Nichols plot
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TheNichols plotis aplotused insignal processingandcontrol design,named after American engineerNathaniel B. Nichols.[1][2][3]
Use in control design
[edit]Given atransfer function,
with theclosed-loop transfer functiondefined as,
the Nichols plots displaysversus.Loci of constantandare overlaid to allow the designer to obtain the closed loop transfer function directly from the open loop transfer function. Thus, the frequencyis the parameter along the curve. This plot may be compared to theBode plotin which the two inter-related graphs -versusandversus) - are plotted.
Infeedback control design,the plot is useful for assessing the stability and robustness of a linear system. This application of the Nichols plot is central to thequantitative feedback theory (QFT)of Horowitz and Sidi, which is a well known method for robust control system design.
In most cases,refers to the phase of the system's response. Although similar to aNyquist plot,a Nichols plot is plotted in aCartesian coordinate systemwhile a Nyquist plot is plotted in aPolar coordinate system.
See also
[edit]References
[edit]- ^Isaac M. Howowitz,Synthesis of Feedback Systems,Academic Press, 1963, Lib Congress 63-12033 p. 194-198
- ^Boris J. Lurie and Paul J. Enright,Classical Feedback Control,Marcel Dekker, 2000,ISBN0-8247-0370-7p. 10
- ^Allen Stubberud, Ivan Williams, and Joseph DeStefano,Shaums Outline Feedback and Control Systems,McGraw-Hill, 1995,ISBN0-07-017052-5ch. 17