Comparison of Neutral-Point Balancing Mechanism in Parallel-Operated T-Type Three-Level PWM AC/DC Interface Converters

Single-operated T-type three level (T3level) PWM AC/DC interface converters suffer from neutral-point potential (NPP) balancing. Methods, such as modified space vector PWM (SVPWM), zero-sequence injection (ZSI) sinusoidal PWM (SPWM), have been proposed to solve the NPP balancing problem. However, NPP balancing reacts differently when T3level AC/DC interface converters operate parallelly. The mechanism of parallel-operated T3level AC/DC interface converters has been proposed by using modified SVPWM and ZSI SPWM. This paper explains the emergence of NPP unbalancing while paralleling T3level PWM AC/DC interface converters, from the SVPWM and ZSI SPWM point of view, respectively. Also, this paper points out the NPP solution equivalence between the above two methods.