Noval Application of a PV Solar plant as STATCOM during Night and Day in a Distribution Utility NetworkABSTRACTPv solar farms produce power during the day are completely idle in the nights .this paper presents utilization of a PvV solar plants as statcom in the night for load reactive power compensation and voltage control .this Statcom functionally wiil also be available to a substantialdegree during daytime with inverter capacity remaining after real power production .the local distribution company london hydro implementingthis new technology ,for the first time in Canada on 10Kw solar system to be installe don the roof top of their head quarters building .The PV solar plant inverter controller will be designed developed and tested in the university laband will be designed ,developed and tested in the university lab and will be designed ,developed and tested in the university lab and will then be installed in fied by spring 2011

Chapter-1PHOTO VOLATIC CELLSPhotovoltaics(PV) is a method ofgenerating electrical powerby convertingsolar radiationintodirect currentelectricityusingsemiconductorsthat exhibit thephotovoltaic effect. Photovoltaic power generation employssolar panelscomposed of a number ofsolar cellscontaining a photovoltaic material. Materials presently used for photovoltaics includemonocrystalline silicon,polycrystalline silicon,amorphous silicon,cadmium telluride, andcopper indium gallium selenide/sulfide.Due to the growing demand forrenewable energysources, the manufacturing of solar cells andphotovoltaic arrayshas advanced considerably in recent years. Solar photovoltaics is 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.[5]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[8]and the levelised cost of electricity (LCOE) from PV is competitive with conventional electricity sources in an expanding list of geographic regions.Net meteringand financial incentives, such as preferentialfeed-in tariffsfor solar-generated electricity, have supported solar PV installations in many countries.[10]Solar CellsPhotovoltaics 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 effectrefers 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 byAlexandre-Edmond Becquerelin 1839. The term photovoltaic denotes the unbiased operating mode of aphotodiodein which current through the device is entirely due to the transduced light energy. Virtually all photovoltaic devices are some type of photodiode.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 modulesare used for grid connected power generation. In this case aninverteris 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 protectionofpipelines.Photovoltaic power generation employssolar panelscomposed of a number ofsolar cellscontaining a photovoltaic material. Materials presently used for photovoltaics includemonocrystalline silicon,polycrystalline silicon,amorphous silicon,cadmium telluride, andcopper indium gallium selenide/sulfide. Due to the growing demand forrenewable energysources, the manufacturing of solar cells andphotovoltaic arrayshas 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.A significant market has emerged in off-grid locations for solar-power-charged storage-battery based solutions. These often provide the only electricity available.[14]The first commercial installation of this kind was in 1966 on Ogami Island in Japan to transitionOgami Lighthousefrom gas torch to fully self-sufficient electrical power.Due to the growing demand for renewable energy sources, the manufacture of solar cells andphotovoltaic arrayshas advanced dramatically in recent years. Solar photovoltaics is 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.[5]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.[5]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 factorsare typically under 25%, which is lower than many other industrial sources of electricity. The EPIA/GreenpeaceAdvanced Scenario shows that by the year 2030, PV systems could be generating approximately 1.8TW 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.[21]Current developments:Photovoltaic panels based oncrystalline siliconmodules are encountering competition in the market by panels that employthin-film solar cells(CdTe[22]CIGS,[23]amorphous Si,[24]microcrystalline Si), which had been rapidly evolving and are expected to account for 31 percent of the global installed power by 2013.[25]However, precipitous drops in prices for polysilicon and their panels in late 2011 have caused some thin-film makers to exit the market and others to experience severely squeezed profits.[26]Other developments includecastingwafers instead of sawing,[27]concentrator modules,'Sliver' cells, andcontinuous printingprocesses.TheSan Jose-based company Sunpower produces cells that have an energy conversion ratio of 19.5%, well above the market average of 1218%.[28]The most efficient solar cell so far is a multi-junction concentrator solar cell with an efficiency of 43.5%[29]produced by theNational Renewable Energy Laboratoryin April 2011. The highest efficiencies achieved without concentration includeSharp Corporationat 35.8% using a proprietary triple-junction manufacturing technology in 2009,[30]and Boeing Spectrolab (40.7% also using a triple-layer design). A March 2010 experimental demonstration of a design by a Caltech group led byHarry Atwaterwhich has an absorption efficiency of 85% in sunlight and 95% at certain wavelengths is claimed to have near perfect quantum efficiency.[31]However, absorption efficiency should not be confused with the sunlight-to-electricity conversion efficiency.

For best performance, terrestrial PV systems aim to maximize the time they face the sun.Solar trackersachieve this by moving PV panels to follow the sun. The increase can be by as much as 20% in winter and by as much as 50% in summer. Static mounted systems can be optimized by analysis of thesun path. Panels are often set to latitude tilt, an angle equal to the latitude, but performance can be improved by adjusting the angle for summer or winter. Generally, as with other semiconductor devices, temperatures above room temperature reduce the performance of photovoltaics.[32]The 2011 European Photovoltaic Industry Association (EPIA) report predicted that, "The future of the PV market remains bright in the EU and the rest of the world," the report said. "Uncertain times are causing governments everywhere to rethink the future of their energy mix, creating new opportunities for a competitive, safe and reliable electricity source such as PV. 2012 could see the installation of 2030GW of PV about the same as in 2011. Unfortunately, the industry's capacity continues to expand, to perhaps as much as 38GW. The resulting glut of supply has crushed prices and profits.[34]By 2015, 131196GW of photovoltaic systems could be installed around the globe.[33]REVENUE MODEL OF PV SOLAR PLANT

Economics: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 theeconomies of scaleneeded 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 emissionswhich 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.

NRELcompilation of best research solar cell efficiencies from 1976 to 2010According toShi Zhengrong, in 2012 unsubsidized PV systems already produce electricity in some parts of the world, more cheaply than coal and gas-fired power plants.[35][36]As PV system prices decline it's inevitable that subsidies will end. "Rapid decline or outright disappearance has already been seen in all the major solar markets except China and India".[36]As of 2011, the price of PV modules per MW has fallen by 60 percent since the summer of 2008, according to Bloomberg New Energy Finance estimates, putting solar power for the first time on a competitive footing with the retail price of electricity in a number of sunny countries. There has been fierce competition in the supply chain, and further improvements in the levelised cost of energy for solar lie ahead, posing a growing threat to the dominance of fossil fuel generation sources in the next few years.[37]As time progresses, renewable energy technologies generally get cheaper,[38][39]while fossil fuels generally get more expensive:The less solar power costs, the more favorably it compares to conventional power, and the more attractive it becomes to utilities and energy users around the globe. Utility-scale solar power can now be delivered in California at prices well below $100/MWh ($0.10/kWh) less than most other peak generators, even those running on low-cost natural gas. Lower solar module costs also stimulate demand from consumer markets where the cost of solar compares very favorably to retail electric rates.[40]As of 2011, the cost of PV has fallen well below that of nuclear power and is set to fall further. The average retail price of solar cells as monitored by the Solarbuzz group fell from $3.50/watt to $2.43/watt over the course of 2011, and a decline to prices below $2.00/watt seems inevitable:[41]For large-scale installations, prices below $1.00/watt are common. In some locations, PV has reached grid parity, the cost at which it is competitive with coal or gas-fired generation. Photovoltaic power is also generated during a time of day that is close to peak demand (precedes it). More generally, it is now evident that, given a carbon price of $50/ton, which would raise the price of coal-fired power by 5c/kWh, solar PV will be cost-competitive in most locations. The declining price of PV has been reflected in rapidly growing installations, totaling about 23 GW in 2011. Although some consolidation is likely in 2012, as firms try to restore profitability, strong growth seems likely to continue for the rest of the decade. Already, by one estimate, total investment in renewables for 2011 exceeded investment in carbon-based electricity generation.[41]

ApplicationsPower stationsMany solarphotovoltaic power stationshave been built, mainly in Europe.[42]As of December 2011, the largest photovoltaic (PV) power plants in the world are theGolmud Solar Park(China, 200 MW),Sarnia Photovoltaic Power Plant(Canada, 97 MW),Montalto di Castro Photovoltaic Power Station(Italy, 84.2 MW),Finsterwalde Solar Park(Germany, 80.7 MW),Okhotnykovo Solar Park(Ukraine, 80MW),Lieberose Photovoltaic Park(Germany, 71.8MW),Rovigo Photovoltaic Power Plant(Italy, 70 MW),Olmedilla Photovoltaic Park(Spain, 60MW), and theStrasskirchen Solar Park(Germany, 54MW).[42]

There are also many large plants under construction. TheDesert Sunlight Solar Farmunder construction inRiverside County, CaliforniaandTopaz Solar Farmbeing built inSan Luis Obispo County, Californiaare both 550MWsolar parksthat will use thin-film solarphotovoltaicmodules made byFirst Solar. TheBlythe Solar Power Projectis a 500 MW photovoltaic station under construction inRiverside County, California. TheAgua Caliente Solar Projectis a 290 megawatt photovoltaic solar generating facility being built inYuma County, Arizona. TheCalifornia Valley Solar Ranch(CVSR) is a 250megawatt(MW)solar photovoltaicpower plant, which is being built bySunPowerin theCarrizo Plain, northeast ofCalifornia Valley.

