# 电气信息类专业英语Part 3 Control Theory.ppt

,Part 3 Control Theory,3.1 Control Engineering 3.2 Basic Control Actions 3.3 Time Response Analysis of Control Systems 3.4 Nonlinear Models and Non-linear 3.5 State-Space Analysis of Control Systems 3.6 Controllability, Observability and Stability,3.1.1 语言现象——形容词的翻译 英语形容词起修饰作用，是修饰名词的。译得准确、生动，与名词搭配相得益彰，可以起到画龙点睛的作用，使文章显得生动活泼，使被修饰的人物、事物跃然纸上。否则，词不达意，晦涩难懂，连名词的意思也黯然失色。因此，应高度重视对英语形容词的准确理解与恰当翻译。,,3.1 Control Engineering,形容词在英文句中一般做表语或修饰名词的定语，因而在翻译时要把形容词与其所修饰的客体统一考虑，对二者的割裂会导致牛头不对马嘴的错误。,,1．正确体会一词多义 有些形容词的词义不是一两个解释所能说清楚的，其含义比较复杂，要先了解它们的本义，抓住其基本概念，再结合被修饰的名词，探索其演变出的各种意义。对形容词词义的理解必须同上下文联系起来，明确它所指的范围，即明确它所修饰的对象，确定它在此表达的意思，再从汉语中挑选恰当的词语，准确恰当地把它表达出来。 heavy的基本词义是“重”，但在翻译时结合修饰的对象则译法各异。如heavy current强电流；heavy crop大丰收；heavy traffic交通拥挤；heavy industry重工业等。,,英语词义对上下文的依赖性是很大的。一个孤立的词，其词义通常是游移不定的，但当词处于特定的联立关系中时，其含义就受到相关词的制约而明朗和稳定了。因此，根据词的联立关系确定词义是词义辨析的重要且最为可行的手段。 universal有“宇宙的、世界的、普遍的、一般的和通用的”等含义。具体用法举例如下： universal meter万用表；universal constant通用常数；universal motor交直流两用电动机；universal use普遍应用；universal agent全权代理人；,,universal access通用存取；universal coupling/ joint万向轴节；universal grammar普遍文法，通用文法；universal gravitation万有引力；universal language通用语言，世界语；Universal Music环球音乐集团(公司名称)；universal serial bus通用串行总线；universal set通用集(合)，泛集，万有集；Universal Studio环球影城(主题公园名)；universal suffrage普选权；universal testing machine 万能试验机；universal time世界时间，格林威治时间，国际标准时间；universal peace世界和平；universal rules一般法则；universal truth普遍真理；universal travel环球旅行等等。,,sophisticated源出希腊语的诡辩家sophist一词，现其使用范围很广。如sophisticated equipment尖端设备，高级设备；sophisticated investor成熟投资者，精明投资人；sophisticated planer精密刨床；sophisticated technology精良工艺；sophisticated arguments强词夺理的论据；sophisticated weapons尖端武器；sophisticated man老于世故的人；the new and sophisticated patterns of intervention花样翻新的干涉活动等等。,,同一个high在high noon中译为正午，在high summer中译为盛夏，在high manner中译为傲慢的态度，而在high voice中译为尖声，这些都和汉语的习惯用法密切相关。 一般的常用专业词组搭配都可以在英汉技术字典中查到，所以对含义不清楚的词组应借助字典来理解，闭门造车式的翻译只能导致主观臆断的错误。 对形容词的翻译还可采取词性转换的技巧，使对原文的表达更通顺和易于理解。,,2．一些原义并无否定意思的形容词和别的词搭配，有时可译成否定句 如： These goods are in short supply. 这些货物供应不足。 This equation is far from being complicated. 这个方程一点也不复杂。,,3．当形容词在句中做表语时，某些情况下可根据汉语习惯，将其和系词合译成动词形式 如： Internet is different from Intranet in many aspects though their spelling is alike． 虽然拼写相像，Internet仍在很多方面不同于Intranet。 If low-cost power becomes available from nuclear power plants，the electricity crisis would be solved． 如能从核电站获得低成本电力，电力紧张问题就会解决。,,4．某些表示事物特征的形容词，可在其后加上“性”、“度”而转化为名词 如： IPC is more reliable than common computer. 工控机的可靠性比普通计算机高。 Experiment indicates that the new chip is about 1.5 times as integrative as that of the old ones. 试验表明，新型芯片的集成度是旧型号的1.5倍。,,5．有时形容词也可根据需要译成副词 如： The same principles of low internal resistance also apply to milli-ammeters． 低内阻原理也同样适用于毫安表。 The modern world is experiencing rapid development of ination technique． 当今世界的信息技术正在迅速地发展。,,词性转换技巧同样适用于其他词类，拘泥于原文的词性进行完全对应的翻译往往会给翻译带来极大的障碍，同时使得译文生涩而难以理解。翻译应从整体着眼，采取适当的词性转换、句子成分转换或句型转换的翻译技巧，可使译文既忠实于原意又通顺可读。,,3.1.2 Specified English Words discipline n. 纪律；学科；训练 vt. 训练，训导；惩戒 regulate vt. 调节，规定；有系统的管理；控制；校准 derive vt. 得自；源于 vi. 起源 actuator n. 执行机构；激励者；促动器 yaw damper 抗偏器；偏航阻尼器 on-site adj. 现场的 Laplace trans 拉普拉斯变换 scan vt. 扫描 vi. 扫描；扫掠 n. 扫描；浏览；审视；细看,,diversify vt. 使多样化，使变化；增加产品种类以扩大 sampled-data 采样数据 nonlinear adj. 非线性的 time-invariant adj. 时不变的 stationary adj. 静止的；固定的；定居的；常备军的 n. 不动的人；驻军 lumped parameter 集合参数；集中参数；总参数 distributed parameter 分散(布)式参数 deterministic adj. 确定性的；命运注定论的 stochastic adj. 随机的；猜测的,,perance criteria 性能标准 overlap n. 重叠；重复 vi. 部分重叠 vt. 与……重叠；与……同时发生,,3.1.3 Text Control Engineering Automatic control has played a vital role in the advancement of engineering and science. In addition to its extreme importance in space-vehicle, missile-guidance, and aircraft-piloting systems, etc, automatic control has become an important and integral part of modern manufacturing and industrial processes. For example, automatic control is essential in such industrial operations as controlling pressure, temperature, humidity,,,viscosity, and flow in the process industries; tooling, handling, and assembling mechanical parts in the manufacturing industries, among many others. The word control is usually taken to mean regulate, direct, or command. Control systems abound in our environment. In the most abstract sense it is possible to consider every physical object as a control system.,,Control engineering or control systems engineering is the engineering discipline that applies control theory to design systems with predictable behaviors. The practice uses sensors to measure the output perance of the device being controlled and those measurements can be used to give feedback to the actuators that can make corrections toward desired perance. When a device is designed to per without the need of human s for correction it is called automatic control (such as cruise control for regulating a car’s speed).,,Multi-disciplinary in nature, control systems engineering focus on implementation of