Design & Analysis of Grid Connected Photovoltaic System

1

Design & Analysis of Grid Connected

Photovoltaic System

Final Year Project Report

Session Fall 2008 – spring 2012

Supervised by

Engr. Naseer Khan

Group Members

Sulaman Muhammad Fa08-EPE-124

Nigar Ahmed Fa08-EPE-129

Sikandar Khan Fa08-EPE-135

Department of

Electrical Engineering

Comsats Institute of Information Technology

Pakistan

2

IN THE NAME OF ALLAH

THE MOST MERCIFUL AND

THE MOST BENEFICIENT

3

A report submitted to

COMSATS institute of information technology,

Abbottabad

as partial fulfillment of requirements

for the award of degree of

Bachelor of Science in Electrical (Power) Engineering

4

Department of Electrical Engineering

Comsats Institute of Information Technology,

Abbottabad

Final Approval

This is to certify that we have read the report submitted by Nigar Ahmed, Sulaman

Muhammad, and Sikandar Khan. It is our judgment that this report is of sufficient

standard to warrant it acceptance by the COMSATS institute of Information Technology,

Abbottabad for the Bachelor degree in Electrical (Power) Engineering.

Committee

Supervisor

Engr. Naseer Khan ………………….


Comsats Institute of information Technology, Abbottabad

Head of department

Dr. Abdur Rashid …………………..


Comsats Institute of information Technology, Abbottabad

5

DEDICATION

To our parents, friends and honorable teachers who always guide us in all respect

of life and give us the proper motivation to explore new innovation in studies and

life.

Design & Analysis Of Grid Connected PV System 6

Acknowledgement

All praise to Almighty Allah under those blessing, we have been able to complete and able to

present this report on “Design & analysis of grid connected photovoltaic system”. It was

concerted effort and cooperation of all near and dear ones was commendable. We are indebted

to them and seek their guidance, help and encouragement in future.

We are very thankful to our parents whose support in those days when we were under great

pressure of completing the task. Without their prayers and motivation we could not have

complete this project.

We are very thankful to our supervisor Engr. Naseer khan, who helped us in every part of this

project. He motivated us to work on this project and support a lot in countering the problems we

faced during the implementation.

Special thanks to Engr. Aamir khalil who helped us a lot in hardware design and simulation.

Project Team


Abstract

Aim of this project is to boost the DC voltage generated by the photovoltaic system to

the required DC value through DC-DC boost converter and then to invert that DC

voltage to AC voltage through H-bridge inverter. The output of the inverter is then

filtered through a low pass filter to get a pure sinusoidal wave form. This output is

then synchronized with the grid by converting the sine wave of grid into square wave

and then compare that square wave with the PWM and then give that output wave of

comparator to H-bridge, so if there is any change in the grid as a result the output of

inverter will also have same change.


Table of Contents

1. Introduction ------------------------------------------------------------ 09

1.1. Grid Synchronization ------------------------------------------- 10

1.2. Photovoltaic System ------------------------------------------- 11

1.3. Pakistan’s Situation ------------------------------------------- 12

1.4. Advantages of PV system ------------------------------------- 13

1.5. Applications -----------------------------------------------------13

2. Literature Review ------------------------------------------------------- 14

2.1. DC-DC Converter ----------------------------------------------- 15

2.2. DC-AC Inverter ----------------------------------------------- 19

2.3. Filter Design --------------------------------------------------- 21

3. Propose System --------------------------------------------------------- 22

3.1. Overview -------------------------------------------------------- 23

3.2. Converter Design ---------------------------------------------- 23

3.3. Inverter Design ------------------------------------------------- 26

3.4. Filter ------------------------------------------------------------- 39

3.5. Inductor Design ------------------------------------------------ 30

3.6. Output Result --------------------------------------------------- 31

3.7. Efficiency ------------------------------------------------------- 32

4. Simulation --------------------------------------------------------------- 34

4.1. DC-AC Inverter ------------------------------------------------- 35

4.2. Grid Synchronization ------------------------------------------ 40

4.3. Project Coding -------------------------------------------------- 46

5. Hardware Implementation--------------------------------------------- 56

5.1. Practical Results ------------------------------------------------ 57

5.2. Components Used ---------------------------------------------- 59

5.3. Components Specifications ----------------------------------- 60

6. References --------------------------------------------------------------- 62


CHAPTER

1

Introduction

1.1 Grid Synchronization

1.2 Photovoltaic system

1.3 Pakistan’s Situation

1.4 Advantages of PV system

1.5 Application


1.1. Grid Synchronization

The main theme of our project is to synchronize the power generated by the photovoltaic

system with the grid. The word synchronization means matching up two things or making two

things to happen at the same time and same speed.

For grid synchronization there are five conditions that must be met before the synchronization

process take place. The five conditions are following:

1. Line voltages

2. Frequency

3. Phase sequence

4. Phase angle

5. Waveforms

Waveforms and phase sequence are fixed by the construction of the photovoltaic system and its

connection to the grid, but voltage, frequency and phase angle must be controlled each time when

photovoltaic system is to be connected with the grid.

The AC voltage generated by the photovoltaic system must be synchronizing with the grid voltage.

There should be no difference in the live voltages of both photovoltaic system and grid.

The frequency of the photovoltaic must also have to be same as the frequency of grid. In Pakistan

the normal frequency of the national grid is 50 Hz. So we also fix the frequency of photovoltaic

system on 50 Hz.

