Optimal Feedback Control of the Poloidal Magnetic Flux Profile in the DIII-D Tokamak based on Identified Plasma Response Models
W. Wehner, W. Shi, E. Schuster, D. Moreau, M.L. Walker, J.R. Ferron, T.C. Luce, D.A. Humphreys, B.G. Penaflor and R.D. Johnson
American Control Conference
Montreal, Canada, June 27-29, 2012
Abstract
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First-principles predictive models based on flux-averaged transport
equations often yield complex expressions not suitable for real-time
control implementations. It is however always possible to reduce these
models to forms suitable for control design while preserving the
dominant physics of the system. If further model simplification is
desired at the expense of less model accuracy and controller
capability, data- driven modeling emerges as an alternative to
first-principles modeling. System identification techniques have the
potential of producing low-complexity, linear models that can capture
the system dynamics around an equilibrium point. This paper focuses on
the control of the poloidal magnetic flux profile evolution in
response to the heating and current drive (H&CD) systems and the total
plasma current. Open-loop data for model identification is collected
during the plasma current flattop in a high-confinement scenario
(H-mode). Using this data a linear state-space plasma response model
for the poloidal magnetic flux profile dynamics around a reference
profile is identified. The control goal is to use the H&CD systems and
the plasma current to regulate the magnetic profile around a desired
target profile in the presence of disturbances. The target profile is
defined close enough to the reference profile used for system
identification in order to stay within the range of validity of the
identified model. An optimal state feedback controller with integral
action is designed for this purpose. Experimental results showing the
performance of the proposed controller implemented in the DIII-D
tokamak are presented.