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.
