09电力机车一班 20097891 江锐 英语翻译作业.doc

09电力机车一班 20097891 江锐 英语翻译作业(原文)Electrical Networks and Power Semiconductor DevicesElectrical NetworksAn electrical circuit or network is composed of elements such as resistors, inductors, and capacitors connected together in some manner. If the network contains no energy sources, such as batteries or electrical generators, it is known as a passive network. On the other hand, if one or more energy sources are present, the resultant combination is an active network. In studying the behavior of an electrical network, we are interested in determining the voltages and currents that exist within the circuit. Since a network is composed of passive circuit elements, we must first define the electrical characteristics of these elements.In the case of a resistor, the voltage-current relationship is given by Ohms law, which states that the voltage across the resistor is equal to the current though the resistor multiplied by the value of the resistance. Mathematically, this is expressed as (1-1A-1) where u=voltage,V; i=current, A; R=resistance, .The voltage across a pure inductor is defined by Faradays law, which states that the voltage across the inductor is proportional to the rate of change with time of the current through the inductor. Thus we have (1-1A-2)Where =rate of change of current, ; L=inductance, H.The voltage developed across a capacitor is proportional to the electric change q accumulating on the plates of the capacitor. Since the accumulation of charge may be expressed as the summation, or integral, of the charge increments dq, we have the equation (1-1A-3)where the capacitance C is the proportionality constant relating voltage and charge. By definition, current equals the rate of change of charge with time and is expressed as i= . Thus an increment of charge dq is equal to the current multiplied by the corresponding time increment, or dq=idt. Eq.(1-1A-3) may then be written as (1-1A-4)where C= capacitance, F.Active electrical devices involve the conversion of energy to electrical form. For example, the electrical energy in a battery is derived from its stored chemical energy. The electrical energy of a generator is a result of the mechanical energy of the rotating armature.Active electrical elements occur in two basic forms: voltage sources and current sources. In their ideal form, voltage sources generate a constant voltage independent of the current drawn from the source. The aforementioned battery and generator are regarded as voltage sources since their voltage is essentially constant with load. On the other hand, current sources produce a current whose magnitude is independent of the load connected to the source. Although current sources are not as familiar in practic, the concept does find wide use in representing an amplifying device, such as the transistor, by means of an equivalent electrical circuit. A common method of analyzing an electrical network is mesh or loop analysis. The fundamental law that is applied in this method is Kirchhoffs first law, which states that the algebraic sum of the voltages around a closed loop is 0, or, in any closed loop, the sum of the voltage rises must equal the sum of the voltage drops. Mesh analysis consists of assuming that currents-termed loop currents-flow in each loop of a network, algebraically summing the voltage drops around each loop, and setting each sum equal to 0.Power Semiconductor DevicesPower semiconductor devices constitute the heart of modern power electronic appartus. They are used in power electronic converters in the form of a matrix of on-off switches. And the switching mode power conversion gives high efficiency.Todays power semiconductor devices are almost exclusively based on silicon material and can be classified as follow: Diode Thyristor or silicon-controlled rectifier (SCR) Triac Gate turn-off thyristor (GTO) Bipolar junction transistor (BJT or BPT) Power MOSFET Static induction transistor (SIT) Insulated gate bipolar transistor (IGBT)MOS-controlled thyristor (MCT) Integrated gate-commutated thyristor (IGCT)（译文）电路与功率半导体器件电路电路或电网络由以某种方式连接的电阻器、电感器和电容器等元件组成。如果网络不包含能源，如电池或发电机，那么就被作为无源网络。换句话说，如果存在一个或多个能源，那么组合的结果为有源网络。在研究电网络的特性时，我们感兴趣的是电路中的电压和电流。因为网络由无源电路元件组成，所以必须首先这些元件的电特性。就电阻元件来说，电压-电流的关系由欧姆定律给出，欧姆定律指出：电阻两端的电压等于电阻上流过的电流乘以电阻值。在数学上表达为： （1-1A-1）式中 u=电压，伏特；i=电流，安培；R=电阻，欧姆。纯电感电压由法拉第定律定义，法拉第定律指出：电感两端的电压正比于流过电感的电流随时间的变化率。因此可以以得到： （1-1A-2）式中di/dt=电流变化率，安培/秒；L=感应系数，亨利。电容两端建立的电压正比于电容两极板上积累的电荷q.因为电荷的积累可以表示为电荷增量dq的和或积分，因此得到的等式为： （1-1A-3）式中电容量C是与电压和电荷相关的比例常数。有定义可知，电流等于电荷随时间的变化率，可表示为i = dq/dt。因此电荷增量dq等于电流乘以相应的时间增量，或dq=idt，那么等式（1-1A-3）可写为 （1-1A-4）式中C=电容量，法拉。有源电气元件涉及其他能量转换为电能，例如电池中的电能来自其储存的化学能，发电机的电能是旋转电枢机械能转换的结果。有源电器元件存在两种基本方式：电压源和电流源。其理想状态为：电压源两端的电压恒定，与从电压源中流出的电流无关。因为负载变化时电压基本恒定，所以上述电池和发电机被认为是电压源。另一方面，电流源产生电流，电流的大小与电源连接的负载无关。虽然电流源在实际中不常见，但其概念的确在表示借助于等值电路的放大器件，比如晶体管中具有广泛应用。分析电网络的方法是网孔分析法或回路分析法。应用于此方法的基本定律是基尔霍夫第一定律，基尔霍夫第一定律指出：一个闭合回路中的电压代数和为0，换句话说，任一闭合回路中的电压升等于电压降。网孔分析法指的是：假设有一个电流即所谓的回路电流流过电路中的每一个回路，求每一个回路电压降的代数和，并令其为零。功率半导体器件功率半导体器件构成了现代电力电子设备的核心。他们以通-断开关矩阵的方式被用于电力电子转换器中。开关式功率变换的效率更高。现今的功率半导体器件几乎都是用硅材料制造，可分类如下： 二极管 晶闸管或可控硅 双向可控硅 门极可关断晶闸管 双集结型晶体管 电力金属氧化物半导体场效应晶体管 静电感应晶体管 绝缘栅双极性晶体管 金属氧化物半导体控制的晶闸管 集成门极换向晶闸管生词列表Semiconductor n.半导体技术 Devices n.装置，设备；设计；策略；图案 dvasComposed v.组成（ compose的过去式和过去分词 ） kmpozdCapacitors n.电容器 Multiplied v.乘（ multiply的过去式和过去分词 ）；（使）相乘 Mathematically adv.算术地 Pure adj.纯正的Proportiona n.比例数 Accumulating v.堆积，积累 Plates vt.镀，在上覆盖金属板 Summat