Optimal Configuration for Distributed Generations in Micro-grid System Considering Diesel as the Main Control Source

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1 Journal of Energy and Power Engneerng 9 (2015) do: / / D DAVID PUBLISHING Optmal Confguraton for Dstrbuted Generatons n Mcro-grd System Consderng Desel as the Man Control Source Xang Chen, Yanbn L, Junmng Xao and Xuehu We Department of Electrc Engneerng, Zhongyuan Unversty of Technology, Zhengzhou , Chna Receved: February 13, 2015 / Accepted: March 11, 2015 / Publshed: May 31, Abstract: Ths paper proposes an optmal confguraton of the dstrbuted hybrd renewable generatons based on the stand-alone mcro-grd system, consderng the desel as the man control source. Due to the natural sources and load of user changes randomly and the non-lnearty of the power output by renewable generatons, an ntellgent optmzaton method based on the mprovement of the genetc algorthm and the control strategy are dscussed. The nstance analyss s compared wth the optmzaton result of the hybrd system based on HOMER (hybrd optmzaton of multple energy resources) and GA (genetc algorthm) method on Matlab software. The smulaton result of the optmal confguraton showed the new hybrd renewable system and would mprove the power supply stuaton whch decreased the cost of energy greatly compared wth the conventonal form of power supply system whch was operated only by desel. The concluson of the comparng result between HOMER and GA method shows the advantages of the strategy for the desel as man control sources. Key words: Dstrbuted generatons, renewable generatons, mcro grd, HOMER, genetc algorthm. 1. Introducton Recently, the applcaton of renewable energy has become one of the solutons to the problems of energy crss and carbon emsson polluton. Besdes, t s hoped to mprove the people s lvelhood who are lvng n the remote areas or slands, whch have dffculty n power supply. So, clean and renewable sources of energy as well as related technologes are beng researched extensvely. The prevous research can lead to a concluson that, the hybrd dstrbuted power systems exhbt the hgher relablty and lower cost compared wth the conventonal power supply system whch was suppled by only one source, such as the sland stand-alone power supply system only used the desel generators. For the dfferent objects of study, consderng the Correspondng author: Xang Chen, master, research felds: mcro grd and new energes. E-mal: cx @hotmal.com. dfferent requrements for the project, the algorthm research turned up multfarously. The stand-alone hybrd power systems were always researched and appled by some models, such as wnd-desel, PV-desel, wnd-pv-desel and wnd-pv-desel-battery. Some researchers dscussed an optmal desgn model that used the form of PV/wnd/battery. Then, they used genetc algorthm to solve the problem of confguraton wth the power sources [1-4]. Consderng controllable load, the study provded an optmzaton method of genetc algorthm and tabu search n an solated sland n Japan [5]. Consderng real-tme dgtal smulator envronment, a fast ntellgent reconfguraton algorthm based on partcle swarm optmzaton was presented n Ref. [6] for an electrc shp s power system. Many hybrd power system projects were appled worldwde purpose for meetng the demand of power supply n sland or other remote areas. Such as, a

2 494 Optmal Confguraton for Dstrbuted Generatons n Mcro-grd System Consderng wnd-pv-desel hybrd system was fund for a vllage n Saud Araba. The study of ths project provded detaled data and senstvty analyss for ths hybrd power system [7]. The result shows the beneft and advantage n solvng the dffculty of power supplyng for the remote vllage and reducng the carbon emsson polluton. In another project n Malaysa, the study of optmal szng and strategy was dscussed for PV and mcro-hydro hybrd system [8]. It amed at the best combnaton of hybrd renewable energy system whch had the lowest total net present cost. For the country has the most slands n the world, especally small slands, to ncrease the electrfcaton rato, they focus the applcatons of the renewable energes whch