major project report "mppt based battery charging using solar energy" (or) solar charge...
TRANSCRIPT
A Major Project Report on
MPPT BASED BATTERY CHARGING USING SOLAR
ENERGY
Submitted in partial fulfillment of the requirement for the Degree of
BACHELOR OF TECHNOLOGY
In ELECTRICAL ENGINEERING
By
ARPIT KUMAR JAIN (121113058)
NIDHISH BARVE (121113063)
NITIN UIKEY (121113057)
VIJAY CHOUDHARY (121113013)
SUYAGYA JAISWAL (121113059)
Under the guidance of Prof . SURESH KUMAR GAWRE
April 2016
DEPARTMENT OF ELECTRICAL ENGINEERING MAULANA AZAD NATIONAL INSTITUTE OF TECHNOLOGY
BHOPAL (M. P.), INDIA– 462003
STUDENT’S DECLARATION
We hereby declare that the work presented in the dissertation entitled “MPPT
Based Battery Charging Using Solar Energy ” in fulfillment of the requirement for
the award of the degree of Bachelor of Technology in Electrical Engineering
submitted in the Department of Electrical Engineering, MANIT, Bhopal is an
authentic record of our own work under the guidance of Prof Suresh Kumar
Gawre.
We have submitted the matter embodied in this dissertation for the award of any other degree.
Name Scholar No. Sign of students
ARPIT KUMAR JAIN (121113058)
NIDHISH BARVE (121113063)
NITIN UIKEY (121113057)
VIJAY CHOUDHARY (121113013)
SUYAGYA JAISWAL (121113059)
CERTIFICATE
This is to certify that the above statements made by us are correct to the best of our knowledge.
Supervisor Prof. Suresh Kumar Gawre
Department of Electrical Engineering ii
Table of Contents STUDENT DECLARATION ........................................................................................................ii CERTIFICATE ...............................................................................................................................ii TABLE OF CONTENT ................................................................................................................ iii LIST OF FIGURES .......................................................................................................................v ABSTRACT...................................................................................................................................vi CHAPTER 1 INTRODUCTION ................................................................................................. 1
1.1 NEED OF RENEWABLE ENERGY .................................................................................. 2 1.2 DIFFERENT SOURCES OF RENEWABLE ENERGY ................................................... 2
1.2.1 WIND ENERGY ....................................................................................................... 2 1.2.2 SOLAR ENERGY .................................................................................................... 2 1.2.3 SMALL HYDRO POWER ........................................................................................ 3 1.2.4 GEOTHERMAL ........................................................................................................ 3
1.3 LITERATURE REVIEW .................................................................................................... 3 1.4 MOTIVATION .................................................................................................................... 4 1.5 OBJECTIVE ...................................................................................................................... 4
CHAPTER 2 MODELLING AND SIMULATION ................................................................... 5
2.1 PV CELL ............................................................................................................................ 6
2.2 PV MODULE ..................................................................................................................... 6
2.3 PV ARRAY......................................................................................................................... 6
2.4 MATLAB SIMULINK MODEL ............................................................................................ 6
2.4.1 MODEL OF PV CELL .............................................................................................. 7 2.4.2 MODEL OF MPPT CONTROL ................................................................................ 8 2.4.3 MODEL OF CONVERTER ...................................................................................... 8 2.4.4 COMPLETE MODEL ............................................................................................... 9
CHAPTER 3 MAXIMUM POWER POINT TRACKING ..................................................... 12
3.1 OVERVIEW OF MPPT ................................................................................................... 13
3.2 CLASSIFICATION OF MPPT TECHNIQUE .................................................................. 13
3.3 DIFFERENT MPPT TECHNIQUE .................................................................................. 15
3.3.1 PERTURBB AND OBSERVE .............................................................................. 15 3.3.2 INCREMENTAL CONDUCTANCE ..................................................................... 16 3.3.3 S C CURRENT .................................................................................................... 18 3.3.4 O C VOLTAGE .................................................................................................... 18 3.3.3 FUZZY LOGIC CONTROL .................................................................................. 19 3.3.3 NUERAL NETWORK .......................................................................................... 19
3.4 DETAILS OF P AND O TECHNIQUE ............................................................................ 20
iii
CHAPTER 4 BUCK CONVERTER DESIGN ...................................................................... 21
4.1 BASICS OF CONVERTER ............................................................................................. 22
4.1.1 INTRODUCTION .................................................................................................. 22
4.1.2 BASIC CONFIGURATION OF BUCK CONVERTER.......................................... 22
4.1.3 NECESSARY PARAMETER OF THE POWER STAGES .................................. 24
4.2 SELECTION OF INDUCTOR AND CAPACITOR ........................................................... 24
4.2.1 INDUCTOR CALCULATION ....................................................................................... 25
4.2.2 CAPACITOR CALCULATION .............................................................................. 26 CHAPTER 5 HARDWARE IMPLEMENTATION OF THE PROJECT ............................. 27
5.1 COMPONENTS USED IN PROJECT ............................................................................. 28
5.1.1 ARDUINO UNO .................................................................................................... 28
5.1.2 CURRENT SENSOR ........................................................................................... 30
5.1.3 VOLTAGE SENSOR ............................................................................................ 31
5.1.4 MOSFET .............................................................................................................. 31
5.1.5 BATTERY ............................................................................................................. 32
5.1.6 OTHER USEFUL COMPONENTS ...................................................................... 32
5.2 TOOLS REQUIRED ........................................................................................................ 33 CHAPTER 6 PROGRAMMING .............................................................................................. 34
6.1 MATLAB COMMAND FOR MPPT CONTROL SIMULATION ........................................ 35
6.2 BUCK CONVERTER TEST CODE ................................................................................. 36
6.3ARDUINO UNO PROGRAMMING.................................................................................... 37 CHAPTER 7 CONCLUSION AND FUTURE SCOPE......................................................... 51
7.1 CONCLUSION .................................................................................................................. 52
7.2 FUTURE SCOPE ............................................................................................................. 52 REFERENCES ........................................................................................................................... 53 APPENDIX .................................................................................................................................. 54
iv
LIST OF FIGURES Figure 2.1 Different solar module…………………………………………………………………………..6 Figure 2.2 MATLAB simulink model of PV cell…………………………………………………………...7
Figure 2.3 MATLAB Simulink model of MPPT control …………………………………………………..8
Figure 2.4 Model of buck converter………………………………………………………………………..8
Figure 2.5 Complete Simulink model………………………………………………………………….…..9
Figure 2.6 I-PV curve…………………………………………………………………………………….....9
Figure 2.7 V-PV curve ……………………………………………………………………………………..10
Figure 2.8(a) Voltage – Current curve .…………………………………………………………………..11
Figure 2.8(b) Power – Voltage curve ...……………………………………………………………….....11
Figure 3.1 Different MPPT technique………………………………………………………………….... 14
Figure 3.2 Flow chart of P & O algorithm………………………………………………………………...16
Figure 3.3 Flow chart of INC algorithm…………………………………………………………………...17
Figure 3.4 P V curve………………………………………………………………………………………..20
Figure 4.1 Buck converter power stages…………………………………………………………………23
Figure 4.2 Wave form of source current………………………………………………………………….24
Figure 5.1 Arduino Uno board……………………………………………………………………………..28
Figure 5.2 Current sensor ACS 712………………………………………………………………………30
Figure 5.3 Voltage divider circuit………………………………………………………………………….31
Figure 5.4 MPPT based solar charge controller…………………………………………………………31
Figure. 8.1 prototype of hardware implementation……………………………………………………………54
v
ABSTRACT
The solar energy is converted to electrical energy by photo-voltaic cells. This energy is
stored in batteries during day time for utilizing the same during night time. Our aim is to obtain
maximum power at the load side from the solar panel. So basic network theorem is applied
called maximum power point theorem. Solar energy obtained is in dc form and dc to dc
converters are used to use the output of solar voltage to load, it can be either stepped up or
stepped down according to requirement. We have used Arduino control board for the duty cycle
control of the converter so that required load voltage can be obtained. For this signal from load
side is given to the Arduino and Maximum Power Point is obtained using P&O technique. At this
MPP, Battery as a load is charged and solar energy is stored in the battery. This stored energy
can be used either directly in the dc form or converted to ac with the help of inverter. Various
MPPT techniques are utilized for the tracking of MPPT but here we have we have P&O
technique.
