DEVELOPMENT OF A MICROCONTROLLER BASED SOLAR ...

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DEVELOPMENT OF A MICROCONTROLLER
BASED SOLAR PHOTOVOLTAIC MPPT
CHARGE CONTROL SYSTEM
Using
INCREMENTAL CONDUCTANCE METHOD
A Thesis
Submitted in partial fulfillment of the
Requirement for the degree of
MASTER OF ELECTRONICS & TELE-COMMUNICATION ENGINEERING
(With Specialization in ELECTRON DEVICE)
By
TANUSREE DUTTA
Reg. No. 105231 of 2008-2009 Exam Roll No. M4ETC10-02
Class Roll No. 000810702003 of 1008-1009
MAY 2010
Under the supervision of
PROF. H. SAHA
FACULTY OF ENGINEERING & TECHNOLOGY
JADAVPUR UNIVERSITY


ACKNOWLEDGEMENTACKNOWLEDGEMENTACKNOWLEDGEMENTACKNOWLEDGEMENT

It gives me immense pleasure to express my deepest sense of gratitude and sincere thanks to my highly
respected and esteemed supervisor Prof. Prof. Prof. Prof. HiranmayHiranmayHiranmayHiranmay Saha,Saha,Saha,Saha, Supervisor,Supervisor,Supervisor,Supervisor, IC Design & fabrication Centre,IC Design & fabrication Centre,IC Design & fabrication Centre,IC Design & fabrication Centre,
JJJJadavpuradavpuradavpuradavpur UniversityUniversityUniversityUniversity, for his revered supervision throughout my dissertation work, which made this task a
pleasant job. It was real pleasure to work under his supervision.

I extend my sincere thanks to Prof. Goutam Bhattacharya, Ramkrishna Mission Vidyamandira, for his keen
interest, continuous encouragement and support.

I am also indebted to my mother, brother, sisters and well wishers who are taking lot of pains for progress in
my life and for their sacrifices, blessing and constant prayers for my advancement.

I express my special thanks to Prof. B.Gupta (HOD,Dept.of ETCE,JU) and Prof. S.K.Sanyal, Dept. of
ETCE,JU, for their kindness and providing me the facilities of the Laboratory to use for my work.

I would also like to thanks all the Research Scholars, staff members and project students of IC Design &
Fabrication Center. Special thanks are due to Mr.A.Mondal, Mr.G.P.Mishra, Mr.A.Kindu. Dr.S.Roy
Choudhury, Mrs.S.Roy, Ms.T.Majhi, Mr.A.Sengupta.

I am also thankful to Prof. R.N.Ghosh, St. Thomas College of Engg. & Tech., Kol. & Mr.Arup Sarkar, Agni
Power Electronics, Kol., for their support.

I also like to thank Dr.S.Mukhopadhya, Secretary, St. Thomas College of Engg. & Tech., Kol. Prof.Mrs.
S.Sen, Principal, St. Thomas College of Engg. & Tech., kol, Mr.Goutam Banerjee, Registrar, St. Thomas
College of Engg. & Tech., kol, for allowing me to pursuing my M.E. in Electronics & Tele-communication at
Jadavpur University.


………………………………………………
TANUSREE DUTTATANUSREE DUTTATANUSREE DUTTATANUSREE DUTTA
Reg. No.Reg. No.Reg. No.Reg. No.105231 of 2008105231 of 2008105231 of 2008105231 of 2008----09,09,09,09,
DATEDATEDATEDATE:::: Roll No.000810702003Roll No.000810702003Roll No.000810702003Roll No.000810702003 of 2008of 2008of 2008of 2008----09090909
Exam Roll No. M4ETC10Exam Roll No. M4ETC10Exam Roll No. M4ETC10Exam Roll No. M4ETC10----02020202
Table of Contents Page No.

1.0 Introduction to Maximum Power Point Tracking (MPPT).
Introduction…………………………………………………. 2
Need for Maximum Power Point Tracking ………………………… 5
How Maximum Power Point is Achieved …………………………… 7
Methods of Maximum Power Point………………………………… 7
Application of MPPT………………………………………………. . 8

2.0 Literature Review…………………………………… 11

3.0 Algorithms for MPPT
Perturb & Observe……………………………………………………… 16
Incremental Conductance …………………………………………… 17
Parasitic Capacitance……………………………………… 18
Voltage Based Maximum Power Point Tracking…………… 18
Current Based Maximum Power Point Tracking……… 18

4.0 Block Diagram of MPPT System.
Basic Block diagram of MPPT…………………………………… 20
What is MPPT…………………………………………………… 20
Solar Photovoltaic Cell ………………………………… 22
DC-DC Converter………………………………. 30
Introduction to Microcontroller…………………………… 34
Characteristics of Battery………………………… 36

5.0 Hardware Description…………………… 39
6.0 Software Description………………………………... 62
7.0 Experimental Setup…………………………………………….
75
8.0 Result…………………………………………………………… 82
9.0 Conclusions & Future Scope ………………………. ………. 85
10.0 References…………… ….…………………………………….. 87
11.0 Annexure……………………………………………………... 88











1

ABSTRACT

Renewable energy sources play an important role in electricity
generation. Various renewable energy sources like wind, solar, geothermal, ocean
thermal and biomass can be used for generation of electricity and for meeting our
daily energy needs. Energy from the sun is the best option for electricity
generation as it is available everywhere and is free to harness. On an average the
sunshine hour in India is about 6hrs annually also the sun shine shines in India for
about 9 months in a year. Electricity from the sun can be generated through the
solar photovoltaic modules (SPV). The SPV comes in various power output to
meet the load requirement. Maximization of power from a solar photo voltaic
module (SPV) is of special interest as the efficiency of the SPV module is very
low. A maximum power tracker is used for extracting the maximum power from
the SPV module .The present work describes the maximum power point tracker
(MPPT) for the SPV module connected to a battery which is used as a load. A
Microcontroller is used for control of the MPPT algorithm. The power tracker is
developed and tested successfully in the laboratory.
Maximum power point tracking (MPPT) is used in photovoltaic (PV)
systems to maximize the photovoltaic array output power, irrespective of the
temperature and irradiation conditions and of the load electrical characteristics. A
new MPPT system has been developed, consisting of a Buck-type dc/dc converter,
which is controlled by a microcontroller-based unit. The main difference between
the method used in the proposed MPPT system and other techniques used in the
past is that the PV array output power is used to directly control the dc/dc
converter, thus reducing the complexity of the system. The resulting system has
high-efficiency, lower-cost and can be easily modified to handle more energy
sources (e.g., wind-generators).

2


`


CHAPTER 1.
Introduction to Maximum Power
Point Tracking (MPPT).



3


Introduction
Develop a Microcontroller based dedicated MPPT controller for solar PV module based on the
incremental conductance method. As people are much concerned with the fossil fuel exhaustion
and the environmental problems caused by the conventional power generation, renewable
energy sources and among them photovoltaic panels and wind-generators are now widely used.
So Solar Energy is a good choice for electric power generation. The solar energy is directly
converted into electrical energy by solar photovoltaic module. Photovoltaic sources are used
today in many applications such as battery charging, water pumping, home power supply,
swimming-pool heating systems, satellite power systems etc. They have the advantage of being
maintenance and pollution-free but their installation cost is high and inmost applications, they
require a power conditioner (dc/dc or dc/ac converter) for load interface. Since PV modules still
have relatively low conversion efficiency, the overall system cost can be reduced using high
efficiency power conditioners which, in addition, are designed to extract the maximum possible
power from the PV module.
The photovoltaic modules are made up of silicon cells. The silicon solar cell which give output
voltage of around 0.7V under open circuit condition. When many such cells are connected in
series we get a solar PV module. Normally in a module there are 36 cells which amount for a
open circuit voltage of about 20V. The current rating of the modules depends on the area of the
individual cells. Higher the cell area high is the current output of the cell. For obtaining higher
power output, the solar PV modules are connected in series and parallel combinations forming
solar PV arrays. A typical characteristic curve of the called current (I) and voltage (V) curve and
power (W) and voltage (V) curve of the module is shown is fig.1.

4


Fig.1 Characteristics of a typical Solar PV Module.


5

Need for maximum power point tracking
Power output of a Solar PV module changes with change in direction of sun, changes in solar
insolation level and with varying temperature as shown in the fig.2 & 3.


Fig.2 Changes in the characteristics of the Solar PV module due to change in the insolation
level.

As seen in the PV (power vs. voltage) curve of the module there is a single maxima of power.
That is there exists a maximum power corresponding to a particular voltage and current. We
know that the efficiency of the solar PV module is low about 13%. Since the module efficiency
is low it is desirable to operate the module at the maximum power point so that the maximum
power can be delivered to the load under varying temperature and insolation conditions. Hence
maximization of improves the utilization of the solar PV module. A maximum power point
tracker (MPPT) is used for extracting the maximum power from the solar PV module and
transferring that power to the load. A dc/dc converter (step up/step down) serves the purpose of
transferring maximum power from the solar PV module to the load. A dc/dc converter acts as an
interface between the load & module in fig.4.
6


Fig.3 Change in the module characteristics due to the change in temperature

By changing the duty cycle the load impedance as seen by the source is varied and matched at
the point of the maximum power with the source so as to transfer the maximum power.


Fig.4 Block diagram of a typical MPPT system

7

How maximum power point is obtained.
As discuss in this chapter the maximum power point is obtained by introducing dc/dc converter
in between the load and the solar PV module. The duty cycle of the converter is changed till the
maximum power point is obtained considering a down converter is used.

