Dynamic Performance of a Small RatingPhotovoltaic (PV) Module

L. Navinkumar Rao I

1 Dept. of Electrical Engg., 1. T.s. Engg colleg, Greater Noida, 201306, U'P; INDIA

email id: navinkamal@rediffmail.com

Abstract--In photovoltaic power system, both photovoltaicmodule and switch-mode converters show non-linear and time-invariant characteristics, which is very difficult control. In thispaper a smaU SOW photovoltaic module BP-3S0 is studied. Theoperating principle is studied and modeling of non-linearequations is done and unknown parameters like series and shuntresistance are calculated. The performance analysis of this SOWphotovoltaic module is presented and simulation results areobtained. The characteristics are plotted by varying at differentinsolation conditions from 100 % to 20 %.Index terms- Photovoltaic (PV), Maximum power point (MPP),Standard test condition (STC)

1. INTRODUCTION

Photovoltaic (PY) generation is gaining increased importanceas a renewable source due to its advantages like absence offuel cost, little maintenance, no noise and wear due to absenceof moving parts, etc. Since the PV generator exhibits anonlinear V-I characteristic, its maximum power (MP) pointvaries with the solar insolation and temperature. At aparticular solar insolation, there is a unique operating point ofthe PV generator at which its power output power is maximum.Therefore, for maximum utilization efficiency, it is necessaryto match PV generator to the load such that the equilibriumoperating point coincides with the MP Point of PV source.This matching of load to PV source is possible by using anintermediate de-de converter, which continuously adjusts thevoltage, current levels and moves the operating point. In orderto understand this tracking mechanism using different de-deconverters it is essential to have exhaustive simulation studiesbefore being the total system experimentally implemented.

Photovoltaic(PY) cell converts part of the solar energy into electricalenergy.The remaining part is converted into heat. This heat inverselyaffects the efficiency of the solar cell. The output power of a PVmodule is product of panel voltage and current. In this paper, anexperiment was conducted to quantify the consequence ofshading in photovoitaic power systems. Fig. 1 showsphoto voltaic BP-350 module, which was installed on theframe in the direction and at the some angle on a roof,allowing them to be tested at the time and under someconditions. Each BP-350 module is comprised of 72photovoltaic cells, as described in [10].

vo

Fig.l Equivalent circuit of the PV cell representing the model parameters.

VI I Characterstics of 50W PV Pannel3.5,.--------~---~---~---~

3_--1 .-1

2.5

,--1-----,2 -

Current

1.5

0.51

o~-------~~--~~--~~~-~a 5 10 15 20 25

Voltage

Fig. 2 Characteristics ofBP 350 solar module at insolation 1000W/m' at 25°C

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Power Vs Voltaqe Charaetersties60,-------~--~---=---~,~--~-------,

I,,

~ -----T------------rI

I

40

Power(W) 30

,

I- - - - - T - - - - - -, - - - - - - r - - - - - - - - - -

,

I, I

____ , L _

I ,,,, ,

-----r-----i-, ,

I

I

20

5 10 15Voltage (V)

25

Fig.3 Characteristics ofBP 3S0 solar module at insolation 1000W/m2 at 2SoC

II. MODELING OF PHOTO VOLTAIC CELL

The electrical power output delivered by a photovoltaic paneldepends on the incident solar radiation, cell temperature, solarincidence angle and load resistance. Manufacturers typicallyprovide only few operational data for photovoltaic panels,such as the open circuit voltage (Voc), the short circuit current(Ise), the maximum power point voltage (Vmpp) and current(lmpp), the temperature drift coefficients at open circuit voltageand short circuit current

V+:RS V +IR<I-T.i.-l~«(j-t:--1)- . -

. Rsn(1)

}Vs; yKTa= (2)

q

The electron charge q and the Boltzmann's constant k areknown values, :v is the usual photovoltaic single cell idealfactor (which value varies within 1-2), Ns is the number ofcells in series and T is the PV panel temperature. The fiveparameters appearing in Eq. (1) corresponding to operation atStandard test condition (STC), are designated: a, IL' 10, Rs, andRSH' In general, these five parameters are functions of the solarradiation incident on the module and the module temperature.Reference values of these parameters are determined for aspecified working condition, such as STC. To evaluate thesefive parameters in Eq. (1), a system of five independentequations is needed. Three current-voltage relations arenormally available from the manufacturer at STC: the shortcircuit current, the open circuit voltage and the current andvoltage at the maximum power point, Eqns ..(3) - (5). Fourthequation results from recognizing that the derivative of thepower at the maximum power point should be zero.

For short circuit:

(3)

For open circuit:

1 = a and V = Vor

!h \~ca = i1 =l» (11 a-i) --"RSli

(4)

At maximum power point A PV cell should be operated at aspecific on its I-V curves to maximize its efficiency over changingconditions. Cell output power at any point is given by P equal to VxI,and by taking the derivative with respect to cell voltage, a usefulrelationship is derived.

I = 111;00 and l = I~;~p

(5)

The derivative of output power with respect to module outputvoltage at maximum power point is zero

IdCVI)1dV I'll?? Id1llrt~p? + Vm?? .-. = 0

·dV i";P?(6)

TABLE I Table showing BP-350 module specifications

Sr o. Typical Electrical Characteristics BP-350

1 Maximum power point (PIM,) SOW

2 Voltage at P1M' (Vmp) 17.3 V

3 Current at Pm" (Imp) 2.89 A

4 Short circuit current I" 3.17 A

S Open circuit voltage Voc 21.8 V

III CALCULA nON OF UNKNOWN PARAMETERS

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h------C2lJ.Ooj

L-------to( ,V_~Dde1

Fig. 4 Schematic diagram for simulation of control mechanism of MPPT

The unknown parameters can be calculated by solvingequations 3-6 for different conditions given in table 1. The firstapproximation is that it is assumed that the short circuitcurrent (Isc) is equal to the generated light current (Id. Theequation that relates the short circuit current and open circuitvoltage becomes

~p.-_ r.1

r =f l'e~-lJ"-~s: ~c \ Rsr.