MPPT algorithm is an important process to ensure the best utilization of the PV panels.
Maximum power point tracking of solar module aiming to improve conversion efficiency of solar
module. Various tracking algorithms are available for this purpose. To implement these
techniques required sensing of the panel voltage, panel current, battery voltage, battery current.
Sensing the voltage is easy and can be made with very less cost. For current sensing standard
Hall-Effect current sensor generally used in the MPPT algorithm.
vi
1
CHAPTER 1
INTRODUCTION
2
1.1 NEED OF RENEWABLE ENERGY
A developing country requires more energy. Nowadays, most of the energy supplied by
fossil fuels such as diesel, coal, petrol, and gas is 80% of our current energy. On top of this
energy demand is expected to grow by almost half over the next two decades. Plausibly this is
causing some fear that our energy resources are starting to run out, with disturbing
consequences for the global economy and global quality of life. Increasing demand of energy
results in two main problem climate change and energy crisis. The global energy demand
increases, the energy related greenhouse gas production increases. It is a global challenge to
reduce the CO2 emission and offer clean, sustainable and affordable energy.
The worldwide increasing energy demand Energy saving is one cost effective solution,
but does not tackle. Renewable energy is a good option because it gives a clean and green
energy, with no CO2 emission. Renewable energy is defined as energy that comes from
resources which are naturally refilled on a human timescale such as sunlight, wind, rain,
tides, waves and geothermal heat.[10]
1.2 DIFFERENT SOURCES OF RENEWABLE ENERGY
1.2.1 Wind Energy
The wind turbine can be used to harness the energy from the airflow. Now a day’s wind
energy can be used from 800 kW to 6 MW of rated power. Science power output is the function
of the wind speed; it rapidly increases with increase in wind speed. In recent time have led to
airfoil wind turbines, which is more efficient due to better aerodynamic structure.
1.2.2 Solar Energy
Solar energy is profusely available that has made it possible to harvest it and utilize it
properly. Solar energy can be a standalone producing system or can be a grid connected
generating unit depending on the availability of a grid nearby. Thus it can be used to produce
power in rural areas where the availability of grids is very low. Solar energy is form of energy
that directly available from sun and convert in to electrical energy, which is best form of energy
without any climatic change and energy crisis. This conversion can be achieved with the help of
PV cell or with solar power plants.[1]
3
1.2.3 Small Hydro Power
Hydropower energy generates power by using a dam or diversion structure to alter the
natural flow of a river or other body of water. This energy can be used by conversion the water
stored in dam into electrical energy using water turbines. Hydropower, as an energy supply,
also provides unique benefits to an electrical system. First, when stored in large quantities in
the reservoir behind a dam, it is immediately available for use when required. Second, the
energy source can be rapidly adjusted to meet demand instantaneously.
1.2.4 Geothermal
Geothermal energy is available in form of thermal energy from heat stored inside the
earth. In this steam produced from reservoirs of hot water found a couple of miles or more
below the Earth's surface. This energy comes from the decay of radioactive nuclei with long
half-lives that are embedded within the Earth, some energy is from residual heat left over from
Earths formation and rest of the energy comes from meteorite impacts.
1.3 LITERATURE REVIEW
Solar power is one of the renewable energy resource that will hopefully lead us away
from coal dependent and petroleum dependent energy resource. The major problem with
photovoltaic charging system is that the energy conversion efficiency of solar panel is poor and
high cost. Solar panels themselves are quite not efficient in their ability to convert sunlight to
energy. The study shows that solar panel convert 35-45% of energy incident on into electrical
energy. So our aim is how to decrease the overall cost and energy conversion efficiency of solar
panel. To store solar energy charging system is also required to efficiently charge battery with
lesser charging time. A Maximum Power Point Tracking algorithm is required to increase the
efficiency of the solar panel.
The most commonly known are [1] hill-climbing, [2] fractional open circuit voltage control,
[3] perturb and observe(P&O), [4] incremental conductance(INC), [5] Neural network control, [6]
fuzzy control based etc. These algorithms are varying due to simplicity, effectiveness, merging
speed, sensor required and cost. The most commonly algorithm based on current and voltage
sensing incremental conductance (INC) and perturb and observe (P&O) is used to track
maximum power point (MPP) due to its simplicity, effectiveness & merging speed.
Under abruptly change in irradiation level as MPP, changes continuously, P & O receipts
4
it as a change in MPP due to perturbation rather than that of irradiation and sometimes ends up
in calculating incorrect MPP. However, this problem gets avoided by an incremental
conductance method in case of the incremental conductance method algorithm takes two
sample of voltage and current to calculate MPP. However, due to higher efficiency, complexity
of incremental conductance algorithm. This MPPT algorithm combines with battery charging
loop to charge lead acid battery with different charging stage like constant current, constant
voltage, float charge. So optimal is charging pattern design to charge Lead acid battery with
three different charging stages that are constant current, constant voltage and float charging.
This charging pattern of battery efficiently charge battery with lesser charging time.[10]
Implementation cost of this pattern very high because both are used voltage and current
sensing device. Voltage sensing directly obtain by connecting voltage divider circuit across the
panel and directly apply to the microcontroller, but current sensing require current sensor
connected between panel and DC-DC converter. Generally, current sensor used for MPP high
efficient LEM current sensor. Due to high cost current sensor and other device make up so PV
charging system cost effective. Our aim is to design charging pattern so that abstract maximum
power from solar module and efficiently charge battery with lesser charging time with low
implementation cost.[2]
1.4 MOTIVATION
Solar energy is one source of power generation that independent away from petroleum
and coal dependent energy resource. The major problem with solar energy is conversion
efficiency poorer and high installation cost. Research going into this area to develop the efficient
control mechanism and provide better control. So the overall installation cost of photovoltaic
charging system reduces. The challenging research work going on in this area is the motivation
behind the project.
1.5 OBJECTIVE
Our objective is to hardware implement the MPPT technique to obtain maximum output
power from solar module. Also to first simulate the same in MATLAB and obtain the desired
results.
5
CHAPTER 2
MODELLING
AND SIMULATION
6
2.1 PHOTOVOLTAIC CELL
A photovoltaic cell or photoelectric cell is a semiconductor device that converts light to
electrical energy by photovoltaic effect. If the energy of photon of light is greater than the band
gap then the electron is emitted and the flow of electrons creates current.
However a photovoltaic cell is different from a photodiode. In a photodiode light falls on
n-channel of the semiconductor junction and gets converted into current or voltage signal but a
photovoltaic cell is always forward biased.
2.2 PV MODULE
Usually a number of PV modules are arranged in series and parallel to meet the energy
requirements. PV modules of different sizes are commercially available. For example, a typical
small scale desalination plant requires a few thousand watts of power.
2.3 PV ARRAY
A PV array consists of several photovoltaic cells in series and parallel connections.
Series connections are responsible for increasing the voltage of the module whereas the
parallel connection is responsible for increasing the current in the array.
