IEEE Power Electronics Magazine September 2022

MOSFETs do not show the same overloading ruggedness which should be taken into account during the thermal and are likely to burn before the fault is identified and design of a fault-tolerant converter [18]. SiC devices used a fuse disconnects the corresponding power device. For in high voltage ports of dc–dc converter shown roughly example, many IGBTs today can withstand the short-cir- 80%/20% distribution between SCF and OCF [18]. It was cuit current for up to 10  µs, thus allowing for sufficient also shown that some devices could fail to conditions time for fault detection and identification (which could between SCF and OCF, but those cases will eventually require less than one switching period) and burning of a converge to either SCF or OCF due to excessive power fuse caused by the short-circuit current [17]. dissipation in a faulty device [19]. The low-voltage Si MOSFETs are most likely to expe- The second FT approach has a redundant capacitors rience SCF with post-fault on-state resistance up to an leg with a midpoint on the input and output sides, as order of magnitude higher than the datasheet value, shown in Figure 1b [20], [21]. It requires four bidirectional Input Bridge (IB) Output Bridge (OB) PWM PWM Q3 OFF OFF Co Vo S1 S3 Q1 ipri Cb TX iLr Lr Cr V2 Q4 +− V1 +− im Q2 vCb Vp Lm vCr +S2 + Vin Cin Vs PWM 1:n PWM SCF S4 Transformer ON (c) Tsw TDT SSS213,,, QQQQ2413 t t V1 t Vin t t VCr Vo/2 t ILr VS1 IS1 VQ1 IQ1 Vo nVin (d) FIG 2 (c) Example of a possible reconfiguration after the fault in the MOSFET switch S1. (d) Idealized steady-state waveforms during post-fault operation. 49 September 2022 z IEEE POWER ELECTRONICS MAGAZINE

auxiliary switches (up to eight discrete switches in solid- are depicted in Figure 2b, where the IBBC is operating as a state implementation) to connect a faulty leg to the cor- typical full-bridge SRC. The IB feeds the transformer with responding midpoint. Unlike the previous FT approach, balanced rectangular voltage pulses, while the OB oper- IB/OB could be realized using IGBT or MOSFET devices, ates as a synchronous rectifier. Its post-fault operation in and the fuses are no longer required. However, only buck and boost modes is based on application of asymmet- OCF could be remedied in the bridge that does not have rical modulations as presented in [11]. a capacitor in series with the transformer winding. The The considered zero redundancy FT SRC can withstand key to this FT approach is to keep the converter running a single fault (either OCF or SCF) in IB and OB semiconduc- after a failure, but as a half-bridge instead of a full-bridge tors, i.e., up to two semiconductor faults when they happen on the faulty side. Similarly, the healthy side should be on the different sides of the converter. Each faulty inverter reconfigured into a half-bridge inverter or rectifier oper- bridge can be easily reconfigured into a half-bridge in the ating synchronously with the other side. After such a case of a semiconductor fault, as shown in Figure 2c for the reconfiguration, the average voltage IB. During the post-fault operation, across the resonance capacitor Cr is The key to this FT the average voltage across Cr equals increased to half of the output volt- approach is to keep half of the output voltage (Figure 2d). age. The auxiliary switches are used the converter running to reconfigure a healthy converter after a failure, but as Similarly, the blocking capacitor Cb side, IB or OB, to ensure post-fault operates at increased voltage stress operation of the FT SRC with the same dc gain as before the fault. In of half the input voltage, assuming that Cb >> Cr·n2. Consequently, the total gain of the case of SCF, the damaged switch a half-bridge instead the converter remains the same is used as a conduction path for the of a full-bridge on the before and after a semiconductor current, while another switch on the fault. This FT approach is compat- same leg is turned off, e.g., S3 should faulty side. ible with both MOSFETs and IGBTs. stay open if S4 causes SCF. The recon- The output voltage of the zero figuration of the healthy bridge into a redundancy FT SRC remains con- half-bridge is functionally similar to stant after a fault, but the RMS cur- commutating auxiliary transformer winding to adjust the rent stresses of the transformer and the semiconductor total converter gain [22], which could be disadvantageous devices are increased to twice the RMS current in the in practice due to the oversized design of the transformer. normal state at the same load, increasing the thermal Since the power supplied by the dc–dc converter is con- loading of the converter components. This FT approach stant before and after the fault, the remaining healthy does not require an additional fuse in series with each components could be overstressed. semiconductor. A shorted semiconductor is used as a current path in the circuit. For any fault type (OCF/SCF) Fault-Tolerant Converters With Zero Redundancy in the IB of the example FT SRC, the healthy OB must be The zero redundancy FT SRC shown in Figure 2a was first reconfigured from the full-bridge into an asymmetrical proposed in [23]. Its basic idea originates from the (Greinacher) voltage doubler rectifier using one of the assumption that the conventional SRC can utilize a short- four possible implementations [22]. This FT approach circuited transistor or continuously turned-on transistor has a thermal loading similar to that in the FT approach as a current conducting path, eliminating auxiliary employing redundant capacitor legs with midpoint con- switches and associated circuitry. Moreover, having only nections but at a much lower cost of implementation. active transistors, this converter can operate as an iso- The comparison between the three presented FT lated buck–boost converter (IBBC) by applying special approaches based on SRC topology is summarized in modulations to IB and OB. Table 1. It can be noted that there is a trade-off between This FT approach is based on the topology morphing adding extra components during the converter design, control (TMC) that enables self-sufficient post-fault con- increasing the converter size and cost to maintain the verter operation without additional components in the pri- same performance after a fault, and having zero redun- mary circuit. The FT SRC implementing the TMC contains dant components, resulting in possible thermal overloads only two hybrid switching bridges at the input and output, after a fault if power curtailment control is not utilized. which can be reconfigured as a full- to a half-bridge after The significantly increased thermal loading after a fault the fault is detected. The blocking capacitor Cb ensures the can also be observed for the FT approach with redundant dc bias in the transformer current is eliminated, avoiding capacitors legs with midpoint connections despite the use saturation of the transformer core after reconfiguration. of extra components. Hence, out of these FT approaches, Additionally, Cb could have a high capacitance not to affect the one with zero redundancy can achieve better effi- the IBBC resonant frequency. The idealized steady-state ciency at a lower cost. It is worth mentioning that fault waveforms of the IBBC during the normal (healthy) state tolerance with zero redundancy and the redundant 50 IEEE POWER ELECTRONICS MAGAZINE z September 2022

capacitors leg both feature reduced voltage swing applied Recent industry trends show that conformal coating is to the isolation transformer. As a result, those techniques a preferred solution to reduce converter weight, cost, are not practical in the dual active bridge-based convert- and shipping fees. On the other hand, this packaging ers, where the power delivery capacity of the converter technology renders any repair unfeasible due to compli- depends directly on the transformer voltage swing [11]. cated and time-consuming disassembly, as shown from the example of the potted PV microconverter presented Application Example of Zero Redundancy in Figure 3(a). Typically, faulty unit is replaced with a Fault-Tolerant DC–DC Converter new one based on a valid warranty or under the terms of a service contract. Owing to low realization cost, the zero-redundancy fault-tolerant approach has already found its applica- Nevertheless, getting a replacement could take a long tion in PV microconverters [24]. PV microconverters time or incur extra-cost for unscheduled maintenance, are typically mounted on the same rail as the PV mod- which results in economic loss due to equipment down- ule it is connected to. Therefore thermal cycling and time. The zero redundancy FT approach based on the exposure to humidity require these devices to be pro- TMC can reduce the downtime time to zero, making the tected according to a high-grade ingress protection PV microconverter operational till the next scheduled code, like IP67 defined in IEC 60529. This makes the maintenance—a great advantage for residential PV instal- converter capable of withstanding snow, rain, wind, lations regardless of possible performance deterioration etc. Thermally conductive and water-resistant epoxy after a fault. Figure 3b shows the power circuit topology resins with moderate viscosity and low hardness are of a zero redundancy FT PV microconverter [24]. It is typically used for potting the converter enclosures. based on the quasi-Z-source series resonant IBBC where Possible location of faulty semiconductors (a) qZS Network Input Bridge (IB) Output Bridge (OB) L1 L2 PWM D1 D3 + 1:1 PWM Cr Co Vo S1 S3 Cb ipri +− TX iLr Lr +− vCb im vCr S2 + Vpv Lm - C2 SqZS PWM 1:n D2 Q4 PWM S4 Transformer C1 (b) FIG 3 (a) Photo of the disassembled industrial PV microconverter with mechanically removed aluminum case and part of the pot- ting compound. (b) Power circuit diagram of the zero redundancy fault-tolerant PV microconverter. 51 September 2022 z IEEE POWER ELECTRONICS MAGAZINE

