Lab Proposal for Integrated Real-time and Control - DCS - UPC

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8Fig. 10.(a) Overshoot controller with/withoutjitters(b) Overshoot controller eliminatingthe jitter problemOvershoot controller: degradation and solutionObservation 12: The problem presented above and its solutioncan be split into several tasks, like analysis and modellingof the new control algorithm, implementation of the controlalgorithm, etc. An interesting issue is how synchronized actuationinstants can be forced in the kernel. For example, asolution could be to use a periodic task for computing u k andanother periodic task for applying u k at the required time.Another solution could be to enforce synchronized executionsat the kernel level, using the EDF tick counter. Moreover,since different solutions to the jitter problem such as [29]or [30] could have also been applied, students more confidentor interested in specific fields can select the solution that bettermeets their preferences.IV. TENTATIVE WORK PLAN AND ITS APPLICATION TO ASPECIFIC COURSEThe previous section has detailed some of the steps requiredto successfully carry out the lab activity presented in this paper.This section summarizes them in order to propose a tentativework plan that is divided into several sessions, each one beinga two-hour lab.S1 - Introduction: Introduction to the activity, and simulationof the open-loop response after obtaining the statespaceform of the RCRC circuit from the circuit differentialequations (1) (consider random values for R and C). Here itis assumed that state-space notation is chosen.S2 - Problem specification (a): This session should beused to specify the problem in terms of the levels for thereference signal and for discrete controller design, whichincludes selecting the sampling period and closed loop polelocations, if pole placement is used. Other control approaches,like optimal control, could also be used.S3 - Problem specification (b): To complement the previoussession, observers should also be designed and simulated.The outcome of this session should be the complete simulationsetup.S4 - Basic implementation (a): Build the RCRC circuitand verify its dynamics in open-loop. Start the controller implementationin a periodic hard real-time task in the processingplatform.S5 - Basic implementation (b): Finish the controllerimplementation and test its correctness.S6 - Multitasking (a): Incorporate a noisy task in thesimulation setup to evaluate the effects of jitter. This stepwould require to use, for example, the TrueTime simulator.S7 - Multitasking (b): Incorporate the noisy task in theimplementation and validate the previous simulation results.S8 - Advanced implementation (a): If degradation in controlperformance is detected in the previous session, simulateadvanced control algorithms or adopt real-time techniques tosolve or reduce the jitter problem.S9 - Advanced implementation (b): Implement the previoussolutions and validate them.Note that the program timing, layout and the set of coveredtopics should be adapted to particular needs/background of thetarget audience or to the goals of the specific curriculum. Forexample, the proposed activity has been introduced as a partof the curriculum of the 2-year master degree on AutomaticControl and Industrial Electronics in the Engineering Schoolin Vilanova i la Geltrú (EPSEVG) of the Technical Universityof Catalonia (UPC) [34]. In particular, since 2007, theexperiment was tailored to become part of the laboratory forthe Control Engineering course, which covers continuous anddiscrete linear time invariant (LTI) control systems, as well asnon-linear control systems, all using state-space formalism.Sessions S1 to S5 were adopted for the laboratory of thediscrete LTI control systems part.The Control Engineering course can be followed by studentseither in the first semester of the first year or in the firstsemester of the second year. Students choosing the secondoption simultaneously attend a course on real-time systems.Therefore, within the same classroom, not all the students arefamiliar with real-time systems. To overcome this apparentdrawback, teams of three students were formed containing atleast a student with competence on real-time systems. Withinsuch heterogeneous teams in terms of skills and theoreticalbackground, it was observed that students took their responsibilitiesand team-work was significantly improved.As in every course edition, after finishing the discrete LTIcontrol systems part, a short and simple questionnaire is givento the students to let them evaluate several aspects of this partof the course. The question Do the laboratory activities permitto better understand the theoretical concepts? is the only onerelated to the laboratories. Looking at the students answers,and taking into account that before introducing the presentedexperiment the lab activities were focused on the simulation of
9an inverted pendulum, the percentage of students appreciatingthe practical part has increased significantly. Although thestandard course evaluation indicates this positive trend, amore complete evaluation tailored to the introduction of thisexperiment is required.V. CONCLUSIONSThis paper has presented a laboratory activity to be integratedin the education curriculum of embedded controlsystems engineers. The activity consists of a real-time controllerof a RCRC electronic circuit. The potential benefits,competences to be acquired, and expected learning outcomesfor students have been presented. The selection of the plant andprocessing platform has been discussed. Extensive details ofa sample implementation have been presented and a tentativework plan for carrying out the activity has been provided.In summary, the proposed activity poses several real challengesto the students that can be met by putting togetherinterdisciplinary skills (electronics, real-time systems, controltheory, programming) towards a single goal: building a workingsystem.REFERENCES[1] D. J. Jackson and P. Caspi, “Embedded systems education: future directions,initiatives, and cooperation”, SIGBED Rev., vol. 2, no. 4, pp. 1-4,Oct. 2005.[2] K.-E. Årzén, A. Blomdell, and B. Wittenmark, “Laboratories and realtimecomputing: integrating experiments into control courses,” IEEEControl Systems Magazine, vol. 25, no. 1, pp. 30-34, Feb. 2005.[3] G. Buttazzo, “Research trends in real-time computing for embeddedsystems”, ACM SIGBED Review, vol. 3, no. 3, Jul. 2006.[4] P. 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Jezernik, “A DSP-based remotecontrol laboratory,” IEEE Transactions on Industrial Electronics, vol. 54,no. 6, pp. 3057-3068, Dec. 2007.[26] K. Ogata, Modern Control Engineering, 4th Edition, Prentice Hall, 2001.[27] C. L. Liu and J. W. Layland, “Scheduling algorithms for multiprogrammingin a hard-real-time environment,” Journal of the Association forComputing Machinery, vol. 20, no. 1, pp. 46–61, Jan. 1973.[28] K.-E. Årzén, A. Cervin, J. Eker, and L. Sha, “An introduction to controland scheduling co-design,” in 39th IEEE Conference on Decision andControl, 2000.[29] J. Skaf and S. Boyd, “Analysis and synthesis of state-feedback controllerswith timing jitter,” IEEE Transactions on Automatic Control, vol.54, no. 3, pp. 652-657, March 2009.[30] P. Balbastre, I. Ripoll, J. Vidal, and A. Crespo, “A task model to reducecontrol delays,” Real-Time Systems, vol. 27, no. 3, pp. 215-236, Sep.2004.[31] C. Lozoya, M. Velasco, and P. Martí, “The one-shot task modelfor robust real-time embedded control systems”, IEEE Transactions onIndustrial Informatics, vol. 4, no. 3, pp. 164-174, Aug. 2008.[32] D. Henriksson, A. Cervin, and K.-E. Årzén, “TrueTime: simulation ofcontrol loops under shared computer resources,” in 15th IFAC WorldCongress, 2002.[33] Y. Wu, E. Bini, and G. Buttazzo, “A framework for designing embeddedreal-time controllers”, in 14th IEEE International Conference on Embeddedand Real-Time Computing Systems and Applications, Aug. 2008.[34] EPSEVG School portal, http://www.epsevg.upc.edu/.
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