MPPT Enabled Solar Photo Voltaic Generators With V-f and P-Q Control in Microgrids

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1 MPPT Enabled Solar Phoo Volaic Generaors Wih V-f and P-Q Conrol in Microgrids T.Jagadeesh 1, Dr. V.Ganesh 2 P.G. Suden [EPS], Deparmen of EEE, JNTUACE Pulivendula, Kadapa, Andhra Pradesh, India 1 Professor, Deparmen of EEE, JNTUACE Pulivendula, Kadapa, Andhra Pradesh, India 2 ABSTRACT: The disribued energy sources are he small energy generaing sources. Combinaion of hese small energy sources will form microgrid o ac in a inerrelaed manner o provide a required amoun of acive power. The conrol approach shows efficacious coordinaion beween paricipaing micro resources while considering he case of charging irradiance and charging baery sae consrain. Micro grids could be conrolled as a single dispach able load which can respond in seconds o mee he needs of he ransmission sysem. The crucial conribuion and novely of he conrol echnique lies in he coordinaion beween MPPT conrol echnique which is used a he PV side or DC supply side, baery conrolling echnique and V-f and P-Q conrol algorihm which are use a inverer side. The PV sysem is designed wih a baery back-up a he condiion of emergencies. This arrangemen helps o keep he microgrid volage and frequency consan and also reliable supply o he criical loads. A coupling inducor is placed in beween PV sysem and grid, for he eliminaion of ripples in he PV oupu curren. The PV source is aached wih he inpu of he inverer hrough a capacior. This capacior injecs reacive power o PV sysem. This presens a perspecive of inerrelaed and inegraed conrol of solar PV generaors wih MPPT echnique and baery sorage echnique o give suppor o volage and frequency (V-f) mainain in islanded condiion. And more over acive and reacive power (P-Q) consrain along wih MPPT and baery sorage is suggesed for he grid conneced condiion. The resuls are verified wih he malab simulink sofware. KEYWORDS: disribued energy resources, maximum power poin racking, volage and frequency conrol, charging baery sae, acive and reacive power. I.INTRODUCTION Now a day he improvemen in power elecronics gives us he possibiliy o use he renewable energy sources in various configuraions. Using power elecronic devices he renewable sources can be added wih disribuion grid or inerconneced wih oher renewable (Solar Phoovolaic, Fuel cells, ec.) and non renewable generaors (Thermal, Nuclear ec.), sorage (Baery) sysems and loads in mirogrids. Micogrid [1] is a small grid. I is he inegraion of large number of disribuion generaors. Microgrids are combinaion of generaing unis and energy sorage unis locaed close o he load cenres. In a microgrid [2], a poin of common coupling (PCC) microresources and sorage devices are aached o medium level volage uiliies. In grid conneced mode microgrid work as a PQ bus. In islanded mode microgrid will be operae on is own, here is no scope of grid. Is own conrol volage and frequency of he microgrid, on ha condiion i will acs as PV bus. Disribuion resources like solar PV are capable of providing ancillary services in he form of reacive power hrough power elecronics inerface, in addiion o he acive power. Non acive power provided by DER can be used o operae he volage a weak elecrical buses in disribuion sysems. Capacior is insalled in disribuion sysem as a cos effecive approach for volage conrol. The conrol of volage and frequency [3], acive and non acive power from inverer based DER s o improve he sysem performance is a come ou area of research. Even so, here are no many research works performed on V-f or P- Q conrol using PV in addiion wih MPPT and baery sysem. The previous works in his opic eiher lack he implemenaion of an energy sorage componen of he volage conrol objecive along wih frequency conrol or he incorporaion of conrol ransiion in various sages. Complee hese gaps by aking all of hese objecives. Copyrigh o IJAREEIE DOI: /ijareeie

