Download Maximum Power Point Tracking

Maximum Power Point Tracking using modified
Perturb & Observe and Incremental Conductance
Techniques
Bilal Masoodi, M. Shahzad Siddiqueii, M. Zia-ul-Haqiii
Department of Electrical Engineering, Superior University, 15-KM Raiwind Road Lahore
Email: [email protected], [email protected], [email protected]
Abstract:
The development of renewable energy has been an
increasingly critical topic in the 21st century with the
growing problem of global warming and other
environmental issues. With greater research, alternative
renewable sources such as wind, water, geothermal and
solar energy have become increasingly important for
electric power generation. Although photovoltaic cells
are nothing new, their use has become more common,
practical, and useful for people worldwide. Although
each cell output is relatively low voltage, if many are
connected in series, a solar photovoltaic (PV) module is
formed. Although the price for such cells is decreasing,
making use of a solar cell module still requires
substantial financial investment. At a given temperature
and insolation level, PV cells supply maximum power at
one particular operation point called the maximum
power point tracking (MPPT). However, the MPP locus
varies over a wide range, depending on PV array
temperature and insolation intensity. Instantaneous
shading conditions and aging of PV cells also affect the
MPP locus. In this research paper two reformed
algorithms have been proposed for MPPT, the most
widely used ones are the ‘Perturb and Observe’ (P&O)
and the Incremental Conductance algorithms. The duty
cycle of the converter will be controlled, so that the
source will send maximum power to the load. The
research paper presents a new reformed technique of
harvesting MPP from PV cells after evaluating the
previous ones. All the previous techniques were
thoroughly studied before making any reform in the
traditional MPP techniques. Both techniques have their
own significance at different situations of weather. In
this paper new technique is introduced by using both of
above P&O and Incremental Conductance.
Keywords – Perturb and Observe (P&O), Maximum Power
Point Tracking (MPPT), Photo Voltaic Cell (PV cell)
I. Introduction:
History of PV Cells
The history of PV dates back to 1839 when a French
physicist, Edmund Becquerel, discovered the first
photovoltaic effect when he illuminated a metal electrode in
an electrolytic solution. Thirty-seven years later British
physicist, William Adams, with his student, Richard Day,
discovered a photovoltaic material, selenium, and made solid
cells with 1~2% efficiency which were soon widely adopted
in the exposure meters of camera. In 1954 the first
generation of semiconductor silicon-based PV cells was
born, with efficiency of 6%, and adopted in space
applications. Today, the production of PV cells is following
an exponential growth curve since technological
advancement of late ‘80s that has started to rapidly improve
efficiency and reduce cost.
Topology about PV Cells
Renewable energy technologies are playing an increasingly
important role in supplying the world’s electricity demands.
In particular, the PV generation system, a promising source
of energy for the future, is evolving rapidly and showing an
industrial growth of approximately 40% per year worldwide.
Solar energy which is free and abundant in most parts of the
world has proven to be an economical source of energy in
many applications. The most important aspect of a solar cell
is that it generates electrical energy directly from sun light
through the photovoltaic module, made up of commonly
silicon cells. The energy, the earth receives from the sun is
so enormous and so lasting that the total energy consumed
annually by the entire world is supplied in as short period as
half an hour. On a clear day, the sun's radiations on the earth
can be 3000 watts per square meter depending on the
location. The sun is a clean and renewable energy source,
which produces neither green-house effect gas nor noxious
waste through its utilization. The photovoltaic process is
completely solid state and self-contained. There are no
moving parts and no materials are consumed or emitted.
Consider the advantages that photovoltaic systems have over
competing power options:
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They are non-polluting with no detectable emissions
or odors.
They can be stand-alone systems that reliably
operate unattended for long periods.
They require no connection to an existing power
source or fuel supply.
They may be combined with other power sources to
increase system reliability.
They can withstand severe weather conditions
including snow and ice.
They consume no fossil fuels - their fuel is abundant
and free.
They can be installed and upgraded as modular
building blocks - as power demand increases; more
photovoltaic modules may be added
Role of MPPT in Solar Energy
The PV systems when connected directly to the load result in
overall poor efficiency where as such MPPT should have
been introduced in PV systems that increase the efficiency of
the system. Solar radiations, load impedance and module
temperature are the three factors which affect the maximum
power extraction from solar PV module. Unlike conventional
energy sources, it is desirable to operate PV systems at its
MPP. [1] Thus, to make a PV module useful, it is necessary
to extract as much energy as possible from such a system. To
achieve operation at the MPP, a time varying matching
network is required that interfaces the varying source and
possibly the varying load [9]. The role of this matching
network, called the MPPT network, is to ensure operation of
the PV array at its MPP, regardless of atmospheric
conditions and load variations. I-V curve of PV module is a
function of insolation and temperature which affects output
current and voltage [10].
