第一章第一篇sectiong
Two variables u(t) and i(t) are the most basic concepts in an electric circuit, they characterize the various relationships in an electric circuitu(t)和i(t)这两个变量是电路中最基本的两个变量，它们刻划了电路的各种关系。 Charge and Current
The concept of electric charge is the underlying principle for explaining all electrical phenomena. Also, the most basic quantity in an electric circuit is the electric charge. Charge is an electrical property of the atomic particles of which matter consists, measured in coulombs (C). 电荷和电流 电荷的概念是用来解释所有电气现象的基本概念。也即，电路中最基本的量是电荷。电荷是构成物质的原子微粒的电气属性，它是以库仑为单位来度量的。
We know from elementary physics that all matter is made of fundamental building blocks known as atoms and that each atom consists of electrons, protons, and neutrons. We also know that the charge e on an electron is negative and equal in magnitude to 1.60210×1019C, while a proton carries a positive charge of the same magnitude as the electron. The presence of equal numbers of protons and electrons leaves an atom neutrally charged. 我们从基础物理得知一切物质是由被称为原子的基本构造
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部分组成的，并且每个原子是由电子，质子和中子组成的。我们还知道电子的电量是负的并且在数值上等于1.602100×10-12C，而质子所带的正电量在数值上与电子相等。质子和电子数量相同使得原子呈现电中性。
We consider the flow of electric charges. A unique feature of electric charge or electricity is the fact that it is mobile; that is, it can be transferred from one place to another, where it can be converted to another form of energy让我们来考虑一下电荷的流动。电荷或电的特性是其运动的特性，也就是，它可以从一个地方被移送到另一个地方，在此它可以被转换成另外一种形式的能量。
When a conducting wire is connected to a battery (a source of electromotive force), the charges are compelled to move; positive charges move in one direction while negative charges move in the opposite direction. This motion of charges creates electric current. It is conventional to take the currentflow as the movement of positive charges, that is, opposite to the flow of negative charges, as Fig.l-1 illustrates. This convention was introduced by Benjamin Franklin (l706～l790), the American scientist and inventor. Although we now know that current in metallic conductors is due to negatively charged electrons, we will follow the universally accepted convention
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that current is the net flow of positive charges. Thus, Electric current is the time rate of charge, measured in amperes (A). Mathematically, the relationship among current i, charge q, and
dqtime t is 当我们把一根导线连接到某一电池上时(一种电动势源)，idt电荷被外力驱使移动；正电荷朝一个方向移动而负电荷朝相反的方向移动。这种电荷的移动产生了电流。我们可以很方便地把电流看作是正电荷的移动，也即，与负电荷的流动方向相反，如图1－1所示。这一惯例是由美国科学家和发明家本杰明－富兰克林引入的。虽然我们现在知道金属导体中的电流是由负电荷引起的，但我们将遵循通用的惯例，即把电流看作是正电荷的单纯的流动。于是电流就是电荷的时率，它是以安培为单位来度量的。从数学上来说，电流i、电荷q以及时间t之间的关系是：
The charge transferred between time t0 and t is obtained by integrating both sides of Eq. (1-1). We obtain从时间t0到时间t所移送的电荷可由方程（1－1）两边积分求得。我们算得：
The way we define current as i in Eq. (1-l) suggests that current need not be a constant-valued function, charge can vary with time in several ways that may be represented by different kinds of mathematical functions我们通过方程（1－1）定义电流的方式表明电流不必是一个恒值函数，电荷可以不同的方式随时间而变化，
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qidtt0t
这些不同的方式可用各种数学函数表达出来。 电压，能量和功率
To move the electron in a conductor in a particular direction requires some work or energy transfer. This work is dwuabperformed by an external electromotive force (emf), typically represented by the battery in Fig.l-1. This emf is also known as voltage or potential difference. The voltage uab between two points a and b in an electric circuit is the energy (or work)
dqneeded to move a unit charge from a to b; mathematically 在导体中朝一个特定的方向移动电荷需要一些功或者能量的传递，这个功是由外部的电动势来完成的。图1－1所示的电池就是一个典型的例子。这种电动势也被称为电压或电位差。电路中a、b两点间的电压等于从a到b移动单位电荷所需的能量（或所需做的功）。数学表达式为：
where w is energy in joules (J) and q is charge in coulombs (C). The voltage uab is measured in volts (V), named in honor of the Italian physicist Alessandro Antonio Volta (l745～l827), who invented the first voltaic battery. Thus, Voltage (or potential difference) is the energy required to move a unit charge through an element, measured in volts (V). 式中w是单位为焦耳的能量而q是单位为库仑的电荷。电压Uab是以伏特为单位来度量的，它是为了纪念意大利物理学家Alessandro Antonio Volta而命名的，这
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位意大利物理学家发明了首个伏达电池。于是电压（或电压差）等于将单位电荷在元件中移动所需的能量，它是以伏特为单位来度量的。 Fig.l-2 shows the voltage across an element (represented by a rectangular block ) connected to points a and b. The plus (+) and minus (-) signs are used to define reference direction or voltage polarity. The uab can be interpreted in two ways: ①point a is at a potential of uab volts higher than point b; ②the potential at point a with respect to point b is uab. It follows logically that in general 图1－2显示了某个元件（用一个矩形框来表示）两端a、b之间的电压。正号（＋）和负号（－）被用来指明参考方向或电压的极性，Uab可以通过以下两种方法来解释。1）在Uab伏特的电位中a点电位高于b点，2）a点电位相对于b点而言是Uab，通常在逻辑上遵循
Although current and voltage are the two basic variables in an electric circuit, they are not sufficient by themselves. For practical purposes, we need to know power and energy. To relate power and energy to voltage and current, we recall from physics that power is the time rate of expending or absorbing energy, measured in watts (W). We write this relationship as 虽然电流和电压是电路的两个基本变量，但仅有它们两个是不够的。
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uab-uba
从实际应用来说，我们需要知道功率和能量。为了把功率和能量同电压、电流联系起来，我们重温物理学中关于功率是消耗或吸收的能量的时率，它是以瓦特为单位来度量的。我们把这个关系式写成：
Where p is power in watts (W), w is energy in joules (J), and
pdwdtt is time in seconds (s). From Eq. (1-1), Eq. (1-3), and Eq.
(1-5), it follows that 式中p是以瓦特为单位的功率，w是以焦耳为单位的能量，t是以秒为单位的时间，从方程（1－1）、（1－3）和（1－5）可以推出
puiBecause u and i are generally function of time, the power p in Eq. (1-6) is a time-varying quantity and is called the instantaneous power. The power absorbed or supplied by an element is the product of the voltage across the element and the current through it. If the power has a plus sign, power is being delivered to or absorbed by the element. If, on the other hand, the power has a minus sign, power is being supplied by the element. But how do we know when the power has a negative or a positive sign？由于u和i通常是时间的函数，方程（1－6）中的功率p是个时间变量于是被称为瞬时功率，某一元件吸收或提供的功率等于元件两端电压和通过它的电流的乘积。如果这个功率的符
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号是正的，那么功率向元件释放或被元件吸收。另一方面，如果功率的符号是负的，那么功率是由元件提供的。但我们如何得知何时功率为正或为负？
Current direction and voltage polarity play a major role in determining the sign of power. It is therefore important that we pay attention to the relationship between current i and voltage u in Fig.1-3(a). The voltage polarity and current i direction must conform with those shown in Fig.1-3(a) in order for the power to have a positive sign. This is known as the passive sign convention. By the passive sign convention, current enters through the positive polarity of the voltage. In this case, p = ui or ui ﹥ 0 implies that the element is absorbing power. However, if p = -ui or ui ﹤ 0, as in Fig.1-3(b), the element is releasing or supplying power. 在我们确定功率符号时，电流的方向和电压的极性起着主要的作用，这就是我们在分析图1－3（a）所显示的电流i和电压u的关系时特别谨慎的重要原因。为了使功率的符号为正，电压的极性和电流的方向必须与图1－3（a）所示的一致。
这种情况被称为无源符号惯例，对于无源符号惯例来说，电流流进电压的正极。在这种情况下，p＝ui或ui>0，表明元件是在吸收功率。而如果p＝－ui或ui<0，如图1－3（b）所示时，表明元件是在释放或提供功率。
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In fact, the law of conservation of energy must be obeyed in any electric circuit. For this reason, the algebraic sum of power in a circuit, at any instant of time, must be zero事实上，在任何电路中必须遵循能量守恒定律。由于这个原因，任一电路中在任何瞬间功率的代数和必须等于零
p0This again confirms the fact that the total power supplied to the circuit must balance the total power absorbed. From Eq. (l-7), the energy absorbed or supplied by an element from time
t0 to time t is这再一次证明了提供给电路的功率必须与吸收的功
率相平衡这一事实。从方程（1－7）可知，从时间t0到时间t被元件吸收或由元件提供的功率等于 Section2
An electric circuit is simply an interconnection of the elements. There are two types of elements found in electric circuits: passive elements and active elements. An active element is capable of generating energy while a passive element is not. Examples of passive elements are resistors, capacitors, and inductors. The most important active elements are voltage or current sources that generally deliver power to the circuit
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wpdtt0t
connected to them. 电路仅仅是元件之间的相互结合。我们发现电路中存在有两种元件：无源元件和有源元件。有源元件能够产生能量而无源元件却不能，无源元件有电阻、电容和电感器等。最重要的有源元件是通常向与它们相连的电路释放能量的电压和电流源。 Independent sources
An ideal independent source is an active element that provides a specified voltage or current that is completely independent of other circuit variables.
