Alternative Energy Generation

8/9/2019 Alternative Energy Generation

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Alternative Energy Distribution

By: Chanakya

[email protected]

Table of Contents

1.0 Overview ............................................................................................................................... 3

2.0 Introduction ........................................................................................................................... 4

3.0 Background ............................................................................................................................ 5

3.1 Traditional Generation Model .................................................................................................. 5

3.1.1 Generation............................................................................................................................ 5

3.1.1.1 Coal-fired power plants: ..................................................................................................... 5

3.1.1.2 Gas turbines and combustion cycle power plants ............................................................... 5

3.1.1.3 Piston engine based power plant ....................................................................................... 6

3.1.1.4 Fuel cell.............................................................................................................................. 6

3.2 Traditional Transmission Model ............................................................................................... 6

3.2.1 Inductance of the three phase Transmission line ................................................................... 9

3.2.2 Corona effect ...................................................................................................................... 11

3.3 Solar power ........................................................................................................................... 11

3.4 Wind power ........................................................................................................................... 13

3.4.1 Background ......................................................................................................................... 13

3.4.1.1 Wind Turbine Issues ......................................................................................................... 14

Technology .................................................................................................................................. 15

4.0 Emerging model and background ......................................................................................... 17

4.1 Battery ................................................................................................................................... 17

4.1.1 Types of Batteries ............................................................................................................... 18

Automotive Batteries................................................................................................................... 18

Vehicle Traction Battery: ............................................................................................................. 18

Stationary battery........................................................................................................................ 18

4.1.2 Batteries in Series ............................................................................................................... 18

4.1.3 Batteries in parallel: ............................................................................................................ 19

4.1.4 Battery Ratings: .................................................................................................................. 19

4.1.5 Battery charging.................................................................................................................. 20

4.2 Induction Motor .................................................................................................................... 22

4.3 Induction Generator: ............................................................................................................. 25

5.0 Models Created ................................................................................................................... 25

Model Assumptions ..................................................................................................................... 255.1 Home Usage Estimate model ................................................................................................. 26


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5.1.1 Load Calculations ................................................................................................................ 28

5.2 Rectifier ................................................................................................................................. 29

5.3 DFIG....................................................................................................................................... 31

5.3.1 The criteria for synchronising two generators ..................................................................... 345.4 Solar Panel ............................................................................................................................. 35

5.5 Combined Model ................................................................................................................... 37

6.0 Simulation Results ............................................................................................................... 39

6.1 Rectifier ................................................................................................................................. 39

6.2 DFIG....................................................................................................................................... 41

6.3 Combined Model ................................................................................................................... 44

7.0 Discussion ............................................................................................................................ 45

7.1 Power Factor Analysis ............................................................................................................ 48

7.2 Fault tolerance ....................................................................................................................... 48

8.0 Further Work ....................................................................................................................... 49

9.0 Conclusion ........................................................................................................................... 50

10.0 Appendices .......................................................................................................................... 50

11.0 References ........................................................................................................................... 57


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1.0 OverviewThe generation of electricity at remote sites or sites located closer to the load has the

potential to reduce transmission costs and losses, and reduce the environmental impact.

However, integrating such smaller generation plant that is distributed throughout the

network raises many issues around load flow analysis, safety, and network operation. This

investigation looks at the integration of distributed electricity generation for residential use,

such as remote communities or those reducing their reliance on the national grid.

Simulations of various network operations were performed using MATLAB and Microcap.

MATLAB was chosen for this project because the output obtained matched the theory.

Models were made of Battery room, Rectifier, Variable voltage source, DFIG [Double Fed

Induction Generation] and tested using different conditions.

In this project, the DFIG model generates electricity on 575V which is transmitted to the

load. The rest of unutilised energy is transmitted back to the grid. The output voltage of

the generator also varies as the grid voltage varies. Though the generation take place on

three phase, only one phase is used for domestic purpose. The distribution transformer is

used to get neutral point as well as to separate one phase out of three.

When the generation depends on weather, i.e. solar or wind, a back-up station is required

so the user can still utilise the electricity when there is not enough generation. To meet thiscriterion, batteries were installed in such manner, that it provided electricity when

generation fails. Apart from that the batteries will charge only when the load demand is less

than the generation. The rectifier circuit is developed to charge these batteries as well as to

remove the transients. As the load is single phase AC, an Inverter is also required to convert

the DC voltage obtained by rectifier.


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2.0 IntroductionThe prices of fossil fuels, particularly oil and natural gas, have risen sharply over the past

few years. As a result, alternative sources of energy used specifically in electricity

generation and transportation are garnering increasing attention although they still meet

only a small percentage of global energy demand, the more commercially viable alternative

energy sources are growing rapidly, presenting investors with the potential for attractive

long-term opportunities. The Idea of generating electricity on one end and transmitting it on

the other end is not more. Now there is an idea of generating electricity near to the load so

one can utilise it whenever they want. Not only this but one can transmits that energy back

to the grid. That also helps to reduce the transmission losses.


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3.0 Background3.1 Traditional Generation Model

The earliest power station had concept of generating electricity on one point and

transmitting it on the other end of the country because of what power drop occurs in

transmitting electricity. The utilisation of electric power is distributed mainly in 3 parts

generation, transmission and distribution

3.1.1 Generation

Alternators are used for generating electricity. Generation is normally performed on 6 KV.

There are lots of methods available for generating electricity by using differ type of prime

movers. As for example in New Zealand especially in North Island most of electricity isgenerated from Lake Taupo.

There are other concepts of generating electricity by.

3.1.1.1 Coal-fired power plants:

Coal is the most important and most widely used fuel for generating electricity. According to

world Energy Council it provides 23% of total global primary energy demand and 38% of

electricity production(Geest and Yeaman 2005). In the plant first of all coal is passed

through cleaning process where they are crushed into small particles so that can burn easily.

And then they are passed through electro static precipitator so that the metal parts can be

removed easily. These coal particles are then send to coal burning plant known as burner

where it burns and release large amount of electricity which is used to boil water and

generates steam on various pressure and temperature measured in Pascal and Celsius. This

generated steam passes through steam turbine on which generator is mechanically coupled

moves turbine thus electricity generates. In short this plant convert chemical energy to

steam, mechanical (kinetic), electric energy.

However, it is expensive to transport coal from one part to another that is one of the main

reasons why power generation companies built power station near to the coal mines.

Another thing is coal is also dirtiest of the fossil fuel and also emits large quantities of ash,

sulphur as a result it cause damage to earth environment.

3.1.1.2 Gas turbines and combustion cycle power plants

Gas turbine power plant works on the same principle as the coal fired power plant works.

The only difference is Gas is used as a source of energy rather than coal. It has more

efficiency with respect to coal fired power plant. However, it is also cheap and available in

large quantity as well as creates less pollution with respect to coal. It has more latent heat

respect to coal that means less fuel has to be used for same generation of electricity.