one of the rectifier diodes is replaced with the MOSFET performance benchmarking of the microconverter cou- to enable the TMC implementation. pled with the 96-cell Silicon PV module before and after the short-circuit fault of a switch S1. In both cases, the Throughout its prognosed lifetime, the microconver- PV microconverter extracted total energy of 1190  Wh ter normally operates as a full-bridge quasi-Z-source and showed the same average maximum power point SRC with the full-bridge rectifier. If the fault occurs in (MPP) tracking efficiency of more than 99%. However, one of the input-side inverter switches, the microconver- the power stage efficiency differs considerably for the ter is reconfigured into a single-switch quasi-Z-source pre- and post-fault operation. Before a fault, it achieves converter. The topology morphing scenario depends on maximum efficiency of 95% at the maximum input the operating point and is realized by applying one of the power, as shown in Figure 4a, which results in the total post-fault modulation sequences [24]. Figure 4 shows the Input voltage VPV, V 47 Input voltage VPV, V 47 46 46 45 45 44 44 43 43 42 42 41 41 250 250 200 150 PPV 200 PPPDVC 100 PDC Power, W Power, W 50 150 0 100 100 99.5 50 99 0 98.5 MPPT Efficiency, % MPPT Efficiency, % 100 98 99.5 97.5 99 97 98.5 98 97.5 97 Converter Efficiency, % 95 Converter Efficiency, % 95 90 2 4 6 8 10 90 Time, hour 85 (a) 85 80 80 75 75 0 0 2 4 6 8 10 Time, hour (b) FIG 4 Experimental benchmarking of the zero-redundancy fault-tolerant PV microconverter coupled with 96-cell PV module using a clear day mission profile in (a) normal operation and (b) post-fault operation. 52 IEEE POWER ELECTRONICS MAGAZINE z September 2022

energy delivered to the output of 1116 Wh during Failure Rate [105 Failure/Year] 1400 Post-fault a day (94% from the extracted PV energy). After Normal a fault, the performance of the microconverter 250 W 200 W 150 W 100 W depends more strictly on the input voltage and, 1200 Maximum operating power consequently, on the operating mode. It features 1000 (a) relatively high efficiency in the buck mode at the Post-fault input voltages above 44 V, which corresponds to 800 the operation during the morning and evening PV Energy Yield Prediction [%] 600 hours, as could be seen from Figure 4b. During 400 the peak solar irradiance hours, the MPP volt- 200 age of the PV module drops below 44 V, and the microconverter starts operating in a boost mode. 0 In that case, the topology is reconfigured into No Limit the quasi Z-source (qZS) single-switch converter that suffers from relatively high current stresses. 100 Normal This results in an efficiency drop of 5%–6% and, consequently, daily output energy yield dropped 80 down to 1070 Wh after a fault, which is 90% of the harvested PV energy. This is an acceptable 60 performance deterioration considering that the converter can continue operating after a semi- 40 conductor switch fault. Post-Fault Operation Issues of Zero- 20 Redundancy Fault-Tolerant Converters The efficiency of the zero redundancy FT dc–dc 0 250 W 200 W 150 W 100 W converters typically deteriorates after a fault, and No Limit the efficiency drop could vary significantly Maximum operating power between the converter operation modes. This (b) observation imposes an issue related to overload- FIG 5 Reliability of the FT PV microconverter before and after the ing of the critical components when attempting to occurrence of a fault with power curtailment, considering the 60-cell Si operate close to the rated power after the fault- residential PV module on the input side coupled with a dc microgrid of induced topology reconfiguration. If the zero 350 V on the output side. (a) Yearly failure rate. (b) Yearly PV energy redundancy FT converter continues delivering the yield predictions. rated power after the fault, the lifespan of the healthy components could be shortened as they will face high thermal stress or even catastrophic switches from the MPP tracking to the power derating failure, depending on design trade-offs. For example, the mode. However, the microconverter input voltage will be low-cost designs use smaller printed circuit boards and different from the MPP voltage. cheaper semiconductors to meet the cost constraints. A trade-off between extending the converter reliabil- Hence the low-cost implementations of zero redundancy ity using power curtailment and associated reduction FT dc–dc converters may require software constraint in the energy yield of the PV system should be consid- (curtailment) of the input power to be introduced in the ered. There are two possible solutions to the power cur- control system to ensure safe post-fault operation. On the tailment problem: operating above and below the MPP other hand, in many applications, including PV, operation voltage. In practice, the power curtailment to the point at the maximum power happens rarely and contributes above the MPP voltage is more beneficial as high step- only a small fraction of the annual energy yield [29]. up converters tend to provide higher efficiency at lower A simple solution to improve the reliability of FT dc– dc gain [26], [27]. In addition, it is simpler to reach that dc converter with zero redundancy and, thus, extend its point when starting MPP tracking from the open-circuit lifetime, is to curtail the converter input power at a cer- voltage of the PV module. tain level during infrequent PV energy production peaks. To define the random failure rate of the converter dur- In the power curtailment mode, the failure rates of the ing its prognosed lifetime, the reliability approach from critical components will be reduced significantly due to the FIDES handbook can be adopted [28]. This method- reduced thermal loading [25]. When the maximum power ology allows for defining how the random failure rate of the PV module becomes higher than the predetermined of components operating under dc stress depends on curtailment power level, the converter control system the variations in component stress resulting from the 53 September 2022 z IEEE POWER ELECTRONICS MAGAZINE

