1. ELECTRICAL DRIVES:
An Application of Power Electronics

2. CONTENTS
Power Electronic Systems
Modern Electrical Drive Systems
Power Electronic Converters in Electrical Drives
:: DC and AC Drives
Modeling and Control of Electrical Drives

3. Power Electronic Systems
What is Power Electronics ?
A field of Electrical Engineering that deals with the application of
power semiconductor devices for the control and conversion of
electric power
Input
Source
- AC
- DC
- unregulated
Reference
sensors
Power Electronics
Power Electronics
Converters
Converters
Load
Load
Output
- AC
- DC
Controller
Controller
POWER ELECTRONIC
CONVERTERS – the
heart of power a power
electronics system

4. Power Electronic Systems
Why Power Electronics ?
Input
Source
- AC
- DC
- unregulated
Reference
sensors
Power Electronics
Power Electronics
Converters
Converters
IDEALLY LOSSLESS !!
Load
IDEALLY LOSSLESS
Load
Output
- AC
- DC
Controller
Controller

5. Power Electronic Systems
Why Power Electronics ?
Other factors:
• Improvements in power semiconductors fabrication
•
Power Integrated Module (PIM), Intelligent Power
Modules (IPM)
• Decline cost in power semiconductor
• Advancement in semiconductor fabrication
•
ASICs
•
Faster and cheaper to implement complex
algorithm
•
FPGA
•
DSPs

6. Power Electronic Systems
Some Applications of Power Electronics :
Typically used in systems requiring efficient control and conversion of
electric energy:
Domestic and Commercial Applications
Industrial Applications
Telecommunications
Transportation
Generation, Transmission and Distribution of electrical energy
Power rating of < 1 W (portable equipment)
Tens or hundreds Watts (Power supplies for computers /office equipment)
kW to MW : drives
Hundreds of MW in DC transmission system (HVDC)

7. Modern Electrical Drive Systems
Classic Electrical Drive for Variable Speed Application :
•
Bulky
•
Inefficient
•
inflexible

8. Modern Electrical Drive Systems
Typical Modern Electric Drive Systems
Electric Motor
Power Electronic Converters
Electric Energy
- Unregulated -
POWER IN
Electric Energy
- Regulated -
Power
Power
Electronic
Electronic
Converters
Converters
Moto
Moto
rr
feedback
Reference
Controller
Controller
Electric
Energy
Mechanical
Energy
Load
Load

9. Modern Electrical Drive Systems
Example on VSD application
Variable Speed Drives
Constant speed
valve
Supply
motor
pump
Power out
Power
In
Power loss
Mainly in valve

10. Modern Electrical Drive Systems
Example on VSD application
Variable Speed Drives
Constant speed
valve
Supply
motor
Supply
pump
PEC
Power out
Power
In
motor
pump
Power out
Power
In
Power loss
Mainly in valve
Power loss

11. Modern Electrical Drive Systems
Example on VSD application
Variable Speed Drives
Constant speed
valve
Supply
motor
Supply
pump
PEC
Power out
Power
In
motor
pump
Power out
Power
In
Power loss
Mainly in valve
Power loss

12. Modern Electrical Drive Systems
Example on VSD application
Electric motor consumes more than half of electrical energy in the US
Fixed speed
Variable speed
Improvements in energy utilization in electric motors give large
impact to the overall energy consumption
HOW ?
Replacing fixed speed drives with variable speed drives
Using the high efficiency motors
Improves the existing power converter–based drive systems

13. Modern Electrical Drive Systems
Overview of AC and DC drives
DC drives: Electrical drives that use DC motors as the prime mover
Regular maintenance, heavy, expensive, speed limit
Easy control, decouple control of torque and flux
AC drives: Electrical drives that use AC motors as the prime mover
Less maintenance, light, less expensive, high speed
Coupling between torque and flux – variable spatial angle
between rotor and stator flux