An independent voltage source is a two-terminal element, such as a battery or a generator, which maintains a specified voltage between its terminals. The voltage is completely independent of the current through the element. The symbol for a voltage source having u volts across its terminals is shown in Fig.1-4(a). The polarity is as shown, indicating that terminal
a is u volts above terminal b. Thus if u > 0, then terminal a
is at a higher potential than terminal b. The opposite is true, of course, if u < 0
一个理想的独立源是产生完全独立于其它电路变量的特定电压或电流的有源元件。一个独立电压源是一个二端口元件，如一个电池或一台发电机，它们在其端部维持某个特定的电压。该电压完全独立于流过元件的电流，在其端部具有u伏电压的电压源的符号如图1－4（a）所示，极性如图所示，它表明a端比b端高u伏。如果u>0，那么a
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端的电位高于b端，当然，如果u<0，反之亦然。
In Fig.1-4(a), the voltage u may be time varying, or it may be constant, in which case we would probably label it U. Another symbol that is often used for a constant voltage source, such as a battery with U volts across its terminals, is shown in Fig.1-4(b). In the case of constant sources we shall use Fig.1-4(a) and 1-4(b) interchangeably.
在图1－4（a）中，电压u可以是随时间而变化，或者可以是恒定的，在这种情况下我们可能把它标为U，对于恒定电压源我们通常使用另一种符号，例如在两端只有U伏电压的电池组，如图1－4（b）所示。在恒定源的情况下我们可以交替地使用于图1－4（a）或图1－4（b） We might observe at this point that the polarity marks on Fig.1-4(b) are redundant since the polarity could be defined by the positions of the longer and shorter lines.
我们可能已经注意到这一点，即图1－4（b）中的极性标号，是多余的因为我们可以根据长天线的位置符，确定电池极性
An independent current source is a two-terminal element through which a specified current flows. The current is completely independent of the voltage across the element. The symbol for an independent current source is shown in Fig.1-5, where i is the specified current. The direction of the current is indicated by the arrow
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一个独立电流源是二端元件在两端之间特定的电流流过，该电流完全独立于元件两端的电压，一个独立电流源的符合如图1－5所示。图中i是特定电流，该电流的方向由箭头标明
Independent sources are usually meant to deliver power to the external circuit and not to absorb it. Thus if u is the voltage across the source and its current i is directed out of the positive terminal, then the source is delivering power, given by p = ui, to the external circuit. Otherwise it is absorbing power. For example, in Fig.1-6 (a) the battery is delivering 24 W to the external circuit. In Fig.1-6(b) the battery is absorbing 24 W, as would be the case when it is being charged. 独立源通常指的是向外电路释放功率而非吸收功率，因此如果u是电源两端的电压而电流i直接从其正端流出，那么该电源正在向对电路释放功率，由式p＝ui算出。否则它就在吸收功率。例如图1－6（a）中电池正在向外电路释放功率24w，在图1－6（b）中，电池就在充电情况，吸收功率24w。 Dependent sources
An ideal dependent (or controlled) source is an active element in which the source quantity is controlled by another voltage or current.
Dependent sources are usually designated by diamond-shaped symbols, as shown in Fig.1-7Since the control of the dependent
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source is achieved by a voltage or current of some other element in the circuit, and the source can be voltage or current, it follows that there are four possible types of dependent sources, namely:
（1）A voltage-controlled voltage source (VCVS). （2）A current-controlled voltage source (CCVS). （3）A voltage-controlled current source (VCCS). （4）A current-controlled current source (CCCS).
Dependent sources are useful in modeling elements such as transistors, operational amplifiers and integrated circuits. 一个理想的受控源是一个有源元件，它的电源量是由另外一个电压和电流所控制。
受控源通常用菱形符号表明，如图1－7所示。由于控制受控源的控制量来自于电路中其他元件的电压或电流，同时由于受控源可以是电压源或电流源。由此可以推出四种可能的受控源类型，即 电压控制电压源（VCVS） 电流控制电压源（CCVS） 电压控制电流源（VCCS） 电流控制电流源（CCCS）
受控源在模拟诸如晶体管、运算放大器以及集成电路这些元件时是很有用的
It should be noted that an ideal voltage source (dependent or
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independent) will produce any current required to ensure that the terminal voltage is as stated, whereas an ideal current source will produce the necessary voltage to ensure the stated current flow. Thus an ideal source could in theory supply an infinite amount of energy. It should also be noted that not only do sources supply power to a circuit, but they can absorb power from a circuit too. For a voltage source, we know the voltage but not the current supplied or drawn by it. By the same token, we know the current supplied by a current source but not the voltage across it.
应该注意的是：一个理想电压源（独立或受控）可向电路提供以保证其端电压为规定值所需的任意电流，而电流源可向电路提供以保证其电流为规定值所必须的电压。还应当注意的是电源不仅向电路提供功率，他们也可从电路吸收功率。对于一个电压源来说，我们知道的是由其提供或所获得的电压而非电流，同理，我们知道电流源所提供的电流而非电流源两端的电压。
第二章第一篇
To say that we live in an age of electronics is an understatement. From the omnipresent integrated circuit to the equally omnipresent digital computer, we encounter electronic devices and systems on a daily basis. In every aspect of our increasingly technological society— whether it is
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science, engineering, medicine, music, maintenance, or even espionage—the role of electronics is large, and it is growing.谈论关于我们生活在一个电子学时代的论调是一种空泛的论调。从无处不在的集成电路到同样无处不在的数字计算机，我们在日常活动中总会遇到电子设备和电子系统。在我们日益发展的科技社会的方方面面——无论是在科学、工程、医药、音乐、维修方面甚至是在谍报方面——电子学的作用是巨大的，而且还将不断增强。
In general, all of the tasks with which we shall be concerned can be classified as \"signal-processing“tasks. Let us explore the meaning of this term一般说来，我们将要涉及到的工作被归结为“信号——处理”工作，让我们来探究这个术语的含义吧。
A signal is any physical variable whose magnitude or variation with time contains information. This information might involve speech and music, as in radio broadcasting, a physical quantity such as the temperature of the air in a room, or numerical data, such as the record of stock market transactions. The physical variables that can carry information in an electrical system are voltage and current. When we speak of \"signalsherefore, we refer implicitly to voltages or currents. However, most of the concepts we discuss can be applied directly to systems with different information-carrying variables. Thus, the behavior of a mechanical system (in which force and velocity are the variables) or a hydraulic system (in which pressure and flow rate are the variables) can often be
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modeled or represented by an equivalent electrical system. An understanding of the behavior of electrical systems, therefore, provides a basis for understanding a much broader range of phenomena. 信号就是其与时间有关的量值或变化包含信息的任何物理变量。这种信息或许像无线电广播的演讲和音乐，或许是像室内温度的物理量，或许像股市交易记录的数字数据。在电气系统中能够载有信息的物理变量是电压和电流。因此当我们谈到“信号”，我们不言而喻指的是电压和电流，然而，我们要讨论的大多数概念是可以被直接应用于载有不同信息的变量的系统，因此，一个机械系统（在这个系统中力和速度是其变量）或者液压系统（在这个系统中压力和流速是其变量）的性能通常可以用一个等效的电气系统来模拟或表示。因此，我们对于电气系统性能的理解为理解更宽领域的现象打下了一个基础。
