1

CHAPTER 1

1. INTRODUCTION TO MAXIMUM POWER POINT TRACKER:

1.1 Energy crisis in ruler India:

The country's per capita consumption of electricity is about 400 kw/hr. We need to add over

1,00,000 mw in next10 years. According to the government, that electricity made available for

all villages by 2016. And 41,000 mw of electricity will be generated during the 10 th plan and

about 65,000 mw during the next five years [1]. Above all to follow the Chaina's electrification

policy and example like the very neighboring country Nepal. Electricity has to be used locally to

avoid transmission loss, micro and mini-projects and the community participation for the suitable

implementation. The rural electrification programme in India faced a similar challenge of

electrifying vast inaccessible areas.

In 1960s, Chaina implemented to electrify around 48% of its total remote areas. It

adopted the now-famous self-construction, self-management and self-consumption policy where

the local administration owned and implemented small hydropower projects. The money comes

from the local sources only. Unlike India, the Chaina government limited its role to that of an

observer. Simultaneously it enforced technical standards and funded research into new

technologies [1]. The result was amazing: around 300 million people in rural areas got electricity

through small hydropower station they built and maintained. In 1975, only 50.6 percent of

villages were electrified, unbelievably in 1996 it reached to 94.3 percent. In 1985 Chain's

ministry of water resources launched an energy based poverty alleviation programme to electrify

300 counties by 2000. They implemented small hydropower projects and fused irrigation and

flood control works with electricity projects.

1.2 MPPT makes the solar system efficient:

The Power point tracker is a high frequency DC to DC converter. They take the DC input from

the solar panels, change it to high frequency AC, and convert it back down to a different DC

voltage and current to exactly match the panels to the batteries. MPPT's operate at very high

audio frequencies, usually in the 20-80 kHz range. The advantage of high frequency circuits is

2

that they can be designed with very high efficiency transformers and small components [3]. The

design of high frequency circuits can be very tricky because the problems with portions of the

circuit "broadcasting" just like a radio transmitter and causing radio and TV interference. Noise

isolation and suppression becomes very important.

There are a few non-digital (that is, linear) MPPT's charge controls around. These are

much easier and cheaper to build and design than the digital ones. They do improve efficiency

somewhat, but overall the efficiency can vary a lot - and we have seen a few lose their "tracking

point" and actually get worse. That can happen occasionally if a cloud passed over the panel - the

linear circuit searches for the next best point, but then gets too far out on the deep end to find it

again when the sun comes out. Thankfully, not many of these around anymore.

The power point tracker (and all DC to DC converters) operates by taking the DC input

current, changing it to AC, running through a transformer (usually a torrid, a doughnut looking

transformer), and then rectifying it back to DC, followed by the output regulator. In most DC to

DC converters, this is strictly an electronic process - no real smarts are involved except for some

regulation of the output voltage. Charge controllers for solar panels need a lot more smarts as

light and temperature conditions vary continuously all day long, and battery voltage changes [3].

The maximum power point is mainly affected by the ambient temperature and the

intensity of sunshine. The intensity of sunshine being constant, the maximum output power

decreases with the rise of the temperature. The temperature being constant, when the sunshine

intensifies, the open circuit voltage of PV battery basically keeps unchanged. But the short

circuit current increases substantially, thus the maximum output power increases substantially.

This SC-MPPT solar controller can intelligently regulate the working voltage of solar panels,

letting the solar panels always work at Maximum Power Point of V-A curve. Compared with

ordinary solar controller, this MPPT controller can increase the efficiency of PV modules by

about 30%. However, due to many different factors, such as the difference in solar panel making,

the change the Sun luminance, change in temperature, the efficiency of the controller etc., the

actually available increased rate is 10%-30%.

1.3 Difference between ordinary charge controller and MPPT: [4]

3

Charge controllers operate at the intermediate stage between solar panel and battery. The main

function of these systems is to charge the battery using the panel generated electric power

avoiding any damages to the battery.

1.31 Basic Charge controller:

In the early stages of development, they used a simple charge controller which was a

mechanically operated relay which does the function of connecting panel to battery when battery

is at low voltage and disconnect when the battery reaches its full charge condition. Problem with

this kind of system is, battery will be in the state of fully charged condition for very long time

and there would be possibility of overcharge damaging battery.

1.42 PWM Charge controller: [4]

These closed-loop systems slowly lower the amount of current dumped into the battery as battery

gets closer to fully charged condition.. And these systems have the ability to keep the battery at

near full charge for indefinite time. Even though the PWM charge controllers meet the

requirement for better battery charging, they don‟t extract the whole power available from the

panel. The solution for this is Maximum Power Point Tracking (MPPT) charge controller!

1.43 Maximum Power Point Tracking:

Frequently referred to as MPPT, is an electronic system that operates the Photovoltaic (PV)

modules in a manner that allows the modules to produce all the power they are capable of. MPPT

is not a mechanical tracking system that “physically moves” the modules to make them point

more directly at the sun. MPPT is a fully electronic system that varies the electrical operating

point of the modules so that the modules are able to deliver maximum available power which

varies with environmental parameters like solar radiation, temperature and wind speed. So

extracting the maximum power from the panel is very important from the system efficiency point

of view. Additional power harvested from the modules is then made available as increased

battery charge current.[4]

1.5 Aim of the project:

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Designing a low cost MAXIMUM POWER POINT TRAKER charge controller with the aim of

extracting maximum power available at the solar panel terminal that will have the following

features:

1. The system detects the voltage of the battery whether is it 12 volts and then proceeds

accordingly.

2. It stores the energy extracted by solar panel in the battery.

3. The system can display the voltage of the battery at any instant, whenever required.

4. It also incorporates a three LED system (Green, Yellow & Red) just to indicate the status

of charging of the battery continuously.

