7/29/2019 Ariel Poster

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Stand Alone Photovoltaic System ModellingMSc in New and Renewable Energy

ntroductiontand-alone PV systems are non-gridonnected photovoltaic systems. They are

ormally used in remote or isolated placeswhere the electric supply from the power-rid is unavailable or not available at aeasonable cost.he scope of this project is to develop a

model of a simple stand-alone PV systemnd to compare the results obtained withrevious work, in order to validate theesults obtained, taking into accountossible inaccuracies.or doing this, the model was developed in

MATLAB/SIMULINK, containing the PVmodule, two batteries in parallel, the chargeontroller, and a constant DC resistor load.

The Systemhe simulations are set to run for data fromouthampton in the United Kingdom, during

he month of December of 2002, and forhe day December 3th of 2002.The PV moduleThe batteriesThe charge controllerThe constant load

he accumulator of the stand-alone systemonsists in tow parallel lead-acid batteries.

Electricalcharacteristics SHARP NT9075

Short-circuit current 3.5 A

Open-circuit voltage 21.8 V

Maximum power 51.5 W

able 1. Values from Sharp NT9075 PVmodule datasheet

Where: closed switch = 1 (true); openwitch = 0 (false); A is the previous state ofwitch A; V is the battery voltage.

Condition A' A

V 14.4 0 0

V 14.4 1 0

12.9 < V < 14.4 0 0

12.9 < V < 14.4 1 1

V 12.9 0 1

V 12.9 1 1

able 2. Truth table for the switch in chargegulation to disconnect or reconnect theV module with the batteries

Figure 1. Schematic representationof the stand-alone PV system

igure 2. Irradiance and ambientemperature, December 2002

The MATLAB/SIMULINKmodelThe stand-alone PV system was developed inMATLAB/SIMULINK to represent its differentcomponents:The components were represented assubsystems and with blocks with embeddedMATLAB functions in the diagram modelled inSIMULINK (figure 6).

Figure 6. Stand-alone PV system structure in SIMULINK

Simulation results

Figure 3. PV current: experimental and simulateddata. December 3 2002

Figure 4. Battery voltage: experimental andsimulated data. December 3 2002

Figure 5. State of charge of the batteries:experimental and simulated data. December 3 2002

Figure 7. Battery voltage: experimental andsimulated data. December 2002

Figure 8. State of charge: experimental andsimulated data. December 2002

The big risings in the voltage that can be seen in thefigure 4, may be due to the current at this point is

positive, meaning that the batteries are in charge mode,and dropping again when the batteries are in dischargemode, to finally achieve an almost constant value ofvoltage.

The decreasing of the SOCof the battery in the figure 5is because there is no current flowing from the PVgenerator to the batteries, so the latter ones are indischarge mode as they are delivering current to theconstant load connected to the stand-alone PV system.

The model developed underestimates the values of thebattery voltage (figure 7), but can be seen that the trendfor the peaks goes with the peaks shown for the curve ofthe real battery voltage values.The discrepancies in figure 8 are due to: battery modelconsidered does not work very well for SOCvalues over0.7-0.8, because overcharge is not considered; themodel considers that the cell of the battery has a higherinternal resistance compared to the resistance that thereal battery has .

CONCLUSIONS The model did not show the effect of the chargecontroller as the values of the battery voltage did notreach the threshold values for disconnecting thebattery with the PV module. The model developed has problems about somemagnitudes, overestimating values of currents andunderestimating values of voltages. The discrepancies are due to the realistic ambientconditions are not all considered in the model, so aretheir specific parameters of the PV generators; thedifference between the measured temperature of thecell, as it is more likely to have it as an approximation;there might be uncertainties in the measurements ofthe experimental data. The model of the battery showed uncertainties for

the values of the voltage in the battery, though therewas a good fit between experimental and simulatedvalues for the state of charge. The discrepancies in the modelling of the batteryare found for the hours with sunlight. Reasons wieldedfor this are the discrepancies that might be consideringthe internal resistance of the battery, and the possibleeffect of temperature on the voltage value of theovercharge state.

Author: Ariel Villaln M.Supervisor: K. Fragaki

ReferencesLorenzo, E., Arajo, G., Cuevas, A., Egido, M.A., Miano, J.C., Zilles,R.Solar Electricity: Engineering of Photovoltaic Systems. [trans.] PhilipDavies. First English Edition. Sevilla : Institute of Solar Energy -

Polytechnic University of Madrid, 1994. p. 316. ISBN: 84-86505-55-0.

Castaer, L., Silvestre, S. Modelling Photovoltaic Systems UsingPSpice. s.l. : John Wiley and Sons Ltd., 2002. p. 358.

Oi, A. Design and Simulation of Photovoltaic Water Pumping System.

San Luis Obispo : s.n., 2005. p. 113. California Polytechnic StateUniversity.

Modelado y anlisis de sistemas fotovoltaicos. Guasch, D. Barcelona :Universitat Politcnica de Catalunya, 2003, p. 224. Tesis Doctoral.

Hansen, A.D., Srensen, P., Hansen, L.H., Bindner, H.Models for aStand-Alone PV System. Ris National Laboratory. Roskilde : s.n., 2000.

p. 78.

Dynamic battery model for photovoltaic applications. Guasch, D.Silvestre, S. 3, s.l. : John Wiley & Sons, Ltd., 30 January 2003, Progressin photovoltaics: research and applications, Vol. 11, pp. 193-206.A general battery model for PV system simulation. Copetti, J.B.,Lorenzo, E., Chenlo, F. s.l. : Wiley, 1993, Progress in Photovoltaics:research and applications, Vol. 1, pp. 283-292.