The 230 MWAntelope Valley Solar Ranchis aFirst Solarphotovoltaic project which is under construction in the Antelope Valley area of the Western Mojave Desert, and due to be completed in 2013.TheMesquite Solar projectis a photovoltaic solar power plant being built inArlington,Maricopa County,Arizona, owned bySempra Generation. Phase1 will have anameplate capacityof 150megawatts. Many of these plants are integrated with agriculture and some use innovative tracking systems that follow the sun's daily path across the sky to generate more electricity than conventional fixed-mounted systems. There are no fuel costs or emissions during operation of the power stations.

In buildings

Photovoltaic wall at MNACTEC Terrassa in SpainPhotovoltaic arrays are often associated with buildings: either integrated into them, mounted on them or mounted nearby on the ground.Arrays are most often retrofitted into existing buildings, usually mounted on top of the existing roof structure or on the existing walls. Alternatively, an array can be located separately from the building but connected by cable to supply power for the building. In 2010, more than four-fifths of the 9,000 MW of solar PV operating in Germany were installed on rooftops.[48]Building-integrated photovoltaics (BIPV) are increasingly incorporated into new domestic and industrial buildings as a principal or ancillary source of electrical power.[49]Typically, an array is incorporated into the roof or walls of a building. Roof tiles with integrated PV cells are also common. A 2011 study using thermal imaging has shown that solar panels, provided there is an open gap in which air can circulate between them and the roof, provide a passive cooling effect on buildings during the day and also keep accumulated heat in at night. The power output of photovoltaic systems for installation in buildings is usually described inkilowatt-peakunits (kWp).In transportPV has traditionally been used for electric power in space. PV is rarely used to provide motive power in transport applications, but is being used increasingly to provide auxiliary power in boats and cars. A self-containedsolar vehiclewould have limited power and low utility, but asolar-charged vehiclewould allow use of solar power for transportation. Solar-powered cars have been demonstrated.[51]

Standalone devices

Solar parking paystation.Until a decade or so ago, PV was used frequently to power calculators and novelty devices. Improvements in integrated circuits and low powerliquid crystal displaysmake it possible to power such devices for several years between battery changes, making PV use less common. In contrast, solar powered remote fixed devices have seen increasing use recently in locations where significant connection cost makes grid power prohibitively expensive. Such applications include water pumps,parking meters, emergency telephones,trash compactors, temporary traffic signs, and remote guard posts and signals.Rural electrificationUnlike the past decade, which saw solar solutions purchased mainly by international donors, it is now the locals who are increasingly opening their wallets to make the switch from their traditional energy means. That is because solar products prices in recent years have declined to become cheaper than kerosene and batteries.In Cambodia, for example, villagers can buy a solar lantern at US$25 and use it for years without any extra costs, where their previous spending on kerosene for lighting was about $2.5 per month, or $30 per year. In Kenya a solar kit that provides bright light or powers a radio or cell phone costs under $30 at retail stores. By switching to this kit Kenyans can save $120 per year on kerosene lighting, radio batteries and cell phone recharging fees.[57]Developing countries where many villages are often more than five kilometers away from grid power are increasingly using photovoltaics. In remote locations in India a rural lighting program has been providing solar powered LED lighting to replace kerosene lamps. The solar powered lamps were sold at about the cost of a few months' supply of kerosene.[58][59]Cuba is working to provide solar power for areas that are off grid.[60]These are areas where the social costs and benefits offer an excellent case for going solar though the lack of profitability could relegate such endeavors to humanitarian goals.

Solar roadways

The 104kW solar highway along the interchange ofInterstate 5andInterstate 205nearTualatin, Oregonin December 2008.In December 2008, the Oregon Department of Transportation placed in service the nations first solar photovoltaic system in a U.S. highway right-of-way. The 104-kilowatt (kW) array produces enough electricity to offset approximately one-third of the electricity needed to light the Interstate highway interchange where it is located.[61]A 45mi (72km) section of roadway in Idaho is being used to test the possibility of installing solar panels into the road surface, as roads are generally unobstructed to the sun and represent about the percentage of land area needed to replace other energy sources with solar power.[62]Solar Power satellitesSpace-based solar power (SBSP) is the concept of collecting solar power inspacefor use onEarth. It has been in research since the early 1970s. SBSP would differ from current solar collection methods in that the means used to collect energy would reside on anorbitingsatelliteinstead of on Earth's surface. Some projected benefits of such a system are: higher collection rate, longer collection period, and elimination ofweatherconcerns. SBSP also introduces several new hurdles, primarily the problem of transmitting energy from orbit to Earth's surface for use.AdvantagesThe 89PWof sunlight reaching the Earth's surface is plentiful almost 6,000 times more than the 15TW equivalent of average power consumed by humans.[63]Additionally, solar electric generation has the highest power density (global mean of 170 W/m) among renewable energies.[63]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[64]and policies are being produced that encourage recycling from producers.[65]PV installations can operate for many years with little maintenance or intervention after their initial set-up, so after the initialcapital costof building any solar power plant,operating costsare 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).[66]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 cellsalready have efficiencies of over 40% in case of concentrating photovoltaic cells[67]and efficiencies are rapidly rising while mass-production costs are rapidly falling.[68]DisadvantagesPhotovoltaic panels are specifically excluded in Europe from RoHS (Restriction on Hazardous Substances) since 2003 and were again excluded in 2011. California has largely adopted the RoHS standard throughEWRA. Therefore, PV panels may legally in Europe and California contain lead, mercury and cadmium which are forbidden or restricted in all other electronics.[69]In some states of the United States of America, much of the investment in a home-mounted system may be lost if the home-owner moves and the buyer puts less value on the system than the seller. The city of Berkeley developed an innovative financing method to remove this limitation, by adding a tax assessment that is transferred with the home to pay for the solar panels.[70]Now known asPACE, Property Assessed Clean Energy, 28 U.S. states have duplicated this solution

Chapter-2Solar cellsAsolar cell(also calledphotovoltaic cellorphotoelectric cell) is asolid stateelectrical device that converts the energy oflightdirectly intoelectricityby thephotovoltaic effect.Assemblies of solar cells are used to makesolar moduleswhich are used to capture energy fromsunlight. When multiple modules are assembled together (such as prior to installation on a pole-mounted tracker system), the resulting integrated group of modules all oriented in one plane is referred to in the solar industry as asolar panel. The electrical energy generated from solar modules, referred to assolar power, is an example ofsolar energy.Photovoltaicsis the field of technology and research related to the practical application of photovoltaic cells in producing electricity from light, though it is often used specifically to refer to the generation of electricity from sunlight.Cells are described asphotovoltaic cellswhen the light source is not necessarily sunlight (lamplight, artificial light, etc.). These are used for detecting light or otherelectromagnetic radiationnear the visible range, for exampleinfrared detectors, or measurement of light intensity.

ApplicationsSolar cells are often electrically connected and encapsulated as amodule. Photovoltaic modules often have a sheet of glass on the front (sun up) side, allowing light to pass while protecting the semiconductorwafersfrom abrasion and impact due to wind-driven debris,rain,hail, etc. Solar cells are also usually connected inseriesin modules, creating an additivevoltage. Connecting cells in parallel will yield a higher current; however, very significant problems exist with parallel connections. For example, shadow effects can shut down the weaker (less illuminated) parallel string (a number of series connected cells) causing substantial power loss and even damaging excessive reverse bias applied to the shadowed cells by their illuminated partners. As far as possible, strings of series cells should be handled independently and not connected in parallel, save using special paralleling circuits. Although modules can be interconnected to create anarraywith the desired peak DC voltage and loading current capacity, using independent MPPTs (maximum power point trackers) provides a better solution. In the absence of paralleling circuits, shunt diodes can be used to reduce the power loss due to shadowing in arrays with series/parallel connected cells.To make practical use of the solar-generated energy, the electricity is most often fed into the electricity grid using inverters (grid-connectedphotovoltaic systems); in stand-alone systems, batteries are used to store the energy that is not needed immediately. Solar panels can be used to power or recharge portable devices.

