Fixed-point based hierarchical MPC control design for a cryogenic refrigerator

•Modular design of local controllers.•The coordinator accesses to few information regarding the subsystems.•The convergence of the fixed-point iterations arising in the negotiation process is proved.•General scheme that can be applied to local PID controller.•Theoretical scheme that is validated through a quite involved cryogenic process. In this paper, a simple, general and scalable hierarchical control framework is proposed and validated through the interconnection of the Joule–Thomson and the Brayton cycle stages of a cryogenic refrigerator. The proposed framework enables to handle the case of destabilizing interconnections through state and/or control signals (which is the case of the cryogenic refrigerator example). Moreover, it offers the possibility to simply change the behavior of the overall system (depending on the context) by only changing the coordinator problem's parameters without changing the set of local controllers used by subsystems which is a common industrial requirement regarding industrial control architectures. Finally, the proposed scheme enables a smooth operator handover on a specific subsystem and/or actuator.