Biogas based Electricity generation plant

Even today in 2013, over 400 million people in India have no access to electricity. Because of the remoteness of much of India’s un-electrified population, renewable energy can offer an economically viable means of undoing this undone. And what better than a biomass power plant. Today, about 32% of the total primary energy use in the country is still derived from biomass and more than 70% of the country’s population depends upon it for its energy needs in some way or the other. Biomass power generation in India is an industry that attracts investments of over Rs.600 crores every year, generating more than 5000 million units of electricity and yearly employment of more than 10 million man-days in the rural areas. We can divide the biomass power plant market in India into 3 categories. Biogas based power projects Present. The current availability of biomass in India is estimated to be approximately640 million metric tones per annum. This converted to cubic meters of biogas comes to 12800 million cubic meters per annum (@ 20 cubic meters of biogas per metric ton of biomass). • This should lead to both electricity and heat generation of 25600 GWh and 51200 GWh per annum respectively (@ 2 KWh of electricity and 4 KWh of heat energy per cubic meter of biogas). • The Government of India has estimated this availability of biomass to a corresponding potential of about 18000 MW generation capacity. • If the above two statements are combined, it comes to around 4 hrs of electricity generation for 365 days a year. Some case studies displayed at MNRE website talk about 6-7 hours of electricity daily in villages using a 10 KW plant. • A total of around 130 biogas power projects have been installed in the country as on date for feeding power to the grid aggregating to 1176.10 MW of generation capacity. Biogas technology, the generation of a combustible gas from anaerobic biomass digestion, is a well-known technology. There are already millions of biogas plants in operation throughout the world. Whereas using the gas for direct combustion in household stoves or gas lamps is common, producing electricity from biogas is still relatively rare in most developing countries. In Germany and other industrialised countries, power generation is the main purpose of biogas plants; conversion of biogas to electricity has become a standard technology. This document will discuss the potentials, obstacles and necessary framework conditions for the utilisation of biogas for small and medium scale electricity generation in developing countries. This paper will not address the biogas production process in general but focus uniquely on electricity generation. The findings presented here are based mainly on available experience from GTZ-related pilot biogas power plants in different countries. They focus on more or less well-documented existing country cases even though little extensive documentation of practical long term operat-ing experience is available. Besides the cases described here, we know of further examples from other GTZ projects (e.g. Bolivia, Tunisia and the Ivory Coast). However, there is not yet sufficient information concerning these to merit inclusion in this assessment. Biogas is gas resulting from an anaerobic digestion process. A biogas plant can convert animal manure, green plants, waste from agro industry and slaughterhouses into combustible gas. Biogas can be used in similar ways to natural gas in gas stoves, lamps or as fuel for engines. It consists of 50-75% methane, 25-45% carbon dioxide, 2-8% water vapour and traces of O2 N2, NH3 H2 H2S. Compare this with natural gas, which contains 80 to 90% methane. The energy content of the gas depends mainly on its methane content. High methane content is therefore desirable. A certain carbon dioxide and water vapour content is unavoidable, but sulphur content must be minimised - particularly for use in engines. The average calorific value of biogas is about 21-23.5 MJ/m³, so that 1 m³ of biogas corre-sponds to 0.5-0.6 l diesel fuel or about 6 kWh (FNR, 2009). The biogas yield of a plant depends not only on the type of feedstock, but also on the plant design, fermentation temperature and retention time. Maize silage for example - a common feedstock in Germany - yields about 8 times more biogas per tonne than cow manure. In most cases, biogas is used as fuel for combustion engines, which convert it to mechanical energy, powering an electric generator to produce electricity. Appropriate electric generators are available in virtually all countries and in all sizes. The technology is well known and maintenance is simple. In most cases, even universally available 3-phase electric motors can be converted into generators. Technologically far more challenging is the first stage of the generator set: the combustion engine using the biogas as fuel. In theory, biogas can be used as fuel in nearly all types of combustion engines, such as gas engines (Otto motor), diesel engines, gas turbines and Stirling motors etc.

Gas turbines are occasionally used as biogas engines, especially in the US. They are very small and can meet strict exhaust emissions requirements. Small biogas turbines with power outputs of 30-75 kW are available on the market, but are rarely used for small-scale applications in developing countries as they are expensive. Furthermore, due to their spinning at very high speeds and the high operating temperatures, the design and manufacturing of gas turbines is challenging and maintenance requires specific skills. External combustion engines such as Stirling motors have the advantage of being tolerant of fuel composition and quality. They are, however, relatively expensive and characterised by low efficiency. Their use is therefore limited to a number of very specific applications. In most commercially run biogas power plants today, internal combustion motors have become the standard technology either as gas or diesel motors.

Solar chimney based Power Plant

The solar updraft tower (SUT) is a renewable-energy power plant for generating electricity from solar power. Sunshine heats the air beneath a very wide greenhouse-like roofed collector structure surrounding the central base of a very tall chimney tower. The resulting convection causes a hot air updraft in the tower by the chimney effect. This airflow drives wind turbines placed in the chimney updraft or around the chimney base to produce electricity. Plans for scaled-up versions of demonstration models will allow significant power generation, and may allow development of other applications, such as water extraction or distillation, and agriculture or horticulture. As a solar chimney power plant (SCPP) proposal for electrical power generation, commercial investment is discouraged by the high initial cost of building a very large novel structure, and by the risk of investment in a feasible but unproven application of even proven component technology for long-term returns on investment—especially when compared to the proven and demonstrated greater short-term returns on lesser investment in coal-fired or nuclear power plants Power output depends primarily on two factors: collector area and chimney height. A larger area collects and warms a greater volume of air to flow up the chimney; collector areas as large as 7 kilometres (4.3 mi) in diameter have been discussed. A larger chimney height increases the pressure difference via the stack effect; chimneys as tall as 1,000 metres (3,281 ft) have been discussed. Heat can be stored inside the collector area. The ground beneath the solar collector, water in bags or tubes, or a saltwater thermal sink in the collector could add thermal capacity and inertia to the collector. Humidity of the updraft and condensation in the chimney could increase the energy flux of the system. Turbines with a horizontal axis can be installed in a ring around the base of the tower, as once planned for an Australian project and seen in the diagram above; or—as in the prototype in Spain—a single vertical axis turbine can be installed inside the chimney. Carbon dioxide is emitted only negligibly as part of operations. Manufacturing and construction require substantial power, particularly to produce cement. Net energy payback is estimated to be 2–3 years. Since solar collectors occupy significant amounts of land, deserts and other low-value sites are most likely. A small-scale solar updraft tower may be an attractive option for remote regions in developing countries. The relatively low-tech approach could allow local resources and labour to be used for construction and maintenance. Locating a tower at high latitudes could produce up to 85 per cent of the output of a similar plant located closer to the equator, if the collection area is sloped significantly toward the equator. The sloped collector field, which also functions as a chimney, is built on suitable mountainsides, with a short vertical chimney on the mountaintop to accommodate the vertical axis air turbine. The results showed that solar chimney power plants at high latitudes may have satisfactory thermal performance. Solar updraft towers can be combined with other technologies to increase output. Solar thermal collectors or photovoltaics can be arranged inside the collector greenhouse. This could further be combined with agriculture The solar updraft tower has a power conversion rate considerably lower than many other designs in the (high temperature) solar thermal group of collectors. The low conversion rate is balanced to some extent by the lower cost per square metre of solar collection. Model calculations estimate that a 100 MW plant would require a 1,000 m tower and a greenhouse of 20 square kilometres (7.7 sq mi). A 200 MW tower with the same tower would require a collector 7 kilometres in diameter (total area of about 38 km²). One 200MW power station will provide enough electricity for around 200,000 typical households and will abate over 900,000 tons of greenhouse producing gases from entering the environment annually. The collector area is expected to extract about 0.5 percent, or 5 W/m² of 1 kW/m², of the solar energy that falls upon it. Concentrating thermal (CSP) or photovoltaic (CPV) solar power plants range between 20% to 31.25% efficiency (dish Stirling). Overall CSP/CPV efficiency is reduced because collectors do not cover the entire footprint. Without further tests, the accuracy of these calculations is uncertain. Most of the projections of efficiency, costs and yields are calculated theoretically, rather than empirically derived from demonstrations, and are seen in comparison with other collector or solar heat transducing technologies. The performance of an updraft tower may be degraded by factors such as atmospheric winds, by drag induced by the bracings used for supporting the chimney, and by reflection off the top of the greenhouse canopy. At present, a number of energy sources are utilized on a large scale such as: coil, oil, gas and nuclear. Continuation of the use of fossil fuels is set to face multiple challenges namely: depletion of fossil fuels reserves, global warming and other environmental concerns and continuing fuel price rise. For these reasons, the existing sources of conventional energy may not be adequate to meet the ever increasing energy demands. Consequently sincere and untiring efforts shall have to be made by the scientists and engineers in exploring the possibilities of harnessing energy from several non-conventional energy sources (solar, biomass, tidal, hydrogen, wind and geothermal energy) which they are seen as possible solution to the growing energy challenges. According to energy experts, unconventional energy sources can be used for electric power generation which receives a great attention. Power generating technology based on green resources would help many countries improve their balance of payments. Being the most abundant and well distributed form of renewable energy, solar energy constitutes a big asset for arid and semi-arid regions. A range of solar technologies are used throughout the world to harvest the sun‘s energy. In the last years, an exciting innovation has been introduced by researchers called ―solar chimney‖. It is a solar thermal driven electrical power generation plant which converts the solar thermal energy into electrical power in a complex heat transfer process. The implementation of this project is of great significance for the development of new energy resources and the commercialization of power generating systems of this type and will help developing countries to promote the rapid development of the solar hot air-flows power generation. The basic physical principles of centralized electricity generation with solar chimney power plants (SCPP‘s) were described by Haaf et al. in 1982. After the pilot plant in Manzanares had gone into operation in June 1982, the first experimental results confirmed the main assumptions of the original physical model. Later, on the basis of experimental data from July 1983 to January 1984, a semi-empirical, parametrical model was proposed for predicting the monthly mean electrical power output of the pilot plant as a function of solar irradiation. The model predictions agreed reasonably with the experimental data for the exceptionally dry months July- October 1983, but the model failed to simulate the wet months following heavy rainfall in winter and spring 1984. It was realized, that natural precipitation entering the collector has a fundamental influence on the collector performance via evaporation, plant growth and infrared absorption in the collector air. A refined parametrical model was therefore proposed, which includes at least the long term, seasonally varying effect on rainwater on the plants performance and allows the simulation of large plants in climates similar to the climate in Manzanares. Solar chimney power plants are an interesting alternative to centralized electricity generation power plants. It is an ideally adapted technology for countries that lack a sophisticated technical infrastructure, where simplicity and uncritical operation of the installation is of crucial importance. A detailed literature survey of this system was performed. The review discusses the principles and characteristics of such a system, its requirements, its construction and its operation. It gives also a brief overview of the present state of research at the solar chimney power plant and future prospects for large-scale plants.

