A fault tolerant control for nonlinear systems with simultaneous actuator and sensor faults. Application to a CSTR

Abstract

In this paper, a novel active fault tolerant tracking control is proposed for nonlinear systems described by Takagi-Sugeno model, the considered systems are affected by simultaneous actuator and sensor faults and have unmeasurable premise variables and depending on the acting faults. Firstly, a mathematical transformation is used to transform the faulty system to an augmented system where all the faults appears as an actuator faults. Secondly, an H-infinity control is conceived to ensure the trajectory tracking in the fault free situation. Then, the system state and the faults are estimated from a proportional integral observer with unknown input (PIUI). The proposed fault tolerant control law is based on the use of the robust tracking control implemented for the system in fault-free case and an additional term related to the estimated faults. The objective is to minimize the deviation of the faulty system compared to the healthy one, even in the presence of actuator and sensor faults. Thus, sufficient conditions are studied with the Lyapunov theory and L2 optimization, and presented in terms of LMIs. Finally, to access the effectiveness of the proposed strategy, a numerical simulation is carried out on a Continuous Stirred Tank Reactor (CSTR), and a comparison with the existing results is made.