Five-Level NPC VSI: Different Ways to Balance Input DC Link Voltages

A five-level Neutral Point Clamped Voltage Source Inverter (NPC-VSI) has several advantages of large capacity, high voltage and low current waveform distortion. However, there is an important problem of the neutral point potential variation. The variation causes an unbalance in the DC link voltage levels and current waveform distortion. In this paper, we propose three ways to control the four input DC voltages. For this, we use in the first case a five-level rectifier/inverter back-to-back and a full clamping bridge, in the second case two three-level PWM rectifiers and a half clamping bridge and in the last one a four two-level PWM current rectifier without any additional circuitry. In all the cases, the rectifiers are controlled by sliding mode control