Solar Ponds A solar Thermal Energy Collector

A solar pond is a pool of saltwater which acts as a large-scale solar thermal energy collector with integral heat storage for supplying thermal energy. A solar pond can be used for various applications, such as process heating, desalination, refrigeration, drying and solar power generation. A solar pond is simply a pool of saltwater which collects and stores solar thermal energy. The saltwater naturally forms a vertical salinity gradient also known as a "halocline", in which low-salinity water floats on top of high-salinity water. The layers of salt solutions increase in concentration (and therefore density) with depth. Below a certain depth, the solution has a uniformly high salt concentration. There are 3 distinct layers of water in the pond: • The top layer, which has a low salt content. • An intermediate insulating layer with a salt gradient, which establishes a density gradient that prevents heat exchange by natural convection. • The bottom layer, which has a high salt content. If the water is relatively translucent, and the pond's bottom has high optical absorption, then nearly all of the incident solar radiation (sunlight) will go into heating the bottom layer. When solar energy is absorbed in the water, its temperature increases, causing thermal expansion and reduced density. If the water were fresh, the low-density warm water would float to the surface, causing a convection current. The temperature gradient alone causes a density gradient that decreases with depth. However the salinity gradient forms a density gradient that increases with depth, and this counteracts the temperature gradient, thus preventing heat in the lower layers from moving upwards by convection and leaving the pond. This means that the temperature at the bottom of the pond will rise to over 90 °C while the temperature at the top of the pond is usually around 30 °C. A natural example of these effects in a saline water body is Solar Lake in the Sinai Peninsula of Egypt. The heat trapped in the salty bottom layer can be used for many different purposes, such as the heating of buildings or industrial hot water or to drive an organic Rankine cycleturbine or Stirling engine for generating electricity. Salinity-gradient solar ponds can collect and store solar heat at temperatures up to 80 °C. As a result, these water bodies act as a renewable source of low grade heat which can be utilized for heating and power generation applications. In this paper, design and test result of the combined system of thermosyphon and thermoelectric modules (TTMs) for the generation of electricity from low grade thermal sources like solar pond is discussed. In solar ponds, temperature difference in the range 40–60 °C is available between the lower convective zone (LCZ) and the upper convective zone (UCZ) which can be applied across the hot and cold surfaces of the thermoelectric modules to make it work as a power generator. The designed system utilizes gravity assisted thermosyphon to transfer heat from the hot bottom to the cold top of the solar pond. Thermoelectric cells (TECs) are attached to the top end of the thermosyphon which lies in the UCZ thereby maintaining differential temperature across them. A laboratory scale model based on the proposed combination of thermosyphon and thermoelectric cells was fabricated and tested under the temperature differences that exist in the solar ponds. Result outcomes from the TTM prototype have indicated significant prospects of such system for power generation from low grade heat sources particularly for remote area power supply. A potential advantage of such a system is its ability to continue to provide useful power output at night time or on cloudy days because of the thermal storage capability of the solar pond. Advantages and disadvantages • The approach is particularly attractive for rural areas in developing countries. Very large area collectors can be set up for just the cost of the clay or plastic pond liner. • The evaporated surface water needs to be constantly replenished. • The accumulating salt crystals have to be removed and can be both a valuable by-product and a maintenance expense. • No need of a separate collector for this thermal storage system. Efficiency The energy obtained is in the form of low-grade heat of 70 to 80 °C compared to an assumed 20 °C ambient temperature. According to the second law of thermodynamics (seeCarnot-cycle), the maximum theoretical efficiency of a cycle that uses heat from a high temperature reservoir at 80 °C and has a lower temperature of 20 °C is 1−(273+20)/(273+80)=17%. By comparison, a power plant's heat engine delivering high-grade heat at 800 °C would have a maximum theoretical limit of 73% for converting heat into useful work (and thus would be forced to divest as little as 27% in waste heat to the cold temperature reservoir at 20 °C). The low efficiency of solar ponds is usually justified with the argument that the 'collector', being just a plastic-lined pond, might potentially result in a large-scale system that is of lower overall levelised energy cost than a solar concentrating system.

Bio Fuels: A fuel for future growth of India

Biofuel development in India centres mainly around the cultivation and processing of Jatropha plant seeds which are very rich in oil (40%). The drivers for this are historic, functional, economic, environmental, moral and political. Jatropha oil has been used in India for several decades as biodiesel for the diesel fuel requirements of remote rural and forest communities; jatropha oil can be used directly after extraction (i.e. without refining) in diesel generators and engines. Jatropha has the potential to provide economic benefits at the local level since under suitable management it has the potential to grow in dry marginal non-agricultural lands, thereby allowing villagers and farmers to leverage non-farm land for income generation. As well, increased Jatropha oil production delivers economic benefits to India on the macroeconomic or national level as it reduces the nation's fossil fuel import bill for diesel production (the main transportation fuel used in the country); minimising the expenditure of India's foreign-currency reserves for fuel allowing India to increase its growing foreign currency reserves (which can be better spent on capital expenditures for industrial inputs and production). And since Jatropha oil is carbon-neutral, large-scale production will improve the country's carbon emissions profile. Finally, since no food producing farmland is required for producing this biofuel (unlike corn or sugar cane ethanol, or palm oil diesel), it is considered the most politically and morally acceptable choice among India's current biofuel options; it has no known negative impact on the production of the massive amounts grains and other vital agriculture goods India produces to meet the food requirements of its massive population (circa 1.1 Billion people as of 2008). Other biofuels which displace food crops from viable agricultural land such as corn ethanol or palm biodiesel have caused serious price increases for basic food grains and edible oils in other countries.

