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

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