An Online Coupling Coefficient Estimation in Wireless Power Transfer Systems with Voltage Loads

This paper presents an online and accurate method for estimating the coupling coefficient in wireless power transfer (WPT) systems with voltage loads using zero-phase angle (ZPA) frequencies. While the characteristics of ZPA-controlled WPT systems have been extensively studied, their applicability has largely been limited to resistive loads. This study investigates the ZPA frequencies of WPT systems with voltage loads, demonstrating that these frequencies depend solely on the coupling coefficient and are largely independent of output voltage in pronounced bifurcation modes. Leveraging this unique characteristic, a rapid and accurate coupling coefficient estimation method is proposed, utilizing self-oscillation to automatically locate ZPA frequencies. The proposed method does not generally affect system design or normal operation, completing the coupling estimation in just 1.5ms. It requires no wireless communication, additional hardware, or complex calculations across the entire coupling range. The effectiveness of the method is validated through simulation and experimental results.