electricdrives-130921022329-phpapp02.pdfBDJHFOHWOIHQ

XNFVKMSBNLNFKHQioe

1. ELECTRIC DRIVES
INTRODUCTION TO ELECTRIC DRIVES
MODULE 1
S. Samsudeen
Electrical Energy Conversion

2. INTRODUCTION TO ELECTRIC DRIVES - MODULE 1
Electrical Drives
Drives are systems employed for motion control
Require prime movers
Drives that employ electric motors as
prime movers are known as Electrical Drives

3. INTRODUCTION TO ELECTRIC DRIVES - MODULE 1
Electrical Drives
•About 50% of electrical energy used for drives
•Can be either used for fixed speed or variable speed
•75% - constant speed, 25% variable speed (expanding)
•MEP 1523 will be covering variable speed drives

4. Example on VSD application
motor pump
valve
Supply
Constant speed Variable Speed Drives
Power
In
Power loss
Mainly in valve
Power out
INTRODUCTION TO ELECTRIC DRIVES - MODULE 1

5. Example on VSD application
motor pump
valve
Supply
motorPEC pump
Supply
Constant speed Variable Speed Drives
Power
In
Power loss
Power out
INTRODUCTION TO ELECTRIC DRIVES - MODULE 1
Power loss
Mainly in valve
Power outPower
In

6. Power loss
Mainly in valve
Power out
motor pump
valve
Supply
motorPEC pump
Supply
Constant speed Variable Speed Drives
Example on VSD application
INTRODUCTION TO ELECTRIC DRIVES - MODULE 1
Power
In
Power loss
Power
In
Power out

7. INTRODUCTION TO ELECTRIC DRIVES - MODULE 1
Conventional electric drives (variable speed)
•Bulky
•Inefficient
•inflexible

8. INTRODUCTION TO ELECTRIC DRIVES - MODULE 1
Modern electric drives (With power electronic converters)
•Small
•Efficient
•Flexible

9. INTRODUCTION TO ELECTRIC DRIVES - MODULE 1
Modern electric drives
•Inter-disciplinary (PE, control system, machine
design, sensors)
•Several research area
•Expanding
Machine design
Speed sensorless
Machine Theory
Non-linear control
Real-time control
DSP application
PFC
Speed sensorless
Power electronic converters
Utility interface
Renewable energy

10. INTRODUCTION TO ELECTRIC DRIVES - MODULE 1
Components in electric drives
Motors
•DC motors - permanent magnet – wound field
•AC motors – induction, synchronous (IPMSM, SMPSM),
brushless DC
•Applications, cost, environment
•Natural speed-torque characteristic is not compatible with load
requirements
Power sources
•DC – batteries, fuel cell, photovoltaic - unregulated
•AC – Single- three- phase utility, wind generator - unregulated
Power processor
•To provide a regulated power supply
•Combination of power electronic converters
•More efficient
•Flexible
•Compact
•AC-DC DC-DC DC-AC AC-AC

11. INTRODUCTION TO ELECTRIC DRIVES - MODULE 1
Components in electric drives
Control unit
•Complexity depends on performance requirement
•analog- noisy, inflexible, ideally has infinite bandwidth.
•digital – immune to noise, configurable, bandwidth is smaller than
the analog controller’s
•DSP/microprocessor – flexible, lower bandwidth - DSPs perform
faster operation than microprocessors (multiplication in single
cycle), can perform complex estimations
•Electrical isolation between control circuit and power circuit is
needed:
•Malfuction in power circuit may damage control circuit
•Safety for the operator
•Avoid conduction of harmonic to control circuit

12. INTRODUCTION TO ELECTRIC DRIVES - MODULE 1
Components in electric drives
Sensors
•Sensors (voltage, current, speed or torque) is normally
required for closed-loop operation or protection
•Electrical isolation between sensors and control circuit is
needed for the reasons previously explained
•The term ‘sensorless drives’ is normally referred to the drive
system where the speed is estimated rather than measured.

13. INTRODUCTION TO ELECTRIC DRIVES - MODULE 1
Overview of AC and DC drives
Extracted from Boldea & Nasar

14. INTRODUCTION TO ELECTRIC DRIVES - MODULE 1
Overview of AC and DC drives
DC motors: Regular maintenance, heavy, expensive, speed limit
Easy control, decouple control of torque and flux
AC motors: Less maintenance, light, less expensive, high speed
Coupling between torque and flux – variable
spatial angle between rotor and stator flux

15. INTRODUCTION TO ELECTRIC DRIVES - MODULE 1
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 (1950s)
•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

16. INTRODUCTION TO ELECTRIC DRIVES - MODULE 1
Overview of AC and DC drives
After semiconductor devices were introduced (1950s)

17. INTRODUCTION TO ELECTRIC DRIVES - MODULE 1
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

18. INTRODUCTION TO ELECTRIC DRIVES - MODULE 1
Classification of IM drives (Buja, Kamierkowski, “Direct torque control of PWM inverter-fed AC motors - a survey”,
IEEE Transactions on Industrial Electronics, 2004.

