15-05-2013, 04:49 PM
Modeling and Simulation of the Photovoltaic Components of a Solar Power System for quick evaluation
Modeling and Simulation.pdf (Size: 1.09 MB / Downloads: 102)
INTRODUCTION
The performance of the PV Generator is critical aspect of the Solar PV System. There is need
for validating Photovoltaic Modules based on the datasheet parameters. This is essential for
preliminary assessment of the PV Modules. Since the solar insolation levels are constantly
changing, real time outdoor performance measurement is very difficult. All the commercially
available Solar Module Testers will be expensive and may have options for creating different
insolation conditions for testing of parameters. But if there was a software for basic performance
evaluation, the performance and efficiency of solar modules could be validated and verified with
the manufacturer’s data sheets and characteristic curves. This is extremely important because
of the importance of the PV components in Solar Photovoltaic Systems. Thus a software tool for
the preliminary evaluation of the PV Modules becomes necessary. If the module can be
modelled, different series and parallel combinations can also be modelled to get the
performance of different Solar Array combinations. This combined with the simulation tools for
the whole Photovoltaic System (On-Grid or Off-Grid) will allow the possibility of quickly
evaluating the system performance.
MATHEMATICAL MODELS FROM EQUIVALENT CIRCUITS
Simple PV Cell Model
The simplest equivalent circuit of a solar cell is a current source in parallel with a diode.
The output of the current source is directly proportional to the light falling on the cell
(photocurrent, Iph). During darkness, the solar cell is not an active device; it works as a diode,
i.e. a p-n junction. It produces neither a current nor a voltage. However, if it is connected to an
external supply (large voltage) it generates a current called diode current or dark current. The
diode determines the I-V characteristics of the cell. Thus a simple PV cell is essentially an ideal
current source in parallel with an ideal diode. The current source represents the current
generated by the PV cell due to the photons received by it, and is constant under constant
irradiance and temperature. The two key parameters most often used to characterize a PV cell
are it short-circuit current and its open-circuit voltage. These values are generally provided on
the manufacturer’s data sheet.
More Accurate PV Cell Model
The simple PV cell model neglects a few parameters. In order to create a more
accurate model, series resistance, parallel resistance, and recombination must be factored into
the equation. Series resistance accounts for any resistance in the current path through the
semiconductor material, the metal grid, contacts, and current collecting bus. The value of the
series resistance is multiplied by the number of series-connected cells. Parallel resistance (or
shunt resistance) is a loss associated with a slight leakage current through a parallel resistive
path to the device. It is not as noticeable as series resistance because the effects are minimal
unless a number of PV modules are connected in parallel for a large system. Recombination in
the depletion region of PV cells provides a non-resistive current path in parallel with the
instrinsic PV cell, and can be represented by a second diode in the equivalent circuit.
SIMULINK IMPLEMENTATION
Simulink is an interactive tool for Modeling, simulating, and analyzing dynamic systems.
It is an excellent resource for Modeling and simulating mathematical systems and subsystems.
Simulink is a simulation programme, which provides a graphical interface for building models as
blocks diagrams. It offers the advantage of building hierarchical models, namely to have the
possibility to view the system at different levels. Simulink provides also the possibility to build
modular models, which have the advantage that in this way the models can be easily connected
together in order to simulate a certain system (stand - alone or on-grid). Such models also help
system designers to optimize the size of the components of a PV system.
CONCLUSIONS
Photovoltaic components of a Solar Power System are mathematically modelled and then
simulated in Matlab/Simulink.
Simulink models are implemented for:
a. Solar Cell
b. Solar PV Module (Current Input Model and Voltage Input Model)
c. A typical Solar Array
Also a Simulink model is implemented for the generating the characteristics curves of PV
Modules. This can be utilised as a Software tool for the PV Module Performance Evaluation
from the Module Data Sheet Parameters. The Data Sheet parameters of two different PV
Modules are utilising for testing the tool as a Software Tool for quick evaluation. The Test
Results are also validated with PV Syst.