International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) V...
International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) V...
International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) V...
International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) V...
International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) V...
International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) V...
International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) V...
International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) V...
International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) V...
International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) V...
International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) V...
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Gaining improved performances of agc in a multi area power system

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Gaining improved performances of agc in a multi area power system

  1. 1. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEME459GAINING IMPROVED PERFORMANCES OF AGC IN A MULTI-AREA POWER SYSTEM WITH ALL POSSIBLE CONSTRAINTS BYCHANGING THE EFFECT OF TURBINES AND CONTROLLERS1Dipayan Guha, 2P.K.Prasad, 3Somalee Mitra, 4Subhankar Mukherjee1,3Assistant Professor, Kanksa Academy of Technology & Management-TIG, Durgapur,West Bengal2Principal, Abacus Technology and Management, Hooghly, West Bengal3Final Year Student, Kanksa Academy of Technology & Management-TIG, Durgapur, WestBengalABSTRACTThe main objective of the present work to study the effect of small load perturbationon a multi-area interconnected power system considering all possible constraints in powersystem. Three thermal areas of reheat turbine either single-stage or two-stage is consideredwith 10% step load perturbation in all the units for study. This paper focused on theeffectiveness of PI and PID controller over conventional I-controller. An attempt is made toinvestigate the proper values of sampling time period (T) and speed regulation parameter(Ri). Further, the effects of variations of reheat gain (Kr) and reheat time constant (Tr) havebeen explored. The performance of single-stage and two-stage turbine has been investigatedwith PID and PI controllers. The dynamic responses are studied in MATLAB-SIMULINKenvironment.INDEX TERMS: Automatic Generation Control, PI and PID controllers, two stage turbine,effect of speed regulation parameter, effect of Kr and Tr , SIMULINK.INTRODUCTIONEveryone expect uninterrupted power supply for their use. However, it is always notpossible for a system to provide continuous power supply to their consumers, since bothactive and reactive powers continuously changes with load variations. Any change in theloads may cause to disrupt the nominal operation of frequency which is highly undesirable,INTERNATIONAL JOURNAL OF ELECTRICAL ENGINEERING& TECHNOLOGY (IJEET)ISSN 0976 – 6545(Print)ISSN 0976 – 6553(Online)Volume 4, Issue 2, March – April (2013), pp. 459-469© IAEME: www.iaeme.com/ijeet.aspJournal Impact Factor (2013): 5.5028 (Calculated by GISI)www.jifactor.comIJEET© I A E M E
  2. 2. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEME460larger change may collapse the system completely. Modern power system networks areinterconnected and exchanging power to the neighbors, the AGC problem is the majorrequirement.The most important part in our daily operation of a power system is the electricalenergy, which must be properly scheduled and controlled. This is the main concern of energycontrol center and implemented automatic generation control program as a part of energymanagement system. The main purpose of power system operation and control to match thegenerations with loads plus losses incurred in the system. The main objective of the LoadFrequency Control (LFC) system is to maintain the frequency and tie-line power to itsnominal values.Number of researches has been found over the past decades in the field of AGC.Literature survey shows that most of the paper studied two-area or multi-area either thermal-thermal or hydro-thermal system using conventional integral controller. Linear perturbationsystem is build for the study of dynamic performances. Less attention is paid for study ofsame for non-linear type of power system. A realistic study may come if the whole system ismodeled with all possible physical constraints, such as Generation Rate Constraints (GRC),Dead Band (DB) and time delays in communication channels. [4] has studied a multi-areasystem considering GRC of turbine using integral controller only. [7] present two-areathermal system considering GRC and single-stage turbine. Literature survey shows that lessattention have been paid in multi-area system considering all possible constraints in powersystem. The main objectives of the present work are as follows –• to study the effect of small step load perturbation in multi-area thermal systems• to compare the performances of single-stage and two-stage turbines with all possibleconstraints• to study the effectiveness of PI and PID controller in lieu of conventional integralcontroller with and without constraints• to study the effect of changes of reheat turbine gain and reheat turbine time constant ondynamic performances three-area system• to investigate the maximum permissible values of speed regulation parameter (Ri) andsampling time period (T) without hampering the dynamic performancesFig. 1: Block diagram of multi-area system considering all possible constraints
