Maximum Power Point Tracking Final Year Report

UNIVERSITI MALAYSIA SABAH SCHOOL OF ENGINEERING AND INFORMATION TECHNOLOGY

Design Project KE 30602

Final Report

Lecturer name

:

Yoong Hou Pin

Team member

:

Albert Ling Hoe Ying (BK09110140) Norrahmah Binti Salleh (BK08110327) Kong Mei Chie (BK09110029) Azahar B. Ali (BK09160210) Nur Fakhriah Binti Mohd Yusuf (BK08160432) Siti Hajar Binti Basuni(BK09110030)

Date of Submission

:

4 June 2012

Final Report Maximum Power Point Tracking (MPPT) Client

: Mr. Yoong

Project Manager : Mr. Yoong Hou Pin Project Leader

: Albert Ling Hoe Ying

Abstract

The project works with maximum power point tracking (MPPT) using the Perturb and Observe (P&O) algorithm. The P&O algorithm is implemented using the controller make up of logic components such as voltage follower, voltage inverter, differentiators, comparators, and X-OR gates. The solar energy harvested from solar panel is fed into the MPPT system to acquire maximum power output at the load. Typical solar panel works with low efficiency such < 15% thus, maximizing from the solar panel energy is a necessity to achieve optimum performance of solar energy. A simple MPPT system is built to maximize the power of solar panel (80W).

TABLE OF CONTENT CHAPTER TITLE

PAGE

ABSTRACT

i

LIST OF TABLE

ii

LIST OF FIGURE

iii-iv

LIST OF ABBREVIATION

1

v

Introduction 1.1 Overview

1

1.2 Power Supply Research

2

1.3 MPPT Research

2

1.4 Objective

3

1.4.1 Problem statement

3

1.4.2 Requirements

3

1.4.3 Safety Feature

4

1.4.4 Tolerance/Accuracy

4

1.4.5 Input/output Definition

4

1.4.6 Operation Environment

4

1.4.8 Hazardous Level

4

1.4.9 Overshoot Protection

4

1.5 Scope of work

5

1.5.1 Academic Review

5

1.5.2 Mathematical Modeling

5

1.5.3 Simulation

5

1.5.4 Hardware Realization

5

1.5.5 Testing

5

1.5.6 Calibration

6

1.6 METHODOLOGY

6

1.6.1 Academic Review

6

1.6.2 Mathematical Modeling

6

1.6.3 Simulation

7

1.6.4 Hardware Realization

7

1.6.5 Testing

7

1.6.6 Calibration

2

3

4

8

LITERATURE REVIEW 2.1 Solar energy

9

2.2 The concepts behind solar panel

10

2.3 The Characteristic of Solar Panel

11

2.4 Side Effect to the Solar Panel

12

2.4.1 Panel Arrangement/ Orientation

12

2.4.2 Roof and Panel Pitch

12

2.4.3 Temperature

12

2.4.4 Partial Shading

13

2.5 Perturb and Observe (P&O) Algorithm

13

2.6 Buck Converter

15

2.6.1 Continuous mode

16

2.7 Impedance matching

18

LIST OF COMPONENT 3.1 Resistor

20

3.2 Capacitor

21

3.3 PIC (Programmable Interface Controllers)

22

3.4 D flip-flop

23

3.5 Operational Amplifier ( Op Amp )

24

OPERATION OF ELECTRONIC PARTS 4.1 Introduction

25

4.2 Solar Array

26

4.3 Controller

27

4.3.1 Voltage Follower

27

4.3.2 Voltage Inverter

28

4.3.3 Analog Multiplier

29

4.3.4 Differentiators

29

4.3.5 Comparators

30

4.3.6 XOR gate

31

4.3.7 D Flip-Flop

32

5

6

7

8

SYSTEM MODELING 5.1 Input and output definition

34

5.2 Detail design and drawing

34

5.3 Operation of MPPT system using P&O algorithm

34

5.4 Buck converter operation

36

5.5 Buck converter detail design

38

5.6 ADC scaling in PIC

39

FABRICATION 6.1

Prototype picture

41

6.2

Comments

41

KEY PERFORMANCE INDEX 7.1

Time performance index

42

7.2

Gantt Chart

43

7.3

Comments on TPI and Gantt Chart

44

7.4

Cost performance index

45

CONCLUSION AND FUTURE WORK 8.1

Conclusion

47

8.2

Future work

47

REFERENCE

48

APPENDIX

49

LIST OF TABLE

TABLE TITLE

PAGE

NUMBER 1

Level of efficiency of different type of material solar panel

10

2

PRE and CLR function table

31

3

Circuit operation of MPPT by P&O algorithm

35

4

Week number in dates

42

5

Weekly TPI for MPPT project

42

6

Simplified schedule of project

44

ii

LIST OF FIGURE

FIGURE TITLE

PAGE

NUMBER 1

I-V Curve of typical solar

3

2

p-n junction of solar panel

10

3

I-V curve of different Solar Panel power

11

4

I-V Photovoltaic Characteristics for four different irradiation levels

14

5

P-V photovoltaic characteristics for four different irradiation levels

15

Thevenin Equivalent circuit

19

Resistor Color Code

21

7(a)