5. The system ensures the rapid as well as safe charging of the battery.

6. The system incorporates the Reverse polarity protection system i.e. if at any instant the

battery voltage is larger than the solar panel voltage the system will prevent the flow of

power from battery to solar panel.

Description of the complete system is given in which interconnection of different blocks and

their working is explained one by one. After that MPPT algorithms and its flow chart is

explained this teaches us how MPPT takes the steps to achieve the maximum power point.

1.6 Steps to complete the project

Step1: Study of journals published related to the topic of MPPT.

Step2: To specified the objective of the project.

Step3: Structuring the block diagram to understand the interconnection of the different units

Step4: Starting of making the circuit on the breadboard in the lab with microcontroller and

other components.

Step5: Interfacing of electronics components MOSFET etc and testing and debugging of the

individual units working.

Step6: Developing the algorithm to get the maximum power from the panel with is changing

dynamically.

Step7: Programming and code burning in PIC16F684.

Step8: Now testing of complete module (software +Hardware).

5

Step9: If module is working as per our objective than fabrication on the PCB.

1.7 What is Maximum Power Point Tracking (MPPT) and how does it Work?

Maximum Power Point Tracking, frequently referred to as MPPT, is an electronic system that

operates the Photovoltaic (PV) modules in a manner that allows the modules to produce all the

power they are capable of. MPPT is not a mechanical tracking system that “physically moves”

the modules to make them point more directly at the sun. MPPT is a fully electronic system that

varies the electrical operating point of the modules so that the modules are able to deliver

maximum available power. Additional power harvested from the modules is then made available

as increased battery charge current. MPPT can be used in conjunction with a mechanical tracking

system, but the two systems are completely different.[5]

To understand how MPPT works, let‟s first consider the operation of a conventional (non-

MPPT) charge controller. When a conventional controller is charging a discharged battery, it

simply connects the modules directly to the battery. This forces the modules to operate at battery

voltage, typically not the ideal

Figure 2: The curve shows that operating voltage with 12 V Battery is different from MPP.

Operating voltage at which the modules are able to produce their maximum available

power. The PV Module Power/Voltage/Current graph shows the traditional Current/Voltage

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curve for a typical 75W module at standard test conditions of 25°C cell temperature and

1000W/m2 of insulation. This graph also shows PV module power delivered Vs module voltage.

For the example shown, the conventional controller simply connects the module to the battery

and therefore forces the module to operate at 12V. By forcing the 75W module to operate at 12V

the conventional controller artificially limits power production to »53W, rather than simply

connecting the module to the battery, the patented MPPT system in a Solar Boost charge

controller calculates the voltage at which the module is able to produce maximum power. In this

example the maximum power voltage of the module (VMP) is 17V. The MPPT system then

operates the modules at 17V to extract the full 75W, regardless of present battery voltage. A high

efficiency DC-to-DC power converter converts the 17V module voltage at the controller input to

battery voltage at the output.

In the future, solar energy will be a very important energy source. Several studies suppose that

more than 45% of the energy in the world will be generated by photovoltaic array. Therefore it is

necessary to concentrate our forces to reduce the application costs and to increment their

performance. In order to reach the last aspect, it is important to note that the output characteristic

of a photovoltaic array is nonlinear and changes with solar irradiation and cell‟s temperature.

Therefore a Maximum Power Point Tracking (MPPT) technique is needed to maximize the

produced energy.

7

CHAPTER 2:

2. BLOCK DIAGRAM OF THE COMPLETE SYSTEM:

By looking at the block diagram of the complete system it become clear that the charge

controller circuit (MPPT) is the interface b/w the solar panel and the battery which ensure rapid

as well as safe charging of the battery while extracting maximum power from the panel by

varying the duty cycle of the PWM output.

Figure 3: Block diagram of complete system

As shown in the block diagram, the charge controller is basically a DC-DC converter, in

which the duty cycle of the switching transistor is controlled by the PWM signal generated by

the microcontroller. Microcontroller will generate the PWM signal whose duty cycle is

determined by the panel and battery electrical parameters as shown in the figure. Different stages

of battery charging are shown in figure 5. Along with the charging this system will have an

equivalent job of operate the panel at its maximum power point. The MPPT algorithm will be

embedded in the microcontroller. Brief description about individual blocks is provided in the

following section

2.1 Description of the complete system:

There are three main components of complete system.

(I). Solar panel. (II). Battery. (III). Charge controller.

8

(I) Solar panel: [5] A photovoltaic module or photovoltaic panel is a packaged

interconnected assembly of photovoltaic cells, also known as solar cells. It takes the solar energy

from the sun and converts it in corresponding electrical energy.

Figure 4: Diagram of practical Solar panel and equivalent circuit of PV cell.

The photovoltaic module, known more commonly as the solar panel, is then used as a

component in a larger photovoltaic system to offer electricity for commercial and residential

applications.

Solar cells are essentially semiconductor junctions under illumination. Light generates

electron-hole pairs on both sides of the junction, in the n-type emitter and in the p-type base. The

generated electrons (from the base) and holes (from the emitter) then diffuse to the junction and

are swept away by the electric field, thus producing electric current across the device. Note how

the electric currents of the electrons and holes reinforce each other since these particles carry

opposite charges. The p-n junction therefore separates the carriers with opposite charge, and

transforms the generation current between the bands into an electric current across the p-n

junction.

The main electrical specification of a solar panel would be, at STC,

Wp: Maximum power available

Isc: Short circuit current

Voc: Open circuit voltage

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Vmp: Voltage at MPP

Imp: Current at MPP

The electrical specifications of solar panel are given below.

Voc-35.7V

Isc-7.94A

Vpm-26.1V

Ipm-6.69A

Variation of power and current of the panel with respect to panel voltage at different radiation &

different solar radiation:[6]

The ideal variation of current and power of PV cell is shown in the given diagram with respect to

change in irradiance and ambient temperature. By these different plots we can have the feel that

how these external causes affect the performance of the system. So study of these curves is very

helpful in designing of the system.