India's total biodiesel requirement is projected to grow to 3.6 million tonnes in 2011–12, with the positive performance of the domestic automobile industry. Analysis from Frost & Sullivan, Strategic Analysis of the Indian Biofuels Industry, reveals that the market is an emerging one and has a long way to go before it catches up with global competitors. The Government is currently implementing an ethanol-blending program and considering initiatives in the form of mandates for biodiesel. Due to these strategies, the rising population, and the growing energy demand from the transport sector, biofuels can be assured of a significant market in India. On 12 September 2008, the Indian Government announced its 'National Biofuel Policy’. It aims to meet 20% of India's diesel demand with fuel derived from plants. That will mean setting aside 140,000 square kilometres of land. Presently fuel yielding plants cover less than 5,000 square kilometres. Biodiesel is a safe alternative fuel to replace traditional petroleum diesel. It has high-lubricity, is a clean-burning fuel and can be a fuel component for use in existing, unmodified diesel engines. This means that no retrofits are necessary when using biodiesel fuel in any diesel powered combustion engine. It is the only alternative fuel that offers such convenience. Biodiesel acts like petroleum diesel, but produces less air pollution, comes from renewable sources, is biodegradable and is safer for the environment. Producing biodiesel fuels can help create local economic revitalization and local environmental benefits. Many groups interested in promoting the use of biodiesel already exist at the local, state and national level. Biodiesel is designed for complete compatibility with petroleum diesel and can be blended in any ratio, from additive levels to 100 percent biodiesel. In the United States today, biodiesel is typically produced from soybean or rapeseed oil or can be reprocessed from waste cooking oils or animal fats such as waste fish oil. Because it is made of these easily obtainable plant-based materials, it is a completely renewable fuel source. BENEFITS OF BIODIESEL Biodiesel can be considered a new technology, taking into account all the years consumers have had to settle for traditional diesel. 1. Biodiesel is not harmful to the environment. A vehicle tends to pollute the environment and emits harmful gasses, if injected with HSD whereas if the engine is using biodiesel it emits no harmful gasses rather keeps the environment pollution free. 2. Biodiesel may not require an engine modification. Biodiesel can be blended with diesel so as to improve the efficiency of the engine without any hassles. 3. Biodiesel is cheap. You can even make biodiesel in your backyard. If your engine can work with biodiesel fuel alone, then you really need not go to the gas station to buy fuel. You can just manufacture some for your own personal use. 4. Any Vehicle using Biodiesel has very low idle stating noise. It is noted that biodiesel has a Cetane number of over 100. Cetane number is used to measure the quality of the fuel’s ignition. If your fuel has a high Cetane number, you can be sure that what you get is a very easy cold starting coupled with a low idle noise. 5. Biodiesel is cost effective because it is produced locally. Biodiesel as a fuel not only helps reducing the pollution, reduces health hazards and gives our society A CLEANER AND GREENER TOMORROW. Advantages of using Biodiesel 1. Easy to use: Biodiesel can be used in existing engines, vehicles and infrastructure with practically no changes. Biodiesel can be pumped, stored and burned just like petroleum diesel fuel, and can be used pure, or in blends with petroleum diesel fuel in any proportion. Power and fuel economy using biodiesel is practically identical to petroleum diesel fuel, and year round operation can be achieved by blending with diesel fuel. 2. Power & Performance: The degree to which fuel provides proper lubrication is its lubricity. Low lubricity petroleum diesel fuel can cause premature failure of injection system components and decreased performance. Biodiesel provides excellent lubricity to the fuel injection system. 3. Emissions & Greenhouse Gas Reduction: Biodiesel provides significantly reduced emissions of carbon monoxide, particulate matter, unburned hydrocarbons, and sulfates compared to petroleum diesel fuel. Additionally, biodiesel reduces emissions of carcinogenic compounds by as much as 85% compared with petro diesel. When blended with petroleum diesel fuel, these emissions reductions are generally directly proportional to the amount of biodiesel in the blend.

Geothermal Energy: A brief Overview

Geothermal energy is the heat from the Earth. It's clean and sustainable. Resources of geothermal energy range from the shallow ground to hot water and hot rock found a few miles beneath the Earth's surface, and down even deeper to the extremely high temperatures of molten rock called magma. Almost everywhere, the shallow ground or upper 10 feet of the Earth's surface maintains a nearly constant temperature between 50° and 60°F (10° and 16°C). Geothermal heat pumps can tap into this resource to heat and cool buildings. A geothermal heat pump system consists of a heat pump, an air delivery system (ductwork), and a heat exchanger-a system of pipes buried in the shallow ground near the building. In the winter, the heat pump removes heat from the heat exchanger and pumps it into the indoor air delivery system. In the summer, the process is reversed, and the heat pump moves heat from the indoor air into the heat exchanger. The heat removed from the indoor air during the summer can also be used to provide a free source of hot water. In the United States, most geothermal reservoirs of hot water are located in the western states, Alaska, and Hawaii. Wells can be drilled into underground reservoirs for the generation of electricity. Some geothermal power plants use the steam from a reservoir to power a turbine/generator, while others use the hot water to boil a working fluid that vaporizes and then turns a turbine. Hot water near the surface of Earth can be used directly for heat. Direct-use applications include heating buildings, growing plants in greenhouses, drying crops, heating water at fish farms, and several industrial processes such as pasteurizing milk. Hot dry rock resources occur at depths of 3 to 5 miles everywhere beneath the Earth's surface and at lesser depths in certain areas. Access to these resources involves injecting cold water down one well, circulating it through hot fractured rock, and drawing off the heated water from another well. Currently, there are no commercial applications of this technology. Existing technology also does not yet allow recovery of heat directly from magma, the very deep and most powerful resource of geothermal energy. Most power plants need steam to generate electricity. The steam rotates a turbine that activates a generator, which produces electricity. Many power plants still use fossil fuels to boil water for steam. Geothermal power plants, however, use steam produced from reservoirs of hot water found a couple of miles or more below the Earth's surface. There are three types of geothermal power plants:dry steam, flash steam, and binary cycle. Dry steam power plants draw from underground resources of steam. The steam is piped directly from underground wells to the power plant, where it is directed into a turbine/generator unit. There are only two known underground resources of steam in the United States: The Geysers in northern California and Yellowstone National Park in Wyoming, where there's a well-known geyser called Old Faithful. Since Yellowstone is protected from development, the only dry steam plants in the country are at The Geysers. Flash steam power plants are the most common. They use geothermal reservoirs of water with temperatures greater than 360°F (182°C). This very hot water flows up through wells in the ground under its own pressure. As it flows upward, the pressure decreases and some of the hot water boils into steam. The steam is then separated from the water and used to power a turbine/generator. Any leftover water and condensed steam are injected back into the reservoir, making this a sustainable resource. Binary cycle power plants operate on water at lower temperatures of about 225°-360°F (107°-182°C). These plants use the heat from the hot water to boil a working fluid, usually an organic compound with a low boiling point. The working fluid is vaporized in a heat exchanger and used to turn a turbine. The water is then injected back into the ground to be reheated. The water and the working fluid are kept separated during the whole process, so there are little or no air emissions. Small-scale geothermal power plants (under 5 megawatts) have the potential for widespread application in rural areas, possibly even as distributed energy resources. Distributed energy resources refer to a variety of small, modular power-generating technologies that can be combined to improve the operation of the electricity delivery system. When a person takes a hot bath, the heat from the water will usually warm up the entire bathroom. Geothermal reservoirs of hot water, which are found a couple of miles or more beneath the Earth's surface, can also be used to provide heat directly. This is called the direct use of geothermal energy. Geothermal direct use dates back thousands of years, when people began using hot springs for bathing, cooking food, and loosening feathers and skin from game. Today, hot springs are still used as spas. But there are now more sophisticated ways of using this geothermal resource. In modern direct-use systems, a well is drilled into a geothermal reservoir to provide a steady stream of hot water. The water is brought up through the well, and a mechanical system - piping, a heat exchanger, and controls - delivers the heat directly for its intended use. A disposal system then either injects the cooled water underground or disposes of it on the surface. Geothermal hot water can be used for many applications that require heat. Its current uses include heating buildings (either individually or whole towns), raising plants in greenhouses, drying crops, heating water at fish farms, and several industrial processes, such as pasteurizing milk. With some applications, researchers are exploring ways to effectively use the geothermal fluid for generating electricity as well. The shallow ground, the upper 10 feet of the Earth, maintains a nearly constant temperature between 50° and 60°F (10°-16°C). Like a cave, this ground temperature is warmer than the air above it in the winter and cooler than the air in the summer. Geothermal heat pumps take advantage of this resource to heat and cool buildings. Geothermal heat pump systems consist of basically three parts: the ground heat exchanger, the heat pump unit, and the air delivery system (ductwork). The heat exchanger is basically a system of pipes called a loop, which is buried in the shallow ground near the building. A fluid (usually water or a mixture of water and antifreeze) circulates through the pipes to absorb or relinquish heat within the ground. In the winter, the heat pump removes heat from the heat exchanger and pumps it into the indoor air delivery system. In the summer, the process is reversed, and the heat pump moves heat from the indoor air into the heat exchanger. The heat removed from the indoor air during the summer can also be used to heat water, providing a free source of hot water. Geothermal heat pumps use much less energy than conventional heating systems, since they draw heat from the ground. They are also more efficient when cooling your home. Not only does this save energy and money, it reduces air pollution.

