Applications such as robotics and factory automation require accurate control of speed and position. This can be accomplished by vector control of induction machines, which emulate the performance of dc motor and brushless dc motor servo drives. Compared with dc and brushless dc motors, induction motors have a lower cost and a more rugged construction.
In any speed and position control application, torque is the fundamental variable that needs to be controlled. The ability to produce a step change in torque on command represents total control over the drives for high performance speed and position control.
This chapter qualitatively shows how a step change in torque is accomplished by vector control of induction-motor drives. For this purpose, the steady-state analysis of induction motors discussed in the previous course serves very well because while delivering a step change in electromagnetic torque under vector control, an induction machine instantaneously transitions from one steady state to another.
Under vector control, induction-motor drives can emulate the performance of dc-motor and brushless-dc motor servo drives discussed in the previous course. These are briefly reviewed in the following sections.
In the dc-motor drive shown in Fig. 4-1a, the commutator and brushes ensure that the armature-current-produced magnetomotive force ...