Analysis, Design, and Implementation of WPT System for EV's Battery Charging Based on Optimal Operation Frequency Range

Charging electric vehicles wirelessly is promising because of its convenience as well as saving of charging cables. However, the existing wireless power transfer systems suffer from high resonant peaks and poor efficiency. Therefore, zero voltage switching (ZVS) operation of inverter should be achieved especially in high transfer power. Based on the variable frequency phase shift control strategy (VFPSC), this paper presents an optimal operation frequency range (OOFR) where the wireless power transfer (WPT) system can realize the required output and ZVS operation of inverter simultaneously without extra dc-dc converters. Meanwhile, based on OOFR, an optimized electrical parameter design method based on VFPSC is proposed with the multiple boundary conditions. Moreover, a novel three-loop control strategy (TLCS) is proposed to make the system operate at any points of OOFR. Especially, an implementation method of the TLCS is proposed, which can dynamically adjust frequency and phase shift to make the system always operate at the preset ZVS angle and realize the required output simultaneously. Finally, a 500-W WPT system is built to verify the correctness of theoretical analysis. The experimental results show that a very high overall efficiency is achieved in the whole charging process and the maximum efficiency can achieve 94.9% with k = 0.2.