电气工程及其自动化专业英语section 9-4.ppt

* Chapter 9 Automation Control System Section 4 Frequency Response Text New Words and Expressions Exercises End Section 4 Frequency Response In conventional control-system analysis there are two basic methods for predicting and adjusting a systems performance without resorting to the solution of the systems differential equation. One of these is the root-locus method, the other is the frequency-response method. For the comprehensive study of a system by conventional methods it is necessary to use both methods of analysis. The principal advantage of the root-locus method is that the actual time response is easily obtained by means of the inverse Laplace transform because the Section 4 Frequency Response precise root locations are known. However, it is sometimes necessary to express performance requirements in terms of the frequency response. Also, the noise, which is always present in any system, can result in poor overall performance. The frequency response of a system permits evaluation of the effect of noise. The design of a passband for the system response may exclude the noise and therefore improve the system performance as long as the dynamic performance specifications are met. The frequency response is also useful in situations Section 4 Frequency Response for which the transfer functions of some or all of the components in a system are unknown. The frequency response can be determined experimentally for these situations, and an approximate expression for the transfer function can be obtained from the graphical plot of the experimental data. The frequency-response method is also a very powerful method for analyzing and designing a robust MIMO system with uncertain plant parameters. Thus, no particular method can be judged superior to the rest. Each has its particular use and advantage in a particular situation. Section 4 Frequency Response Design of control systems by state variable techniques is often based upon achieving an