Tidal Energy: A Introduction & Technical Aspects

Tidal energy is one of the oldest forms of energy used by humans. Indeed, tide mills, in use on the Spanish, French and British coasts, date back to 787 A.D.. Tide mills consisted of a storage pond, filled by the incoming (flood) tide through a sluice and emptied during the outgoing (ebb) tide through a water wheel. The tides turned waterwheels, producing mechanical power to mill grain. We even have one remaining in New York- which worked well into the 20th century. Tidal power is non-polluting, reliable and predictable. Tidal barrages, undersea tidal turbines – like wind turbines but driven by the sea – and a variety of machines harnessing undersea currents are under development. Unlike wind and waves, tidal currents are entirely predictable. Tidal energy can be exploited in two ways: 1. By building semi-permeable barrages across estuaries with a high tidal range. 2. By harnessing offshore tidal streams. Barrages allow tidal waters to fill an estuary via sluices and to empty through turbines. Tidal streams can be harnessed using offshore underwater devices similar to wind turbines. Most modern tidal concepts employ a dam approach with hydraulic turbines. A drawback of tidal power is its low capacity factor, and it misses peak demand times because of 12.5 hr cycle of the tides. The total world potential for ocean tidal power has been estimated at 64,000 MWe. The 25-30 ft tidal variations of Passamaquoddy Bay (Bay of Fundy) have the potential of between 800 to 14,000 MWe Tidal range may vary over a wide range (4.5-12.4 m) from site to site. A tidal range of at least 7 m is required for economical operation and for sufficient head of water for the turbines. Hammerfest Traditional tidal electricity generation involves the construction of a barrage across an estuary to block the incoming and outgoing tide. The dam includes a sluice that is opened to allow the tide to flow into the basin; the sluice is then closed, and as the sea level drops, the head of water (elevated water in the basin) using traditional hydropower technology, drives turbines to generate electricity. Barrages can be designed to generate electricity on the ebb side, or flood side, or both. Tidal range may vary over a wide range (4.5-12.4 m) from site to site. A tidal range of at least 7 m is required for economical operation and for sufficient head of water for the turbines. A 240 MWe facility has operated in France since 1966, 20 MWe in Canada since 1984, and a number of stations in China since 1977, totaling 5 mWw. Tidal energy schemes are characterised by low capacity factors, usually in the range of 20-35%. The waters off the Pacific Northwest are ideal for tapping into an ocean of power using newly developed undersea turbines. The tides along the Northwest coast fluctuate dramatically, as much as 12 feet a day. The coasts of Alaska, British Columbia and Washington, in particular, have exceptional energy-producing potential. On the Atlantic seaboard, Maine is also an excellent candidate. The undersea environment is hostile so the machinery will have to be robust. Currently, although the technology required to harness tidal energy is well established, tidal power is expensive, and there is only one major tidal generating station in operation. This is a 240 megawatt (1 megawatt = 1 MW = 1 million watts) at the mouth of the La Rance river estuary on the northern coast of France (a large coal or nuclear power plant generates about 1,000 MW of electricity). The La Rance generating station has been in operation since 1966 and has been a very reliable source of electricity for France. La Rance was supposed to be one of many tidal power plants in France, until their nuclear program was greatly expanded in the late 1960’s. Elsewhere there is a 20 MW experimental facility at Annapolis Royal in Nova Scotia, and a 0.4 MW tidal power plant near Murmansk in Russia. UK has several proposals underway. Studies have been undertaken to examine the potential of several other tidal power sites worldwide. It has been estimated that a barrage across the Severn River in western England could supply as much as 10% of the country’s electricity needs (12 GW). Similarly, several sites in the Bay of Fundy, Cook Inlet in Alaska, and the White Sea in Russia have been found to have the potential to generate large amounts of electricity. WHAT IS THE IMPACT ON THE ENVIRONMENT? Tidal energy is a renewable source of electricity which does not result in the emission of gases responsible for global warming or acid rain associated with fossil fuel generated electricity. Use of tidal energy could also decrease the need for nuclear power, with its associated radiation risks. Changing tidal flows by damming a bay or estuary could, however, result in negative impacts on aquatic and shoreline ecosystems, as well as navigation and recreation. The few studies that have been undertaken to date to identify the environmental impacts of a tidal power scheme have determined that each specific site is different and the impacts depend greatly upon local geography. Local tides changed only slightly due to the La Rance barrage, and the environmental impact has been negligible, but this may not be the case for all other sites. It has been estimated that in the Bay of Fundy, tidal power plants could decrease local tides by 15 cm. This does not seem like much when one considers that natural variations such as winds can change the level of the tides by several metres. WHAT ARE THE COSTS OF TIDAL ENERGY? Tidal power is a form of low-head hydroelectricity and uses familiar low-head hydroelectric generating equipment, such as has been in use for more than 120 years. The technology required for tidal power is well developed, and the main barrier to increased use of the tides is that of construction costs. There is a high capital cost for a tidal energy project, with possibly a 10-year construction period. Therefore, the electricity cost is very sensitive to the discount rate. The major factors in determining the cost effectiveness of a tidal power site are the size (length and height) of the barrage required, and the difference in height between high and low tide. These factors can be expressed in what is called a site’s “Gibrat” ratio. The Gibrat ratio is the ratio of the length of the barrage in metres to the annual energy production in kilowatt hours (1 kilowatt hour = 1 KWH = 1000 watts used for 1 hour). The smaller the Gibrat site ratio, the more desireable the site. Examples of Gibrat ratios are La Rance at 0.36, Severn at 0.87 and Passamaquoddy in the Bay of Fundy at 0.92. Offshore tidal power generators use familiar and reliable low-head hydroelectric generating equipment, conventional marine construction techniques, and standard power transmission methods. The placement of the impoundment offshore, rather than using the conventional “barrage” approach, eliminates environmental and economic problems that have prevented the deployment of commercial-scale tidal power plants. Three projects (Swansea Bay 30 MW, Fifoots Point 30 MW, and North Wales 432 MW) are in development in Wales where tidal ranges are high, renewable source power is a strong public policy priority , and the electricity marketplace gives it a competitive edge. Q. What are some of the devices for tidal energy conversion? The technology required to convert tidal energy into electricity is very similar to the technology used in traditional hydroelectric power plants. The first requirement is a dam or “barrage” across a tidal bay or estuary. Building dams is an expensive process. Therefore, the best tidal sites are those where a bay has a narrow opening, thus reducing the length of dam which is required. At certain points along the dam, gates and turbines are installed. When there is an adequate difference in the elevation of the water on the different sides of the barrage, the gates are opened. This “hydrostatic head” that is created, causes water to flow through the turbines, turning an electric generator to produce electricity. Electricity can be generated by water flowing both into and out of a bay. As there are two high and two low tides each day, electrical generation from tidal power plants is characterized by periods of maximum generation every twelve hours, with no electricity generation at the six hour mark in between. Alternatively, the turbines can be used as pumps to pump extra water into the basin behind the barrage during periods of low electricity demand. This water can then be released when demand on the system its greatest, thus allowing the tidal plant to function with some of the characteristics of a “pumped storage” hydroelectric facility. WHAT ARE SOME OF THE DEVICES FOR TIDAL ENERGY CONVERSION? The technology required to convert tidal energy into electricity is very similar to the technology used in traditional hydroelectric power plants. The first requirement is a dam or “barrage” across a tidal bay or estuary. Building dams is an expensive process. Therefore, the best tidal sites are those where a bay has a narrow opening, thus reducing the length of dam which is required. At certain points along the dam, gates and turbines are installed. When there is an adequate difference in the elevation of the water on the different sides of the barrage, the gates are opened. This “hydrostatic head” that is created, causes water to flow through the turbines, turning an electric generator to produce electricity. Electricity can be generated by water flowing both into and out of a bay. As there are two high and two low tides each day, electrical generation from tidal power plants is characterized by periods of maximum generation every twelve hours, with no electricity generation at the six hour mark in between. Alternatively, the turbines can be used as pumps to pump extra water into the basin behind the barrage during periods of low electricity demand. This water can then be released when demand on the system its greatest, thus allowing the tidal plant to function with some of the characteristics of a “pumped storage” hydroelectric facility. WHY TIDAL ENERGY? The demand for electricity on an electrical grid varies with the time of day. The supply of electricity from a tidal power plant will never match the demand on a system. But, due to the lunar cycle and gravity, tidal currents, although variable, are reliable and predictable and their power can make a valuable contribution to an electrical system which has a variety of sources. Tidal electricity can be used to displace electricity which would otherwise be generated by fossil fuel (coal, oil, natural gas) fired power plants, thus reducing emissions of greenhouse and acid gasses. Tidal power, also called tidal energy, is a form of hydropower that converts the energy of tides into useful forms of power, mainly electricity. Although not yet widely used, tidal power has potential for future electricity generation. Tides are more predictable than wind energy and solar power. Among sources of renewable energy, tidal power has traditionally suffered from relatively high cost and limited availability of sites with sufficiently high tidal ranges or flow velocities, thus constricting its total availability. However, many recent technological developments and improvements, both in design (e.g. dynamic tidal power, tidal lagoons) and turbine technology (e.g. new axial turbines, cross flow turbines), indicate that the total availability of tidal power may be much higher than previously assumed, and that economic and environmental costs may be brought down to competitive levels. Historically, tide mills have been used both in Europe and on the Atlantic coast of North America. The incoming water was contained in large storage ponds, and as the tide went out, it turned waterwheels that used the mechanical power it produced to mill grain. The earliest occurrences date from the Middle Ages, or even from Roman times. It was only in the 19th century that the process of using falling water and spinning turbines to create electricity was introduced in the U.S. and Europe. The world's first large-scale tidal power plant is the Rance Tidal Power Station in France, which became operational in 1966. Tidal power is taken from the Earth's oceanic tides; tidal forces are periodic variations in gravitational attraction exerted by celestial bodies. These forces create corresponding motions or currents in the world's oceans. Due to the strong attraction to the oceans, a bulge in the water level is created, causing a temporary increase in sea level. When the sea level is raised, water from the middle of the ocean is forced to move toward the shorelines, creating a tide. This occurrence takes place in an unfailing manner, due to the consistent pattern of the moon’s orbit around the earth.[5] The magnitude and character of this motion reflects the changing positions of the Moon and Sun relative to the Earth, the effects of Earth's rotation, and local geography of the sea floor and coastlines. Tidal power is the only technology that draws on energy inherent in the orbital characteristics of the Earth–Moon system, and to a lesser extent in the Earth–Sun system. Other natural energies exploited by human technology originate directly or indirectly with the Sun, including fossil fuel, conventional hydroelectric, wind, biofuel, wave and solar energy. Nuclear energy makes use of Earth's mineral deposits of fissionable elements, while geothermal power taps the Earth's internal heat, which comes from a combination of residual heat from planetary accretion (about 20%) and heat produced through radioactive decay (80%). A tidal generator converts the energy of tidal flows into electricity. Greater tidal variation and higher tidal current velocities can dramatically increase the potential of a site for tidal electricity generation. Because the Earth's tides are ultimately due to gravitational interaction with the Moon and Sun and the Earth's rotation, tidal power is practically inexhaustible and classified as a renewable energy resource. Movement of tides causes a loss of mechanical energy in the Earth–Moon system: this is a result of pumping of water through natural restrictions around coastlines and consequent viscous dissipation at the seabed and in turbulence. This loss of energy has caused the rotation of the Earth to slow in the 4.5 billion years since its formation. During the last 620 million years the period of rotation of the earth (length of a day) has increased from 21.9 hours to 24 hours; in this period the Earth has lost 17% of its rotational energy. While tidal power will take additional energy from the system, the effect is negligible and would only be noticed over millions of years.[8]

