Design and Analysis of an Integral Sliding Mode Fault Tolerant Control Scheme

Abstract

One of the important elements necessary for achieving FTC, is the availability of redundant actuators. This provides increased freedom in terms of controller design to mitigate the effects of faults and failures. Although these ‘redundant’ actuators are often designed for different purposes, in the event of an emergency (such as faults or failures to the primary actuators), they can be used to retain satisfactory performance. This chapter is concerned with the development of fault tolerant controllers for a class of linear systems with redundant actuators. This redundancy will be exploited to achieve tolerance to a specified class of faults/failures, which includes the possibility of total failure to certain primary actuators. Furthermore the precise class of total actuator failure which can be accommodated is identified. The idea is to design an ISM controller based on a ‘virtual’ system. The associated virtual control signal is then translated into actual control surface deflections using CA. This distinctive design strategy is beneficial since only one controller is designed to cover a wide range of fault/failure cases, while the CA redistributes the signals to the available ‘healthy’ actuators. The scheme uses the measured or estimated effectiveness level of the actuators to redistribute the control effort during faults/failures to maintain close to nominal closed-loop performance without reconfiguring the controller. The relative error in the estimation of the actuator effectiveness gains is also taken into consideration. The stability test in this chapter allows an effective synthesis procedure to be employed using Linear Matrix Inequality (LMI) optimisation to compute the parameters involved in the control law. The effectiveness of the scheme against faults or failures is tested in simulation based on a large transport aircraft model.