Vol. 9, No. 3 pelsmagazine.ieee.org September 2022 For your engineering success 81 Features Departments 16 Wide Bandgap-Based Power Electronics & Columns for Aerospace Applications 4 From the Editor Wide Bandgap Devices Continue to Evolve Jin Wang for Aerospace Applications Ashok Bindra 26 Wide Bandgap Semiconductor-Based Power 8 President’s Message Electronics for Aviation IEEE PELS: 35 Years of Growth and Excellence Liuchen Chang Fei (Fred) Wang, Ruirui Chen, and Kaushik Rajashekara 12 PSMA Corner 37 Totem-Pole PFC Reliability and Performance Accelerating the Transition to Vehicle Electrification Improvement With Advanced Controls Renee Yawger Zhong Ye, Danyang Zhu, and Hailong Yang 65 Women in Engineering Getting Involved With IEEE Power Electronics 45 Full-Bridge Fault-Tolerant Isolated DC–DC Society: Successful APEC Event for WIE, YP, and You! Converters: Overview of Technologies and Stephanie Watts Butler Application Challenges 72 Expert View Abualkasim Bakeer, Andrii Chub, and Dmitri Vinnikov Silicon Alternatives to the Ubiquitous MLCC Mukund Krishna 56 Ranking Qi Wireless Power Transmitters 76 Society News by Efficiency 91 Event Calendar 96 White Hot You can’t get there from here John Perzow Which Came First? Part I Robert V. White On the cover Aerospace Applications for WBG Devices IMAGES LICENSED BY INGRAM PUBLISHING, ELECTRIC AIRCRAFT—©SHUTTERSTOCK.COM/ RYAN FLETCHER, EXTERNAL POWER RECEPTACLE PLUG— ©SHUTTERSTOCK.COM/ AUTTZ Digital Object Identifier 10.1109/MPEL.2022.3197966 1September 2022 z IEEE POWER ELECTRONICS MAGAZINE
IEEE Power Electronics Magazine Editor-in-Chief Alan Mantooth Navid R. Zargari Sanjib Kumar Panda Ashok Bindra Senior Past President Rockwell Automation, Canada TC 12: Energy Access and Austin, TX, USA Long Range Planning Off-Grid Systems +1 631 672-2875 Committee Chair 2024 Members-at-Large [email protected] [email protected] [email protected] Stephanie Watts Butler Mario Pacas WattsButler LLC Advertising Sales Deputy Editors-in-Chief VP Global Relations USA Kathy Naraghi Stephanie Watts Butler (Industry) [email protected] Shinzo Tamai WelComm, Inc., WattsButler LLC Pat Wheeler Toshiba Mitsubishi-Electric Industrial [email protected] USA VP Technical Operations Systems Corp., Japan +1 858 279-2100 [email protected] [email protected] Ulrike Grossner Leon M. Tolbert (Academic) Brad Lehman ETH Zurich, Switzerland IEEE Power Electronics Society Staff Min H. Kao Professor VP Products Giovanna Oriti Mike Kelly Electrical Engineering and President-Elect Naval Postgraduate School, USA Executive Director Computer Science [email protected] Axel Mertens [email protected] The University of Tennessee Johan Enslin Leibniz Universität Hannover, Germany Jane Celusak 520 Min H. Kao Bldg VP Standards Maryam Saeedifard Project Manager Knoxville, TN, 37996-2250, USA [email protected] Georgia Tech, USA [email protected] +1 865 974-2881 Jian Sun Alicia Tomaszewski [email protected] VP Conferences Technical Committee Chairs Project Manager Transportation [email protected] Al-Thaddeus Avestruz Electrification Community Magazine Advisory Board Mark Dehong Xu TC 1: Control and Modeling of [email protected] Leon M. 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From the Editor by Ashok Bindra Wide Bandgap Devices Continue to Evolve for Aerospace Applications F rom electric aircrafts to satellites high-voltage, encountered in these electronics will be even more chal- and unmanned aerial vehicles applications, the article highlights ther- lenging. Furthermore, it shows that (UAVs), the need for fuel saving mal management, EMI mitigation and WBG-based power electronics can and greenhouse reduction continues dv/dt filter designs, and current sharing also play an important role for satel- relentlessly. As a result, electrification between power modules as additional lites, future space stations, lunar- seems to be catching rapidly in aero- challenges for aerospace applications. based electric power systems, and space and aviation applications. This Consequently, lab safety needs more other space exploration applications. demands new generation of power con- attention because of the involvement of verters, motor drives, and solid-state high-voltage, low air pressure, radia- The third feature “Totem-Pole PFC circuit breakers with unprecedented tion, and cryogenic temperature, which Reliability and Performance Improve- power density, efficiency, and reliability. are not generally encountered in other ment with Advanced Controls” by Wide bandgap (WBG) power devices, applications. So, as per Wang’s article, Zhong (John) Ye, Danyang Zhu, and such as silicon carbide (SiC) MOSFETs safety rules, procedures, and related Hailong Yang unveils a novel continu- and gallium nitride (GaN) high-electron trainings are needed. Also, the article ous conduction mode (CCM) totem- mobility transistors (HEMTs) and gate suggests that there will soon be a lack pole PFC analog controller, which is injection transistors (GITs), are regard- of workforce due to the rapid develop- combined with a 2.5 kW SiC MOSFET ed as critical candidates for such appli- ment of more electric aircraft (MEA), to demonstrate the robustness and cations. While WBG devices have been electric vertical take-off and landing performance improvement of totem- serving the needs of commercial and (eVTOL) aircrafts, UAV, electric propul- pole PFC prototype. The fourth fea- industrial systems for more than a sion, and space exploration. Conse- ture “Fault-Tolerant Isolated DC-DC decade, there are still many challenges quently, more investment from Converters: Survey of Technologies for WBG devices and their circuits for governments and industry are needed and Application Challenges” by aviation applications, which include to attract and train students and engi- Abualkasim Bakeer, Andrii Chub, and radiation hardness, extreme operation neers to work on WBG-based power Dmitri Vinnikov discusses three fault temperature, high altitude, high-voltage, electronics for aerospace systems, con- tolerant (FT) approaches to overcom- high dv/dt, and high di/dt operation cludes the author. ing semiconductor faults in galvani- induced issues. cally isolated dc–dc converters using The second feature “Wide Bandgap series resonant converter as the refer- In the cover feature “Wide Bandgap Semiconductor Based Power Elec- ence topology. Amongst them, the Based Power Electronics for Aero- tronics for Aviation” by Fei (Fred) zero redundancy FT approach shows space Applications,” by Jin Wang, the Wang, Ruirui Chen, and Kaushik the lowest implementation cost but author shows that WBG devices are Rajashekara, also focuses on the requires some degree of power cur- gradually finding their ways into cover theme. This article suggests tailment after a fault. In essence, it aerospace applications. Besides dis- that many of the same WBG-based shows that the zero-redundancy FT cussing the common challenges, such power electronics technologies can approach is the best for numerous as radiation hardness, extreme opera- also be extended to future electrified emerging applications where the cost tion temperature, high altitude, and spacecraft applications, where the of implementation is essential while requirements on power density, spe- the performance of the post-fault Digital Object Identifier 10.1109/MPEL.2022.3196232 cific power, efficiency, reliability, and operation is allowed to deteriorate Date of publication: 28 September 2022 the operating environment for power reasonably. 4 IEEE POWER ELECTRONICS MAGAZINE z September 2022
Finally, the feature “Ranking Qi vehicle electrification workshop that announcement of logo and photo Wireless Power Transmitters by Effi- will offer latest technologies and future contest winners. Additionally, it ciency” by John Perzow discusses the trends surrounding vehicle electrifica- reveals Prof. Kaushik Rajashekara proposed efficiency test protocol for tion. The “Expert View” column by has been awarded the prestigious the U.S. EPA, intended to rank Qi Mukund Krishna emphasizes the need Global Energy Prize for 2022. Finally, wireless power transmitters on the for silicon alternatives to ubiquitous the “Event Calendar” provides power transfer efficiency. MLCCs, which have reached their limits a year’s listing of conferences in terms of ESL, area, and profile. In the and workshops. Columns, Society News, and More “White Hot” column “Which Came First? Part I,” Bob White investigates Hopefully, we will return to nor- In the column President’s Message, the history of power electronics with an malcy soon. Thanks to you, both print IEEE Power Electronics Society emphasis on the effect of each major and digital versions of the magazine (PELS) President Liuchen Chang high- advance in devices. are being delivered on time to our lights PELS’ growth and excellence readers. IEEE Power Electronics for 35 years. Plus, he adds, “Our soci- Next, the “Women in Engineering” Magazine is committed to bringing ety has become the eighth largest soci- (WIE) column “Getting Involved With timely articles, columns, and news ety within IEEE, and is continuing its IEEE Power Electronics Society” by items of interest and value to practic- steady growth in membership Stephanie Watts Butler underlines ing power electronics engineers throughout the world, including high- the efforts of WIE volunteers in pro- worldwide. To serve you better and er quality in publications, more agility moting PELS and its activities keep this magazine a valuable in technical programs, and excellence amongst potential members, namely resource for working power electron- in conferences and expositions.” Addi- young professionals, diverse mem- ics engineers around the world, we tionally, the column points to the bers, and industrial members. look forward to your feedback and many initiatives started by PELS to suggestions. Now, we have a website fully serve its members. As usual, Society News brings (https://pelsmagazine.ieee.org/) where activities from PELS chapters and you can easily provide your feedback. Likewise, in the column “PSMA Cor- student branches around the world, Stay safe and healthy! ner,” Renee Yawger focuses on a virtual and celebrates PELS Day with the
President’s Message by Liuchen Chang IEEE PELS: 35 Years of Growth and Excellence T he IEEE Power Electronics at other conferences including EPE fessionals, and researchers) from the Society (PELS) celebrates the 2022 – ECCE Europe in Hannover, country. The PELS Education Steer- 35th anniversary in 2022 for Germany, and IEEE Energy Conver- ing Committee has made significant its establishment as a full IEEE soci- sion Congress and Exposition (ECCE) efforts in defining a suitable platform ety by the visionary pioneers of the 2022 in Detroit, MI, USA. For more for posting the education videos on power electronics community. Many details, please see the article of this power electronics known as PELS- PELS Chapters and Student Branch magazine written by Stephanie Watts Tube. The first batch of contributions Chapters around the world have orga- Butler (the leading organizer of the was submitted for review. nized virtual or in-person events to APEC breakfast event and the Chair of celebrate the PELS Day throughout PELS Industry Committee), titled “Get- PELS VP Products and President- June this year. You may have seen the ting Involved With IEEE Power Elec- Elect Brad Lehman has noted that it fascinating photos of these events tronics Society: Successful APEC is interesting to see what some of the posted on our PELS website. Now our Event for WIE, YP, and You!” emerging technical trends are appear- society has become the eighth largest ing in the papers. For example, society within IEEE, and is continu- Lots have happened after my last machine learning papers are begin- ing its steady growth in membership report. We are very pleased to ning to emerge to enable new designs throughout the world, including announce that IEEE has approved the in improving reliability, magnetics, higher quality in publications, more IEEE PELS Graduate Studies Scholar- and PCB designs. Several years ago, agility in technical programs, and ship, including the IEEE PELS Jan these topics could not be found in any excellence in conferences and exposi- Abraham “Braham” Ferreira Scholar- of our publications. There also seems tions. In addition, PELS is expanding ship and the IEEE PELS Graduate to be an increased interest to publish initiatives to fully serve its members. Studies Fellowship, including IEEE in open access journals, such as our PELS John G. Kassakian Fellowship, newer IEEE OPEN JOURNAL OF POWER Starting with IEEE Applied Power as noted by Mario Pacas, VP Global ELECTRONICS, established in 2020. This Electronics Conference and Exposi- Relations. These student award pro- is no doubt being accelerated by tion (APEC) 2022 in March, in-person grams will be launched soon. At a vir- European Funding Agencies’ require- interactions have returned to most of tual meeting held in July, our AdCom ments requiring researchers to make our major conferences and events in members provided excellent advice their publications freely available to 2022. The breakfast event of “WIE, YP, on strengthening PELS education the public, as outlined in Plan S. How- and You: How to become involved with activities, which will lead to several ever, we are noticing that some other PELS and PSMA too” was a huge suc- new initiatives and programs enhanc- countries are also leaning toward cess at APEC 2022. Please stay tuned ing the service to our students and new public access requirements for the announcement of similar professionals. In addition to the ongo- (India), although they are less restric- events and receptions organized by ing Ph.D. Schools in Europe and Asia, tive. PELS is well positioned, since our Young Professionals (YP) Commit- the second Ph.D. School in Mexico authors can also optionally select (for tee, Women in Engineering (WIE) will be held in a hybrid format in Sep- modest charges) to make any of their Committee and Students Committee tember in San Luis Potosí, with key- papers open access. Perhaps, though, notes from seven distinguished one of the more interesting mandates Digital Object Identifier 10.1109/MPEL.2022.3193859 scientists and more than 100 partici- that might begin to influence author Date of publication: 28 September 2022 pants (Ph.D. students, industry pro- submissions to our PELS journals is 8 IEEE POWER ELECTRONICS MAGAZINE z September 2022 2329-9207/22/$31.00©2022IEEE
that China has recently required industry trends, issues, and design tees in the future. Previous FEPPCONs researchers to publish one third of topics. Maybe some industry authors have significantly impacted the techni- their papers in domestic Chinese jour- might enjoy the exposure and write cal programs of PELS and have led to nals. However, this guideline has not some articles? First contact our mag- establishing International Technology seemed to reduce the number of sub- azine editor with your ideas. Roadmap for Wide Bandgap Power missions to any of PELS journals Under the leadership of Mark Semiconductors (ITRW), IEEE Work- from our authors in China. This is Dehong Xu (VP Membership) and shop on the Electronic Grid (eGrid), likely because of the prestige, high Sanjib Panda (Region 10 Chair), PELS IEEE Empower A Billion Lives (EBL) impact factors, and huge readership Membership Committee-China and Competition, Cyber Security Initiative of all PELS journals. Some other high- Membership Committee-India were (and Technical Committee 10: Design lights in our publications include: established in order to further Methodologies), and more. A series of ■ Review times for letters in IEEE strengthen the support and service to articles reporting the details of the PELS Chapters and members in these technical programs and outcomes of TRANSACTIONS ON POWER ELECTRONICS countries. It is expected that more FEPPCON XI will be published in a or even full papers in IEEE OPEN countries and regions will establish future issue of this magazine. JOURNAL OF POWER ELECTRONICS are similar committees in the future. normally below four weeks (Wow!!). IEEE Future of Electronic Power Many hybrid events are in plan- ■ IEEE TRANSACTIONS ON POWER ELEC- Processing and Conversion (FEP- ning for the remaining 2022, including TRONICS was (again) the most down- PCON) XI was held in early June in Ice- our AdCom meeting, PELS Townhall loaded IEEE TRANSACTIONS in the land. As part of PELS strategic planning meeting, and other committee meet- first six months of 2022. process, FEPPCON has provided our ings during ECCE 2022 in October. ■ Columns in IEEE Power Electronics society an avenue to identify the emerg- Most technical committees will run Magazine are all open access and ing technological areas and trends their leadership elections this year. I free to the public. PELS membership which enable PELS to develop new pro- am looking forward to the opportuni- is required to access the feature arti- grams and even new technical commit- ties to say “hello!” to you in-person at cles, though. The columns discuss some of these events. MOTOR DRIVE CONTROL RAPID PROTOTYPING from Matlab® Simulink® online store on imperix.com
