This paper presents a new switching scheme for resonant inverters. The proposed method bases on the tracking algorithm of the resonant frequency. Therefore, the proposed method can keep unity output displacement factor at the load-impedance varying conditions. In order to control the output power, the proposed scheme uses pulse width modulation (PWM) method. Thus, since the proposed PWM scheme needs load-circulating operations, it can be adopted in the full-bridge inverter, but not in the conventional half-bridge inverters. In response to that, this paper also proposes a new half-bridge resonant inverter having load-circulating operation modes. In this paper, detailed switching schemes and control circuits of the proposed PWM method are described. Experimental results of the prototype experimental setup to verify the validity of the proposed method are presented and discussed.