can be operated stand-alone and better economy than desel whch was used conventonally. Many studes were carred out usng the HOMER (hybrd optmzaton of multple energy resources) software for achevng the performance analyss the desel-renewable mxed mcro-grd system n Refs. [9, 10]. The confguraton of the hybrd renewable power supply system s closely lnked to the control strategy. In Ref. [11], Sajjad, et al. proposed sx mode control strategy for a stand-alone hybrd power system. The strategy was used to control the power flow to meet the demand of users load based on the measurable system varables. Ths paper proposes an optmal algorthm n confguraton of the hybrd renewable power system, consderng the desel generators as the man control energy source. For the demonstraton project n the sland, the model of wnd-pv-desel-battery was used as the form of stand-alone power supply system. Then the economc ndcators would be evaluated by TPNC (total net present cos. Referenced the smulaton result operated by the soft of HOMER whch was used n research for mcro-grd and dstrbuted generaton power system. The dstrbuted generators combnaton depends on the value of TPNC. 2. Research Methodology Genetc algorthm s a conventonal methodology to solve the problems of the optmal confguraton wth the dstrbuted power systems. In ths study, the desel generators were consdered as the man control source. Therefore, the conventonal genetc algorthm was used to mprove the new system, and the new control strateges were formulated to mprove the economy of the system. Ths paper manly consdered the output power of wnd, PV, desel and the capacty of battery as the manly nfluence factors for the economy research of the system. 2.1 Wnd Turbne Model For the wnd turbne, the factors of the output power are related to wnd speed and tower heght. Accordng to the formula of the wnd turbne output power by pece wse functon as Eq. (1): 0, v( vc 3 av( bpr, vc v( vr Pwt ( Pr, vr v( v (1) co 0, v( vco where, P, v r c, v co, v r, mean rated power, cut-n wnd speed, cut-out wnd speed, rated wnd speed, respectvely. Besdes, we gnore the nfluence caused by tower heght n ths paper. 2.2 PV Model Consderng the solar energy, the electrcal power supply s affected by the solar radaton, the panel sze and PV cell temperature. Then, the power of the photo-voltac output hourly s gven by Eq. (2): GAC PPV PSTC ( 1 k( Tc Tr )) (2) GSTC where, PPV means the output power of the photo-voltac; P STC stands for the max output power n text method under the standard test condton. 2 Always t equals 1 /m when the envronment temperature s 25 C, G AC means llumnaton ntensty; k s the temperature coeffcent of output power; T c s the PV temperature; T r s the PV

3 Optmal Confguraton for Dstrbuted Generatons n Mcro-grd System Consderng 495 temperature under standard test condtons. 2.3 Desel Generator Model The economy of the desel generator s determned by the ol consumpton of unt power. The fuel cost can be calculated as Eq. (3): 2 CF( P ) a P b P c (3) t where, CF ( P t ) s hourly consumpton; P t means the rated power of the desel; a, b and c are the fuel curve coeffcent. 2.4 Battery Bank Model Consderng the confguraton of the sze of the battery bank, the battery s charge and dscharge are the man factors. The SOC (state of charge) of the battery bank can be calculated as Eq. (4): t t SOC() t (1 Q) SOC( t 1) P () t e / E (4) where, SOC( and SOC(t 1) are the battery bank state of charge at tme t and t 1; Q s hourly dschargng rate; E s the total energy; e cd s effcency of charge and dscharge. 2.5 Constrants Model and Control Strategy For the complexty of the dstrbuted generatons n the hybrd renewable system, the dspatch strateges are curous. In ths study, to ensure the relablty and electrc power qualty of power supply, the desel was operated as the man control source. So the control and dspatch strateges were dscussed as a man pont. In the economc model, the object s to obtan the lowest cost for the stand-alone mcro-grd system, and the nfluencng factors of the cost contan not only the cd cd Fg. 1 Control strategy of the hybrd renewable power system.

