Maximum Efficiency Tracking in Wireless Power Transfer for Battery Charger: Phase Shift and Frequency Control

This paper presents a maximum efficiency point tracking algorithm for Wireless Power Transfer (WPT) to match the load impedance to that of the source impedance. Conventionally, the load is considered only resistive in the literature. In most of the applications the battery is the end load and the equivalent circuit of battery consists of resistive and reactive elements. Therefore, to improve the overall efficiency of the system, load impedance has to be matched with source impedance. In this paper, a maximum efficiency power tracking (MEPT) algorithm is presented to match source impedance to load impedance. Proposed algorithm varies both frequency and phase shift of the inverter output voltage to minimize input power, whereas output power is kept constant by a dc-dc converter. Battery voltage and current regulation are maintained by the output side dc-dc converter. A brief mathematical analysis is provided to verify the proposed concept. Further, a laboratory prototype with a power rating of 600W is developed, and results are provided to verify the effectiveness of the concept.