A Genetic algorithm based optimization of DG/capacitors units considering power system indices

Transcription

1 A Genetc algorthm based optmzaton of DG/capactors unts consderng power system ndces Hossen Afrakhte 1, Elahe Hassanzadeh 2 1 Assstant Prof. of Gulan Faculty of Engneerng, ho_afrakhte@gulan.ac.r 2 Elahehassanzadeh@yahoo.com Abstract: In ths paper, both Dstrbuted Generators (DG) unts and shunt capactors are allocated and szed optmally and smultaneously for lne loss reducton, voltage profle mprovement and the relablty rsng of the power system. The objectve functon whch ncludes power losses (actve and reactve), voltage profle and relablty ndces s maxmzed usng genetc algorthm. Power system operaton lmts are consdered as constrants. The problem of optmal dstrbuted generaton and capactor szng and placement s solved for a 9-buses test system and the results of applyng the proposed method llustrate the best answer s found by optmzng both DGs and capactors n dstrbuton networks. Keywords: Capactors, Dstrbuton Generaton (DG), Genetc Algorthms (GA), Power Loss, Relablty, Voltage Profle. 1. Introducton The prmary and man functon of electrc utltes s provdng a relable and secure energy supply for customers wth specfc voltage and stable frequency. So, they try to obtan ths goal by means of dfferent solutons such as the applcaton of Dstrbuted Generaton (DG) unts and shunt capactors. Technologcal progress, economcal analyses, envronmental consderatons, and power system deregulaton are known as effcent reasons of DG employment. DG could contan any small power generators near to utlzaton ponts that complement central power statons regardless of energy source. The mpact of DG n system operatng characterstcs needs to be evaluated properly because the performance of power system can be mproved or destroyed va proper locaton and szng of DG and system operatng condtons [1]-[2]. Shunt capactors can also be consdered n parallel wth DG unts due to ther applcatons n voltage stablzaton, power/energy loss mnmzaton, system capacty release, and relablty enhancement [3]-[4]. A wde varety of research work has been done to address the placement and szng of DG and capactor va dfferent methods and for dfferent reasons. In [1] a lnear programmng and Genetc algorthm were used to determne the optmal sttng and szng of DG wth mult-system constrants. In [3] a smulated annealng s proposed to determne the locatons, the types and szes of capactors and the control settngs of them. A PSO based mult objectve formulaton was proposed n [4] for optmal capactor placement ncorporatng the cost of relablty, coasts of losses and nvestments as objectve functon and n [5] to optmze the cost of power losses and energy not suppled n presence of DG. Ref [6] represented a Fuzzy model for optmal DG sttng and szng and determnes ts operaton mode (PV or PQ). In [7], the dstrbuted generaton mpacts on total losses, voltage profle and short crcut currents were used as objectve functon based on a steady-state analyss to search the best ponts for connectng dstrbuted generators. In [8,] the problem of the optmal allocaton and szng of capactors n unbalanced dstrbuton systems s formulated as a mult-objectve optmzaton problem by usng a mcro genetc algorthm. Ref [9] proposed a approach for capactor placement through senstvty factors and self adaptve hybrd dfferental evoluton (SaHDE) technque. In ths paper, the genetc algorthm s appled to determne the optmal locaton and sze of a DG unt along wth four shunt capactors for power losses reducton, voltage profle and relablty mprovements. 2. Problem Formulaton Determnng the optmum locaton and szng of DG and capactor unts and studes ther mpact on loss, voltage profle and relablty s the overall goal of ths paper. The objectve functon s composed of actve and reactve power losses, voltage profle and relablty ndces that are explaned below: 2.1 Power Loss Studes have ndcated that as much as 13% of total power generated s wasted n the form of losses at the dstrbuton level [10]. One of the man advantages offered by DG s the lne loss reducton because of ts proxmty to the load canters. ٦٤١

