solar powered palnt

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

Department of Electronics & Tele-communication Engineering

JADAVPUR UNIVERSITY,

KOLKATA- 700032, INDIA

FACULTY OF ENGINEERING & TECHNOLOGY

JADAVPUR UNIVERSITY

CERTIFICATE OF APPROVAL *

The foregoing thesis is hereby approved as a creditable study of an engineering subject and

presented in a manner satisfactory to warrant acceptance as pre-requisite to the degree for which

it has been submitted. It is understood that by this approval the undersigned do not necessarily

endorse or approve any statement made, opinion expressed or conclusion drawn there in but

approve the thesis only for which it is submitted.

Committee on final examination

For the evaluation of the Thesis

……………………………………….

……………………………………….

Examiners

* Only in case the thesis is approved

A CK N O W L E D G E M E N TA CK N O W L E D G E M E N TA CK N O W L E D G E M E N TA CK N O W L E D G E M E N T

It gives m e im m ense pleasure to express m y deepest sense of gratitude and sincere thanks to m y highly

respected and esteem ed supervisor P rof. P rof. P rof. P rof. H iranm ayH iranm ayH iranm ayH iranm ay Saha,Saha,Saha,Saha, Supervisor,Supervisor,Supervisor,Supervisor, IC D esign & fabrication Centre,IC D esign & fabrication Centre,IC D esign & fabrication Centre,IC D esign & fabrication Centre,

JJJJadavpuradavpuradavpuradavpur U niversityU niversityU niversityU niversity , for h is revered supervision throughout m y dissertation w ork, w hich m ade this task a

pleasant job. It w as real p leasure to w ork under his supervision.

I extend m y sincere thanks to P rof. G outam B hattacharya, R am krishna M ission V idyam andira, for h is keen

interest, continuous encouragem ent and support.

I am also indebted to m y m other, brother, sisters and w ell w ishers w ho are taking lot of pains for progress in

m y life and for their sacrifices, blessing and constant prayers for m y advancem ent.

I express m y special thanks to P rof. B .G upta (H O D ,D ept.of E TCE ,JU ) and Prof. S .K .Sanyal, D ept. of

E TCE ,JU , for their k indness and providing m e the facilities of the L aboratory to use for m y w ork.

I w ould also like to thanks all the R esearch Scholars, staff m em bers and project students of IC D esign &

F abrication Center. Special thanks are due to M r.A .M ondal, M r.G .P .M ishra, M r.A .K indu. D r.S .R oy

Choudhury, M rs.S .R oy, M s.T .M ajhi, M r.A .Sengupta.

I am also thankful to P rof. R .N .G hosh, St. Thom as College of E ngg. & Tech., K ol. & M r.A rup Sarkar, A gn i

Pow er E lectronics, K ol., for their support.

I also like to thank D r.S .M ukhopadhya, Secretary, St. Thom as College of E ngg. & Tech., K ol. P rof.M rs.

S .Sen, P rincipal, St. Thom as College of E ngg. & Tech., kol, M r.G outam B anerjee, R egistrar, St. Thom as

College of E ngg. & Tech., kol, for allow ing m e to pursuing m y M .E . in E lectronics & Tele-com m unication at

Jadavpur U niversity.

… … … … … … … … … … … … … … … … … …

TA N U SR E E D U TTATA N U SR E E D U TTATA N U SR E E D U TTATA N U SR E E D U TTA

R eg. N o.R eg. N o.R eg. N o.R eg. N o.105231 of 2008105231 of 2008105231 of 2008105231 of 2008 ----09,09,09,09,

D A TED A TED A TED A TE :::: R oll N o.000810702003R oll N o.000810702003R oll N o.000810702003R oll N o.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.

