Fuzzy logic controller for the maximum power point tracking in photovoltaic system

Transcription

1 Intrnational Journal of Computr Applications ( ) Fuzzy logic controllr for th maximum powr point tracking in photovoltaic systm G. Balasubramanian Assistant Profssor Dpartmnt of Elctrical Enginring Annamalai Univrsity Annamalainagar-68 2, INDIA S. Singaravlu Associat Profssor Dpartmnt of Elctrical Enginring Annamalai Univrsity Annamalainagar-68 2, INDIA ABSTRACT This papr prsnts afuzzy logic controllr for maximum powr point tracking (MPPT) in photovoltaic systm.an asy and accurat mthod of modling photovoltaic arrays is proposd. Th modl and fuzzy basd control stratgis ar combind to form intllignt controllrs that ar mor accurat and robust.th modl basd controllr is dsignd such that th rfrnc signal for PWM gnrator of th convrtr can b adjustd to achiv maximum powr gnration from th photo voltaic systm. Th proposd fuzzy logic controllr shows bttr prformancs compard to th and MPPT basd approach.a MATLAB basd modling and simulation schm along with MPPT and fuzzy logic controllr is proposd which ar suitabl for studying th I-V and P-V charactristics of a PV array undr a non-uniform irradiation and diffrnt tmpratur. Th modl has bn xprimntally validatd. Gnral Trms Photovoltaic Array, DC-DC Boost convrtr, Fuzzy Logic Kywords MPPT convrtr, Non-linar approach, Choppr, Photovoltaic charactristics 1. INTRODUCTION In rcnt yars, rnwabl nrgy sourcs bcom mor significant sourc of nrgy. Among th rnwabl nrgy sourcs, solar nrgy is sustainabl with lss carbon missions [1-2].Th output powr of a PV array varis according to th sunlight conditions such as solar irradiation, shading and tmpratur. To obtain maximum powr from photovoltaic array, photovoltaic powr systm usually rquirs maximum powr point tracking (MPPT) controllr [3]. Various approachs hav bn rportd to implmnt MPPT such as prturb and obsrv () mthod [4-5], th incrmntal conductanc mthod, constant voltag mthod and short-circuit currnt mthod [6]. Using this mthod th maximum powr point can b found for spcifid solar irradiation and tmpratur condition but thy display oscillatory bhaviour around th maximum powr point undr normal oprating conditions. Morovr th systm will not rspond quickly to rapid changs in tmpratur or irradianc. On th othr hand th convntional controllrs ar fixdgain fdback controllrs. Thrfor thy cannot compnsat th paramtr variations in th procss and cannot adapt changs in th nvironmnt. -controlld systm is lss rsponsiv to ral and rlativly fast altrations in stat and so th systm will b slowr to rach th st point. Rcntly intllignt basd schms hav bn introducd [7-9].Among th intllignt basd mthods fuzzy logic controllr has its own mrits such that th MPPT algorithm can b asily formd. Th shap of th mmbrship function of th fuzzy logic controllrs can b adjustd such that th gap btwn th opration point and maximum powr point can b optimizd. Thrfor in th prsnt papr, an intllignt control tchniqu using fuzzy logic control associatd with a MPPT controllr ar usd to improv nrgy convrsion fficincy of th photovoltaic systm. Th proposd intllignt fuzzy logic procss compriss of xprt knowldg which xtracts maximum powr from a PV modul undr varying solar irradiation, tmpratur and load condition. Mathmatical modling of th systm and th simulation rsults using MATLAB / SIMULINK ar prsntd. Th fuzzy logic controllr basd rsults ar compard with th convntional tchniqus such as and controlling mthods which validat it mrits.an xprimntal stup of th proposd schm has bn built and th rsults obtaind on a PV arrayof 74.8W, 21.2 V, 4.4A rating is prsntd. 