Solar Cells Solar Panel Solar Panel
(4 cells ) (Module) (Multiple Module)
Figure 2.1 Different solar modules
Here in these project Monocrystalline PV Module is used and its electrical specification
and characteristic table is as shown below
7
Table 2.1 Electrical Characteristic of PV Module
Mono crystalline cell:
Advantages-
1. It has highest efficiency (15%-20%)
2. Space efficient
3. Its life is long
4. perform better than poly crystalline cell at low light condition.[4]
Disadvantages-
1. These cells are expensive
2. If it is partially covered with shade, snow & dirt, the entire circuit may break down.
2.4 MATLAB SIMULINK MODEL
2.4.1 MATLAB Simulink Model of Photovoltaic Cell
Figure 2.2 Matlab Simulink Model of Photovoltaic Cell
Maximum Power – Pmax 40 W
Voltage at Pmax – Vmax 16.4 V
Current at Pmax – Imax 0.61 A
Short - circuit current – Isc 0.71 A
Open – voltage circuit – voc 17.2 V
Total number of cells in series (Ns) 36
Total number of array in parallel (Np) 4
8
2.4.2 MATLAB Simulink Model of MPPT Control of PWM Generation
Figure 2.3 Matlab Simulink Model of MPPT control and PWM generation
2.4.3 MATLAB Simulink Model of Buck Converter and PWM Pulse
Figure 2.4 Matlab Simulink Model of Buck converter and PWM pulse.
9
2.4.4 Complete MATLAB Simulink Model
Figure. 2.5 Complete Matlab Simulink Model
2.5 MATLAB Simulink Result
Figure 2.6 I_PV CURVE
10
Figure 2.7 V_PV AND OUTPUT VOLTAGE CURVE
11
Figure 2.8(a) VOLTAGE – CURRENT CURVE
Figure 2.8(b) POWER – VOLTAGE CURVE
12
CHAPTER 3
MAXIMUM POWER POINT
TRACKING
13
3.1 AN OVERVIEW OF MAXIMUM POWER POINT TRACKING
A typical solar panel converts only 30 to 40 percent of the incident solar irradiation into
electrical energy. Maximum power point tracking technique is used to improve the efficiency of
the solar panel. According to Maximum Power Transfer theorem, the power output of a circuit is
maximum when the Thevenin impedance of the circuit (source impedance) matches with the
load impedance. Hence our problem of tracking the maximum power point reduces to an
impedance matching problem. In the source side we are using a buck convertor connected to a
solar panel in order to enhance the output voltage so that it can be used for different
applications like motor load. By changing the duty cycle of the buck converter appropriately we
can match the source impedance with that of the load impedance.[5]
3.2 CLASSIFICATION OF MPPT TECHNIQUE
There are different ways of classifying MPPT techniques, some based on the number of
variables used to track MPP like one variable or two variable methods, and some based on the
type of techniques used to track MPP. The different MPPT control techniques are classified into
broadly three groups: Offline (indirect), Online (direct) and other techniques, mainly on the basis
of parameters required to track MPP. Offline control techniques usually use technical data of PV
panels to estimate the MPP. These data includes prior information like, I–V and P–V curves of
the panels for different climatic conditions, different mathematical models etc. of PV panels.
Online (direct) methods on the other hand use real time, PV voltages and/or current
measurements for tracking MPP. These methods do not require the measurement of
temperature and solar irradiance and also the PV array model. The offline methods are cost
effective but performance wise less effective than online and other methods. Other methods
include either modification or combination of these methods or methods based on indirect
calculations.[10]
14
Figure.3.1 Different types MPPT techniques.
15
3.3 DIFFERENT MPPT TECHNIQUE
There are different techniques used to track the maximum power point. Few of the most
popular techniques are:
1. Perturb and observe (hill climbing method)
2. Incremental Conductance method
3. Fractional short circuit current
4. Fractional open circuit voltage
5. Neural networks
6. Fuzzy logic
3.3.1 Perturb & Observe
Perturb & Observe (P&O) is the simplest method. In this we use only one sensor,
that is the voltage sensor, to sense the PV array voltage and so the cost of implementation is
less and hence easy to implement. The time complexity of this algorithm is very less but on
reaching very close to the MPP it doesn’t stop at the MPP and keeps on perturbing on both the
directions. When this happens the algorithm has reached very close to the MPP and we can set
an appropriate error limit or can use a wait function which ends up increasing the time
complexity of the algorithm. However the method does not take account of the rapid change of
irradiation level (due to which MPPT changes) and considers it as a change in MPP due to
perturbation and ends up calculating the wrong MPP. Perturb and observe (P&O) is one of the
famous algorithm due to its simplicity used for maximum power point tracking. This algorithm
based on voltage and current sensing based used to track MPP. In this controller require
calculation for power and voltage to track MPP. In this voltage is perturbed in one direction and
if power is continuous to increase then algorithm keep on perturb in same direction. If new
power is less than previous power then perturbed in opposite direction. When module power
reach at MPP there is oscillation around MPP point.[3]
16
Figure 3.2 Flow chart of Perturb and observe algorithm
3.3.2 Incremental Conductance
Incremental conductance method uses two voltage and current sensors to sense the
output voltage and current of the PV array. The left hand side is the instantaneous conductance
of the solar panel. When this instantaneous conductance equals the conductance of the solar
then MPP is reached. Here we are sensing both the voltage and current simultaneously. Hence
the error due to change in irradiance is eliminated. However the complexity and the cost of
implementation increases. As we go down the list of algorithms the complexity and the cost of
implementation goes on increasing which may be suitable for a highly complicated system. This
is the reason that Perturb and Observe and Incremental Conductance method are the most
widely used algorithms.[3]
17
In this technique, the controller measures incremental change in module voltage and
current to observe the effect of a power change [1] . This method requires more calculation
but can track fast than perturb and observe algorithm (P&O). Under abruptly change in
irradiation level as maximum power point changes continuously, P&O receipts it as a change
in MPP due to perturb rather than that of isolation and sometimes ends up in calculating
incorrect MPP. However this problem get avoided by incremental conductance (INC).In this
method algorithm takes two sample of voltage and current to maximize power from solar
module. However due to effectiveness and complexity of incremental conductance algorithm
very high compare to perturb and observe. Like the P&O algorithm, it can produce
oscillations in power output. This study on realizing MPPT by improved incremental
conductance method with variable step-size [6]. So these are two advantage of incremental
conductance method. So in our implementation to achieve high efficiency this method utilize
incremental conductance (dI/dV) of the photovoltaic array to calculate the sign of the change
in power with respect to voltage (dP/dV). The controller maintains this voltage till the isolation
changes and the process is repeated.
Figure 3.3 Flow chart of incremental conductance algorithm
18
3.3.3 Fractional short circuit current MPPT
Fractional ISC results from the fact that, under varying atmospheric conditions, IMPP is
approximately linearly related to the ISC of the PV array.
IMPP =k2 Isc Where k2 is a proportionality constant.
Just like in the fractional VOC technique, k2 has to be determined according to the PV
array in use. The constant K2 is generally found to be between 0.78 and 0.92. Measuring ISC
during operation is problematic. An additional switch usually has to be added to the power
converter to periodically short the PV array so that ISC can be measured using a current sensor.
3.3.4 Fractional open circuit voltage MPPT
The near linear relationship between VMPP and VOC of the PV array, under varying
irradiance and temperature levels, has given rise to the fractional VOC method.
VMPP = k1 Voc where k1 is a constant of proportionality. Since k1 is dependent on the
characteristics of the PV array being used, it usually has to be computed beforehand by
empirically determining VMPP and VOC for the specific PV array at different irradiance and
temperature levels. The factor k1 has been reported to be between 0.71 and 0.78. Once k1 is
known, VMPP can be computed with VOC measured periodically by momentarily shutting down
the power converter.However; this incurs some disadvantages, including temporary loss of
power.Fractional open circuit (FOCV) fast and simple way of MPPT tracking. This algorithm not
able to track exact maximum power point. Reason is that when irradiation level and temperature
of module changes correspondingly MPP point change but this algorithm work on fixed value of
voltage at MPP. This algorithm work on principle that voltage at MPP is nearly equal to open
circuit voltage of module by factor N. Value of N basically braying from .68 to .80 that depend on
type of module used.[4]
19
3.3.5 Fuzzy Logic Control
Microcontrollers have made using fuzzy logic control popular for MPPT over last
decade. Fuzzy logic controllers have the advantages of working with imprecise inputs, not
needing an accurate mathematical model, and handling nonlinearity.
