Environmental Engineering Reference
In-Depth Information
The above example serves as a good transition to discussion on the various
types of electric machines. The following sections of this chapter carry this analysis
to greater depths. The types of machines considered in this chapter are contained in
a broader scope or taxonomy of electric machines shown in Figure 5.6.
Electric machines for
hybrid vehicle ac drives
Asynchronous
Synchronous
Induction
cage rotor
Induction
wound rotor
Induction
doubly fed
Permanent
magnet
Variable
reluctance
Unipolar
Brushed
DC
Doubly fed
reluctance
Switched
reluctance
Interior PM
Inset PM
Surface PM
IM
IPM
SPM
VRM
Figure 5.6 Survey of electrical machine types
5.2 Brushless machines
The electromagnetic interaction responsible for torque production is the Lorenz
force defined with the help of Figure 5.7. In this illustration, a pair of magnets force
magnetic flux across a gap in which reside a pair of conductors that are free to
rotate. When current is injected into the conductor turn, there will be a magnetic
flux encircling the conductor that interacts with the field flux (depicted as lines),
resulting in a force on the currents in that conductor and oriented orthogonal to both
the flux and the current. The resultant Lorenz force is a vector cross-product of the
flux and the current, with the seat of the force resting on the current in the con-
ductors. The term seat of the force is used to dispel the notion that the force acts on
the copper conductor or on some other member. For example, the electron beam in
a cathode ray tube (CRT) is formed by thermionic emission of electrons from a
caesium-coated tungsten wire cathode. The electron cloud is subsequently focused
into a beam and accelerated by a high potential at the CRT anode (a conductive
coating on the inside walls of the tube). A raster is scanned on the CRT face by
horizontal and vertical deflection coils placed around the neck of the CRT that form
a cross-field into which the electron stream passes. When encountering the mag-
netic field (shaped very similar to that in Figure 5.7), the electrons experience the
Lorenz force and are deflected orthogonal to both their velocity vector (initially
down the
z
-axis of the tube) and to the field itself (the
x
- and
y
-axes). As further
