VARIABLE SPEED CONTROLLER FOR AC MOTOR

摘要

PROBLEM TO BE SOLVED: To operate the resistances of primary and secondary resistors, respectively, without rotating an AC motor at the time of variable speed control thereof. SOLUTION: A variable speed control circuit 30 comprises an AC signal generation circuit 31, a secondary resistance operating circuit 32 and a primary resistance operating circuit 33. A DC excited state is brought about immediately before starting an induction motor and an AC signal having microamplitude outputted from the AC signal generation circuit 31 is superposed on an M axis current command value in order to vary the DC exciting current. Primary and secondary resistances of the motor are then operated by the primary and secondary resistance operating circuits 33, 32.