TheoryThe solar cell works in three steps:1. Photonsinsunlighthit the solar panel and are absorbed by semiconducting materials, such as silicon.2. Electrons(negatively charged) are knocked loose from their atoms, causing an electric potential difference. Current starts flowing through the material to cancel the potential and this electricity is captured. Due to the special composition of solar cells, the electrons are only allowed to move in a single direction.3. An array of solar cells converts solar energy into a usable amount ofdirect current(DC) electricity.EfficiencyThe efficiency of a solar cell may be broken down into reflectance efficiency, thermodynamic efficiency, charge carrier separation efficiency and conductive efficiency. The overall efficiency is the product of each of these individual efficiencies.Due to the difficulty in measuring these parameters directly, other parameters are measured instead: thermodynamic efficiency,quantum efficiency,integrated quantum efficiency, VOCratio, and fill factor. Reflectance losses are a portion of the quantum efficiency under "external quantum efficiency". Recombination losses make up a portion of the quantum efficiency, VOCratio, and fill factor. Resistive losses are predominantly categorized under fill factor, but also make up minor portions of the quantum efficiency, VOCratio.Thefill factoris defined as the ratio of the actual maximum obtainablepower, to the product of the open circuit voltage and short circuit current. This is a key parameter in evaluating the performance of solar cells. Typical commercial solar cells have a fill factor > 0.70. Grade B cells have a fill factor usually between 0.4 to 0.7. The fill factor is, besides efficiency, one of the most significant parameters for the energy yield of aphotovoltaic cell.[14]Cells with a high fill factor have a low equivalent series resistance and a high equivalent shunt resistance, so less of the current produced by light is dissipated in internal losses.Single p-n junction crystalline silicon devices are now approaching the theoretical limiting power efficiency of 33.7%, noted as theShockleyQueisser limitin 1961. In the extreme, with an infinite number of layers, the corresponding limit is 86% using concentrated sunlight.[15]CostThe cost of a solar cell is given per unit of peak electrical power. Manufacturing costs necessarily include the cost of energy required for manufacture. Solar-specific feed in tariffs vary worldwide, and even state by state within various countries.[16]Such feed-in tariffs can be highly effective in encouraging the development of solar power projects.

High-efficiency solar cells are of interest to decrease the cost of solar energy. Many of the costs of a solar power plant are proportional to the area of the plant; a higher efficiency cell may reduce area and plant cost, even if the cells themselves are more costly. Efficiencies of bare cells, to be useful in evaluating solar power plant economics, must be evaluated under realistic conditions. The basic parameters that need to be evaluated are the short circuit current, open circuit voltage.[17]The chart below illustrates the best laboratory efficiencies obtained for various materials and technologies, generally this is done on very small, i.e., one square cm, cells. Commercial efficiencies are significantly lower.

Reported timeline of solar cell energy conversion efficiencies (from National Renewable Energy Laboratory (USA))Grid parity, the point at which photovoltaic electricity is equal to or cheaper thangrid power, can be reached using low cost solar cells. It is achieved first in areas with abundant sun and high costs for electricity such as inCaliforniaandJapan.[18]Grid parity has been reached inHawaiiand other islands that otherwise usediesel fuelto produce electricity.George W. Bushhad set 2015 as the date for grid parity in the USA.[19][20]Speaking at a conference in 2007,General Electric's Chief Engineer predicted grid parity without subsidies in sunny parts of the United States by around 2015.[21]The price of solar panels fell steadily for 40 years, until 2004 when high subsidies in Germany drastically increased demand there and greatly increased the price of purified silicon (which is used in computer chips as well as solar panels). Thegreat recessionof 2008 and the onset of Chinese manufacturing caused prices to resume their decline with vehemence. In the four years after January 2008 prices for solar modules in Germany dropped from 3 to 1 per peak watt. During that same times production capacity surged with an annual growth of more than 50%. China increased market share from 8% in 2008 to over 55% in the last quarter of 2010.[22]Recently, since the middle of 2010, the price has been dropped to $1.21.5/Wp (crystalline modules).[citation needed]

MaterialsThe cost of a solar cell is given per unit of peak electrical power. Manufacturing costs necessarily include the cost of energy required for manufacture. Solar-specific feed in tariffs vary worldwide, and even state by state within various countries.[16]Such feed-in tariffs can be highly effective in encouraging the development of solar power projects.High-efficiency solar cells are of interest to decrease the cost of solar energy. Many of the costs of a solar power plant are proportional to the area of the plant; a higher efficiency cell may reduce area and plant cost, even if the cells themselves are more costly. Efficiencies of bare cells, to be useful in evaluating solar power plant economics, must be evaluated under realistic conditions. The basic parameters that need to be evaluated are the short circuit current, open circuit voltage.[17]The chart below illustrates the best laboratory efficiencies obtained for various materials and technologies, generally this is done on very small, i.e., one square cm, cells. Commercial efficiencies are significantly lower.

Reported timeline of solar cell energy conversion efficiencies (from National Renewable Energy Laboratory (USA))Grid parity, the point at which photovoltaic electricity is equal to or cheaper thangrid power, can be reached using low cost solar cells. It is achieved first in areas with abundant sun and high costs for electricity such as inCaliforniaandJapan.[18]Grid parity has been reached inHawaiiand other islands that otherwise usediesel fuelto produce electricity.George W. Bushhad set 2015 as the date for grid parity in the USA.[19][20]Speaking at a conference in 2007,General Electric's Chief Engineer predicted grid parity without subsidies in sunny parts of the United States by around 2015.[21]The price of solar panels fell steadily for 40 years, until 2004 when high subsidies in Germany drastically increased demand there and greatly increased the price of purified silicon (which is used in computer chips as well as solar panels). Thegreat recessionof 2008 and the onset of Chinese manufacturing caused prices to resume their decline with vehemence. In the four years after January 2008 prices for solar modules in Germany dropped from 3 to 1 per peak watt. During that same times production capacity surged with an annual growth of more than 50%. China increased market share from 8% in 2008 to over 55% in the last quarter of 2010.[22]Recently, since the middle of 2010, the price has been dropped to $1.21.5/Wp (crystalline modules).[citation needed]ManufactureBecause solar cells are semiconductor devices, they share some of the same processing and manufacturing techniques as other semiconductor devices such ascomputerandmemorychips. However, the stringent requirements for cleanliness and quality control of semiconductor fabrication are more relaxed for solar cells. Most large-scale commercial solar cell factories today make screen printed poly-crystalline or single crystalline silicon solar cells.Poly-crystalline silicon wafers are made by wire-sawing block-cast silicon ingots into very thin (180 to 350 micrometer) slices or wafers. The wafers are usually lightlyp-typedoped. To make a solar cell from the wafer, a surface diffusion ofn-typedopants is performed on the front side of the wafer. This forms a p-n junction a few hundred nanometers below the surface.Anti-reflection coatings, to increase the amount of light coupled into the solar cell, are typically next applied. Silicon nitride has gradually replaced titanium dioxide as the anti-reflection coating, because of its excellent surface passivation qualities. It prevents carrier recombination at the surface of the solar cell. It is typically applied in a layer several hundred nanometers thick using plasma-enhanced chemical vapor deposition (PECVD). Some solar cells have textured front surfaces that, like anti-reflection coatings, serve to increase the amount of light coupled into the cell. Such surfaces can usually only be formed on single-crystal silicon, though in recent years methods of forming them on multicrystalline silicon have been developed.The wafer then has a full area metal contact made on the back surface, and a grid-like metal contact made up of fine "fingers" and larger "bus bars" are screen-printed onto the front surface using asilverpaste. The rear contact is also formed by screen-printing a metal paste, typically aluminium. Usually this contact covers the entire rear side of the cell, though in some cell designs it is printed in a grid pattern. The paste is then fired at several hundred degrees Celsius to form metal electrodes inohmic contactwith the silicon. Some companies use an additional electro-plating step to increase the cell efficiency. After the metal contacts are made, the solar cells are interconnected by flat wires or metal ribbons, and assembled intomodulesor "solar panels". Solar panels have a sheet oftempered glasson the front, and apolymerencapsulation on the back.

