ABSTRACT
Photovoltaic
(PV) system is one of the revolutionary renewable sources that are grabbing place rapidly instead of traditional
energy sources. Industries are now designing solar roof, solar tree leaves,
solar roadways, solar vehicles and even flexible solar cells for clothing. In
the meantime, The International Energy Agency (IEA) reports that, last year,
renewable overtook coal as the world‟s largest source of new power capacity.
Yet, effective power generation or power extraction from renewable sources remain
relatively low, and this must rise fast, as people transition to a more green
and environment-friendly energy future. The demand or future work is looking
for high efficiency, more reliable and low economical price of every components
used in a PV system. PV charge controller (CC) is one of the most important
parts of a PV system. CC circuit is used to extract the power of a solar panel
during its less than optimum conditions. Under reduced incident solar
radiation, due to the cloudy weather the low power level supplied by the solar
cell normally would not be adequate to operating a load and charging up the
storage or battery, but with the presence of the controller circuit, the low
power generated by the solar panel would be accumulated to a high enough level
to overcome the energy barrier of the battery or the load. In this research, a
solar charge controller is designed based on Maximum Power Point Tracking
(MPPT) technique. Microcontroller PIC 16F877A integrated circuit (IC) works as
control unit, which reduced complexity in the number of electronic components
and increased monitoring and regulative functions. The benefit of this charge
controller is maximum power tracking capability from the solar panel, as well
as customized programmable control unit, remote control and monitoring facility
interfacing with smart phone or laptop applications, external device charging
unit, Liquid Crystal Display (LCD) for displaying the system status including
both of panel and battery voltage, current, power, charging state of battery in
percentage and load status. Experimental results demonstrate that proposed MPPT
charge controller increase 11% efficiency of 85W, 12V standalone PV systems.
TABLE OF CONTENTS
Board of Examiners ……………………………………………………… i
Declaration ……………………………………………………………….. ii
Dedication ………………………………………………………………... iii
Acknowledgement ……………………………………………………….. iv
Abstract …………………………………………………………………... v
List of Figures ……………………………………………………………. xi
List of Tables …………………………………………………………….. xiv
List of Abbreviations …………………………………………………….. xv
List of Symbols …………………………………………………………... xvii
1 INTRODUCTION 1
1.1 Introduction
………………………………………………….......... 1
1.2
Background of the Thesis ………………………………………… 2
1.3 Literature
Review ………………………………………………… 3
1.4 Problem
Statement ………………………………………………... 4
1.5 PV
System and Charge Controller (CC) ………………………….. 6
1.6 Significance of This Research
………………………………… 7
1.7 Scope
of the Thesis …………………………………………… 8
1.8 Objective of
the Research ………………………………………… 8
1.9 Outline of Methodology ……………………………………………… 9
1.10 Organization
of the Thesis ………………………………………... 9
2 PHOTOVOLTAIC SYSTEM 11
2.1
Introduction ………………………………………………….......... 11
2.2 Photovoltaic
(PV) System ………………………………………… 11
2.3
Classifications of PV System ………………………………........... 12
2.3.1
Standalone or Off-grid …………………………………….. 12
2.3.2 Grid-tie ……………………………………………………. 13
2.3.3 Grid-tie
with Power Backup or Grid Interactive ………….. 13
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2.3.4 Grid Fallback
…………………………………………........
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14
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2.3.5 Grid-tie and Standalone
Systems …………………………..
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14
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2.4 Photovoltaic Cells and
PV Panels …………………………………
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15
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2.5 Electric Model of
Photovoltaic Cell ………………………………
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16
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2.6 Charger Unit
..……………………………………………………..
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19
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2.7 DC/DC Converter
…………………………………………………
|
19
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2.7.1 Converter Topology ……………………………………
|
20
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2.7.2 Theory of Operation
……………………………………
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20
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2.7.3 Sizing of the Output Filter
……………………………..
|
21
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2.7.4 Value of the Inductor, L
………………………………..
|
22
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2.7.5 Value of the Capacitor, C
………………………………
|
23
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2.8 Maximum Voltage Output
for Duty Cycle Ratio Control ……………
|
24
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2.9 Maximum Power Point
Tracking (MPPT) ……………………………
|
26
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2.10
Control Unit
………………………………………………….........
|
27
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2.10.1 Microcontroller PIC16F877A
………………………….
