Q. Show the Overall output limitations of Speed Control?

The overall output limitations are as shown in Figure. With base speed defined as the full-field speed of themotor at the normal armature voltage, speeds above base speed are obtained by motor-field control at approximately constant horsepower, and speeds below base speed are obtained by armature-voltage control at approximately constant torque. The development of solid- state controlled rectifiers capable of handling many kilowatts has opened up a whole new field of solid-state dc motor drives with precise control of motor speed. The control resistors (in which energy is wasted) are eliminated through the development of power semiconductor devices and the evolution of flexible and efficient converters. Thus, the inherently good controllability of a dc machine has been increased significantly.