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A Simulated annealing global maximum power point tracking method for photovoltaic systems experiencing non-uniform environmental conditions

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Lynden, SL (2015) A Simulated annealing global maximum power point tracking method for photovoltaic systems experiencing non-uniform environmental conditions. PhD thesis, University of Tasmania.

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Abstract

Photovoltaic (PV) systems have immense potential due to the abundance of
available solar energy and the capability of these systems to be implemented in
a distributed manner. This clean, renewable and sustainable energy source can
provide a solution to concerns about the shortage of fossil fuels, global warming,
greenhouse gas emissions and pollution in general. Residential PV systems
enable consumers to take control of generating electricity to satisfy their own
load requirements and potentially export any excess energy to the distribution
grid. Investing in a PV system requires significant initial capital and PV cells
have a very limited efficiency. Residential customers who invest in a PV system
expect to be able to have the best return on their investment by utilising the
power available in the sunlight to the greatest extent possible. The potential
power available from such systems can be dramatically reduced due to shading
of the modules and ineffective control strategies to overcome the influence of
shading. PV cells exhibit a non-linear Power-Voltage (P-V) characteristic leading
to a unique point corresponding to optimal operation. This point is referred to as
the Maximum Power Point (MPP), and varies depending on the environmental
conditions. Typical conditions in a residential environment involve obstacles
such as trees, houses and power poles which may cause shading across all or
part of the PV system throughout the day. Shading from these obstacles leads
to increased non-linearity in the P-V characteristic as multiple maxima can be
exhibited. Traditionally, Maximum Power Point Tracking (MPPT) techniques
have been developed to track a single maximum on the P-V characteristic
based on simple techniques such as hill climbing. These techniques inherently
fail when multiple maxima are exhibited under Partial Shading Conditions (PSC).
The work documented in this thesis consists of two main parts. In the first part,
a study of modelling PV cells and an extensive shading study for an eight-module
PV system is conducted. This analysis has led to the classification of partial
shading phenomena based on the time scale as either constant, static or transient
partial shading, and exploring the effect that each aspect of partial shading
has on the relative location of the Global Maximum Power Point (GMPP).
The second part comprehensively explores the concept of MPPT and presents
a review of techniques proposed in the literature with consideration of their
performance under non-uniform environmental conditions. A Global MPPT
(GMPPT) method is proposed based on the global optimisation technique of
Simulated Annealing (SA) and its performance is verified through simulations
and experimental application.
The key contributions of this thesis include proposing a shading classification
based on the time of influence of the shading and studying how this affects the
relative location of the GMPP, development and optimisation of a SA based
GMPPT method, and the merging of these results to develop a comprehensive
and enhanced GMPPT strategy.
The main concerns associated with modelling PV cells and modules are introduced
and a model of the BP380 PV module is developed based on the
commonly used Single Diode Model (SDM) for PV modules. The SDM provides
a good balance between accuracy and simplicity and is shown to model the
experimentally measured P-V and Current-Voltage (I-V) characteristics of the
BP380 modules with acceptable accuracy. A model is also developed and
experimentally validated based on combining two series-connected modules
modelled using the SDM to explore PSC.
A PV system comprised of eight series-connected PV modules, modelled based
on the BP380 PV modules, is developed to explore the influence of PSC. A
methodology for calculating the position of the shadow tip and determining
which cells are shaded by an object is proposed and used to perform five case
studies exploring the effects of constant, static and transient partial shading.
Constant partial shading is defined as a mismatch in the potential of the modules
in a system based on factors such as manufacturing tolerance, cell degradation
and damage over time. This type of shading should remain roughly the same
for all time. Static partial shading is considered as shading that moves much
slower than the movement of clouds across the sky and represents the shading
that occurs on the modules due to the presence of obstacles in the environment.
Finally, transient shading is the quickest shading phenomena and is represented
by the changing irradiance due to the movement of clouds across the sky.
An extensive review of maximum power extraction strategies is presented. Each
technique is assessed against key criteria identified as being essential for a
universally applicable GMPPT strategy. In particular, the methods are assessed
on whether they can locate a global maximum reliably, the method complexity
and its ease of application to other PV systems. The analysis suggests that
a global maximum power extraction strategy with moderate complexity and
limited dependence on system specific parameters is needed.
The proposed SA based GMPPT method is introduced in the form of simple
studies showing the effectiveness of the method in converging to a GMPP based
on a two module PV system, eight module PV system, basic grid connected
system and through experimental verification on the two series-connected BP380
PV modules. The key parameters of the SA method are explored in more detail
to assess their influence on the effectiveness of the proposed method.
The main advantages of the proposed methodology for GMPPT is that it is not
significantly more complex than the common perturb and observe (P&O) MPPT
technique, yet has far superior performance in converging to the GMPP. Additionally,
when compared to the Particle Swarm Optimisation (PSO) method
which is commonly used for GMPPT, the SA based method has less complexity
yet similar performance in converging to the GMPP. By incorporating understanding
of the relative location of the GMPP under different PSC, the technique
is enhanced to improve accuracy and convergence time. In residential environments
one of the key factors is minimising cost and ensuring maximum effciency.
For this reason, a low cost and low complexity MPPT method that can achieve
GMPP identification is essential, to enable systems implemented in residential
environments to be utilised to the greatest extent possible.

Item Type: Thesis (PhD)
Keywords: Photovoltaic, Maximum Power Point Tracking, Simulated Annealing, Partial Shading Conditions
Copyright Holders: The Author
Copyright Information:

Copyright 2015 the author

Date Deposited: 03 Aug 2016 23:24
Last Modified: 03 Aug 2016 23:24
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