Download V/F control

Speed control of squirrel cage
induction machine using V/F
control
Prepared by:
Luis Fernando Montoya
Chun-Ju Huang
Ashish K. Solanki
1
Agenda
 Introduction
 Applications of AC drives
 Types of Methods to control the speed of Induction machine
 V/F control
 Power Converters
 Simulation Model
 Simulation Results
 Conclusion
 Reference
2
Introduction
An electric drive system consisting of electric motor, its power
controller and energy transmitting shaft consisting of load
Types of Drive system
(1)DC Drive
(2)AC Drive
AC Drives are mostly used in Industry.
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Advantages and disadvantages of AC
Drives compare to DC Drives
 Advantages of ac drives
1. For the same rating, ac motors are lighter in weight as compared
to dc motors.
2. AC motors require low maintenance.
3. AC motors are less expensive.
4. AC motors can work in dangerous areas like chemical,
petrochemical etc.
 Disadvantage of ac drives
1.Power converters for the control of ac motors are more complex.
2.Power converter for ac drives are more expensive.
3.Power converters for ac drives generate harmonics in the supply
system and load circuit.
4
Industrial applications
Induction motors with squirrel cage rotors are the workhorse of
industry because of their low cost and rugged construction.
When Squirrel cage induction machine is operated directly from
the line voltages(60 Hz/50 Hz essentially constant voltage) an
Induction motor is operated at constant speed. However in the
industry we required to vary the speed of an Induction motor.
This can be done by Induction motor drives.
Main application of Induction Motor drives:
Fans, Compressor, Pumps, blowers, machine tools like lathe,
drilling machine, lifts, conveyer belts etc.
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Methods of Speed Control
of Induction motors
(1) Stator voltage Control
(2) Stator Frequency Control
(3) Stator Current Control
(4) V/F Control
(5) Slip power recovery Control ( Wound Rotor Induction
Machine)
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Curve of the behavior of the
Induction Machine
• During start up. Normally
draws up to seven times the
rated current.
• Normally delivers
approximately 1.5 the rated
torque, when starting
• When operating at base
speed if the load is
increased, the motor will
start slowing down and the
slip will increase.
•But if the load is increased
beyond the Break down
torque, the machine wont
be able to recover.
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V/Hz Theory Background
 The induction motor draws
the rated current and
delivers the rated torque at
the base speed.
 As mentioned before the
motor can take up to 2.5 load
increase, with 20% drop in the
speed.
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Description of the principle
 Assume the voltage applied to the Motor is AC, and the voltage
drop across the Armature resistance very small. Then at the
steady state we get:


