A New Output Integral Sliding Mode Fault-Tolerant Control and Fault Estimation Scheme for Uncertain Systems

This paper describes a new fault-tolerant control technique for over-actuated uncertain linear systems that compensates for actuator faults and failures using an output integral sliding mode-based control allocation strategy. An observer-based fault estimation unit is first proposed to estimate the system states and the actuator&#x2019;s effectiveness level. Based on the estimated state&#x2019;s information, a nominal virtual control law is created to achieve the desired specification of the perturbed system. A nonlinear output integral sliding manifold is incorporated with the nominal virtual control law that provides resilience to the closed-loop system against the uncertainty caused by the actuator&#x2019;s faults and failure, states estimation error, and fault estimation error. Finally, depending on anticipated actuator efficacy from the fault estimation unit, the control allocation reroutes the virtual control input signals among the redundant actuators. A small-gain theorem is used to demonstrate the augmented closed-loop system stability. The observer and controller gains are synthesized using the linear matrix inequality technique. Finally, simulations on an aircraft system are performed to verify the efficacy of the suggested FTC technique. Compared with the existing work, the proposed approach is better able to handle actuator redundancy in faulty conditions and cater to the fault estimation error up to a certain level. <italic>Note to Practitioners</italic>&#x2014;The aim of this paper is to address the reliability issues of industrial systems that contain sufficient input redundancy and are particularly designed to tolerate the faults and failures issues during the system operation. Existing fault-tolerant control schemes based on control allocations have limitations in terms of effective utilization of actuator redundancy, handling of fault estimation error, and applicability of reconfigurable control law. In this paper, we developed a fault-tolerant control strategy that is capable of addressing all the aforementioned concerns. The output integral sliding mode control-based control allocation scheme, proposed in this paper, is applicable to the class of over-actuated systems. The reconfiguration of fault-tolerant control law based on the estimated states and fault information is capable to cover a wider class of faults and failures while maintaining robustness against the system dynamics and uncertainty. The control reconfiguration is equally applicable to the class of systems that contains both rank-deficient and in-deficient input distribution matrices. The proposed scheme assumed the bounded external disturbance, therefore in future work, the adaptive law will be incorporated with sliding mode controller and results will be extended to a generalized class of affine nonlinear systems.