Electrolytic Capacitors (Electrochemical type capacitors)

22

7(b)

Ceramic Capacitors

22

8

PIC (Peripheral Integrated Circuit)

22

9

D flip-flop Diagram

23

10

D flip–flop: (a) Truth Table and (b)Timing Diagram

23

11

Operational Amplifier ( Op Amp )

24

12

MPPT Charge Controller Circuit

25

13

Specifications of solar panel (Sharp NE-80E2EA)

26

14

Voltage follower connection

27

15

Inverting Op-amp connection

28

16

Connection of analog multiplier AD633

29

17

Voltage and Power Differentiator Connection

30

5.1 6

iii

18

Power and voltage comparators

31

(a) Connection diagram of IC7486, (b) XOR truth table, (c) Connection of 19

32 XOR gate in the circuit

20

74HC74 D-Flip-flop connection

32

21

Simple block diagram for overall system.

34

22

Full schematic diagram for MPPT system and Buck Converter

35

23

Flow chart for MPP tracking

35

24

The Circuit operation chart.

36

25

Circuit diagram of Buck Converter

38

26

Voltage Divider Using Resistor

40

iv

LIST OF ABBREVIATION

CPI

Cost Performance Index

KPI

Key Performance Index

MPP

Maximum Power Point

MPPT

Maximum Power Point Tracking

P&O

Perturb and Observe

PV

Photovoltaic

TPI

Time Performance Index

VMPP Voc X-OR

Maximum power point voltage Open circuit voltage Excusive OR

v

CHAPTER 1

INTRODUCTION

1.1 Overview The development of renewable energy has been an increasingly critical topic in the 21 st century with the growing problem of global warming and other environmental issues. With greater research, alternative renewable sources such as wind, water, geothermal and solar energy have become increasingly important for electric power generation. Although photovoltaic cells are certainly nothing new, their use has become more common, practical, and useful for people worldwide. The most important aspect of a solar cell is that it generates solar energy directly to electrical energy through the solar photovoltaic module, made up of silicon cells. Although each cell outputs a relatively low voltage, if many are connected in series, a solar photovoltaic module is formed. A photovoltaic module is used efficiently only when it operates at its optimum operating point. Unfortunately, the performance of any given solar cell depends on several variables. At any moment the operating point of a photovoltaic module depends on varying insolation levels, sun direction, irradiance, temperature, as well as the load of the system. The amount of power that can be extracted from a photovoltaic array also depends on the operating voltage of that array. As we will observe, a maximum power point (MPP) will be specified by its voltage-current (V-I) and voltage-power (V-P) characteristic curves. Solar cells have relatively low efficiency ratings. Thus, operating at the MPP is desired because it is at this point that the array will operate at the highest efficiency. With constantly changing atmospheric conditions and load variables, it is very difficult

1

to utilize all of the solar energy available without a controlled system. For the best performance, it becomes necessary to force the system to operate at its optimum power point. The solution for such a problem is a Maximum Peak Power Tracking system (MPPT).

1.2 Power Supply Research A battery is a source portable electric power. A storage battery is a reservoir, which may be used repeatedly for storing energy. Energy is charged and drained from the reservoir in the form of electricity, but it is stored as chemical energy. But, for our design we use capacitor for storing the energy. In a way, a capacitor is a little like a battery. Although they work in completely different ways, capacitors and batteries both store electrical energy. Inside the battery, chemical reactions produce electrons on one terminal and absorb electrons on the other terminal. A capacitor is much simpler than a battery, as it can't produce new electrons -- it only stores them. Inside the capacitor, the terminals connect to two metal plates separated by a non-conducting substance, or dielectric. It won't be a particularly good capacitor in terms of its storage capacity, but it will work. In theory, the dielectric can be any non-conductive substance. However, for practical applications, specific materials are used that best suit the capacitor's function. Mica, ceramic, cellulose, porcelain, Mylar, Teflon and even air are some of the non-conductive materials used. The dielectric dictates what kind of capacitor it is and for what it is best suited. Depending on the size and type of dielectric, some capacitors are better for high frequency uses, while some are better for high voltage applications.

1.3 MPPT Research The Maximum Power Point Tracker (MPPT) is needed to optimize the amount of power obtained from the photovoltaic array to the power supply. The output of a solar module is characterized by a performance curve of voltage versus current, called the I-V curve. See Figure 1. The maximum power point of a solar module is the point along the I-V curve that corresponds to the maximum output power

2

possible for the module. This value can be determined by finding the maximum area under the current versus voltage curve.

Figure 1: I-V Curve of typical solar panel 1.4 Objective The objective of the project is to design a Maximum Power Point Tracking (MPPT) charge collecter which operate with photovoltaic module and produce maximum power to solar power collector. This component optimized the amount of power obtained from the photovoltaic array and charged the power supply.