real-life yearly mission profile. The reliability was evalu- and the shorted faulty switch as a current path in the post- ated under a yearly mission profile of solar irradiance and fault topology. ambient temperature adopted from Aalborg, Denmark As a result, post-fault maintenance can be delayed at [29]. Figure 5a shows the predicted random failure rate no extra cost compared to the other two FT approaches. for the considered FT PV microconverter. In the pre-fault The most reasonable approach could be keeping the main- conditions, the PV microconverter experiences a moder- tenance schedule after a fault occurred and was remedied ate failure rate. After a fault appears, the control system to avoid costly urgent maintenance events. This helps curtails the maximum input power. avoid power outages and allows for Preliminary calculations showed a faster return on investment. The that this PV microconverter would The main obstacle in main obstacle in designing zero experience new faults next time it redundancy systems is in achiev- attempts to process the rated power designing zero redun- ing a trade-off between the cost of of 300  W. If the input power is cur- dancy systems is in the converter and the level of post- tailed at the level of 250 W, the con- fault power curtailment. The power verter can continue operation after achieving a trade-off curtailment reduces post-fault ther- the topology reconfiguration but between the cost of mal loading of the critical converter with much increased yearly random components and even avoids cata- failure rate. The curtailment level the converter and the strophic failure. Depending on the should be reduced to 200 W to retain level of post-fault application and climate conditions, the random failure rate of a healthy power curtailment after a fault does microconverter. A further reduction power curtailment. not necessarily penalize the gener- of the curtailment level to 150  and ated energy. It may be needed just 100  W shows a further reduction in to avoid catastrophic failure during the failure rate. rare moments of peak power genera- On the other hand, the PV microconverter with a low tion or processing. Therefore, the zero-redundancy fault curtailment level cannot efficiently utilize the avail- tolerance approach suits the best for numerous emerging able PV energy, as predicted in Figure 5b. A healthy FT applications where the cost of implementation is essen- PV microinverter is predicted to deliver total energy of tial while the performance of the post-fault operation is 309  kWh/year at the output terminals during the nor- allowed to deteriorate reasonably. mal operation before the fault occurrence. The case of no power curtailment during the post-fault opera- Acknowledgments tion is avoided in Figure 5 as these conditions lead This research was supported by the Estonian Research to a guaranteed catastrophic failure anytime the PV Council grants: PSG206 - literature review and classifica- microconverter attempts to process powers close to tion of methods, and PRG1086 - fault-tolerant PV micro- the rated power. When the maximum operating power converter related research. of 250 W is used, the PV microconverter loses only 9% of its energy yield estimated for the output side of the About the Authors converter. Hence, it can continue its operation without Abualkasim Bakeer received the B.Sc. and M.Sc. catastrophic failures. For the power curtailment level degrees in electrical engineering from Aswan University, of 100 W, the PV microconverter can still provide a lit- Aswan, Egypt, in 2012 and 2017, respectively. He is cur- tle over 60% of the initial energy yield. It is worth men- rently pursuing the Ph.D. degree with the Department of tioning that the dependence between the curtailment Electrical Power Engineering and Mechatronics, Tallinn power level and energy yield loss would be much more University of Technology, Estonia. In 2014, he joined the substantial in southern climates, where more energy is Electrical Engineering Department, Faculty of Engineer- produced at higher power levels compared to the refer- ing, Aswan University, as a Demonstrator, and then ence case from Northern Europe. became an Assistant Lecturer in 2017. His main research topics are dc–dc converters, fault diagnosis and fault tol- Conclusions and Discussion erance, impedance-source power converters, and model The article has discussed three FT approaches to over- predictive control. coming semiconductor faults in galvanically isolated Andrii Chub received the B.Sc. and M.Sc. degrees in dc–dc converters using SRC as the reference topology. electronic systems from Chernihiv State Technological Among them, the zero redundancy FT approach shows University, Ukraine, in 2008 and 2009, respectively, and the lowest implementation cost but requires some degree the Ph.D. degree in electrical engineering from the Tal- of power curtailment after a fault. This approach is based linn University of Technology, Estonia, in 2016. He was on the topology morphing control principle that allows with Kiel University in 2017 and Federico Santa Maria converter topology reconfiguration using healthy switches Technical University from 2018 to 2019. He is currently 54 IEEE POWER ELECTRONICS MAGAZINE z September 2022

a Senior Researcher with the Power Electronics Group, [10] T. Li and L. Parsa, “Design, control, and analysis of a fault-tolerant Tallinn University of Technology. He has coauthored soft-switching DC–DC converter for high-power high-voltage applica- more than 100 articles on power electronics and appli- tions,” IEEE Trans. Power Electron., vol. 33, no. 2, pp. 1094–1104, Feb. cations. His research interests include advanced dc–dc 2018. converter topologies, renewable energy conversion sys- [11] A. Chub, G. Buticchi, V. Sidorov, and D. Vinnikov, “Zero-redundancy tems, energy-efficient buildings, reliability, and fault- fault-tolerant resonant dual active bridge converter for more electric air- tolerance of power electronic converters. crafts,” in Proc. PEDG, Kiel, Germany, Jun. 2022, p. 6. [12] L. F. Costa and M. Liserre, “Failure analysis of the DC–DC converter: Dmitri Vinnikov ([email protected]) A comprehensive survey of faults and solutions for improving reliability,” received the Dipl.Eng., M.Sc., and Dr.Sc.techn. degrees in IEEE Power Electron. Mag., vol. 5, no. 4, pp. 42–51, Dec. 2018. electrical engineering from the Tallinn University of Tech- [13] G. K. Kumar and D. Elangovan, “Review on fault-diagnosis and fault- nology, Tallinn, Estonia, in 1999, 2001, and 2005, respec- tolerance for DC–DC converters,” IET Power Electron., vol. 13, no. 1, tively. He is currently the Head of the Power Electronics pp. 1–13, Jan. 2020. Group, Department of Electrical Power Engineering and [14] S. S. Khan and H. Wen, “A comprehensive review of fault diagnosis Mechatronics, Tallinn University of Technology. More- and tolerant control in DC–DC converters for DC microgrids,” IEEE over, he is one of the founders and leading researchers Access, vol. 9, pp. 80100–80127, 2021. of ZEBE—Estonian Centre of Excellence for zero energy [15] F. Deng et al., “Protection scheme for modular multilevel converters and resource efficient smart buildings and districts. He under diode open-circuit faults,” IEEE Trans. Power Electron., vol. 33, no. has authored or coauthored two books, five monographs, 4, pp. 2866–2877, Apr. 2018. and one book chapter as well as more than 400 published [16] W. Zhang, D. Xu, P. N. Enjeti, H. Li, J. T. Hawke, and H. S. Krish- articles on power converter design and development, and namoorthy, “Survey on fault-tolerant techniques for power electronic is the holder of numerous patents and utility models in converters,” IEEE Trans. Power Electron., vol. 29, no. 12, pp. 6319–6331, this field. His research interests include applied design of Dec. 2014. power electronic converters and control systems, renew- [17] D. Xing et al., “1200-V SiC MOSFET short-circuit ruggedness evalua- able energy conversion systems (photovoltaic and wind), tion and methods to improve withstand time,” IEEE J. Emerg. Sel. Topics impedance-source power converters, and implementa- Power Electron., in press, doi: 10.1109/JESTPE.2022.3144995. tion of wide bandgap power semiconductors. He is the [18] A. Bakeer, A. Chub, and D. Vinnikov, “Fault diagnosis of output-side Chair of the IEEE Estonia Section, and a Senior Member diode-bridge in isolated DC–DC series resonant converter,” in Proc. IEEE of IEEE. 7th Int. Energy Conf. (ENERGYCON), May 2022, pp. 1–6. [19] M. Gleissner and M.-M. Bakran, “Failure characteristics of discrete References power semiconductor packages exceeding electrical specifications,” in Proc. 16th Eur. Conf. Power Electron. Appl., Aug. 2014, pp. 1–10. [1] L. F. Costa, G. D. Carne, G. Buticchi, and M. Liserre, “The smart trans- [20] L. Costa, G. Buticchi, and M. Liserre, “A fault-tolerant series-resonant former: A solid-state transformer tailored to provide ancillary services to DC–DC converter,” IEEE Trans. Power Electron., vol. 32, no. 2, pp. the distribution grid,” IEEE Power Electron. Mag., vol. 4, no. 2, pp. 56–67, 900–905, Feb. 2017. Jun. 2017. [21] L. Costa, G. Buticchi, and M. Liserre, “Bidirectional series-resonant [2] M. M. Jovanovic´ and B. T. Irving, “On-the-fly topology-morphing con- DC–DC converter with fault-tolerance capability for smart transform- trol-efficiency optimization method for LLC resonant converters operating er,” in Proc. IEEE Energy Convers. Congr. Expo. (ECCE), Sep. 2016, in wide input- and/or output-voltage range,” IEEE Trans. Power Electron., pp. 1–7. vol. 31, no. 3, pp. 2596–2608, Mar. 2016. [22] X. Pei, S. Nie, Y. Chen, and Y. Kang, “Open-circuit fault diagnosis and [3] S. Poshtkouhi and O. Trescases, “Flyback mode for improved low- fault-tolerant strategies for full-bridge DC–DC converters,” IEEE Trans. power efficiency in the dual-active-bridge converter for bidirectional PV Power Electron., vol. 27, no. 5, pp. 2550–2565, May 2012. microinverters with integrated storage,” IEEE Trans. Ind. Appl., vol. 51, [23] D. Vinnikov, A. Chub, O. Korkh, and M. Malinowski, “Fault-tolerant no. 4, pp. 3316–3324, Jul./Aug. 2015. bidirectional series resonant DC–DC converter with minimum number [4] A. Blinov, R. Kosenko, A. Chub, and V. Ivakhno, “Analysis of fault- of components,” in Proc. IEEE Energy Convers. Congr. Expo. (ECCE), tolerant operation capabilities of an isolated bidirectional current-source Sep. 2019, pp. 1359–1363. DC–DC converter,” Energies, vol. 12, no. 16, p. 3203, Aug. 2019. [24] D. Vinnikov, A. Chub, D. Zinchenko, V. Sidorov, M. Malinowski, and [5] A. Chub, D. Vinnikov, R. Kosenko, and E. Liivik, “Wide input volt- S. Bayhan, “Topology-morphing photovoltaic microconverter with wide age range photovoltaic microconverter with reconfigurable buck–boost MPPT voltage window and post-fault operation capability,” IEEE Access, switching stage,” IEEE Trans. Ind. Electron., vol. 64, no. 7, pp. 5974–5983, vol. 8, pp. 153941–153955, 2020. Jul. 2017. [25] H. Tarzamni et al., “Reliability assessment of conventional iso- [6] T. Rahimi et al., “Fault-tolerant performance enhancement of DC–DC lated PWM DC–DC converters,” IEEE Access, vol. 9, pp. 46191-46200, converters with high-speed fault clearing-unit based redundant power 2021. switch configurations,” in Proc. IEEE Electr. Power Energy Conf. (EPEC), [26] X. Li, H. Wen, Y. Zhu, L. Jiang, Y. Hu, and W. Xiao, “A novel sensor- Oct. 2021, pp. 492–497. less photovoltaic power reserve control with simple real-time MPP [7] Z. W. Khan, H. Minxiao, Y. Jinggang, A. U. Rehman, B. G. Teshagar, and estimation,” IEEE Trans. Power Electron., vol. 34, no. 8, pp. 7521–7531, L. K. Tuan, “An overview of fault tolerant high power DC–DC converters Aug. 2019. for application in DC grid,” in Proc. IEEE 6th Int. Conf. Eng. Technol. [27] J. M. Riquelme-Dominguez and S. Martinez, “A photovoltaic power Appl. Sci. (ICETAS), Dec. 2019, pp. 1–7. curtailment method for operation on both sides of the power-voltage [8] M. Farhadi, M. Abapour, and B. Mohammadi-Ivatloo, “Reliability analy- curve,” Energies, vol. 13, no. 15, p. 3906, Jul. 2020. sis of component-level redundant topologies for solid-state fault current [28] Fides Guide 2009 Edition A-Reliability Methodology for Electronic limiter,” Int. J. Electron., vol. 105, no. 4, pp. 541–558, Sep. 2017. Systems, AIRBUS France, Eurocopter, Nexter Electron., MBDA Missile [9] F. Bento and A. J. M. Cardoso, “A comprehensive survey on fault diag- Syst., Thales Systèmes Aéroportés SA, Thales Avionics, Thales Corporate nosis and fault tolerance of DC–DC converters,” Chin. J. Electr. Eng., vol. Services SAS, Thales Underwater Syst., FIDES Group, Ghaziabad, India, 4, no. 3, pp. 1–12, Sep. 2018. 2014. [29] A. Chub, D. Vinnikov, S. Stepenko, E. Liivik, and F. Blaabjerg, “Photo- voltaic energy yield improvement in two-stage solar microinverters,” Ener- gies, vol. 12, no. 19, p. 3774, Oct. 2019.  55 September 2022 z IEEE POWER ELECTRONICS MAGAZINE