|
28
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2.10.2 Integrated Circuit SG3524
…………………………………
|
29
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2.11 Low Pass Filter ……………………………………………………
|
29
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2.12 Battery ……………………………………………………….........
|
30
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2.13
Conclusion ………………………………………………………..
|
30
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3 SOLAR CHARGE CONTROLLER
|
31
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3.1 Introduction
…………………………………………………………...
|
31
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3.2 Evolution of Solar Charge Controller
………………………………..
|
32
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3.3 Operating Principle
………………………………………………......
|
33
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3.3.1
Relay Type Switch ……………………………........................
|
34
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3.3.2
Solid State Switch ……………………………………............
|
34
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3.4 Charge Controller Types
……………………………………………...
|
35
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3.4.1
Shunt Controller ………………………………………….........
|
35
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3.4.2
Series Controller …………………………………………........
|
36
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3.5 Switching Mechanism of
Charge Controller ………………………….
|
37
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3.5.1
On-Off mechanism ……………………………………….........
|
37
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3.5.2
PWM …………………………………………………......... 38
3.5.3
MPPT ……………………………………………………… 38
3.5.3.1
Perturb & Observe (P&O) or Hill Climbing Method ……………………………………………. 40
3.6 Characteristics of MPPT ……………………………………………... 42
3.7 Charge Controller Selection
………………………………….............. 44
3.8 Charge Regulation Set Points ………………………………………... 44
3.8.1 Voltage Regulation (VR) Set
Point …………………………… 45
3.8.2 Voltage
Regulation Hysteresis (VRH) ………………………... 45
3.8.3 Low Voltage
Disconnect (LVD) ……………………………… 45
3.8.4 Low Voltage Disconnect
Hysteresis (LVDH) ………………... 45
3.8.5 Effect of Duration
of Load on Set Point ……………………… 46
3.8.6 Depth
of Charge Effect… …………………………….............. 46
3.8.7 Effect
of Temperature of Battery …………………………….. 46
3.9 Conclusion ……………………………………………………………. 46
4 MODELLING AND SIMULATION 47
4.1 Introduction …………………………………………………………... 47
4.2 PV Module Modeling ………………………………………………… 47
4.2.1
Ideal Factor ……………………………………………………. 49
4.2.2 Open
Circuit Voltage …………………………………………. 49
4.2.3
Short Circuit Current ………………………………….............. 49
4.2.4 Short Circuit Current
Temperature Coefficient ………………. 49
4.2.5
Cells Series Number …………………………………………... 50
4.2.6 Cells
Parallel Number ………………………………………… 50
4.2.7
Reference Temperature ……………………………….............. 50
4.2.8
Subsystem of PV Module …………………………….............. 51
4.3 Battery Modeling …………………………………………….............. 51
4.3.1
Battery Type …………………………………………………... 52
4.3.2
Nominal Voltage (V) ………………………………………….. 52
4.3.3
Rated Capacity (Ah) …………………………………………... 53
4.3.4
Initial State-of-Charge (SOC) ………………………………… 53
4.3.5
Full Charge Voltage …………………………………………... 53
4.3.6 Internal
Resistance (Ohms) …………………………………… 53
4.3.7 Capacity @ Nominal Voltage ………………………………… 53
4.3.8
Exponential Zone ……………………………………………... 53
4.3.9
Units …………………………………………………………... 53
4.4 Buck-boost Converter Modeling ……………………………………... 54
4.5 MPPT Modeling ……………………………………………………… 55
4.6 SIMULINK Model of Charge Controller ……………………………. 56
4.7 Simulation Results …………………………………………………… 57
4.8 Conclusion ……………………………………………………………. 59
5 HARDWARE DESIGN AND FIELD TEST 60
5.1 Introduction …………………………………………………………... 60
5.2 Hardware Implementation ……………………………………………. 60
5.2.1 Buck
Converter Design ………………………………........ 62
5.2.1.1 Inductor Selection ………………………………… 62
5.2.1.1.1 Inductor Peak Current
…………………... 64
5.2.1.2
Capacitor Selection ………………………………... 64
5.2.1.3 MOSFET Selection ………………………………. 65
5.2.2
MOSFET Driver …………………………………………... 66
5.2.3
Voltage Regulator ……………………………………......... 66
5.2.4
Voltage Sensor …………………………………………….. 67
5.2.5
Current Sensor …………………………………………….. 68
5.2.5.1 ACS712 Current Sensor ………………………….. 69
5.2.6 Wireless
Data Transfer ……………………………………. 70
5.2.7
External Device Charging Unit ………………………........ 70
5.2.8
Liquid Crystal Display (LCD) …………………………….. 71
5.2.9 LED
Indication ……………………………………………. 71
5.3 Solar Panel …………………………………………………………… 72
5.4 Battery or Storage ……………………………………………………. 73
5.4.1
Lead-Acid Batteries ……………………………………….. 73