3.3.6 Neural Network
Another technique of implementing MPPT which are also well adapted for
microcontrollers is neural networks. Neural networks commonly have three layers: input, hidden,
and output layers. The number nodes in each layer vary and are user dependent. The input
variables can be PV array parameters like VOC and ISC, atmospheric data like irradiance and
temperature, or any combination of these. The output is usually one or several reference signals
like a duty cycle signal used to drive the power converter to operate at or close to the MPPT [4].
TABLE 3.1 COMPARISONS OF DIFFERENT MPPT TECHNIQUES
20
3.4 DETAIL OF P &O TECNIQUE
The Perturb & Observe algorithm states that when the operating voltage of the PV panel is
perturbed by a small increment, if the resulting change in power P is positive, then we are going
in the direction of MPP and we keep on perturbing in the same direction. If P is negative, we are
going away from the direction of MPP and the sign of perturbation supplied has to be changed
[5].
Figure 3.4 Solar panel Characteristic showing MPP and Operating point A & B
21
CHAPTER 4
BUCK CONVERTER DESIGN
22
4.1 BASICS OF CONVERTER
4.1.1 Introduction
There are three basic types of dc-dc converter circuits, termed as buck, boost and buck-boost.
In all of these circuits, a power device is used as a switch. This device earlier used was a
thyristor, which is turned on by a pulse fed at its gate. In all these circuits, the thyristor is
connected in series with load to a dc supply, or a positive (forward) voltage is applied between
anode and cathode terminals. The thyristor turns off, when the current decreases below the
holding current, or a reverse (negative) voltage is applied between anode and cathode
terminals. So, a thyristor is to be force-commutated, for which additional circuit is to be used,
where another thyristor is often used. Later, GTO’s came into the market, which can also be
turned off by a negative current fed at its gate, unlike thyristors, requiring proper control circuit.
The turn-on and turn-off times of GTOs are lower than those of thyristors. So, the frequency
used in GTO-based choppers can be increased, thus reducing the size of filters. Earlier, dc-dc
converters were called ‘choppers’, where thyristors or GTOs are used. It may be noted here that
buck converter (dc-dc) is called as ‘step-down chopper’, whereas boost converter (dc-dc) is a
‘step-up chopper’. In the case of chopper, no buck-boost type was used.
These converters are now being used for applications, one of the most important being
Switched Mode Power Supply (SMPS). Similarly, when application requires high voltage,
Insulated Gate Bi-polar Transistors (IGBT) are preferred over BJTs, as the turn-on and turn-off
times of IGBTs are lower than those of power transistors (BJT), thus the frequency can be
increased in the converters using them. So, mostly self-commutated devices of transistor family
as described are being increasingly used in dc-dc converter.[6]
4.1.2 Basic Configuration of Buck Converter
A buck converter (dc-dc) is shown in Fig.3.1. Only a switch is shown, for which a device as
described earlier belonging to transistor family is used. Also a diode (termed as freewheeling) is
used to allow the load current to flow through it, when the switch (i.e., a device) is turned off.
The load is inductive (R- L) one. In some cases, a battery (or back emf) is connected in series
with the load (inductive). Due to the load inductance, the load current must be allowed a path,
23
which is provided by the diode; otherwise, i.e., in the absence of the above diode, the high
induced emf of the inductance, as the load current tends to decrease, may cause damage to the
switching device. If the switching device used is a thyristor, this circuit is called as a step-down
chopper, as the output voltage is normally lower than the input voltage. Similarly, this dc-dc
converter is termed as buck one, due to reason given later.is provided by the diode; otherwise,
i.e., in the absence of the above diode, the high induced emf of the inductance, as the load
current tends to decrease, may cause damage to the switching device. If the switching device
used is a thyristor, this circuit is called as a step-down chopper, as the output voltage is
normally lower than the input voltage. Similarly, this dc-dc converter is termed as buck one, due
to reason given later.
The basic operation of the buck converter has the current in an inductor controlled by two
switches (usually a transistor and a diode). In the idealized 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 as being infinite).[4]
Fig. 4.1 Buck Converter (dc-dc) Power Stage
24
Fig.4.2 Waveforms of source current
4.1.3 Necessary Parameters of the Power Stage
The following four parameters are needed to calculate the power stage:
1. Input voltage range: VIN(min) and VIN(max)
2. Nominal output voltage: VOUT
3. Maximum output current: IOUT(max)
4. Integrated circuit used to build the buck converter. This is necessary because some
parameters for the calculations must be derived from the data sheet.
If these parameters are known, the power stage can be calculated.
4.2 Selection of Inductor and Capacitor
First calculate Maximum duty cycle
………………… (1)
Where,
VIN(max) = maximum input voltage
VOUT = output voltage
η = efficiency of the converter, e.g., estimated 90%
25
4.2.1 Inductor calculation
Data sheets often give a range of recommended inductor values. If this is the case, choose an
inductor from this range. The higher the inductor value, the higher is the maximum output
current because of the reduced ripple current.
In general, the lower the inductor value, the smaller is the solution size. Note that the
inductor must always have a higher current rating than the maximum current, this is because
the current increases with decreasing inductance. [7]
For parts where no inductor range is given, the following equation is a good estimation for the
right inductor:
……………………….(2)
Assume:
We are designing for a 40 W solar panel and 12 V battery
Input voltage (Vin) =16.4 V
Output Voltage (Vout)=12 V
Output current (Iout) =40W/12V =3.33 A (approx)
Switching Frequency (Fsw)=50 KHz
Duty Cycle (D) =Vout/Vin= 12/16.4 =0.71 or 71%
Calculation
L= ( Vin-Vout ) x D x 1/Fsw x 1/ dI ……………………………….(3)
Where dI is Ripple current
For a good design typical value of ripple current is in between 30 to 40 % of load current.
Let dI =35% of rated current
dI=35% of 3.33=0.35 x 3.33 =1.17A
So L= (16.4.0-12.0) x 0.71 x (1/50k) x (1/1.17) = 57.65uH =58uH (approx)
26
Inductor peak current =Iout+dI/2 = 2.4+(1.17/2) = 3A
4.2.2 Output Capacitor Calculation
...………………………... (4)
The out put capacitor ( Cout)= dI / (8 x fs x dV) ……………………………(5)
Where
dV is ripple voltage
Let voltage ripple( dV ) = 20mV
Cout= 1.17/ (8 x 50000 x 0.02 ) = 183.75 uF
By taking some margin, select 220uF electrolytic capacitor.
27
CHAPTER 5
HARDWARE
IMPLEMENTATION OF
PROJECT
28
5.1 COMPONENTS USED IN PROJECT
5.1.1 ARDUINO UNO
Arduino Uno is a microcontroller board based on the ATmega328P. It has 14 digital input/output
pins (of which 6 can be used as PWM outputs), 6 analog inputs, a 16 MHz quartz crystal, a USB
connection, a power jack, an ICSP header and a reset button. It contains everything needed to
support the microcontroller; simply connect it to a computer with a USB cable or power it with a
AC -to-DC adapter or battery to get started. You can tinker with your UNO without worrying too
much about doing something wrong, worst case scenario you can replace the chip for a few
Rupees and start over again [8].
Figure 5.1 Arduino Uno board
29
Table 5.1 Technical specification of Arduino Uno board
Microcontroller ATmega328P
Operating Voltage 5 V
Input Voltage (recommended) 7-12 V
Input Voltage (limit) 6-20 V
Digital I/O Pins 14 (of which 6 provide PWM output)
PWM Digital I/O Pins 6
Analog Input Pins 6
DC Current per I/O Pin 20 Ma
DC Current for 3.3V Pin 50 Ma
Flash Memory 32KB(ATmega328P)
of which 0.5 KB used by bootloader
SRAM 2 KB (ATmega328P)
EEPROM 1 KB (ATmega328P)
Clock Speed 16 MHz
Length 68.6 mm
30
5.1.2 Current Sensor
For current measurement we have used a Hall Effect current sensor ACS 712(5A).