©IMAGE LICENSED BY INGRAM PUBLISHING Ranking Qi Wireless Power Transmitters by Efficiency You can’t get there from here by John Perzow T he Wireless Power Consortium (WPC) Energy protocol for the U.S. Environmental Protection Agency Star Task Force (ESTF), comprised of engi- (EPA), intended to rank Qi wireless power transmitters on neers from major cellphone and consumer the basis of power-transfer efficiency. Key to this test pro- electronics manufacturers, test houses, and tocol is the assumption that a single, optimally designed others, developed a proposed efficiency-test test receiver may be used to accurately assess transmitter efficiency and enable ranking. The possibility exists that Digital Object Identifier 10.1109/MPEL.2022.3195597 phones using different power receiver designs (e.g., differ- Date of publication: 28 September 2022 ent “friendly metal” profiles, different electrical designs) will interact with transmitters and report different 56 IEEE POWER ELECTRONICS MAGAZINE z September 2022 2329-9207/22©2022IEEE

rankings for a given transmitter, thus invalidating the pro- Introduction posed test protocol. Experiments to prove or disprove the assumption that a single optimized receiver can be used The latest market research finds that “battery life remains as a proxy to fairly compare and rank the real-world a top-ranked factor in consumer smartphone purchase power-transfer efficiency performance of Qi wireless intentions in Europe, China, and the U.S. At the same power transmitters were conducted. As a result of these time, consumer satisfaction with both battery life and bat- experiments, the WPC has concluded that because of tery charging times are stubborn pain points, consistently receiver–transmitter interaction, it is not possible to rank appearing each year at the bottom of the list of user expe- transmitters by efficiency for more than one receiver riences.” [1] Wireless charging has been the most impact- design but decreasing the transmitter’s standby power ful feature introduced to address this problem since the could save as much energy over a 24-h period as improv- lithium-ion battery. Wireless charging entered the mass- ing full-power efficiency by 10%. market growth phase when Apple adopted the Qi wireless charging interface standard in early 2017, effectively end- ing the wireless charging standards battle [2]. The Wireless Charging Attach Rate of Global Smartphone Shipments (Rx) 50% 45% 40% 35% 30% 25% 20% 15% 10% 5% 0% 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023 2024 2025 FIG 1 Percent of wirelessly charged cell phones shipped. Source: Strategy Analytics, Needham, MA USA: “2021 Wireless Charging Insights” (published Oct. 2021). Qi-Certified Charging Unit Sales (RX + TX) (Global, Unit Volume, Millions) 1800 1600 25.5% 1400 5-yr CAGR 1200 1000 22.9% 800 600 400 200 0 2020 2021 2022 2023 2024 2025 2019 Qi-Certified Wireless Charging (RX) Qi-Certified Wireless Charging (TX) *Includes phones, tablets, wearables & associated after-market accessories, embedded charging in vehicles and venues FIG 2 Five-year CAGR for Qi receivers and transmitters. 57 September 2022 z IEEE POWER ELECTRONICS MAGAZINE

