Variable-characteristic d.c. machines

The paper deals with the application of pulsed voltage waveforms to the field windings of separately excited d.c. machines, and describes the development of an unusual form of control scheme, which holds the field current and the armature current in a fixed relationship. A wide range of torque/speed characteristics are shown to be possible, using simple and inexpensive control apparatus. One arrangement, which allows the separately excited machine to behave as a series machine in the motoring region, and as a constant-torque machine in the braking region, is described in detail, and its possible application as a battery electric traction drive is discussed.