This special issue addresses fault diagnosis and fault tolerant control, two fields in which research is very active, being motivated by many real life applications, e.g. flight control systems, chemical systems, power systems and other safety critical systems, in order to enhance the reliability and fault tolerant capability of practical systems. Faults that occur in sensors and actuators, in process hardware and software components, in human operators’ decisions (not even speaking of transgressions), may have catastrophic consequences, because not only are nominal specifications no longer fulfilled, but also these faults may result in heavy damage to the operators, the system and the environment.
Fault diagnosis has been the subject of intensive research for more than 30 years, and fruitful results have been reported. The fault tolerant control design is an emerging topic, whose foundation is not yet completely stabilized, but whose understanding is getting deeper and deeper. Several journals have published special issues on fault diagnosis and fault tolerant control in the last two years, showing the importance of this research field.
The present issue gathers some of the best international specialists, and reveals new trends in fault diagnosis and fault tolerate control for linear, nonlinear, hybrid and networked control systems. The most significant research problems are studied that are currently tackled by the control community: activated fault diagnosis, network-based fault diagnosis, and fault tolerant control under actuator outages, friction and supervisory fault tolerant control.
The first paper is by J. Stoustrup and H. Niemann, in which two active fault diagnosis methods for additive, parametric or multiplicative faults are proposed. Both methods are based on controller reconfiguration. The first method is based on a number of alternate observers, each designed to be sensitive to one or more faults. Periodically, the observer part of the controller is changed into the sequence of fault sensitive observers. The second method periodically adds a term to the controller that for a short period of time renders the system unstable if a fault has occurred, which facilitates rapid fault detection.
Three papers have considered communication network based fault diagnosis issues: The work, conducted by X. He, Z. Wang, Y. D. Ji and D. H. Zhou, provided H-infinity fault detection filters for a class of discrete-time linear systems in network environment, where the plant and its controller are located at diverse places, and are connected over network. In the paper by Y. Zhao and H. Gao, the authors investigated the fault detection problem for continuous time systems with network communication links. Three types of incomplete measurements are simultaneously addressed. W. Li and S. Ding studied the remote fault detection problem over unreliable communication channels encountering bit errors and data losses, where data transmissions could be centralized and decentralized. The proposed method is based on model matching approaches.
Three papers have tackled some difficult and important problems in fault tolerant control field: In the work by M. Staroswiecki and D. Berdjag, the authors introduced a general frame where several controllers are designed, each of them being dedicated to a subset of faults. This frame includes the classical passive and active strategies, and extends the reliable control strategy. Its performance evaluation and optimization is carried out by setting a decision frame in which the trade-off between the FTC complexity and the probability to face a non recoverable situation is explicitly addressed. The paper by R. Patton, D. Putra and S. Klinkhieo proposed a new approach to friction compensation which is based on the theory of robust fault estimation. The friction forces are viewed as actuator faults with time-varying characteristics to be estimated and compensated within a fault tolerant control scheme, so that the limitations arising from the use of a friction model are obviated. The work by B. Jiang, H. Yang and P. Shi discussed the fault tolerant control issue from an energy point of view. The dissipativity theory and switching control theory are introduced into the design of fault detection and a unique scheme that simultaneously performs fault isolation and fault tolerant control. The proposed framework relies on a simple dissipativity-based switching among a family of pre-computed candidate controllers without any additional model or filter.
We hope this special issue will provide a useful reference for people working in the diagnosis and fault tolerant control areas, and help academics, scientists and engineers explore new methodologies in both theory investigation and practical applications.
We would like to thank all the contributors and reviewers for their excellent work and timely support, which have made the special issue possible and successful. In particular, we are very grateful to Professor Peter Fleming, EIC of IJSS, for giving us the opportunity to edit this special issue, and all the very helpful advice during the process.