DC Out DC Out DC Out A B C WPT Transmitter ½ Bridge DriverWPT Receiver Synchronous DC-DC DC Buck Regulator Input Battery Charger FIG 3 Various efficiency test points used in published industry studies. FIG 4 Three-coil Qi transmitter. Source: WPC archives. one’s daily travel (home, car, office, etc.), thereby encour- aging frequent charge “top-ups.” The proliferation of wire- industry-wide adoption of the Qi standard enables con- less chargers at home and in public infrastructure is sumers freedom of choice and the resulting increased forecast to drive transmitter shipments to 435M units in competition drives better products. About 5% of new 2025, a 23% cumulative average growth rate from 2019 phones shipped worldwide in 2016 had wireless charging through 2025 [1] (Figure 2). and that is expected to grow to 45% by 2025 [1] (Figure 1). Wireless charging transmitters are intended to address the All these wireless receivers and transmitters con- problem of battery life by being available throughout form to the Qi standard, which ensures interoperability between the various products. Broad-market adoption and interoperability of a standard creates consumer choice, so it would be useful to consumers and govern- ments if transmitters could be ranked by their power- transfer efficiency (as external power supplies are categorized, ranked, and regulated [5], [7]). As is seen in the wired external power supply market, efficiency ratings help consumers make better-informed purchase decisions and motivates manufacturers to continually improve their power-transfer efficiency characteristics. Measuring the efficiency of wired external ac-to- dc adapters (aka external power supplies, or EPS) is well understood and presents few technical challenges. As they are, appropriately, defined by DOE as volt- age sources, the test methods and load conditions are DCin DCload Amp Volt Volt Meter Meter Meter Amp Compensating Transmitter Under Test Meter Programmable Resistive DC Source Calibrated Receiver Load FIG 5 WPC efficiency protocol test-points. hsys = Pload/Pin, where Pin = DCin × Iin and Pload = DCload × Iload. Source: WPC, Energy Star Test Method for Wireless Power Transmitters, Rev. June 19, 2018. 58 IEEE POWER ELECTRONICS MAGAZINE z September 2022

well defined and controlled, which results in little test transmitters in this class use near-field techniques and variability [5]. are intended to support charging distances (z-distance) For the purposes of efficiency measurement, wireless up to 50 mm. The goal was to establish a uniform, repeat- power transmitters can best be compared to external able, fair, and generally accepted method for measuring power supplies. They are both used in a voltage-source power-transfer efficiency where test labs could look at configuration and are both used to the unit under test (UUT or trans- supply power to charging and non- mitter) as a “black box,” and where charging circuits (task lights, etc.), For the purposes low-cost, off-the-shelf test equip- just as ac-USB wall-warts are used. of efficiency ment could be employed. The WPC The problem is, it is an external task force used the Energy Star test power supply broken into two pieces; measurement, guidelines [4] as the starting point where the primary-side electronics wireless power of the test protocol design: That is, are in the transmitter and the sec- the test must be; repeatable, not ondary-side electronics and magnet- transmitters can best overly burdensome, unambiguous, ics are in the receiver. Consequently, be compared to reproducible, anticipate technology wireless power-transfer efficiency changes, harmonize with related is poorly defined and difficult to external power EPA/DOE test procedures, represen- measure. Wireless power transmit- supplies. tative, discourage circumvention, ters have been characterized by dif- and be consistent with legal author- ferent manufacturers as voltage or ity. current sources, efficiency has been described in the industry as “coil-to-coil,” “dc-in to dc- Overview of WPC Proposed Efficiency Test Protocol out,” “power-in to power-out,” etc. The “dc out test point The WPC test protocol compares dc power into the load may be located after rectifier (dc out A), after the dc–dc to dc power into the transmitter. Four key independent regulator (dc out B) or at the actual load (dc out C)” (Fig- variables that need to be controlled to ensure accuracy ures 3 and 7). and fairness were identified as follows. Seldom do efficiency claims also include conditions 1) Power Class: The transmitter’s stated output power like load resistance or how the relative position between rating is used to place the device into one of five the receiver and transmitter is controlled (x-, y-, and classes. These classes tend to correspond to use- z-axis). Additional factors like random user placement cases, which are useful in determining the load char- of the receiver on the transmitter (for systems that offer acteristics for the test setup (Table 1). The classes are open placement) and the fact that the Qi standard does 2.5 W (wearables), 7  W (phones), 15 W (phones and not strictly define the receiver further complicate test tablet computers), 30 W (small notebook computers), approaches. and 100 W (large notebook computers). To address the lack of an industry-wide definition and method for wireless power system-efficiency test- ing, the WPC initiated a task force to draft an efficiency Test Receiver Location Template test protocol that would represent all inductive wire- 50.0 less power systems regardless of underlying operating Y-axis (%) 40.0 Active principle. The scope of the test protocol was limited 30P.0eak Coil charging to magnetic induction-based wireless power transmit- C2o0u.0pling (kmax) ters designed to supply up to 100 W and intended to 10.0 area power or charge consumer electronics products like cell 0.0 phones, tablets, audio equipment, task lights, etc. All ––Table 1. Qi receiver power classes, 2018. -10.0 Spec Version Power Class Fixed DC Output -20.0 TBD 2.5W 5V Qi 1.1 7.5W 5V -30.0 Qi 1.2 15 12V TBD 30 12V -40.0 TBD 100 19.5V -50.0 -50.0 -30.0 -10.0 10.0 30.0 50.0 X-axis (%) FIG 6 Polar grid generator, a tool used to assign receiver test locations. 59 September 2022 z IEEE POWER ELECTRONICS MAGAZINE

2) Load Characteristics: Rather than assigning a real- receiver design size and cost constraints that are the world load resistance for power loading, some wire- reality of consumer product designs, we set out to less power efficiency studies optimized the dc load exceed the power efficiency of the consumer devices resistance to equal the system coil/antenna imped- intended to be used with the transmitter and thereby ance and adjusted the output voltage in order to maxi- eliminate receiver variability from the equation. mize the system power transfer-efficiency. This is not By controlling these independent variables, we assumed representative of real-world conditions. The test the observed efficiency differences between the device receiver in this protocol incorporates a regulated dc– under test was the function of one dependent variable, dc converter that outputs a fixed voltage appropriate e.g., the wireless power transmitter design. for the power class. For example, a 7.5 W class trans- mitter with a 5 W nameplate is most often used for cell Primary Elements of the Proposed Efficiency Test phone charging, so the output voltage is 5 V and the Protocol and Reporting Results maximum load resistance is 5 Ω, which mimics the input to a cell phone charging circuit. Figure 7 provides primary elements of the proposed effi- ciency test protocol. 3) Test Receiver Position: It has been observed that 1) A reference receiver is used as a proxy for a consumer placing the receiver a few millimeters off-center (the coil-to-coil alignment that results in peak coil cou- device. Its definition depends on the magnetic induc- pling, or kmax,) could reduce the power transfer-effi- tion standard, maximum output power (power class) ciency by as much as 10% in some transmitter designs. of the transmitter being measured, and output voltage Therefore, the relative position between the receiver defined for the receiver in the standard. It was assumed and the load was strictly controlled. In addition to the that a “best-in-class efficiency” receiver could be used center point, testing was done at other prescribed x, to fairly compare transmitter efficiency, and that the y locations and the results were averaged. This results would represent real-world behavior. approach requires a template to assign “random and 2) The reference receiver presents a dc load appropriate repeatable” test locations to simulate actual user for the intended application. This value is adjusted placement behavior. A tool we called a “Polar Grid down by the programable load so that 25%, 50%, 75%, Generator” was developed to assign points in fixed and 100% active load conditions are measured in each concentric rings (Figure 6). The test house then picks receiver placement location. two points at random from each ring for location test- 3) The four load measurements are taken with the ing and records the coordinates for repeatability. The receiver placed at the center of the Tx active area and number of rings and points are proportional to the at other selected points. A “Polar Grid Generator” was charging area. developed to identify receiver placement locations other than the center to model actual user behavior (in 4) Test Receiver Definition: This test receiver was systems that do not have a fixed-placement design that intended to yield a fair proxy with which to compare forces transmitter–receiver alignment). Fixed-location transmitter efficiency performance. By eliminating systems are measured at only one location. WP transmitter (Tx): UUT Calibrated WP receiver (Rx) End-of-Charge Swich C1 Vac_out Vdc_out C2 + + Inverter Rectifier DC-DC Programmable Converter Calibration Load DC L_Tx L_Rx (Resistive) -- FIG 7 WPC efficiency test block diagram. 60 IEEE POWER ELECTRONICS MAGAZINE z September 2022