Another requirement for the synchronization process, the phase angles of the photovoltaic system

must be same as the phase angles of the grid. In our project we match the phase angles of

photovoltaic system with the grid by phase loop lock generally known as PLL.

As the line voltage, frequency and phase angles of the grid is constant and we cannot change them,

so for the purpose of synchronization we have to design the system in such a way that its line

voltage, frequency and phase angles should be same as the that of the grid.

a. Why Synchronization is needed

Here the question raises that why synchronization is needed? If the system is not

synchronizing with the grid we cannot inject power into it nor can take power from the grid. The

synchronization failed when fault occurs. If there if difference between the frequency of system

and the grid, it will show to us as a fault. Same as if there is any difference between the phase

angle and line voltages it will indicate as a fault.


There are different methods for synchronizing a system with grid like three-lamp method,

PLL etc. But in our project we use PLL for synchronization.

1.2. Photovoltaic system

Photovoltaic systems (PV system) use solar panels to convert sunlight into electricity. A

system is made up of one or more solar panels, usually a controller or power converter, and the

interconnections and mounting for the other components. A small PV system may provide energy to

a single consumer, or to an isolated device like a lamp or a weather instrument. Large grid-

connected PV systems can provide the energy needed by many customers.

Due to the low voltage of an individual solar cell (typically ca. 0.5V), several cells are wired in

series in the manufacture of a "laminate". The laminate is assembled into a protective weatherproof

enclosure, thus making a photovoltaic module or solar panel. Modules may then be strung together

into a photovoltaic array. The electricity generated can be either stored, used directly (standalone

plant) or fed into a large electricity grid powered by central generation plants (grid-connected) or

combined with one or many domestic electricity generators to feed into a small grid (hybrid

plant). Depending on the type of application, the rest of the system ("balance of system" or "BOS")

consists of different components. The BOS depends on the load profile and the system type.

Systems are generally designed in order to ensure the highest energy yield for a given investment.

a. Grid Connected System

A grid connected system is connected to a large independent grid (typically the public

electricity grid) and feeds power into the grid. Grid connected systems vary in size from residential

(2-10kW) to solar power stations (up to 10s of MW). This is a form of decentralized electricity

generation. In the case of residential or building mounted grid connected PV systems, the electricity

demand of the building is met by the PV system. Only the excess is fed into the grid when there is

an excess. The feeding of electricity into the grid requires the transformation of DC into AC by a

special, grid-controlled solar inverter.

In kW sized installations the DC side system voltage is as high as permitted (typically 1000V

except US residential 600V) to limit ohmic losses. Most modules (72 crystalline silicon cells)

generate about 160W at 36 volts. It is sometimes necessary or desirable to connect the modules

partially in parallel rather than all in series. One set of modules connected in series is known as a

'string'.


b. Stand-Alone system

A standalone system does not have a connection to the electricity grid. Standalone

systems vary widely in size and application from wristwatches or calculators to remote buildings or

spacecraft. If the load is to be supplied independently of solar insulation, the generated power is

stored and buffered with a battery. In non-portable applications where weight is not an issue, such

as in buildings, lead acid batteries are most commonly used for their low cost and tolerance for

abuse. A charge controller may be incorporated in the system to:

a) Avoid battery damage by excessive charging or discharging and

b) Optimizing the production of the cells or modules by maximum power point tracking (MPPT).

However, in simple PV systems where the PV module voltage is matched to the battery voltage, the

use of MPPT electronics is generally considered unnecessary, since the battery voltage is stable

enough to provide near-maximum power collection from the PV module. In small devices (e.g.

calculators, parking meters) only direct current (DC) is consumed. In larger systems (e.g. buildings,

remote water pumps) AC is usually required. To convert the DC from the modules or batteries into

AC, an inverter is used.

1.3. Pakistan’s Situation

As the condition of power sector in Pakistan is very worst. There is about shortfall of 8000

MW in peer hours. So in this condition photovoltaic system is strongly recommended for Pakistan.

The people of Pakistan are also now attracting toward the photovoltaic system. The weather

condition in Pakistan is also very suitable for photovoltaic system.

There have been some efforts to install and expand the use of solar energy in Pakistan. The average

amount of daily sunlight in Pakistan is nine and a half hours; there are a few cloudy days even in the

wettest regions. Eight power generation plants have been installed and eleven are in various stages

of completion. Further feasibility studies are undergoing. In December 1981 the first

solar photovoltaic system was commissioned, located in Mumniala (a village 60 km

from Islamabad). Four solar systems has been commissioned in Khukhera (Lasbela district), Ghakar

(Attock district), Malmari (Thatta district)(now that system is unserviceable) and Dittal Khan

Leghari, Digri (Mirpurkhas district).

A practical example of the use of solar energy can be seen in some rural villages of Pakistan where

houses have been provided with solar panels that run electric fans and energy saving bulbs. One

notable and successfully implemented case was the village of Narian Khorian (about 50 kilometers


from Islamabad) which employs the use of 100 solar panels installed by a local firm, free of cost;

these panels have provide energy through lights and fan facilities to some 100 households.

1.4. Advantages of Photovoltaic System

The 89 PW of sunlight reaching the Earth's surface is plentiful – almost 6,000 times more

than the 15 TW equivalent of average power consumed by humans. Additionally, solar electric

generation has the highest power density (global mean of 170 W/m2) among renewable energies.

