elimination of harmonics in multi level converter

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Dept. Of EEE SKIT Page 1

1. INTRODUCTION

With increasing concern of global warming and the depletion of fossil fuel

reserves, many are looking at sustainable energy solutions to preserve the earth for the future

generations. Other than hydro power, wind and photovoltaic energy holds the most

potential to meet our energy demands. Alone, wind energy is capable of supplying large

amounts of power but its presence is highly unpredictable as it can be here one moment and

gone in another. Similarly, solar energy is present throughout the day but the solar

irradiation levels vary due to sun intensity and unpredictable shadows cast by clouds, birds,

trees, etc. The common inherent drawback of wind and photovoltaic systems are their

intermittent natures that make them unreliable. However, by combining these two

intermittent sources and by incorporating maximum power point tracking (MPPT)

algorithms, the systems power transfer efficiency and reliability can be improved

significantly.

When a source is unavailable or insufficient in meeting the load demands, the other

energy source can compensate for the difference. Several hybrid wind/PV power systems

with MPPT control have been proposed and discussed in works. Most of the systems in

literature use a separate DC/DC boost converter connected in parallel in the rectifier stage as

shown in Figure 1.1 to perform the MPPT control for each the renewable energy power

sources. A simpler multi input structure has been suggested by that combine the sources

from the DC-end while still achieving MPPT for each renewable source. The structure

proposed by is a fusion of the buck and buck-boost converter. The systems in literature

require passive input filters to remove the high frequency current harmonics injected into

wind turbine generators.


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The harmonic content in the generator current decreases its lifespan and increases the

power loss due to heating. In this project, an alternative multi-input rectifier structure is

proposed for hybrid wind/solar energy systems. The proposed design is a fusion of the Cuk

and SEPIC converters.

The features of the proposed topology are:

1)

The inherent nature of these two converters eliminates the need for separate

input filters for PFC;

2) It can support step up/down operations for each renewable source (can support

wide ranges of PV and wind input);

3)

MPPT can be realized for each source;

4)

Individual and simultaneous operation is supported.

Figure 1.1: Hybrid system with multi-connected boost converter.


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2. ENERGY

Inphysics,energy is an indirectly observed quantity. It is often understood as the

ability aphysical system has to dowork on other physical systems. The word energyderives

from the Greek word n rg i , which possibly appears for the first time in the work

ofAristotle in the 4th century BCE. The energy cannot be created nor destroyed. It is

changed from one form to another form. This is called Conservation of energy.

2.1. Energy Resources:

A source of energy is one that can provide adequate amount of energy in a use full

form over a long period of time. Energy is important input for development. The energy

need of a country is taken as the index of the development of that country.

There are 2 types of energy resources. They are

I.

Non-renewable (or) Conventional energy resources

II. Renewable (or) Non-conventional energy resources

2.2. Non-renewable energy resources:

A non renewable resourceis anatural resource which cannot be produced, grown,

generated, or used on a scale which cansustain its consumption rate, once depleted there is

no more available for future needs. Also considered non-renewable are resources that are

consumed much faster than nature can create them.Fossil fuels (such ascoal,petroleum,

andnatural gas),nuclear power (uranium) and certainaquifers are examples. In contrast,

resources such astimber (whenharvested sustainably) or metals (which can berecycled)

are consideredrenewable resources.
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2.2.1. Fossil fuel:

Natural resources such ascoal,petroleum (crude oil) andnatural gas take thousands of

years to form naturally and cannot be replaced as fast as they are being consumed.

Eventually natural resources will become too costly to harvest and humanity will need to

find other sources of energy.

At present, the main energy source used by humans are non-renewable fossil fuels, as

a result of continual use since the firstinternal combustion engine in the 17th century, the

fuel is still in high demand with conventionalinfrastructure andtransport which are fittedwith the combustion engine. The continual use of fossil fuels at the current rate will

increaseglobal warming and cause more severeclimate change.

Advantages:

These can be found in lots of places in the world.

These can be easily transported to the power stations.

These are relatively cheap energy sources.
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Disadvantages:

Environmental damage can be caused when dig up them.

Coal, Oil and gas are not renewable, so once the supplies are used, they will run out.

Burning these fuels releases greenhouse gases into the air. This may add to global

warming.

2.2.2. Radioactive fuel:

The use ofnuclear technology requires aradioactive fuel.Uraniumore is present in

the ground at relatively low concentrations andmined in 19 countries. The uranium

resource is used to create plutonium, uranium-238 isfissionable and istransmuted into

fissileplutonium-239 in anuclear reactor.Nuclear fuel is used for the production ofnuclearweapons and innuclear power stations to create electricity.

Advantages:

Nuclear fuel does not make harmful greenhouse gases.

You only need a very small amount of nuclear fuel to make a lot of energy

Disadvantages:

The waste that is produced when using nuclear fuel is radioactive and very harmful.

It needs to be disposed of carefully

Nuclear power stations are at risk from terrorist attack and sabotage.

World uranium supplies may run out in about 50 years.
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2.3. Renewable energy resources:

Renewable energy isenergy which comes fromnatural resources such as sunlight,

wind, rain,tides,andgeothermal heat,which arerenewable (naturally replenished). About

16% of global final energy consumption comes from renewables, with 10% coming from

traditionalbiomass,which is mainly used forheating,and 3.4% fromhydroelectricity.New

renewables (small hydro, modern biomass, wind, solar, geothermal, and biofuels) accounted

for another 3% and are growing very rapidly. The share of renewables in electricity

generation is around 19%, with 16% of global electricity coming from hydroelectricity and

3% from new renewables.

2.3.1. Solar Power:

Solar power is the conversion ofsunlight into electricity, either directly using

photovoltaics (PV), or indirectly usingconcentrated solar power (CSP). Concentrated solar

power systems use lenses or mirrors and tracking systems to focus a large area of sunlight

into a small beam. Photovoltaics convert light into electric current using thephotoelectric

effect.

2.3.2. Wind Power:

Wind poweris the conversion ofwind energy into a useful form of energy, such as

usingwind turbines to make electricity,windmills for mechanical power, windpumps for

water pumping ordrainage,orsails to propel ships.

