A state-space modeling and a neutral point voltage control for an NPC power converter

Fluctuations of the neutral point voltage in NPC power converters cause problems such as excessively high voltage applied to their power devices. This paper presents a novel method of controlling the neutral point voltage by adjusting the dead-time that is required to prevent a DC-link short circuit. To analyze the dynamic effects of dead-time, a state-space averaged model for an NPC power converter is derived. This control method is applicable to single-phase NPC power converters, independent of the polarity of power flow, and free from the undesired variation of switching frequency of PWM. Experimental results have revealed satisfactory control performance.