电子专业毕业设计论文外文文献及翻译-全双桥电机保护驱动器a3976(编辑修改稿)

电子专业毕业设计论文外文文献及翻译-全双桥电机保护驱动器a3976(编辑修改稿)内容摘要：

stances, the quantity of energy source is limited. unlimited usage of energy source results in energy crisis. At present, most of the energy consumed by humans is produced from fossil fuels. The greatest recoverable fossil is in the form of coal and lignite. Although world coal resources are enomous and potentially can fill energy needs for a century or two, their utilization is limited by environmental disruption from mining and emissions of carbon dioxide and sulfur dioxide. These would bee intolerable long before coal resources were exhausted. Only a small percentage of coal and lignite has been utilized to date, whereas much of the recoverable petroleum and natural gas has already been consumed. Petroleum has several characteristics that make it superior to coal as a source of energy. Its extraction causes less environmental damage than does coal mining. It is a more concentrated source of energy than coal, and it burns with less pollution, and it can be moved easily through pipes. These characteristics make it an ideal fuel for automobiles. Since first mercial oil well in 1859, somewhat more than 100 million barrels of oil have been produced in the United States, most of it in recent years. In 1990 world petroleum consumption was at a rate of about 65 million barrels per day. Projected use of petroleum and natural gas indicates rapid depletion. Alaskan oil can help the petroleum supply only temporarily. Peak world petroleum resources production will be reached within a few years. Since the first energy crisis of 19731974, some concrete actions have even taken place. However, the severalfold increase in crude oil prices since 1973 has extacted a toll. In the . and other industrialized nations, the economy has been plagued by inflation, recession, unemployment, and obsolescence of industrial equipment. The economies of some petroleumdeficient developing countries have been devastated by energy prices. Energy crisis was acpanied by worldwide shortages of some foods and minerals, followed in some cases by surpluses, such as the surplus wheat resulting from increased planting and a copper surplus resulting from the efforts of copperproducing nations to acpuire foreign currency by copper export. As known to all,the availability and cost of energy has bee dominant factors in society today. Obviously, solving the energy crisis makes good sense. Many schemes has been proposed for conserving present energy resources and for developing new ones. It is always possible to use less energy in any process. Therefore, energy engineer is created and developed. The first goal of energy engineer is to determine the methods by which energy utilization is reduced but the output remains the same, or even second goal is to determine which methods of using less energy。