【正文】 portional to the total . of the field windings, the constant of proportionality being the directaxis airgap permeance. The outstanding advantages of . machines arise from the wide variety of operating characteristics that can be obtained by selection of the method of excitation of the field windings. The field windings may be separately excited from an external . source, or they may be selfexcited。 for convenience we shall continue to assume a sinusoidal fluxdensity wave in the air gap. The torque can then be found from the magic field viewpoint. The torque can be expressed in terms of the interaction of the directaxis airgap flux 4 per pole d? and spacefundamental ponent 1Fa of the armature . With the brushes in the quadrature axis the angle between these fields is 90 electrical degrees, and its sine equals unity. For a P pole machine 2122 dPT Fa? ???? ???? （ 11） In which the minus sign gas been dropped because the positive direction of the torque can be determined from physical reasoning. The space fundamental 1Fa of the sawtooth armature is 28? times its peak. Substitution in above equation then gives ()2 a aaPCT i N mm ???? （ 12） Where, aI =current in external armature circuit。 從網上下載的中英文對照文章按不合格論。 英文翻譯包括英文全文和翻譯兩部分 （ 中文 翻譯不少于 2020字） 。 1 畢業(yè)設計（論文） 外文翻譯 題 目 ： 直流電機控制系統(tǒng) 專 業(yè) ： 電子信息工程 班 級 ： 08 級 學 生 ： 辛國鵬 指導教師 ： 湯曉方 西安理工大學高科學院 2020 年 2 說 明 英文翻譯 是畢業(yè)設計（論文）答辯委員會對 學生答辯資格審查的依據(jù)材料之一。學生應當在畢業(yè)設計（論文）工作 期內完成， 英文翻譯 不合格者不得參加答辯。 所選英文 資料 內容應與本 人 專業(yè)或本人論文題目有關。 3 英文全文 Introduction to . Machines . machines are characterized by their versatility. By means of various binations of shunt, series, and separately excited field windings they can be designed to display a wide variety of voltampere or speedtorque characteristics for both dynamic and steady state operation. Because of the ease with which they can be controlled, systems of . machines are often used in applications requiring a wide range of motor speeds or precise control of motor output. The essential features of a . machine are shown schematically. The stator has salient poles and is excited by one or more field coils. The airgap flux distribution created by the field winding is symmetrical about the centerline of the field poles. This is called the field axis or direct axis. As we know, the . voltage generated in each rotating armature coil is converted to . in the external armature terminals by means of a rotating mutator and stationary brushes to which the armature leads are connected. The mutatorbrush bination forms a mechanical rectifier, resulting in a . armature voltage as well as an armature . Wave then is 90 electrical degrees from the axis of the field poles, . in the quadrature axis. In the schematic representation the brushes are shown in quadrature axis because this is the position of the coils to which they are connected. The armature . Wave then is along the brush axis as shown. (The geometrical position of the brushes in an actual machine is approximately 90 electrical degrees from their position in the schematic diagram because of the shape of the end connections to the mutator.) The magic torque and the speed voltage appearing at the brushes are independent of the spatial waveform of the flux distribution。 aC =total number of conductors in armature winding。 . the machine may supply its own excitation. The method of excitation profoundly influences not only the steadystate characteristics, but also the dynamic behavior of the machine in control systems. The connection diagram of a separately excited generator is given. The required field current is a very small fraction of the rated armature current. A small amount of power in the field circuit may control a relatively large amount of power in the armature circuit。 excitation poles and winding。 end shield with ball or sliding bearings。 the terminal box. － The rotor which is the moving part of the machine. It is made up of a core mounted on the machine shaft. This core has uniformly spaced slots into which the armature winding is fitted. A mutator, and often a fan, is also located on the machine shaft. The frame is fixed to the floor by means of a bedplate and bolts. On low power