Design of marine half-ship electrical power system with base load, hotel load, bow thrusters and electric propulsion

The principal components of the system are: 30 MVA Gas Turbine, Round Rotor Alternator 5 MVA Diesel Generator, Salient Pole Alternator 11.5 MVA Base Load 6 MVA Switched Hotel Load 20 MVA Average-Value Propulsion Rectifier 1 MVA Direct Online Start, Squirrel Cage Bow Thrusters

The sequence of events during the simulation is: 10 seconds - Hotel Load disconnected 20 seconds - Propulsion begins ramping up 30 seconds - Full power ahead 40 seconds - Propulsion begins ramping down 50 seconds - Bow Thrusters start up 60 seconds - Hotel Load connected

Design of Three phase to DC zener regulated supply for DC battery charging

Description The Zener diode block modeled in this example presents a practical implementation that uses parameters commonly provided on datasheets. These parameters are (1) Zener Voltage Vz (2) Dynamic Impedance Zzt (3) Knee Impedance Zzk (4) Max Continuous Current Izm (5) Forward Voltage Drop Vf (6) On Resistance Ron This block can effectively model three regions of operation of the zener diode I-V characteristics - forward-biased, reverse-biased before breakdown and reverse-biased after breakdown. Beyond the maximum reverse continuous current Izm, the zener is assumed to burn up and is treated as an open circuit. The implementation of the zener diode can be seen by looking under the mask of the block. Zener diodes are commonly employed in applications as voltage regulators. The circuit shows an AC source fed to a step-down transformer. The output of the transformer is then rectified using a diode bridge and smoothened using a capacitive filter. The zener diode then acts to regulate the output voltage to the zener voltage 10V. The input current into the zener is limited by the resistor Rlimit to permissible values. The programmable voltage source is setup to increase its output voltage at 0.1s. As the source output increases, so does the voltage applied at the input of the zener. However, the zener can regulate the output only as long as its input current is below the maximum specified value. This current increases as we increase the source voltage and the zener ultimately fails at about 0.112s. With the zener acting as an open-circuit at fault, voltage regulation is lost and the output of the capacitive filter gets applied to the load. Result:

Modelling of Electrical components in Simpower system

Advantages of MATLAB modelling: • Libraries of application-specific models, including models of common AC and DC electric drives, flexible AC transmission systems (FACTS), and renewable energy systems • Discretization and phasor simulation modes for faster model execution • Ideal switching algorithm for accelerated simulation of power electronic devices • Analysis methods for obtaining state-space representations of circuits and computing load flow for machines • Basic models for developing key electrical technologies • Ability to extend component libraries using the Simscape language • Support for C-code generation SimPowerSystems model (left) of an asynchronous motor and diesel-generator uninterruptible power supply (UPS). The Simulink scope (right) shows stator currents and speed of the asynchronous machine.

SimPowerSystems supports the development of complex, self-contained power systems, such as those in automobiles, aircraft, manufacturing plants, and power utility applications. The models you create support your entire development process, including hardware-in-the-loop simulations. Modeling Electrical Power Systems SimPowerSystems provides libraries for modeling electric machines, transformers, and power converters. You can connect components, such as generators, transmission lines, breakers, and motors, to model electrical power systems. Application-specific libraries are also provided, enabling you to model electric drives, aircraft power networks, and renewable energy systems. Connecting these systems with control systems modeled in Simulink lets you test integrated electrical power systems in a single environment. In addition to the traditional input-output or signal flow connections used in Simulink, SimPowerSystems uses physical connections that permit the flow of power in any direction. Models of electrical power systems built using physical connections (or acausal models) closely resemble the network they represent, and are easy to understand and share. You can define your three-phase connections using individual connections for each phase, enabling you to perform tests such as injecting a single-line-to-ground fault. You can also create single-line diagrams, where the three phases are represented by a single line, making the diagram easy to read. SimPowerSystems components are parameterized using the per-unit system, which is widely used in the power system industry and simplifies the parameterization and analysis of your system.

SimPowerSystems model (left) of a permanent magnet synchronous motor and inverter sized for use in a typical hybrid vehicle. The model includes the electrical connections (single-phase and three-phase) and signal flow connections, and the scope (right) shows the stator currents in the PMSM. Creating Custom Components You can add components from other physical modeling products to your SimPowerSystems model. The Foundation libraries in Simscape contain blocks in hydraulic, thermal, magnetic, and other physical domains. Integrating these domains into your SimPowerSystems model using physical connections helps you model other aspects of your system in a single environment. The Simscape language is an object-oriented language based on MATLAB that enables you to create your own physical modeling components and libraries. You can define custom components complete with parameterization, physical connections, and equations represented as acausal implicit differential algebraic equations (DAEs). Within your component’s Simscape language file, you can use MATLAB to analyze parameter values, perform preliminary computations, and initialize system variables. The Simulink block and dialog box for your custom component are automatically created from the file.

