ABSTRACT
As the sources of
conventional energy deplete day by day, resorting to alternative sources of
energy like solar and wind energy has become essential of the hour. Solar-powered
lighting systems are readily available in rural as well as urban areas. These
include solar lanterns, solar home lighting systems, solar street lights, solar
garden lights and solar power packs. All of them consist of four components:
solar photovoltaic module, rechargeable battery, charge controller and load. In
the solar-powered lighting system, the solar charge controller plays an
important role as the battery’s overall life depends mainly on it. In this
point of view, this project presents designing a Solar Charge Controller for
the Solar Battery Charging Station with the function to disconnect and
reconnect battery and load during battery over charging or discharging. Instead
of using readily available microcontroller board (Eg. Arduino), here Arduino microcontroller (Atmega328) has been used to
make the system cost-effective. The source code for the Arduino microcontroller
is written in Arduino software.
Furthermore, to ensure the full charge and to avoid over discharge the SOC of
the battery has been properly determined by sensing the terminal voltage of the
battery and the charging or discharging current. Normal charge controller has
four set-points which are fixed, but here the set-points will be automatically
adjusted depending on the level of charging and discharging current. As a
current sensor ACS712 hall current sensor has been used. The system has been
simulated and practically implemented.
Performance study of the system shows that it works
properly within the range 10A maximum.
TABLE OF CONTENTS
Declaration of Authorship i
Certificate of Authorship
ii
Acknowledgements
iii
Abstract iv
CHAPTER
1 Introduction 1-13
1.1
Background of the work 2
1.2
Objectives of this project 4
1.3
Purposes of the thesis 5
1.4
Literature survey 7
1.5
Project Outline 13
CHAPTER
2 Theoretical Backgrounds 14-33
2.1
Introduction 15
2.2
Basics of Charge Controller Theory
15
2.2.1
Two Stage Charge Controller
16
2.2.2
Voltage Regulation (VR) Set-point 16
2.2.3
Array Reconnect Voltage (ARV) Set-point 17
2.2.4
Voltage Regulation Hysteresis (VRH) 18
2.2.5
Low Voltage Disconnect (LVD) 18
2.2.6
Load Reconnect Voltage (LRV) Set-point 18
2.2.7
Low Voltage Disconnect Hysteresis (LVDH) 19
2.3 Effect
of Battery Internal Resistance 19
2.3.1 Battery Internal Resistance 19
2.3.2 Effect of IR and Charging or Discharging
Current 20
2.4 Hall
current sensor 23
2.4.1 Introduction
23
2.4.2 Theory
23
2.4.3 Sensitivity and output of ACS712 26
2.5
Microcontroller 28
2.5.1 Importance of Microcontroller 29
2.5.2
Microcontroller versus Microprocessor 29
2.5.3
Architecture of Atmega328
30
2.6 Battery
32
2.6.1 Active Material
33
CHAPTER 3 Designs and
Development of the System 34-51
3.1 Hardware Design 35
3.1.1 Voltage sensing Circuit
36
3.1.2 Current Sensing Sector
37
3.1.3 Voltage Regulator Section
38
3.1.4 Switching Section
40
3.1.4.1
Switching unit between PV and Battery 40
3.1.4.2 Switching unit between Load and Battery 41
3.1.4.3 Opto-coupler
41
3.1.5 Control Section
42
3.2 The Flow Chart for the
Program
46
3.3
Schematic Diagram of the System 47
3.4 Software Design 48
3.4.1 Programming Language
49
3.4.2 About Arduino
50
3.4.3 Why Arduino
51
CHAPTER 4 Simulated and Practical Results 52-57
4.1
Introduction 53
4.2
Simulation Part 54
4.2.1 Voltage Regulation (VR) Set-point 54
4.2.2 Array Reconnect Voltage (ARV) Set-point 54
4.2.3 Low Voltage Disconnect (LVD) 55
4.2.4 Load
Reconnect Voltage (LRV) Set-point 55 4.2.5 Data table of
battery voltage and set points
at
different current
55
4.3
Prototype Testing 56
CHAPTER 5 Conclusion and Future work
58-63
5.1
Conclusion 59
5.2
Future work 60
Glossary 60 References
62
CHAPTER 1
INTRODUCTION
1.1 INTRODUCTION
Bangladesh Government has set up
the goal of providing electricity to all by 2020 and to ensure reliable and
quality supply of electricity at a reasonable and affordable price. Sustainable
social and economic development depends on adequate power generation capacity
of a country. There is no other way for accelerating development except to
increase the power generation by fuel diversification. Development of Renewable
Energy is one of the important strategies adopted as part of Fuel
Diversification Program. In line with the Renewable Energy policy 2009, the
