Feed-forward frequency compensator for APWM HB flyback converter

A feed-forward frequency compensator for the asymmetrical pulse-width modulated (APWM) half-bridge (HB) flyback converter is proposed to increase power conversion efficiency. Under variable input voltage, the APWM HB flyback converter cannot be satisfied with the soft commutation of the output rectifier because the variation of the PWM duty cycle induces an improper turn-off duration. It means that the resonance of the primary current can be out of the ZCS condition with respect to the input voltage variation. The proposed feed-forward frequency compensator can properly change the operating frequency of the converter to preserve the soft commutation of the output rectifier with respect to the input voltage variation. Experimental results using a 240 W prototype converter were obtained to verify that the proposed compensation algorithm can improve the power conversion efficiency under the input voltage and load variations.