Analysis and Design of Overcurrent Protection for WPT Systems With Class-D Inverter

In comparison with full-bridge inverter, half-bridge inverter, and single-switch inverter, class-D inverter presents a simpler structure with fewer switches and lower voltage stresses of switches, which makes class-D inverter suitable for wireless power transfer (WPT) systems. However, the class-D inverter may suffer from a large output current due to accidental variations of the load resistance and mutual inductance, which may potentially lead to device damage. Two passive overcurrent protection (OCP) circuits for WPT systems with class-D inverter are proposed in this article. The class-D inverter’s output current can be automatically protected to a safe value by the proposed OCP circuits. Compared to active protection, the current detection circuit and related control circuit are not required in the proposed method, which reduces the control complexity and is easy to implement. In addition, the proposed system can automatically return to the normal operation mode after the overcurrent event is over. The proposed OCP will not affect the inherent characteristics of the original compensation topologies, such as load-independent constant output and zero phase angle (ZPA). The operating principle of the proposed OCP circuits is analyzed. An experimental prototype is designed and established to validate the feasibility of the proposed method.