Prepared by: Luis Fernando Montoya Chun-Ju Huang Ashish K. Solanki Speed control of squirrel cage induction machine using V/F control 1.

Prepared by: Luis Fernando Montoya

Chun-Ju HuangAshish K. Solanki

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Introduction Applications of AC drives Types of Methods to control the speed of Induction machine V/F controlPower ConvertersSimulation ModelSimulation Results Conclusion Reference

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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.

Introduction

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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 drives1.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 applicationsInduction 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

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• 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.

V/Hz Theory BackgroundThe 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 PrincipleSince 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

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Torque

Synchronousfrequency

V/Hz control Closed loop

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Three Phase Full Bride Uncontrolled Rectifier

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DC-DC Boost Converter

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DC-DC Boost Converter

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3 Phase PWM Inverter

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Block Diagram of Simulation Model

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Simulation Model

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Uncontrolled Rectifier and DC-DC Boost Converter Simulation Model

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3 phase inverter with Squirrel Cage Induction Motor

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Simulation ResultsInput Voltage for 3 phase uncontrolled Rectifier

4.14 4.145 4.15 4.155 4.16 4.165 4.17 4.175

-400

-300

-200

-100

0

100

200

300

Time(s)

Inpu

t V

olta

ge t

o re

ctifi

er(V

)

Voltage input to rectifier

Vin A

Vin BVin C

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Simulation ResultsOutput Voltage of three phase uncontrolled rectifier

0.08 0.1 0.12 0.14 0.16 0.18 0.2 0.22 0.24

-300

-200

-100

0

100

200

300

Time(s)

Out

put

Voltage o

f R

ectif

ier(

V)

Vin A

Vin B

Vin C

Rectified Output voltage

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Simulation ResultsOutput Voltage of DC/DC Boost converter

0 2 4 6 8 10 12 14 16 18 200

50

100

150

200

250

300

350

400

Time(s)

Out

put V

olta

ge o

f DC

DC C

onve

rter(V

)

Output Voltage of DC DC Converter

Vdc out

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Simulation ResultsOutput Voltage of 3 Phase PWM inverter before filter

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5-500

0

500

Time(s)Voltag

e Outp

ut inv

erter(

V))

Output Voltage of Inverter before filter

Vout inv A

Vout inv BVout inv C

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5-500

0

500

Time(s)

Voltag

e Outp

ut inv

erter

phase

A(V))

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5-500

0

500

Time(s)

Voltag

e Outp

ut inv

erter

phase

B(V))

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5-500

0

500

Time(s)

Voltag

e Outp

ut inv

erter

phase

C(V))

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Simulation ResultsOutput Voltage of Inverter after filter

( Controlled Input voltage given to Induction motor)

0 2 4 6 8 10 12 14 16 18 20-250

-200

-150

-100

-50

0

50

100

150

200

250

Time(s)

Vol

tage

Inpu

t to

Mac

hine

(V)

Output Voltage of Inverter after filter(input Voltage to Machine)

Vin m A

Vin m BVin m C

3.68 3.7 3.72 3.74 3.76 3.78 3.8 3.82 3.84 3.86 3.88

-200

-150

-100

-50

0

50

100

150

200

Time(s)

Voltage I

nput

to M

achin

e(V

)

Output Voltage of Inverter after filter(input Voltage to Machine)

Vin m A

Vin m B

Vin m C

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Simulation ResultsStator Current

3.55 3.6 3.65 3.7 3.75 3.8 3.85 3.9

-10

-8

-6

-4

-2

0

2

4

6

8

10

Time(s)

Sta

tor

Curr

ent(

A)

Stator Current

Istator A

Istator BIstator C

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Simulation ResultsRotor Reference speed and Actual Speed

Here the reference speed is 1000 rpm= 104.72 rad/sec

0 2 4 6 8 10 12 14 16 18 20-20

0

20

40

60

80

100

120

Time(s)

Roto

r S

peed (

rad/s

ec)

Rotor Speed

Reference Speed

Actual Speed

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Simulation ResultsWithout Filter after the PWM inverter , rotor speed is fluctuating

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Simulation ResultsRotor Reference speed and Actual Speed

0 2 4 6 8 10 12 14-10

0

10

20

30

40

50

60

70

80

90

100

Time(s)

Roto

r S

peed (

rad/s

ec)

Rotor Speed

Reference Speed

Actual Speed

0 2 4 6 8 10 12 14 16 18 20-20

0

20

40

60

80

100

120

140

Time(s)

Roto

r S

peed (

rad/s

ec)

Rotor Speed

Reference Speed

Actual Speed

0 2 4 6 8 10 12 14 16 18 20-20

0

20

40

60

80

100

120

140

160

180

Time(s)

Roto

r S

peed (

rad/s

ec)

Rotor Speed

Reference Speed

Actual Speed

Reference speed is 1300 rpm=136.14 rad/sec

Reference speed is 600rpm= 62.83 rad/sec

Reference speed is 1500rpm= 157.08 rad/sec

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Rotor Reference speed and Actual Speed

Reference Speed is changed from 104.71 rad/sec to 92.24 rad/sec

0 2 4 6 8 10 12 14 16 18 20-20

0

20

40

60

80

100

120

Time(s)

Roto

r S

peed (

rad/s

ec)

Rotor Speed

Reference Speed

Actual Speed

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ConclusionIn 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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