26 k. subramanian

12/10/2013 8:15 AM Power Electronics and Drives Division ,VIT University,Vellore,TamilNadu, India 632 014 1

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

Implementation Of Vernier Mode Operation Using STATCOM For Terminal

Voltage Regulation Of a 3-Ø Stand-Alone Self-excited Induction Generator

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 energyconversion 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. A3-Ø, 415 V capacitor bank of 100μF (in each phase) is connected across the statorterminals of the machine for its self-excitation. The results show a good agreementbetween the simulation and experiment.

Abstract


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.


2. System Configuration


Single line diagram of proposed system is shownin Fig.5.1. It comprises of thyristor/triacswitched inductor, VSC-STATCOM and self-excited induction generator.

It supplies power to a three-phase R-L load. Thefull 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 leadingVAr to mitigate the load lagging VAr.

The switched inductor LSR and Cadd areconnected in parallel with load. This combinationresonates with the system frequency at all loadconditions and VSC-STATCOM will operate inVernier control of SEIG for terminal voltageregulation.

Fig.1 Single line diagram of SEIG supplying power to R-L load with switched reactor

3. Equivalent circuit Analysis [10] &[11]


Fig. 2 Single-phase steady state equivalent circuit of SEIG with VSC

)2(ZsIs

)1(F

X

F

Xc

F

Xceqt VSC

)3(

FXmjZ;F

XCeqtZ

jFXF

RZ:XFjRZ

ZmZ

ZmZ

RZc

RZcZZ

,Where

mC

Lr

2LS1

2

2

eqt

eqt1S

)4(0AXAF)AXA(F)AXA(F)AXA(F,XP 8m76m524m332m1m

)5(0BF)BXB(F)BXB(F,XQ 54m322m1m

)6(IVPandF

RI3P;RIV;

ZR

ZII;

ZZ

ZIIr;