Solar power is pollution-free during use. Production end-wastes and emissions are manageable

using existing pollution controls. End-of-use recycling technologies are under development and

policies are being produced that encourage recycling from producers.

PV installations can operate for many years with little maintenance or intervention after their initial

set-up, so after the initial capital cost of building any solar power plant, operating costs are

extremely low compared to existing power technologies.

Grid-connected solar electricity can be used locally thus reducing transmission/distribution losses

(transmission losses in the US were approximately 7.2% in 1995).

Compared to fossil and nuclear energy sources, very little research money has been invested in the

development of solar cells, so there is considerable room for improvement. Nevertheless,

experimental high efficiency solar cells already have efficiencies of over 40% in case of

concentrating photovoltaic cells and efficiencies are rapidly rising while mass-production costs are

rapidly falling.

1.5. Application of Grid connected PV system

Following are the advantages of grid connected photovoltaic system.

1. Saving commercial units

2. Backup power supply

3. Environmental friendly

4. Ever green system


CHAPTER

2

Literature Review

2.1 DC-DC Converter

2.2 DC-AC Inverter

2.3 Filter Design


2.1. DC-DC Converter

A DC-DC converter is also known as chopper, and is commonly used to obtain a variable

DC voltage from a constant voltage DC source. The average value of the output voltage is varied by

changing the proportion of the time during which the output is connected to the input. This

conversion can be achieved with the combination of an inductor and capacitor and a solid state

device operate in a high-frequency switching mode.

In high-voltage and high-current applications, the switching devices used in a chopper circuit are

thyristors. When power transistors BJT’s, MOSFETS or GTO thyristors are used, they can be

turned off easily by controlling the base or gate current.

There are two fundamental type kinds of chopper circuits

1. Buck choppers

2. Boost choppers

The buck chopper produce output voltage that is less than the input voltage.

The boost choppers produce output voltage that is greater than the input voltage.

Pulse width modulation is the switching technique used in DC choppers. In this method, the pulse

width Ton is varied while the overall switching period T is kept constant. The fig 2.1 shows, how the

output waveform vary as the duty cycle is increased.

Fig 2.1 PWM waveform with fixed switching frequency


Buck Choppers (Step-Down)

In buck choppers the output voltage is varied several times less than the input voltage.

The fig 2.2 shows the basic circuit diagram of a buck chopper. The circuit includes a switch S,

diode D and an inductor L.

Fig 2.2 Basic circuit of Buck Chopper

When PWM is provided to the switch S, the switch S is then closed, the diode D is OFF, since it is

reversed-biased. It will stay off as long as switch S remain closed. The equivalent circuit shown in

the fig 2.3 when the switch S is closed and diode D is open. The input current builds up

exponentially and flows through the inductor L and the load. The output voltage is equal to Vi. The

switch S is kept on for time Ton and then turned OFF.

Fig 2.3 equivalent circuit for ON state


Now when no PWM is provided to the gate of switch S, the switch become open, the current

through the inductor start decaying to zero. It cannot change instantaneously but will decrease

slowly to zero. This cause an inductor voltage with opposite polarity across the inductor. The

inductor voltage forward biases the diode, and the current flowing through the inductor now

freewheels through the diode D and the load. The purpose of the diode therefore is to provide a path

for the load current when switch S is off. Therefore, turning off switch S automatically turns ON

diode D. the new circuit configuration is shown in fig 2.4. The voltage across the load is zero, and

the current decays toward zero as long as switch S remains OFF, that is for period Toff. The energy

stored in the inductor L is delivered to the load.

Fig 2.4 equivalent circuit for OFF state

Boost Choppers (step-up)

Boost choppers produce DC voltage several times greater than the input voltage. The basic

circuit diagram of step-up DC-DC converter is shown in the fig 2.5. The circuit includes switch S,

inductor L and capacitor C. The switch S operates on PWM.

Fig 2.5 Basic circuit of Boost Chopper


When PWM is provided in the gate of the switch S, the switch S is then turned ON. As shown in fig

2.6. The inductor is connected to the input supply. The voltage across the inductor VL jumps

instantaneously to source voltage Vi, but the current through the inductor iL increases linearly and

source energy in the inductor L. at this time the capacitor energy supplies the load voltage.

Fig 2.6 Equivalent circuit when switch is ON

Now when there is no PWM on the gate of switch, the switch S become open as shown in the fig

2.7, the current collapse and the energy stored in the inductor L transferred to the capacitor C

through the diode D. the induced voltage VL across the inductor reverse, and the inductor voltage

adds to the source voltage to increase the output voltage. The current that was flowing through

switch S now flows through L, D and C to the load. Therefore, the energy stored in the inductor is

released to the load and the output voltage increase.

Fig 2.7 Equivalent circuit when switch is OFF


When switch S is again closed, D becomes reverse-biased, the capacitor energy supplies the load

voltage, and the cycle repeats.

The voltage across the load is:

Vo = Vi + VL

Vo is the output voltage

Vi is the input voltage

VL is the voltage released by the inductor

Vo will always be greater than the Vi because the polarity of the VL is always same as that of Vi.

The diode current iD behave as follow:

ID = 0 when switch is closed (on)

ID = ii when switch is open (off)

2.2. DC-AC Inverter

Inverts are static circuits that convert DC power into AC power at a desired output voltage

or current and frequency. The output voltage of an inverter has a periodic waveform. There are

many types of inverters, and they are classified according to number of phases, use of power

semiconductor devices, communication principals, and output waveform.

