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Robust control : PID vs. fractional control design, a case study Martínez, Arturo

Abstract

This thesis presents a systematic procedure to design PID and CRONE controllers to regulate the hypnotic state of anesthesia with the intravenous administration of propofol. The hypnotic state of the patient is assessed by means of the WAV index, a processed hypnotic index based on a deterministic analysis of the EEG. The objective of the controllers is to provide an adequate drug administration regime of propofol, depending on the hypnotic set point, to avoid under or over dosage of the patients. Propofol is assumed to be administered by a commercial Graseby 3400 infusion pump. The two model-based controllers are designed to compensate for the patients inherent drug-response variability (uncertainty), to achieve good output disturbance rejection, and to attain good set point response. The drug-response model consists of two parts: a pharmacokinetic model that characterizes the drug movement in the body, and pharmacodynamic model that relates the drug concentration in the brain to the WAV hypnotic index. An anti-windup scheme is also implemented to protect the system against performance degradation in the event of actuator saturation. The performance of the controllers is assessed by calculating typical time domain measures (overshoot, settling and rise times), and using the median performance error, median absolute performance error, divergence, and wobble of the system's output. Overall, the CRONE controller was shown to have better output disturbance rejection, and to be less sensitive to the drug-response variability of the patients.

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