A New Concept on Intelligent Distribution Voltage Control for Dc Micro Grids Using Fuzzy Control and Gain-Scheduling Technique

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1 New onept on Intelligent Distriution Voltge ontrol for D Miro Grids Using Fuzzy ontrol nd GinSheduling Tehnique R.Shnthi Priy PG Student, Deprtment of EEE, Mll Reddy Engineering ollege. STRT: Instlltion of mny distriuted genertions (DGs) ould e detrimentl to the power qulity of utility grids. Miro grids filitte effortless instlltion of DGs in onventionl power systems. In reent yers, D mirogrid hve gined populrity euse D output soures suh s photovolti systems, fuel ells, nd tteries n e interonneted without /d onversion, whih ontriutes to totl system effiieny. Moreover, highqulity power n e supplied ontinuously when voltge sgs or lkouts our in utility grids. It is proposed lowvoltge ipolr type D mirogrid nd desried its onfigurtion, opertion, nd ontrol sheme, through simultions. However, D miro grids should hve two or more energy storge units for system redundny. Therefore, we modified the system y dding nother energy storge unit in simultion model. Severl kinds of droop ontrols hve een proposed for prllel opertions, some of whih were pplied for or d miro grids. If ginsheduling ontrol sheme is dopted to shre the storge unit outputs, the storge energy would eome unlned. This projet therefore presents new voltge ontrol tht omines fuzzy ontrol with ginsheduling tehniques to omplish oth power shring nd energy mngement. The simultion results will e otined for the D distriution voltges were within 340 V ± 5%, nd the rtios of the stored energy were P.Kmlkr ssoite Professor, Deprtment of EEE, Mll Reddy Engineering ollege. pproximtely equl, whih implies tht d voltge regultion nd stored energy lning ontrol n e relized simultneously in MTL Softwre. I. INTRODUTION: Inresed in reent yers euse of the redution in greenhouse gses nd depletion of fossil fuels. fter the 0, Tohoku erthquke nd tsunmi, the trends hve elerted even more in Jpn. s it is well known, instlltion of mny DGs ould e detrimentl to the power qulity of utility grids; therefore, mirogrids hve een studied s one of the ndidtes to support smooth instlltion of DGs. In prtiulr, d distriution mirogrids hve een studied for few yers. prt from redution in /d onversions losses, d mirogrids n supply ontinuous highqulity power when voltge sgs or lkouts our in utility grids. For instne, d power supplies re ommonly used in teleommunition uildings nd internet dt enters where highqulity power is needed We previously proposed lowvoltge ipolrtype d mirogrids, nd desried the onfigurtion, opertion, nd ontrol sheme, whih were demonstrted through experimentl result. In the experiment, we used one energy storge unit with d/d onverter to sustin dus voltge when the system ws in intentionl islnding opertion. fuzzy ontrol ws pplied to mximum power point trking ontrol of photovolti system in n isolted mirogrid to improve the response ginst rpidly hnging wether onditions. Pge 90

