An improved CBPWM method to balance the output voltage of eight-switch three-phase inverter under neutral-point potential unbalance condition

This paper investigates the neutral-point (NP) potential unbalance of the fault tolerant topology of three-level neutral-point-clamped (NPC) inverter, namely the eight-switch three-phase inverter (ESTPI). It is illustrated in this paper that the conventional carrier-based pulse width modulation (CBPWM) will cause the NP potential unbalance of ESTPI. Moreover, the NP potential unbalance will lead to the output voltage unbalance, which seriously deteriorates the system performance of ESTPI. As a consequence, an improved CBPWM, where the upper and lower triangular carriers have different amplitudes, is proposed to guarantee a three-phase balanced output voltage of ESTPI. The simulation results demonstrate that the proposed scheme can suppress the unbalance of three-phase output voltage effectively.