Method and apparatus for specifying and visualizing robust tuning of model-based controllers

Abstract

A method includes obtaining information identifying uncertainties associated with multiple parameters of a model for an industrial model-based controller. The method also includes obtaining information identifying multiple tuning parameters for the controller. The method further includes generating a graphical display identifying (i) one or more expected step responses of an industrial process that are based on the tuning parameters of the controller and (ii) an envelope around the one or more expected step responses that is based on the uncertainties associated with the parameters of the model. The parameters could include a process gain, a time constant, and a time delay associated with the model. The uncertainties associated with the parameters of the model could include, for each parameter of the model, an uncertainty expressed in the time domain. The information identifying the tuning parameters could include a settling time and an overshoot associated with the controller.

What is claimed is: 
     
         1 . A method comprising:
 obtaining information identifying uncertainties associated with multiple parameters of a model for an industrial model-based controller;   obtaining information identifying multiple tuning parameters for the controller; and   generating a graphical display identifying (i) one or more expected step responses of an industrial process that are based on the tuning parameters of the controller and (ii) an envelope around the one or more expected step responses that is based on the uncertainties associated with the parameters of the model.   
     
     
         2 . The method of  claim 1 , wherein the parameters comprise a process gain, a time constant, and a time delay associated with the model. 
     
     
         3 . The method of  claim 2 , wherein the uncertainties associated with the parameters of the model comprise, for each parameter of the model, an uncertainty expressed in the time domain. 
     
     
         4 . The method of  claim 1 , wherein obtaining the information identifying the tuning parameters comprises obtaining a settling time and an overshoot associated with the controller. 
     
     
         5 . The method of  claim 4 , further comprising:
 determining the one or more expected step responses based on a reference tracking performance ratio and a disturbance rejecting performance ratio associated with the controller.   
     
     
         6 . The method of  claim 5 , wherein determining the one or more expected step responses comprises using an iterative process to identify a value of the reference tracking performance ratio and a value of the disturbance rejecting performance ratio using a constrained optimization problem. 
     
     
         7 . The method of  claim 6 , wherein the iterative process comprises:
 tuning the disturbance rejecting performance ratio to obtain an optimal settling time for a fixed value of the reference tracking performance ratio;   tuning the reference tracking performance ratio to activate a constraint based on the overshoot; and   optimizing the settling time with respect to the reference tracking performance ratio.   
     
     
         8 . The method of  claim 1 , further comprising:
 identifying, for different combinations of values for the parameters of the model, multiple expected step responses of the industrial process at multiple time instances; and   identifying the envelope by identifying, for each time instance, a maximum value of the step responses at that time instance and a minimum value of the step responses at that time instance;   wherein the envelope defines a range of step responses given the uncertainties associated with the parameters of the model.   
     
     
         9 . The method of  claim 1 , wherein obtaining the information identifying the uncertainties associated with the parameters of the model comprises receiving the information identifying the uncertainties from a user. 
     
     
         10 . An apparatus comprising:
 at least one memory configured to store (i) information identifying uncertainties associated with multiple parameters of a model for an industrial model-based controller and (ii) information identifying multiple tuning parameters for the controller; and   at least one processing device configured to generate a graphical display that identifies (i) one or more expected step responses of an industrial process that are based on the tuning parameters of the controller and (ii) an envelope around the one or more expected step responses that is based on the uncertainties associated with the parameters of the model.   
     
     
         11 . The apparatus of  claim 10 , wherein:
 the parameters comprise a process gain, a time constant, and a time delay associated with the model; and   the uncertainties associated with the parameters of the model comprise, for each parameter of the model, an uncertainty expressed in the time domain.   
     
     
         12 . The apparatus of  claim 10 , wherein:
 the information identifying the tuning parameters comprises a settling time and an overshoot associated with the controller; and   the at least one processing device is configured to determine the one or more expected step responses based on a reference tracking performance ratio and a disturbance rejecting performance ratio associated with the controller.   
     
     
         13 . The apparatus of  claim 12 , wherein the at least one processing device is configured to determine the one or more expected step responses using an iterative process to identify a value of the reference tracking performance ratio and a value of the disturbance rejecting performance ratio using a constrained optimization problem. 
     
     
         14 . The apparatus of  claim 13 , wherein the at least one processing device is configured during the iterative process to:
 tune the disturbance rejecting performance ratio to obtain an optimal settling time for a fixed value of the reference tracking performance ratio;   tune the reference tracking performance ratio to activate a constraint based on the overshoot; and   optimize the settling time with respect to the reference tracking performance ratio.   
     
     
         15 . The apparatus of  claim 10 , wherein the at least one processing device is configured to:
 identify, for different combinations of values for the parameters of the model, multiple expected step responses of the industrial process at multiple time instances; and   identify the envelope by identifying, for each time instance, a maximum value of the step responses at that time instance and a minimum value of the step responses at that time instance;   wherein the envelope defines a range of step responses given the uncertainties associated with the parameters of the model.   
     
     
         16 . A method comprising:
 obtaining information identifying uncertainties associated with multiple parameters of a model for an industrial model-based controller; and   identifying multiple tuning parameters for the controller based on the uncertainties and one or more tuning specifications, wherein the one or more tuning specifications include constraints on a settling time and an overshoot associated with the controller.   
     
     
         17 . The method of  claim 16 , wherein identifying the multiple tuning parameters comprises identifying the multiple tuning parameters based on a reference tracking performance ratio and a disturbance rejecting performance ratio associated with the controller. 
     
     
         18 . The method of  claim 17 , wherein identifying the multiple tuning parameters further comprises using an iterative process to identify a value of the reference tracking performance ratio and a value of the disturbance rejecting performance ratio using a constrained optimization problem. 
     
     
         19 . The method of  claim 18 , wherein the iterative process comprises:
 tuning the disturbance rejecting performance ratio to obtain an optimal settling time for a fixed value of the reference tracking performance ratio;   tuning the reference tracking performance ratio to activate the constraint on the overshoot; and   optimizing the settling time with respect to the reference tracking performance ratio.   
     
     
         20 . The method of  claim 16 , wherein:
 the parameters comprise a process gain, a time constant, and a time delay associated with the model; and   the uncertainties associated with the parameters of the model comprise, for each parameter of the model, an uncertainty expressed in the time domain.