We are discussed deeply about solar and wind powers in next chapters.
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3. Solar Power

Solar power

is the conversion ofsunlight into electricity, either directly using

photovoltaics (PV), or indirectly usingconcentrated solar power(CSP). Concentrated solar

power systems use lenses or mirrors and tracking systems to focus a large area of sunlight

into a small beam. Photovoltaics convert light into electric current using thephotoelectric

effect.

Commercial concentrated solar power plants were first developed in the 1980s. The

354 MWSEGS CSP installation is the largest solar power plant in the world, located in

theMojave Desert of California. Other large CSP plants include theSolnova Solar Power

Station (150 MW) and theAndasol solar power station (150 MW), both in Spain. The 200

MWGolmud Solar Park inChina,is theworlds largestphotovoltaic plant.

3.1. Photovoltaics:

Asolar cell, or photovoltaic cell (PV), is a device that converts light into electric

current using thephotoelectric effect.The first solar cell was constructed byCharles Fritts inthe 1880s. In 1931 a German engineer, Dr Bruno Lange, developed a photo cell using silver

selenide in place of copper oxide. Although the prototypeselenium cells converted less than

1% of incident light into electricity, bothErnst Werner von Siemens andJames Clerk

Maxwell recognized the importance of this discovery. Following the work ofRussell Ohl in

the 1940s, researchers Gerald Pearson,Calvin Fuller and Daryl Chapin created the

silicon solar cell in 1954. These early solar cells cost 286 USD/watt and reached efficiencies

of 4.56%. Photovoltaic power generation employssolar panels composed of a number

ofsolar cells containing a photovoltaic material. Materials presently used for photovoltaics

include monocrystalline silicon,polycrystalline silicon,amorphous silicon,cadmium

telluride,andcopper indium gallium selenide/sulfide.
http://en.wikipedia.org/wiki/Sunlighthttp://en.wikipedia.org/wiki/Electricityhttp://en.wikipedia.org/wiki/Photovoltaicshttp://en.wikipedia.org/wiki/Concentrated_solar_powerhttp://en.wikipedia.org/wiki/Photoelectric_effecthttp://en.wikipedia.org/wiki/Photoelectric_effecthttp://en.wikipedia.org/wiki/SEGShttp://en.wikipedia.org/wiki/Mojave_Deserthttp://en.wikipedia.org/wiki/Solnova_Solar_Power_Stationhttp://en.wikipedia.org/wiki/Solnova_Solar_Power_Stationhttp://en.wikipedia.org/wiki/Andasol_solar_power_stationhttp://en.wikipedia.org/wiki/Huanghe_Hydropower_Golmud_Solar_Parkhttp://en.wikipedia.org/wiki/Chinahttp://en.wikipedia.org/wiki/List_of_photovoltaic_power_stationshttp://en.wikipedia.org/wiki/List_of_photovoltaic_power_stationshttp://en.wikipedia.org/wiki/Photovoltaic_planthttp://en.wikipedia.org/wiki/Solar_cellhttp://en.wikipedia.org/wiki/Photoelectric_effecthttp://en.wikipedia.org/wiki/Charles_Frittshttp://en.wikipedia.org/wiki/Seleniumhttp://en.wikipedia.org/wiki/Ernst_Werner_von_Siemenshttp://en.wikipedia.org/wiki/James_Clerk_Maxwellhttp://en.wikipedia.org/wiki/James_Clerk_Maxwellhttp://en.wikipedia.org/wiki/Russell_Ohlhttp://en.wikipedia.org/wiki/Calvin_Fullerhttp://en.wikipedia.org/wiki/Siliconhttp://en.wikipedia.org/wiki/Solar_panelhttp://en.wikipedia.org/wiki/Solar_cellhttp://en.wikipedia.org/wiki/Monocrystalline_siliconhttp://en.wikipedia.org/wiki/Polycrystalline_siliconhttp://en.wikipedia.org/wiki/Amorphous_siliconhttp://en.wikipedia.org/wiki/Cadmium_telluridehttp://en.wikipedia.org/wiki/Cadmium_telluridehttp://en.wikipedia.org/wiki/Copper_indium_gallium_selenidehttp://en.wikipedia.org/wiki/Copper_indium_gallium_selenidehttp://en.wikipedia.org/wiki/Cadmium_telluridehttp://en.wikipedia.org/wiki/Cadmium_telluridehttp://en.wikipedia.org/wiki/Amorphous_siliconhttp://en.wikipedia.org/wiki/Polycrystalline_siliconhttp://en.wikipedia.org/wiki/Monocrystalline_siliconhttp://en.wikipedia.org/wiki/Solar_cellhttp://en.wikipedia.org/wiki/Solar_panelhttp://en.wikipedia.org/wiki/Siliconhttp://en.wikipedia.org/wiki/Calvin_Fullerhttp://en.wikipedia.org/wiki/Russell_Ohlhttp://en.wikipedia.org/wiki/James_Clerk_Maxwellhttp://en.wikipedia.org/wiki/James_Clerk_Maxwellhttp://en.wikipedia.org/wiki/Ernst_Werner_von_Siemenshttp://en.wikipedia.org/wiki/Seleniumhttp://en.wikipedia.org/wiki/Charles_Frittshttp://en.wikipedia.org/wiki/Photoelectric_effecthttp://en.wikipedia.org/wiki/Solar_cellhttp://en.wikipedia.org/wiki/Photovoltaic_planthttp://en.wikipedia.org/wiki/List_of_photovoltaic_power_stationshttp://en.wikipedia.org/wiki/Chinahttp://en.wikipedia.org/wiki/Huanghe_Hydropower_Golmud_Solar_Parkhttp://en.wikipedia.org/wiki/Andasol_solar_power_stationhttp://en.wikipedia.org/wiki/Solnova_Solar_Power_Stationhttp://en.wikipedia.org/wiki/Solnova_Solar_Power_Stationhttp://en.wikipedia.org/wiki/Mojave_Deserthttp://en.wikipedia.org/wiki/SEGShttp://en.wikipedia.org/wiki/Photoelectric_effecthttp://en.wikipedia.org/wiki/Photoelectric_effecthttp://en.wikipedia.org/wiki/Concentrated_solar_powerhttp://en.wikipedia.org/wiki/Photovoltaicshttp://en.wikipedia.org/wiki/Electricityhttp://en.wikipedia.org/wiki/Sunlight


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Due to the growing demand forrenewable energy sources, the manufacturing of solar

cells andphotovoltaic arrays has advanced considerably in recent years. Solar photovoltaics

are growing rapidly, albeit from a small base, to a total global capacity of

67,400megawatts (MW) at the end of 2011, representing 0.5% of worldwide electricity

demand. The total power output of the worlds PV capacity run over a calendar year is equal

to some 80 billion kWh of electricity.