1.4.1

Problem statement

To fight against the global warming and any other problem that related with fossil fuels, most countries are switching to renewable energy source like sunlight, biomass, hydro and wind. Eventhough some countries already use renewable energy source, the renewable energy technologies are not appropriate in some application and location. However, among several renewable energy source, photovoltaic array are used in many application such as water pumping, battery charging and street lighting. In this application the load can be demand more power than photovoltaic (PV) system can deliver. Therefore to achieve the power required, power conversion system is used to maximize the power from PV system.

1.4.2

Requirements

3

MPPT is able to maximize power up to 80W. It also can used to operate up to 20 panel in parallel. The load used is water pumping. The system has display to show the power.

1.4.3

Safety Feature

All electronic part only consumes 5V. To prevent damage on the solar electronic devices, a regulator is used to regulate the dc supply to 5V.

1.4.4

Tolerance/Accuracy

The MPPT systems have temperature tolerance of +/-2⁰C.

1.4.5

Input/Output Definition

Input is solar power. Output is load.

1.4.6

Operation Environment

This device operate in outdoor when there have sufficient sun light during day time.

1.4.7

Hazardous Level

MPPT system operate outdoor in order to collect the solar power which is all the device expose to disturbance like temperature, environment and else. The overheated wire connection is possible to cause the system fail to operate.

1.4.8

Overshoot Protection

The IP56 is used to hold the electronic device of the MPPT system. The wire need casting to protect the wire from overheating.

4

1.5 Scope of work 1.5.1

Academic Review

Before the MPPT project taken out, the background research for the MPPT was collected. MPPT and photovoltaic cell research need to consider since the MPPT was design according to the solar panel system. Information and data from the analysis will combine to get the idea how to design and how the MPPT system will work.

1.5.2

Mathematical Modeling

The maximum power of MPPT system will calculated based on the maximum power from Solar Panel. It includes the calculation for the system loading effect where the internal resistance can be obtained. The MPPT circuits also need to calculate the power, voltage and current for the input and output of the load.

1.5.3

Simulation

Circuit will simulate using the Proteus or Pspice Software to ensure whether the installation of the circuit can be running or not. The circuit will be tested using different sorts of input to get the desired output. The most important device in this system is Peripheral Interface Controller (PIC). It will control the whole system and display the load output.

1.5.4

Hardware Realization

After the simulation done, circuit will be construct. The collected power from solar panel will and the maximum power that can archive will record to ensure it ready to be connected to the circuit. The final stage to complete this circuit is combined the circuit with the final structure. The IP56 casing will be use for the safety future.

1.5.5

Testing

5

The Solar Panel will be connected as input to the MPPT system and the motor pump will be used as the output. The flow of testing process is:

1.5.6

i.

Monitoring system test

ii.

Temperature control test

iii.

Power absorbed test

iv.

Electrical safety test

Calibration

Calibration will be done according to an error of the system, which is help to improve the system accuracy. The device with the known or assigned correctness is called the standard. Then the conceptual design of MPPT should be achieved.

1.6

METHODOLOGY

1.6.1

Academic Review

Firstly, research about the meaning of the Maximum Power Point Tracking (MPPT) device and its function with photovoltaic cell will be done. Via internet and other resources, circuit of the MPPT device will be learned as well as method of how the MPPT device controls the power which will supply directly to the load. In addition, some useful equations will be reviewed as well so that the modeling can be done easily.

1.6.2

Mathematical Modeling

The modeling part will divided into three parts. The first part is the photovoltaic cell (also known as solar cell). Photovoltaic has a method for generating power using solar cells to convert energy from the sun into the flows of electrons.

Solar cells have a complex relationship between solar irradiation,

temperature and total resistance that will produces non-linear output efficiency. Secondly, MPPT system is used to sample the output of the cells and apply the proper resistance (load) to obtain maximum power

6

for any given environmental conditions. MPPT system will be build according to the desired output and supply to the desired load.

1.6.3

Simulation

After modeling the desired part of the system, all of the system will be simulated using proper software (Pspice or Proteus) to ensure that the desired output will be obtained. The software we will use allows for the division of a stimulated system into numbers of subsystems. This subsystems can be model and test individually and then interconnected later. This makes it possible to build the physical subsystems such as the solar panel, MPPT and other system as independent units and verify their proper functionality. Display blocks and graphs can be attached to any interconnecting line to monitor the corresponding signal's behavior. The monitored signal can also be written to a workspace variable for further evaluation and analysis.

1.6.4

Hardware Realization

After all the stimulation, all of the circuit will be constructing according to the designed. In this part, we are more focusing on the MPPT system, controller and the load. For the solar system, the solar panel used in our system will provided by School of Engineering and Information Technology.

PIC

microcontroller is use in the MPPT system to control the output which will be the supply of the load. Software for the controller can be developed, deployed, and tested by using C/C++ assembler. For the circuit side, Printed Circuit Board (PCB) will be used and the circuit drawn as per designed. After all the circuit is being done, the circuit will place into the appropriate housing or casing which we will use IP56 case and for the cable, we use cable trunking so that our design look need and tidy.

1.6.5

Testing

After all the circuit and hardware have been successfully attached, the device will be tested to know the performance of each device. First of all, the solar panel will be connected to the MPPT device and

7

monitoring the output of the system which display by the LCD display board. The control system will control and set the desire output and supply to the load.

