A simple capacitor voltage balancing method for nested neutral point clamped inverter

A simple flying-capacitor voltage balancing method for nested neutral point clamped (NNPC) inverter is proposed in this paper. The NNPC inverter is a newly developed four-level voltage source inverter (VSI) with new topology. There are two flying-capacitors in series in each leg in the NNPC inverter. The voltage across each capacitor should be controlled to balance at one-third of DC bus voltage to make the inverter operate normally and all switching devices share the same voltage stress. The proposed capacitor voltage balancing method, which employs proper redundant phase switching states to control capacitor voltages and uses simple control tables to implement the procedure, requiring very few computations, is simple, effective and easy to integrate with any PWM schemes. The proposed method is verified by simulation results.