This document contains lecture slides from an ECE 442 Power Electronics course. The slides cover various topics relating to DC motor drives, including: 1) controlled and chopper-fed separately excited DC motor drives, 2) equivalent circuits of separately excited and series DC motors, 3) operating modes of DC motors such as motoring, regenerative braking, dynamic braking and plugging, 4) single phase half-wave, semi-converter, full-converter and dual-converter DC motor drives, and 5) their characteristics including quadrants of operation and waveform summaries.

1. ECE 442 Power Electronics 1
Controlled-Rectifier Fed Drive
Armature Field

2. ECE 442 Power Electronics 2
Chopper-Fed Drive
Armature Field

3. ECE 442 Power Electronics 3
Equivalent Circuit of a Separately-Excited
DC Motor

4. ECE 442 Power Electronics 4
f
f f f f
a
a a a a g
g v f
d t f a
d L
di
v R i L
dt
di
v R i L e
dt
e K i
T K i i
d
T J B T
dt



 
  


  

5. ECE 442 Power Electronics 5
0
f f f
g v f
a a a g
a a a v f
d t f a
d L
d d
Steady state
d
dt
V R I
E K I
V R I E
V R I K I
T K I I
T B T
P T








 
 

 


6. ECE 442 Power Electronics 6
a a a v f
a a a a a a
v f f
v
f
V R I K I
V I R V I R
K I V
K
R


 
 
 
 
 
 
 
Solve for the motor speed

7. ECE 442 Power Electronics 7
Control of the motor speed
• Control armature
voltage, Va
– Voltage control
• Control the field
current, If
– Current control
• Control the armature
current, Ia
a a a
f
v
f
V I R
V
K
R



 
 
 
 

8. ECE 442 Power Electronics 8
Magnetization Characteristic

9. ECE 442 Power Electronics 9
Characteristics of Separately-Excited Motors
Rated
speed
Use field-current control
Use armature
voltage control

10. ECE 442 Power Electronics 10
Equivalent circuit of a DC Series Motor

11. ECE 442 Power Electronics 11
( )
( )
( )
g v a
a a f a g
a a f a v f
d t a f
d L
a a f a
v f
E K I
V R R I E
V R R I K I
T K I I
T B T
V R R I
K I





  
  

 
 


12. ECE 442 Power Electronics 12
Controlling the Motor Speed
• Control the armature
voltage, Va
• Control the armature
current, Ia
( )
( )
a a f a g
a a f a v
d t a f
d L
a a f a
v f
V R R I K I
T K I I
T B T
V R R I
K I



  

 
 


13. ECE 442 Power Electronics 13
Characteristics of DC Series motors

14. ECE 442 Power Electronics 14
Operating Modes
• In variable-speed applications, a dc motor
may be operating in one or more of the
following “Modes”
• Motoring
• Regenerative braking
• Dynamic braking
• Plugging

15. ECE 442 Power Electronics 15
Motoring Mode
“Back emf”, Eg is < supply voltage Va
Both Ia and If are positive
Developed torque meets load demand

16. ECE 442 Power Electronics 16
Regenerative Braking Mode
Motor acts as a Generator
Eg becomes > supply Voltage Va
Ia becomes negative
Kinetic energy of the motor is returned to the supply

17. ECE 442 Power Electronics 17
Dynamic Braking
Replace the supply voltage with a resistor
Power dissipated in the resistor rather than given back
to the source

18. ECE 442 Power Electronics 18
Plugging
Reverse the armature terminals while running
Va and Eg act in the same direction
Ia is reversed, producing “braking” torque

19. ECE 442 Power Electronics 19
Four-Quadrant Operation

20. ECE 442 Power Electronics 20
Single-Phase DC Drive
Change Va by changing firing angle 
Inductor Lm is a “smoothing” Inductor to prevent
discontinuous current

21. ECE 442 Power Electronics 21
Armature Reversal

22. ECE 442 Power Electronics 22
Field Reversal

23. ECE 442 Power Electronics 23
Single-Phase Half-Wave Converter Drive
(1 cos )
2
0
(1 cos )
0
m
a a
a
m
f f
f
V
V
V
V


 


 
 
 
 
 

24. ECE 442 Power Electronics 24
Quadrant of Operation

25. ECE 442 Power Electronics 25
Waveform Summary

26. ECE 442 Power Electronics 26
Single-Phase Semiconverter Drives
(1 cos )
0
(1 cos )
0
m
a a
a
m
f f
f
V
V
V
V


 


 
 
 
 
 

27. ECE 442 Power Electronics 27
Quadrant(s) of Operation
Semiconverter – one quadrant converter
One polarity of output voltage and current

28. ECE 442 Power Electronics 28
Waveform Summary

29. ECE 442 Power Electronics 29
Single-Phase Full-Converter Drives

30. ECE 442 Power Electronics 30
Quadrant(s) of Operation
Full converter – two quadrant converter
Output voltage polarity can be positive or negative
Output current has one polarity

31. ECE 442 Power Electronics 31
Waveform Summary

32. ECE 442 Power Electronics 32
Single-Phase Dual-Converter Drives
Dual converter can operate in all four quadrants
Output voltage and current can be positive or negative