Attenuation of low frequency distortion components of the output voltage waveform of a thyristor cycloconverter

The limit on the practical range of output frequencies of a cycloconverter for a.c. motor speed control is due mainly to the presence of low frequency distortion components in the output voltage waveform. This paper presents the results of an investigation which showed that these distortion components can be attenuated by applying the communications engineering principles of sampling and pulse position modulation to the control strategy of the cycloconverter. The results of this work suggest that the conventional cosinusoidal control techniques are not the best that can be devised for cycloconverters, and that with the availability of the microprocessor, considerable scope exists for innovation in this area.