A sliding mode approach for active fault tolerant control and estimation

This proposal will consider the use of sliding mode concepts for active fault tolerant control and estimation in an 'active aircraft'. Sliding mode controllers have strong robustness properties to a certain class of uncertainty and have been shown to provide inherent fault tolerant control with respect to actuator faults. Sliding mode observers have an ability to reconstruct un-measurable signals within a dynamic system by appropriate scaling and filtering of the so-called 'equivalent output error injection'. This is a unique property of sliding mode observers which emanates from the fact that the introduction of a sliding motion forces the outputs of the observer to exactly track the plant measurements. Previous work has investigated the potential of sliding mode ideas for fault tolerant control in a civil aircraft with 'conventional' control surfaces. In an active control environment a key challenge will be to apply these ideas in a less traditional setting in which there is a proliferation of 'unconventional' actuators or sensor arrays. A problem formulation will be developed during the project so that the signals to be reconstructed represent unmeasured or unmeasurable external quantities which impact on the aircraft system - either externally (environmental conditions) or internally (associated with the airframe itself).