4 敏感性分析简介.ppt

4__敏感性分析简介,敏感性分析的步骤,单因素敏感性分析,什么是敏感性分析,敏感性分析,敏感性分析计算公式,敏感性分析法,敏感性分析例题,盈亏平衡分析,敏感性分析 excelChapter 4 Feedback Control System Characteristics
The main topic of chapter 4 is to introduce the definitions of open- and closed –loop control system and to discuss the sensitivity of a system to a parameter change.
系统的敏感性:系统参数变化对系统性能的影响
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Open- and Closed-Loop control system.
Fig An open-loop system
An open-loop (direct) system operates without feedback and directly generates the output in response to an input signal.
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Fig An closed-loop system
An closed-loop system uses a measurement of the output signal and parison with the desired output to generate an error signal that is applied to the actuator.
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反馈控制利用偏差信号来激励系统。
Where
denotes the error signal.
, we have
Solving for
The error signal is
It is clear that, to reduce the error, the magnitude of
must be greater than one over the range of s under consideration.
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Sensitivity of control systems to parameter variations
A process, represented by the transfer function , whatever its nature, is subject to a changing environment, aging, ignorance of the exact values of the process parameters, and other natural factors that affect a control process.
In the open-loop system, all these errors and changes result in a changing and urate output. However, a closed-loop system senses the change in the output due to the process changes and attempts to correct the output.
So a primary advantage of a closed-loop feedback control system is its ability to reduce the system’s sensitivity.
闭环系统的作用就是减少系统的敏感性。
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For the closed-loop case, if GH(s)>>1 for plex frequencies of interest, we can obtain
If H(s)=1 , we have the desired result; that is, the output is equal to the input.
Therefore, the first advantage of a feedback syste