自动控制理论10

,单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,Lecture 15,Bode Diagrams,North China Electric Power University,Sun Hairong,1,Topics,of this class,What is called Bode diagrams?,Elemental Bode diagrams.,Bode diagrams of compound transfer functions,(Reading Module 15),Sample problems,2,1. Bode diagrams of simple transfer function,We begin the study by means of the following open-loop transfer function,Suppose its Bode diagram is required.,It is known from previous, The bode diagrams consistes of two parts.,the,magnitude,the,phase,3,one: Magnitude part,In the magnitude part of the bode diagrams,The x-coordinate is the frequency,v,but it is graduated by,lg,v,.,And the Y-coordinate is modulus,M,but the modulus is expressed in decibels,M,db,.,4,two: Phase part,In the phase part of the bode diagrams,The x-coordinate is the frequency,v,but it is graduated by,lg,v,.,And the Y-coordinate is phase angle .,Plotted on a logarithmic scale,Plotted on a horizontal scale,5,2. Elemental Bode diagrams,In this section, the bode diagrams of some classic elements will be talked about,Gain element,The integral element,First-order lag element,The inverse of the first-order lag element,The second-order lag element,The inverse of the second-order lag element,6,Accurate magnitude of,the second-order lag element with the damping ratio changing,7,3. Bode diagrams of compound transfer function,In this section, we will talk about how to determine the bode diagrams of compound transfer function by using the classic elements,Suppose we wish to draw the Bode diagram of the open-loop transfer function,The transfer function consists of four separate transfer functions(,classic elements,),8,Plot,M,db,against,v,Adding the component plots for magnitude.,9,Plot,f,against,v,Adding the component plots for phase.,10,The basic method for drawing Bode diagrams,The bode diagram for the compound transfer function is obtained by adding the component plots for both magnitude and phase.,11,Examples 1:,An open-loop system has a transfer function of the form , draw the Bode diagrams,Solution:,There are three separate elements.,Two break frequency,The slope of the low-frequency is,zero.,The phase-frequency is,12,Examples 2:,An open-loop system has a transfer function of the form , draw the Bode diagrams,Solution:,There are three separate elements.,Two break frequency,The slope of the low-frequency is,-40db/dec,.,The phase-frequency is,13,There are three separate elements.,Two break frequency,The slope of the low-frequency is,-40db/dec,.,The phase-frequency is,Examples 3:,An open-loop system has a transfer function of the form , draw the Bode diagrams,Solution:,14,The end,15,