Voltage Slope-sensing Based Zero Voltage Switching Detection for 6.78 MHz Wireless Power Transfer Application

Zero voltage switching (ZVS) has been widely implemented to improve the efficiency and robustness of high switching frequency converters. However, once the converter loses ZVS, the abrupt increase in switching loss decreases efficiency and may damage the converter. In this paper, a voltage slope-based detection method is proposed to detect ZVS status and prevent the converter from continuously hard switching. This detection circuit converts the voltage slope of the switching node to a dc voltage, which is compared with a reference voltage for the ZVS criterion. When hard switching occurs, two actions can be chosen: either shutting down the converter or adjusting the dead time to regain ZVS. The detection is achieved with simple circuitry and little control effort. A 6.78 MHz inverter for WPT application is used to verify this detection method. Experimental results show that ZVS status is detected effectively.