【正文】 Control systems exist in a virtually infinite, both in type of application and level of sophistication. The heating system and the water heater in a house are systems in which only the sign of the difference between desired and actual temperatures is used for control. If the temperature drops below a set value, a constant heat is switched on, to be switched off again when the temperature rises above a 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 39 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 diaphra gm 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 for the use of feedback control. For the example, pressure variations upstream of V can be important disturbances affecting inflow and outflow, and hence level. In a steel rolling mill, very large disturbance torques in the drive motor of the rolls when steel slabs enter or leave affect speeds. For the water Level example, a sudden or gradual change of flow resistance of the valves due to foreign matter or valve deposits represents a system parameter values are different at 20% and 100% of full power. In a valve, the relation, between pressure drop and flow rate is often nonlinear, and as a res。必須對那些仿真軟件平臺進行研究分析和大量的二次開發(fā)工作，包括遠程實驗、仿真平臺的理論研究、平臺的搭建、數(shù)據(jù)的傳輸、數(shù)據(jù)的安全、數(shù)據(jù)的共享、實驗在線監(jiān)視系統(tǒng)、學生實驗情況的專家知識庫、利用知識庫提供在線操作指導等等。同時可以降低對運行的硬件平臺的要求，降低軟件的投入，減少軟件運行維護的費用，降低客戶機的配置要求。 我們所設計的虛擬實驗系統(tǒng) 軟件只是一個單機的仿真軟件，對于用戶而言，必須每臺客戶機都裝有一套軟件，軟件投入資金大，同時，對客戶機的要求又高，以運行很龐大的仿真軟件。在設計控制系統(tǒng)時，根軌跡法是有效的，因為它指出了系統(tǒng)開環(huán)極點和零點應該怎樣變化，才能使系統(tǒng)的性能滿足設計指標。 除建模外，我對系統(tǒng)根軌跡有了較深刻的理解。 MATLAB 語言的數(shù)值計算和繪圖功能非常強大，而且精度可以滿足要求，這就直接省去了我們的繪圖時間。等三部分都生成好后，就可以打印出實驗報告，本次實驗結束。下面我們具體舉根軌跡實驗說明。可實現(xiàn)資源共享和多任務并行的要求。 其中，‘ tanhuang’ 、‘ dianlu’ 、‘ zidong’分別是彈簧小車模型、電路模型、自動化控制模型的 M 文件。Call39。,39。clear all39。Z)39。 state=uimenu(fzsyxm,39。Call39。,39。clear all39。D)39。 虛擬實驗系統(tǒng)主界面 實驗操作窗口 模型元件庫 仿真模型 幫助 仿真試驗項目 輸入元件庫 輸出元件庫 連續(xù)線性環(huán)節(jié)元件庫 非線性元件庫 離散線性環(huán)節(jié)元件庫 彈簧小車模型 電路模型 自動化模型 自動控制系統(tǒng)穩(wěn)定性 根軌跡實驗窗口 頻域分析窗口 自控系統(tǒng)靜態(tài)誤差 線性二階系統(tǒng) 實驗指導 關于虛擬實驗系統(tǒng) 退出實驗 數(shù)字PID控制 退出MATLAB 完成 31 state=uimenu(fzsyxm,39。Call39。,39。clear all39。T)39。 state=uimenu(fzsyxm,39。Call39。,39。首先新建一個 GUI（圖形用戶界面），根據(jù)主界面的模型框架，在菜單編輯器建立菜單，然后運行，得到相應的 M 文件。 5