Sliding-mode fault-tolerant control using the control allocation scheme

This paper is devoted to the design of a novel fault-tolerant control (FTC) using the combination of a robust sliding-mode control (SMC) strategy and a control allocation (CA) algorithm, referred to as a CA-based sliding-mode FTC (SMFTC). The proposed SMFTC can also be considered a modular-design control strategy. In this approach, first, a high-level SMC, designed without detailed knowledge of systems' actuators/effectors, commands a vector of virtual control signals to meet the overall control objectives. Then, a CA algorithm distributes the virtual control efforts among the healthy actuators/effectors using the real-time information obtained from a fault detection and reconstruction mechanism. As the underlying system is not assumed to have a rank-deficient input matrix, the control allocator module is visible to the SMC module resulting in an uncertainty. Hence, the virtual control, in this scheme, is designed to be robust against uncertainties emanating from the visibility of the control allocator to the controller and imperfections in the estimated effectiveness gain. The proposed CA-based SMFTC scheme is a unified FTC, which does not need to reconfigure the control system in the case of actuator fault or failure. Additionally, to cope with actuator saturation limits, a novel redistributed pseudoinverse-based CA mechanism is proposed. The effectiveness of the proposed schemes is discussed with a numerical example.