1.6.6

Calibration

All the testing and troubleshooting will be doing it in the same time when there is failure and problem occurs while doing testing. Some calibration will be carry out in order to get the desire output.

8

CHAPTER 2

LITERATURE REVIEW

2.1

Solar energy

Solar energy is imperative to support critical energy sources on earth. Basically, it work to grow our food, light our days, manipulate weather patterns, provide heat, and can be used to generate solar electricity. Solar electricity relies upon man-made devices such as solar panels or solar cells in order to provide a source of clean, or we can speak as a low cost renewable energy. The fully system of solar electricity are involved from the critical part called solar panel. It‟s should be the main part that absorbed the sun energy then convert it into another energy to ensure the voltage and power are produced. As solar energy technologies become more advanced, we are able to develop the energy we receive from the sun to provide a greater, significant amount of our electricity. Being implicit in several characteristic of how solar panel works make our ability to produce the maximum power are closed.

2.2

The concepts behind solar panel

Solar cells are usually made from silicon, the same material used for transistors and integrated circuits. The silicon is treated or "doped" so that when light strikes it electrons are released, so generating an electric current. There are three basic types of solar cell which is Monocrystalline, Polycrystalline and Amorphous. Monocrystalline cells are cut from a silicon ingot (bar) grown from a single large crystal of silicon whilst polycrystalline cells are cut from an ingot made up of many smaller crystals. The third type is the amorphous or thin-film solar cell.

9

Table 1: Level of efficiency of different type of material solar panel Material

Level of efficiency %

Monocrystalline silicon

14 to 17

Polycrystalline silicon

13 to 15

Amorphous silicon

5 to 7

We should be familiar with concepts of "Doping", it‟s the intended introduction of chemical elements, with which one can obtain a surplus of either positive charge carriers (p-conducting semiconductor layer) or negative charge carriers (n-conducting semiconductor layer) from the semiconductor material. If two differently contaminated semiconductor layers are combined, then a socalled p-n-junction results on the boundary of the layers.

Figure 2: p-n junction of solar panel At this junction, an interior electric field is built up which leads to the separation of the charge carriers that are released by light. Through metal contacts, an electric charge can be tapped. If the outer circuit is closed, meaning a consumer is connected, and then direct current flows. Finally, metal contacts on the cell allow connection of the generated current to a load. A transparent anti-reflection film protects the cell and decreases reflective loss on the cell surface.

10

2.3

The Characteristic of Solar Panel

The characteristic is usually different based on the types of solar panel material. For analysis through characteristic, we always refer to the voltage-current V-I characteristic.

Figure 3: I-V curve of different Solar Panel power Every model of solar panel has unique performance characteristics which can be graphically represented in a chart. The graph in Figure 3 is called an “I-V curve”, and it refers to the module‟s output relationship between current (I) and voltage (V) under existing conditions of sunlight and temperature. Theoretically, every solar panel has multiple I-V curves (several of which are shown above for one particular module) one each for all the different combinations of conditions that would affect the STC rating parameters above: temperature, air mass, irradiance and so on. Because of Ohm‟s Law (and the equation Power = Voltage x Current), the result of reduced voltage is reduced power output. The ideal position on any I-V curve, the sweet spot where we can collect the most power from the module is at the “knee”. That‟s the maximum power point (MPP), and we can see that its position changes with temperature and irradiance. The objective for a system to constantly track the P-V curve to keep the operating point as close to the maxima while energy is extracted from the PV array.

11

2.4

Side Effect to the Solar Panel

Basically, we need to construct an experiment while „playing‟ with solar panel as our source energy from sun ray. The general concept or theory according to the parameters like current-voltage behavior, maximum power produced from opened-circuit and closed-circuit or the efficiency normally different to the real world while testing.

2.4.1

Panel Arrangement/ Orientation

Solar panels are installed differently based on our geographic locations throughout the world. The idea behind this is simple; the sun is in a different place in the sky, so panels need to be directed according to this positioning. The ideal situation is when the sun is hitting the panels at a perfectly perpendicular angle (90°). This maximizes the amount of energy striking the panels and being produced. The two factors that such an angle is controlled by are the orientation (North/South/East/West) and the angle of the panels from the surface of the Earth.

2.4.2

Roof and Panel Pitch

The most application using the solar panel is placed at the highest part of building. The “pitch” or tilt of our roof can affect the number of hours of sunlight we receive in an average day throughout the year. Large commercial systems have solar tracking systems that automatically follow the sun‟s tilt through the day. These are expensive and not necessary to the normal type of application such as 12 Volt output devices.

2.4.3

Temperature

This is the huge problem always facing to the small component devices. Some panels like it hot but most don‟t. So, panels typically need to be installed a few inches above the roof with enough air flow to cool them down. As a result the power output will be reduced by between 0.25% (amorphous cells) and 0.5%

12

(most crystalline cells) for each degree C of temperature rise. This reduction in efficiency may be important to us if we have a high electricity demand to the devices.