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3.1.1.3 Piston engine based power plant

In above two power plants external combustion engines were used. But this plant consists

of internal combustion engines which work in four strokes Intake, Compression, Power and

Exhaust. Here generators are connected to flywheel and as the fly wheel rotates generator

shafts and generates electricity. This plant has more advantages as It is available in small

size from 1KW to 65000KW(Breeze 2005). Petrol or diesel can be used as a fuel though

diesel engine does not have any spark plugs. It is more efficient than external combustion

engines. It has efficiency of 70-80 percent for four stroke engines only.(Breeze 2005)

3.1.1.4 Fuel cell

The fuel cell is an electromechanical device, closely related to the battery which harnesses

chemical reaction between two reagents to produce electricity. This method is the best

among the others as it consumes hydrogen and oxygen which can be supplies from water by

hydrolysis method. The outcome of the cell is only water so no carbon foot prints aregenerated. The cell itself has no moving part and also can be operate for long period of time

without maintenance, far longer than any turbine- or engine- based generating system. It

does not generate unwanted noise as there are no moving parts used. The only problem

with this technology is primary cost. (Breeze 2005)

There are also plenty of the techniques available as for example, Bio massed power

generation, Nuclear power and geothermal power.

3.2 Traditional Transmission Model

Generated voltages are transmitted to load centre by using conductors. The diameter and

length of this conductors are choose according to materials they are made of, allowable

impedance, length of networks etc. generated voltages are not enough high to transmit to a

long distance. Because as per the power formula KW (P) = V I Cos If the power factor

remains constant then load will consumes more current for low voltage with respect to high

voltage. So as the current increases the power losses also increase by I2Z, where Z is the

impedance of the network providing current to that load. 3 phase / transformers or Y/

step up transformers are used to step up the voltage level by 66kv or 120kv. Now on the

same voltage low current has to be drag by the load so there will be less transmission losses

as well as it helps to reduce the size of conductor and that cause less installation cost and

reduce the number of supports.

Normally the power distributed to small office lets say domestic loads are provided on

single phase which is 230 volt. This is done by using 3 phase step down /Y transformer

which transforms 11kv/400v. Generally 400v 3 phase connection is provided to small

engineering companies, shopping centres, large buildings etc(AUT 2009)


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In New Zealand there are some private companies whom are given power on 11kv near to

the distribution transformers then they provide the same power to their own

customers.(AUT 2009)

The transmission lines are made of conductors which have their own resistance reactanceand capacitance. As the temperature changes this parameters also changes but it does not

affect the transmission parameters as these values are negligible enough to ignore.

The resistance of the conductor is more important in transmission evolution and economic

studies. The dc resistance of solid round conductor at constant temperature is.

R = l/A where, ,l,A are resistivity, length and diameter of the area.

This is not the term when ac flows in conductor; because of screen effect [higher current

density on the surface] this resistance is more than normal resistance called impedance (Z).

When ac current flows in conductors it creates self and mutual inductance lets say, for

single phase two wire system, the predefine value of self inductance is 0.5e-7

. And the value

of mutual inductance between two points can be define by L = 2e-7

where D2 is the

distance between two conductors and D1 = r1

In single phase two wire system

Lext = 2e-7

H/m where, D is the distance between two conductors, r is redius of the

conductor.

Total inductance for conductor 1 is then

L1 = Lself+ L mutual

L1 =2e-7 ;

L1 = 2e-7

+ 2e-7

where, r1 = H/m


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Same way,

L2 = 2e-7

+ 2e-7

where, r2 =

The second term of the above equation is known as inductance spacing factor.

In single phase both the conductor has same current to flow and therefore they generates

same inductance of both conductor has same diameter then, r1 = r2 = r and hence L1 = L2 =L.

The ELCB (Earth Leakage Circuit Breaker) is based on the same principle as the. When there

is no current flow through earth, same current pass through neutral. So both phase and

neutral induces the same amount of flux which compensate the system. As the current start

flowing from phase to earth neutral does not generates flux for more and the latch operates

and circuit breaker trips.

While energising the grid for first time it is important to divide a whole grid in to small partsand then charge it. If it is connected directly with the generators then it will absorbed lots of

power as it is charging and fail the system.

Considering L11, L22 as mutual inductance and L12 = L21 as a self inductance of the line then

flux linkage is given by

1 = L11I1 + L12I2 as each conductor has its own self and mutual inductance.

2 = L22I2 + L21I1

as I2 = -I1

1 =

2 =

These calculations were for single phase two wire systems in three phase this scenario

changes.


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3.2.1 Inductance of the three phase Transmission line

Consider three conductors lay down in delta for symmetrical distance from each other.

Assuming balance load condition the final formula for flux linkage is.

a =

In balance load condition a= b= c. As

For three phase asymmetrical distances.

Line inductance of each line can be found from following equation

a =

b =

c =

if is a reference means and where = 1(120o and

= 1(240o

a= a/Ia it is easy to find a value of inductance.

s conductor has inductance it has capacitance too. It causes because of the potential

difference between two lines. Of course this value is not constant and varies with

temperature and moisture in air as the permittivity of air also affects capacitance. The

amount of capacitor is a function of conductor size, spacing between two conductors and

height above the ground.

C = q/V


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If V12is the voltage drops from pint 1 relative to 2 is

V12 =

Considering one meter length of a single-phase line consisting two long solid roundconductors having a radius r.

Assuming conductor 1 alone to have a charge of q1, the voltage between conductor 1 and 2is

V12 (q1) =

Now assuming only conductor 2, having charge of q2, the voltage between conductor 2 and

1 is

V21 (q2) =

Since,V12(q2) = -V21(q2)

V12(q1) =

Now the potential difference due to presence of both charges will be

V12 = V12(q1) + V12(q2) = +

For single phase line -q1 =q2 = -q

V12 =


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By formula C= q/v

C12 = F/m

Above equation gives line to line capacitance between conductors. The effect of the ground

is neglected as it is very law with respect to line capacitance.

The magnetic field generates in transmission line induces voltages in the objects having

considerable length parallel to line such as telephone line, pipe line and fences. Apart from

that there is a reason while doing maintenance of transmission line it is isolated and

discharge, as it has capacitance in it. The magnetic field is affected by the presence of earth

return currents. For balance three phase system zero current flows in earth return path.

Magnetic fields have been reported to affect blood composition, growth, behaviour,

immune systems, and neutral functions.(Saadat 2002)

3.2.2 Corona effect

According to the author, Hadi Saadat. when the surface potential gradient of a conductor

exceeds the dielectric strength of the surrounding air, ionization occurs in the area close of

the conductor surface. This partial ionization is known as corona it produces the distortion

in nearest radio and television signals. This is the reason while turning on the radio near to

the line does not catch the AM [amplitude modulation] signals.

In New Zealand in some rural area this transmission takes place by single wire earth return

system. This system was introduced in earlier 1930, when great recession was running on.And it keep going until 1940, second world war. In this system only one conductor is

installed and the return path is gained by earth. Though this system can be installed in low

cost but it is very inefficient as the impedance of the system varies according to ground

condition. As the ground becomes wet its resistance decreases. This system also increases

the capacitance between two lines as the distance between two conductor increases, finally

the impedance of the system increases.

3.3 Solar power

Solar energy is the most important source of energy available to the earth and its

inhabitants. it is the energy source that drives the photosynthesis reaction. The energy

radiated by sun on the surface of earth is distinguished by ultraviolet light visible light and

infrared light which are around 7%, 47% and 46% respectively.(Breeze 2005) Each year

around 1500 million TWh of solar energy reached the earth(Breeze 2005). There are some

of the energy is absorbed by ozone layer some is reflected back by clods but still around 700

million Twh of energy is available on surface of earth. Most of this energy strikes the oceans

which are almost in accessible parts. (Breeze 2005)


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(Fig 3.1) Solar power

Solar power can be generated anywhere on the earth but it would be wise to consider sites

before installing it. Places where clouds are cover commonly is not that preferable than theplace where sunlight is frequently available for whole of the year.