2 In pas decade solar PV microgrid is used for eiher grid conneced mode or islanded mode separaely. In his projec coordinaed he volage, frequency and acive, non acive power conrol. In his several conrol algorihm are implemened hrough which he solar capabiliy of PV generaors for volage and frequency (V-f) conrol and acive and non acive/reacive power (P-Q) conrol in islanded and grid conneced microgrid[9] could be harnessed. The locaions of conrollers are arranged as MPPT conrolling echnique is used a PV side, baery conrolling echnique and V-f or P-Q conrolling echnique used a inverer. These conrolling echniques a hree places are joinly linked wih he power equaing objecives a he DC as inpu of he inverer and AC as oupu of he inverer. The radiional synchronous generaor frequency conrol, droop conrol echniques [4], abc-dqo echnique are used for he volage and frequency algorihm, acive and non acive power conrol. The used conrol mehods are developed using he RMS/average values of volage and acive and reacive power. The remaining paper deals he rough explanaions of modelling of he solar cell and characerisics in nex secion. Afer ha nex secion describes he modelling of he conrol algorihms of MPPT, volage and frequency and acive and reacive power II.SOLAR PV MODELLING Solar cells are he building blocks of a PV array [5]. The commonly used solar PV cell model is single diode model. Solar cells are he building blocks of a PV array. Basically solar cell is a P-N diode. When sun ligh srikes solar cell i generae elecriciy. The circui diagram of solar PV cell is shown below fig: 2. i is one diode equivalen circui. In his circui I ph is he elecriciy generaed by P-N Juncion diode of solar cell from sun ligh i.e. curren source. R sh & R s are shun and series resisances of solar cell respecively. These cells are conneced in series and parallel o form module. The mahemaical represenaion equaions of solar cell are shown below. I ph I scr Ki T 298 / 1 (1) Reserve sauraion curren of module is I rs I scr / exp qvoc / N skat1 (2) G D R s R s Fig1. Equivalen circui of solar PV Maximum power (P MPP ) Table I Solar module specificaion 2W Volage a maximum power (V MPP ) 26.3V Curren a maximum power (I MPP ) 7.61A Open circui volage (V OC ) 32.9V Shor circui volage (I SC ) 8.21A Copyrigh o IJAREEIE DOI: /ijareeie

3 The sauraion curren I o is 3 T q Eg 1 1 I I rs exp Tr Bk Tr T The PV Module oupu curren is q V PV I PV Rs I PV N P I ph N p I exp 1 N s AkT Fig2. I-V&P-V characerisics of solar module (3) (4) Where B is irradiaion, T ref is Reference emperaure E go is Energy band gap (for Si =1.1ev), Ns is series conneced cells, N P is Parallel conneced cells, V OC is Open circui volage, I SC is shor circui curren, k is Bolzmann consan ( J/K), A is Idealiy facor, K i is he shor-circui curren co-eff is.17a per deg cenigrade, q is Charge of elecron ( C), Rs is series resisance, R sh is shun resisance. III.SYSTEM DESCIPION A. PV Sysem Configuraion: Fig3 presens he PV sysem arrangemen for V-f and P-Q echnique wih MPPT inclusive of baery backup. I is a wo-sage arrangemen where a DC-DC boos converer is used for MPPT conrol. The baery backup will mainain he sysem volage and frequency consan and also rying o supply he criical loads. A baery sysem is arranged in parallel o he PV a he inverer inpu o injec or o ake acive power hrough a bidirecional DC-DC converer. When he baery is absorbing power, he converer operaes in he buck mode and when baery is injecing power o he grid, i operaes in he boos mode.in beween he solar PV sysem and grid a coupling Inducor (L c ) is placed which is filer ou he ripple in he PV oupu currens. The node poin beween inducor and grid is known as he poin of common coupling (PCC). The node volage is denoed as v. The res is conneced wih he inducive load. The generaed PV power is conneced hrough he C dc o inverer. Here he capacior is acs as he reacive power generaor o he sysem. B. Baery Modelling: In his paper, he baery model is aken from he MATLAB simpower sysem library which will be used for he proposed V-f and P-Q conrols. Because of he flucaing and uncerain naure of solar power and more over he high varying load demands, lead acid baeries are used. These are he more efficacious ype of baeries sysem used in microgrid execuions. These baeries will give he maximum capaciy when uilized. So, in he modeling of sysem, a baery is aken as a lead acid baery wih suiable choice of parameers for deep cycle uilizaion. LA (Lead acid) baery can charge up o SOC of 8% and can be discharged up o SOC of 2%. The scienific modelled baery has wo equaions represening he baery discharge and charge model for a LA baery is given bellow V baey V baery Q V R i K i Exp Q i Q Q V R i K i K Exp i Q Q i.1 (5) (6) Copyrigh o IJAREEIE DOI: /ijareeie

