On Current THD Extreme Switching Sequences for a Single-Phase Cascade H-Bridge Inverter with Phase-Shifted PWM and Non-Equal DC Sources

Cascade H-bridge inverter with Phase-Shifted Pulse Width Modulation (PS-PWM) is an attractive choice for integration of DC sources of different nature. Non-equal DC sources compromise current Total Harmonic Distortion (THD) by introducing undesirable low frequency subharmonics. This paper suggests that, for more than 3 H-bridges, there are two unique current Total Harmonic Distortion (THD) extreme DC source switching sequences on a PWM period-the best that minimizes undesirable low frequency current harmonic content (minimal THD) and the worst that delivers maximal current THD. These extreme sequences depend solely on DC source voltage inequality relationships.