(Voltage applied at the stator, and Flux)
Since the V/f relation keeps constant, then the flux remains
constant and the torque is independent of the supplied
frequency.
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Description of the Principle
 Since the flux is maintained
constant, the toque developed
depends only on the slip speed.
 Huge starting torque can be
obtained without heating-up the
machine
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V/Hz Open Loop
Torque
Synchronous
frequency
11
V/Hz control Closed loop
12
Three Phase Full Bride Uncontrolled Rectifier
13
DC-DC Boost Converter
14
DC-DC Boost Converter
15
3 Phase PWM Inverter
16
Block Diagram of Simulation Model
17
Simulation Model
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Uncontrolled Rectifier and DC-DC Boost
Converter Simulation Model
19
3 phase inverter with Squirrel Cage
Induction Motor
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Simulation Results
Input Voltage for 3 phase uncontrolled Rectifier
Voltage input to rectifier
Vin A
Vin B
Vin C
300
200
Input Voltage to rectifier(V)
100
0
-100
-200
-300
-400
4.14
4.145
4.15
4.155
4.16
4.165
4.17
4.175
Time(s)
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Simulation Results
Output Voltage of three phase uncontrolled rectifier
Vin A
Vin B
Vin C
Rectified Output voltage
300
200
Output Voltage of Rectifier(V)
100
0
-100
-200
-300
0.08
0.1
0.12
0.14
0.16
Time(s)
0.18
0.2
0.22
0.24
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Simulation Results
Output Voltage of DC/DC Boost converter
Output Voltage of DC DC Converter
400
Vdc out
350
Output Voltage of DC DC Converter(V)
300
250
200
150
100
50
0
0
2
4
6
8
10
Time(s)
12
14
16
18
20
23
Simulation Results
Voltage Output inverter phase
Voltage
Voltage
Voltage
Output inverter phase
Output inverter phase
C(V))
B(V))
A(V)) Output inverter(V))
Output Voltage of 3 Phase PWM inverter before filter
Output Voltage of Inverter before filter
500
Vout inv A
Vout inv B
Vout inv C
0
-500
0
0.05
0.1
0.15
0.2
0.25
Time(s)
0.3
0.35
0.4
0.45
0.5
0
0.05
0.1
0.15
0.2
0.25
Time(s)
0.3
0.35
0.4
0.45
0.5
0
0.05
0.1
0.15
0.2
0.25
Time(s)
0.3
0.35
0.4
0.45
0.5
0
0.05
0.1
0.15
0.2
0.25
Time(s)
0.3
0.35
0.4
0.45
0.5
500
0
-500
500
0
-500
500
0
-500
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Simulation Results
Output Voltage of Inverter after filter
( Controlled Input voltage given to Induction motor)
Output Voltage of Inverter after filter(input Voltage to Machine)
250
Output Voltage of Inverter after filter(input Voltage to Machine)
Vin m A
Vin m B
Vin m C
200
Vin m A
Vin m B
Vin m C
200
150
150
100
100
Voltage Input to Machine(V)
Voltage Input to Machine(V)
50
50
0
-50
0
-50
-100
-100
-150
-150
-200
-200
-250
0
2
4
6
8
10
Time(s)
12
14
16
18
20
3.68
3.7
3.72
3.74
3.76
3.78
Time(s)
3.8
3.82
3.84
3.86
3.88
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Simulation Results
Stator Current
Stator Current
10
Istator A
Istator B
Istator C
8
6
4
Stator Current(A)
2
0
-2
-4
-6
-8
-10
3.55
3.6
3.65
3.7
3.75
3.8
3.85
3.9
Time(s)
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Simulation Results
Rotor Reference speed and Actual Speed
Here the reference speed is 1000 rpm= 104.72 rad/sec
Rotor Speed
120
Reference Speed
Actual Speed
100
Rotor Speed (rad/sec)
80
60
40
20
0
-20
0
2
4
6
8
10
Time(s)
12
14
16
18
20
27
Simulation Results
Without Filter after the PWM inverter , rotor speed is fluctuating
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Simulation Results
Rotor Reference speed and Actual Speed
Rotor Speed
100
Reference Speed
Actual Speed
90
80
70
Reference speed is 600rpm= 62.83 rad/sec
Rotor Speed (rad/sec)
60
50
40
30
20
10
0
-10
0
2
4
6
Rotor Speed
8
10
12
14
Time(s)
140
Reference Speed
Actual Speed
120
100
Rotor Speed (rad/sec)
80
Reference speed is 1300 rpm=136.14 rad/sec
60
40
20
0
-20
0
2
4
6
8
180
10
Time(s)
Rotor Speed
12
14
16
18
20
Reference Speed
Actual Speed
160
140
120
100
Rotor Speed (rad/sec)
Reference speed is 1500rpm= 157.08 rad/sec
80
60
40
20
0
-20
0
2
4
6
8
10
Time(s)
12
14
16
29
18
20
Rotor Reference speed and
Actual Speed
Reference Speed is changed from 104.71 rad/sec to 92.24 rad/sec
Rotor Speed
120
Reference Speed
Actual Speed
100
Rotor Speed (rad/sec)
80
60
40
20
0
-20
0
2
4
6
8
10
Time(s)
12
14
16
18
20
30
Conclusion
 In Case of Squirrel cage induction motor the slip
cannot be increase above certain limit, the operating
speed range is very less. By applying the V/F control
we can get the large operating range by keeping V/F
ratio constant.
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Reference
 [1] Modern Power Electronics and AC drives by Bose, Bimal K.
 [2] POWER ELECTRONICS Converters, Applications and Design




by Ned Mohan
[3] Power electronics Lecture Notes by Prof. Nasiri
[4] Lecture Notes by Dr. Omar
[5] AC Induction Motor Control using Constant V/Hz Principe
and Space Vector PWM Technique with TMS320 C240
[6] Speed Control of 3-Phase Induction Motor Using PIC18
Microcontrollers
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