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

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.