Size Optimized Load Independent Constant Current and Constant Voltage Wireless Charging System for EVs

Efficient and compact wireless charging system (WCS) for electric vehicles requires a constant current-constant voltage (CC-CV) output, which ensures the safety and longer life span of Lithium-ion batteries. In this article, a simple, size-optimized WCS is designed using a series-series compensation topology to achieve load independent CC-CV output. The seamless transition from CC to CV mode is achieved by changing the switching frequency assisted by a simple analog switch (DG 201). Transmission line parameter based simplified technique is proposed to derive switching frequencies for CC-CV output. Furthermore, from the load independent voltage and current gain using frequency-domain analysis, switching frequencies for CC-CV mode is verified. In addition, all inverter switches are designed to operate with zero voltage switching (ZVS) at turn-<sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> and zero current switching at turn-<sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small> during CC charging and ZVS at turn <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> during CV charging. To improve power density a kVA/kW optimization technique is employed, which minimizes the size of reactive components. An optimized kVA/kW ratio of 19.95 is achieved at Q = 4.47 for a coupling coefficient 0.2. A 600 W prototype has been designed and developed to validate the proposed WCS. It operates at 115.6 kHz in CC mode and 129 kHz in CV mode with a coupling coefficient of 0.2 and achieves a peak efficiency of 92%.