A delta–sigma-modulated speed control system for induction motors

The electronic control techniques used in static frequency changers differ considerably, depending on the type of system considered and the particular specifications and requirements. Mark-space ratio control and pulse-width modulation are among techniques already well-established for use with induction motors to provide a variable-speed a.c. drive. The project is concerned with the applicability of delta-sigma modulation as the basis of a novel method of electronic speed control. The techniques involved are well-known in communication systems, where they are extensively used in the transmission of speech signals. With a sine wave at the input, a delta–sigma modulator produces an output quantised in both voltage and frequency, which enables power control to be achieved from a fixed d.c. supply using only a single power controller. [Continues.]