Government is committed to facilitate both public and private sector investment
in Renewable Energy projects to substitute indigenous non- renewable energy
supplies and scale up contributions of existing Renewable Energy based
electricity productions. The Renewable Energy Policy envisions that 5% of total
energy production will have to be achieved by 2015 and 10% by 2020. To achieve
this target, GOB is looking for various options preferably Renewable Energy
resources. Under the existing generation scenario of Bangladesh, Renewable
Energy has a very small share to the total generation. The share of Renewable
Energy exceeds more than 1% till now. The present Government is placing
priority on developing Renewable Energy resources to improve energy security
and to establish a sustainable energy regime alongside of conventional energy
sources. Government has already launched "500 MW Solar Power Mission" to promote the use of Renewable
Energy to meet the increasing demand of electricity.
Solar Energy, radiation produced
by nuclear fusion reactions deep in the Sun’s core. The Sun provides
almost all the
heat and light Earth
receives and therefore
sustains every living being.
Bangladesh being a country being concerned about environmental problems,
sustainable energy sources is becoming more and more popular here.
Photovoltaic (PV) is the direct
process of converting solar energy into electricity. It is considered as a
clean and environmental-friendly source of energy. Photovoltaic power systems,
a promising source of energy for the future, are actually solar panels are
referred to by the industry as solar electric modules or photovoltaic (PV)
modules. Module or panel, they are flat arrangements of series-connected
silicon solar cells. There are generally 30 to 36 solar cells per module. The
modules can be wired as series or parallel arrays to produce higher voltages
and currents. Typical small PV systems use a single panel to charge a 12-volt
battery. In general, a PV system consists of
a PV array,
which converts sunlight
to direct-current electricity,
a control system,
which regulates battery charging,
and operation of the load, energy storage in the form of secondary
batteries and loads
or appliances. A
charge controller is
one of functional
and reliable major components in PV systems.
Since the brighter,
the sunlight, the
more voltage the
solar cells produce, the
excessive voltage and
current could damage
the batteries. A charge
controller is used to control charging and discharging function to prevent
damage and long-life of batteries. As
the input voltage
from the solar
array varies with
time, the charge
controller regulates the charge
to the batteries
preventing any overcharging.
The charge controller
also prevent over discharging of
batteries as load
are connected with
it always. Therefore, a good, solid and reliable PV
charge controller is a key component of any PV battery charging system to
achieve low cost and the benefit that user can get from it. The algorithm or
control strategy of a battery charge controller determines the effectiveness of
battery charging and PV array utilization, and ultimately the ability of the
system to meet the load demands. An intelligent charge controller should be
designed to prolong
the battery's lifetime
and stabilize the
voltage from is has
photovoltaic panel.
Important functions of battery charge controllers
and system controls are
Prevent Battery Overcharge: To limit the energy supplied to the
battery by the PV array when the battery becomes fully charged.
Prevent Battery Over-discharge: To
disconnect the battery
from electrical loads
when the battery reaches low
state of charge.
Provide Load Control Functions: To automatically connect and
disconnect an electrical load at a specified time, for example operating a
lighting load from sunset to sunrise.
Prevent Battery Undercharge: The battery industry pays less
attention to undercharging than to overcharging. Still it is better to prevent
undercharging.
Figure
1.1 shows the
block diagram for
a controller that
employs hysteresis on
charge and discharge, selective
load disconnect.
Figure-1.1: Block diagram of a charge
controller
Ideally, a charge controller will
make full use of the output power of the PV array, charge the batteries
completely and stop the discharge of the batteries at exactly the prescribed
set-point, without using any power itself.