5.4.2
Battery Charging Algorithms ……………………………... 75
5.5 Hardware Schematic …………………………………………………. 76
5.6 PCB Design ………………………………………………………….. 78
5.7 Final Design ………………………………………………….............. 79
5.8 Cost Analysis ………………………………………………………… 79
5.9 Experimental Setup …………………………………………………... 81
5.10 Experimented
Data ……………………………………………….. 81
5.11 Testing
Results ………………………………………………........ 83
5.11.1
LCD Display …………………………………………......... 83
5.11.2 Wireless
Data Transfer ……………………………………. 84
5.11.3 External
Device Charging ……………………………........ 85
5.12 Conclusion
………………………………………………………... 85
6 CONCLUSIONS AND FUTURE WORK 86
6.1 Summary ……………………………………………………………... 86
6.2 Future Work ………………………………………………….............. 88
6.3 Industrial Scaling
…………………………………………….............. 89
REFERENCES ………………………………………………………..... 90
APPENDIX
………………………………………………………… 93
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LIST OF FIGURES
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Fig.
1.1 A solar home system (SHS)
|
07
|
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Fig.
2.1 Block diagram of standalone PV
system.
|
12
|
|
Fig.
2.2 Block diagram of standalone PV
system
|
13
|
|
Fig.
2.3 Block diagram of grid-tie PV
system
|
13
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Fig.
2.4 Ideal I-V Curve for a PV cell
|
15
|
|
Fig.
2.5 Typical current-voltage (I-V)
curve
|
15
|
|
Fig.
2.6 Solar cell electrical equivalent
model
|
16
|
|
Fig.
2.7 Block diagram of the charging
unit
|
18
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|
Fig.
2.8 Electrical model – DC/DC
converter (buck topology)
|
19
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Fig. 2.9 (a) Switch operation – DC/DC converter
when Switch M1
closed
|
20
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Fig.
2.9 (b) Switch operation – DC/DC
converter when Switch M1 open
|
20
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Fig. 2.10 Inductor current
waveform of output filter
|
22
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Fig. 2.11 Inductor current waveform used to
illustrate capacitor charging
|
23
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Fig. 2.12 Switching
operation of DC/DC converter
|
24
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Fig. 2.13 Inductor current
waveform
|
25
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Fig. 2.14 Schematic diagram of
microcontroller connections that it controls
|
28
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Fig. 2.15 Average value of
PWM signal
|
29
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Fig. 2.16 Construction of
Lead-acid battery
|
30
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Fig.
3.1 Simple block diagram of a charge
controller
|
31
|
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Fig.
3.2 On-off charge controller
|
32
|
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Fig.
3.2 Solid state series controller
|
32
|
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Fig.
3.4 Micro-processor based series
controller
|
32
|
|
Fig.
3.5 Block diagram of operation of
charge controller
|
33
|
|
Fig.
3.6 Rely type switch used for solar
charge controller
|
34
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Fig.
3.7 Solid state switch for solar
charge controller
|
34
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Fig.
3.8 Block diagram of a shunt charge
controller
|
35
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Fig.
3.9 Block diagram of a series charge
controller
|
36
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Fig. 3.10 Schematic diagram
of PWM
|
38
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Fig. 3.11 Schematic diagram
of MPPT
|
38
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Fig. 3.12 Characteristic PV
array power curve
|
40
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Fig. 3.13 Divergence of
hill climbing/P&O from MPP
|
40
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Fig. 3.14 Block diagram of the PV system using the hill
climbing and
P&O
methods
|
41
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Fig. 3.15 The flowchart of
P&O control technique
|
41
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Fig. 3.16 Charge controller
set points
|
44
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Fig.
4.1 Block of PV Module: SM-85KSM
model
|
48
|
|
Fig.
4.2 Function block parameters of PV
Module: SM-85KSM
|
48
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Fig. 4.3 Subsystem implementation of generalized PV Module: SM-
85KSM
|
51
|
|
Fig.
4.4 Block of 12V, 100Ah lead-acid
battery
|
52
|
|
Fig.