2. MODEL OF A PV ARRAY A PV cll can b rprsntd by an quivalnt circuit [1]as shown in Fig. 1. Th charactristics of this PV cll can b obtaind using standard quation (1). I PV D R P R S I PV R Load Fig 1: Equivalnt circuit of PV cll VPV I = I PV I O xp V+R S I 1 V+R SI V t a R p (1) I PV = photovoltaic currnt I O = saturation currnt V t = N S k T/q, thrmal voltag of array Ns = cll connctd in sris T = is th tmpratur of th p-n junction k = Boltzmann constant q = lctron charg R S = quivalnt sris rsistanc of th array R P = quivalnt paralll rsistanc of th array a = diod idality constant 22

2 Intrnational Journal of Computr Applications ( ) Fig. 1 shows th singl diod modl. A singl solar cll will produc only a limitd powr. Thrfor it is usual practic in ordr to gt dsird powr rating th solar clls ar connctd in paralll and sris circuits which form a modul. Such moduls ar again connctd in paralll and sris to form a solar array or panl to gt rquird voltag and currnt. Th quivalnt sris and paralll rsistanc of th array ar dnotd by th symbol R S and R P rspctivly in th quivalnt circuit. From th gnral I-V charactristic of th practical photovoltaic dvic on can b obsrv that th sris rsistanc R S valu will dominat in th voltag sourc rgion and th paralll rsistanc R P valu will dominat in th currnt sourc rgion of opration. Th gnral quation of a PV cll dscribs th rlationship btwn currnt and voltag of th cll. Sinc th valu of shunt rsistanc R P is high compard to valu of sris rsistanc R S th currnt through th paralll rsistanc can b nglctd. Th light gnratd currnt of th photovoltaic cll dpnds linarly on th solar irradiation and is also influncd by th tmpratur [11] givn by th quation (2) I PV = I PV,n + K I T G G n (2) I PV,n = is th light gnratd currnt at nominal condition (25 C and 1 W/ m 2 ) Δ T = T T n T = actual tmpratur [K] T n = nominal tmpratur [K] K I = currnt cofficints G = irradiation on th dvic surfac [W/m 2 ] G n = nominal irradiation Th currnt and voltag cofficints K V and K I ar includd as shown in quation (3) in ordr to tak th saturation currnt I O which is strongly dpndnt on th tmpratur. I O = I sc,n +K I T xp V oc,n +K V T 1 av t K V = voltag cofficints K I = currnt cofficints Th output voltag is incrasd (whr th currnt rmain unchangd) proportionally on numbr of idntical PV moduls connctd in sris(n sr ). Similarly th output currnt is incrasd (whr th voltag rmain unchangd) proportionally on numbr of idntical PV moduls connctd in paralll (N par ). It can b notd that th quivalnt sris and paralll rsistanc ar dirctly proportional to th numbr of sris moduls and invrsly proportional to th numbr of paralll moduls rspctivly. Th quation for array composd of N sr x N par givn by quation (4) I = I PV N par I O N par xp V+R S Nsr Npar V t an sr V+R S N sr Npar R P N sr Npar I 1 Th paramtr of solar array (KCP-1275 at 25 C, 1W/m 2 ) usd for thortical and xprimntal stup is givn in tabl-1. I (3) (4) PV Array I mp 4.4 A V oc 21.2 V V mp 17. V a 1.3 P max 74.8 W R s.511 Ω I sc 5.2 A R sh Ω N s 36 K v mv/ I O,n 9.83 x 1-8 A K I 2.8 ma/ DC-DC