19. INTRODUCTION TO ELECTRIC DRIVES - MODULE 1
Elementary principles of mechanics
M
v
F
m
F
f
()
dt
Mvd
FF
fm=-
Newton’s law
Linear motion, constant M
•First order differential equation for speed
•Second order differential equation for displacement
()
Ma
dt
xd
M
dt
vd
MFF
2
2
fm
===-
x

20. INTRODUCTION TO ELECTRIC DRIVES - MODULE 1
Elementary principles of mechanics
•First order differential equation for angular frequency (or velocity)
•Second order differential equation for angle (or position)
( )
2
2
m
le
dt
d
J
dt
d
JTT
q
=
w
=-
With constant J,
Rotational motion
- Normally is the case for electrical drives
( )
dt
Jd
TT
m
le
w
=-
q
T
e
, w
m
T
l
J

21. INTRODUCTION TO ELECTRIC DRIVES - MODULE 1
Elementary principles of mechanics

22. INTRODUCTION TO ELECTRIC DRIVES - MODULE 1
dt
d
JTT
m
le
w
+=
For constant J,
()
dt
d
J
mw
Torque dynamic – present during speed transient
()
dt
d
mw Angular acceleration
Larger net torque and smaller J gives faster acceleration
0.19 0.2 0.21 0.22 0.23 0.24 0.25
-200
-100
0
100
200
s
p
e
e
d

(
r
a
d
/
s
)
0.19 0.2 0.21 0.22 0.23 0.24 0.25
0
5
10
15
20
t
o
r
q
u
e

(
N
m
)
Elementary principles of mechanics

23. INTRODUCTION TO ELECTRIC DRIVES - MODULE 1
dt
d
JTT
m
le
w
+=
Elementary principles of mechanics
dt
d
JTT
m
mlmem
w
w+w=w
dt
d
Jpp
m
mLD
w
w+=Þ
Driving
power
Load
power
Change
in KE
•A step change in speed requires an infinite driving power
•Therefore w is a continuous variable

24. INTRODUCTION TO ELECTRIC DRIVES - MODULE 1
dt
d
JTT
m
le
w
+=
Elementary principles of mechanics
dt
d
JTT
m
mlmem
w
w+w=w
dt
d
Jpp
m
mLD
w
w+=Þ
Integrating the equation with time and setting the initial speed w(0) =
0, we obtain the following:
w
D
=p
D
dt
0
t
ò =p
L
dt
0
t
ò+w
m
J
dw
m
dt
0
t
ò dt
w
D=w
L+Jw
m
0
w
òdw
m
w
D
=w
L
+
1
2
Jw
m
2

25. INTRODUCTION TO ELECTRIC DRIVES - MODULE 1
Elementary principles of mechanics
A drive system that require fast acceleration must have
•small overall moment of inertia
•large motor torque capability
As the motor speed increases, the kinetic energy also increases.
During deceleration, the dynamic torque changes its sign and thus
helps motor to maintain the speed. This energy is extracted from the
stored kinetic energy:
J is purposely increased to do this job !

26. INTRODUCTION TO ELECTRIC DRIVES - MODULE 1
Elementary principles of mechanics
()
dt
vd
MFF
le=-
Combination of rotational and translational motions
r r
w
T
e,
w
T
l
F
l
F
e
v
M
T
e
= r(F
e
), T
l
= r(F
l
), v =rw
dt
d
MrTT
2
le
w
=-
r
2
M - Equivalent moment inertia of the
linearly moving mass

27. INTRODUCTION TO ELECTRIC DRIVES - MODULE 1
Elementary principles of mechanics – effect of gearing
Motors designed for high speed are smaller in size and volume
Low speed applications use gear to utilize high speed motors
Motor
T
e
Load 1,
T
l1
Load 2,
T
l2
J
1
J
2
w
m
w
m1
w
m2
n
1
n
2

28. INTRODUCTION TO ELECTRIC DRIVES - MODULE 1
Motor
T
e
Load 1,
T
l1
Load 2,
T
l2
J
1
J
2
w
m
w
m1
w
m2
n
1
n
2
Motor
T
e
J
equ
Equivalent
Load , T
lequ
w
m
2
2
21equ JaJJ +=
T
lequ
= T
l1
+ a
2
T
l2
a
2
= n
1
/n
2
=w
2
/w
1

