A new tool for the analysis of modal control laws: the `pole attractors´

In the design of modal control laws, the choice of the closed-loop eigenvalues is emphasized. In the output feedback case, this choice becomes more and more crucial as the degrees of freedom appearing in the control design are decreasing. Then, the assignment of right eigenvectors often induces weakly observable poles. The reluctance of the feedback to move these poles away can be represented by some attracting zones of the complex plane called pole attractors. The pole attractors are presently geometrically defined and their attraction is quantified. The usefulness of such a concept for synthesizing modal control laws is illustrated on a realistic aircraft autopilot design