Convrtr (Boost) MPPT and Boost Controllr Tabl-1 3. DC DC BOOST CONVERTER A dual stag powr lctronic systm comprising a boost typ dc-dc convrtr and an invrtr is usd to fd th powr gnratd by th PV array to th load. To maintain th load voltag constant a DC-DC stp up convrtris introducd btwn th PV array and th invrtr.th block schmatic of th proposd schm is shown in Fig.2. In this schm a PV array fds DC-DC convrtr usd in stp-up configuration. Th voltag across th DC-DC convrtr is fd to a thr-phas, six-stp, quasisquar-wav IGBT invrtr a thr-phas fixd amplitud and fixd frquncy supply is obtaind to fd an isolatd load. Invrtr Control Logic Load Fig 2: Systm configuration for PV-basd systm fding powr to th load For a dc-dc boost convrtr, by using th avraging concpt, th input output voltag rlationship for continuous conduction mod is givn by Vo/Vin=1/(1 D) (5) Whr, D = duty cycl. Sinc th duty ratio D is btwn and 1 th output voltag must b highr than th input voltag in magnitud. It should b notd that th control logic of such dc-dc convrtr has to b diffrnt whn it is fd from a stiff DC sourc. Th duty ratio of th choppr is found to incras linarly with incras in cll tmpratur and hnc th intnsity. It has bn obsrvd that whn a PV array is connctd to a boost convrtr, incrasing th duty cycl incrass th avrag PV array currnt and as a rsult, PV array voltag dcrass. Thus, an incras in duty-cycl rsult in shifting th oprating point to th lft on th V-I charactristics of th PV array. Similarly dcrasing th duty cycl dcrass th avrag PV array currnt and as th PV array voltag incrass rsulting in shifting th oprating point of PV array to th right. As th invrtr DC voltag varis with irradiation to obtain constant amplitud and constant frquncy supply from th invrtr, a closd loop fuzzy controllr is incorporatd to automatically vary th duty-cycl of th DC-DC convrtr to obtain constant DC voltag at th invrtr input trminals.th invrtr output is thn applid to an isolatd load. 23

3 Intrnational Journal of Computr Applications ( ) 4. LOGIC MPPT CONTROLLER Th convntional controllrs ar fixd-gain fdback controllrs. Thrfor thy cannot compnsat th paramtr variations in th procss and cannot adapt changs in th nvironmnt. -controlld systm is lss rsponsiv to ral and rlativly fast altrations in stat and so th systm will b slowr to rach th st point. On th othr hand mthod for MPPT tracking will not rspond quickly to rapid changs in tmpratur or irradianc. Thrfor th fuzzy control algorithm is capabl of improving th tracking prformanc as compard with th classical mthods for both linar and nonlinar loads. Also, fuzzy logic is appropriat for nonlinar control bcaus it dos not us complx mathmatical quation. Th block diagram of fuzzy logic controllr (FLC) is shown in Fig.3. Th two FLC input variabls ar th rror E and chang of rror CE. Th bhavior of a FLCdpnds on th shap of mmbrship functions of th rul bas. Knowldg bas mthod. Hr w ar using MIN-MAX fuzzy implication mthod. 