2.4.4

Partial Shading

Basically, shade is the enemy of solar power. With poor solar design, even a little shade on one panel can shut down energy production on all of your other panels. Before we design a system for our devices, we‟ll conduct a detailed shading analysis of our roof to reveal its patterns of shade and sunlight throughout the year. There may be situations where this cannot be avoided, and the effects of partial shading should be considered as part of energy absorption.

2.5

Perturb and Observe (P&O) Algorithm

Solar cells produce energy by performing two basic tasks: (1) absorption of light energy to create free charge carriers within a material and (2) the separation of the negative and positive charge carriers in order to produce electric current that flows in one direction across terminals that have a voltage difference. Solar cells perform these tasks with their semiconducting materials. The separation function is typically achieved through a p-n junction. Solar cell regions are made up of materials that have been “doped” with different impurities. This creates an excess of free electrons (n-type) on one side of the junction, and a lack of free electrons (p-type) on the other. This behavior creates an electrostatic field with moving electrons and a solar cell is essentially, a large-area diode (Richard, 2006). Researches on renewable energies have received much attention due to their capability of reducing the fossil fuels usage and mitigating the environmental issues such as the green house effect and air pollution (Liu and Huang, 2011). Among the renewable energies, the photovoltaic (PV) generation system has become increasingly important as a renewable source due to its advantages such as absence of fuel costs, low maintenance requirement and environmental friendliness. However, in PV generation system, the conversion efficiency is very low, especially under low irradiation, and the amount of the electric power generated by solar cells varies with weather conditions. Therefore, a maximum power point tracking (MPPT) method is used to

13

maximize the harvested solar energy from the solar panel. In the MPPT system, the system works to find the maximum power point (MPP) via powerful microcontroller. There are many ways of distinguishing and grouping methods that seek the MPP from a photovoltaic (PV) generator (Salas et al, 2006). All the different algorithms has its own pro and cons. In addition, each PV has its own voltage-current (V-I) characteristics. Figure 4 shows the V-I characteristics of a PV under different irradiance. Figure 5 shows the P-V photovoltaic characteristics for four different irradiation levels.

Figure 4: I-V Photovoltaic Characteristics for four different irradiation levels.

14

Figure 5: P-V photovoltaic characteristics for four different irradiation levels From Figure 4 and Figure 5, the MPP can be determined. It is used widely in seeking it using different algorithms. There are many algorithms in tracking the MPP, for instances, Perturb and observe algorithm, incremental conductance algorithm, parasitic capacitances, constant voltage control, constant current control, pilot cell, artificial intelligent method (Algazar et al, 2012).

2.6

Buck Converter

A buck converter is a step-down DC to DC converter. Its design is similar to the step-up boost converter, and like the boost converter it is a switched-mode power supply that uses two switches (a transistor and a diode), an inductor and a capacitor. The operation of the buck converter is fairly simple, with an inductor and two switches (usually a transistor and a diode) that control the inductor. It alternates between connecting the inductor to source voltage to store energy in the inductor and discharging the

15

inductor into the load. For the purposes of analysis it is useful to consider an idealised buck converter. In the idealised converter all the components are considered to be perfect. Specifically the switch and the diode have zero voltage drop when on and zero current flow when off and the inductor has zero series resistance. Further it is assumed that the input and output voltages do not change over the course of a cycle (this would imply the output capacitance being infinitely large).

2.6.1

Continuous mode

A buck converter operates in continuous mode if the current through the inductor (IL) never falls to zero during the commutation cycle. In this mode, the operating principle is described by the plots in figure 4: 

When the switch pictured above is closed (On-state, top of figure 2), the voltage across the inductor is

. The current through the inductor rises linearly. As the diode is reverse-biased

by the voltage source V, no current flows through it; 

When the switch is opened (off state, bottom of figure 2), the diode is forward biased. The voltage across the inductor is

(neglecting diode drop). Current IL decreases.

The energy stored in inductor L is

Therefore, it can be seen that the energy stored in L increases during On-time (as IL increases) and then decreases during the Off-state. L is used to transfer energy from the input to the output of the converter. The rate of change of IL can be calculated from:

With VL equal to

during the On-state and to

during the Off-state. Therefore, the increase

in current during the On-state is given by:

, t{on} = DT

16

Identically, the decrease in current during the Off-state is given by:

, t{off} = (1-D)T If we assume that the converter operates in steady state, the energy stored in each component at the end of a commutation cycle T is equal to that at the beginning of the cycle. That means that the current I L is the same at t=0 and at t=T (see figure 4). So we can write from the above equations:

It is worth noting that the above integrations can be done graphically: In figure 4, to the area of the yellow surface, and

is proportional

to the area of the orange surface, as these surfaces are

defined by the inductor voltage (red) curve. As these surfaces are simple rectangles, their areas can be found easily:

for the yellow rectangle and

for the orange one. For steady

state operation, these areas must be equal. As can be seen on figure 4,

and

. D is a scalar called the duty cycle with a value

between 0 and 1. This yields:

From this equation, it can be seen that the output voltage of the converter varies linearly with the duty cycle for a given input voltage. As the duty cycle D is equal to the ratio between t On and the period T, it cannot be more than 1. Therefore,

. This is why this converter is referred to as step-down

converter.