4 Fig3 schemaic diagram of PV sysem Where V baery is he baery volage (V), V is he baery consan volage (V), K is polarizaion consan (V/Ah) or polarisaion resisance (Ω), Q is baery capaciy (Ah), R is he inernal resisance (Ω), i is baery curren (A), and i is filered curren (A). The capaciy of he baery is chosen as o provide a maximum backup power o recompense for he PV oupu if and only if a very small or no irradiance level. In he simulaion model he sysem is designed wih MPP of PV model a STC is 1 kw. From his, he baery capaciy is aken as o give his amoun of power a mos of 1 hour wih an energy conen of 1 kwh. The baery backup is considered for shor duraion operaions like conrol of frequency of sysem and criical loads power supplying in he posiion of emergency condiions. One hour of baery backup is aken as sufficien for oher backup sources o ake over he conrols in he microgrid emergency siuaions. IV.CONTROL METHODS A. MPP Tracking Mehod: As we know power conversion efficiency of solar module very low. To increase efficiency of solar module proper impedance maching requires increasing efficiency of solar module. Differen ypes of MPPT mehod are developed by researchers in recen years. Every mehod has is advanage and disadvanage. MPPT algorihms are varying due o simpliciy, efficiency, racking speed, sensor required and cos. I is seen ha he V-I characerisics of he solar module is nonlinear and exremely affeced by he solar irradiaion and emperaure. To maximize he oupu power of solar module, i has o be operaed a fixed value of load resisance. This requires a separae power converer circui for he MPPT. In his model design, a Boos ype DC DC converer is uilized o ake he maximum power from solar module. There are differen mehods are here o implemen MPPT algorihm hese are Perurb and observer mehod, Proporional inegral mehod and Incremenal conducance[6] mehod ec. Fig4. block diagram of MPPT and V-f and P-Q conrolling Incremenal conducance mehod: This mehod is based on he slope of he PV curve of solar PV Module. The slope of he curve is zero a MPP, Posiive a lef side and Negaive a righ side as given by Copyrigh o IJAREEIE DOI: /ijareeie

5 dp, A MPP dv dp, Lef Side of MP Sep (1) dv dp, Righ Side of MPP dv dp d(iv) di I V Sep (2) dv dv dv From (1) and (2), we ge di I, A MPP dv V di I, Lef of MPP Sep (3) dv V di I, Righ of MPP dv V By differeniaing insananeous conducance o he incremenal conducance he MPP can be racked as shown in following flowchar. In his mehod o sense he oupu volage and oupu curren uses he volage and curren sensors The duy cycle generaed in his MPPT algorihm is given o he DC o DC conroller swiches. The inducor and capacior values are L s =.91µH, C 1 =9mF, C 2 =.9F. This boos conroller will give maximum power from solar PV generaor o inver. Fig5. Flow char of MPPT INC mehod B. V-f conrolling mehod : This conrol mehod conains wo mehod conaining wo loops one loop for volage conrol and anoher loop for frequency conrol. From fig6 he down loop for volage conrol which has feedback PI conroller PI 2. In his loop PCC volage is couned and he rms value of v is compued. Then his value is differeniaed wih reference volage V which is given by grid and he difference given o he PI conroller. Then he oupu volage of inverer is in phase wih he PCC volage, and he magniude of he inverer oupu volage is jurisdicion wih respec o he reference volage. The mahemaical expression is given as bellow Copyrigh o IJAREEIE DOI: /ijareeie