4 496 Optmal Confguraton for Dstrbuted Generatons n Mcro-grd System Consderng cost of the generaton devces, but also that of operatons and the power output for the each generatons. Though we use the same wnd turbnes, many factors lke the locatons and wnd energy always nfluence the objectve functon. The objectve functon for the total cost of the system was made as Eq. (5), and each model was used for calculatng the power output for each generaton wth the resources data nput. m n h (5) mn( T ) mn ap b P c P uv c w j sj k dk st 1 j 1 k 1 where, T c s total cost of the dstrbuted generatons of mcro grd system; P w s the power out of the wnd turbne n number I; P sj s the power out of the PV n number j; P dk s the power out of the desel n number k; V st s the capacty of the battery; a s the coeffcent of the cost for the wnd turbne n number ; b j s the coeffcent of the cost for the wnd n number j; c k s the coeffcent of the cost for the desel n number k; u s the coeffcent of the cost for unt capacty of battery. Accordng to the dspatch strategy, the cost of power generaton n hybrd renewable system whch conssts of dstrbuted generatons cost, transmsson devces cost, operaton and management cost, respectvely. In Fg. 1, wth the strategy of the desel generaton as the man control source, the code of the search algorthm whch the GA (genetc algorthm) was consdered at present amed to obtan the optmzaton results, and another new search algorthm would be studed for the better results n the future. necessary. In ths study, we referenced the optmzaton operated by the software of HOMER. 3.1 Smulaton wth HOMER HOMER s desgned for the hybrd renewable and dstrbuted generaton system, and developed by the natonal renewable energy lab n USA. In ths study, HOMER works off grd, and shows how to cost-effectvely combne renewable systems wth grd power for maxmum relablty. The purpose s to meet the electrcal load whle savng fuel maxmally. The nformaton requred for the analyss was provded by the local meteorologcal department and electrc power bureau. The fnal optmal confguraton depends on the value of COE (cost of energy). The model based of HOMER software whch s showed n next fgure. In Fg. 2, the man components consdered n ths hybrd system were wnd turbne, PV, desel generator, battery, converter, respectvely. In ths study, we referenced the brand of wnd turbne manufacturers called Xnsa, the model s XFHJ-100k, the wnd turbne s rated power s 100, and unt prce s RM700,000 calculated n ths study. The prce of the PV s RM27,460/. Other nformaton requred s showed n Table 1. In Fg. 3, t shows the dagrammatc of the annual solar radaton n the sland. The best radaton month s July, and the worst s February. Fg. 4 shows the dagrammatc of the wnd speed n the wnd farm of 3. Research Methodology Snce the natural sources such as the wnd and solar energy are n a good condton n ths place, the renewable energes have a good prospect. Besdes, electrc vehcle and electrc buses wll be supported by government and the publc chargng statons were to be under constructon. The flexblty of mcro-grd system control would be ncreased greatly. The study of the confguraton of the hybrd power system s Fg. 2 The model of hybrd renewable system setup.

5 Optmal Confguraton for Dstrbuted Generatons n Mcro-grd System Consderng 497 Table 1 The nput nformaton for the hybrd system. Component Sze Captal Cost Replacement Lfe-tme () (RMB/k) (years) Wnd turbne PV 50 1,400 1, Desel Battery 3k.Ah, 6k Converter Daly radaton (h/m 2 ) Fg. 3 Global horzon radaton Jan. Feb. Mar. Apr. May. Jun. Jul. Aug. Sep. Oct. Nov. Dec. The annual solar radaton. Wnd resource Jan. Feb. Mar. Apr. May. Jun. Jul. Aug. Sep. Oct. Nov. Dec. Fg. 4 The annual wnd speed. the sland. The best month s November and the worst month s Aprl or May. Ths two knd of natural source has some complementary to each other n the overall trend. Then, the user load n sland s showed by Fg. 5. The weather changes randomly, but the statstc data of the natural sources reflect the characterstcs regonally and seasonally. So, the hybrd renewable system can use the natural sources complementarly. Wth the smulaton operated by the soft of HOMER, thousands of smulaton confguratons were showed by COE (cost of energy) n Fg. 6. It shows the hybrd system consstng of wnd turbne, PV, desel generator, and battery. Make sure every component of the hybrd RE system, the deal optmzaton results were showed n Fg. 6. The model of wnd-pv-desel-battery has the lowest TNPC (total net present cos, the same to the COE of the system approxmately RMB2.426/h. Meanwhle, the mnmum COE, whose model only has the desel and battery, s hgher than the model of wnd-pv-desel-battery system. From the nformaton collected by the local electrc power bureau, the COE of the conventonal power supply generated by desel Max Daly hgh Mean Daly low Man Fg. 5 The annual load. Jan. Feb. Mar. Apr. May. Jun. Jul. Aug. Sep. Oct. Nov. Dec. Ann. Intal captal Operaton cost (RM/yr) Fg. 6 Optmzaton results for the RE system wth HOMER. Jan. Feb. Mar. Apr. May. Jun. Jul. Aug. Sep. Oct. Nov. Dec. Fg. 7 Monthly electrc producton of the hybrd RE system.

