Model Predictive Control with Integral Action for the Rotational Transform Profile Tracking in NSTX-U
Z.O. Ilhan and E. Schuster
IEEE Multi-conference on Systems and Control
Buenos Aires, Argentina, September 19-22, 2016
Abstract
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Active control of the toroidal current density profile is among
those plasma control milestones that the National Spherical Tokamak
eXperiment - Upgrade (NSTX-U) program must achieve to realize its
next-step operational goals, which are characterized by high-performance,
long-pulse, MHD-stable plasma operation with neutral beam heating. As
a first step towards the realization of these goals, a first-principles-driven,
control-oriented model has been proposed earlier to predict the
spatial-temporal evolution of the current density profile by combining
the poloidal magnetic flux diffusion equation with empirical correlations
obtained at NSTX-U for the electron density, electron temperature, and
non-inductive current drives. In this work, the proposed 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 account for various modeling
uncertainties and external disturbances. The neutral beam powers,
electron density, and total plasma current are used as actuators. The
effectiveness of the proposed MPC strategy in regulating the current
density profile in NSTX-U is demonstrated in closed- loop nonlinear
simulations.