6 V ( ) V ( ) K V ( ) V ( ) d v 1 v ( ) 1 K 2 2. (7) c P I Where K P2 and K I 2 are he conroller gain consans. In above equaion 1 has been added o he righ-hand side such ha when here is no injecion from he PV generaor, he PV oupu volage is exacly he same as he erminal volage. The frequency is conrolling by conrolling he acive power oupu a he inverer side which is shown in he firs loop. 6Hz is aken as he reference frequency for microgrid. I is checked wih measured value for error if any error exiss, i is given o he PI conroller PI 3. I provide phase shif angle 1. Then he volage waveform in ime scale is shifed. Here acive power is injeced o mainain he reference frequency. The equaions are given bellow. Fig7. Baery SOC conrolling schemaic diagram f f K f f d Fig6. V-f conrolling mehod schemaic diagram 1 K P3 ref measured I 3 ref (8) measurd 2 K P4 1.2 PAC PDC K I PAC PDC d (9) The phase shif conribuions respecively from DC and AC sides, 1 and 2 o obain he final phase shif, of he volage, v c1 which, hen, generaes he volage reference signal are hen averaged as given in bellow v for he inverer PWM. Measured AC power is muliplied wih he facor 1.2 due o he acive DC power is 12% of AC acive power. Here inverer is having 98%. The DC acive power is compared wih he AC acive power. The resulan signal is given o he PI 4 conroller. The equaion for his conroller is given bellow. / (1) The average of hese wo phase shif signals are given o he PWM pulse generaor. This is coupled wih volage conrol loop. To conrol he DC side volage based on AC side volage. To suppor frequency conrol and supply or absorb acive power, baery wih power conrol sysem is incorporaed wih PV sysem. Wheher here is excess solar power and for frequency conrol required acive power is less han PV MPP, charging of baery will sar. If here is required amoun of solar power solar power availabiliy is less and also for he frequency conrol he acive power requiremen is more han PV MPP, hen he defici power will supplied by he baery o sysem. Copyrigh o IJAREEIE DOI: /ijareeie c

7 TABLE II V-f Conrol gain parameers Volage conrol loop K p2.41 K i2.5 Frequency conrol K p K i P DC loop K p K i Baery loop K p K i mainain sysem frequency 6Hz. These conrol mechanism is shown in figure7. C. P-Q Conrolling Mehod: The inverer side P-Q conrol is similar o ha of V-f conrol. This conrol loop is oal works on he associaion of acive and non acive power [7] a PCC wih inverer. The oupu phase and volage magniude equaions are given blow and corresponding conrol loop fig shown above. Based on figures down loop he measured reacive power injecion a PCC is subraced wih he menioned reacive load and he resulan signal is passed o he PI conroller, PI 2. Then, he oupu obained is muliplied wih he erminal volage v o obain he reference volage v c1 which is in phase wih v. The conrol loop 3 in Fig8 handles acive power conrol hrough he conroller, PI 3 o generae he phase shif conribuion α 1 and a he same ime insure he acive power balance beween AC and DC sides hrough he conroller, PI 4. The equaions for P-Q conrol are given below. (11) v K Q Q K Q Q d. v c p ref acual I ref acyal α K P P K P P d. 1 P3 ref acual I3 ref acual α K 12. P P K. P P P ACmeasu DC I ACmeasu DC Fig8. P-Q conrolling mehod schemaic diagram (12) d. α α α / (14) Equaion (1) denoes he reacive power conrol loop. (11) Denoes he acive power conrol loop, and (12) denoes he acive power balance beween he inpu DC side and oupu AC side of he inverer. Equaion (13) averages he phase shif conribuion obained from he acive power conrol a he AC and DC sides such ha he acive power conrol a AC side and power balance objecive are aken ino accoun. The baery conrol algorihm is same as above secion. (13) Copyrigh o IJAREEIE DOI: /ijareeie

8 TABLE III P-Q CONTROL GAIN PARAMETERS Volage conrol loop Frequency conrol P DC conrol loop Baery conrol loop K p K i K p K i K p K i K p K i V. SIMULATION RESULTS Figure9. Shows he resuls a he islanding mode of operaions and a his condiion microgrid only supply he power o load. Figure1. Shows he resuls a grid conneced mode. A his condiion sysem acive and non acive power conrolling are given (a) (b) (c) (d) Fig9. V-f Conrolling graphs. (a) Inverer inpu power, (b) inverer oupu power, (c) frequency of he sysem, (d) PV generaor oupu volage. Copyrigh o IJAREEIE DOI: /ijareeie

