1. Control of a self-excited squirrel
cage induction machine based
wind energy conversion system
Vikram Roy Chowdhury

2. 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.

3. 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.

4. Self excitation process for an induction
machine
Rs
F
R
F
Vt
F jX
jXls
jXlr
Ir
Is
jX c
F2
Rr
F
Vg
F
jXm
V

5. Equations in the self excited mode
=
+
=
(
+j
)+ (
+
)
Magnetization characteristics of the
machine.

6. Characteristics of the chosen machine in self
excited mode
Variation of terminal voltage with active power output
Variation of per unit frequency with active power output
260
0.962
0.96
C=680
255
0.958
250
0.956
----------------------->F
----------------->Vt
C=650
C=620
245
0.954
C=620
0.952
0.95
C=650
0.948
240
0.946
C=680
0.944
235
0
1
2
3
---------------->Po
4
5
6
Terminal Voltage versus active power
output
0.942
0
1
2
3
-------------------->Po
4
5
Per Unit frequency versus active
power output
6

7. 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

8. Control strategy of SVC in grid connected
mode
Control strategy of SVC under grid connected mode of
operation

9. Configuration of the STATCOM used

10. Equation of an inverter in the voltage oriented
reference frame
P=
Q=
P=
(Active Power)
Q=
(Reactive power)

11. Unit vector generation or defining axes for
transformations
where

12. d-AXIS CONTROLLER FOR THE
STATCOM
DC bus voltage and current controller

13. q-AXIS CONTROLLER FOR THE
STATCOM
Terminal voltage(standalone mode)/VAR(grid mode)
controller and current controller

14. Pitch angle control scheme for the system
For standalone mode

15. Contd…
For grid connected mode

16. Results for Voltage control and VAR control
with SVC
Reactive power control with SVC in grid connected mode
Terminal voltage of the machine with SVC as compensator
10
Reference
Actual
---------------->KVAR control in grid connected mode
---------------->Terminal voltage of the machine
300
250
200
150
100
50
19.8 19.82 19.84 19.86 19.88 19.9 19.92 19.94 19.96 19.98
---------------->Time(secs)
Control of terminal voltage by
SVC
20
Reference
Actual
5
0
-5
-10
-15
-20
33
33.02 33.04 33.06 33.08 33.1 33.12 33.14 33.16 33.18
---------------->Time(secs)
33.2
Control of reactive power by
SVC
Operating Condition: Load 15 KW 220 V 50 Hz 0.7 power factor lag

17. Results obtained with STATCOM
Results for d-axis quantities
Reference Vdc* and actual Vdc
Reference Id* and actual Id
950
50
Reference
Actual
940
30
920
20
---------------->Id(ampere)
930
---------------->Vdc(volts)
Reference
Actual
40
910
900
890
880
10
0
-10
-20
870
-30
860
-40
850
46.9 46.92 46.94 46.96 46.98 47 47.02 47.04 47.06 47.08
---------------->Time(secs)
DC bus voltage
47.1
-50
46.95 46.96 46.97 46.98 46.99 47 47.01 47.02 47.03 47.04 47.05
---------------->Time(secs)
d-axis current
Operating Condition: Load 15 KW 220 V 50 Hz 0.7 power factor lag

18. Contd…
Results obtained for q-axis quantities
Reference Iq* and actual Iq
Reference Vt* and actual Vt
80
320
Reference
Actual
310
70
290
65
---------------->Iq(ampere)
300
---------------->Vterminal(volts)
Reference
Actual
75
280
270
260
60
55
50
250
45
240
40
230
35
220
46.9 46.92 46.94 46.96 46.98 47 47.02 47.04 47.06 47.08
---------------->Time(secs)
Terminal voltage
47.1
30
46.95 46.96 46.97 46.98 46.99 47 47.01 47.02 47.03 47.04 47.05
---------------->Time(secs)
q-axis current
Operating Condition: Load 15 KW 220 V 50 Hz 0.7 power factor lag

19. Grid Voltage and current with SVC and
STATCOM
Grid voltage and grid current with SVC connected
Grid voltage and current before and after the connection of STATCOM
300
300
200
Voltage
Current
---------------->Vgrid(volts),Igrid(ampere)
---------------->Vgrid(volts),Igrid(ampere)
Current
Voltage
100
0
-100
-200
200
100
0
-100
-200
-300
34.2 34.22 34.24 34.26 34.28 34.3 34.32 34.34 34.36 34.38
---------------->Time(secs)
34.4
Grid voltage and current with
SVC
-300
94.9
94.95
95
95.05
95.1
95.15
---------------->Time(secs)
95.2
Grid voltage and current with
STATCOM
Operating Condition: Load 15 KW 220 V 50 Hz 0.7 power factor lag
95.25

20. VAR control in grid connected mode with
transient
KVAR(Reference and Actual)
2
Reference
Actual
---------------->Reactive Power(KVAR)
1.5
1
0.5
0
-0.5
-1
-1.5
-2
94.5
95
95.5
---------------->Time(secs)
96
96.5
Actual VAR and its reference as wind speed suddenly changes
from 8m/s to 9m/s

21. DC bus voltage required with SVM technique
Reference Vdc* and actual Vdc with SVM
800
Reference
Actual
790
---------------->Vdc(volts)
780
770
760
750
740
730
720
710
700
49
49.02
49.04
49.06
49.08
49.1 49.12 49.14
---------------->Time(secs)
49.16
49.18
49.2

22. Result of frequency control for standalone
mode of operation
Actual frequency and its reference
55
Reference frequency
Actual frequency
54
---------------->Frequency(Hz)
53
52
51
50
49
48
47
46
45
46.5
46.6
46.7
46.8
46.9
47
---------------->Time(secs)
47.1
47.2
Actual frequency and its reference during load switching
(from 15 KW to 20 KW) at t=47 seconds
47.3

23. 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.

24. 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.

25. QUESTIONS??

26. THANK YOU

27. Data of the machine used for simulation
Quantities
Values
Rated Voltage( L-L)
400 V
Rated Line Current
67.6 A
Number of poles
4
Stator resistance
0.191Ω
Stator leakage reactance
1.20mH
Rotor resistance referred
to stator
Rotor reactance referred
to stator
Rated speed
0.0812Ω
Voltage(V)
100
150
200
210
220
230
Current(A)
5.78
8.68
12.44
13.89
16.20
19.10
1.79mH
240
23.15
1440 rpm
250
260
270
28.94
36.46
46.30
Rated H.P. of the machine
50.4
Operating frequency
50 Hz

28. Magnetization Characteristics of the chosen
machine