Microprocessor control system for PWM IGBT inverter feeding three-phase induction motor

In this work a three-phase PWM IGBT voltage source inverter has been introduced. The PWM control signals are produced using a microprocessor, so the complex control circuit hardware of the inverter can be replaced by microprocessor software. The suboptimal PWM switching strategy is proposed, which closely approximates and exhibits many of the desirable performance characteristics of optimized PWM strategies based on minimized total harmonic distortion. The drive system hardware includes the implementation of microprocessor system, transistorized inverter, interface circuits, isolating circuits and driving circuits. The IGBTs are used as efficient switching devices for the inverter power circuits, so simple and efficient transistor drive circuits can be used. Also, the overlap protection is taken into consideration. The PWM inverter is to feed an induction motor with adjustable voltage to frequency in a proper relation to maintain approximately constant rated flux in the machine over the operating frequency range (1-50 Hz). Hence, the drive system is used to control the speed of a three-phase induction motor from very low speed to the motor rated speed at a constant torque. The test results were obtained experimentally. The waveforms and the spectrum analysis of PWM control signals are given together with voltage and current of the motor at different frequencies