电气工程专业英语+unit6

1、电气工程及其自动化专业英语电气工程及其自动化专业英语主编主编 杨勇杨勇 邓秋玲邓秋玲Unit 6 Automatic Control6.2 Feedback Control6.1 Introduction6.3 Control Methods6.4 Control Technologies6.5 Further Reading 6.1 Introduction New Words and Expressionsinterrelated adj. 相关的相关的direct v. 引导引导regulate v. 调节调节exert v. 运用；施加运用；施加restraint n. 约束约束per

2、formance characteristics 运行特性运行特性physical property 物理性质物理性质plant n. 装置；设备装置；设备agency n. 机构机构manipulated variable 操纵变量操纵变量feedback n. 反馈反馈 6.1 Introduction New Words and Expressionscomparator n. 比较器比较器disturbance n. 扰动扰动actuate v. 开动开动flipping n. 翻转翻转illuminate v. 照亮照亮constitutev. 组成组成luminous flux 光

3、通量光通量lumensn. 流明流明variable n. 变量变量accelerator depression对加速的抑制对加速的抑制accelerator pedal加速踏板加速踏板6.1 Introduction New Words and Expressionscarburetor butterfly valve化油器阀门化油器阀门light bulb灯泡灯泡relayn. 继电器继电器photocell n. 光电池光电池mechanical alarm clock机械闹钟机械闹钟audible sound可听见的声音可听见的声音bell hammer铃锤铃锤be subdivide

4、d into被分为被分为follow-up system随动系统随动系统external intervention外部干预外部干预6.1 Introduction New Words and Expressionsmanual adj. 手动的手动的intelligent adj. 智能的智能的interdependent elements相互依存的元件相互依存的元件stimulin. 激励激励thermostat control 恒温控制恒温控制aileronn. 副翼副翼ruddern. 方向舵方向舵cowl flap 整流罩整流罩6.1 Introduction6.1.1 Element

5、ary Concept of Control Systems textA control system is an interrelated collection of elements that directs or regulates (controls) energy or exerts restraint, from a source point to a usage point. To be acceptable, it must have physical properties and performance characteristics that satisfy all con

6、cerned observers. Physical properties can be peculiar to an application, and they are usually subject to economic constraints presenting their own challenge to the designer. However, different physical systems have performance similarities that logically lead to a unified control-system theory. Note

7、：不定式短语to be acceptable为目的状语，意思是“要得到认可”。be subject to意思是“受到的制约”。6.1.1 Elementary Concept of Control SystemsThere are some definitions and terminology related to control system.(1) The plant is the original or basic system over which control is desired; it is also called the controlled system.(2) The

8、control element, or controller, is the agency that applies a control signal to the plant. The signal represents a change in a manipulated variable of the system.(3) The controlled variable is that characteristic of the plant which is being regulated. Usually, plant output is the controlled variable.

9、Note：that applies a control signal to the plant为定语从句，修饰the agency。 6.1.1 Elementary Concept of Control Systems(4) The reference command or reference input is an external signal applied to a control system in order to bring about a specific action of the plant (i.e., a specific value of the controlle

10、d variable).(5) Disturbance inputs are undesired stimuli of the plant which affect the value of the controlled variable.(6) A comparator is a control system element that compares (by addition or subtraction) two or more signals.Note：此句中bring about是“引起、带来、实现”的意思。text6.1.1 Elementary Concept of Contro

11、l Systems(7) Feedback is that property of a control system whereby the output (controlled variable) is compared to the reference input, and an actuating signal or control force, depending on both the output and the input, is generated. This signal actuates the controller. In control systems without

12、feedback, the reference input serves as the actuating signal.(8) A feedback element converts the controlled variable into a form (the feedback signal) which may be directly compared with the reference command.Note：此句中whereby是连词“凭借”，depending on both the output and the input为现在分词短语作定语。text6.1.2 Class

13、ification and Applications of Control SystemsControl systems are first of all classified according to their requirements of external interventions. In a manual control system, an intelligent being forms one of the interdependent elements. A control system for which all interdependent elements are no

14、n-intelligent components is called an automatic control system; it is this latter type on which most control system theory centers.Note：此句中first of all作状语，意思为“首先”，center on是“集中在、着重在”。text6.1.2 Classification and Applications of Control SystemsAs an example, a man flipping a light switch to illuminat

15、e a darkened room constitutes a manual control system. The switch and light bulb are the plant, with luminous flux (measured in lumens) as controlled variable or output. The movement of the switch handle is the actuating signal or control force. An automobile driver adjusting the degree of accelerat