6 498 Optmal Confguraton for Dstrbuted Generatons n Mcro-grd System Consderng Table 2 Optmzaton results for the RE system based GA. Component WT (100 ) PV (50 ) Desel (50 ) Bat (6 3,000 Ah) Quantty COE (RM/h) s approxmately RMB3.03/h. The applcaton of the hybrd renewable system can mprove the power supply of the current stuaton greatly. In Fg. 7, t shows the monthly average electrc producton. The composton of the electrcty consumpton and producton can be seen from Fg. 7. Sum to the nformaton, the hghest consumpton s n September as t s the tourst rush season. The new comng toursts ncrease the burden of power supply. On the contrary, the lowest consumpton s n Aprl as the toursts rarely come for the bad weather, such as the rany weather. In another aspect, the wnd turbnes afford the major power source from October to February as the monsoon clmate has brought more wnd resources, and t s extremely rch regon for the wnd resources. For the PV, t provdes the power on steady. 3.2 Smulaton wth Genetc Algorthm by MATLAB In ths study, genetc algorthm was dscussed to fnd the optmal confguraton of the hybrd system, and the genetc algorthm codes were operated on the MATLAB to gan the optmzaton result. In the MATLAB smulaton, for the desel generator was consdered as the man control source, some new condtons were added nto the smulaton. Compared wth the conventonal research on the confguraton of dstrbuted generatons, the mproved genetc algorthms reflect the dfferences n constrant condton and control strateges. The rated power of the desel generator s the 50 each, and make sure one of the desel generators work all the tme. The smaller sze of desel generators would ncrease the flexblty of the strateges desel generators. The am of ths desgn s to have more knowledge about the most economc capacty of dstrbuted generatons. We gnore the cost of the mantenance caused by ncreased desel generators. The detal control strategy s showed n Fg. 1. In these studes, the prce of desel s 7.5 RMB per lter. In the MATLAB smulaton, the orgnal populatons have 20, and the smulaton was executed by 200 maxmum generatons. The crossover value s 0.25 and the mutaton value s 0.1. The ftness value s the recprocal of the COE and the best value s The best result s 13 wnd generatons, 3 PV generaton, 27 desel generatons and 50 6 batteres. The result of the optmzaton shows n Table 2. From Table 2, we can see the optmzaton result calculated by the mproved GA method. The COE s 1.88 RM/h. Compared wth the optmzaton result operated by HOMER, the GA optmzaton has a great mprovement. Ths method gnores many engneerng nfluences. For example, we consder the lmtng case n real engneerng so that the desel can supply the peak load. In ths GA method, the nsuffcent capacty of the desel generators s made up by batteres when the peak load s comng. And the batteres strategy contrbuted the great mprovement of result. But t s based on the accurate load forecastng technques. Ths result s referenced the average load value n recent years. The load forecastng technques s an mportant part of these studes of the next stages. Consderng the desel generator as the man control source of the power supply, ths strategy has a hgher relablty, a hgher power qualty, as well as much easer control operaton and control methods. The optmzaton result would be put n applcaton. What s more, the smple control strateges avod the frequent operatons of the facltes and equpment, also savng the cost of the operatng and management, prolongng the servce lfe of the equpment. 4. Conclusons In ths paper, the desel generator was consdered as

