Abstract: A power converter having improved efficiency and useful, for example, in the propulsion system of an electric vehicle. The power converter includes a dual chopper having an output level variable over a rather wide range for controlling the speed of the vehicle from stop to cruising. A commutating inverter is transformer coupled to the chopper for commutating thyristors in the chopper. Efficiency is considerably enhanced by programming the amount of energy in the commutating inverter in accordance with the power being delivered by the chopper so as to minimize power losses and thereby increase the range of the vehicle.

Abstract: A propulsion system for an electric vehicle in which a chopper is used to provide controlled DC power to a separately excited DC propulsion motor. In order to provide increased torque for comparatively short intervals to meet on-the-road requirements, the propulsion motor is provided with two sets of shunt field windings, and switch means are provided for connecting the windings in series or in parallel dependent upon the torque demands on the system. Normally the system is operated with the shunt field windings in series. To meet transient demands for increased torque, such as rapid acceleration from a stop light or improved gradability on hills, means are provided for detecting such increased torque demands and switching the field windings from series to parallel configuration thereby increasing the field flux and causing the motor to produce increased torque. The parallel connected field windings compensate for the demagnetizing effect of high armature currents without the need for a series field winding.

Abstract: A variable duty cycle power converter operable in a current controlled loop and having means for delivering increased load current at low duty cycles for efficient use of the switching elements in the converter. A current limit is established for maximum duty cycle which allows current flow through the power switching elements near but within the ratings of the devices. The maximum limit is programmed as a function of duty cycle to allow increased load current flow while maintaining the current through the power switching devices within ratings. As a result substantially increased current can be provided at low duty cycles without the need for using power switching devices of increased rating.