A COMPARITVE STUDY BETWEEN VECTOR CONTROL AND DIRECT TORQUE CONTROL OF INDUCTION MOTOR USING MATLAB SIMULINK Submitted by Fathalla Eldali Department of Electrical and Computer Engineering For the Degree of Master of Science Colorado State University Fall 2012 1
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A COMPARITVE STUDY BETWEEN
VECTOR CONTROL AND DIRECT
TORQUE CONTROL OF INDUCTION
MOTOR USING MATLAB SIMULINK
Submitted by
Fathalla Eldali
Department of Electrical and Computer Engineering
For the Degree of Master of Science
Colorado State University
Fall 2012
1
WHEN HAVE I BEEN INTERESTED IN
MOTOR DRIVE AND MATLAB?
BSC Senior Design
LIM + PLC
MATLAB/Simulink as A Modeling TOOL
2
THESIS OUTLINES Introduction
Induction Motor Principles
Induction Motor Modeling
Electric Motor Drives
Vector Control of Induction Motor
Direct Torque Control
Theoretical Comparison Vector Control and Direct Torque Control
Simulation Results
Simulation Results in the normal operation case
The effect of Voltage sags and short interruption on driven
induction motors
The characteristics of the voltage sag and short interruption
Conclusion & Future Work
3
INTRODUCTION Motors are needed
Un driven Motors and power consumption
Power Electronics, DSP revolution help
Rectifiers
Inverters
Sensors
Control Systems Theories
4
OLD STUDIES & MOTIVATION
Many studies have been done about FOC & DTC
individually
Few studies were published as a comparison
studies as [17-19]
Voltage Sag & Short Interruption faults were not
considered in the comparison
5
INDUCTION MOTOR PRINCIPLES
Nikola Tesla first AC motors 1888
AC motors
-Induction Motors
-Permanent Magnet Motors
Why are Induction Motors are mostly used ?
Supplied through stator only
Easy to manufacture and maintain
Cheap
6
INDUCTION MOTOR CONSTRUCTION
Stator :
laminated sheet steel (eddy current loses reduction) attached to
an iron frame
stator consists of mechanical slots
insulated copper conductors are buried inside the slots and then Y
or Delta connected to the source.
7
Two Types of Rotor
A-wound rotor:
-Three electrical phases just as the stator does and they
(coils) are connected wye or delta.
B-squirrel-cage’s rotor
-contains bars of aluminum or copper imbedded in the
rotor, which are short circuited at the end of each bar by an end
disc
8
INDUCTION MOTOR ROTOR TYPES (A)
WOUNDED ROTOR (B) SQUIRREL-CAGE
ROTOR.
9
ELECTRIC AC MOTOR DRIVES Practically, induction motor doesn’t work at its rated speed
Switching the (motor) on/off is possible by mechanically
stressful
decreasing the rotation speed is a better way to save energy
and reduce mechanical stress
10
PURPOSES OF ELECTRIC AC MOTOR DRIVES
11
INDUCTION MOTOR MODELING To model IM, We should know the electrical and mechanical
equations that describe it in the transient and steady state
The Electrical equations are for the Voltage, current, Flux
The Mechanical equations for the speed, position and Torque
12
IDEALIZED CIRCUIT MODEL OF THREE PHASE
INDUCTION MACHINE
13
ELECTRICAL EQUATIONS
14
MECHANICAL EQUATIONS
15
MACHINE MODEL IN ARBITRARY REFERENCE
FRAMES
Purpose of those Transformations:
Eliminate the effect of inductance changing with time
It is more convenient to be used in Unbalanced voltage
cases.
The other advantage is that we can observe any variable
at any instance.
16
17
RELATIONSHIP BETWEEN ABC AND QD
ARBITRARY COORDINATE REFERENCE FRAMES.
18
INDUCTION MOTOR MODELING
MATLAB/SIMULINK
Three phase to d-q stationary reference frame
d-q stationary frame to d-q synchronous frame
Electromagnetic Torque Equation modeling
19
THREE PHASE TO D-Q STATIONARY
REFERENCE FRAME
2
Vds_s
1
Vqs_s
u[1]
Vqs-s
f(u)
Vds-sVcs
Vbs
Vas
20
D-Q STATIONARY FRAME TO D-Q
SYNCHRONOUS FRAME
2
Vds_e
1
Vqs_e
Repeating
Sequence
Mux
Mux
f(u)
Fcn1
f(u)
Fcn
2
Vqs_s
1
Vds_s
21
ELECTROMAGNETIC TORQUE AND SPEED
EQUATION MODELING
22
1
Te
Product1
Product
-K-
Gain4
Add
4
Iqr-e
3
Ids-e
2
Idr-e
1
Iqs-e
Te
1
Speed
TL
1
s
Integrator
B
Gain2
-K-
1/J
1
Te
Wm
23
Vqs_s
Vds_s
Vqs_e
Vds_e
d-q (S) To d-q (E) Transformation
Wr
u[1]
Vqs-s
f(u)
Vds-s
Vcs
Vbs
Vas
Te
Vqr-e
d(Iqs-e)/dt
Ids-e
Wr
Idr-e
d(Iqr-e)/dt
Iqr-e
Subsystem3
Vds-e
Iqs-e
Iqr-e
d(Idr-e)/dt
d(Ids-e)/dt
Ids-e
Subsystem2
Vqs-e
d(Iqr-e)/dt
Ids-e
Idr-e
d(Iqs-e)/dt
Iqs-e
Subsystem1
Vdr-e
Iqs-e
Wr
Iqr-e
d(Ids-e)/dt
d(Idr-e)/dt
Idr-e
Subsystem
Step
1
s
Integrator
B
Gain2
-K-
Gain1
Iqs-e
Idr-e
Ids-e
Iqr-e
Te
Electromagnetic Torque
Calculation
0
Constant
Iqs-e
Iqs-e
Ids-eIds-e
Overall IM Model 24
1-VECTOR CONTROL OF INDUCTION MOTOR
Torque in separately excited dc motor
Principles of vector control of Induction motor
Torque equations for Vector Control
Vector Control MATLAB/SIMULINK
25
TORQUE IN SEPARATELY EXCITED DC MOTOR
26
SIMPLE REPRESENTATION OF SEPARATELY
EXCITED DC MOTOR.
