Control of a self-excited squirrel cage induction machine based

wind energy conversion system

Vikram Roy Chowdhury

Outline

• Introduction & Background• Operation and design of the SCIG based system.• Controllers Design

Machine terminal voltage in standalone mode

VAR controller in grid connected mode

DC bus voltage control.

Overall current control.

Overall pitch control scheme.

• Comparison of the system operation with SVC and STATCOM

• Verification of the above control scheme in MATLAB/SIMULINK platform.

Literature review/Background

• VAR control with STATCOM and SVC are well reported in literature in grid connected mode.

• Pitch control over rated speed is reported in literature.• Self excited induction machine characteristics are well reported

in many literatures.• Back to back connected converter control of wind systems are

well reported in literature.• A new type of pitch control method is being proposed.• Utilization of SVC and STATCOM for standalone application is

successfully demonstrated.• Overall electrical control by only shunt compensators are

demonstrated.

Self excitation process for an induction machine

lsjX lrjXF

R s

F

R

jX

sI rI

VF

Rr

mjXF

Vt 2F

jXc

F

Vg

Equations in the self excited mode

= + +j

= ( ) + ( + )

Magnetization characteristics of the machine.

Characteristics of the chosen machine in self excited mode

Terminal Voltage versus active power Per Unit frequency versus active

output power output

0 1 2 3 4 5 6235

240

245

250

255

260

---------------->Po

------

------

----->

Vt

Variation of terminal voltage with active power output

C=680

C=620

C=650

0 1 2 3 4 5 60.942

0.944

0.946

0.948

0.95

0.952

0.954

0.956

0.958

0.96

0.962

-------------------->Po

------

------

------

----->

F

Variation of per unit frequency with active power output

C=620

C=650

C=680

Topology of SVC used with its control strategy in standalone mode for voltage control

The configuration of the SVC with its equivalent reactance

Control voltage generation for firing the SVC for standalone mode

Control strategy of SVC in grid connected mode

Control strategy of SVC under grid connected mode of operation

Configuration of the STATCOM used

Equation of an inverter in the voltage oriented reference frame

P=

Q=

P= (Active Power)

Q= (Reactive power)

Unit vector generation or defining axes for transformations

where

d-AXIS CONTROLLER FOR THE STATCOM

DC bus voltage and current controller

q-AXIS CONTROLLER FOR THE STATCOM

Terminal voltage(standalone mode)/VAR(grid mode) controller and current controller

Pitch angle control scheme for the systemFor standalone mode

Contd…For grid connected mode

Results for Voltage control and VAR control with SVC

19.8 19.82 19.84 19.86 19.88 19.9 19.92 19.94 19.96 19.98 2050

100

150

200

250

300

---------------->Time(secs)

------

------

---->

Term

inal

vol

tage

of t

he m

achi

ne

Terminal voltage of the machine with SVC as compensator

Reference

Actual

Control of terminal voltage by SVC

33 33.02 33.04 33.06 33.08 33.1 33.12 33.14 33.16 33.18 33.2-20

-15

-10

-5

0

5

10

---------------->Time(secs)

------

------

---->

KV

AR

con

trol i

n gr

id c

onne

cted

mod

e

Reactive power control with SVC in grid connected mode

Reference

Actual

Control of reactive power by SVC

Operating Condition: Load 15 KW 220 V 50 Hz 0.7 power factor lag

Results obtained with STATCOMResults for d-axis quantities

46.9 46.92 46.94 46.96 46.98 47 47.02 47.04 47.06 47.08 47.1850

860

870

880

890

900

910

920

930

940

950

---------------->Time(secs)

------

------

---->

Vdc

(vol

ts)

Reference Vdc* and actual Vdc

Reference

Actual

46.95 46.96 46.97 46.98 46.99 47 47.01 47.02 47.03 47.04 47.05-50

-40

-30

-20

-10

0

10

20

30

40

50

---------------->Time(secs)

------

------

---->

Id(a

mpe

re)

Reference Id* and actual Id

Reference

Actual

DC bus voltage d-axis current

Operating Condition: Load 15 KW 220 V 50 Hz 0.7 power factor lag

Contd…Results obtained for q-axis quantities

46.9 46.92 46.94 46.96 46.98 47 47.02 47.04 47.06 47.08 47.1220

230

240

250

260

270

280

290

300

310

320

---------------->Time(secs)

------

------

---->

Vte

rmin

al(v

olts

)

Reference Vt* and actual Vt

Reference

Actual

46.95 46.96 46.97 46.98 46.99 47 47.01 47.02 47.03 47.04 47.0530

35

40

45

50

55

60

65

70

75

80

---------------->Time(secs)