2 In this pper, we fous on pplition of fuzzy ontrol to ginsheduling ontrol nd demonstrte the vlidity of the proposed ontrol through experiments. D MIROGRID FOR RESIDENTIL OMPLEX System onfigurtion We proposed d mirogrid for residentil omplex, s shown in Fig.. There re round houses in the system, eh hving miro omined het nd power unit (mirohp unit) suh s gs engine or fuel ell. The mirohp units re onneted to d distriution line (three wire,±70 V), nd the eletri power is shred mong the houses. ogenerted hot wter is either used y individul house or shred etween djent houses. The utility grid is onneted to the system y retifier. t the lod side, vrious forms of eletri power (suh s 00 V nd d 48 V) n e otined from the onverters. EDLs re used s the min energy storge unit euse of their dvntges suh s fst response, sfety (espeilly ompred with Liion tteries), esy mesurement of the stored energy, nd no toxiity of the onstituent mterils. In verifition test of energy storge system using n EDL unit, the voltge, nd mximum energy were 500 V nd 5 MJ, respetively. From this, EDL is onsidered vile s n energy storge system in smll grid. The pitl ost per kilo wtt hour (kwh) for EDL is dollrs, while tht for ledid nd Liion tteries is nd dollrs, respetively. In ddition, EDLs n hndle mny hrge dishrge yles, nd therefore hs lowost per yle onsidering its long life. The pitl ost per kwhper yle for EDL is 4 ents, while tht for ledid nd Liion tteries is 0 00 nd 5 00 ents, respetively. The disdvntge of EDL is its lowenergy density. If lrge energy pity is needed for mirogrid, reltively lrge EDL is required. However, lrgeenergy pity is not neessry for the proposed d mirogrid euse the mirohp units re operted to prevent over hrge/dishrge of the EDLs s desried in the following setion. Fig..4 System onfigurtion of the d mirogrid for residentil omplex. Fig..5 Interonneted opertion. PURPOSE ND RHITETURE OF THE D MIRO GRID SYSTEM Following three terms re riefly summrized purposes of the D miro grid system. () Inrese the introdution of distriuted PV units. () Redue energy dissiption nd fility osts resulting from /D onversion y integrting the juntion etween ommeril grid nd D us whih onnets PV units nd umultors. (3) Supply power to lods vi regulr distriution lines (not exlusive lines for emergeny) even during the lkout of ommeril grids. II. D MIRO GRID SYSTEM onverters. These onverters lwys trk the mximum power point of the D power soures whih flututes depending on the intensity of solr rdition. onventionl pplines n e used s they re if n inverter is instlled in eh house to hnge the D power into 00 V / 00 V power, ut D power feeding will spred widely euse of its high effiieny, one sfe nd ompt gers, suh s rekers nd outlets, re stndrdized in the future. Storge tteries of the ommunity re lso linked to the D us. The Dsed distriution system redues fility osts nd energy dissiption ssoited with /D onversion euse the PV units nd ttery re D onneted nd most of the urrent energysving pplines operte on D due to the progress of inverter tehnology. This is why we should push hed with the D system. The system doesn t require long trnsmission lines to onvey solr power from remote res euse the PV units hve een distriuted in the demnd re. Power soures nd lods re losely loted to eh other in ommunity. Pge 9

