High efficient four-level NNPC inverter with capacitor voltage control algorithm

- Four-level NNPC (Nested Neutral Point Clamped) inverters have fewer components compared to other 4-level inverters and can operate from 2.4 kV to 7.2 kV without the need for additional switching devices. The 4-level NNPC inverter outputs the final switching signal in consideration of the output current and the capacitor voltage state, since the flying capacitor voltage of each phase should be controlled to Vdc / 3 and normal control is possible. A carrier based pulse width modulation (CBPWM) method is used meanwhile, a new capacitor voltage control algorithm is proposed to reduce the switching loss for the conventional capacitor voltage control. In this paper, a 4 - level NNPC inverter was designed for experimental setup was made for the experiment. The validity of the capacitor voltage control algorithm is verified through experimental results. Copyright The Korean Institute of Electrical Engineers