elimination of harmonics in multi level converter
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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.
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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.
http://en.wikipedia.org/wiki/Solar_cellhttp://en.wikipedia.org/wiki/Solar_inverterhttp://en.wikipedia.org/wiki/Grid-connected_photovoltaic_power_systemhttp://en.wikipedia.org/wiki/Stand-alone_power_systemhttp://en.wikipedia.org/wiki/File:PV-system-schematics-residential-Eng.pnghttp://en.wikipedia.org/wiki/Stand-alone_power_systemhttp://en.wikipedia.org/wiki/Grid-connected_photovoltaic_power_systemhttp://en.wikipedia.org/wiki/Solar_inverterhttp://en.wikipedia.org/wiki/Solar_cell -
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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.
3.4shows the current paths that are active at this stage.
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.
3.6shows the current paths that are active at this stage.
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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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