PSMA Corner by Renee Yawger Accelerating the Transition to Vehicle Electrification G lobally, governments are the PSMA Transportation Electronics The workshop will take place on mandating a switch from Committee will offer a virtual work- two consecutive Tuesdays, 13 and 20 internal combustion engine shop focused on the latest technolo- September, at 9:00 A.M.–2:30 P.M. CDT (ICE) technology to electric-drive gies and future trends surrounding (2:00–7:30 P.M. GMT). The full agenda vehicles in 100s of millions of vehicles vehicle electrification. can be found at: https://www.psma. to combat climate change. For exam- com/2022vehicle_workshop_agenda ple, on 29 June 2022, the European PSMA Vehicle Electrification Union (EU) agreed to a framework to Workshop The 2022 PSMA Vehicle Electrifi- eliminate carbon emissions from new cation Workshop is being promoted cars and vans by 2035, effectively The September 2022 Transportation along with ITEC+EATS 2022 and reg- removing the ICE option for large- Electronics Committee Workshop will istration is open at https://psma.com/ scale auto manufacturers [1]. Auto- focus on topics of interest for any technical-forums/transportation- makers are already moving quickly to engineer or manager that is involved power-electronics/workshop innovate, reduce electric drive costs in vehicle electrification. This includes and leverage technology to respond not only those in the automotive Vehicle Electrification Trend to this new environment. industry, but also those in the off-road in Brief and heavy-duty industries. The global trend towards According to the International Energy increased vehicle electrification cre- Each session will lead off with key- Agency (IEA), as the cost of batteries ates significant opportunities for the note speakers and conclude with Q&A and EVs falls and charging infrastruc- power semiconductor industry. There and a roundtable discussion. The first ture expands, EV fleets are expanding are opportunities within the pow- session keynote will be offered by Kia at a fast pace in multiple markets [2]. ertrain of the electric vehicle (EV), in Motors with a presentation of the More than 10 million electric cars the charging infrastructure including “Evolution of the EV Market.” There were on the roads in 2020 with many the on-board charger and wireless are two keynotes in the second ses- manufacturers predicting a minimum charging, and in advanced battery sion; the first will be offered by the of 50% of vehicle sales to be electric technology. A driving goal of the Department of Energy with an “Over- by the year 2030 as shown in Figure 1. Power Sources Manufacturers Asso- view of Current EV Charging Projects ciation (PSMA) (www.psma.com) is Supported by the Department of Ener- The electrification of buses and to improve the knowledge of techno- gy.” The second keynote of this session heavy-duty truck offerings, including logical and other developments relat- will be by Oakridge National Laborato- everything from garbage trucks to ed to power sources and conversion ry with a presentation on “Materials to long-haul freight trucks are also devices and vehicle electrification Help Battery Life. Recycling Trends in expanding. Proposed government reg- provides an opportunity for PSMA Testing – All Chemistries.” ulations are further accelerating the member companies to align their transition to vehicle electrification. product roadmaps to meet the needs A wide range of topics will be The ‘Fit for 55’ initiative in the EU of this industry. In September of 2022, addressed by experts in the field, means that all new cars or vans placed including the latest technologies in in the market from 2035 onward will Digital Object Identifier 10.1109/MPEL.2022.3193861 fast charging and wireless charging, be zero-emission vehicles [3]. Similarly, Date of publication: 28 September 2022 what to do about high EMI, dc–dc the U.S. administration has set a goal converter trends, battery testing and of 50% EV sales by 2030 [4]. With the management, and many more topics. Vehicle Electrification Workshop, 12 IEEE POWER ELECTRONICS MAGAZINE z September 2022
Original equipment manufacturer 2021 2022 2023 2024 2025 2026 2027 2028 2029 2030 BMW Group 25 15-25% 10 % of sales electric BAIC Group 2 1.3 50% Annual sales (million) 33 Changan Automobile (Group) 10 25% 50% New EV models (number) Daimler 1 30% 1 1 11 Cumulative sales (million) Dongfeng Motor Co 40% FAW 40 60% * European market only Ford 22 100%* ** Chinese and US markets only GM Group 30 1 1 T Includes both EVs and FCEVs Honda 40%T Hyundai-Kia 1 29 Mazda 1 5% Renault-Nissan 20 20% Maruti Suzuki 1 1.5 SAIC 30% 30 Stellantis 38%* 70%* 31%** 35%** Toyota Group 1 15 >1 Volkswagen 20% 70%* 26 50%** 13 75 Volvo (Geely Group) 1 1 1 1 50% 100%* FIG 1 Original equipment manufacturer announcements related to electric light-duty vehicles. Source: https://www.iea. org/reports/global-ev-outlook-2021/trends-and-developments-in-electric-vehicle-markets PSMA is offering the power engineering community, the opportunity to better understand the significant opportunities that the vehicle electrification trend offers the power semiconductor industry. About the Author Renee Yawger is the Director of Marketing at Efficient Power Conversion Corporation (EPC) and the Director of Corporate Marketing at EPC Space. She has over 25 years of sales and marketing experience within the semi- conductor industry. Prior to joining EPC, she was at Vishay Siliconix for nearly 15 years in various positions in sales support, customer service, and regional market- ing. At EPC, she is responsible for the product marketing and marketing communication functions globally. She is also the Vice President of the Board of Directors, PSMA. References [1] The Associated Press. (Jun. 29, 2022). EU nations reach deal to eliminate carbon emissions from new cars by 2035—National. Global News. Accessed: Jul. 7, 2022. [Online]. Available: https://glo- balnews.ca/news/8955504/eu-climate-deal-reached [2] IEA, Paris, France. (2021). Global EV Outlook 2021. [Online]. Avail- able: https://www.iea.org/reports/global-ev-outlook-2021 [3] European Union. (2022). Fit for 55: Why the EU is Toughening CO2 Emission Standards for Cars and Vans. [Online]. Available: https://www. consilium.europa.eu/en/infographics/fit-for-55-emissions-cars-and-vans/ [4] J. Ewing. (Aug. 5, 2021). President Biden sets a goal of 50 percent electric vehicle sales by 2030. The New York Times. Accessed: Jul. 6, 2022. [Online]. Available: https://www.nytimes. com/2021/08/05/business/biden-electric-vehicles.html 14 IEEE POWER ELECTRONICS MAGAZINE z September 2022
©SHUTTERSTOCK.COM/IMMERSION IMAGERY Wide Bandgap-Based Power Electronics for Aerospace Applications by Jin Wang Aerospace applications are not new but potentially vertical take-off and landing (eVTOL) aircraft, and future the final frontiers for power electronics hybrid and turbo electric propulsion call for a new genera- research and developments. On the aviation tion of power converters, motor drives, and solid-state cir- side, because of the need for fuel saving and cuit breakers with unprecedented power density, greenhouse gas reduction, more electric air- efficiency, and reliability [1], [2], [3], [4], [5], [6], [7], [8], craft (MEA), unmanned aerial vehicles (UAVs), electric [9], [10], [11]. On the space side, lunar, Mars, and deep space expeditions, will need light-weight and highly effi- Digital Object Identifier 10.1109/MPEL.2022.3197346 cient power electronics systems to work reliably at places Date of publication: 28 September 2022 that no man has gone before, where space radiation and extreme operation conditions present more challenges to power devices and circuits [12], [13], [14]. 16 IEEE POWER ELECTRONICS MAGAZINE z September 2022 2329-9207/22©2022IEEE
Class E Airspace High energy primary cosmic ray (proton, electron or heavy ion) Altitude ~36km Terrestrial cosmic shower starts Typical “aircraft cruising altitude” Altitude ~19km n n mu 1n/cm2s < p pn n neutron flux (for E>10MeV) nn mu n < 3n/cm2s n mu Class B, C, D, G, E... Airspace Class A Airspace Altitude ~ 13km n kn pi Altitude ~ 9km n 0.1n/cm2s < p neutron flux (for E>10MeV) < 0.5n/cm2s n Altitude ~ 5km Denver ~1.6km np Altitude ~ 0km NY ~0km 0.001n/cm2s < Miami ~0km neutron flux (for E>10MeV) < 0.004n/cm2s Neutron flux for E>10MeV ~ Neutron flux for 10MeV>E>1MeV FIG 1 Terrestrial neutron radiation [19]. Wide bandgap (WBG) power devices, such as silicon Radiation Hardness carbide (SiC) junction barrier Schottky (JBS) diodes and In space, cosmic rays from the Sun, our own galaxy, and power MOSFETs and gallium nitride (GaN) high-elec- distant galaxies contains mainly protons, electrons, and a tron mobility transistors (HEMTs) relatively smaller number of heavy and gate injection transistors (GITs), ions, traveling nearly at the speed of are regarded as natural candidates Recent tests show that the light. Heavy ions can cause single for aerospace applications. With event effects (SEEs), such as degra- great efforts from device manufac- SiC power MOSFETs dations, interrupts, as well as dam- turers and system integrators, these exhibit latent damage age. As shown in Figure 1, when the devices are either already or close to the gate oxide at heavy ions bombard atmospheric to being implemented in different gases, terrestrial neutron flux will be power converters, actuator drives, drain to source bias generated. The intensity of neutron and circuit breakers for aerospace voltages much lower flux is high at typical aircraft cruising applications [15], [16], [17]. The altitude [19]. main remaining challenges for WBG than the rated break- Recent studies show that SiC devices and their circuits for avia- down voltages. power MOSFETs are more reliable tion applications include: than their Si counterparts when it ■■radiation hardness; comes to terrestrial neutron flux. The ■■extreme operation temperature; and terrestrial neutron induced failure ■■high altitude, high voltage, high rates in SiC devices are much lower dv/dt, and high di/dt operation induced issues such as than failure rates in similarly rated Si devices [19]. Thus, lower partial discharge inception voltage and higher in terms of radiation hardness, for many aviation applica- EMI noises. tions, SiC is already a better choice than Si. 17 September 2022 z IEEE POWER ELECTRONICS MAGAZINE
However, when it comes to space applications, where 400 V rated devices, SEB can happen at 375 V. Also, after heavy ions are the main radiation sources, SiC power radiation, tested GIT devices exhibit increased dynamic MOSFETs so far cannot reach the same level of reliabil- on resistance when they are biased at voltages much ity of their silicon (Si) counterparts. Recent tests show lower than their rated voltages. The same effect was not that SiC power MOSFETs exhibit latent damage to the observed when the devices were biased at their rated gate oxide at drain to source bias voltages much lower voltages [21]. than the rated breakdown voltages. As shown in Figure 2, most tested devices will have single event burnout Extreme Operation Temperature (SEB) at voltages lower than 50% their rated voltage. On Both aviation and space applications require power elec- the contrary, their Si counterpart usually do not exhibit tronics to work at extreme temperatures. For high tem- latent gate damage and often pass the radiation tests perature, limited by the packaging and supporting without SEBs. This difference is partially due to the electronics, the suggested maximum junction tempera- much higher electric field stress in SiC MOSFETs’ gate tures of WBG devices are usually 175 °C or lower. Active oxide [18], [20]. cooling of these devices at high ambient temperature is Recently, GaN HMETs and GITs have also been evalu- often required. ated against heavy ion radiation [21], [22]. Test results In terms of extremely low temperature, cryogenic show that lower voltage rated (≤200 V) GaN HEMTs can evaluations of WBG devices and circuits have been car- pass radiation tests at their rated voltages, thus can be ried out in recent years [23], [24], [25], [26]. These studies considered as radiation hardened. But for devices rated show that most tested SiC and GaN devices can work at at 600 V, SEBs occurred at a voltage as low as 350 V. For cryogenic conditions very well. The breakdown voltage of these devices are often not quite affected by the temperature. SiC devices show 1500 No Effect Latent Gate Degradation ΔID=ΔIG ΔID>>ΔIG (to 3300) increased on resistance at lower tem- 1400 perature whereas GaN devices often see 1300 SEB decreased on resistance at lower temper- 1200 ature. GIT devices showed 55%–70% on Drain-Source Voltage (V) 1100 No Data resistance reduction at low temperature. 1000 The threshold voltages for most evaluated SiC varies from device to device. At cryo- 900 genic temperature, some devices showed 800 decreased switching losses while some 700 showed increased switching losses. A 600 summary of cryogenic evaluation of GaN 500 400 devices is shown in Table I. 300 In terms of passive components, mul- No Data 200 tiple studies of cryogenic operations of 100 M1 M2 M3 M4 M5 M2 M3 M4 M6 M7 M8 ceramic and film capacitors had also Device0: M1 M2 M7 Ar 11 Cu 24 Age 49 Xe 66 been carried since late 1990s. Most of Ion/LET: B 1.0 Ar 9.3 the results show that tested film capaci- [MeV-cm2/mg(SiC)] tors (polypropylene and polycarbonate) FIG 2 Impact of multiple types of heavy ion radiations on eight different SiC have relatively minor characteristics MOSFETs from four manufacturers [18]. changes at liquid nitrogen temperature –– Table I. Cryogenic (4.2 k) evaluation results of GaN devices [25]. GaN Device Voltage Rating Vth CMP to Room Ron CMP to RT Soft-SW Loss CMP Hard-SW Loss CMP RT Temperature (RT) to RT (by Eoss) T1: HEMT 650 V 17% of Ron(RT) No Change (On-Si) 650 V 55% of Vth(RT) 17% of Ron(RT) No Change No Change 600 V 123% of Vth(RT) 70% of Ron(RT) 155% of Esoft(RT) T2: HEMT 600 V 115% of Vth(RT) 55% of Ron(RT) 80% of Esoft(RT) 90% of Ehard(RT) (Cascode) 107% of Vth(RT) No Change T3: GIT 1 No Change T4: GIT 2 18 IEEE POWER ELECTRONICS MAGAZINE z September 2022
whereas some ceramic capacitors show significant busbars, connectors, aviation wires, and cables which are decreases in capacitance. More studies on cryogenic all essential for power converters. operations of different types of capacitors and induc- tors with new core and insulation materials are still B. High-Speed Switching needed [37], [38], [39]. With WBG devices, partial discharge becomes a more pressing issue because of the higher switching speed. Stud- Partial Discharge ies show that PDIV of all types of insulation structures will decrease with decreased rise and fall time of applied volt- Currently, for MEAs, both ac and dc power distribution ages [28], [29]. Figure 5 shows a SiC-based 2 kV 1 MVA inte- have been implemented. For example, Boeing 787 has grated modular motor drive (IMMD) and the detailed view over 1 MVA of electric power distribution, both 115 V 400 of a power electronics submodule. Hz ac distribution and ±270 V dc distribution are utilized. One of the main reasons that the dc voltage is limited to As indicated in the figure, PD is more prone to happen ±270 V is partial discharge at high altitude. Partial dis- at surfaces of stacked PCB boards, external connection charge (PD) is a localized discharge that only partially terminals, edges of busbars and the triple points inside bridges the insulation between conductors under high power modules. As shown in Figure 6, to study the PD voltage stress. Corona at the surface of conductor or insu- of triple points, test coupons were designed and tested. lation material and cavity discharge inside insulation Test results show that at short pulses, shorter rise time material are two common PD phenomena. A. High Altitude Breakdown Voltage vs. Pressure The Paschen’s curve, as shown in Figure 3, (Air - 0.1 inch Gap) indicates that the breakdown of the air can happen just slightly above 300 V when the 100000 air pressure is low. Figure 4(a) shows a motorette sample under tests in an altitude Breakdown Voltage 10000 V chamber, which emulates a section of the 1000 stator of an electric machine, being tested in an altitude chamber. Figure 4(b) shows 100 1.00E-01 1.00E+00 1.00E+01 1.00E+02 1.00E+03 the partial discharge inception voltage 1.00E-02 Pressure - Torr (PDIV) and partial discharge extinction voltage (PDEV) of the motorette at differ- FIG 3 Paschen curve for the air [27]. ent pressures. It can be seen that at 50 torr, which is roughly the air pressure at 62 000 ft (18897.6 m) above the sea level, PDIV of the motorrete occurs at 270 V. At high alti- tude, reduced PDIV can be observed for Test results within Phase AVoltage (V) 550 500 450 400 350 300 250 PDIV-Phase A PDEV-Phase A 200 0 100 200 300 400 500 600 700 Pressure (Torr) (a) (b) FIG 4 (a) A motorette being tested in an altitude chamber. (b) PDIV and PDEV of the sample at different air pressure (altitude). 19 September 2022 z IEEE POWER ELECTRONICS MAGAZINE
