英文翻譯(英文).doc

蘭州交通大學(xué)畢業(yè)設(shè)計(jì)英文翻譯（英文）Applications of Power Electronics Technique in Power SystemElectric power electronics(Power Electronics) is apply realm at the electric power technique in of electronics , be called an electric power electronics a technique(the Technique of the Power Electronic) in the engineering the application . It with make use of a big power electronics a spare part to the electric power carry on transformation and control for study a contents , is 1 and electronics , control and the electric power close and related edge academics . Its of the creation and the usage in the electric power built up a kind of relation , under this kind of relation , the creation of electric power , transport to have a very high efficiency with usages all , and various different loads can get what it expect the best energy a supply form and the best control . Therefore, electricity dint electronics technique not only in great quantities used for traditional electric power system in of hand over direct current to lose to change to give or get an electric shock device , more extensively applied at the industry produce hand over of various electrical engineering direct current in each realm to adjust soon , the material processes various energy of heating power supply(such as medium the high Pin respond heating power supply , weld power supply.etc.) in the realm to output a control etc. Along with the technical development , drive by electric voltage of various all control the power spare part of a Gao Pin2 Da4 and its power mold piece to appear one after anotherr , this is various for manufacturing cleverly made and easy and convenient , the function be stable high-efficiency with the high-quality high Pin switch power supply provided a condition , this power supply currently extensively used for various communication equipments , calculator is to each kind of appliance product . Modern electric power electronics technique(the Electronic Technique of the Modern Power) mainly with that in the middle of the realm those behind rise of , have development foreground most currently of all control an electric power electronics spare part such as the Power-MOSFET, IGBT, MCT , PIC etc. introduces their basic structure , the work principle , main parameter for the background , applied characteristics , and spare part application medium of drive , protection etc. basic problem , introduce in the hard PWM switch respectively and soft PWM switch under the condition of each kind of transformation electricity road , like DC-DC , DC-AC , AC-AC , the basic principle, electric circuit characteristics of the AC-DC etc . transformation electric circuit , wave load with analytical and various form to electric circuit work of influence analysis and first step design, calculation . Over the last 30 years power electronics devices typically have been employed tostabilize voltages and to control motor speed .With the development of high power thyristor ,a static compensator (STATCOM) allows both leading or lagging power factor to be corrected seamlessly with a minimum of installed capacitance ,allowing voltage stabilization and load seamlessly with a minimum of installed capacitance , allowing voltage stabilization and load balancing . A converter-based united power flow controller (UPFC) controls power flow ,voltage and power factor , allowing optimmal and stable use of existing line . A dynamic voltage restorer (DVR) instantly reacts to drop (eg . battery ) . Notable application of power electronics is HVDC power transmission over long distance . All of these have relied on phase controlled thyristors (PCT) , offering the higher power control . During the early 1980s the transistor-based structures were pushed towands higher powers Gate Turn-off (GTO) thyristor and by the early 1990s Insulated Gate Bipolar Transistor (IGBT) had become very high power . In thermal power plant , the major load of the auxiliary system is fan and pump , especially the FD and ID fans and feed-water pumps that have large influence on the auxiliary power . The energy saving of these equipment can improve the plant efficiency remarkably . The requirement to the partial load running of large fans and pumps becomes higher and higher . There are four methods to control the flow of the fans and pumps : baffle (throttle) adjustment , impeller adjustment , fluid coupling adjustment and motor speed ( frequency conversion and voltage transformation) adjustment . The first three methods are the conventional adjustment methods in power plants . These methods apply mechanical principle . Frequency conversion method changes the flow through changing the frequency of power source applied on the motor so that the rotating speed of the fan or pump is changed . This method changes the input power of the motor . Although all above four methods can be used to adjust the flow of the fans and pumps , their shaft powers are remarkably different . Frequency inverter can make the air flow control close to the required curve , without throttle , so the fan can use minimum power while providing the same air flow and its efficiency is the highest .The technology of large power electronic has developed from SCR , Gate Turn-off Thyristor (GTO) to Integrated Insulated Gate Bipolar Transistor (IGBT) . The control mode has developed from early U/f control mode to vector control technology and pulse width modulation . The frequency inverters has a function of variable voltage and implements some complete control algorithm that can not be implemented by traditional analog circuit . The frequency conversion device has many advantages : large capacity , high accuracy , high controllability , high RAS(Reliability Availability Service-ability) , etc. Especially the development inverter of the IGBT technology of high voltage and large capacity makes frequency inverter of large fans and water pumps possible in the large power plant . Beside the frequency speed control technology , soft-startup is another new developing technology in recent years . It adopts SCR with large power to establish the voltage adjustment circuit , so the AC motor can be started with low voltage . Because of digital control technology based on microprocessor , the startup characteristics , shutdown characteristics and startup current can be set accurately . It has a very good protection function . It is suitable to devices that started frequently or under a heavy load condition .Soft-startup has the following advantages : (1) It can conjugate with startup characteristics and shutdown characteristics of various machines accurately , so it can work optimally ;(2) It is a starter without contact , thus has higher reliability and maintainability ;(3) Because of its constant soft-startup characteristics , it decreases the startup current and reduces the impact on the transformer and motor itself ;(4) It decreases the startup torque , so it reduces the impulsion to the mechanical devices and prolongs service life ;(5) It can improve the power factor of the motor when it is under low load or no l