Design of a helicopter output feedback control law using modal and structured-robustness techniques

A procedure is described for designing output-feedback control laws based on a mixture of modal and frequency domain approaches. In the first step of this procedure, a state-feedback control law is synthesized. The modal approaches are used for dealing with dynamic performances whilst the robustness is optimized by using frequency domain criteria. Note that the robustness measure adopted here is based on structured singular values in such a way that not only the stability but also the damping ratio are robust against uncertainties. In the second step, a minimal-order observer output-feedback control law, defined in an eigenstructure setting, is performed in such a way that both modal and robustness properties are recovered. The robustness of the technique is illustrated using a realistic helicopter problem.