P. E. McDermott

University of California, Santa Barbara, Santa Barbara, CA, United States

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Publications (9)7.1 Total impact

  • P. E. McDermott, D. A. Mellichamp
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    ABSTRACT: This paper describes a new multivariable self-tuning controller that specifically handles different time delays between each of the input-output pairs (multiple delays), and deals with unknown or varying time delay (variable dead time compensation) without requiring an explicit estimate of each delay. The new algorithm can control unstable and/or non-minimum phase processes; it eliminates both set-point and load offsets without having to maintain integral action continuously; it decouples the loops, both dynamically and at steady state. The effective decoupling algorithm not only minimizes significant interactions among the control loops, it permits the use of a very simple design criterion, namely the approximate assignment of the primary closed-loop poles to prespecified locations. A straightforward autotuning technique locates the closed-loop poles on-line so as to optimize the system set-point step responses. One desirable side-effect is to account for inexact decoupling.The controller is demonstrated using a simulated paper machine head box having an unusually large amount of (off-diagonal) interaction, a simulated two-input, two-output distillation column with time-varying parameters (varying gains and time delays), and a highly interacting unstable and non-minimum phase system on which the autotuning technique is demonstrated. These three processes place stringent requirements on any control method, and two of them have been used extensively in the literature to test various multivariable and/or self-tuning algorithms. Hence, the success of the new technique indicates that it is a very promising candidate to deal with intransigent processes, i.e. those characterized as unstable, non-minimum phase, time-varying (non-linear), and interacting.
    Optimal Control Applications and Methods 12/2006; 7(1):55 - 79. · 1.06 Impact Factor
  • P. E. McDermott, D. A. Mellichamp, R. G. Rinker
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    ABSTRACT: A pole-placement self-tuning controller has been used to control a fixed-bed autothermal reactor conducting the water-gas shift reaction at both an upper stable state and a middle unstable state. Excellent set-point tracking and disturbance rejection characteristics were obtained using a single manipulated variable, the heat input at the entrance to the catalyst bed, to control a single bed temperature. Excellent set-point tracking during the transition from the upper state to the middle state was obtained by using a technique that tuned the closed-loop poles on-line so as to give an optimal response.
    AIChE Journal 06/2004; 32(6):1004 - 1014. · 2.49 Impact Factor
  • P. E. McDermott, D. A. Mellichamp, R. G. Rinker
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    ABSTRACT: The multiinput/multioutput pole-placement self-tuning controller (MIMO PPSTC) previously developed by McDermott and Mellichamp is used to control a fixed-bed autothermal reactor with internal countercurrent heat exchange. The performance of the controller is demonstrated using step changes in the set points and in the primary disturbance variables. It is shown that the complete temperature profile can be maintained by controlling two temperatures in the catalyst bed: one just before the hot spot and the other at the exit of the bed. Simulated results using a 36th-order nonlinear reactor model operating at both an open-loop upper stable steady state and an open-loop unstable steady state are presented. Experimental results for a fixed-bed autothermal reactor operating at an upper stable state are presented.
    AIChE Journal 05/1986; 32(6):1015 - 1024. · 2.49 Impact Factor
  • P.E. McDermott, H.-C. Chang, R.G. Rinker
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    ABSTRACT: “Snap-through” Hopf bifurcations are induced in a laboratory autothermal reactor by the destabilizing effects of a single proportional controller. These unexpected and dramatic phenomena are predicted a priori by a bifurcation analysis of the model equations with the controller gain as the bifurcation parameter. The experimental bifurcation data are used in a parameter estimation study which yields an extremely accurate dynamic model for the nonlinear system.
    Chemical Engineering Science. 01/1985;
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    ABSTRACT: Counterflow reactor models fall into three classes of partial differential equations: hyperbolic, parabolic, and mixed hyperbolic-parabolic. These have been analyzed to determine the behavior of their eigenvalues and their modal contributions. Using an asymptotic analytical technique (WKB theory), hyperbolic p.d.e. systems and mixed p.d.e. systems with characteristics similar to hyperbolic systems were found to have a “defective” internal structure, making them generally undesirable for modeling or control applications requiring low-order models. Parabolic systems, or mixed systems with characteristics similar to parabolic systems, were found to be “well-behaved”. Hence, where it is possible to choose the type of model to apply to a specific reactor, the choice of the parabolic form is strongly suggested to mitigate potential structural problems.
    Chemical Engineering Communications 12/1984; 31(1-6):263-287. · 1.05 Impact Factor
  • P.E. McDermott, D.A. Mellichamp
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    ABSTRACT: For a class of discrete-time pole-placement controllers that utilize a single non-zero pole, the effect of varying the control sampling period, both on the optimal location of the closed-loop pole and on the size of the feasible pole location region, has been considered. With both deterministic and stochastic optimality measures, fast sampling yields an optimal pole location close to 1 with a very narrow feasible operating region. Conversely, slow sampling yields an optimal pole location at 0 with a much wider feasible operating region; however, the closed-loop response characteristics for slow sampling are much poorer. Sampling at a rate which yields an optimal closed-loop pole in the range 0.2-0.7 is seen to avoid the excessive system sensitivity (as when located closer to 1) and a somewhat degraded system response (when located at 0). These results suggest the basis of an ad hoc design technique for on-line selection of the sampling period which is demonstrated using a nonlinear model of a fixed-bed chemical reactor.
    American Control Conference, 1984; 07/1984
  • P. E. McDERMOTT, D. A. MELLICHAMP
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    ABSTRACT: An explicit self-tuning controller is described that incorporates closed-loop pole location as the principal design criterion for the objective function of Clarke and Gawthrop. The algorithm includes several minor extensions to improve robustness : a variable dead-time compensator to deal with unknown or time-varying delay, and a method of treating steady-state offset that avoids retaining an integrator in the loop continuously. A new technique has been developed and included in the algorithm that enables the controller to be auto-tuning in the sense that the closed-loop pole(s) and sampling period can be determined on-line so as to optimize the system set-point step response, leaving the system designer to specify only internal model orders and noise characteristics on which to initiate retuning. The resulting controller is quite robust and can easily handle unstable, non-minimum phase systems in a single-loop configuration, as is demonstrated by several simulations including a non-linear model of a fixed-bed autothermal reactor operating over such a large range that auto-tuning of the poles is a necessity.
    International Journal of Control - INT J CONTR. 01/1984; 40(6):1131-1147.
  • Patrick E. McDermott, Hsueh-Chia Chang
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    ABSTRACT: The global dynamics of an autothermal reactor stabilized at an (open-loop) unstable steady-state by a single proportional controller is studied as a bi
    Chemical Engineering Science. 01/1984;
  • P.E. McDermott, D.A. Mellichamp
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    ABSTRACT: An explicit self-tuning controller is developed that incorporates closed-loop pole location as the principal design criterion for the method of Clarke and Gawthrop. The algorithm includes a variable dead-time compensator to deal with unknown or time-varying delay, and a new method of treating steady-state offset. A technique has been developed and included in the algorithm that enables the controller to be "nearly self-tuning" in the sense that the closed-loop pole(s) and/or sampling period can be determined on-line so as to optimize the system set-point step response, leaving the system designer only to specify internal model orders and noise characteristics on which to initiate retuning. This controller can easily handle unstable, nonminimum phase systems in a single-loop configuration, as is demonstrated by several simulations including a non-linear model of a fixed-bed autothermal reactor.
    American Control Conference, 1983; 07/1983