Fault tolerant control using virtual actuators and set-separation detection principles

In this paper we combine a set-separation approach to fault detection and identification (FDI), recently proposed by the authors, with the virtual actuator approach to controller reconfiguration of Steffen and Lunze. The FDI approach is based on the separation of sets that characterize the system operation under different actuator fault situations that can occur in the plant. The derivation of these sets takes into account the closed-loop system reconfigured by means of the virtual actuator under all considered actuator faults. Analytic conditions in terms of closed-loop system parameters and bounds on external signals can be deduced from the required set separation which, in turn, guarantees closed-loop stability, setpoint tracking, and optimal performance properties of the scheme under all considered fault situations. Thus, the main contribution of this paper is twofold. First, it provides an integrated strategy for fault tolerant control by adapting two existing techniques for FDI and for controller reconfiguration to work in combined form. Second, and more importantly, it endows the resulting combined scheme with guaranteed closed-loop stability, setpoint tracking and optimal performance properties under actuator faults and in the presence of disturbances