Life spanMost commercially available solar panels are capable of producing electricity for at least twenty years.[citation needed]The typical warranty given by panel manufacturers is over 90% of rated output for the first 10 years, and over 80% for the second 10 years. Panels are expected to function for a period of 30 to 35 years.

Chapter-3Voltage-Source InverterA typical voltage-source PWM converter performs the ac to ac conversion in two stages: ac to dc and dc to variable frequency ac. The basic converter design is shown in figure 1.1. The grid voltage is rectified by the line rectifier usually consisting of a diode bridge. Presently, attention paid to power quality and improved power factor has shifted the interest to more supply friendly ac-to-dc converters, e.g. PWM rectifier. This allows simultaneously active filtering of the line current as well as regenerative motor braking schemes transferring power back to the mains. The dc voltage is filtered and smoothed by the capacitor C in the dc bus (figure 1.1). The capacitor is of appreciable size (2-20 mF) and therefore a major cost item [Bose 97]. Alternatively, the inverter can be supplied from a fixed dc voltage. The filtered dc voltage is usually measured for control purpose. Because of the nearly constant dc bus voltage, a number of PWM inverters with their associated motor drives can be supplied from one common diode bridge. The inductive reactance L between rectifier and ac supply is used to reduce commutation dips produced by the rectifier, to limit fault current and to soften voltages spikes of the mains.

Neglecting the voltage drop of the inductances (current depending) and diodes (Ud 1V if i > 0), the positive potential of the dc bus voltage equals the highest potential of the three phases and the negative potential equals the lowest potential of the three phases. Since each phase owns one negative and one positive maximum potential during one period of the net frequency, the rectifier input voltage equals the maximum of the positive and negative line voltages, respectively. Thus, the rectifier input voltage traces six pulses as shown in figure 1.2 by the thick line

Figure 1.2 presents typical voltage and current waveforms of a B6-diode bridge supplied by a stiff grid. As indicated by the dashed lines, the rectifier current iB6 increases, if the absolute value of a line voltage is higher than the dc voltage. Consequently, the dc voltage increases slightly. A dc voltage higher than the current voltage supply causes a reduction of the rectifier input current until the current equals zero and the diode bridge blocks the supply voltage. The rectifier current iB6 is identically reflected by the line currents. The sign of each line current depends on the two non-blocking diodes each conducting the positive and negative rectifier current, respectively. During the conducting period, the difference of line and dc voltage is active as voltage drop over the line inductances and resistances. The higher the line inductances, the smaller the line current peaks. However, the value of the line inductances is limited due to economic and efficiency reasons. Furthermore, the average dc voltage depends on the line inductances and the inverter output power. The maximum dc voltage (no load) is equal to the maximum amplitude of the line voltages. Due to voltage drops of line inductances, resistances and rectifier diodes, the dc voltage slightly decreases with increasing load. For more details concerning the rectifier, see [Bose 97], [Dub 89] et al. According to figure 1.1, the dc voltage is switched in a three-phase PWM inverter by six semiconductor switches in order to obtain pulses, forming three-phase ac voltage with the required frequency and amplitude for motor supply. The switching devices must be capable of being turned on as well as turned off. During the last years, major progress has been made in the development of new power semiconductor devices. The simpler requirement driving the power switches and the higher maximum switching-frequency, enabling higher operating frequencies (higher motor speed), provide continually rising output power. The new generation of switching devices is capable of conducting more current and blocking higher voltages. The alternatives at present are gate turn-off thyristor (GTO), MOS controlled thyristor (MCT), bipolar junction transistor (BJT), MOS field effect transistor (MOSFET) and insulated gate bipolar transistor (IGBT).

The IGBT is a combination of power MOSFET and bipolar transistor technology and combines the advantages of both. In the same way as a MOSFET, the gate of the IGBT is isolated and its driving power is very low. However, the conducting voltage is similar to that of a bipolar transistor. Presently, IGBTs dominate the medium-power range of variable speed drives. Since the maximal current rating of IGBT modules is around 1 kA and the voltage rating is approximately 3 kV, they will gradually replace GTOs at higher power levels [Vas 99]. Parallel to the power switches, reverse recovery diodes are placed conducting the current depending on the switching states and current sign. These diodes are required, since switching off an inductive load current generates high voltage peaks probably destroying the power switch. Exemplary for one inverter leg, figure 1.3 presents the basic configuration and the inverter output voltage depending on the switching state and current sign. The basic configuration of one inverter output phase consists of upper and lower power devices T1 and T4, and reverse recovery diodes D1 and D4.

When transistor T1 is on, a voltage Udc is applied to the load. Considering an inductive load, the current increases subsequently. If the load draws positive current, it will flow through T1 and supply energy to the load. To the contrary, if the load current ia is negative, the current flows back through D1 and returns energy to the dc source.

Figure 1.3: Basic configuration of a half-bridge inverter and center-tapped inverter output voltage. Left: Switching states and current direction. Right: Output voltage and line current. Similarly if T4 is on, which is equal to T1 off, a voltage - Udc is applied to the load and the current decreases. If iis positive, the current flows through D4 returning energy to the dc source. A negative current yields T4 conductinand supplying energy to the load. According to figure 1.3, with T1 on and drawing positive load current ia, the output voltage ua0 will be less than Udc by the on-state voltage drop of T1. When the load current reverses, the output voltage will be higher than Udc by the voltage drop across D1. Similarly, the output voltage is slightly changed by the voltage drop of the lower devices T4 and D4.

Normally, the on-state voltage and diode drops (1 V) are ignored and the center-tapped inverter is represented as generating the voltage Udc and - Udc, respectively. Neglecting additionally the dead-time interval dead, the behavior of the power devices together with the reverse recovery diode is equally described by ideal two-position switche

Chapter-4POWER FACTOR CORRECTION.Capacitive Power Factor correction is applied to circuits which include induction motors as a means of reducing the inductive component of the current and thereby reduce the losses in the supply. There should be no effect on the operation of the motor itself. An induction motor draws current from the supply, that is made up of resistive components and inductive components. The resistive components are:1) Load current.2) Loss current. and the inductive components are:3) Leakage reactance.4) Magnetizing current.The current due to the leakage reactance is dependant on the total current drawn by the motor, but the magnetizing current is independent of the load on the motor. The magnetizing current will typically be between 20% and 60% of the rated full load current of the motor. The magnetizing current is the current that establishes the flux in the iron and is very necessary if the motor is going to operate. The magnetizing current does not actually contribute to the actual work output of the motor. It is the catalyst that allows the motor to work properly. The magnetizing current and the leakage reactance can be considered passenger components of current that will not affect the power drawn by the motor, but will contribute to the power dissipated in the supply and distribution system. Take for example a motor with a current draw of 100 Amps and a power factor of 0.75 The resistive component of the current is 75 Amps and this is what the KWh meter measures. The higher current will result in an increase in the distribution losses of (100 x 100) /(75 x 75) = 1.777 or a 78% increase in the supply losses.In the interest of reducing the losses in the distribution system, power factor correction is added to neutralize a portion of the magnetizing current of the motor. Typically, the corrected power factor will be 0.92 - 0.95 Some power retailers offer incentives for operating with a power factor of better than 0.9, while others penalize consumers with a poor power factor. There are many ways that this is metered, but the net result is that in order to reduce wasted energy in the distribution system, the consumer will be encouraged to apply power factor correction. Power factor correction is achieved by the addition of capacitors in parallel with the connected motor circuits and can be applied at the starter, or applied at the switchboard or distribution panel. The resulting capacitive current is leading current and is used to cancel the lagging inductive current flowing from the supply.Capacitors connected at each starter and controlled by each starter is known as "Static Power Factor Correction" while capacitors connected at a distribution board and controlled independently from the individual starters is known as "Bulk Correction".

