H_∞-based model following method in autolanding systems

Probably the most important part during a flight is the landing phase because most of the accidents occur in this phase. Automatic landing systems (ALS) take over the control during this phase to avoid potential pilot-induced risks. However, some external disturbances such as windshear can jeopardize the safe landing. In this paper, the flare part of ALS is handled in a different way. A combination of some useful design methods is brought together to improve the performance of the conventional ALS even under severe weather conditions. Model following method is combined with the H_∞ synthesis method to find out the optimal solution for a given cost function. Resultant H_∞ optimal control problem is solved using Linear Matrix Inequalities (LMIs) and then a dynamic controller is constructed. On the other hand, the overall system is formed into P-K configuration, thus the system can be reconfigured easily when there exists a change in the system such as addition or removal of disturbance, noise and so on. We achieved significant performance on the system without any disturbance. In addition to that, the robustness takes an important role for the flight systems and needs to be handled correctly. Therefore, two kinds of windshear are taken care of and their effects minimized in a way that the tracking performance remains unaffected. Thus, highly considerable results are obtained using the proposed method even under severe weather conditions.