4.5 Block parameters for lead-acid
battery
|
52
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Fig. 4.6 Block of buck-boost converter model
Fig.
4.7 Subsystem implementation of
buck-boost converter
|
54
54
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Fig.
4.8 Dialog box of MPPT block
|
55
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Fig.
4.9 MPPT unit of simulation
|
55
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Fig. 4.10 Subsystem
implementation of P&O MPPT block
|
55
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Fig. 4.11 MATLAB/SIMULINK
based full solar MPPT system
|
56
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Fig. 4.12 Subsystem of
case1
|
56
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Fig. 4.13 Scope wave forms
of buck-boost converter
|
58
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Fig. 4.14 Discharge
characteristics of battery
|
58
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Fig. 4.15 Scope wave forms
of complete circuit
|
58
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Fig. 4.16 Scope wave forms
of extracting power from PV panel
|
59
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Fig.
5.1 (a) 0.37 μH Inductor
|
63
|
|
Fig.
5.1 (b) 470 μF Capacitor
|
63
|
|
Fig.
5.2 IRFZ44N MOSFET
|
65
|
|
Fig.
5.3 (a) MOSFET Driver
|
66
|
|
Fig.
5.3 (b) Pin layout of MOSFET driver
|
66
|
|
Fig.
5.4 (a) Voltage regulator LM7805
|
66
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|
Fig.
5.4 (b) Voltage regulator LM7812
|
66
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|
Fig.
5.5 Voltage sensor flowchart
|
67
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|
Fig.
5.6 (a) Voltage divider circuit
|
67
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|
Fig.
5.6 (b) ACS712 current sensor
|
67
|
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Fig.
5.7 Current sensor flowchart
|
68
|
|
Fig.
5.8 Wireless data transfer by
Bluetooth module JU-MCU
|
70
|
|
Fig.
5.9 Mobile charger unit by Proteus
|
71
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Fig. 5.10 LCD display from
JHD
|
71
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Fig. 5.11 (a) Solar panel
of SM-85KSM by KYOCERA
|
72
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Fig. 5.11 (b) Specification
label
|
72
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Fig. 5.12 Charging process
for a typical lead-acid battery
|
74
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Fig. 5.13 Block diagram of
the researched charge controller system
|
76
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Fig. 5.14 Schematic circuit
layout of designed solar charge controller
|
77
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Fig. 5.15 PCB design of
solar MPPT charge controller
|
78
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Fig. 5.16 Designed MPPT
solar charge controller
|
79
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Fig. 5.17 Experimental
setup of the designed solar charge controller
|
81
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Fig. 5.18 Graphical
representation of the charge controller efficiency
|
82
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Fig. 5.19 LCD display is
working properly
|
84
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Fig. 5.20 Wireless data
transfer to smart phone
|
84
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Fig. 5.21 External device
charging unit
|
85
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LIST OF TABLES
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Table 2.1 Electrical
Specifications SM-85KSM
|
18
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Table 3.1 Pros and Cons of
Both Types of Controllers
|
43
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Table 5.1 Component List
|
61
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Table 5.2 Electrical
Performance Under Standard Test Conditions (*STC)
|
72
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Table 5.3 Module
Characteristics
|
73
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Table 5.4 Component List
with Unit Price
|
80
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Table 5.5 Experimented Data with Efficiency of the Designed
Charge
Controller
|
82
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Table 5.6 Average
Efficiency for Experimented Days
|
83
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LIST OF
ABBREVIATIONS
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PV
|
Photovoltaic
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SHS
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Solar Home System
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CC
|
Charge Controller
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MPPT
|
Maximum Power Point
Tracking
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PWM
|
Pulse Width Modulation
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LCD
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Liquid Crystal Display
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P&O
|
Perturb & Observe
|
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INC
|
Incremental
Conductance
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CV
|
Constant Voltage
|
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FLC
|
Fuzzy Logic Control
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ANN
|
Artificial Neural Network
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MPP
|
Maximum Power Point
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Li-ion
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Lithium-ion
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LED
|
Light Emitting Diode
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PIC
|
Peripheral Interface
Controller
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PCB
|
Printed Circuit Board
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CC
|
Charge Controller
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LVD
|
Low Voltage Disconnect
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HVD
|
High Voltage Disconnect
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SOC
|
State of Charge