27
PRINCIPLES OF VECTOR CONTROL OF
INDUCTION MOTOR
28
PRINCIPLES OF VECTOR CONTROL
(DECOUPLING BETWEEN ROTOR FLUX
AND TORQUE)
29
DERIVATION OF THE ORIENTATION CONDITION
30
PROCEDURE IN THREE MAIN POINTS
31
THE PROCEDURE USING MATLAB/SIMULINK
32
33
The last step is to convert the gotten component of stator current
in stationary reference frame to the desired three phase currents
to be the base of control the inverter
34
THE SIMULINK MODEL OF THE FIELD
ORIENTATION CONTROL (FOC) OF
INDUCTION MOTOR.
ids
iqs
Rotor flux angle
Actual speed
Stator currents
Output
To Workspace
Time
Terminator
Scope
Reference
Speed
ev iqs*
PI
Load
0.8
Landa_r*
Vabc
TL
iabc
N
Te
Landa_s
th
Landa_dr
Landa_qr
IM1
iabc*
iabc
Vabc
Determing the state
of the PWM
ids
iqs
th
iabc*
Current decoupling
controller
-K-
.
Overall FOC Model
35
2-DIRECT TORQUE CONTROL
The basic concept of (DTC) method was proposed by
Takahashi and Noguchi in 1986
It is more used in controlling the induction motor because it is
considered a simple and robust method
It has a very fast response and simple structure which makes it
to be more popular used in industrial world
It implies a comparative control of the torque and the stator
fluxes which must fall into two separate certain bands (limits)
to be applicable
36
SPACE VECTOR MODULATION OF
THREE PHASE VOLTAGE SOURCE
INVERTER WITH DTC
voltage vector is shifted (lag or lead) with respect to the
stator flux vector by an angle which is not more than 90°,
this causes the flux to increase and vice versa
The torque is then directly controlled by selecting the
inverter situation in order to boost the stator flux up or
buck it down.
37
SV-PWM
38
SV-PWM
39
BASIC PRINCIPLES OF SWITCHING TABLE
40
THE HYSTERESIS BAND CONTROLS THE STATOR
FLUX VOLTAGE AND
Increase Increase
Increase Decrease
Decrease Decrease
Decrease Increase
41
THE SIMULINK MODEL OF DIRECT TORQUE
CONTROL (DTC) OF INDUCTION MOTOR.
Step
Scope3
Repeating
Sequence
Relay1
Relayev Te*
PI
Output
Interpreted
MATLAB Fcn
MATLAB Fcn
0.8
Landa_s*
Vabc
TL
iabc
N
Te
Landa_s
th
IM
Overall DTC Model
42
LOOK-UP TABLE (SWITCHING TABLE)
Sectors
I II III IV V VI
FU TU V2 V3 V4 V5 V6 V1
FU TD V6 V1 V2 V3 V4 V5
FD TN V7 V0 V7 V0 V7 V0
FD TU V3 V4 V5 V6 V1 V2
FD TD V5 V6 V1 V2 V3 V4
FD TN V0 V7 V0 V7 V0 V7
43
THEORETICAL COMPARISON VECTOR CONTROL
AND DIRECT TORQUE CONTROL
44
SIMULATION RESULTS DTC Vs. FOC
Speed
Electromagnetic Torque
Flux
Three phase current
45
MOTOR SPEED RESPONSE.
0 1 2 3 4 5 6 70
50
100
150
200
250
300
350
400
Time (sec)
Moto
r speed (
r.p.m
)
FOC DTC
46
TORQUE RESPONSE
FOC DTC
47
FLUX RESPONSE
0 1 2 3 4 5 6 70
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
Time (sec)
Sta
tor
Flu
x (
Wb)
0 1 2 3 4 5 6 70
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
Time (sec)
Sta
tor
Flu
x (
Wb)
FOC DTC
48
THREE PHASE MOTOR CURRENT
0 1 2 3 4 5 6 7-4
-3
-2
-1
0
1
2
3
4
Time (sec)
Thre
e p
hase m
oto
r curr
ent
(Am
p)
0 1 2 3 4 5 6 7-15
-10
-5
0
5
10
15
20
Time (sec)
Thre
e p
hase m
oto
r curr
enr
(Am
p)
FOC DTC
49
THE DISTORTION OF THREE PHASE CURRENT
FOC DTC
50
THE EFFECT OF VOLTAGE SAGS AND SHORT
INTERRUPTION ON DRIVEN INDUCTION
MOTORS
(ASD) is considered as one of the sensitive loads to the
voltage sag and short interruption
That might cause the motor protection relay to trip,
because the undervoltage of the DC link
The ac current, which is feeding the motor, increases.
The speed usually deviates and the torque varies [29]
51
THE CHARACTERISTICS OF THE VOLTAGE SAG
AND SHORT INTERRUPTION
Two main types of Voltage Sag and interruptions
Balanced and Unbalanced
7 types of sags could happen as shown
52
SIMULATION RESULTS FOR THE CHOSEN PQ
ISSUES
The voltage sag types, which are used in this project thesis, are
Type A (Balanced) and Type B (Unbalanced). The short
interruption is applied on the two driving techniques too.