Fig,15 The equivalent circuit of a solar cell

Fig.16 The schematic symbol of a solar cell

To understand the electronic behavior of a solar cell, it is useful to create a model which is

electrically equivalent, and is based on discrete electrical components whose behavior is well

known. An ideal solar cell may be modelled by a current source in parallel with a diode; in

practice no solar cell is ideal, so a shunt resistance and a series resistance component are added

to the model. The resulting equivalent circuit of a solar cell is shown in fig. Also shown, on the

right,is the schematic representation of a solar cell for use in circuit diagrams.

Characteristic equation

From the equivalent circuit it is evident that the current produced by the solar cell is equal to

that produced by the current source, minus that which flows through the diode, minus that

which flows through the shunt resistor:

25

I = IL − ID − ISH

where

I = output current (amperes)

IL = photogenerated current (amperes)

ID = diode current (amperes)

ISH = shunt current (amperes)

The current through these elements is governed by the voltage across them:

Vj = V + IRS

where

Vj = voltage across both diode and resistor RSH (volts)

V = voltage across the output terminals (volts)

I = output current (amperes)

RS = series resistance (Ω)

By the Shockley diode equation, the current diverted through the diode is:

where

I0 = 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, volts.

By Ohm’s law, the current diverted through the shunt resistor is:

26

Where RSH = shunt resistance

Substituting these into the first equation produces the characteristic equation of a solar cell,

which relates solar cell parameters to the output current and voltage:

An alternative derivation produces an equation similar in appearance but with V on the left-hand

side. The two alternatives are identites; that is, they yield precisely the same results.

In principle, given a particular operating voltage V the equation may be solved to determine the

operating current I at that voltage. However, because the equation involves I on both sides in a

transcendental function the equation has no general analytical solution. However, even without

a solution it is physically instructive. Furthermore, it is easily solved using numerical methods.

(A general analytical solution to the equation is possible using Lambert’s W function, but since

Lambert's W generally itself must be solved numerically this is a technicality.)

Since the parameters I0, n, RS, and RSH cannot be measured directly,the most common

application of the characteristic equation is nonlinear regression to extract the values of these

parameters on the basis of their combined effect on solar cell behavior.

Open-circuit voltage and short-circuit current

When the cell is operated at open circuit, I = 0 and the voltage across the output terminals is

defined as the open-circuit voltage. Assuming the shunt resistance is high enough to neglect the

final term of the characteristic equation, the open-circuit voltage VOC is:

Similarly, when the cell is operated at short circuit, V = 0 and the current I through the terminals

is defined as the short-circuit current. It can be shown that for a high-quality solar cell (low RS

and I0, and high RSH) the short-circuit current ISC is:

27

Effect of physical size

The values of I0, RS, and RSH 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 I0 because it has twice the junction area across which current can

leak. It will also have half the RS and RSH 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/cm2)

JL = photogenerated current density (amperes/cm2)

Jo= reverse saturation current density (amperes/cm2)

rS = specific series resistance (Ω-cm2)

rSH = specific shunt resistance (Ω-cm2)

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 J0 or lower values of rSH 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 I0. (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 I0 increases in proportion

to exp(T). The net effect is to reduce VOC (the open-circuit Voltage) linearly with increasing

temperature. The magnitude of this reduction is inversely proportional to VOC; that is, cells with

higher values of VOC 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 IL 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 ISC, the short-circuit current. Very high values of RS

will also produce a significant reduction in ISC; 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 VOC. Very low values of RSH will produce a significant reduction in VOC.

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 VOC:

Thus, an increase in I0 produces a reduction in VOC proportional to the inverse of the logarithm

of the increase. This explains mathematically the reason for the reduction in VOC 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, +VIN, is impressed

across the inductor and the diode prevents the capacitor from discharging +VOUT 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:

VL= 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, tOFF, for an output voltage. Because

34

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

circuit.