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IC
|
Integrated Circuit
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CCM
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Continuous Conduction Mode
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DCM
|
Discontinuous Conduction
Mode
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ICD
|
In Circuit Debugger
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A/D
|
Analog to Digital
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I2C
|
Inter Integrated Circuit
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USART
|
Universal Asynchronous Receiver Transmitter
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LPF
|
Low Pass Filter
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Wi-Fi
|
Wireless Fidelity
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USB
|
Universal Serial Bus
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MOSFET
|
Metal Oxide Semiconductor Field Effect Transistor
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ESR
|
Equivalent Series
Resistance
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STC
|
Standard Test Condition
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NOCT
|
Nominal Operating Cell
Temperature
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AGM
|
Absorbed Glass Mat
|
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BDT
|
Bangladeshi Taka
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USD
|
US Dollar
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LIST OF SYMBOLS
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Isc
|
Current Source
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Io
|
Diode Saturation Current
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m
|
Diode Ideality Constant
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VT
|
Thermal Voltage of Array
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Ns
|
Cell Connected in Series
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T
|
Temperature of PN Junction
|
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K
|
Boltzmann Constant
|
Electron
Charge
Equivalent Series Resistant of the Array
Equivalent Parallel Resistant of the Array
Net
Current
Voltage
Source
Open
Circuit Voltage
Inductor
Current
Average
Inductor Current
|
iLmax iLmin
fpwm ic
MV τ
E
V0
|
Maximum Inductor Current
Minimum Inductor Current
Commutation Frequency
Capacitor Current
Voltage Factor
Time Constant
Internal Battery Voltage
Constant Voltage
|
CHAPTER 1
INTRODUCTION
1.1 Introduction
Photovoltaic (PV) system is one of the renewable energy
resources that recently have become broader in energy sectors. The demand or
future work is looking for high efficiency, more reliable and economical price
PV charge controller which is come in portable size has become very popular in
PV system. PV charge controller is very important in PV system. This thesis
proposed a controller circuit that is used to extract the power of a solar cell
during its less than optimum conditions. Under reduced incident solar
radiation, due to the cloudy weather the low power level supplied by the solar
cell normally would not be adequate to operating a load and charging up the
storage or battery, but with the presence of the controller or power extractor
circuit, the low power generated by the solar panel would be accumulated to a
high enough level to overcome the energy barrier of the battery or the load. In
this research work, a Photovoltaic (PV) Maximum Power Point Tracking (MPPT)
charge controller is designed based on microcontroller PIC 16F877A, which
reduced complexity in the number of electronic components and increased
monitoring and regulative functions. This project used dc-dc buck converter
circuit which has been simulated using software of MATLAB SIMULINK. Pulse width
modulation (PWM) will be implemented on the PIC 16F877A to control duty cycle,
voltage and current in the PV system and is programmed using software of
microC. Bluetooth device is used to remote monitoring using smart phone or
laptop apps. Liquid Crystal Display (LCD) is used to display the voltage and
current from rechargeable battery. The benefit of this thesis is an improvement
of efficiency depend on duty cycle and voltage change. Experimental results
proof that proposed MPPT charge controller increase 11% efficiency of an 85 W,
12 V PV standalone systems and prevents high power level to component failure
during the normal operation of the solar cell. This charge controller or power
extractor circuit can also be used in other power sources to utilize the
portion of power which normally would have been lost.
1.2 Background of the Study
Solar power is one of the clean and
renewable sources of energy that have mass market appeal among the others being
wind, geothermal steam, biomass, and hydroelectric etc. Solar power uses energy
from the sun to provide passive heating, lighting, hot water, and active
production of electricity through photovoltaic (PV) solar cells. PV‟s are the
most promising of active solar power which directly convert sunlight into
electricity. However, PV panels are very expensive, in terms of high production
cost and low efficiency. Significant works have been done to improve the
efficiency of the photovoltaic array. One of the earliest improvements is the
addition of a battery. Without the battery, the photovoltaic array can supply
electrical power directly to a load. The major drawback of this configuration
is the uneven distribution of solar energy: during daylight operation, the
photovoltaic array can produce excess power while during night time or periods
of reduced sun light, there is no power supplied from the photovoltaic array.
With the addition of a battery, the battery can be charged by the photovoltaic
array during periods of excessive solar radiation, e.g. daylight, and the
energy stored in the battery can then be used to supply electrical power during
nighttime. The theorem known as the maximum power theorem
(Jacobi's Law) states: “Maximum power
is transferred when the internal resistance of the source equals the resistance
of the load, when the external resistance can be varied, and the internal
resistance is constant.”
