Apparatus and method for calculating proxy limits to support cascaded model predictive control (MPC)

An apparatus comprising:

• a master model predictive control (MPC) controller comprising:
• at least one network interface configured to:
• send multiple inquiry optimization calls to a slave MPC controller, each inquiry optimization call associated with a different direction among multiple directions within a variable space;
• and
• receive in response to each of the enquiry optimization calls, from the slave MPC controller, information indicating to what extent the slave MPC controller is able to change a manipulated variable of multiple manipulated variables in the direction associated with the respective enquiry optimization call within the variable space without violating process variable constraints of the slave MPC controller, the variable space including a first feasibility region defined by the process variable constraints;
• and
• at least one processing device configured to:
• estimate a second feasibility region associated with the slave MPC controller using the information, the second feasibility region identifying a portion of the first feasibility region in which combinations of manipulated variable values of the multiple manipulated variables satisfy the process variable constraints;
• and
• perform plantwide optimization using the second feasibility region, wherein a solution generated during the plantwide optimization includes one of the combinations of manipulated variable values within the second feasibility region;
• wherein the at least one processing device is configured to receive proxy limit values from the slave MPC controller in response to the inquiry optimization calls;
• and
• wherein each proxy limit value identifies a maximum distance in one of the directions within the variable space that the slave MPC controller is able to change the manipulated variables without violating the process variable constraints.

A non-transitory computer readable medium containing a computer program, the computer program comprising computer readable program code that when executed causes at least one processing device to:

• send multiple inquiry optimization calls from a master model predictive control (MPC) controller to a slave MPC controller, each inquiry optimization call associated with a different direction among multiple directions within a variable space;
• receive, at the master MPC controller from the slave MPC controller in response to each of the inquiry optimization calls, information indicating to what extent the slave MPC controller is able to change a manipulated variable of multiple manipulated variables in the direction associated with the respective enquiry optimization call within the variable space without violating process variable constraints of the slave MPC controller, the variable space including a first feasibility region defined by the process variable constraints;
• estimate a second feasibility region associated with the slave MPC controller using the information, the second feasibility region identifying a portion of the first feasibility region in which combinations of manipulated variable values of the multiple manipulated variables satisfy the process variable constraints;
• and
• perform plantwide optimization at the master MPC controller using the second feasibility region, wherein a solution generated during the plantwide optimization includes one of the combinations of manipulated variable values within the second feasibility region;
• wherein the information comprises proxy limit values from the slave MPC controller;
• and
• wherein each proxy limit value identifies a maximum distance in one of the directions within the variable space that the slave MPC controller is able to change the manipulated variables without violating the process variable constraints.