Elementary principles of mechanics – effect of gearing

29. INTRODUCTION TO ELECTRIC DRIVES - MODULE 1
Torque-speed quadrant of operation
w
T
12
34
T +ve
w +ve
P
m
+ve
T -ve
w +ve
P
m
-ve
T -ve
w -ve
P
m
+ve
T +ve
w -ve
P
m
-ve
•Quadrant of operation is
defined by the speed and
torque of the motor
•Most rotating electrical
machines can operate in 4
quadrants
•Not all converters can
operate in 4 quadrants

30. INTRODUCTION TO ELECTRIC DRIVES - MODULE 1
Torque-speed quadrant of operation
w
T
T
e
w
m
T
e
T
e
T
e
w
m
w
m
w
m
•Quadrant of operation is
defined by the speed and
torque of the motor
•Most rotating electrical
machines can operate in 4
quadrants
•Not all converters can
operate in 4 quadrants
Quadrant 1
Forward motoring
Quadrant 2
Forward braking
Quadrant 3
Reverse motoring
Quadrant 4
Reverse braking

31. INTRODUCTION TO ELECTRIC DRIVES - MODULE 1
Motor steady state torque-speed characteristic (natural
characteristic)
Synchronous mch
Induction mch
Separately / shunt DC mch
Series DC
SPEED
TORQUE
By using power electronic converters, the motor characteristic
can be change at will

32. INTRODUCTION TO ELECTRIC DRIVES - MODULE 1
Load steady state torque-speed characteristic
SPEED
TORQUE
Frictional torque (passive load)
•Exist in all motor-load drive
system simultaneously
•In most cases, only one or two
are dominating
•Exists when there is motion
T~ C
Coulomb friction
T~ w
Viscous friction
T~ w
2
Friction due to turbulent flow

33. a
T
L
T
e
Vehicle drive
INTRODUCTION TO ELECTRIC DRIVES - MODULE 1
Load steady state torque-speed characteristic
Constant torque, e.g. gravitational torque (active load)
SPEED
TORQUE
Gravitational torque
gM
F
L
T
L
= rF
L
= r g M sin a

34. INTRODUCTION TO ELECTRIC DRIVES - MODULE 1
Load steady state torque-speed characteristic
Hoist drive
Speed
Torque
Gravitational torque

35. INTRODUCTION TO ELECTRIC DRIVES - MODULE 1
Load and motor steady state torque
At constant speed, T
e
= T
l

Steady state speed is at point of intersection between T
e
and T
l
of the
steady state torque characteristics
T
l
T
e
Steady state
speed
w
r
Torque
Speed
w
r2w
r3
w
r1

36. INTRODUCTION TO ELECTRIC DRIVES - MODULE 1
Torque and speed profile
10 25 45 60 t (ms)
speed
(rad/s)
100
The system is described by: T
e
– T
load
= J(dw/dt) + Bw
J = 0.01 kg-m2, B = 0.01 Nm/rads-1 and T
load
= 5 Nm.
What is the torque profile (torque needed to be produced) ?
Speed profile

37. INTRODUCTION TO ELECTRIC DRIVES - MODULE 1
Torque and speed profile
10 25 45 60 t (ms)
speed
(rad/s)
100
0 < t <10 ms Te = 0.01(0) + 0.01(0) + 5 Nm = 5 Nm
10ms < t <25 ms Te = 0.01(100/0.015) +0.01(-66.67 + 6666.67t) + 5
= (71 + 66.67t) Nm
25ms < t< 45ms Te = 0.01(0) + 0.01(100) + 5 = 6 Nm
45ms < t < 60ms Te = 0.01(-100/0.015) + 0.01(400 -6666.67t) + 5
= -57.67 – 66.67t
le
TB
dt
d
JT +w+
w
=

38. INTRODUCTION TO ELECTRIC DRIVES - MODULE 1
Torque and speed profile
10 25 45 60
speed
(rad/s)
100
10 25 45 60
Torque
(Nm)
72.67
71.67
-60.67
-61.67
5
6
t (ms)
t (ms)
Speed profile
torque profile

39. INTRODUCTION TO ELECTRIC DRIVES - MODULE 1
Torque and speed profile
10 25 45 60
Torque
(Nm)
70
-65
6
t (ms)
For the same system and with the motor torque profile
given above, what would be the speed profile?
J = 0.001 kg-m2, B = 0.1 Nm/rads-1
and T
load
= 5 Nm.

