Protection Strategy for Wireless Charging Electrical Vehicles

Wireless charging has become increasingly popular for electric vehicles (EVs) in recent years. However, possible device damage may happen because of the sharp variations of inverter output current and the ZVS angle due to the alignment variation between resonant coils especially while charging. To design a protection strategy, the characters of the inverter output current and phase angle are analyzed when the wireless charging EV leaves. The protection strategy is composed of the insufficient angle protection, overcurrent protection, and the excessive angle protection. A detection circuit is designed to measure the variation of inverter output current and phase angle. A wireless charging EV prototype is established to validate the proposed methods. The experimental results show that the designed detection circuit and protection strategy can catch the abnormal working state of the system when the wireless charged EV leaves and take measures immediately to protect the main circuit of the system from device damages.

I. Introduction

Wired charging is used for traditional EVs where the charging cables and sockets are exposed, which faces optional electric sparks and other safety issues in high power applications. Alternatively, wireless charging is safer because of neither direct physical connection nor shortcut circuit and leakage. Additionally, the wireless charging can be automatically started without manual operation required once the EV is detected in the proper position. Furthermore, the primary side can be built under the ground without occupying ground space. Because of the advantages mentioned above, the wireless charging for EVs has become a research hotspot [1]–[3].