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Capacitive Power Transfer for Contactless Charging

Capacitive Power Transfer for Contactless Charging. Mitchell Kline Igor Izyumin Prof. Bernhard Boser Prof. Seth Sanders. Why Wireless Power?. The Powermat.

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Capacitive Power Transfer for Contactless Charging

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  1. Capacitive Power Transfer for Contactless Charging Mitchell Kline Igor Izyumin Prof. Bernhard Boser Prof. Seth Sanders

  2. Why Wireless Power?

  3. The Powermat

  4. “…I started to wonder if the magnet on the iPhone case was safe in my pocket where I also keep my credit cards… I was told that I should remove my iPhone from the case after charging because [it] was not intended for daily use. ” Thomas Scholle1 star amazon review

  5. “you'll need to invest another $40 per device to get the full functionality as you see it advertised. Too pricey for me!” J. Lincoln 2star amazon review

  6. Wireless Power Technology Close-coupled wireless power transfer 1. Inductive Power Source Power Source Load Load 2. Capacitive

  7. Capacitive Power Transfer System 2 1 Powertrain optimization Alignment and load sensitivity

  8. Requirements • 3.5 pF/cm2(¼ mm air gap) with ~50 cm2gives 150 pF • Need >2.5 W (USB spec.)

  9. Prior Art A. Hu. 2008. Soccer Playing Robot 13.9 nF 217 kHz ~40 W? 44% efficient E. Culurciello. 2008. Inter-chip power transfer 10 fF 15 MHz ~100 uW? ~1% efficient?

  10. Optimization Approach C Given Pout and C, how do we maximize the efficiency? or What is the minimum required C to achieve a particular Pout and efficiency? Pout

  11. Powertrain Architecture

  12. Efficiency Expression Minimize: Increase voltage Minimize: Large switch Small inductor Fixed Maximize Does not consider switching losses => Eliminate with ZVS

  13. Approximate ZVS Analysis

  14. Approximate ZVS Analysis Initial charge qt = Charge removed by inductor

  15. ZVS Condition From integration: ZVS requires: Refactored as: qt = Charge removed by inductor

  16. Example Design Pout = 4 W, VS = 35 V, and RonCoss = 44 ps

  17. Example Design • Choose • η = 0.9, Q = 40 • Minimum C is 147 pF • Optimum VD/VS is 0.8 • Optimum switch size Coss = 13 pF

  18. Simulation Results

  19. Prototype Powertrain Circuit 8 pF 125 pF 28 V 35 V 3.5 Ω 12 uH Q = 42 Coilcraft 1812LS Siliconix Si1029X NXP Schottky PMEG6002EJ

  20. Experimental Results

  21. Capacitive Power Transfer System 2 1 Powertrain optimization Alignment and load sensitivity

  22. Automatic Frequency Tuning

  23. Automatic Frequency Tuning

  24. Automatic Duty Cycle Control VS ½ LresidualIL2 IL Load ½ Csw VS2 Light-load condition: not enough current in tank to get Zero Voltage Switching (ZVS)

  25. Automatic Duty Cycle Control SHUTDOWN Supply Current DC Output Voltage

  26. Capacitive Power Transfer System IS Csw - + VL Load

  27. With 6 by 10 cm2, we transfer 3.8 W at 83% efficiency over a 0.5 mm air gap.

  28. Controller H-Bridge & Inductors

  29. Rectifier Buck Converter

  30. Conclusion Power transfer over small capacitors is enabled by • Zero Voltage Switching Enable moderate voltage, high frequency operation • Automatic Tuning Robust to changes in coupling capacitance • Duty cycle adjustment without RX feedback Preserve efficiency at light loads

  31. Thank You! Acknowledgements Dr. Mei-Lin Chan Dr. Simone Gambini Prof. David Horsley Dr. MischaMegens James Peng Richard Przybyla Kun Wang Prof. Ming Wu This material is based upon work supported by the Defense Advanced Research Projects Agency (DARPA) under Contract No. W31P4Q-10-1-0002

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