A signal can carry information in two different forms. In an analog signal the continuous variation of the voltage or current with time carries the information. An example, in Fig.2-l, is the voltage produced by a thermocouple pair when the two junctions are at different temperatures. As the temperature difference between the two junctions varies, the magnitude of the voltage across the thermocouple pair also varies. The voltage thus provides an analog representation of the temperature difference. 一个信号可以以两种形式来承载信息。在一个模拟信号中电压或电流随时间而产生的连续变化载有信息。在图2-1中，当一对热电偶的接头处于不同的温度时由热电偶所产生的电压就是一个例
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子。当两个接头之间的温度差改变时，一对热电偶两端的电压也将改变。于是电压就提供了温度差的模拟表现形式
The other kind of signal is a digital signal. A digital signal is one that can take on values within two discrete ranges. Such signals are used to represent ON-OFF or YES-NO information. An ordinary household thermostat delivers a digital signal tocontrol the furnace. When the room temperature drops below a preset value, the thermostat switch closes turning on the furnace. Once the room temperature rises high enough, the switch opens turning off the furnace. The current through the switch provides a digital representation of the temperature variation: ON equals \"too cold\" while OFF equals \"not too cold\". 另一种的信号是数字信号。数字信号是在两个离散的范围内能够呈现一定数值的信号。这种信号常用以表示“开—关”或“是—不是”信息。一个普通的家用恒温器传递一种数字信号来控制炉子当房间的温度下降到预定温度以下时，恒温器的开关合上使炉子开始加热；一旦房间的温度上升到足够高，开关就断开使炉子关闭。流过开关的电流提供了温度变化的数字表示：ON即为“太冷”而OFF即为“不太冷”
A signal-processing system is an interconnection of components and devices that can accept an input signal or a group of input signals, operate on the signals in some fashion either to extract or improve the quality of the information, and present the information as an output in the proper form at the proper time. 一个信号处理系统是某些元件或设备之间的
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相互连接，这些元件和设备能够接收一个输入信号或一组输入信号，信号处理系统以某种方式来处理这些信号即提取这些信号或提高这些信号的品质，然后在适当的时间以适当的形式把这个信号表示为输出量。
Fig.2-2 illustrates the components in such a system. The central circles represent the two types of signal processing (digital and analog), while theblock between the two signal- processing blocks represents the conversion of an analog signal to equivalent digital form (A/D=Analog-to-Digital) and the reverse conversion of a digital signal to the corresponding analog form (D/A=Digital-to-Analog). The remaining blocks involve inputs and outputs— getting signals into and out of the processing system. 图2-2显示了这样一个系统的组成部分。中间的圆圈代表了两种类型的信号处理（数字和模拟），而处于信号处理框之间的方框表示模拟信号向等效数字形式（A/D即模拟到数字）的转换，以及从数字信号向相应的模拟形式（D/A即数字到模拟）的逆转换。剩下的方框涉及输入和输出——取得信号以及从处理系统输出信号。 Many electrical signals derived from physical systems are obtained from devices called transducers. We have already encountered an example of an analog transducer, the thermocouple pair. It converts temperature difference (the physical variable) to a voltage (the electrical variable). Generally, a transducer is a device that converts a physical or mechanical variable to an equivalent voltage or current signal. Unlike the
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thermocouple example, however, most transducers require some form of electrical excitation to operate从物理系统获得的很多电气信号是从被称为传感器的器件中输入的。我们已经碰到了一个模拟传感器的例子。即热电偶。它把温度的变化（物理变量）转换成电压（电气变量）。通常，传感器是一种将物理或机械变量转换成等效电压或电流信号的器件。然而，不同于热电偶例子，大多数传感器需要一些形式的电激励以驱动传感器
The output from a system can be in many forms, depending on the use to be made of the information contained in the input signals. One can seek to display the information, either in analog form (using a meter, for example, in which the needle position indicates the size of the variable of interest) or in digital form (using a set of digital display elements that are lit up with a number corresponding to the variable of interest). Other possibilities are to convert the output to sound energy (with a loudspeaker), or to use the output asan input signal to another system, or to use the output as a control signal to initiate some action. 个系统的输出可以有多种形式，这取决于包含在输入信号中的信息所起的作用。我们可以选择何种方式显示这些信息，无论是以模拟形式（例如，使用一种仪表，仪表的指针的位置指明我们所感兴趣的变量的大小）或是以数字形式（使用一套数字显示元件，显示对应于我们所感兴趣的变量的数字）。其它的可能的情况下是将输出转换成声能（利用扬声器），或是将输出作为另一个系统的输入，或是利用输出作为控制
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信号来产生某个动作 第二篇
The mathematics of computers and other digital electronic devices have been developed from the decisive work of George Boole (l815～l864) and many others, who expanded and improved on his work. The body of thought that is known collectively as symbolic logic established the principles for deriving mathematical proofs and singularly modified our understanding and the scope of mathematics. 布尔代数也称为逻辑代数。它是英国数学家乔治－布尔（1815－1864）于1849年创立的。在当时，这种代数纯粹是一种数学游戏。在布尔代数里，布尔构思出一种关于0和1的代数系数，用基础的逻辑符号系统描述物体和概念。这种代数不仅广泛于概率和统计等领域，更为重要的是，它为数字计算机开关电路设计提供了最重要的数学方法。
Only a portion of this powerful system is required for our use. Boole and others were interested in developing a systematic means of deciding whether a proposition in logic or mathematics was true or false, but we shall be concerned only with the validity of the output of digital devices. True and false can be equated with one and zero, high and low, or on and off. These are the only two states of electrical voltage from a digital element. Thus, in this remarkable algebra performed by logic gates, there are only two values, one and zero; anyalgebraic combination or manipulation can yield only these two values. Zero and
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one are the only symbols in binary arithmetic这种很有用的系统中只有一部分内容为我们所应用。布尔等人感兴趣的是推导出一种用来判断某个命题在逻辑上或在数学上是真还是假的系统性的方法，但我们要关注的仅仅是数字设备的输出的正确与否。真或假可以等同于一和零 ，或者等同于开和关。这是电子元件中电压的两种唯一的状态。因此，由逻辑门所完成的这个奇异的代数中，只有两种值，一和零，任何代数组合或者计算只能产生这两种值。零和一是二进制运算中唯一的符号
The various logic gates and their interconnections can be made to perform all the essential functions required for computing and decision-making. In developing digital systems the easiest procedure is to put together conceptually the gates and connections to perform the assigned task in the most direct way. Boolean algebra is then used to reduce the complexity of the system, if possibl，ewhile retaining the same function. The equivalent simplified combination of gates will probably be much less expensive and less difficult to assemble不同的逻辑门和它们之间的相互连接可以用来完成计算以及判断所要求的必要的功能。在开发数字系统时最简单的做法是把逻辑门以及它们之间的连接根据概念排放在一起 以最直接的方式完成 设定的任务。于是我们采用布尔代数来减小系统的复杂程度，如果可能的话，与此同时应保留其相同的功能。逻辑门之间等效的简单的组合可能使得费用更加便宜而在装配上更加容易。
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Boolean algebra has three rules of combination, as any algebra must have: the associative, the commutative, and the distributive rules. To show the features of the algebra we use the variables A, B, C, and so on. To write relations between variables each one of which may take the value 0 or l, we use to mean “not A,” so if A = l , then = 0. Thecomplement of every variable is expressed by placing a bar over the variable; the complement of