Vo=D*Vi ( Vo is output voltage and Vi is input voltage)
D is the duty cycle of the PWM.
Io = D*Ii
So the Output Power
Pout = Vo * Io
Input Power,
Pin = Vi * Ii
By varying the duty cycle of the PWM, maximum power point is extract from the Solar PV
module by using a different algorithm.


Fig.5 DC/DC converter helps in tracking the maximum power point.

Methods of Maximum Power Point Tracking.
The maximum power is reached with the help of a dc/dc converter by adjusting its duty
cycle.Now question arises how to vary the duty cycle and in which direction so that maximum
power is reached. Whether manual tracking or automatic tracking? Manual tracking is not
possible so automatic tracking is preferred to manual tracking. An automatic tracking can be
performed by utilizing various algorithms.
a. Perturb and observe
b. Incremental Conductance
c. Parasitic Capacitance
d. Voltage Based Maximum Power Tracking
e. Current Based Maximum power Tracking
8

The algorithms are implemented in a microcontroller to implement the maximum power point
tracking. The algorithm changes the duty cycle of the dc/dc converter to maximize the power
output of the module and make it operate at the maximum power point of the module.

Applications of Maximum Power Point Trackers.
MPPT systems are used mainly in systems where source of power is nonlinear. Such as the
solar PV modules or the wind generator systems. MPPT systems are generally used in solar PV
applications such as battery chargers and grid connected stand alone PV systems.

a) Battery charging: Charging of battery (lead acid/NiCad) which is used for the storage of
electrical energy. This energy if it comes from the solar PV systems then fast charging of
the battery can be done with the help of the MPPT charge controller.



Fig.6.Battery charging application of MPPT

b) Grid connected and standalone PV systems: In grid connected or stand alone PV systems.The
solar arrays supply power to the grid or to the local load. A dc/dc converter is used as the
array voltage is dc and as grid voltage is ac an dc/ac converter must be used.





Fig.7.Grid connected application using MPPT

9

Before a dc/ac converter a dc/dc converter (normally step up) is used which serves the purpose
of the maximum power point tracking as explained earlier. Due to maximum power tracking
always the maximum power is transferred to the grid or the local load.

c) Water pumping applications: Solar PV arrays can be used to run dc motors which drive the
pump for supplying the water in the fields. By using the maximum power point tracker the
power to the motor can be increased and so the output flow rate of the pump will also increase.



Fig.8. Pumping application of the MPPT.


10


CHAPTER 2.
Literature Review.


11


The following literature survey for the current report consists of various papers published in the
IEEE conferences and the journals.
1)Development of a Microcontroller-Based Solar Photovoltaic Maximum Power Point
Tracking Control System.
Eftichios Koutroulis, Kostas Kalaitzakis, Member, IEEE, and Nicholas C. Voulgaris

The authors have developed a new MPPT algorithm based on the fact that the maximum power
operating point of a PV generator can be tracked accurately by comparing the incremental and
instantaneous conductance’s of the PV array. The work was carried out by experiment,with
results showing that the developed incremental conductance(IntCond) algorithm has
successfully tracked the MPOP using Microcontroller,even in cases of rapidly changing
atmospheric conditions, and has higher efficiency than ordinary algorithms in terms of total PV
energy transferred to the load.
A very common MPPT technique is to compare the PV array voltage (or current) with a
constant reference voltage (or current), which corresponds to the PV voltage (or current) at the
maximum power point, under specific atmospheric conditions. The resulting difference signal
(error signal) is used to drive a power conditioner which interfaces the PV array to the load.
Although the implementation of this method is simple, the method itself is not very accurate,
since it does not take into account the effects of temperature and irradiation variations.

In the PV current-controlled MPPT system shown in Fig.9, the PV array output current is
compared with a reference current calculated using a microcontroller, which compares the PV
output power before and after a change in the duty cycle of the dc/dc converter control signal.

The PI controller regulates the PV output current to match the reference current.The incremental
conductance method is based on the principle that at the maximum power point.

dP/dV = 0 and since P=VI ,it yields, dI/dV= -I/V
where P,V,I are the PV array output power, voltage and current respectivly.This method is
implemented as shown in Fig.10 .A PI controller is used to regulate the PWM control signal of
the dc/dc converter until the condition:
(dI/dV) + (I/V) = 0 is satisfied. This method has the disadvantage that the control circuit
complexity results in a higher system cost.

12


Fig.9 MPPT system with the incremental conductance control method.


Fig.10 Feed-forward maximum power tracking control system.

In this method the power converter is controlled using the PV array output power. The MPPT
control algorithm is based on the calculation of the PV output power and of the power change
by sampling voltage and current values. The power change is detected by comparing the present
and previous voltage levels, in order to calculate a reference voltage which is used to produce
the PWM control signal.The dc/dc converter is driven by a DSP-based controller for fast-
response and the overall system stability is improved by including a PI controller which is so
used to match the array and reference voltage levels. However, the DSP-based control unit
increases the implementation cost of the system.
2). Control of DC/DC Converters for Solar Energy System with Maximum Power
Tracking.
Chihchiang Hua and Chihming Shen.
The object of this paper is to analyze and design DC/DC converters of different types in a solar
energy system to investigate the performance of the converters.A simple method which
combines a discrete time control and a PI compensator is used to track the Maximum power
points (MPP's) of the solar array. The system is kept to operate close to the MPPT's, thus the
maximum possible power transfer from the solar array is achieved. The implementation of the
proposed converter system was based on a digital signal processor (DSP). Experimental tests
where carried out for buck, boost and buck-boost converters using a simple maximum power
13

point tracking (MPPT) algorithm. The efficiencies for the system with different converters are
compared. The paper is use full in evaluating the response of step up, step down converter for
the MPPT system. Paper proposes that the Step down converter is the best option for the use in
the MPPT system as it give higher efficiency.
3)
Maximum Power Tracking for Photovoltaic Power Systems.
Joe-Air Jiang1,
Tsong-Liang Huang2, Ying-Tung Hsiao2* and Chia-Hong Chen2.

The authors have developed a new MPPT algorithm based on the fact that the MPOP(maximum
peak operating point) of a PV generator can be tracked accurately by comparing the incremental
and instantaneous conductance’s of the PV array. The work was carried out by both simulation
and experiment, with results showing that the developed incremental conductance(IntCond)
algorithm has successfully tracked the MPOP, even in cases of rapidly changing atmospheric
conditions, and has higher efficiency than ordinary algorithms in terms of total PV energy
transferred to the load.
4) A New Algorithm for Rapid Tracking of Approximate Maximum Power Point in
Photovoltaic Systems. Sachin Jain, Student Member, IEEE, and Vivek Agarwal.
A robust oscillation method is used for implementing the maximum power point tracking for
the solar arrays. The method uses only one variable that is load current for detecting the
maximum power.This method is suitable for the battery charging application where MPPT is to
be implemented.The algorithm is implemented through a simple circuit.The paper gives detailed
discussion about design of a step down converter used for the MPPT.

5). Microprocessor-Controlled New Class of Optimal Battery Chargers for Photovoltaic
Applications.
Mohamad A. S. Masoum, Seyed Mahdi Mousavi Badejani, and Ewald F. Fuchs.

The authors discuss a control system of a residential photovoltaic system.The paper explains a
perturb and observe algorithm and how can it be implemented using a microprocessor. This
paper is one of the basic papers which explains the Incremental Conductance algorithm.Also
controller design using PI scheme obtained.
14

6) Implementation of a DSP-controlled Photovoltaic Peak Power Tracking system.
Chihchiang Hua, Member, IEEE, Jongrong Lin, and Chihming Shen
The corresponding authors have proposed a new kind of maximum power point tracking
algorithm based on Incremental Conductance algorithm.The algorithm is fast acting which
eliminate the ripple in the module voltage. The module voltage and current that are taken for
processing are not averaged but are instantaneous this speed ups the process of peak power
tracking. Also the paper implements the new algorithm on the real time platform.The software
used was DSP.
7). Comparative Study of Maximum Power Point Tracking Algorithms Using an
Experimental, Programmable, Maximum Power Point Tracking Test Bed.
D. P. Hohm, M. E. Ropp.
The authors have compares all the different kinds of algorithm that are used for the maximum
power point tracking.This helps in proper selection of the algorithm.Preliminary results indicate
that perturb and observe compares favorably with incremental conductance and constant
voltage. Although incremental conductance is able to provide marginally better performance in
case of rapidly varying atmospheric conditions, the increased complexity of the algorithm will
require more expensive hardware and therefore may have an advantage over perturb and
observe only in large PV arrays.
8) Theoretical and Experimental Analyses of Photovoltaic Systems With Voltage and
Current-Based Maximum Power-Point Tracking.
Mohammad A. S. Masoum, Hooman Dehbonei, and Ewald F. Fuchs

Detailed theoretical and experimental analyses of two simple, fast and reliable maximum
power-point tracking (MPPT) techniques for photovoltaic (PV) systems are presented. Voltage-
based (VMPPT) and the Current-based (CMPPT) approaches.A microprocessor-controlled
tracker capable of online voltage and current measurements and programmed with VMPPT and
CMPPT algorithms is constructed.The load of the solar system is either a water pump or
resistance. The paper has given a simulink model of the Dc/Dc converter and a solar PV
module.
The literature review consists of vast survey of papers from the various conferences. The
literatures give sufficient idea about the basics of the MPPT algorithm and how the MPP
tracking is takes place.
15



CHAPTER 3.
Algorithms to track the Maximum
Power Point.