This is sufficient to cover the annual power supply needs of over 20 million

households in the world. More than 100 countries use solar PV. Installations may be

ground-mounted (and sometimes integrated with farming and grazing) or built into the roof

or walls of a building (building-integrated photovoltaics).

Driven by advances in technology and increases in manufacturing scale and

sophistication, the cost of photovoltaics has declined steadily since the first solar cells were

manufactured and the levelised cost of electricity (LCOE) from PV is competitive with

conventional electricity sources in an expanding list of geographic regions. Net metering and

financial incentives, such as preferentialfeed-in tariffs for solar-generated electricity, have

supported solar PV installations in many countries.

3.2. Solar cells:

Photovoltaics are best known as a method for generating electric power by using solar

cells to convert energy from the sun into a flow of electrons. Thephotovoltaic effect refers to

photons of light exciting electrons into a higher state of energy, allowing them to act as

charge carriers for an electric current. The photovoltaic effect was first observed by

Alexandre-Edmond Becquerel in 1839. The term photovoltaic denotes the unbiased

operating mode of aphotodiode in which current through the device is entirely due to the

transduced light energy. Virtually all photovoltaic devices are some type of photodiode.
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Fig 3.1: Solar cells produce electricity directly from sunlight.

Solar cells produce direct current electricity from sun light, which can be used to

power equipment or torecharge a battery.The first practical application of photovoltaics was

to power orbiting satellites and otherspacecraft, but today the majority ofphotovoltaic

modules are used for grid connected power generation. In this case aninverter is required to

convert the DC to AC. There is a smaller market for off-grid power for remote dwellings,

boats, recreational vehicles, electric cars, roadside emergency telephones,remote sensing,

andcathodic protection ofpipelines.

Photovoltaic power generation employssolar panels composed of a number ofsolar

cells containing a photovoltaic material. Materials presently used for photovoltaics include

monocrystalline silicon,polycrystalline silicon,amorphous silicon,cadmium telluride,and

copper indium gallium selenide/sulfide. Due to the growing demand forrenewable energy

sources, the manufacturing of solar cells andphotovoltaic arrays has advanced considerably

in recent years.

Cells require protection from the environment and are usually packaged tightly

behind a glass sheet. When more power is required than a single cell can deliver, cells are

electrically connected together to form photovoltaic modules, or solar panels. A single

module is enough to power an emergency telephone, but for a house or a power plant the

modules must be arranged in multiples asarrays.
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A significant market has emerged in off-grid locations for solar-power-charged

storage-battery based solutions. These often provide the only electricity available. The first

commercial installation of this kind was in 1966 on Ogami Island in Japan to transition

Ogami Lighthouse from gas torch to fully self-sufficient electrical power.

Due to the growing demand for renewable energy sources, the manufacture of solar

cells andphotovoltaic arrays has advanced dramatically in recent years.

Solar photovoltaics are growing rapidly, albeit from a small base, to a total global

capacity of 67,400megawatts (MW) at the end of 2011, representing 0.5% of worldwide

electricity demand. The total power output of the worlds PV capacity run over a calendar

year is equal to some 80 billion kWh of electricity. This is sufficient to cover the annual

power supply needs of over 20 million households in the world. More than 100 countries use

solar PV. World solar PV capacity (grid-connected) was 7.6 GW in 2007, 16 GW in 2008, 23

GW in 2009, and 40 GW in 2010. More than 100 countries use solar PV. Installations may be

ground-mounted (and sometimes integrated with farming and grazing) or built into the roof

or walls of a building (building-integrated photovoltaics).

Photovoltaic power capacity is measured as maximum power output under

standardized test conditions (STC) in "Wp" (Watts peak). The actual power output at a

particular point in time may be less than or greater than this standardized, or "rated," value,

depending on geographical location, time of day, weather conditions, and other factors. Solar

photovoltaic arraycapacity factors are typically under 25%, which is lower than many other

industrial sources of electricity.

The EPIA/Greenpeace Advanced Scenario shows that by the year 2030, PV systems

could be generating approximately 1.8 TW (Terawatt=1012) of electricity around the world.

This means that, assuming a serious commitment is made toenergy efficiency,enough solar

power would be produced globally in twenty-five years time to satisfy the electricity needs

of almost 14% of the worlds population.
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3.3. Photovoltaic power systems:

Fig 3.2: Photovoltaic power system circuit.

Solar cells produce direct current (DC) power, which fluctuates with the intensity of

the irradiated light. This usually requires conversion to certain desired voltages or alternating

current (AC), which requires the use of theinverters. Multiple solar cells are connected

inside the modules. Modules are wired together to form arrays, then tied to inverter, which

produces power with the desired voltage and frequency/phase (when itsAC).

