Single-Stage Soft-Switching Low-Distortion Bipolar PWM Modulation High-Frequency-Link DC–AC Converter With Clamping Circuits

A single-stage soft-switching low-distortion bipolar pulsewidth modulation (BPWM) modulation high-frequency-link (HFL) dc-ac converter with clamping circuits is proposed in this paper. The converter consists of a primary side half bridge high-frequency inverter, a secondary side cycloconverter, and clamping circuits composed of a two-switch forward active clamping circuit and a passive clamping circuit. The clamping circuits recycle the energy in leakage inductances and output filter inductor during the dead time of the cycloconverter, clamp the voltage spike across bidirectional switches, and achieve soft switching of secondary side cycloconverter under BPWM modulation. Compared with unipolar PWM HFL dc-ac converter, BPWM HFL dc-ac converter has no duty cycle loss and narrow pulse in transformer primary, thus zero-crossing distortion is reduced. In this paper, soft switching and low zero-crossing distortion of the proposed dc-ac converter are analyzed. Experimental results of a 200 W prototype of the proposed dc-ac converter designed as audio amplifier are presented to verify the analysis results. Experimental results show that peak efficiency is 93.5% and ultralow output voltage total harmonic distortion +noise (THD + N) is lower than 0.2%.