Figure 5: I-V curves for different temperatures (at 1000 w/m2)

10

Figure 6: I-V curves for different Irradiances (at 250

C).

The PV current is increasing with respect to increment in irradiance as well as temperature but

the only difference is that open circuit voltage (Voc) is increasing in case of increment in

irradiance while it is decreasing in the case of increment in temperature.[6]

Figure 7: P-V curves for different temperatures (at 1000 w/m2)

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Figure 8: P-V curves for different Irradiances (25deg)

Solar Irradiance is a measure of how much solar power you are getting at your location. This

irradiance varies throughout the year depending on the seasons. It also varies throughout the day,

depending on the position of the sun in the sky, and the weather. Solar insulation is a measure of

solar irradiance over of period of time - typically over the period of a single day. The curve

below shows that radiation coming from the sun is varying throughout the day in the Gaussian

fashions we should take care of it in designing of the system.[6]

Figure 9: Variation in sun irradiance in a sample day.

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(II) Battery:

It is used to store the electrical energy received from solar panel. The lead-acid storage battery,

an important energy storage device, is the most widely used secondary storage cell by

automobile and other industries. Storage cells are devices which release a flow of electron

through an external circuit as a result of reactions occurring between the active electrode

materials and ions transported by the electrolyte. The cells in which the reactions are reversible

are called secondary cells. In these cells the active materials can be returned to their original state

by applying electrical current from an external source in the opposite direction to the flow of the

cells discharge current.

The charging of the battery is done in three modes. These are described as follows:

Bulk Charge mode [7]

Absorption mode

Float charge mode

Figure 10: Three different charging modes of Battery.

(III) Charge controller:

It is an electronic system which operates the PV modules in a manner that allow the modules to

produce all the power they are capable of. So that the module is able to deliver maximum

available power which varies with environmental parameters like solar radiation, temperature

13

hence the efficiency of the system is increased. A charge controller consist of three main blocks

buck converter, pulse width modulator, and microcontroller. Microcontroller senses the panel

voltage and current as well as battery voltage. And provide the signal to PWM to vary the duty

cycle of the rectangular pulse which controls the switching action of the MOSFET switch

deployed in buck converter. And a equation holds here.[8]

[V (battery) = V(panel) * Duty cycle]

The variation of duty cycle is done by a microcontroller (16F684) which can follow any of given

algorithm. But the concept of the all algorithms is same which is to achieve maximum power

extracted from the panel by forcing the solar panel to operate at particular Voltage and current

(Vm, Im).

Buck Converter [8]

A basic buck converter circuit is as shown in figure. Assuming an ideal switch (MOSFET Q1)

and instantaneous input output voltages Vin and Vout, we can arrive at following equation:

Figure 11: Buck converter basic circuit.

Vout=D*Vin

Where, D=Ton/T, is the duty cycle.

Ton: Switch on duration, T: period (1/switching frequency)

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Fluctuation in output is diminished by using a low pass filter consisting L1 and C1. The problem

of stored inductive energy is overcome by using diode. The corner frequency of the LPF is

selected to be much lower than the switching frequency, thus essentially eliminating the

switching frequency ripple in the output voltage. During the interval when switch is on, the diode

D1 becomes reverse biased and the input provides energy to the load as well as to the inductor.

During the interval when switch is off, inductor current flows through diode, transferring some

of its stored energy to the load.

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CHAPTER: 3

3. BASIC CONCEPTS OF IMPLEMENTATION OF ALGORITHUM

I started with the very basic experiment of duty cycle control of PWM signal by varying analog

input voltage to the pin of microcontroller PIC16F684. Actually it is inbuilt property of

PIC16F684. First of all if we select any of the pin of controller as an analog input the

corresponding higher eight bit digital value stores in ADRESH register automatically. And if we

want to change the duty cycle we will have to change the value of register CCPR1L. As duty

cycle is directly related to the content of this register by given formula.[8]

So what we do just put the value of ADRESH into CCPR1L and get the duty cycle changed. This

is the only key of algorithum of MPPT .At one pin I have taken the value of voltage and at some

other pin current as an input to the controller and get it multiplied to come out with power. And

keep on comparing the present power to previous power to decide that duty cycle has to be

incremented or decremented . if P(present) > P(prev) by increasing voltage than increase Duty

cycle by increasing the contant of CCPR1L. if P(prev)> P(present) tby increasing voltage reduce

the Duty cycle .

3.1 My basic experiment in lab with PIC16F684 :

I started with the PWM generation using PIC 16F684 with operating frequency 250 Hz. I was

able to vary the duty cycle and thereby varying the LED brightness by varying resistance of

potentiometer. This experiment helped me in the later stage to verify the duty cycle at maximum

power extraction. The structure of this LED brightness variation is given below. The voltage

variation due to potentiometer resistance change is read by the analog channel RA0, and the

equivalent hex values stored in registers ADH, ADL are scaled suitably and put in the register

CCPR1L which affects the duty cycle ratio. The PWM runs in the single and active-high mode,

thus coming out at pin PC5 by default and leaving 3 other PWM-related registers available for

other usage. The PWM period 1μsec·16·256 = 4.096msec (which corresponds to approx. 244Hz

16

frequency) is provided by setting PR2 with the value of 255 and using Timer2 1:16 presale. The

program starts with a necessary setup of the control registers and then falls into an infinite loop.

At each iteration of this loop the PIC reads the voltage at PIC RA0 digitizes it and updates the

duty cycle ratio of PWM. The 8 higher bits of the ADC are available in ADRESH register, while

the two lower bits are in ADRESL. Those two bits are first shifted twice to the right to come to a

proper place and then are ANDed with the other bits of the corresponding control register. After

a 20msec delay this process repeats over and over. The oscillograms below show the output at

pin RC5, corresponding to a dimmer and brighter LED, respectively.[8]

Figure 12: LED brightness control by Duty cycle variation of PWM signal.