The ACS712 (5A) sensor read the current value and converts it into a relevant voltage value;
the value that links the two measurements is sensitivity [9]. As per data sheet for ACS 712 (5A)
models:
1. Sensitivity is 185mV/A.
2. The sensor can measure positive and negative currents (range -5A…5A),
3. Power supply is 5V
4. Middle sensing voltage is 2.5V when no current
Figure 5.2 Current Sensor ACS 712
Table 5.2 Rating of Current Sensor ACS 712
31
5.1.3 Voltage Sensor
Arduino’s analog inputs can be used to measure DC voltage between 0 and 5V (when using the
standard 5V analog reference voltage) and this range can be increased by using two resistors to
create a voltage divider. The voltage divider decreases the voltage being measured to within the
range of the Arduino analog inputs. We can use this to measure the solar panel and battery
voltages.[6]
Figure 5.3 Voltage Divider Circuit
5.1.4 MOSFET
The vital component of a buck converter is MOSFET.Choosing a right MOSFET from the variety
of it available in the market is quite challenging task.
These are few basic parameters for selecting right MOSFET.
1. Voltage Rating: Vds of MOSFET should be greater than 20% or more than the rated voltage.
2. Current Rating: Ids of MOSFET should be greater than 20% or more than the rated current.
3. ON Resistance (Rds on) : Select a MOSFET with low ON Resistance (Ron)
4. Conduction Loss: It depends on Rds(ON) and duty cycle. Keep the conduction loss minimum.
5. Switching Loss: Switching loss occurs during the transition phase. It depends on switching
frequency, voltage, current etc. Try to keep it minimum.[2]
32
Table 5.3 Rating of Mosfet IRFZ44N
Also we have provided mosfet heat sink
5.1.5 Battery
-lead acid battery
-nominal voltage :12 V
-capacity : 1.3 Ah
5.1.6 Other useful components
1. Capacitor
2. Inductor
3. Diodes
4. Resistor
5. Wires and Jump wires
6. Fuses
7. Heat sink
8. LCD display
9. LED
10. Screw terminals
33
5.2 TOOLS REQUIRED :
1. Soldering Iron
2. Glue Gum
3. Cordless Drill
4. Knife
5. Wire Cutter
6. Wire Stripper
7. Screw Driver
8. Ruler and pencil
5.3 SCHEMATIC DIAGRAM OF MPPT BASED SOLAR CHARGE CONTROLLER
Figure 5.4 MPPT based solar charge controller
34
CHAPTER 6
PROGRAMMING
35
6.1 MATLAB COMMAND FOR MPPT CONTROL SIMULATION:
function D = PandO(Param, Enabled, V, I)
% MPPT controller based on the Perturb & Observe algorithm.
% D output = Duty cycle of the boost converter (value between 0 and 1)
% Enabled input = 1 to enable the MPPT controller
% V input = PV array terminal voltage (V)
% I input = PV array current (A)
%
% Param input:
Dinit = Param(1); %Initial value for D output
Dmax = Param(2); %Maximum value for D
Dmin = Param(3); %Minimum value for D
deltaD = Param(4);%Increment value used to increase/decrease the duty
cycle D
% ( increasing D = decreasing Vref )
%
persistent Vold Pold Dold;
dataType = 'double';
if isempty(Vold)
Vold=0;
Pold=0;
Dold=Dinit;
end
P= V*I;
dV= V - Vold;
dP= P - Pold;
if dP ~= 0 & Enabled ~=0
if dP < 0
if dV < 0
D = Dold + deltaD;
else
D = Dold - deltaD;
end
else
if dV < 0
D = Dold - deltaD;
else
D = Dold + deltaD;
end
end
else D=Dold;
end
if D >= Dmax | D<= Dmin
D=Dold;
36
end
Dold=D;
Vold=V;
Pold=P;
6.2 BUCK CONVERTER TEST CODE:
#include <TimerOne.h>
void setup()
{ // Initialize the digital pin as an output.
// Pin 13 has an LED connected on most Arduino boards
pinMode(13, OUTPUT);
pinMode(9, OUTPUT);
pinMode(8, OUTPUT);
digitalWrite(8, HIGH);
Timer1.initialize(20);
// set a timer of length 8uS
//Timer1.attachInterrupt( timerIsr );
// attach the service routine here
//Set duty cycle
// Timer1.pwm (9,256); // 25% duty cycle
// Timer1.pwm (9, 512); // 50% duty cycle
Timer1.pwm (9, 768); // 75% duty cycle
}
void loop()
{
// Main code loop
// TODO: Put your regular (non-ISR) logic here
}
// Custom ISR Timer Routine
void timerIsr()
{ // Toggle LED
//digitalWrite( 13, digitalRead( 13 ) ^ 1 );
}
37
6.3 ARDUINO MPPT SOLAR CHARGE CONTROLLER (ARDUINO UNO
PROGRAMMING):
// This code is for an arduino Uno based Solar MPPT charge controller.
// Specifications :
// 1.Solar panel power = 40W
// 2.Rated Battery Voltage= 12V ( lead acid type )
// 3.Maximum current = 5A
// 4.Maximum load current =10A
// 5. In put Voltage = Solar panel with Open circuit voltage from 16
to 20V
////////////////////////////////////////////////////////////////
#include "TimerOne.h" // using Timer1 library from
http://www.arduino.cc/playground/Code/Timer1
#include <LiquidCrystal_I2C.h> // using the LCD I2C Library from
https://bitbucket.org/fmalpartida/new-liquidcrystal/downloads
#include <Wire.h>
//--------------------------------------------------------------
//////// Arduino pins Connections////////
// A0 - Voltage divider (solar)
// A1 - ACS 712 Out
// A2 - Voltage divider (battery)
// A4 - LCD SDA
// A5 - LCD SCL
// D2 - ESP8266 Tx
// D3 - ESP8266 Rx through the voltage divider
// D5 - LCD back control button
// D6 - Load Control
// D8 - 2104 MOSFET driver SD
// D9 - 2104 MOSFET driver IN
// D11- Green LED
// D12- Yellow LED
// D13- Red LED
///////// Definitions /////////
#define SOL_VOLTS_CHAN 0 // defining the adc channel to
read solar volts
#define SOL_AMPS_CHAN 1 // Defining the adc channel to
read solar amps
#define BAT_VOLTS_CHAN 2 // defining the adc channel to
read battery volts
#define AVG_NUM 8 // number of iterations of the
adc routine to average the adc readings
// ACS 712 Current Sensor is used. Current Measured = (5/(1024
*0.185))*ADC - (2.5/0.185)
#define SOL_AMPS_SCALE 0.026393581 // the scaling value for raw
adc reading to get solar amps // 5/(1024*0.185)
#define SOL_VOLTS_SCALE 0.029296875 // the scaling value for raw
adc reading to get solar volts // (5/1024) *(R1+R2)/R2 // R1=100k and
38
R2=20k
#define BAT_VOLTS_SCALE 0.029296875 // the scaling value for raw
adc reading to get battery volts
#define PWM_PIN 9 // the output pin for the pwm
(only pin 9 avaliable for timer 1 at 50kHz)
#define PWM_ENABLE_PIN 8 // pin used to control shutoff
function of the IR2104 MOSFET driver (When high, the mosfet driver is
on)
#define PWM_FULL 1023 // the actual value used by the
Timer1 routines for 100% pwm duty cycle
#define PWM_MAX 100 // the value for pwm duty cyle 0-
100%
#define PWM_MIN 60 // the value for pwm duty cyle 0-
100% (below this value the current running in the system is = 0)
#define PWM_START 90 // the value for pwm duty cyle 0-
100%
#define PWM_INC 1 //the value the increment to the
pwm value for the ppt algorithm
#define FALSE 0
#define ON TRUE
#define OFF FALSE
#define TURN_ON_MOSFETS digitalWrite(PWM_ENABLE_PIN, HIGH) //
enable MOSFET driver
#define TURN_OFF_MOSFETS digitalWrite(PWM_ENABLE_PIN, LOW) //
disable MOSFET driver
#define ONE_SECOND 50000 //count for number of interrupt in
1 second on interrupt period of 20us
#define LOW_SOL_WATTS 5.00 //value of solar watts // this is
5.00 watts
#define MIN_SOL_WATTS 1.00 //value of solar watts // this is
1.00 watts
#define MIN_BAT_VOLTS 11.00 //value of battery voltage // this
is 11.00 volts
#define MAX_BAT_VOLTS 14.10 //value of battery voltage// this
is 14.10 volts