------

------

---->

Iq(a

mpe

re)

Reference Iq* and actual Iq

Reference

Actual

Terminal voltage q-axis current

Operating Condition: Load 15 KW 220 V 50 Hz 0.7 power factor lag

Grid Voltage and current with SVC and STATCOM

34.2 34.22 34.24 34.26 34.28 34.3 34.32 34.34 34.36 34.38 34.4-300

-200

-100

0

100

200

300

---------------->Time(secs)

----

-----

-----

-->V

grid

(vol

ts),

Igrid

(am

pere

)

Grid voltage and grid current with SVC connected

Current

Voltage

94.9 94.95 95 95.05 95.1 95.15 95.2 95.25-300

-200

-100

0

100

200

300

---------------->Time(secs)

----

----

----

----

>V

grid

(vol

ts),

Igrid

(am

pere

)

Grid voltage and current before and after the connection of STATCOM

Voltage

Current

Grid voltage and current with SVC

Grid voltage and current with STATCOM

Operating Condition: Load 15 KW 220 V 50 Hz 0.7 power factor lag

VAR control in grid connected mode with transient

94.5 95 95.5 96 96.5-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

---------------->Time(secs)

----

----

----

----

>R

eactive P

ow

er(

KV

AR

)

KVAR(Reference and Actual)

Reference

Actual

Actual VAR and its reference as wind speed suddenly changes from 8m/s to 9m/s

DC bus voltage required with SVM technique

49 49.02 49.04 49.06 49.08 49.1 49.12 49.14 49.16 49.18 49.2700

710

720

730

740

750

760

770

780

790

800

---------------->Time(secs)

----

----

----

----

>V

dc(v

olts)

Reference Vdc* and actual Vdc with SVM

Reference

Actual

Result of frequency control for standalone mode of operation

46.5 46.6 46.7 46.8 46.9 47 47.1 47.2 47.345

46

47

48

49

50

51

52

53

54

55

---------------->Time(secs)

----

----

----

----

>F

requency(H

z)

Actual frequency and its reference

Reference frequency

Actual frequency

Actual frequency and its reference during load switching (from 15 KW to 20 KW) at t=47 seconds

CONCLUSION AND FUTURE WORK

• By this method both standalone and grid connected systems can be operated satisfactorily.

• Grid connection is also possible with appropriate control.

• Frequency control by pitch control with a slew rate of 12 degrees per second gives good dynamic response.

• Though STATCOM control strategy is complex it gives better performance both in steady state and under dynamic conditions .

• Voltage control and VAR control by some other converter topology may be proposed.

• From the results it can be inferred that with SVM lower DC bus voltage is required indicating better dc bus utilization.

REFERENCES

• [1] Wind electrical systems by D. Kastha, S.N. Bhadra and S. Banerjee• [2] Understanding FACTS TECHNOLOGY OF FLEXIBLE AC TRANSMISSION

SYSTEMS by Narain G. Hingorani and Laszlo Gyugyi• [3] N.H. Malik and S.E. Hague, "Steady state analysis and performance of an

isolated self-excited induction generator", IEEE Trans. on Energy Conversion, Vol. EC-1, No. 3, pp.134-139, September 1986.

• [4] T.F. Chan, "Analysis of self-excited induction generators using an iterative method", IEEE PES 1995 Winter Meeting, New York, Jan 29 to Feb 2, 1995.

• [5] Analysis and development of a distribution STATCOM for power quality compensation Ph.D thesis by Parthasarathi Sensarma

• [6]Synchronous reference frame strategy based STATCOM for reactive and harmonic current compensation M.tech thesis by Arun Karppaswamy B

• [7] R. Datta and V. T. Ranganathan, “A simple position-sensorless algorithm for rotor-side field-oriented control of wound-rotor induction machine,” IEEE Trans. Ind. Electron., vol. 48, no. 4, pp. 786–793, Aug. 2001.

QUESTIONS??

THANK YOU

Data of the machine used for simulation

Quantities Values Voltage(V) Current(A) Rated Voltage( L-L) 400 V 100 5.78Rated Line Current 67.6 A 150 8.68Number of poles 4 200 12.44Stator resistance 0.191Ω 210 13.89Stator leakage reactance 1.20mH 220 16.20Rotor resistance referred to stator

0.0812Ω 230 19.10

Rotor reactance referred to stator

1.79mH 240 23.15

Rated speed 1440 rpm 250 28.94Rated H.P. of the machine 50.4 260 36.46Operating frequency 50 Hz 270 46.30

Magnetization Characteristics of the chosen machine