Analysis of starting performance of an inverter fed induction motor

Abstract

This thesis investigates the starting performance of inverter fed induction motors. Smooth starting with good control is an important requirement for an induction motor. The major requirement of industries are soft start and variable speed of machine. This thesis shows how sine pulse width modulation (SPWM) can be used to achieve the above requirements. Theoretical ag well as practical investigations were carried out to prove that SPWM inverter fed motors successfully fulfill the requirements. For present thesis work pwm inverter is selected. The waveform synthesis of pwm inverter is not simple. A simple technique of pwm inverter waveform synthesis is proposed and used for harmonic analysis in this thesis. The inverter waveforms were analysed using time domain analysis. Since conventional Fourier series method takes more computational time, the time domain method is used. For theoretical prediction d-q axes motor model has been used and Euler's method has been employed to solve the motor equations numerically. Frequency domain analysis takes more computational time because it solves motor equation for many harmonics. The method is inaccurate as frequency domain analysis has to truncate Fourier series to limit computational time. The inaccuracy may increase if pwm waveform is generated by asynchronous method. In asynchronous pwm, the modulated wave mayor may not be periodic of fundamental frequency. This phenomenon causes subharmonics to be presented in the pwm wave which cannot be detected by usual Fourier series method. Time domain representation of invert~r waveform and subsequent motor equations solution are free from these drawbacks.