control systems mainly derived by mathematical modeling of systems of a diverse range. Control systems designed by humans are used to extend their physical capabilities, to compensate for their physical limitations, to relieve them of routine or tedious tasks, or to save money. In a modern aircraft, for example, the power boost controls amplify the force applied by the pilot to move the control surfaces against large aerodynamic forces.,,The reaction time of a human pilot is too slow to enable him or her to fly an aircraft with a lightly damped Dutch roll mode without the addition of a yaw damper system. An autopilot (flight control system) relieves the pilot of the task of continuously operating the controls to maintain the desired heading, altitude, and attitude. Freed of this routine task, the pilot can per other tasks, such as navigation and/or communications, thus reducing the number of crew required and consequently the operating cost of the aircraft.,,In many cases, the design of control system is based on some theory rather than intuition or trail-and-error. Control theory is used for dealing with the dynamic response of a system to commands, regulations, or disturbances. Control engineering consists of analysis and design of control configurations. Analysis is the investigation of the properties of an existing system. It is concerned with determination of the response of a plant (the controlled object) to commands, disturbances, and changes in the plant parameters. The design problem is one choice and arrangement of system components to per a specific task. If the dynamic response is satisfactory, there need be no second phase.,,If the response is unsatisfactory and modification of the plant is unacceptable, a design phase is necessary to select the control elements (the controller) to improve the dynamic perance to acceptable levels. There are two major divisions in control theory, namely, classical and modern. The scope of classical control theory is limited to single- and single-output (SISO) system design. The system analysis is carried out in time domain using differential equations,,,in complex-s domain with Laplace trans or in frequency domain by transing from the complex-s domain. The systems are assumed to be second order and single variable, and higher-order system responses and multivariable effects are ignored. A controller designed using classical theory usually requires on-site tuning due to design approximations. Yet, due to easier physical implementation of classical controller designs as compared to systems designed using modern control theory,,,these controllers are preferred in most industrial applications. The most common controllers designed using classical control theory are PID controllers. In contrast, modern control theory is carried out in the state space, and can deal with multi- and multi-output (MIMO) systems. This overcomes the limitations of classical control theory in more sophisticated design problems, such as fighter aircraft control.,,In modern design, a system is represented as a set of first order differential equations defined using state variables. Nonlinear, multivariable, adaptive and robust control theories come under this division. Being fairly new, modern control theory has many areas yet to be explored. Scholars like Rudolf E. Kalman and Aleksandr Lyapunov are well known among the people who have shaped modern control theory. Control systems are classified in terms that describe either the system itself or its variables:,,Open-loop and closed-loop control systems (see Fig. 3.1). An open-loop system is one in which the control action is independent of the output. A closed-loop system, however, the of the plant is somehow dependent on the actual output. Since the output is fed back in a functional determined by the nature of the feedback elements and then subtracted from the , a closed-loop system is referred to as a negative feedback system or simply as a feedback system.,,,Fig. 3.1 open-loop control system and closed-loop control system,Continuous and discrete systems. The system that all its variables are continuous functions of time is called continuous-variable or analog system; the describing equations are differential equations. A discrete-variable or digital system has one or more variables known only at particular instants of time, as in Fig. 3.2, the equations are difference equations. If the time intervals are controlled, the system is termed a sampled-data system.,,Discrete variables occur naturally, as from a scanning radar that obtains position data once per scan or a data channel that transmits many pieces of ination in turn. A discrete variable will obviously approach a continuous variable as the sampling interval is decreased.,,,Fig. 3.2 Continuous system and discrete system,Discontinuous variables, such as shown in Fig.3.2(c) occur in “on-off” or “bang-bang” control systems