The advantage of this technology is solar panel does not require large amount of continues

area as it can be installed on various place where the space and sunlight available. The other

advantage is it does not generate any carbon emission. Apart from that there is no running

cost or maintenance cost for solar plants. However, it also has disadvantages like it

generates power only during morning time and does not generate any electricity at night or

when sunlight is not available. It also requires more space than other plants for generating

same capacity of electricity. It generates D.C power so there should be some extra device

requires which can convert DC voltage to A.C. e.g. inverter. It would be wise step to

installed backup system so that can supply power in peak period or at night. The solar cell

has life of about 10 years. Apart from that the output of solar panel does not remains

constant through the end. Its generating capacity decrease with the duration. it is costly

and also requires good skills to install panels.(Solar 2009)

There is another way to generates electricity by concentrating solar rays. The solar thermal

generation involves using the sun simply as a source of heat. This heat is captured,

concentrated on point by which heat engine runs. The heat engine may be conventional

steam turbine, in case the heat will be used to generate steam.

There are also other ways of concentrating solar rays on the receiver side.

Parabolic troughs:


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The parabola is ideal shape for a solar reflector because it concentrates all the light incident

on it from the sun at single point called focus. In this type of construction through is built

with the parabolic cross section reflectors which suppose to bring the sunlight to focus at a

line rather than a single point like in parabola. The reflecting panels can be made of mirror

glass or reflecting materials like foil.

Remember for obtaining optimum efficiency it is necessary to install reflector across the sky

facing towards sun. Once the beam concentrated on plate it converts heat to steam and the

same process starts.

3.4 Wind power

3.4.1 Background

Wind causes due to difference in pressure at two points and it flows from high pressure

zone to low pressure zone. It has enormous amount of energy in it and nowadays new

technology has introduce which can utilise this energy which means it can convert that

kinetic energy to electric energy by using bunch of equipments and machines. Wind mill is

divided mainly in two parts called wind turbine and generator (Induction motor type or

DFIG).(Energy 2009)

Wind turbine can be horizontal axis or vertical axis.


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3.4.1.1 Wind Turbine Issues

A wind turbine generator has no output at all until the wind speed exceeds its low wind cut-

in speed, which is typically between 14 and 22 km/h. Power output then rises until rated

output is reached at wind speed of about 54km/h. After which output power remains

unchanged until wind speed reach to the cut-out wind speed about 90km/h. For greed

security it is necessary to control voltage at the output terminals of the wind turbine

generator. It is also necessary to maintaining consistent output during faults on the grid

where voltage can be drop suddenly. It is likely to maintain output over a range of grid

frequencies around the nominal 50Hz frequency at which New Zealand grid operates.(Geest

and Yeaman 2005)

There are such factors which are limiting Integration of wind energy in to national power

grid. Those are as follows...

Frequency management;

Short term variation in wind farm output;

Generation scheduling;

Frequency management

In New Zealand, Electricity is transmitted on 50Hz of frequency. If the frequency

varies then the safe limits which are between 49.8Hz and 50.2Hz, it causes damage

to generators and loads. The change in frequency occurs when the difference

between generation and demand changes. So if the demand is constant and

generation increases then frequency will increase.

The change in frequency f in a short time interval t is given approximately by;


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f/t = (Generation - Load)/H Generation

Where, H is the constant of inertia of turbine.

Short term variation in wind farm output

As we the wind speed never stays constant. It varies from time to time and as the

wind speed varies the power which is almost Vs3

also varies and hence the output of

wind generator also varies. That situation causes a change in frequency. To reduce

the change in frequency it is necessary to have a backup power station so that can

full fill the changes in the grid and can be helpful to reduce frequency variation. In

New Zealand we are lucky because we already have hydro-electric generating plant

which can be used as a backup. We also have thermal power plant but it takes more

time to start up with respect to hydro plant.

Generation Scheduling

Another problem related with wind farm is the future, the next day. There is some

uncertainty about broadcasting wind data. If there will not be any wind next day also

known as dry day, then there will not be any generation take place. Finally the

potential of large scale wind energy can increase the uncertainty around the need to

start large scale backup stations.

Apart from that in New Zealand there are large scales of power take place from

hydro power station. This is the energy that we have to use it or lose it. It is almostimpossible to store the flow of river.

There is lots of more detail available about integrating generated electricity to the national

power grid of New Zealand. There is point need to be considered by owner of the wind farm

like dispatch time, pre-dispatch time two hour rule etc....(Geest and Yeaman 2005)

Technology

The wind mill is divided in two main parts, wind turbine and wing generators. as we knowthere are new technology in the market are available for WTG[Wind Turbine Generators]

which is known as DFIG[Double Fed Induction Generators]. Before that we will go through

the other technology as well as DFIG.

As we already know A WTG is typically connected to hub to form the rotor assembly. The

rotor hub is connected with shaft and gear train which transmit the power to WTG. And the

output is directly connected to grid. There are currently four technology is being used for

WTGs.

Asynchronous Induction Generator


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This technology has been used for a long time and uses standard squirrel cage

induction motor which is connected to the main grid in manner to supply excitation

to the field. The whole system consists of turbine- gearbox and generator. In this

type of generator turbine shaft is connected to the generator via gear box. The

reactive power can also be supplied by capacitors. The value of the capacitors can be

defined by considering a generator running as a motor with unity power factor. This

kind of generator does not have any control on reactive power and it provides only

active power.(Geest and Yeaman 2005)

Asynchronous Double Fed Induction Generator [DFIG]

The double fed induction generator is the motor with the slip rings, which can be

accessed externally. This technology allows user to control rotor current by which

user can control speed or torque. This technology has ability to provide reactive

power, voltage as well as frequency regulation. As the stator windings are connected

to the grid, it can contribute overall power system inertia. The present project model

delivers 50% of the active power though the stator.An Example of this kind of

generator is Vestas V90 3MW WTG proposed by trust-power for stage III of the

Tararua wind farm.(Geest and Yeaman 2005)

Synchronous Unsynchronised

This technology uses either permanent magnets or a standard excitation system,

hence it does not have to be connected with grid. User can connect is to the gridonce generator starts delivering power. The mechanical connections are made as

same as above two generators. The generator is connected directly to the turbine

and allows for variable speed operation over a wide range. The generator frequency

potentially being different to the grid frequency, a four quadrant power converter is

used to connect the generator to the grid. This system can provide reactive power,

voltage and frequency regulation. This generator cannot contribute to system inertia

owing to the presence of power electronic in the stator connections.(Geest and

Yeaman 2005)

Synchronous Synchronised

This technology is used by only few power stations. One of the generators based on

this technology has been located at Gebbies Pass, near Christchurch. (Geest and

Yeaman 2005)This technology uses standard synchronous generator. In this type of

generator the generator frequency can be vary with the RPM because of what a

variable speed control gearbox is connected in between turbine shaft and generator

shaft.


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4.0 Emerging model and backgroundNowadays there is a new trend of generating power is taking place. For that wind and solar

power generation is the best option for generating electricity near to the load and if theowner is not using that electricity, then he or she is able to transmit the same back to the

grid. That will reduce the transmission losses as well as it is the sustainable way to generate

electricity before that it is necessary to understand problems and requirement to transmit

generated electricity back to the grid provided by Trans power (network operators in New

Zealand).

