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Prior to the introduction of SCRs, mercury-arc rectifiers were used for controlling electrical power, but such rectifier circuits were part of industrial electronics and the scope for applications of mercury-arc rectifiers was limited. Once the SCRs were available, the application area spread to many fields such as drives, power supplies, aviation Power electronics is the application of electronic circuits to energy conversion. You may have more interaction with power electronics than you think. If you drive a car, use a computer, cook with a microwave, talk on any type of telephone, listen to a stereo, or make holes with a cordless drill, then you come in contact with power electronics. Thanks to power electronics, the electricity needed to run the things you use everyday is processed, filtered, and delivered with maximum efficiency, smallest size and minimal weight. In formal terms, "This technology encompasses the use of electronic components, the application of circuit theory and design techniques, and the development of analytical tools toward efficient electronic conversion, control, and conditioning of electric power." The main areas of power electronics research include: • Electronic devices (like diodes and transistors) • Power converter circuit design and work with various topologies for converter circuits • Magnetic components (such as transformers and inductors) • Electronic circuit packaging and manufacturing • Control of electrical motors Power electronics has applications that span the whole field of electrical power systems, with the power range of these applications extending from a few VA/Watts to several MVA / MW. The main task of power electronics is to control and convert electrical power from one form to another. The four main forms of conversion are: • Rectification referring to conversion of ac voltage to dc voltage, • "Electronic power converter" is the term that is used to refer to a power electronic circuit that converts voltage and current from one form to another. In addition, SCRs and other power semiconductor devices are used as static switches. Importance and Uses of Power Electronics Power electronics is everywhere you look. For example, power electronics is used in • space systems and satellites • Alternative energy (like solar and wind). All modern computers rely on switch-mode power converters for their dc supply needs. These power electronic supplies range from battery management converters for laptops to multiple redundant converters for advanced server clusters. Only with power electronics is it feasible to build small power supplies with the many separate outputs and voltages needed for a computer, its peripherals, and its display. Many of today's advances involve distributed power methods. A distributed-architecture power supply for a computer system consists of an off-line active power factor correction (PFC) circuit followed by a dc-dc converter and multiple point-of-load dc-dc converters. Such a arrangement differs from the conventional bulk power converter architecture since it includes an extra power conversion stage, and because it uses an intermediate dc level for distribution. In the near future, we can expect computer designers to use 12 V buses and even 48 V buses to deliver power to individual boards and subsystems. Power electronics is answering a new challenge for the development of extremely dynamic, low-voltage applications such as high performance microprocessor computer systems. These devices demand tight regulation of extremely low voltage outputs (now reaching below 2 V) as well as very fast response to large load transitions. Applications such as this which demand high power density, low power consumption, high efficiency, and innovative packaging are inspiring new technologies including synchronous rectification, polyphase interleaving, on-board power conversion, GaAs semiconductor devices, and board-level interconnect modeling. In the next few years, we will begin to see a further advance to chip-level interconnects and power conversion. Another nearly universal power electronics application is the automobile's ignition system. Thousands of volts are required to ignite the fuel-air mixture inside a cylinder so that internal combustion can occur. Today's cars employ all-electronic ignition systems, which have replaced the traditional spark plugs with boost converters coupled to transformers. A third example, now being used in some models, is an all-electronic power steering system. This system uses power electronics to control electric motors and assist in moving the steering rack. This system is replacing the traditional, belt-driven hydraulic pump. The results are improved steering response, lower energy consumption, and the elimination of noisy belt drives. Electric air conditioning systems are starting to appear as well. The high-intensity lamps now appearing in headlights, and the bright LEDs appearing in taillights all require power electronics to deliver electrical energy in the correct form. Power electronics is a major growth area within the automotive industry. Electronic ignitions, power semiconductor voltage regulators, automatic motor controls, and audio systems are some of the most common applications. But in the future, electronic systems ranging from small motor controls for windows and seats up to high-power traction controls for electric drive systems will be present on cars. Perhaps most significant is the move to a higher-voltage electrical system. Cars of the near future will be designed around a 40 V to 50 V electrical supply in place of today's 10 V to 15 V systems. Many people are curious about new electric and hybrid cars -- in which the primary electrical system is dominated by power electronics. Electric cars offer high performance, zero tailpipe emissions, and low costs, but are still limited in range by the need for batteries. Hybrid car designs use various strategies to combine both an engine and electrical elements to gain advantages of each. In both cases, inverters and dc-dc converters rated for many kilowatts serve as primary energy control blocks. Power Electronics in Telecommunications Power electronics is widespread in the telecommunications industry. It is actually one of the largest users of power supplies and batteries. The uses range from ultra-reliable backup power systems that keep telephones working under all conditions to small supplies for cordless phones.A typical power system for a "central office" in a telephone network might have a a 5-kW power converter system for telecommunication system. This might comprise a front-end off-line