16

Different algorithms help to track the maximum power point of the solar pv module
automatically.
The various algorithms used are:

a) Perturb and Observe.
b) Incremental Conductance.
c) Parasitic Capacitance.
d) Voltage Based Peak Power Tracking.
e) Current Based peak power Tracking
a) Perturb and Observe method - In this algorithm a slight perturbation is introduced in
the system. Due to this perturbation the power of the module changes. If the power increases
due to the perturbation then the perturbation is continued in that direction. After the peak power
is reached the power at the next instant decreases and hence after that the perturbation reverses.


Fig.11 Perturb and observe algorithm


When the steady state is reached the algorithm oscillates around the maximum point. In order to
keep the power variation small the perturbation size is kept very small.The algorithm is
developed in such a manner that it sets a reference voltage of the module corresponding to the
maximum voltage of the module. A Microcontroller then acts moving the operating point of the
module to that particular voltage level. It is observed that there some power loss due to this
perturbation also the fails to track the power under fast varying atmospheric conditions. But still
this algorithm is very popular and simple.
17

Implemented Method

b) Incremental conductance method:- The disadvantage of the perturb and observe
method to track the maximum power under fast varying atmospheric condition is overcome by
Incremental conductance method. The algorithm makes use of the equation:

P=V*I
(where P= module power,V=module voltage, I=module current);

Diff. with respect to dV
dP/dV=I+V*dI/dV
Depending on this equation the algorithm work at maximum power point

dP/dV=0

dI/dV=-I/V


Fig.12.Incremental conductance method.

If operating point is to the left of the power curve then we have

dP/dV>0
dI/dV>I/V

By using this equation, algorithm works.
The incremental conductance can determine that the MPPT has reached the MPP and stop
perturbing the operating point.If this condition is not met, the direction in which the MPPT
18

operating point must be perturbed can be calculated using the relationship between dl/dV and -
I/V. This relationship is derived from the fact that dP/dV is negative when the MPPT is to the
right of the MPP and positive when it is to the left of the MPP. This algorithm has disvantages
over perturb and observe in that it can determine when the MPPT has reached the MPP, where
perturb and observe oscillates around the MPP. Also, incremental conductance can track rapidly
increasing and decreasing irradiance conditions with higher accuracy than perturb and
observe.One disadvantage of this algorithm is the increased complexity when compared to
perturb and observe method.
Others Method
c) Parasitic capacitances :- The parasitic capacitance method is a refinement of
incremental conductance method that takes into account the parasitic capacitances of the solar
cells in the PV array . Parasitic capacitance uses the switching ripple of the MPPT to perturb the
array. To account for the parasitic capacitance, the average ripple in the array power and
voltage,generated by the switching frequency, are measured using a series of filters and
multipliers and then used to calculate the array conductance.The incremental conductance
algorithm is then used to determine the direction to move the operating point of the MPPT. One
disadvantage of this algorithm is that the parasitic capacitance in each module is very small, and
will only come into play in large PV arrays where several module strings are connected in
parallel. Also, the DC-DC converter has a sizable input capacitor used filter out small ripple in
the array power.This capacitor may mask the overall effects of the parasitic capacitance of the
PV array.
d) Voltage control maximum point tracker:- It is assumed that a maximum power
point of a particular solar PV module lies at about 0.75 times the open circuit voltage of the
module. So by measuring the open circuit voltage a reference voltage can be generated and feed
forward voltage control scheme can be implemented to bring the solar pv module voltage to the
point of maximum power.One problem of this technique is the open circuit voltage of the
module varies with the temperature. So as the temperature increases the module open circuit
voltage changes and we have to measure the open circuit voltage of the module very often.
Hence the load must be disconnected from the module to measure open circuit voltage. Due to
which the power during that instant will not be utilize.
e) Current control maximum power point tracker:- The maximum power of the
module lies at the point which is at about 0.9 times the short circuit current of the module. In
order to measure this point the module or array is short-circuited. And then by using the current
mode control the module current is adjusted to the value which is approx 0.9 times the short
circuit current. The problem with this method is that a high power resistor is required which can
stain the short-circuit current. The module has to be short circuited to measure the short circuit
current as it goes on varying with the changes in insolation level.

19



CHAPTER 4.
BLOCK DIAGRAM OF MPPT SYSTEM


20





Fig.13
What is MPPT ?
A MPPT, or maximum power point tracker is an electronic DC to DC converter that
optimizes the match between the solar array (PV panels), and the battery bank, utility power,
DC motor, or DC pump.
.

Fig.14 Characteristic curve of solar photovoltaic MPPT system



21

what do we mean by "optimize"?

Most PV panels are built to put out a nominal 12 volts. The catch is nominal. In actual fact,
most all are designed to put out from 16 to 36 volts. The problem is that a nominal 12 volt
battery is pretty close to an actual 12 volts - 10.5 to 12.7 volts, depending on state of charge.
Under charge, most batteries want from around 13.2 to 14.2 volts to fully charge , quite a bit
different than what most panels are designed to put out.This is electronic tracking, and has
nothing to do with moving the panels. Instead, the controller looks at the output of the panels,
and compares it to the battery voltage. It then figures out what is the best power that the panel
can put out to charge the battery. It takes this and converts it to best voltage to get maximum
AMPS into the battery. Most modern MPPT's are around 92-97% efficient in the conversion.
You typically get a 20 to 45% power gain in winter and 10-15% in summer. Actual gain can
vary widely depending weather,temperature, battery state of charge, and other factors.

MPPT's are most effective under these conditions:
Winter, and/or cloudy or hazy days - when the extra power is needed the most.
Cold weather - solar panels work better at cold temperatures, but without a MPPT we are losing
most of that. Cold weather is most likely in winter - the time when sun hours are low and you
need the power to recharge batteries the most. Low battery charge - the lower the state of charge
in your battery, the more current a MPPT puts into them - another time when the extra power is
needed the most. You can have both of these conditions at the same time. The Power point
tracker is a high frequency DC to DC converter. They take the DC input from the solar panels,
change it to high frequency AC, and convert it back down to a different DC voltage and current
to exactly match the panels to batteries. MPPT's operate at high audio frequencies, usually in
the 20-80 kHz range. Most newer models of MPPT controllers available are Microcontroller
based. They know when to adjust the output that it is being sent to the battery, and they actually
shut down for a few microseconds and "look" at the solar panel and battery and make any
needed adjustments.


22

SOLAR PHOTOVOLTAIC CELL
Simple explanation
Photons in sunlight hit the solar panel and are absorbed by semiconducting materials,such as
silicon.Electronics (negatively charged) are knocked loose from their atoms, allowing them to
flow through the material to produce electricity. Due to the special composition of solar cells,
the electrons are only allowed to move in a single direction.The complementary positive
charges that are also created (like bubbles) are called holes and flow in the direction opposite of
the electrons in a silicon solar panel.An array of solar cells converts solar energy into a usable
amount of direct (DC) electricity.
Photogeneration of charge carriers
When a photons hits a piece of silicon, one of three things can happen:
1)The photon can pass straight through the silicon — this (generally) happens for lower energy
photon.
2)The photon can reflect off the surface,
3)The photon can be absorbed by the silicon, if the photon energy is higher than the silicon band
gap value.This generates an electron-hole pair and sometimes heat,depending on the band
structure.
When a photon is absorbed, its energy is given to an electron in the crystal lattice.Usually this
electron is in the valence band, and is tightly bound in covalent bonds between neighboring
atoms, and hence unable to move far. The energy given to it by the photon "excites" it into the
conduction band,where it is free to move around within the semiconductor. The covalent bond
that the electron was previously a part of now has one fewer electron — this is known as a hole.
The presence of a missing covalent bond allows the bonded electrons of neighboring atoms to
move into the "hole," leaving another hole behind, and in this way a hole can move through the
lattice. Thus, it can be said that photons absorbed in the semiconductor create mobile electron-
hole pairs
A photon need only have greater energy than that of the band gap in order to excite an electron
from the valence band into the conduction band. However, the solar frequency specturm
approximates a black body spectrum at ~6000 K, and as such, much of the solar radiation
reaching the Earth is composed of photons with energies greater than the band gap of silicon.
These higher energy photons will be absorbed by the solar cell, but the difference in energy
23

between these photons and the silicon band gap is converted into heat (via lattice vibrations —
called phonons) rather than into usable electrical energy.
Charge carrier separation
There are two main modes for charge carrier separation in a solar cell:
1)drift of carriers, driven by an electrostatic field established across the device.
2)diffusion of carriers from zones of high carrier concentration to zones of low carrier
concentration (following a gradient of electrochemical potential).
In the widely used p-n junction solar cells, the dominant mode of charge carrier separation is by
drift. However, in non-p-n-junction solar cells (typical of the third generation solar cell research
such as dye and polymer solar cell), a general electrostatic field has been confirmed to be
absent, and the dominant mode of separation is via carrier diffusion.
The p-n junction
Main articles: semiconductor and p-n junction.
The most commonly known solar cell is configured as a large-area p-n junction made from
silicon. As a simplification,one can imagine bringing a layer of n-type silicon into direct contact
with a layer of p-type silicon.In practice, p-n junctions of silicon solar cells are not made in this
way, but rather, by diffusing an n-type dopant into one side of a p-type wafer (or vice versa).
If a piece of p-type silicon is placed in intimate contact with a piece of n-type silicon,then a
diffusion of electrons occurs from the region of high electron concentration (the n-type side of
the junction) into the region of low electron concentration (p-type side of the junction). When
the electrons diffuse across the p-n junction, they recombine with holes on the p-type side. The
diffusion of carriers does not happen indefinitely however, because of an electric field which is
created by the imbalance of charge immediately on either side of the junction which this
diffusion creates. The electric field established across the p-n junction creates a diode that
promotes charge flow, known as drift current,that opposes and eventually balances out the
diffusion of electron and holes. This region where electrons and holes have diffused across the
junction is called the depletion region because it no longer contains any mobile charge carriers.
It is also known as the "space charge region".
Connection to an external load
Ohomic metal-semiconductor contacts are made to both the n-type and p-type sides of the solar
cell, and the electrodes connected to an external load. Electrons that are created on the n-type
side, or have been "collected" by the junction and swept onto the n-type side, may travel
through the wire, power the load, and continue through the wire until they reach the p-type
semiconductor-metal contact. Here, they recombine with a hole that was either created as an
24

electron-hole pair on the p-type side of the solar cell, or are swept across the junction from the
n-type side after being created there.
The voltage measured is equal to the difference in the quasi fermi levels of the minority carriers
i.e. electrons in the p-type portion, and holes in the n-type portion.

