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 power converter, with outputs of 0.8, 1.6, and 3.2 MVA, which use IGBTs. The inverter and converter are suitable for industrial drive applications, such as rolling mills, water pumps, etc., 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 achieve current balance among the parallel connected IGBTs, low inductance laminated bus bars are designed by using an electro-magnetic simulator, and switching waveforms of IGBTs are evaluated by the circuit simulator SPICE using power device models. A variable capacitance snubber circuit is also presented for the NPC inverter to reduce both switching voltage swing and power consumption.