Dynamic-Space-Vector Discontinuous PWM for Three-Phase Vienna Rectifiers with Unbalanced Neutral-Point Voltage

Neutral-point (NP) voltage imbalance is an inherent issue of three-level converters. The alternating input current distortion is generated by using the conventional discontinuous pulsewidth modulation (DPWM) scheme without NP voltage balance control. In this article, the deviation vector between the synthesis vector and the reference vector, which is the fundamental cause of alternating input current distortion under NP voltage unbalance conditions, is revealed. Then, by optimizing the subsector division and the switching state sequence, a dynamic-space-vector DPWM (DSV-DPWM) is proposed to eliminate the deviation vector. Further, the comparisons of the proposed DSV-DPWM, the conventional DPWM, and an existing triangle carrier-based DPWM (TCB-DPWM), are addressed. Finally, a 10-kW prototype was built to verify the effectiveness of the proposed DSV-DPWM scheme. Experimental results show that, compared with the conventional DPWM scheme and the TCB-DPWM scheme, both the current THD performance and efficiencies can be significantly improved by the proposed DSV-DPWM scheme under unbalanced NP voltage conditions.