A synchronous rectification method with a high-speed comparator for a megahertz frequency BWPT system to enhance efficiency

In bidirectional wireless power transfer (BWPT) systems, the phase synchronization accuracy of the secondary synchronous rectification (SR), or active rectification signal directly determines energy transfer efficiency and overall system stability. In traditional SR solutions, current transformers increase system losses. The auxiliary coil and RF line connection are susceptible to electromagnetic interference, resulting in signal delays, that lead to reduced system efficiency. This paper proposes a secondary-side self-synchronized rectification method that utilizes a high-speed comparator to perform real-time zero-crossing detection (ZCD) of the voltage across the secondary compensation capacitor, thereby generating a synchronization signal on the secondary side. By sampling the compensation capacitor, the obtained synchronization signal demonstrates high stability and strong immunity to interference. By studying synchronization signal acquisition at a switching frequency of 1 MHz, the proposed method enhances the stability of secondary-side synchronous rectification, enables soft switching, reduces system losses, and supports high-efficiency BWPT at 1 MHz. In this experiment, a BWPT system prototype incorporating a synchronous rectification method was developed. The system utilizes GaN devices in combination with an S-S compensation network and operates at a frequency of 1 MHz. SR is achieved on the secondary side, delivering an output power of 336.57 W, with a transmission efficiency of 96.48%.