Single solar cell normally produces
voltage and current much less than the typical requirement of a load. A
photovoltaic cell typically provides 0.2
̴ 1.4 V and 0.1 ̴ 5 A, depending
on the photovoltaic cell and its operating conditions, e.g. direct sun light,
cloudy, etc., while the load might need about 5
̴ 48 V, 0.1 ̴ 20 A. Thus a number
of photovoltaic cells are arranged in series to provide the needed voltage
requirement, and arranged in parallel to provide the needed current
requirement. These arrangements are critical since if there is a weak cell in
the formation, the voltage or current will drop and the solar cell array will
not be functioning properly. Thus for example, it is normal to see a
photovoltaic array arranged for 17V to provide 12V to a battery. The additional
5V provides a safety margin for the variation in solar cell manufacturing and
solar cell operation, e.g. reduced sun light conditions. Since the current
produced by these photovoltaic cell arrays is constant, in the best of lighting
condition, the photovoltaic array loses efficiency due to the fixed voltage of
the battery. Different techniques are available to reduce the losses, among the
techniques Maximum Power Point tracking (MPPT) method performs better in this
arena, where the PV voltage is tracked and converted it to the battery level
voltage by a Buckboost converter. This MPPT method can recover the 30% power
loss and the power consumed by the MPPT circuitry is not excessive. Together
with MPPT technique, various methods and circuits have been developed to
improve the efficiency and applications of solar cell array. However, the basic
assumption of all these methods and circuits is always that the photovoltaic
array can produce at least the necessary power to operate the battery or the
load. So far, no charge controller has been designed based on microcontroller
to capture the power of a solar cell during the reduced sunlight
conditions.
1.3 Literature Review
Renewable energy is generally defined
as energy that comes from resources which are naturally replenished and
regenerated after a regular time cycle. In its various forms, it derives
directly from the sun, or from heat generated deep within the earth. Included
in the definition is electricity and heat generated from solar, wind, ocean,
hydro power, biomass, geothermal resources, and bio-fuels and hydrogen derived
from renewable resources.
As people are much concerned with the
fossil fuel exhaustion and the environmental problems caused by the
conventional power generation, renewable energy sources are taking full
concentration in this regards. And among them photovoltaic panels and
wind-generators are now widely used. Photo voltaic (PV) sources are used today
in many applications such as battery charging [1], lighting [2], water pumping
[3], satellite power systems [4], irrigation etc. They have the advantage of
being maintenance and pollution free but their main drawbacks are high
fabrication cost, low energy conversion efficiency, and nonlinear
characteristics. PV modules still have relatively low conversion efficiency.
High efficiency power trackers can be significantly improve the conversion
efficiency which is designed to extract the maximum possible power from the PV
module [5]. Energy extraction process from renewable sources like solar, wind,
speed breaker [6] etc. has become more difficult. Some techniques are vastly
used to extract energy from PV systems. Particularly, perturb and observe
(P&O) [7], incremental conductance (INC) [8], constant voltage (CV) [9],
short current pulse [10], fuzzy logic control (FLC) [11]-[12], artificial
neural network (ANN) [13] and some other techniques [14] offer an efficient
energy extraction process. Proposed controller has designed based on perturb
& observe method. Different MPPT techniques have been developed and
implemented [14][16]. Literature review evident that none of those have
employed a microcontroller based MPPT technique. These proposed methods ensure
a safe and fast battery charging process. Which can be significantly improved
the system at the point of simplicity, highest efficiency and high flexibility.
In short, real time measurements of panel open circuit voltage are used to
detect the maximum power point of the solar panel.
Due to high energy densities and long
life times, Lithium-ion (Li-ion) batteries are increasingly used in systems
such as portable electronics, electric vehicles among others. The optimization
designs of these batteries have been built in order to study its internal
dynamics [17]-[19]. To minimize the cost of total system lead-acid battery is
used. In this thesis a simple dynamic model based on capacitor/resistor
networks is implemented in MATLAB SIMULINK environment in order to predict the
charging time and optimize the use of the battery [20]. Battery charge rate is
continuously adjusted in a way that the system operating point is forced near
the detected maximum power point of the solar panel. Theoretical and
experimental analyses are used to demonstrate the reliability and validity of
the proposed technique.
1.4 Problem Statement
With the advancement of renewable
energy, energy extraction process from renewable sources has not become more
efficient. The efficiency of an energy extraction process can further be
improved considering the Current-Voltage (I-V) characteristic of a solar cell.