9 (a) (b) (c) (d) (e) Fig1. P-Q Conrolling graphs. (a) acive and reacive power wih references, (b) generaed DC volage, (c) acive and reacive power of gride, (d) per uni PCC volage, (e) grid frequency. VI.CONCLUSION This paper presens various conrolling mehods for microgrid wih baery sorage sysem. In he conrolling mehod MPPT conrolling is used a PV side, V-f/P-Q, baery conrol algorihm a inverer side. PV generaor gives maximum power hrough MPPT conrol. Smoohened power will be given as inpu o he inverer. The menioned conrol sraegy gives a fla ransform from P-Q conrol in grid mode which is operaed in grid conneced condiion o V-f conrolling mode in islanded condiion. Comparing o radiional mehods hese mehods gives very accepable performance. This paper gives in showing he conrol sraegy wih efficacious coordinaion beween inverer V-f/P-Q conrol, and energy sorage. Copyrigh o IJAREEIE DOI: /ijareeie

10 REFERENCES [1] R.H.Lasseer Microgrid: A Concepual soluion IN PROC 35 TH IEEE PESC CONFERENCE, AACHEN, GERMANY. JUNE [2] S. Papahanassiou. D.Georgakis. N. Haziagyrious, A. Engler and Ch. Hard, Operaion of prooype Microgrid sysem based on micro resources equipped wih fas acing power elecronic inerfaces, IN PROC 35 TH IEEE PESC CONFERENCE, AACHEN, GERMANY. JUNE [3] H. Laaksonen, P. Saari, and R. Komulainen, Volage and frequency conrol of inverer based weak LV nework microgrid, presened a he In. Conf. Fuure Power Sys., Amserdam, The Neherlands, Nov.18, 25. [4] J. C. Vasquez, R. A. Masromauro, J. M. Guerrero, and M. Liserre, Volage suppor provided by a droop-conrolled mulifuncional inverer, IEEE Trans. Ind. Elecron., vol. 56, pp , 29. [5] Pandiarajan.N and Dr. Ranganah Muhu (211) "Developmen of Power Elecronic Circui Oriened Model of Phoovolaic Module", Inernaional Journal of Advanced Engineering Technology, E-ISSN Vol.II1 Issue IV.olume 3 ISSN [6] Saravana selava. D Modeling and simulaion of Incremenal Conducance MPPT Algorihm for Phoo Volaic Applicaion. In proc IJSET213 volume 2, issue No.7 pp: July 213. [7] Y.Xu, H.Li, D.T.Rizy, F.Li,and J.D.Kueck, Insananeous acive and nonacive power conrol of disribued energy resources wih a curren limier, in Proc. IEEE Energy Conversion Congr. Expo., 21, pp [8] Sanam Singh, A.N. Tiwari, Volage and Frequency conroller for self exied inducion generaor in micro hydro power plan, in proc. IJARECE volume 2,Issue 2,February 213. ISSN: X. [9] M.G.Molina and P.E.Mercado, Modeling and conrol of grid-conneced phoovolaic energy conversion sysem used as a dispersed generaor, in Proc. 28 IEEE/PES Transm. Disrib. Conf. Expo.: Lain America, pp BIOGRAPHY T.JAGADEESH, Received his B.Tech degree from ASCET, Gudur and currenly pursuing M.Tech degree from JNTUA College of Engineering Pulivendula. His doing specializaion on Elecrical Power Sysem.. Dr.V.GANESH, Professor, Deparmen of Elecrical and Elecronics Engineering, JNTUA College of Engineering Pulivendula, His area of ineress are elecrical disribuion sysems, applicaion of arificial inelligence o elecrical engineering, FACTS and renewable energy sysems. He is a reviewer of many journals on power and energy sysems. Presenly he is guiding 6 Ph.D scholars. Copyrigh o IJAREEIE DOI: /ijareeie