RZRZZ

RZEIs Ltout

r2r

ineqtLtceqt

cSL

m2

mS

eqtceqtc1

eqtcg

4. Modeling of the system


)7(1/035.0089.0/1;e54.0/116C;V

R;AVC5.0P 211/1651p3pT

T

)8(/PT TTT

Fig. 3 Simulated wind turbine characteristics

Modeling of the system cont…


Fig. 4 D-Q Equivalent circuit of SEIG with load

)9(Vdt

di

C

1

dt

diL

dt

diLiR cq

qsqsm

qslsqss

)10(dt

di

C

1

dt

diL

dt

diLiR drr

qrqsm

qrlrqrr

)11(Vdt

di

C

1

dt

diL

dt

diLiR cd

dsdrm

qslsdss

)12(dt

di

C

1

dt

diL

dt

diLiR qrr

drdrm

drlrdrr

)13(VIZC

)14(0000C;idriqriiI;kkVVV

where11

ds1

dqcdcq qs

)15(

pLRLpLL

LpLRLpL

pL0pC

1pLR0

0pL0pC

1pLR

Z

rrrrmmr

rrrrmrm

mlss

mlss

)16(iiiii 2drds

2qrqsm

)17(iLE mmg

)18(ifL mm

)19(pP2JTeTand

iiiiL2P23Trshaftdsqrqsdrme

)20(TTeJ2Pp shaftr


4.3 STATCOM model [9]

Modeling of the system cont…

Fig. 5 VSC based STATCOM

)24(dcCSCcciSBcbiSAcaipVdc

)25(SASCVeSCSBVeSBSAVe

dc

dca

c

b dc

)26(0iii

ipLireipLirvipLireaipLirv

cc

cccccbcb

cbcbcaca

cbcabb

a

)29(L3ir3ev2revpi

&L3ir3ev2revpi;L3ir3ev2revpi

fcafababcbccfcafababcbcbfcafababcbca

)27(ccipLiripLireipLirv cccacabcbcbb

)28(ri2riebvpLi2pLi

ririeavpLipLicacabccbca

cacaabcbca


STATCOM Control

)30(VVV32V 2c

2b

2at

)31(VVuVVuVVu

tcc

tbb

aa t

)32(

32uu2u3W

32uu2u3W

3u3uW

cbaa

cbab

caa

4.4.1 Quadrature Component of Reference Source Current

)33(VVV tmeatreferr

)34(VKVVKII errnewerrolderrnewpsmsqoldsmqnew i**

)35(WII;andWII;WII cscqnewscqbsbqnewsbqasaqnewsaq******

4.4.2 in Phase Component of Reference Source Current

)36(VVV dcmeadcreferrdc

)37(VKVVKII dcerrnewdcerrolddcerrrnewpsmsdoldsmdnew i**

)38(uII;anduII;uII csmdnewscdbsmdnewsbdasmdnewsad******

4.4.3 Total Source Current

)39(

III

III

III

scdscqsc

sbdsbqsb

sadsaqsa

***

***

***

4.4.4 PWM Current Controller

)40(

III

III

III

scscscerr

sbsbrsberr

sasasaerr

*

*

*

4.4.5 Voltage Magnitude at Point of Common Coupling (PCC)

)41(0VVV

C3iiiiiipVC3iiiiiipV

cba

stalcbstalcab

stalbbstabaa l

5. Experimental work


Fig.6 Photograph of SEIG with rotating STATCOM and load connection

The induction motor draws inductive currentif the load on the generator increases.

In order to compensate the lagging VArrequired by the induction machine andchange in magnetizing reactance, thesynchronous motor is excited in anoverexcited mode i.e, excitation is greaterthan the normal excitation thereby yieldingthe required leading VAr.

The corresponding terminal voltage at PCC ismeasured and noted, Table-1, without andwith TSR, VSC-STATCOM. The correspondingcharacteristics are shown in Fig.7.

6. RESULT AND DISCUSSION


using the above cited model of theproposed SEIG-STATCOM is wired usingbuilt in libraries of power system toolboxin MATLAB/SIMULINK software version9.0 and simulated for 10seconds.The simulated results of SEIG are showin Figs.7 (a) and (b) with lagging powerfactor loads. The loads are divided into¼, ½, ¾ and full load.It is switched on at 2, 4, 6 and 6seconds. The STATCOM compensated theSEIG terminal voltage drop (Vdrop) ineach step.The experimental and simulated loadcharacteristics of SEIG with and withoutcontroller are show in Figs.8 (a) and (b)respectively

Fig. 7 Terminal voltage variation of SEIG with time (a) without controller (b) with controller

Results and Discussion cont…


Sl.

No.

Load Power

(Watts)

Terminal voltage (volts) with FC =100μF

Without

VSC-TATCOM

With

VSC-TATCOM

1 00 240 240

2 300 180 240

3 500 165 239

4 600 136 238

5 700 40 237

Table 1 Load characteristics (experimental) of SEIG

The corresponding terminal voltage at PCC is measured and noted,Table-1, without and with TSR, VSC-STATCOM. The correspondingcharacteristics are shown in Fig.7.

7. CONCLUSION

From Figures 7 and 8, it is observed that load terminal voltage of theself-excited induction generator is drooping with load.

This fact brings out essentiality of external control mechanism formaintaining the load terminal voltage with varying load. Theterminal voltage is thus regulated, 8(b).


Fig. 8 Load characteristics of SEIG with full load excitation capacitor

REFERENCES

[1] Basset E. D and Potter F. M.(1935), “Capacitive Excitation For Induction Generators,” AIEE

E committee of Electrical Engineering, pp.535-545.

[2] 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.

[3] 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.

[4] R. C. Bansal (2005), “Three-Phase Self-Excited Induction Generators: Over View,” IEEE

Trans. on Energy Conversion, vol. 20, No.2, pp.292–299.

[5] 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.

[6] 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.

[7] 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.

[8] 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.


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] 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.

[12] 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.

[13] D. M. Egglestonnad F.S. Stoddard, “Wind Turbine Engineering Design”, New York:Van

Nostrand Reinhold Co. 1987

[14] 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.

[15] Mat lab/Simulink Software Version.9.0


THANK YOU


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26 k. subramanian