1、 毕业设计（外文翻译） 题 目 电路与功率二极管器件 系 （院） 自动化系 专 业 电气工程与自动化 学生姓名 陈芬 学 号 2007090403 指导教师 刘应乾 职 称 助 教 2011 年 6 月 15 日 1 Electrical Networks and Power Semiconductor Devices Electrical Networks An electrical circuit or network is composed of elements such as resistors, inductors, and capacitors connected togethe
2、r 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,
3、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,
4、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 iRu (1-1A-1) where u=voltage,V； i=current, A； R=resistance, . The voltage across a pure inductor is defined by Faradays law, w
5、hich 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 dtdiLu (1-1A-2) Where dtdi =rate of change of current, sA ； L=inductance, H. The voltage developed across a capacitor is proportional to the electric cha
6、nge 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 dqcu 1 (1-1A-3) where the capacitance C is the proportionality constant relating voltage and charge. By definition, cu
7、rrent equals the rate of change of charge with time and is expressed as i= dtdq . 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 2 idtcu 1 (1-1A-4) where C= capacitance, F. Active electrical devices
8、 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: v
9、oltage 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, cu
10、rrent 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 co
11、mmon 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
12、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 Devices Power semiconductor devices constitute the heart of moder
13、n 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)
