Optimal PWM of neutral point charge minimum for three-level inverter at high modulation index

摘要

This paper aims to suppress the neutral point voltage ripple of optimal PWM for NPC three-level inverter at low switching frequency and high modulation index. A new optimal PWM method with minimum neutral point charge is proposed. New pulse pattern with negative pulses and an additional switching angle is adopted. Pulse sequence is calculated with the new method, which introduces the weighting factor λ to compromise the THD and neutral point charge. Simulation and experiment results show that the new method can effectively suppress the neutral point voltage ripple and stabilize the output voltage level while ensuring that the current harmonic is acceptable.