Improved neural-aided sliding mode controller for autolanding under actuator failures and severe winds

In this paper, the fault tolerant capabilities of the neural aided sliding mode controller for autolanding under actuator failures and severe winds developed earlier are improved significantly by incorporating a novel anti-windup strategy and a phase compensation scheme. This controller further increases the size of the fault tolerance envelope for various types of control surface stuck faults and provides complete coverage at every point within the envelope boundaries. Earlier work by the authors showed the existence of a neural-aided sliding mode controller which could handle a wide range of actuator stuck faults. One of the major drawbacks of this earlier controller is that it does not ensure that all points within the range of minimum and maximum bounds of the fault tolerance envelope are covered. The anti-windup proposed in this paper is a generalization of the scheme used for proportional-derivative-integral controllers to the cascaded trajectory following controllers designed by the authors. This scheme can handle requirements of state limiting as well as multiple redundant control surface saturation. The proposed anti-wind up design is a simplification over the command filter approach used for adaptive backstepping. The approach is demonstrated for a fixed-wing aircraft undergoing unknown actuator stuck failures and subject to severe wind disturbances during autolanding. An example of three control surface failures (both ailerons and rudder) handled by this controller is also presented.