Sven Bodenburg

Experimental evaluation of a fault-tolerant plug-and-play controller

Networked control systems use the network connection to exchange data and signals. In plug-and-play control the communication of control algorithms and system models over a shared network is concerned with the intention to adjust control laws automatically after the occurrence of changes in the plant structure or in the control objectives. An application scenario is the break down of a sensor or an actuator as studied in fault-tolerant control. This paper investigates such a situation in the sense of plug-and-play control. The diagnostic task and reconfiguration task are separated and assigned to predestined computational units: an onboard unit allocated at the plant with access to the plant signal and a remote off-board unit concerning the expensive computation. The onboard diagnostic unit detects and identifies the failure at runtime and transmits the model of the faulty plant to the offboard reconfiguration unit over a shared network. Using the reconfiguration strategy of the virtual sensor and virtual actuator the reconfigured controller is automatically designed and transmitted to the control station to replace the original control algorithm. In the whole sequence no human interaction is necessary. The main contributions of this paper are the combination of a diagnosis method and a reconfiguration method to perform a completely automated sequence, the implementation of this concept and the evaluation by experiments on a thermal fluid process.

Plug-and-play control of interconnected systems with a changing number of subsystems

This paper proposes a new method for designing decentralised controllers of interconnected systems with a changing number of subsystems. When a new subsystem is added to an existing interconnected system, the control station of this subsystem should be designed by the design agent of this new subsystem based only on local information and some gathered model information over the network. As the dynamics of the overall system depends upon all existing subsystems, the main difficulty of this design problem is to ensure the stability of the overall interconnected system based on limited information and, furthermore, to evaluate the overall input-output performance locally. The main results of this paper are conditions that can be used to analyse the overall system by means of a limited amount of model information. As a consequence, the new subsystem can be “plugged in”, its design agent collects relevant model information over the network to check the conditions and the new control station “plays” together with the existing controllers. The method is illustrated by its application to a multizone furnace for crystal growth.

Plug-and-Play Control — Definition and Realisation in MATLAB

Abstract Technological plants are live systems which are subject to persistent changes. For instance, instrumentations fail or are added, operation modes are changed or communication network topologies are modified. This paper presents a concept to adjust control algorithms to new configurations of the closed loop. The introduced Plug-and-Play Control utilises a communication network to exchange control algorithms between physically separated components. This paper elucidates the concept and describes a realisation of the algorithm exchange by remote procedure calls and model construction functions provided by MATLAB. Experiments on a fluid process illustrate the performance of Plug-and-Play Control and point out the necessary application requirements. Zusammenfassung Technische Anlagen unterliegen während ihrer Laufzeit ständigen Veränderungen. So fallen z. B. Sensoren aus oder kommen neu hinzu, oder es wird zwischen verschiedenen Arbeitsmodi oder Netzwerktopologien umgeschaltet. In diesem Beitrag wird ein Konzept vorgestellt, um Regelungsalgorithmen an die neuen Systemkonfigurationen anzupassen. Plug-and-Play Control nutzt dabei ein Kommunikationsnetzwerk, um Regelungsalgorithmen zwischen getrennten Komponenten auszutauschen. Der Beitrag erläutert das Konzept und zeigt eine Realisierung der Regelungsalgorithmen mit Hilfe von entfernten Prozeduraufrufen und model construction Funktionen von MATLAB. Abschließend wird über die Erprobung des Konzepts an einem Demonstrationsprozess berichtet.

A design method for plug-and-play control of large-scale systems with a varying number of subsystems

This paper presents an online procedure to design decentralised controllers for a large-scale system when subsystems are added or removed. As the dynamics of all subsystems depend upon each other through the physical couplings, the main challenge of the controller design is to ensure global I/O stability and a required I/O performance of the overall large-scale system. For this purpose, plug-and-play control is devoted to the following two issues: first, the set-up of a model to describe the global system behaviour by limited model information only. Second, the design of the control station of the added subsystem based on this model with respect to local design requirements in order to guarantee the satisfaction of global system specifications. Furthermore, it is allowed to adjust neighbouring control stations to ensure a good overall system performance neighbouring subsystems are allowed to adjust their control stations. As a consequence, a new subsystem can be “plugged-in” and automatically “plays” together with the existing subsystems to guarantee a global performance. The overall procedure is experimentally evaluated by application to a thermo-fluid plant.

Plug-and-Play control - Theory and implementation

Technological systems are live systems which are subject to persistent changes. For instance, instrumentations fail or are added, operation modes are changed or communication network topologies are modified. This paper presents a concept to adjust control laws and reference trajectory models to new configurations of the closed loop. The introduced Plug-and-Play Control utilises a communication network to exchange control algorithms between physically separated components. This paper elucidates the concept and describes an implementation of the algorithm exchange by remote procedure calls and model construction functions provided by MATLAB. Experiments on a fluid process illustrate the performance of Plug-and-Play Control and point out the necessary application requirements.

Cooperative reconfiguration of locally interconnected systems with limited model information: A plug-and-play approach

This paper proposes a cooperative reconfiguration approach after faults have occurred in a locally interconnected system. Although the impact of the fault has effects to all other subsystems through the physical couplings, only the control station of the faulty subsystem should be reconfigured together with neighbouring control stations. The focus of this paper is on the organisation of the reconfiguration process without a central coordinator. Design agents exist for every subsystem which store the model of the respective subsystem. A local search algorithm is presented for the design agent of the faulty subsystem to find supportive design agents and to procure their local models to set-up an adequate model describing the faulty subsystem under the influence of the physical interactions. Furthermore, cooperative reconfiguration conditions are proposed to recover the global performance by the reconfiguration of the assigned control stations based on the limited model information. As a consequence, after the “plug-in” of the control stations into the hardware they “play” together to cooperatively act against the fault. This plug-and-play reconfiguration method is applied to a multizone furnace.

Plug-and-play diagnosis of locally interconnected systems with limited model information

This paper proposes a novel method to organise the design of a diagnostic unit that should detect faults in a decentralised controlled interconnected system. A fault at a subsystem should be detected by a local model-based diagnostic unit that only evaluates the local signals of the faulty subsystem. The focus of this paper is on the organisation of the design process of the diagnostic unit without a central coordinator. Design agents exist for each of the subsystems which store the subsystem model. A local algorithm is presented to gather models from neighbouring design agents with the aim to set-up a model which describes the behaviour of the faulty subsystem used by the diagnostic unit. Based on a proposed detectability condition the amount of model information is determined in order to guarantee the detection of the fault. As a consequence, with the plug-in of the diagnostic unit into the control hardware, the detection of the fault is ensured. The proposed plug-and-play diagnosis is applied to a multizone furnace.

A local search algorithm for plug-and-play reconfiguration of interconnected systems

Abstract This paper proposes a novel method to organise the reconfiguration process of decentralised controllers after actuator failures have occurred in an interconnected system. If an actuator fails in a subsystem, only the corresponding control station should be reconfigured, although the fault has effects on other subsystems through the physical couplings. The focus of this paper is on the organisation of the reconfiguration process without a central coordinator. Design agents exist for each of the subsystems which store the subsystem model. A local algorithm is presented to gather models from neighbouring design agents with the aim to set-up a model which describes the behaviour of the faulty subsystem including its neighbours. Furthermore, local reconfiguration conditions are proposed to design a virtual actuator so as to guarantee stability of the overall system. As a consequence, the design agents “play” together to gather the model of the faulty subsystem before the reconfigured control station is “plugged-in” the control hardware. Plug-and-play reconfiguration is illustrated by an interconnected tank system.