Many residential systems are connected to the grid wherever available, especially in

the developed countries with large markets. In these grid-connected PV systems, use of

energy storages are optional. In certain applications such as satellites, lighthouses, or in

developing countries, batteries or additional power generators are often added as back-ups,

which formsstand-alone power systems.
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3.4. Economics:

Photovoltaic power

worldwideGWp

2005 5.4

2006 7.0

2007 9.4

2008 15.7

2009 22.9

2010 39.7

2011 67.4

Year end capacities

Financial incentives for photovoltaics,such asfeed-in tariffs,have often been offered

to electricity consumers to install and operate solar-electric generating systems. Government

has sometimes also offered incentives in order to encourage the PV industry to achieve the

economies of scale needed to compete where the cost of PV-generated electricity is above

the cost from the existing grid. Such policies are implemented to promote national or

territorialenergy independence,high techjob creation and reduction ofcarbon dioxide

emissions which cause global warming. Due to economies of scale solar panels get less costly

as people use and buy more as manufacturers increase production to meet demand, the

cost and price is expected to drop in the years to come.
http://en.wikipedia.org/wiki/Gigawatt-peakhttp://en.wikipedia.org/wiki/Gigawatt-peakhttp://en.wikipedia.org/wiki/Gigawatt-peakhttp://en.wikipedia.org/wiki/Financial_incentives_for_photovoltaicshttp://en.wikipedia.org/wiki/Feed-in_tariffshttp://en.wikipedia.org/wiki/Economies_of_scalehttp://en.wikipedia.org/wiki/Energy_independencehttp://en.wikipedia.org/wiki/High_techhttp://en.wikipedia.org/wiki/Carbon_emissionshttp://en.wikipedia.org/wiki/Carbon_emissionshttp://en.wikipedia.org/wiki/Carbon_emissionshttp://en.wikipedia.org/wiki/Carbon_emissionshttp://en.wikipedia.org/wiki/High_techhttp://en.wikipedia.org/wiki/Energy_independencehttp://en.wikipedia.org/wiki/Economies_of_scalehttp://en.wikipedia.org/wiki/Feed-in_tariffshttp://en.wikipedia.org/wiki/Financial_incentives_for_photovoltaicshttp://en.wikipedia.org/wiki/Gigawatt-peak


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3.5. Advantages:

The 89PW(Petawatt=1015)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/m) 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 interventionafter their initial set-up, so after the initialcapital 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, experimentalhigh 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.

3.6. Disadvantages:

It is relatively expensive to build solar power stations.

When it is cloudy or at night there is not enough light so no electricity can be made.

Some people dont like the look of solar panels.
http://en.wikipedia.org/wiki/Orders_of_magnitude_(power)#petawatt_.281015_watts.29http://en.wikipedia.org/wiki/Orders_of_magnitude_(power)#petawatt_.281015_watts.29http://en.wikipedia.org/wiki/Capital_costhttp://en.wikipedia.org/wiki/Operating_costhttp://en.wikipedia.org/wiki/High_efficiency_solar_cellshttp://en.wikipedia.org/wiki/High_efficiency_solar_cellshttp://en.wikipedia.org/wiki/Operating_costhttp://en.wikipedia.org/wiki/Capital_costhttp://en.wikipedia.org/wiki/Orders_of_magnitude_(power)#petawatt_.281015_watts.29


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4. Wind Energy

The Earth is unevenly heated by the sun, such that the poles receive less energy from

the sun than the equator; along with this, dry land heats up (and cools down) more quickly

than the seas do. The differential heating drives a globalatmospheric convection system

reaching from the Earth's surface to thestratosphere which acts as a virtual ceiling. Most of

the energy stored in these wind movements can be found at high altitudes where continuous

wind speeds of over 160 km/h (99 mph) occur. Eventually, the wind energy is converted

through friction into diffuse heat throughout the Earth's surface and the atmosphere.

The total amount of economically extractable power available from the wind is

considerably more than present human power use from all sources. Axel Kleidon of the Max

Planck Institute in Germany did a "top down" calculation on how much wind energy there

is, starting with the incoming solar radiation that drives the winds by creating temperature

differences in the atmosphere. He concluded that somewhere between 18 TW and 68 TW

could be extracted. Cristina Archer andMark Z. Jacobson presented a "bottom-up" estimate,

which unlike Kleidon's are based on actual measurements of wind speeds, and found that

there is 1700 TW of wind power at an altitude of 100 meters over land and sea. Of this,

"between 72 and 170 TW could be extracted in a practical and cost-competitive manner".

4.1. Distribution of wind speed:

The strength of wind varies, and an average value for a given location does not alone

indicate the amount of energy a wind turbine could produce there. To assess the frequency

of wind speeds at a particular location, a probability distribution function is often fit to the

observed data. Different locations will have different wind speed distributions.

TheWeibull model closely mirrors the actual distribution of hourly wind speeds at many

locations. The Weibull factor is often close to 2 and therefore aRayleigh distribution can be

used as a less accurate, but simpler model.
http://en.wikipedia.org/wiki/Convection#Atmospheric_convectionhttp://en.wikipedia.org/wiki/Stratospherehttp://en.wikipedia.org/wiki/Mark_Z._Jacobsonhttp://en.wikipedia.org/wiki/Weibull_distributionhttp://en.wikipedia.org/wiki/Rayleigh_distributionhttp://en.wikipedia.org/wiki/Rayleigh_distributionhttp://en.wikipedia.org/wiki/Weibull_distributionhttp://en.wikipedia.org/wiki/Mark_Z._Jacobsonhttp://en.wikipedia.org/wiki/Stratospherehttp://en.wikipedia.org/wiki/Convection#Atmospheric_convection


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4.2. Wind Power:

Wind poweris the conversion ofwind energy into a useful form of energy, such as

usingwind turbines to make electricity,windmills for mechanical power, windpumps for

water pumping ordrainage,orsails to propel ships.