3.1 BULK CORRECTION:The Power factor of the total current supplied to the distribution board is monitored by a controller which then switches capacitor banks In a fashion to maintain a power factor better than a preset limit. (Typically 0.95) Ideally, the power factor should be as close to unity as possible. There is no problem with bulk correction operating at unity.3.2 Static Correction:As a large proportion of the inductive or lagging current on the supply is due to the magnetizing current of induction motors, it is easy to correct each individual motor by connecting the correction capacitors to the motor starters. With static correction, it is important that the capacitive current is less than the inductive magnetizing current of the induction motor. In many installations employing static power factor correction, the correction capacitors are connected directly in parallel with the motor windings. When the motor is Off Line, the capacitors are also Off Line. When the motor is connected to the supply, the capacitors are also connected providing correction at all times that the motor is connected to the supply. This removes the requirement for any expensive power factor monitoring and control equipment. In this situation, the capacitors remain connected to the motor terminals as the motor slows down. An induction motor, while connected to the supply, is driven by a rotating magnetic field in the stator which induces current into the rotor. When the motor is disconnected from the supply, there is for a period of time, a magnetic field associated with the rotor. As the motor decelerates, it generates voltage out its terminals at a frequency which is related to it's speed. The capacitors connected across the motor terminals, form a resonant circuit with the motor inductance. If the motor is critically corrected, (corrected to a power factor of 1.0) the inductive reactance equals the capacitive reactance at the line frequency and therefore the resonant frequency is equal to the line frequency. If the motor is over corrected, the resonant frequency will be below the line frequency. If the frequency of the voltage generated by the decelerating motor passes through the resonant frequency of the corrected motor, there will be high currents and voltages around the motor/capacitor circuit. This can result in severe damage to the capacitors and motor. It is imperative that motors are never over corrected or critically corrected when static correction is employed.Static power factor correction should provide capacitive current equal to 80% of the magnetizing current, which is essentially the open shaft current of the motor.The magnetizing current for induction motors can vary considerably. Typically, magnetizing currents for large two pole machines can be as low as 20% of the rated current of the motor while smaller low speed motors can have a magnetizing current as high as 60% of the rated full load current of the motor. It is not practical to use a "Standard table" for the correction of induction motors giving optimum correction on all motors. Tables result in under correction on most motors but can result in over correction in some cases. Where the open shaft current can not be measured, and the magnetizing current is not quoted, an approximate level for the maximum correction that can be applied can be calculated from the half load characteristics of the motor. It is dangerous to base correction on the full load characteristics of the motor as in some cases, motors can exhibit a high leakage reactance and correction to 0.95 at full load will result in over correction under no load, or disconnected conditions.Static correction is commonly applied by using on e contactor to control both the motor and the capacitors. It is better practice to use two contactors, one for the motor and one for the capacitors. Where one contactor is employed, it should be up sized for the capacitive load. The use of a second contactor eliminates the problems of resonance between the motor and the capacitors.3.3 INVERTER:Static Power factor correction must not be used when the motor is controlled by a variable speed drive or inverter. The connection of capacitors to the output of an inverter can cause serious damage to the inverter and the capacitors due to the high frequency switched voltage on the output of the inverters.The current drawn from the inverter has a poor power factor, particularly at low load, but the motor current is isolated from the supply by the inverter. The phase angle of the current drawn by the inverter from the supply is close to zero resulting in very low inductive current irrespective of what the motor is doing. The inverter does not however, operate with a good power factor. Many inverter manufacturers quote a cos of better than 0.95 and this is generally true, however the current is non sinusoidal and the resultant harmonics cause a power factor (KW/KVA) of closer to 0.7 depending on the input design of the inverter. Inverters with input reactors and DC bus reactors will exhibit a higher true power factor than those without.The connection of capacitors close to the input of the inverter can also result in damage to the inverter. The capacitors tend to cause transients to be amplified, resulting in higher voltage impulses applied to the input circuits of the inverter, and the energy behind the impulses is much greater due to the energy storage of the capacitors. It is recommended that capacitors should be at least 75 Meters away from inverter inputs to elevate the impedance between the inverter and capacitors and reduce the potential damage caused. Switching capacitors, Automatic bank correction etc, will cause voltage transients and these transients can damage the input circuits of inverters. The energy is proportional to the amount of capacitance being switched. It is better to switch lots of small amounts of capacitance than few large amounts.3.4 SOLID STATE SOFT STARTER:Static Power Factor correction capacitors must not be connected to the output of a solid state soft starter. When a solid state soft starter is used, the capacitors must be controlled by a separate contactor, and switched in when the soft starter output voltage has reached line voltage. Many soft starters provide a "top of ramp" or "bypass contactor control" which can be used to control the power factor correction capacitors.The connection of capacitors close to the input of the soft starter can also result in damage to the soft starter if an isolation contactor is not used.

The capacitors tend to cause transients to be amplified, resulting in higher voltage impulses applied to the SCRs of the Soft Starter, and the energy behind the impulses is much greater due to the energy storage of the capacitors. It is recommended that capacitors should be at least 50 Meters away from Soft starters to elevate the impedance between the inverter and capacitors and reduce the potential damage caused.Switching capacitors, Automatic bank correction etc, will cause voltage transients and these transients can damage the SCRs of Soft Starters if they are in the Off state without an input contactor. The energy is proportional to the amount of capacitance being switched. It is better to switch lots of small amounts of capacitance than few large amounts.3.5 CAPACITOR SELECTION:Static Power factor correction must neutralize no more than 80% of the magnetizing current of the motor. If the correction is too high, there is a high probability of over correction which can result in equipment failure with severe damage to the motor and capacitors. Unfortunately, the magnetizing current of induction motors varies considerably between different motor designs. The magnetizing current is almost always higher than 20% of the rated full load current of the motor, but can be as high as 60% of the rated current of the motor. Most power factor correction is too light due to the selection based on tables which have been published by a number of sources. These tables assume the lowest magnetizing current and quote capacitors for this current. In practice, this can mean that the correction is often less than half the value that it should be, and the consumer is unnecessarily penalized. Power factor correction must be correctly selected based on the actual motor being corrected. The Electrical Calculations software provides two methods of calculating the correct value of KVAR correction to apply to a motor. The first method requires the magnetizing current of the motor. Where this figure is available, then this is the preferred method. Where the magnetizing current is not available, the second method is employed and is based on the half load power factor and efficiency of that motor. These figures are available from the motor data sheets.

FOR EXAMPLE:Motor A is a 200 KW 6 pole motor with a magnetizing current of 124A. From tables, the correction applied would be 37KVAR. From the calculations, this would require a correction of 68.7 KVAR Motor B is a 375KW 2 pole motor with a half load efficiency of 93.9% and a half load power factor of 0.805, the correction recommended by the tables is 44 KVAR while the calculations reveal that the correction should be 81.3KVAR Electrical Calculations is a shareware program which means that you can try it before you buy it. You can freely distribute copies to anyone you please, but if you find it to be useful, as I'm sure you will, then you must purchase it at $NZ35.00 Registered copies of Busbar will be eligible for continued updates, and registered users will be advised of all major upgrades as they become available.

Static Power factor correction can be calculated from known motor characteristics for any given motor, either the magnetizing current and supply voltage (method 1) or half load efficiency and half load power factor(method 2), or, as a last resort, table values can be used. These will almost always result in under correction.Bulk power factor correction can be calculated from known existing power factor, required new powerfactor, line voltage and line current.3.6 SUPPLY HARMONICS:Harmonics on the supply cause a higher current to flow in the capacitors. This is because the impedance of the capacitors goes down as the frequency goes up. This increase in current flow through the capacitor will result in additional heating of the capacitor and reduce it's life. The harmonics are caused bu many non linear loads, the most common in the industrial market today, are the variable speed controllers and switchmode power supplies. Harmonic voltages can be reduced by the use of a harmonic compensator, which is essentially a large inverter that cancells out the harmonics. This is an expensive option. Passive harmonic filters comprising resistors, inductors and capacitors can also be used to reduce harmonic voltages. This is also an expensive exersize.In order to reduce the damage caused to the capacitors by the harmonic currents, it is becomming common today to install detuning reactors in series with the power factor correction capacitors. These reactors are designed to make the correction circuit inductive to the higher frequency harmonics. Typically, a reactor would be designed to create a resonant circuit with the capacitors above the third harmonic, but sometimes it is below. (Never tuned to a harmonic frequency!!) Adding the inductance in series with the cpacitors will reduce their effective capacitance at the supply frequency. Reducing the resonant or tuned frequency will reduce the the effective capacitance further. The object is to make the circuit look as inductive as possible at the 5th harmonic and higher, but as capacitive as possible at the fundemental frequency. Detuning reactors will also reduce the chance of the tuned circuit formed by the capacitors and the inductive supply being resonant on a supply harmonic frequency, thereby reducing damage due to supply resonances amplifying harmonic voltages caused by non linear loads.3.7 DETUNING REACTORS:Detuning reactors are connected in series with power factor correction capacitors to reduce harmonic currents and to ensure that the series resonant frequency does not occur at a harmonic of the supply frequency. The reactors are usually chosen and rated as either 5% or 7% reactors. This means that at the line frequency, the capacitive reactance is reduced by 5% or 7%.Using detuning reactors results in a lower KVAR, so the capacitance will need to be increased for the same level of correction. When detuning reactors are used in installations with high harmonic voltages, there can be a high resultant voltage across the capacitors. This necessitates the use of capacitors that are designed to operate at a high sustained voltage. Capacitors designed for use at line voltage only, should not be used with detuning reactors. Check the suitability of the capacitors for use with line reactors before installation. The detuning reactors can dissipate a lot of heat. The enclosure must be well ventillated, typically forced air cooled. The detuning reactor must be specified to match the KVAR of the capacitance selected. The reactor would typically be rated as 12.5KVAR 5% meaning that it is a 5% reactor to connect to a 12.5KVAR capacitor.