Terminals DC- AC DC+ 3D Printed Insulation DC-link PCB Busbar Triple Housing points Encapsulation Stage 1: DC - Busbar Necessary wire Die 1334 V / 2000 V APS Board DC + Busbar bounding Solder Baseplate Nylon Spacer DBC Gate Drive Board ceramic 0 V / 2 kV Zoomed in Currenty Sensor & Power Module Dc inputs AC Busbar 178 mm 120 mm IMMD power converter unit Power module unit Stage 3: Stage 2: Potential PD locations (sources) for power converter 0 V / 667 V 667 V / 1334 V system Integrated modular motor • High voltage terminals (DC and AC) drive (IMMD) and the motor • Busbar edges • Device surfaces (PCB and power module) • Power module interior FIG 5 Potential PD locations of power electronics submodules for a 1 MVA IMMD for electrified propulsion. Copper Silicone gel Copper Direct wire bonding HV 5.5 tr=200 ns (DBC) GND HV Silicone gel tr=150 ns GND PDIV /kV 5.0 tr=100 ns AIN Protrusion Back copper 4.5 (a) (b) 4.0 Triple point Surface roughness Silicone gel HV 3.5 GND 0 200 400 600 800 Ceramic Pulse width /µs Floating (c) FIG 6 Triple point, direct bond copper (DBC) test coupons, and PDIV versus rise time and pulse width [29]. (faster switching) will result in lower PDIV. This is largely will need be much higher than current ±270 V. Thus, the because that shorter rise time will have more impact on expected high voltage, together with the high altitude and the voltage integration over time when the applied voltage high switching speed call for innovations in insulation pulses are short. material, insulation design and grounding strategies. The decreasing PDIV with fast switching speed means more challenges in the insulation EMI design of SiC and GaN power mod- At cryogenic The higher switching speed and ules, especially for aerospace applica- higher switching frequency of WBG tions where there is a need to further temperature, some devices will improve the efficiency reduce footprints of baseplates for devices showed and power quality of power electron- power modules for weight reduction ics circuits. But at the same time, purposes. decreased switching more EMI related issues could be For future hybrid and turbo elec- losses while some expected. For motor drives, as shown in Figure 7, the common mode cur- tric propulsion, the required electric power is estimated to be 20 MW for showed increased rent largely is a result of the common a commercial regional single aisle switching losses. mode voltage at the neutral point of aircraft. This means that the dc dis- the electric machine and distributed tribution voltage for these aircrafts parasitic capacitance of the motor, 20 IEEE POWER ELECTRONICS MAGAZINE z September 2022
Power Source Variable frequency drive Motor M + – ICM Parasitic capacitance Common GND Vcm (V) 200 Vcm (V) 200 Higher 100 Si to WBG 100 Devices 0 0 Higher Switching –100 Speeds & frequency –100 –200 –200 1 1 1 1 1 1 1 11 0.0001 0.00015 1 1 1 1 1 111 0.4 0.4 0.45 Icm (A) Icm (A) 0.2 0.2 0 0 –0.2 –0.2 –0.4 –0.4 0.1 0.15 0.2 0.25 0.3 0.35 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 Times (ms) offset=0 Times (ms) offset=0 Common mode voltage at the neutral point of the three-phase motor and resulting common mode current. FIG 7 Common mode voltage and current in a typical motor drive. the power converter and power source. When Si devices The Si inverter was controlled to switch at 30 kHz and the are replaced by SiC or GaN devices, the rising edges of the SiC inverter was controlled to switch at 30 kHz and then common mode voltage will become sharper, with similar 60 kHz. As shown in Figure 8, the measured conducted layout of the power electronics and electric machine struc- EMI for SiC and Si inverter are similar when both were ture, the peak value of the common mode current will switching at 30 kHz. It was pointed out that the tested SiC increase due to the higher switching speed. If higher inverter will need EMI filters to pass MIL-STD-461 part switching frequencies are implemented, the repeating fre- CE102, the size of the required filter will be similar to the quency of the common mode current pulses will also size of the filter that is required by its Si counterpart [31]. increase [30], [31]. However, on the bright side, the Design and Product Examples fundamental frequency of typi- In the last few years, there have been cal electric machines for MEA and With WBG devices, great design examples of WBG-based future electric propulsion are usu- partial discharge power converters and motor drives ally in the range of few hundred of for aerospace applications. Figure 9 Hertz to couple kiloHertz. Though becomes a more press- shows a 600 W GaN-based noninvert- potential implementations of per- ing issue because of ing buck–boost (NIBB) converter manent magnet machines will result the higher switching designed for photovoltaic panels in in lower leakage inductance, which space applications. The converter has requires higher switching frequency speed. integrated maximum power point to achieve reasonable power qual- tracking (MPPT) function and has ity, the switching frequency of SiC- been tested at –140 °C successfully. based machine drives will most The measured efficiency of the con- possibly stay below 60 kHz, which does not significantly verter at –110 °C is 98.31%. The specific power of the con- change the conductive EMI spectrum [31]. A recent study verter is 3.76 W/g [32]. compared the EMI performance of commercial-off-the- In Figure 10, a 10-level 18.9 kW flying capacitor mul- shelf (COTS) 250-kW SiC MOSFET-based inverter and a tilevel inverter module is shown. The module is based 250-kW Si IGBT-based inverter with similar construction. on 150 V GaN devices and achieves 98.95% efficiency, 21 September 2022 z IEEE POWER ELECTRONICS MAGAZINE
(a) W Conducted EMI: Si vs. SiC (Active lnversion) L 120 SiC - 60 kHz L x W x H = 95 x 69 x 25 [mm] Si FIG 9 600 W GaN-based NIBB for space applications [32]. SiC 110 461G Mag (dBµV) 100 90 As newest development, multiple medium voltage mega- watt PD free demonstrations of SiC-based propulsion 80 drives are being developed and tested by both industry and university led teams. Figure 13(a) shows a submodule 70 for a 2-kV 1-MVA integrated modular motor drive (IMMD) 60 that is currently being developed under a project funded by NASA and led by The Ohio State University (OSU) in col- 50 laboration with the University of Wisconsin, the University 106 107 of Maryland, and North Carolina A&T University. The sub- Freq (Hz) module utilizes SiC power modules from Wolfspeed. Fig- ure 13(b) shows the submodule during tests in the altitude (b) chamber. The submodule achieves PD free operation at 700 FIG 8 (a) A 250 kW SiC inverter that can switch at 60 kHz (left) V and 87 torr [air pressure at 56 000 ft (17068.8 m)]. Figure and a 250 kW Si inverter that switches at 30 kHz (right). (b) 14(a) shows three stages of these submodules configured Conductive EMI Si versus SiC when both motor drives work in in series for a 2-kV, 1-MVA test with inductive loads. Fig- the inversion mode [31]. ure 14(b) shows three phase “B” currents, each from a dif- ferent stage. During the test, the SiC power modules were 1.0355 MHz effective frequency, and a 38.4 kW/kg specific switching at 40 kHz. Based on results of double pulse tests power density [33], [34]. and the inductive load tests, the estimated efficiency of all Product developments and research demonstration stages together is higher than 99%. The power density of of SiC-based power converters for aerospace applica- the submodule is 35.36 kW/kg [36]. tions have been more focused on Figure 15(a) and (b) shows over- high power electric machine drives. all design and current assembly sta- Figure 11 shows GE Aviation’s 200 The higher switching tus of the 2-kV, 1-MVA IMMD. Figure kW integrated starter generator con- speed and higher 15(c) shows the configuration of troller for MAE. The unit utilizes planned IMMD tests inside an alti- GE’s 1200 V SiC MOSFETs packed switching frequency of tude chamber at the NASA Electric in liquid cooled power modules that WBG devices will Aircraft Testbed (NEAT). If success- features GE’s Power Overlay technol- improve the efficiency ful, this would be the first megawatt ogy. The maximum coolant tempera- level integrated motor drive with PD ture can reach 105 °C. and power quality of free operation at high altitude. Figure 12 shows a 2.4-kV1- power electronics Summary and Thoughts MW 3-level active neutral-point- clamped (ANPC) inverter for circuits. But at the WBG devices are gradually finding hybrid-electric propulsion, which same time, more EMI their ways into aerospace applica- was designed and demonstrated by tions. Besides the challenges that GE. The inverter features a SiC+Si related issues could were discussed in this article, ther- hybrid approach and achieves 99% be expected. mal management, EMI mitigation efficiency and a power density of and dv/dt filters designs, and current 12 kVA/kg [35]. sharing between power modules 22 IEEE POWER ELECTRONICS MAGAZINE z September 2022
Phase A id S9A S8A S7A S6A S5A S4A S3A S2A S1A Cd + ia La io Vd Cd C8 C7 C6 C5 C4 C3 C2 C1 + + Phase B va Ca vo S9B S8B S7B S6B S5B S4B S3B S2B S1B AC Sense FPGA Controller NPO Flying X6S Flying Modular Circuitry Phase B (9 x Gate Signals per phase) Capacitors Capacitors GaNFETs Heat Sinks Output Filter Phase B DC Input Neutral 5V Logic Neutral Phase A Signal lsolators Power lsolators 3D Printed Air Inlet Baffle AC DC Input Output Phase A NPO Input 0–80 SMT Mounting Nuts Output Filter Capacitors FIG 10 150 V GaN-based 10-level 18.9 kW flying capacitor multilevel inverter module for aviation motor drives [33]. SiC MOSFET Modules Cold Plate FIG 11 GE Aviation’s 200 kW integrated starter generator Heavy-Copper PCB controller for MAE with 1.2 kV SiC power modules [16]. Snubber Caps DC-Bus Caps during breaking for solid state circuit breakers are few FIG 12 2.4-kV, 1-MW 3-level SiC+Si hybrid ANPC for hybrid- key additional challenges. In general, lab safety needs electric propulsion [35]. more attention because of the involvement of high volt- age, altitude chamber, radiation, and cryogenic tempera- Additional Information ture, which generally are not encountered in other applications. So, safety rules, procedures and related In the IEEE Power Electronics Society (PELS), seeing the trainings are needed. Also, there will soon be a lack of rapid increasing numbers of participating researchers in workforce due to the rapid development of MEA, eVTOL, the related area, a Technical Committee on Aerospace UAV, electric propulsion, and space exploration. More Power (TC11) was formed in 2021. The committee estab- investment from governments and industry are needed lished an annual workshop on Power Electronics for to attract and train students and engineers to work on Aerospace Applications (PEASA). Each year, the work- WBG-based power electronics for aerospace. shop will focus on a specific topic, such as electric pro- pulsion, electromagnetic interference, control and 23 September 2022 z IEEE POWER ELECTRONICS MAGAZINE
Stage I Stage II Stage III A1 B1 C1 A2 B2 C2 C4 B4 A4 C3 B3 A3 A5 B5 C5 A6 B6 C6 (a) (a) DC input PMT Submodule (b) Pressure FIG 14 (a) Three stages with nine submodules in a series con- meter figuration for the inductive 2-kV 1-MVA test. (b) Test waveforms from the test that shows three phase B currents with one from (b) each stage. FIG 13 (a) A submodule for a 2-kV 1-MVA integrated motor drive with a power density of 38.45 kW/kg. (b) The submodule under partial discharge evaluation in an altitude chamber at 87 torr. (a) (b) (c) FIG 15 (a) 2-kV, 1-MVA IMMD. (b) The IMMD under initial test. (c) Test configuration of the IMMD inside a large altitude chamber at NASA’s NEAT facility. Source: NASA NEAT facility. protection of onboard power distribution systems, had participated to share their insight, showcase recent eVTOL, power converters for space applications, radia- developments, and discuss remaining challenges for the tion hardened designs, reliability, etc. The inaugural work- road ahead. shop, as part of the IEEE/AIAA Transportation Electrification Conference and Electric Aircraft Technolo- The 2023 workshop will be hosted at the Univer- gies Symposium was held in June 2022. To build a techni- sity of Nottingham with a focus on electric propulsion. cal foundation for future workshops, the 2022 workshop The 2024 workshop will be focusing on EMI with loca- had focused on high voltage related challenges for aero- tion yet to be decided. Volunteers and suggestions on space power electronics. Experts representing NASA, future workshop topics and locations are welcome. industry, academia, the Technical Committee on Transpor- tation Electrification at the IEEE Dielectrics and Electri- About the Author cal Insulation Society, and SAE high voltage committees Jin Wang ([email protected]) is a Professor at The Ohio State University, Columbus, OH, USA. He conducts 24 IEEE POWER ELECTRONICS MAGAZINE z September 2022