The basic circuit diagram of inverter consists of four switches; here we use MOSFETS as a switch.

And every MOSFET has its own driver known as MOSFET driver.

Fig 2.8 Basic circuit diagram of H-bridge Inverter

Full bridge can be constructed by combining two half -bridges. Fig 2.8 shows the basic circuit of a

single phase full bridge inverter.


Fig 2.9 (a) Fig 2.9 (b)

In fig 2.9 (a) switch S1 & S4 is closed

In fig 2.9 (b) switch S2 & S3 is closed

To operate this H-bridge we use PWM. The switches are turned on an OFF in diagonal pairs, so

either switch S1 and S4 or S2 and S3 are turn for half cycle. Therefore, the DC source is connected to

the load alternately in opposite directions. First when current start flowing in the circuit the switch

S1 and S4 become close and act as a short circuit. When S1 and S4 become short the output wave for

half cycle is shown in the fig 2.10. After that when S2 and S3 become short and the direction of the

current become opposite and the waveform for this cycle is also shown in the fig 2.10.

Fig 2.10 Square wave output of H-bridge Inverter

This is the output waveform of DC-AC inverter. In first half cycle the switch S1 and S4 is short and

it give us a positive waveform. In second cycle when switch S2 and S3 is short since the direction of

current is opposite and give us a negative waveform.


2.3. Filter Design

Filter is used for the smoothing of wave form. I.e. if we have a sinusoidal waveform but

that is not in pure sinusoidal shape, we use filter for the to smooth our waveform and get it into pure

sinusoidal shape.

Fig 2.11 basic circuit diagram of Filter

The basic circuit diagram of filter is shown in fig 2.11. The circuit consists of an inductor and a

capacitor in series.

There are three types of filters:

1. Low-pass filter

2. High-pass filter

3. Band-pass filter

Low-pass filter is a filter that passes frequencies below a certain value and rejects frequencies

above that value. A low-pass filter is an electronic filter that passes low frequency signals but

rejects signals with frequencies higher than the cutoff frequency. The actual amount of attenuation

for each frequency varies from filter to filter. It is sometimes called a high-cut filter, or treble cut

filter when used in audio applications. A low-pass filter is the opposite of a high-pass filter.

High-pass filter is a filter that passes frequencies above a certain value and rejects frequencies

below that value. A high-pass filter is an electronic filter that passes high frequency signals

but rejects signals with frequencies lower than the cutoff frequency. The actual amount of

attenuation for each frequency varies from filter to filter. A high-pass filter is usually modeled as

a linear time-invariant system. It is sometimes called a low-cut filter or bass-cut filter.

Band-pass filter is a filter that passes frequencies within a certain range and rejects (attenuates)

frequencies outside that range.


CHAPTER

3

Propose System

3.1 Overview

3.2 Converter Design

3.3 Inverter Design

3.4 Filter

3.5 Inductor design

3.6 Output Result

3.7 Efficiency


3.1 Overview:

The aim of our project is to convert solar energy into electrical energy and then synchronize

that power with grid. We use solar penal as a source and take DC power from that penal, we then

boost that DC power and then invert that DC into AC voltage. And then filter the AC voltage to get

pure sine wave. And then synchronize our output voltage, frequency and phase with the grid.

3.2 Converter Design

Fig 3.1 shows Circuit Diagram of the DC-DC converter which is implemented in hardware.

DC battery, inductor, capacitor, power diode and switch (MOSFET) is used. MOSFET has 3

terminals Drain, Gate and Source. Its rating is given on the basis of withstand voltage of Drain to

Source. Gate has its own rating which is less than the voltage rating of Drain to Source. At gate of

the MOSFET pulses are given via opto-coupler or MOSFET drivers to maintain the rated input

voltage at the gate. Here MOSFET is used as a switch and at its gate PWM (high frequency) is

given which is made by 2 methods, either by square wave oscillator with DC shift or by using

microcontroller. In microcontroller it is generated by coding. Basically PWM is ON and OFF, in

micro controller language it is said as SET (on) and RESET (off).

vi

Inductor , L

S

capacitor output

Power diode

Fig 3.1 Circuit diagram of DC-DC boost converter


Working

When MOSFET in ON (short circuit) then diode is reverse biased and no current flows

to output. At that time capacitor discharges and output current is flown. When MOSFET is OFF

(open circuit) the inductor changes its polarity because it opposes change in current so at that time

diode is forward biased. At this moment the inductor act as another battery and both input voltage

and voltage of inductor is added, at this vary moment the capacitor is charged and also output

current flows.

In this DC-DC booster the input voltage is 25v DC which is boosted to the 80v DC.

Theoretically the boosted voltage is:

Vo = Vi / (1-d)

Where d is the duty cycle which is settled to 0.7.

When Vi = 25v

Vo = 83.33v

Practically the output Vo = 81.30 v

Inductor design

For designing inductor for the DC-DC booster first of all its value is calculated that which value is

required for the booster.