3.8 SUPPLY RESONANCE:Capacitive Power factor correction connected to a supply causes resonance between the supply and the capacitors. If the fault current of the supply is very high, the effect of the resonance will be minimal, however in a rural installation where the supply is very inductive and can be a high impedance, the resonances can be very severe resulting in major damage to plant and equipment. Voltage surges and transients of several times the supply voltage are not uncommon in rural areas with weak supplies, especially when the load on the supply is low. As with any resonant system, a transient or sudden change in current will result in the resonant circuit ringing, generating a high voltage. The magnitude of the voltage is dependant on the 'Q' of the circuit which in turn is a function of the circuit loading. One of the problems with supply resonance is that the 'reaction' is often well removed from the 'stimulus' unlike a pure voltage drop problem due to an overloaded supply. This makes fault finding very difficult and often damaging surges and transients on the supply are treated as 'just one of those things'. To minimize supply resonance problems, there are a few steps that can be taken, but they do need to be taken by all on the particular supply. 1) Minimize the amount of power factor correction, particularly when the load is light. The power factor correction minimizes losses in the supply. When the supply is lightly loaded, this is not such a problem.2) Minimize switching transients. Eliminate open transition switching - usually associated with generator plants and alternative supply switching, and with some electromechanical starters such as the star/delta starter.3) Switch capacitors on to the supply in lots of small steps rather than a few large steps.4) Switch capacitors on o the supply after the load has been applied and switch off the supply before or with the load removal.Harmonic Power Factor correction is not applied to circuits that draw either discontinuous or distorted current waveforms.Most electronic equipment includes a means of creating a DC supply. This involves rectifying the AC voltage, causing harmonic currents. In some cases, these harmonic currents are insignificant relative to the total load current drawn, but in many installations, a large proportion of the current drawn is rich in harmonics. If the total harmonic current is large enough, there will be a resultant distortion of the supply waveform which can interfere with the correct operation of other equipment. The addition of harmonic currents results in increased losses in the supply. Power factor correction for distorted supplies can not be achieved by the addition of capacitors. The harmonics can be reduced by designing the equipment using active rectifiers, by the addition of passive filters (LCR) or by the addition of electronic power factor correction inverters which restore the waveform back to its undistorted state. This is a specialist area requiring either major design changes, or specialized equipment to be used.3.9 Benefits of Power Factor CorrectionMost people associate electricity and energy with kilowatts (kW). In fact, kW only makes up a part of the overall energy usage in a home, commercial building or an industrial manufacturing plant. In the world of AC power, there are actually three types of power: Apparent Power (measured in Volt-Amps) Real Power (measured in Watts) Reactive Power (measured in VARs)The relationship between Apparent Power and the other two is influencedby what is called Power Factor (PF). The PF can be thought of as a measure of electrical efficiency ina power system.Numerous benefits can be derived by providing power factor correction to a facility. Benefit: Reduced Utility BillsUtilities have several different rate structures that may be used for billing. kVA Billing straight charges for all apparent power consumed kVAr Billing additional charges for reactive power Power Factor Penalty charges based on the customers actual power factor Adjusted kW Demand the real power demand is adjusted by a formula and is based on the customers actual power factor In all cases, the power factor of a customer will become a direct or indirect factor in the utility bill.Power bills may be reduced by introducing capacitors to the facility, which can reduce the need for kVAr required from the utility. Capacitors have the added effect of reducing line losses which can reduce the amountof kW hours required by a facility. Additional benefits of reducing linelosses will be discussed later in this document.Benefit: Electrical System Capacity Capacitors in a facility produce reactive energy that motors require to produce magnetizing current for induction motors and transformers. This reduces the overall current needed from the power supply. This translates into reduced loads on both transformers and feeder circuits.Capacitors Provide Reactive Power

Reduced loads on transformers can have a variety of positive impacts that include but are not limited to: less maintenance, reduced breaker trips, and higher full-load capacity.Benefit: Improved Voltage LevelsLow voltage may be caused by a lack of reactive energy. Additionally, voltage drops are often caused by dynamic load changes. In both cases, the effects can be harmful. In facilities with motors, low voltage reduces motor efficiency and can cause overheating. Interference may be introduced by low voltage in lighting and other electrical instruments (i.e. Computers). Welding plants in particular, may suffer from voltage drops. The quality of a weld is directly proportional to the voltage. These voltage drops can cause bad welds which translate into scrap or possible product recalls if allowed to persist. Real-time capacitor systems ( , the STATCOM supplies reactive power to the ac system. If V V i T< , the STATCOM absorbs reactive power. State of the art for STATCOM is by the use of IGBT (Insulated Gate Bipolar Transistors). By use of high frequency Pulse Width Modulation (PWM), it has become possible to use a single converter connected to a standard power transformer via air-core phase reactors. The core parts of the plant are located inside a prefabricated building. The outdoor equipment is limited to heat exchangers, phase reactors and the power transformer. For extended range of operation, additional fixed capacitors, thyristor switched capacitors or an assembly of more than one converter may be used.

The semiconductor valves in a STATCOM respond almost instantaneously to a switching order. Therefore the limiting factor for the comple plant speed of response is determined by the time needed for voltage measurements and the control system data processing. A high gain controller can be used and a response time shorter than a quarter of a cycle is obtained. The high switching frequency used in the IGBT based STATCOM concept results in an inherent capability to produce voltages at frequencies well above the fundamental one. This property can be used for active filtering of harmonics already present in the network. The STATCOM then injects harmonic currents into the network with proper phase and amplitude to counteract the harmonic voltages. By adding storage capacity to the DC side of STATCOM, it becomes possible not only to control reactive power, but also active power. As storage facility, various kinds of battery cells can be used, depending on the requirements on the storage facility. The result, STATCOM with energy storage (Fig. 7), is expected to come into use in years to come as dynamic storage facility particularly of renewable energy (wind, solar).

Impact of FACTS in interconnected networks The benefits of power system interconnection are well established. It enables the participating parties to share the benefits of large power systems, such as optimization of power generation, utilization of differences in load profiles and pooling of reserve capacity. From this follows not only technical and economical benefits, but also environmental, when for example surplus of clean hydro resources from one region can help to replace polluting fossil-fuelled generation in another. For interconnections to serve their purpose, however, available transmission links must be powerful enough to safely transmit the amounts of power intended. If this is not the case, from a purely technical point of view it can always be remedied by building additional lines in parallel with the existing, or by uprating the existing system(s) to a higher voltage.

This, however, is expensive, time-consuming, and calls for elaborate procedures for gaining the necessary permits. Also, in many cases, environmental considerations, popular opinion or other impediments will render the building of new lines as well as uprating to ultra-high system voltages impossible in practice. This is where FACTS is coming in. Examples of successful implementation of FACTS for power system interconnection can be found among others between the Nordic Countries and between Canada and the United States. In such cases, FACTS helps to enable mutually beneficial trade of electric energy between the countries. Other regions in the world where FACTS is emerging as a means for AC bulk power interchange between regions can be found in South Asia as well as in Africa and Latin America. In fact, AC power corridors equipped with SVC and/or SC transmitting bulk power over distances of more than 1.000 km are a reality today.

