Online Photovoltaic Curve Tracer Using SEPIC DC-DC Converter

International Journal of Pure and Applied MathematicsVolume 118 No. 24 2018ISSN: 1314-3395 (on-line version)url: http://www.acadpubl.eu/hub/Special Issuehttp://www.acadpubl.eu/hub/Online Photovoltaic Curve Tracer usingSEPIC DC-DC Converter*R. Ramaprabha1 , L. Deepak2 ,R. R. Hari Prasath3 , S. Dhilip4Associate Professor1 and UG Students2,3,4Department of Electrical and Electronics Engineering,SSN College of Engineering, Kalavakkam 603110, Indiaramaprabhar@ssn.edu.in1 ; deepaklouis1998@gmail.com2 ;hari97rr@gmail.com3 ; dhilipsekar1998@gmail.com4*Corresponding authorMay 10, 2018AbstractThe knowledge of real characteristic curves of a PV panel/arrayenables the user to know their actual production and, bycomparing the curves over time, to assess their degree ofdegradation by weathering. In this paper, a photovoltaic VI characteristic curve tracer which operates autonomously,with no need to be disconnected from its load is presented.This tracer uses single-ended primary inductance converter(SEPIC). This curve tracer is a simple, cost effective andcompact for online monitoring system. The effective sketching of the tracer is proved for normal and partial shadedcondition operating conditions of PV through MatLab simulations.Index Terms:PV array; SEPIC; Online curve tracer;MatLab.1

International Journal of Pure and Applied Mathematics1INTRODUCTIONDue to the dramatic growth in population and needs, the usage offossil fuels becomes limited due to their depletion. Nowadays, theseenergy sources are becoming too expensive and too environmentallydamaging to retrieve. Hence, the conventional energy seemed to bea better alternative and in no time, will definitely become the basicnecessity. Of the various renewable sources available, solar energyholds the greater potential to meet the raising demand, which canbe realized through a photovoltaic module or panel that generallyconverts light energy into electrical energy [1]-[3]. It is mandatoryto determine the PV panel/array efficiency, robustness, and deterioration. The proper continuous monitoring system is required toknow the real power production and forecast. The curve tracers arevery popular for accomplishing this job [4]-[5].The current-voltage curve postulates a level of perception intothese attributes unsurpassed by many supervising efforts [6]-[7].However, the current approach of curve tracing prevails in an abominable form (i.e.) the module has to be removed from the load andassociated to a device for the sole purpose of curve tracing. Thisis troublesome for the reason that a qualified mentor is required tooperate. Furthermore, consuming more time to detach and attachthe panels.In this paper, a curve tracer which functions individually andprovides a highly efficient and effective test and diagnostic solution for PV systems while eliminating the possibility of detachingthe panel from the load is presented. The tracer is achieved usingSEPIC (Single Ended Primary Inductance Converter). It is a DCDC converter, which receives its input (DC) from the PV moduleand administers the output voltage [8]. The block diagram of thesystem is shown in Fig. 1. The main components include PV array,SEPIC and inverter which may be connected to AC load or grid. Toprove the technology, the proper PV panel/array model is required.In Chapter II, the modelling of PV panel is discussed. Chapter IIIdiscusses the design of SEPIC converter components and ChapterIV presents the integration and simulation results.2Special Issue

International Journal of Pure and Applied MathematicsSpecial IssueFig. 1. Block diagram of the proposed systemChapter V concludes with major inferences observed throughsimulation studies.2MODELLING OF PHOTOVOLTAICARRAY UNDER NORMAL AND PARTIAL SHADED CONDITIONSThe electrical equivalent of the PV panel is shown in Fig. 2. Thismodel is well developed in literature and capable of well representing the PV panel/array characteristics [8]-[10].Fig. 2. Electrical circuit representing PV panelThe following equations are used for the mathematical modeling ofPV panel [9]. The output current from PV panel is given asIpv Iph ID Ish(1)Photon generated current of the PV panel, Iph is given asIph {Ki (T Tn ) Ipvn }GGn(2)The current through the diode is calculated asID Ir {exp (Vpv Ipv Rse )Vta 1 }3(3)

