Environmental Engineering Reference
In-Depth Information
The main technologies of electric machines used for electric road vehicles are:
DC motors, induction motors, permanent-magnet brushless, DC-switched reluc-
tance motors [
2
]. These different types of electric machines are analyzed in the
following sections of this chapter.
5.2.1 DC Electric Machines
The DC motor, whose basic principle is shown in Fig.
5.2
, represents the simplest
typology of electric machine, widely used for many domestic and industrial
applications.
The most common DC machine, also called brushed DC motor, is characterized
by the presence of a collector, which is essentially a set of electric contacts
electrically insulated among them. The rotor windings are equally distributed
along the rotor surface and their terminals depart from and arrive to each contact of
the collector. The application of a DC voltage to the rotor windings, by means of
carbon brushes in contact with the collector, generates a magnetic field with a
polarity spatially changed by the position of brushes with respect to the collector.
At the same time a stationary magnetic field is generated in the stator part, by
means of permanent magnets or winding collocated on a magnetic structure. The
interaction of these two magnetic fields generates a rotation of the rotor with
respect to the stator.
Classic brushed DC motors present limitations due to the need for brushes to
press against the collector, with the consequence of friction resistance. At higher
Fig. 5.2 Principle of opera-
tion of a DC machine
Armature
Brush
-
Armature
conductor
N
S
Commutator
+
Rotor