research on high-power converters for transportation [18] J.-M. Lauenstein, M. C. Casey, R. L. Ladbury, H. S. Kim, A. M. Phan, and A. D. Topper, “Space radiation effects on SiC power device reliability,” in electrification and renewable energy integration. He has Proc. IEEE Int. Rel. Phys. Symp. (IRPS), Mar. 2021, pp. 1–8. [19] A. Akturk et al., “Terrestrial neutron-induced failures in silicon car- published over 200 IEEE conference papers and journal bide power MOSFETs and diodes,” IEEE Trans. Nucl. Sci., vol. 65, no. 6, pp. 1248–1254, Jun. 2018. articles. He received the Nagamori Award in 2020 and [20] C. Abbate et al., “Gate damages induced in SiC power MOSFETs during heavy-ion irradiation—Part I,” IEEE Trans. Electron Devices, vol. 66, no. 10, IEEE Power Electronics Emerging Technology Award in pp. 4235–4242, Oct. 2019. [21] J.-B. Sauveplane et al., “Heavy-ion testing method and results of nor- 2021 for pioneering research and development of wide mally OFF GaN-based high-electron-mobility transistor,” IEEE Trans. Nucl. Sci., vol. 68, no. 10, pp. 2488–2495, Oct. 2021. bandgap power device-based high power density electric [22] E. Mizuta et al., “Single-event damage observed in GaN-on-Si HEMTs for power control applications,” IEEE Trans. Nucl. Sci., vol. 65, no. 8, machine drives and power converters. He initiated and pp. 1956–1963, Aug. 2018. [23] Z. Zhang et al., “Characterization of wide bandgap semiconductor served as the General Chair for the 1st IEEE Workshop devices for cryogenically-cooled power electronics in aircraft applica- tions,” in Proc. AIAA/IEEE Electr. Aircr. Technol. Symp. (EATS), 2018, on Wide Bandgap Power Devices and Applications in pp. 1–8. [24] H. Gui et al., “Characterization of 1.2 kV SiC power MOSFETs at cryo- 2013. He currently serves as the Chair for the PELS Tech- genic temperatures,” in Proc. IEEE Energy Convers. Congr. Expo. (ECCE), Sep. 2018, pp. 7010–7015. nical Committee on Aerospace Power. He is a Fellow [25] L. Nela, N. Perera, C. Erine, and E. Matioli, “Performance of GaN power devices for cryogenic applications down to 4.2 k,” IEEE Trans. Power Elec- of IEEE. tron., vol. 36, no. 7, pp. 7412–7416, Jul. 2021. [26] R. Chen and F. F. Wang, “SiC and GaN devices with cryogenic cooling,” References IEEE Open J. Power Electron., vol. 2, pp. 315–326, 2021. [27] Paschen Curve: Voltage Breakdown vs Pressure. Accessed: May 15, [1] P. Wheeler and S. Bozhko, “The more electric aircraft: Technology and 2022. [Online]. Available: http://www.highvoltageconnection.com/articles/ challenges,” IEEE Electrific. Mag., vol. 2, no. 4, pp. 6–12, Dec. 2014. paschen-curve.html [2] B. Sarlioglu and C. T. Morris, “More electric aircraft: Review, challenges, [28] A. A. Abdelmalik, A. Nysveen, and L. Lundgaard, “Influence of fast rise and opportunities for commercial transport aircraft,” IEEE Trans. Trans- voltage and pressure on partial discharges in liquid embedded power elec- port. Electrific., vol. 1, no. 1, pp. 54–64, Jun. 2015. tronics,” IEEE Trans. Dielectr. Electr. Insul., vol. 22, no. 5, pp. 2770–2779, [3] M. J. Armstrong et al. Architecture, Voltage, and Components for Oct. 2015. a Turboelectric Distributed Propulsion Electric Grid Final Report. [29] H. You, Z. Wei, B. Hu, Z. Zhao, R. Na, and J. Wang, “Partial discharge Accessed: May 15, 2022. [Online]. Available: https://ntrs.nasa.gov/ behaviors in power modules under square pulses with ultrafast dv/dt,” IEEE citations/20150014237 Trans. Power Electron., vol. 36, no. 3, pp. 2611–2620, Mar. 2021. [4] Clean Sky 2. A European Initiative. Accessed: May 15, 2022. [Online]. [30] D. Han, S. Li, Y. Wu, W. Choi, and B. Sarlioglu, “Comparative analy- Available: https://www.clean-aviation.eu/ sis on conducted CM EMI emission of motor drives: WBG versus Si [5] R. Jansen, C. Bowman, A. Jankovsky, R. Dyson, and J. Felder, “Overview devices,” IEEE Trans. Ind. Electron., vol. 64, no. 10, pp. 8353–8363, of NASA electrified aircraft propulsion (EAP) research for large subsonic Oct. 2017. transports,” in Proc. 53rd AIAA/SAE/ASEE Joint Propuls. Conf., Jul. 2017, [31] W. Perdikakis, M. J. Scott, K. J. Yost, C. Kitzmiller, B. Hall, and K. A. pp. 1–25. Sheets, “Comparison of Si and SiC EMI and efficiency in a two-level aero- [6] C. L. Bowman, T. V. Marien, and J. L. Felder, “Turbo- and hybrid-elec- space motor drive application,” IEEE Trans. Transport. Electrific., vol. 6, trified aircraft propulsion for commercial transport,” in Proc. AIAA/IEEE no. 4, pp. 1401–1411, Dec. 2020. Electr. Aircr. Technol. Symp. (EATS), Jul. 2018, pp. 1–8. [32] M. D’Antonio, C. Shi, B. Wu, and A. Khaligh, “Design and optimization of [7] L. Dorn-Gomba, J. Ramoul, J. Reimers, and A. Emadi, “Power electronic a solar power conversion system for space applications,” IEEE Trans. Ind. converters in electric aircraft: Current status, challenges, and emerging tech- Appl., vol. 55, no. 3, pp. 2310–2319, May 2019. nologies,” IEEE Trans. Transport. Electrific., vol. 6, no. 4, pp. 1648–1664, [33] N. Pallo, S. Coday, J. Schaadt, P. Assem, and R. C. N. Pilawa- Dec. 2020. Podgurski, “A 10-level flying capacitor multi-level dual-interleaved [8] N. Swaminathan and Y. Cao, “An overview of high-conversion high- power module for scalable and power-dense electric drives,” in Proc. voltage DC–DC converters for electrified aviation power distribution IEEE Appl. Power Electron. Conf. Expo. (APEC), Mar. 2020, pp. system,” IEEE Trans. Transport. Electrific., vol. 6, no. 4, pp. 1740–1754, 893–898. Dec. 2020. [34] R. C. N. Pilawa-Podgurski, “Emerging circuit techniques to utilize wide- [9] A. Barzkar and M. Ghassemi, “Electric power systems in more and bandgap semiconductors in compact, lightweight, and efficient power con- all electric aircraft: A review,” IEEE Access, vol. 8, pp. 169314–169332, verters,” in IEDM Tech. Dig., Dec. 2021, pp. 5.6.1–5.6.4. 2020. [35] D. Zhang, J. He, and D. Pan, “A megawatt-scale medium-voltage high- [10] J. He, D. Zhang, and D. Torrey, “Recent advances of power electronics efficiency high power density `SiC+Si’ hybrid three-level ANPC inverter for applications in more electric aircrafts,” in Proc. AIAA/IEEE Electr. Aircr. aircraft hybrid-electric propulsion systems,” IEEE Trans. Ind. Appl., vol. 55, Technol. Symp. (EATS), Jul. 2018, pp. 1–8. no. 6, pp. 5971–5980, Nov./Dec. 2019. [11] V. Madonna, P. Giangrande, and M. Galea, “Electrical power generation [36] Y. Cong et al., “Submodule design of a 2 kV 1 MW integrated modular in aircraft: Review, challenges, and opportunities,” IEEE Trans. Transport. motor drive for aviation applications,” in Proc. IEEE 8th Workshop Wide Electrific., vol. 4, no. 3, pp. 646–659, Sep. 2018. Bandgap Power Devices Appl. (WiPDA), Nov. 2021, pp. 345–350. [12] NASA Artemis Mission. Accessed: May 15, 2022. [Online]. Available: [37] R. L. Patterson, A. Hammond, and S. S. Gerber, “Evaluation of capaci- https://www.nasa.gov/specials/artemis/ tors at cryogenic temperatures for space applications,” in Proc. Conf. Rec. [13] Z. Zhang et al., “Characterization of wide bandgap semiconductor IEEE Int. Symp. Electr. Insul., vol. 2, Jun. 1998, pp. 468–471. devices for cryogenically-cooled power electronics in aircraft applica- [38] C. Park, O. Obadolagbonyi, and L. Graber, “Cryogenic power electron- tions,” in Proc. AIAA/IEEE Electr. Aircr. Technol. Symp. (EATS), 2018, ics: Capacitors and inductors,” IOP Conf. Ser., Mater. Sci. Eng., vol. 756, pp. 1–8. no. 1, Mar. 2020, Art. no. 012010. [14] P. Li et al., “Radiation hardness assurance of single event [39] F. Teyssandier and D. Prêle, “Commercially available capacitors at effects on components for space application,” in Proc. 4th Int. cryogenic temperatures,” in Proc. 9th Int. Workshop Low Temp. Electron. Conf. Radiat. Effects Electron. Devices (ICREED), May 2021, (WOLTE), Guarujá, Brazil, Jun. 2010, pp. 1–5. pp. 1–6. [15] NASA Issues Contracts to Mature Electrified Aircraft Propulsion Technologies. Accessed: May 15, 2022. [Online]. Available: https://www. nasa.gov/press-release/nasa-issues-contracts-to-mature-electrified-aircraft- propulsion-technologies [16] GE Aviation SiC Based Products for Aviation Applications. Accessed: May 15, 2022. [Online]. Available: https://www.geaviation.com/ systems/electrical-power [17] EPC GaN Devices for Space Applications. Accessed: May 15, 2022. [Online]. Available: https://epc-co.com/epc/Applications/SpaceApplica- tions.aspx 25 September 2022 z IEEE POWER ELECTRONICS MAGAZINE
©SHUTTERSTOCK.COM/GORODENKOFF Wide Bandgap Semiconductor-Based Power Electronics for Aviation by Fei (Fred) Wang, Ruirui Chen, and Kaushik Rajashekara T here is a growing trend in aircraft electrification, power to electric power requires architecture changes, which can reduce green-house gas emissions, more electric power, and improvements in electric power reduce audible noise, reduce maintenance generation, distribution, and conversion. There are two needs, lower cost, and improve safety. Moving main categories of aircraft electrification in aviation indus- from mechanical, pneumatic, and hydraulic try: the more-electric aircraft (MEA), which replaces sec- ondary aircraft systems traditionally supplied by pneumatic, Digital Object Identifier 10.1109/MPEL.2022.3194225 hydraulic, or mechanical power with electrical systems; and Date of publication: 28 September 2022 the electrified aircraft propulsion (EAP), which includes turbo-electric, hybrid-electric, and all-electric architectures. 26 IEEE POWER ELECTRONICS MAGAZINE z September 2022 2329-9207/22©2022IEEE
Power electronics play a crucial role for aircraft electri- of WBG devices, passive components can be reduced. As a fication. At the heart of power electronics are power semi- result, power electronics equipment efficiency, power den- conductor devices. The emergence of wide bandgap (WBG) sity, specific power, and/or temperature capability can be semiconductor devices are profoundly changing power improved. 2) Topology simplification due to lower power electronics. The superior performance of WBG devices loss, higher voltage, and higher switching frequency capa- over silicon (Si) devices can improve efficiency, power den- bility of WBG devices. For example, complex Si-based soft sity, specific power, and reliability of power electronics, the switching topologies to avoid high switching loss can be characteristics that are particularly important for aviation replaced with simpler WBG-based hard switching topolo- applications. Authors have been involved in the develop- gies. Higher voltage and faster switching WBG devices ment of several power electronics equipment prototypes offer an opportunity to replace the Si-based multilevel utilizing WBG devices for aircraft applications. All of them topologies with the simple two-level or other topologies have achieved significantly improved efficiency and spe- with reduced levels, which can still achieve the needed cific power over the comparable, state-of-the-art Si-based performance, such as low harmonics and fast dynamics. commercial equipment. On the other hand, the fast switch- Therefore, the converter design, control, and operation can ing WBG devices and the aviation environment also pose be greatly simplified, resulting in higher density, higher reli- unique challenges for the design and application of power ability, and lower cost. 3) Enabling system-level benefits. electronics. Fast switching speed can cause high dv/dt WBG-based power electronics can have better dynamic and di/dt slew rates, leading to increased electromagnetic performance and more system-level functionalities as a interference (EMI), and higher parasitics induced overvolt- result of higher switching frequency and higher control age and power loss. Aviation environment includes low bandwidth, which can lead to system-level benefits. For pressure, strong cosmic ray radiation, and wide tempera- example, high control bandwidth can enhance the stability ture range associated with the flight environmental condi- and power quality, and reduce the design margin and filter tions. Addressing these issues and requirements in design needs in a system, which can directly translate into weight and application is critical to the successful utilization and reduction in an aircraft electrical system. 4) Enabling new maximizing the benefits of WBG-based power electronics applications. With lower loss and faster switching capa- in aviation. bilities of WBG devices, some of the mechanical or other nonelectrical functions can be replaced by electrical ones. I. Benefits of WBG-Based Power Electronics Examples include solid-state transformers (SSTs), solid- Generally, the physical properties including bandgap energy, state circuit breakers (SSCBs), and high-speed motor breakdown electric field, saturation drift velocity, and ther- drives. There are Si-based SSTs and SSCBs in the market mal conductivity are all significantly higher for WBG semi- but their efficiency and related performance are gener- conductors, as compared to Si. Therefore, WBG devices can ally inferior to their mechanical counterparts. To improve achieve lower specific on-resistance, faster switching speed, their efficiency, hybrid solutions with both mechanical and higher operating temperature, and better radiation harden- electrical portions have been introduced for high power ing capability. Additionally, certain WBG devices exhibit applications, which will add weight and complexity, and superior performance at cryogenic temperatures. For exam- therefore not ideal for aviation applications. With WBG ple, GaN high electron mobility transistors (HEMTs) show devices, the power loss can be significantly reduced. In significantly reduced specific on-resistance (>4X) at cryo- addition, SSTs and SSCBs will introduce valuable system- genic temperatures [1]. Therefore, WBG devices are advan- level benefits. For example, SSCBs can interrupt fault cur- tageous for aviation applications, where cosmic radiation rents at least an order of magnitude faster, in less than and extreme temperature can be a concern. Also, for avia- hundreds of microseconds instead of milliseconds or tion applications, high efficiency, high power density, and high specific power of power electronics are essential. The benefits of utilizing WBG Generator devices in power electronics can be realized in four ways. 1) Direct substi- VF HV AC bus tution of Si devices with WBG devices. AC/AC AC/DC AC/DC Lower on-state resistance, faster CF LV AC bus (ATRU) (TRU) switching speed, and less diode reverse HV DC bus LV DC bus recovery of WBG devices can lead to lower power loss and therefore higher DC/AC DC/AC efficiency. Together with higher oper- HV AC LV AC HV DC HV AC LV AC HV AC ating temperature of WBG devices, loads loads loads loads loads loads cooling needs can be reduced. More- over, with higher switching frequency FIG 1 MEA architecture. 27 September 2022 z IEEE POWER ELECTRONICS MAGAZINE
Generator HV AC bus AC/DC HV DC bus DC/AC DC/AC DC/DC LV DC bus DC/AC HV AC HV AC HV DC Propulsion fans LV AC LV DC loads loads loads (a) loads loads Generator HV AC bus Energy storage system AC/DC HV DC bus DC/AC DC/AC DC/DC LV DC bus DC/AC HV AC HV AC HV DC Propulsion fans LV AC LV DC loads loads loads (b) loads loads Energy storage system HV DC bus DC/AC DC/AC DC/DC LV DC bus DC/AC HV AC HV DC Propulsion fans LV AC LV DC loads loads loads loads (c) FIG 2 Examples of EAP-based electrical architecture. (a) Turbo-electric architecture. (b) Series hybrid-electric architecture. (c) All-electric architecture. 28 IEEE POWER ELECTRONICS MAGAZINE z September 2022
Dr C1 Di Input Filter Protection AC Load C2 Dn FIG 3 AC–AC converter system diagram. longer needed for mechanical breakers, which will lead electric propulsion architectures. Figure 2 shows examples to reduced design margins needed for aircraft electrical of the electrical architectures for EAP [2]. Several ac–dc, system components like cables, capacitors, and inductors. ac–ac, dc–ac, and dc–dc converters are required depend- These system-level benefits, together ing on the main bus configuration with much reduced power loss, will and the propulsion technology. Note justify the applications of WBG- Clearly, WBG-based that for EAP, distributed propulsion based SSTs and SSCBs, especially for can be easily achieved with multiple aviation applications. The high-speed power electronics can fans distributed on the aircraft for a motor drive will be a key enabler for be a critical enabling more effective propulsion, and each aviation electrification, where the fan is driven by its own dc/ac inverter fundamental frequency is high and technology for avia- motor drive. Some large EAP aircraft the high-speed motor is preferred tion electrification, are under investigation. For example, for smaller size and lower weight. It NASA’s single-aisle STARC-ABL and would be challenging to realize a Si- with their benefits N3X airplane projects aim for dc/ac based high-power high-speed motor both at the equipment inverters rated at a minimum of 1 MW drive without incurring high switch- with a dc bus level between 1000 and level and the system ing loss and/or using some complex 3000 V [3]. multilevel topologies. level. Various types of faults can occur in the aircraft electrical system, such II. Examples of WBG-Based Power as short circuit, overload, and arc- Electronics for Aviation ing. Protection devices are required Clearly, WBG-based power electronics can be a critical to isolate and clear faults, and to ensure safe flying condi- enabling technology for aviation electrification, with their tions. Mechanical circuit breakers are still predominantly benefits both at the equipment level and the system level. used in conventional aircraft. However, they are not This section overviews power electronics in MEA and EAP suitable for systems with high dc voltages. On the other applications, and presents several WBG-based power elec- tronics development examples for these applications, mainly from the authors’ experience. A. Power Electronics in Aviation FIG 4 10 kW SiC JFET-based ac-dc-ac converter prototype. MEA technologies have been implemented in large com- mercial aircraft, including Boeing 787 and Airbus A380. Fig- ure 1 shows a typical electrical architecture of the MEA [2]. The variable frequency (VF) high voltage ac (HVAC) bus is rated at 115 V and 360–800 Hz (A380 case), or 230 V ac and 360–800 Hz (B787 case). The constant frequency (CF) low voltage ac (LVAC) bus is rated at 115 V and 400 Hz. The high voltage dc (HVDC) bus is rated at 270 VDC (A380 case) or 540 VDC (B787 case). The low voltage dc (LVDC) bus is rated at 28 V. EAP is the next step for aviation electrification and is gaining much research and development interest. Turbo- electric, hybrid-electric, and all-electric are the three main 29 September 2022 z IEEE POWER ELECTRONICS MAGAZINE