Using the Simscape language, you can control exactly which effects are captured in the models of your physical components. This approach enables you to balance the tradeoff between model fidelity and simulation speed. Custom Simscape implementation of a permanent magnet synchronous motor, used as a generator. The MATLAB editor shows Simscape language source code of the electrical and mechanical equations, and the scope shows the three-phase AC currents and DC current at the load. Simulating Models You can simulate your SimPowerSystems models using any of three solution methods for your power system network, as well as an ideal switching algorithm that improves simulation performance for systems with high-frequency switching. Selecting SimPowerSystems Simulation Mode Choose simulation mode (continuous, discrete, or phasor) using SimPowerSystems™. Analyze transient effects and magnitudes of circuit voltages. Continuous methods perform highly accurate simulations of power system models, varying the step size to capture the dynamics of your system. Discrete methods enable you to control the precision of your simulation by selecting the size of the time step. Phasor simulation replaces the differential equations representing the network with a set of algebraic equations at a fixed frequency, making it possible to do transient stability studies of systems with multiple machines. The ideal switching algorithm in SimPowerSystems enables fast and accurate simulation of systems containing power electronic devices. This algorithm uses an improved method of calculating the state-space representation of the system instead of relying on current sources with high-impedance snubbers to model power electronic devices. This method gives you greater flexibility in selecting a solver and results in shorter simulation times. SimPowerSystems interface for selecting simulation options. Continuous, discrete, and phasor simulation modes are supported, with the option of enabling an ideal switching algorithm for faster simulation. Analyzing Models SimPowerSystems provides tools for analyzing models, visualizing simulation results, and calculating advanced block parameters, enabling you to: • Display steady-state voltage and currents • Display and modify initial state values • Perform load flows and machine initialization • Perform harmonic analysis • Display impedance vs. frequency measurements The load flow computational engine computes initial currents of synchronous and asynchronous machines. You specify the desired steady-state machine conditions in your circuit, and SimPowerSystems computes the load flow. The resulting rotor position, initial currents, and internal fluxes are automatically entered into the parameters for the machines. SimPowerSystems lets you analyze the electrical network topology and compute the equivalent state-space model of your circuit without running a simulation. You can link the state-space model to the Linear System Analysis app in Control System Toolbox™ to obtain time-domain and frequency-domain responses. The SimPowerSystems FFT analysis tool. The frequency spectrum of a voltage waveform is displayed, and power quality is measured by calculating total harmonic distortion.

SimPowerSystems Release Notes R2015a

Simscape Components Asynchronous machines with SI parameterization Synchronous Machine Model 2.1 blocks Zigzag-Delta1-Wye and Zigzag-Delta11-Wye Transformer blocks Average-Value Inverter block Ideal Rectifier block name change Featured Examples Specialized Technology PV Array block Annotation and export options for Load Flow Tool power_customize function for creating custom Specialized Technology blocks Three-limb core option for three-phase transformer blocks Interpolation and Store State-Space Matrices options for Tustin solver​​ New machine block dialog boxes and function access New powergui dialog box and tools Block library changes Phasor Simulation Method examples

Simulating AC to DC to AC PWM converter

A 60 Hz, voltage source feeds a 50 Hz, 50 kW load through an AC-DC-AC converter. The 600V, 60 Hz voltage obtained at secondary of the Wye/Delta transformer is first rectified by a six pulse diode bridge. The filtered DC voltage is applied to an IGBT two-level inverter generating 50 Hz. The IGBT inverter uses Pulse Width Modulation (PWM) at a 2 kHz carrier frequency. The circuit is discretized at a sample time of 2 us The load voltage is regulated at 1 pu (380 V rms) by a PI voltage regulator using abc_to_dq and dq_to_abc transfomations. The first output of the voltage regulator is a vector containing the three modulating signals used by the PMW Generator to generate the 6 IGBT pulses. The second output returns the modulation index. The Multimeter block is used to observe diode and IGBT currents. In order to allow further signal processing, signals displayed on Scope1 block (sampled at simulation sampling rate of 2us ) are stored in a variable named 'psbbridges_str' (structure with time). Simulation Start the simulation. After a transient period of approximately 50 ms, the system reaches a steady state. Observe voltage waveforms at DC bus, inverter output and load on Scope1. The harmonics generated by the inverter around multiples of 2 kHz are filtered by the LC filter. As expected the peak value of the load voltage is 537 V (380 Vrms). In steady state, the mean value of the modulation index is m = 0.80 and the mean value of the DC voltage is 778 V. The fundamental component of 50 Hz voltage buried in the chopped inverter voltage is therefore: Vab = 778 V * 0.612 * 0.80 = 381 V rms Once simulation is completed, open the Powergui and select 'FFT Analysis' to display the 0 - 7000 Hz frequency spectrum of signals saved in the 'psbbridges_str' structure. The FFT will be performed on a 2-cycle window starting at t=0.1-2/50 (last 2 cycles of recording). Select input labeled 'Vab Load' . Click on Display and observe the frequency spectrum of last 2 cycles. Notice harmonics around multiples of the 2 kHz carrier frequency. Maximum harmonic is 1.4 % of fundamental and THD is 2%. Observe diode currents on trace 1 of Scope2, showing commutation from diode 1 to diode 3. Also observe on trace 2 currents in switches 1 and 2 of the IGBT/Diode bridge (upper and lower switches connected to phase A). These two currents are complementary. A positive current indicates a current flowing in the IGBT, whereas a negative current indicates a current flowing in the antiparallel diode.