16、or depression to maintain a desired speed also constitutes a manual control system.Note：此句中lumens是光通量的计量单位。flipping a light switch to illuminate a darkened room为现在分词短语结构，说明主语A man 的动作；最后一句中，adjusting the degree of accelerator depression也是现在分词短语结构，说明主语An automobile driver的动作。text6.1.2 Classification

17、and Applications of Control SystemsMovement of the accelerator pedal, linkage, and carburetor butterfly valve is the actuating signal. The engine and drive train can be considered the plant. A light bulb switched on by a relay activated by circuitry that senses degree of darkness through use of a ph

18、otocell is an automatic control system.Note：此句中有3个定语，由switched on引出的过去分词短语作主语A light bulb的定语，过去分词短语activated by作a relay的定语，that引出定语从句修饰circuitry。6.1.2 Classification and Applications of Control SystemsA mechanical alarm clock forms an automatic control system, in which the bell (plant) generates an

19、audible sound (controlled variable). The control force is retraction of the bell hammer stop by the clocks time-indicating movement and linkage. textNote：此句的in which 引导非限制性定语从句修饰control system。stop是名词，表示“止动装置”。6.1.2 Classification and Applications of Control SystemsA regulator system has as its prim

20、ary function to maintain the controlled variable within a specified range, regardless of the presence of disturbance inputs; its reference command is changed infrequently. A follow-up system is one that is required to maintain a close correspondence between a frequently changed reference command and

21、 the controlled variable.Note：该句中的as its primary function为方式状语，夹在谓语成分has to的中间。text6.1.2 Classification and Applications of Control SystemsIn a continuous (-variable) system, all variables are continuous, differentiable functions of time; behavior of the system is therefore described by differential

22、 equations. A discrete (-variable) system has at least one variable known only at particular instants in time, necessitating description by difference equations.Note：此句中continuous, differentiable是修饰名词functions的两个并列形容词，中间用逗号分隔。现在分词短语necessitating description by.进一步修饰A discrete (-variable) system。为了适应

23、汉语的表达习惯该句译文的语序有调整。text6.2 Feedback ControlNew Words and Expressionspreliminary n. 准备；初步措施 adj.初步的 adj.初步的 flame n. 火焰flyball-governed 离心式调速器restraining spring 限制弹簧differential equation 微分方程independent variable 独立变量Laplace transform 拉普拉斯变换transmission n. 传输路径 New Words and Expressionsratio n. 比率initi

24、al condition 初始条件relaxed adj. 放松的；松懈的；随意的energized adj. 激励的；使通电的assumption n. 假设restriction n. 限制super-position 叠加性is associated with 与联系terminals n. 端口New Words and Expressionsopen-circuit 开路filter network 滤波器网络s-domain s域dynamic response 动态响应transient response 瞬态响应whereas conj. 然而steady-state resp

25、onse 稳态响应anti aircraft gun turret 高射炮6.2 Feedback Control6.2.1 Transfer Functions and Block DiagramsThe workings of a control system may be represented in such a flow diagram as Fig.6.1, called the functional block diagram of the system. It is to be understood that any or all of r(t), q(t) and c(t)

26、may represent multiple signals.textNote： It is to be understood that是一种固定表达结构，意思是“是需要理解的”。Fig.6.1 Functional block diagram of a control system6.2.1 Transfer Functions and Block DiagramsOrdinarily the functional block diagram is drawn as a preliminary to establishing the formal mathematical relations

27、hip connecting c(t) with r(t) and q(t).Note： 句中is drawn为被动语态，to establishing 为介词加现在分词短语作定语，修饰名词preliminary，其中to为介词。text6.2.1 Transfer Functions and Block DiagramsFig.6.2 shows a functional block diagram of an open-loop room heating system that consists of a gas-fired space heater, with a broken wind

28、ow pane constituting a disturbance. Air heated by the flame and cold air through the broken window pane are forcing functions in the heat flow equation that describes the room heating process and determines the room temperature as the system output.Note：第一个that引出的定语从句修饰an open-loop room heating syst

29、em，with和现在分词短语一起构成独立主格结构，作方式状语；第二个that引导的定语从句有两个谓语动词describes和determines，共同说明主语的动作。text6.2.1 Transfer Functions and Block DiagramsFig.6.2 Block diagram of an open-loop room heating systemtext6.2.1 Transfer Functions and Block DiagramsFig.6.3 Block diagram of the flyball-governed engineA functional b

