文档介绍：Massachusetts Institute of Technology
Department of Electrical Engineering puter Science
Electric Machinery
Class Notes 10: Induction Machine Control and Simulation February 11, 2004
c 2003 James L. Kirtley Jr.
1 Introduction
The inherent attributes of induction machines make them very attractive for drive applications.
They are rugged, economical to build and have no sliding contacts to wear. The difficulty with
using induction machines in servomechanisms and variable speed drives is that they are “hard to
control”, since their torque-speed relationship plex and nonlinear. With, however, modern
power electronics to serve as frequency changers and digital electronics to do the required arithmetic,
induction machines are seeing increasing use in drive applications.
In this chapter we develop models for control of induction motors. The derivation is quite brief
for it relies on what we have already done for synchronous machines. In this chapter, however, we
will stay in “ordinary” variables, skipping the per-unit normalization.
2 Volts/Hz Control
Remembering that induction machines generally tend to operate at relatively low per unit slip, we
might conclude that one way of building an adjustable speed drive would be to supply an induction
motor with adjustable stator frequency. And this is, indeed, possible. One thing to remember is
that flux is inversely proportional to frequency, so that to maintain constant flux one must make
stator voltage proportional to frequency (hence the name “constant volts/Hz”). However, voltage
supplies are always limited, so that at some frequency it is necessary to switch to constant voltage
control. The analogy to DC machines is fairly direct here: below some “base” speed, the machine
is controlled in constant flux (“volts/Hz”) mode, while above the base speed, flux is inversely
proportional to speed. It is easy to see that the maximum torque varies inversely to the square of
flux, or