毕 业 设 计（论文） 外文文献翻译文献、资料中文题目文献、资料英文题目：System compensation 文献、资料来源： 文献、资料发表（出版）日期：院（部）：专 业： 电气与自动化班 级： 姓 名：学 号：指导教师：翻译日期：2017.02.14毕业设计（论文）外文文献翻译附 件： System compensationSystem compensation1 IntroductionIt was mentioned earlier that performance of a control system is measured by its stability, accucacy , and speed of response .in general these items are specified when a system is being designed to satisfy a specific task .Quite often the simultaneous satisfaction of all these requirements cannot be achieved by using the basic elements in the control system .Even after introducing controllers and feedback , we are limited as to the choice we may exercise in selecting a certain transient response while requiring a small steady state error. We will show how the desired transient as well as the steady state behavior of a system may be obtained by introducing compensatory elements (also called equalizer networks)into that control system loop .These compensation elements are designed so that they help achieve system performance , i. e .bandwidth, phase margin ,peak overshoot ,steady state error ,etc. without modifying the entire system in a major way .Form our experience so far we recognize that any changes in system performance can be achieved only though varying the forward loop gain .Consider the third-order unity feedback system with the following forward loop transfer function,G (s)=s (s + a)( s + b)From the Routh-Hurwitz criterion we know that stability requires K K cNow consider the same system but with the addition of a zero,G (s) H (s) =K (兀3 + s (sr 1 +1)(兀 2 +1)This is the type of function we obtain if we were to add derivative and proportional control to a third-order servomechanism .The characteristic equation becomess3T 2 + s2(T 1 +T 2)+ (KT 3 + 1)S + K _ S(ST 1 + 1)(ST 2 + 1)And the zeros of the characteristic equation are determined byS3T 1T 2 + S2(T 1 +T 2) + (KT 3 + 1)s + k _ 0The Routh array becomesS 3T T( KT + 1)1 23T + TKb(KT+1)(T +T )- KTTS2o 312 1121T + T12S1bbb =0122S0cw1c _ K1For stability b、 0, and thereforeK ( T 1T 3 + TT - T T ) +2312(T1+T2）0Clearly ,with a proper selection of the time constants ,this may be satisfied .The Nyquist plot for thisis shown in Fig.1Fig.13 CASCADED COMPENSATIONAs indicated inFig.2, cascaded compensation consists of placing elements in series with the forward loop transfer function .Such compensation may be classified into the following categories:(a) Phase-lag compensation(b) Phase-lead compensation(c) feedback compensationFig.2 Type of compensation(e) Lag-lead compensation(f) Compensation by cancellation.The details of these methods is the subject of this section.Phase-lag compensationConsider a unity feedback control system whose forward loop transfer function represents a third-order system with its Nyquist plot show in Fig.3.It is required that the gain be K 1 for satisfying the margin of stability but K2 for satisfying the steady state performance .This seemingly contradictory requirement may be satisfied if we were to reshape the plot to the one indicated by thedotted lines .The reshaped plot may be obtained if the low-frequency part of K 1 is rotated clockwise while the high-frequency part of K1 must lag ,the type of compensation used to achieve this is phase-lag compensation. Such compensation is obtained by a phase-lag element.Fig.3When the output of an element lags the input in phase and the magnitude decrases as a function of frequency ,the element is called a phase-lag element .Consider the lag network.The transfer function for this is1 + aTs1 + TWhereaT 二 RC；Ra二2