30、lock diagram of the flyball-governed engine is drawn in Fig.6.3, where the restraining spring acts as the reference command and engine speed is the controlled variable.text6.2.1 Transfer Functions and Block DiagramsThe first requirement for analysis of a (linear) control system is that one must be a

31、ble to describe each physical component of the system by a mathematical function. These mathematical models are then combined to produce a composite mathematical model of the system, which usually takes the form of a differential equation with time as the independent variable. The Laplace transform

32、methods provide the easiest way of solving such an equation.Note：句子中的which引导非限制性定语从句，which是从句的主语，指代a composite mathematical model of the system；介词短语with time as the independent variable作状语。text6.2.1 Transfer Functions and Block DiagramsThe transfer function of a transmission path through a system co

33、mponent is defined as the ratio of the Laplace transform of the components output signal to the Laplace transform of the components input signal, with all initial conditions taken to be zero (i.e., the component is initially “relaxed,” or energized). This assumption represents no real restriction, s

34、ince any nonzero initial conditions can be introduced later as input.Note：句子中用with引出一个过去分词短语，作条件状语，进一步补充说明前面的内容。textIf q(t)=0 (no disturbance input) in Fig.6.1, the transfer function of the plant is: (6.1)Assume that the plant of Fig.6.1 is linear and that a disturbance input exists. By super-positi

35、on, c(t) has a component due to x(t) and a component due to q(t); hence, a transfer function is associated with either input-output path. These transfer functions are , as found in Eq.(6.1), and , computed with . Then we have: (6.2)1( )( )( )C sGsX s12 ( )( )( )( ) ( )L c tG s X sG s Q s6.2.1 Transf

36、er Functions and Block DiagramsNote：句子中Assume that 省略主语，介词By意思是“根据，由”，be associated with的意思是“与有关联”。textSo that the controlled variable is given by: (6.3)As an example, the calculation of transfer functions of electrical circuit elements was: (6.4)112( )( )( )( ) ( )c tLG s X sG s Q sinitial conditio

37、n 0outputTransfer function( )inputLG sL6.2.1 Transfer Functions and Block DiagramstextFig.6.4 The RC network circuitAs another example, a RC network is shown in Fig.6.4, where and are considered the input and the output, respectively. Terminals are open-circuit.By Kirchhoffs voltage law (KVL): （6.5）

38、ii1( )( )( ) dv tR ti ttCFig.6.4 The RC network circuit6.2.1 Transfer Functions and Block DiagramstextAssume zero initial conditions and apply the Laplace transform to Eq.(6.5)to obtain: (6.6)Solving Eq.(6.6) for the ratio of output and input transforms gives the transfer function of the network of

39、Fig. 6.4 as: (6.7)Voltage division, applied to the s-domain version of Fig.6.4, gives at once: (6.8)i1( )( )( )VsRI sI sSCi()()()1Iss CFsVss R C0i( )1/1( )( )(1/)1V ssCF sV sRsCRCs6.2.1 Transfer Functions and Block Diagramstext6.2.2 Dynamic Response of Control SystemsWhen a system is subjected to a

40、test input, the response in time may be divided in two parts. The first part of the response immediately after the application of the input is called transient response whereas the response long after the application of the input, as is known as steady-state response. Note：whereas是并列连词，表达转折的意思“然而”，由

41、它把全句分为前半和后半部分，两部分结构相似，但内容具有对比意义。副词immediately修饰after。textIn stable control systems, the transient response dies as time becomes large compared to the smallest time constant of the system and the steady-state response begins. The time response of an analog control system, denoted by, can, in general,

42、 be written in terms of its two components as: (6.9)where denotes the transient response, and denotes the steady-state response.tss()()()yty ty t6.2.2 Dynamic Response of Control SystemstextBoth the steady-state and the transient response are important for a control system. For example, consider the

43、 case of controlling the position of an anti aircraft gun turret. A schematic diagram for controlling gun turret in one plane is shown in Fig.6.5. The very nature of application demands that the gun is aligned to the enemy target in minimum possible time following a step input. The analysis will sho

44、w that such systems should have a fast rise time in the transient response even though it may be accompanied by large overshoot and undershoot.6.2.2 Dynamic Response of Control SystemstextFig.6.5 Schematic diagram for controlling the position of a gun turret6.2.2 Dynamic Response of Control SystemsN

45、ow consider another servo position control system, which is used for controlling the position of hull of a big ship, where the large overshoot and undershoot cannot be tolerated but a slower response is acceptable if the final steady-state error is small. Even though, both the control systems are us

