15-10-2012, 01:24 PM
A Photovoltaic Array Simulation Model for Matlab-Simulink GUI Environment
A Photovoltaic Array.pdf (Size: 203.97 KB / Downloads: 122)
Abstract
A photovoltaic array (PVA) simulation model to be
used in Matlab-Simulink GUI environment is developed and
presented in this paper. The model is developed using basic
circuit equations of the photovoltaic (PV) solar cells including the
effects of solar irradiation and temperature changes. The new
model was tested using a directly coupled dc load as well as ac
load via an inverter. Test and validation studies with proper load
matching circuits are simulated and results are presented here.
INTRODUCTION
HE use of new efficient photovoltaic solar cells (PVSCs)
has emerged as an alternative measure of renewable green
power , energy conservation and demand-side
management. Owing to their initial high costs, PVSCs have
not yet been a fully attractive alternative for electricity users
who are able to buy cheaper electrical energy from the utility
grid. However, they have been used extensively for water
pumping and air conditioning in remote and isolated areas
where utility power is not available or is too expensive to
transport. Although PVSC prices have decreased considerably
during the last years due to new developments in the film
technology and manufacturing process [1], PV arrays are still
widely considered as an expensive choice compared with
existing utility fossil fuel generated electricity. After building
such an expensive renewable energy system, the user naturally
wants to operate the PV array at its highest energy conversion
output by continuously utilizing the maximum available solar
power of the array. The electrical system powered by solar
arrays requires special design considerations due to varying
nature of the solar power generated resulting from
unpredictable and sudden changes in weather conditions
which change the solar irradiation level as well as the cell
operating temperature. Salameh and Dagher [2] have proposed
a switching system that changes the cell array topology and
connections or the structural connections of the arrays to
establish the required voltage during different periods of a
day.
PVA MODELING FOR SIMULINK
A general block diagram of the PVA model for GUI
environment of Simulink is given in Fig. 2 along with filter
and load models. The block called PVA model for GUI is the
last stage of the model. This block contains the sub models
that are connected to build the final model. A diode (D1) is
connected in series with the load circuit to prevent the reverse
current flow. A filter is connected before the load to maintain
a stable voltage. The filter contains a series R-L and parallel C
elements. The PVA consists of 8 PV cells all connected in
series to have a desired voltage output. Depending on the load
power required, the number of parallel branches can be
increased to 2 or more. The effects of the temperature and
solar irradiation levels are represented by two variables gains.
They can be changed by dragging the slider gain adjustments
of these blocks named as variable temperature and variable
solar irradiation.
SIMULATION RESULTS
The proposed PVA model is simulated using the scheme
given in Fig. 2. The system supplies power to a mainly
resistive dc load and an RLC ac load with 500 W, 200 VAr
inductive and 500 VAr capacitive. The system does not have
any controller. The loads are just chosen to match the power
generated by the PVA. Actually the voltage at dc load bus and
the both voltage and frequency at ac load bus must be
controlled and kept constant for the users. The control part is
also done as a part of this work. However, only the PVA
modeling is included in this paper since both parts require
more space.
The current-voltage (I-V) characteristic of the PVA during
operation is given in Fig. 5. Since the voltage of the PVA is
equal to the open circuit voltage at stand-still, the I-V
characteristics start at open circuit voltage with current equal
to zero. As the simulation starts an the loads begin draw
current from the PVA, the voltage and the current start moving
toward the operating values, which are shown in Figs.
CONCLUSIONS
This paper introduces a simulation model for photovoltaic
arrays (PVA) to be used in Matlab-Simulink GUI
environment. The proposed model has a generalized structure
so that it can be used as a PV power generator along with
wind, fuel cells and small hydro system by establishing proper
interfacing and controllers. The model is simulated connecting
a three phase inverter showing that, the generated dc voltage
can be converted to ac and interfaced to ac loads as well as ac
utility grid system. Therefore the model proposed here can be
considered as a part of distributed power generation systems.