Analysis of neutral-point voltage balancing problem in three-level neutral-point-clamped inverters with SVPWM modulation

In this paper, the evolution and the control options of the neutral point potential in NPC inverters with SVPWM modulation are analysed. In this analysis, the different components that can be found in the phase current are taken into account: fundamental, dc current and harmonics. Firstly, the current injected in the neutral point by the non-redundant medium vectors is evaluated for each phase current component. The only components that inject dc current in neutral point are demonstrated to be the even and non-multiple of 3 current harmonics. This dc current tends to unbalance the neutral point potential. Finally, the compensation of this dc current by means of both the small redundant vectors and the fundamental component of the phase current is analysed. This study allows the maximum amplitude of the phase current harmonics to be determined without losing the neutral point potential control with the SVPWM modulation.