So by varing the analog value at pin RA0 tha brightness og LED is also varing with is

nothing but the change in duty cycle of PWM signal at tha pin RC5. 470 ohm resister is for the

current limiting purpose. Time period of PWM signal is given by below relation. The

programming associated with this LED brightness control is given in programming section.

3.2 Experiment done for implementing MPPT algorithm:

I took two analog signals from external power supply at the pin number 3 and 13 of the

PIC16F684. And vary each signal individually with the help of two potentiometer by vary any of

the signal the duty cycle of the PWM signal was varying. Actually both the signal was taken as a

current and voltage respectively in the programming which was done for the controller. And the

duty cycle was varying according to the multiplication value of both the signal as per the

programming.

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Figure 13: Experimental set up for PWM signal generation on bread board

We can see two complemented wave form which has been produced at the pin number 5 and 6

respectively that was the real base for making one MOSEFET ON another MOSFET OFF in the

buck converter. This ON OFF mode was selected by keeping the value of register

CCP1CON<3,0> equal to 1100 PWM mode which put P1A, P1C active high and P1B, P1D

active high. The value of PR2 is set to 0x27 for PWM signal produced at 25 kHz frequency.

Also the green and yellow LED‟s brightness are showing the Duty cycle of the PWM

signal and its complemented signal produced by the controller it means as much as the green

LED is brighter the yellow LED become faded and vice versa. So from this experiment one can

feel that the complementary signals are produced by the microcontroller at pin 5 and pin 6 that is

if duty cycle of one signal is increasing than Duty cycle of other signal is decreasing. For coding

refer to Appendix.

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3.3 Schematic diagram of complete module:

The selection of the components is based on requirement and capability of handling the power

levels of these requirements. For switching n-channel MOSFETs IRF630 and as blocking diode

between battery and panel p-channel MOSFETs IRF5210 are used.

Figure 14: Schematic of MPPT solar charge controller.

19

3.4 Circuit description:

Figure shows the schematic of MPPT solar charge controller. The upper part of parallel

MOSFETS represents the switch These MOSFETs are driven by a driver IC IR2110 which is

operated from the signals HIGHIN, LOWIN signals coming from the microcontroller. For this

design PIC16F684 is used for incorporating MPPT and PWM generation. IR2110 is used for the

Synchronous Rectification. As we can see, the combination of parallel MOSFETs on right are

used for Synchronous Rectification where, when the transistor is switched off it acts as the diode

which does the operation of diode D1 described earlier.[9]

In the synchronous buck converter, the efficiency is increased by replacing the diode with

a low side MOSFET. The four parallel MOSFETs must be driven in a complimentary manner

with a small dead time between their conduction intervals. The synchronous buck converter

always operates in continuous conduction. In this design, IR2110 is used with bootstrap

capacitor configuration to create the supply required by the high side driving of the top switch.

The supply required by microcontroller and enable signal of IR2110, is created by 5V voltage

regulator 7805In the schematic shown above, a 12V zener is provided at the Panel+ terminal to

limit the gate-source voltage of the p-channel MOSFET to maximum 12V. And a diode is

provided between the terminals panel+ and panel-terminals to provide the protection in case the

panel terminals are reversed. P-channel MOSFETs function as a blocking diode between panel

and battery, so that when the panel is at lower voltage than that of battery reverse current flow

should not occur from battery to panel.

The current sensing block will sense the current being dumped into the battery. Here the

current flowing through the inductor is sensed as it is almost equal to the output current flowing

into the battery. So, the aim will be to maximize this current by adjusting the duty cycle based on

the voltage level of the battery which is continuously monitored by the microcontroller. In the

above developed schematic the current sensor is realized using an op amp. The voltage across the

current sense resistor R12 is translated across R21 of current sensor block. And the current

through the path flows through R20 to create a voltage which will be sensed by the PIC analog

channel. Panel and battery voltage sensing is done by voltage divider arrangements. Temperature

is sensed by 1k thermistor. Linearizing series resistance is calculated and added. Charging and

discharging of battery is indicated by LEDs connected with PIC.

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3.5 Selection of the components of the buck converter based on the design

parameter:

The main design parameters to design a buck converter are:[8]

Input voltage range.

Output voltage.

Peak to peak ripple current.

Peak to peak ripple voltage.

Switching frequency.

For the above proposed design, the values of inductor & capacitor are calculated as below:

V in is ranging from (20V to 30V) and I max = 20A.

At fully charged battery Output voltage level, V out = 13.5V.

Switching frequency, f=50 kHz

As D (duty cycle) =Vout/Vin

According to the limits of Vout & Vin.

I calculated D min = 0.3 & D max = 0.675.

Peak to peak ripple current,

I ripple (p-p) = [V in*D* (1-D)*T/L] = 0.6 amp.

Therefore inductor, L = 75 uH.

Peak to peak ripple voltage V ripple (p-p)= Vout. (1-D)/ (8.L.C.f2) = 5 mv.

Therefore capacitor, C = 415 uF.

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3.6 Experimental setup of the complete module of MPPT:

The complete set up of MPPT is made on breadboard in NMR Lab. For developing the hardware

design schematic of the MPPT charge controller, there has been very extensive experimental

work carried out at the NMR Lab, IDDC, IIT Delhi to arrive at the final design. The NMR Lab

has provided me a very great environment to work with all the required facilities and

components to carry out hardware, programming and testing part of my project work. The

complete module of MPPT setup consists of many of the major components like.[10]

P channel MOSFETs

N channel MOSFETs

IR2110 MOSFET driver IC

PIC16F684 microcontroller IC

Inductor & Capacitor

LM7805 voltage regulator IC

OP27, Opamp IC.

