Controlling Common-Mode Voltages in Multilevel Inverters

This paper proposes a novel method based on pulse width modulation techniques toreduce and control the common-mode voltage in three-phase multilevel inverters. Besides controllingthe common-mode voltage, this method is capable of controlling capacitors voltages and load currentswith low switching losses and harmonic contents. In fact, due to the existence of different pulsepatterns and the possibility of choosing the optimum patterns based on the most important criteria, thecontrollability of this method has risen properly. Furthermore, the controller randomly selects one ofthe optimum pulse patterns, which has another advantage of spreading the spectrum contents of theoutput voltage for low electromagnetic interferences and mechanical vibration. This method can beapplied to a three-phase, three-level inverter with the flying capacitor topology. Another advantage ofthis method is that the technique can be applied to more voltage levels without significantly changingthe control algorithm. The simulation results of a five-level inverter in this paper indicate that theproposed technique can be used to implement a multilevel inverter.