A neutral-point potential balancing method for three-level inverters based on improved virtual space vector modulation

A new modulation method is proposed to solve the unbalancing problem of neutral-point potential in the DC side in three-level (3L) three-phase neutral-point-clamped (NPC) voltage source inverters. Based on properties of current balancing of three phases and redundant short vectors, different short vectors have different time distribution factors, which can be used to improve the control of the neutral-point current. The neutral-point voltage is under control by adjusting the time of the virtual vector, therefore the distortion of the output voltage waveform and the voltage across switch devices will be reduced. Simulation results show the validity of the method.