14. Modern Electrical Drive Systems
Overview of AC and DC drives
Before semiconductor devices were introduced (<1950)
• AC motors for fixed speed applications
• DC motors for variable speed applications
After semiconductor devices were introduced (1960s)
• Variable frequency sources available – AC motors in variable
speed applications
• Coupling between flux and torque control
• Application limited to medium performance applications –
fans, blowers, compressors – scalar control
• High performance applications dominated by DC motors –
tractions, elevators, servos, etc

15. Modern Electrical Drive Systems
Overview of AC and DC drives
After vector control drives were introduced (1980s)
• AC motors used in high performance applications – elevators,
tractions, servos
• AC motors favorable than DC motors – however control is
complex hence expensive
• Cost of microprocessor/semiconductors decreasing –predicted
30 years ago AC motors would take over DC motors

16. Modern Electrical Drive Systems
Overview of AC and DC drives

17. Power Electronic Converters in ED Systems
Converters for Motor Drives
(some possible configurations)
DC Drives
DC Source
AC Source
DC-AC-DC
DC-AC-DC
AC-DC
AC-DC
AC Drives
AC-DC-DC
AC-DC-DC
DC Source
AC Source
DC-DC
DC-DC
AC-DC-AC
AC-DC-AC
Const.
DC
Variable
DC
AC-AC
AC-AC
NCC
FCC
DC-AC
DC-AC
DC-DC-AC
DC-DC-AC

18. Power Electronic Converters in ED Systems
Converters for Motor Drives
Configurations of Power Electronic Converters depend on:
Sources available
Type of Motors
Drive Performance - applications
- Braking
- Response
- Ratings

19. Power Electronic Converters in ED Systems
DC DRIVES
Available AC source to control DC motor (brushed)
AC-DC
AC-DC
AC-DC-DC
AC-DC-DC
Uncontrolled Rectifier
Control
Controlled Rectifier
Single-phase
Three-phase
Single-phase
Three-phase
Control
DC-DC Switched mode
1-quadrant, 2-quadrant
4-quadrant

20. Power Electronic Converters in ED Systems
DC DRIVES
AC-DC
AC-DC
400
200
0
+
50Hz
1-phase
Vo =
Vo
2Vm
cos α
π
Average voltage
over 10ms
−
-200
-400
0.4
0.405
0.41
0.415
0.42
0.425
0.43
0.435
0.44
0.405
0.41
0.415
0.42
0.425
0.43
0.435
0.44
10
5
0
0.4
500
0
50Hz
3-phase
+
Vo
-500
Vo =
3VL −L,m
π
0.4
cos α
0.405
0.41
0.415
0.42
0.425
0.43
0.435
0.44
0.405
0.41
0.415
0.42
0.425
0.43
0.435
0.44
30
20
−
Average voltage
over 3.33 ms
10
0
0.4

21. Power Electronic Converters in ED Systems
DC DRIVES
AC-DC
AC-DC
2Vm
π
+
50Hz
1-phase
Vo =
Vo
2Vm
cos α
π
90o
90o
Average voltage
over 10ms
−
−
180o
180o
2Vm
π
3VL −L,m
50Hz
3-phase
π
+
Vo
−
Vo =
3VL −L,m
π
cos α
Average voltage
over 3.33 ms
−
3VL −L ,m
π

22. Power Electronic Converters in ED Systems
DC DRIVES
AC-DC
AC-DC
ia
Vt
+
3-phase
supply
Vt
Q2
Q1
−
Q3
Q4
- Operation in quadrant 1 and 4 only
Ia

23. Power Electronic Converters in ED Systems
DC DRIVES
AC-DC
AC-DC
3phase
supply
+
3-phase
supply
Vt
−
ω
Q2
Q1
Q3
Q4
T

24. Power Electronic Converters in ED Systems
DC DRIVES
AC-DC
AC-DC
R1
F1
3-phase
supply
+
Va
F2
R2
ω
Q2
Q1
Q3
Q4
-
T

25. Power Electronic Converters in ED Systems
DC DRIVES
AC-DC
AC-DC
Cascade control structure with armature reversal (4-quadrant):
iD
ω
ωref +
_
Speed
Speed
controller
controller
iD,ref +
Current
Current
Controller
Controller
_
iD,ref
iD,
Armature
Armature
reversal
reversal
Firing
Firing
Circuit
Circuit

