Mixed-Integer MPC Strategies for Fueling and Density Control in Fusion Tokamaks

Model predictive control (MPC) is promising for fueling and core density feedback control in nuclear fusion tokamaks, where the primary actuators, frozen hydrogen fuel pellets fired into the plasma, are discrete. Previous density feedback control approaches have only approximated pellet injection as...

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Bibliographic Details
Published in:IEEE control systems letters 2023-01, Vol.7, p.1-1
Main Authors: Orrico, Christopher A., van Berkel, Matthijs, Bosman, Thomas O. S. J., Heemels, W. P. M. H., Krishnamoorthy, Dinesh
Format: Article
Language:English
Subjects:
Constrained control
Fuels
Hybrid systems
Magnetic materials
Mathematical models
Optimization
Photonic crystals
Plasma temperature
Plasmas
Predictive control for nonlinear systems
Tokamaks
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Summary:Model predictive control (MPC) is promising for fueling and core density feedback control in nuclear fusion tokamaks, where the primary actuators, frozen hydrogen fuel pellets fired into the plasma, are discrete. Previous density feedback control approaches have only approximated pellet injection as a continuous input due to the complexity that it introduces. In this letter, we model plasma density and pellet injection as a hybrid system and propose two MPC strategies for density control: mixed-integer (MI) MPC using a conventional mixed-integer programming (MIP) solver and MPC utilizing our novel modification of the penalty term homotopy (PTH) algorithm. By relaxing the integer requirements, the PTH algorithm transforms the MIP problem into a series of continuous optimization problems, reducing computational complexity. Our novel modification to the PTH algorithm ensures that it can handle path constraints, making it viable for constrained hybrid MPC in general. Both strategies perform well with regards to reference tracking without violating path constraints and satisfy the computation time limit for real-time control of the pellet injection system. However, the computation time of the PTH-based MPC strategy consistently outpaces the conventional MI-MPC strategy.
ISSN:2475-1456
2475-1456
DOI:10.1109/LCSYS.2023.3282891