Research On Transient Fault Recovery And Safety Control Of Networked Control System

Networked control system (NCS) has become the mainstream form of the automation industry, and the operational safety of them has gradually caused extensive concern. However, with the increasing scale and complexity, the threats of the transient faults brought up by the design flaws and the external interference are stood out to the operation safety of this type of system. To date, the systematic methods for the detection and recovery of transient faults are scarce. In this paper, a novel approach based on transient fault propagation analysis is proposed for the recovery and safety control of transient faults in NCS. In which, NCS is modeled by object-centered abstraction models and system-centered workflow models from the entire system knowledge, the fault propagation analysis is conducted based on the relationships among the elements of the models, and hierarchical fault detection and recovery strategies are provided to discover and recover transient faults in a limited area the fault influenced according to the transient fault effects, which is to ensure the system performance when the transient fault occurs. The main contents of this paper are summarized as follows:The causes and characteristics of transient faults in NCS are summarized firstly. After analyzing the requirements of the detection and the recovery of transient faults, the key technologies for transient fault detection and recovery are pointed out and the implementations of them are discussed. Besides, a close-loop control framework for the recovery and safety control of transient faults are recommended, which contains five steps as system monitoring, transient fault propagation analysis, transient fault detection, strategy-making for transient fault recovery and strategy-implementation.As a cornerstone for transient fault tolerance, the ontology-based fault propagation analysis approach is illustrated then. To make up the lack of modeling in existing fault propagation analysis approaches, the systematic models form ontological knowledge of NCS are proposed for analyzing transient fault propagation, namely, the function, behavior and structure models and workflow models. And from them, the fault effects and the effect traces are excavated by object-centered and system-centered ontology based fault propagation analysis. To verify the ontology-based fault propagation analysis approach, a simulation platform is developed to unify the two-aspect models from AADL (Architecture Analysis Design Language) and its extensions, and the efficiency of the proposed fault propagation analysis approach is validated by a case. Due to the characteristics of high occurrence rate, various manifestations, and difficulty detection about locations, the hierarchical detection scheme is proposed to discover the transient faults under the situation that they are hard to be located and their detection generally depends on the propagation effects. Considering the difference of the fault symptoms in the node level and in system level, parameter matches and model-based detections are employed to conduct the detection in node-level and system-level, in which the detectors are deployed according to the fault propagation analysis on the FBS models. And a networked control liquid mixer system which models are described by AADL is used to promise the effectiveness of the detection scheme.As a resource-constrained and time-constrained system, the recovery strategies for the transient faults in NCS are provided based on the fault propagation effect traces. And then an optimal process for multiple available recovery strategies is illustrated. In which, the recovery points are selected according to the fault propagation effects and traces, and the recovery strategy pool is established according to the data and control effects influenced by transient faults. The optimization algorithm is proposed based on schedulability analysis and recovery performance assessments. And with the simulation models of a simplified networked position control system, a case study is conducted to verify the effectiveness of the recovery methods.To verify the approach, a case of actual application is illustrated. Aiming at satisfying with the safety requirements of the tunnel construction wireless monitoring and control systems, the hierarchical transient fault detection and recovery scheme is drew out based on the methods mentioned above after analyzing the transient faults and their effects in the system. With a prototype system, different faults are injected to the nodes for verifying the safety of the system, and the results show the effectiveness of the recovery design, by which the operation safety of the system is promoting.The full text of this paper is summarized at last, the deficiencies are explained and the future works of the recovery and safety control technologies for transient faults in NCS are prospected.