Research on Carrier-Based Virtual Space Vector Modulation and DC Voltage Offset Compensation Method for Three-Level NPC Inverter

Neutral-point voltage (NPV) balance control is the key issue of the neutral-point-clamped (NPC) inverter. Compared to SVPWM, virtual space vector modulation (VSVM) can reduce the triple frequency fluctuation of the NPV at any modulation index and power factor, but cannot eliminate the DC voltage offset caused by accumulated errors. Besides, the vector dwell time calculation of VSVM is complicated. To solve the above problems, the equivalent modulation wave of VSVM is firstly deduced in this paper, and the carrier-based VSVM (CBVSVM), which can simplify the calculation of VSVM significantly, is further proposed. Then, for the five different regions of VSVM, the relation between the moving direction of modulation wave and DC voltage offset is analyzed respectively. On this basis, the DC voltage offset compensation method without changing the output voltage amplitude is researched. Finally, the effectiveness of the proposed CBVSVM and DC voltage offset compensation method are verified by simulation and experiment.