Aalborg Universitet Design of Integrated Systems for The

View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by VBN Aalborg Universitet Design of Integrated Systems for the Control and Detection of Actuator/Sensor Faults Stoustrup, Jakob; Grimble, M.J.; Niemann, H.H. Published in: Sensor Review Publication date: 1997 Document Version Tidlig version også kaldet pre-print Link to publication from Aalborg University Citation for published version (APA): Stoustrup, J., Grimble, M. J., & Niemann, H. H. (1997). Design of Integrated Systems for the Control and Detection of Actuator/Sensor Faults. Sensor Review, 138-149. General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. ? Users may download and print one copy of any publication from the public portal for the purpose of private study or research. ? You may not further distribute the material or use it for any profit-making activity or commercial gain ? You may freely distribute the URL identifying the publication in the public portal ? Take down policy If you believe that this document breaches copyright please contact us at [email protected] providing details, and we will remove access to the work immediately and investigate your claim. Downloaded from vbn.aau.dk on: December 25, 2020 Introduction Research articles In the control of industrial systems, it is rare Design of integrated that a control system functions continuously systems for the control without shutdown throughout the scheduled life cycle of the plant and controller hardware. and detection of Owing to wear of mechanical and electrical actuator/sensor faults components, both actuators and sensors can fail in more or less critical ways. For safety- critical processes, it is of paramount impor- Jakob Stoustrup tance to detect when faults are likely to M.J. Grimble and happen and then to identify these faults as fast as possible once they have occurred. Henrik Niemann To meet such industrial needs, a number of schemes for fault detection and isolation (FDI) have been put forward in the literature on automatic control. Much of the research The authors has dealt with the design of filters which Jakob Stoustrup is a Professor at the Department of monitor a process and generate alarms when Control Engineering, Aalborg University, Fredrik Bajersvej 7, faults have occurred. In most cases, the filters DK-9220 Aalborg East, Denmark. Tel: (45) 9815 8522; are model-based devices which act indepen- Fax: (45) 9815 1739; E-mail: [email protected]. dently of the computer-implemented digital M.J. Grimble is Professor and Director at the Industrial controllers. In this paper, however, the advan- Control Centre, University of Strathclyde, Graham Hills tages of combining the control algorithm and Building, 50 George Street, Glasgow G1 1QE, UK. E-mail: the FDI filter in a single module will be dis- [email protected] cussed, and a relatively simple methodology Henrik Niemann is Associate Professor at the Depart- to design such combined modules will be ment of Automation, Technical University of Denmark, described. Building 326, DK-2800 Lyngby, Denmark. E-mail: It will be shown that a combined module [email protected] will be beneficial in terms of implementation and reliability, but it will also be shown that Abstract the quality of control and the quality of detec- Considers control systems operating under potentially tion will not improve by using the integrated faulty conditions. Discusses the problem of designing a design – compared with the individual designs single unit which not only handles the required control of two components – provided that a good action but also identifies faults occurring in actuators and nominal model is available. This result is sensors. In common practice, units for control and for shown to be very general. A special case using diagnosis are designed separately. Attempts to identify an algebraic Riccati equation approach was situations in which this is a reasonable approach and cases presented in Tyler and Morari (1994). in which the design of each unit should take the other into On the other hand, if the quality of the consideration. Presents a complete characterization for available model is poor, the design of the each case and gives systematic design procedures for both control system and of the diagnosis system the integrated and non-integrated design of control and diagnosis units. Shows how a combined module for has to be undertaken simultaneously in order control and diagnosis can be designed which is able to to improve overall functionality. follow references and reject disturbances robustly, control Useful surveys about early work on FDI the system so that undetected faults do not have disas- can be found in Frank (1990) and Patton et al. trous effects, reduce the number of false alarms and (1989). Many of these techniques are observ- identify which faults have occurred. er-based, such as Magni and Mouyon’s (1991). These methods have since been refined and extended. A more recent work in this line of research is that of Frank and Ding (1994). The original idea of using the infor- mation already available in the “observer” Sensor Review Volume 17 · Number 2 · 1997 · pp. 138–149 part of a controller for diagnostic purposes © MCB University Press · ISSN 0260 2288 was given in Nett et al. (1988). 