Three-Phase Multimodule VSIs Using SHE-PWM to Reduce Zero-Sequence Circulating Current

A modular voltage-source inverter (MVSI) uses individual three-phase modules in a shunt connection to allow lower power rated inverters to be implemented in higher power applications. It is standard practice to implement each module with the same pulsewidth-modulation (PWM) pattern. This paper proposes a new PWM approach for MVSIs for which each module is made to operate with a different PWM pattern. It is shown in this paper how more output voltage harmonics can be eliminated with the new approach than with the standard approach and how the new approach can be expanded to significantly reduce zero-sequence current that circulates among the inverter modules. The mathematical formulations needed to generate appropriate PWM patterns for the new PWM approach and experimental results obtained from a prototype MVSI are presented in this paper as well.