Keywords: pulse width modulation, microcontrollers, THD, AC induction motors, induction motor control, three–phase inverters, constant torque zone, constant power zone, look–up tables, AT89C52, PIC18F4431, current distortion, feedforward control, total harmonic distortion
Low distortion three–phase sine PWM using a general purpose micro–controller
Three–phase balanced sine–PWM pulses are required for the purpose of generation of sinusoidal output voltage and/or currents from inverters, used for UPS/motor–control applications. Such pulse–generation is possible using micro–controllers/DSPs with PWM output pins. This paper discusses a simple algorithm to generate low distortion balanced three–phase sine–PWM pulses from a general purpose micro–controller, without using PWM pins. It is shown via simulation and experimentation that such an algorithm is capable of achieving current–distortions well below 5%. An inverter, controlled by such an algorithm, is also tested for three–phase AC induction motor control application in V/f mode, using a feed–forward control–methodology. A performance–comparison is made between a general–purpose micro–controller (using the above strategy) and a micro–controller (used for motor–control applications) for the above application–area.