International Journal of Pure and Applied MathematicsandIr Ki (T Tn ) Iscnexp[(Vpv Ipv Rse )Vta 1]Special Issue(4)In this paper, 2 series connected panels are taken for the purpose oftracing normal and partial shaded conditions [11]. Table 1 enliststhe specification of the PV system used here.TABLE 1 PV ARRAY SPECIFICATIONSThe MatLab model of 21 PV array is shown in Fig.3.Fig. 3. MatLab sub system to represent PV modelThe electrical power generated by a PV panel is a function of voltage and current characteristics. The association between currentand voltage is measured while changing the load linked to the PVmodule from open circuit to short circuit produces characteristicscurves as shown in Fig. 4.4

International Journal of Pure and Applied MathematicsFig. 4. Characteristics of a PV panelThe key points in the characteristic curves are short circuit current(Isc ), open circuit voltage(Voc ), maximum power point (Pmpp ) andassociated maximum power point voltage (Vmpp ) and current (Impp ).The power curve is obtained by multiplying voltage and current.Under partial shaded conditions, the V-I curve with multiple stepsand V-P curve with multiple peaks are observed. This is discussedin detail in Chapter IV. The modeled PV array is interfaced toinverter and load via the SEPIC curve tracer.3DESIGN AND SIMULATION OF SEPICDC-DC CONVERTERSIMULATIONRESULTSThe curve tracing is affiliated with high cost owing to the manualfacet of presently available I-V curve tracers. Therefore, it must becommercially feasible. A curve tracer is fixed between a PV module and the inverter as shown in Fig. 1. It is provided with SEPICwhich is integrated to the PV module so that it tracks the characteristic continuously. During normal process, the curve tracermay not be included in the PV system. At periodic intervals andduring occurrences of fair conditions, the curve tracer will becomea mandatory part of the circuit. The DC-DC converter (SEPIC)in the curve tracer sweeps the voltage on the panel side from opencircuit voltage to short circuit current; At the same time maintaining the voltage on the side of inverter constant, This means thecurve tracer requires no external load when included as part of thecircuit.5Special Issue

International Journal of Pure and Applied MathematicsThe circuit for SEPIC is shown in Fig. 5. The design of components is based on the equations presented in [12]-[14].Fig. 5. SEPIC based tracerThe working of SEPIC is tested with DC input of 16 V (equal tothe Vmpp of the panel) with closed loop in regulatory mode [15].For observing buck and boost operation a step reference is given.Till 0.5s, boost operation occurs as the reference is set greater thaninput voltage; After that, as reference is set lower than the inputvoltage, buck operation occurs. The waveforms are shown in Fig.6.It is observed from Fig. 6 that the designed SEPIC works wellas regulator. This ensures the design components of SEPIC.Fig. 6. Simulated SEPIC regulator waveforms6Special Issue

International Journal of Pure and Applied Mathematics4INTEGRATION AND SIMULATIONOF CURVE TRACERThe system shown in Fig. 1 is simulated with resistive load. Parameters are decided based on the equations present in [6]. Table2 listed the parameters used in simulation studies.Fig. 7. MatLab integration of SEPIC curve tracer with PV arrayTABLE 2 SIMULATION PARAMETERS USED IN V-ITRACERThe V-I curves produced by the SEPIC based curve tracer undernormal and partial shaded conditions are presented in vide Fig. 8to Fig. 13. Fig. 8 and Fig. 9 shows the time domain observation ofthe voltage and current under normal & partial shaded conditions.The voltage and current are fed to X-Y scope to observe the V-Icurves (Fig. 10 and Fig. 12) respectively. For partial shading 1panel is kept at low insolation (G 600 W/m2 ). Fig. 11 and Fig.13 are obtained from the Figs. 10 & 12 by multiplying voltage andcurrent.7Special Issue

