An Intelligent Voltage Controller For Static Var Tors

An Intelligent Voltage Controller for Static VAR Compensators A.M. Sharaf

L.A. Snider

University of New Brunswick Canada

Nanyang Technological University Singapore

Abstract

extra high voltage transmission networks. new emerging smic converter topologies: flexible AC transmission systems )FACTS) based on current injection (CSI) or voltage injection (VCI) line committed voltage source or current source inverter interface schemes. The effectiveness of static var compensators [9 - 1 3 is determined largely by the control strategy, system interactions and contingencies: fault types, location. duration and protective or restorative actions on the network. SVC's are utilized in multitudes of applications includins voltage stability, reactive compensation power factor correction, steady state power flow enh,mcement on we,A .4C tr'ansmission lines. steady state dynamic synchronous fist swing stability. capacity release on overloaded tie lines 'and suppleinenmy use in damping s t e m turbine torsional sub-synchronous oscillations iwd shaft vibrations. The p.?per presents a novel rule based zonal action. p i n adjustable. error driven voltage stabilizer. The control action [ 17 - 181 is scaled by the length of the voltage error excursions in the voltage error phase portrait. 4.

The paper presetrrs a novel AI-rule based itrtelligeirt conrroller for fired capacitor-thyristor controlled reactor (FC-TCR)static VAR Compensator (SVC). The brrelligenr rolrage regulator is based on the concept of the error escrrrsiorr plarie where the stubilizing actiow is scaled by the magnitude of the excursion voltage error I'ector, irr order to etuure adequate compensation. The proposed ride based voltage regulator is validated using ATPIEMTP and is compared with an optimized con\*entional proporrional plus ititegt-a1 voltage controller. The proposed rule based desigti is robust and tolerares system parameter rariatiorrs as well as nwdellirig inaccrrracirs. sincc the control lewl is only scaled by the location of the Ldrage e.\-cursioti error wctor in the (e,-?,,) error plane. The schenre is ralidaredfor fwo large system conringencies eonrprisitig load rejectiotr and a three phase short circrtir furtlt followed b y loss of U transmission line.

1. Introduction

2. Sample study system

Electrical power systems are complex interconnected. highly nonlinear networks with ever vxying conditions causing vohge fluctuations. vruiations in active and reactive power generation. 'and power flow on tr"mission lines. Reactive power changes produced by load viuiations ;tnd line switching can cause adverse effects on system voltage stability and the inrerconnwted system security. St;itic v;u c i q " t o r s (SVC's) are utilized to enhance tlie integ~itedAC system voltage smbility. SVC's [ 1-91 c'an be classi!ied into four categ:gories: 1. thyristor switched capiicitor banks (TSC). 3. thyristor controlled reactor banks (TCR). 3. combinations of ( I ) and (2) wirli the switched or fixed capacitor. thyristor conlroller reactor ;IS tlie most cost effective solution to voltage instability and reactive compensation of high voltage ;mi

Figure 1 depicts a sample EHV - SO0 kV interconnected AC svstem of two AC "m with double circuit 400 Km. 500 kV tr'mmission lines. The static v x compensi1tor is a fixed capacitor. thyristor controlled reactor type with a rating of +SO0 MVAR. The parameten are given in the Appendix. The ATP/EMTP electromagnetic transient sirnuhiion S O ~ ~ Ww X s ~ used to vdidilte the W \ V de-b:lsed \.olt;iprt reyulator structure:, in comparison to the convenriond proportional plus integral controller. operating on ;I 3-phiSe 6-pulse thyristor controlled re:ictor bank. The convention;J controller is depicted in Figure 2 .

3. Zonal action rule based voltage stabilizer

239 0-8186-5320-5/94 $03.00 0 1994 IEEE

The AI-rule-based zonal action stabilizer is based on the concept of on-line gain scheduling and adjustment based on the length of the voltage error excursion vector. Figures 3a 'and 3b depict the detailed block diagram 'and controller gain scheduling action using the on-line measurement of the length of the excursion vector in the (e,-e,) zonal phase portrait. The full system and controllers were modeled using ATPEMTP with ;I time step of 100 11s. The control equations are summarized ;is follows:

4. Sample digital simulation results The sample study system shown in Figure 1 with the fixed capacitor and thyristor controlled reactor SVC system was simulated using ATPEMTP. Both conventional proportional plus integral (PI), and rule based error driven controllers were studied and compared for two large system contingencies, namely 1. Load rejection of approximately 1000 MVA at the receiving end bus. This was effected by disconnection of the 500 MVA const'mt impedance load and an increase in the receii-inp end system impedance. 2. Temporary three phase short circuit fault for 6 cycles which was cleared by removing the f:iulred line, near the SVC bus. depict the controller's dynamic Figure 4, S performance for the case of temporary three phase short circuit fault near the SVC bus at the line side.