46、ed for controlling the angular position of mechanical loads, the transient response is of paramount importance in one in contrast to the zero steady-state error in the other.6.2.2 Dynamic Response of Control SystemsNote：which和where分别引出两个非限制性定语从句，修饰servo position control system。Note：Even though引导的让步状

47、语从句之后的句子不出现but；X is paramount importance in A in contrast to Y in B为一固定句型，意思是“X对A的重要性比Y对B的重要性要大得多”。textIf the steady-state response of the output does not agree exactly with the input, the system is said to have a finite steady-state error.The study of a control system in the time domain essentially

48、 involves the evaluation of the transient and the steady-state responses of the system. In the design stage of a controller, specifications are usually given in terms of the transient and the steady-state performance, which are to be satisfied by the closed loop system.6.2.2 Dynamic Response of Cont

49、rol Systemstext6.2.3 Steady-state Error of Linear SystemsFig.6.6 Transient responseThe steady-state error (ESS) of the system is simply the final position error, which is the difference between where the controlled variable is and where it should be. Fig.6.6 Transient responsetext6.2.3 Steady-state

50、Error of Linear Systems In Fig.6.6, ESS is shown as the position error after the oscillations have died out. This error is the result of friction, loading, and feedback-sensor accuracy. A sophisticated controller can reduce steady-state error to practically zero.text6.2.4 Classification of Feedback

51、Control SystemsThere are two major classifications of feedback control systems: servomechanisms and process control. Servomechanisms are usually mechanical motion systems. Analysis of some servomechanisms may require a highly mathematical approach. Process control refers to a system that attempts to

52、 keep some process at a constant value. Process control systems are usually slower than servomechanisms, and empirical data may need to be used in the design.text6.2.4 Classification of Feedback Control SystemsFig.6.7 shows block diagrams of the two major classifications of feedback control systems:

53、 process control and servomechanisms. For a process control system shown in Fig.6.7(a), the job of the controller is to maintain a stationary set point despite disturbances.For example, maintaining a constant temperature in an oven whether the door is opened or closed. Often, in a process control sy

54、stem, the set point is established by another controller acting in a supervisory role. text6.2.4 Classification of Feedback Control SystemsIn a servomechanism shown in Fig.6.7(b), the job of the controller is to have the controlled variable track a moving set pointfor example, moving a robot arm fro

55、m one position to another. text6.2.4 Classification of Feedback Control SystemsFig.6.7 Feedback-control block diagrams6.3 Control MethodsNew Words and Expressionsmanipulated variable 操纵变量proportional term 比例项proportional gain 比例增益tuning parameter 整定参数instantaneous time 瞬时时间retain vi. 保持the bulk of 大

56、部分integral term积分项accumulated offset累积偏移量6.3 Control MethodsNew Words and Expressionsresidual adj. 剩余的；残余的derivative term 微分项slope n. 斜率 with respect to关于；至于termvt. 把称为overshoot n. 过冲sufficiently adv. 足够地；充分地trade-off （为此）付出的代价due to 由于6.3 Control MethodsNew Words and Expressionstune vt. 调整offline a

57、dv. 脱机的；离线的subject vt. 使服从；使隶属；使遭遇online adv. 在线地fuzzy logic 模糊逻辑generalized adj. 普遍的；概括的；广义的fuzzifier module模糊器模块fuzzy inference engine模糊推理机6.3 Control MethodsNew Words and Expressionsdefuzzifier module 去模糊器模块vagueness n. 模糊性linguistic adj. 语言的； 语言学的antecedent and the consequence 前因和后果comprises vt.

58、 构成；包含The PID control scheme is named after its three correcting terms, whose sum constitutes the manipulated variable (MV). Hence: (6.10)where Pout, Iout, and Dout are the contributions to the output from the PID controller from each of the three terms, respectively, as defined below.outoutoutMV( )

59、 tPID6.3.1 PID ControlNote：句中whose 引导定语从句，用来修饰terms。text6.3.1 PID Control(1) Proportional Term The proportional term makes a change to the output that is proportional to the current error value. The proportional response can be adjusted by multiplying the error by a constant Kp, called the proportio

60、nal gain. The proportional term is given by: (6.11)outp( )PK e ttext6.3.1 PID Controlwhere Pout is proportional output; Kp is proportional gain(a tuning parameter); e is an error which equals (setpoint(SP) product value(PV); t is time or instantaneous time (the present). A high proportional gain res