L=[R×TON × (1-D)]/2 (1)

D=Ton/T (2)

For D=0.7

And calculating T from f (15 KHz)

T=66.6us

So putting values for Ton in eq. 2:

Ton=46.6us

Now putting values in eq.1 to get the value of L

L=3.5mH


Specifications used for inductor Following are the inductor specifications:

1. EI shape inductor

2. 36 gauge wire

3. 125 turns

Practical results

Input Dc voltage Output DC voltage

12v 36.75v

15v 46.48v

18v 56.39v

21v 66.78v

25v 81.30v


3.3 Inverter Design

Construction For inverting DC voltage into AC voltage H-Bridge is used. Its construction is similar to

‘H’, in h bridge 4 switches are used here for switching MOSFETS are used. For switching of the

MOSFETS micro controller is also used in the circuit for each MOSFET opto-coupler is used

because a pulse cannot be given directly to the gate of MOSFET.

Block Diagram of inverter

Working

H-Bridge inverts DC to AC voltage. For this switching is done, in switching first of all

switch 1 & 4 is ON meanwhile switch 2 & 3 are OFF and vice versa. When switch 1&4 are ON

then at that time current direction is different from the other when switch 2 & 3 are ON. So it is said

that DC is inverted to AC, because the current direction changes with the change in switching of

MOSFETS.

Fig 3.2 shows the circuit diagram of H-Bridge. For switching, at gate the opto couplers or

MOSFETS drivers are used through which pulses are given to the MOSFETs. At the gate of

MOSFET’s pulses in the form of sinusoidal PWM is given. Sinusoidal PWM can be made by 2


methods either by comparing sine wave and ramp wave or by making a code in micro-controller.

Both of the methods can be practically implemented. For sine and ramp wave first of all oscillators

are made which gives output in the form of sine and ramp respectively. This method is analogue

method. in coding output port is set and reset according to our need. As for inverter’s H-Bridge

sinusoidal PWM is needed so loops are used so at one time the set time varies meanwhile the reset

time also varies. If set time increases so at that time reset time should reduce and vice versa. This

method of generating PWM is digital method. usually analogue methods are faster than the digital

methods because in digital methods certain time is used by each command written in coding, for

execution. But here the digital method is preferred because coding is simple and small which don’t

take more time, its almost take the same time as of analogue method and secondly here if analogue

method is used so sine and wave oscillators will be required which will result in the complex

circuitry and there is more probability of errors in analogue method and its difficult to sort it out.

Fig 3.2 Circuit diagram of H-Bridge

As in H-Bridge (diagonal/off diagonal) 2 switches are ON at one time. Switching between switch

S1&S4 and switch S2&S3 determine the output frequency which is settled to a nominal value 50 Hz.

In coding the switching of switch 1 & 4 and switch 2 & 3 is controlled, so the output frequency can

be controlled by the coding here the requirement is 50 Hz.


Practical results

DC voltage Inverted AC

36.75 V 31.67 V

46.48 V 40.39 V

56.39 V 48.61 V

66.78 V 54.43 V

81.30 V 75.65 V


3.4. Filter

Filter is used for the smoothing of wave form. i.e. if we have a sinusoidal waveform

but that is not in pure sinusoidal shape, we use filter for the to smooth our waveform and get it into

pure sinusoidal shape.

Here we use Low-pass Filter.

Low-pass Filter

A low-pass filter is an electronic filter that passes low frequency signals

but attenuates (reduces the amplitude of) signals with frequencies higher than the cutoff frequency.

The actual amount of attenuation for each frequency varies from filter to filter. It is sometimes

called a high-cut filter, or treble cut filter when used in audio applications. A low-pass filter is the

opposite of a high-pass filter. A band-pass filter is a combination of a low-pass and a high-pass.

Fig 3.3 shows the circuit diagram of a low pass filter. Filter is necessary to be connected after H

Bridge because the output of the H Bridge is in the form of PWM’s (both positive and negative). So

to get the smooth output of sine wave the filter is used. Here low pass filter is used where an

inductor is used and a capacitor is connected in the parallel to the output load.

Fig 3.3 Circuit diagram of a low pass filter


3.5. Inductor Design

To calculate the value of inductor:

Lfi=Vb / (4h x Fs)

Vb: Input DC voltage

Vb= 80v

h: hysteresis (h=0.5Io)

Io =Po/Vo

Io= 2.75 A

Fs: switching freq.

Fs=15 KHz

Lfi =1.5mH

Inductor specification

Core used: ferrite core

Wire: 22 SWG

No. of turns: 150


Capacitor Value The value of capacitor can be find as followed:

2Fs /10=1/2π (√ (Lfi * Cfi))

Solving for Cfi

Cfi =100/(16*π^2*Fs ^2 * Lfi)

Cfi =8.2uF

To get the desired value of capacitor we used a bulk of four capacitors each of 3uF in parallel and

series by making its combinations. All of the capacitors used in the filter are non-polar.