The idea of generating electricity close to the load applied at various places. In India as the

sunlight is available during the eight months the idea of installing solar panels has been

widely spread. Many solar panels give an output of 18v and 60w though it can be varied

with temperature and solar intensity. This generated electricity is store in batteries and one

can use that any time when the user wants. The idea of generating electricity close to the

demand has many advantages on both user side and generation side. For example as the

distance between generation and utilisation point decrease, the less energy required to

transfer, which means less transmission losses. Reduce the size of conductor, less supports

need to be installed, less installation cost. If one use wind or solar energy to generates

electricity then there will be no carbon emission and that helps to reduce the carbon foot

print.

As per earlier discussion I am going to discuss some point about Matlab.

Creating an own model or start working directly on model is not good enough to research

for this project. That is why the model was built using SimPowerSystems. SimPowerSystems

extends Simulink with tools for modeling and simulating the generation, transmission,

distribution, and consumption of electrical power. It provides models of many components

used in these systems, including three-phase machines, electric drives, and libraries of

application-specific models such as Flexible AC Transmission Systems (FACTS) and wind-

power generation. Harmonic analysis, calculation of Total Harmonic Distortion (THD), load

flow, three phase load, wind generators, IGBTs, machines, DFIG, working models and so on.

4.1 Battery

Battery is the device which stores electric charge in form of chemical energy. So

basically it is the transducer which changes a form of energy. There are lots of terms

about battery before discussing that we have to understand a simple concept of DC

network. Battery is consisting of numbers of cells which gives output of 2 volts in

normal condition and in full charge condition it gives an output of 2.1 volt per cell.

That means there are 3 cells suppose to be connected in series to build six volt of

battery. 12 cells for 24V battery.


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Nowadays, various kinds of batteries are available. But fundamentally it is divided in

two parts, primary and secondary. Primary cell is also called non rechargeable, use

and throw cell. The best example of this is AA or AAA dry cell available in market

easily which gives an output of 1.5 volt.

In simple terms secondary cell means rechargeable cell. We know the car batteries

we can easily recharge those batteries by the source. In practical life secondary cells

are more likely to use than the primary cell for backup system. Secondary batteries

are classified based on their use.(T.R.Crompton)

4.1.1 Types of Batteries

Automotive Batteries

These kinds of batteries are used for starting, lighting, Ignition [SLI] in internalcombustion engines. Batteries used in car [Lead-Acid] are best example of this.

Vehicle Traction Battery:

This is also called motive power or industrial batteries because of their use.

These are available in many different electrolytes. As for example, Lead-Acid,

Nicle-Iron, Silver-Zink etc This type of batteries has ability to withstand against

high temperature. In fully charge condition the energy density range of

electrolyte is in between 100-120 wh/kg.(T.R.Crompton)

Stationary battery

Stationary batteries are mostly use for backup system but it is divided in to two

groups one type of battery is used for standby power system. It is used

intermittently E.g. UPS [uninterrupted power supply]. Another type of battery is

used for load levelling system E.g. in large power stations this type of battery

room are built to meet the peak demand when demand is more than generation.

(T.R.Crompton)

4.1.2 Batteries in Series

As we know battery has the unit of Ampere hour. That means the capacity of battery

measures in AH. As the number of AH increase the more energy it can store in it.


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In above figure shows number of cells connected in series. In series connection

voltages add together for example in above figure six batteries of 2 volt are use so at

terminal we receive 2+2+2+2+2+2 = 12 v. the more numbers of batteries the more

output voltage. Remember connecting a battery in series does not increase AH

capacity. It only increases output voltage.

It is already known that the current is equal at all points in a series circuit, so

whatever amount of current there is in any one of the series-connected batteries,

must be the same for all the others as well. For this reason, each battery must have

the same amp-hour rating, or else some of the batteries will become depleted

sooner than others, compromising the capacity of the whole bank.

4.1.3 Batteries in parallel:

As shown in above figure in parallel connection the output voltage of the battery

remain same. But it increases the ampere hour capacity of the battery. Now as we

know that the voltage is equal across all branches of a parallel circuit, so we must be

sure that these batteries are of equal voltage. If not, we will have relatively large

currents circulating from one battery through another, the higher-voltage batteriesoverpowering the lower-voltage batteries which can cause unwanted

effects.(B.L.Theraja and A.K.Theraja 2005)

Apart from that there are some other terms called battery ratings which are also

important while using a battery in a particular conditions..

4.1.4 Battery Ratings:

Reserve capacity: It is one of the newly developed rating standards. And it is more

realistic because it provides double check on Ah capacity. as the rating increase the

more one has to pay.

Zero Cranking Power: This is also called Zero degree performance. While testing the


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battery to get rating. it has to be chilled up to -18 degrees and then load is applied

on that battery only for 5 seconds. The test is held continuously until the output

voltage of that battery drops to 5v. As higher both the digits, better the battery

quality. As higher the number the price increases.

Cold cranking Power: This simple rating is applied to all 12 v storage batteriesregardless of that size. The battery is chilled up to -18

oC which is called (0

oF) until the

output voltage of battery drops to 7.2V. On the same time the output current is

measured for 30 seconds. Remember Higher the output better the battery.(T.R.Crompton)

4.1.5 Battery charging

When load is applied to battery it starts discharging and as it discharges the output

voltage also reduces of course not fast as the Ah. Remember while checking a battery

output voltage it is necessary to check it on load other vise owner always find full

voltage on battery and cannot be sure that whether battery is charged or not. Oncebattery is fully discharge it is necessary to charge it. If it remains discharge for a long

time than it will not work properly because it occurs problem in electrolyte. There are

two type of charging methods are available for batteries constant current charging and

constant voltage charging. Both has their own advantages and disadvantages..

Constant current charging

Constant current charging

The above figure shows the circuit diagram for constant current charging in this

method. This means the charger supply uniform current constantly. As the battery

start receiving that current the density of electrolyte increases and battery startcharging. As the battery charges the density of electrolyte increases not only this but

the temperature of battery also increases. It is necessary that battery temperature

should not increase then the optimum temperature which is provided by

manufacturers. Constant current charging helps to eliminate imbalance of cells and

batteries connected in series. Constant current chargers are mostly used for cyclic

operation where battery is supposed to charge overnight. Remember the voltage of

the charger may vary with time. It has disadvantages such as it takes longer time to

charge. Apart from that it is necessary to keep an eye on battery temperature and it

should not exceed than rated temperature in any condition.

As the battery start charging the amount of charging current decreases.


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The battery charging current-time characteristic is given below

Constant voltage charging

In this method, the charging voltage remains constant at any instant of time.when

battery is discharge and its terminal voltage is low, a large amount of chargingcurrent flows. As the battery start charging its back e.m.f. increases and the amount

of charging current decrease. It is notable that with this method the charging time

decreases by half with respect to constant current charging. It also increase storage

capacity by 20% but reduce the efficiency by 10%.

If there is a secondary cell in charging the back e.m.f. acts opposite to the appliedvoltage. in above figure V is the supplied voltage which drives charging current

towards battery against back e.m.f. Eb. then the power spent in overcome is Eb I isstored in form of chemical energy. The charging current can be found from following

equation.

