New variable speed drive with proven motor friendly performance for medium voltage motors

A medium voltage VSD is described, where existing standard motors can be connected. The sinusoidal quality of its output voltage is proven by AC machine manufacturer tests. No additional motor losses exist compared to operation direct on line. For quadratic loads like pumps and fans, self-ventilated motors can be operated at variable speed without cooling problems. This paper describes a newly developed voltage source inverter (VSI) based on the principle of the neutral-point clamped (NPC) inverter. The new converter is equipped with an LC output filter in order to feed the motor with a sinusoidal output voltage. Because of the sinusoidal motor voltage, existing motors can be fed without any derating, without reinforcing the insulation and without substantial additional motor noise. The inverter uses an integrated gate commutated thyristor (IGCT).