DUT 24 Figure of Merrit Range: 32.3 to 55.7 DUT 27 10 20 30 40 50 60 DUT 21 DUT 13 DUT 17 DUT 8 DUT 3 DUT 14 DUT 10 DUT 26 DUT 18 DUT 25 DUT 5 DUT 4 DUT 2 DUT 22 DUT 9 DUT 23 DUT 11 Dut 7 DUT 19 DUT 15 DUT 16 DUT 6 DUT 20 DUT 29 DUT 1 DUT 12 DUT 28 0 FIG 8 Experiment 1 FOM range. Standby Power Range Table 2. Experiment 1b, sample test 22mW to 1.6W –– with multiple receivers. UUT 3 Rank by Test Receiver UUT 23 UUT 24 Tx ID Rx1 Rx2 Rx3 Rx4 Mean UUT 1 UUT 1 1 121 1.25 UUT 7 UUT 2 3 432 3 UUT 12 UUT 3 2 213 2 UUT 4 4 899 7.5 0.000 0.500 1.000 1.500 2.000 UUT 5 5 345 UUT 6 6 564 4.25 Power (W) UUT 7 8 756 5.25 UUT 8 9 988 6.5 FIG 9 Experiment 1 standby power range. UUT 9 7 677 8.5 Biggest delta from mean 3.5 1.25 –1.5 –1.5 6.75 4) Quiescent power, or transmitter power-dissipation when no receiver is present, is measured per ANSI/   CTA-2042.3 and recorded. The Big Assumption 5) Reporting the result is done by averaging all active power measurements into a single “Figure of Merit” The integrity of this test protocol hinges on the assump- (FOM). The FOM is compared to other transmitters in tion that a single reference receiver may be used the power class to establish a ranking. The wireless in the test setup for each class of wireless power transmit- power transmitter with the highest score got the ter. To test this assumption, the WPC conducted “Number 1” ranking. Random receiver placement seen two experiments. in real-world use makes it impossible for a consumer to replicate the reported FOM. Therefore, this protocol Experiment 1: Using a third-party laboratory familiar reports a ranking and not a statement of real-world with DOE/EPA testing of consumer products, 29 different efficiency performance. 61 September 2022 z IEEE POWER ELECTRONICS MAGAZINE

Mains AC/DC Transmitter Power Adapter Under Test Watt-Hour Cellular Logger Handset FIG 10 Experiment 2 test setup. 7.5 W-class transmitters were tested per the WPC pro- of this experiment was to rank transmitters by comparing posed efficiency test protocol described above. This exer- the accumulated power (Watt-hours) into each transmit- cise, completed in May 2018, was designed to assess the ter over the charge cycle (10%–90%) of a cell phone (using difficulty and repeatability of our test approach, look at the phone’s fuel gauge) (Figure 10). This test was per- differences between single and multicoil transmitter formed in three locations on the transmitter in order to designs and assess the range of efficiency and quiescent capture the impact of user phone-placement behavior. power for transmitters available in the market (to see if This test was also done with two different phone models there is opportunity for meaningful energy savings that to assess the interaction of different receiver–transmitter justifies an EnergyStar program). Subsequently, a sample pairs. The average accumulated power for the three tests of nine transmitters were retested using four different on a given transmitter is the final outcome or “score” for a receiver designs, four loads (100%, 75%, 50%, and 25% of given transmitter/phone pair. The transmitter that mea- full rated power) at the center location. We refer to this as sures the lowest average power over the three test loca- “Experiment 1b.” tions should be the most efficient transmitter in the group and presumably, the transmitters will rank similarly for Experiment 1 Observations: each phone. 1) A figure of merit range of 32–56 (1.7:1) was reported The WPC supplied eight transmitters with three test (Figure 8), which justifies an EnergyStar program. locations identified on the transmitter’s charging surface, 2) A surprisingly wide standby power range of 130–810 (determined by 100%, 90%, and 80% of RF signal strength). The two phones were common handsets designed and mW (73:1) was reported (Figure 9), which also justifies built by different well-known manufacturers. an energy-saving program. 3) One receiver/transmitter pair (UU4/Rx1) reported an Experiment 2 Observations: outlying FOM number (Table 2). Understanding the 1) Transmitter efficiency rankings are not consistent mechanics of this interaction could help drive design improvements. between two receivers (25% of transmitters are ranked 4) There were different rankings between the two test the same between two receivers in multipoint tests, 0% approaches, and there was a different ranking in the rank the same between the two receivers in the center small sample experiment 1b based on the receiver that point test) (Table 3). was used (Table 2). This inconsistency caused the 2) Efficiency rankings are different for single-point and ESTF to commission experiment 2, with which to multipoint tests. assess the validity of the assumption that a single test 3) More test locations decrease ranking differences between receiver could be used as a proxy with which phones (bad idea to rank by center position only). to compare wireless power transmitter efficiency 4) The receiver design variable makes it impossible to performance. fairly rank wireless transmitters based on efficiency. 5) Our second experiment yielded a typical energy usage Experiment 2: The ESTF designed a “total Watt-hour” of 22 Wh to charge a commonly available phone experiment that utilized a test approach closer to the effi- (measured in three locations on a transmitter with a ciency test protocol defined by the U.S. Department of free-placement design). Improving the efficiency by Energy to assess battery charger efficiency [6]. The goal 10%, which is a stretch, would save about 2.2 Wh over a 62 IEEE POWER ELECTRONICS MAGAZINE z September 2022

–– Table 3. Transmitter rankings. Multi-Position Ranking Center-Position Only Ranking Transmitter ID Phone 1 Ranking Phone 2 Ranking Phone 1 Ranking Phone 2 Ranking Average Difference by Tx UUT 1 11 21 UUT 2 22 53 0.50 UUT 3 34 16 1.00 UUT 4 45 34 3.00 UUT 5 57 78 1.00 UUT 6 63 42 1.50 UUT 7 78 67 2.50 UUT 8 86 85 1.00 Average difference by Rx 2.50 1.25 2   Standby Power W Range 130mW to 810mW UUT 7 Transmitter UUT 4 UUT 1 0.2 0.4 0.6 0.8 1 0 mW FIG 11 Sample of common wireless transmitters in 2021. 24-h period. However, it is well within reach to reduce this problem and discover alternative approaches to quiescent power by 50%. Looking at seven popular solving this need. The following bullets summarize our wireless transmitters introduced in 2021, we observed top findings. a narrower standby power range of 130–810 mW, with ■■Wireless power systems for consumer applications the median value (after removing the 810 mW outlier) of 210  mW (Figure 11). This is up from the 180 mW have entered mass-adoption. Energy savings improve- median value we saw in the first experiment (Figure 9). ment programs that target these systems will provide a Cutting standby power to 100 mW would save 2.6 Wh meaningful societal benefit. over a 24-h period. ■■Because of receiver–transmitter interaction, it is not possible to quantify or rank a stand-alone wireless Conclusion power transmitter based on efficiency. ■■A more narrowly defined receiver specification will As a result of the efforts by the WPC Energy Star Task help measure and help the industry improve wireless force to develop and validate a fair and repeatable test, power system efficiency. we are disappointed to conclude that we were not able ■■It is possible to quantify and rank the power-transfer to meet the goal of proposing an efficiency-test proto- efficiency of a transmitter–receiver pair if the receiver col for the U.S. Environmental Protection Agency design is fixed and the x-, y-, and z-coordinates are (EPA) that could rank Qi wireless power transmitters carefully controlled. based on power-transfer efficiency. We hope the indus- ■■The test receiver in an efficiency test protocol must try and academic institutions will continue to research present a real-world load-resistance profile. 63 September 2022 z IEEE POWER ELECTRONICS MAGAZINE

