A two-feedback-loop robust helicopter controller based on eigenspace techniques and H∞ synthesis

The design of a robust helicopter control law is described. A two-loop structured feedback is proposed. The first loop is static and computed using eigenstructure assignment. Its objective is to provide decoupling between the different axes. The second loop is designed using H_∞ synthesis. The objective of the outer loop is to improve performance in terms of minimizing the error between the reference and output signals and robustness against additive perturbations due to plant uncertainties. This procedure allows the compensator order to be reduced with respect to more classically derived H_∞ solutions