自动控制原理2008（双语）chapter5.pptVIP

The Principle of Automatic Control自动控制原理 Lecturers：Prof. Jiang Bin Dr. Lu Ningyun College of Automation Engineering NUAA，2008. Autumn NUAA-The Principle of Automatic Control Chapter 5 Frequency Response 频域响应 What we have learned? Mathematical model ODE model -> TF model Time-domain analysis 1st order, 2nd order, higher order Unit Step response Root Locus method Suitable to low order systems to analyze the stability, time-domain responses etc. For high order system??? The time response of a control system is usually more difficult to determine analytically, especially for high-order systems. On the other hand, in the frequency domain, there is a wealth of graphical methods available that not limited to low-order systems. Furthermore, there are relations between the frequency-domain and the time-domain performances in linear systems. Start from an example Frequency Response means… The steady-state response of a system to a sinusoidal input In frequency-response method, we vary the frequency of the input signal over a certain range and study the resulting response. Outline of Chap 5 5-1 Frequency characteristics frequency characteristic Amplitude ratio of the output sinusoid to the input sinusoid? magnitude characteristic (幅值特性） Physical meaning of frequency characteristic The differential equation: The transfer function: Frequency characteristic: A few conclusions from the example Physical meaning of FC:表示系统或环节对不同频率正弦信号的跟踪能力或复现能力。确定了在不同频率正弦信号作用下,系统或环节输入与输出的单值对应关系。 Properties of FC: G(jw)只与系统或环节本身的结构参数有关,是系统或环节本身的属性,与输入信号和初始条件无关。 频率法就是利用稳态的频率响应，间接地研究系统的动态特性，从而避免了求解高阶微分方程的困难。 1. Polar coordinate plot (Nyquist plot) 当输入正弦信号的频率从0变到+∞时,矢量 的终端便在复平面上描绘出一条轨迹,这条轨迹就是G(jw)的极坐标图,通常又称为幅相频率特性曲线，也称Nyquist曲线。 Why use the logarithmic magnitude in Bode plot? Multiplication of magnitudes can be converted into addition. A simple method for sketching an approximate log-magnitude curve is available. (detailed in 5.2) L(w)=20lgA(w) VS w ? loga