4.3 Dfuzzification Onc fuzzification is ovr, output fuzzy rang is locatd. Sinc at this stag a non-fuzzy valu of control is availabl a dfuzzification stag is ndd.cntroid dfuzzification mthod[12] is usd for dfuzzification in th proposd schm. nb nm ns zr ps pm pb Dgr of mmbrship1 Fig 5 (a): Mmbrship function plots for Inputs E(k) CE (k) Fuzzification Intrfac Dcision Making Logic Infrnc ngin Fig 3: Block of Fuzzy controllr Dfuzzification Intrfac Outp nb nm ns zr ps pm pb Dgr of mmbrship1 Fig 5(b): Mmbrship function plots for Δ Vr + Fuzzy logic - modl Vo Z-1 Procss Fig 4: Fuzzy logic control schm In this papr a fuzzy logic control schm (Fig.4) is proposd for maximum solar powr tracking of th PV array with an invrtr for supplying isolatd loads. Thy hav advantags to b robust and rlativly simpl to dsign sinc thy do not rquir th knowldg of th xact modl. On th othr hand th dsignr nds complt knowldg of th PV systm opration. 4.1 Fuzzification Thmmbrship function valus ar assignd to th linguistic variabls using svn fuzzy subst calld ngativ big (nb), ngativ mdium (nm), ngativ small (ns), zro(zr), positiv small (ps),positiv mdium (pm),positiv big (pb).fuzzy associativ mmory for th proposd systm is givn in Tabl-2.Variabl and Δ ar slctd as th input variabls, whr is th rror btwn th rfrnc voltag (Vr) and actual voltag (Vo) of th systm, Δ is th chang in rror in th sampling intrval. Th output variabl is th rfrnc signalfor PWM gnrator U. Triangular mmbrship functions ar slctd for all ths procss. Th rang of ach mmbrship function is dcidd by th prvious knowldg of th proposd schm paramtrs. 4.2 Infrnc ngin Infrnc ngin mainly consist of Fuzzy rul bas and fuzzy implication sub blocks. Th inputs ar now fuzzifid ar fd to th infrnc ngin and th rul bas is thn applid. Th output fuzzy st ar thn idntifid using fuzzy implication U Vo nb nm ns zr ps pm pb Dgr of mmbrship1 Fig 5(c): Mmbrship function plots for U U Tabl 2 Fuzzy associativ mmory for thproposd systm Δ nb nm ns zr ps pm pb nb nb nb nb nm nm ns zr nm nb nb nm nm ns zr ps ns nb nm nm ns zr ps pm zr nm nm ns zr ps pm pm ps nm ns zr ps pm pm pb pm ns zr ps pm pm pb pb pb zr ps pm pm pb pb pb Th mmbrship function of th variabls rror, chang in rror and chang in rfrnc signal for PWM gnrator ar shown in Fig. 5a-5c rspctivly. 5. RESULTS AND DISCUSSION A MATLAB basd modling and simulation schm (Appndix) along with MPPT and fuzzy logic controllr is proposd which ar suitabl for studying th I-V andp-v charactristics of a PV array undr a non-uniform irradiation and diffrnt tmpratur. Th fuzzy logic controllr basd rsults ar compard with th convntional tchniqus such as and controlling mthods which validat it mrits. 24

4 Control signal Panl Powr (W) Currnt (A) Powr (W) Intrnational Journal of Computr Applications ( ) 5.1 Simulation of Photovoltaic charactristics Th bhavior th PV clls and its charactristics ar discussd in this sction. It is found that th st of P-V&I-V charactristics ar highly nonlinar and dpndnt on solar irradianc of th PV array. Th combination of V and I that maximizs th output dpnds on irradiation and is also affctd by th tmpratur of th cll. 25 C 5 C 75 C 1 C 125 C Powr (W) Currnt (A) 1 W/m 2 8 W/m 2 6 W/m 2 4 W/m 2 2 W/m 2 Voltag (V) Fig 6(a): I-V Charactristics for diffrnt irradiations Voltag (V) Fig 6(b): P-V Charactristics Voltag (V) Fig 6(c): I-V Charactristics Voltag (V) Fig 6(d): P-V Charactristics for diffrnt tmpratur Fig.6(a)shows I-V charactristics of a PV cll. It can b obsrvd that as th cll tmpratur rmain constant, thpv output voltag rmains narly constant whil th PV output currnt incrass with incrasing solar intnsity. Fig.6(b)& Fig.6(c) shows P-V&I-V charactristics of a PV cll rspctivly. Fig.6(d) shows P-V curv plottd for diffrnt valus of tmpratur. 