Integral Sliding Mode Fault Tolerant Control Schemes with Control Allocation

The key attribute of a Fault Tolerant Control (FTC) system is to maintain overall system stability and acceptable performance in the face of faults and failures within the system. In this thesis new integral sliding mode (ISM) control allocation schemes for FTC are proposed, which have the potential to maintain the nominal fault free performance for the entire system response, in the face of actuator faults and even complete failures of certain actuators. The incorporation of ISM within a control allocation framework uses the measured or estimated values of the actuator effectiveness levels to redistribute the control effort among the healthy actuators to maintain closed-loop stability. This combination allows one controller to be used in both fault free as well as in fault or failure situations. A fault tolerant control allocation scheme which relies on an a posteri approach, building on an existing state feedback controller designed using only the primary actuators, is also proposed. Retro-fitting of an ISM scheme to an existing feedback controller is advantageous from an industrial perspective, because fault tolerance can be introduced without changing the existing control loops. To deal with a wider range of operating conditions, the fault tolerant features of ISM are also extended to linear parameter varying systems. A FTC scheme considering only the availability of measured system outputs is also proposed, where now the feedback controller design is based on the estimated states. In each of the ISM fault tolerant schemes proposed, a rigorous closed-loop analysis is carried out to ensure the stability of the sliding motion in the face of faults or failures. A high fidelity benchmark model of a large transport aircraft is used to demonstrate the efficacy of the new FTC schemes.