Improving three-phase induction machines power factor using single phase auxiliary winding fed by an active power filter

This paper presents a three-phase induction machine that employs a single phase auxiliary winding, which is only magnetically coupled to the stator main winding, and controlled by an active power filter. The active filter consists mainly of a two leg PWM voltage source inverter, which together with the auxiliary winding serves to supply leading reactive power to the machine. With sufficient ampere-turn capability of the auxiliary winding and an adequate control algorithm, the computer simulation results show that it is possible to obtain nearly unity power factor operation at the terminals of the main winding over a range of load conditions including rated load. The simulated power factor of this scheme is compared with the measured result for a typical practical induction motor.