Fig 4.1: Wind power worldwide installed capacity

Fig 4.2: Wind power worldwide installed capacity forecast

Fig 4.3:Burbo Bank Offshore Wind Farm,at the entrance to theRiver Mersey in North West

England
http://en.wikipedia.org/wiki/Wind_energyhttp://en.wikipedia.org/wiki/Wind_turbinehttp://en.wikipedia.org/wiki/Windmillhttp://en.wikipedia.org/wiki/Windpumphttp://en.wikipedia.org/wiki/Water_pumpinghttp://en.wikipedia.org/wiki/Drainagehttp://en.wikipedia.org/wiki/Sailhttp://en.wikipedia.org/wiki/Burbo_Bank_Offshore_Wind_Farmhttp://en.wikipedia.org/wiki/River_Merseyhttp://en.wikipedia.org/wiki/File:Pretty_flamingos_-_geograph.org.uk_-_578705.jpghttp://en.wikipedia.org/wiki/File:GlobalWindPowerCumulativeCapacity-withForcast.pnghttp://en.wikipedia.org/wiki/File:GlobalWindPowerCumulativeCapacity.pnghttp://en.wikipedia.org/wiki/File:Pretty_flamingos_-_geograph.org.uk_-_578705.jpghttp://en.wikipedia.org/wiki/File:GlobalWindPowerCumulativeCapacity-withForcast.pnghttp://en.wikipedia.org/wiki/File:GlobalWindPowerCumulativeCapacity.pnghttp://en.wikipedia.org/wiki/File:Pretty_flamingos_-_geograph.org.uk_-_578705.jpghttp://en.wikipedia.org/wiki/File:GlobalWindPowerCumulativeCapacity-withForcast.pnghttp://en.wikipedia.org/wiki/File:GlobalWindPowerCumulativeCapacity.pnghttp://en.wikipedia.org/wiki/River_Merseyhttp://en.wikipedia.org/wiki/Burbo_Bank_Offshore_Wind_Farmhttp://en.wikipedia.org/wiki/Sailhttp://en.wikipedia.org/wiki/Drainagehttp://en.wikipedia.org/wiki/Water_pumpinghttp://en.wikipedia.org/wiki/Windpumphttp://en.wikipedia.org/wiki/Windmillhttp://en.wikipedia.org/wiki/Wind_turbinehttp://en.wikipedia.org/wiki/Wind_energy


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A largewind farm may consist of several hundred individualwind turbines which are

connected to theelectric power transmission network. Offshore wind power can harness the

better wind speeds that are available offshore compared to on land, so offshore wind powers

contribution in terms of electricity supplied is higher. Small onshore wind facilities are used

to provide electricity to isolated locations and utility companies increasinglybuy back

surplus electricity produced by small domestic wind turbines. Although a variable source of

power, theintermittency of wind seldom creates problems when using wind power to supply

up to 20% of total electricity demand, but as the proportion rises, increased costs, a need to

use storage such aspumped-storage hydroelectricity,upgrade the grid, or a lowered ability to

supplant conventional production may occur. Power management techniques such as excess

capacity, storage, dispatchable backing supply (usually natural gas), exporting and importing

power to neighboring areas or reducing demand when wind production is low, can mitigate

these problems.

Wind power, as an alternative tofossil fuels, is plentiful,renewable, widely

distributed, clean, produces nogreenhouse gas emissions during operation, and uses little

land. In operation, the overall cost per unit of energy produced is similar to the cost for new

coal and natural gas installations. The construction of wind farms is not universally

welcomed, but anyeffects on the environment from wind power are generally much less

problematic than those of any other power source.

4.3. Wind Farms:

A wind farm is a group ofwind turbines in the same location used for production of

electric power. A large wind farm may consist of several hundred individual wind turbines,

and cover an extended area of hundreds of square miles, but the land between the turbines

may be used for agricultural or other purposes. A wind farm may also be located offshore.
http://en.wikipedia.org/wiki/Wind_farmhttp://en.wikipedia.org/wiki/Wind_turbinehttp://en.wikipedia.org/wiki/Electric_power_transmissionhttp://en.wikipedia.org/wiki/Net_meteringhttp://en.wikipedia.org/wiki/Net_meteringhttp://en.wikipedia.org/wiki/Intermittent_power_sourceshttp://en.wikipedia.org/wiki/Pumped-storage_hydroelectricityhttp://en.wikipedia.org/wiki/Fossil_fuelhttp://en.wikipedia.org/wiki/Renewable_energyhttp://en.wikipedia.org/wiki/Greenhouse_gashttp://en.wikipedia.org/wiki/Environmental_impact_of_wind_powerhttp://en.wikipedia.org/wiki/Wind_turbinehttp://en.wikipedia.org/wiki/Wind_turbinehttp://en.wikipedia.org/wiki/Environmental_impact_of_wind_powerhttp://en.wikipedia.org/wiki/Greenhouse_gashttp://en.wikipedia.org/wiki/Renewable_energyhttp://en.wikipedia.org/wiki/Fossil_fuelhttp://en.wikipedia.org/wiki/Pumped-storage_hydroelectricityhttp://en.wikipedia.org/wiki/Intermittent_power_sourceshttp://en.wikipedia.org/wiki/Net_meteringhttp://en.wikipedia.org/wiki/Net_meteringhttp://en.wikipedia.org/wiki/Electric_power_transmissionhttp://en.wikipedia.org/wiki/Wind_turbinehttp://en.wikipedia.org/wiki/Wind_farm


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Many of the largest operational onshore wind farms are located in the US. As of

November 2010, theRoscoe Wind Farm is the largest onshore wind farm in the world at

781.5 MW, followed by theHorse Hollow Wind Energy Center (735.5 MW). As of

November 2010, theThanet Wind Farm in the UK is the largest offshore wind farm in the

world at 300 MW, followed byHorns Rev II (209 MW) in Denmark.

4.4 Offshore Wind Power:

Fig 4.4: aerial view of offshore wind power

Offshore wind power refers to the construction of wind farms in bodies of water togenerate electricity from wind. Better wind speeds are available offshore compared to on

land, so offshore wind powers contribution in terms of electricity supplied is higher.