Assume that the ratio between Voc and RSH is negligiblebecause of RSH is typically several kilo-ohms; the diodesaturation current determines the open-circuit voltage (Voc) ofPV module.

(7)

(8)

IV. SIMULATION OF BP-350 PHOTO-VOLTAICMODULE

~---- ~D

D~t...==.J

V-4 et...r.I:ff'K1C.5 d SoI.at rnoOMs-aN~bN~~

'-'

Fig. 5 Schematic diagram for simulation of photo-voltaic cell

Using MATLAB simulink software along with its SIMULINKand SIMPOWERSYSTEM toolboxes, this PV Cell issimulated. FigA shows the Schematic diagram for simulationof control mechanism to track maximum power point (MPP)at different insolation conditions. The control strategy shouldbe applied to operate the cell at MPP. Since PV-cellcharacteristics are non-linear it is difficult to track MPP. Fig.5 shows the schematic diagram for simulation of BP-350photovoitaic module

V-I Characteristics3.5 - - - - - - - - - - -

100%I

3~ -_-_-_- __-_-_--r ~2.5~----"""-------------~

~ 2 ~-~-~-~-~~- ~ __co1!<3 1.5 --------------~---

1-

0.5

°0L.---~5---1-'-0- -~15---l.UlL---:25

Voltage V(0

Fig.6 Simulated V-I curves ofBP-350 under varying 20% to 100%insolation condition at 25°C.

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Power vs Voltage

100%

35r -

~ 30fc,

~ 25Loo,_ _ J

15r

10~ -

0--=-----o 10 15Voltage V(0

20 25

Fig.7 Simulated Power and voltage relationship curves under varying 20% to100% insolation condition at 25°C

V. RESULTS AND DISCUSSION

Fig. 6 has shown the V-I characteristics ofBP-350 module. Itshows non-linear behaviour of PV cell. Initially current isconstant and equal to light generated current, with decrease inload current decreases and becomes zero at open circuitcondition. Using simulation MPP is calculated for a particularcurrent and voltage condition. Table I shows the specificationof BP-350 solar module at a standard test condition of atemperature 25°C. Fig.7 shows simulated power and voltagerelationship curves under different insolation condition atconstant temperature of 25°C.

VI. CONCLUSIONSThis paper has discussed the modeling of photovoltaic cell inwhich analysis and modeling is done to discover thecharacteristics of a small rhotovoltaic module BP-350 atstandard test condition of 25 C. It has also presented the MPPtracking at a particular value of voltage and current.

REFRENCES

[I) S. Gerbex, R. Cherkaoui, and A. J. Germond, "Optimal location ofmulti type FACTS devices in a power system by means of geneticalgorithms," IEEE Trans. Power Systems, vol. 16, pp. 537-544, August.2001.

[2) E. Koutroulis, K. Kalaitzakis, and N. C. Voulgaris, "Development ofamicrocontroller-based, photovoltaic maximum power point trackingcontrol system," IEEE Trans. Power Electron., vol. 16, no. I, pp. 46-54,Jan. 2001.

[3) N. Femia, G. Petrone, G. Spagnuolo, and M. Vitelli, "Optimization ofperturb and observe maximum power point tracking method," IEEETrans. Power Electron., vol, 20, no. 4, pp. 963-973, Jul. 2005.

[4) M. A. S. Masoum, H. Dehbonei, and E. F. Fuchs, 'Theoretical andexperimental analyses of photovoltaic systems with voltageandcurrent-based maximum power-point tracking," IEEE Trans. EnergyConversion, vol. 17, no. 4, pp. 514-522, Dec. 2002.

[5) G. C. Goodwin, S. F. Graebe, and M. E. Salgado, Control SystemDesign. Upper Saddle River, NJ: Prentice-Hall, 2001.

[6) W. Xiao, W. G. Dunford, and A. Capel, "A novel modeling methodfor photovoltaic cells," in Proc. IEEE 35th Annual Power Electron.Spec. Conf., Aachen, Germany, Jun. 2004, pp. 1950-1956.

(7) R. D. Middlebrook, "Small-signal modeling of pulse-width modulatedswitched-mode power converters," Proc. IEEE, vol. 76, no. 4, pp. 343-354, Apr. 1988.

[8) K. J. Astr6m, "Model uncertainty and robust control," in LectureNotes on Iterative Identification and Control Design. Lund, Sweden:Lund Inst. Of Technol., Jan. 2000, pp. 63-100.

[9) I. Zverev, "Switching frequency related trade off's in a hard switchingCCM PFC boost convert," in Proc. 18th Annu. IEEE Appl. PowerElectron. Con! and Expo., Miami, FL, 2003, vol, 2, pp. 671-676.

[10) 50 Watt Photovoltaic Module-BP350. (2003, Aug.). [Online).Availab Ie:http://www.rfindustries.com.auirfiproducts/solarfBP350U _v2.pdf

L Navinkumar Rao received the BE and M-Tech. degree in engineering from VNIT,Nagpur, India, in 1999 and 2002, respectively.He is currently working toward the Ph.D.degree from GB Technical University. Hisareas of interests are de-de converters andrenewable energy.

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