电气工程及其自动化专业英语 Chapter9 Automation Control System.ppt

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1、Chapter 9Automation Control System Section 1 Introductionn Textn New Words and Expressionsn Exercisesn Endn Scientific Thesis Writing:Main BodySection 1 Introduction Automatic control systems permeate life in all advanced societies today.Such systems act as catalysts in promoting progress and develo

2、pment.They are integral components of any industrial society and are necessary for the production of goods required by an increasing world population.Technological developments have made it possible to travel to the moon and to explore outer space.The successful operation of space vehicles,the space

3、 shuttle,space stations,and reconfigurable flight control systems depends on the proper functioningSection 1 Introductionof the large number of control systems used in such ventures.The DC shunt motor of Fig.9-1 is an example for open-loop control systems.For a given value of field current,a require

4、d value of voltage is applied to the armature to produce the desired value of motor speed.In this case the motor is the dynamic part of the system,the applied armature voltage is the input quantity,and the speed of the shaft is the output quantity.A variation of the speed from the desired value,due

5、to a change of mechanical loadSection 1 Introductionon the shaft,can in no way cause a change in the value of the applied armature voltage to maintain the desired speed.Therefore,the output quantity has no influence on the input quantity.Section 1 Introduction Fig.9-1 Open-loop control system(a)elec

6、tric motor;(b)functional block diagram Section 1 Introduction System in which the output quantity has no effect upon the input quantity are called open-loop control systems.The example just cited is represented symbolically by a functional block diagram,as shown in Fig.9-1(b).The desired speed of th

7、e motor is the command input;the selection of the value of time on the value of voltage applied to the motor armature is represented by the reference-selector block;and the output of this block is identified as the reference input.The reference input is applied to the dynamic unit that performs the

8、desiredSection 1 Introductioncontrol function,and the output of this block is the desired output.A person could be assigned the task of sensing the actual value of the output and comparing with the command input.If the output does not have the desired value,the person can alter the reference-selecto

9、r position to achieve this value.Introducing the person provides a means through which the output is fed back and is compared with the input.Any necessary change is then made in order to cause the output to equal the desired value.TheSection 1 Introductionfeedback action,therefore,controls the input

10、 to the dynamic unit.Systems in which the output has a direct effect upon the input quantity are called closed-loop control systems.To improve the performance of the closed-loop system so that the output quantity is as close as possible to the desired quantity,the person can be replaced by a mechani

11、cal,electrical,or other form of comparison unit.The functional block diagram of a single-input single-output(SISO)closed-loop control system is illustrated in Fig.9-2.ComparisonSection 1 Introductionbetween the reference input and the feedback signal results in an actuating signal that is the defere

12、nce between these two quantities.The actuating signal acts to maintain the output at the desired value.This system is called a closed-loop control system.The designation closed-loop implies the action resulting from the comparison between the output and input quantities in order to maintain the outp

13、ut at the desired value.Thus,the output is controlled in order to achieve the desired value.Section 1 IntroductionFig.9-2 Functional block diagram of a closed-loop control system Section 1 Introduction The fundamental difference between the open-and closed-loop systems is the feedback action,which m

14、ay be continuous or discontinuous.Continuous control implies that the output is continuously fed back and compared with the reference input.In one form of discontinuous control the input and output quantities are periodically sampled and compared;i.e.,the control action is discontinuous in time.This

15、 is commonly called a digital,discrete-data,or sampled-data feedback control system.A discrete-data control system may incorporate a digital Section 1 Introductioncomputer,which improves the performance achievable by the system.In another form of discontinuous control system the actuating signal mus

16、t reach a prescribed value before the system dynamics reacts to it;i.e.,the control action is discontinuous in amplitude rather than in time.This type of discontinuous control system is commonly called an on-off or relay feedback control system.Both forms may be present in a system.Section 1 Introdu

17、ction A signification date in the this history of automatic feedback control systems is 1934,when Hazens paper Theory of Servomechanisms was published in the Journal of the Franklin Institute,marking the beginning of the very intense interest in this new field.It was in this paper that the word serv

18、omechanism originated,from the words servant(or slave)and mechanism.Blacks important paper on feedback amplifiers appeared in the same year.After World War II,control theory was studied intensively and applications have proliferated.Section 1 IntroductionMany books and thousands of articles and tech

19、nical papers have been written,and the application of control systems in the industrial and military fields has been extensive.This rapid growth of feedback control systems was accelerated by the equally rapid development and widespread use of computer.Section 1 Introduction The control theory devel

