Loss Unbalance Issue of the Full-bridge Inverter with Reactive Power Injection

The unbalanced power losses of the semiconductor switches affect the thermal loading, and thus, the reliability of power converters is challenged. In this paper, the unbalance loss distribution of power devices has been analyzed in a full-bridge (FB) PV inverter, which employs the traditional hybrid unipolar pulse width modulation (UPWM) for reactive power injection. This analysis serves to improve the design and control of the FB inverter to enhance its reliability. More importantly, a new modulation method is proposed to balance the power losses, resulting in good thermal performance and increase lifetime. The proposed method periodically changes the switching operation modes at the grid frequency to ensure equal power losses, and thus, the almost identical junction temperature of each power switch. Simulation and experimental results have validated the effectiveness of the loss analysis and the proposed modulation scheme.