= \"not B\". Two fixed quantities also exist. The first is identity, I = l; the other is null, null = 0
布尔代数与任何代数一样具有结合律、交换律和分配律。为了表示代数的特性我们使用变量A,B和C以及诸如此类的变量。为了写出这些可能取值为0或1的各个变量之间的相互关系，我们采用来Ā表示“非A”，因此如果A＝1，那么Ā＝0。每个变量的补码用每个变量上方加一横线来表示，B的补码就是Ā也即“非B”。同时还存在两个固定的量。第一个量是单位量，即I＝1，另外一个量是零，即null＝0。 Boolean algebra applies to the arithmetic of three basic types of gates: an OR-gate, an AND-gate and the inverter. The symbol and the truth tables for the logic gates are shown in Fig.2-3, the truth table illustrate that the AND-gate corresponds to multiplication, the OR-gate corresponds to addition, and the inverter yield the complement of its input variable. 布尔代数应用于三种基本类型的逻辑门的运算：一种是或门，一种是与门，还有一种是反相器（非门）。逻辑门的符号和真值表如图2－3所
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示，真值表显示与门对应于乘，或门对应于加，而反相器产生其输入变量的补码
We have already found that AB = \"A AND B\" for the AND-gate and A + B = \"A OR B\"
for the OR-gate我们已经算出对于与门来说 AB=“A AND B”而对与或门来说 A+B=“A OR B”
The AND, or conjunctive, algebraic form and the OR, or disjunctive, algebraic form must each obey the three rules of algebraic combination. In the equations that follow, the reader may use the two possible values 0 and l for the variables A, B, and Cto verify the correctness of each expression. Use A = 0, B = 0, C = 0; A = l, B = 0, C = 0; and so on, in each expression. The associative rules state how variables may be grouped.对于“与”，即逻辑乘，以及“或”，即析取，它们的代数形式必须遵循代数组合的三个法则。在接下来的等式中，读者可以把变量A,B,C设为两个可能的值0和1来证明每个表达式的正确性。例如采用A=0,B=0,C=0，或A=1, B=0,C=0等等，在每个表达式中，结合律表明如何把变量进行重组
For AND (AB)C = A(BC) = (AC)B,
and for OR (A + B) + C = A + (B + C) = (A + C) + B 对于“与”有（AB）C＝A（BC）＝（AC）B而对于“或”有（A＋B）＋C＝A＋（B＋C）＝（A＋C）＋B
the rules indicate that different groupings of variables may be used
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without altering the validity of the algebraic expression这个法则表明我们可以采用变量的不同组合而不改变代数表达式的正确性。交换率表明了变量的顺序
The commutative rules state the order of variables. For AND AB = BA and for OR A+B = B+A
the rules indicate that the operations can be grouped and expanded as shown
对于“与”有AB＝BA，而对于“或”有A＋B＝B＋A。这个法则表明了可以如上式所示进行运算的组合和展开
Before we show the remaining rules of Boolean algebra for digital devices, let us confirm the distributive rule for AND by writing the truth table, Table 2-l. We will discover soon how we knew that we could write AB + C = (A + C)(B + C), which is proved by the truth table to be a proper expansion. 在我们展示数字设备布尔代数的剩下的那个法则之前，让我们通过写出真值表的方式即真值表2－1来验证对于“与”的分配律。我们将很快发现如何写出等式AB＋C＝（A＋C）（B＋C），这一等式由真值表证明了是一个正确的展开式。
The more complex expression and its simpler form yield identical values. Because binary logic is dominated by an algebra in which a sum of ones equals one, the truth table permits us to identify the equivalence among algebraic expressions. A truth table may be used to find a simpler
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equivalent to a more complex relation among variables, if such an equivalent exists. We will see shortly how the reduction of complexity may be achieved in a systematic manner with truth tables and other techniques更为复杂的表达式和它的一次式产生了相等的值。由于二进制逻辑取决于某一代数，其单个变量之和等于一个变量，所以真值表允许我们在代数表达式中找出等效值，我们可以使用真值表来求出一个等效于变量之间较复杂的关系式的一次表达式。如果这样的等效关系存在，我们将很快看到利用真值表以及其它方法以一种系统性的方式如何完成这样一个复杂步骤的简化工作。
Some additional relations in the algebra, which use identity and null, are worth nothing. Here we illustrate properties of the AND and OR operations that use the distributive rules and the fact that I is always l and null is always 0. AND
AI = A or A1 = AOR
A = null
A+ null = A
A + 0 = AAND A = 0OR A + A null = null A0 =
AA = AOR
A + A
= I A + =1 0OR = A
AND
A + I = I A + 1 = 1AND
The relation points out an important fact, that is, that I, the identity, is the universal set. Null is called the empty set.代数中另外的一些关系式，这些式子中使用单位一和零，是没有意义的，这里我们列举了运用分配律后“与”和“或”运算的性质，结果是1永远是1而
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零永远是0。
与：AI＝A即A1＝A或：A＋null＝A即A＋0＝A与： 即或： 即 与：Anull＝0即A0＝0或：A＋I＝I即A＋1＝与：AA＝A或：A＋A＝A关系式A＋A＝I指出了一个重要事实，即I，也就是单位量，是全集，而零被称为空集。
We have considered several logical relations. For the two-value Boolean algebra of digital electronics, the choice of the technique depends upon the nature of the function whose reduction is desired. Some simple functions may be easily reduced by examining their truth table; others require the manipulation of Boolean algebra to reveal the relationship . When we consider the circuit foradding binary numbers, we see that Boolean algebra is required to discover a simplification in that particular application我们已经研究了几种逻辑关系。对于电子学的二值布尔代数来说，选择何种方法取决于我们所期望的简化函数的性质。一些简单的函数可以通过观察它们的真值表很容易进行简化；而另一些函数需要通过计算布尔代数来揭示它们的关系。当我们研究有关二进制数相加的电路时，我们将看到需要布尔代数来揭示该特定应用中的简化过程
Semiconductor switches are very important and crucial components in power electronic systems.these switches are meant to be the substitutions of the mechanical switches,but they are severely limited by the properties of the
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semiconductor materials and process of manufacturing. 在电力电子系统，中半导体开关是非常重要和关键部件。半导体开关将要替换机械开关,但半导体材料的性质和生产过程严重限制了他们。
Switching losses开关损耗
Power losses in the power eletronic converters are comprised of the Switching losses and parasitic losses. 电力电子转换器的功率损耗分为开关损耗和寄生损耗
the parasitic losses account for the losses due to the winding resistances of the inductors and transformers,the dielectric losses of capacitors,the eddy and the hysteresis losses. 寄生损失的绕组电感器、变压器的阻力、介电损耗的电容器,涡流和磁滞损耗
the switching losses are significant and can be managed. 这个开关损耗是非常重要的,可以被处理。they can be further divided into three components:(a)the on-state losses,(b)the off-state losses and the losses in the transition states. 他们可以分为三个部分: 通态损耗，断态损耗和转换过程中产生的损耗。
On-State Losses通态损耗：
The electrical switches conduct heavy current and have nonzero voltage across the switch in the on-state.The on-state power losses are given by Pon=Uson if.这个电子开关能导通大电流，并且在通态时有非零的压降。这个通态功率损耗的公式为Pon=Uson if.
The Uson and If are respectively the switch voltage in the on-state and the forward current through the switch.For example,the typical power diodes and the power transistors have nearly 0.5 to l volt across them in the on-state.The forward currents can be hundreds to thousands of amperes.The on-state power losses are very significant. 其中Uson是通态时开关上的压降，if是流过开关的电流。例如，典型的功率二极管和功率晶体管有近似0.5~1伏的通态压降。而电流会有数百到数千安培。这个通态损耗非常重要。
Off-State Losses断态损耗
The electrical switches withstand high voltages and have nonzero leakage current through the switch in the off-state.The off-state power lesses are given by Poh=Uoff ir在关断状态时，电子开关到经受得起高电压，并会有非零的漏电流。断态损耗的公式
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为Poh=Uoff ir.