2 In the heavy load condtons, the cost of losses wll be added to customers' costs. Therefore, n feeders wth hgh losses, usng small-scale dstrbuted generaton (10-20% of the feeder load) could cause a sgnfcant reducton of losses [11]. DG and capactor operatons n mnmzng the loss are smlar. The dfference s that the DG unts cause mpact on both the actve and reactve power, whle the capactor banks only have mpact on the reactve power flow. The lne losses ndex s gven as: F1 Pl PlwDGorC m 1 Ql Ql C wdgor m 1 Pl m 1 Ql m 1 Where, Pl and Ql are the total actve and reactve lne losses of th total actve and reactve lne losses wth DG and capactors. Hgh value of ndex F1 ndcates low power losses meanng better system performance. Actve and reactve load models are presumed constant and the grd total MVA s expressed as [12]: 1 / 2 2 P PDG S 2 Q QDG QC QDG 0 asynchrono us generators 2.2 Voltage Profle Proper locaton and szng of DG and capactors lead to boost the voltage profle of the grd Voltage profle at the customer ste s mproved dependng on the amount of reactve power njected by the shunt capactor. In addton, DG releves the load demand that wll cause an mprovement n the voltage magntude. The proposed ndex of voltage profle mprovement has been determned as: (1) (2) F2 VPDG or C VP (3) 1 V Vmn V max V VP m1 1Vmn V max 1 Where, VP and VP DGor C are the voltage profle of system n the case of wthout and wth DG and capactor respectvely. V s the voltage magntude of the th bus, Vmn and V max are the mnmum and maxmum allowed operaton voltages. A Hgh ndex F 2 value ndcates hgh qualty voltage profle. 2.3 Relablty Man Power system ablty n securng the supply of electrcty and delverng an acceptable qualty of power to the customers s mentoned as a relablty concept whch s one of the most mportant crtera and must be consdered durng power system plannng and operaton. The man ndces (load pont) used to assess the relablty of dstrbuton networks are [13]: λ = Falure rate r = Mantenance tme U = λ r = average annual off tme In ths paper, the ES ndex (the amount of energy that has not been suppled) has been used as a relablty mprovement ndex llustrated as: ES ESDG or C F (4) 3 ES 1 ES L U (KWh/year) (5) Where, L s the average load connected to load pont n kw. ES, ES DG or C are the total average energy not suppled when the fault happened n all sectons of system n the case of wthout and wth DG and capactor respectvely. 2.4 Objectve Functon OF Max w1 F1 w2 F2 w3 F3 (6) Vmn V Vmax Pl Plmax mn max Subject to : PDG PDG PDG mn max QDG QDG QDG PFmn PF PFmax 3 w 1 w 0 1 (7) 1 ٢ ٣ ٤ Table I shows w values (weght coeffcents) for ndces. Those values may vary accordng to the network operator s concerns. TABLE I: Weght Coeffcents w 1 w 2 w GA Setup and Codng of the Soluton Genetc algorthms work by optmzng the ftness functon (formed by addng the objectve functon and penalty terms for constrants volatons). When applyng Genetc Algorthms to optmze the DG/shunt capactors allocaton and szng problems, an mportant aspect s the codng of the potental solutons. The ntal populaton (coded varables) s the canddate locatons and szes of DG/capactor unts. Each chromosome s represented by a vector. The chromosome codng n ths study as seen n Fg. 1 s defned as a two- ٦٤٢

3 vector chromosome n whch the frst secton s a strng of bus numbers that DG/capactor are nstalled, the secondary secton explans the DG/capactors capactes. Fg. 1: Chromosome codng BUS s a dscrete number between 1 and the total number of buses. P DG and Q CA are contnuous numbers rangng from zero to the maxmum value of DG capacty (MW) and capactor capacty (MVAR) respectvely. Genetc Algorthm searches for the best answer n a contnuous way between boundary lmts; consequently the optmal case s GA output. Genetc Algorthm parameters used for all system were: Populaton sze: 50, umber of generaton: 300, Crossover functon: Arthmetc, Mutaton functon: Gaussan, Mutaton Rate: 0.7, Selecton type: Roulette Wheel. The eltsm mechansm s adopted for ensurng the survval of the best performng combnaton. For each locaton of DG/capactor unts n GA, an optmal power flow s used to defne ther avalable szes. The utlzaton of ths structure s varous extensons mplementng to the standard OPF problem and easly addng the new varables, constrants and costs to t. Calculatng of optmal power flow s used to evaluate the branch current, bus voltage, real and reactve power flows for the generaton and load condtons at each bus. The flow chart for the proposed method based on the GA s gven n the Fg Smulaton Results The test system for the proposed methodology s a 9- bus, sngle feeder, radal dstrbuton network [14] shown n Fg.3. The substaton lne voltage s 23kV and detals of the feeder and the load characterstcs are gven n Table II. In ths work, the falure rate for all branches s assumed to be 0.1 f /km-year that "f" represents the falure frequency. Therefore, the falure rates of the test system are n the range [0.1, 0.5] (f/year) whch the longer lne wth hghest mpedance has the bggest falure rate. The repar tme s 4 h and the swtchng tme s 0.5h. By runnng the power flow wthout DG and capactors, calculated values of actve and reactve power losses are MW and 0.64 MVAR and the average of bus voltage s Fg. 3: Case study Then, the proposed algorthm s carred out for one DG unt and four capactor banks ndvdually and smultaneously. Capactor and DG szes are randomly selected from [150, 300, 450, 600, 750, and 900] KVAR and [0.1, 0.4] MW respectvely. The total ES value of grd before DG/capactor placements s about KWh/year, after 4 capactors allocated n ther proper locatons (3, 4, 5 and 9) s KWh/year, after one DG optmum locatng (bus 9) and szng (379 KW) reduce to KWh/year and after DG/capactors smultaneously nstallng (DG at bus 8, capactors at buses 3, 4, 6, and 7) reduce to KWh/year. Relablty calculatons of the test system are gven n Table III. The values of r and U at each branch and for each case are not ncluded because of the lack of suffcent space. Tables IV shows a comparson between the results related to a system of dfferent DG/Capactor confguratons that llustrates a bg dfference among the system results wthout a DG/capactor and other cases. As mentoned, choosng both DGs and capactors are necessary for mnmzng the actve and reactve power losses and boostng the voltage profle of network. However, DG has more effcency at mprovng system relablty. Changng optmum locaton and sze of DG and capactors when they nstalled smultanety, s an mportant ssue. Fg. 2: Flowchart of genetc algorthm ٦٤٣