power-factor-correction (PFC) boost converter to support any possible ac utility input, followed by two 2.5-kW forward converters to support high output current for the telehone system's 48 V dc distributed bus. The difficulties of generating and storing power in space provide a fertile ground for power electronics research. Design constraints such as weight, efficiency, and reliability consistently push power electronics research efforts to the limits of today's technology. The primary sources of power and energy storage for satellites and space probes have included solar cells, fuel cells, thermoelectric nuclear power, batteries, and flywheels. In most cases these power sources provide low power with uncertain electrical behavior. The energy must be converted into a useable form with the lowest possible loss. Modern space systems have very large power systems. A typical communications satellite, for example, might operate with hundreds of independent dc sources for maximum reliability at every network node. The International Space Station has sophisticated redundant power feeds and sources to maintain science operations and life support systems. In the space power context, thermal management is extremely important, since all lost energy must be dissipated into outer space by radiation cooling. Reliability, especially under exposure to large temperature swings and intense radiation, is a difficult challenge. Many of today's fundamental power electronics designs derive originally for space power systems. Early dc-dc converters and fuel cell systems were developed for 1960s space projects, including the Apollo moon missions. Today, NASA, the European Space Agency (ESA), and their major technology suppliers are the international leaders in advanced power electronics. Processing power from current sources such as solar cells, thermoelectric generators, and fuel cells requires a boost converter to transform input current at low voltage to a voltage appropriate for charging the on-board battery or flywheel storage system. Electronic Ballasts and Other Lighting Applications Compact fluorescent lamps, high-intensity discharge (HID) lighting, high-brightness LEDs, dimming and control systems for all types of lighting -- these are some examples of the applications of power electronics to lighting. For more conventional fluorescent tubes, electronic ballast offer better performance, lower energy consumption, and less wear and tear than more traditional magnetic ballasts. Lighting technology is changing rapidly, and power electronics is the primary enabler of this change. Modern electronic ballasts operate at frequencies of a few tens of kilohertz to eliminate flicker and acoustic noise associated with discharge lighting. Small sizes and fast operation allow advanced lamps to be used in applications from cameras to cars. Power Electronics in Alternative Energy Wind, water, and sunlight are the keys to a new generation of power sources. Fuel cells and microturbines offer efficiency ways to convert fuels to electricity. The raw power from these sources must be conditioned before it can be used by standard electrical loads. This power conditioning function is where power electronics plays an important role. Solar power is generally used to convert the sun's energy into either of two more readily useable forms: hot liquid such as in a solar water heating plant or solar thermal power plant, or directly into electric current such as generated by photovoltaic cells. Hot liquid systems can be used to generate steam to drive turbines and generators. The largest demonstration systems even include thermal energy storage so power can be produced continuously. Photovoltaic systems can use static power inverters to convert their initial low-voltage dc power into ac power suitable to run a given load or to feed into the power grid. The electrical current available from photovoltaic systems is supplied at very low voltages that depend on a number of factors including the angle of the sunlight and level of cloud cover. This variation of output voltage and output power means that we need some way of regulating controlling the output of the photovoltaic system; this task is often accomplished using adjustable boost converters that can keep the output voltage of a solar cell bank constant regardless of sun angle. Once a constant voltage is available, an inverter converts the solar power to ac so it can be fed into the power grid. Photovoltaic current is now more than ever becoming a growing source of power. Thanks to recent developments in thin film photovoltaics, the cost per kilowatthour is not far above a target level of US $0.10/kWhr. Throughout the world, electric power is used at an average rate of 12 billion kilowatts every hour of every day of every year. With few exceptions, the majority of this electrical power is not used in the form in which it was initially produced. Rather, it is re-processed to provide the type of power needed in the technology that is being employed. Power electronics is the engineering discipline that is utilized when converting electrical power from one form to another. In terms of commerce, the impact of power electronics is huge. Sales of power electronics equipment exceed $60 billion each year and affect another $1 trillion in hardware electronics sales. The prospect of improvements in the technology of such a dynamic market is exciting. Industrial firms could introduce products that are more powerful, more dependable, more durable, smaller in size, lighter in weight, and less costly to the consumer. The impact of power electronics is perhaps equally striking in terms of our environment. Power electronics systems are expected to control up to 80 percent of all electricity used by the year 2010. With the improvements in power electronics technology that the Center for Power Electronics Systems (CPES) has planned, the U.S. will be able to reduce its energy consumption by 30 percent. Recognizing the tremendous challenges involved in realizing these types of improvements in power electronics technology, five universities and more than 80 corporations joined forces in 1998 to create CPES. In order to achieve vision, many active countries are working on this technology and they are optimistic that by using power electronics they will reduce 70 percent power consumption . Development of power electronics processes using an integrated systems approach ; improve the quality, reliability, and cost-effectiveness of power electronics systems; and reduce both the time and effort associated with design cycles for systems application Bibliography: Word Count: 2111
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