#define BATT_FLOAT 13.60 // battery voltage we want to stop
charging at
#define HIGH_BAT_VOLTS 13.00 //value of battery voltage // this
is 13.00 volts
#define LVD 11.5 //Low voltage disconnect setting
for a 12V system
#define OFF_NUM 9 // number of iterations of off
charger state
//---------------------------------------------------------------------
//Defining led pins for indication
#define LED_RED 11
39
#define LED_GREEN 12
#define LED_YELLOW 13
//---------------------------------------------------------------------
// Defining load control pin
#define LOAD_PIN 6 // pin-6 is used to control the load
//---------------------------------------------------------------------
// Defining lcd back light pin
#define BACK_LIGHT_PIN 5 // pin-5 is used to control the lcd back
light
//---------------------------------------------------------------------
////////////////////////////BIT MAP ARRAY///////////////////////
//---------------------------------------------------------------------
byte solar[8] = //icon for solar panel
{
0b11111,
0b10101,
0b11111,
0b10101,
0b11111,
0b10101,
0b11111,
0b00000
};
byte battery[8]= // icon for battery
{
0b01110,
0b11011,
0b10001,
0b10001,
0b11111,
0b11111,
0b11111,
0b11111,
};
byte _PWM [8]= // icon for PWM
{
0b11101,
0b10101,
0b10101,
0b10101,
0b10101,
0b10101,
0b10101,
0b10111,
};
//--------------------------------------------------------------
40
// global variables
float sol_amps; // solar amps
float sol_volts; // solar volts
float bat_volts; // battery volts
float sol_watts; // solar watts
float old_sol_watts = 0; // solar watts from previous time
through ppt routine
unsigned int seconds = 0; // seconds from timer routine
unsigned int prev_seconds = 0; // seconds value from previous
pass
unsigned int interrupt_counter = 0; // counter for 20us interrrupt
unsigned long time = 0; // variable to store time the
back light control button was pressed in millis
int delta = PWM_INC; // variable used to modify pwm
duty cycle for the ppt algorithm
int pwm = 0; // pwm duty cycle 0-100%
int back_light_pin_State = 0; // variable for storing the state
of the backlight button
int load_status = 0; // variable for storing the load
output state (for writing to LCD)
enum charger_mode {off, on, bulk, bat_float} charger_state; //
enumerated variable that holds state for charger state machine
// set the LCD address to 0x27 for a 20 chars 4 line display
// Set the pins on the I2C chip used for LCD connections:
// addr, en,rw,rs,d4,d5,d6,d7,bl,blpol
LiquidCrystal_I2C lcd(0x27, 2, 1, 0, 4, 5, 6, 7, 3, POSITIVE); // Set
the LCD I2C address
//---------------------------------------------------------------------
// This routine is automatically called at powerup/reset
//---------------------------------------------------------------------
void setup() // run once, when the sketch starts
{
pinMode(LED_RED, OUTPUT); // sets the digital pin as output
pinMode(LED_GREEN, OUTPUT); // sets the digital pin as output
pinMode(LED_YELLOW, OUTPUT); // sets the digital pin as output
pinMode(PWM_ENABLE_PIN, OUTPUT); // sets the digital pin as output
Timer1.initialize(20); // initialize timer1, and set a 20uS period
Timer1.pwm(PWM_PIN, 0); // setup pwm on pin 9, 0% duty
cycle
TURN_ON_MOSFETS; // turn off MOSFET driver chip
Timer1.attachInterrupt(callback); // attaches callback() as a
timer overflow interrupt
Serial.begin(9600); // open the serial port at 9600
bps:
pwm = PWM_START; // starting value for pwm
charger_state = on; // start with charger state as
off
pinMode(BACK_LIGHT_PIN, INPUT); // backlight on button
41
pinMode(LOAD_PIN,OUTPUT); // output for the LOAD MOSFET
(LOW = on, HIGH = off)
digitalWrite(LOAD_PIN,HIGH); // default load state is OFF
lcd.begin(20,4); // initialize the lcd for 16
chars 2 lines, turn on backlight
lcd.noBacklight(); // turn off the backlight
lcd.createChar(1,solar); // turn the bitmap into a
character
lcd.createChar(2,battery); // turn the bitmap into a
character
lcd.createChar(3,_PWM); // turn the bitmap into a
character
}
//---------------------------------------------------------------------
// Main loop
//---------------------------------------------------------------------
void loop()
{
read_data(); // read data from inputs
run_charger(); // run the charger state machine
print_data(); // print data
load_control(); // control the connected load
led_output(); // led indication
lcd_display(); // lcd display
}
//---------------------------------------------------------------------
// This routine reads and averages the analog inputs for this system,
solar volts, solar amps and
// battery volts.
//---------------------------------------------------------------------
int read_adc(int channel)
{
int sum = 0;
int temp;
int i;
for (i=0; i<AVG_NUM; i++) { // loop through reading raw adc
values AVG_NUM number of times
temp = analogRead(channel); // read the input pin
sum += temp; // store sum for averaging
delayMicroseconds(50); // pauses for 50 microseconds
}
return(sum / AVG_NUM); // divide sum by AVG_NUM to get
average and return it
}
//---------------------------------------------------------------------
// This routine reads all the analog input values for the system. Then
it multiplies them by the scale
// factor to get actual value in volts or amps.
//---------------------------------------------------------------------
42
void read_data(void) {
sol_amps = (read_adc(SOL_AMPS_CHAN) * SOL_AMPS_SCALE -12.01);
//input of solar amps
sol_volts = read_adc(SOL_VOLTS_CHAN) * SOL_VOLTS_SCALE;
//input of solar volts
bat_volts = read_adc(BAT_VOLTS_CHAN) * BAT_VOLTS_SCALE;
//input of battery volts
sol_watts = sol_amps * sol_volts ;
//calculations of solar watts
}
//---------------------------------------------------------------------
// This is interrupt service routine for Timer1 that occurs every 20uS.
//---------------------------------------------------------------------
void callback()
{
if (interrupt_counter++ > ONE_SECOND) { // increment
interrupt_counter until one second has passed
interrupt_counter = 0; // reset the counter
seconds++; // then increment
seconds counter
}
}
//---------------------------------------------------------------------
// This routine uses the Timer1.pwm function to set the pwm duty cycle.
//---------------------------------------------------------------------
void set_pwm_duty
(void) {
if (pwm > PWM_MAX) { // check limits of
PWM duty cyle and set to PWM_MAX
pwm = PWM_MAX;
}
else if (pwm < PWM_MIN) { // if pwm is less than
PWM_MIN then set it to PWM_MIN
pwm = PWM_MIN;
}
if (pwm < PWM_MAX) {
Timer1.pwm(PWM_PIN,(PWM_FULL * (long)pwm / 100), 20); // use
Timer1 routine to set pwm duty cycle at 20uS period
//Timer1.pwm(PWM_PIN,(PWM_FULL * (long)pwm / 100));
}
else if (pwm == PWM_MAX) { // if pwm set to
100% it will be on full but we have
Timer1.pwm(PWM_PIN,(PWM_FULL - 1), 20); // keep
switching so set duty cycle at 99.9%
//Timer1.pwm(PWM_PIN,(PWM_FULL - 1));
}
}
//---------------------------------------------------------------------
// This routine is the charger state machine. It has four states on,
43
off, bulk and float.
