CONTROLLER OF INDUCTION MOTOR

PROBLEM TO BE SOLVED: To avoid the stop of a device so as to improve the operation efficiency by preventing an instantaneous overcurrent from occurring in an output current at the return operation to the reference voltage of supply voltage. SOLUTION: The power supplied from a power source PS is inverted into specified control power through a power inverter circuit 20 and is outputted to an induction motor CM, while the power inverter circuit 20 is controlled so that the supply frequency and the supply voltage of the induction motor CM may change, based on the preset reference voltage frequency property, and also the supply frequency of the induction motor CM is controlled for the variable speed control of the induction motor CM. Furthermore, the supply voltage is adjusted so that the current of the induction motor CM may be minimum by making the supply voltage of the induction motor CM ripple small with the specified quantity of ripples, and also the quantity of ripples per unit time of the supply voltage is set to a very small value and it is returned gradually to the reference voltage value gradually, when there is a request for returning the supply voltage to the reference voltage value.