1. 18
Special-Purpose Electric Machine

2. Figure 18.1(a) Two-pole brushless DC motor with three-phase stator winding

3. Figure 18.3 Transistor and SCR drives for a brushless DC motor
Variable
DC supply T 4 a b c
Stator a' c' b' 1 5 2 6 3
Transistor supply for brushless DC motor + _
Vari
able S
SCR supply for brushless DC motor

4. Figure 18.4 Phase voltages and transistor (SCR) switching sequences for the brushless DC motor drive of Figure 18.3 T 2 1 3 4 5 6
1 = Transistor on
0 = Transistor off 60
120
180
240
300
360
Electrical degrees
Phase-to-phase
stator voltage V
a-b
b-c
c-a

5. Figure 18.5 Performance and efficiency characteristics of brushless DC motor
Speed, rev/min
100
150
200
250
300
350
400 50
500
Efficiency Curve
475
407
339
272
204
136 68
80%
85%
90%
94%
(b)
1000
1500
2000
2500
Performance Curve
(a)
Torque, lb-ft
Torque, Nm

6. Figure 18.8 Stepping motor configurations
(a) Permanent-mag
net
stepping motor
(b) Variable-reluctance
(c) Hybrid stepping motor
Torque