Three-Phase Multi-Module VSIs Using SHE-PWM with Reduced Zero-Sequence Circulating Current

A Modular Voltage-Source Inverter (MVSI) uses individual three-phase modules in a shunt connection to share the total power in a symmetrical manner. The operation of paralleled inverters, however, results in the appearance of zero-sequence current that circulates among the inverter modules. Moreover, conventional PWM techniques do not take advantage of the modular structure of MVSIs to improve harmonic content. In this paper, a new selective harmonic elimination (SHE) PWM technique that eliminates more harmonics than convention techniques current is proposed in the paper. In the paper, the basic principles of conventional SHE-PWM are reviewed, then the proposed PWM technique is introduced and explained, and then it is shown how the proposed technique can be just as good in reducing zerosequence circulating current as conventional methods. The concepts discussed in the paper are confirmed with results obtained from an experimental prototype.