The Usoff and Ir are respectively the reverse bias voltage in the off-state and the reverse current through the switch.For example,the typical power diodes and the power transistors have high reverse voltages in hundreds to thousands of volts and microamps to milliamps through them in the off state. 其中Uoff在断态时的反向偏置电压，ir是流过开关的反向漏电流。例如，典型的功率二极管和功率晶体管有很高的反向压降几百到几千伏和几微安到几毫安的漏电流。
Transition-State Losses转换损耗：
The practical switching devices have limited capabilities of rate of voltage transition and the rate of current steering.These nonabrupt transition rates give rise to power losses in the switching devices.We will examine these switching losses in two cases separately:the inductive and capacitive loads. 在实际的开关装置限制了电压变换率和电流变化率。非突变引起了开关装置的功率损耗。我们测试开关损耗时分两种情况：感性负载和容性负载。
Switching with Inductive Load接感性负载的开关：
The indutor is assumed to be large so that the current through it in steady state is nearly constant Io.Assume that initially the switch is off.The inductor current is +Io and freewheels through diode V1.When the switch is turned on,the current through the switch begins to build up linearly(an assumption)to+Io while the diode V1 is still on.The on diode has zero voltage across it(an ideal diode),hence,the voltage on the switch is held constant at+Us.When the current buildup is over,the diode V1 ceases to conduct and the voltage on the switch ramps linearly(again an assumption)down to zero. 假设电感无穷大，即在稳定时流经电感的电流是恒定的Io，假定开始时开关处于关断状态。电感电流为+Io惯性流过二极管V1。当开关闭合后，电流流经开关开始建立线性上升+Io此时二极管扔导通。二极管压降为0，此时开关两端电压维持在+Us当电流建立完成后，二极管V1截止，开关两端电压线性下降为0。
When the switch is turned off ,the voltage begins to build up linearly to +us while the diode V1 is off. while the diode is off the current through the switch equals the inductor current,which is constant I0 After the switch voltage reaches
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aero, the current through the switch begins to decrease below I0,as the remaining current is now steered through the diode V1 which has now turned on The current through the swithch ramps down to zero ultimately. Switching waveforms with inductive load are shown in Fig.3-1开关打开后，开关两端电压线性上升至Us。此时二极管仍截止，二极管截止，流过开关的电流相当于流过电感的电流，维持在恒定的Io。开关电压到0时，通过开关的电流开始上升到Io以下。此时余留的电流正转向二极管V1，V1导通。最终通过开关的电流下降到0，开关过程的波形的电感负载波形见图3-1 The switching losses are given by : Psw=1/2UsIo[……….]fs 开关损耗的公式是Psw=1/2UsIo[……….]fs
The switching power losses increase linearly with the switching requency like in the resistive case but about six times more. The upper bound on the switching frequency is also about half. 开关功率损耗线性增加随着开关频率 此时的损耗要比阻性负载损耗的6倍还多。当f取最大时 Psw=1/2UsIo。 Switching with capacitive Load开关接有容性负载
The capacitor is assumed to be large so that the voltage through is in stedy state is nearly constant U0.Assume that initially the switch is on,hence,the cuttent through the switch is IS.The capacitor voltage is U the voltage across the switch is zero and the diode V1is reverse biased.When the switch is turned off,the switch voltage begins to ramp up to+U0 while the diode V1 is still off.During this buildup,the current through the switch is held constant at Is.Wheng the voltage buildup is over,the diode V1begins to conduct and the voltage on the switch is clamped at U0,and the current through the switch ramps linearly(again an assumption)down to zero. 假设电容器很大，致使在稳定状态下其两端电压接近为常数Uo。假使开关初始状态为闭合，则通过开关的电流为Is。电容器的电压为Uo开关两端的电压为零，二极管V1反向偏置。当开关打开后，开关两端电压开始上升到Uo，此时二极管一直关断。当电压等于Uo时，二极管V1开始导通并且开关两端电压被钳位在Uo。流过开关的电流线性下降到零。
When the switch is closed,the current begins to build up linearly to Is while the diode V1 is still on .The voltage on the switch remains clamped at U0.After the switchcurrent reaches Is ,the diode turns off and the voltage on the switch begins to ramp down to zero. 当开关闭合，电流开始上升至Is，
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此时V1仍然导通，开关两端电位被钳位在Uo。当开关电流等于Is时，二极管关断并且开关两端电压线性下降至0。
The switching power losses in the case of capacitive load also have similar dependence as in the case of inductive loads. 当开关闭合，电流开始上升至Is，此时V1仍然导通，开关两端电位被钳位在Uo。当开关电流等于Is时，二极管关断并且开关两端电压线性下降至0。
The switching power losses in the case of capacitive load also have similar dependence as in the case of inductive loads. 接容性负载情况下的开关功率损耗的决定因素与感性负载情况下有相似之处。
The switching losses can be usually minimized in two ways; 1divert the energy from the switch to a loss or non-loss circuit or 2switch at either zero current or at zero voltage.The first is called snubbering and the later is known as zero-voltage and zero-current swithching. 开关损耗一般被归为两点：1。开关的能量转化成了损耗或无损耗电流或开关的过0电流或过0电压，第一个被称为缓冲，最后一个被成为过0电流或过0电压的开关。
The basic principle of operation of an induction machine is illustrated by the revolving horseshoe magnet and copper-disk experiment pictured in Fig.4-1. When the horseshoe magnet is rotated, the moving magnetic field passing across the copper disk induces eddy currents in the disk. These eddy currents are in such a direction as to cause the disk to follow the rotation of the horseshoe magnet. With the direction of rotation shown in the figure, the eddy currents will be as displayed in Fig.4-1 according to Fleming's right-hand rule
一台感应电机的基本工作原理如图4－1中的旋转的U形磁铁和铜圈盘的实验图所示。当U形铁旋转时，运动的磁场穿过铜圆盘从而在铜圆盘中产生涡流。这些涡流的方向是这样的以致于使圆盘顺着U
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形磁铁的转向旋转。在图示的旋转方向下，根据弗莱明右手定则涡流的方向将如图4－1所示。
Fleming's right-hand rule: Place the thumb and the first and second fingers of the right hand so that all three are mutually perpendicular. With the hand in this position, the first finger is pointed in the direction of the field, the thumb is in the direction of motion of the relative motion of the conductor, and the second finger is the direction of the induced voltage. Note that the relative motion of the conductor is opposite to the rotation of the direction of rotation of the magnetic field.
弗莱明右手定则：伸出右手大拇指、食指以及中指并使它们相互垂直。保持右手处于这种状态，使食指指向磁场的方向，拇指指向导体相对运动的运动方向，那么中指所指的方向就是感应电压的方向，要注意的是导体的相对运动与磁场的旋转方向的运动相反。
By applying Fleming's right-hand rule, the force on the copper disk is determined to be in the direction of rotation of the magnet.
通过应用弗莱明右手定则，我们确定作用在铜圆盘上的力与磁铁的旋转方向一致
Fleming's left-hand rule: Place the thumb and the first and second finger of the left hand so that all three are mutually perpendicular to each other. With the first finger in the direction of the field and the second finger in the direction of the current, the thumb indicates the direction of the force. 弗莱明左手定则：伸出左手大拇指、食指以及中指并使它们相互垂直。
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使食指指向磁场的方向，中指指向电流的方向，那么拇指所指的方向是力的方向
Whereas the copper disk will rotate in the same direction as the rotating magnetic field, it will never reach the same speed as the rotating magnet, because if it did, there would be no relative motion between the two and therefore no current induced in the copper disk. The difference in speed between the rotating magnetic field and the copper disk is known as slip, which is essential to the operation of an induction motor. In induction motors the rotating magnetic field is set up by windings in the stator, and the induced currents are carried by conductorsin the rotor. The rotating horseshoe magnet and copper disk are considerably different in structure from today's induction motor, but the basic principles of operation are the same.
尽管铜圆盘将顺着旋转磁场的方向而旋转，然而它却永远也达不到旋转磁铁的速度，因为如果铜圆盘的速度等于旋转磁铁的速度，那么在两者之间就不存在相对运动因而在铜圆盘中不会感应出电流。旋转磁铁和铜圆盘之间的速度差被称为转差（率），转差（率）对于感应电机的运行是必要的，在感应电机中旋转磁场是通过定子绕组建立的，并且感应电流是由转子导体承载的。旋转U形铁和铜圆盘与目前感应电动机的结构有相当大的不同，但基本工作原理是一样的。 The rotating magnetic field is essential to the functioning of an induction motor. In practical machines this rotating magnetic field is achieved by a
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combination of a space displacement of the windings and a time-phase displacement of the exciting voltage.
旋转磁场对于一台感应电动机来说是必要的。在实际的电机中，旋转磁场是通过绕组在空间上的交替布置和励磁电压在时间相位上的相互交替这两者的结合来实现的。
The rotor is formed from laminated electrical steel punching, and the rotor winding consists of bars contained in slots punched in the laminations. These bars are short-circuited at both ends by a short-circuiting ring. A bar-end ring structure, without the laminated core, is called a squirrel cage, as shown in the Fig.4-2. In small- and medium-horsepower sizes, rotors are made by casting aluminum into the rotor core. In the larger sizes of ac motors, cast-aluminum rotor are not practical, and copper bars are inserted into the slots. Thesecopper bars are short-circuited at both ends by a copper end ring, and the end ring is brazed or soldered onto the bars. Sometimes bronzes or other alloys are used to replace copper in making the cage and end ring. The sizes at which the transition between cast-aluminum and copper rotors takes place varies among rotor manufacturers, but virtually all rotors in motor sizes of several thousand horsepower and above are built with bar-type rotors.