20、oped through the late 1950s may be categorized as conventional control theory and is effectively applied to many control-design problems,especially to SISO systems.Since then,control theory has been developed for the design of more complicated systems and for multiple-input multiple-output(MIMO)syst

21、ems.Space travel has become possible only because of the advent of modern control theory.Areas such as trajectory optimization and minimum-time and/or minimum-fuel problems,which are very importantSection 1 Introductionin space travel,can be readily handled by multivariable control theory.The introd

22、uction of micro-processors as control elements,i.e.,performing control functions in contrast to being used solely as computational tools,has had an enormous impact on the design of feedback control systems that achieve desired control-system specifications.Section 1 Introduction The early studies of

23、 control systems were based on the solution of differential equations by classical means.Other than for simple systems,the analysis in this approach is tedious and does not readily indicate what changes should be made to improve system performance.Use of the Laplace transform simplifies this analysi

24、s somewhat.Nyquists paper published in 1932 dealt with the application of steady-state frequency-response techniques to feedback amplifier design.This work was extended by Black and Bode.Hall and Harris appliedSection 1 Introductionfrequency-response analysis in the study of feedback control systems

25、,which furthered the development of control theory as a whole.Another advance occurred in 1948,when Evans presented his root-locus theory.This theory affords a graphical of the stability properties of a system and permits the graphical evaluation of both the time and the frequency response.Laplace t

26、ransform theory and network theory are joined in the root-locus calculation.Section 1 Introduction The Laplace transform and the principles of linear algebra are used in applying state variable methods to system analysis and design.The nth-order differential equation describing the system can be con

27、verted into a set of n first-order differential equations,expressed in terms of the state variables,that can be written in matrix notation for simpler mathematical manipulation.Matrix equations lend themselves very well to computer solution.This characteristic has enabled modern control theory to so

28、lve many problems,such as nonlinear andSection 1 Introductionoptimization problems,that could not be solved by conventional control theory.Mathematical models are used in the linear analysis.Once a physical system has been described by a set of mathematical equations,they are manipulated to achieve

29、an appropriate mathematical format.When this has been done,the subsequent method of analysis is independent of the nature of the physical system;i.e.,it does not matter whether the system is electrical,mechanical,or something else.This technique helps the designer to spot similarities based upon pre

30、vious experience.Section 1 Introduction The reader should recognize that no single design method is intended to be used to the exclusion of the others.Depending upon the known factors and the simplicity or complexity of a control-system problem,a designer may use one method exclusively or a combinat

31、ion of methods.With experience in the design of feedback control systems comes the ability to use the advantages of each method.Section 1 Introduction The modern control theory includes the method for the assignment of the complete eigenstructure,which consists of both the closed-loop eigenvalue spe

32、ctrum and the associated set of eigenvectors.This method is an extension of previous methods that assigned only the closed-loop eigenvalues.The eigenvectors can be selected from identifiable subspaces that are associated with the system plant and control matrices.This method provides great potential

33、 for shaping the system output response to meet desired performance standards.ReturnNew Words and Expressionsautomatic control system自动控制系统reconfigurablea.可重构的，可再构的open-loop control system开环控制系统functional block diagram功能框图feedbackn.反馈closed-loop control system闭环控制系统single-input single-output(SISO)单输

34、入单输出continuous control 连续控制 New Words and Expressionsdiscontinuous control断续控制periodicallyad.周期地samplen.采样，取样，样品，试件；v.采样discrete-data离散数据的sampled-data采样数据的relay feedback control system 继电反馈控制系统servomechanism n.伺服机构，伺服系统，随动系统multiple-input multiple-output(MIMO)多输入多输出 New Words and Expressionsmodern c

35、ontrol theory现代控制理论trajectory n.轨迹，轨道multivariable多变量differential equation微分方程Laplace transform拉普拉氏变换frequency-response 频率响应root-locus 根轨迹time response时域响应New Words and Expressionsstate variable 状态变量nth-ordern阶matrixn.矩阵mathematical model数学模型eigenstructuren.特征结构eigenvaluen.特征值eigenvectorn.特征向量Return

36、Scientific Thesis Writing:Main Body 正文是学术论文的核心部分，占主要篇幅。其宗旨是要阐明作者研究成果或所提出理论、方法的基本内容、理论依据、正确性、实现方法、仿真或实验的验证方法及其结果分析。要求推理论证严密、论述简明准确、分析与介绍条理清晰而重点突出，全文层次清楚、结构严谨、合乎逻辑。Scientific Thesis Writing:Main Body 正文可按内容和目的划分为若干部分，每部分采用小标题，用阿拉伯数字编号；小标题下还可设子标题，其编号采用：小标题数字.子标题数字。由于学科、专题、研究方法和实验手段等的不同，正文的结构并非千篇一律。学术论文