3 The exess nd defiieny of power re vrile ftors whih should e ompensted for good lne etween supply nd demnd. The ompenstion system, whih onsists of storge tteries nd idiretionl power onverter, keeps good power lne in the ommunity y soring short term power flututions. Sine long term flututions, suh s those etween dy nd night, re lso smoothed y the ttery system, the miro grid system seems to e smll soure or lod for the outer widere grid. onsequently, this sheme redues the ost for the stiliztion of ommeril grids. The stte of hrge (SO) of the storge ttery lwys indites the time integrl of differene etween supply nd demnd in the D miro grid system. The SO e omes full with exess power, wheres it rehes the lower limit in defiieny. The mount nd diretion of the power flow from ommeril grid is ontrolled ording to the SO, nd power supply is mintined in the miro grid. However, power supply to the miro grid might e regulted to stilize the power flow of the ommeril grid. Fig..6. Shemti digrm of D miro grid system The ove mentioned D miro grid requires storge tteries nd ontrol units s its key omponents. To respond to short term power surplus or defiieny, the storge tteries hve to repet hrge nd dishrge opertion frequently under the ondition where the urrent vries rp idly. The D miro grid requires tteries tht quikly respond to hnges in the urrent nd ensures high durility in suh demnding opertion. Lrge pity (from severl hundred kwh to few MWh) should e ville for ommunity tht onsists of severl dozens or hundreds of households. Furthermore, preise detetion of the SO during the frequent hnge in opertion is lso indispensle to mnge the power lod nd ontrol the mount of power purhsed from or sold to the ommeril grid. redox flow ttery (RF ttery) stisfies the ove mentioned four onditions: quik response, high durility, lrge pity, nd preise SO detetion. Figure shows the si onept of the RF ttery. The ttery works y redutionoxidtion retion in the eletrolyti solution whih irultes etween ells nd tnks. The ells, where ions exhnge eletrons, re seprted from the tnks, where the solution is stored. While most tteries re nmed fter their tive mterils, the RF ttery is so lled euse of its speil rhiteture. Redox is n revited word of redution nd oxidtion. Flow phrses the irultion of n eletrolyti solution. The tive mterils of oth the positive nd the negtive eletrodes re vndium ions. ttery retion proeeds s the ions hnge their vlene in the solution without ny solid de posit on eletrodes. Therefore, the ell retion is very fst. There is no degrdtion y the hrgedishrge yle, too. lrge sle ttery is lso esily uilt due to its simple rhiteture. In ft, 6 MWh RF ttery system used to e utilized for smoothing the output flutution of wind frm where mny erogenertors were instlled(). nother signifint dvntge of the RF is the preise nd simultneous detetion of the SO while urrent flows in ells. The ove mentioned fetures of the RF ttery re est suited for D miro grid systems, ut the energy density of the RF ttery is lower thn tht of other seondry tteries, nd onsequently, it requires lrge footprint. 4. SupplyDemnd lne Test for RF ttery n experimentl fility ws onstruted to demonstrte lned opertion etween supply nd demnd in the D miro grid., Fig..6 the speifition of the experimentl fility, omposition, nd ppernes of min devies, respetively. Sine the purpose of this experiment is to demonstrte the lned opertion etween supply nd demnd, the fility ws disonneted from outer power soures. Pge 9

4 Fig..7 oneptul digrm of redox flow ttery In omprison with tul ses, the experimentl fility uses the sme length of lines ut dels with % to 0% of eletri power. In the D us, the trget voltge is 350 V, nd the totl length is km. The exlusive RF ttery hs een developed for this experiment, nd it hs 4 kw of mximum output nd 0 kwh of umulting pity. The ttery ws onneted t the enter of the D us through idiretionl DD onverter. The PV units nd n ero genertor were distriuted on the D us. The totl output of these genertors is out 8 kw. The PV system onsists of three different types of modules: polyrystlline silion modules nd IGS ompound modules, oth of whih re ommonly used, nd onentrtor photovolti (PV) modules tht we hve developed. The PV module ollets strong sunlight with lenses y preisely trking the sun nd genertes eletri power with multijuntion ells with extremely high onversion effiieny, therey yielding out twie the power generted y generl polyrystlline silion module on sunny dy. OOPERTIVE VOLTGE ONTROL SHEME IN D MIROGRID Voltge Drop Prolem in Rdil D Mirogrid System In typil D mirogrid with rdil topology, power flows from its point of ommon oupling(p) to the end us in one diretion. Therefore, voltge drop prolem n our with line voltge drop nd the lowest us voltge is formed t the reeiving end in the system. The vlue of the line voltge drop inreses in proportion to the lod urrent mgnitude nd the line length in the mirogrid. Figure shows typil voltge profile in D mirogrid. In this instne, some us voltges, normlly t theend of system, re out of the dmitted voltge rnge s the distriution line eomes longer. Moreover, ertin sensitive lods without voltge ompenstor ould mlfuntion nd the voltge stility might deteriorte further s the us voltges eome seriously diminished. Therefore, voltge ontrol method is needed to mintin the system us voltge within n pproprite rnge. Fig 5.3. The proposed voltge ontrol topology in rdil D mirogrid In n power system, vriety of devies, suh s shunt pitors, shunt retors, trnsformers, stti VR ompenstors (SV), STTOMs, re used to ontrol system voltges euse the voltges re influened onsiderly y retive power. However, there is no retive power in D system, nd system voltges re determined y tive powerflow. Therefore, different sheme from n system is needed to regulte system voltges in D system. In this pper, gridonneted onverter nd ontrollle distriuted genertor, whih inludes n energy storge devie, re used for the oopertive voltge ontrol in D mirogrid s shown in Figure. dvntges of eh devie ould e emphsized through the oopertive voltge ontrol euse the devies hve opposite hrteristis. Grid onneted onverter (G) ts s n onlod tphnging trnsformer in n power system from voltge ontrol point of view, nd it n effiiently ontrol ll system voltges t the seondry side of the onverter y PWM swithing opertion. The onverter is loted t the P in the proposed ontrol sheme to ontrol the voltges t ll uses in D mirogrid. Therefore, the G is used for voltge ontrol t the P only, nd n dditionl series onverter is not onsidered in this pper. Pge 93