Power Electronics, converters, research and Applications: A Brief overview

Power electronics is the application of solid-state electronics for the control and conversion of electric power. It also refers to a subject of research in electronic and electrical engineering which deals with design, control, computation and integration of nonlinear, time varying energy processing electronic systems with fast dynamics. The capabilities and economy of power electronics system are determined by the active devices that are available. Their characteristics and limitations are a key element in the design of power electronics systems. Formerly, the mercury arc valve, the high-vacuum and gas-filled diode thermionic rectifiers, and triggered devices such as the thyratron and ignitron were widely used in power electronics. As the ratings of solid-state devices improved in both voltage and current-handling capacity, vacuum devices have been nearly entirely replaced by solid-state devices. Power electronic devices may be used as switches, or as amplifiers. An ideal switch is either open or closed and so dissipates no power; it withstands an applied voltage and passes no current, or passes any amount of current with no voltage drop. Semiconductor devices used as switches can approximate this ideal property and so most power electronic applications rely on switching devices on and off, which makes systems very efficient as very little power is wasted in the switch. By contrast, in the case of the amplifier, the current through the device varies continuously according to a controlled input. The voltage and current at the device terminals follow a load line, and the power dissipation inside the device is large compared with the power delivered to the load. Several attributes dictate how devices are used. Devices such as diodes conduct when a forward voltage is applied and have no external control of the start of conduction. Power devices such as silicon controlled rectifiers and thyristors (as well as the mercury valve and thyratron) allow control of the start of conduction, but rely on periodic reversal of current flow to turn them off. Devices such as gate turn-off thyristors, BJT and MOSFET transistors provide full switching control and can be turned on or off without regard to the current flow through them. Transistor devices also allow proportional amplification, but this is rarely used for systems rated more than a few hundred watts. The control input characteristics of a device also greatly affect design; sometimes the control input is at a very high voltage with respect to ground and must be driven by an isolated source. As efficiency is at a premium in a power electronic converter, the losses that a power electronic device generates should be as low as possible. Devices vary in switching speed. Some diodes and thyristors are suited for relatively slow speed and are useful for power frequency switching and control; certain thyristors are useful at a few kilohertz. Devices such as MOSFETS and BJTs can switch at tens of kilohertz up to a few megahertz in power applications, but with decreasing power levels. Vacuum tube devices dominate high power (hundreds of kilowatts) at very high frequency (hundreds or thousands of megahertz) applications. Faster switching devices minimize energy lost in the transitions from on to off and back, but may create problems with radiated electromagnetic interference. Gate drive (or equivalent) circuits must be designed to supply sufficient drive current to achieve the full switching speed possible with a device. A device without sufficient drive to switch rapidly may be destroyed by excess heating. Power electronic circuit’s process and control electrical energy, and are critical elements in many kinds of systems. The rapid evolution of technology is generating a demand for power electronics whose capabilities greatly exceed what is presently achievable. Challenges of particular importance include miniaturization and integration of power electronics, and improving their cost and dynamic performance. Miniaturization is difficult in part because the magnetic components used in most power circuits scale down poorly in size. Likewise, achieving integration and low cost is difficult because of the diverse materials and assembly methods that are required for contemporary designs. My research interest includes working to address these challenges through a combination of new technologies. One research focus is on the development of improved power passive components. Passive components such as inductors and capacitors often dominate the size and cost of power circuits, and limit their efficiency, noise attenuation, and transient performance. In one effort, we are developing means to improve the performance of passive filter components by compensating for their parasitic. These efforts have led to new integrated filter components with much better performance than conventional passives. Likewise, we are developing new types of power passive components that better scale to small sizes and high frequencies. Construction of these components using micro fabrication techniques is also being explored, with the goal of enabling integrated fabrication of power converters. A second research focus is the development of techniques to achieve greatly increased switching frequencies in power converters. Higher frequencies are desirable because they enable faster transient response and reduce passive component requirements. Moreover, at sufficiently high frequencies, batch fabrication of many circuit components may become possible, enabling higher levels of integration to be achieved. We are exploring new system architectures, circuit designs, and control methods that together enable substantial increases in operating frequency over the present state of the art. It is anticipated that the technologies under development will lead to miniaturized, highly integrated power electronics. In addition to developing fundamental power conversion technologies, we are applying them in a variety of applications. Automotive power generation and control is one such area. For example, we have investigated the application of power electronics to enhance the efficiency, power, and transient performance of automotive alternators. We have also developed dc/dc converters and other power electronics for automotive applications, with the goal of enabling improved performance, safety, and comfort in vehicles. Other areas of interest include power components and circuits for industrial, commercial, consumer, and medical applications where improved size, efficiency, and performance are of importance. Applications of power electronics range in size from a switched mode power supply in an AC adapter, battery chargers, fluorescent lamp ballasts, through variable frequency drives and DC motor drives used to operate pumps, fans, and manufacturing machinery, up to gigawatt-scale high voltage direct current power transmission systems used to interconnect electrical grids. Power electronic systems are found in virtually every electronic device. For example: • DC/DC converters are used in most mobile devices (mobile phones, PDA etc.) to maintain the voltage at a fixed value whatever the voltage level of the battery is. These converters are also used for electronic isolation and power factor correction. A power optimizer is a type of DC/DC converter developed to maximize the energy harvest from solar photovoltaic or wind turbine systems. • AC/DC converters (rectifiers) are used every time an electronic device is connected to the mains (computer, television etc.). These may simply change AC to DC or can also change the voltage level as part of their operation. • AC/AC converters are used to change either the voltage level or the frequency (international power adapters, light dimmer). In power distribution networks AC/AC converters may be used to exchange power between utility frequency 50 Hz and 60 Hz power grids. • DC/AC converters (inverters) are used primarily in UPS or renewable energy systems or emergency lighting systems. Mains power charges the

DC battery. If the mains fail, an inverter produces AC electricity at mains voltage from the DC battery. Solar inverter, both smaller string and larger central inverters, as well as solar micro-inverter are used in photovoltaic as a component of a PV system. Motor drives are found in pumps, blowers, and mill drives for textile, paper, cement and other such facilities. Drives may be used for power conversion and for motion control. For AC motors, applications include variable-frequency drives, motor soft starters and excitation systems. In hybrid electric vehicles (HEVs), power electronics are used in two formats: series hybrid and parallel hybrid. The difference between a series hybrid and a parallel hybrid is the relationship of the electric motor to the internal combustion engine (ICE). Devices used in electric vehicles consist mostly of dc/dc converters for battery charging and dc/ac converters to power the propulsion motor. Electric trains use power electronic devices to obtain power, as well as for vector control using pulse width modulation (PWM) rectifiers. The trains obtain their power from power lines. Another new usage for power electronics is in elevator systems. These systems may use thyristors, inverters, permanent magnet motors, or various hybrid systems that incorporate PWM systems and standard motors.

How to Write a Great Research Paper

MATLAB Electric Power System

Solar photo voltaic power generation system

Photovoltaic (PV) technology converts one form of energy (sunlight) into another form of energy (electricity) using no moving parts, consuming no conventional fossil fuels, creating no pollution, and lasting for decades with very little maintenance. The use of a widely available and reasonably reliable fuel source the sun with no associated storage or transportation difficulties and no emissions makes this technology eminently practicable for powering remote scientific research platforms [2]. Indeed, numerous examples of successfully deployed systems are already available around the globe [7, 8]. The completely scalable nature of the technology also lends itself well to varying power requirements i.e. from the smallest autonomous research platforms to infrastructure-based systems. This technology can be limited, however, by annual fluctuations in solar insolation, especially at extreme latitudes. Based on semiconductor technology, solar cells operate on the principle that electricity will flow between two semiconductors when they are put into contact with each other and exposed to light (photons). This phenomenon, known as the Photovoltaic effect was first discovered by

Fig. 2.1 Solar cell Edmund Becquerel in 1839. Actual development of PV technology began in the 1950s and gained greater impetus through the NASA space program during the 1960s. Research continues today at national laboratories and within private industry, focusing on increasing conversion efficiencies and mass production strategies to further lower the cost of producing PV modules. Solar photovoltaic systems convert solar energy directly into electrical energy. Basic conversion device used is known as a solar photovoltaic cell or a solar cell as shown in fig. 2.1. Although other light sources may also produce photovoltaic electricity, only sunlight based PV cells are considered in this chapter. A solar cell is basically an electrical current source, driven by flux of radiation. Solar cells were first produced in 1954 and were rapidly developed to provide power for space satellites based on semiconductor electronics technology. Its terrestrial applications were considered seriously only after the oil crisis of 1973, when a real need of alternative energy source was felt globally. Efficient power utilization depends not only on efficient generation in the cell but also on the dynamic load matching in the in the external circuit. Major advantages of solar PV systems over conventional power systems are as under: 1. It converts solar energy directly into electrical energy without going through thermal mechanical link. 2. Solar PV system is reliable, modular, and durable and generally maintenance free. 3. These systems are quiet, compatible with almost all environmental, respond instantaneously to solar radiation and have an expected life span of 20 years or more. 4. It can located at the place of use i.e. onsite and hence no distribution network is required. It also suffers from some drawbacks which can be overcome by the technology in future, such as: 1. At present the cost of solar cells are high, making them economically uncompetitive with other conventional power sources. 2. The efficiency of solar cell is low. 3. As solar energy is intermittent, some kind of electrical energy storage e.g. battery is required which makes the whole system more expensive. 2.2 Components of Photovoltaic system 2.2.1 PV Panels PV panels tend to work much better in cold weather than in hot climates (except for amorphous silicon panels). Add a reflective snow surface and the output can sometimes exceed the rating for the panel. Array currents up to 20% greater than the specified output have been reported. In general, PV materials are categorized as either crystalline or thin film as shown in fig. 2.2 and they are judged on two basic factors: efficiency and economics. For remote installations where the actual space available for PV panels is often quite limited, the greater conversion efficiency of crystalline technology seems to have the advantage. It is also worth noting that the conversion efficiency of thin-film panels tends to drop off rather rapidly in the first few years of operation. Decreases of more than 25% have been reported. This performance deterioration must be taken into account when sizing the array for a multi-year project. However, there are still applications where the lighter weight and greater flexibility of the thin-film panels may be more suitable. Which PV technology is more appropriate for a given application will need to be determined on a case-by-case basis [14].