4 TABLE II: Load and lne data of 9-bus system Branch P L (KW) Q L (KWAR) R + j X (Ω) j j j j j j j j j3.026 λ (f/year) TABLE III: Relablty calculatons of test system for 4 cases (1- wthout DG/Capactor, 2-wth Capactor, 3-wth DG and 4- wth DG/Capactor) Feeder Falure rate (f/year) ES (KWh/year) secton λ 1 λ 2 λ 3 λ 4 ES 1 ES 2 ES 3 ES total Actve and reactve power losses of system are shown n Fgs 4 and 5 before and after the nstallaton of DG and capactors respectvely. To analyse the voltage profle of the test system, Fg 6 s plotted. Comparng the results llustrates that the ntegraton of both DG and capactor nto the network can mprove the voltage more than the other stuatons. The value of falure rate and ES wth and wthout DG and capactors are shown n Fgs 7 and 8 respectvely. Table V shows the objectve functon value. Fg. 5: etwork reactve power loss Fg. 4: etwork actve power loss Fg. 6: Impact of dfferent DG/Capactor confguratons on voltage profle ٦٤٤

5 TABLE V: Objectve functon value F1 F2 F3 OF Capactor ١٨ 0.1١ DG ٢٣ 0.١٩٦ DG& Capactor ٢٨ 0.2٤ References Fg. 7: etwork Falure Rate Fg. 8: etwork ES ndex TABLE IV: Comparson of dfferent DG/capactor arrangements P ( KW) Q ( KVAR) ES (KWh/yr) DG bus P+jQ DG sze j 102 Capactor bus , 4, 5, j , 4, 6, 7 Capactor sze KVAR 900, 900, 750, , 750, 600, 300 [1] A.A. Abou El-Ela, S.M. Allam and M.M. Shatla, Maxmal optmal benefts of dstrbuted generaton usng genetc algorthms, Electrc Power Systems Research, Volume 80, Issue 7, July 2010, Pages [2] R. Rntamak, Kauhanem, Applyng modern communcaton technology to loss-of-mans protecton, CIRED 2009, Paper [3] Hsao-Dong Chang, Jn-Cheng Wang, Orvlle Cocktgs and Hyoun-Duck Shn, Optmal Capactor Placements n Dstrbuton Systcns: Part 1: A ew Formulaton and the Overall Problem IEEE Transactons on Power Delvely, Vol. 5, o. 2, Aprl [4] A. H. Etemad, M. Fotuh-Fruzabad, Dstrbuton System Relablty Enhancement usng Optmal Capactor Placement IET, Generaton, Transmsson & Dstrbuton, Vol. 2, pp , September [5] Amn Hajzadeh, EhsanHajzadeh, PSO-Based Plannng of Dstrbuton Systems wth Dstrbuted Generatons, World Academy of Scence, Engneerng and Technology [6] H. Shayegh, B. Mohamad, Mult-Objectve Fuzzy Model n Optmal Sttng and Szng of DG for Loss Reducton, Internatonal Journal of Electrcal Power and Energy Systems Engneerng, 2:3, [7] Lus F. Ochoa, Antono Padlha-Feltrn, Gareth P. Harrson, Evaluatng Dstrbuted Generaton Impacts wth a Mult objectve Index, IEEE Transactons on Power Delvery, [8] Gudo Carpnell, Chrstan oce, Danela Proto, Multobjectve Optmal Allocaton of Capactors n Dstrbuton Systems: A ew Heurstc Technque Based on Reduced Search Space Regons and Genetc Algorthms, 20th Internatonal Conference on Electrcty Dstrbuton Prague, 8-11 June [9] S. Vjayabaskar, T. Mangandan, Capactor Placement n Radal Dstrbuton System Loss Reducton usng Self Adaptve Hybrd Dfferental Evoluton and Loss Senstvty Factors, European Journal of Scentfc Research, Vol. 87 o 2 September, 2012, pp [10] Y. H. Song, G. S. Wang, A. T. Johns and P.Y.Wang, Dstrbuton network reconfguraton for loss reducton usng Fuzzy controlled evolutonary programmng, IEEE Trans. Gener., trans., Dstr., Vol. 144, o.4, July [11] F. L. Alvarado, Locatonal Aspects of Dstrbuted Generaton, Proceedng of IEEE PES Wnter Meetng, Volume 1, pp. 140, Oho, [12] D. Sngh, R.K. Msra, and D. Sngh, Effect of Load Models n Dstrbuted Generaton Plannng, IEEE Transacton on Power Systems, vol. 22, 2007, pp [13] R. Bllnton, R.. Allan, Relablty Evaluaton of Power Systems, Plenum Press, ew York, [14] Baghzouz. Y. and Ertem S, Shunt Capactor Szng for Radal Dstrbuton Feeders wth Dstorted Substaton Voltages, IEEE Trans. on Power Delvery, Vol. 5, pp , ٦٤٥