AL + K1 B C C 28 V M 50 A FIG 5 AC–DC converter system diagram. C – 270V K2 5.5A P S1H & S3H S1H S3H S2H S2H O iL S2L S1L & S3L S3L S2L N S1L FIG 7 Phase-leg of the 3L-ANPC converter and corresponding modulation. FIG 6 1.5 kW GaN-based ac–dc converter prototype. frequency was selected to be 70 kHz as it is the optimal point for the overall weight, in particular, considering the hand, SSCBs can provide fast protection and be adapted EMI filter weight reduction. The 70 kHz switching fre- to protect either ac or dc circuits. Traditionally, SSCBs quency was enabled by the SiC devices. available are mostly rated at 28 V dc and several hundred amperes, or 270–540 V dc and several tens of amperes Figure 4 shows the converter hardware. One innovation with limited efficiencies. With the huge increase in power of this converter is the SiC JFET modules that were custom and voltage ratings, especially in the case of EAP, higher packaged with planar structure and are capable of operating current capabilities and corresponding breakers at high at 250 °C junction temperature. The prototype was tested ver- dc voltage are needed. ifying key performance requirements including compliance with the power quality and EMI standards. With the ambient B. Examples of WBG-Based Power Electronics temperature designed for 65 °C, the prototype achieved > 95% for MEA and EAP efficiency and 3.59 kW/kg specific power, which was about an order of magnitude lighter than the commercially available 1) 10 kW SiC-based high power density ac-fed motor drive Si-based ac-fed motor drives at the time. for MEA. A 10 kW high density three-phase ac–dc–ac converter was 2) 1.5 kW GaN-based high power density ac–dc universal developed more than a decade ago using the first available charger for MEA. SiC devices at the time, the 1.2 kV normally-on SiC junc- A 1.5 kW high density ac/dc converter utilizing 650 V GaN tion-gate field-effect transistors (JFETs) and SiC Schottky HEMTs was designed as a universal battery charger for diodes [4]. As shown in Figure 3, the converter topology potential aircraft applications. As shown in Figure 5, the consists of a three-level Vienna-type rectifier as an active topology is based on a three-level Vienna-type rectifier and a front-end with a two-level voltage source inverter. Note that three-level dual output dc–dc converter. The ac voltage is a protection circuit was added on the dc link to take care of 115 or 235 V rms with 360–800 Hz frequency. The dual dc the potential failures of the normally-on JFETs. This topol- output are 28 V/50 A (range 20–33.6 V) and 270 V/5.5 A ogy was selected as it can lead to a higher specific power. (range 180–302 V). The ac phase voltage was 235 V rms with 360–800 Hz fre- quency, similar to that of Boeing 787. The switching The prototype of the hardware with both power stage and EMI filters, shown in Figure 6, was tested under full power operation. The hard switching ac–dc stage achieved 30 IEEE POWER ELECTRONICS MAGAZINE z September 2022
97.9% efficiency at 112.5 kHz switching frequency and coupled inductors to achieve 1 MW power while reduc- 95.3% efficiency at 450 kHz switching frequency. The LLC ing harmonic ripples and EMI noise. Dc and ac side EMI and buck modes of dc/dc stage achieved 95.1% efficiency filters are employed to meet DO-160 standards on both and 97.8% efficiency, respectively. The specific power is sides. Figure 8 shows the system configuration of the 1 2 kW/kg. MW inverter. 3) 1 MW SiC-based high power density cryogenically-cooled As mentioned above, GaN HEMTs exhibit excellent dc–ac converter for EAP. performance at cryogenic temperatures. However, in A 1 MW inverter was developed for future EAP applica- order to build a MW-level inverter, too many discrete GaN tions utilizing cryogenic cooling [5]. This inverter is dc- HEMT devices need to be paralleled since there were no fed from ±500 V bus and capable of three-phase output commercial GaN modules available. Even with the com- up to a fundamental frequency of 3 kHz. The inverter uti- mercial modules, their package is not built to operate at lizes a three-level active neutral point clamped cryogenic temperatures. As a result of these practical (3L-ANPC) topology, with one of its three phase-legs and limitations, the 900 V/800 A SiC MOSFET power module corresponding low-loss modulation scheme shown in was adopted. Figure 7. Two 500 kW inverters are paralleled through Figure 9 illustrates the 1 MW inverter system layout and Figure 10 shows the actual hardware. The EMI filters + Three-Level Coupled AC EMI Motor – ANPC Inductors Filter DC EMI Three-Level Filter ANPC + – FIG 8 1 MW inverter system configuration. Liquid tubing AC Output Control AC EMI Filter Gas tubing Inverter #2 Coupled Inductor Inverter #1 DC EMI Filter FIG 9 Integrated cryogenically cooled 1 MW inverter. DC Input 31September 2022 z IEEE POWER ELECTRONICS MAGAZINE
ACDM Coupled DCCM inductor SSPC is shown in Figure 11. Two SiC inductors inductors Inverter #1 modules are paralleled for the 500 A rated operation condition. Inverter #2 Control board The SSPC prototype as shown in Figure 12 was fully tested at rated conditions with protection functions verified. The overall loss is 2400 W, which corresponds to an efficiency of 99.52%. The total weight with and without enclosure are 4.45 and 3.16 kg, respectively, corresponding to specific power of 112.4 and 158.2 kW/ kg. The power rating and the specific power are both significantly higher than the previously reported SSPCs. FIG 10 1 MW SiC-based cryogenically cooled inverter prototype. III. Challenges and Solutions of WBG-Based Power Electronics for itvs,ea Energy absorption Aviation itvs,ov TVS diode While WBG devices can significantly Overvoltage clamping improve power electronics, to fully TVS diode utilize their superior characteristics poses unique challenges and, in many cases, requires iload + id – – comprehensive new design approaches. In particular, + vgs these characteristics include high switching frequency, S1 vds S2 high dv/dt, high di/dt, and high/low temperatures. Avia- tion applications certainly desire to fully utilize WBG FIG 11 Bi-directional dc SSPC topology. capabilities and also need to consider special operation requirements, including EMI standard compliance and are directly cooled with liquid nitrogen while the inverter high altitude environment. Special considerations are power stage is cooled with cold gaseous nitrogen. The gas- needed for power electronics design with WBG devices eous nitrogen is used to regulate the SiC MOSFET junction in order to apply them effectively and reliably for avia- temperature to be around room temperature at full load for tion. Several key aspects on WBG-based power electron- better loss performance, and also to avoid the SiC MOSFET ics design challenges and potential solutions are module temperature to be too low due to the packaging discussed in this section. limitations. A. Cross-Talk and Short Circuit Protection The 1 MW prototype was tested at full load opera- High dv/dt during a fast switching transient of a WBG device tion. The inverter half load efficiency is above 99% and will affect its complementary device in the same phase-leg the weight is 55.6 kg corresponding to a specific power of and this interaction between two switches is termed cross- 18 kW/kg, which provides a promising solution to achieve talk. Cross-talk is a clear hazard for the safe operation of high specific power and high efficiency for future EAP WBG devices, with their lower threshold voltage, lower neg- applications. ative gate breakdown voltage, and faster switching speed. 4) 1 kV/500 A SiC-based high power density solid-state power To suppress cross-talk without sacrificing fast switch- controller (SSPC) for EAP. ing, gate assist circuits including gate impedance control The SSPC is a SSCB plus intelligence for fault detection, and gate voltage control were developed [7]. In general, diagnostics, and management. A 1 kV/500 A dc SSPC for dv/dt can be reduced through intelligent gate control or future EAP utilizing 1.2 kV SiC MOSFET was developed soft switching circuits. For example, the gate driving volt- [6]. The common source SiC module HT3220 from Wolf- age can be programmed to a specific pattern that results speed intended for bidirectional applications was selected in a smoothed drain–source voltage of the switching as the main switch. The main circuit topology for the device. This requires a programmable gate driving volt- age or impedance, e.g., by switching on/off multiple gate resistors, multilevel gate voltage or current source-based gate drivers. Compared with Si devices, the short circuit protection of WBG devices is more challenging. Because of smaller 32 IEEE POWER ELECTRONICS MAGAZINE z September 2022
chip area and higher current density, SiC MOSFETs and can have multiple switching commutation loops, which GaN HEMTs have poorer short circuit withstand capability can make the overvoltage issue more severe and compli- compared with Si devices. Si devices usually have a >10 µs cated. Considering the 3L-ANPC inverter as an example, short circuit withstand time, while the typical short circuit both short loop (consisting of two switches, e.g., S3L and withstand time of SiC MOSFETs is several microseconds [8] S1L in Figure 7) and long loop (consisting of four switches, and for GaN HEMTs it is several hundreds of nanoseconds e.g., S3H, S2H, S2L and S1L) exist. For the modulation scheme [9], [10]. As a result, WBG devices require faster response shown in Figure 7, some devices (e.g., S1L and S3L) switch of their protection circuits. Under high dv/dt and di/dt of at high frequency and some (e.g., S2L and S2H) switch at line WBG devices, it is challenging for a short circuit protec- frequency. The switching commutation between two high tion scheme to achieve fast response time and strong noise switching frequency devices in the short loop (e.g., S1L and immunity simultaneously. One robust scheme is desatura- S3L) will also induce overvoltage on the off-state nonactive tion-based protection with optimized circuit scheme and line switching frequency device in the long loop (e.g., S2H). parameters were proposed for SiC MOSFET short-circuit The line switching frequency device usually experiences protection [11]. A three-step short-circuit protection strat- higher overvoltage than the high switching frequency egy was developed for GaN HEMTs [12]. First, an ultrafast device as the long loop usually has larger loop inductance detection circuit detects the sudden phase-leg voltage dip than the short loop. The nonlinearity of the device output when short circuit occurs. Then an active gate voltage capacitance has significant influence on the overvoltage clamping circuit lowers the gate voltage to limit short-cir- level. The modulation shown in Figure 7, which keeps the cuit current. Finally, the desaturation-based protection cir- nonactive high switching devices (e.g., S1H and S3H) in the cuit turns-off the device. negative half line cycle off, will build some initial voltage on the off-state line switching frequency device (e.g., S2H B. Overvoltage in Figure 7) before the switching transient, reducing the Overvoltage on a switching device occurs during its turn-off device output capacitance nonlinearity and thus reducing transient or the turn-on transient of its complementary its overvoltage. Laminated busbar and vertical loop layout device in a phase-leg configuration. High voltage spikes dur- are preferred in the 3L-ANPC inverter to fully utilize the ing switching transients can lead to device breakdown or magnetic cancelling effect to reduce both the short loop failure. WBG devices with high switching speed capability and long loop parasitic inductances [13]. and small on-state resistance will exacerbate the issue. Good device and module packaging techniques and optimal C. Converter Interactions With Load and Source layout design to minimize loop parasitics are general Pulse-width-modulated (PWM) voltages can cause harmful approaches to reduce the overvoltage. interactions between converters and their sources/loads, such as generators, motors, cables, and transformers. For Three-level converters, such as the Vienna-type rec- example, in the case of an inverter driving a motor through tifier (Figure 3) and 3L-ANPC (Figure 7) converter, can a cable, it is well known that PWM voltages can lead to volt- be preferred topologies for high power aviation applica- age doubling at the motor terminals due to the cable trans- tions, due to their lower device rating, lower power loss, mission line effect. High dv/dt and high switching frequency and lower harmonics and EMI. However, these converters Grounding CAN communication connector Power Input Auxiliary Coolant terminals power connector supply (a) Without enclosure FIG 12 1 kV/500 A dc SSPC prototype. (a) Without enclosure. (b) With enclosure. (b) With enclosure 33 September 2022 z IEEE POWER ELECTRONICS MAGAZINE
of the WBG-based converters will exacerbate interactions which is an important EMI noise source. Four-leg con- between converters and their loads/sources. The critical verter topology can also be used for CM EMI noise elimi- cable length for voltage doubling depends on dv/dt, and will nation [17], [18]. The variable switching frequency PWM, decrease from tens of meters for Si-based inverters to only which spreads the narrow band harmonics to a wide several meters for WBG-based inverters. PWM voltages can frequency range and thus reduces the EMI noise peak, is also produce common mode (CM) voltages on motor shaft, also a potential solution. For paralleled converters, the which in turn can induce detrimental bearing current interleaving angle can be optimized to minimize EMI [19]. through parasitic capacitance and bearing lubricant break- In fact, the 1 MW inverter in Figures 8–10 adopted two down. The high dv/dt and high switching frequency of WBG- paralleled and interleaved 500 kW inverters for reduced based motor drives will increase the capacitive bearing EMI filters. current and accelerate bearing degradation. The issue can be mitigated through specially designed motor to electri- For a given attenuation requirement, techniques are cally insulate bearings from the motor frame, which will add also available to reduce size, weight, and power loss of EMI cost. The charging and discharging of the cable and load/ filters. Multistage filter topology can be utilized to achieve source parasitic capacitances during switching will intro- higher-order attenuation than single-stage topology. The duce extra switching loss, which will be exacerbated with hybrid active–passive filter can attenuate low frequency high switching frequency. noise via an active filter with small size and light weight, such that a much smaller and lighter passive filter can be Commonly used solutions to mitigate converter and designed only for high frequency noise attenuation [20]. load/source interactions due to high dv/dt include: the intel- Advanced materials, cooling, and geometry can be used ligent gate control techniques for dv/dt reduction as dis- for EMI filter size and weight reduction. For example, the cussed previously, and the dv/dt filter at the ac terminals filter inductor for the 1 MW inverter in Figure 12 utilized a of the WBG converters to limit the dv/dt seen by the load or 3-D printed housing to realize cryogenically cooled induc- source [14]. The motor terminal filter to eliminate voltage tor windings for overall filter weight reduction. reflection is also effective but less flexible. Note that the dv/dt filter will not help with high dv/dt induced converter E. High Altitude Impact internal issues such as the cross-talk. Additionally, multi- Power electronics must be designed to work under their level converters, which have lower output harmonics and intended environmental conditions. For aviation applica- lower dv/dt due to more levels in the output voltage, can be tions, they need to be designed for high altitude environ- utilized to reduce converter output dv/dt and CM voltage, ment, considering low pressure, low temperature, and albeit at the cost of increasing the number of components. high cosmic ray radiation. Low pressure will adversely affect the health of electrical insulation materials used in D. EMI Filter power electronics. Partial discharge (PD) phenomenon is In aviation applications, EMI filters are generally required a primary aging mechanism in dielectrics. A study of for power electronics equipment to attenuate EMI noise power module PD in [21] demonstrates that a void that is and to meet stringent EMI standards such as DO-160. Since harmless at sea level can turn into an additional source of EMI filters are commonly made of passive inductors and aging and couple with other voids to escalate PD intensity capacitors, they can be bulky, heavy, and lossy, and often by a factor of two or more. WBG devices with higher dv/dt contribute to 50% or more of the total equipment weight. may suffer more severe PD issues compared to Si devices For a converter with given power and voltage, the size of as PD behavior is influenced by dv/dt of the excitations. A the EMI filter is generally determined by its cutoff fre- study in [22] shows that, under square pulses with ultra- quency. WBG-based converters with high switching fre- fast dv/dt (>100 V/ns), SiC power module PD inception quency capabilities are generally beneficial to EMI filters voltage decreases with decreasing rise times if the pulses with their increased switching frequencies and correspond- are short (e.g., <300 µs). ing increased EMI filter cutoff frequencies. In fact, both the ac-fed motor drive in Figure 4 and the universal charger in Low pressure thin air at high altitude will reduce the Figure 6 took advantage of the high switching frequency air heat dissipation capability and impact the cooling sys- capabilities of SiC and GaN devices for reduced EMI filters. tem of power electronics. Cosmic ray at high altitude can increase failure-in-times (FITs) of devices, which calls for Even with much reduced EMI filters in WBG-based significant voltage derating for Si devices. As mentioned converters, they are still main contributors to overall con- earlier, one superior characteristic of WBG devices is their verter weight, size and power loss. To further reduce the better radiation hardening capability against cosmic rays EMI filters, an effective approach is the EMI noise source due to their wide energy bandgap. In this regard, the WBG- reduction, which refers to techniques of directly reducing based power electronics are ideal for aviation applications. the converter input/output EMI emission. PWM technolo- gies, such as the active zero state PWM [15] for two-level F. High and Low Temperatures converters, and CM elimination PWM [16] for three-level WBG semiconductor materials are capable of operating at converters, can be utilized to reduce the CM voltage, much higher temperatures (>500 °C) compared to Si 34 IEEE POWER ELECTRONICS MAGAZINE z September 2022
