91% Efficient Wireless Transfer of 25kW across 21cm
During last week's IEEE Applied Power Electronics Conference (APEC 2016) Mariusz Bojarski, Hevo Power Inc., Erdem Asa, Hevo Power Inc. and New York University, United States, Kerim Colak, Istanbul Ulasim A.S., and Dariusz Czarkowski, New York University presented a paper titled, "A 25kW Industrial Prototype Wireless Electric Vehicle Charger". The prototype design was experimentally verified at output power levels from 0 to 25kW. The measured system efficiency was up to 91%.
This wireless charger consists of three-phase power factor corrector (PFC), three-phase resonant inverter, primary and secondary coils with series resonant compensation, and a rectifier. In the proposed design, PFC provides a constant voltage dc bus and the whole output regulation is done by the resonant inverter. It simplifies the rectifier structure to the simple full-bridge topology. The operating frequency of the converter was 85- to 88-kHz.
Combining the two traditional modulation, phase shift modulation and frequency control, phase-frequency hybrid control strategy is implemented in this work. The principle of operation is to utilize the phase shift for regulating the system output and the frequency to operate as close to the resonant frequency as possible.
For the control loops, the phase detector, loop filter and digital control delay loop (DCDL) are implemented in a Spartan6 XC6SLX9 FPGA and the feedback controller is managed by a TMS320F28335PGFA microcontroller. The phase detector finds the phase error between a reference value and the output signal. Its output is filtered by the loop filter and applied to the microprocessor.
The hybrid control strategy evaluates the tuning frequency and phase shift function based on the reference and output signals and sends the needed signal to the DCDL. The FPGA outputs are used to control the gate drivers.
Experimental results showed that the proposed phase-frequency hybrid control strategy performs well. Firstly, the proposed concept provides full-range regulation from zero to full power without losing ZVS conditions. Secondly, it keeps the operating frequency range narrow (in this instance between 85kHz and 88kHz) and it can operate within the frequency range suggested by SAE J2954 for wireless charging electric vehicles. And thirdly, the presented inverter has high efficiency in a wide range of operation parameters.