4.5. Electricity Generation:

In awind farm,individual turbines are interconnected with a medium voltage (often

34.5 kV), power collection system and communications network. At a substation, this

medium-voltage electric current is increased in voltage with atransformer for connection to

the high voltageelectric power transmission system.
http://en.wikipedia.org/wiki/Roscoe_Wind_Farmhttp://en.wikipedia.org/wiki/Horse_Hollow_Wind_Energy_Centerhttp://en.wikipedia.org/wiki/Thanet_Wind_Farmhttp://en.wikipedia.org/wiki/Horns_Revhttp://en.wikipedia.org/wiki/Wind_farmhttp://en.wikipedia.org/wiki/Transformerhttp://en.wikipedia.org/wiki/Electric_power_transmissionhttp://en.wikipedia.org/wiki/File:Sund_mpazdziora.JPGhttp://en.wikipedia.org/wiki/Electric_power_transmissionhttp://en.wikipedia.org/wiki/Transformerhttp://en.wikipedia.org/wiki/Wind_farmhttp://en.wikipedia.org/wiki/Horns_Revhttp://en.wikipedia.org/wiki/Thanet_Wind_Farmhttp://en.wikipedia.org/wiki/Horse_Hollow_Wind_Energy_Centerhttp://en.wikipedia.org/wiki/Roscoe_Wind_Farm


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Fig4.5:Typical components of a wind turbine (gearbox,rotor shaft and brake assembly)

being lifted into position

The surplus power produced by domestic micro generators can, in some jurisdictions,

be fed into the network and sold to the utility company, producing a retail credit for the

micro generators' owners to offset their energy costs.

4.6. Advantages:

Wind is free and will not run out so the cost is in building the wind turbine.

Wind power generation does not create greenhouse gases.

There are very few safety risks with wind turbines.

4.7. Disadvantages:

We can only use windmills in areas where there is a lot of wind. Sometimes there

may be days where there is little wind.

We need a lot of turbines to make a lot of electricity.

Some people dont like the way wind turbines look, they think they spoil the

countryside.
http://en.wikipedia.org/wiki/Gearboxhttp://en.wikipedia.org/wiki/File:Scout_moor_gearbox,_rotor_shaft_and_brake_assembly.jpghttp://en.wikipedia.org/wiki/Gearbox


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2.1 Introduction:

In general increasing the switching frequency in voltage source inverters (VSI) leads to

the better output voltage/current waveforms. Harmonic reduction in controlling a VSI with

variable amplitude and frequency of the output voltages of importance and thus the conventional

inverters which are referred to us two level in inverters have required increase switching

frequency along with various PWM switching strategies in the case of high power / high voltage

applications ,however, the two level inverters has some limitations to operate at high frequency

mainly du e to switching losses and construction of rating itself, moreover, in the semi conductor

switching devices should be used in such a manner series /parallel combination s to obtain

capability of handling high power . Now a days the use of multilevel approach is believed to be

provision alternative in such a very high power conversion processing system. Advantages ofthis multilevel approach include good power quality, good electromagnetic compatibility (EMC),

low switching looses and high voltage capability.

Power electronics converters of a family of electrical circuits which converts electrical

energy from level of voltages / current/ frequency to another using semi conductor based

electronic switch. The essential characteristics of these types of circuits are that the switches are

operated only in one of two states either fully on or off.

The process of switching the electronic devices in a power electronic converter from one

state to another state is called modulation. Each family of power converters has proffered

modulation strategies associated with it that aim to optimize the circuit operation for the target

criteria most appropriate for the family .parameters such a switching frequency , distortion

,losses, harmonic generation ,and speed of responses are the issues which must be considered

when developing modulation strategizes for a particular family of converters .


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2.7 COMPARISON BETWEEN FOUR DIFFERENT FIVE-LEVEL

INVERTERS TOPOLOGIES:

Table 1:Comparison table for four different MLI

The above table compares the power component requirement per phase leg among the

four multilevel inverter topologies mentioned above. It shows that the number of main

switches, main diodes, and capacitors needed by the inverters to achieve the same no of voltage

levels. From the above comparison table we can say that auxiliary H-Bridge inverter is very

much suitable, and the no of components required are very less. As the no of components

reduces THD of the circuit will reduce.


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2.8 Simplified Block diagram of H-Bridge inverter:

Fig2.4Block diagram of H-BRIDGE inverter

2.9 AUXILLARY H-BRIDGE INVERTER:

Fig 2.5 H-Bridge Inverter

The proposed circuit is the single phase five level inverter. The schematic circuit of the

proposed is shown above. The above proposed inverter might be preferred not only under the

aspect of harmonic content reduction ,due to several level of the output voltage as an essential

feature of multilevel scheme, but also under the aspect of full utilization of semiconductor

devices in case that high voltage of dc-link could be applied.


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The five level inverter has very simple commutation sequence which could make it

possible to freely change output phase voltages between arbitrary two voltage levels, requiring

no additional commutation circuitry.

Commutation procedure between some levels should be divided in to each one level

commutation of unit change of voltage in order to guarantee voltage stress of both main switches

and main diodes with in limit level voltage even during transient time. One level commutation

can be carried out by first turning of the most upper (lower) main switch in one state and turning

on the opposite lower (upper) main switch in of state after required dead time. It should be noted

that such commutation sequence facilitates utilization of switching devices even with different

turn off times.


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CHAPTER 3

CONFIGURATION ANDMODES OF OPERATION OF

AUXILARY H-BRIDGE

INVERTER

3.1 Auxiliary H-Bridge:


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Fig 3.1 Auxiliary H-Bridge

3.2 MODES OF OPERATION OF THE H-BRIDGE INVERTERCIRCUIT:

3.2.1 MODE1: To get +Vs Level

Fig 3.2Switching combination required to generate output voltage level Vs

3.2.2 MODE2: To get + Vs/2 level:


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Fig 3.3 Switching combination required to generate output voltage level +Vs/2

3.2.3 MODE3: To get Zero level:

Fig 3.4 Switching combination required to generate output voltage level Vs=0

3.2.4 MODE4: To get - Vs/2 level:


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Fig 3.5 Switching combination required to generate output voltage level -Vs/2

3.2.5 MODE5: To get -Vs Level:

Fig 3.6 Switching combination required to generate output voltage level Vs.

3.2.6 Power Stage Operation:


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The required five voltage output levels (Vs, Vs/2, 0, -Vs/2, -Vs) are generated as

follows:

1) Maximum positive output, Vs: Switch S1 is ON, connecting the load positive terminal to

Vs, and switch S4 is ON, connecting the load negative terminal to ground. All other

controlled switches are OFF; the voltage applied to the load terminals is Vs. Fig.

