1. Implementation Of Vernier Mode Operation Using STATCOM For Terminal
Voltage Regulation Of a 3-Ø Stand-Alone Self-excited Induction Generator
by
K. Subramanian, S. P. Sabberwal, M. Arunachalam and D. P. Kothari
Over View: of the Presentation
Abstract
Key words
1. Introduction
2. System Configuration
3. Equivalent Circuit Analysis
4. Modeling of the Proposed System
5. Experimental Work
6. Results and Discussion
7. Conclusion
References
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2. Abstract

This paper describes regulated voltage operation of a 3-Ø self-excited induction generator
(SEIG) supplies power to an isolated power system comprises of R and R-L loads.

A wind turbine drives the rotor of SEIG generating voltage with variable magnitude and
frequency. Therefore, the problem is to control both voltage and frequency.

For frequency control, an active power balancing technique is applied. A 3-Ø
thyristor/triac switched reactor (TSR) with STATCOM is employed to regulate the terminal
voltage of SEIG.

Instantaneous reactive power theory based control logic developed and implemented to
control the power drawn by the additional load (dump load).


Mathematical model of the proposed system derived using steady state equivalent circuit
followed by MATLAB/SIMULINK based simulation is executed.
To validate the proposed system, a laboratory model of an isolated wind energy
conversion scheme (WECS) is rigged up using conventional induction motor of 3Hp,3-Ø,
415V, 4.9A, and 1440 rpm coupled with a 220V, 20A separately excited d.c motor drive. A
3-Ø, 415 V capacitor bank of 100μF (in each phase) is connected across the stator
terminals of the machine for its self-excitation. The results show a good agreement
between the simulation and experiment.
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3. 1. Introduction
The power generated mainly through the induction machines has a poor voltage regulation in
particular isolated mode [5]-[6]. Different controller is used to control the voltage and
frequency of SEIG is presented in detail [7]. Tarek Ahmed et al [8] present terminal voltage
regulation of SEIG under different load conditions functioning in three distinct steps with static
VAr compensator. However, there is a need for economic operation on a continuous basis. Bhim
Singh et al [9] presented a stand-alone generating system using self-excited induction
generators in the extraction of petroleum products; costly STATCOM is used for voltage
regulation of the generator in full-scale range.
The aim of this work is to implement a three-phase Voltage Source converter (VSC) based static
reactive volt-ampere (VAr) compensator (STATCOM) employed to act as a Vernier between two
steps is presented. Attempt is made to study the performance of SEIG for continuous load
variation. The advantages of the proposed scheme are:
 Rating and cost of STATCOM is low because it operates in Vernier control mode
 If an active energy storage system like battery is connected on d.c side of
STATCOM, it is called VSI-STATCOM; it aids to regulate the system voltage by
supplying active power partially during low wind velocity.
The VSC-STATCOM operating in Vernier mode such that it mitigates the excess VAr generated
by the full load capacitance along with switched inductor. As soon as the load reactance varies,
the generator operation shifts from resonant condition. In order to maintain resonance, the
effective reactance of the load, magnetising reactance and switched reactance has to be
altered. A simple control circuit is designed and implemented.
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4. 2. System Configuration
Single line diagram of proposed system is shown
in Fig.5.1. It comprises of thyristor/triac
switched inductor, VSC-STATCOM and selfexcited induction generator.
It supplies power to a three-phase R-L load. The
full load excitation capacitor CFC is split into two;
one is used to excite the generator at no-load
(Cno-load) the other (Cadd.) will supply the leading
VAr to mitigate the load lagging VAr.
The switched inductor LSR and Cadd are
connected in parallel with load. This combination
resonates with the system frequency at all load
conditions and VSC-STATCOM will operate in
Vernier control of SEIG for terminal voltage
regulation.
Fig.1 Single line diagram of SEIG supplying power
to R-L load with switched reactor
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5. 3. Equivalent circuit Analysis
Xceqt
Xc
X VSC
F
F
F
Is
[10] &[11]
(1)
Zs
(2)
Where,
ZS
Z1
ZC
Zc R eqt
Z1
RS
Zc R eqt
j F XL :
XCeqt
F
Z 2 Zm
; Zm
Z2
Z2
Zm
Rr
jFX L
F
(3)
j FXm
P X m , F (A1X m A 2 )F 3 (A 3 X m A 4 )F 2 (A 5 X m A 6 )F A 7 X m A 8 0
Q X m , F (B1X m B 2 )F 2 (B 3 X m B 4 )F B 5 0
Is
E g Z c R eqt
Z1 Z c R eqt
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Z c R eqt
