Chris Mi , Ph.D, Fellow IEEE Professor, Department of Electrical and Computer Engineering

1. High Efficiency Wireless Charging of Electric Vehicles for Safe and Economic Future Transportation Chris Mi, Ph.D, Fellow IEEE Professor, Department of Electrical and Computer Engineering Director, DOE GATE Center for Electric Drive Transportation University of Michigan-Dearborn, (313)583-6434; mi@ieee.org

2. Conventional EV Charging 1 2 3 Battery swapping Investment of battery packs; standardization is difficult; swapping stations need a lot investment, space and manpower; safety and reliability is of concern Normal charging AC charging using level 1 or level 2，voltage at 110V, 220V，6-10 hours per charge Charge at home or public space, need large installation of charge stations Fast charging Mostly DC charging in 15 to 30 minutes. For an EV with a 24kWh battery pack, charging in 15 minutes means 96kW. This is way over the power available in private homes.

3. Issues of Con. Charging and Battery Swapping Electric safety is of concern: electric shock due to rain, etc. Charge station, plug and cable can be easily damaged, stolen Charge/swap station takes a lot of space and affect the views Wireless Charging

4. Definition of WPT • Wireless power transfer (WPT) • Inductive power transfer (IPT) • Contactless power system (CPS), • Wireless energy transfer • Strongly coupled magnetic resonance • High-efficiency inductive-power distribution • The essential principles are the same given the distances over which the power is coupled is almost always within one quarter of a wavelength and therefore, the fundamental operation of all of these systems can be described by simple coupled models Grant Covicand John Boys, “Modern Trends in Inductive Power Transfer for Transportation Applications,” IEEE journal of emerging and selected topics in power electronics, vol. 1, no. 1, march 2013

5. Methods of Wireless Power Transfer Electromagnetic Induction 电磁感应式 Radio wave 无线电波 • In 1830’s, Faraday's law of induction • In 1890’s, Tesla had a dream to send energy wirelessly • GM EV1used an Inductivecharger in the 1990’s • 2007, MIT demonstrated a system that can transfer 60W of power over 2 m distance at very low efficiency • Wireless/inductive chargers are available on the market • Qualcomm, Delphi (Witricity), Plugless Power, KAIST, etc. have developed EV wireless charger prototypes Wireless Power Transfer 电能的无线传输 Microwave 微波 Radiation 辐射式 Laser 激光 Electromagnetic Resonance 电磁谐振式 Ultrasound 超声波 Predicted Wireless Charging Market $17 Billion in 2019

6. Problems and Difficulties • Magnetic field is diminishing proportional to1/r3 • Often the mutual inductance is less than 20% or 10% of the self inductance • Analytical calculation of coil mutual inductance is next to impossible • Further analytical method is needed • Numerical simulation and coupled field - lumped parameter simulation is also of paramount importance • High frequency HFSS instead of static FEM for high frequency High cost Low efficiency Need novel designs and methods to study these systems Large size Limited distance Sensitive to vehicle alignment

7. A Wireless Power Transfer System • Secondary controlled WPT Covic, G.A.; Boys, J.T., "Inductive Power Transfer," Proceedings of the IEEE , vol.101, no.6, pp.1276,1289, June 2013.

8. Equivalent Circuit Series-Series L1, L2 – Self inductance Lm – Mutual inductance L1=L1σ+Lm; L2= L2σ+Lm Series-Series Resonance Structure

9. Power Transferred • Power of output side • Power of the input side • Efficiency Calculated efficiency

10. System Topology at UMD • Key inventions: • Optimized multi-coil design for maximum coupling, with bipolar architecture • LCC topology for soft switching to further increase efficiency and frequency • Distributed circuit parameters to minimize the capacitor size and voltage rating • Bidirectional LCL Power factor correction circuit to maximize the front end efficiency and reduce system cost • Foreign object detection and electromagnetic field emissions for human and animal safety for the developed system.

11. Double-sided LCC Compensated Wireless Power Transfer • Topology • Important Characteristic: • The output current at resonant frequency: • The output power can be expressed as:

12. Comparison of Coil Design (a) Circular pads, (b) flux-pipe pads (c) DD-DDQ bipolar pads Trong-Duy Nguyen, Siqi Li, Weihan Li, Chunting Chris Mi, Feasibility Study on Bipolar Pads for Efficient Wireless Power Chargers, IEEE Applied Power Electronics Conference, Fort Worth, TX, USA, March16-20, 2014

13. Typical Misalignment • Door-to-door (right-left)is more difficult • Front-rear is easier to align Rectangular bipolar pads Rectangular Unipolar pads

14. Five Studied Cases Z (height) Coils: Similar area Ferrites: Similar volume Y (width) X (depth / length)

15. X & Y Misalignment 1. The maximum coupling coefficient decreases with the increase of coil’s X-length The topology with bigger Y-size has a better Y-misalignment tolerance Z (height) 2. X-misalignment tolerance increases with the coil’s X-length Y (width) X (length)

16. Angular Misalignment Typically, when a driver parks an EV, the worst angular misalignment can be limited at about 30°

17. Coupling coefficient vs x, y, theta Finite element analysis using Maxwell 3D Z Y X

18. Coupling Coefficient Profile versus Door-to-door and Front-to-rear Misalignments

19. Safety issues Range of flux density is within 1-1.2 meters, => It is safe to install this WPC in an electric vehicle chassis, typically about 1.8meter door-to-door size with chassis - perfectly aligned position With chassis - maximum misaligned position

20. Exposed field to a human of 1.8-meter high Human body is exposed to maximum about 1.6uTesla in foot area while about 0.06uT in head area. Human’s height [in meter]

21. Experimental Verification Input voltage Output current Input current Output voltage Max power: 8kW Max Eff.: 97%

22. Experiment Results Xmis=0mm, Gap =200mm Xmis=300mm, Gap =200mm Xmis=125mm, Gap =400mm

23. (Rectifier + PFC) + Buck + Wireless • PFC – power factor correction >0.98 • Buck for charge control • WPT: fixed frequency, auto-tuned system. WPT

24. System Efficiency for Different Vbat

25. Dynamic In-Motion Charging Buried tracks

26. Results of Foreign Object Test #1 Experiment Result: the gum wrapper was burned and there left an imprint, which means the temperature is high.

27. Conclusions • Misalignment tolerance was analyzed and discussed • Two kinds of coupling coefficient detection methods were proposed • 8 kW wireless charger prototype with 200mm gap and 300mm door-to-door misalignment tolerance had been built and tested • Coupling coefficient maintains at 18.8%~31.1% • With a 200mm gap, 95.66% efficiency (at about 8kW) from DC to DC was obtained at desired position • 95.39% efficiency (at about 4kW) at 300mm X-misalignment and 200mm Gap

28. Acknowledgement • Department of Energy • GATE Program • DENSO International • US China Clean Energy Center • GATE Industrial Partners • Chrysler, Ford, DENSO International, Mathworks, dSPACE, ANSYS, Hp Pelzer, EDTA, PSIM, GaN Systems

29. IEEE Workshop and TPEL Special Issue on Wireless Power • 2015 WoWSponsored by six Societies of IEEE • PELS, IAS, IES, VTS, MAG, PES • June 5-6 (Fri.-Sat.), 2015, Daejeon, Korea • Held just after the 2015 ECCE-Asia (June 1-4) in Seoul • General Chairs: Dr. Chun Rim, Dr. Chris Mi • TPC: Dr. John Miller • http://www.2015wow.org • IEEE Transactions on Power Electronics (Guest-EIC) • IEEE Journal on Emerging and Selected Topics on Power Electronics (Guest-EIC)