VIN × tON = tOFF × VL

and because:

VOUT = VIN + VL

We can then establish the relationship:

VOUT = VIN × (1 + tON/tOFF)

using the relationship for duty cycle (D):

tON/(tON + tOFF) = D

Then for the boost circuit:

VOUT = VIN/(1-D)

Similar derivations can be had for the buck circuit:

VOUT = VIN × D

and for the inverter circuit (flyback):

VOUT = VIN × 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 µA

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 PVARRAY

LOADBUCKCONVETERAMPLIFIER

LCDDISPLAY

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

5PD2

20

3

2 TL084

-12V

+5V

1N4148

0.uF

470E

100uF

100uF

6PD3

9

4

3

1N4148

3

SPV

0.1uF

VI

PD410

5

+5V

2.2K

1K

+12V

0.1E

VO

+5V

0.75mH

PD58

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

19PB4

10K

1N4148

1K

SW Push button

IRF9640

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)



INTO- External interrupt source 0 to the MCU.


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.


ICP1-Timer/Counter1 input capture pin.


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.


/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.


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.


MISO-Data output pin for memory uploading or SPI.


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.


ADC0-Analog to Digital input ADC0.






46




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.



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

AA

1 2AA

1 2A'

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-coupleroutput

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 CONVERTER3.3mH

IRF 9640MOSFET

100uF

0.1uF

Output ofBuck 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 I1 to I2 in time t1,

Vs – Va = L ( I2-I1/t1) = L ∆I/t1

Or t1 = ∆IL/(Vs- Va)

and the inductor current falls linearly from I2 to I1 in time t2,

-Va = - L ∆I/t2

55

t2 = ∆IL/Va

where ∆I=I2 – I1 is the peak-peak ripple current of the inductor L. equating the

value of ∆I,

∆I = (Vs – Va)t1/L = Va t2/L

Substituting t1 = kT and t2 = (1 - k)T yields the average output voltage as

Va = Vs t1/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 = t1 +t2 = ∆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/(8LCf2 Vs)

∆Vc = Vsx k (1-k)/(8LCf2)

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/(8xLxCxf2) = 2xVa = 2xkxVs

Which gives the critical value of the capacitor Cc as

Cc =C = 1-k/(16xLxf2)

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.

R1 = 47K

57

R2 = 10K

R2/(RI + R2) 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.

R1 = 22K

R2 = 10K

R2/(R1 + R2)X15 = 10K/(10K + 22K) x 15 V = 4.68V

22K

10K

Buck Converter O/P

1N4148

1N4148

1K

+5V

Fig.41

Current to Voltage Converter:

10K

-5V

0.1E

+5V

10K

3

2

74

6

1

5+

-

V+

V-

OUT

OS1

OS2

1K

3

2

74

6

1

5+

-

V+

V-

OUT

OS1

OS2

47K

12V,7A-h Battery

O/P of the Buck ConverterorSolar 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 0.1Ω resistance which is

connected in series with the Battey. So Maximum Voltage is drpped across 0.1Ω

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

Rf = 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 Rf = Rin =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

ICTC7660

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.

At First detect the SPV Voltage(Vi1) & SPV Current (Ii1)for a particular Duty Cycle of the

PWM.

And detect the Buck Converter Output Voltage (Vb1) & Battery Current (Ib1).

Now Increase the Duty Cycle by 1.

Again, detect the SPV Voltage(Vi2) & SPV Current (Ii2).

And detect the Buck Converter Output Voltage (Vb2) & battery Current (Ib2).

Now Again Increase the Duty Cycle by 1.

Detect the SPV Voltage(Vi3) & SPV Current (Ii3).

And detect the Buck Converter Output Voltage (Vb3) & Battery Current (Ib3).

Compute the Change in Voltages & Currents.

dV1=Vb2-Vb1

dI1 =Ib2-Ib1

dV2= Vb3-Vb2

dI2=Ib3-Ib2

Now Compute the Change in Conductance

S1=dI1/dV1

S2=dI2/dV2

If S2>S1 then Duty Cycle is increased by 1

And similarly, If S2<S1 then Duty Cycle is decreased by 1.