17

2.7

Impedance Matching

Maximum power transfer occur when the impedance of the source equals to the load. The maximum possible power is delivered to the load when the impedance of the load (load impedance or input impedance) is equal to the complex conjugate of the impedance of the source (its internal or output impedance). For two impedance to be complex conjugate conjugate their resistance must be equal, and their reactances must be equal in magnitude but of opposite signs. Suppose we have a two terminal circuit and we want to connect a load resistance RL such that the maximum possible power is delivered to the load. To analyze this problem, we go through Thevenin equivalent circuit as shown in Figure 2.10. The current flowing through the load resistance is given by 𝑖𝐿 = 𝑅

𝑉𝑠

(2.4)

𝑆 +𝑅𝐿

The power delivered to the load is 𝑃𝐿 = 𝑖𝐿2 𝑅𝐿

(2.5)

Substituting for the current, we have 𝑃𝐿 =

𝑉𝑠2 𝑅𝐿 𝑅𝑆 +𝑅𝐿 2

(2.6)

To find the value of the load resistance that maximizes the power delivered to the load, we set the derivative of 𝑃𝐿 with respect to 𝑅𝐿 equal zero: 𝑑𝑃𝐿 𝑑𝑅𝐿

=

𝑉𝑠2 𝑅𝑆 +𝑅𝐿 2 −2𝑉𝑠2 𝑅𝐿 𝑅𝑆 +𝑅𝐿 𝑅𝑆 +𝑅𝐿 4

=0

(2.7)

Solving for the load resistance, we have 𝑅𝑆 = 𝑅𝐿

(2.8)

Thus, the load resistance that absorbs the maximum power from a two-terminal circuit is equal to the thevenin resistance. The maximum power is found by substituting 𝑅𝑆 = 𝑅𝐿 into 𝑉2

𝑃𝐿 = 4𝑅𝑠

𝑆

(2.9)

18

Figure 5.1 : Thevenin Equivalent circuit

19

CHAPTER 3

LIST OF COMPONENTS

3.1

Resistor

A resistor is a passive two-terminal electrical component that implements electrical resistance as a circuit element. The current through a resistor is in direct proportion to the voltage across the resistor's terminals. Thus, the ratio of the voltage applied across a resistor's terminals to the intensity of current through the circuit is called resistance. This relation is represented by Ohm's law, where I is the current through the conductor in units of amperes, V is the potential difference measured across the conductor in units of volts, and R is the resistance of the conductor in units of ohms.

The electrical resistance is equal to the voltage drop across the resistor divided by the current through the resistor. Resistors are used as part of electrical networks and electronic circuits. Resistor has their own color code, where the color code is is determine the value and tolerance of the resistor. Figure 6 shows the table on how to read the value and tolerance of resistor using the color code.

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Figure 6: Resistor Color Code 3.2

Capacitor

The capacitor's function is to store electricity, or electrical energy. The capacitor also functions as a filter, passing alternating current (AC), and blocking direct current (DC). The capacitor is constructed with two electrode plates facing each other, but separated by an insulator. When DC voltage is applied to the capacitor, an electric charge is stored on each electrode. While the capacitor is charging up, current flows. The current will stop flowing when the capacitor has fully charged. The capacitance of a capacitor is generally very small, so units such as the microfarad (10-6F ), nanofarad ( 10-9F ), and picofarad (10-12F ) are used. Recently, an new capacitor with very high capacitance has been developed. The Electric Double Layer capacitor has capacitance designated in Farad units.

Figure 7(a): Electrolytic Capacitors (Electrochemical type capacitors) Aluminum is used for the electrodes by using a thin oxidization membrane. Large values of capacitance can be obtained in comparison with the size of the capacitor, because the dielectric used is

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very thin. The most important characteristic of electrolytic capacitors is that they have polarity. They have a positive and a negative electrode.

Figure 7(b): Ceramic Capacitors Ceramic capacitors are constructed with materials such as titanium acid barium used as the dielectric. Internally, these capacitors are not constructed as a coil, so they can be used in high frequency applications. Typically, they are used in circuits which bypass high frequency signals to ground. These capacitors have the shape of a disk. Their capacitance is comparatively small.

3.3

PIC (Programmable Interface Controllers)

A PIC microcontroller is a processor with built in memory and RAM and you can use it to control your projects (or build projects around it). It has been already mentioned that microcontrollers differs from other integrated circuits. Most of them are ready for installation into the target device just as they are, this is not the case with the microcontrollers. In order that the microcontroller may operate, it needs precise instructions on what to do. In other words, a program that the microcontroller should execute must be written and loaded into the microcontroller.

Figure 8: PIC (Peripheral Integrated Circuit) They can be programmed to be timers or to control a production line and much more. They are found in most electronic devices such as alarm systems, computer control systems, phones, in fact almost

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any electronic device.PIC Microcontrollers are relatively cheap and can be bought as pre-built circuits or as kits that can be assembled by the user.

