Power factor correction of induction machine using PWM inverter fed auxiliary stator winding

This thesis deals with a scheme for power factor correction of an induction machine by using an auxiliary stator winding in conjunction with a PWM voltage inverter and a capacitor on the dc side of the inverter. The aim of this scheme is to use PWM technique as means to reduce the reactive components such as capacitor and filter circuits.;The basic principle of power factor correction has been elaborated by describing various methods of power factor correction for an induction motor.;The operating principle of the proposed scheme is explained with the help of an equivalent circuit and phasor diagram. Mathematical models are developed to simulate the proposed scheme. Mathematical analysis shows that the scheme does not give the best performance if the power factor is corrected to unity. A criterion has been developed to select the optimum value of power factor at which the scheme gives best performance. Fourier analysis of the PWM inverter output voltage waveform is performed and the effect of the harmonics on the performance of the scheme is investigated. The simulation and experimental results show that harmonic components in the PWM output voltage can be reduced by operating the PWM inverter with a higher frequency ratio and the distortion factor in the main input current can be reduced to get a nearly sinusoidal current waveform.;The proposed scheme is an alternative to the fixed capacitor thyristor controlled reactor scheme. The proposed scheme requires only a low cost dc capacitor rather than three units of ac capacitors and does not need any filter circuit. Hence the proposed scheme could be an economical scheme.