Experimental evaluation of input designs for multiple-input multiple-output open-loop system identification

A procedure is presented for input design in MIMO system identification that explicitly takes system gain directionality into account. For ill-conditioned systems, the dynamics tend to be different in the various gain directions. The advantage of this procedure is that the dynamics in all gain directions can be identified. The procedure can be used for any type of excitation signal, e.g., step, PRBS or multi-sinusoidal signals. The superiority of the proposed input designs over more standard designs is demonstrated on a pilot-scale distillation column. The main conclusion of the study is that it is crucial that the various gain directions in a MIMO system are properly excited. The type of input signal (e.g., step or PRBS), or the way of exciting the gain directions, appears to be less important.