I =

Where R = Total circuit resistance including internal resistance of the battery

I = Charging current

As Eb increases the V- Eb decreases cause a reduction in charging current, but by

variable resistor I can be keep constant.(B.L.Theraja and A.K.Theraja 2005)


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Constant voltage charging

4.2 Induction MotorTo understand the concept of induction generator it is necessary to understand

induction motor first. There are two types of induction motors available based on

rotor type squirrel cage and wound rotor (slip ring type). An induction motor is

made of two parts stator and rotor. A stator carries three phase windings and the 3

phase supply is connected to the terminals. It generates rotating magnetic field

which has synchronous speed of (120f/P) where f and P are frequency and number

of poles respectively.

A squirrel cage rotor has copper bar on it and they are permanently short circuited.

The rotor slots are not parallel to the shaft but they are little bit skew because 1) ithelps to reduce humming while rotor is rotating. And 2) it helps to reduce attraction

between stator and rotor so that rotor and stator windings do not magnetically lock

each other. In this type of rotor it is not possible to add external resistor to provide

extra mechanical torque.

In phase wound rotor the rotor is wounded for same number of poles as the stator

has. it is always wounded in three phase. It is possible to add external resistance to

control the torque.

Working principle:


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Here 1,2 and 3 are in black red and blue colured.

When three phase windings are placed at 120 degrees apart from each other and supplied

current, it provides resultant magnetic flux, which rotates in space by synchronous speed.

When = 0o

;

Here 1 = 0 ;2 = -3/2 m,3 = 3/2 m

So r = 2 m cos (60o/2)

r = 3/2 m

When = 60o

;

Here Here 1 =3/2 m,2 = -3/2 m,3 = 0

So r = 2 m cos (60o/2)

r = 3/2 m

When = 120o

Here 1= 3/2 m, 2= 0, m,3 = -3/2 m

So r = 2 m cos (60o/2)

r = 3/2 m

Now it is proved that in any condition r = 3/2 m.


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From above results we can say that.

The resultant flux has constant value which is 1.5 times maximum flux per phase m. As

well as the resultant flux rotates around the stator at synchronous speed Ns.

Fundamental concept of Rotor:

Due to relative speed between the rotating flux and stationary conductors, Emf is

induced in the rotor according to faradays law of electromagnetic induction e = Blv or by

e = N (/t)

The frequency of induced emf is same as supply voltages

Its magnitude is proportional to relative velocity between flux and conductor given by

Flemings right hand rule.


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Because of current flows in rotor it also produce magnetic flux but in opposite

direction.[Lenz Law]the reason which produce the rotor current is the relative velocity

between rotating flux of stator and the rotor

Hence to reduce relative speed the rotor starts running in the same direction of flux and

tries to catch up with rotating flux.

4.3 Induction Generator:

Induction generator is the same device as the induction motor. When run faster than

its synchronise speed Ns, an induction motor runs as a generator known as induction

generator. It is the reciprocal of induction motor as it takes mechanical energy and

generates electrical energy. In general an ordinary squirrel-cage motor which is

driven by petrol engine and connected to three phase line. As the shaft speed

increases then the synchronous speed, motor start delivering power. For creating its

own magnetic field it absorbs reactive power Q from grid with whom it is connected.

The Q flows opposite direction to active power P.

The active power generated is directly proportional to the slip above the

synchronous speed Ns. in some cases the reactive power supplied by a group of

capacitors connected across the terminals. The generated frequency is little bit less

than the shafts rotating frequency.

The terminal voltage increases with the capacitance. If the capacitors are

insufficient, the generator voltage will not build up so it is necessary to make sure

that enough reactive power be supplied by the capacitor bank to induction motor.

It is already discussed in induction motors that the flux generated by three phase

windings are 1.5 times more than maximum flux that is one of the reason why

induction generators are used as it delivers 1.5 times more electric power than

mechanical input.(B.L.Theraja and A.K.Theraja 2005)

Pele = 1.5 Pmech

5.0 Models CreatedThis project it based on generating electricity near to the load centre. To research onthis project it is necessary to work on models. For that few models were created by

using Simulation software MATLAB. The model was created on based of some

assumptions

Model Assumptions

The internal resistance is supposed to be constant during the charge and the discharge

cycles and doesn't vary with the amplitude of the current. The parameters of the model

are reduced from discharge characteristics and assumed to be the same for charging.

The capacity of the battery doesn't change with the amplitude of current. The modeldoesn't take the temperature into account. The Self-Discharge of the battery is not


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represented. It can be represented by adding a large resistance in parallel with the

battery terminals. The battery has no memory effect.

5.1 Home Usage Estimate model

The sine wave generator is already available in this MATLAB. For primary condition

the sine wave generator was used as the voltage source which provides 230v RMS

[root mean square] value. it is not possible to use DFIG or Induction generator model

as the usage model. Because it was created to use in phasor type power gui. While

this model works on continues type power gui. We cannot use the both together on

the same time.

Before generating electricity it is important to know about its utilisation. The plant

capacity can be define by the capacity of generator to provide electricity to theamount of load. First of all, it is a good idea to know about load demand and

maximum demand [peak demand]. By creating a load demand we can know about

load factor and peak load. In this project load demand chart is generated on the

basis of some general information. There could be difference in KW values of

appliances as they are available in wide range. Nowadays, electrical appliances are

available with energy ratings, as these ratings go higher the better appliance.


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The above graph is based on excel sheet, attached with this document.

To create a backup system it is not important to learn about load calculation. The

battery provides the active power and the same way the load use the same active

power. This active power is measured by KW-h meters installed in line. This domestic

meter measures only active power used by user. Because normally the power factor

of this domestic load is close to unity. But in commercial distribution industry has to

maintain a power factor. According to electricity rules, if the power factor of

particular industry drops then allowable value, then that company might be asked to

pay penalty.

To analyse DFIG model or generating electricity the owner must have the concept of

1 & 3 phase load so that he can isolate some of the loads to reduce peak demand. In

New Zealand during some periods the supply of water heaters are isolated to drop

the peak demand. In some industries maximum demand Indicators are installed. As

the maximum demand increases the more one owner has to pay.

0

2000

4000

6000

8000

10000

12000

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

TOTAL ENERGY-DEMAND W

solar KD210GX-LP 210 wh

wind H6.4-5000W 45-5kwh

Peak-demand


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5.1.1 Load Calculations

Single Phase

The instantaneous power P(t) = v(t) i(t) =

Active Power P(t) = VI Cos where, V and I are rms value, = (v- i)

The reactive power occurs because of inductance and reactance in the circuit. It has the zero

average value.

Q = VI sin

Apparent power (S) =

Power Triangle

From the law of energy conservation it is already proved that the total power supplied by

the source to sink is the sum of all the power flown in sinks. Thus, P = P1 + P2 + P3

Three phase load

One of the reason why three phase transmission take place is because it has ability

to delivered more power with respect to single phase. The instantaneous power

delivered by three phase is near to constant not pulsating like single phase.


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A power system has Y- connected generators. Loads can be in star or delta.

Generators are rarely -connected, because if the load is not balanced then return

current flows through the circuit. While in Y-connection if the load is unbalanced

then return current will flow from neutral.

For Y-connected Load

VPH= 3 VL where, VPH and VL are phase voltage and line voltage respectively. In this

Y-connection line current and phase current has the same value.

IL = IPH

In -connected load the value of line voltage and phase voltage are same as there is

not any neutral point. But line current is 3 times higher that phase current.

VL = VPH & IL= 3 IPH

The three phase instantaneous power is ....

P3 = 3 VPHIPHCos

Same way reactive power is

Q3 = 3 VPHIPHSin

Apparent power S3 = 3 VPHIPH = P3 + j Q3 (B.L.Theraja and A.K.Theraja 2005)

5.2 Rectifier

Rectifier is the unit which converts alternative current to direct current by means of

p-n junction diodes. It helps to provide a backup supply for which batteries are used.