■■Measuring the power-transfer efficiency of a wireless About the Author transmitter with open placement capability requires mea- suring over the power profile of the transmitter at multi- John Perzow has recently retired as the owner of ASM ple x and y locations. Ideally, an x, y table is used to Consultants, LLC, which provided market research, prod- move the receiver in 1 mm (or smaller) increments within uct, market, and corporate development consulting ser- the charging area. vices for analog and mixed-signal semiconductor and system manufacturers. He was the vice president of mar- ■■Wireless power transmitters should be classified as ket development for the Wireless Power Consortium and external power supplies as they are used as voltage continues to consult for the WPC as the Chair of the WPC sources to provide power to battery and non-battery EnergyStar Task Force. Prior to founding his consulting receivers. group in 2010, he was the Marketing Director for Analog Devices’ Power Management Group, the Marketing Direc- ■■A program that reduces the average standby power of tor and the Product Line Manager for the Power Group of wireless power transmitters by 50% could save as much Broadcom Corporation and the Marketing Director for energy in a 24-h period as improving the full-power effi- National Semiconductor’s Power Group. He began his ciency by 10%. career as part of the start-up team of Comlinear Corpora- tion, which designed high-speed amplifiers and data con- Discussion verters. He received the B.S. degree in electrical engineering education from Colorado State University and Given the physical attributes of a tightly coupled trans- the M.B.A. degree from the University of Colorado, USA. former, where the coil structures, magnetic materials and He is conamed in six patents in power electronic circuit physical design are well controlled and not variable, it is design and was on the Industrial Advisory Board, Colo- easy to see how transformers can be optimized for maxi- rado State University, from 2010 to 2017. mum power transfer between the primary and secondary coils. Now imagine a transformer where the primary and References secondary windings and magnetic structures are in sepa- rate packages; and imagine that multiple secondary-side [1] 2021 Wireless Charging Insights, Strategy Analytics, Needham, MA, solutions will operate with a single primary-side device. It USA, Oct. 2021. is easy to see how the secondary-side device design, with [2] (May 2016). Wireless Charging of Consumer Electronics-Rubbish widely varying magnetic and electrical elements will Heap or Mass Adoption? [Online]. Available: https://www.standardsuni- impact total system performance. versity.org/e-magazine/june-2016/wireless-charging-consumer-electronics- rubbish-heap-mass-adoption/ Apparently in Maine they have an adage, “you can’t get [3] (Jun. 2021). Analysis: Global Smartphone Sales Forecast for Wire- there from here” [9] (spoken in a Maine accent), said when less Charging 2008 to 2026, Data Analytics. Accessed: Jan. 2022. giving directions as an observation of the impossibility [Online]. Available: https://www.strategyanalytics.com/access-services/ of traveling a direct route between certain places. That devices/mobile-phones/device-technologies/reports/report-detail/anal- seems to be the case here, too. We are unable to define ysis-global-smartphone-sales-forecast-for-wireless-charging-2008-to- a representative efficiency test for inductive wireless 2026?slid=1796916&spg=3 power transmitters that can interoperate with more than [4] (Dec. 13, 2021). DOE Appendix A to Subpart C of Part 430—Proce- one receiver design. dures, Interpretations, and Policies for Consideration of New or Revised Energy Conservation Standards and Test Procedures for Consumer Any wireless power system-efficiency can be mea- Products and Certain Commercial/Industrial Equipment. Accessed: sured, but controlling the variables is more compli- Jan. 2022. [Online]. Available: https://www.federalregister.gov/docu- cated than with common power supply measurement ments/2021/12/13/2021-25725/energy-conservation-program-for-appliance- approaches. Spatial positioning and load characteristics standards-procedures-interpretations-and-policies-for must be designed to mimic real-world conditions. Con- [5] (Feb. 10, 2016). External Power Supply Test, National Archives, Code trolling these variables makes it possible to accurately of Federal Regulations, Title 10, Chapter II, Subchapter D, Part 430, Sub- measure the efficiency of a wireless power transmitter if part C, 430.32. Accessed: Jan. 2022. [Online]. Available: https://www.ecfr. it is coupled to only one receiver design. gov/current/title-10/chapter-II/subchapter-D/part-430/subpart-C/section- 430.32#p-430.32(w)(2) The need to regulate wireless chargers for the ben- [6] (Feb. 21, 2016). Battery Charger Test: Appendix Z to Subpart B of efit of society is real, so, how can we address this prob- Part 430—Uniform Test Method for Measuring the Energy Consump- lem? There are two short-term solutions: 1) standardize tion of External Power Supplies National Archives, Code of Federal the receiver more precisely and 2) decrease quiescent Regulations, Title 10, Chapter II. Accessed: Jan. 2022. [Online]. Avail- (standby) power. able: https://www.ecfr.gov/current/title-10/chapter-II/subchapter-D/part- 430/subpart-B/appendix-Appendix%20Z%20to%20Subpart%20B%20of%20 Standardizing the receiver design could diminish Part%20430 receiver-influenced efficiency variability and allow the [7] (2016). Level VI, Energy Star. Accessed: Apr. 2020. [Online]. Available: industry to make reliable efficiency improvements. The https://www.cui.com/efficiency-standards Qi specification does not presently strictly define the [8] DOE Energy Conservation Program for Consumer Products: 10 CFR mechanical or electrical properties of the receiver, which Part 430, Subpart B, Appendix Y (‘Appendix Y’), U.S. Dept. Energy, allows for a wide range of unpredictable system efficiency Washington, DC, USA, Jan. 2016. behavior. [9] (Dec. 22, 2009). On the Quirkiness of Rural New England and Maine Culture. Accessed: Jan. 2022. [Online]. Available: http://andywoodruff. com/blog/you-cant-get-there-from-here/ and https://en.wikipedia.org/wiki/ Bert_%26_I  64 IEEE POWER ELECTRONICS MAGAZINE z September 2022

by Stephanie Watts Butler Women in Engineering Getting Involved With IEEE Power Electronics Society: Successful APEC Event for WIE, YP, and You! An insurmountable wall of jargon too large of an obstacle. [2]. Some conferences create a role acronyms glued together PELS’s five-year strategic plan lists of “New Volunteer Chair” to help with complex organiza- and cites engagement of its member- onboard new volunteers, but also tional dynamics can present a com- ship several times, especially with make clear the requirements for plicated scenario for those wanting respect to diversity and inclusion each volunteer position, how to to become more involved with the a nd industr ia l membership [1]. apply, and how to climb the ladder IEEE Power Electronics Society Therefore, the leadership of PELS, of conference leadership. The WIE (PELS). This wall can feel even more with the assistance of the PELS committee decided to mold this con- unsurmountable to those new to Women in Engineering (WIE) Com- cept into a live event where clarity engaging with the IEEE, especially mittee, have been investigating best would be provided for a variety of students, recent graduates, or practices for increasing engagement committees, roles, and activities diverse members. Industry members levels and satisfaction. (“topics”) across PELS in addition may struggle to find relevant oppor- to the opportunity to network with tunities, and non-native English A 2021 panel presentation on volunteers and leaders. The need for speakers may find understanding the diversity and inclusion work within the event, and the ability of the professional societies and confer- event to increase engagement, is Digital Object Identifier 10.1109/MPEL.2022.3193860 ences provided examples of best revealed in the story of one of the Date of publication: 28 September 2022 practices proven to support accessi- event volunteers. During the recent bility of volunteering opportunities FIG 1 IEEE APEC 2022 event hands out information on volunteering for IEEE PELS. Source: APEC 2022. 65September 2022 z IEEE POWER ELECTRONICS MAGAZINE