3.2shows the current paths that are active at this stage.

2) Half-level positive output, Vs/2: The auxiliary switch S5 is ON, connecting to load

terminal through diodes D5 and D8, and S4 is ON, connecting to another load terminal to

the ground. All other controlled switches are OFF; the voltage applied to the load

terminals is Vs/2. Fig. 3.3shows the current paths that are active at this stage.

3) Zero output: Two main switches S3 and S4 are ON, short-circuiting the load. All other

controlled switches are OFF; the voltage applied to the load terminals is Zero. Fig.


4) Half-level negative output,- Vs/2: The auxiliary switch S5 is ON, connecting to load

terminal through diodes D6 and D7, and S2 is ON, connecting to another load terminal to

the ground. All other controlled switches are OFF; the voltage applied to the load

terminals is -Vs/2. Fig. 3.5shows the current paths that are active at this stage.

5) Maximum negative output, -Vs: Switch S2 is ON, connecting the load negative terminal

to Vs, and switch S3 is ON, connecting the load positive terminal to ground. All other

controlled switches are OFF; the voltage applied to the load terminals is Vs. Fig.



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3.2.7 SWITCHING COMBINATIONS REQUIRED TO GENERATE THE

FIVE-LEVEL OUTPUT VOLTAGE WAVEFORM SHOWN IN TABLE

FORMAT:

Table 3.1 switching combinations required to generate the five-level output voltage

CHAPTER 4


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Modulation topologies

For

Multilevel Inverters

4.1 INTRODUCTION:

The multilevel topology involves several modulation techniques. Each technique involves

different modulation methods.

Multilevel Modulations

Fundamental

Frequency Switching

PWM


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Fig 4.1 : Multilevel modulation techniques.

4.2 Pulse width modulation techniques:

The advent of the transformer less multilevel inverter topology has brought forth various

pulse width modulation (PWM) schemes as a means to control the switching action of the active

devices in each of the multilevel voltage levels in the inverters. The most efficient method of

controlling the output voltage is to incorporate pulse width modulation control within the

inverters.

In this method a fixed dc input voltage is supplied to the inverter and a controlled ac output

voltage is obtained by adjusting the ON and OFF periods of the inverter devices. Voltage type

PWM inverters have been applied widely to power supplies systems and motor driving systems.

This is because:

1) Inverters are well adapted for high speed self turn-off switching devices.

2) They can operate stably and can be easily controlled.

The PWM control has the following advantages:

1)

The output voltage can be controlled easily without inducing any additional

components.

2) With this type of control technique, lower order harmonics can be eliminated and

higher order harmonics can be filtered out easily.

The commonly used PWM control techniques are:

Space Vector PWMSinusoidal PWM


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(a) Sinusoidal pulse width modulation

(b) Space vector PWM

The performance of each of these control methods is usually judged based on the

following parameters:

(a) Total harmonic distortion (THD) of the voltage and current at the output of the inverter,

(b)Switching losses with in the inverter,

(c) peak to peak ripple in the load current, and

(d) Maximum inverter output voltage for a given dc voltage.

From the above all mentioned PWM control methods, the sinusoidal pulse width

modulation is applied to the proposed inverter since it has various advantages over the other

techniques. SPWM inverter provides an easy way to control amplitude, frequency, and harmonic

contents of the output voltage.

4.2.1 Sinusoidal pulse width modulation:

In the sinusoidal pulse width modulation scheme as the switch is turned ON and OFF

several times during each half cycle, the width of the pulses is varied to change the output

voltage. Lower order harmonics can be eliminated are reduced by selecting the type of

modulation for the pulse widths and the number of pulses per half cycle. Higher order harmonics

may increase, but these are not consider as they can be filtered out easily using filters. The

SPWM aims at generating a sinusoidal inverter output voltage without lower order harmonics.

This is possible if the sampling frequency is compared to the fundamental output frequency of

the inverter.

In this method of modulation several pulses per half cycle are used. The width of each

pulse is varied proportional to the amplitude of a sine wave evaluated at the center of the same


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pulse. By comparing a sinusoidal reference signal with a triangular carrier wave, the gating

signals are generated. The below figure shows the most common carrier technique, the

conventional SPWM technique, which is based on the principle of comparing the triangular

signal with a sinusoidal reference waveform (Natural sample)

Fig 4.2 Sinusoidal PWM Technique

4.3 Proposed modulation technique:

The modulation technique used for the proposed inverter is multicarrier modulation, i.e.

carrier based PWM or Multi carrier technique.

4.3.1 Multicarrier or Carrier based PWM:


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These are the classical and most widely used method of pulse width modulation. They

has common characteristic sub cycles of constant time duration , a sub cycle being defined as the

total duration Ts during which an active inverter like assumes to consecutive switching states of

opposite voltage polarity . Operation at sub cycles of constant duration is reflected in the

harmonic spectrum by two salient side bands, centered around the carrier frequency and

additional frequency bands around integral multiples of the carrier.

The multicarrier modulation technique is very suitable for a multilevel inverter circuit.

By employing this technique along with the multilevel topology, the low THD output waveform

without any filer circuit is possible. Switching the devices turn ON and OFF only one time per

cycle, that can overcome the switching loss problem, as well as EMI problem. The SPWM

switching patterns developed for the proposed inverter is given below.

4.3.2 SIMULINK MODEL OF MULTI CARRIER SINUSOIDAL PWM

GENERATOR:


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Fig 4.3: Simulink model MCSPWM generator

4.3.3 SCOPE of the Simulink model of MCSPWM:


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Fig 4.4: Triggering signals generated using MCSPWM technique.

6. Proposed multi-input rectifier stage

A system diagram of the proposed rectifier stage of a hybrid energy system is shown

in Figure 6.1, where one of the inputs is connected to the output of the PV array and the

other input connected to the output of a generator. The fusion of the two converters is

achieved by reconfiguring the two existing diodes from each converter and the shared

utilization of the Cuk output inductor by the SEPIC converter. This configuration allows

each converter to operate normally individually in the event that one source is unavailable.

