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1、第6章 英文资料翻译6.1控制理论基础Background of Control Theory(控制理论基础) 1 System and Control TheoryAccording to the Encyclopedia Americana, a system is “an aggregation or assemblage of things so combined by nature or man as to form an integral and complex whole” .Mathematical systems theory is the study, of the int
2、erruptions and behavior of such an assemblage of “things” when subjected to certain conditions or inputs. The abstract nature of systems theory is due to the fact that it is concerned with mathematical properties rather than the physical form of the constituent parts. 按照美国大百科全书的解释，所谓系统就是反映“一个各种物体的集合
3、，根据其性质或人的愿望而结合起来以至形成一个集中、复杂的整体”。数学中的系统理论就是对这种由若干“物体”构成的集合当其受到某些条件和输入作用的行为和阻断进行研究的一门学问。系统理论的抽象性质源于这样一个事实：系统理论更关心物体组成部件的数学性质而不是其物理形式。Control theory is more often concerned with physical application. A control systems is considered to be any system which exists for the purpose of regulating or controll
4、ing the flow of energy, information, money, or other quantities in some desired fashion. In more general terms, a control system is an interconnection of many components or functional units in such a way as to produce a desired result, in this book, control theory is assumed to encompass all questio
5、ns related to design and analysis of control systems.控制理论通常与实际应用有关。一般认为，控制系统是任意一个这样的系统：其目的是为了以某种期望的方式来调节或控制诸如能量、信息、资金等等牧师量的流动。从更一般的意义上讲，控制系统就是一个按照一定方式由很多元件或功能单元构成的结合体，其目的是为了获得期望的结果。本书中，假定控制理论包括所有与控制系统设计和分析问题有关的内容。Fig.37.1 is a general representation of an open-loop control system. The input or contr
6、ol u(t) is selected based on the goals for the system and all available a priori knowledge about the system. The input is in no way influenced by the output of the system, represented by y(t).If unexpected disturbances act upon an open-loop system, or if its behavior is not completely understood, th
7、en the output will not behave precisely as expected.图37。1是对开环控制系统的一般性表示。输入变量或控制作用U（T）是根据本系统的目标以及所有可获取的先验知识而选定的。输入变量决不会受到Y（T）所表示的系统输出变量的影响。如果有不期望的振动作用在开环系统上，或者如果其行为不能完全掌握的话，则该系统的输出就不会完全如预期般动作。Another general class of control systems is the closed-loop or feedback control system, as illustrated in Fig
8、.37.2.In the closed-loop system, the control u(t) is modified in some way by information about the behavior of the system output. A feedback system is often better able to cope with unexpected disturbances and uncertainties about the systems dynamic behavior. However, it need not be true that closed
9、-loop control is always superior to open-loop control. When the measured output has errors which are sufficiently large, and when unexpected disturbances are relatively unimportant, closed-loop control can have a performance which is inferior to open-loop control.另一类常见的控制系统是闭环或反馈控制系统，如图37。2所示。闭环控制系统
10、中，控制作用U（T）被以某种方式由与系统输出行为有关的信息所校正。一个反馈系统经常能更好的应付不期望的振动作用以及系统动态性能的不确定性。然而，闭环控制并不一定总是优于开环控制。当输出的测量误差足够大或不期望的振动无关紧要时，闭环控制的性能就会比开环控制的差。2 Introduction to Modern Control Theory现代控制理论导论Several factors provided the stimulus for the development of modern control theory(a) The necessity of dealing with more re
11、alistic models of systems.处理更加真实的系统模型的必要性。(b) The shift in emphasis towards optimal control and optimal system design.研究重点朝向最优控制和最优系统设计的转移。(c) The continuing developments in digital computer technology.数字计算机技术的不断发展。(d) The shortcomings of previous approaches.原有方法的短缺。(e) A recognition of the applicab
12、ility of well0known methods in other fields of knowledge。对二将熟知方法在其他知识领域中应用的广泛认同。The transition from simple approximate models, which are easy to work with , to more realistic models produces two effects, First, a larger number of variables must be included in the mode Second, a more realistic model
13、is more likely to contain nonlinearities and time-varying parameters. Previously ignored aspects of the system, such as interactions and feedback through the environment , are more likely to be included.模型中必须包含众多的变量。其次，更为真实的模型往往具有非线性和时变参数。以前往往忽略的一些系统问题例如关联问题以及通过环境形成的反馈等，现在却需要考虑。With an advancing tec
14、hnological society, there is a trend towards more ambitious goals. This also means dealing with complex systems with larger number of interaction components. The need for greater accuracy and efficiency has changed the emphasis on control system performance. The classical specifications in terms of
15、percent overshoot, settling time, abandwidth, etc, have in many cases given way to optimal criteria such as minimum energy, minimum cost, and minimum operation. Optimization of these criteria makes it even more difficult to avoid dealing with unpleasant nonlinear. Optimal control theory often dictat
16、es that nonlinear time-varying control laws be used, even if the basic system is linear and time-invariant.在不断发展先进的社会中，朝着更加宏伟目标的发展趋势是很明显的。这也就意味着要处理具有大量相互关联部件的复杂系统。对二更加精确和更加有效的需求已经改变了对控制系统性能要求的重点。以百分超调量、调节时间、带宽等来表示的经典技术指标已经在很多场合让位二最优性准则，例如最小能耗、最低成本和最短时间操作等。依据这些准则的最优化合得想要避免处理讨厌的非线性一中变得更为困难。即使基本受近期系统是线性和时不变的，最优控制理论也经常规定要采用非线性、时变的控制规律。The continuing advances in computer technology have had three principal effects on the controls field