// It's called once each time through the main loop to see what state
the charger should be in.
// The battery charger can be in one of the following four states:
// On State - this is charger state for MIN_SOL_WATTS < solar watts <
LOW_SOL_WATTS. In this state isthe solar
// watts input is too low for the bulk charging state but not low
enough to go into the off state.
// In this state we just set the pwm = 99.9% to get the most of
low amount of power available.
// Bulk State - this is charger state for solar watts > MIN_SOL_WATTS.
This is where we do the bulk of the battery
// charging and where we run the Peak Power Tracking alogorithm.
In this state we try and run the maximum amount
// of current that the solar panels are generating into the
battery.
// Float State - As the battery charges it's voltage rises. When it
gets to the MAX_BAT_VOLTS we are done with the
// bulk battery charging and enter the battery float state. In
this state we try and keep the battery voltage
// at MAX_BAT_VOLTS by adjusting the pwm value. If we get to pwm =
100% it means we can't keep the battery
// voltage at MAX_BAT_VOLTS which probably means the battery is
being drawn down by some load so we need to back
// into the bulk charging mode.
// Off State - This is state that the charger enters when solar watts
< MIN_SOL_WATTS. The charger goes into this
// state when there is no more power being generated by the solar
panels. The MOSFETs are turned
// off in this state so that power from the battery doesn't leak
back into the solar panel.
//---------------------------------------------------------------------
void run_charger(void) {
static int off_count = OFF_NUM;
switch (charger_state) {
case on:
if (sol_watts < MIN_SOL_WATTS) { // if watts
input from the solar panel is less than
charger_state = off; // the
minimum solar watts then
off_count = OFF_NUM; // go to
the charger off state
TURN_OFF_MOSFETS;
}
else if (bat_volts > (BATT_FLOAT - 0.1)) { // else if
the battery voltage has gotten above the float
charger_state = bat_float; // battery
float voltage go to the charger battery float state
}
else if (sol_watts < LOW_SOL_WATTS) { // else if
44
the solar input watts is less than low solar watts
pwm = PWM_MAX; // it means
there is not much power being generated by the solar panel
set_pwm_duty(); // so we just
set the pwm = 100% so we can get as much of this power as possible
} // and stay
in the charger on state
else {
pwm = ((bat_volts * 10) / (sol_volts / 10)) + 5; // else if
we are making more power than low solar watts figure out what the pwm
charger_state = bulk; // value
should be and change the charger to bulk state
}
break;
case bulk:
if (sol_watts < MIN_SOL_WATTS) { // if watts
input from the solar panel is less than
charger_state = off; // the
minimum solar watts then it is getting dark so
off_count = OFF_NUM; // go to
the charger off state
TURN_OFF_MOSFETS;
}
else if (bat_volts > BATT_FLOAT) { // else if the
battery voltage has gotten above the float
charger_state = bat_float; // battery
float voltage go to the charger battery float state
}
else if (sol_watts < LOW_SOL_WATTS) { // else if
the solar input watts is less than low solar watts
charger_state = on; // it means
there is not much power being generated by the solar panel
TURN_ON_MOSFETS; // so go to
charger on state
}
else { // this is
where we do the Peak Power Tracking ro Maximum Power Point algorithm
if (old_sol_watts >= sol_watts) { // if
previous watts are greater change the value of
delta = -delta; // delta to make pwm
increase or decrease to maximize watts
}
pwm += delta; // add
delta to change PWM duty cycle for PPT algorythm (compound addition)
old_sol_watts = sol_watts; // load
old_watts with current watts value for next time
set_pwm_duty(); // set pwm duty
cycle to pwm value
}
break;
case bat_float:
45
if (sol_watts < MIN_SOL_WATTS) { // if watts
input from the solar panel is less than
charger_state = off; // the
minimum solar watts then it is getting dark so
off_count = OFF_NUM; // go to
the charger off state
TURN_OFF_MOSFETS;
set_pwm_duty();
}
else if (bat_volts > BATT_FLOAT) { // If we've
charged the battery abovethe float voltage
TURN_OFF_MOSFETS; // turn off
MOSFETs instead of modiflying duty cycle
pwm = PWM_MAX; // the
charger is less efficient at 99% duty cycle
set_pwm_duty(); // write
the PWM
}
else if (bat_volts < BATT_FLOAT) { // else if
the battery voltage is less than the float voltage - 0.1
pwm = PWM_MAX;
set_pwm_duty(); // start
charging again
TURN_ON_MOSFETS;
if (bat_volts < (BATT_FLOAT - 0.1)) { // if the
voltage drops because of added load,
charger_state = bulk; // switch
back into bulk state to keep the voltage up
}
}
break;
case off: // when we
jump into the charger off state, off_count is set with OFF_NUM
TURN_OFF_MOSFETS;
if (off_count > 0) { // this
means that we run through the off state OFF_NUM of times with out doing
off_count--; //
anything, this is to allow the battery voltage to settle down to see if
the
} // battery
has been disconnected
else if ((bat_volts > BATT_FLOAT) && (sol_volts > bat_volts)) {
charger_state = bat_float; // if
battery voltage is still high and solar volts are high
}
else if ((bat_volts > MIN_BAT_VOLTS) && (bat_volts < BATT_FLOAT)
&& (sol_volts > bat_volts)) {
charger_state = bulk;
}
break;
default:
TURN_OFF_MOSFETS;
46
break;
}
}
//--------------------------------------------------------------
//////////////////////////LOAD CONTROL//////////////////////////
//--------------------------------------------------------------
void load_control(){
if ((sol_watts < MIN_SOL_WATTS) && (bat_volts > LVD)){ // If the
panel isn't producing, it's probably night
digitalWrite(LOAD_PIN, LOW); // turn the
load on
load_status = 1; // record
that the load is on
}
else{ // If the
panel is producing, it's day time
digitalWrite(LOAD_PIN, HIGH); // turn the
load off
load_status = 0; // record
that the load is off
}
}
//--------------------------------------------------------------
// This routine prints all the data out to the serial port.
