Abstract: Regenerative braking controller for controlling a direct current motor adapted to drive a railway tramcar, an electric automobile or the like, comprises a direct current power supply, a series circuit composed of the armature and the field coil of the motor and a smoothing reactor, a chopper circuit connected in parallel with the series circuit and a diode inserted between the parallel circuit and the direct current power supply. The apparatus is characterized by an excitation circuit for exciting the field of coil of the d.c. motor with the voltage of the d.c. power supply so that a current may flow to the d.c. source due to voltage generated by the d.c. motor, and for supplying a power necessary for the operation of the chopper circuit from the d.c. source at the time of a low regenerating voltage of the d.c. motor.

Abstract: A system for controlling a thyristor chopper used for the speed control of a d.c. motor driving an electric car, in which means are provided for generating turn-on pulses and turn-off pulses at the maximum chopping frequency of the chopper, dividing the frequency of the turn-on pulses and turn-off pulses stepwise in response to the application of chopping frequency instruction signals, and applying these frequency-divided turn-on and turn-off pulses to the chopper for controlling the chopper, so that the motor can be smoothly controlled by the chopper whose chopping frequency varies stepwise from a low to a high valve with conductive rate-control.