Duty and Phase Control of a Self-Synchronized Class E Rectifier for High-Frequency Wireless Power Transfer System

This article proposes a high-frequency (HF) wireless power transfer (WPT) system using duty and phase control of a self-synchronized class E rectifier considering the nonlinear internal capacitance of field-effect transistors (FETs). In HF WPT systems ($>$$ \text{13.56}\,\text{MHz}$), the self-synchronized class E rectifier provides a precise gate signal by compensating for the propagation delay. However, when controlling the output power of the HF WPT system, the nonlinear capacitance $C_{\text{oss}}$ of FETs distorts the shape of the drain-voltage waveform, which reduces the efficiency due to nonzero-voltage switching or partial diode operation. To mitigate this issue, we propose an $\alpha$ (=duty ratio) and $\beta$ (=phase delay) control method for a self-synchronized class E rectifier while considering the nonlinear $C_{\text{oss}}$ of FET. To achieve robust control and performance of the HF WPT system, we employed a regression method to estimate the value of $C_{\text{oss}}$ more accurately. Specifically, considering the impact of $C_{\text{oss}}$ on the performance of the HF WPT system, we selected two optimized control points $P_{\text{max}}$ and $P_{\text{min}}$ and developed a first–order polynomial equation representing the relationship between $\alpha$ and $\beta$. Following the determined $\alpha$$\beta$ relationship, the output power of the WPT was adjusted by hysteresis control while maintaining the highest efficiency. In the experimental validation, the proposed WPT system achieved a conversion efficiency of 82% to 76% in the 160–90 W output power range. Finally, the effectiveness of the proposed control method was also verified in closed-loop control during dynamic operation from 160 to $100\,\mathrm{W}$, with a minimal ripple (1.7%) in the output power.