1.2 OBJECTIVES OF THE PROJECT
§ To design an automatic charge controller circuit with variable
set-points
§ Use hall current sensor
to vary the set points according to the amount of current
§ To construct a intelligent charge controller circuit intelligent
in the breadboard § Test for its
functionality
1.3 PURPOSES OF THE PROJECT
Batteries are often blamed for
power system failures, but batteries are only the most vulnerable part of the
system. No battery can overcome the faults of a bad charging system. Best
battery performance is achieved when the characteristics of the battery are
matched to the charging source. This is the job of the charge control system.
Small PV power systems at remote sites face two charge control problems that
indoor float systems connected to the power grid do not. First, the amount of
solar power is highly variable and influenced by uncontrollable factors such as
the weather. Second, the power system may have to cope with temperature
extremes. Both of these can cause too much or too little battery charging.
Premature battery failure is the result.
A battery becomes overcharged when it is forced to accept
more current than it can chemically store. This happens either when charging
currents are too high or when the battery is fully charged and current
continues to flow through the battery. Overcharging damages batteries through electrolyte
water loss and grid corrosion. One of the ways a battery dissipates overcharge
current is to use it to decompose electrolyte water. Water is broken down into
hydrogen and oxygen gases. This process is referred to as gassing. Unless the gases are recycled or the water is replaced,
the loss is permanent. Battery capacity is permanently lost when the
electrolyte dries out.
In small PV systems, undercharging is as responsible
as overcharging for early battery failure.
The problem with undercharging is salfation. As a battery discharges, the
active material on both plates is changed to lead sulfate. When the battery
recharges, the lead sulfate is changed back to active material and sulfate ions
return to the electrolyte. Sulfate ions do this easily if they are not part of
a larger lead sulfate crystal structure. However, if recharge is delayed, there
is time for crystal growth and it can become difficult or impossible to change
the entire lead sulfate back into active material. Battery self-discharge
contributes to crystal growth. By delaying full recharge, undercharging allows
lead sulfate to form more perfect crystal structures. In extreme cases, surface
lead sulfate crystal barriers block whole plates and the battery is unable to
recharge. Such a battery is said to have "sulfated" because its plates
have "hardened".
Electrolyte
freezing is another problem caused
by severe undercharging. Electrolytes with low specific gravities freeze at
higher temperatures. Frozen electrolytes expand and injure plates.
Table 1 shows
the freezing point of electrolytes with different specific gravities.
|
SPECIFIC GRAVITY
|
FREEZING
POINT
̊C
|
|
SPECIFIC GRAVITY
|
FREEZING
POINT
̊C
|
|
1.300
1.280
1.260
1.240
1.220
1.200
|
-70
-68
-58
-44
-34
-25
|
1.180
1.160
1.140
1.120
1.100
1.000
|
-21
-16
-12
-10
-08
0
|
Table 1 Electrolyte
freezing point at various specific gravities (BCI, 1995)
Some of the other critical issues are listed in the
following.
• Premature failure and lifetime prediction of batteries are major
concerns within the PV industry.
• Batteries experience a wide range of operational conditions in
PV applications, including varying rates of charge and discharge, frequency and
depth of discharges, temperature fluctuations, and the methods and limits of
charge regulation. These variables make it very difficult to accurately predict
battery performance and lifetime in PV systems.
• Battery performance in PV systems can be attributed to both battery
design and PV system operational factors. A battery, which is not designed and
constructed for the operational conditions experienced in a PV system, will
almost certainly fail prematurely.
•
Battery manufacturers’
specifications often do not provide sufficient information for PV applications.
The performance data presented by battery manufacturers is typically based on
tests conducted at specified, constant conditions and is often not
representative of battery operation in actual PV systems.
On the other
hand, during periods of below average isolation and/or during periods of
excessive electrical load usage, the energy produced by the PV array may not be
sufficient to keep the battery fully recharged. When a battery is deeply
discharged, the reaction in the battery occurs close to the grids, and weakens
the bond between the active materials and the grids. When a battery is
excessively discharged repeatedly, loss of capacity and life will eventually
occur. In some cases, the electrical loads in a PV system must have
sufficiently high enough voltage to operate. If batteries are too deeply
discharged, the voltage falls below the operating range of the loads, and the
loads may operate improperly or not at all
Therefore, a charge controller is
important to prevent battery overcharging, excessive discharging, reverse
current flow at night and to protect the life of the batteries in a PV system.
