26-05-2012, 03:09 PM
Evaluation of Micro Controller Based Maximum Power Point Tracking Methods Using dSPACE Platform
[attachment=23179]
INTRODUCTION
The word photovoltaic (PV) literally means conversion
of sunlight directly to electricity. It is clean, easymaintenance
and long lifespan (>25 years)
characteristics gained a lot of attention in the recent
decade. The annual growth of solar energy installation
nowadays is around 30% and this number is still
climbing [1].
A typical photovoltaic system consists of two major
parts: the solar panels that generate DC power from
sunlight, and the power electronics that convert DC into
standard AC voltages. Most solar cells on the market can
achieve 13 ~ 15% of energy conversion, and over 20%
in lab environments [2]. While research goes on to
improve the PV cell efficiency, it is fundamentally the
power electronics that provide controllability over this
renewable energy source. In particular, good control to
track the maximum power that the PV cells can provide
is critically important because the photovoltaic energy is
subject to weather changes, and the amount of electricity
produced by solar panels is highly unpredictable
throughout the day.
MPPT ALGORITHMS
The weather and load changes cause the operation of a
PV system to vary almost all the times. A dynamic
tracking method is necessary to ensure maximum power
is extracted from the PV arrays. The following
algorithms are the most fundamental MPPT algorithms,
and they can be developed using micro controllers.
Perturb and Observe Method
The Perturb and Observe method (P&O) is the most
commonly used MPPT method because of its simplicity
[4]. Fig 2.1 below shows the Power-Voltage curve of a
typical PV array. During the operation, the terminal
voltage is continuously perturbed and power is measured.
If the power increases due to a perturbation of voltage to
a given direction, it indicates the operating point is
moving towards MPP. Therefore the voltage should be
changed in the same direction in the next cycle. If the
power decreases, it indicates the operating point has
passed the MPP and must be changed in the opposite
direction.
Incremental Conductance Method
The incremental conductance method (IncCond) has the
advantage over P&O method in that it calculates the
direction of the perturbation without constantly varying
the voltage. The operating principle of incremental
conductance method is based on the following
characteristic of the P-V curve
Simulation Results
All three methods were simulated with the same boost
converter block under the same loading and weather
conditions. Full sunlight and partial cloudy conditions
were used to test the algorithms. The results are shown
in the following figures. The voltage and current are
sampled at a sampling frequency of 100Hz for all three
methods.
In the following diagrams only the tracking performance
under full sunlight are shown. Please refer to appendix I
for the equation used to simulate the partial cloudy
weather condition.
[attachment=23179]
INTRODUCTION
The word photovoltaic (PV) literally means conversion
of sunlight directly to electricity. It is clean, easymaintenance
and long lifespan (>25 years)
characteristics gained a lot of attention in the recent
decade. The annual growth of solar energy installation
nowadays is around 30% and this number is still
climbing [1].
A typical photovoltaic system consists of two major
parts: the solar panels that generate DC power from
sunlight, and the power electronics that convert DC into
standard AC voltages. Most solar cells on the market can
achieve 13 ~ 15% of energy conversion, and over 20%
in lab environments [2]. While research goes on to
improve the PV cell efficiency, it is fundamentally the
power electronics that provide controllability over this
renewable energy source. In particular, good control to
track the maximum power that the PV cells can provide
is critically important because the photovoltaic energy is
subject to weather changes, and the amount of electricity
produced by solar panels is highly unpredictable
throughout the day.
MPPT ALGORITHMS
The weather and load changes cause the operation of a
PV system to vary almost all the times. A dynamic
tracking method is necessary to ensure maximum power
is extracted from the PV arrays. The following
algorithms are the most fundamental MPPT algorithms,
and they can be developed using micro controllers.
Perturb and Observe Method
The Perturb and Observe method (P&O) is the most
commonly used MPPT method because of its simplicity
[4]. Fig 2.1 below shows the Power-Voltage curve of a
typical PV array. During the operation, the terminal
voltage is continuously perturbed and power is measured.
If the power increases due to a perturbation of voltage to
a given direction, it indicates the operating point is
moving towards MPP. Therefore the voltage should be
changed in the same direction in the next cycle. If the
power decreases, it indicates the operating point has
passed the MPP and must be changed in the opposite
direction.
Incremental Conductance Method
The incremental conductance method (IncCond) has the
advantage over P&O method in that it calculates the
direction of the perturbation without constantly varying
the voltage. The operating principle of incremental
conductance method is based on the following
characteristic of the P-V curve
Simulation Results
All three methods were simulated with the same boost
converter block under the same loading and weather
conditions. Full sunlight and partial cloudy conditions
were used to test the algorithms. The results are shown
in the following figures. The voltage and current are
sampled at a sampling frequency of 100Hz for all three
methods.
In the following diagrams only the tracking performance
under full sunlight are shown. Please refer to appendix I
for the equation used to simulate the partial cloudy
weather condition.