5 Vgrid I onn onn Susystem [Iq] [Id] POWER REGULTOR V_inv I_inv Id_ref Iq_ref Vlod Inverter g Id_ref Iq_ref V_inv Ilod I_inv Freq Sin_os Vlod Ilod G_PULSES URRENT REGULTOR Id_ref Iq_ref I_inv P & Q Susystem wt V I P & Q Susystem3 PI PI In RMS Disrete RMS vlue3 0 G_PULSES 3 I_inv /se Vgrid Igrid sin_os dq0 sin_os dq0 Vgrid Igrid PI PI P & Q Susystem Uref Pulses V I Id_ref /se3 [Id] Iq_ref [Iq] z Supply SG Sg 50e3 REFERENE POWER REF POWER VD Susystem v [FV] FV F F onn onn Furthermore, the line voltge drop inreses with lod urrent, espeilly t low us voltge,whih uses lrge voltge differene etween some uses in rdil D mirogrid. In the se where lrge voltge differene exists etween some uses nd only the G ontrols the system voltges, mintining ll system voltges in the dmitted rnge n e prolem. This prolem nnot e solved with the G only, euse voltge ontrol of the G is performed either y inresing or deresing system voltges. OPTIML DG LLOTION LGORITHM Voltge ontrol y DG hs lrge dependeny on its lotion in power system. Moreover, voltge ontrol in D mirogrid neessittes power genertion from DG. Therefore, the more ontrolled the us voltge is, the lrger the mount of power needed from DG. This involves inresing the pity nd thus, the instlltion ost of the DG. Therefore, n optiml DG llotion is essentil for eonomil voltge ontrol with minimum pity nd power genertion from DG. III. SIMULTION RESULTS SIMULTION MODEL: Fig 6.4: susystem of ttery energy storge lok onstnt Gin RESULTS: K V K onstnt 0 onstnt sin sin sin SG Trigonometri Funtion Trigonometri Funtion Trigonometri Funtion Produt Produt Produt node 0 Fig 6.5:three phse sinwve genertion Fig. 6.6 Gind/d onverter output power hrteristis. (Voltge vrition %). s s s V V V 3 Disrete, Ts = e006 s. pow ergui ThreePhse reker ThreePhse Series RL Lod ThreePhse Series RL Lod Fig 6.: Simultion model Fig. 6.7 Gind/d onverter input power hrteristis. (Voltge vrition %). Fig 6.:susystem of power regultor Distriution Voltge Fig 6.3:susystem of urrent regultor Pge 94

6 Rtio of EDL hnge Rtio of EDL Fig Simultion results (ginsheduling ontrol nd droop ontrol, Kv = 50) (Initil ondition W /W 0.5). Fig. 6.8 Simultion results (ginsheduling ontrol nd droop ontrol, Kv = 0) (Initil ondition W /W ). Rtio of EDL rtio Rtio of EDL Fig. 6.. Simultion results (ginsheduling ontrol nd fuzzy ontrol) (Initil ondition W /W 0.5). Droop ontrol EDL terminl Voltge () Fuzzy ontrol EDL terminl Voltge () Fig. 6.9 Simultion results (ginsheduling ontrol nd droop ontrol, Kv = 50) (Initil ondition W /W ). Fig. 6.. Reltions etween input Xk nd voltge referene Vd. Distriution Voltge Pge 95