  3. 3. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEME461SYSTEM INVESTIGATEDThe AGC system investigated comprises an interconnection of three areas of equalsize. All areas comprising reheat type thermal unit, turbines are either single-stage or two-stage. Appropriate values of physical constraints are considered for study. The nominalvalues of all parameter with physical constraints are given in appendix-1. Fig. 1 shows thebasic block diagram of three-area system with constraints present in power system.TWO-STAGE REHEAT TURBINEThe approximated Transfer Function (T.F) of two-stage reheat turbine is modeled in[2]. This has been used to demonstrate the effect of small load perturbation in AGC system.Fig. 2(a) and 2(b) shows the schematic and T.F representations of two-stage reheat turbine,respectively. It comprises four main cylinders as very high pressure (VHP), high pressure(HP), intermediate pressure (IP) and low pressure (LP). MW rating of each cylinder is α, β, γ,and δ so that( )1=+++ δγβα .Fig. 2(a): Schematic diagram of two-stage turbineFig. 2(b): T.F model of two-stage turbineLinear approximated T.F of two-stage turbine is defined by eqn: [1]{ } ]1[)1)(1)(1()(1)(2121222211−+++++++=rrtrrrrrrrTsTsTsTTTsTKTTKssG
  4. 4. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEME462CONTROLLERSMW frequency control or AGC problem is that sudden small load perturbation maycontinuously disturb the system operation. To maintain system stability the system isoperated with different types of controllers, hence selection of proper controller is veryimportant so far system stability is concerned. This paper is focused on the effectiveness ofProportional (P), Integral (I), Proportional-Integral (PI), Proportional-Integral-Derivative(PID) controller on system dynamics. The transfer function model of PI and PID controllerare as follows –GC(s) = )2(−−−+sKK iP [for PI-controller]GC(s) = )3(−++ DiP sKsKK [for PID-controller]The optimum values of KP, KI & KD are considered as 0.8036, 0.6356 and 0.1832respectively [4].SIMULINK RESULTSFig. 3: Frequency error in single-stage 3-area system with different controllersFig. 4: Frequency error in single-stage 3-area system for different Ri with PID-controllers
  5. 5. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEME463Fig. 5: Frequency error in single-stage 3-area system with constraints for different controllersFig. 6: Frequency error of single stage system with constraints with PID-controllersFig. 7: Frequency error of two-stage system without constraints using different controllers
  6. 6. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEME464Fig. 8: Frequency error of two-stage 3-area system for different values of Ri using PIDcontrollerFig. 9: Frequency error in 3-area system without constraints using PID-controllersFig. 10: Frequency error in 3-area system with constraints using PID-controllers
  7. 7. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEME465Fig. 11: Frequency error in two-stage 3-area system with constraints using differentcontrollersFig. 12: Frequency error in two-stage system with constraints for different values of RiFig. 13: Frequency error in single-stage 3-area system with constraints for different values ofKr
  8. 8. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEME466Fig. 14: Frequency error in single-stage 3-area system with constraints for different values ofTrFig. 15: Frequency error in two-stage 3-area system with constraints for different values ofKrFig. 16: Frequency error in two-stage 3-area system with constraints for different values of Tr
  9. 9. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEME467Fig. 17: Frequency error in 3-area system with different values of T using PID controllersEFFECT OF SPEED REGULATION CONSTANTThis paper demonstrates the effect of speed regulation parameter on dynamicperformances of a multi-area system without deteriorating the system performances. 10%load perturbation in all area considered for this study. Initially, frequency error ( fi) isobtained considering Ri of 4% (2Hz/p.u MW) for all areas. The system has been investigatedin two stages-(i) without constraints and (ii) with constraints. Fig.3 (for single-stage) & Fig.7(for two-stage) and Fig.5 (for single-stage) & Fig.11 (for two-stage) show the responses atnominal value of Ri for without and with constraints, respectively. Then, value of Ri isincreased gradually step by step from 4% to 8% and responses are shown in Fig.4 (for single-stage), Fig.8 (for two-stage) and Fig.6 (for single-stage), Fig.12 (for two-stage), respectively.It is observed form the foregoing results that in both the cases the oscillations are deterioratedand system approaches to instability.EFFECT OF CHANGE OF KRThe effects of change of gain of reheat turbine on system dynamicshave been observed. To study the effectiveness of Kr, it is being changed by ±25% ofnominal value (i.e., 0.5) and responses are shown in Fig.13 and 15. It is clearly seen from theresults that the settling time as well as steady state error gets minimized at a faster rate forhigher value of Kr.EFFECT OF CHANGE OF TRThe effects of change of time constant of reheat turbine on systemdynamics have been observed. To study the effectiveness of Tr, it is being changed by ±25%of nominal value (i.e., 10 sec) and responses are shown in Fig.14 and 16. It is clearly seenfrom the results that the settling time as well as steady state error gets minimized at a fasterrate for lower value of Tr.
