Use of an LC filter to achieve a motor-friendly performance of the PWM voltage source inverter

By putting an LC filter between a PWM voltage source inverter and induction motor, standard industrial motors can also be utilized for adjustable speed drive applications. In this paper, the application of an LC filter to medium voltage motors fed by inverters with switching frequencies below 1000 Hz is described. For different filter topologies, rules for the electrical design are discussed as well as solutions for the stability problem. Also discussed are solutions against common mode voltage stress on the motor terminals. An example shows the implication of the filter on the minimum inverter power which has to be installed to feed a given motor.