"fb

&

=

/=

-

pu

(3)

where €& is a small daid zone to avoid control hunting 'and instability. At any sampling time instant k: Aa@) = K, &(k)re"(k)+Ye,Ql (4)

5. Conclusions

where IC,, y are the selected modulation constmts, which crtn be optimized using ,an off-line error based performance index J, defined as follo\vs:

The paper presents a novel AI-rule b'weci voltnpe controller design for static var compensitors. This rule based controller utilized the voltage error. voltage error rxcf and the excursion vector magnitude to adjust the control level. This on-line gain scheduling feature, 'and the us? of the concept of zonal action enhance the controlltr robustness in terms of tolerating different fault t j p s . location. duration, system 'and control interactions as ell as uncertainties in the modelling. The control level is tailored at anytime by the level of the excursion error "nfested in the excursion vector (R,). The control acrion is both fast 'and self adjusting. hence provides for ;in intelligent, simple, robust and easy t o implement vo1r:i~cf regulator structure. The new AI rule-based volrii92 regulator was validated using ATPEMTP and irr effectiveness was compared with a conventional optimizzd PI controller. 1 he sane error based excursion planc a i d control structure concept c'an be extended to other SVC conrr\d tasks, such as reactive power compensation. power fiiitor correction, first swing transient sk?hility damping :mi steady state tie line power flow enhancement. I t W;L< also validated for speed and torque resuliitiilri of motor hi\ zs.

N

where N=-T-


is selected in the range

Tszmple

(2-3) of supply frequency cycles. a,. a,. 'and a3 are relative weightings. To include current limiting action, equation (4) above c'an be modified to include a current dependent gain K,, so: A atk)=I(O-qR,Qre"O +Ye"QI (6) where K, is the current limiter gain calculated iit each time step using nns current measurements. (7)

I=o In the ATPEMTP simulation results shown in the paper. the current limiting nction was not required due to the large size (FC+TCR)SVC used (+SO0 MVAR). The final firing angle control action resembles a proportional plus iii~egmlregulation with firing deliiy angle a. (90°
6. Appendix - System Parameters System 1 - scndinp end: 20 GVA fault level x,Jx, = 0.3 volt;i~z: 1.02 PU. 0 degrees trxnsformc'r: 3000 hlVA. 105 . Q= 100 240

System 2 - receiving end: 40 GVA fault level x d X l = 0.3 voltage: 1.00 PU, -35 degrees transformer: 2000 MVA, IO%, Q=l00