  10. 10. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEME468OBSERVATIONFollowing points are observed from the SIMULINK results –1. Fig. 3, 5 and 7 reveals that undershoots and settling time both are reducing using PIDcontrollers2. Fig. 4 show with increasing of Ri, system undershoots increases while the settling time isalmost constant3. Fig. 6 and 12 reveals that system responses exhibits fast oscillations with increases of Riand system gradually moves towards instability4. Dynamic responses get improved when system operating with two-stage turbine compareto single-stage turbine, Fig.9.5. The performances of two-stage turbine with all possible constraints is quit better when itworks with PI-controller in lieu of other two controllers, Fig. 10 and 11.6. The settling time and overshoots both are minimized with increase of reheat turbine gain(Kr), Fig. 13 and 15.7. The settling time and overshoots both are minimized with decrease of reheat turbine timeconstant (Tr), Fig. 14 and 16.CONCLUSIONThis paper made an attempt to study the effect of system constraints on dynamics ofmulti-area interconnected power system. The system gets non-linear with addition of systemconstraints. It is seen that dynamics of power system is improved with PID-controller in lieuof PI or I controllers. It is also concluded from the preceding discussion that systemundershoots increases with physical constraints, especially due to the effect of transportationlag in communication channels. Neglecting the constraints such as GRC, DB and TDdecreases the efficiency of the controller, hence for getting improved responses these must beconsidered. The performance with two-stage turbine is much better than single-stage turbineworking with PID controllers.REFERENCES[1] Prof. C.S.Indulkar, “Analysis of MW frequency control problem using sampled datatheory”, IEEE, vol.73, June 1992[2] J.Nanda et. al., “Sampled data Automatic Generation Control of Hydro-Thermal systemconsidering GRC-a sensitivity analysis”, IEEE, vol.71, June 1990[3] Ibraheem et. al., “Recent philosophies of Automatic Generation Control strategies inPower system”, IEEE trans. on Power system, vol.20, no.1, 2005[4] J.Nanda et. al., “Some New findings on Automatic Generation Control of anInterconnected Hydro-Thermal System with Conventional controllers”, IEEE Trans. onEnergy Conversion, Vol. 3, No. 1, 2006[5] J.Nanda et. al, “Automatic Generation Control of a multi-area system with conventionalintegral controllers”[6] K.S.S Ramakrishnan et. al., “Automatic Generation Control of interconnected powersystem with diverse sources of power system”, Int. Journal of Engg., Science andTechnology, vol.2, no.5, 2010, pp: 51-65
  11. 11. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEME469[7] Hemin Golpira et. al., “Effect of physical constraints on AGC dynamic behavior in aninterconnected power system”, Int. Journal of Advanced Mechartronics Syst., vol. 3, no.2, 2011, pp: 79 – 87[8] Naimul Hasan et. Al.,‘Real Time Simulation of Automatic Generation Control forInterconnected Power System’, International Journal on Electrical Engineering andInformatics ‐ Volume 4, Number 1, March 2012, pp: 40 – 51[9] Elegerd, O.l., “Eletric energy system theory-an Introduction”, second edition, TMH.[10] Tan Qian Yi, Gowrishankar Kasilingam and Raman Raghuraman, “Optimal-Tuning ofPID Power System Stabilizer in Simulink Environment for a Synchronous Machine”International Journal of Electrical Engineering & Technology (IJEET), Volume 4,Issue 1, 2013, pp. 115 - 123, ISSN Print : 0976-6545, ISSN Online: 0976-6553.[11] Preethi Thekkath and Dr. G. Gurusamy, “Effect of Power Quality on Stand by PowerSystems”, International Journal of Electrical Engineering & Technology (IJEET),Volume 1, Issue 1, 2010, pp. 118 - 126, ISSN Print : 0976-6545, ISSN Online: 0976-6553.[12] Deepika Yadav, R. Naresh and V. Sharma, “Fixed Head Short Term Hydro ThermalGeneration Scheduling using Real Variable Genetic Algorithm”, International Journalof Electrical Engineering & Technology (IJEET), Volume 3, Issue 2, 2012,pp. 430 - 443, ISSN Print : 0976-6545, ISSN Online: 0976-6553.APPENDIX – 1Pr = rated power in two areas = 2000MWf = nominal frequency of operation = 50HzT12 = T23 = T31 = synchronizing time constant = 0.086 secBi = biasing factor = 0.425Kps = gain of power system = 120Tps = time constant of power system = 20 secTt = turbine time constant = 0.3 secTsg = speed governor time constant = 0.08 secKsg = gain of speed governor = 1Kr1 = Kr2 = steam turbine reheat constant = 0.5Tr1 = Tr2 = steam turbine reheat time constant = 10 secRi = speed regulation constant =2 Hz/p.u MWKI = gain of Integral controller = 0.6356KP = gain of proportional controller = 0.8036KD = gain of derivative controller = 0.1832GRC = Generation rate constraint = 5.0±DB = Dead band = 0.036 secTime delay (TD) in communication channel = 1 sec

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