Charge controllers prevent excessive battery overcharge by interrupting or
limiting the current flow from the array to the battery when the battery
becomes fully charged and prevent battery over-discharge by open-circuiting the
connection between the battery and system load once the battery reaches a low
state of charge condition. Consequently overcharge and over-discharge effects
can be removed.
1.4 LITERATURE SURVEY
Before proceeding with our work, a
literature survey has been conducted.
Among them the following topics, which are closely related with our
work, are given below. As our thesis work is commercial project (related to
application of microcontroller) it is difficult to know more about which
technique is used to make such product only their application or operation is
given on company website. Such companies are:
1. Company name: Outback Power System
Website:
http://www.outbackpower.com/products/charge_controllers/flexmax/
Product name:
FLEXmax-Continuous Maximum Power Point Tracking Charge Controllers
Product Model: FLEXmax 80 Features:
• Increases PV Array Output by up to 30%
• Advanced Continuous Maximum Power Point Tracking
• Full Power Output in Ambient Temperatures up to 104°F
(40°C)
• Battery Voltages from 12 VDC to 60 VDC
• Fully Out Back Network Integrated and Programmable
• Programmable Auxiliary Control Output
• Built-in 128 days of Data Logging
Cost – 539$
2. Company name: Sunforce
Website:
http://www.sunforceproducts.com/product_details.php?PRODUCT_ID=152 Product name: 10 Amp Digital Charge
Controller Features:
• Protect battery form Overcharge and Discharge
• For use with 12V solar panels and batteries only
• Handles up to 10 Amps of current
• Handles up to 50 Watts of Solar Power
•
Maintenance Free Protection
of your solar panels and batteries LCD
digital display
Cost – 87.23$
3. Company name: Xantrex Technology
Inc.
Website:http://www.wholesalesolar.com/products.folder/controllerfolder/xantrexXWSC
C.html
Product name:
XW Solar Charge Controller
Product model:
XW-MPPT 60-150
Features and General Information:
• Maximum Power Point
Tracking (MPPT) delivers
maximum available power from PV array to battery bank
• Integrated PV ground-fault protection
• Ultra-reliable,
convection-cooled design does
not require a
cooling fan -
large, aluminum, die-cast heat-sink
allows full output
current up to
45°C without thermal derating
• Selectable two or
three-stage charging algorithms
with manual equalization
to maximize system performance and improve battery life
• Configurable auxiliary output
• Two-line,
16-character liquid crystal
display (LCD) and
four buttons for configuration and system monitoring
• Input over-voltage and
under-voltage protection, output
over-current protection, and back
feed (reverse current) protection (warning and fault messages appear on LCD
when unit shuts down as a protective measure)
• Over-temperature protection and power derating when output power and ambient temperature are high 18
• Battery Temperature Sensor (BTS) included - automatically provides temperature
compensated battery charging
Cost- $475.00$
4. Company name: Beijing EPsolar Technology Co. Ltd
Website:
http://www.epsolarpv.com/en/index.php/Product/pro_content/id/233/am_id/136 Product name: eTracer series MPPT Solar
Charge Controller (45A/60A) &
(12/24/36/48V)
Product model: LS1024RP / LS2024RP Features:
•
Waterproof design
•
High efficient Series PWM
charging
•
Gel, Sealed and Flooded
battery type option
•
Widely used, automatically
recognize day/night
•
Intelligent timer function
with 1-15 hours option
•
Use MOSFET as electronic
switch
•
Digital LED menu with
simple setting and easy using
•
Temperature
compensation
•
Reverse protection: any
combination of solar module and battery
•
Prevent Over discharging,
Over charging and Overheating
•
Prevent Load overload and
Load short circuit and PV short circuit
In our project,
we are designing a series controller. The most simple series controller is the
series-interrupting type, turning the array charging current either on or off.