37、在体裁上属说明文。目的是解释事物，说明道理。解释事物时可以通过定义、分类、举例、比较和对比，分析其因果关系和提供数据等手段。在构思正文段落时，可以灵活地运用这些方式。Scientific Thesis Writing:Main Bodyl 定义定义 定义是揭示概念的内涵或者词语意义的方法。在解释事物时，往往需要对一些概念或者词语下个明确的定义。A substation is an assemblage of equipment for the purpose of switching of changing or regulating the voltage of electricity.在下

38、定义时，常用的词语有：be,be defined as,be known as,be called,mean,refer to,involve,deal with,be concerned with。Scientific Thesis Writing:Main Bodyl 分类分类 分类是把具有共同特性的有关事物分成属类。分类方法可以达到有效地组织文章的作用。Main classifications of the substations are as follow:Step-up substation,primary grid substation,secondary substation a

39、nd distribution.（对变电站进行了分类）对事物分类常用的词语有：class,group,category,kind,sort,be classified into,be classed into,be divided into,fall into,group into,be made up of。Scientific Thesis Writing:Main Bodyl 举例举例 举例是使用例子说明要点。它是最常见，也是最有效的一种说明方式。举例时，常用的词语有：like,an example of,such as,be illustrated by,for example,as

40、illustrated by,for instance。Scientific Thesis Writing:Main Bodyl 比较与对比比较与对比 比较是确定事物异同关系的思维过程和方法。对比是把两种不同的事物作对照，互相比较。对事物进行比较和对比时，常用的词语有：comparison,contrast,both,similar,difference,different,similarities,like,while,although,alike,same,on the other hand,in a similar way,on the contrary,however,comparin

41、g to,instead,unlike。Scientific Thesis Writing:Main Bodyl 因果分析因果分析 因果分析是用于阐述和分析某事件产生的原因和结果。解释原因和结果常用的词语有：as,because,since,accordingly,consequently,hence,therefore,thus,so,as a result,thus,so because of,account for。ReturnExercises I.Choose the best answer into the blank 1.The system in which the outpu

42、t is controlled in order to achieve the desired value is call-ed .A.a open-loop control system B.a close-loop control system C.a sequential control system D.an automatic control system2.In the form of the output is continuously fed back fed back and compared with the reference input.A.continuous con

43、trolB.discontinuous control C.discrete-data controlD.sampled-data control Exercises I.Choose the best answer into the blank 3.Theory of Servomechanisms that marks the beginning of the automatic feedback control system is published in .A.1932 B.1934 C.1948 D.19504.The root-locus theory was presented

44、by .A.Nyquist B.Bode C.Black D.Evans Exercises I.Choose the best answer into the blank 5.The state equations are .A.a set of n first-order differential equations B.a n-order differential equation C.a set of n first-order algebraic equations D.a n-order algebraic equationExercises II.Answer the follo

45、wing questions according to the text 1.What is the difference between the open-loop control system and the close-loop control system?2.What is the difference between the continuous control system and the discontinuous control system?3.What systems does conventional control theory suit to?SISO or MIM

46、O?4.Whose paper dealt first with the application of steady-state frequency-response techniques to feedback amplifier design?Exercises III.Translate the following into Chinese Practically all control systems that are implemented today are based on computer control.A computer-controlled system can be

47、described schematically as in Fig.9-3.The output from the process y(t)is a continuous-time signal.The output is converted into digital form by the analog-to-digital(A-D)converter.The A-D converter can be included in the computer or regarded as a separate unit,according to ones preference.The convers

48、ion is done at the sampling times,tk.The computerExercises III.Translate the following into Chinese interprets the converted signal,y(tk),as a sequence of numbers,processes the measurements using an algorithm,and gives a new sequence of numbers,u(tk).This sequence is converted to an analog signal by

49、 a digital-to-analog(D-A)converter.The events are synchronized by the real-time clock in the computer.The digital computer operates sequentially in time and each operation takes some time.The D-A converter must,however,produce a continuous-time signal.This is normally done byExercises III.Translate

50、the following into Chinese keeping the control signal constant between the conversions.In this case the system runs open loop in the time interval between the sampling instants because the control signal is constant irrespective of the value of the output.The computer-controlled system contains both