Then New value is stored in the previous value.

Now we check the battery condition,

If Ib3<Imax ,Vb3 should be less than Vmax.

If Ib3>Imax ,Vb3 should be greater than Vmax.

If Vb3 greater than Vmax after some delay it will return back to the initial condition.

If Vb3<Vmax it again compute the Incremental Conductance

70

Modified Incremental Conductance Method

NO YES

NO

YES N

YES N

YES

START

Detect Vi,Ii,Vmax,Imax,Vb,Ib

Duty Cycle= D

Compute dV1 ,dV2,Ib1,Ib2

For D=1 ;dV1 =Vb2-Vb1; dI1 = Ib2 – Ib1

For D=D+1; dV2 = Vb3-Vb2; dI1 = Ib3-Ib2

Compute change in conductance

S1=dI1/dV1, S2 =dI2/dV2

S2>S1

D=D+1 D=D-1

S1=S2

DELAY

Ib3<Imax

Vb3<Vmax

Vb3>Vmax

71

Coding of modified Incremental Conductance Method

'$sim

$regfile = "m8def.dat"

$crystal = 8000000

' //////////////////////////////////////////////////////////////////////////////////////////////’

Config Adc = Single , Prescaler = Auto , Reference = Avcc

Start Adc

'//////////////////////////////////////////////////////////////////////////////////////////////’

Dim Vb1 As Word ‘buck o/p voltage1’



Dim Ib1 As Word ‘battery current1’



Dim Vmax As Word 'max O/P voltage'

Dim Imax As Word 'max O/P current'

Dim Vi As Word 'spv voltage’

Dim Ii As Word ‘spv current’

Dim Wi As Word ‘spv power’

Dim P1 As Word 'change in voltage1'

Dim P2 As Word 'change in voltage2'

Dim Q1 As Word 'change in current1'

Dim Q2 As Word 'change in curent2'

Dim S1 As Word 'change in conductance1'

Dim S2 As Word 'change in conductance2'

' ///////////////////////////////////////////////////////////////////////////////////////////////////////

Config Portb.3 = Output

Config Timer2 = Pwm , Prescale = 8 , Pwm = On , Compare PWM = Clear Up

'//////////////////////////////////////////////////

Dim Gp As Integer 'duty cycle of PWM'

‘//////////////////////////////////////////////////////////////////////////////////////////////’

M:

Gp = 1

Vmax = 1000

Imax = 1000

Vi = Getadc(3)

Ii = Getadc (4)

W = Vix Ii

72

X:

Compare2 = Gp

Waitms 200 'delay 200ms'

Vb1 = Getadc(1)

Waitms 100

Ib1 = Getadc(2)

Waitms 100

' ////////////////////////////////////////////////////

Y:

Gp = Gp + 1 'Duty cycle is increased by 1'

Compare2 = Gp

Waitms 200

Vb2 = Getadc(1)

Waitms 100

Ib2 = Getadc(2)

Waitms 100

'////////////////////////////////////////////////////////////

Z:

Gp = Gp + 1 'Duty cycle is increased by 1'

Compare2 = Gp

Waitms 200

Vb3 = Getadc(1)

Waitms 100

Ib3 = Getadc(2)

Waitms 100

'/////////////////////////////////////////////////////////////////////

P1 = Vb2 - Vb1

P2 = Vb3 - Vb2

Q1 = Ib2 - Ib1

Q2 = Ib3 - Ib2

'////////////////////////////////////////////////////////////////////

S1 = Q1 / P1

S2 = Q2 / P2

'/////////////////////////////////////////////////////////////////////

If S2 > S1 Then

Goto A

Else

73

Goto B

End If

' ////////////////////////////////////////////////////

A:

Gp = Gp + 1

Compare2 = Gp

Waitms 100

S1 = S2

'////////////////////////////////////////////////////////////////////////////////////////////////////////’

B:

Gp = Gp - 1

Compare2 = Gp

Waitms 100

S1 = S2

'//////////////////////////////////////////////////////////////////////////////////////////////////’

’

If S1 = S2 Then

If Ib3 < Imax Then

Goto C

Else

Goto D

End If

End If

'///////////////////////////////////////////////////////////////////////////////////////////////’

C:

If Vb3 < Vmax Then

Goto Z

Else

Wait 5

Goto M

End If

D:

If Vb3 > Vmax Then

Wait 5

Goto M

Else

Goto Z

End If

End 'end program

74

CHAPTER 7.

EXPERIMENTAL SETUP

75

Implementation of the hardware for the MPPT system is done using AVR Microcontroller. A personal computer (PC) is used for implementing the control. System components .

The hardware setup of the MPPT consists of a - Solar PV module - Dc/Dc converter(step down) with driving circuit of P-Channel MOSFET that acts as a switch. - A load (12V,7AH Battery ) Personal computer(installed with BASCOM software & Ponyprog Programmer through which microcontroller programmed was burned.)

Hardware Setup Fig.45

76

1).Solar PV module:- Solar PV module used is a 38W module having 17.7Vp and 2.2Ap at 25degree Celsius and 1000W/m2. The module is multicrystalline having 36 cells. The module is shown in the fig.

. SOLAR PV MODULE

Fig.46

2).Dc/Dc converter:-

The dc/dc converter is the main component of the MPPT system it acts as an interface between

the module and the load. The experiment is carried out using the step down converters. The

detailes of the converters are explain in the chapter 5.The converters are controlled through the

Duty Cycle of PWM that is generated form a AVR Microcontroller .

A driver circuit is used to drive the MOSFET.For reliable operation a MOSFETt of rating

100V and 25A was selected. MOSFET is P- Channel IRF9640. The other components of the

dc/dc converter isinductor and capacitor where selected according to the thumb rule.

3).Software Programming Language BASCOM & Ponyprog Programmer through

which microcontroller Programme was burned are installed on Personal Computer:-

77

Personal computer is used for Compile the program into the AVR Atmega8 Microcontroller

The selected algorithm is implemented by using a BASCOM software.

The algorithm developed and simulation in the BASCOM is downloaded in the AVR

Microcontroller through serial Port of the PC using Ponyprog Programmer.

LOAD:- Load used is a purely a 12V, 7 A-H Battery.

STEP DOWN DC-DC CONVERTER USING IC 3524

Fig.47

78

HARDWARE SETUP FOR MPPT CHARGE CONTROLLER(1)

Fig.48

79

HARDWARE SETUP FOR MPPT CHARGE CONTROLLER(2)

Fig.49

80

GENARATED PWM SIGNAL ON DIGITAL STORAGE OSCILLOSCOPE

Fig.50

81

CHAPTER 8.

RESULT

82

DATA TABLE OF MPPT SYSTEM

O/P VOLTAGE(V) O/P CURRENT(I) O/P POWER(P)

1 0 0 0

2 1 2.5 2.5

3 2 3 6

4 3 2.6 8

5 4 3.25 13

6 5 3.2 16

7 6 3.16 19

8 7 3.14 22

9 8 3.125 25

10 9 3.11 28

11 10 3 30

12 11 2.91 32

13 12 2.83 34

14 13 2.61 34

15 14 2.28 32

16 15 2 30

17 6 0 0

83

VOLTAGE Vs POWER CURVE OF THE MPPT SYSTEM

0 5 10 15 20

-5

0

5

10

15

20

25

30

35

O/P

Po

we

r)

O/P Voltage

Fig.51

84

CHAPTER 9.

Conclusions & Future Scope

85

Conclusions:

1).Power output of module improves by using MPPT system.It is observed that the module

gives the output maximum power of 29W at on time(12:00 noon).In early morning it gives

power of about 10W same power is obtained in the evening. The temperature has effect on the

maximum Power.