7 Optmal Confguraton for Dstrbuted Generatons n Mcro-grd System Consderng 499 the man control source for the power supply n stand-alone mcro-grd system. Wth the study, the nfluencng factors can be dvded nto several aspects, such as the renewable generatons of whch the output power s nonlnear, the natural sources whch changes randomly and rregularly and short-term users load whch also changes randomly and n lable. What s more, the prce of the ol s changng all the tme but advancng n long term. So the ways of research n optmal confguraton were dscussed n these aspects, respectvely, such as, modelng the dstrbuted generatons, makng sure the objectve functons and constrants, makng the control strategy, collectng the weather source data for years, codng the optmzaton algorthm, and analyzng the optmzaton result. Besdes, the optmal confguraton was also studed wth HOMER based on the nstance of an sland demonstraton project n Chna, and the optmzaton result was compared wth that mproved by the GA method. Fnally, the result would be referenced n the constructon of practcal engneerng. References [1] Ekren, O., and Ekren, B. Y Sze Optmzaton of a PV/Wnd Hybrd Energy Converson System wth Battery Storage Usng Response Surface Methodology. Appled Energy 85 (11): [2] Ekren, O., Ekren, B. Y., and Ozerdem, B Break-Even Analyss and Sze Optmzaton of a PV/Wnd Hybrd Energy Converson System wth Battery Storage A Case Study. Appled Energy 86 (7): [3] Ekren, O., and Ekren, B. Y Sze Optmzaton of a PV/Wnd Hybrd Energy Converson System wth Battery Storage Usng Smulated Annealng. Appled Energy 87 (2): [4] Rajkumar, R. K., Ramachandaramurthy, V. K., and Yong, B. L Techno-economcal Optmzaton of Hybrd PV/Wnd/Battery System Usng Neuro-Fuzzy. Energy 36 (8): [5] Asato, B., Uchda, K., and Goya, T Optmal Operaton for Desel Generators n Small Isolated Island Power System Cosderng Controllable Load. In Proceedngs of the ICEMS (Electrcal Machnes and Systems), 2010 Internatonal Conference on IEEE (Insttute of Electrcal and Electroncs Engneers), [6] Mtra, P., and Venayagamoorthy, G. K Implementaton of an Intellgent Reconfguraton Algorthm for an Electrc Shp s Power System. IEEE Transactons on Industry Applcatons 47 (5): [7] Rehman, S., Mahbub Alam, M., and Meyer, J. P Feasblty Study of a Wnd-PV-Desel Hybrd Power System for a Vllage. Renewable Energy 38 (1): [8] Qas, A., Othman, M. M., and Khams, N Optmal Szng and Operatonal Strategy of PV and Mcro-hydro. In Proceedngs of the 2013 IEEE 7th Internatonal PEOCO (Power Engneerng and Optmzaton Conference), [9] Lambert, T., Glman, P., and Llenthal, P Mcropower System Modelng wth HOMER. Integraton of Alternatve Sources of Energy 1 (15): [10] Razak, N. A., Bn Othman, M. M., and Musrn, I Optmal Szng and Operatonal Strategy of Hybrd Renewable Energy System Usng Homer. In Proceedngs of the th Internatonal IEEE PEOCO (Power Engneerng and Optmzaton Conference), [11] Sajjad. M., Chowdhury, A. R., and Saha, S Sx Mode Control Strategy for a Stand-Alone Hybrd Power System. In th Internatonal Conference on IEEE ICECE (Electrcal Computer Engneerng),