//--------------------------------------------------------------
void print_data(void)
{
Serial.print(seconds,DEC);
Serial.print(" ");
Serial.print("Charging = ");
if (charger_state == on) Serial.print("on ");
else if (charger_state == off) Serial.print("off ");
else if (charger_state == bulk) Serial.print("bulk ");
else if (charger_state == bat_float) Serial.print("float");
Serial.print(" ");
Serial.print("pwm = ");
Serial.print(pwm,DEC);
Serial.print(" ");
Serial.print("Current (panel) = ");
Serial.print(sol_amps);
Serial.print(" ");
Serial.print("Voltage (panel) = ");
Serial.print(sol_volts);
Serial.print(" ");
47
Serial.print("Power (panel) = ");
Serial.print(sol_volts);
Serial.print(" ");
Serial.print("Battery Voltage = ");
Serial.print(bat_volts);
Serial.print(" ");
Serial.print("\n\r");
//delay(1000);
}
//--------------------------------------------------------------
//------------------------Led Indication------------------------
//--------------------------------------------------------------
void led_output(void)
{
if(bat_volts > 14.1 )
{
leds_off_all();
digitalWrite(LED_YELLOW, HIGH);
}
else if(bat_volts > 11.9 && bat_volts < 14.1)
{
leds_off_all();
digitalWrite(LED_GREEN, HIGH);
}
else if(bat_volts < 11.8)
{
leds_off_all;
digitalWrite(LED_RED, HIGH);
}
}
//--------------------------------------------------------------
// This function is used to turn all the leds off
//--------------------------------------------------------------
void leds_off_all(void)
{
digitalWrite(LED_GREEN, LOW);
digitalWrite(LED_RED, LOW);
digitalWrite(LED_YELLOW, LOW);
}
//--------------------------------------------------------------
//-------------------------- LCD DISPLAY -----------------------
//--------------------------------------------------------------
void lcd_display()
{
back_light_pin_State = digitalRead(BACK_LIGHT_PIN);
48
if (back_light_pin_State == HIGH)
{
time = millis(); // If any of the buttons
are pressed, save the time in millis to "time"
}
lcd.setCursor(0, 0);
lcd.print("SOL");
lcd.setCursor(4, 0);
lcd.write(1);
lcd.setCursor(0, 1);
lcd.print(sol_volts);
lcd.print("V");
lcd.setCursor(0, 2);
lcd.print(sol_amps);
lcd.print("A");
lcd.setCursor(0, 3);
lcd.print(sol_watts);
lcd.print("W ");
lcd.setCursor(8, 0);
lcd.print("BAT");
lcd.setCursor(12, 0);
lcd.write(2);
lcd.setCursor(8, 1);
lcd.print(bat_volts);
lcd.setCursor(8,2);
if (charger_state == on)
{
lcd.print(" ");
lcd.setCursor(8,2);
lcd.print("on");
}
else if (charger_state == off)
{
lcd.print(" ");
lcd.setCursor(8,2);
lcd.print("off");
}
else if (charger_state == bulk)
{
lcd.print(" ");
lcd.setCursor(8,2);
lcd.print("bulk");
}
else if (charger_state == bat_float)
{
lcd.print(" ");
lcd.setCursor(8,2);
lcd.print("float");
}
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//-----------------------------------------------------------
//--------------------Battery State Of Charge ---------------
//-----------------------------------------------------------
lcd.setCursor(8,3);
if ( bat_volts >= 12.7)
lcd.print( "100%");
else if (bat_volts >= 12.5 && bat_volts < 12.7)
lcd.print( "90%");
else if (bat_volts >= 12.42 && bat_volts < 12.5)
lcd.print( "80%");
else if (bat_volts >= 12.32 && bat_volts < 12.42)
lcd.print( "70%");
else if (bat_volts >= 12.2 && bat_volts < 12.32)
lcd.print( "60%");
else if (bat_volts >= 12.06 && bat_volts < 12.2)
lcd.print( "50%");
else if (bat_volts >= 11.90 && bat_volts < 12.06)
lcd.print( "40%");
else if (bat_volts >= 11.75 && bat_volts < 11.90)
lcd.print( "30%");
else if (bat_volts >= 11.58 && bat_volts < 11.75)
lcd.print( "20%");
else if (bat_volts >= 11.31 && bat_volts < 11.58)
lcd.print( "10%");
else if (bat_volts < 11.3)
lcd.print( "0%");
//--------------------------------------------------------------
//-------------------------Duty Cycle---------------------------
//--------------------------------------------------------------
lcd.setCursor(15,0);
lcd.print("PWM");
lcd.setCursor(19,0);
lcd.write(3);
lcd.setCursor(15,1);
lcd.print(" ");
lcd.setCursor(15,1);
lcd.print(pwm);
lcd.print("%");
//-------------------------------------------------------------
//------------------------Load Status--------------------------
//-------------------------------------------------------------
lcd.setCursor(15,2);
lcd.print("Load");
lcd.setCursor(15,3);
if (load_status == 1)
{
lcd.print(" ");
lcd.setCursor(15,3);
lcd.print("On");
}
else
50
{
lcd.print(" ");
lcd.setCursor(15,3);
lcd.print("Off");
}
backLight_timer(); // call the backlight timer function in every
loop
}
void backLight_timer(){
if((millis() - time) <= 15000) // if it's been less than the
15 secs, turn the backlight on
lcd.backlight(); // finish with backlight on
else
lcd.noBacklight(); // if it's been more than 15
secs, turn the backlight off
}
51
CHAPTER 7
CONCLUSIONS AND
FUTURE SCOPE
52
CONCLUSIONS:
This method presented here control lead acid battery charging faster and efficiently.
The control algorithm execute P&O method allow module to operate at maximum power point
according to solar irradiation, and match load with the source impedance to provide
maximum power. This MPPT model is more suitable because of less cost, easier circuit
design. And efficiency of the circuit is increased by 20-25% in case of MPPT solar charge
controller compare to a circuit without MPPT. And also saved the extra energy required in
mechanical tracking. As Arduino based controlling is used, it maintained constant 12V at the
output terminal i.e. at the battery terminal.
FUTURE SCOPE:
1) Hybrid of MPPT with mechanical tracking will give more efficiency, project can be
extended in this direction.
2) Battery output is directly utilized to feed power in the dc grid which can be used for
charging electronic devices like laptop, mobile directly.
3) By adding wifi module we can record our data in the system and optimize the data
for better use.
4) Solar panel installed on urban and sub-urban areas with modified technology will
lead in saving of our bill.
53
REFERENCES:
[1]. G.C Hsieh, C.Y. Tsai, and H.I. Hsieh, “Photovoltaic Power‐Increment Aided Incremental‐ Conductance Maximum Power Point Tracking Controls,” in Proc. IEEE PEDG, pp. 542-549, Aalborg, Denmark, 2012.
[2]. G.C. Hsieh, S.W. Chen, and C .Y. Tsai, “Interleaved Smart Burp PV Charger for Lead Acid
Batteries with Incremental Conductance MPPT,” in Proc. IEEE ECCE, Phoenix, pp. 3248-3255, 2011.
[3]. Azadeh Safari and Saad Mekhilef, “Simulation and Hardware Implementation of Incremental
Conductance MPPT With Direct Control Method Using Cuk Converter”, IEEE Trans. Ind. Electron, vol. 58, no. 4, pp. 1154 – 1161, April 2011. [4]. M. Gradella, J. Rafael, E. Ruppert,” Comprehensive approach to Modeling and simulation of
photovoltaic arrays”, IEEE Trans. Power Electron. vol. 24, no. 5, May 2009. [5]. B. Liu, S. Duan, F. Liu, and P. Xu, “Analysis and improvement of maximum power point
tracking algorithm based on incremental conductance method for photovoltaic array,” inProc. IEEE PEDS, 2007, pp. 637–641.
[6]. Z. Yan, L. Fei, Y. Jinjun, and D. Shanxu, “Study on realizing MPPT by improved incremental
conductance method with variable step-size,” inProc. IEEE ICIEA, Jun. 2008, pp. 547–550. [7]. W. Xiao,M. G. J. Lind,W. G. Dunford, and A. Capel, “Real-time identification of optimal
operating points in photovoltaic power systems,” IEEE Trans. Ind. Electron., vol. 53, no. 4, pp. 1017–1026, Jun. 2006.
[8]. S. Minami, Y. Onishi, S. J. Hou, and A. Kozawa, “A New Intense Pulse charging Method for
the Prolongation of Life in Lead-acid Batteries” Journal Asian Electric Vehicles, Vol. 2, No. 1, pp. 541-544, 2004.
[9]. D.P Hohm, M. E. Ropp, “Comparative Study of Maximum Power Point Tracking Algorithms
Using an Experimental, Programmable, Maximum Power Point Tracking Test Bed”, Photovoltaic Specialists Conference, 2000. Conference Record of the Twenty-Eighth
IEEE,pp 1699 – 1702, 15-22 Sept. 2000.
[10] Pallavee Bhatnagar, R.K. Nema,” Maximum power point tracking control technique: State of art in photovoltaic application.”
54
APPENDIX:
FIG. 8.1 Prototype of Hardware Implementation
55
56