Solutions to Reduce Leakage Current and Extend the Operating Range of Power Factor for a Single-Phase Full-Bridge Inverter with DC Bypass

A full bridge inverter with DC bypass (FB-DCBP) topology is not only capable of withstanding twice as much voltage stress as FB structure but also alleviates the leakage current that the FB registers. However, the improvement in leakage current of the FB-DCBP depends on the parameter consistency of the DCBP circuit such as the propagation time of the photocoupler and the turn-on and turn-off times of the power transistors. The parameter inconsistency of the DCBP circuit would incur asymmetric operation that causes two unequal clamping voltages and worsens the leakage current. In addition, because the clamping diodes of FB-DCBP are not controllable, a slight phase lead/lag in AC current with respect to grid voltage would result in PWM failure and deteriorate AC power quality and leakage current. To balance the clamping voltages on the DC capacitors, a duty ratio compensator (DRC) is presented to cope with the overdischarged DC capacitor due to the inconsistency in DCBP circuit. To further avert malfunction in PWM voltage, an improved topology with two MOSFETs in place of the clamping diodes of FB-DCBP is presented. Experimental results validate the effectiveness of the proposed approaches.