Neutral-point-clamped inverter with parallel driving of IGBTs for industrial applications

This paper describes the design and construction of a neutral-point-clamped (NPC) inverter and converter, with outputs of 0.8, 1.6, and 3.2 MVA, which use insulated gate bipolar transistors (IGBTs). The inverter and converter are suitable for industrial drive applications, such as rolling mills, water pumps, and so on, and they are composed of multi-inverter units in parallel. Each inverter unit is composed of four pairs of parallel IGBTs connected in series. In order to share current among the parallel-connected IGBTs, influences of wiring inductance and device characteristics are evaluated by simulation using novel power device models and experimental results. To reduce both switching voltage swing and power consumption, a variable-capacitance snubber circuit is also presented for the NPC inverter.