Constraint and limit feasibility handling in a process control system optimizer
First Claim
1. A method of controlling a process, comprising:
- running an optimizer that uses an objective function to develop a solution defining a set of target values;
determining if the solution is feasible with respect to a set of process variable constraints;
if the solution is not feasible;
(1) redefining the process variable constraints for at least one process variable to define a new upper and lower process variable constraint limit for the one process variable;
(2) developing a new objective function by adding a penalty variable to the objective function for the one process variable, wherein the penalty variable penalizes the objective function based on the amount by which the one process variable differs from one of the new process variable constraint limits for the one process variable; and
(3) rerunning the optimizer with the new objective function to develop a new solution defining a new set of target values with the new process variable constraint limits for the one process variable;
providing the target values or the new target values to a controller; and
running the controller using the target values or the new target values to develop a set of control signals for controlling the process.
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Abstract
An optimization technique for use in driving a process plant controller, such as a model predictive controller, uses an organized, systematic but computationally simple method of relaxing or redefining manipulated, control and/or auxiliary variable constraints when there is no feasible optimal solution within pre-established constraints, to thereby develop an achievable solution for use by the controller. The optimization routine uses penalized slack variables and/or redefines the constraint model in conjunction with the use of penalty variables to develop a new objective function, and then uses the new objective function to determine a control solution that bests meets the original constraint limits.
171 Citations
53 Claims
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1. A method of controlling a process, comprising:
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running an optimizer that uses an objective function to develop a solution defining a set of target values;
determining if the solution is feasible with respect to a set of process variable constraints;
if the solution is not feasible;
(1) redefining the process variable constraints for at least one process variable to define a new upper and lower process variable constraint limit for the one process variable;
(2) developing a new objective function by adding a penalty variable to the objective function for the one process variable, wherein the penalty variable penalizes the objective function based on the amount by which the one process variable differs from one of the new process variable constraint limits for the one process variable; and
(3) rerunning the optimizer with the new objective function to develop a new solution defining a new set of target values with the new process variable constraint limits for the one process variable;
providing the target values or the new target values to a controller; and
running the controller using the target values or the new target values to develop a set of control signals for controlling the process. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. A system adapted to be implemented with a processor for use in controlling a process, comprising:
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a computer readable medium;
an optimizer routine stored on the computer readable medium and adapted to be executed on the processor to use an objective function to develop a solution defining a set of target values;
a feasibility handling routine stored on the computer readable medium and adapted to be executed on the processor to determine if the solution is feasible with respect to a set of process variable constraints and if the solution is not feasible;
to redefine the process variable constraints for at least one process variable to define a new upper and lower process variable constraint limit for the one process variable;
to develop a new objective function by adding a penalty variable for the one process variable to the objective function, wherein the penalty variable penalizes the objective function based on the amount by which the one process variable differs from one of the new process variable constraint limits for the one process variable; and
to rerun the optimizer routine with the new objective function to develop a new solution defining a new set of target values with the new process variable constraint limits for the one process variable; and
a controller routine stored on the computer readable medium and adapted to be executed on the processor to use the target values or the new target values to develop a set of control signals for controlling the process. - View Dependent Claims (13, 14, 15, 16, 17, 18, 19, 20, 21, 22)
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23. A method of controlling a process comprising:
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defining at least one constraint associated with each of a set of process variables;
defining an objective function to include one of more economic unit costs associated with the process variables and a penalty variable associated with one of the process variables violating the constraint for the one of the process variables, wherein the penalty variable has a unit penalty that is greater than each of the economic unit costs; and
using the objective function to develop a set of process control signals for use in controlling the process. - View Dependent Claims (24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36)
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37. A system for use with a processor to control a process, comprising:
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a computer readable medium;
a first routine stored on the computer readable medium and adapted to be executed on the processor to store at least one constraint associated with each of a set of process variables;
a second routine stored on the computer readable medium and adapted to be executed on the processor to store an objective function that defines one or more economic unit costs associated with the process variables and a penalty variable associated with at least one of the process variables violating the constraint for the one of the process variables, wherein the penalty variable has a unit penalty that is greater than the;
economic unit costs; and
a third routine stored on the computer readable medium and adapted to be executed on the processor to use the objective function to develop a set of process control signals for use in controlling the process. - View Dependent Claims (38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53)
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Specification