The first unit is of the module is reverse polarity protection system it is made of P

channel MOSFETs. A 12 volt Zener diode is connected to the circuit ensure that the VGS never

become less than (-12) volts. If in any case the battery voltage becomes greater than the panel

voltage the power should not flow in reverse direction because of this unit of the circuit.

N channel MOSFETs are connecting in parallel to keep the resistance lower. As we know

the parallel resistance always makes the overall resistance lower than individual resistance. One

pair of MOSFET is working as the switch and another pair is as a diode of buck converter.[10]

IR2110 is driving both of the pair of MOSFETs. To make it sure that if one pair is ON

than at this time other one is OFF and vice versa. So that buck converter is working properly.

IR2110 IC is generating the signal called TOP and BOTTOM switching signal. The IR2110 is

high voltage, high speed power MOSFET and IGBT drivers with independent high and low side

referenced output channels. Proprietary HVIC and latch immune CMOS technologies enable

ruggedized monolithic construction. Logic inputs are compatible with standard CMOS or LSTTL

output, down to 3.3V logic. The output drivers feature a high pulse current buffer stage designed

for minimum driver cross-conduction. Propagation delays are matched to simplify use in high

22

frequency applications. The floating channel can be used to drive an N-channel power MOSFET

or IGBT in the high side configuration which operates up to 500 or 600 volts. Floating channel

designed for bootstrap operation, fully operational to +500V or +600V Tolerant to negative

transient voltage. (dV/dt) immune .Gate drive supply range from 10 to 20V. Under voltage

lockout for both channels 3.3V logic compatible. Separate logic supply range from 3.3V to 20V.

Logic and power ground ±5V offset. CMOS Schmitt-triggered inputs with pull-down. Cycle by

cycle edge-triggered shutdown logic. Matched propagation delay for both channels. Outputs in

phase with inputs.

Figure 15: Complete setup of MPPT module with display unit.

23

Figure 16: Isometric view of the MPPT setup realized on the bread board.

Figure 17: Top view of the MPPT setup realized on the bread board.

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PIC16F684 is the very important component of the MPPT module. It generates the PWM

signal according to the algorithm implemented in the coding of the controller. At pin no. 5 it

produces the PWM signal which works to operate the switch of the buck converter by keeping as

ON and OFF. As well as it generates a complementary signal of PWM at pin 6, which drives the

diode (made of n channel MOSFETs) of the buck converter either ON or OFF. Both the signals

are complemented, with the help of these two signals MOSFET driver IR2110 generates the TOP

and BOTTOM switching signals.[11]

The main features of PIC 16F684 from the requirement point of view of my project:

12 I/O pins with individual direction control

A/D converter of 10 bit resolution & 8 channels

PWM mode with 10 bit resolution

Software selectable precision internal oscillator for the frequency range of 8 MHz to 125

KHz

The value of inductor and capacitors are decided with the designing parameters of the

buck converter, which decide the value of ripple current and ripple voltage at the output side of

the buck converter. Apart from this the IC LM7805 is used to generate the +5V at the circuit,

which is very much essential to provide the Vcc for all IC used in the circuit. Apart from this

OP27 is used for the current sensing unit of the module, which is explained in the description of

the schematic diagram of the MPPT. It senses the voltage drop across the 25mΩ resistance and

brings this voltage with respect to the ground after some amplification. Now this voltage is given

to the pin 3. This voltage is directly proportional to the current going towards the load or battery.

In the Figure 14 the complete module of the MPPT with display unit is shown. Its shows

that when we have given 12.31 volts at the input (Panel voltage) of MPPT system and the PWM

signal has the duty cycle approximately 50% (shown in picture) and the output voltage is 5.57V

(shown by right sided multimeter). This justifies the relation of battery voltage, panel voltage and

duty cycle.

25

The hardware implementation was carried out step by step. First, the basic building

blocks of MPPT solar charge controller were implemented and successfully tested. This includes

PIC programming, PWM Generation, duty cycle variation, top and bottom switch signal

generation from PIC, driving top & bottom switches (MOSFETs) with MOSFET driver IR2110,

successful implementation of driving circuit with bootstrap capacitor to generate high side

supply of IR2110, buck converter, current sensing circuit, MPPT algorithm development and

finally implementation of whole system of MPPT Solar Charge Controller on breadboard. The

system was tested in the laboratory and the design was verified successfully. The results got were

satisfactory and the real time MPPT operation with the power supply was verified many times.

The main features of the developed system are explained below.

A very low cost and efficient design.

The design includes protection against panel terminal reversing and reverse flow

of power from battery to panel at night, over current protection, prevents

consumption of power by the electronics at night time when charging is not done.

The design is modular. Several such modules can be connected together with

multiple panels to meet greater power requirement.

Multiple number of this module can be used with different sources of renewable

energy to make a Hybrid Charge Controller System.

The use of microcontroller allows the designer to include other features like LCD

display, data transmission via serial communication etc (if needed) without

requiring any change in the basic schematic design.

LED indicators for battery state of charge of the battery.

The display unit is able to display the direct battery voltage and charging current

of the battery.

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3.7 Programming & code burning of the microcontroller PIC16F684:

The programming of the microcontroller is done in C language. The „perturb & observe‟ method

based algorithm is implemented in the microcontroller. For code please refer the coding section.

I have used MPLAB IDE v8.46 with HI-TECH C Compiler for coding, compiling and debugging

of the PIC programming. And for burning these codes into the PIC chip, I have used PICSTART

Plus development programmer. The burning of the code was successfully done in NMR lab.

Figure 18: PIC programmer (PICSTART Plus) & PIC programming environment

Figure 19: In picture window showing the successful burning of the code for PIC16F684.

