Pulse Width Modulated Inverters for AC Motor Drives

The use of pulse width modulation techniques applied to thyristor inverters to obtain variable frequency-variable voltage waveforms is reviewed. A number of basic modes of modulation are analyzed; harmonic content and principles of wave generation are investigated and compared to conventional forms of synthesis. The prime advantage of such systems is to preserve a near sine wave envelope rather than to eliminate specific harmonics. This allows a potentially wider range of speed control by keeping the harmonics in fixed but small proportions relative to the fundamental frequency. The principal harmonics which are presen-t are those induced by pulse modulation; these normally can be filtered by the inherent delays of the motor.