This rectifier unit supply dc current to battery bank and help them to charge so in

case of emergency or power failure owner can use it. There are two models created

on different software one was on matlab and another was microcap. There is no

particular one kind of diode is available on matlab. In microcap model the diode

name 1N4007 are used as a bridge rectifier. The data sheet for that diode is given in

another section.

Now, the generated voltage is 230v rms. and the forward voltage is 0.7. This means

there will be 0.7 of voltage drop in each diode while conducting. Now according to

diode theory and formulas..

Vrms = Vp/2 where Vp is the peak voltage

Lets say transformer ration is 10 : 1 then voltage at secondary will be ten times less

then primary voltages called Vp2.

VDC is called DC average value also called Vavg which will be


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VDC = Vp2/ for half wave ideal condition but in real condition for full wave bridge

rectifier, there are two diodes conducts at same instant so there will be a voltage

drop of 1.4 voltages.

VDC= (2 Vp)/ *Ideal condition+

VDC = (2(Vp-1.4))/

Now the output comes from diode is almost equal to VDC which is less then rms

value. But steel it is not good enough as it has many ripple in it. To smooth, it is

necessary to filter it and this can be done by adding filter circuit. In this model RC

filter is used which has following formulas.

After removing ripples from out put the smooth dc output will smooth enough for

batteries to charge

Calculation for ripple voltage is.

Vripple = VDC/ (2 R f C); where R, f and C are resistor frequency of ripple voltage

and capacitance in micro faradays respectively.

The final output of the voltage is VDC = VDC + (Vripple/2)

This device was tested on microcap software.

The rectifier unit on Microcap


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Rectifier unit of MATLAB

5.3 DFIG

The DFIG is the kind induction generator with slip rings so here the generated power is

dragged by two sights stator and rotor. There are power electronic devices like rectifier

and inverter unit is connected on rotor and grid side respectively. Between this DC link a

dc capacitor is connected as a filter unit which can be helpful to remove the ac

component from the rectifier voltage and also helps to maintain constant voltage levels.

The inverter unit converts this smooth DC to Ac at the required frequency close to 50Hz

and then feeds to the main grid. While the output from stator can be directly fed to the

main grid where another generators are already synchronised. As per earlier discussion

neither wind speed nor does load remain constant at any instant because of what it

because a change in frequency and as the frequency varies the impedance of the

transmission lines also varies by equation 2fL and 1/2fC. Which means voltage drop

varies. Finally it can damage the instruments connected on grid.


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In DFIG technology, the harmonics injected in the grid can be removed by the rotor side

converter. Not only has this, it transmitted reactive power to support grid.


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In this model DFIG generates power at 60Hz 575 Volts. Though normally generation

take place on 11kv.gererated voltages comes at terminal A, B, C. 400volt is the line

voltage. This block has two inputs wind and trip. The wind speed in Kmph has to be

entered in the system. If someone wants to fed external power then need to check

external mechanical torque option given in block parameter Turbine data. If that

option is selected then wind terminal from main block will disappear and Pm

terminal will be enable through which it is possible to feed external mechanical

torque generated by turbine. Here in this model a variable wind speed model is used

which varies the speed of wind with respect to time.

The trip is stand for the getting signals for tripping the whole unit. It is not necessary

to feed this signal manually. In this model this tripping device gets signal from

[Trip_WT]. Now once the voltage generated and there is no problem in the circuit

then DFIG keep giving output on 575V 60Hz.With the help of the three phase twowinding transformers of ratings 12 MVA. As it is necessary to provide reactive power

to DFIG as it absorbs that reactive component and provide the active power. And in

this model this power is provided by means of three capacitors connecting in star

which provides 500kw of power to the grid. The neutral of this star point is

connected directly to the ground to make the system more reliable. Once this

generated voltage is good enough to transmit to the load centre which is almost

10km far from DFIG generating station. The transmission line can be overhead or

underground or could be made of copper or aluminium. The aluminium provides less

weight and cheap solution, but it has more impedance with respect to copperconductor. Not only has this, but to transmit same amount of power aluminium

conductor had to be more in diameter with respect to copper conductor. With the

help of the pi section line it is easy to transmit voltage on 25kv for 10km far from the

point of generation. This PI- section has parameters of frequency, resistance

inductance and capacitance in both positive and zero sequence. In this model the

value of frequency, resistance inductance and capacitance is 50HZ, 0.1153, 1.05e-3,

11.33e-009 respectively for positive sequence. This data are calculated on the basis

of type of conductor, shape, operating temperature, and distance between two

conductors. Finally this pi section creates impedance of 0.115 ohms (), by equation

Z2=R

2+ (XL - XC)

2where, R, XL and XC are resistance, and capacitance respectively. In

this model no need to find the value of XL and XC but it is easy to find its value by

following formula. XL= 2fL and XC= 1/2fC where L and C are the values of inductor

in Henry and capacitor in farad. After 30km this voltage is step-down by another Y/

transformer whose star point (on primary side) is grounded to earth this helps to

stabilise the system as well as also helps to remove humming and also provide

neutral point. Then it is ready for the further distribution.

The grid is fed power not only by DFIG, but also by another source which has abilityto provide electricity supply as backup or extra electricity to the load in case of peak


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period. This three phase programmable voltage source provides electricity on 120kv

which is further step-up to 25kv so that can be synchronised with another source.

5.3.1 The criteria for synchronising two generators

The generated voltage should be same. If these criteria do not match then reversecurrent flows from one generator to another from high voltage to low voltage. This

reverse current can damage the windings of the generator.

Frequency of the both generator should be same.

While synchronising two generators it is necessary to check phase sequence if the both

generated. The face sequence of the both generator must be same.

Although, it is hard to build a devices which have same impedance. But if the impedance

of two generators matches then it gives optimum performance.

To check the data and flow of power three phase V-I measurement both is installed near

to the both generator DFIG and programmable source. Here in this model the output

graph can be shown with help of scope. The term Vabc and Iabc provide this data to wind

turbine data acquisition which check the data at each instant of the time and if there is

any error found in that then this device will isolate the turbine section from generator.

It is very difficult to generate electricity without load. While designing a whole system,

engineer has to consider the point of impedance matching for optimum output of the

generator, as impedance plays important role in the system. In this model 2MVAof loadis used to stabilise the whole system. This load is consisting of three phase delta star

transformer which step-down the voltage to 2.3kv. a three phases breaker is used as

buffer between line and motor. The motor consumes 1.68 MW at 0.936 power factor. To

maintain power factor 200kw of capacitors are connected to grid. The plant and motor

connection is also installed in this system.


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Model generated for analysing and testing

5.4 Solar Panel

There is no particular model is available for solar panel. But that is sure that the whole

system works on photovoltaic system. By looking at fundamental theory it is easy to say that

the simplest equivalent circuit of a solar cell is a current source in parallel with a diode.

The output of the current source is directly proportional to the intensity of light falls on the

surface of cell (photo current Iph). If the light is not available lets say in night it works as a p-


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n junction diode. It produces neither a current nor a voltage. If it is connected to large

supply voltage, it produces the diode current which determines the I-V characteristic of cell.

This current called dark current.

It is already known that the output of the photo cell varies as the temperature varies. In

above circuit the series resistance Rs gives more accurate shape between maximum power

point and the open circuit voltage. It causes the voltage drops.