; Ir
IS Z m
Z2 Zm
;I L
Fig. 2 Single-phase steady state equivalent
circuit of SEIG with VSC
(4)
(5)
IS Zc
R eqt
Zc
; Vt I L R eqt ; Pin
3 I2 R r
r
F
and Pout Vt I L (6)
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6. 4. Modeling of the system
PT 0.5C p AV 3 ;
TT PT /
TR
V
;C p
116/
1
0.4
5e
165/ 1 ; 1
1/
0.089 0.035/
2
1
(7)
(8)
T
Fig. 3 Simulated wind turbine characteristics
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7. Modeling of the system cont…
R s i qs L ls
R r i qr L lr
R r i dr L lr
Z
where
V Vcq
I
dt
di qs
dt
di dr
dt
di qs
Lm
Lm
1 di qs
dt
C dt
di qs
dt
1 di qr
Lm
1 di ds
dt
C dt
di dr 1 di dr
dt
(9)
(10)
r dr
C dt
di dr
Lm
Vcq
C dt
Vcd
(11)
(12)
r qr
Fig. 4 D-Q Equivalent circuit of SEIG with load
V
Vcd
R s pLls
Z
dt
di qr
R s i ds L ls
C
di qs
(13)
kq
1
pC
0
pLm
r Lm
k d 1; I
i qs
0
R s pLls
r Lm
pLm
i ds
iqr
idr 1 ; C
pLm
1
pC
pLm
R r pLr
r Lr
r Lr
R r pLr
(14)
i qs i qr 2
im
Eg
0
0
0 0 0 0 1
(15)
i ds i dr 2
(16)
Lm im
Lm f im
(17)
(18)
Te 3 2 P 2 L m i dr i qs i qr i ds
and
Tshaft T e J 2 P p r
p r P 2J Te Tshaft
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(19)
(20)
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8. Modeling of the system cont…
4.3
STATCOM model
[9]
pVdc i ca SA i cbSB i ccSC C dc
e a V dc SA SB
e b Vdc SB SC
e c V dc SC SA
v a r i ca L p i ca ea r i cb L p i cb
v b r i cb L p i cb e b r i cc L p i cc
i ca i cb i cc 0
v b r i cb pL i cb
eb
r i ca pL i ca
r i cc
pL i cc
pLi ca pLi cb v a e ab ri ca ri ca
pLi ca 2pLi cb v b e bc ri ca 2ri ca
pi ca
pi cb
pi cc
v b e bc r 2 v a e ab 3rf i ca 3L f ;
v b e bc r 2 v a e ab 3rf i ca 3L f &
v b e bc r 2 v a e ab 3rf i ca 3L f
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(24)
(25)
(26)
(27)
(28)
Fig. 5 VSC based STATCOM
(29)
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9. STATCOM Control
4.4.3 Total Source Current
Vt
2 3 Va 2 Vb 2 Vc 2
(30)
u a Va Vt
u b Vb Vt
u c Vc Vt
Wa
ua
I *sa I *saq I *sad
I *sb I *sbq I *sbd
I *sc I *scq I *scd
(31)
3
uc
Wb
3u a 2
Wa
3u a 2
3
ub uc
ub
4.4.4 PWM Current Controller
2 3
(32)
I saerr I *sa I sa
I sberr I *sbr I sb
I scerr I *sc I sc
uc 2 3
4.4.1 Quadrature Component of Reference Source Current
Verr Vtref
(39)
Vtmea
I *smqnew I *smsqold K p Verrnew Verrold
(40)
4.4.5 Voltage Magnitude at Point of
Common Coupling (PCC)
(33)
K i Verrnew
(34)
I *saq I *saqnew Wa ; I *sbq I *sbqnew Wb and ; I *scq I *scqnew Wc
(35)
pVa i a i lb i sta
pVb i a i lc i sta
Va Vb Vc 0
i b i lb i sta 3C
i b i lc i sta 3C
(41)
4.4.2 in Phase Component of Reference Source Current
Vdcerr Vdcref
Vdcmea
I *smdnew I *smsdold K p Vdcerrrnew Vdcerrold
(36)
K i Vdcerrnew
(37)
I *sad I *smdnew u a ; I *sbd I *smdnew u b and ; I *scd I *smdnew u c
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(38)
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10. 5. Experimental work
The induction motor draws inductive current
if the load on the generator increases.
In order to compensate the lagging VAr
required by the induction machine and
change in magnetizing reactance, the
synchronous motor is excited in an
overexcited mode i.e, excitation is greater
than the normal excitation thereby yielding
the required leading VAr.
The corresponding terminal voltage at PCC is
measured and noted, Table-1, without and
with TSR, VSC-STATCOM. The corresponding
characteristics are shown in Fig.7.
Fig.6 Photograph of SEIG with rotating STATCOM and load connection
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11. 6. RESULT AND DISCUSSION
using the above cited model of the
proposed SEIG-STATCOM is wired using
built in libraries of power system toolbox
in MATLAB/SIMULINK software version
9.0 and simulated for 10seconds.
The simulated results of SEIG are show
in Figs.7 (a) and (b) with lagging power
factor loads. The loads are divided into
¼, ½, ¾ and full load.
It is switched on at 2, 4, 6 and 6
seconds. The STATCOM compensated the
SEIG terminal voltage drop (Vdrop) in
each step.
The experimental and simulated load
characteristics of SEIG with and without
controller are show in Figs.8 (a) and (b)
respectively
Fig. 7 Terminal voltage variation of SEIG with time (a) without controller (b) with controller
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12. Results and Discussion cont…
Table 1 Load characteristics (experimental) of SEIG
Terminal voltage (volts) with FC =100μF
Without
With
VSC-TATCOM
VSC-TATCOM
Sl.
No.
Load Power
(Watts)
1
00
240
240
2
300
180
240
3
500
165
239
4
600
136
238
5
700
40
237
The corresponding terminal voltage at PCC is measured and noted,
Table-1, without and with TSR, VSC-STATCOM. The corresponding
characteristics are shown in Fig.7.
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13. 7. CONCLUSION
Fig. 8 Load characteristics of SEIG with full load excitation capacitor