Chapter-7PV SOLAR PLANT CONTROL CIRCUIT

Chapter-8INTRODUCTION TO MATLAB

MATLAB is a software package for computation in engineering, science, and applied mathematics.

It offers a powerful programming language, excellent graphics, and a wide range of expert knowledge. MATLAB is published by and a trademark of The MathWorks, Inc.

The focus in MATLAB is on computation, not mathematics: Symbolic expressions and manipulations are not possible (except through the optional Symbolic Toolbox, a clever interface to maple). All results are not only numerical but inexact, thanks to the rounding errors inherent in computer arithmetic. The limitation to numerical computation can be seen as a drawback, but its a source of strength too: MATLAB is much preferred to Maple, Mathematical, and the like when it comes to numerics.

On the other hand, compared to other numerically oriented languages like C++ and FORTRAN, MATLAB is much easier to use and comes with a huge standard library.1 the unfavorable comparison here is a gap in execution speed. This gap is not always as dramatic as popular lore has it, and it can often be narrowed or closed with good MATLAB programming. Moreover, one can link other codes into MATLAB, or vice versa, and MATLAB now optionally supports parallel computing. Still, MATLAB is usually not the tool of choice for maximum-performance Computing.The MATLAB niche is numerical computation on workstations for non-experts in computation.

This is a huge nicheone way to tell is to look at the number of MATLAB-related books on mathworks.com. Even for supercomputer users, MATLAB can be a valuable environment in which to explore and fine-tune algorithms before more laborious coding in another language.Most successful computing languages and environments acquire a distinctive character or culture.In MATLAB, that culture contains several elements: an experimental and graphical bias, resulting from the interactive environment and compression of the write-compile-link-execute analyze cycle; an emphasis on syntax that is compact and friendly to the interactive mode, rather than tightly constrained and verbose; a kitchen-sink mentality for providing functionality; and a high degree of openness and transparency (though not to the extent of being open source software).

The fifty-cent tourWhen you start MATLAB, you get a multipaneled desktop. The layout and behavior of the desktop and its components are highly customizable (and may in fact already be customized for your site). The component that is the heart of MATLAB is called the Command Window, located on the 1Here and elsewhere I am thinking of the old FORTRAN, FORTRAN 77. This is not a commentary on the usefulness of FORTRAN 90 but on my ignorance of it.

INTRODUCTION

Right by default. Here you can give MATLAB commands typed at the prompt, >>. Unlike FORTRAN and other compiled computer languages, MATLAB is an interpreted environmentyou give a command, and MATLAB tries to execute it right away before asking for another.

At the top left you can see the Current Directory. In general MATLAB is aware only of files in the current directory (folder) and on its path, which can be customized. Commands for working with the directory and path include cd, what, addpath, and editpath (or you can choose File/Set path. . . from the menus). You can add files to a directory on the path and thereby add commands to MATLAB; we will return to this subject in section 3.Next to the Current Directory tab is the Workspace tab. The workspace shows you what variable names are currently defined and some information about their contents. (At start-up it is, naturally, empty.) This represents another break from compiled environments: variables created in the workspace persist for you to examine and modify, even after code execution stops. Below the CommandWindow/Workspace window is the Command History window. As you enter commands, they are recorded here. This record persists across different MATLAB sessions, and commands or blocks of commands can be copied from here or saved to files.

As you explore MATLAB, you will soon encounter some toolboxes. These are individually packaged sets of capabilities that provide in-depth expertise on particular subject areas. There is no need to load them explicitlyonce installed, they are always available transparently. You may also encounter Simulink, which is a semi-independent graphical control-engineering package not covered in this document.Graphical versus command-line usage

MATLAB was originally entirely a command-line environment, and it retains that orientation.But it is now possible to access a great deal of the functionality from graphical interfacesmenus, buttons, and so on. These interfaces are especially useful to beginners, because they lay out the available choices clearly.2 As a rule, graphical interfaces can be more natural for certain types of interactive work, such as annotating a graph or debugging a program, whereas typed commands remain better for complex, precise, repeated, or reproducible tasks. One does not always need to make a choice, though; for instance, it is possible to save a figures styles as a template that can be used with different data by pointing and clicking. Moreover, you can package code you want to distribute with your own graphical interface, one that itself may be designed with a combination of graphical and command-oriented tools. In the end, an advanced MATLAB user should be able to exploit both modes of work to be productive.

That said, the focus of this document is on typed commands. In many (most?) cases these have graphical interface equivalents, even if I dont explicitly point them out.In particular, feel free to right-click (on Control-click on a Mac) on various objects to see what you might be able todo to them.WHAT IS SIMULINK

Simulink (Simulation and Link) is an extension of MATLAB by Math works Inc. It works with MATLAB to offer modeling, simulating, and analyzing of dynamical systems under a graphical user interface (GUI) environment. The construction of a model is simplified with click-and-drag mouse operations. Simulink includes a comprehensive block library of toolboxes for both linear and nonlinear analyses. Models are hierarchical, which allow using both top-down and bottom-up approaches. As Simulink is an integral part of MATLAB, it is easy to switch back and forth during the analysis process and thus, the user may take full advantage of features offered in both environments. This tutorial presents the basic features of Simulink and is focused on control systems as it has been written for students in my control systems .

Getting StartedTo start a Simulink session, you'd need to bring up Matlab program first. From Matlab command window, enter:>> simulinkAlternately, you may click on the Simulink icon located on the toolbar as shown

To see the content of the blockset, click on the "+" sign at the beginning of each toolbox.To start a model click on the NEW FILE ICON as shown in the screenshot above.Alternately, you may use keystrokes CTRL+N.A new window will appear on the screen. You will be constructing your model in this window. Also in this window the constructed model is simulated. A screenshot of a typical working (model) window that looks like one shown below:

To become familiarized with the structure and the environment of Simulink, you are encouraged to explore the toolboxes and scan their contents.

You may not know what they are all about but perhaps you could catch on the organization of these toolboxes according to the category. For instant, you may see Control System Toolbox to consist of the Linear Time Invariant (LTI) system library and the MATLAB functions can be found under Function and Tables of the Simulink main toolbox. A good way to learn Simulink (or any computer program in general) is to practice and explore. Making mistakes is a part of the learning curve. So, fear not, you should be.

A simple model is used here to introduce some basic features of Simulink. Please follow the steps below to construct a simple model.

STEP 1: CREATING BLOCKS.

From BLOCK SET CATEGORIES section of the SIMULINK LIBRARY BROWSER window, click on the "+" sign next to the Simulink group to expand the tree and select (click on) Sources.

A set of blocks will appear in the BLOCKSET group. Click on the Sine Wave blockand drag it to the workspace window (also known as model window)

A set of blocks will appear in the BLOCKSET group. Click on the Sine Wave blockand drag it to the workspace window (also known as model window)

I am going to save this model under the filename: "simexample1". To save a model, you may click on the floppy diskette icon. Or from FILE menu, select Save or CTRL+S. All Simulink model file will have an extension ".mdl". Simulink recognizes file with .mdl extension as a simulation model (similar to how MATLAB recognizes files with the extension .m as an MFile).

Continue to build your model by adding more components (or blocks) to your model window. We'll continue to add a Scope from Sinks library, an Integrator block from Continuous library, and a Mux block from Signal Routing library.

NOTE: If you wish to locate a block knowing its name, you may enter the name in the SEARCH WINDOW (at Find prompt) and Simulink will bring up the specified block.

To move the blocks around, simply click on it and drag it to a desired location.Once all the blocks are dragged over to the work space should consist of the following components:

You may remove (delete) a block by simply clicking on it once to turn on the "select mode" (with four corner boxes) and use the DEL key or keys combination CTRL-X.

STEP 2: MAKING CONNECTIONSTo establish connections between the blocks, move the cursor to the output port represented by ">" sign on the block. Once placed at a port, the cursor will turn into a cross "+" enabling you to make connection between blocks.To make a connection: left-click while holding down the control key (on your keyboard) and drag from source port to a destination port.

The connected model is shown below.

A sine signal is generated by the Sine Wave block (a source) and is displayed by the scope. The integrated sine signal is sent to scope for display along with the original signal from the source via the Mux, whose function is to multiplex signals in form of scalar, vector, or matrix into a bus.

