【正文】 set maximum. Variations of such relay or onoff control systems, sometimes quite sophisticated, are very mon in practice because of their relatively low cost. In the nature of such control systems, the controlled variable will oscillate continuously between maximum and minimum limits. For many applications the control is not sufficiently smooth or accurate. In the Power steering of a car, the controlled variable or system output is the angle of the front wheels, it must follow the system input, the angle of the steering wheel, as closely as possible but at a much higher Power level. In the Process industries, including refineries and chemical plants, there are many temperatures and level to be held to usually constant values in the presence of various disturbance. of an electric power generation Plant, controlled values of voltage and frequency are outputs, but inside such a plant there are again many temperatures, levels, pressures, and, other variables to be controlled. In aerospace, the control of aircraft, missiles, and satellites is an area of often very advanced system. One Classification of control systems Is the following: 1. Process control or regulator systems: The controlled variable, or output, must be held as close as possible to a usually constant desired value, or input, despite any disturbances. 2. Servomechanisms: The input varies and the output must be made to follow it as closely as possible. Power steering is One example of the second class, equivalent to systems for positioning control surfaces on aircraft. Automated manufacturing machinery, such as numerically controlled machine tools, uses servos extensively for the control of positions or speeds. This last example brings to mind the distinction between continuous and discrete systems. The latter are inherent in the use of digital puters for control. The classification into linear nonlinear control systems should also be mentioned at this point. Analysis and design are in general much simpler for the former, to which most of this book is devoted. Yet most systems bee nonlinear if the variables more over wide enough ranges. The importance in practice of linear techniques relies on linearization based on the assumption that the variables stay close enough to a given operating point. OPENLOOP CONTROL AND CLOSEDLOOP CONTROL To introduce the subject, it is useful to consider an example. In , let it be desired to maintain the actual water level in the tank as close as possible to a desired level. The desired level will be called the system input, and the actual level the controlled or system output. Water flows from the tank via valve Vo and enters the 40 tank a supply via a control valve Vc. The control valve is adjustable, either manually or by some type of actuator. This may be an electric motor or a hydraulic or pneumatic cylinder. Very often it would be pneumatic diaphragm actuator, indicated in Fig 2. Increasing the pneumatic pressure above the diaphragm pushes it down against