Remediating the Effects of Time Delays in Axisymmetric Plasma Controllers via Optimal Tuning and Predictor Augmentation
R. Arastoo, E. Schuster, M. Walker
Division of Plasma Physics (DPP) Annual Meeting of the American Physical Society (APS)
Atlanta, Georgia, November 2-6, 2009
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Abstract
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Introducing extra time delays into the axisymmetric control loops of
certain superconducting tokamaks can have significant detrimental
consequences. This study exposes and quantifies these effects by
focusing on plasma current and radial position control in a
vertically-stable circular plasma in KSTAR. Delays in the power
supplies, data acquisition, and vessel structure are taken into account.
Extremum-seeking-based optimal tuning of PID controllers is proposed
as a possible method for remediating the negative effects of time
delays. In addition, an augmentation of the control loop by the
introduction of a predictor is proposed to improve the performance of
the time-delayed closed-loop system. It is shown that the proposed
predictor is robust against uncertainties in the values of the delays.
The dual-locus technique is employed to assess stability of the
closed-loop systems in the presence of time delays.
