Hedi Dhouibi

Diagnosis of hybrid systems through Observers and Timed Automata

This paper deals the diagnosis of hybrid systems. The objective is the integration of these two modeling tools: Observers and Timed Automata for the design of a global diagnostic model. The latter allows to detect and locate faults, minimize repair time and provide a reliable diagnosis and easily readable despite the complexity of the equipment. As regards methodology, the work consists in automate model generation procedures and failure indicators in formal form and interchangeable to integrate them into the diagnostic system. On the implementation plan, the results were applied to a hydraulic system with two tanks.

Multiple fault diagnosis using mathematical models

Multiple fault diagnosis is a challenging problem because the number of candidates grows exponentially in the number of faults. The multiple fault problems is important, since the single fault assumption can lead to incorrect or failed diagnoses when multiple faults occur. In this work, we present an approach for diagnosing multi faults based on model using techniques of detection and localization. We use an observer to generate residuals for a decision in a stage of monitoring and diagnostic system when disruptions or defects occur. Our contribution is the proposal of a diagnostic method when multiple faults type actuators or sensors affect the system.

Diagnostic and prognostic of hybrid dynamic systems: Modeling and RUL evaluation for two maintenance policies

In the industrial sector, maintenance plays a very important role in carrying out production by increasing system reliability and availability. Thee maintenance decision is based primarily on diagnostic modules, prognostics and decision support. Diagnostic consists of detection and isolation of faults, while prognostic consists of prediction of the remaining useful life of systems. Moreover, recent industrial systems are naturally hybrid: their dynamic behavior is both continuous and discrete. This paper presents an integrating architecture of diagnostic and prognostic in a hybrid dynamic system. Indeed, the diagnostic system is based on controlling task execution times during system operation. This method is based on a general modeling approach using hybrid automata. The model proposed is detailed by studying a two-tank system. To validate the model, a Stateflow controller is used. These failures are anticipated by a prognostics process based on a prediction of the remaining life for each component by taking maintenance policy into account. Two new methods are compared: ABAO (As Bad As Old) and AGAN (As Good As New), based on the type of repair strategy.

Modeling and Fault Diagnosis Using Mixed Approach: Hybrid Dynamical Systems with Unknown Disturbances

A hybrid dynamical system (HDS) results from the interaction between a continuous dynamics and a discrete. The continuous dynamics represents the system behaviour which may change from a functioning mode to another depending on the discrete dynamics. The HDS is often subject to disturbances arising from external phenomena due to the environment, or internal phenomena linked to changes in the system. This paper proposes a diagnosis approach of disturbed complex HDS by combining using State Observers and Timed Automata (TA). The proposed method combines the advantages of Observer and TA in order to obtain the best performance in the presence of disturbances, particularly in the fault location phase. Thus, for complex systems, the observer-based approach is used to generate fault indicators for fault detection and the fault isolation procedure consists in analysing the fault signatures matrix. The TA, which are commonly used in discrete event systems enables to take into account temporal aspects and to follow up the system dynamic evolution as well as fault propagation effects. To refine fault location, a diagnoser based on TA is built. The simulation results show the dynamic behaviour of the system variables with performance evaluation of the proposed fault diagnostic approach.

Using timed automata and fuzzy logic for diagnosis of multiple faults in DES

This paper proposes a design method of a support tool for detection and diagnosis of failures in discrete event systems (DES). The design of this diagnoser goes through three phases: an identification phase and finding paths and temporal parameters of the model describing the two modes of normal and faulty operation, a detection phase provided by the comparison and monitoring time operation and a location phase based on the combination of the temporal evolution of the parameters and thresholds exceeded technique. Our contribution lays in the application of this technique in the presence of faults arising simultaneously, sensors and actuators. The validation of the proposed approach is illustrated in a filling system through a simulation.

Diagnosis and prognosis of hybrid dynamic systems

System in which the dynamical behavior evolves based on the interaction between the continuous and discrete dynamics, present in the system, are called hybrid systems. For these systems, maintenance and repair are an increasing part of the total cost of final product. Efficient diagnosis and prognosis techniques have to be adopted to detect, isolate and anticipate faults. This paper presents a novel integrated framework for diagnosis and prognosis in a hybrid dynamic system. The formalism used for hybrid diagnosis is enriched in order to be able to follow the evolution of an aging law for each faults of the system.

Using mixed approach in modeling and multiple fault identification of hybrid systems

Despite the technological advances and progress in the industrial systems, the fault diagnosis of the system remains a very important task. Indeed, an effective diagnosis contributes to the improvement of the reliability and also to the decrease in maintenance costs. This paper presents an approach to diagnosis of hybrid systems thanks to the use of the Bond Graph, of Observer and Timed Automata. This approach allows to detect and locate not only simple faults but also multiple faults, to minimize repair time and to provide a reliable diagnosis and easily interpretable despite the complexity of the equipment. The proposed approach is validated by simulation tests to a two tanks hydraulic system.