The charge controller constantly monitors battery voltage, and disconnects or
open-circuits the array in series once the battery reaches the regulation
voltage set point. When battery voltage drops to the array reconnect voltage set
point, the array and battery are reconnected, and the cycle repeats.
Assume that the battery is fully
charged when the terminal voltage reaches 14 volts with a specific charging
current. Assume also that when the terminal voltage reaches 14 volts, the array
will be disconnected somehow from the batteries and that when the terminal
voltage falls below 14 volts, the array will be reconnected. Now note that when
the array is disconnected from the terminals, the terminal voltage will drop
below 14 volts, since there is no further voltage drop across the battery
internal resistance. The controller thus assumes that the battery is not yet
charged and the battery is once again connected to the PV array, which causes
the terminal voltage to exceed 14 volts, which causes the array to be
disconnected. This oscillatory process continues until ultimately the battery
becomes overcharged or until additional circuitry in the controller senses the
oscillation and decreases the charging current. One way to eliminate overcharging
resulting from the oscillatory process is to introduce hysteresis into the
circuit, so that the array will not reconnect to the batteries until the
batteries have discharged somewhat.
Figure 1.2 Hysteresis loops in charge controller
for voltage sensing
Now consider the discharge part of
the cycle. Assume the battery terminal voltage drops below the prescribed
minimum level. If the controller disconnects the load, the battery terminal
voltage will rise above the minimum and the load will turn on again, and once
again, an oscillatory condition exists. Thus, once again an application for
hysteresis is identified.
Generally,
charge controller is divided into 3 main portions, which are Atmega328
microcontroller, input parts and output parts. The input part for the charge
controller is battery voltage sensing circuit. It is used to detect the voltage
of the battery and send the data to the Atmega328 microcontroller to analyze
and Atmega328 microcontroller will operate according to the program written
inside its memory. For the output part, it consists panel-battery connect/
disconnect circuit, sources load connect/ disconnect circuit, low voltage
warning, fully charged indicator and normal indication. A crystal oscillator of
4MHz/20MHz clocks the microcontroller. Circuit power at 5V is derived from a
L7805 voltage regulator connected to the battery. Two power MOSFETs (IRF540)
are used as solid-state switch for the panel-battery line and batteryload line.
LEDs of differing colors are used to display the system status.
**Here, Atmega328 microcontroller is used to control the
operation of charging control and data acquisition task in this project.
Atmega328 contains 19 I/O ports which are suitable for the development of the
charge controller. Port A to is used to
perform the analog to digital conversion, which is used in input parts like
battery voltage sensing circuit and current sensing circuit. Port C controls
disconnect or reconnect operations for photovoltaic panel or load and provide
the information of battery charging status. Port B is used as to show different
battery voltage condition indicated by LEDs. Block diagram of charge controller
is shown in Figure 1.0
Figure-1.3 Block diagram of
Microcontroller based charge controller**
The other features of this designed charge
controller are listed as below.
•
Solar charging current: 50
Amps continuous
•
Nominal battery voltage:
12V
•
Photovoltaic panel voltage
ratings: Up to 50 KWP
•
Battery type: lead-acid
•
Hysteresis Control Option
•
Over voltage and under
voltage protection
•
Excess temperature
protection
•
Battery voltage status
indication by LEDs
•
Three LED indicators to
show the status of the charge controller which are battery charging, battery discharging, and charging
& discharging
•
Adjustable output voltage
1.5 THESIS OUTLINES
This project is divided into 4 chapters:
Chapter
1: An introduction of charge
controller. Some recent works related to our project are studied. The basic
elements of the proposed system are described in short.
Chapter 2: In
the 2nd chapter, we have studied the theories in details related to this work.
Definition of microcontroller, Families of microcontroller, the internal
architecture of Atmega328
microcontroller are described. MCU needs to configure at first, how it
should be configured is discussed in this chapter.
Chapter 3: Mainly focused on
methodologies for the design & development of Photovoltaic Charge
Controller. This chapter also includes the development & testing process of
the program. Chapter 4: This chapter includes the Simulation and Practical
Result of the program. Details on the progress of the thesis are explained in
this chapter.
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