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3.8 Finalized algorithm for MPPT:

Now my algorithm is to get MPP, is based on the fact that the maximum power point is obtained

near to 70% of open circuit voltage of the panel at that instant. So after reaching to this voltage

the exact location of MPP will be traced with the help of perturb and observe method. The

benefit of applying these two concepts together is that first we will reach near to Vmpp in only

one instruction after that with in very few steps of changing duty cycle it will reach at the exact

location of maximum power point. This is explained with the help of given curve.[12]

Figure 20: By keeping the duty cycle at 70% we reach near to MPP.

After reaching near to MPP further Perturb & Observe method is applied to trace exact Vmpp

(i.e. panel voltage where maximum power point is obtained).

3.9 Description of the P&O method:

Perturb-and-observe (P&O) method is dominantly used in practical PV systems for the MPPT

control due to its simple implementation, high reliability, and tracking efficiency. Fig. 2 shows

the flow chart of the P&O method. The present power P (k) is calculated with the present values

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of PV voltage V (k) and current I (k) and is compared with the previous power P(k-1). If the

power increases, keep the next voltage change in the same direction as the previous change.

Otherwise, change the voltage in the opposite direction as the previous one.

Figure 21: Tracking of MPP when (dP/dV) >0 So D(k+1)D(k)+∆D

Figure 22: Tracking of MPP when (dP/dV) <0. So D(k+1) [D(k)-∆D]

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3.10 Flow chart of the finalized algorithm:

Figure 23: shows the flow chart of the MPPT algorithm

The P&O Maximum Power Point Tracking algorithm is mostly used, due to its ease of

implementation. On the other hand, its main drawbacks are the waste of energy in steady state

conditions, when the working point moves across the MPP and the poor dynamic performances

exhibited when a step change in solar irradiance or in temperature occurs. In this paper, a

modified variable step size P&O MPPT algorithm is proposed, the step size is automatically

tuned according to the operating point. Compared with the conventional fixed step size method,

the proposed approach can effectively improve the MPPT speed and efficiency simultaneously.

When the MPP is reached, the system then oscillates around the MPP. In order to minimize the

Oscillation, the perturbation step size should be reduced. However, a smaller step size slows

down the MPPT. So step size should be compromise between both the things.

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3.11 DISPLAY UNIT:

This unit is used for the purpose of display of battery voltage and charging current of the battery.

The system consists of four major blocks.

1) Three LEDs (G, Y, R). 3) PIC16F88 microcontroller.

2) Hall IC ACS712T 4) 16X1 LCD.

LEDs (G, Y, R):

It is used to indicate the charging status of the Lead acid battery. By using the fact that if the

battery voltage is >12.5 V the battery is fully charged. And it is indicated by the green LED, or if

it is less than 12.5V But greater than 11.5V than yellow LED will glow. This indicates that

battery is charged but it requires charging. If the battery voltage is less than 11.5V than battery

needs to be charged and in this case red LED glows and battery is almost discharged in this case.

Hall IC (ACS712T):

It is used for sensing the current. The principle of working off hall IC is based on Hall Effect.

For detail about hall IC refer to Appendix. Tie pin 1 and 2 are connected as well as 3 and 4 are

also connected the current has to be measure is passed though pin (1-2) to pin (3-4) and this

current is sensed by the IC and produce the voltage at pin 7. Without any current passing, the

reading of the IC at the pin 7 is 2.52V and this value is increased by the 0.186 V per amp of

current, i.e. the sensitivity of the Hall IC is 186mV per amp of current. It can with stand the

current up to 5 amps. Pin 6 and 5 are connected by a capacitor which will determine the value of

bandwidth. [13]

PIC16F88:

The IC and all other components are connected to this IC only. It is 18 pin IC whose pin no 6 to

pin no 13 are connecting to the 16x1 LCD‟s data bit D0, D1…..D7. Pin 14 is VCC. And Pin 5 is

used as the GND. The 5 volt Vcc is produced by the voltage regulator IC LM7805. For more

detail refer the schematic diagram of Display unit.

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16X1 LCD:

It used to display either voltage or current at a time one thing, related to the battery or load .and

this is done by the help of a switch if it is on than voltage otherwise current. The LCD is run by

the microcontroller PIC16F88. The power supply needed for LCD is also 5V which is also

coming from voltage regulator IC LM7805. For detail programming code refer the appendix.

The schematic diagram of complete module of LCD Display unit is shown below.

Figure 24: Schematic diagram of the complete display module the schematic

Above diagram makes it very clear that how the different blocks are connected together to make

the display unit of the system. This display unit can display up to 15V maximum and the coding

of IC support the 13 amp maximum display of the current. For detail coding refer to coding

section.

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Figure 25: Complete display module on bread board measuring Voltage.

3.12 State of charge Vs battery voltage (at no load condition):

(Table shows at 10.5 volts = fully discharged, and 77 degrees F). Voltages are for a 12 volt

battery system. For 24 volt systems multiply by 2, for 48 volt system, multiply by 4. VPC is the

volts per individual cell - if you measure more than a .2 volt difference between each cell, you

need to equalize, or your batteries are going bad, or they may be sulfated. These voltages are for

batteries that have been at rest for 3 hours or more. Batteries that are being charged will be

higher - the voltages while under charge will not tell you anything, you have to let the battery sit

for a while. For longest life, batteries should stay in the green zone. Occasional dips into the

yellow are not harmful, but continual discharges to those levels will shorten battery life

considerably. It is important to realize that voltage measurements are only approximate. The best

determination is to measure the specific gravity, but in many batteries this is difficult or

impossible. Note the large voltage drop in the last 10%.[14]

Here the state of charge Vs voltage characteristic of lead acid battery is explained with

the help of graph given below it shows that above 12.5V the battery is about 90% charged and at

10.5 volt battery is about fully discharge.

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Figure 26: It shows the State of charge of the battery Vs battery voltage

If the switch is off it display the current in ampere. At the time of measuring the current the

display module are shown below in the other diagram.

