DSP-based adaptive digital control method for frequency tracking and impedance angle control of MCR–WPT systems

Aiming at the problem where the transmission power and transmission efficiency are affected by frequency detuning in wireless power transfer (WPT), a frequency tracking method using current-over-zero comparison and a digital control method using a dynamic time lag is proposed based on the digital signal processing (DSP) technology. The proposed method only needs to determine the time when current passes the zero point and start current sampling. Then a simple digital phase-locked loop (PLL) can be accomplished by comparing the current sampling value with the setting current value at the zero point. Combined with voltage–current double closed-loop phase-shift control, constant current or voltage output is realized. Finally, a DSP-based experimental setup with an output power of 300 W is designed for a series of verification experiments. The findings show that the method can achieve fast frequency tracking as well as phase adjustment when the air-gap distance and load are changed. It also satisfies constant current or voltage output. More importantly, the transmission efficiency of the weak inductive state achieved by the proposed method is better than that of the fixed-frequency and resonant-frequency state. In addition, it is 5% higher than that of the fixed-frequency state.