Robust state and sensor fault estimation for switched nonlinear systems based on asynchronous switched fuzzy observers

This article aims to address state and sensor fault estimation issue for a class of continuous-time nonlinear switched systems, modelled as Takagi-Sugeno (T-S) models with nonlinear consequent parts and subject to L2$$ {L}_2 $$ norm bounded disturbances. This modelling approach helps to prevent Unmeasured Premise Variables (UPVs) problem. The primary contribution of this study consists of proposing robust H infinity$$ {H}_{\infty } $$ asynchronous switched observers to simultaneously estimate state and sensor faults under state-dependent switching. Based on a candidate multiple Lyapunov function, the design of the proposed observer is formulated in terms of Linear Matrix Inequalities (LMIs) conditions. These conditions are dwell-time-independent and less conservative compared with similar previous studies, thanks to some usual relaxation techniques and the incremental quadratic constraints applied on unmeasured nonlinear consequent parts. Another contribution consists to perform the estimation of the attraction domain of the estimation error using an optimization procedure. In order to illustrate the effectiveness of the proposed design approach, two simulation examples are considered. The first one concerns the conservatism reduction brought by our proposal compared with previous studies, while the second one is dedicated to show through an illustrative example the performance of the proposed switched T-S observers under mismatching switching laws.