40. INTRODUCTION TO ELECTRIC DRIVES - MODULE 1
Ratings of converters and motors
Torque
Speed
Power limit for
continuous torque
Continuous
torque limit
Maximum
speed limit
Power limit for
transient torque
Transient
torque limit

41. INTRODUCTION TO ELECTRIC DRIVES - MODULE 1
Thermal considerations
Unavoidable power losses causes temperature increase
Insulation used in the windings are classified based on the
temperature it can withstand.
Motors must be operated within the allowable maximum temperature
Sources of power losses (hence temperature increase):
- Conductor heat losses (i
2
R)
- Core losses – hysteresis and eddy current
- Friction losses – bearings, brush windage

42. INTRODUCTION TO ELECTRIC DRIVES - MODULE 1
Thermal considerations
Electrical machines can be overloaded as long their temperature
does not exceed the temperature limit
Accurate prediction of temperature distribution in machines is
complex – hetrogeneous materials, complex geometrical shapes
Simplified assuming machine as homogeneous body
p
2
p
1
Thermal capacity, C (Ws/
o
C)
Surface A, (m
2
)
Surface temperature, T (
o
C)Input heat power
(losses)
Emitted heat power
(convection)
Ambient temperature, T
o

43. INTRODUCTION TO ELECTRIC DRIVES - MODULE 1
Thermal considerations
Power balance:
21
pp
dt
dT
C -=
Heat transfer by convection:
)TT(Ap
o2
-a=
C
p
T
C
A
dt
Td
1
=D
a
+
D
Which gives:
( )
t-
-
a
=D
/th
e1
A
p
T
A
C
a
=t , where
With DT(0) = 0 and p
1
= p
h
= constant ,
, where a is the coefficient of heat transfer

44. INTRODUCTION TO ELECTRIC DRIVES - MODULE 1
Thermal considerations
t
t
TD
t
t
t-
×D=D
/t
e)0(TT
TD
( )
t-
-
a
=D
/th
e1
A
p
T
Heating transient
Cooling transient
A
p
h
a
)0(TD

45. INTRODUCTION TO ELECTRIC DRIVES - MODULE 1
Thermal considerations
The duration of overloading depends on the modes of operation:
Continuous duty
Short time intermittent duty
Periodic intermittent duty
Continuous duty
Load torque is constant over extended period multiple
Steady state temperature reached
Nominal output power chosen equals or exceeds continuous load
TD
t
A
p
n1
a
t
p
1n
Losses due to continuous load

46. INTRODUCTION TO ELECTRIC DRIVES - MODULE 1
Thermal considerations
Short time intermittent duty
Operation considerably less than time constant, t
Motor allowed to cool before next cycle
Motor can be overloaded until maximum temperature reached

47. t
1
t
INTRODUCTION TO ELECTRIC DRIVES - MODULE 1
Thermal considerations
Short time intermittent duty
A
p
s1
a
max
TD
A
p
n1
a
t
TD
p
1
p
1n
p
1s

48. t
1
INTRODUCTION TO ELECTRIC DRIVES - MODULE 1
Thermal considerations
Short time intermittent duty
t
t
TD
( )
t-
-
a
=D
/ts1
e1
A
p
T
max
TD
A
p
n1
a
( )
t-
-
a
=
a
/ts1n1 1
e1
A
p
A
p
( )
t-
-³
/t
s1n1
1
e1pp
1
/t
n1
s1
te1
1
p
p
1
t
»
-
£
t-

49. INTRODUCTION TO ELECTRIC DRIVES - MODULE 1
Thermal considerations
Periodic intermittent duty
Load cycles are repeated periodically
Motors are not allowed to completely cooled
Fluctuations in temperature until steady state temperature is reached

50. INTRODUCTION TO ELECTRIC DRIVES - MODULE 1
Thermal considerations
Periodic intermittent duty
p1
t
heatingcoolling
coolling
coolling
heating
heating

51. INTRODUCTION TO ELECTRIC DRIVES - MODULE 1
Thermal considerations
Periodic intermittent duty
Example of a simple case – p
1
rectangular periodic pattern
p
n
= 100kW, nominal power
M = 800kg
h= 0.92, nominal efficiency
DT
¥
= 50
o
C, steady state temperature rise due to p
n
kW91
1
pp
n1 =
÷
÷
ø
ö
ç
ç
è
æ
-
h
= Also, C/W180
50
9000
T
p
A
o1
==
D
=a
¥
If we assume motor is solid iron of specific heat c
FE
=0.48 kWs/kg
o
C,
thermal capacity C is given by
C = c
FE
M = 0.48 (800) = 384 kWs/
o
C
Finally t, thermal time constant = 384000/180 = 35 minutes

52. INTRODUCTION TO ELECTRIC DRIVES - MODULE 1
Thermal considerations
Periodic intermittent duty
Example of a simple case – p
1
rectangular periodic pattern
For a duty cycle of 30% (period of 20 mins), heat losses of twice the nominal,
0 0.5 1 1.5 2 2.5
x 10
4
0
5
10
15
20
25
30
35