138 Systems for the control and detection of actuator/sensor faults Sensor Review Jakob Stoustrup, M.J. Grimble and Henrik Niemann Volume 17 · Number 2 · 1997 · 138–149 Early work on FDI experienced problems z w c =Gs() d owing to modelling uncertainties. In some yc uc cases, false alarms were common due to Gs() Gs()w imperfect modelling. This called for issues of =11 12 d robustness to be incorporated into the FDI Gs21() Gs22() uc design algorithm. Specific robustness solu- CsIA(±)±1 B+ D tions to FDI problems were discussed in =1 111 CsIA(±)±1 B+ D Bokor and Keviczky (1994); Mangoubi et al., 2 121 (1995); Murad et al., (1996); Patton and CsIA(±)±1 B+ D w 1 212 d. Chen (1991); Qiu and Gertler (1993); and ±1 (1) CsIA(±)BD+ uc Wang and Wu (1993). All these methods used 2 222 frequency domain techniques in contrast to For the standard problem shown in Figure 1, a controller K(s), making the transfer function Ajbar and Kantor’s (1993), which used l∞ techniques. from wd to zc small, can be found by standard An interesting application of FDI tech- control optimization tools. Popular control niques was presented in works by Blanke et al. design methods that support standard problem optimization comprise: LQG (or ) methods (1995), Jørgensen et al. (1995), Grainger et al. H2 (Zhou et al., 1996), methods (Zhou et (1995) and Garcia et al. (1995), which sug- H∞ al.,1996), L methods (Dahleh and Pearson, gested using a diesel-engine actuator as an 1 1987) and µ methods (Zhou et al., 1996). FDI benchmark problem. Usually, the model G(s) will contain the plant model itself, but it can also contain Problem formulation models of disturbances, measurement noise, time variations, non-linearities and unmod- Figure 1 illustrates a control problem in the elled dynamics. Hence, making the transfer standard system configuration (see, for exam- function from wd to zc small ensures a number ple, Zhou et al. (1996) for an introduction to of performance and robustness properties. the standard configuration paradigm). Here, The everyday operation of such a feedback wd can be thought of as a collection of unde- system depends on reliable actuators and sired signals (disturbances) entering the sensors. However, in most industrial environ- system G(s) or as set-points. The signals yc are ments actuators and sensors can fail. One way the measurements used by the controller K(s), to model this is depicted in Figure 2. generating the control signals uc in order to Here, the measurements used by the con- make the outputs to-be-controlled z suffi- c troller are y = yc + fs rather than yc and the ciently small. controls acting on the plant are uc + fa rather ≡ ≡ The system in Figure 1 can be described in than uc. For example yc + fs 0 or uc + fa 0 either the state space formulation: can represent completely defective sensors or xÇAB Bx actuators, respectively. 12 = For safety-critical processes in particular, zcCD11112 Dwd faults must be identified and action taken yCD Du c 22122c immediately. Two main paths of action can be or, alternatively, in transfer matrix function taken: either the control design algorithm can form: be modified to tolerate minor errors; or, using Figure 1 Control system in standard control configuration Figure 2 Control system with actuator and sensor faults 139 Systems for the control and detection of actuator/sensor faults Sensor Review Jakob Stoustrup, M.J. Grimble and Henrik Niemann Volume 17 · Number 2 · 1997 · 138–149 an estimator, the faulty signal can be identi- ξξÇ =+ÄÄ + Ä ABwBu12 fied and action taken by the operator or a =+ÄÄξ + Ä zC11112 DwDu (3) supervisory system. In most applications, the yC=+ÄÄξ DwDu + Ä latter would be preferable. 22122 A method is now described which allows for or in transfer function matrix form: either, or both, approaches to be incorporated z wGsÄ () GsÄ ()w =GsÄ() = 11 12 . Ä Ä into a single design step that also comprises y uGsGs21() 22()u the controller design. This is achieved using a (The explicit formulae are given below.) single module which generates both the con- Using standard control optimization meth- trol action and the fault estimates.

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