25

I = I
L
− I
D
− I
SH

where I = output current (amperes)
I
L
= photogenerated current (amperes)
I
D
= diode current (amperes)
I
SH
= shunt current (amperes)
The current through these elements is governed by the voltage across them:
V
j
= V + IR
S

where V
j
= voltage across both diode and resistor R
SH
(volts)
V = voltage across the output terminals (volts)
I = output current (amperes)
R
S
= series resistance (￿)
By the Shockley diode equation, the current diverted through the diode is:
where I
0
= reverse saturation current (amperes)
n = diode ideality factor (1 for an ideal diode)
q = elementary charge
k = Boltzmann’s constant
T = absolute temperature
For silicon at 25°C,
26


27

Effect of physical size
The values of I
0
, R
S
, and R
SH
are dependent upon the physical size of the solar cell. In
comparing otherwise identical cells, a cell with twice the surface area of another will, in
principle, have double the I
0
because it has twice the junction area across which current can
leak. It will also have half the R
S
and R
SH
because it has twice the cross-sectional area through
which current can flow. For this reason, the characteristic equation is frequently written in terms
of current density, or current produced per unit cell area:

Where,
J = current density (amperes/cm
2
)
J
L
= photogenerated current density (amperes/cm
2
)
J
o
= reverse saturation current density (amperes/cm
2
)
r
S
= specific series resistance (-cm
2
)
r
SH
= specific shunt resistance (-cm
2
)
This formulation has several advantages. One is that since cell characteristics are referenced to a
common cross-sectional area they may be compared for cells of different physical dimensions.
While this is of limited benefit in a manufacturing setting, where all cells tend to be the same
size, it is useful in research and in comparing cells between manufacturers. Another advantage
is that the density equation naturally scales the parameter values to similar orders of magnitude,
which can make numerical extraction of them simpler and more accurate even with naive
solution methods.
A practical limitation of this formulation is that as cell sizes shrink certain parasitic effects grow
in importance and can affect the extracted parameter values. For example, recombination and
contamination of the junction tend to be greatest at the perimeter of the cell, so very small cells
may exhibit higher values of J
0
or lower values of r
SH
than larger cells that are otherwise
identical. In such cases, comparisons between cells must be made cautiously and with these
effects in mind.

28

Cell temperature

Fig.17 Effect of temperature on the current-voltage characteristics of a solar cell

Temperature affects the characteristic equation in two ways: directly, via T in the
exponential term, and indirectly via its effect on I
0
. (Strictly speaking, temperature affects all of
the terms, but these two far more significantly than the others.) While increasing T reduces the
magnitude of the exponent in the characteristic equation, the value of I
0
increases in proportion
to exp(T). The net effect is to reduce V
OC
(the open-circuit Voltage) linearly with increasing
temperature. The magnitude of this reduction is inversely proportional to V
OC
; that is, cells with
higher values of V
OC
suffer smaller reductions in voltage with increasing temperature. For most
crystalline silicon solar cells the reduction is about 0.50%/°C, though the rate for the highest-
efficiency crystalline silicon cells is around 0.35%/°C. By way of comparison, the rate for
amorphous silicon solar cells is 0.20-0.30%/°C, depending on how the cell is made.
The amount of photogenerated current I
L
increases slightly with increasing temperature because
of an increase in the number of thermally generated carriers in the cell. This effect is slight,
however: about 0.065%/°C for crystalline silicon cells and 0.09% for amorphous silicon cells.
The overall effect of temperature on cell efficiency can be computed using these factors in
combination with the characteristic equation. However, since the change in voltage is much
stronger than the change in current, the overall effect on efficiency tends to be similar to that on
voltage. Most crystalline silicon solar cells decline in efficiency by 0.50%/°C and most
amorphous cells decline by 0.15-0.25%/°C. The figure to the right shows I-V curves that might
typically be seen for a crystalline silicon solar cell at various temperatures.

29

Series resistance

Fig.18 Effect of series resistance on the current-voltage characteristics of a solar cell
As series resistance increases, the voltage drop between the junction voltage and the terminal
voltage becomes greater for the same flow of current. The result is that the current-controlled
portion of the I-V curve begins to sag toward the origin, producing a significant decrease in the
terminal voltage V and a slight reduction in I
SC
, the short-circuit current. Very high values of R
S

will also produce a significant reduction in I
SC
; in these regimes, series resistance dominates and
the behavior of the solar cell resembles that of a resistor. These effects are shown for crystalline
silicon solar cells in the I-V curves displayed in the figure to the right.
Shunt resistance


Fig.19 Effect of shunt resistance on the current–voltage characteristics of a solar cell
As shunt resistance decreases, the current diverted through the shunt resistor increases for a
given level of junction voltage. The result is that the voltage-controlled portion of the I-V curve
begins to sag toward the origin, producing a significant decrease in the terminal current I and a
slight reduction in V
OC
. Very low values of R
SH
will produce a significant reduction in V
OC
.
Much as in the case of a high series resistance, a badly shunted solar cell will take on operating
characteristics similar to those of a resistor.These effects are shown for crystalline silicon solar
cells in the I-V curves displayed in the figure to the right.

30

Reverse saturation current


Fig.20 Effect of reverse saturation current on the current-voltage characteristics of a solar cell
If one assumes infinite shunt resistance, the characteristic equation can be solved for V
OC
:

Thus, an increase in I
0
produces a reduction in V
OC
proportional to the inverse of the logarithm
of the increase. This explains mathematically the reason for the reduction in V
OC
that
acompanies increases in temperature described above. The effect of reverse saturation current
on the I-V curve of a crystalline silicon solar cell are shown in the figure to the right. Physically,
reverse saturation current is a measure of the "leakage"of carriers across the p-n junction in
reverse bias. This leakage is a result of carrier recombination in the neutral regions on either
side of the junction.
4.4) DC-DC CONVERTER


Introduction.
The power switch was the key to practical switching regulators. Prior to the invention of the
Vertical Metal Oxide Semiconductor (VMOS) power switch, switching supplies were generally
not practical.The inductor's main function is to limit the current slew rate through the power
switch. This action limits the otherwise high-peak current that would be limited by the switch
resistance alone. The key advantage for using an inductor in switching regulators is that an

A linear regulator uses a resistive voltage drop to regulate the voltage,losing power (voltage
drop times the current) in the form of heat.A switching regulator’s inductor does have a voltage
drop and an associated current but the current is 90 degrees out of phase with the voltage.
Because of this,the energy is stored and can be recovered in the discharge phase of the
switching cycle.This results in a much higher efficiency and much less heat.
31


What is a Switching Regulator?
A switching regulator is a circuit that uses a power switch,an inductor,and a diode to transfer
energy from input to output. The basic components of the switching circuit can be rearranged to
from a step-down(buck) ,step-up(boost).or an inverter (flyback). These design are shown in fig.
21,22 ,23 & 24 respectively,where Figures 23 & 24 are the same except for the transformer and
the diode polarity.Feedback and control circuitry can be carefully nested around these circuits to
regulate the energy transfer and maintain a constant output within nornmal operating conditions.


Fig.21 Buck converter topologies


Fig..22 simple boost converter


Figure 23. Inverting topology.

32


Figure 24.Transformer flyback topology.

Why Use a Switching Regulator?

Switching regulators offer three main advantages compared to a linear regulators. First,
switching efficiency can be much better than linear. Second, because less energy is lost in the
transfer smaller components and less thermal management are required. Third, the energy stored
by an inductor in a switching regulator can be transformed to output voltages that can be greater
than the input (boost), negative (inverter), or can even be transferred trough a transformer to
provide electrical isolation with respect to the input.
Linear regulators provide lower noise and higher bandwidth ,their simplicity can sometimes
offer a less expensive solution. These are the advantages of the linear regulators.

There are, admittedly, disadvantages with switching regulators.They can be noisy and require
energy management in the form of a control loop.The solution to these control problems is
found integrated in modern switching modes controller chips.

Charge Phase
A basic boost configuration is depicted in fig.25. Assuming that the switch has been open for a
long time and that the voltage drop across the diode is negative, the voltage across the capacitor
is equal to the input voltage. When the switch closes, the input voltage, +V
IN
, is impressed
across the inductor and the diode prevents the capacitor from discharging +V
OUT
to ground.
Because the input voltage is DC, current through the inductor rises linearly with time at a rate
proportional to the input voltage divided by the inductance.


33


Figure 25. Charging phase: when the switch closes, current ramps up through the inductor.
Discharge Phase

Fig.26
shows the discharge phase. When the switch opens again, the inductor current continues
to flow into the rectification diode to charge the output.As the output voltage rises,the slope of
the current ,di/dt though the inductor reverses. The output voltage rises until equilibrium is
reached or: V
L
= L×di/dt
In other words, the higher the inductor voltage, the faster inductor current drops.