3.4

D flip-flop

The D flip-flop tracks the input, making transitions with match those of the input D. The D stands for data. This flip-flop stores the value that is on the data line. It can be thought of as a basic memory cell. A D flip-flop can be made from a set/reset flip-flop by tying the set to the reset through an inverter. The result may be clocked.

Figure 9: D flip-flop Diagram The D (Data) flip-flop has an input D, and the output Q will take on the value of D at every triggering edge of the clock pulse and hold it until the next triggering pulse. The D flip-flop is usually positive edge triggered. CLK

D

Q

Condition

0

1

0

Start

Raising edge

1

1

Store 1

0

0

Q

No Charge

Raising edge

0

0

Store 0

(a)

(b) Figure 10: D flip–flop: (a) Truth Table and (b)Timing Diagram

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3.5

Operational Amplifier ( Op Amp )

The Operational Amplifier (Op Amp ) can be used in many different ways. The Op-amp has two inputs an inverting input ( - ) and a non-inverting input ( + ) and one output. A signal applied to the inverting input will have its polarity reversed on the output. A signal applied to the non-inverting input will retain its polarity on the output. The gain or amplification of the signal is determined by a feedback resistor that feeds some of the output signal back to the inverting input. The smaller the resistor, the lower the gain.

Figure 11: Operational Amplifier (Op Amp )

The name operational amplifier was originally adopted for a series of high performance DC amplifiers used in analog computers. These amplifiers were used to perform mathematical operations applicable to analog computation such as summation, scaling, subtraction, integrating and essentially any feedback operation.

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CHAPTER 4

OPERATION OF ELECTRONIC PART

4.1

Introduction

This part will cover all components used in the MPPT charge controller circuit and its operation. There will be details of the function of each components used and its operations. The circuit was divided into 3 parts which are solar array, control circuit and lastly the power stage. The MPPT charge controller referred is shows below.

Figure 12: MPPT Charge Controller Circuit

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4.2

Solar Array For the solar array, the model of the solar panel we used is Sharp NE-80E2EA. This solar

module is able to output a maximum power of 80 Watt. The specifications of the solar module are supplied by the manufacturer‟s datasheet as shown in figure 13 below.

Figure 13: Specifications of solar panel (Sharp NE-80E2EA).

4.3

Controller

The controller circuit consists of voltage follower, an analog inverter, a multiplier, two differentiators, two comparators, a XOR-gate and a D Flip-Flop.

4.3.1

Voltage Follower Voltage follower achieved using op-amp. Op-amp is a DC coupled high gain electronic voltages

amplifier with a differential inputs and single-ended output. The function of op-amp is to amplify the input voltages and produce larger output.

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Varray

Figure 14: Voltage follower connection In the referred circuit, the array was connected to a voltage divider before fed into the voltage follower. LM318 op-amp was used as voltage follower. The used of 51k ohm and 200k ohm voltage divider is to have high impedances input at multiplier as the voltage follower is then connected as the input of the multiplier. The supply voltage of the op-amp were set to V+ = 5V and V– = -5V. The output voltage of the voltage follower is V+= =

R3 Varray R2 + R3 200k Varray 200k + 51K

= 0.7968 𝑉𝑎𝑟𝑟𝑎𝑦 𝑉𝑜𝑢𝑡 = 𝑉 − =𝑉+ = 0.7968 𝑉𝑎𝑟𝑟𝑎𝑦

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4.3.2

Voltage Inverter Another application of op-amp was inverting the voltage and fed into the op-amp. The current

array was measured in term of voltage connecting the array with small value of resistor. The input into the voltage inverter is negative of array current multiply, -IARRAY with the value sensing resistor, Rs. The output voltage, VOUT of will be to positive value multiplying with resistance R4 and R6 connecting the op-amp. Then output voltage waveform of the will be the same as the input waveform shape but the value is invert from negative to positive and also based on value of R4 and R6. The op-amp being used in the circuit is LM318.

Figure 15: Inverting Op-amp connection The output voltage of LM318 voltage inverter is; −𝐼𝑎𝑟𝑟𝑎𝑦 𝑅𝑠 − 𝑉 − 𝑉 − − 𝑉𝑜𝑢𝑡 = 𝑅4 𝑅6 𝑉 − = 0𝑉 𝑉𝑜𝑢𝑡 = =

𝑅6 𝐼𝑎𝑟𝑟𝑎𝑦 𝑅𝑠 𝑅4 36𝑘 × 0.47 × 𝐼𝑎𝑟𝑟𝑎𝑦 1𝑘

= 16.92𝐼𝑎𝑟𝑟𝑎𝑦

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The output voltage of inverting op-amp is then fed into the multiplier. The current of the op-amp was inverted due to have positive value of power at the multiplier. 4.3.3

Analog Multiplier Analog multiplier is an electronic device that evaluated the product of two analog signals which it

is output. Analog multiplier is use to calculate power of the array by multiplying the array voltage and the array current. AD633 is an analog multiplier, four quadrants. It includes high impedance, differential X and Y inputs and high impedance summing input, Z. This analog multiplier was built using differential op-amps, multiplier and a voltage follower.

