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Home , AC motor, Direct torque control, Electric machine, Electric motor, Vector control (motor)

A COMPARITVE STUDY BETWEEN AND DIRECT CONTROL OF USING MATLAB SIMULINK

Submitted by Fathalla Eldali Department of Electrical and Computer For the Degree of Master of Science Colorado State University Fall 2012

1 WHEN HAVE I BEEN INTERESTED IN AND MATLAB?

 BSC Senior Design  LIM + PLC  MATLAB/Simulink as A Modeling TOOL

2 THESIS OUTLINES  Introduction  Induction Motor Principles  Induction Motor Modeling  Drives  Vector Control of Induction Motor   Theoretical Comparison Vector Control and Direct Torque Control  Simulation Results  Simulation Results in the normal operation case  The effect of sags and short interruption on driven induction motors  The characteristics of the voltage sag and short interruption 3  Conclusion & Future Work

INTRODUCTION  Motors are needed  Un driven Motors and power consumption  , DSP revolution help   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

first AC motors 1888  AC motors -Induction Motors -Permanent Motors  Why are Induction Motors are mostly used ?  Supplied through only  Easy to manufacture and maintain  Cheap

6

INDUCTION MOTOR CONSTRUCTION

 Stator :  laminated sheet steel ( loses reduction) attached to an frame  stator consists of mechanical slots  insulated conductors are buried inside the slots and then Y or Delta connected to the source.

7  Two Types of 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

13 ELECTRICAL EQUATIONS 

14 MECHANICAL EQUATIONS

15 MACHINE MODEL IN ARBITRARY REFERENCE FRAMES

 Purpose of those Transformations:  Eliminate the effect of 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

u[1] 1 Vas Vqs_s Vqs-s

Vbs

f(u) 2 Vds_s Vds-s Vcs

20 D-Q STATIONARY FRAME TO D-Q SYNCHRONOUS FRAME

1 Vds_s Mux 2 f(u) 1 Vqs_s Vqs_e Fcn

f(u) 2 Vds_e Fcn1 Mux Repeating Sequence

21 ELECTROMAGNETIC TORQUE AND SPEED EQUATION MODELING

22 1 Iqs-e

Product1 2 Idr-e

Gain4

Add -K- 1 Te Te 3 Ids-e

4 Product Iqr-e 1 Te 1 -K- 1 s Wm Speed 1/J Integrator

TL

B 23

Gain2 Vqs-e d(Iqs-e)/dt Vas d(Iqr-e)/dt

u[1] Vqs_s Vqs_e Ids-e Iqs-e Vbs Iqs-e Vqs-s Idr-e Iqs-e Te

Subsystem1

f(u) Vds_s Vds_e Vcs Iqs-e Vds-e Vds-s Wr d(Ids-e)/dt Idr-e d-q (S) To d-q (E) Transformation Iqs-e 1 Te -K- Iqr-e Ids-e s Gain1 Ids-e Ids-e Integrator d(Idr-e)/dt Ids-e Iqr-e

Subsystem2 Electromagnetic Torque Calculation Vqr-e d(Iqr-e)/dt d(Iqs-e)/dt B Ids-e 0 Wr Gain2 Iqr-e Idr-e Constant Subsystem3 Step

Vdr-e d(Idr-e)/dt Iqs-e Wr Iqr-e Idr-e d(Ids-e)/dt Subsystem 24 Overall IM Model 1-VECTOR CONTROL OF INDUCTION MOTOR

 Torque in separately excited  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. Scope Time 0.8 -K- ids iabc Landa_r* . ids iabc* N Vabc Vabc iqs iabc* Te iqs iabc Landa_s ev iqs* th Determing the state th Reference PI of the PWM TL Speed Current decoupling Landa_dr Output controller Landa_qr Terminator To Workspace IM1

Load

Stator currents

Rotor flux angle

Actual speed 35

Overall FOC Model 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 41 Decrease Decrease

Decrease Increase THE SIMULINK MODEL OF DIRECT TORQUE CONTROL (DTC) OF INDUCTION MOTOR.

0.8

Landa_s*

Output

Interpreted iabc ev Te* Vabc MATLAB Fcn N Relay1 Repeating PI MATLAB Fcn Te Sequence Landa_s TL th Step IM Scope3

42 Overall DTC Model

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.

FOC DTC

400

350

300

250

200 Motor speed (r.p.m) Motor speed 150

100

50

0 0 1 2 3 4 5 6 7 Time (sec)

46 TORQUE RESPONSE

FOC DTC

47 FLUX RESPONSE

FOC DTC

0.9 0.9

0.8 0.8

0.7 0.7

0.6 0.6

0.5 0.5

0.4 0.4

Stator Flux (Wb) Stator Flux (Wb)

0.3 0.3

0.2 0.2

0.1 0.1

0 0 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 Time (sec) Time (sec) 48 THREE PHASE MOTOR CURRENT

FOC DTC

4 20

3 15

2 10

1

5

0

0

-1 Three phase motor current (Amp) motor current phase Three

Three phase motor currenr (Amp) motor currenr phase Three -5 -2

-10 -3

-4 -15 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 Time (sec) Time (sec) 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.

