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TH Lee

Publications and source records attributed to TH Lee.

7 recordsLinked to original sources
PubMed2000

Simultaneous online automatic tuning of cascade control for open loop stable processes

In this paper, we present a new simultaneous online automatic tuning method for cascade control using a relay feedback approach. Departing from the traditional approach towards tuning of cascade control systems where the secondary and primary loops are tuned in strict sequence, the proposed approach is to carry out the entire tuning process in one experiment. For ease of practical applications, the entire procedure of controller design may be automated and carried out online. A direct controller tuning approach to tune the controllers is proposed here. Robustness analysis of the new cascade control design is further carried out in the paper by drawing on existing results for SISO feedback systems. Simulations are provided to illustrate the applicability and effectiveness of both the online autotuning approach and the new cascade control design.

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PubMed2000

Development of a GPC-based PID controller for unstable systems with deadtime

Till now, traditional low-order control schemes have never been applicable to unstable systems with deadtime. In this paper, we present the first application of a PID controller with time-scheduled gains to unstable systems with deadtime, consisting of a single unstable pole. The control gains are designed based on a generalised predictive control (GPC) approach. The only user specifications required are simple and classical desired properties as in the natural frequency and the damping ratio of the closed-loop system. An approach is further developed to subsequent on-line self-tuning of control weights so that the overall control system remains applicable and effective in the face of disturbances and slowly varying dynamics. A detailed analysis of the closed-loop stability of the thus designed control system is further provided in the paper. Based on stability conditions developed, the prediction horizon for the GPC-based controller may be effectively computed. Finally, simulation examples illustrate the performance of the control system.

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PubMed2000

Robust on-line relay automatic tuning of PID control systems

In this paper, a robust on-line relay automatic tuning method for PID control systems is developed which expand on the application domain of Astrom's renowned relay autotuning method. In the proposed configuration, a relay is applied to an inner loop of a controller-stabilised process in the usual manner. Using the induced limit cycle oscillations from the closed-loop system, the controller settings may be re-tuned non-iteratively to achieve enhanced performance without disrupting closed-loop control. Two control tuning methodologies are developed -- a direct and an indirect method based on an explicit process model. Simulation examples and a real-time experiment are provided to illustrate the practical appeal and potential advantages of the proposed method over the basic one.

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PubMed1999

Foreword

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PubMed1998

Correlation of redox potential with state variables in cultures under controlled dissolved oxygen concentration and pH

In batch cultures for L-ornithine production in which dissolved oxygen concentration and pH were closely controlled, time changes of redox potential were observed in connection with the profiles of cell, glucose, and ornithine concentrations. It was found that the redox potential profile had four different phases reflecting the physiological state of the culture and that it was closely related to cell concentration change. Effects of glucose and ornithine on the redox potential were identified in a separate series of experiments. On the basis of the experimental results, a correlation of redox potential to glucose, cell, and ornithine concentrations has been proposed. The proposed correlation can be used for on-line estimation of ornithine concentration from on-line data of redox potential, glucose concentration, and cell concentration.

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PubMed1996

Emergency Department Observation Units: Has the Time Come?

Background: Economic pressures for efficiency in health care have led to the need for new strategies for the care of patients with acute chest pain. Methods: Chest pain observation units have been developed in many hospitals and are widely considered to have the potential to provide rapid and safe evaluations for low-risk patients with acute chest pain. Critical pathways are also an increasingly used strategy for the management of this patient population. Results: Available data suggest that chest pain observation units can decrease 6 month resource utilization compared with patients admitted to traditional sites of care. However, the potential exists for these units to increase resource utilization by encouraging admissions to the hospital of patients who otherwise would have been discharged directly home. Conclusions: Chest pain observation units appear to be an important innovation for the care of patients with a low risk for acute myocardial infarction. Use of guidelines for the se units may permit true increases in efficiency without compromising quality.

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