26. Power Electronic Converters in ED Systems
DC DRIVES
AC-DC-DC
AC-DC-DC
control

27. Power Electronic Converters in ED Systems
DC DRIVES
AC-DC-DC
AC-DC-DC
DC-DC: Two-quadrant Converter
Va
+
T1
D1
ia
Vdc
−
T2
D2
Q2
Q1
Ia
+
Va
-
T1 conducts → va = Vdc

28. Power Electronic Converters in ED Systems
DC DRIVES
AC-DC-DC
AC-DC-DC
DC-DC: Two-quadrant Converter
Va
+
T1
D1
ia
Vdc
−
T2
D2
Q2
Q1
Ia
+
Va
-
D2 conducts → va = 0
Va
T1 conducts → va = Vdc
Eb
Quadrant 1 The average voltage is made larger than the back emf

29. Power Electronic Converters in ED Systems
DC DRIVES
AC-DC-DC
AC-DC-DC
DC-DC: Two-quadrant Converter
Va
+
T1
D1
ia
Vdc
−
T2
D2
Q2
Q1
Ia
+
Va
-
D1 conducts → va = Vdc

30. Power Electronic Converters in ED Systems
DC DRIVES
AC-DC-DC
AC-DC-DC
DC-DC: Two-quadrant Converter
Va
+
T1
D1
ia
Vdc
−
T2
D2
Q2
Q1
Ia
+
Va
-
T2 conducts → va = 0
Va
D1 conducts → va = Vdc
Eb
Quadrant 2 The average voltage is made smallerr than the back emf, thus
forcing the current to flow in the reverse direction

31. Power Electronic Converters in ED Systems
DC DRIVES
AC-DC-DC
AC-DC-DC
DC-DC: Two-quadrant Converter
2vtri
+
vA
vc
Vdc
-
0
vc
+

32. Power Electronic Converters in ED Systems
DC DRIVES
AC-DC-DC
AC-DC-DC
DC-DC: Four-quadrant Converter
leg A
+
Q1
leg B
D3
D1
+
Va
−
Q3
Vdc
−
Positive current
va = Vdc
when Q1 and Q2 are ON
Q4
D4
D2
Q2

33. Power Electronic Converters in ED Systems
DC DRIVES
AC-DC-DC
AC-DC-DC
DC-DC: Four-quadrant Converter
leg A
+
Q1
leg B
D3
D1
+
Va
−
Q3
Vdc
−
Q4
D4
Positive current
va = Vdc
when Q1 and Q2 are ON
va = -Vdc
when D3 and D4 are ON
va = 0
when current freewheels through Q and D
D2
Q2

34. Power Electronic Converters in ED Systems
DC DRIVES
AC-DC-DC
AC-DC-DC
DC-DC: Four-quadrant Converter
leg A
+
Q1
leg B
D3
D1
+
Va
−
Q3
Vdc
−
Q4
D4
Positive current
va = Vdc
when Q1 and Q2 are ON
va = -Vdc
when D3 and D4 are ON
va = 0
when current freewheels through Q and D
D2
Q2
Negative current
va = Vdc
when D1 and D2 are ON

35. Power Electronic Converters in ED Systems
DC DRIVES
AC-DC-DC
AC-DC-DC
DC-DC: Four-quadrant Converter
leg A
+
Q1
leg B
D3
D1
+
Va
−
Q3
Vdc
−
Q4
D4
Positive current
D2
Q2
Negative current
va = Vdc
when Q1 and Q2 are ON
va = Vdc
when D1 and D2 are ON
va = -Vdc
when D3 and D4 are ON
va = -Vdc
when Q3 and Q4 are ON
va = 0
when current freewheels through Q and D
va = 0
when current freewheels through Q and D