The shunt resistance Rsh provides the leakage current to the ground which ie very less with

respect to load current so that will be good to neglect it.

In an ideal, it is assumed that cell has Rsh = Rs = 0.

In above model the output current I is the difference of IL and normal diode current Io:

As per Shockley diode equation I = Is ( - 1) where I is the diode current, Is is the

reverse bias VD is the voltage across diode. And VT is the thermal voltage which is consider as

the voltage at normal temperature which is 25.85 mV at 300 K.

VT =

Where

q is the magnitude of charge on an electron 1.602 10-19

,

k is Boltzmanns constant,

T is the absolute temperature of the p-n junction in Kelvin.

I =IL- Io ( - 1) [for solar cell model]

The model included temperature dependence of the photo current IL and the saturation

current of diode Io.

IL = IL (T1) + Ko(T-T1)

Where

IL (T1) = Isc (T1,nom)

Ko =

I = Io

(T1)

Io (T1) =

A series resistance Rs was included; which represent the resistance inside each cell in the

connection between cells.

Rs = -

Xv = I0 (T1) -


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The current voltage curve for solar cell:

This characteristic shows the relation between voltage and current on the graph.

Current voltage I-V curve for a solar cell

As we know if the R is small then solar cell is suppose to operate in between region M and

N. where it delivers constant current to the load. In case if the R is large then the cell will

operate in region P-S. Then the solar cell will give constant voltage as the output which is

almost equal to Voc. [open circuit voltage]

Description:

This model is known as MSX60 PV. It is chosen because of its well known use and

application. In this model if the user change parameters according to new kind of

cells then he will be able to change an output of cell.

5.5 Combined Model


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Combine model single phase backup system

The whole model consists of variable voltage source rectifier charger unit, batteries to

Provide backup, inverter and single phase load.

The description of the whole model is given below:

In this model DFIG generates 400v 3 phase A.C. which will be transform to 230v Ac by using

/Y transformer by the formula 400/3 = 230.9 say 230 volts single phase. This electricity is

fed to linear single phase transformer which gives an output of 15.42 volts. Though it is not

the normal ratio of 10: 1 or something but no need to consider at this stage.

The output comes from charger [rectifier ] unit is pure dc and is feed to battery bank which

are 10 batteries connected in series to charge which are lead acid and has nominal voltage

of 1.2 volts and 1.5 Ah of capacity and internal resistance of 0.02 ohms() . In this model

those are fully discharged.

There is a current limiting resistance of 200 is added to limit current as well as it is a part

of RC filter. Remember that the rectifier unit can be work as both constant current charging

and constant voltage charging.

After that the same dc supply is connected to 3 levels IGBT inverter which converts Dc

current to Ac current. This unit will provide the output of 12v Ac which is not enough to

connect to the main bus. So there is a step up transformer is used to transform 12v to 230Vac with 50 Hz frequency. There is no particular VA ratings are available for this system.

Now this 230v Ac is synchronised with main bus of owners house. And as we know there is

already a load connected there so whenever there is an electricity generating near to the

load, then the load is supposed to use the generated electricity. And if the load is off then

that electricity will charge the batteries apart from that if the batteries are charged and load

is off then the generated electricity will transmitted to power grid so that the other user can

use it. There are some assumptions taken while creating a model.

Now, the calculation for above descriptions is as below:


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Somehow, the generated voltages are 230V rms. And is fed to 230v/15.42 step down

transformer. So the peak value will be .

Vrms = Vp/2

Vp = 27.33 2

Vp = 38.6 V

Now, Avg Value VDC = Vavg

VDC = (2(38.61.4))/

VDC = 25.5 volt.

Now the current limiting resistor R of 5100 is used as filter and capacitor of 100F. With

small amount of capacitance matlab takes too much time to run the model.

Now, Vripple = VDC/2 (R f C);

= 25.5/ (51001000.0001)

= 0.5 V.

So as per formula the final output is 25.75 say 26V as shown in test results.

Actually that would be best option to provide regulated power supply by using Zener Diode

or voltage regulated IC normally IC 78XX where XX stand for output voltage here we can use

7812. To get exact output regulated supply

6.0 Simulation Results6.1 Rectifier


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Fig. 6.1.1 The out of rectifier unit tested in Microcap

The above waveform is the output of the rectifier unit tested in microcap. The blue line

shows the input AC voltage which has zero average value. And as discussed in the rectifier

theory it gives the output of 25.899 V, which is shown in red line.

Fig. 6.1.2 Output waveform of variable voltage source.

The above waveforms are of variable voltage device which generates voltage and changesits amplitude with respect to time. The parameters are entered such as the output voltage

VDC with ripple

voltage of 0.5V


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start at 255V at 0 seconds, At 0.25 S the voltage set to 230 V and once again increase to

285V and after 0.10S, the voltage level again set to 230V.

6.2 DFIG

Fig 6.2.1 The output of DFIG

As shown in above waveform, the grid and DFIG are same voltage levels 565V. The outputvoltage of the Grid is 326V which is phase voltage. Though there is a variation in the current

waveform of the both DFIG and grid, but still it varies between 2.724 and 2.724, and 0.8363

to 0.8363 Amps respectively. This waveform shows the values in respect to magnitude. It

does not show frequency. After 150 seconds the average value of the current remains

constant and does not varies with time.


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Fig 6.2.2 Testing results of DFIG [High grid voltage]

The output voltage of the DFIG increases as the Grid voltage increase. And the current of the DFIG

increases to 4.5A, which is almost double than the normal condition (2.7A).

Fig 6.2.3 Testing results of DFIG [Low grid voltage]

Fig 6.2.3 shows the output of the DFIG in low voltage condition. as the grid voltage drop by 15 V

current of the DFIG also reduces and set to nearly 2.15 V.


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Fig 6.2.4 Output of Load @ 565V

The above figure shows that the two loads of 1000W and 833W drags the current of 1.023A and

0.85A respectively. It remains costant during the whole period and chages only when the supply

voltage changes.

Fig 6.2.5 starting of DFIG

From figure 6.2.5 it can be shown that the DFIG stats delivering current after 1 second. Before that it

act as a motor and absorbs current from the grid which helps to charge the stator windings of the

system.


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6.3 Combined Model

Fig 6.3.1 The output of combine model with variable voltage.

As shown in figure the output of the inverter varies as the input DC voltage varies. In first

few seconds as the DC voltage is not smooth enough and is also rising, the output voltage ofthe inverter also increases. And set down to the certain value only when the DC voltage

becomes stable.


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Fig 6.3.2 The output of combine model without variable voltage

In the above figure it is easy to conclude that the output voltage of the inverter set to 230V

AC, only when the DC voltage of the battery is set to about 38V. The whole system takes 0.1

second to set the DC and AC voltage level. The vertical white line in the output of thesecondary windings shows the power loss cause because of the copper and iron losses in

the transformer.

7.0 DiscussionThe model used in this project emits 1.525 KW of active power at 565 V which is shown in

figure 6.2.1

The background material presented in Section 5.2 shows that...

The generated voltage is AC and also does not remains constant as the wind speed varies

every second. Therefore it is necessary to convert it in to DC so that energy can be stored in

batteries as a backup. The input and output wave forms are shown in figure 6.1 the output

DC has ripple of 0.5V only. Thus this unit provide smooth DC voltage of 25.904V, which will

charge the batteries only when the demand is lower than generation.

