Division of accelerators, cryogenics and magnetism

Modelling and model-based-control of large cryorefrigerators

Large superconducting tokamak devices produce significant pulsed heat loads on magnets, due to huge eddy currents encountered in the magnetic system, AC losses and neutron flux radiations coming from the plasma. Such high pulsed loads disturb the cryogenic plant that are cooling magnets, and make it necessary to use appropriate control strategies. The aim is to maintain the stability of the overall process subject to the variable thermal load and to satisfy operational and safety constraints (turbine operational temperature range, maximum capacity of the helium tank, compressor suction and discharge pressures, etc.). Currently, technological solutions are studied to smooth the effect of the thermal disturbance on the cryoplant and to avoid the over-dimensioning of the process. These solutions have to be combined with specific control algorithms, resulting in optimally designed closed-loop systems that can operate near their maximum capacity without the need for too conservative security margins. The recent interest in advanced control methodologies has motivated many studies on modelling and control of cryogenic plants. In particular, several dynamic simulators have been proposed for operator training, dimensioning and/or control design. Based on a better dynamic modelling of the underlying process, advanced control schemes have been proposed which were often dedicated to a particular key variable.

This seminar will be about control-oriented-modelling and model-based designed control of cryorefrigerators. Equations to model cryogenics will be presented, and then the Simcryogenics library for MATLAB/Simulink/Simscape will be introduced. We will see why these equations are compatible for control scheme generation and several advanced control applications, with associated simulation and experimental results, including simulation and control of the JT60-SA cryogenic system.