Modeling and Analysis of a Strongly Coupled Series-Parallel-Compensated Wireless Power Transfer System

In the wireless charging of high-power electric buses or low-power consumer electronics, the charging distance is normally very small, leading to a strong coupling. Current distortion occurs for a wireless power transfer (WPT) system with a strong coupling. This paper investigates the strongly coupled series-parallel (SP)-compensated WPT system, where the first harmonic approximation (FHA) is no longer valid. A mathematical model of an SP-compensated WPT system based on differential equations is built. There are two sinusoidal components with significantly different frequencies existing in the transmitter and receiver currents, which cause the current distortion. The proposed model and FHA are compared, and the proposed model is more accurate than FHA. The estimations of the current root-mean-square values from FHA tend to be smaller than those from the proposed model and the measured values. In addition, it is found that with the increasing rectifier dc current, the system transits from zero voltage switching to zero current switching. The critical rectifier dc current decreases with the increasing operating frequency. The experimental results verify the effectiveness of the proposed model. The proposed model promotes a better design of an SP-compensated strongly coupled WPT system.