A novel space vector modulation method of three-level inverter based on the synthesized middle space vectors

This paper proposes a space-vector modulation method for three-level neutral point clamped (NPC) inverter. The concept of middle-vectors is proposed and applied to restrain the neutral point (NP) voltage variations. By using the synthesized middle-vector method, the average current across the NP can be controlled to almost zero, while the neutral point voltage is not affected at every sampling instant. Moreover, the variation of neutral point voltage due to unbalanced capacitor voltages can be adjusted by controlling the proposed middle-vectors. The effectiveness of compensation for departure of NP potential during the system dynamic processes is guaranteed by distributing the active time of middle voltage vectors to the corresponding small voltage vectors. Detailed mathematical analysis is presented to illustrate the proposed middle vector synthesizing method. To verify the theoretical analysis, digital simulation using Matlab/Simulink is conducted and experiment setup is also built, both simulation and experimental results confirmed the validity and effectiveness of the proposed method.