转子是由电工钢冲压叠片形成的，并且转子绕组是由叠片中冲出的槽中的导条组成的。这些导条被两端的短路环所短路。一个没有叠片铁
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心的导条—端环结构被称为鼠笼，如图4－2所示。在中小型电机中，转子是通过在转子槽中铸铝来制成的。在大型交流电动机中，铸铝转子是不实用的，我们将铜导条插入转子槽中。这些铜导体被两端的铜环所短路，并且端环被焊接在导条上。有时我们在制作笼条和端环时用青铜或其他合金来代替铜。铸铝与铜转子之间的尺寸的变化在不同的电机制造商之间有所不同，但实际上功率等于几千马力以及功率大于几千马力的所有电动机的转子都是导条类型的转子。
Another construction feature dependent on motor size is the type of coil winding used. In small- and medium-size ac motors, most coils are random-wound. These coils are made with round wire, which is wound into the stator slots and assumes a diamond shape in the end turns; however, the wires are randomly located within a given coil, and hence the name \"random-wound\". For large ac motors and particularly for high-voltage motors, 2300V and above, form-wound coils are used. These coils are constructed from rectangular wire, which is bentinto shape around forms and then taped. The coil is formed to the proper size so that the complete coil can be inserted into the stator slots at the time the stator is wound. Form-wound coils are used for high-voltage windings because it is relatively easy to add extra insulation on the individual coils before inserting them into the stator.
另一个取决于电动机尺寸大小的结构特征是我们所采用的线圈绕组类型。在中小型交流电动机中，大多数的线圈是散绕的，这些线圈是
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由圆导线制成的，它们被绕进定子槽中并且假设其端部线匝为菱形，然而，由于这些导线被随意地放置在给定的线圈中，因此就得到了“散绕”（线圈）这个名称对于大型交流电动机特别是电压等于2300V或大于2300V的高压电动机，我们采用模绕线圈，这些线圈采用矩形截面的导线构成，将它们弯曲成型后缠上绝缘带。在制作定子绕组时，线圈被做成适当的尺寸，以便将整个线圈放入定子槽内。模绕线圈被作为高压绕组使用这是由于在把这些线圈放置入定子槽之前我们可以相对容易地在其单个线圈上增加额外的绝缘。
Most people can formulate a mental picture of a computer, but computers do so many things and come in such a variety of shapes and sizes that it might seem difficult to distill their common characteristics into an all-purpose definition. At its core, a computer is a device that accepts input, processes data, stores data, and produces output, all according to a series of stored instructions.
Computer input is whatever is put into a computer system. Input can be supplied by a person, by the environment, or by another computer. Examples of the kinds of input that a computer can accept include the words and symbols in a document, numbers for a calculation, pictures, temperatures from a thermostat, audio signals from a microphone, and instructions from a computer program. An input device, such as a keyboard or mouse, gathers input and transforms it into a series of
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electronic signals for the computer.
In the context of computing, data refers to the symbols that represent facts, objects, and ideas. Computers manipulate data in many ways, and we call this manipulation processing. The series of instructions that tell a computer how to carry out processing tasks is referred to as a computer program, or simply a \"program.\" These programs form the software that sets up a computer to do a specific task. In a computer, most processing takes place in a component called the central processing unit (CPU), which is sometimes described as the\"brain\" of the computer.
A computer stores data so that it will be available for processing. Most computers have more than one location for storing data, depending on how the data is being used. Memory is an area of a computer that temporarily holds data that is waiting to be processed, stored, or output. Storage is the area where data can be left on a permanent basis when it is not immediately needed for processing.
Output is the results produced by a computer. Some examples of computer output include reports, documents, music, graphs, and pictures. An output device displays, prints, or transmits the results of processing. Computers are versatile machines, which are able to perform a truly amazing assortment of tasks, but some types of computer are better suited to certain tasks than other types of computers. Computers can be
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categorized as personal computer, handheld computers, workstations, mainframes, supercomputers , and servers.
大多数人可以制订一个电脑精神的图片，但电脑做很多事情，出现这样的形状和大小不同，它似乎难以提炼成一个全能的定义，它们的共同特点。在其核心，一台计算机是一种装置，它接受输入，处理数据，存储数据，并产生输出，根据对所有存储一系列指示。 什么是计算机输入到计算机系统的压力。输入可提供的一人，由环境，或由另一台计算机。对输入的各种例子，一个计算机可以接受包括文字和符号的文件，规定计算，图片，从恒温器的温度数字，音频信号从一个麦克风，从电脑程序指令。一个输入设备，如键盘或鼠标，集输和转换成一个电子信号的计算机的一系列。
在计算中，数据是指以符号代表的事实，对象和想法。计算机操作在很多方面的数据，我们称之为操作处理。一系列的指令，告诉计算机如何进行处理任务，被称为一个计算机程序，或只是一个“程序”。这些方案形成了软件，建立了计算机做特定的任务。在计算机中，大部分处理发生在一个组件的地方称为中央处理单元（CPU），有时为“大脑的计算机”来形容。
计算机存储数据，以便它会被用作处理可用。大多数计算机有多个用于存储数据的位置，这取决于数据如何被使用。内存是计算机的一个领域，数据是暂时持有等待处理，存储或输出。在数据存储，是可以在一个地区长期离开时，没有立即处理所需。
输出是由电脑产生的结果。电脑输出的一些例子包括报告，文件，
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音乐，图形，图片。输出设备显示，打印，或传送的处理结果。 电脑是多功能机，它能够执行各种各样的任务十分惊人，但某些类型的计算机更适合比其他类型的计算机的某些任务。计算机可以被归类为个人电脑，掌上电脑，工作站，大型机，超级计算机和服务器。
A personal computer is a type of microcomputer, designed to meet the computing needs of an individual. It typically provides access to a wide variety of computing applications, such as word processing, photo editing, e-mail, and Internet access. Personal computers are available as desktop computers or notebook computers. 个人计算机是一种微型计算机，它能够满足个人的计算需要，它特别提供了适应各种各样计算应用的方法，比如说文字处理、相片编辑、电子邮件以及进入互联网，个人计算机可以被当作台式计算机以及笔记本电脑一样使用 A handheld computer is designed to fit into a pocket, run on batteries, and be used while you are holding it. Also called a PDA (Personal Digital Assistant) and a palmtop computer, a computer in this category is typically used as an electronic appointment book, address book, calculator, and notepad. With its slow processing speed and small screen, a handheld compute is not powerful enough to handle many of the tasks that can be accomplished by desktop or notebook personal computers. A handheld computer is designed to bea computing accessory, rather than your primary computer掌上电脑被设计成能够放
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进口袋，能依靠电池工作，并且当你放在手上它时能够运行。它也被称作PDA（个人数字助手）和手掌上的电脑，这种类型的计算机典型性地被作为电子图书、通讯录、计算器以及记事本来使用。由于其速度较慢且显示屏较小，所以掌上电脑功能不够强大无法执行台式计算机及个人电脑所能完成的很多任务。掌上电脑旨在成为计算助手而非成为你的主要计算机。
Computers advertised as workstation are usually powerful desktop computers designed for specialized tasks. A workstation can tackle tasks that require a lot of processing speed, such as medical imaging and computer-aided design. Some workstations contain more than one microprocessor, and most have circuitry specially designed for creating and displaying three-dimensional and animated graphics . Because of its cost, a workstation is often dedicated to design tasks, and is not used for typical microcomputer applications, such as word processing, photo editing, and accessing the Web. 被人们大力宣传为工作站的计算机通常是指设计来完成特定任务的功能强大的台式计算机。工作站能够处理需要快速处理的任务，例如医学成像以及计算机辅助设计。某些工作站包含不止一个微处理器，并且大多数具有特别为产生和显示三维和动画图像而设计的电路。由于其成本高，所以一个工作站通常用来设计任务，而不是用来作为典型的微型计算机来应用，例如文字处理、图像编辑以及网络访问
Ordinary personal computers that are connected to a local area
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network can also be called as workstations. A computer network is two or more computers and other devices that are connected for the purpose of sharing data and programs. A LAN (local area network) is simply a computer network that is located within a limited geographical areasuch as a school computer lab or a small business与局域网相连接的普通的个人计算机也可以被称为工作站。计算机网络是由两台或多台计算机以及其它连接在一起为了共享数据和程序的设备而组成的。一个LAN（局域网）仅仅是一个限定地理区域内的计算机网络，例如一个学校计算机实验室或一个小商行。
A mainframe computer ( or simply a \"mainframe\" ) is a large and expensive computer that is capable of simultaneously processing data for hundreds or thousands of users. Mainframes are generally used by businesses or governments to provide centralized storage, processing, and management for large amounts of data. Mainframes remain the computer of choice in situations where reliability, data security, and centralized control are necessary. 主机（或简写为“mainframe”）是一种大型昂贵的能够同时为成百上千用户处理数据的计算机。主机通常由商行或政府使用用来提供对大量数据的集中存储、处理以及管理。主机使我们在需要可靠性、数据安全性以及集中处理的情况下提供了可选择的计算机。
A computer falls into the supercomputer category if it is, at the time of construction, one of the fastest computers in the world. Because of
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their speed, supercomputers can tackle complex tasks that just would not be practical for other computers. Typical uses for supercomputers include breaking codes, modeling worldwide weather systems, and simulating nuclear explosions. One impressive simulation designed to run on a supercomputer tracked the movement of thousands of dust particles as they were tossed about by a tornado如果某种计算机在其制造的时代是世界上最快的计算机之一，那么这种计算机就属于超级计算机类型。由于它们的速度，超级计算机能够处理其它计算机所不能处理的复杂任务。超级计算机的典型的作用包括破解密码、建立世界范围的天气系统模型以及模拟核爆炸。超级计算机上所完成的一个使人留下深刻印象的仿真是对数以千计的尘埃微粒的运动进行追踪，这些尘埃微粒就象被一场龙卷风所抛掷一样。
In the computer industry, the term \"server\" has several meanings. It can refer to computer hardware, to a specific type of software, or to a combination of hardware and software. In any case, the purpose of a server is to \" serve \" the computers on a network ( such as the Internet or a LAN ) by supplying them with data. A personal computer, workstation, or software that requests data from a server is referred to as a client. For example, on a network, a server might respond to a client's request for a Web page. Another server might handle the. steady stream of e-mail that travels among clients from all over the Internet. A server might also allow clients within a LAN to share files or access a centralized printer.
