Abstract: A control apparatus for controlling the main circuit for driving an AC electric motor consisting of a diode converter and a pulse width modulation (PWM) power converting device, in which it is arranged that the DC current as the output of the diode converter is detected by a current detector, the AC component of this DC current is filtered through a high-pass filter, and a pulse-width-modulation control is exercised by a control circuit in response to the output of the high-pass filter so that the DC current as the output of the diode converter may be smoothed out in the main circuit by the PWM power converting device. By such arrangement, this control apparatus of an electric motor is made smaller in size and simplified in structure and enabled to control the power factor of the power source of the diode converter to close to 1.0.

Abstract: An A.C. current control system for an A.C. power supply device for feeding a load comprises a closed control loop for controlling the power supply device on the basis of results of comparison between an output signal from a reference current waveform generator for generating a reference current waveform and an output signal from a load current waveform detector for detecting the waveform of load current. A load voltage detector is provided, the output signal from which is positively fed back to the closed control loop for compensating deviation in the current control due to electromotive force or like factors of the load.