SPEED AND TORQUE CONTROL

SPEED AND TORQUE MOTOR
 
The objective of this chapter is to discuss various techniques for the control of
electric machines. Since an in-depth discussion of this topic is both too extensive
for a single chapter and beyond the scope of this book, the presentation
here will necessarily be introductory in nature. We will present basic techniques for
speed and torque control and will illustrate typical configurations of drive electronics
that are used to implement the control algorithms. This chapter will build upon the
discussion of power electronics in Chapter 10.
Note that the discussion of this chapter is limited to steady-state operation. The
steady-state picture presented here is quite adequate for a wide variety of electricmachine
applications. However, the reader is cautioned that system dynamics can play
a critical role in some applications, with concerns ranging from speed of response to
overall system stability. Although the techniques presented here form the basis for
dynamic analyses, the constraints of an introductory textbook are such that a more
extensive discussion, including transient and dynamic behavior, is not possible.
In the discussion of torque control for synchronous and induction machines,
the techniques of field-oriented or vector control are introduced and the analogy is
made with torque control in dc motors. This material is somewhat more sophisticated
mathematically than the speed-control discussion and requires application of the
dq0 transformations developed in Appendix C. The chapter is written such that this
material can be omitted at the discretion of the instructor without detracting from the
discussion of speed control.

CONTROL OF DC MOTORS

BeFore the widespread application of power-electronic drives to control ac machines,
dc motors were by far the machines of choice in applications requiring flexibility of
control. Although in recent years ac drives have become quite common, the ease of
control of dc machines insure their continued use in many applications.