International Journal of Pure and Applied MathematicsFig. 8. V-I curve in time domain under normal operatingconditionFig. 9. V-I curve in time domain under partial shaded condition8Special Issue

International Journal of Pure and Applied MathematicsFig. 10. Traced V-I curve under normal operating conditionFig. 11. Computed V-P curve under normal operating conditionFig. 12. Traced V-I curve under partial shaded conditionFig. 13. Traced V-P curve under partial shaded condition9Special Issue

International Journal of Pure and Applied MathematicsIt is inferred from the above figures, SEPIC is capable of acting asa quick V-I tracer and capable in tracing the key points mentionedin Fig. 4.5CONCLUSIONIn this paper, SEPIC based V-I tracer is presented. The followingpoints are derived from the simulation studies. This method of tracing allows changing the sweep speed anddirection. By suitably changing the duty cycle of the converter, specificzones of the characteristic curve can be partially examined. The system can be expanded just connecting other convertersin parallel depending on the requirement. High fidelity is achieved even for high speed sweeping. A fast response of operation is particularly interesting becauseit ensures that all points in the curve are obtained with thesame climatic conditions. It provides the opportunity for a quick first test of the module.Observing the above points and comparison presented in [16],it can be concluded that the SEPIC based curve tracer has moreadvantages which include flexibility, modularity, fidelity, fast response and direct display. The cost is also reasonable comparedwith available curve tracers.References[1] B. Hodge, Alternative Energy Systems and Applications, Wiley, Hoboken, NJ (2010)[2] Photovoltaic systems technology, University Kassel, Kassel,Germany, 2003.10Special Issue

International Journal of Pure and Applied Mathematics[3] REN21. Renewables 2016 Global Status Report; REN21 Secretariat: Paris, France, 2016.[4] P. Hernday, Field Applications for I-V Curve Tracers, (Online). ProField applications of I-V-Curve-Tracers-Hernday.pdf.[5] Guide to Interpreting I-V Curve Measurements of PV Arrays(Online). Available: http:// resources.solmetric.com/ get/Guide% 20to% 20 Interpreting% 20I-V % 20Curves.pdf Solmetric, Application Note PVA-600-1, 1 March 2011.[6] C.W. Riley and L.M. Tolbert, An online autonomousIV tracer for PV monitoring applications, in IEEEPower & Energy Society General Meeting, 2015. DOI:10.1109/PESGM.2015.7286146[7] Willoughby A.A, Omotosho T.V, Aizebeokhai A.P, A simple resistive load I-V curve tracer for monitoring photovoltaicmodule characteristics, in the proceeding of 2014 IEEE IREC(5th International Renewable Energy Congress), pp. 1 6, Hammamet, 25-27 March 2014.[8] Natarajan Pandiarajan, Ramabadran Ramaprabha, andRanganathMuthu, Application of CircuitModel for Photovoltaic Energy Conversion System, International Journal ofPhoto energy, Volume 2012, Article ID 410401, 14 pages,doi:10.1155/2012/410401.[9] Marcelo Gradella Villalva, Jonas Rafael Gazoli, and ErnestoRuppert Filho, Comprehensive Approach to Modeling andSimulation of Photovoltaic Arrays, IEEE Transactions onPower Electronics, vol. 24, no. 5, 2009, pp.1198-1208.[10] M. Edouard and D. Njomo, Mathematical Modeling and Digital Simulation of PV Solar Panel using MATLAB Software,vol. 3, no. 9, pp. 2432, 2013.[11] R.Ramaprabha and Dr.B.L.Mathur,Modelling and Simulationof Solar PV array Under Partial Shaded condition s,Proc. ofIEEE Int. Conf. on Sustainable Energy Technologies, pp. 1216, Singapore, Nov 24-27, 2008.11Special Issue