Output filter considerations for PWM drives with induction motors

PWM drives using insulated gate bipolar transistors (IGBTs) have become the preferred standard for variable speed control of induction motors because of their high reliability, good performance, and relatively low cost. Despite the many benefits these drives offer it is important to understand the consequences they can place on the motor insulation system. This is particularly important when considering the fast rise time of the inverter output voltage pulses when applied to installations using long connection cables between the inverter and motor. This paper first describes the potential problem a motor insulation system might experience when subjected to fast rise time inverter output voltage pulses in combination with long connection cables between the motor and inverter. Subsequently it reviews various inverter output filter arrangements that can be used to minimize motor insulation stress