In this paper, a robust unknown input observer (UIO) for the joint state and fault estimation in discrete-time Takagi-Sugeno (TS) systems is presented. The proposed robust UIO, by applying the H∞ framework, leads to a less restrictive design procedure with respect to recent results found in the literature. The resulting design procedure aims at achieving a prescribed attenuation level with respect to the exogenous disturbances, while obtaining at the same time the convergence of the observer with a desired bound on the decay rate. An extension to the case of unmeasurable premise variables is also provided. Since the design conditions reduce to a set of linear matrix inequalities (LMIs), that can be solved efficiently using the available software, an evident advantage of the proposed approach is its simplicity. The final part of the paper presents an academic example and a real application to a multi-tank system, which exhibit clearly the performance and effectiveness of the proposed strategy.
This paper addresses the problem of fault estimation in wind turbines using a joint fault and state estimation scheme. The scheme assumes a set of possible faults affecting the dynamics of the wind turbine. Then, a joint process fault and state estimation scheme is developed considering that process disturbances and sensor noises are unknown but bounded in an ellipsoid. Two subcases are considered depending of the satisfaction of a rank condition. The proposed scheme is applied to a well-known wind turbine benchmark proposed in a international competition. From the results obtained, a satisfactory fault estimation is achieves against a set of pre-defined fault scenarios.
This paper aims at providing two competitive solutions to the problem of estimating state as well as sensor and actuator faults. The development starts with a common system description, which is transformed into a nonlinear descriptor system-like form. The appealing property of such an approach is that the sensor fault is eliminated from the output equation by suitably extending the state vector. Subsequently, a novel fault estimation scheme is proposed and its error dynamics are carefully described. Having such a unified framework, two competitive design procedures are proposed. One is based on the celebrated H ∞ while the other employs the quadratic boundedness strategy. With the estimators, the paper provides a unified framework for assessing the uncertainty of the resulting estimates in the form of uncertainty intervals. Thus, both solutions can be compared from the theoretical perspective. The final part of the paper contains a numerical simulation example concerning a twin-rotor system that clearly shows the comparison and performance of the above approaches. Subsequently, an experimental study concerning a multi-tank system using real data is reported.
For isotropic materials with a significant fraction of micro-pores, the cumulative water intake per unit of inflow surface area typically yields a linear function of the square root of time elapse. The authors postulate that this dependence has a limited range of validity. The validity of this approximation starts from an initial period that is inversely proportional to the rate of water intake and ends much before the material reaches the capillary moisture content. Experimental investigation presented here uses a differential presentation of the cumulative water inflow and clearly indicates that material such as calcium silicate or brick belong to a broad class of materials characterized by a constant water absorption coefficient (A-coefficient). Initial period varies from ½ to 4 minutes. On the other hand, materials with a multiple pore-system such as an Aerated Autoclaved Concrete (AAC) may display a systematically varying A-coefficient. Authors propose a test procedure limited to 1-hour duration that can be used to derive a practical and reproducible value of A-coefficient.
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