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在计算机工业中，“服务器”这个术语有多种含义。它可以指计算机硬件、特定类型的软件或是指硬软件结合。在任何场合，一个服务器的目的是通过向计算机提供数据而为网络上的（例如互联网或局域网）计算机服务。一台个人计算机、服务站或者向服务器申请数据的软件被称为客户，例如在网络上，一个服务器可能会用一个网页来回应客户的要求。另外的服务器可能会处理来往于所有互联网上的客户的电子邮件的稳定的数据流。一个服务器可能还会允许同一局域网内的客户共享文件或可以使用同一台中央打印机。
A computer system usually refers to a computer and all of the input, output, and storage devices that are connected to it. At the core of a personal computer system is a desktop or notebook computer. 一个计算机系统通常是指一台计算机以及与它相连的输入、输出以及存储设备。就实质内容来说，一个个人计算机系统就是一台台式计算机或一台笔记本电脑。除个人计算机之间装饰部分不同以外，一个个人计算机系统通常包括以下几种设备：
Despite cosmetic differences among personal computers, a personal computer system usually includes the following equipment:
（1）Computer system unit. The system unit is the case that holds the main circuit boards, microprocessor, power supply, and storage devices. The system unit for most notebook computers holds a built-in keyboard and speakers too.
（2）Display device. Most desktop computers use a separate monitor
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as a display device, whereas notebook computers use an flat panel LCD screen (liquid crystal display screen) that is attached to the system unit. （3）Keyboard. Most computers are equipped with a keyboard as the primary input device. 1）计算机系统单元 系统单元包括主电路板、微处理器、电源以及存储设备，对于大多数笔记本电脑系统单元还包括一个机内键盘和喇叭。
2）显示设备 大多数台式计算机使用一个单独的监视器作为显示器，然而笔记本电脑使用一个与系统单元相连的LCD屏（液晶显示屏）作为显示器。
3）键盘 大多数计算机配有一个键盘作为主要输入设备。 （4）Mouse. A mouse is an alternative input device designed to manipulate on-screen graphical objects and controls. 4）鼠标 鼠标是另外一个旨在显示屏上处理图像目标和控制的输入设备
（5）Floppy disk drive. A floppy disk drive is a storage device that reads data from and writes data to floppy disks. A floppy disk is a round piece of flexible mylar plastic covered with a thin layer of magnetic oxide and sealed inside a protective casing . The floppies most commonly used ontoday's personal computers are 3 1/2 disks with a capacity of 1.44MB.
（6）Hard disk drive. A hard disk contains one or more metallic disks encased within a disk drive, which can store billions of characters of data in the form of magnetized spots. The storage capacity of a
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hard-disk unit is many times that of a floppy disk and much faster. It is usually mounted inside the computer's system unit.
5）软盘驱动器 软盘驱动器是从软盘上读取数据或向软盘写入数据的存储设备。一个软盘是一张柔软的聚酯薄膜塑料圆盘，圆盘上覆盖着一层薄的磁性氧化物并被封装在一个保护套里。大多数通常使用在目前个人计算机中的软盘是尺寸为4又1/3寸而容量为1.44MB的盘子。
6）硬盘驱动器 硬盘包含一个或多个装入硬盘驱动器内的金属盘片，硬盘可以用磁道来储存数十亿的数据符号。一个硬盘单元的存储容量是软盘的好几倍并且存储速度要快得多，硬盘通常安装在计算机系统单元内部。
（7）CD-ROM or DVD drive. A CD-ROM (compact disc read-only memory) drive is
or audio CDs. A DVD (digital video disc) drive can read data from computer CDs, audio CDs, computer DVDs, or DVD movie disks. CD-ROM and DVD drives typically cannot be used to write data onto disks. The \"RO\" in \"ROM\" stands for \"read-only\" and means that the drive can read data from disks, but cannot be used to store new data on them. 7）CD-ROM驱动器以及DVD驱动器 一个CD-ROM（盒装的磁盘只读存储器）驱动器是一个使用激光技术来读永久存储在计算机中或音频CD中的数据的存储设备。一个DVD（数字视频磁盘）驱动器能够从计算机CD、音频CD、计算机DVD或DVD电子磁盘
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中读取数据。CD-ROM驱动器和DVD驱动器不能用来在磁盘上写数据，“ROM”中的“RO”表示“只读”，意味着驱动器可以从磁盘上读取数据，而不能用来将数据反复写在磁盘上。 （8）CD-writer.
Many
computers-especially
desktop
models——include a CD-writer that can be used to create and copy CDs. （9）Sound card and speakers. Desktop computers have a rudimentary built-in speaker that's mostly limited to playing beeps. A small circuit board, called a sound card, is required for high-quality music, narration, and sound effects. A desktop computer's sound card sends signals to external speakers. A notebook's sound card sends signals to speakers that are built into the notebook system unit8）刻录机 很多计算机——特别是台式计算机——包含一台可用来产生和复制CD的刻录机。
9）声卡和喇叭 台式计算机有一个基本的内置的喇叭，这种喇叭仅限于发出哗哗声。如果要产生高品质音乐、讲话以及音乐效果，就需要一块小电路板，这块电路板称为声卡。台式计算机的声卡将信号传送到外接的音箱。一台笔记本电脑的声卡将信号发送到内置在笔记本电脑系统单元的喇叭中。
（10）Modem. Virtually every personal computer system includes a built-in modem that can be usedto establish an Internet connection using a standard telephone line.
（11）Printer. A computer printer is an output device that produces
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computer-generated text or graphical images on paper.
