Model Predictive Control with Integral Action for Current Density Profile Tracking in NSTX-U
Z.O. Ilhan, W.P. Wehner, E. Schuster and D. Boyer
Division of Plasma Physics (DPP) Annual Meeting of the American Physical Society (APS)
San Jose, CA, USA, October 31 - November 4, 2016
Abstract
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Active control of the toroidal current density profile may play a
critical role in non-inductively sustained long-pulse, high-beta
scenarios in a spherical torus (ST) configuration, which is among the
missions of the NSTX-U facility. In this work, a previously developed
physics- based control-oriented model is embedded in a feedback
control scheme based on a model predictive control (MPC) strategy to
track a desired current density profile evolution specified indirectly
by a desired rotational transform profile. An integrator is embedded
into the standard MPC formulation to reject various modeling
uncertainties and external disturbances. Neutral beam powers, electron
density, and total plasma current are used as actuators. The proposed
MPC strategy incorporates vari- ous state and actuator constraints
directly into the control design process by solving a constrained
optimization problem in real-time to determine the optimal actuator
requests. The effectiveness of the proposed controller in regulating
the current density profile in NSTX-U is demonstrated in closed-loop
nonlinear simulations.