3.6. Hardware Output Results The output results of the designed hardware are as follows:

Input DC Boosted DC Inverted AC

12 V 36.75 V 31.67 V

15 V 46.48 V 40.39 V

18 V 56.39 V 48.61 V

21 V 66.78 V 54.43 V

25 V 81.30 V 75.65 V


3.7 Efficiency

As there are two parts of hardware DC-DC converter and DC-AC Inverter. We have

calculated the efficiency of both parts separately. The efficiency of both the DC-DC converter and

DC-AC inverter are as follows:

Efficiency of DC-DC boost converter

Vin = 25 V

Iin = 2 A

Pin = 50 W

Vout = 81.3 V

Iout = 0.51 A

Pout = 41.5 W

η = Pout / Pin

η = 83%

Efficiency of DC-AC Inverter

Vin = 81.30 v

Iin = 3 A

Pin = 244 W

Vrms = 75.65 V

Irms = 2.75 A

Pout = 206 W

η = Pout / Pin


η = 84%

Overall Efficiency

ηoverall = 0.83 × 0.84

ηoverall = 72.04%


CHAPTER

4

Simulation

4.1 DC-AC Inverter

4.2 Grid Synchronization

4.3 Project Coding


4.1 DC-AC Inverter

Fig 4.1 Block diagram of DC-AC inverter

The fig 4.1 shows the block diagram of DC-AC inverter. In Inverter the phase and

frequency of the output voltage is controlled with the help of square wave. As for MOSFETS

sinusoidal PWM is required which is generated from the comparison of sine and ramp wave. Fig 4.2

shows the comparison of ramp and sine wave.

Fig 4.2 Comparison of ramp and sine wave

The frequency of the ramp wave determines the frequency of the PWM. Greater the frequency of

ramp wave greater will be the frequency of the PWM and which will result in smooth sine wave.

Fig 4.3 shows the PWM generated by the comparison of sine and ramp wave.


Fig 4.3 PWM waveform

In H-Bridge it is necessary that either diagonal MOSFETS are ON or OFF diagonal MOSFETS are

ON at a time. For that PWM should be divided such that at a single instant MOSFET 1 & 4 are ON

and MOSFET 2&3 OFF and vice versa. It is done by comparing the PWM with the square wave,

Phase and frequency will determine the phase and frequency of the output of the project.


Fig.4.4 square wave with DC offset

This square wave is compared through comparator with the PWM generated from comparison of

sine and ramp wave. We take the square wave from function generator. The wave form of the

square wave is shown above in the figure 4.4.

First this simple square wave is compared with the PWM to get the PWM for the switching of

MOSFET 1 & 4 then for MOSFET 2 & 3 the NOT of the square wave is compared with the PWM

to get PWM.


The waveform for MOSFET 1 and 4 is given below in fig 4.5. This is produced by the comparison

of square wave with PWM.

There is a vacant place in the centre of PWM, this is because in this region the sine wave is

maximum and the ramp is not able to cut that maximum sine wave that’s why this place is vacant.

Fig 4.5 PWM for switch 1 & 4


The waveform for MOSFET 2 and 3 is given below in fig 4.5. This is produced by the comparison

of square wave with PWM.

Fig 4.6 PWM for switch 2 & 3

After division of PWM into two sets it is given to opto-couplers through which it is given at gate of

the MOSFETS which inverts the DC voltage into AC. This PWM is only used as pulses at gate

which is needed for on and off of MOSFET. Its amplitude has no relation with the amplitude of

output voltage. The waveform of output AC voltage is given in the fig 4.7 below. This is the AC

wave form which is not filtered.


Fig 4.7 Output inverted AC waveform

4.2. Grid synchronization

In our project we synchronize the output AC voltage, phase and frequency with the grid.

We did the simulation of our grid synchronization.

Necessary conditions for synchronization

There are few conditions that must be met before the synchronization process takes place. The

conditions are as follows:

1) Equal line voltage

2) Frequency

3) Phase

4) Waveform

Our focus is to synchronize the phase of our system and the grid because frequency is already

settled to a nominal value (50HZ) in switching of MOSFETS through microcontroller and here it is


assumed that the Grid is ideal and has a constant frequency. The output voltage of out inverter and

grid is also constant and equal. By synchronizing the phase the wave form can also be

synchronized. Waveforms and phase sequence are fixed by the construction of the photovoltaic

system and its connection to the grid, but voltage, frequency and phase angle must be controlled

each time when photovoltaic system is to be connected to a grid.

The AC voltage generated by the photovoltaic system must be synchronizing with the grid voltage.

There should be no difference in the live voltages of both photovoltaic system and grid.

The frequency of the photovoltaic must also have to be same as the frequency of grid. In Pakistan

the normal frequency of the national grid is 50 Hz. So we also fix the frequency of photovoltaic

system on 50 Hz.

Another requirement for the synchronization process, the phase angles of the photovoltaic system

must be same as the phase angles of the grid. In our project we match the phase angles of

photovoltaic system with the grid by phase loop lock generally known as PLL.

As the line voltage, frequency and phase angles of the grid is constant and we cannot change them,

so for the purpose of synchronization we have to design the system in such a way that its line

voltage, frequency and phase angles should be same as the that of the grid. Synchronization in

electrical generating system is the combination or synchronization of two electrical inputs by

matching the output-voltage waveform of one electrical system with the voltage waveform of

another system. Synchronization can be between two or more generating systems or between

generating systems and a utility supply

How Grid synchronization is done

As explained in inverter that square wave determines the phase and frequency of output

waveform. For grid synchronization here a new technique is used. In this technique the output of

grid utility is used. As the grid is considered ideal so it has constant voltage and frequency so here

phase is only controlled. The sine wave of grid is converted into square wave, as square wave

determines the phase and frequency. This new square wave is given as an input to the system i.e. for

the comparison of this square wave with the PWM for diagonal switch and then comparing not of

this square wave with the PWM for the other switches. Now the new PWM made due to this square

wave form will be used for inverter for switching.

Fig 4.8 shows the block diagram of grid synchronization


Fig 4.8 block diagram of grid synchronization

Conversion of Grid Sine Wave into Square Wave

As for grid synchronization we have to convert the sine wave of grid into square wave

for the purpose to give it as an input to compare it with PWM.

