A High-Efficiency Wireless Power Transfer System With Variable Capacitor Technique for Compensating Coil Misalignment

This paper introduces a novel variable capacitor module (VCM) for a wireless power transfer (WPT) systems system. It operates based on the principle that ceramic capacitance changes with the variation of DC bias voltage. By generating a controllable pulse current through a driver circuit, the capacitor bias voltage can be adjusted, thereby altering the compensation capacitance to enhance system stability. In comparison to previous literature, the proposed module features a simple circuit topology with fewer circuit components, and also the power switch in the driver circuit exhibits zero-current switching (ZCS) characteristics, further reducing circuit power losses. To validate the feasibility of the proposed concept, this paper implemented a 200W WPT system. The VCM adjusts the compensation capacitance of the transmitter side (Tx) coil to achieve optimal transmission efficiency. The experimental results demonstrate that the VCM has an adjustment range of 105nF to 122nF. By using VCM, the overall system efficiency achieves an improvement of 2.74% in coil misalignment conditions and approximately 3% enhancement in resonant tank power transfer efficiency. When the coils are precisely aligned, the system can achieve an efficiency of 87%. Employing the proposed full-bridge phase shift modulation technique ensures stable control of the output voltage at 48V. Based on test results, highlighting its reliable performance.