STEP 3: RUNNING SIMULATION

You now can run the simulation of the simple system above by clicking on the play button (alternatively, you may use key sequence CTRL+T, or choose Start submenu under Simulation menu).

Double click on the Scope block to display of the scope.

INTRODUCTION

SimPowerSystems and other products of the Physical Modeling product family work together with Simulink to model electrical, mechanical, and control systems.

SimPowerSystems operates in the Simulink environment. Therefore, before starting this users guide, you should be familiar with Simulink. For help with Simulink, see the Simulink documentation. Or, if you apply Simulink to signal processing and communications tasks (as opposed to control system design tasks), see the Signal Processing Block set documentation.

The Role of Simulation in Design

Electrical power systems are combinations of electrical circuits and electromechanical devices like motors and generators. Engineers working in this discipline are constantly improving the performance of the systems.Requirements for drastically increased efficiency have forced power system designers to use power electronic devices and sophisticated control system concepts that tax traditional analysis tools and techniques. Further complicating the analysts role is the fact that the system is often so nonlinear that the only way to understand it is through simulation.

Land-based power generation from hydroelectric, steam, or other devices is not the only use of power systems. A common attribute of these systems is their use of power electronics and control systems to achieve their performance objectives.

What Is SimPowerSystemsSimPowerSystems is a modern design tool that allows scientists and engineers to rapidly and easily build models that simulate power systems.SimPowerSystems uses the Simulink environment, allowing you to build a model using simple click and drag procedures. Not only can you draw the circuit topology rapidly, but your analysis of the circuit can include its interactions with mechanical, thermal, control, and other disciplines. This is possible because all the electrical parts of the simulation interact with the extensive Simulink modeling library. Since Simulink uses MATLAB as its computational engine, designers can also use MATLAB toolboxes and Simulink block sets. SimPowerSystems and Sim Mechanics share a specialPhysical Modeling block and connection line interface.

SimPowerSystems Libraries

You can rapidly put SimPowerSystems to work. The libraries contain models of typical power equipment such as transformers, lines, machines, and power electronics. These models are proven ones coming from textbooks, and their validity is based on the experience of the Power Systems Testing and Simulation Laboratory of Hydro-Qubec, a large North American utility located in Canada, and also on the experience of cole de Technologie Suprieure and Universit Laval. The capabilities of SimPowerSystems for modeling a typical electrical system are illustrated in demonstration files. And for users who want to refresh their knowledge of power system theory, there are also self-learning case studies.The SimPowerSystems main library, power lib, organizes its blocks into libraries according to their behavior. The power lib library window displays the block library icons and names. Double-click a library icon to open the library and access the blocks. The main SimPowerSystems power lib library window also contains the Powergui block that opens a graphical user interface for the steady-state analysis of electrical circuits.

Nonlinear Simulink Blocks for SimPowerSystems ModelsThe nonlinear Simulink blocks of the power lib library are stored in a special\block library named powerlib_models. These masked Simulink models are used by SimPowerSystems to build the equivalent Simulink model of your circuit. See Chapter 3, Improving Simulation Performance for a description of the powerlib_models library

You must have the following products installed to use SimPowerSystems: MATLAB Simulink

3.4. PULSE WIDTH MODULATION TECHNIQUE:

The advent of the transformerless multilevel inverter topology has brought forth various pulse width modulation (PWM) schemes as a means to control the switching of the active devices in each of the multiple voltage levels in the inverter. The most efficient method of controlling the output voltage is to incorporate pulse width modulation control (PWM control) within the inverters. In this method, a fixed d.c. input voltage is supplied to the inverter and a controlled a.c. output voltage is obtained by adjusting the on andoff periods of the inverter devices. Voltage-type PWM inverters have been applied widely to such fields as power supplies and motor drivers. This is because: (1) such inverters are well adapted to high-speed self turn-off switching devices that, as solid-state power converters, are provided with recently developed advanced circuits; and (2) they are operated stably and can be controlled well.

The PWM control has the following advantages:

(i) The output voltage control can be obtained without any additional components.(ii) With this type of control, lower order harmonics can be eliminated or minimized along with its output voltage control. The filtering requirements are minimized as higher order harmonics can be filtered easily.The commonly used PWM control techniques are:(a) Sinusoidal pulse width modulation (sin PWM)(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 within the inverter, c) Peak-to-peak ripple in the load current, and d) Maximum inverter output voltage for a given DC rail voltage.

From the above all mentioned PWM control methods, the Sinusoidal pulse width modulation (sinPWM) is applied in the proposed inverter since it has various advantages over other techniques. Sinusoidal PWM inverters provide an easy way to control amplitude, frequency and harmonics contents of the output voltage.

Sinusoidal Pulse Width ModulationIn 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 or 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 of concern because they can be eliminated easily by filters. The SPWM aims at generating a sinusoidal inverter output voltage without low-order harmonics. This is possible if the sampling frequency is high compared to the fundamental output frequency of the inverter. Sinusoidal pulse width modulation is one of the primitive techniques, which are used to suppress harmonics presented in the quasi-square wave. SAMPLING TECHNIQUEIn this method of modulation, several pulses per half-cycle are used. Instead of maintaining the width of all pulses, the width of each pulse is varied proportional to the amplitude of a sin-wave evaluated at the centre of the same pulse. By comparing a sinusoidal reference signal with a triangular carrier wave, the gating signals are generated. The frequency of reference signal determine the inverter output frequency and its peak amplitude, controls the modulation index, M, and then in turn the RMS output voltage. Fig.3.2 shows the more common carrier technique, the conventional sinusoidal pulse width modulation (SPWM) technique, which is based on the principle of comparing a triangular carrier signal with a sinusoidal reference waveform (natural sampling).

The figure below gives the sinusoidal pulse width modulation.

(a)

(b)

(c) (a) Modulating/reference and carrier waveform . (b) Line-to-neutral switching pattern. (c) Line-to-line output waveform.Graph. 3.1 (a), (b), (c) Sinusoidal Pulse Width Modulation (SPWM).

By varying the modulation index M, the RMS output voltage can be varied. It can be observed that the area of each pulse corresponds approximately to the area under the sine-wave between the adjacent midpoints of off periods on the gating signals. The phase voltage can be described by the following expressions:

where wm is the angular frequency of modulating or sinusoidal signal.wc is the angular frequency of the carrier signal.M is modulation index

.

E is the dc supply voltage. f is the displacement angle between modulating and carrier signals.and Jo and Jn are Bessel functions of the first kind.The amplitude of the fundamental frequency components of the output is directly proportional to the modulation depth. The second term of the equation gives the amplitude of the component of the carrier frequency and the harmonics of the carrier frequency. The magnitude of this term decreases with increased modulation depth. Because of the presence of sin(m /2), even harmonics of the carrier are eliminated. Term 3 gives the amplitude of the harmonics in the sidebands around each multiple of the carrier frequency. The presence of sin((m+n) / 2) indicated that, for odd harmonics of the carrier, only even-order sidebands exist, and for even harmonics of the carrier only oddorder sidebands exist. In addition, increasing carrier or switching frequency does not decrease the amplitude of the harmonics, but the high amplitude harmonic at the carrier frequency is shifted to higher frequency. Consequently, requirements of the output filter can be improved. However, it is not possible to improve the total harmonic distortion without using output filter circuits. In multilevel case, SPWM techniques with three different disposed triangular carriers were proposed as follows:

1. All the carriers are alternatively in opposition (APO disposition)2. All the carriers above the zero value reference are in phase among them, but in opposition with those below (PO disposition)3. All the carriers are in phase (PH disposition)4. Multi carrier modulation techniqueIn the proposed inverter circuit the multi carrier modulation technique is employed.

PROPOSED MODULATION TECHNIQUE:3.5.1 MULTICARIER MODULATIONThis technique involves the carrier based PWM3.5.2 CARRIER BASED PWMThese are the classical and most widely used methods of pulse width modulation. They have as common characteristic subcycles of constant time duration, a subcycle being defined as the total duration Ts during which an active inverter leg assumes two consecutive switching states of opposite voltage polarity. Operation at subcycles of constant duration is reflected in the harmonic spectrum by two salient sidebands, centered around the carrier frequency, and additional frequency bands around integral multiples of the carrier. The multi carrier modulation technique is very suitable for a multilevel in