Solar photovoltaic (PV) systems are distributed energy sources that are an environmentally friendly
and renewable source of energy. However, solar PV power fluctuates due to variations in radiation
and temperature levels. Furthermore, when the solar panel is directly connected to the load, the power
that is delivered is not optimal. A maximum peak power point tracker is therefore necessary for
maximum efficiency.
A complete PV system equipped maximum power point tracking (MPPT) system includes a solar
panel, MPPT algorithm, and a DC-DC converter topology. Each subsystem is modeled and simulated
in a Matlab/Simulink environment; then the whole PV system is combined with the battery load to
assess the overall performance when subjected to varying weather conditions.
A PV panel model of moderate complexity based on the Shockley diode equation is used to predict
the electrical characteristics of the cell with regard to changes in the atmospheric parameter of
irradiance and temperature.
In this dissertation, five MPPT algorithms are written in Matlab m-files and investigated via
simulations. The standard Perturb and Observe (PO) algorithm along with its two improved versions
and the conventional Incremental Conductance (IC) algorithm, also with its two-stage improved
version, are assessed under different atmospheric operating conditions. An efficient two-mode MPPT
algorithm combining the incremental conductance and the modified constant voltage methods is
selected from the five ones as the best model, because it provides the highest tracking efficiencies in
both sunny and cloudy weather conditions when compared to other MPPT algorithms.
A DC-DC converter topology and interface study between the panel and the battery load is performed.
This includes the steady state and dynamic analysis of buck and boost converters and allows the
researcher to choose the appropriate chopper for the current PV system. Frequency responses using
the state space averaged model are obtained for both converters. They are displayed with the help of
Bode and root locus methods based on their respective transfer functions. Following the simulated
results displayed in Matlab environment for both choppers, an appropriate converter is selected and
implemented in the present PV system. The chosen chopper is then modeled using the Simulink
Power Systems toolbox and validates the design specifications.
The simulated results of the complete PV system show that the performances of the PV panel using
the improved two-stage MPPT algorithm provides better steady state and fast transient characteristics
when compared with the conventional incremental conductance method. It yields not only a reduction
in convergence time to track the maximum power point MPP, but also a significant reduction in
power fluctuations around the MPP when subjected to slow and rapid solar irradiance changes. / Thesis (M.Sc.Eng)-University of KwaZulu-Natal, Durban, 2011.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ukzn/oai:http://researchspace.ukzn.ac.za:10413/8321 |
| Date | January 2011 |
| Creators | Nkashama, Cedrick Lupangu. |
| Contributors | Saha, Akshay Kumar. |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
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