The increased temperature decreases the open circuit voltage
(Voc) while increased intensity of solar radiations increases
short circuit current (Isc).
The concept of MPPT is to monitor the terminal voltage and
current continuously and update the control signal
accordingly to achieve maximum power point (MPP) [2]. A
DC/DC convertor with MPPT algorithm is used between PV
module and load to extract maximum available power [11].
An example of MPPT with a typical cell of voltage and
current is shown in figure below. It shows where the
maximum power point lies for that typical cell is.
Figure 1. Typical forward bias I-V characteristics of a PV cell
II. Techniques:
A Short Review on Conventional MPPT Techniques
The conventional P&O algorithm is easy to implement and
is most commonly used in battery charging with commercial
PV modules. In this method, the operating voltage or current
of the PV module, is perturbed and then the power obtained
is observed to decide the direction of further changes in the
voltage or current [8]. If the power is increased by the
perturbation then voltage or current is kept on changing in
the same direction until the power begins to fall. The
algorithm measures the instant voltage (Vt) and current (It)
to calculate the power (Pt) and then compares it with last
calculated power (Pt-1) [7]. The algorithm continuously
perturbs the system if the operating point variation is
positive, otherwise the direction of perturbation is changed.
Here is the flow chart for the conventional P&O algorithm
Figure 2. Flow Chart of P&O Algorithm
The second one is the conventional Incremental Conductance
(INC) method. The incremental conductance algorithm of
MPPT was developed by K. H. Hussein, I. Muta, T. Hoshino
and M. Osakada, however the concept technique was
developed by O. Wasyneczuk. They used derivative of
conductance to determine the maximum power point (MPP)
[12]. The MPP is determined by comparing instant
conductance I/V to the incremental conductance ΔI/ΔV and
the INC technique is based on the fact that slope of P-V
curve is zero at MPP as shown in Fig. 3. [3] This algorithm
performs better than P&O algorithm in rapidly varying
environment and is robust to the rapidly varying solar
radiation. The MPPT speed and accuracy was improved by
introducing automatically adjustable variable step size to
conventional INC technique [4]. When MPP is far from
operating point, the step size is large for fast tracking while
during operating point closer to MPP, the step size becomes
small to reduce steady state oscillation.
accurate and effective than most commonly used P&O
algorithms at low solar radiations. Therefore these
algorithms are combined with P&O and INC algorithms to
increase their effectiveness. The P&O based algorithms
oscillate around the MPP in slow varying atmospheric
conditions. Therefore to decrease losses due to oscillations,
the P&O based algorithms are suitable in only rapidly
changing atmospheric conditions and the constant voltage
method is fast and sufficient for constant conditions. The two
mode control algorithm combines these two algorithms by
using incremental conductance method for more than 30%
normalized solar radiations and constant voltage method for
less than 30% normalized radiations. The flow chart of the
algorithm of this method is shown in Fig 4.
Figure 3. Flow chart of Incremental Conductance
Algorithm
The algorithm is modified and the derivative of resistance
(dV/dI) is used in place of derivative of conductance. The
modified algorithm is variable step-size incremental
resistance (INR) algorithm is based on the fact that slope of
P-I curve is zero at MPP, positive on the left of MPP, and
negative on the right of MPP [13].
Figure 4. Flow Chart of Modified hybrid techniques
using two mode control method algorithm
III. Modified P&O with INC Algorithm
The Modified P&O with INC Algorithm consists of hybrid
algorithm using a different algorithm technique along with
the P&O method for faster and accurate tracking of MPP [5].
The voltage and current controlled algorithms are more
IV. Conclusion
In the above research we reviewed previous MPP techniques
and also their algorithms. Both of the above techniques have
their own significance for faster and slow changing weather
conditions. We proposed a new techniques say hybrid both
of P&O and INC which actually works in both slow and
faster changing conditions of weather. This is basically an
advancement in conventional P&O and INC method. From
this research we also came to know that both techniques are
really efficient for MPPT.
[12]. A. Yafaoui., B. Wu and R. Cheung, Implementation of
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7627~7633 e-ISSN: 2087-278X
THE 8th INTERNATIONAL SYMPOSIUM ON
ADVANCED
TOPICS
IN
ELECTRICAL
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Bilal Masood, Senior Faculty Member and
Research Supervisor of Electrical Power & Renewable
energy systems at Department of Electrical Engineering,
Superior University Lahore
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M. Shahzad Siddique, Final Year Student
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iii
M. Zia-ul-Haq, Final Year Student and
active Researcher at Department of Electrical Engineering,
Superior University Lahore