Two input-output pairing strategies based on linear quadratic Gaussian (LQG) control are suggested. In the first strategy, denoted linear quadratic interaction index (LQII), input-output pairing suggestions are found from a minimization of the output signal variance. This index not only guides to what pairing should be tried, it also gives a direct measure of how much better a full MIMO controller can perform. The second proposed interaction measure, denoted integrating linear quadratic index array (ILQIA), focuses more on the low frequency behaviour of the considered plant, such as load disturbances. The strategies are used to compare the expected performance of decentralized control structures in some illustrative examples. The pairing suggestions are compared with the recommendations previously obtained using other interaction measures such as the relative gain array (RGA), the Hankel interaction index array (HIIA) and the participation matrix (PM). The new strategies are easy to interpret and give suitable pairing recommendations where other methods may fail.
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