Abstract: The invention relates to a chopper circuit with free commutation for the supply of power to a load from a source of direct current. It comprises a principal thyristor with a return diode, a series resonant circuit as the commutation circuit and a free-wheeling diode. The free-wheeling diode is parallel to the capacitor of the resonant circuit so that the coil serves both as the commutation circuit and the coil to limit variations of the current in the thyristor. The circuit is particularly suitable for use with electric traction motors.

Abstract: A direct current motor includes a chopper in series with the field coil of the motor to regulate the current flowing through the armature of the motor during electrical braking when the motor functions as a generator to produce current. In addition, a shunting device is connected to the field coil to regulate the current flowing through the coil so that it is maintained at a value less than the armature current.

Abstract: This invention pertains to a direct current, series excited traction motor, the armature coil of which is connected in series with the field coil and a smoothing coil, and the power supply of which is adjusted by a current chopper. The inductor includes, in addition, a shunting device for reduction of excitation, and a free wheeling diode is in parallel with the motor and the smoothing coil. This device is unique in that the field coil is divided into at least two series connected partial coils to generate additive flux, one of them only being provided with the shunting device. The chopper is advantageously of a type which may operate in a continuous conduction mode.