BLANC - Blanc

Cryogenic HElium for Optimised System – CHEOPS

Submission summary

The aim of this project is to develop a new general method for controlling large cryogenic refrigerators. This method should be operational over the entire working range of these complex machines, covering the initial start-up at a temperature of 300K down to 4.2K or 1.8K as well as nominal working conditions. The target is to achieve overall dynamic control of these systems by taking into account two recent requirements: - withstanding without risk large fluctuations in thermal load, - reducing operating costs by optimising electrical energy consumption. Changing needs have led to a rise in unit powers (several MW of electricity) and an increase in complexity. This in turn is reflected in greater needs for automatic control to manage all stages of operation and ensure operating safety. Cryogenic refrigerators are plants producing cold conditions at temperatures of less than 80K. They are used in two main types of application: - cooling superconducting magnets for instruments requiring high magnetic fields, - gas liquefaction (He, H2, N2, etc.) whether for the production of industrial cryogenic fluids of for storing liquid fuels (H2) for the development of NTEs. Based on current technology, cryogenic refrigerators are adapted to stable or lightly variable thermal loads. Energy consumption problems are taken into account only very partially. This is because these systems are controlled by multiple PID-type multiple loops that are independently tuned empirically when the plant is brought on stream for the first time. This method is sufficient as long as the plant runs in a neighbourhood of its nominal operating point. However, the coupling effects between the dynamics of the different regulators and also the lack of anticipation make this type of control unsuitable when the refrigeration load is subject to random or cyclical perturbations of variable amplitude. In addition, during the start-up stages of these machines (initial cooling in particular) the solutions implemented consist in catenating partially automatic sequences, often adapted on a case-by-case basis. With the aim being to achieve fully automated and optimum operation, it is clearly apparent that much work still needs to be done to achieve these targets. Overall dynamic control consists in reconsidering these methods from top to bottom. Starting with the reality of a refrigerator, i.e., a complex and highly nonlinear process presenting critical operating phases, the initial aim must be to based on a comprehensive and faithful modelling of the process with a parametrisation adaptable to all the machines. Then, the most appropriate automatic control methods must then be designed and adapted to address the problem. The aim being to achieve the desired dynamic performance by guaranteeing safer and more robust operation while at the same time simplifying tuning procedures. The CEA and manufacturers of large refrigerators are focusing their development efforts essentially on the cryogenic aspect of the machines. But there is also an urgent need to address the control-command aspect by launching an ambitious specific project on this subject. The ideal conditions are now in place for undertaking this study. For example, the Low Temperature Service of CEA/Grenoble (SBT), possesses a very well-instrumented representative cryogenic test facility (STATION 400W @ 1.8K), as well as specialist teams in cryogenics, instrumentation and control and monitoring. In addition, the Department of Advanced Technologies (DTA) at Air-Liquide in Sassenage provides its expertise in the fields of construction and operation of cryogenic refrigerators and expansion turbines. It is ready to participate in this development project, the results of which will be directly applicable to its own production. Finally the Laboratoire d'Automatique de Grenoble (Grenoble Automatic Control Laboratory, now known as the automatic Control department of GIPSA Lab since 2007), which has considerable expertise in complex process regulation, has already joined forces with SBT on a variety of subjects concerning the control-command of cryogenic systems. After three years, the project will have developed a control approach method for cryogenic refrigerators that should be operational and easily applicable to plants on the market. Research and development conducted on this project could open up new prospects in nonlinear control.

Project coordination

Patrick BONNAY (Organisme de recherche)

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

Help of the ANR 390,000 euros
Beginning and duration of the scientific project: - 36 Months

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