From Figures 7 and 8, it is observed that load terminal voltage of the
self-excited induction generator is drooping with load.

This fact brings out essentiality of external control mechanism for
maintaining the load terminal voltage with varying load. The
terminal voltage is thus regulated, 8(b).
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14. REFERENCES
[1]
[2]
[3]
[4]
[5]
[6]
[7]
[8]
Basset E. D and Potter F. M.(1935), “Capacitive Excitation For Induction Generators,” AIEE
E committee of Electrical Engineering, pp.535-545.
G. Raina and O. P. Malik (1983), “Wind Energy Conversion Using a Self-Excited Induction
Generator,” IEEE Trans. Power App. Syst., Vol. PAS- 102,no.12, pp. 3933-3936.
R. C. Bansal, T. S. Bhatti and D. P. Kothari (2003), “Bibliography on the application of
Induction Generators in non-conventional energy system”, IEEE Trans. on Energy
Conversion, Vol. 18, No.3, pp. 433-439.
R. C. Bansal (2005), “Three-Phase Self-Excited Induction Generators: Over View,” IEEE
Trans. on Energy Conversion, vol. 20, No.2, pp.292–299.
N. P. A. Smith (1996), “Induction Generators For Stand Alone Micro-Hydro Systems,” IEEE
proceeding of International conference on Power Electronics drives and Energy System For
Industrial Growth, pp 669 - 673.
S. S. Murthy, B. P. Singh, C. Nagamani and K. V. V. Satynarayana (1988), “Studies of the
Conventional Induction Motor as SEIGs”, IEEE Trans. On Energy Conversion, Vol.3, No.4,
pp 842 - 848.
Yogesh K., Chauhan, Sanjay K. Jain, and Bhim Singh (2010), “A prospective on voltage regu
lation of self-excited induction generators for industry applications, IEEE Tran. On Industry
Applications, Vol. 46, No.2, pp 720-730.
T. Ahmed, O. Noro, E. Hiraki and M. Nakaoka (2004). “Terminal voltage regulation character
istics by Static VAr compensator for a 3-Ø
SEIG”, IEEE Trans. On Industry Appl., Vol.40,
No.4, pp.978 - 988.
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15. Ref. cont…
[9]
B. Singh, S. S. Murthy and S. Gupta (2010). “A stand-alone generating system using SEIG
s in the extraction of petroleum products”, IEEE Trans. On Industry applications,Vol.46, No
.1, pp. 94 - 101
[10] Luiz A.C. Lopres and Rogerio G. Almedia (2006). “Wind-driven self-excited induction generat
or and frequency regulated by a reduced rating VSI”, IEEE Trans. On Energy Conversion,
Vol.21, No. 2, pp. 297-304.
[11]
[12]
[13]
[14]
[15]
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Murthy, S.S., B. Singh, S. Gupta and B. M. Gulati (2003). “General steady
state analysis
of three phase self-excited induction generator feeding three-phase un balanced load /
single phase load for stand-alone applications”, Proc., IEE, Gen.Trans. Dist, Vol.150, No.1,
pp. 49-55.
Murthy, S. S., O. P. Malik and A.K. Tandon (1982). “Analysis of self-excited induction
generators”, Proc., IEE, Gen. Trans. Dist., Vol. 123, No. 6, pp.
260-265.
D. M. Egglestonnad F.S. Stoddard, “Wind Turbine Engineering Design”, New York:Van
Nostrand Reinhold Co. 1987
Andrew miller, Ed. Muljadi, Donald S. Zinger (1997),“A variable speed wind turbine power
control”, IEEE Trans. On Energy Conversion, Vol. 12,No. 2, pp. 181-186.
Mat lab/Simulink Software Version.9.0
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16. THANK YOU
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