applications", IEEE Transactions on Power Apparatus and Systems, Vol. PAS-101, No. 10, Oct. 1982, pp. 3761-3769. 4. R. Hauth, R. Moran, "Introduction to static var systems for voltage and var control, IEEE Tutorial text 78EH01354)WR. IEEE Summer PAS Meeting, Los Angles, CA, July 1978. pp. 4548. 5. C.H. Titus, J.L. Fink, D.M. Demarest. F.H. Ryder. "The influence of the Eel River HVDC conversion facility performance on the design of future HVDC terminals". Paper No. 14-06, CIGRE Intemational Conference on Large High Voltage Electrical Systems, Paris, France, Aug. 21-29, 1974.. 6. F.J. Ellert, R. Moran, "HVDC and static var control applications of thyristors", IEEE/IAS International Semiconductor Power Converter Conference, Lake Ruena Vista, Florida. March 27031, 1977. 7. R. Hauth. R. Moran. "The performance of thyristorcontroller static var systems in HVXC applications - Part 1: Fundamental relationships". IEEE Tutorial Text 78EH 13.54PWR, pp. 56-61. IEEE Summer PAS Meeting,Los Angles. C.A. July 1978. 8. K. Reichert, et al, "Controllable reactor compensator for more extensive utilization of high voltage transmission systems. Paper 31-04, CIGRE Conference, Paris. France, Aug., 1974. 9. H. Becker. et al. "Three phase shunt reactors for long distance bulk power lines". Electric Review. 1969, pp. 940-94.3. 10. E. Friedlander. et al. "Saturated reactors for long distance hulk power lines", Electric Review. 1969. pp. 940-943. 11. H. Sche\veichart. et a.. "Closed loop control of static var sources (SVS) on EHV transmission lines. IEEE paper A78135-6. IEEE/PAS 1979 Winter Power Meeting. New York. New York. Feb. 1978. 17. Y. Baghzouz. M.D. Cos, "Optinid shunt compensation tor unbalanced linear bads \vith nonsinusoidal supply \'oltage". Electric Machines and Power Systems. 1991. pp. 171-183. 13. G. Gueth. P. Enstedt. .4.Rey. R.W. hlenzies, "Individual phase control of a static compensator for load compensation and voltage halancinp and regulation". IEEE Trans. on Po\ver Systems. 1987. pp. 898-904. 14. L. Gyugyi. R..4. 0tto.T.H. Putman. "Principles and applications of static thyristor-controller shunt coinpensatnrs;". IEEE Trans. on Power Apparatus and Systems, 1079, pp. 1 9 3 1945. 15. P.M. Anderson. R.L. Xgrs\val. J.E. Van Ness. "Suhsynchronous resonance in p o w r s rel="nofollow"> steins". IEEE Press. Ne\\ York, 1990. 16. A.M. Shard. J. Heydeiiiann and G . Honderd. "Application of regression analysis in novel po\ver s\-stem stabilizer design". Electric Power Systems Research Joumal. Vol. 22. 1991. pp. 181188. 17. A.M. Sharaf. A. Ghosh. " S p e d 2nd torque regulation <.i permanent magnet DC inotors using rule bclsed fuzzy lopic control". Proceaiings IEEE - Intelligent Vehicles Syniposiurn. Tokyo, Japan, July 14-16, 1993.

Transmission lines: length: 200 k m rl= 0.0248R/km. 1,= 0.8746 mH/km, c,= 0.01326 pf/km r,,= 0.2026f2/km, 1,= 3.291 mH/km, c,= 0.000846 pS/km Receiving end shunt load: I F : constant impedance 500 MVA. 0.8 PF size

svc: FCDCR inductive A = 100 MVAR capacitive Q= 500 MVAR, series connected with R 'and L to form 5th h"nonic filter transformer: 500 M V A . 5%. Q=l00 tYW

PI controller K, = 0.817. K,= 1.0. ~=0.05.I$=O.001.

K, = 0.2

Rule based controller K, = 0.817. K,= 1.0. ~=C).05. '~0.001,tl = 0.002 k,,= 17.0. R, = 0.005

7. Acknowledgements The authors acknowledge the support of N'myang Technological University. Singapore and The University of New Brunswick. Canah.

8. References 1. K. Engtvrg and S . Torsent "Reactors and capacitors controller hy thyristors for optimum power system VAR control", Proceedings: EPRIEL-1017SR WS-78-108 Special Report 1979 on Transmission Static VAR Systems Seminar. pp. 1-17. 2. R. Hauth and R. M o m . "The bsics of applyins static var systems on HVDC power networks". Proceedings: EPRIEL1047SR WS-78-108 Special Report 1979 on Transmission Static VAR Systems Seininar. pp. 5-1 pp 5-32. 3. R.L. Hauth. S.A. hliske. Jr. and F. Nizaru. "The role and benefits of static var systems in high voltage poa.er systems

241

2 GVA

2 GVA 10 %

SYSTEM 1 20 OVA

Figure 1 Sample Study System

Figure 2 Conventional PI Controller

zonal adion phase portrait

integrator

Figure 3a: Rule Based Zonal Contmller Structure

242

Figure3b Rule BasedVoltage Controller Block Diagram

-1

I

I

Figure .a: Voltage error vs. time

- -

1 I-

Y

I=

Total SVC current vs. time

Figure

FigureLf: Three phase fanlt followed by tripping of line: Dynamic PerfOrmamr of SVC with conventional controller

Figure

EN

d:

Voltage error vs. time

Figure

b Total SVC cuttent vs. time

_;ewe r:m

Figure c: e,d(q)/dt, R, vs. time

Figure d: d(e,)/dt vs. e,

Figure5:Three phase fault followed by tripping of line: Dynamic performanceof SVC with rule based controller

243

.Id