2).Power output should be increased by increasing the current rating. To increase the power,

biasing power should be decreased.

3)The power delivered to the load in case of step-down converter is about 30W. Output voltage

of the Buck Converter is decreased which is about 15Volt.

4).Temperature of the module is an important parameter. The power output of the module

changes by about 0.5% for every degree rise in temperature.Due to the increase in temperature

the power output decreases very sharply.

5) The module placement also plays an important role in power output. Module is kept south

facing hat is the path of the sun for around the year . Buts its elevation angle must be adjusted

every month to get high power output. The axial tracking for the individual module which are

not too heavy (10W to 60W) can be obtained automatically. Where as for the panel or arrays the

automatic tracking is not feasible due to large torque required to rotate the arrays. So in these

cases a manual tracking/automatic tracking can be performed by adjusting the array direction

for three times a day. i.e. morning, afternoon and evening. This type of tracking can add to the

power in the module.

Future scope: 1) Development of different Microcontroller based dedicated MPPT controller for solar PV module based on the different algorithm such as observe & perturbation, computational method etc. This can be a low cost embedded controller.

2)Automatic recording and monitoring of the temperature and insolation level on the module to

predict the maximum power of the module.

3) Development of a high Power Output MPPT system.

4)Converting the whole system into a single Integrated Circuit.

86

CHAPTER 10.

References

87

References: 1) Eftichios Koutroulis, Kostas Kalaitzakis, Member, IEEE, and Nicholas C. Voulgaris,

“Development of a Microcontroller Based solar Photovoltaic Maximum Power Point Tracking

Control System”.

IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 16, NO. 1, JANUARY 2001

2) Chihchiang Hua and Chihming Shen.

“Control of DC/DC Converters for Solar Energy System with Maximum Power Tracking”.

3) Joe-Air Jiang1, Tsong-Liang Huang2, Ying-Tung Hsiao2*and Chia-Hong Chen2,

“Maximum Power Tracking for Photovoltaic Power Systems”.

Department of Bio-Industrial Mechatronics Engineering, National Taiwan University Taipei, Taiwan

106, R.O.C. Department of Electric Engineering, Tamkang UniversityTamsui, Taiwan 251, R.O.C.

4) Sachin Jain, Student Member, IEEE, and Vivek Agarwal Senior Member, IEEE

“A New Algorithm for Rapid tracking of Approximate Maximum Power Point in Photovoltaic

systems”.

IEEE POWER ELECTRONICS LETTERS, VOL. 2, NO. 1, MARCH 2004

5) Mohamad A. S. Masoum, Seyed Mahdi Mousavi Badejani, and Ewald F. Fuchs.IEEE,

“Microprocessor-Controlled New Class of Optimal Battery Chargers for Photovoltaic

Applications”.

6) Chihchiang Hua, Member, IEEE, Jongrong Lin, and ChihmingShen “Implementation of a DSP-

controlled Photovoltaic Peak Power Tracking system”, IEEE TRANSACTIONS ON INDUSTRIAL

ELECTRONICS, VOL. 45, NO. 1, FEBRUARY 1998.

7).D. P. Hohm, M. E. Ropp,”Comparative Study of Maximum Power Point Tracking Algorithms

Using an Experimental, Programmable, Maximum Power Point Tracking Test

Bed”,IEEE,2000.pp.1699-1702.

8) “Mohammad A. S. Masoum, Hooman Dehbonei, and Ewald F. Fuchs,

“Theoretical and Experimental Analyses of Photovoltaic Systems With Voltage and Current-

Based Maximum Power-Point Tracking”.IEEE TRANSACTION ON ENERGY

CONVERSION,VOL.17,No.4.DECEMBER 2002.

9) www.ieeexplore.ieee.org.

10) www.atmel.com

11) BASCOM AVR Software

88

CHAPTER 11.

ANNEXURE

THANK YOU

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