A Microcomputer-Based Control Signal Generator for a Three-Phase Switching Power Inverter

A three-phase electronic switching inverter has been firmly established as a power source for ac motors in variable-speed applications. In generating control signals for such an inverter, microcomputers are playing an increasingly important role. A micro- computer-based system (using 8051 from Intel) for the generation of pulsewidth modulated (PWM) control signals for a transistorized voltage controlled three-phase inverter is described. The computational algorithm is based on modification of the triangular modulation strategy. The polarity of the triangular timing wave is made the same as the polarity of the reference wave. This eliminates the potential hazard of a "shoot-through" at each zero crossing of the control signal. The widths of the pulses, their positions along the time axis, and the number of pulses per period of the output signal are computed in real time.