Optimizing Efficiency in Brushless DC Motor Drives

1. 18 Special-Purpose Electric Machine

2. a N b' c' S b c a' (a) Figure 18.1(a) Two-pole brushless DC motor with three-phase stator winding

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

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

5. Efficiency Curve 475 350 85% 80% 407 300 Performance Curve 350 475 339 250 90% 300 407 272 200 250 339 Torque, Nm Torque, lb-ft Torque, Nm 204 Torque, lb-ft 200 272 150 94% 150 204 136 100 100 136 68 50 50 68 500 1000 1500 2000 2500 500 100 150 200 250 300 350 400 0 0 0 0 0 0 0 Speed, rev/min Speed, rev/min (a) (b) Figure 18.5 Performance and efficiency characteristics of brushless DC motor

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