materials, which can be very valuable for aviation applica- been developed and tested in battery-powered EAP systems tions. With high temperature capability, power electronics for small aircraft, such as electric vertical take-off and land- can be placed in the harsh environment, e.g., near the jet ing (eVTOL) aircraft and unmanned aerial vehicles (UAVs). engine with an ambient temperature range between –55 °C and 225 °C, which is desirable in some cases. Another For large commercial aircraft, WBG-based power elec- benefit to operate power electronics at high temperature tronics will likely be first adopted in MEA with HVDC bus is to reduce the cooling need, as in the case of the high- voltage at several hundreds of volts and converter power density motor drive in Figure 4, which employed a custom around tens to hundreds of kilowatts, similar to the Boe- packaged module operating at 250 °C junction tempera- ing 787 case. As the next step of aircraft electrification ture. However, it is difficult to find low cost commercial moves from MEA to EAP, the required electric power will power devices with junction temperature capability >175 be increased to megawatt and tens of megawatt level. To °C. High temperature power electronics are limited by reduce the electrical system weight, especially, the cable device packaging, gate drive ICs, and passive components weight, the system voltage needs to be increased from [23]. With these limitations, the maximum ambient tem- hundreds of volts to several kilovolts. As a result, power perature capability of power electronics today is in the electronics must be capable of handling kilovolts and kilo- range of 210 °C–240 °C. amperes for aviation operating conditions. High-voltage and high-power power electronics with consideration for As presented earlier, certain WBG devices such as GaN electrical insulation, thermal, and radiation performance at HEMTs exhibit improved performance as temperature high altitude will need to be developed. High-voltage WBG decreases. The low temperature capability and superior devices, e.g., the 10 kV SiC MOSFET power modules cur- characteristics of WBG-based power electronics can also rently available only as engineering prototypes, can help to be valuable for aviation applications. They can be used in enable the high-voltage EAP system. low temperature environments, including high altitude and cryogenically cooled environments. On the other hand, low With the help of WBG devices, the specific power of MW- temperature power electronics are even less mature than level motor drives for EAP applications is approaching 20 high temperature power electronics. Commercially avail- kW/kg and the peak efficiency can be above 99%. Cryogenic able power semiconductor modules often employ silicone cooling, which can be realized by using liquid hydrogen fuel gel as encapsulant. These device modules cannot be used and liquefied natural gas as the coolant, has great potential at cryogenic temperatures as the mechanical integrity and to further reduce the weight and power loss of the WBG- electrical insulation performance of silicone gel will dete- based power electronics by taking advantage of the superior riorate significantly once the temperature is below –60 °C performance of WBG semiconductors at cryogenic tempera- [24]. Epoxy could be a promising candidate of encapsulant ture. On the other hand, high temperature capability of WBG material as most epoxies can work properly at cryogenic semiconductors can also be utilized for harsh environment temperature. Magnetic materials such as ferrite and nano- and reduced cooling needs. Materials, components, packag- crystalline materials will survive but exhibit significant ing, data, models, and standards will need to be developed performance degradation at cryogenic temperature [25]. for low and high temperature power electronics. Other auxiliary components such as commercially available gate driver ICs, isolated power supplies, and sensors are not The EAP in large aircraft will likely adopt distributed designed for extremely low temperature and their function- propulsion architecture. Integrated power electronic ality at cryogenic temperature need further investigation. inverters with electric motors can help to further increase As in the case of high temperature WBG power electronics, system power density and specific power. The integrated much research and development work are needed for low motor drive system can have shared mechanical structure temperature WBG power electronics as well. and cooling for the inverter and motor, and reduced con- nections to enable overall weight and volume savings. The IV. Future Perspectives superior temperature capability of the WBG devices will help such integration. For both the regular motor and the With their compelling benefits at both the equipment and cryogenically cooled superconducting motor, the high or system level, WBG-based power electronics are expected to low temperature capability of the WBG semiconductors dominate future aviation electrification applications. While can be utilized in the converter and motor integration. SiC and GaN devices are still being developed and evolving rapidly, the low voltage (1200 V or below for SiC and 650 V With the fast dynamics enabled by fast switching speed or below for GaN) devices are already quite mature in terms and high switching frequency, WBG-based power electron- of performance, cost, and reliability. These commercially ics are also expected to be designed and utilized for system- available devices have been successfully employed in many level functions and benefits in future aviation applications. terrestrial applications, including relatively high-power The benefit of the SSCB or SSPC to quickly interrupt a applications, such as electric vehicles, photovoltaic invert- fault is already explained. The other functions and benefits ers, battery energy storage systems, datacenter power sup- include but not limited to stability enhancement, power plies., and more. For aviation, SiC-based motor drives have quality improvement, transient ride through, and coordi- nated protection. All these can translate to reduced design margin needs and reduced system weight. 35 September 2022 z IEEE POWER ELECTRONICS MAGAZINE
This article has focused on aviation applications. Con- [3] R. Jansen, C. Bowman, A. Jankovsky, R. Dyson, and J. Felder, “Overview ceivably, many of the same WBG-based power electron- of NASA electrified aircraft propulsion (EAP) research for large subsonic ics technologies can also be applied to future electrified transports,” in Proc. 53rd AIAA/SAE/ASEE Joint Propuls. Conf., Atlanta, spacecraft applications, where the requirements on power GA, USA, Jul. 2017, p. 4701. density, specific power, efficiency, reliability, and the oper- [4] R. Lai et al., “A high-power-density converter,” IEEE Ind. Electron. Mag., ating environment for power electronics will be even more vol. 4, no. 4, pp. 4–12, Dec. 2010. challenging. WBG-based power electronics can also play [5] R. Chen et al., “A cryogenically-cooled MW inverter for electric aircraft an important role for satellites, future space stations, lunar- propulsion,” in Proc. AIAA/IEEE Electr. Aircr. Technol. Symp. (EATS), New based electric power systems, and other space exploration Orleans, LA, USA, 2020, pp. 1–10. applications. [6] Z. Dong, R. Ren, and F. Wang, “Development of high-power bidirectional DC solid-state power controller for aircraft applications,” IEEE J. Emerg. Acknowledgement Sel. Topics Power Electron., early access, Dec. 31, 2022, doi: 10.1109 /JESTPE.2021.3139903. This article is in part based on the work sponsored by Boe- [7] Z. Zhang, F. Wang, L. M. Tolbert, and B. J. Blalock, “Active gate driver for ing, NASA, and ARPA-E. The contributions of the colleagues crosstalk suppression of SiC devices in a phase-leg configuration,” IEEE and students from The University of Tennessee, Knoxville Trans. Power Electron., vol. 29, no. 4, pp. 1986–1997, Apr. 2014. and Virginia Tech are acknowledged. [8] Z. Wang et al., “Temperature-dependent short-circuit capability of silicon carbide power MOSFETs,” IEEE Trans. Power Electron., vol. 31, no. 2, About the Authors pp. 555–1566, Feb. 2016. [9] H. Li et al., “Robustness of 650-V enhancement-mode GaN HEMTs under Fei (Fred) Wang ([email protected]) (Fellow, IEEE) has various short-circuit conditions,” IEEE Trans. Ind. Appl., vol. 55, no. 2, been a Professor and the Condra Chair of Excellence in pp. 1807–1816, Mar. 2019. Power Electronics at the University of Tennessee, Knoxville [10] R. Chen, Z. Yang, and F. Wang, “Overcurrent and short-circuit capability (UTK), USA, since 2009. He is a Founding Member and the experimental investigation for GaN HEMT at cryogenic temperature,” in Proc. Technical Director of the NSF/DOE Engineering Research IEEE Appl. Power Electron. Conf. Expo. (APEC), Jun. 2021, pp. 382–388. Center CURENT. He also holds a joint appointment with [11] Z. Wang, X. Shi, Y. Xue, L. M. Tolbert, F. Wang, and B. J. Blalock, “Design Oak Ridge National Laboratory. Prior to UTK, he also and performance evaluation of overcurrent protection schemes for silicon worked at GE and Virginia Tech. His research interests are carbide (SiC) power MOSFETs,” IEEE Trans. Ind. Electron., vol. 61, no. 10, mainly on WBG power electronics, and power electronics pp. 5570–5581, Oct. 2014. for grid and transportation applications. He is a fellow of the [12] X. Lyu et al., “A reliable ultrafast short-circuit protection method for U.S. National Academy of Inventors. E-mode GaN HEMT,” IEEE Trans. Power Electron., vol. 35, no. 9, pp. 8926– 8933, Sep. 2020. Ruirui Chen (Member, IEEE) has been a Research [13] H. Gui et al., “Methodology of low inductance busbar design for three- Assistant Professor at the University of Tennessee, Knox- level converters,” IEEE J. Emerg. Sel. Topics Power Electron., vol. 9, no. 3, ville, TN, USA, since 2020. He worked at FSP-Powerland pp. 3468–3478, Jun. 2021. Technology Inc., China. His research interests include WBG [14] J. He et al., “Multi-domain design optimization of dv/dt filter for SiC devices and applications, medium voltage power electron- based three-phase inverters in high-frequency motor-drive applications,” ics, cryogenic power electronics, EMI, and power electron- IEEE Trans. Ind. Appl., vol. 55, no. 5, pp. 5214–5222, Sep./Oct. 2019. ics for electrified transportation and grid applications. [15] Y. Lai, P. Chen, H. Lee, and J. Chou, “Optimal common-mode voltage reduction PWM technique for inverter control with consideration of the Kaushik Rajashekara (Fellow, IEEE) has been a dead-time effects—Part II: Applications to IM drives with diode front end,” Distinguished Professor at the University of Houston, TX, IEEE Trans. Ind. Appl., vol. 40, no. 6, pp. 1613–1620, Nov./Dec. 2004. USA, since 2016. Prior to that, he worked at GM, Delphi, [16] H. Zhang, A. V. Jouanne, S. Dai, A. K. Wallace, and F. Wang, “Multilevel Rolls-Royce Corporation, and the University of Texas at inverter modulation schemes to eliminate common-mode voltages,” IEEE Dallas, USA. His research interests include power/energy Trans. Ind. Appl., vol. 36, no. 6, pp. 1645–1653, Nov./Dec. 2000. conversion, transportation electrification, renewable [17] A. L. Julian, G. Oriti, and T. A. Lipo, “Elimination of common-mode volt- energy, and microgrid systems. He is a member of the U.S. age in three-phase sinusoidal power converters,” IEEE Trans. Power Elec- National Academy of Engineering, a fellow of the Indian tron., vol. 14, no. 5, pp. 982–989, Sep. 1999. National Academy of Engineering, and a member of the [18] R. Chen et al., “Investigation of fourth-leg for common-mode noise Chinese Academy of Engineering. He has received a num- reduction in three-level neutral point clamped inverter fed motor drive,” ber of awards, including the IEEE Medal on Environment in Proc. IEEE Appl. Power Electron. Conf. Expo. (APEC), Mar. 2019, & Safety Technologies, the IEEE Richard Harold Kaufmann pp. 2582–2588. Award for his contributions to electrification of transpor- [19] R. Chen et al., “Modeling, analysis, and reduction of harmonics in paral- tation and renewable energy, and the Global Energy Prize. leled and interleaved three-level neutral point clamped inverters with space vector modulation,” IEEE Trans. Power Electron., vol. 35, no. 4, pp. 4411– References 4425, Apr. 2020. [20] S. Wang, Y. Y. Maillet, F. Wang, D. Boroyevich, and R. Burgos, “Investiga- [1] R. Chen and F. F. Wang, “SiC and GaN devices with cryogenic cooling,” tion of hybrid EMI filters for common-mode EMI suppression in a motor drive IEEE Open J. Power Electron., vol. 2, pp. 315–326, Apr. 2021, doi: 10.1109/ system,” IEEE Trans. Power Electron., vol. 25, no. 4, pp. 1034–1045, Apr. 2010. OJPEL.2021.3075061. [21] M. Borghei and M. Ghassemi, “Characterization of partial discharge [2] L. Dorn-Gomba, J. Ramoul, J. Reimers, and A. Emadi, “Power electronic con- activities in WBG power converters under low-pressure condition,” Ener- verters in electric aircraft: Current status, challenges, and emerging technolo- gies, vol. 14, no. 17, p. 5394, Aug. 2021, doi: 10.3390/en14175394. gies,” IEEE Trans. Transport. Electrific., vol. 6, no. 4, pp. 1648–1664, Dec. 2020. [22] H. You et al., “Partial discharge behavior in power modules under square pulse with ultrafast dv/dt,” IEEE Trans. Power Electron., vol. 35, no. 36 IEEE POWER ELECTRONICS MAGAZINE z September 2022 9, pp. 8926–8933, Sep. 2020. [23] Y. Xiao, Z. Zhang, M. S. Duraij, G. Zsurzsan, and M. A. E. Ander- sen, “A review of high-temperature power electronics converters,” IEEE Trans. Power Electron., early access, Feb. 4, 2022, doi: 10.1109 /TPEL.2022.31481922019. [24] T. A. T. Vu, J.-L. Auge, and O. Lesaint, “Low temperature partial dis- charge properties of silicone gels used to encapsulate power semiconduc- tors,” in Proc. IEEE Conf. Electr. Insul. Dielectr. Phenomena, Aug. 2009, pp. 421–424. [25] R. Chen et al., “Core characterization and inductor design investigation at low temperature,” in Proc. IEEE Energy Convers. Congr. Expo. (ECCE), Sep. 2018, pp. 4218–4225.