I-V characteristic of a solar cell is nonlinear and varies with irradiation and
temperature [14]-[16]. There is a unique point on the I-V or Power-Voltage
(P-V) curve of the solar array called Maximum power point (MPP) at which the
entire PV system operates with maximum efficiency and produces its maximum
output power. When a PV array is directly connected to a load, the systems
operating point will be at the intersection of the I-V curves of the PV array.
However, under most conditions this operating point is not at the MPP [15].
Therefore it is desirable to ensure that the load line passes through the MPP
to continuously deliver the maximum power to the output.
For example, a photovoltaic array
rated 85 W, 19.7 V will have a maximum current of 85/19.7=4.31 A. During direct
sunlight, the photovoltaic array produces 19.7 V and 4.31A, but since the
battery is rated at 12V, the power transferred is only 12*4.31=51.78W, Power
loss, 85W-51.78W=33.22W for a loss of about 39%. This is a significant power
loss; however, it is not desirable to reduce the maximum possible voltage
provided by the photovoltaic array because in the reduced sunlight condition,
the current and voltage produced by the photovoltaic array will drop due to low
electron generation, and thus might not able to charge the battery.
In order to reduce the power losses
and improve the efficiency of the photovoltaic array, a method of Maximum Power
Point Tracking (MPPT) is introduced where the voltage provided by the
photovoltaic array is tracked and converted to the battery voltage by a
DC-to-DC converter before the power is supplied to the battery. 30% power loss
can recover utilizing these MPPT techniques. Most of the PV charge controller
nowadays just uses LED to indicate the operating status of the rechargeable
battery. It is hard to know the values of the rechargeable battery that have
been used such as voltage, current and others. Besides most of PV charge
controller is expensive depends on the total cost of PV system that has been
used.
Literature review evident that none
of those have employed a microcontroller based MPPT technique. These proposed methods ensure a safe and fast
battery charging with different control and protection topologies. Which can be
significantly improved the system at the point of simplicity, highest
efficiency and high flexibility. In short, real time measurements of panel open
circuit voltage are used to detect the maximum power point of the solar panel.
Simulation has been executed with the MATLAB SIMULINK environment.
1.5 PV
System and Charge Controller (CC)
Both rural and urban electrification
through solar PV technology is becoming more popular day by day in the whole
world. Every single PV system or stand-alone PV system is known as solar home
systems (SHS). SHS are highly decentralized and particularly suitable for
remote, inaccessible areas. Solar program mainly targets those areas, which
have no access to conventional electricity and little chance of getting
connected to the grid. SHS‟s can be used to light up homes, shops, fishing
boats, high ways, office, school-colleges etc. It can also be used to charge
cellular phones, run televisions (TV), radios and cassette players. SHSs have
become increasingly popular among users because of offering an attractive
alternative to conventional electricity. It also facilitates to avoid monthly
bills, fuel cost, negligible repair and maintenance costs, easy installation at
anywhere etc.
Globally SHS provide power to
hundreds of thousands of households in remote locations where electrification
by the grid is not feasible. SHS usually operate at a rated voltage of 12V DC
or 24V DC. Provide power for low power
DC appliances such as light, fan, radio and TV for about three to five hours a
day. Furthermore appliances such as cables, switches, mounts, structural parts,
power conditioners and inverters may also used. Inverter is used to invert 12V
or 24V DC power to 240V AC power. A SHS
typically includes one or more PV modules consisting of solar panels, a charge
controller which distributes power and protects the batteries and appliances
from damage and at least one battery to store energy for use when the sun is
not shining. Fig. 1.1 shows a solar home system. Solar panel, battery and loads
are connected through the charge controller (CC). CC is an electronic device, used
to control the operation of battery, load and solar panel of any PV system. PV
modules produces energy from sunlight, CC extract this energy from panel and
distribute to the load and store in the battery in most efficient and effective
manner.
Fig.
1.1 A solar home system (SHS)
It is used to control the storage of
electricity in the battery. This stored electricity can be used in later
specially at night to for household purpose. Main function of charge controller
is to prevent the battery from being overcharged. In addition, it can perform
some other functions such as disconnecting the load at low voltage, giving
indication to show state of charge, battery voltage, amount of current flowing,
fault condition etc. Battery is used for back up of power. Inverter can be used
to convert DC voltage to AC voltage.
