Inverse Nyquist array

Interaction among control loops in a multivariable system has been the subject of much research over the last 20 years. Various types of decouplers were explored to separate the loops. Rosenbrock presented the inverse Nyquist array (INA) to quantify the amount of interaction. Bristol, Shinskey, and McAvoy developed the relative gain array (RGA) as an index of loop interaction... 

Rosenbrock, H. H., "Design of Multivariable Control Systems Using the Inverse Nyquist Array," Proc. IEEE, 1969, 116, 1929. 

Although most existing columns do not have composition control at both ends, some columns are so equipped. Most of those reported in the literature (references 8 and 9, for example) apparently are not badly aSlicted with interaction. At least dual composition control was accomplished without decouplers. For a laboratory column Waller and associates studied six approaches to dual composition control, including those of modem control theory. Tyreus" discusses multivariable control of an industrial column whose design was performed via a technique called the inverse Nyquist array. 

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