Figure 27: Display module on bread board measuring current

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Advantage of the display module is that that it can show the charging status of the battery and the

charging current is also displayed with the help of this. This is very much helpful to protect the

battery system from excessive current. Apart from this the three LED systems directly indicate

the status of the battery when it should be charged and when it should be disconnected from the

charging.

3.13 PIC programming for 16F88:

The code burning for display of current and voltage for IC PIC16F88 is done in the environment

of MPLAB IDE v8.46 with HI-TECH C Compiler for coding, compiling and debugging of the

programs. And for burning these codes into the PIC chip, PICKit 2 v2.61. was used. The diagram

given below shows that programming of the 16F88 was build successfully and the code burning

was also completed. To follow the complete code refers to the coding section.

Figure 28: PIC programming environment (code burning for PIC16F88)

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CHAPTER.4 RESULT: 4.1 (Test & observation .1)

With the help of power supply and series resistance (5 ohms and 20 watts) available in

the NMR Lab the MPPT module was tested. The observed values of current, voltage and power

are shown in the Table given below. The reading shows that the maximum power is obtained

near to the 50 percent duty cycle.

Duty Cycle V_in (Volts) I_in (Amp) Power(Watts)

10 16.80 0.56 09.40

15 16.70 0.62 10.35

20 16.65 0.69 11.48

25 16.56 0.76 12.58

30 16.51 0.80 14.19

35 16.38 0.90 14.74

40 16.26 1.05 17.07

45 16.20 1.15 18.63

50 16.08 1.12 18.00

55 15.90 1.10 17.49

60 15.83 1.08 17.14

65 14.70 1.17 17.20

70 14.02 1.09 16.80

75 13.51 1.19 16.01

80 12.90 1.20 15.52

85 12.60 1.16 14.62

90 12.14 1.14 13.91

95 11.78 1.11 13.08

Table: 1

Figure 29: Power Vs Duty cycle graph (Plotted in Microsoft Excel).

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4.2 (Test & observation: 2)

This test was performed on slightly higher voltage than the previous test. Again it shows the

maximum power is extracted near by 50 percent of duty cycle.

Duty Cycle V_in (Volts) I_in (Amp) Power(Watts)

10 20.30 0.59 11.97

15 20.02 0.72 14.41

20 19.35 0.89 17.22

25 18.56 0.98 18.18

30 17.46 1.04 18.15

35 17.08 1.30 20.66

40 16.86 1.32 21.25

45 16.40 1.33 21.81

50 15.33 1.47 22.53

55 14.90 1.41 21.14

60 13.83 1.38 19.08

65 13.04 1.37 17.86

70 12.02 1.29 15.50

75 11.21 1.18 13.22

80 10.90 0.93 10.13

85 10.80 0.91 09.81

90 10.14 0.77 07.80

95 09.78 0.72 07.04

Table: 2

Figure 30: Power Vs Duty cycle graph for Test. 2 (Plotted in Excel).

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4.3 Top and bottom switching for different duty cycle:

Figure 31: Top & bottom switching for different duty cycle ratio from 5 to 45%.

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Figure 32: Top & bottom switching for different duty cycle ratio from 50 to75%.

39

Figure 33: Top & bottom switching for different duty cycle ratio from 80 to 85 %.

In diagrams we observe that as much as the duty cycle of the one PWM is increasing the

duty cycle of another (complementary PWM) is decreasing it means the IR2110 produce the Top

& bottom switching in such a manner which ensure if switch of buck converter is ON than diode

of Buck converter is OFF and Vice versa. This justifies the operation of buck converter. The gate

charge for the high side MOSFET is provided by the bootstrap capacitor which is charged by the

15V supply through the bootstrap diode during the time when the device is off (assuming that VS

swings to ground during that time, as it does in most applications). Since the capacitor is charged

from a low voltage source the power consumed to drive the gate is small. The input commands

for the high side channel have to be level-shifted from the level of COM to whatever potential

the tub is floating at which can be as high as 500V.The on/off commands are transmitted in the

form of narrow pulses at the rising and falling edges of the input command. They are latched by

a set/reset flip-flop referenced to the floating potential.

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4.4 Observations:

We observed that the duty cycle at which the system was stabilizing was same as the duty cycle

at which maximum power is extracted. It means according to the algorithm of MPPT (P&O

method) the duty cycle of the PWM signal keeps on changing until or unless it reaches the

maximum power point. As it is stabilizing near to 50% of the duty cycle it means maximum

power should be available near to 50% of duty cycle. And this is proved by tests taken in the

Lab. Hence MPPT is verified for all tests. The switching of top and bottom switches functioned

properly for varying duty cycles. The output voltage obtained across the load was free from

ripples as desired.

The PWM waveform of the microcontroller 16F684 is shown below on which the system was

stabilized. It is having approximately fifty percent duty cycle.

Figure 34: The PWM waveform for which MPPT module was stabilized.

Apart from this the Display module was also tested in the Lab, it is functioning properly for

displaying the battery voltage and charging current. It can display the voltage up to 15 volts. So

finally, it can be concluded that the system designing (MPPT as well as LCD display) was done

successfully in the Laboratory. And its performance was also found satisfactory as per desired.

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4.5 SCOPE FOR FUTURE WORK:

The development of products like low cost MPPT Solar Charge Controllers is one of the most

important needs of today‟s renewable energy world. That too for a country like India it has

become extremely important to have its own indigenous technology in the rapidly growing

renewable energy sector. The MPPT Solar Charge Controller developed is really a great step

towards having our own indigenous technology and making the product available at very low

cost.

The scope of this project was simply to create a working prototype of a MPPT system.

This system successfully uses the simple P&O algorithm to reach the MPP. The additional

resources (labor) needed to implement the more complex incremental conductance algorithm is

quite modest. Reaching a stable, true MPP at steady state instead of oscillating around this point

would improve the system's efficiency and increase reliability. Thus implementing the

incremental conductance algorithm is a good choice in continuing this project.