Fig. 2.2 Types of solar cells

Fig. 2.3 OFF grid Residential Solar PV system Mono-crystalline silicon panels should be utilized when a higher voltage is desirable. This would be in an instance where the DC power has to travel some distance before being utilized or stored in a battery bank as shown in fig. 2.3. These panels are also the most efficient PV technology, averaging 14% to 17%. New technology charge controllers, which allow for a higher array voltage than the battery bank voltage, somewhat obviate the advantages of the mono-crystalline panels. Polycrystalline silicon panels have efficiencies of 12% to 14% and can often be purchased at a lower cost per watt than mono-crystalline silicon panels. This type of panel sees the widest use in polar applications. Thin-film technologies include amorphous silicon, cadmium telluride, copper-indium dieseline, and others (refer fig. 2.2). Although the cost of these panels appears attractive at first, it is important to note that the efficiencies are comparatively low. The 8% to 10% efficiencies seen in new panels quickly degrade to about 3% to 6% after several months of exposure to sunlight. Furthermore, amorphous silicon and cadmium telluride modules are sensitive to a much narrower band of colors, and the winter shift to redder sunlight results in slightly poorer performance. Newer, triple-junction thin film technologies appear to have higher efficiencies and less degradation over time, but they are still subject to the same problems mentioned above, if to a lesser degree. The somewhat flexible nature of thin-film technology may make it appropriate for some applications, but in general, the higher efficiencies and more robust nature of the crystalline silicon modules make them a better choice for polar applications. Regardless of the technology employed, the researcher would be well advised to look for modules with heavy-duty aluminum frames, UL ratings, easy-to-use junction boxes, and a long warranty (20+ years). All of these are indicative of a quality unit that will withstand the rigors of the polar environment.

Fuel cell for automobiles and power generation

A fuel cell is a device that generates electricity by a chemical reaction. Every fuel cell has two electrodes, one positive and one negative, called, respectively, the anode and cathode. The reactions that produce electricity take place at the electrodes. Every fuel cell also has an electrolyte, which carries electrically charged particles from one electrode to the other, and a catalyst, which speeds the reactions at the electrodes. Hydrogen is the basic fuel, but fuel cells also require oxygen. One great appeal of fuel cells is that they generate electricity with very little pollution–much of the hydrogen and oxygen used in generating electricity ultimately combine to form a harmless byproduct, namely water. One detail of terminology: a single fuel cell generates a tiny amount of direct current (DC) electricity. In practice, many fuel cells are usually assembled into a stack. Cell or stack, the principles are the same. The purpose of a fuel cell is to produce an electrical current that can be directed outside the cell to do work, such as powering an electric motor or illuminating a light bulb or a city. Because of the way electricity behaves, this current returns to the fuel cell, completing an electrical circuit. (To learn more about electricity and electric power, visit "Throw The Switch" on the Smithsonian website Powering a Generation of Change.) The chemical reactions that produce this current are the key to how a fuel cell works. There are several kinds of fuel cells, and each operates a bit differently. But in general terms, hydrogen atoms enter a fuel cell at the anode where a chemical reaction strips them of their electrons. The hydrogen atoms are now "ionized," and carry a positive electrical charge. The negatively charged electrons provide the current through wires to do work. If alternating current (AC) is needed, the DC output of the fuel cell must be routed through a conversion device called an inverter. Oxygen enters the fuel cell at the cathode and, in some cell type, it there combines with electrons returning from the electrical circuit and hydrogen ions that have traveled through the electrolyte from the anode. In other cell types the oxygen picks up electrons and then travels through the electrolyte to the anode, where it combines with hydrogen ions. The electrolyte plays a key role. It must permit only the appropriate ions to pass between the anode and cathode. If free electrons or other substances could travel through the electrolyte, they would disrupt the chemical reaction. Whether they combine at anode or cathode, together hydrogen and oxygen form water, which drains from the cell. As long as a fuel cell is supplied with hydrogen and oxygen, it will generate electricity. Even better, since fuel cells create electricity chemically, rather than by combustion, they are not subject to the thermodynamic laws that limit a conventional power plant (see "Carnot Limit" in the glossary). Therefore, fuel cells are more efficient in extracting energy from a fuel. Waste heat from some cells can also be harnessed, boosting system efficiency still further. Alkali fuel cells operate on compressed hydrogen and oxygen. They generally use a solution of potassium hydroxide (chemically, KOH) in water as their electrolyte. Efficiency is about 70 percent, and operating temperature is 150 to 200 degrees C, (about 300 to 400 degrees F). Cell output ranges from 300 watts (W) to 5 kilowatts (kW). Alkali cells were used in Apollo spacecraft to provide both electricity and drinking water. They require pure hydrogen fuel, however, and their platinum electrode catalysts are expensive. And like any container filled with liquid, they can leak. Molten Carbonate fuel cells (MCFC) use high-temperature compounds of salt (like sodium or magnesium) carbonates (chemically, CO3) as the electrolyte. Efficiency ranges from 60 to 80 percent, and operating temperature is about 650 degrees C (1,200 degrees F). Units with output up to 2 megawatts (MW) have been constructed, and designs exist for units up to 100 MW. The high temperature limits damage from carbon monoxide "poisoning" of the cell and waste heat can be recycled to make additional electricity. Their nickel electrode-catalysts are inexpensive compared to the platinum used in other cells. But the high temperature also limits the materials and safe uses of MCFCs–they would probably be too hot for home use. Also, carbonate ions from the electrolyte are used up in the reactions, making it necessary to inject carbon dioxide to compensate. Phosphoric Acid fuel cells (PAFC) use phosphoric acid as the electrolyte. Efficiency ranges from 40 to 80 percent, and operating temperature is between 150 to 200 degrees C (about 300 to 400 degrees F). Existing phosphoric acid cells have outputs up to 200 kW, and 11 MW units have been tested. PAFCs tolerate a carbon monoxide concentration of about 1.5 percent, which broadens the choice of fuels they can use. If gasoline is used, the sulfur must be removed. Platinum electrode-catalysts are needed, and internal parts must be able to withstand the corrosive acid. Proton Exchange Membrane (PEM) fuel cells work with a polymer electrolyte in the form of a thin, permeable sheet. Efficiency is about 40 to 50 percent, and operating temperature is about 80 degrees C (about 175 degrees F). Cell outputs generally range from 50 to 250 kW. The solid, flexible electrolyte will not leak or crack, and these cells operate at a low enough temperature to make them suitable for homes and cars. But their fuels must be purified, and a platinum catalyst is used on both sides of the membrane, raising costs. Solid Oxide fuel cells (SOFC) use a hard, ceramic compound of metal (like calcium or zirconium) oxides (chemically, O2) as electrolyte. Efficiency is about 60 percent, and operating temperatures are about 1,000 degrees C (about 1,800 degrees F). Cells output is up to 100 kW. At such high temperatures a reformer is not required to extract hydrogen from the fuel, and waste heat can be recycled to make additional electricity. However, the high temperature limits applications of SOFC units and they tend to be rather large. While solid electrolytes cannot leak, they can crack.

Multi level inverters topologies and their simulation in Matlab/Simulink

In this study, a review of cascaded H-bridge multilevel inverter topology and control schemes was conducted. Multilevel inverter topology (MLI) H-bridge cascade is implemented to reduce harmonic for high power applications. Applications of multilevel converters are able to reduce the number of harmonics contained in the system of low-voltage electrical distribution. Each topology has their own advantages and disadvantages. The cascaded H-bridge multilevel inverter topology requires only a single DC power source with both input and output, high availability, and the control of power flow in the regenerative version. The selected switching technique to control the inverter will also have an effective role on harmonic elimination while generating the ideal output voltage. Intensive studies have been performed on carrier-based, sinusoidal, space vector and sigma delta PWM methods in open loop control of inverters. The results from this study represent a beneficial basis for matching of inverter topology and the best control scheme according to different application areas. In general, increasing the switching frequency in voltage source inverters (VSIs) leads to better output voltage and current waveforms. Harmonic reduction in controlling a VSI with variable amplitude and frequency of the output voltage is important, and thus, conventional inverters which are referred as two-level inverters require increased switching frequency along with various PWM switching strategies. The multilevel fundamental switching scheme is used to control the needed power electronics switches. Also, a method is presented where switching angles are computed such that a desired fundamental sinusoidal voltage is produced and at the same time certain higher order harmonics are eliminated. The generalized multilevel inverter topology can balance each voltage level by itself regardless of the inverter control and load characteristics. The concept of multilevel converters has been introduced since 1975. The usage of these applications has become more diverse and affects a wide field of electrical engineering from a few watts to several hundred megawatts. Converting static structures that comprise mainly applications of power electronics is becoming increasingly powerful, and the technology has had to adapt to the growth of the power to convert. Multilevel inverter topologies are the Neutral-Point Clamped (NPC) inverters (or DiodeClamped inverters), the cascaded H- bridge inverters (CHB), and the Flying Capacitor (FC) inverters (or Capacitor Clamped inverters), as shown in Figure 1. In this paper, a review of multilevel inverter based on cascaded h-bridge topology and control schemes was conducted. The advantages of this multilevel approach include good power quality, good electromagnetic compatibility (EMC), low switching losses, and high voltage capability.