Speed Control of Three Phase Squirrel Cage Induction Motor (original) (raw)

The paper describes the open loop control of the 3 phase induction motor at variable speed using a 3 phase inverter. The 3 phase inverter is supplied from a 400V DC supply. The 3 phase inverter with 3 legs use IGBTs as switches for the generation of 3 phase output. The switches are controlled by pulses created by the PIC microcontroller. The PWM technique used in this project is sinusoidal pulse width modulation. PIC mi crocontroller is used to generate PWM signals. These low voltage signals are given to opto-couplers. The opto-coupler isolates the controller from high voltage level circuit and raises the voltage level of output. The output is fed to the driver circuit for a half bridge of IGBT. For the protection of IGBTs against the over voltages and from short circuiting we have used bootstrapping arrangement. The PIC microcontroller is used to generate PWM signals at variable frequencies. The frequency can be varied using a manual input to the controller.