In addition to these equipment mentioned above, some other peripheral devices might be added to a computer system to enhance its functionality, such as a digital camera, scanner, joystick, or graphics tablet
10）调制解调器 实际上所有的个人计算机系统包括一个内置的调制解调器，它可以被用来通过标准电话线与互联网相连接。 11）打印机 一台计算机的打印机是能够在纸上产生计算机输出文本或绘画图像的输出设备。
除以上提到的这些设备以外，某些其它的外围设备可以连接在计算机系统上来增强计算机的功能，例如数码相机、扫描仪、游戏杆或图形板。
Electric Power Systems 电力系统 Section 1 Introduction 第一节介绍
The modern society depends on the electricity supply more heavily than ever before. 现代社会的电力供应依赖于更多地比以往任何时候。 It can not be imagined what the world should be if the electricity supply were interrupted all over the world. 它无法想象的世界应该是什么，如果电力供应中断了世界各地。 Electric power systems (or electric energy systems), providing electricity to the modern society, have become indispensable components of the industrial world. 电力系统（或电力能源系统），提供电力到现代社会，已成为不可缺少的组成部分产业界的。
The first complete electric power system (comprising a generator, cable, fuse, meter, and loads) was built by Thomas Edison – the historic Pearl Street Station in New York City which began operation in September 1882. 第一个完整的电力系统（包括发电机，电缆，熔断器，计量，并加载）的托马斯爱迪生所建-站纽约市珍珠街的历史始于1882年9月运作。 This was a DC system consisting of a steam-engine-driven DC generator supplying power to 59 customers
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within an area roughly 1.5 km in radius. The load, which consisted entirely of incandescent lamps, was supplied at 110 V through an underground cable system. 这是一个半径直流系统组成的一个蒸汽发动机驱动的直流发电机面积约1.5公里至59供电范围内的客户。负载，其中包括完全的白炽灯，为V提供110通过地下电缆系统。 Within a few years similar systems were in operation in most large cities throughout the world. With the development of motors by Frank Sprague in 1884, motor loads were added to such systems. This was the beginning of what would develop into one of the largest industries in the world. In spite of the initial widespread use of DC systems, they were almost completely superseded by AC systems. By 1886, the limitations of DC systems were becoming increasingly apparent. They could deliver power only a short distance from generators.
在一个类似的系统在大多数大城市在世界各地运行数年。随着马达的弗兰克斯普拉格发展在1884年，电机负载被添加到这些系统。这是什么开始发展成为世界上最大的产业之一。在最初的直流系统广泛使用尽管如此，他们几乎完全被空调系统所取代。到1886年，直流系统的局限性也日益明显。他们可以提供功率只有很短的距离从发电机。
To keep transmission power losses ( I 2 R ) and voltage drops to acceptable levels, voltage levels had to be high for long-distance power transmission. Such high voltages were not acceptable for generation and consumption of power; therefore, a convenient means for voltage transformation became a necessity. 为了保持发射功率损失（我2 R）和电压下降到可接受的水平，电压等级，必须长途输电高。如此高的电压不发电和电力消耗可以接受的，因此，电压转换成为一个方便的手段的必要性。
The development of the transformer and AC transmission by L. Gaulard and JD Gibbs of Paris, France, led to AC electric power systems. 在发展的变压器，法国和交流输电由L.巴黎戈拉尔和JD吉布斯导致交流电力系统。
In 1889, the first AC transmission line in North America was put into operation in Oregon between Willamette Falls and Portland. 1889年，第一次在北美交流传输线将在俄勒冈州波特兰之间威拉梅特大瀑布和实施。
It was a single-phase line transmitting power at 4,000 V over a distance of 21 km. With the development of polyphase systems by Nikola Tesla, the AC system became even more attractive. By 1888, Tesla held several patents on AC motors, generators, transformers, and transmission systems. Westinghouse bought the patents to these early inventions, and they formed the basis of the present-day AC systems.这是一个单相线路
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传输功率为4,000公里，超过21 V系统的距离。随着交流的发展多相系统由尼古拉特斯拉，成为更具吸引力的。通过1888年，特斯拉举行交流多项专利电动机，发电机，变压器和输电系统。西屋公司购买了这些早期的发明专利，并形成了系统的基础，现在的交流。
In the 1890s, there was considerable controversy over whether the electric utility industry should be standardized on DC or AC. By the turn of the century, the AC system had won out over the DC system for the following reasons: 在19世纪90年代，有很大的争议或交流电力行业是否应该统一于直流。到了世纪之交的，在交流系统赢得了原因出在下面的直流系统为：
（1）Voltage levels can be easily transformed in AC systems, thus providing the flexibility for use of different voltages for generation, transmission, and consumption. （1）电压水平可以很容易地改变了空调系统，从而提供了传输的灵活性，发电用不同的电压和消费。
（2）AC generators are much simpler than DC generators. （2）交流发电机简单得多比直流发电机。
（3）AC motors are much simpler and cheaper than DC motors. （三）交流电机和电机便宜简单得多，比直流。
The first three-phase line in North America went into operation in 1893——a 2,300 V, 12 km line in southern California. 前三个阶段的美国北线投产于1893年- 1 2300五，南加州12公里路线研究。 In the early period of AC power transmission, frequency was not standardized. 在电力传输初期交流，频率不规范。 Many different frequencies were in use: 25, 50, 60, 125, and 133 Hz. 有许多不同频率的使用：25，50，60，125，和133赫兹。 This poses a problem for interconnection. Eventually 60 Hz was adopted as standard in North America, although 50 Hz was used in many other countries. 这对互连的问题。最后60赫兹标准获得通过，成为美国在北美，虽然是50赫兹在许多其他国家使用。
The increasing need for transmitting large amounts of power over longer distance created an incentive to use progressively high voltage levels. To avoid the proliferation of an unlimited number of voltages, the industry has standardized voltage levels. In USA, the standards are 115, 138, 161, and 230 kV for the high voltage (HV) class, and 345, 500 and 765 kV for the extra-high voltage (EHV) class. In China, the voltage levels in use are 10, 35, 110 for HV class, and 220, 330 (only in Northwest China) and 500 kV for EHV class . 较长的距离越来越需要大量的电力传输多激励他们逐步使用高压的水平。为了避免电压增殖数量无限，业界标准电压水平。在美国，标准是115，138， 161，和230千伏的高电压（高压）类，345，500和765千伏级的特高电压（超高压）。在中国，各级使用电压为10，35，110级高压， 220，
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中国330（仅在西北）和500千伏超高压类。
The first 750 kVtransmission line will be built in the near future in Northwest China. 第一个750 kVtransmission线将建在不久的将来在中国西北地区。
With the development of the AC/DC converting equipment, high voltage DC (HVDC) transmission systems have become more attractive and economical in special situations. 随着交流的发展/直流转换设备，高压直流高压直流（HVDC）传输系统已经成为更具吸引力的经济和情况特殊。 The HVDC transmission can be used for transmission of large blocks of power over long distance, and providing an asynchronous link between systems where AC interconnection would be impractical because of system stability consideration or because nominal frequencies of the systems are different. 在高压直流输电可用于输电块以上的大长途电话，并提供不同系统间的异步连接在AC联网系统将是不切实际的，因为稳定考虑，或因标称频率的系统。
The basic requirement to a power system is to provide an uninterrupted energy supply to customers with acceptable voltages and frequency. 基本要求到电源系统是提供一个不间断的能源供应，以客户可接受的电压和频率。 Because electricity can not be massively stored under a simple and economic way, the production and consumption of electricity must be done simultaneously. A fault or misoperation in any stages of a power system may possibly result in interruption of electricity supply to the customers. 由于电力无法大量储存在一个简单的方法和经济，电力的生产和消费必须同时进行。系统的故障或误操作的权力在任何阶段可能导致电力供应中断给客户。 Therefore, a normal continuous operation of the power system to provide a reliable power supply to the customers is of paramount importance. 因此，一个正常的电力系统连续运行的，提供可靠的电力供应给客户的重要性是至关重要的。
Power system stability may be broadly defined as the property of a power system that enables it to remain in a state of operating equilibrium under normal operating conditions and to regain an acceptable state of equilibrium after being subjected to a disturbance. 电力系统稳定，可广泛定义为干扰财产的权力系统，可继续经营的状态下正常运行的平衡条件和后向遭受恢复一个可以接受的平衡状态。
Instability in a power system may be manifested in many different ways depending on the system configuration and operating mode. 在电力系统的不稳定可能会表现在经营方式和多种不同的方式取决于系统配置。
Traditionally, the stability problem has been one of maintaining
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synchronous operation. Since power systems rely on synchronous machines for generation of electrical power, a necessary condition for satisfactory system operation is that all synchronous machines remain in synchronism or, colloquially \"in step\". This aspect of stability is influenced by the dynamics of generator rotor angles and power-angle relationships, and then referred to \" rotor angle stability \". 传统上，稳定性问题一直是一个保持同步运行。由于电力系统的发电电力，一个令人满意的系统运行的必要条件是，依靠同步电机同步电机都留在同步或通俗的“步骤”。这一方面是受稳定的发电机转子的动态角度和功角的关系，然后提到“转子角稳定”
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