5.2 Simulation of, and Fuzzy logic MPPT Controllrs An xtnsiv simulation work nsurd ralizd MATLAB nvironmnt is prformd. Som slctd rsults ar prsntd with a comparison btwn systm incorporating diffrnt configurations as, and Fuzzy MPPT controllrs. To highlight th proposd systm good prformancs, th following simulation wr prsntd for fast solar irradianc [13] from 5 to 1 W/m 2 at fixd tmpraturof 25 C and fast dcras and incras in tmpratur variations from 4 C to 2 C and 2 C to 4 C rspctivly at fixd solar irradiancof 1w/m 2. From th simulation rsults, it can b dducd that th fuzzy controllr is fastr than controllr and in th transitional stat, and prsnt also much smothr signal with lss fluctuation in stady stat. 8 6 Fuzzy Tim (Sc) Tim (Sc) Fig 7: Rspons of th PV panl for a fast solar irradianc from 5 to 1W/m 2 at 25 c 25

5 Control Signal Panl Powr (W) Control Signal Panl Powr(W) Intrnational Journal of Computr Applications ( ) Tim(Sc) Tim(Sc) Fig 8: Rspons of th PV panl for a fast tmpratur variation from 4 c to 2 c at a solar irradianc of 1W/m E Tim(sc) Tim(Sc) Fig 9: Rspons of th PV panl for a fast tmpratur variation from 2 c to 4 c at a solar irradianc of 1W/m 2 6. EXPERIMENTAL INVESTIGATION Th PV array in th proposd schm shown in Fig.1(b) consist of solar PV array of 74.8W, 21.2V, 4.4A (15 panls connctd in sris). A load of 8Ω pr-phas was connctd in star across th invrtr trminals. A DC-DC convrtr (L=4μH, C=.25F) was constructd with IGBT (4 A, 6 V) as a switch with a switching frquncy of 2 KHz shown in Fig.1 (a). Th closd loop firing schm was mployd to triggr th DC-DC convrtr.a 5Hz, thr-phas IGBT invrtr was fabricatd, and a microcontrollr C 16F877A was usd to triggr th IGBT in 18 dgr conduction mod. Th abov schm was tstd for diffrnt conditions of irradiations. Fig 1(a): DC-DC-Convrtr - Invrtr Fig 1(b): Solar Panl 26

6 Intrnational Journal of Computr Applications ( ) Th simulatd thr phas voltag and currntwavform at th output of th invrtr shown in Fig. 11(a). Th simulatd currnt wavform (Fig. 11(b)) shows, vn though th load is applid at.8 sconds th voltag across th load rmains constant. Currnt (A) Voltag (V) Currnt (A) Voltag (V) Tim (sc) Fig 11(a): Simulatd Voltag & currnt wavform at output of th invrtr undr nominal load Tim (sc) Fig 11(b): Simulatd Voltag & currnt wavform at output of th invrtr undr suddn chang in load Fig 12: Voltag and currnt wavform (xprimntal) (On phas alon shown for clarity) Th xprimntal voltag and currnt wavform (on phas alon shown for clarity) at th output of th invrtr is shown in Fig. 12. Som harmonics hav bn introducd in th proposd schm found in th wavforms it can b liminatd by introducing ncssary filtrs. 7. CONCLUSION A simpl powr lctronic controllr for intrfacing photovoltaic arrays with DC-DC convrtr has bn dvlopd. By applying th puls width modulation (PWM) control schm with appropriat MPPT algorithm to th powr switchs and th DC-DC convrtr can draw maximum powr from photovoltaic array. Th rsults obtaind from th xprimntal invstigation and simulation studis of th proposd schm ar compard and it has bn found that th simulation rsults closly agr with th xprimntally obtaind rsults, thus validating th xprimntal powr circuit and control circuits of th invrtr. So, th fuzzy logic control is an ffctiv tool to track and xtract maximum powr to th isolatd load. 8. ACKNOWLEDGEMENT Th authors thank th authoritis of Annamalai Univrsity for th facilitis providd. 