OUR MAIN virtual PELS townhall meeting [4], Radha Krishna COMPONENT Moorthy asked the first question, which was “how IS TRUST to become involved with PELS.”  I (Stephanie) shared with her that WIE would be sponsoring an ITG delivers common mode choke event on how to become involved with PELS and solutions for every application. she immediately accepted the invite to become a You’ll get quick turnarounds, custom solutions, and volunteer for the event. Radha volunteered to orga- one-on-one support from the industry’s top, high-volume nize the technical committee table so she could magnetics manufacturer. Our design engineers offer a learn about technical committees and also helped full-range of solutions for a wide variety with the standards table collateral too. Although of industries and applications. Radha unfortunately wasn’t able to attend the event in person, she noted “I was able to engage with the Trusted Innovation leaders of the activities in which I’m interested. Based on volunteering for this event and those Magnetics & EMI Filters interactions, I’m not only involved more with WIE now, but I’m establishing my engagement Engineering Electronics Partnership www.ITG-Electronics.com with Technical Committees 4 and 8 via the since 1963 associated conferences.” This event brought together a number of different collaborators: the Young Professionals (YP) Commit- tee served as a co-host and the Power Supply Manu- facturers Association (PSMA) also contributed information about how to work across similar orga- nizations which impact our field. Since PSMA mem- bers are typically companies, this partnership also became a way to provide increased opportunities for industrial members of PELS. The 2022 IEEE Applied Power Electronics Conference and Exposition (APEC) was chosen as the inaugural location for this new style of event titled “WIE, YP, and You: How to become involved with IEEE PELS and PSMA too.” With the mission statement “Join us and learn all the ways you can engage with PELS and PSMA, network with volunteers and officers, and uncover all the exciting opportunities behind these acronyms.” At APEC, 13 high-top round tables were placed around a room and a breakfast buffet was pro- vided (Figure 1). Each table had its topic blazoned on a sign above the table, and was hosted by lead- ers and current volunteers of that topic. Each table also had collateral for the attendees—handouts that gave an overview of the topic, ways to get involved, and expected frequently asked questions (FAQs) with answers. These handouts are also available on the PELS website to support contin- ued accessibility of information on how to be more involved at various levels [3]. Attendees picked up breakfast and wandered around the room, stopped at tables with topics that interested them, picked up FAQs, and networked with the leaders and vol- unteers (Figure 2). At the end of the event, each participant was invited to fill out a survey, includ- ing identifying topics in which they wanted to vol- unteer or learn more about. Several different metrics show the success of the event. For instance, 100% of respondents want to see this specific event organized again and ranked the handout collateral as good or excellent. 66 IEEE POWER ELECTRONICS MAGAZINE z September 2022

FIG 2 Attendees picked up breakfast and wandered around to gather PELS volunteer information. Source: APEC 2022. TRANSFORM SMART PRODUCT DEVELOPMENT PSIM ACQUISITION BOLSTERS ALTAIR’S SIMULATION PORTFOLIO The latest release of Altair Simulation augments Altair’s circuit board and electronic design tools, giving users more power to design and implement smart components, products, and systems. It also ushers in new tools for power electronics and motor drives, including PSIM, which delivers world-class simulation and design capabilities for power supplies, motor drives, control systems, and microgrids. Learn more about Altair Simulation 2022’s new abilities, features, and tools at altair.com/simulation-2022 © Altair Engineering Inc. All Rights Reserved. / altair.com / Nasdaq: ALTR / #ONLYFORWARD 67 September 2022 z IEEE POWER ELECTRONICS MAGAZINE

High Voltage The survey asked what topics the attendee wanted Capacitor Charging to learn more about or volunteer for, and the respon- Power Solutions dents could select as many topics as they preferred; 85% of all respondents wanted to volunteer for at least The 402 Series - robust charging power one topic or a future WIE or YP event, and 6% didn’t want to volunteer, but they did want to learn more Š Outputs from 0-1kV to 0-50kV about a given topic. Figure 3 provides the list of topics Š 5kJ/sec peak charge rate along with what percentage of survey respondents Š Comprehensive local/remote control wanted to volunteer for or learn more about that topic. Š Worldwide three phase AC inputs As shown in Figure 3, many attendees want to volun- teer for a variety of topics or gain more information. Visit us: https://www.us.lambda.tdk.com Folks could register in advance to express interest in Email: [email protected] one of the topics (even if they were unable to attend Call: +1-732-795-4100 APEC) demonstrating the thirst for learning how to become more involved in PELS (those responses were The best of both worlds! B AT T E R Y not included in the statistics for this article). A S S E M B LY Mersen and F & K DELVOTEC SOLUTIONS Figure 4 shows the age distribution from the have joined forces to develop a respondents. Because the event was cosponsored by standardized battery platform LAMINATED BUS BAR YP, one would expect a large number of younger par- solution using a laser welding WITH MONITORING ticipants—indeed nearly half of the attendees were connector process to enable below the age of 30. On the other hand, several experi- leading $/kW and kWh/Kg FEATURE enced industrial participants marched into the room efficiency for 21700 battery series. with myopic focus; they had recently realized engag- ing with PELS could assist their career or help them LASER WELDED solve a problem at work and they were excited to BUS BAR attend an event to help them engage. Consequently, the distribution of age and experience was quite CONNECTIONS broad. Figure 5 shows the range of organizational affiliations. As would be expected at a conference, DC FUSE COMPACT AND LOW academia was well represented. Breaking down the PROFILE VACUUM attendance statistics, the following trends were noted. BRAZED COLD PLATE ■ 68% of attendees were associated with Aca- E P. M E R S E N . C O M demia—faculty-staff, researchers, or students. ■ If academic researchers and students are com- 68 IEEE POWER ELECTRONICS MAGAZINE z September 2022 bined together, an approximate 1/3–1/3–1/3 distri- bution results between student/researcher–facul- ty–industry. ■ Approximately 1/3 of respondents were from out- side the USA. ■ Approximately 2/3 were male and 1/3 female or gender variant/nonconforming. Almost 75% would volunteer at a future YP or WIE event, an important response since successful events like this one take volunteers. Approximately 40 volunteers and IEEE staff worked together to cre- ate this successful event, including many volunteers who were unable to attend APEC, but wanted to help create permanent collateral that PELS can use to facilitate greater engagement in various opportuni- ties. IEEE PELS staff participation gave attendees the opportunity to meet the people who strongly sup- port the various PELS activities with administrative and program management assistance. The chairs for the event were myself (Stephanie Watts Butler) and Christina DiMarino, representing the PELS WiE Committee, and Nayara Brandao de Freitas, repre- senting the PELS YP Committee.

While the FAQs and handouts concept of personally inviting folks survey, found the table topic of inter- were deemed important by about 1/3 to PELS events was one of the calls est, and any other task that was of attendees, almost all attendees to action in a previous column [5]. needed. The students also found the cited the discussions, networking, experience rewarding. Anna Corbitt and socializing as what was most One personal invite that became summarized it well: important to them. Thus, having net- very helpful was Prof. Alan Man- working and roundtable discussion tooth from the University of Arkan- “Aside from networking and events that are structured and with a sas personally inviting several meeting new people, the main purpose appear to be the most suc- students to the event and to volun- thing I learned at the APEC cessful events. The importance of a teer. Four students became critical PELS event was how to stay structured event was obvious from volunteers during the live event, involved in the future. Before the survey results, 0% said the ensuring folks signed in, did the attending APEC, I was a fairly event should be less structured, 85% said structure was just right, Optimize the electrification properties and 15% thought should be more of your EV power electronics structured. As WIE has shifted & electric propulsion systems its programming development to be more professional and per- 75+ YEARS sonal development oriented, OF CUSTOMER rather than purely networking driven, we have seen a significant SERVICE increase in event engagement and participation—an important © take-away for other committees and event organizers A critical component to the success of any event is how to not only engage volunteers, but how to reach the desired audi- ence of attendees—especially since in this case the target audi- ence were folks who might have zero PELS engagement today, other than attending the APEC conference. One of the APEC ple- nary talks covered an important PELS initiative—Empower a Bil- lion Lives (EBL)—and the speak- ers gave a shout-out for this event. Thus, a reasonable assumption would be this men- tion during the well-attended Ple- nary Session drove attendance. However, about 50% of attendees learned about the event from a colleague—more than twice that of the APEC website, PELS Newsletter, or social media (although a posting by a col- league might have been viewed as learning from a colleague rather than social media). So just like my reaching out to Radha led to her volunteering, reaching out 1:1 is what most greatly impacts attendance. This grass- roots distributed engagement 69 September 2022 z IEEE POWER ELECTRONICS MAGAZINE