Control of induction motors

Induction motors have existed for many years but were always limited in their application because the supply needed for variable speed control could only be provided by rotary converters, otherwise a three-phase fixed supply could be used to give a fixed-speed control. For this reason induction motors have been used in industrial installations for some time but their use for traction systems has only recently gained widespread acceptance with the advent of cheaper, higher ratings of static inverters and cheaper microprocessors with enough processing power to handle the control. It is assumed in this paper that other authors explain the details of induction motor operation and power electronic inverters; only the aspects relevant to controlling induction motors will be dealt with here