Figure 16: Connection of analog multiplier AD633

4.3.4

Differentiators Another application of op-amp is to differentiate the voltage fed into the op-amp. This application

was achieve connect a capacitor in series with the op-amp and a resistor at the feedback. In the MPPT circuit referred, the measured power and voltage of the array is approximately differentiated using high pass filter. The op-amp used as in differentiator circuit is LM318. The connection for power and voltage differentiator is shown below. It can be seen that the parameter of capacitors, and resistors used in the differentiator circuit is same. The differentiated value power and voltage of array is measured as the value is needed to evaluate to track the MPP.

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Figure 17: Voltage and Power Differentiator Connection

4.3.5

Comparators The comparators also using op-amp which compares two voltages or currents and switches its

output to indicate which one is larger. From the referred circuit, the outputs of differentiators‟ dV/dt and dP/dt were fed into the comparator. At the comparators both the differentiated voltage and array was compared to ground. The op-amp being used as the comparators were LM311. Although an ordinary opamp can be used as comparator, there is special integrated circuit intended for use as comparators. LM311 chips are designed for very fast response and aren‟t in the same league as other op-amp.

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Figure 18: Power and voltage comparators The comparators will produce output 1 if the input value is greater than zero while it produce zero if the input value is lower than zero.

4.3.6

XOR gate In the referred MPPT charge controller circuit, both output of comparators to the XOR gate.

There is pull-out resistors connected parallel in between the comparators and XOR gates. This connection is to provide additional power to drive the XOR gate. In the pull-out resistor, 4.7k ohm resistor connected in series with 5V voltage source and shunted in between comparators and XOR gate. The XOR being used in the circuit was IC7486. Since there were two inputs to the XOR gate, then there will be 4 conditions. The truth table of the XOR gate showing the output of each condition is shown as well as its connection in the circuit.

(a)

Xv

Xp

output

0

0

0

0

1

1

1

0

1

1

1

0

(b) 31

(c) Figure 19: (a) Connection diagram of IC7486, (b) XOR truth table, (c) Connection of XOR gate in the circuit

4.3.7

D Flip-Flop

Flip-flop is an electronic circuit that has two stable states and thereby is capable of serving one bit of memory. It usually controlled by one or two signals and/or a gate or clock signal. The output of D-flipflop, Q looks a delay of input D. In the referred circuit, the D flip flop that being used is 74HC74 D flipflop. The connection to flip-flop is shown below.

Figure 20: 74HC74 D-Flip-flop connection

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𝑃𝑅𝐸 and 𝐶𝐿𝑅 must be connected high logic (1) to enable the flip-flop to operate where output was determined by input, D. According to table 2 below, flip-flop will operate if 𝑃𝑅𝐸 and 𝐶𝐿𝑅 are set to HIGH logic. Table 2: PRE and CLR function table

The output of XOR is connected to flip-flop before fed to switch because to prevent high frequency switching chattering and to minimize the unavoidable interference generate by the buck converter‟s switching action [David and Yan, 2000]. This interference occurs immediately after the clock transition and is over before the next, so latch never samples it.

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CHAPTER 5

SYSTEM MODELING

5.1

Input and output definition

The input of our design MPPT system is the DC power supply from the solar panel. The output of this system is the output voltage to the load supplying 80 W to the DC motor. The power that is harvested from solar panel is maximized using the MPPT system by using P&O algorithm. Basically, to have the maximum power transfer to the load, an impedance matching circuit design is required. Hence, our overall design can be divided into four simple stages as in figure 21. Figure 21 shows the input solar panel is fed into the MPPT system and impedance matching to have the desired output at the load. Solar Panel

MPPT

Impedance matching

Load- DC motor

Figure 21: Simple block diagram for overall system.

5.2

Detail design and drawing

The overall design of MPPT is built based on logic components such as, voltage follower, voltage inverter, analog multiplier, differentiators, voltage comparators, X-OR gate, and D-flip flop. These components are used to track the MPP by using the P&O algorithm. The DC-DC buck converter is used to step down to 12V for the load use. The overall design schematic is as follows,

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Figure 22: Full schematic diagram for MPPT system and Buck Converter 5.3

Operation of MPPT system using P&O algorithm

MPPT system tracks the maximum power point of the solar panel and supplies it to the buck converter. The overall operation of the operation is simplified as in flow chart in Figure 23. Figure 23 shows the flow of tracking the MPP of solar panel. dV/dt Voltage follower

Varray Differentiators

Parray Inverting Amplifiers

Multiplier

Comparator

dP/dt Differentiators

Switch

Comparator

X-OR

D-flip flop

Figure 23: Flow chart for MPP tracking

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Power, W

MPP Pmax A B

Voltage, V Vmax Figure 24: The Circuit operation chart.

The solar panel will exhibit the PV curve as in Figure 24. Refer to the P-V curve in Figure 24, the P&O algorithm is implemented using the MPPT controller circuit. By referring to the Maximum Power Point (MPP), the voltage array is increased or decreased by charging or discharging of capacitors.

At point A, V