Abstract: A method for generating pulse width modulated (PWM) control signals from a reference waveform uses a unipolar timing waveform to modulate the reference waveform thereby avoiding the need for lock-out intervals to prevent shoot-through in power inverters supplied by the PWM control signals. Further, a sinusoidal reference waveform is approximated by a trapezoid, simplifying the computation of switching points located at intersections between the reference and timing waveforms.

Abstract: A control system is provided in which a signal proportional to the actual rotor speed of an induction motor is coupled to a variable gain amplifier. Changes in the commanded gain of the amplifier electronically control the ratio between rotor speed and the output signal amplitude of the variable gain amplifier. The output of the variable gain amplifier determines the commanded stator frequency. Disks optically encoded with a PWM pattern are driven at a speed which corresponds to the commanded stator frequency. Optical sensors read the pattern and provide switching signals to an inverter coupled to an induction motor.