Fig.26 Discharge phade:when the switch opens,current flows to the load through the rectifying
diode

In a steady-state operating condition the average voltage across the inductor over the entire
switching cycle is zero. This implies that the average current through the inductor is also in
steady state. This is an important rule governing all inductor-based switching topologies. Taking
this one step further, we can establish that for a given charge time ton and a given input voltage
and with the circuit in equilibrium, there is a specific time, t
OFF
, for an output voltage. Because

34

the average inductor voltage in steady state must equal zero, we can calculate for the boost
circuit.


V
IN
× t
ON
= t
OFF
× V
L


and because: V
OUT
= V
IN
+ V
L


We can then establish the relationship: V
OUT
= V
IN
× (1 + t
ON
/t
OFF
)

using the relationship for duty cycle (D): t
ON
/(t
ON
+ t
OFF
) = D

Then for the boost circuit: V
OUT
= V
IN
/(1-D)

Similar derivations can be had for the buck circuit:
V
OUT
= V
IN
× D

and for the inverter circuit (flyback): V
OUT
= V
IN
× D/(1-D)


Introduction to Microcontroller A Microcontroller has a CPU in addition to a fixed amount of RAM,ROM,I/O ports, and a timer
all on a single chip.In other words,the processors,RAM,ROM,,I/Oports,and timer are all
embedded together on one chip; therefore, the designer cannot add any external memory, I/O,or
timer to it.The fixed amount of on-chip ROM,RAM and number of I/O ports in microcontrollers
makes them ideal for many applications in which cost and space are critical.In many
applications,for example a TV remote control,there is no need for the computing power of a 486
or even an 8086 microprocessor.

35

Block Diagram of Microcontroller:


CPU RAM ROM
I/O Timer Serial COM Port

Criteria for choosing a microcontroller


The first and foremost criterion in choosing a microcontroller is that it must the task at hand
efficiently and cost effectively. In analyzing the needs of a microcontroller-based project,we
must first see whether an 8-bit,16-bit,or 32-bit microcontroller can best handle the computing
needs of the task most effective
Among other considerations in this category are:
Speed
Packaging
Power consumption
The amount of RAM & ROM chip.
The number of I/O pins and the timer on the chip.
How easy to upgrade to higher-performance or lower power-consumption version.
Cost per unit.
All these criterion are fulfill by using a AVR ATMEGA8 Microcontroller

Features of AVR ATMEGA8 Microcontroller
￿ High-performance, Low-power AVR® 8-bit Microcontroller
￿ Advanced RISC Architecture
￿ 130 Powerful Instructions – Most Single-clock Cycle Execution
￿ 32 x 8 General Purpose Working Registers
￿ Fully Static Operation
￿ Up to 16 MIPS Throughput at 16 MHz
￿ On-chip 2-cycle Multiplier
￿ High Endurance Non-volatile Memory segments
￿ 8K Bytes of In-System Self-programmable Flash program memory
￿ 512 Bytes EEPROM
￿ 1K Byte Internal SRAM
￿ Write/Erase Cycles: 10,000 Flash/100,000 EEPROM
36

￿ Data retention: 20 years at 85°C/100 years at 25°C(1)
￿ Optional Boot Code Section with Independent Lock Bits
￿ In-System Programming by On-chip Boot Program
￿ True Read-While-Write Operation
￿ Programming Lock for Software Security

￿ Peripheral Features
￿ Two 8-bit Timer/Counters with Separate Prescaler, one Compare Mode
￿ One 16-bit Timer/Counter with Separate Prescaler, Compare Mode, and Capture

￿ Mode
￿ Real Time Counter with Separate Oscillator
￿ Three PWM Channels
￿ 8-channel ADC in TQFP and QFN/MLF package

￿ Eight Channels 10-bit Accuracy
￿ 6-channel ADC in PDIP package

￿ Six Channels 10-bit Accuracy

￿ Byte-oriented Two-wire Serial Interface
￿ Programmable Serial USART
￿ Master/Slave SPI Serial Interface
￿ Programmable Watchdog Timer with Separate On-chip Oscillator
￿ On-chip Analog Comparator

￿ Special Microcontroller Features
￿ Power-on Reset and Programmable Brown-out Detection
￿ Internal Calibrated RC Oscillator
￿ External and Internal Interrupt Sources
￿ Five Sleep Modes: Idle, ADC Noise Reduction, Power-save, Power-down,
andStandby

￿ I/O and Packages
￿ 23 Programmable I/O Lines
￿ 28-lead PDIP, 32-lead TQFP, and 32-pad QFN/MLF
￿ Operating Voltages
￿ 2.7 - 5.5V (ATmega8L)
￿ 4.5 - 5.5V (ATmega8)
￿ Speed Grades
37

￿ 0 - 8 MHz (ATmega8L)
￿ 0 - 16 MHz (ATmega8)
￿ Power Consumption at 4 Mhz, 3V, 25°C
￿ Active: 3.6 mA
￿ Idle Mode: 1.0 mA
￿ Power-down Mode: 0.5 A

LOAD (BATTERY
):

The current limiting method is required to charged the liead-acid batteries.The charge time of a
sealed lead-acid battery is 12-16 hours (up to 36 hours for larger capacity batteries). With higher
charge currents and multi-stage charge methods, the charge time can be reduced to 10 hours or
less. Lead-acid cannot be fully charged as quickly. It takes about 5 times as long to recharge a
lead-acid battery to the same level as it does to discharge.
A multi-stage charger first applies a constant current charge, raising the cell voltage to a preset
voltage. Stage 1 takes about 5 hours and the battery is charged to 70%. During the topping
charge in Stage 2 that follows, the charge current is gradually reduced as the cell is being
saturated. The topping charge takes another 5 hours and is essential for the well being of the
battery. If omitted, the battery would eventually lose the ability to accept a full charge. Full
charge is attained after the voltage has reached the threshold and the current has dropped to 3%
of the rated current or has leveled off. Fig. shows the charging characteristics of battery.




Fig.27 Charging Characteristics of Battery

38


CHAPTER 5.
HARDWARE DESCRIPTION



39

CIRCUIT ANALYSIS & DESCRIPTION

To track the Maximum power point, a Hardware section is required which consist of different
parts. Each part performs the different function.
The different hardware parts are:

• Microcontroller
• Buffer
• Opto –coupler
• Transistor Amplifier
• Buck converter
• Current to Voltage converter using OP-AMP
• Positive voltage to Negative Voltage Converter
• Micro switch which connected to Port of microcontroller
• LED which connected to Port of microcontroller
• Positive 5V regulated Power Supply
• LCD (Liquid Crystal Display)
Specification of the MPPT Solar Charge Controller :


Design for 1Amp Current
Consider the,
Solar Photovoltaic Module Voltage = 25 Volt,
which is the Input of the Buck Converter so ,Vin = 25V
Required Voltage for Charging a 12V Battery about 13.5Volt,
So we consider the Output of the Buck converter,
Vout = 15Volt and consider the Output current Iout = 1Amp

40


Now

DESIGNING OF BUCK CONVERTER


Fig.28 Buck converter using IC3524



41

Vin = 25 Volt
Vout = 15Volt
Iout = 1Amp
f = 31.25 KHz
L =( 2.5 x 25 x 15)/31.25 x 1000 x ( 15 + 25 ) x 1

= 0.75 Mh
Consider, ∆Vo = 50mV

Co = 1 x 15 / 0.05 x 31.25 x1000 (15 +25)
= 240 µF
Nearest available value is 220µF, 35V.
To reduce the ripple component a 0.1 µF Non-electrolytic capacitor is connected in parallel
with the electrolytic capacitor.

Now Enhancement of the Output Current


Design for 5Amp Current
Vin = 25 Volt
Vout = 15Volt
Iout = 5Amp
f= 31.25 KHz
L =( 2.5 x 25 x 15)/31.25 x 1000 x ( 15 + 25 ) x 5

= 0.15mH
Ripple Voltage
∆Vo = 50mV

Co = 5 x 15 / 0.05 x 31.25 x1000 (15 +25)
= 1200 µF
Nearest available value is 1000uF, 35V & 220µF.
These two are connected in parallel to get 1220µF
42


BLOCK DIAGRAM OF THE CIRCUIT


SWITCH
(micro)
LED
BUFFER
AVR ATMEGA8 MICROCONTROLLER
OPTO-COUPLER
SOLAR PV
ARRAY
LOAD
BUCK
CONVETER
AMPLIFIER
LCD
DISPLAY

Fig.29

43

CIRCUIT DIAGRAM OF MPPT CHARGE CONTROLLER



1K
1N4148
1N4148
+5V
100E
21
1000uF
1
PD1 3
+12V
1
10E
1N4148
1N4148
+12V
0.1uF
10K
4
22
2
1
1N4148
1K
100nF
1K,1/2W
0.1uF
2
5
PD2
20
3
2 TL084
-12V
+5V
1N4148
0.uF
470E
100uF
100uF
6
PD3
9
4
3
1N4148
3
SPV
0.1uF
VI
PD4
10
5
+5V
2.2K
1K
+12V
0.1E
VO
+5V
0.75mH
PD5
8
6
11
1N4148
0.1E
+5V
1 3
TL084
LM7805
R17
PD6
7
7
C4
1n
12
1N4148
+5v
2
+
ATMEGA 8 MICRO CONTROLLER
TC7660
47K
PD7
23
8
13
Batt.
-12V
1N4148
ADC0
-
47K
PB0
10uF
14
330E
1K
10K
1K
+5V
PB1
ADC1 24
15
330E
5K
SW Push button
10K
10uF
PB2
SW Push button
ADC2 25
16
330E
1K
47K
+5V
CD4049
BA159
10K
10K
PB3
ADC3 26
17
LCD DISPLAY 16X2
47K
10K
PC817
10K
ADC4 27
18
10K
10K
+5V
BD139
100uF
10uF
+5V
ADC5 28
19
PB4
10K
1N4148
1K
SW Push button
IRF
9640
100uH
+12v
0.1uF
PD0 2
1
PB5


