Performance Comparison of Primary Side PFM and Secondary Side PWM for SS Wireless Power Transfer CC/CV Control Strategy

Abstract

Wireless Power Transfer (WPT) system for Electric Vehicle (EV) battery charging application popularity is increasing due to the safety, convenience, and eco-friendly issue. Nowadays, Lithium-Ion battery is well known as one of the potential options for EV. However, Constant Current/Constant Voltage (CC/CV) control strategy needs to be adopted for achieving high efficiency charging and maintaining battery lifetime. By analyzing the gain curve, Pulse Frequency Modulation (PFM) can be used to perform CC/CV charging due to the load variation. The operating switching frequency needs to be considered and limited to prevent instability of the system. A typical drawback in the PFM control is the use of serial communication module for feedback data transmission from the secondary to the primary side. Therefore, the rectifier side controlled WPT can be a solution to remove the feedback communication part. In this paper, Pulse Width Modulation (PWM) applied in the secondary side (rectifier) for achieving CC/CV charging is investigated and compared with the traditional PFM control. The comparison study is verified by implementing a 3kW Series-Series (SS) WPT topology in the Power Simulation (PSIM) software. It shows that the secondary side PWM control strategy can achieve 94% efficiency during the $35 \Omega $ load in CC mode, while the primary side PFM control only can achieve 88% efficiency.