Nonlinear Backstepping Control for the Fuel Diffusion Lag in Fusion Reactors
E. Schuster, M. Krstic and G. Tynan
IFAC World Congress on Automatic Control
Barcelona, Spain, July 2002
Abstract
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Control of plasma density and temperature magnitudes, as well as their
profiles, are among the most fundamental problems in fusion reactors.
Existing efforts use control techniques based on linearized models. In
this work, a zero-dimensional nonlinear model involving approximate
conservation equations for the energy and the densities of the species
was used to synthesize a nonlinear feedback controller for stabilizing
the burn condition of a fusion reactor. The model addresses the issue
of the lag due to the finite time for the fresh fuel to diffuse into
the plasma center. Nonlinear backstepping is used to deal with this
imposed lag. In this way we make our control system independent of the
fueling system and the reactor can be fed either by pellet injection
or by gas puffing. The controller exhibits excellent properties of
robustness and the boundness of the state variables is guaranteed for
a large set of values of the lag constant. In addition the nonlinear
controller proposed guarantees a much larger region of attraction than
the previous linear controllers, it is capable of rejecting
perturbations in initial conditions leading to both thermal excursion
and quenching, and its effectiveness does not depend on whether the
operating point is an ignition or a subignition point.