Abstract: A motor control apparatus to supply current from a D-C source to an electric motor has a thyristor chopper circuit, the duty factor of which is controlled depending on a current instruction signal. The thyristor chopper circuit is provided between the terminals of the D-C source in series with an electric motor, and has main and auxiliary thyristors. A series connection of a capacitor and a reactor, forming commutating elements, is connected across the auxiliary thyristor and oscillates to generate a pulse of current through a forward diode in order to turn off the main thyristor when the auxiliary thyristor is turned on. In addition, a saturable current transformer is so provided that through a primary winding thereof chopper current flows, and the secondary winding operates as the reactance of the commutating elements. Current flowing through the secondary winding therefore depends on the chopper current flowing through the primary winding.

Abstract: A control apparatus for an electric motor vehicle includes a control system to increase the duty cycle of a chopper circuit driving an electric drive motor of the vehicle when a spontaneous backward movement takes place upon starting of the vehicle at an uphill gradient, thereby to increase the armature and field current of the drive motor and hence the counter current braking effort or so-called plugging effort. The control apparatus assures a reliable starting of the vehicle even at an uphill gradient road.

Abstract: A system for detecting an output of a controllable semiconductor device includes a controllable semiconductor device, a magnetic amplifier to which an output of the semiconductor device is fedback to control the semiconductor device, and a monitor device for monitoring an output of the magnetic amplifier. The monitor device serves for determining that the output of said semiconductor device exceeds a predetermined level, when the output of the magnetic amplifier is in a remanent output region of the magnetic amplifier.