Abstract: In order to maintain high transmission efficiency when different loads are being charged, a dual-switch buck-boost conventer is proposed at the load end. By adjusting the duty cycle of the converter, the equivalent load resistance can be always equal to the optimal load resistance to achieve maximum efficiency. And the expected output power value is set, the corresponding output voltage according to different load resistance is calculated sending to the controller as a reference voltage, the phase shift angle of the inverter is adjusted through closed-loop phase shift control, and output the corresponding voltage stably realizing constant power control. The simulation shows that the transmission efficiency remains constant at 85% and the output power remains constant at 4 200 W when the load resistance varys between 10 ~ 40Ω.

Key words: impedance matching, dual-switch buck-boost converter, duty cycle, phase shift control , constant power control