The load of the house does not remain constant it can be vary every hours, minutes and so

on. As the load varies it drag more or less current from the inverter hence, the load current

changes. Thus by the formula Vripple = IL/2fC the ripple voltage changes and thus the output

of the rectifier varies as per the load varies.

According to the law of energy conservation Energy neither be created nor be destroyed

thus the generated electricity must be utilise or should be stored. In the model named

Domestic purpose DFIG.mdl, if the load is not available or somehow the generation is more

than demand then the generated electricity will stored in batteries in the form chemical

energy. As the batteries have their own capacity and it cannot be overcharged, in case if the

batteries are fully charged then this generated energy will be transmitted to grid.

The models creation as the part of simulation revealed that...

To make DFIG working it is necessary to connect a load with it. Two loads of 1000W and

833W are selected randomly. Hence this load of 1000W and 833W drag current of 1.023

and 0.85 ampere respectively at 565 V. This is shown in figure 6.2.4. The amount of the

current drag by the load can be found from the formula P = 3 VL IL Cos where VL and IL are

line voltage and line current respectively.

The models created as a part of the simulation proves that...

In normal condition the maximum output current drag from the computer can be 2.7A.From which 1.023 + 0.85 A flows in to the load. And the rest of the current flow back to the


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grid. This theory can be solved by the applying Kirchhoffs law of current. Thus, IDFIG = ILOAD1 +

ILOAD2 + IGRID. The results says that in peak hours if the load drag more current than generated

then DFIG provides the same output at 2.7A but the rest of current will be drag from the

grid thus this model also comply with peak hours.

From the tests shows that when DFIG is connected to the grid then the output voltage does

not varies with wind speed just because of connected directly to the grid. But the output

current of the generator becomes zero for few seconds. After that generator starts acting as

an induction motor of 1500W [2 H.P.] and drag current of 2.7A from grid. On the same time

if the wind starts again then it can damage the windings of the generated as the block rotor

condition. To secure this unwanted condition it is important to install circuit breakers which

can isolate the device whenever the reverse flow of current occurs or wind speed varies.

This device also known as STATCOM.

The tests also results that... In such condition if the grid voltage varies then the output of

the DFIG also varies as the grid voltage increases the flux related with stator and rotor

winding increases by formula ( = LI) where I = V/Z *windings+. Finally the energy stored in

coil increases by 0.5 LI2

and the output voltage as well as current increases for fraction of

seconds and then as the grid voltage set to its original value the whole system balanced

itself. But during this period DFIG provides output on 4.5A which is almost double than the

2.7A. This situation can cause damage in DFIG windings. So, it is important to keep an eye on

grid voltages. apart from that when the grid voltage increase the small amount of reverse

current also flow in generator for fraction of second which has enough ability to damage thewinding. But somehow if the condition keeps continue than the above event occurs and

DFIG delivers more current. The whole event showed in figure 6.2.2.

The model demonstrates that

As per the value of the stator and rotor impedance the DFIG generates 565.6 V and delivers

1.525 KW which means maximum amount of the current can be drag from this generator is

2.7A at 565V.

By looking at the wind turbine characteristic of the minimum Turbine requirement of the

wind speed is 8 m/s. And it should remain in between 8 and 11 m/s. The mechanical power

varies as the wind speed varies it can be define by the formula Pmech. = 0.5 R2CpV

3

where, Cp and R is the power coefficient and Radius of turbine respectively. If the DFIG is

not synchronised and if the wind speed varies then the terminal voltage of the generator

also varies. Once the generator is synchronised with the grid then voltage does not varies as

per the speed but the output power of the generator varies as per the torque varies. Where

torque can be define by the formula Pmech= 2NT/60 where, N is RPM ,T is torque and Pmech

is mechanical power


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Another requirement for the DFIG is to connect it to the grid because it does not contain

any PMMC device. Only the stator of the DFIG can be connected to the grid. Engineer must

not connect the rotor windings to the grid because rotor contain electronic device such as

rectifier and inverter.This generator absorbs reactive component from the grid and delivers

active power.

Va = -Ria -

=

where,

Ls &Ms are self and mutual inductance of armature coil. a is the flux linkage with coil.

(Grainger and Jr.) So if the grid is not connected then there will not be any ia [rotor current]

so there will not be any generation.

Losses: In this project the loads are used near to the generating station so there should not

be any transmission losses. But as shown in fig 6.2.4, the voltage of the 1000w load is

0.0816V less then generated voltage. The reason behind that problem is the transformer.

This linier ground transformer is used to get the neutral point, which means it does not

step-up or step-down voltage level but by locking at the parameters it can be said that the

impedance of secondary winding is smaller than primary. Apart from that it is impossible to

build a transformer without losses [hysteresis-Iron-copper losses]. So because of that iron

and copper losses the voltage on the secondary side reduced by 0.0816V.

From figure 6.2.5 it can be define that DFIG takes almost 1 second to stable the current. At

zero seconds windings are fully discharged and the grid is providing current to load. At 0.01

second DFIG start generating electricity and deliver to load and grid, because of what the

current drops down after few seconds and DFIG start absorbing current back from grid. The

whole process occurs till 1.1 second and after that the current stops fluctuating and start

developing from 0.6 A to 2.7 A full load.

Normally grid voltage and frequency remains constant through the time, but in case such as

the sudden increase in load or somehow, the generators stops delivering power. If the grid

voltage drops suddenly then DFIG will start delivering more current in respect to set the

voltage back to the normal. Apart from that at low voltage, load will drag more current from

the system. Hence, after few seconds DFIG will be overloaded and stops working. But if the

grid voltage drops linearly than the output of the DFIG also decrease as stator drag less

current for excitation. This is shown in figure 6.2.3.

Finally the tests done on combine model contain generator, backup system and inverter

shows that


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Considering the batteries are full charged and if the load demand is more than the

generation then the rest of the current will provided by the batteries. In condition such as

the batteries are completely discharged than the rest of the current will be provided by the

grid. Same way, if the demand is less than the generation then the rest of the current will be

used to charge the batteries. If the batteries are fully charged, than the rest of the currentwill be sent to grid.

As shown in the figure 6.3.2 if the DC voltage, fed the inverter remains constant than the

output of the system remains constant. But in case if the DC voltage of the system varies

than the output of the rectifier also varies. This is show in figure 6.3.1. If the filter capacitors

are not fully charged than as the voltage varies the output of DC rectifier also varies. If the

filter capacitors are charged enough, it can help to maintain voltage level.

7.1 Power Factor Analysis

Power factor is the cosine angle of difference between voltage and current drawn by load

from source. When current leads the voltage p.f. is called leading otherwise lagging. When

the value of Cos = 1, the power factor called unity and that means both the voltage and

current are in phase with each other.

The facts related to power factor are given below.

If the circuit is purely inductive then the current leads voltage by 90o and the average power

is zero. Same way, if the circuit is purely capacitive then the current lags voltage by 90o and

the average power is zero. It is impossible to build purely inductive or capacitive circuit and

that is why when the capacitors of large amount are kept on for long time absorbs active

power because of the resistance. And user has to pay for that.

In this project the load is purely resistive hence, the power factor is unity for the whole

system.

7.2 Fault tolerance

The output of the DFIG does not remain constant. The variable voltage source was used in

this model to make it more realistic. That is why the variable voltage source was built.


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Variable voltage source

This model varies the output voltage by e

Alternative Energy Generation

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