Fig 4.9 shows the sine to square converter in which AC supply from grid, DC supply, virtual OP-

AMP and a NOT gate is used. Here the AC and DC are compared through op amp. The AC supply

is from GRID utility. As sine wave for first half cycle is positive and in second half cycle it is

negative. When positive half cycle of sine wave and DC voltage is compared then op amp gives

Vcc at output similarly for negative cycle AC is negative but DC is positive so it is not compared so

op amp give zero at output as the other pin of the op amp is grounded. Here, the not gate has

similar working as that of in inverter. As diagonal/off diagonal MOSFETS are ON and OFF so this

not will make the square wave inverted. Once from node 3 this square wave is compared with the

PWM and then from node 4 it is compared with the PWM. So again the PWM is divided for H-

Bridge.


Fig.4.9 sine to square converter

As sine wave is converted into square wave so if a shift occurs in grid’s sine wave so a shift will

occur in the square wave accordingly a shift will occur in PWMs for switches and a shift will occur

in the output of the project which will be synchronized with the grid.

Fig 4.10 sine to square converter with wave forms


Fig 4.11 Full diagram of grid synchronization

Output wave comparison For 0 degree shift:

As in the Grid sine wave there is 0 degree phase shift, so same as that in output wave

form there is also 0 degree phase shift, because we have synchronize out output waveform with the

grid. The 0 degree phase shift result is shown in the fig 4.12.


Fig 4.12 Simulation output for 0 degree phase shift

For 10 degree phase shift:

As in the Grid sine wave there is 10 degree phase shift, so same as that in output wave

form there is also 10 degree phase shift, because we have synchronize out output waveform with the

grid. The 10 degree phase shift result is shown in the fig 4.13.


Fig 4.13 Simulation output for 0 degree phase shift

4.3 Project Code For the generation of PWM we used micro-controller and the coding has been done in Kiel.

mov p1,00h mov a,00h

START: CLR P1.3 SETB P1.1 SETB P1.2 SET P1.4 ACALL DELAY1 CLR P1.1 CLR P1.2 ACALL DELAY1 SETB P1.1 SETB P1.2 ACALL DELAY1


ACALL DELAY1 CLR P1.1 CLR P1.2 ACALL DELAY1 SETB P1.1 SETB P1.2 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 CLR P1.1 ACALL DELAY1 SETB P1.1 SETB P1.2 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 CLR P1.1 CLR P1.2 ACALL DELAY1 SETB P1.1 SETB P1.2 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 CLR P1.1 CLR P1.2 ACALL DELAY1 SETB P1.1 SETB P1.2 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 CLR P1.1 CLR P1.2 ACALL DELAY1 SETB P1.1 SETB P1.2 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 CLR P1.1


CLR P1.2 ACALL DELAY1 SETB P1.1 SETB P1.2 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 CLR P1.1 CLR P1.2 ACALL DELAY1 SETB P1.1 SETB P1.2 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 CLR P1.1 CLR P1.2 ACALL DELAY1 SETB P1.1 SETB P1.2 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 CLR P1.1 CLR P1.2 ACALL DELAY1

SETB P1.1 SETB P1.2 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1


ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 CLR P1.1 CLR P1.2 ACALL DELAY1 SETB P1.1 SETB P1.2 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 CLR P1.1 CLR P1.2 ACALL DELAY1 SETB P1.1 SETB P1.2 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 CLR P1.1 CLR P1.2 ACALL DELAY1 SETB P1.1 SETB P1.2 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 CLR P1.1 CLR P1.2 ACALL DELAY1 SETB P1.1 SETB P1.2 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1


ACALL DELAY1 ACALL DELAY1 CLR P1.1 CLR P1.2 ACALL DELAY1 SETB P1.1 SETB P1.2 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 CLR P1.1 CLR P1.2 ACALL DELAY1 SETB P1.1 SETB P1.2 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 CLR P1.1 CLR P1.2 ACALL DELAY1 SETB P1.1 SETB P1.2 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 CLR P1.1 CLR P1.2 ACALL DELAY1 SETB P1.1 SETB P1.2 ACALL DELAY1 ACALL DELAY1 CLR P1.1 CLR P1.2 ACALL DELAY1 SETB P1.1 SETB P1.2 ACALL DELAY1 CLR P1.1 CLR P1.2 ACALL DELAY1 CLR P1.4 CLR P1.2 CPL P1.4 MOV 1.5,1.4 SETB P1.1 SETB P1.3


ACALL DELAY1 CLR P1.1 CLR P1.3 ACALL DELAY1 SETB P1.1 SETB P1.3 ACALL DELAY1 ACALL DELAY1 CLR P1.1 CLR P1.2 ACALL DELAY1 SETB P1.1 SETB P1.3 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 CLR P1.1 ACALL DELAY1 SETB P1.1 SETB P1.3 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 CLR P1.1 CLR P1.3 ACALL DELAY1 SETB P1.1 SETB P1.3 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 CLR P1.1 CLR P1.3 ACALL DELAY1 SETB P1.1 SETB P1.3 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 CLR P1.1 CLR P1.3 ACALL DELAY1 SETB P1.1 SETB P1.3


ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 CLR P1.1 CLR P1.3 ACALL DELAY1 SETB P1.1 SETB P1.3 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 CLR P1.1 CLR P1.3 ACALL DELAY1 SETB P1.1 SETB P1.3 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 CLR P1.1 CLR P1.3 ACALL DELAY1 SETB P1.1 SETB P1.3 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 CLR P1.1 CLR P1.3 ACALL DELAY1


SETB P1.1 SETB P1.3 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 CLR P1.1 CLR P1.3 ACALL DELAY1 SETB P1.1 SETB P1.3 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 CLR P1.1 CLR P1.3 ACALL DELAY1 SETB P1.1 SETB P1.3 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 CLR P1.1 CLR P1.3 ACALL DELAY1 SETB P1.1 SETB P1.3 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 CLR P1.1 CLR P1.3


ACALL DELAY1 SETB P1.1 SETB P1.3 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 CLR P1.1 CLR P1.3 ACALL DELAY1 SETB P1.1 SETB P1.3 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 CLR P1.1 CLR P1.3 ACALL DELAY1 SETB P1.1 SETB P1.3 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 CLR P1.1 CLR P1.3 ACALL DELAY1 SETB P1.1 SETB P1.3 ACALL DELAY1 ACALL DELAY1 ACALL DELAY1 CLR P1.1 CLR P1.3 ACALL DELAY1 SETB P1.1 SETB P1.3 ACALL DELAY1 ACALL DELAY1 CLR P1.1 CLR P1.3 ACALL DELAY1 SETB P1.1 SETB P1.3 ACALL DELAY1 CLR P1.1


CLR P1.3 ACALL DELAY1 CLR P1.5 JMP START

delay1: mov tmod,#01 mov tl0,#0b2h mov th0,#0ffh setb tr0

again: jnb tf0,again clr tr0 clr tf0 ret


CHAPTER

5

Hardware Implementation

5.1 Practical Circuits

5.2 Components Used

5.3 Components Specifications


5.1. Practical Circuits

The implemented hardware is composed of Converter, Inverter and Filter.

DC-DC Boost Converter

Fig 5.1 Practical circuit of DC-DC boost converter.


DC-AC Inverter

Fig 5.2 Practical circuit of DC-AC Inverter

Filter Design

Fig 5.3 Practical circuit of Filter


5.2. Components Used

Components used in DC-DC Converter MOSFET 17N40

Opto-coupler 4N35

Power Diode schottky diode

Inductor E-I Shape

Capacitor Non-polar

µ-Controller PIC 18F452

Regulator IC 7705

Components used in DC-AC Inverter MOSFETS 17N40

Opto-coupler PC123

µ -Controller PIC 18F452

Components used in Filter Inductor 1.5 mH

Capacitor non-polar


5.3. Components Specifications

MOSFET 17N40 Symbols Parameters FQP17N40 Unit

VDSS Drain-source voltage 400 Volts

ID Drain-current 16 Amperes

VGSS Gate-source voltage 30 Volts

PD Power dissipation 1.35 Watt/ Celsius

Opto-coupler 4N35

Reverse voltage 6 volts

Peak fwd current 3 amperes

Power dissipation 300 mW

µ-Controller

Features 18f452

Operating frequency 40Mhz

Program memory 32 K

i/o ports Port A,B,C,D,E

Timers 4


Opto-coupler PC 123

Parameter Symbol Rating unit

I/P

Fwd Current IF 50 mA

Peak IF IFM 1 A

Reverse voltage VR 6 V

Power dissipation P 70 mW

O/P

Collector-Emitter-

Voltage

VCEO 70 V

Emitter-Collector-

Voltage

VECO 6 V

Collector-Current IC 50 mA

Collector power

dissipation

PC 150 mW


References

http://www.alldatasheet.com/datasheet-pdf/pdf/43321/SHARP/PC123.html

www.datasheetcatalog.org/datasheet/Sharp/mXrwuqw.pdf

www.fairchildsemi.com/ds/FQ/FQP17N40.pdf

www.ic2ic.com/search.jsp?sSearchWord=FQP%2017N40%20MOSFET

www.datasheetcatalog.org/.../1/03tgz200g5x4946jka7isojyj5wy.pdf

www.datasheetarchive.com/opto%20coupler%204n35-d

www.datasheetdir.com/4N35+Optocouplers

www.alldatasheet.com/view.jsp?Searchword=18F452

www.datasheetarchive.com/18f452-datasheet.html

http://www.easycalculation.com/physics/electromagnetism/inductance.php

http://powermagnetics.co.uk/calculator.html

http://www.alldatasheet.com/datasheet-pdf/pdf/43321/SHARP/PC123.html

http://www.datasheetcatalog.org/datasheet/Sharp/mXrwuqw.pdf

http://www.fairchildsemi.com/ds/FQ/FQP17N40.pdf

http://www.ic2ic.com/search.jsp?sSearchWord=FQP%2017N40%20MOSFET

http://www.datasheetcatalog.org/.../1/03tgz200g5x4946jka7isojyj5wy.pdf

http://www.datasheetarchive.com/opto%20coupler%204n35-d

http://www.datasheetdir.com/4N35+Optocouplers

http://www.alldatasheet.com/view.jsp?Searchword=18F452

http://www.datasheetarchive.com/18f452-datasheet.html

http://www.easycalculation.com/physics/electromagnetism/inductance.php

http://powermagnetics.co.uk/calculator.html

Date post:	14-Feb-2017
Category:	Engineering
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