9. REFERENCES [1] Mayssa Farhat and Lassaad Sbita, Advancd Fuzzy MPPT Control Algorithm for Photovoltaic Systm, Scinc Acadmy Transactions on Rnwabl Enrgy Systms Enginring and Tchnology, 211, vol. 1, no. 1, pp , Mar [2] T. Tafticht, K. Agbossou, M.L. Doumbia, and A. Chriti, An Improvd Maximum powr point tracking mthod for photovoltaic systm, Rnwabl nrgy, vol.33, pp , 28. [3] Yun Tiam Tan, Danil S. Kirschn, and Nicholas Jnkins, A Modl basd PV Gnration suitabl for stability analysis, IEEE trans. on nrgy conv., vol.19, no.4, pp , Dc.24. [4] C. R. Sullivan and M. J. Powrs, A high-fficincy maximum powr point trackr for photovoltaic array in a solar-powrd rac vhicl, in Proc. IEEE PESC, [5] N. Fmia, Optimizing Duty-cyclPrturbation of MPPT Tchniqu,35th Annual IEEE Powr ElctronicsSpcialists Confrnc.,24. [6] E. Koutroulis E, K. Kalaitzakis, and NC. Voulgaris, Dvlopmnt of a microcontrollr basd photovoltaic maximum powr point tracking control sytm, IEEE trans. on Powr Elctronics, vol. 16, no. 1, pp , 21. [7] Abdulhadi Varnham, M. Abdulrahman, Al-Ibrahim, S. Gurvindr, Virk, and Djaml Azzi, Soft computing modl basd controllrs for incrasd photovoltaic plant fficincis, IEEE trans. on nrgy conv., vol. 22, no. 4, pp , Dc. 27. [8] A. Damak1, A. Gusmi and A. Mami, Modling and fuzzy control of a photovoltaic-assistd watring systm, Journal of Enginring and Tchnology Rsarch, Vol.1, pp. 7-13, 29. [9] B.Krishna Kumar, Matlab basd Modlling of Photovoltaic Panls and thir Efficint, Utilization for Maximum Powr Gnration, 1st National Confrnc on Intllignt Elctrical Systms, NCIES, Salm, India, pp ,

7 Intrnational Journal of Computr Applications ( ) [1] M.G.Villalva, J.R.Gazol, and E.R.Filho, Comprhnsiv Approach to Modling and Simulation of Photovoltaic Arrays", IEEE trans. on Powr Elctronics, vol.24, no.5, pp , May 29. [11] H. Patl, and V. Agarwal, MATLAB basd modling to study th ffcts of partial shading on PV array charactristics, IEEE trans. on nrgy conv., vol. 23, no.1, pp , Mar. 28. [12] Timothy, andj. Ross, Fuzzy logic with nginring applications, McGraw hill intrnational ditions, Elctrical nginring sris, Nw York, [13] C. Larbs, S.M. AitChikh and T. Obidi, Gntic alogorithms optimizd fuzzy logic control for th maximum powr point tracking in photovoltaic systm, Rnwabl Enrgy., vol. 34, no.1, pp , Oct. 29. APPENDIX A MATLAB basd modling and simulation schm along with MPPT and fuzzy logic controllr is proposd (Fig. 13) which ar suitabl for studying th I-V and P-V charactristics of a PV array undr a non-uniform irradiation and diffrnt tmpratur. Th configuration of th proposd schm is simulatd undr diffrnt condition of irradiations (.4 kw/m 2 to1kw/m 2 ) in th powr systm block st platform of th MATLAB. Th simulatd currnt wavform (Fig.11(b)) shows, vn though suddn chang in load is applid at.8 sconds th voltag across th load rmains constant. In ordr to achiv th load voltag constant th actual voltag fd to th invrtr is compard with th rfrnc maximum voltag that can b obtaind at th load for a givn V oc and I sc.th rror is calculatd and accordingly th rfrnc signal to th PWM gnrator is changd in ordr to maintain th load voltag constant. Fig 13: Photovoltaic and MPPT Fuzzy controllr implmntd in SIMULINK 28