©SHUTTERSTOCK.COM/BUTUSOVA ELENA Totem-Pole PFC Reliability and Performance Improvement With Advanced Controls by Zhong Ye, Danyang Zhu, and Hailong Yang T otem-pole power factor correction (PFC) is a current reversing prevention at input voltage drop, light- simple and highly efficient topology. It is being ning surge protection, current harmonic reduction, and ac widely used in high-density and high-efficiency crossover current spike elimination. These challenges are power supply design. However, engineers still not closely related to each other and there is no single face many design challenges, including PFC control that can solve all the design issues. This article reviews the main design challenges and provides compre- Digital Object Identifier 10.1109/MPEL.2022.3194285 hensive solutions to these issues. Most of the solutions are Date of publication: 28 September 2022 novel or are used for the first time in PFC control. These solutions are integrated into the industry’s first continuous 2329-9207/22©2022IEEE 37September 2022 z IEEE POWER ELECTRONICS MAGAZINE
conduction mode (CCM) totem-pole PFC analog controller supplies to move from platinum efficiency level to titanium IVCC1102 [1]. A 2.5 kW SiC-based totem-pole PFC proto- level. It also changes power supply design landscape since type [1] is built to demonstrate the robustness and perfor- only a small or no heatsink is needed and power density can mance improvement with the proposed solutions. be increased substantially. Introduction With WBG device cost declining rapidly, it is foreseeable that the TPPFC will become a mainstream circuit in the With increasing maturity of silicon carbide (SiC) and gal- near future. While the TPPFC is becoming more popular, it lium nitride (GaN) wide bandgap (WBG) technology and is imperative to have a reliable control to support this appli- rapid adoption of the WBG switching devices, the CCM cation. Since most TPPFCs use two Si MOSFETs to rectify totem-pole topology becomes a preferred PFC circuit used the ac input, the additional need of the gate drive compli- in high-efficiency and high-density ac–dc power converter cates the circuit control and may impact the converter’s design. The totem-pole PFC (TPPFC) is of the simplest cir- reliability. On the whole, there are still five aspects posing cuit structure among several available bridgeless PFC topol- significant challenges to the circuit design and control: ogies [2]–[6]. A simplified totem-pole PFC circuit diagram is 1) boost inductor current reversing prevention at input shown in Figure 1. Note that the bridge consisting of D1, D2, D3 and D4 is for ac input surge and inrush protection. They voltage drop; do not conduct current during normal operation. 2) ac crossover current spike elimination; 3) lightning surge protection and control; Figures 2 and 3 show the equivalent TPPFC circuit in posi- 4) THD reduction and fast step-load response; and tive and negative ac cycles. Q3 and Q4 are used to rectify the 5) control robustness under Vac severe distortion. ac input and switch at the ac line frequency. As such, silicon (Si) MOSFETs are often used for cost reason. Q2 and Q3 are These five aspects are not closely related and will be dis- WBG devices and operate at high switching frequencies. cussed and concluded separately in each of the following five sections. Compared with a traditional PFC shown in Figure 4, the TPPFC has only two semiconductor devices instead of Boost Inductor Current Reversing Prevention three conducting in its current paths. By replacing the two at AC Drop rectifier diodes with one synchronous MOSFET (SynFET) in the current paths, the TPPFC can gain over 0.5% and 1% A traditional PFC’s current is regulated by a multiplier- efficiency for high line and low line inputs, respectively [7], based average-current loop, as shown in Figure 5. The [8]. 1% seems less significant, but the power loss is actually current loop’s compensator is located after the current reduced by 50% for a converter to increase its efficiency command multiplier in the signal path. Abrupt change of from 98% to 99%. It is the most effective step for power Vac doesn’t appear at the compensator’s output right away Si MOS SiC/GaN Q1 Si MOS SiC/GaN Q3 A Co Q3 Q1 Vo Vac IL IL A Co RL lac Vac D1 D3 L RL EMI lac Filter L D2 D4 Q4 Q2 Q4 Q2 FIG 1 Totem-pole PFC circuit diagram. FIG 3 Equivalent TPPFC circuit in ac negative cycle. Si MOS SiC/GaN D5 Do Q3 Q1 Vo IL Co Vo RL L RL Vac IL A Co Q1 L Vac D1 D3 EMI lac Filter Q4 Q2 D2 D4 IL FIG 2 Equivalent TPPFC circuit in ac positive cycle. FIG 4 Traditional PFC circuit diagram. 38 IEEE POWER ELECTRONICS MAGAZINE z September 2022
due to the compensator’s bandwidth limit. That means feathers the PWM duty cycle and regulates the PFC’s that the PFC’s duty cycle cannot be updated in time to current to be in phase with Vac. This direct feedforward maintain voltage-second balance anymore. A totem-pole control evidently works very well to prevent the current PFC with ac input synchronous rectification is essentially reversing but this application has not been reported before. a bidirectional converter. Vac’s sudden dropping to zero at The proposed control diagram is shown in Figure 6, where ac outage could cause a large reverse current [9]. The C is the sensed Vac signal and is used for the feedforward reverse current discharges the output capacitor and control. Figure 7 is the 2.5 kW TPPFC prototype. Figure reduces the hold-up time, which is the most needed for 8 shows the ac voltage and current waveforms at ac drop some applications, such as servers to backup critical data. test. It can be seen clearly that there is no reverse current Moreover, the reverse current is not controllable; the cur- occurring. rent could reach a catastrophic level and damage the power switches. AC Crossover Current Spike Elimination Van de Sype [10] and Chen and Sun [11] introduce a Unlike a traditional PFC where the input ac current is rec- direct Vac feedforward control. The control, based on volt- tified naturally by a diode bridge, a totem-pole PFC with age-second balance, computes PFC PWM duty cycle with ac synchronous rectification MOSFETs (SynFETs) com- instantaneous input Vac and output Vo values. pletely relies on its precise control. Alternating the two SynFETs on and off too early or too late can result in a In ideal case, the duty cycle is Vac short circuit. To mitigate this issue, a deadtime should be inserted, during which all four MOSFETs are turned Don(t) = 1– |Vac(t)| / Vo. off. However, a large deadtime can lead to a flat zero cur- rent at ac crossover area, which contributes to the third With the same Vac and Vo sensing scaler and the pro- order harmonic and deteriorates the THD. Furthermore, if posed feedforward gain KF = 2 [1], the current loop’s the EMI filter’s residual current is not low enough, it can compensator output maintains almost unchanged. It just + Gid = ^iL / d^ Gvi = V^o / ^iL |Vac| iL L iD VO – Q C d R Current Loop Voltage Loop Kl Comp Traditional – gmi – Controller + KVI +OTA D I_Comp KVO C Multiplier Vramp X/X gmv – OTA V_Comp + Vrms2 Vref FIG 5 Traditional PFC control loop. 39September 2022 z IEEE POWER ELECTRONICS MAGAZINE
+ Gid = ^iL / d^ Gvi = V^o / ^iL |Vac| iL L iD VO – Q C d R Kl = Current Loop 5.5 – + Voltage Loop Comp IVCC1101/2 KVI – gmi – KVO +OTA + Duty-Ratio I_Comp C KF = 2 1.4V Vramp = 4V C gmv – OTA KL GSH V_Comp + 2.0V Duty cycle Low line: 1 2xfac feed forward High line: 0.3 FIG 6 Average mode current loop with direct input voltage duty cycle feed forward. FIG 7 2.5 kW TPPFC prototype. cause a current ringing when the four MOSFETs are FIG 8 AC voltage and current waveforms at Vac drop test (test turned off simultaneously, as indicated in Figure 9(a). A conditions: Vac = 110 V, Vdc (=Vo) = 400 V, Po = 1.25 kW). proper deadtime, such as 150–200 μs, can minimize the current distortion and give a good deadtime margin for crossing over, Q3’s Coss, as shown in Figure 2, has already safe operation. To reduce the SynFETs’ conduction loss, been fully charged to the bus voltage Vo, the duty cycles of Q1 low Rds_on MOSFETs are often used. However, the low- (main FET) and Q2 (freewheel FET) are near 1 and 0 respec- Rds_on Si MOSFETs always come with a large Coss. The tively. After the Vac crossover point, Q2 becomes the main Coss stores significant energy and can cause a large cur- FET and its duty cycle jumps from near 0 to near 1, which rent spike when it is discharged to the boost inductor essentially applies the Coss voltage, Vo, directly across the abruptly, as shown in Figure 9(a) [12], [13]. boost inductor. As a result, a large current spike can occur. Figure 9(a) shows the key signals during Vac crossing over from a positive half cycle to a negative one. Just before Vac 40 IEEE POWER ELECTRONICS MAGAZINE z September 2022
To mitigate this issue, a soft PWM +Vth Dead Band duty cycle startup can be used to discharge the Coss and ramp up the ac current gradually. During the crossover period, the control Inductor Crossover –Vth loop is frozen to avoid potential Current point compensator windup. Therefore, the PWM duty cycle has to ramp up in an open loop. In order to ramp the ac current up smoothly Q4(SynFET_L) EMI filter current ringing Large current ripple and linearly discharge the Coss, it can be concluded with the voltage- D ramping up at switching frequency Q3(SynFET_H) second balance rule that linearly Q1 off ramping up the duty cycle should be used. Figure 9(b) shows the Q2 off Q2 off duty cycle ramps up linearly at a higher switching frequency and switching frequency narrower Vac crossover range. (a) A higher ramping up switch- +Vth Dead Band ing frequency is able to reduce the current ripple and smooth the crossover current. Figure 10 shows the test waveform of Coss –Vth being discharged with duty cycle linearly ramping up at around 200 Inductor Current Crossover kHz, namely about three times point of the normal 65 kHz switching frequency. To ensure VSW (Chn Q4(SynFET_L) Smooth crossover 3) can be fully discharged to current zero volts, the duty cycle should D ramping up at a higher Q3(SynFET_H) be ramped up to 100% (or near switching frequency 100%) before the soft-start period Q1(High Side) Q1 off Q2 off expires. The number of the soft- Q2(Low Side) Q2 off start switching cycles required is dependent on the maximum switching frequency allowed current spike. For the (b) recommended 100 µs soft-start period, 10 to 20 switching cycles FIG 9 (a) Current waveform and signal transition during Vac crossover. (b) Optimal Vac cross- is sufficient to smooth out the cur- over control. rent. More switching cycles can result in a better result. However, no further improvement was observed when more switching cycles are used. Figures 10 and 11 are the waveforms tested at 220 Vac input and 2.5 kW output. Figure 11 shows the zoom- out current waveform. It can be seen that a smooth crossover current is achieved. FIG 10 AC crossover soft start waveforms from a positive ac Lightning Surge Protection Control cycle to a negative ac cycle. Since lightning surges could hit a power grid at any ac phase angle and polarity, PFC controllers must be able to detect the Vac with minimum delay and execute a right control logic to avoid circuit damage. Lightning surge test is one of the toughest challenges to the reliability of a TPPFC circuit. Unfortunately, the problem seems to be more like an engineering issue than an academic topic. There are rare good articles found on this topic. 41 September 2022 z IEEE POWER ELECTRONICS MAGAZINE
FIG 11 Clean ac current waveform at high line. FIG 15 Out-of-phase lightning surge test. Si MOS SiC/GaN When a lightning surge voltage has the same polarity of the Vac input, as shown in Figure 12, it Vac D1 D3 Q3 Q1 Vo appears to be an ac over voltage. Diodes D2 and D3, Vac + in a positive ac cycle as an example, clamp the Vac IL A Co to the output capacitor Co. Depending on the surge EMI lac L RL energy, the controller is normally be able to detect – Filter one of or both Vac over voltage and Vo over voltage, and all the four switches are turned off to avoid cir- D2 D4 Q4 Q2 cuit damage. FIG 12 Lightning surge in phase with Vac. When the lightning surge voltage has the oppo- site polarity of the Vac input, the case becomes Vac Si MOS SiC/GaN more complicate. Vac D1 D3 Q3 Q1 As an example shown in Figure 13, since Q4 – Co is on for positive ac half cycles, the surge voltage IL L A always causes a short circuit initially until the EMI lac Q2 Vo negative Vac voltage is detected and Q4 is turned + Filter off. Even though the Vac is shorted by Q4 and D2, Short circuit the Vac is still able to change its polarity due to RL EMI filter’s impedance. As soon as the Vac polar- D2 D4 Q4 ity changing is detected, the controller executes a regular ac crossover control procedure-turning FIG 13 Lightning surge out of phase with Vac. off the four MOSFETs and then soft starting. Thanks to the fast Vac detection, the ac SynFET FIG 14 In-phase lightning surge test. Q4 only needs to stand the surge current for a short period, such as a few microseconds. After the four switches are turned off, the surge protec- tion diodes D1 and D4 take over the surge current and clamp the Vac surge voltage to the output capacitor, which avoids overstress on the four switches. Figures 14 and 15 show the key waveforms of the in-phase and out- of-phase lightning surge tests. The tests were conducted under 1500 V surge voltage with 2 Ω impedance without using MOV surge protection devices. Channel 1 (dark blue) is Vac measured at the EMI filter’s X cap; Channel 2 IAC (light blue) is the input ac current; Channel 3 GDL (green) is the low-side high-frequency switch’s gate sig- nal; Channel 4 FSL (purple) is the low-side low-frequen- cy’s gate signal. The test results show the fast and precise response of the controller. The whole responding proce- dures are illustrated in detail in the figures. 42 IEEE POWER ELECTRONICS MAGAZINE z September 2022
Pin Po AC Crossover lac Vac Track N Hold Vo Vo_avg 0 FIG 19 0–2.5 kW full-load step response test (test conditions: Vac = 220 V, Vdc = 400 V). FIG 16 Vo average value sensing with second order harmonic Vo is sensed at Vac crossover points by a track-and-hold rejection. circuit. The value is exactly the average Vo when PF = 1, as shown in Figure 16. For most PFC converters, their PFs are Non-Linear Track N Hold VO near 1 at heavy loads. At light loads, the PF may reduce, but Gain feedback since Vo ripple becomes smaller in the meantime, the sensed voltage still well represents the average Vo. In this way, there VAO le gmv – is no harmonic injected into the voltage loop. Since the volt- age error signal is updated in each of a half ac cycle, the volt- C3 C1 + 2V AC Crossover + age loop is slowed down, which can deteriorate the step load R2 DC Mode + response. To minimize Vo overshoot and undershoot at step Non-Linear Mode + responses, a nonlinear voltage loop is used to boost the volt- Burst Mode FIG 17 Track-and-hold circuit and nonlinear control diagram. age loop response when the Vo error exceeds the set value [14], THD Reduction With Second Harmonic Rejection Control [15]. Figure 17 depicts the detail of the voltage loop compensa- tor and the track-and-hold circuit block shown in Figure 6. To achieve a good THD, the traditional PFC control has to lower the voltage loop’s bandwidth to attenuate the second When the nonlinear control is activated, the track-and- harmonic more. However, a low-bandwidth voltage loop hold circuit is bypassed, so there is no detection delay always leads to a poor step-load response, or vice versa, the of Vo error. The tests show that low THD and fast step response can be achieved with the control. Figures 18 and control can have a good step response but at the cost of 19 show the excellent THD and Vo step response results, THD [17], [18]. To solve this dilemma, a second order har- compared with the data in [17] and [18]. monic rejection Vo sensing scheme is introduced to acquire the Vo’s average value. Control Robustness Under Vac Severe Distortion It is a major concern and a design challenge for engineers to develop a reliable totem-pole PFC control. 30 In different application scenarios, the input ac voltage can be distorted more or less in 25 terms of shapes and amplitudes [16]. Under 230V any circumstances, the control must main- 20 110V tain a correct logic for the circuit’s safe operation. It is desired to maintain a unity THD / % power factor, namely that the ac current is 15 in phase with Vac and the PFC input appears to be an ideal resistive load. Thanks 10 to the direct Vac feedforward control afore- mentioned, the PFC duty cycle can follow Vac variation and be adjusted instanta- 5 neously. The current loop compensator just feathers the PWM duty cycle in a small 0 750 1000 1250 1500 1750 2000 2250 2500 amplitude but with a much higher equiva- 0 250 500 Output Power / W lent bandwidth. Figures 20 and 21 show two test results of 32 Vac distortion standard FIG 18 THD test data. tests [16]. 43 September 2022 z IEEE POWER ELECTRONICS MAGAZINE
