Abstract
This paper examines the neutral voltage variations on a neutral point clamped (NPC) inverter circuit and proposes a new PWM technique which allows a great reduction in the capacitor values. Conventional and advanced control methods of the neutral point potential are analyzed demonstrating that the use of medium size vectors generates voltage fluctuations which can only be reduced by increasing the capacitor values. In this paper a new PWM control method is introduced. Different from former techniques, the use of the medium size vectors is avoided, increasing the neutral voltage controllable region to the whole range of operation under any load conditions making it possible to operate the NPC inverter with very small DC-link capacitors. The suitable voltage vector is carefully selected to reduce the output waveform distortion. The proposed PWM technique is experimentally verified on a low-power prototype and is compared with advanced control methods. The simulation and experimental results have shown that the proposed technique allows a great reduction in the capacitor values.
