Networked control with delay measurement and estimation

As future industrial communication network solutions move towards industrial Ethernet based solutions, monitoring and control of network parameters and control of the network will gain more attention than previously in order to achieve unperturbed performance. The main challenges in implementation of Ethernet based solutions in control applications come from the fact that the performance of the network is priory nondeterministic and may change according to the load in the network. Respectively, this perturbed operation of the communication network may affect on efficiency and performance of the control application. This work focuses on performance improvement of a control application that is controlled over a switched Ethernet network. In such networks main network parameter that may pose perturbation in performance is the network-induced delay. With novel network instrumentation and network performance estimation methods the behavior of the network-induced delay in the switched Ethernet network is described. The outputs of these methods are used in the control strategies to compensate for the deterious effect of the network. First, a method for measuring the network information, particularly the network-induced transmission delay, is presented. Next, this information is utilized in control design. Two control approaches are developed, which differ with respect to the time-variant behavior of the delay measurements. A Smith predictor based approach is proposed for the case where network time delay variation is low, and polynomial system based time variant controller and observer design is proposed for the case where time variation is high. Second, methods for estimating the network-induced transmission delay, is presented and utilized in control design. Two control approaches based on robust control theory are developed, which differ with respect to ability to take into account in addition of delay variation also other uncertainty sources, such as model uncertainty and measurement errors. The developed control designs are tested with simulations as well as on the experimental platform. From the results it is clear that utilization of the methods improve performance of the application. From the results it is also clear that no single method is suitable for all the cases, but the choice should be based on detail investigation of available instrumentation, magnitude of network delay variation, and uncertainty sources coming from the process

Use of upper bound delay estimate in stability analysis and robust control compensation in networked control systems

Recent interest in networked control systems (NCS) has instigated research in various areas of both communication networks and control. The analysis of NCS has often been performed either from the network, or the control point of view and not many papers exist were the analysis of both is done in the same context. Here a simple overall analysis is presented. In the paper the procedure of obtaining the upper bound delay value in the switched Ethernet network is proposed and the obtained delay estimate is used in stability analysis of the feedback loop and in the control compensation. The upper bound delay algorithm is based on the network calculus theory, the stability analysis uses the small gain theorem, and control compensating strategy is based on Smith predictor, where however the upper bound delay is utilised in obtaining the delay estimate.Comment: 6 page

Control compensation based on upper bound delay in networked control systems

Recent interest in networked control systems (NCS) has instigated research in both communication networks and control. Analysis of NCSs has usually been performed from either the network or the control point of view, but not many papers exist where the analysis of both is done in the same context. In this paper an overall analysis of the networked control system is presented. First, the procedure of obtaining the upper bound delay value for packet transmission in the switched Ethernet network is presented. Next, the obtained delay estimate is utilised in delay compensation for improving the Quality of Performance (QoP) of the control systems. The presented upper bound delay algorithm applies ideas from network calculus theory. For the improvement of QoP, two delay compensation strategies, the Smith predictor based and the robust control based delay compensation strategies, are presented and compared.Comment: 6 page

Säätöpiirien suorituskykyindeksien muuttaminen taloudellisiksi suureiksi

Tyypillisessä prosessiteollisuuden tehtaassa on satoja säätöpiirejä, joista tutkimusten mukaan suuri osa toimii huonosti. Yhtenä syynä tähän on pidetty säätöpiirien virittämiskäytäntöä. Säätöpiirit yleensä viritetään toimimaan optimaalisesta tietyille toimintaolosuhteille ja viritys on tapahtunut käyttöönoton yhteydessä. Virityksen jälkeen operaattoreilla ei ole ollut tietoa säätöpiirien suorituskyvystä. Viime aikoina on aktiivisesti tutkittu ja sovellettu käytäntöön säätöpiirien suorituskykyindeksejä säätöpiirien tilan monitorointiin. Kehitetyt indeksit ovat kuitenkin matemaattisia, ja niiden tulkitseminen vaatii taustatietoa. Tästä syystä tehtailla suorituskykyindeksien käyttöönotto on ollut hidasta. Työn tavoitteena on ollut muuttaa säätöpiirien suorituskykyindeksit taloudellisuussuureiksi, jolloin indeksien tulkittavuus helpottuisi. Työn kirjallisuusosassa esitetään lyhyesti säätöpiirien suorituskykyindekseihin liittyvä teoria. Tämän jälkeen esitetään kirjallisuudessa ja kaupallisissa ohjelmistoissa esitetyt suorituskykyindeksien muuntamistavat. Lisäksi tarkastellaan yleisiä säädön taloudellisuuden arviointimenetelmiä. Työn kokeellisessa osassa tarkastellaan säätöpiirien suorituskykyindeksien taloudellisuuksia Siilinjärven ja Pyhäsalmen rikastamoilta saadulla testidatalla. Lopuksi on ehdotettu analysointistrategia, jolla voidaan arvioida säätöpiirien taloudellisuuksia suorituskykyindeksien avulla

New time variant control system design for networked control systems

Peer reviewe

DATA BASED FAULT DETECTION OF THE ONLINE ANALYSERS IN A DEAROMATISATION PROCESS

Fault diagnosis methods based on process history data have been studied widely in recent years, and several successful industrial applications have been reported. In this paper a comparison of four monitoring methods, PCA, PLS, subspace identification and self-organising maps, for fault detection of the online analysers in a dearomatisation process is presented. The effectiveness of different statistical process monitoring methods in FDI of the online analysers is evaluated on the basis of a large number of simulation studies. Finally the results are presented and discussed.Peer reviewe

Evaluation of control performance: methods, monitoring tool and applications in a flotation plant

Evaluating control performance has attracted considerable interest in recent years. A set of performance indices appropriate to monitoring and assessment in flotation cells is presented and discussed in this paper. A graphical, user-friendly and interpretable program for displaying performance indices for operators has been developed. Finally, the testing results from flotation cells in a zinc plant are presented and discussed.Peer reviewe

Support vector machines for detection of analyzer faults- a case study

The aim of the work presented in this paper is to assess the ability of support vector machines (SVM) for detecting measurement faults. Two different support vector machine approaches for detecting faults are tested and compared to neural networks. The first method is based on a SVM regression model together with an analysis of the residuals whereas the second method is based on a SVM classifier. The methods were applied to a rigorous first principles based dynamic simulator of a dearomatization process.Peer reviewe