Digital control of a variable-speed, thyristor-controlled, commutatorless machine

An investigation was conducted concerning the reasons for the inadequate performance of digital logic which had been designed to control variable speed electric machines. The inadequate performance had been related to a failure to control the instantaneous speed with sufficient accuracy. Corrective approaches were developed and tested on the digital speed-control system designed by Dunworth (1970). The need for thyristor firing-angle control with its production of undesirable large harmonic currents could be eliminated by combining the principles of induction machine operation with some of the concepts used in thyristor-controlled, commutatorless machines. Experimental and theoretical work performed on the resulting stepped-field induction machine is discussed.