7 Fig Integrl of the squre of the urrent (IEDL nd IEDL). Fig 6.4: Integrl of the squre of the urrent with three ontrollers (Droop ontrol, Fuzzy ontrol nd Model referene dptive ontrol) Fig Simultion results (ginsheduling ontrol nd fuzzy ontrol) (Initil ondition W /W ). RESULTS MODIFIED Fig Simultion results (ginsheduling ontrol only) (Initil ondition W /W ). Fig Simultion results (ginsheduling ontrol nd droop ontrol, Kv = 0) (Initil ondition W /W ). Rtio of EDL rtio Pge 96

8 Droop ontrol EDL terminl Voltge () Fuzzy ontrol EDL terminl Voltge () Fig. 6.8 Simultion results (ginsheduling ontrol nd droop ontrol, Kv = 50) (Initil ondition W /W ). Fig. 6.. Reltions etween input Xk nd voltge referene Vd. Rtio of EDL Fig. 6.9Simultion results (ginsheduling ontrol nd droop ontrol, Kv = 50) (Initil ondition W /W 0.5). Fig. 6.. Integrl of the squre of the urrent (IEDL nd IEDL). Fig 6.3 :Integrl of the squre of the urrent with three ontrollers (Droop ontrol, Fuzzy ontrol nd Model referene dptive ontrol) Fig Simultion results (ginsheduling ontrol nd fuzzy ontrol) (Initil ondition W /W. 0.5). IV. ONLUSION: This projet presented new d distriution voltge ontrol for d/d onverters with n energy storge unit. The proposed ontrol omines ginsheduling tehnique with fuzzy ontrol. The experimentl results show tht the d distriution voltge ws within 340 V ± 5%, nd the rtios of the storge units were pproximtely equl. This indites tht d voltge regultion nd stored energy lning ontrol re relized simultneously. Pge 97

9 The min dvntge of the proposed ontrol is presented for the ses where the model is unknown or is mthemtilly omplex. Therefore, the proposed ontrol is reltively esy to introdue to rellife projets ompred with the modern ontrol theories tht utilize the timedomin stte spe representtion. However, for this purpose, tril nd error methods might e dopted to djust the memership funtions in prtie, whih is time onsuming proess. Our future study will ttempt to estlish the design proedure of the memership funtions. REFERENES: olde,.i. Piti,. Lsu, G.D. ndreesu, L. Tutele, F.ljerg nd P.Sndholdt, DTF SVM motion sensorless ontrol of PM ssistne relutne synhronous mhine s strterlterntor for hyrid eletri vehiles, IEEE Trns,Power Eletron.,vol,no 3, pp.7 79,My 006. J. Lee, J.Hong, K.Nm, R.Orteg,L.Prly nd.stolfi Sensorless of surfe mount permnent mgnet synhronous motors sed on nonliner oserver, IEEE Trns,Power Eletron.,vol 5,no, pp.9097,fe 00. H.S.Kng,.K.Kim nd Y.S,Kim, Position ontrol for interior permnent mgnet synhronous motors using n dptive integrl inry oserver, J.Eletr.Tehnol.,vol 4,no, pp.40 48,Jun 009. J.G.Lee, K.H.Nm, S.H.Lee,S.H.hoi, nd S.W.Kwon, lookup tle sed loss minimizing ontrol for FEV permnent mgnet synhronous motors, J.Eletr.Tehnol.,vol 4,no, pp.0 0,Jun 009. W.T.Su nd.m.liw, dptive position ontrol for LPMSM drive sed on dpted inverse model nd roust disturne oserver, IEEE Trns,Power Eletron.,vol,no, pp ,Mr 006. Pge 98