Fig.30

44

PIN CONFIGURATION OF AVR ATMEGA8 MICROCONTROLLER




PIN FUNCTION


PIN 1: PC6- Generic IO pin PC6(Port C6)
/RESET- Reset Pin for MCU, active at low
PIN 2: PD0- Generic IO pin PD0 (Port D0)
PIN 3: PD1- Generic IO pin PD1 (Port D1)
PIN 4: PD2- Generic IO pin PD2 (Port D2)
INTO- External interrupt source 0 to the MCU.
PIN 5: PD3- Generic IO pin PD3 (Port D3)
INT1- External interrupt source 1 to the MCU.
PIN 6: PD4- Generic IO pin PD4(Port D4)
T0- Timer/Counter0 clock source
XCX- USART external clock
PIN 7: Vcc – Power Supply(+5V)
PIN 8: GND – Common Ground
PIN 9: PB6- Generic IO pin PB6(Port B6)
XTAL1-Pin for external clock source (crystal,resonator) for MCU(input) TOSC1-Timer
Oscillator Pin1-clock source for asynchronous clocking of
45

Timer/counter1
PIN 10: PB7- Generic IO pin PB6(Port B7) XTAL2-Pin for external clock source
(crystal,resonator) for MCU(inTOSC2-Timer Oscillator Pin2-clock source for asynchronous
clocking of Timer/counter1
PIN 11: PD5- Generic IO pin PD5(Port D5) T1-Timer/Counter1 clock source.
PIN 12: PD6- Generic IO pin PD6(Port D6) N0: AIN0 Analog comparator Positive
input.When configured as an input and with the internal MOS pull-up resistor switched
off,thin film also serves as the positive input of the on chip analog comparator.
PIN 13: PD7- Generic IO pin PD7(Port D6)AIN1: AIN1 Analog comparator Negative input.
When configured as an input and with the internal MOS pull-up resistor switched off, thin
film also serves as the negative.
PIN 14: PB0- Generic IO pin PB0(Port B0)
ICP1-Timer/Counter1 input capture pin.
PIN 15: PB1- Generic IO pin PB1(Port B1)
OC1A-Output Compare matchA output.The pin can serve as an external output for the
Timer/Counter1 output CompareA.The pin has to be configured as an output to serve the
function. The OC1A pin is also the output pin for the PWM mode timer function.
PIN 16: PB2- Generic IO pin PB2(Port B2)
/ss-slave select pin for using with SPI.
OC1A-Output Compare matchB output.The pin can serve as an external output for the
Timer/Counter1 output CompareB.The pin has to be configured as an output to serve the
function. The OC1A pin is also the output pin for the PWM mode timer function.
PIN 17: PB3- Generic IO pin PB3(Port B3)
OC2-Timer/Counter2 output compare match output. The pin can serve as an external output
for the timer/counter2 output compare.the pin has to be configured as an output to serve this
function.The OC2 pin is also the output pin for the PWM mode timer function.
PIN 18: PB4- Generic IO pin PB4(Port B4)
MISO-Data output pin for memory uploading or SPI.
PIN 19: PB5- Generic IO pin PB5(Port B5)
SCK-Clock input pin for memory up/downloading or SPI.
PIN 20: AVCC- Power supply for AD Converter.
PIN 21: AREF- Reference voltage for AD converter.
PIN 22: GND- Common Ground.
PIN 23: PC0- Generic IO pin PC0(Port C0)
ADC0-Analog to Digital input ADC0.
PIN 24: PC1- Generic IO pin PC1(Port C1)
ADC1-Analog to Digital input ADC1.
PIN 25: PC2- Generic IO pin PC2(Port C2)
ADC2-Analog to Digital input ADC2.
PIN 26: PC3- Generic IO pin PC3(Port C3)
46

ADC3-Analog to Digital input ADC3.
PIN 27: PC4- Generic IO pin PC4(Port C4)
ADC4-Analog to Digital input ADC4.
SDA-2-wire serial bus Data.When the TWEN bit in TWCR is Set (one to enable the 2-wire
serial interface, pin is disconnected from the port and becomes the erial Data I/O pin for the 2-
wire serial interface.
PIN 28: PC5- Generic IO pin PC5(Port C5)
ADC5-Analog to Digital input ADC5.
SCL-2-wire serial Interface Clock. When the TWEN bit in TWCR is Set (one to enable the 2-
wire serial interface, pin is disconnected from the port and becomes the serial Clock I/O pin for
the 2-wire serial interface.

To track the Maximum Power Point, Solar Photo Voltaic Array acts as a source which is
connected to a Buck Converter. Buck Converter is a step down converter which is used to
step down the voltage which is generated from a solar photo voltaic array. The output of
the Buck Converter is controlled by a switch. MOSFET acts as a switch. This switch is
controlled by the duty cycle of the PWM (Pulse Width Modulation) which is connected to
a Gate of the MOSFET.
This PWM is generated from a AVR ATMEGA8 Microcontroller.

Pin No. 15,16,17 of Microcontroller generates the PWM.
.
Generation of PWM from the Microcontroller

Timer/Counter2 is a general purpose, single channel, 8-bit Timer/Counter module.The main
features are:

• Single Channel Counter
• Clear Timer on Compare Match (Auto Reload)
• Glitch-free, phase Correct Pulse Width Modulator (PWM)
• Frequency Generator
• 10-bit Clock Prescaler
• Overflow and Compare Match Interrupt Sources (TOV2 and OCF2)
• Allows Clocking from External 32 kHz Watch Crystal Independent of the I/O Clock.

47


A simplified block diagram of the 8-bit Timer/Counter.


Fig.31

The Timer/Counter (TCNT2) and Output Compare Register (OCR2) are 8-bit registers.
Interrupt request.signals are all visible in the Timer Interrupt Flag Register (TIFR).All interrupts
are individually masked with the Timer Interrupt Mask Register (TIMSK).

Definitions:
Many register and bit references in this document are written in general form. A lower case “n”
replaces the Timer/Counter number, in this case. However, when using the register or bit
defines in a program, the precise form must be used (i.e., TCNT2 for accessing Timer/Counter2
counter value and so on).
48


Timer/Counter
Clock Sources:
The Timer/Counter can be clocked by an internal synchronous or an external asynchronous
clock source. The clock source clkT2 is by default equal to the MCU clock, clk I/O. When the
AS2 bit in the ASSR Register is written to logic one, the clock source is taken from the
Timer/Counter Oscillator connected to TOSC1 and TOSC2.

Counter Unit:
The main part of the 8-bit Timer/Counter is the programmable bi-directional counter unit.

Counter Unit Block Diagram


Fig.32
Signal description (internal signals):
count Increment or decrement TCNT2 by 1.
direction Selects between increment and decrement.
clear Clear TCNT2 (set all bits to zero).
clkT2 Timer/Counter clock.
TOP Signalizes that TCNT2 has reached maximum
value.

BOTTOM Signalizes that TCNT2 has reached minimum
Value (zero)
Fast PWM Mode: The fast Pulse Width Modulation or fast PWM mode (WGM21:0 = 3) provides a high PWM
waveform generation option. The fast PWM differs from the other PWM option by its single-
slope operation. The counter counts from BOTTOM to MAX then restarts from BOTTOM. In
non-inverting Compare Output mode, the Output Compare (OC2) is cleared on the Compare
Match between TCNT2 and OCR2, and set at BOTTOM.In inverting Compare Output mode,
the output is set on Compare Match and cleared at BOTTOM.Due to the single-slope operation,
the operating frequency of the fast PWM mode can be twice as high as the phase correct PWM
mode that uses dual-slope operation. This high frequency makes the fast PWM mode well
49

suited for power regulation, rectification, and DAC applications. High frequency allows
physically small sized external components (coils, capacitors), and therefore reduces total
system cost.

Fast PWM Mode, Timing Diagram

Fig.33

This 8-bit PWM is connected to a buffer IC.

Digital Buffer:

Output of the NOT gate is the "complement" or inverse of its input signal. For example, when
its input signal is "HIGH" its output state will NOT be "HIGH" and when its input signal is
"LOW" its output state will NOT be "LOW", it inverts. Another single input logical device used
a lot in electronic circuits and which is the reverse of the NOT gate is called a Digital Buffer.
A Digital Buffer is another single input device that does no invert or perform any type of
logical operation on its input signal as its output exactly matches that of its input signal. In other
words, its Output equals its Input. It is a "Non-inverting" device and so will give us the Boolean
expression of: A = Q.
Then we can define the operation of a single input Digital Buffer as being:
"If A is true, then Q is true"
A Digital Buffer can also be made by connecting together two NOT gates as shown below. The
first will "invert" the input signal A and the second will "re-invert" it back to its original level.
50

1
2
BUFFER
A
A
1
2
AA
1
2
A'

Fig.34

Truth Table


A Q
0 0
1 1

HEX INVERTER IC CD4049 used as a buffer
when two inverter are connected i.e
output of the one inverter is connected to the other that produces the buffer. Buffer is
used to boost up the PWM signal & also used for High impedance matching at the
output.