1.6 Significance of this Thesis
Solar home system or standalone PV
system come with a rechargeable battery, under the cloudy weather conditions
that do not allow the solar cell array to produce adequate power to charge the
battery. In this research, to extract maximum power in any types of weather
condition, Microcontroller based MPPT charge controller has been designed. This
controller can significantly reduce the power losses and improve 11% efficiency.
In this proposed system of 85W, 12V PV system used for performance test of the
charge controller and theoretical losses of this standalone system is 39.08%,
where using this controller circuit it has been reduced to 28.14%. The proposed
study intends using the mathematical models and MATLAB SIMULINK environment to
simulation in combination with experimental data to determine the maximum power
extracting capability of the proposed controller of solar cells.
1.7 Scope of the Study
Solar charge controller is the heart
of solar home system. Using low quality charge controllers greatly diminishes
the efficiency of solar PV system. Infrastructure Development Company Limited
(IDCOL) has specified some standards which should be followed by all the charge
controller manufacturers. Technical appraisal and analysis of the available
charge controllers in the market is highly necessary. In this thesis, a
microcontroller based solar charge controller is designed that follow maximum
power point tracking techniques (MPPT). MPPT techniques were well known for
increasing the output of a solar panel. Using MPPT in the charge controllers is
a great way of increasing the efficiency of solar home system. In this thesis,
four MPPT algorithms were studied and modeled. Comparative analysis of their
efficiency were made using MATLAB/SIMULINK.
1.8 Objective of the Study
The main goal of this thesis is to
design a microcontroller based maximum power point tracker (MPPT) for off-grid
standalone PV system, which is basically known as solar MPPT charge controller.
Another purpose of this thesis is to develop an efficient controller circuit
that can extract maximum power from Photovoltaic (PV) or solar panel. This will
assist to recover power losses by increasing the efficiency with low price.
Analyzing and evaluating the results of the experimental data with that from
existing techniques, mathematical models and simulation packages used to
validate the proposed charge controlling technique. Specific objectives of the
thesis are:
a. To design MPPT charge controller by using PIC microcontroller.
b. To improve existing charge controller models including some
additional features like data logging, external device charging unit, liquid
crystal display (LCD) display for monitoring voltage and current status.
c. To evaluate proposed design of charge controller both software
and hardware performance test will validate for a complete PV system.
1.9 Outline of Methodology
A substantial number of
literature/papers have been reviewed pertaining to different MPPT methods
published for solar PV system. This review is intended to design and establish
a MPPT technique base on microcontroller. Necessary experimental setup has been
prepared in a laboratory of MIST. Key points of the proposed research are
summarized below:
a. A design layout including circuit diagram has developed for the
proposed MPPT system followed by its implementation and performance analysis
with necessary testing and developments. Thereby a prototype of solar charge
controller have been developed and validated.
b. Additionally, attractive features like, A LCD display will
continuously show the system status. A charging unit for direct charging of
smart phones or gadgets will be used. A Bluetooth module added, which could be
helpful in getting data continuously from the PV system using a smart phone or
laptop have been added to make the system smarter than existing
controllers.
c. A final version of the MPPT controller circuit designed on
Printed Circuit Board (PCB) using Sprint-Layout and Proteus software utilizing
experimented experience on prototype.
1.10 Organization of the Study
Chapter 1 gives a brief description
of the total research work and basically is an introduction of the thesis. A
typical solar home system and the role of charge controller are introduced.
This chapter provides the background of the thesis, objectives, scope of the
research, problem statement, and brief evolution of charge controller and the
thesis outline.
Chapter 2 deals with different
features of a charge controller. Specifically charge controller design,
switching mechanisms, different set points, operating characteristics are
discussed in this chapter.
Chapter 3 presents a clear concept of
solar charge controller. Description in details about the solar charge
controller including the operating principle, classification, switching
mechanisms and the different charge regulation set points are demonstrates
well. Selection of a charge controller, PWM and MPPT techniques are also
discussed.
Chapter 4 mainly focused on
methodologies for the development of charge controller. Details on the progress
of the simulation and hardware design are explained in this chapter. Full
simulation has been executed by MATLAB SIMULINK environment.
Chapter 5 presents the experimental
results obtained from the hardware and the limitation of the project. All
discussions are concentrating on the field test result and performance of
photovoltaic charge controller.
Chapter 6 includes the conclusion of
the thesis. Obstacle faced and recommendation for future work also discussed in
this chapter. Additionally, brief concept for industrialization is discussed
here.
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