Another extension of this project would be to directly power the microcontroller and other

circuits from the solar panel instead of from a power supply. Or to incorporate a power supply

into the system that draws energy from the solar panel or an energy storage element that is in

turn charged by the solar panel. This extension would allow the system to be deployed to remote

locations.

Yet another more useful system would be one that could directly power a DC or AC load. An

additional DC-DC converter would be needed to supply a regulated DC signal. An inverter is

needed to supply an AC signal. If the AC signal is meant to connect to the grid, it is necessary to

synchronize the frequency of the signal with that of the grid in addition to limiting the voltage to

no higher than the grid voltage.

This digital controller would allow us to add these features to our system with relative

ease thanks to its high performance and many peripherals. The work allowed to detailed analysis

of a photovoltaic generator composed by the association of a solar panel, Buck converter with

MPPT control and loads type resistive or battery by means of computer aided simulation. From

mathematical modeling of the solar panel, it was developed a flexible structure to the simulation

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accounting the effects of changes in solar irradiation and temperature. A Buck converter was

designed for the desired operating conditions. The system was implemented in on bread board

and the results confirm the good performance of the maximum power point tracking of the solar

panel.

The hardware implementation was carried out step by step. First, the basic building blocks of

MPPT solar charge controller were implemented and successfully tested. This includes PIC

programming, PWM Generation, duty cycle variation, top and bottom switch signal generation

from PIC, driving top & bottom switches (MOSFETs) with MOSFET driver IR2110, successful

implementation of driving circuit with bootstrap capacitor to generate high side supply of

IR2110, buck converter, current sensing circuit, MPPT algorithm development and finally

implementation of whole system of MPPT Solar Charge Controller on breadboard. The system

was tested in the laboratory and the design was verified successfully. After the finalization, PCB

layout is made and all the components were mounted. The system was then tested in NMR Lab.

The results got were satisfactory and the real time MPPT operation was found working.

The performance of the system developed was satisfactory in terms of output voltage and

current ripple, tracking of the maximum power point by varying the duty cycle at different

atmospheric conditions. Hence it can be concluded that the presented work done on MPPT Solar

Charge Controller provides a right direction to develop a fully commercial system which would

aim at promoting the utilization of solar energy among common people. The main objective of

developing a low cost system for rural applications is met by the system designed which is a

simple, scalable and very low part count structure. As mentioned in the main features of MPPT

Solar Charge Controller, the system is modular. Therefore there is an advantage of just using

multiple modules with multiple solar panels or combination of different renewable sources

(hybrid system). The project aims at storing the energy in terms of battery charge. But the DC

output of charge controller can be fed to the inverter to run the home appliances or to drive the

motor of a solar powered electric vehicle. There are lot many such options which provide a huge

scope for future works of this project work.

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4.6 REFERENCES:

[1]A.K.Agarwala, “Notes on Switched Mode Power Conversion”,January 2002

[2].Book „Power Electronics‟ By MD Singh KB Khanachandani. McGraw-Hill publication

[3].ADVANCED ALGO FOR MPPT CONTROL OF PHOTOVOLTAIC SYSTEMS Research

Paper by Liu, B. Wu and R. Cheung University, Toronto page 2 to 4.

[4]. Development of Generalized Photovoltaic Model Using MATLAB/SIMULINK Huan-Liang

Tsai, Ci-Siang Tu, and Yi-Jie Su, Member, IAENG

[5] en.wikipedia.org/wiki/Solar_panel.1].Chihchiang Hua, ,Jongrong Lin, and Chihming

Shen,“Implementation of a DSPControlled Photovoltaic System with Peak Power

Tracking”,IEEE TRANSACTIONS ON, INDUSTRIAL ELECTRONICS, VOL. 45, NO. 1,

FEBRUARY 1998 pp 99-107.

[6].Chihchiang Hua and Chihming Shen, “Control of DC/DC Converters for Solar Energy

System with Maximum Power Tracking”.

[7].Prabhat Yadav, laxmi kant dwivedi,R.K. Saket “ MATLAB based modelling and maximum

power point tracking (MPPT) method for photovoltaic system under partial shading conditions”

IRJET, vol-3,issu-7, july-2016.. [8]. K. H. Hussein et al, “Maximum Photovoltaic Power Tracking: An Algorithm for rapidly

changing atmospheric conditions,” Proc. Inst. Elect. Eng. vol. 142, pt. G, no. 1,pp. 5964, Jan.

1995.

[9].C.R. Sullivan and M.J. Powers, “A High-Efficiency Maximum Power Point Tracking for

Photovoltaic Arrays in a Solar-Power Race Vehicle”, IEEE PESC„93, 1993, pp.574-580.

[10].B.K. Bose, P.M. Szczesny and R.L. Steigerwald,,“Microcomputer Control of a Residential

Photovoltaic Power Conditioning System”, IEEE Trans. on Industry Applications, vol. IA-21,

no. 5,Sep. 1985, ppll82-1191.

[11].Xuejun Liu and A.C.Lopes,,“An Improved Perturbation and Observe Maximum Power

Point Tracking Algorithm for PV Arrays” IEEE PESC „2004, pp.2005-2010.

[12].D. P. Hohm, M. E. Ropp,“Comparative Study of Maximum Power Point Tracking

Algorithms Using an Experimental, Programmable, Maximum Power Point Tracking Test

Bed”,IEEE,2000.pp.1699-1702.

[13]. Laxmi Kant Dwivedi1, Prabhat Yadav, Dr. R.K. Saket “Photovoltaic System Analysis for

Solar Cell Parameters Variation” IJESC-2016, VOL-6,ISSU-7,PP. 1795-1799.

[14]. N. Mohan et al., “Power Electronics—Converter, Applications, and Design”.New York:

Wiley, 1995.

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