OPTO-COUPLER


Output of the Buffer is connected to a Opto-coupler. Opto-coupler is used as a
isolator. It isolate the digital section from the high voltage power section. This isolator
is used to save the low voltage digital circuit from the high voltage power circuit.
PC817 used as a Opto-coupler.



51


Theory of Optocoupler


The optical coupler is a venerable device that offers the design engineer new freedoms in
designing circuits and systems. Problems such as ground loop isolation,common mode noise
rejection, power supply transformations, and many more problems can be solved or simplified
with the use of an optical coupler.
Operation is based on the principle of detecting emitted light. The input to the coupler is
connected to a light emitter and the output is a photodector, the two elements being separated by
a transparent insulator and housed in a light–excluding package. There are many types of
optical couplers; for example, the light source could be an incandescent lamp or a light emitting
diode (LED). Also,the detector could be photovoltaic cell, photoconductive cell, photodiode,
phototransistor, or a light–sensitive SCR. By various combinations of emitters and detectors, a
number of different types of optical couplers could be assembled. Once an emitter and detector
have been assembled as a coupler, the optical portion is permanently established so that device
use is only electronic in nature. This eliminates the need for the circuit designer to have
knowledge of optics.
COUPLER CHARACTERISTICS
The PC817 is an optical coupler consisting of a gallium arsenide (GaAs) LED and a silicon
phototransistor.
INPUT
For most applications the basic LED parameters IF and VF are all that are needed to define
the input. Fig.36 shows these forward characteristics, providing the necessary information to
design the LED drive circuit. Most circuit applications will require a current limiting resistor in
series with the LED input.
OUTPUT
The output of the coupler is the phototransistor. The basic parameters of interest are the
collector current IC and collector emitter voltageVCE.Figure37 is a curve of VCE(sat) versus
IC for two different drive level.
COUPLING
To fully characterize the coupler, a new parameter, the dc current transfer ratio or coupling
efficiency () must be defined. This is the ratio of the transistor collector current to diode
current IC/IF.


52


RESPONSE TIME
The speed is fairly slow compared to switching transistors, but is typical of phototransistors
because of the large base–collector area. The switching time or bandwidth of the coupler is a
function of the load resistor RL because of the RLCO time constant where CO is the parallel
combination of the device and load capacitances.

Fig.35 Opto-Coupler


Fig.36 Input Characteristic of Opto-Coupler


53



Fig.37 Output Characteristic of Opto-Coupler
AMPLIFIER


Output of the Opto-coupler is connected to a Transistor Amplifier which is used to amplify
the DC level of the PWM signal. BD139 power transistor is used as a Amplifier when
proper biasing is applied to the circuit.

Circuit Diagram of the Amplifier:

Opto-coupler
output
1K,1/2W
2.2K
100E
SPV
O/P of Amplifier


Fig.38

This Amplifier output is used to drive the Gate of MOSFET. So this amplifier is used as a
driver circuit of the MOSFET.
MOSFET used as a switch for Buck Converter
54


Why we use Buck Converter:
We know that for charging a 12Volt battery minimum required voltage is 13.5 Volt, but
Solar PV Module produces a 25Volt.So to step down the voltage Buck Converter or Step-
Down converter is required.


BUCK CONVERTER
3.3mH
IRF 9640
MOSFET
100uF
0.1uF
Output of
Buck conve
1K,1/2 W
100E
Amplified PWM
SPV Voltage

Fig.39

Buck Converter:
In a regulator ,the average output voltage Va,is less than the input voltage,Vs hence the name
“buck”, a very popular regulator. The circuit diagram of a buck regulator using a MOSFET.The
circuit operation can be divided into two modes. Mode 1 begins when MOSFET is switched on
at t=0. The input current,which rises,flows through filter inductor L, filter capacitor C and load
resistor R.Mode2 begins when MOSFET is switched off at t=t1.The freewheeling diode Dm
conducts due to energy stored in the inductor and the inductor current continues to flow through
L,C,load and diode Dm. The inductor Current falls until MOSFET is switched on again in the
next cycle. The equivalent circuits for the modes of operation are shown in figure.39.The
waveforms for the voltage & current flows continuously in the inductor L.It is assumed that the
current rises and falls linearly in practical circuits, the switch has a finite, nonlinear
resistance.Its effect can generally be negligible in most applications. Depending on the
switching frequency, filter inductance and capacitance the inductor current could be
discontinuous.
The voltage across the inductor L is , in general
eL = L di/dt
Assuming that the inductor current rises linearly from I
1
to I
2
in time t
1
,
Vs – Va = L ( I
2
-I
1
/t
1
) = L ∆I/t
1

Or t1 = ∆IL/(Vs- Va)
and the inductor current falls linearly from I2 to I1 in time t2,
-Va = - L ∆I/t
2

55

t
2
= ∆IL/Va
where ∆I=I
2
– I
1
is the peak-peak ripple current of the inductor L. equating the
value of ∆I,
∆I = (Vs – Va)t
1
/L = Va t
2
/L
Substituting t
1
= kT and t
2
= (1 - k)T yields the average output voltage as
Va = Vs t
1
/T = kVs
Assuming a lossless circuit Vs x Is = Va x Ia=KxVsxIa and the average input current Is = k x Ia
The switching period T can be expressed as
T = 1/f = t
1
+t
2
= ∆IL/(Vs – Va) + ∆IL/Va = ∆ILVs/(Va(Vs - Va))
Which gives the peak-to-peak ripple current as
∆I = Va(Vs - Va)/fLVs
∆I = Vsk(1 - k) /fL
Using Kirchhoff’s current law, we can write the inductor current iL as
iL = ic +io
If we assume that the load ripple current ∆io is very small and negligible, ∆iL = ∆ic.
The average capacitor current, which flows into for t1 +t2 = T/2 is
Ic = ∆I/4
The cacitor voltage is expressed as
Vc=1/C ic dt +vc (t=0)
And the peak-to-peak ripple voltage of the capacitor is
∆Vc =Vc – Vc(t = 0)=1/C T/ 2 ∆I/4 dt = ∆I T/8x C= ∆I
0
Substituting the value of ∆I from Eq,
∆Vc = Va (Vs – Va0/(8LCf
2
Vs)
∆Vc = Vsx k (1-k)/(8LCf
2
)

Condition for Continuous Inductor Current and Capacitor Voltage:


If IL is the average inductor current , the inductor ripple current ∆I = 2IL
We get,
Vs(1 - k)k/fL = 2IL = 2 Ia = 2kVs/R
Which gives the critical vaule of the inductor Lc as Lc = L = (1 - k) R/2f
If Vc is the average capacitor voltage, the capacitor ripple voltage ∆Vc = 2Va
We get
Vs x (1-k) x k/(8xLxCxf
2
) = 2xVa = 2xkxVs
Which gives the critical value of the capacitor Cc as
Cc =C = 1-k/(16xLxf
2
)
The buck converter requires only for on-off the MOSFET and has efficiency greater than
90%.The di/dt of the load current is limited by inductor L. However, the input current is
discontinuous and a smoothing input filter is normally required.
56


The output of the Buck Converter produces the voltage which is less from the solar
PV Module array voltage. The Output of the Buck Converter is used to charging a
12V,7Amp-hr Lead acid Battery.



The Battery is charged by the Maximum Power Point tracking (MPPT) method using
Microcontroller. To track the Maximum Power Point, it is required to scene the solar PV
module voltage & Current and also required to scene the Buck Converter Output Voltage
& also Current which is used to charged the battery.

We know that Microcontroller is a Digital system and its operating voltage is +5V.But
Solar PV Module & Buck Converter produces the High voltage. It is required to reduced
in +5V by using a voltage divider method. After reducing the high voltage analog signal
become a digital signal. These digital signal are read by the ADC(A-to-D) port of the AVR
ATMEGA8 Microcontroller.

Similarly, current of the Solar PV module & current which is produced by the Buck
Converter is converted into a voltage. These voltages are also read by the ADC Port of the
AVR ATMEGA8 Microcontroller.


Now the Voltage Divider Method:


Solar PV Voltage
10K
1N4148
1N4148
1K
+5V
47K

Fig.40

Solar PV Module Voltage = 25V
It is required to reduce the maximum upto to +5V.
R
1
= 47K
57

R
2
= 10K
R
2
/(R
I
+ R
2
) x 25 = 10K/(10K + 47K) x 25 V = 4.38V

This voltage is connected to a ADC port of the ATMEGA8 Microcontroller.
Similarly, Output of the Buck Converter is required to reduced upto +5V.
Output of Buck Converter = 15V.
R
1
= 22K
R
2
= 10K
R
2
/(R
1
+ R
2
)X15 = 10K/(10K + 22K) x 15 V = 4.68V
22K10K
Buck Converter O/P
1N4148
1N4148
1K
+5V

Fig.41

Current to Voltage Converter:

10K
-5V
0.1E
+5V
10K
3
2
7
4
6
1
5
+-
V+V-
OUT
OS1
OS2
1K
3
2
7
4
6
1
5
+-
V+V-
OUT
OS1
OS2
47K
12V,7A-h Battery
O/P of the Buck Converter
or
Solar PV Voltage
+5V
-5V


Fig.42

It is an Inverting amplifier using Op-Amp TL084.
If Battery is charged by the 1A Current. We connect a 0.1 resistance which is
connected in series with the Battey. So Maximum Voltage is drpped across 0.1
is 0.1V.
58

Now this Voltage is amplified by using a Inverting amplifier.

For Inverting Amplifier,
Vo/Vin = -Rf/Rin
Vo should be maximum 5V.
Gain hould be Maximum (5/0.1)=50
We consider the Rin = 1k
R
f
= 50K

We consider the 47K resistor because nearest available Value of 50k resistor is 47K.It is
Inverting amplifier so it produces a -4.7V. To obtain a +4.7V output a similar amplifier is
designed whose gain is 1. So we consider R
f
= R
in
=10K.