Figure 6.2 illustrates the case when only the wind source is available. In this case, D1 turns

off and D2 turns on; the proposed circuit becomes a SEPIC converter and the input to output

voltage relationship is given by (1). On the other hand, if only the P source is available, then

D2 turns off and D1 will always be on and the circuit becomes a Cuk converter as shown in

Figure 6.3 the input to output voltage relationship is given by (2). In both cases, both


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converters have step-up/down capability, which provide more design flexibility in the

system if duty ratio control is utilized to perform MPPT control.

Figure 6.4 illustrates the various switching states of the proposed converter. If the

turn on duration of M1 is longer than M2, then the switching states will be state I,II, IV.

Similarly, the switching states will be state I, III, IV if the switch conduction periods are vice

versa. To provide a better explanation, the inductor current waveforms of each switching

state are given as follows assuming that d2 > d1; hence only states I, III, IV are discussed in

this example. In the following, Ii, PV is the average input current from the PV source; Ii, W

is the RMS input current after the rectifier (wind case); and Idc is the average system output

current.

The key waveforms that illustrate the switching states in this example are shown in

Figure 6.5. The mathematical expression that relates the total output voltage and the twoinput sources will be illustrated in the next section.

State I (M1 on, M2 on):

State III (M1 off, M2 on):


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State IV (M1 off, M2 off):

Figure 6.1: Proposed rectifier stage for a Hybrid wind/PV system.


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Figure 6.2: Only wind source is operational (SEPIC)

Figure 6.3: Only PV source is operation (Cuk)


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Figure 6.4 (I-IV): switching states within a switching cycle

Find an expression for the output DC bus voltage, Vdc, the volt-balance of the output

inductor, L2, is examined according to Figure 6.5 with d2 > d1. Since the net change in the

voltage of L2 is zero, applying volt-balance to L2 results in (3). The expression that relates


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the average output DC voltage (Vdc) to the capacitor voltages (vc1 and vc2) is then obtained

as shown in (4), where vc1 and vc2 can then be obtained by applying volt-balance to L1 and

L3. The final expression that relates the average output voltage and the two input sources

(VW and VPV) is then given by (5). It is observed that Vdc is simply the sum of the two

output voltages of the Cuk and SEPIC converter. This further implies that Vdc can be

controlled by d1 and d2 individually or simultaneously.

The switches voltage and current characteristics are also provided in this section. The

voltage stress is given by (6) and (7) respectively. As for the current stress, it is observed from

Figure 6 that the peak current always occurs at the end of the on-time of the MOSFET. Both

the Cuk and SEPIC MOSFET current consists of both the input current and the capacitors

(C1 or C2) current. The peak current stress of M1 and M2 are given by (8) and (10)

respectively. Leq1 and Leq2, given by (9) and (11), represent the equivalent inductance of

Cuk and SEPIC converter respectively.

The PV output current, which is also equal to the average input current of the Cuk

converter is given in (12). It can be observed that the average inductor current is a function


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of its respective duty cycle (d1). Therefore by adjusting the respective duty cycles for each

energy source, maximum power point tracking can be achieved.


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CHAPTER 5

SIMULATION OF THEAUXILIARY H-BRIDGE

INVERTER AND ITS

RESULTS

5.1 MATLAB Introduction:

MATLAB is a high-performance language for technical computing. It integrates

computation, visualization, and programming in an easy-to-use environment where problems and

solutions are expressed in familiar mathematical notation. Typical uses include:

Math and computation

Algorithm development Data acquisition

Modeling, simulation, and prototyping

Data analysis, exploration, and visualization

Scientific and engineering graphics

Application development, like graphical user interface building


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MATLAB is an interactive system whose basic data element is an array that does not require

dimensioning. This allows you to solve many technical computing problems, especially those

with matrix and vector formulations, in a fraction of the time it would take to write a program in

a scalar non interactive language such as C or FORTRAN. The name MATLAB stands for

matrix laboratory. MATLAB was originally written to provide easy access to matrix software

developed by the LINPACK and EISPACK projects. Today, MATLAB engines incorporate the

LAPACK and BLAS libraries, embedding the state of the art in software for matrix computation.

MATLAB has evolved over a period of years with input from many users. In university

environments, it is the standard instructional tool for introductory and advanced courses in

mathematics, engineering, and science. In industry, MATLAB is the tool of choice for high-

productivity research, development, and analysis. MATLAB features a family of add-on

application-specific solutions called toolboxes. Very important to most users of MATLAB,

toolboxes allow you to learn and apply specialized technology. Toolboxes are comprehensive

collections of MATLAB functions (M-files) that extend the MATLAB environment to solve

particular classes of problems. Areas in which toolboxes are available include signal processing,

control systems, neural networks, fuzzy logic, wavelets, simulation, and many others.

The proposed circuit connected in MATLAB/SIMULINK is shown below.


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Fig 8.1: Simulation circuit.

The output wave forms of current and voltage before the inverter i.e. D.C and after

the inverter i.e. at the load (A.C) are shown below.


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Fig 8.2: Voltage and Current wave forms before the inverter.

Fig 8.3: Voltage and Current wave forms after the inverter.

The wave forms shown above are continuous. We get the output voltage of 220V

(approximately) at the output and the current is 1.15A. So from this circuit we get the

continuous power whether both solar and wind are present or any one i.e. only solar or

wind present or both are absent.


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The internal block diagrams of PV system and Wind AC are shown below.

Fig 8.4: Internal circuit of PV system.

Fig 8.5: Internal circuit of Wind AC system.


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CONCLUSION

In this paper a new multi-input Cuk-SEPIC rectifier stage for hybrid

wind/solar energy systems has been presented.

The features of this circuit are:

1)

Additional input filters are not necessary to filter out high frequency

harmonics.

2) Both renewable sources can be stepped up/down (supports wide ranges of PV

and wind input).

3)

MPPT can be realized for each source.

4)

Individual and simultaneous operation is supported.

Simulation results have been presented to verify the features of the proposed topology.


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REFERENCES

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