FIG 20 2nd, 5th, 7th, and 8th mixed harmonic injection test. and the Ph.D. degree in power electronics from the Univer- FIG 21 1 kHz harmonic injection test. sity of Toledo, USA. He is a Senior Member of IEEE and the The tests demonstrate the PFC control can achieve CTO of Inventchip Technology. He was with Texas Instru- nearly unity power factor even with severely distorted Vac input. The tests also show the robustness of the Vac cross- ments as the System and Application Manager, and with over control logic. The circuit is able to operate safely and reliably with the abnormal multiple-time Vac crossing over. Lucent Bell Labs/Tyco Power Systems as the Technical Conclusion Manager and DMTS, working on motor drive, power supply The five most challenging aspects of the totem-pole PFC design, power management IC, and wide bandgap power design were discussed and solutions were proposed and vali- dated by using the new PFC controller IVCC1102. The direct device development. Vac feedforward control was proven for the first time to be an effective way to prevent the boost inductor current Danyang Zhu ([email protected]) reversing; the control with proper Vac and Vo scalers demon- strated an excellent current loop response and enabled the received the B.S. and M.S. degrees in electrical engineer- PFC to maintain nearly unity power factor even with severely distorted Vac input. Soft-start PWM switching at a ing from Tsinghua University, Beijing, China, in 2000 and higher frequency is able to smooth out ac crossover current. The same ac crossover control was tested with high order ac 2002, respectively. He is leading IC products development harmonic injection and ac line lighting surge, and was proven to be very robust. It was able to maintain a correct for InventChip Technology. He was with Fairchild Semi- control logic even under line lightning surge and abnormal multiple-time Vac crossing-over conditions. The combination conductor and Texas Instruments, working on IC products of second harmonic rejection control and nonlinear control achieved both excellent THD and step load response. development. About the Authors Hailong Yang ([email protected]) received Zhong (John) Ye ([email protected]) received the B.S. and M.S. degrees from the Inner Mongolia University of the B.S. and M.S. degrees from Fuzhou University, China, Technology, China. As an exchange student, he worked with the Energy Systems Laboratory, Mie University, Japan, for one year. He is an Applications Engineer with Inventchip Technology. References [1] 2.5 kW Totem-Pole PFC Reference Design and IVCC1102 Datasheet. Accessed: Apr. 2022. [Online]. Available: https://www.inventchip.com.cn [2] S. Chellappan, “A comparative analysis of topologies for a bridgeless-boost PFC circuit,” Texas Instrum. Analog Des. J., vol. 3, pp. 1–4, 3rd Quart., 2018. [3] Q. Huang and A. Q. Huang, “Review of GaN totem-pole bridgeless PFC,” CPSS Trans. Power Electron. Appl., vol. 2, no. 3, pp. 187–196, Sep. 2017. [4] J. Zhang and B. Luo, “Design considerations of digital controlled totem pole PFC,” Power Electron. News, Tech. Rep., Apr. 2020. [Online]. Avail- able: https://www.powerelectronicsnews.com [5] Z. Ye, A. Aguilar, Y. Bolurian, and B. Daugherty, “GaN FET-based high CCM totem-pole bridgeless PFC,” in Proc. Texas Instrum. Power Supply Design Seminar (SEM), 2014, pp. 6-1--6-11. [6] M. U. Alam, “Investigation of bridgeless single-phase solutions for AC– DC power factor corrected converters,” Ph.D. dissertation, Univ. British Columbia, Vancouver, BC, Canada, Jul. 2017. [7] High Efficiency CCM Bridgeless Totem Pole PFC Design Using GaN E-HEMT, GS665BTP-REF rev170905. Accessed: Jan. 2018. [Online]. Avail- able: https://www.gansystems.com [8] S. Dusmez and Z. Ye, “Designing a 1 kW GaN PFC stage with over 99% efficiency and 155 W/in3 power density,” in Proc. IEEE 5th Workshop Wide Bandgap Power Devices Appl. (WiPDA), Nov./Oct. 2017, pp. 225–232. [9] B. Sun, “Control challenges in a totem-pole PFC,” Texas Instrum. Ana- log Appl. J., vol. 2, pp. 1–4, 2nd Quart., 2017. [10] D. M. Van de Sype, K. De Gusseme, A. P. M. Van den Bossche, and J. A. Melkebeek, “Duty-ratio feedforward for digitally controlled boost PFC con- verters,” IEEE Trans. Ind. Electron., vol. 52, no. 1, pp. 108–115, Feb. 2005. [11] M. Chen and J. Sun, “Feedforward current control of boost single-phase PFC converters,” IEEE Trans. Power Electron., vol. 21, no. 2, pp. 338–345, Mar. 2006. [12] B. Sun, “How to reduce current spikes at AC zero-crossing for totem- pole PFC,” Texas Instrum. Analog Appl. J., vol. 4, pp. 1–32, 4th Quart., 2015. [13] Z. Ye and B. Sun, “Advanced digital controls improve PFC performance,” in Proc. Texas Instrum. Power Supply Design Seminar (SEM), 2012, pp. 7-1--7-16. [14] N. A. Hawkins, M. L. McIntyre, and J. A. Latham, “Nonlinear control for power factor correction of a dual-boost bridgeless circuit,” in Proc. 44th Annu. Conf. IEEE Ind. Electron. Soc. (IECON), Oct. 2018, pp. 1368–1373. [15] M. Chen, A. Mathew, and J. Sun, “Nonlinear current control of single- phase PFC converters,” IEEE Trans. Power Electron., vol. 22, no. 6, pp. 2187–2194, Nov. 2007. [16] Technology Specification of Switching Power Supply for Power Line Distortion Immunity, China Power Supply Society, China, Issue 1007, 2020. [17] Digital Control IC for Interleaved PFCs. Accessed: 2017. [Online]. Available: https://www.st.com/content/dam/technology-tour-2017/ses- sion-2_track-5_digital-control-pfc.pdf [18] Power Factor Correction (PFC) Handbook. Accessed: Apr. 2014. [Online]. Available: https://www.onsemi.com/pub/Collateral/HBD853-D.PDF 44 IEEE POWER ELECTRONICS MAGAZINE z September 2022
©SHUTTERSTOCK.COM/ANDRII STEPANIUK Full-Bridge Fault- Tolerant Isolated DC–DC Converters: Overview of Technologies and Application Challenges by Abualkasim Bakeer, Andrii Chub, and Dmitri Vinnikov Nowadays, energy generation is on the path from microgrids that facilitate direct integration of energy centralized to distributed generation paradigm sources, storage, and dc loads. Also, most consumer and to improve the efficiency and resilience of industrial devices are naturally dc devices or contain a dc power systems. One of the major developments link, which makes them compatible with dc microgrids. in the energy sector was the introduction of dc Hence, dc distribution is an efficient tool for combining dc energy sources and battery energy storage with typical Digital Object Identifier 10.1109/MPEL.2022.3196565 loads that are predominantly compatible with dc Date of publication: 28 September 2022 microgrids. In the foreseeable future, widespread adoption 2329-9207/22©2022IEEE 45September 2022 z IEEE POWER ELECTRONICS MAGAZINE
of dc microgrids will rely on the ubiquitous use of dc–dc is also possible, but could be costly due to the high converters. Apart from cost concerns, the long-term reli- number of extra components [6]. Scaling up the typical ability of power electronic systems is under scrutiny by the dc–dc converters to the medium and high power levels power industry, which prefers simple but highly reliable/ typically requires a parallel connection of several dc–dc available solutions. converter cells, which suggests (N + 1) redundancy for Among isolated dc–dc converter topologies, flyback fault tolerance implementation. Operation with medium and forward converters are used the most in low-power to high voltages requires the implementation of multi- applications. These topologies are switch topologies to match block- simple and, thus, cost-efficient, but ing voltage requirements [7], which they do not allow for fault-tolerance In the foreseeable enables component-level fault tol- implementation. They could be erance by adding a few extra sub- overdesigned for higher reliability, future, widespread modules or series switches [8], [9]. but their cost would render their adoption of dc Moreover, fault tolerance could be adoption unfeasible. Conventional implemented at the level of each (N + 1) redundancy could be used microgrids will rely on submodule [10]. in a limited number of mission- the ubiquitous use of This article discusses the imple- critical systems where the cost mentation possibilities of full- of implementation is a secondary dc–dc converters. bridge fault-tolerant galvanically issue. However, the cost of imple- isolated dc–dc converters and their mentation and maintenance still practical limitations. The known play an essential role in most appli- approaches are categorized into cations. Therefore, fault-tolerant (FT) dc–dc converters two groups: those with redundant components and are becoming increasingly popular as a tool enabling with zero redundancy (Table 1). Both types can oper- a deferred after-fault maintenance of mission-critical ate after a semiconductor fault until the next scheduled systems [1]. maintenance. The main implementation principles are The literature on the isolated fault-tolerant dc–dc demonstrated using series resonant dc–dc converter converters presents full-bridge topologies primarily due (SRC) topology as it was used the most in the literature. to their control versatility offering various switching Moreover, some phase-shifted topologies, like the dual patterns. They are capable of on-the-fly topology mor- active bridge, are not feasible in implementation with phing into equivalent topologies with a reduced number zero redundancy and thus cannot be used as a case of switches, like half-bridge, flyback, or single-switch study [11]. Only semiconductor faults are considered as [2]–[5], providing ample opportunities for a semicon- they were reported to be the most frequent in isolated ductor fault remedy. Component-level fault tolerance dc–dc converters [12]. Fault detection techniques are Ta–b– le 1. Comparison between different FT approaches for full-bridge galvanically isolated dc–dc converters. Item Redundant active Redundant capacitors Zero redundancy [22]–[24] Example leg [16] leg [20], [21] IB/OB switch type Figure 1(a) Figure 1(b) Figures 2(a) and (c) and 3(a) Reported power range IGBT MOSFET/IGBT Post-fault overloading > 350 W > 350 W MOSFET/IGBT of components Power curtailment No Yes < 350 W Extra components Not Needed Needed Yes ■■4 Aux. switches ■■4 Aux. switches Power density ■■4 Semiconductors ■■0 Semiconductors Needed Cost ■■12 Fuses ■■0 Fuses ■■0 Aux. switches ■■0 Semiconductors XXX XX ■■0 Fuses $$$ $$ X Reported applications ■■UPS ■■UPS ■■Data Center ■■Data Center $ ■■Residential PV ■■Battery charger ■■Light-emitting diodes X is the smallest design, XXX is the biggest design. $ is the cheapest, $$$ is the most expensive. 46 IEEE POWER ELECTRONICS MAGAZINE z September 2022
Active Leg Input Bridge (IB) Output Bridge (OB) Active Leg PWM PWM Q7 PWM PWM PWM PWM S7 S1 S3 Q1 Q3 S5 F F TX iLr Lr Cr F F Q5 im Lm +− F F S2 S4 vCr +Vin Cin Co Vo ++S6Q6 Q8 F ++PWM + PWM Q4 PWM 1:n PWMF S8 Transformer PWMQ2 PWM (a) Cap. Leg Input Bridge (IB) Output Bridge (OB) Cap. Leg Cin1 PWM PWM Q3 Co1 PWM PWM Q5 S1 S3 Q1 Cr Q6 S5 TX iLr Lr +− Q4 Co2 im Lm vCr Vin Vo S6 PWM 1:n PWM Cin2 PWM Transformer PWM S2 S4 Q2 (b) FIG 1 A fault-tolerant isolated dc–dc converter using redundant components on the input and output sides. (a) FT SRC with a redundant active leg [16]. (b) FT SRC with a redundant capacitors leg with midpoint connection [20], [21]. not presented as they have been reviewed and catego- converters suffer the most from semiconductor faults, as rized in [9], [13], and [14]. the statistics report that input-side semiconductors are The article overviews three main approaches to the the most vulnerable components [12]. In general, the realization of the fault tolerance to semiconductor faults converter semiconductors have two typical fault states in full-bridge galvanically isolated dc–dc converters. It depending on the failure mechanism: an open-circuit demonstrates a trade-off between fault (OCF) and short-circuit fault using extra components or reduc- (SCF) [15]. After fault detection and ing converter operating power after The known approaches identification, an FT converter can a fault to avoid overheating healthy be revived by the control system. components or penalizing the con- are categorized into The auxiliary switches (i.e., S5,6 verter efficiency after a fault. two groups: those with and Q5,6) operate in an on/off mode and can be implemented as an elec- Fault-Tolerant Converters With redundant compo- tromechanical relay, a static solid- Redundant Components nents and with zero state relay (SSR), or using two MOSFETs connected in the back-to- Using redundant components to overcome converter failure condi- redundancy. back configuration. This group of FT tions is the most common way to approaches is tolerant to both the prevent power outages in mission- OCF and the SCF in the input/output critical applications [1], extending bridge (IB/OB) semiconductors. The converter useful life and availability. This refers to redun- auxiliary switch connects unused redundant components dancy at the component level within a single converter depending on the fault location on either the input or using additional hardware, like semiconductors, capaci- output side. tors, auxiliary switches, and fuses to isolate the faulty The first FT approach (Figure 1a) uses redundant component, as shown in Figure 1. Isolated dc–dc switching legs (i.e., active legs) on the input and output 47 September 2022 z IEEE POWER ELECTRONICS MAGAZINE
sides. It requires a fuse (designated as “F” in Figure 1a) in the redundant leg in the FT converter compromises the series with each semiconductor in the converter to iso- converter cost as redundant switches require extra gate late an SCF and transform it into an OCF after thermal drives and auxiliary power supply circuitry. fuse breakdown [16]. By following this way, to achieve complete isolation of the faulty leg from the converter On the other hand, with this FT approach, the con- operation, the healthy switch in the faulty leg should be verter components can handle the same power before turned off continuously. One of the drawbacks of using and after the fault occurrence without overloading the fuses is that they dissipate power losses during nor- the components. The switches of the redundant leg are mal operation and thus affect the converter efficiency dimensioned or selected in the same way as for the main [12]. In addition, the presence of the fuse will increase inverter legs. This FT approach is limited to implementa- parasitic inductance in the power circuit [16]. Moreover, tions with IGBTs, as these transistors can survive rela- tively long overcurrent intervals before the fuse burns. Input Bridge (IB) Output Bridge (OB) PWM PWM PWM PWM S1 S3 Q1 Q3 ipri Cb TX iLr Lr Cr V2 Co Vo +− V1 +− im Q2 Q4 vCb Vp vCr +S2 + Vin Cin Lm Vs PWM 1:n PWM PWM S4 Transformer PWM (a) Tsw TDT SS21,,34,, QQ21,,34 t t V1 t Vin t t VCr t ILr VS1 IS1 VQ1 IQ1 Vo nVin (b) FIG 2 The FT SRC with a zero redundancy and TMC-based post-fault control [22]. (a) Main circuit. (b) Idealized steady-state wave- forms during normal operation. 48 IEEE POWER ELECTRONICS MAGAZINE z September 2022
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