Fault tolerant control using sliding modes with on-line control allocation

Abstract

Sliding Mode Control Sliding mode control was conceived in the USSR during the 1950's and spread to the 'west' after the end of the 'cold war'. Sliding mode control (SMC) is a nonlinear type of control methodology and a special case of variable structure control. An interesting account of early developments in this area appears in [26]. SMC is a robust control methodology and it is quite unique compared to other controller design paradigms, since the performance of the controller depends on the design of the 'sliding surface' and not the state tracking directly. The idea of sliding mode control is to force the trajectory of the states onto a predefined surface in the state space. Once reached (usually in finite time), the states are forced to remain on that surface for all subsequent time. Sliding mode control has an inherent robustness property to a certain type of uncertainty which makes SMC a strong candidate for passive fault tolerant control (FTC). Recent accounts of the theory associated with sliding modes appear in [14, 27]. Sliding mode control systems are, in theory, completely insensitive to a class of uncertainty called matched uncertainty [14]. This represents uncertainty which occurs in the channels associated with the control inputs. Intuitively this suggests SMC schemes should inherently have passive FTC capability with respect to actuator faults. The work by Hess & Wells [19] argues that sliding mode control has the potential to become an alternative to reconfigurable control and has the ability to maintain the required performance without requiring fault detection and isolation (FDI). © 2010 Springer-Verlag Berlin Heidelberg.