and are treated separately in a subsequent paper. Linear and nonlinear systems. A system is linear if all its elements are linear, and nonlinear if any element is nonlinear. Time-invariant and time-variant systems. A time-invariant (or stationary) system is one whose parameters do not vary with time. The output of a stationary system is independent of the time at which an is applied, and the coefficients of the describing differential equations are constants.,,A time-variant (or nonstationary) system is a system with one or more parameters that vary with time. The time at which an is applied must be known, and the coefficients of the differential equations are time-dependent. Lumped parameter and distributed parameter systems. Lumped parameter systems are those for which physical characteristics are assumed to be concentrated in one or more “lumps” and thus independent of any spatial distribution.,,In effect, bodies are assumed rigid and treated as point massed; springs are massless and electrical leads resistanceless, or suitable corrections are made to the system mass or resistance; temperatures are uni; etc. In distributed parameter systems, the continuous spatial distribution of a physical characteristic is taken into account. Bodies are elastic, springs have a distributed mass, electrical leads have a distribute resistance, and the temperatures vary across a body.,,Lumped parameter systems are described by ordinary differential equations; while distributed parameter systems are described by partial differential equations. Deterministic and stochastic systems. A system or variable is deterministic if its future behavior is both predictable and repeatable within reasonable limits. If not, the system or variable is called stochastic or random. Analyses of stochastic systems and of deterministic system with stochastic s are based on probability theory.,,Single-variable and multivariable system. A single-variable system is defined as one with only one output for one reference or command and is often referred to as a single single output (SISO) system. A multivariable (MIMO) system has any number of s and outputs. At many universities, control engineering courses are taught in Electrical and Electronic Engineering, Mechatronics Engineering, Mechanical engineering, and Aerospace engineering; in others it is connected to computer science, as most control techniques today are implemented through computers, often as Embedded systems (as in the automotive field).,,The field of control within chemical engineering is often known as process control. It deals primarily with the control of variables in a chemical process in a plant. It is taught as part of the undergraduate curriculum of any chemical engineering program, and employs many of the same principles in control engineering. Other engineering disciplines also overlap with control engineering, as it can be applied to any system for which a suitable model can be derived.,,Control engineering has diversified applications that include science, finance management, and even human behavior. Students of control engineering may start with a linear control system course dealing with the time and complex-s domain, which requires a thorough background in elementary mathematics and Laplace trans (called classical control theory). In linear control, the student does frequency and time domain analysis. Digital control and nonlinear control courses require Z transation and algebra respectively, and could be said to complete a basic control education.,, Notes 1．For example, automatic control is essential in such industrial operations as controlling pressure, temperature, humidity, viscosity, and flow in the process industries. 例如，在对压力、温度、湿度、粘度、流量实施的工业过程的控制中，必须进行自动控制。 2．The reaction time of a human pilot is too slow to enable him or her to fly an aircraft with a lightly damped Dutch roll mode without the addition of a yaw damper system. 飞行员的反应速度太慢，如果不附加阻尼偏航系统，就无法通过小阻尼的荷兰滚方式来驾驶飞机。,,3．Since the output is fed back in a functional determined by the nature of the feedback elements and then subtracted from the … 因为输出会以由反馈元件特性决定的函数形式反馈回来，然后从输入中减去…… 4．Students of control engineering may start with a linear control system course dealing with the time and complex-s domain, which requires a thorough background in elementary mathematics and Laplace trans.,,学习控制工程可以从线性控制系统起步，线性控制系统涉及时域及复域两个方面，要求必须具有良好的数学基础，掌握拉普拉斯变换。,,3.1.4 Reading Materials Types of Feedback When feedback acts in response to an event/phenomenon, it can influence the signal in one of two ways. An in-phase feedback signal, where a positive-going wave on the leads to a positive-going change on the output, will amplify the signal, leading to more modification. This is known as positive feedback. A feedback signal which is inverted,,,where a positive-going change on the leads to a negative-going change on the output, will dampen the effect of the signal, leadin