So, all the Voltage & Current of a Solar PV Module & Buck Converter are converted into
+5V.

Now all the voltage & Current of a Solar PV Module & Buck Converter are connected to
a ADC Port of a Microcontroller.
Pin No.23,24,25,26 of a Microcontroller used as a ADC Channel.

The Micro Switches are connected to a Port D4 & D5 to Set or Reset the Microcontroller.

Pin No.6,11 of a Microcontroller used as a Port D4 & D5.


Light Emitting Diode (LED) are connected to a Port B0,B1,B2 to indicate the different
operating condition.

Pin No.14,15,16 of a Microcontroller used as a Port B0, B1 & B2.


Maximum Power Point Tracking (MPPT) Method:


Maximum Power Point Tracking is performed by using a very advanced method
(Incremental Conductance Method) which is independent of temperature, other
atmospheric condition that is used to track the maximum Power Point very quickly.
Maximum Power Point is tracked by using a microcontroller. So, to track the maximum
power point, Solar PV Module voltage is connected to a source of the p- channel MOSFET
and also connected to a ADC of the Microcontroller. Solar PV module Current is also
converted into a Voltage and is connected to a ADC of the microcontroller.
59

Similarly, Buck converter output Voltage is connected to a ADC of the microcontroller.
The output of the Buck is used to charging a Battery.So the current of the Buck Converter
is converted to a voltage which is connected to a ADC of the microcontroller.

For Maximum Power Point tracking Solar PV Module voltage is connected to a Buck
Converter which is controlled by the duty cycle of the PWM. The PWM is generated from
the AVR ATMEGA 8 Microcontroller.

So, to track the Maximum Power Point ,
For a particular duty cycle of the PWM,
Measure the

Solar PV Module Voltage ( Vin1)
Solar PV Module Current (Iin1)
Buck Converter Output Voltage (Vout1)
Buck Converter Output Current (Iout1)

Now increase the duty cycle by 1
Measure the

Solar PV Module Voltage ( Vin2)
Solar PV Module Current (Iin2)
Buck Converter Output Voltage (Vout2)
Buck Converter Output Current (Iout2)

Now measure the difference between the Voltage & current to obtain the conductance
∆Vin = Vin2 – Vin1
∆Iin = Iin2 – Iin1
∆Vout = Vout2 – Vout1
∆Iout = Iout2 – Iout1
So the Incremental Conductance (S1) = ∆Iin / ∆Vin
And instanteneous Conductance (S2) = - ( Iin2/ Vin2)
Then the Maximum Power Point will tracked that means MPPT will performed.

So to track the Maximum Power Point a Software Programming is required to adjust the
duty cycle automatically & extract the Maximum Power from the Solar PV Module for
every change in Voltage & Current of the PV module.

60


Votage Converter Circuit:
NC
10uF
10uF
NC
-12Volt
NC
+12Volt
IC
TC7660

Fig.43
This circuit is used to convert from +12Volt to -12Volt supply. We know that Output of
the battery produce +12Volt.There is no any -12Volt supply.But in this circuit amplifier is
used which is made by Operational-Amplifier(Op-Amp).For biasing of the Op-Amp
+12Volt & -12volt both are required.
At last Output is displayed on a LCD .Solar PV module Voltage & Current and also
Buck Converter Output Voltage & Current all are read from the LCD(Liquid crystal
Display).
It is a 16*2 Character LCD.

Fig.44

61


CHAPTER 6.
SOFTWARE DESCRIPTION.


62


SOFTWARE SECTION

The Solar Photovoltaic Maximum Power Point Tracking charge Controller is controlled by the
variation of the duty cycle of the PWM which is used to control the Buck Converter.

This control is done by the microcontroller. There are different programming language which is
used in Microcontroller such as Assembly, C language ,Basic etc.

Here, a special type of Software is used to compile the programmed in microcontroller. Name
of the Software is AVR BASCOM. In the BASCOM software we can write the program in
different languages such as Assembly, C language ,Basic etc.

But in this project Program is written by the AVR BASCOM BASIC language. This language
is very easy to write and also very easy to debug the error.

So to write the Software coding, a algorithm is required. Here a special type of algorithm is
used to track the Maximum Power Point. The Algorithm is Incremental Conductance method.
This algorithm is independent of temperature, other atmospheric condition.

63


DESCRIPTION OF THE ALGORITHM (Incremental Conductance Method):
Detetc the Solar PV Module Volage V1 & Output Current I1 for a particular duty cycle of the
PWM.
Measure the Power P1 =V1xI1.
Now increase the duty cycle by 1 and measure the Solar Module Voltage V2 & O/P Current I2
.

Measure the Power P2 =V2xI2
Measure ∆V = V2 – V1
∆I = I2 – I1

If ∆V = 0 then ∆I = 0
If ∆I = 0 then output voltage remains the same

If ∆I ≠ 0 & If ∆I > 0 decrease the duty cycle by 1

If ∆I < 0 increase the duty cycle by 1

If ∆V≠ 0 then ∆I/∆V = - (I2/ V2)

If ∆I/∆V = - (I2/ V2) then output remains same

If ∆I/∆V ≠ - (I2/ V2) then if ∆I/∆V > - (I2/ V2)

Increase the duty cycle by 1
if ∆I/∆V < - (I2/ V2) then decrease the duty cycle by 1

64

FLOW CHART OF MPPT using (INC)






YES

NO
YES YES
NO NO
YES YES
NO NO
NO
Detect
V(k) &I(k)
Compute dV & dI

dV=V(k)-V(k-1)
dI=I(k)
-
I(k
-
1)

START

dV=0
Renew V(k) & I(k)
V(k-1)=V(k)
I(k-1)=I(k)
dI/dV
=
-
I/V

dI/dV
>
-
I/V

dI>0

Decrease O/P
voltage
Increase O/P
Voltage
Decrease
O/P Voltage
dI=0

O/P Voltage remains
the same
Increase O/P
voltage
O/P
Volt.remains
the same

65


Coding of Incremental Conductance Method
(Using AVR BASCOM BASIC Language)
'$sim
$regfile = "m8def.dat"
$crystal = 8000000
' /////////////////////////////////////////////////////////////////////////////////////////////'
Config Adc = Single , Prescaler = Auto , Reference = Avcc
Start Adc
'//////////////////////////////////////////////////////////////////////////////////////////////'
Dim W1 As Word 'spv voltage1'
Dim W2 As Word 'o/p current1'
Dim W3 As Word 'spv voltage2'
Dim W4 As Word 'o/p current2'
Dim S1 As Integer 'change in voltage'' '
Dim S2 As Integer 'change in current''
Dim R1 As Single 'change in conductance'
Dim R2 As Single 'instanteneous conductance'
'////////////////////////////////////////////////////////////////////////////////////////////////////////’
Config PortB.3 = Output
Config Timer2 = Pwm , Prescale = 8 , Pwm = On , Compare Pwm = Clear Up
'///////////////////////////////////////////////////////////////////////////////////////////////////////////’
Dim Gp As Integer 'duty cycle of Pwm'
Gp = 1
Main:
Compare2 = Gp
Waitms 200
B:
W1 = Getadc(2)
Waitms 200
W2 = Getadc(3)
Waitms 200
'//////////////////////////////////////////////////////////////////////////////////////////////'
Gp = Gp + 1 'duty cycle is increased by 1'
Compare2 = Gp
Waitms 200
Start:
W3 = Getadc(3)
Waitms 200
W4 = Getadc(2)
66


'///////////////////////////////////////////////////////////////////////////////////////////'
S1 = W3 - W1
S2 = W4 - W2
'///////////////////////////////////////////////////////////////////////////////////////// ‘

If S1 = 0 Then
Goto C
Else
Goto D
End If
'/////////////////////////////////////////////////////////////////////////////////////'
C:
If S2 = 0 Then
Goto E
Else
Goto F
End If
'//////////////////////////////////////////////////////////////////// /////////////////////// ‘
D:
R1 = S2 / S1
R2 = W4 / W3
'///////////////////////////////////////////////////////////////////////////////////////// ‘
If R1 = R2 Then
Goto G
Else
Goto H
End If
'/////////////////////////////////////////////////////////////////////////////////////////// '
E:
Gp = Gp
Compare2 = Gp
Goto End
F:
If S2 > 0 Then
Goto I
Else
Goto J
End If
'////////////////////////////////////////////////////////////////////'
67


G:
Gp = Gp
Compare2 = Gp
Goto End
H:
If R1 > R2 Then
Goto K
Else
Goto L
End If
'/////////////////////////////////////////////////////////////////////////'
I:
Gp = Gp + 1
Compare2 = Gp
If Gp > 200 Then
Gp = 200
Compare2 = Gp
End If
Goto End
'/////////////////////////////////////////////////////////////////////////////////////////////////'
J:
Gp = Gp - 1
Compare2 = Gp
If Gp = 255 Then
Gp = 0
End If
Goto End
K:
Gp = Gp + 1
Compare2 = Gp
If Gp > 200 Then
Gp = 200
Compare2 = Gp
End If
Goto End
'////////////////////////////////////////////////////////////////////////////////////////////////////////////////////'

68


L:
Gp = Gp - 1
Compare2 = Gp
If Gp = 255 Then
Gp = 0
End If
Goto End
End:
W3 = W1
W4 = W2
Goto Start
'



69


Description of the Algorithm (Modified Incremental Conductance Method):

Vmax & Imax are the maximum desiarable voltage & Current