53 SIMULATION RESULTS FOR THE CHOSEN PQ ISSUES

 The affected DC Link Voltage  For FOC Vs. DTC , I observe the following:  Speed Variation  Three Phase Current

54 THE AFFECTED DC LINK VOLTAGE

One phase short interruption’s effect on DC link voltage (Type B) 55 DC VOLTAGE WAVE SHAPE UNDER THE EFFECT OF TWO TYPES OF VOLTAGE SAG CONDITION

56 TABLE THE DC LINK VOLTAGE IN DIFFERENT VOLTAGE SAG PERCENTAGES AND DIFFERENT DURATIONS (TYPE A)

Sag Duration (Cycles) 18 cycles 22 cycles 26 cycles 30 cycles

Voltages Sag (%)

20 % 314.75 314.6 314.51 314.2

40 % 236.5 236.4 236.4 236.4

60 % 159.7 156.28 156.26 156.26

80 % 155.4 126.2 102.49 83.55

100 % (interruption) 155.3 126.15 102.4 83.15 57 THE DC LINK VOLTAGE IN DIFFERENT VOLTAGE SAG PERCENTAGES AND DIFFERENT DURATIONS (TYPE A) 350 DC link in the normal operation is 400 Volt 18 cycles 22 cycles 26 cycles 300 30 cycles

250

200 DC link DC Voltage (Volt)

150

100

50 58 20 30 40 50 60 70 80 90 100 Voltage Dip (Sag) % SPEED VARIATION (DEVIATION) VOLTAGE SAG TYPE A

FOC DTC

70 100

18 cycles 18 cycles 90 22 cycles 60 22 cycles 26cycles 26 cycles 80 30cycles Motor Stall 30 cycles 50 70

60 40

50

30 40

Speed Drop % from speed the Drop desired Speed 30 20 % from speed the desired Drop Speed

20

10 10

0 0 20 30 40 50 60 70 80 90 100 59 20 30 40 50 60 70 80 90 100 Voltage Dip (Sag) % Voltage Dip (Sag) % SPEED VARIATION TYPE A

FOC DTC

Sag Duration 18 cycles 22 cycles 26 cycles 30 cycles Sag Duration 18 cycles 22 cycles 26 cycles 30 cycles (Cycles) (Cycles)

Voltages Sag (%) Voltages Sag (%)

20 % 0% 0% 0% 0% 20 % 0% 0% 0% 0%

40 % 0% 0% 0% 0% 40 % (0,+0.5)% (0,+0.5)% (0,+0.5)%

60 % 60 % (0,+0.5)% (0,+0.5)%

80 % (-15, +19) % (-43,+54) % (-66, +85) % 80 % STALLS

100 % (-16, +19) % (-43,68) % (-67, +170) % 100 % STALLS (interruption) (interruption) 60 PEAK CURRENT DURING VOLTAGE SAG TYPE A

FOC DTC

7 30 18 cycles 22 cycles 26 cycles 6 25 30 cycles 3.67A "Normal current" 5

20

4

15

3 Motor Current (Amp) Motor Current

Three phase current (Amp) current phase Three 10 18 Cycles 2 22 Cycles

26 Cycles

5 1 30 Cycles Motor stalls 4.5A "normal current"

0 0 20 30 40 50 60 70 80 90 100 20 30 40 50 60 70 80 90 100 Voltage Dip (sag) % Voltage Dip (Sag) % 61 PEAK CURRENT DURING VOLTAGE SAG TYPE A

FOC DTC

Sag Duration 18 cycles 22 cycles 26 cycles 30 cycles Sag Duration 18 cycles 22 cycles 26 cycles 30 cycles (Cycles) (Cycles)

Voltages Sag (%) Voltages Sag (%)

20 % 3.67 3.67 3.67 3.67 20 % 4.5 4.5 4.5 4.5

40% 3.67 3.67 3.67 3.67 40 % 4.5 4.5 4.5 4.5

60 % 3.95 3.98 4.1 4.06 60 % 4.6 4.84 4.5 4.5

80% 4.17 13.28 27.8 25.6 80 % 4.7 4.84 6.8 1.5-3

100 % 4.19 13.34 27.84 26.45 100 % 4.84 4.87 6.8 1.5-3 (interruption) (interruption) 62 CONCLUSION Comparison Aspects FOC DTC

Speed Response Faster and more robust

Torque response Faster but spiky better torque response

flux response Slower and it is affected by the Faster and stable load easiness of Complicated because of the Easy implementation transformation

V-sag/ Interruptions Speed deviates gradually Speed reaches 0 at certain point Current increases gradually Current doesn’t increase and it falls suddenly

63 General Good Good RECOMMENDED FUTURE WORK

 Detailed analysis in comparing those two important methods

 RT simulation should be done for full analysis of the other power quality issues

 In addition simulation should consider the protection system for both under voltage and overvoltage

64 REFERENCES

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