Microcontroller based PWM inverter control

Abstract

Electric motor converts electrical energy into mechanical energy. In industry, even in every household appliance electric motors are using for this conversion. A three-phase induction motor has for over 100 years proven to be an extremely reliable electromechanical conversion device. But speed control of induction motor is a crying need in industrial application. We know the speed of an induction motor is directly proportional to the frequency and inversely proportional to the number of poles. By changing the number of poles, precise control of speed is not possible. Therefore for the precise control of speed of induction motor the only option is to change the frequency. Therefore, to achieve the goal of speed control of induction motor there is no alternative of inverters. By means of power electronic converters it is possible to vary the speed of an induction motor. The main objective of static power converter is to produce an ac output waveform from a dc power supply. Moreover, inverter not only control the speed of induction motor but it has also some unique features like frequency control, voltage control, torque control, power factor correction, auto breaking, power saving, built in protection systems, etc. These features have made the inverter essential motor driving equipment in industrial as well as household appliances. With the availability of high speed power semiconductor devices the three phase inverters play the key role for variable speed ac motor drives. The objective of the present project is to design and construct a three-phase PWM inverter and necessary control circuits to run a three-phase squirrel cage induction motor. Control will involve computer interface with inverter control circuitry.