文档介绍：Massachusetts Institute of Technology
Department of Electrical Engineering puter Science
Electric Machines
Class Notes 7: Permanent “Brushless DC” Motors February 11, 2004
c 2003 James L. Kirtley Jr.
1 Introduction
This document is a brief introduction to the design evaluation of permanent motors, with
an eye toward servo and drive applications. It anized in the following manner: First, we
describe three different geometrical arrangements for permanent motors:
1. Surface Mounted s, Conventional Stator,
2. Surface Mounted s, Air-Gap Stator Winding, and
3. Internal s (Flux Concentrating).
After a qualitative discussion of these geometries, we will discuss the elementary rating param-
eters of the machine and show how to arrive at a rating and how to estimate the torque and power
vs. speed capability of the motor. Then we will discuss how the machine geometry can be used to
estimate both the elementary rating parameters and the parameters used to make more detailed
estimates of the machine performance.
Some of the more involved mathematical derivations are contained in appendices to this note.
2 Motor Morphologies
There are, of course, many ways of building permanent motors, but we will consider only a
few in this note. Actually, once these are understood, rating evaluations of most other geometrical
arrangements should be fairly straightforward. It should be understood that the “rotor inside” vs.
“rotor outside” distinction is in fact trivial, with very few exceptions, which we will note.
Surface Machines
Figure 1 shows the basic ic morphology of the motor with s mounted on the surface
of the rotor and an otherwise conventional stator winding. This sketch does not show some of
the important mechanical aspects of the machine, such as the means for fastening the permanent
s to the rotor, so one should look at it with a bit of caution. In addition, this sketch and
the other sketches to follow are not necessarily to a scale