a spring and increases valve opening. In this form of Control, the valve is adjusted t0 make output c equal to input r, but not, readjusted continually to keep the two equal. Open loop control, with certain safeguards added is very mon, for example, in the context of sequence control, that is, guiding a process through a sequence of predetermined steps. However, for systems such as the one at hand, this form of control will normally not yield high performance. A difference between input and output, a system error e = rc would be expected to develop, due to two major effect: 1. Disturbances acting on the system 2. Parameter variation of the system These are prime motivations。還要感 謝我們 03 電氣所有的同學(xué)，正是可愛的你們，我的大學(xué)生活才如此的豐富多彩！ 最后要感謝的，是 我的家人，同時將這篇論文送給他們。正是由于我們的努力，整個設(shè)計才能進行的那么順利。在論文的編寫過程中，他給我提出寶貴的意見，并且給與細(xì)致的指導(dǎo)。這正是該項目的難點，也是我們繼續(xù)要開發(fā)研究的。大大減少實驗室的投入，降低辦學(xué)成本。我需要一個基于網(wǎng)絡(luò)平臺的遠程實驗、仿真系統(tǒng)。 對于給 定被 控系統(tǒng)，按照預(yù)先給定系統(tǒng)的參數(shù)繪制出系統(tǒng)的根軌跡圖，并按照給定的瞬態(tài)性能指標(biāo)要求用根軌跡分析法設(shè)計串聯(lián)校正補償器以及求出校正前后系統(tǒng)的傳遞函數(shù)。 根軌跡法是一種求解閉環(huán)特征方程根的簡便圖解方法，它根據(jù)系統(tǒng)的開環(huán)傳遞函數(shù)極點和零點的分布，依據(jù)一些簡單的規(guī)則，研究開環(huán)系統(tǒng)某一參數(shù)變化時，閉環(huán)系統(tǒng)極點和零點在 s 平面上的軌跡 。我還了解了 MATLAB 的控制系統(tǒng)工具箱，它是 MATLAB 中的一個重要的領(lǐng)域型工具箱，主要用于線性定常系統(tǒng)的分析、設(shè)計與仿真。 35 5 總結(jié)和展望 本次畢業(yè)設(shè)計我們用 MATLAB 設(shè)計了《自動控制原理》虛擬實驗系統(tǒng)，主要設(shè)計友好的人機界面供學(xué)生做實驗使用。 33 在此，我們以根軌跡實驗為例簡要地說明本虛擬實驗系統(tǒng)在《自動控制原理》實驗中的應(yīng)用，展示一下本虛擬實驗系統(tǒng)的功能。對用戶而言，操作簡單易學(xué)且無須編程，參數(shù)輸人與修改是活．具有多次或重復(fù)仿真運行的控制能力，可 以 顯示校正前后系統(tǒng)的特性曲 線，能很直觀漂亮地繪 制出控制系統(tǒng)的階躍響應(yīng)曲線、伯德圖、乃氏 圖和根軌跡圖．這些很強的交互能力使其在自動控制原理的實驗中可以發(fā)揮理想的效果。 最后生成新的 M 文件 : 文件 ,在運行該文件 ,得到圖的主界面 圖 虛擬實驗系統(tǒng)的主界面 32 4 系統(tǒng)設(shè)計成果及實驗舉例 系統(tǒng)設(shè)計成果 經(jīng)過三個月的努力，我們建立了一個用戶界面良好的《自動控制原理》虛擬實驗系統(tǒng) 。,39。界面仿真方式 (amp。)。,39。Label39。,39。界面仿真方式 (amp。)。,39。Label39。,39。界面仿真方式 (amp。)。,39。Label39。,39。仿真模型 (amp。在得到的 M文件中，定義變量，進行各個模塊的調(diào)用。 6)完成 ： 是為了在用戶結(jié)束使用的時候退出 MATLAB 或退出實驗窗口所設(shè) 30 立的。 2)模型元件庫： 這個部分包含有 5 個元件庫，是配合實驗操作窗口所設(shè)計的，是為了方便用戶的建模，使得用戶不需要再進入 MATLAB 的 SIMULINK 來調(diào)用相應(yīng)的模塊。 利用上述對象和 MATLAB 進行界面設(shè)計的方法，進行周密的組織、設(shè)計，來設(shè)計出一個界面良好、操作簡便、功能強大的圖形用戶界面。具體地講，可以通過下述 3 個函數(shù)來獲得對象句柄值。在 MATLB 中的 GUI 對象層次結(jié)構(gòu)如圖所示： 圖 MATLAB中的 GUI對象層次結(jié)構(gòu)圖 在 MATLAB 中，每個圖形對象都是由一個 數(shù)字來標(biāo)識，叫句柄 (Handle)。 2)下拉式菜單對象 (uimenu):能建立下拉式菜單和子菜單等圖形用戶界面對象。 27 圖 校正前實驗結(jié)果 圖 校正后實驗結(jié)果 28 3． 3 主界面的設(shè)計 設(shè)計思想及目標(biāo) 作為強大的科學(xué)計算軟件， MATLAB 也提供了圖形用戶界面的設(shè)計和開發(fā)功能。根據(jù)用戶進行的不同系統(tǒng)分析，在主界面中調(diào)用相應(yīng)的 fig 文件，顯示不同的實驗分析結(jié)果。這樣在運行主程序的時候，該 m 文件會被自動調(diào)用，彈出“實驗?zāi)康呐c原理”界面，見圖 ： 圖 ‘“ 實驗 原理 與 目的”界面 26 ② 實 驗步驟的生成 利用 MATLAB 軟件的 GUI 界面編程，生成一個 m 文件，再將實驗的詳細(xì)步驟寫入 m 文件。實驗報告生成完成以后，由系統(tǒng)原先給定的參數(shù)及特性，再根據(jù)實驗過程中的四種不同的校正方法，用戶可以根據(jù)自己的需要，通過點擊“實驗報告生成”這個按鈕，隨心所欲地顯示校正前后系統(tǒng)的特性，如根軌跡圖以及傳遞函數(shù)等。最后得出根軌跡的窗口 : 圖 根軌跡分析窗口 24 實驗報告生成模塊的設(shè)計 (1)設(shè)計思想及目標(biāo) 為了使實驗過程中的實驗?zāi)康呐c原理、實驗步驟、數(shù)據(jù) 、框圖以及分析和設(shè)計結(jié)果等能夠在實驗?zāi)K界面中顯示，我們做了實驗報告