Continuously Scheduled Model Parameter Based Adaptive Controller

• US 20090319060A1
• Filed: 06/22/2009
• Published: 12/24/2009
• Est. Priority Date: 06/20/2000
• Status: Active Grant

• Current Assignee: Fisher-Rosemount Systems Incorporated (Emerson Electric Company)
• Original Assignee: Fisher-Rosemount Systems Incorporated (Emerson Electric Company)
• Inventors: Blevins, Terrence Lynn, Wojsznis, Wilhelm K., Wojsznis, Peter
• Granted Patent: US 8,280,533 B2
• Time in Patent Office: Days
• US Class Current: 700/30
• CPC Class Codes: G05B 11/42 for obtaining a characteristic which is both proportional and time-dependent, e.g. P. I., P. I. D.
• CPC Class Codes: G05B 13/042 in which a parameter or coefficient is automatically adjusted to optimise the performance
• CPC Class Codes: G05B 17/02 electric

Abstract

An adaptive process controller performs continuously scheduled process model parameter interpolation to determine a particular set of process model parameters which are used to develop controller tuning parameters for controller tuning. More particularly, a state-based, adaptive PID controller described herein uses a new technique to determine an appropriate process model to be used to perform adaptive tuning over the various operating regions of the plant, and in particular, uses a process model parameter determination technique that enables continuously scheduled process model parameter update over the various plant operating regions or points. The use of this continuously scheduled process model parameter update method provides for smoother transitions between tuning parameters used in the PID controller during adaptive tuning procedures which are implemented based on changes in the operating region or the operating point of the process, thereby providing for better overall control.

Claims

1. An adaptive controller for use in controlling a process, comprising:

a controller input to receive an process variable input signal from the process;

a controller output to provide a process control signal for use in controlling the process;

a control block coupled between the controller input and the controller output that determines the control signal by implementing process control calculations using the input signal and a set of controller tuning parameters; and

a tuning block that determines new values for the set of controller tuning parameters during operation of the process using a set of stored process model parameter values and a process state variable, wherein the set of stored process model parameter values includes a process model parameter value for a particular process model parameter for each of a plurality of different process operating points defined by the process state variable;

the tuning block including;

a model adaptation routine that determines the stored process model parameter value for the process model parameter at each of the plurality of different process operating points;

a model parameter determination routine that determines a particular process model parameter value for a particular process operating point based on the process state variable value and the set of stored process model parameter values; and

a controller tuning parameter routine that determines the set of controller tuning parameters for the particular process operating point from the determined process model parameter value and a stored tuning rule.

2. The adaptive controller of claim 1, wherein the model adaptation routine stores an interpolation function parameter for determining a process model parameter value at process operating points between two or more of the plurality of different process operating points associated with the set of stored process model parameter values using an interpolation technique, and wherein the model parameter determination routine further determines the particular process model parameter value for the particular process operating point using the interpolation function parameter in the interpolation technique.

3. The adaptive controller of claim 2, wherein the interpolation technique is a linear or a non-linear interpolation technique.

4. The adaptive controller of claim 2, wherein the interpolation technique is a linear sigmoidal interpolation technique.

5. The adaptive controller of claim 2, wherein the interpolation technique is a non-linear sigmoidal interpolation technique.

6. The adaptive controller of claim 1, wherein the model adaptation routine updates the set of stored process model parameter values by determining a new process model parameter value for a specific process operating point and changing the set of stored process model parameter values based on the new process model parameter value for the specific process operating point.

7. The adaptive controller of claim 6, wherein the model adaptation routine stores an interpolation function parameter for determining a process model parameter value at process operating points between two or more of the different process operating points associated with the set of stored process model parameter values, and wherein the model adaptation routine determines the set of stored process model parameter values by changing the interpolation function parameter based on the new process model parameter value for the specific process operating point.

8. The adaptive controller of claim 6, wherein the model adaptation routine uses an interpolation function parameter for determining a process model parameter value at process operating points between two or more of the different process operating points associated with the set of stored process model parameter values, and wherein the model adaptation routine updates the set of stored process model parameter values by changing one or more of the stored process model parameter values for the different process operating points based on the interpolation function parameter and based on the new process model parameter value for the specific process operating point.

9. The adaptive controller of claim 6, wherein the model adaptation routine updates the set of stored process model parameter values based on the new process model parameter value for the specific process operating point by storing the new process model parameter value for the specific process operating point as one of the set of stored process model parameter values, and culling the set of stored process model parameter values if the number of process model parameter values within the set of stored process model parameters values reaches a threshold.

10. The adaptive controller of claim 6, wherein the model adaptation routine changes the set of stored process model parameter values based on the new process model parameter value for the specific process operating point by changing two or more of the set of stored process model parameter values without changing their associated process operating points, based on the new process model parameter value at the specific process operating point.

11. The adaptive controller of claim 10, wherein the model adaptation routine changes the two or more of the set of stored process model parameter values using an interpolation technique and the new process model parameter value at the specific process operating point.

12. The adaptive controller of claim 10, wherein the model adaptation routine changes the two or more of the set of stored process model parameter values using a linear interpolation technique based on the new process model parameter value at the specific process operating point.

13. The adaptive controller of claim 10, wherein the model adaptation routine changes the two or more of the set of stored process model parameter values using a non-linear interpolation technique based on the new process model parameter value at the specific process operating point.

14. The adaptive controller of claim 1, wherein the control block implements a feedforward/feedback controller technique.

15. The adaptive controller of claim 1, wherein the set of controller tuning parameters include a feedforward tuning parameter and a feedback tuning parameter.

16. The adaptive controller of claim 1, wherein the particular process model parameter includes a process gain, a deadtime or a time constant.

17. The adaptive controller of claim 1, wherein the control block implements a proportional, integral, derivative controller technique.

18. A method of adaptively tuning a process controller used to control a process, the method comprising:

storing a set of model parameter values characterizing the operation of the process during operation of the process, each of the model parameter values characterizing the operation of the process at a different process operating point with each of the different process operating points being associated with a different process state variable value;

collecting process data during the operation of the process and performing a model characterization procedure based on the collected process data to determine a new model parameter value for one or more process operating points;

updating the stored set of model parameter values with the new model parameter value; and

tuning the process controller using the stored set of model parameter values, including;

determining a current model parameter value for a current process operating point using two or more of the set of stored model parameter values and the process state variable;

using the determined current model parameter value and a process model based tuning rule to define a set of controller tuning parameter values; and

updating the process controller with the determined set of controller tuning parameter values.

19. The method of adaptively tuning a process controller of claim 18, including using an interpolation function to determine a model parameter value at a process operating point between two or more of the different process operating points associated with the stored set of model parameter values, and determining the current model parameter value for the current process operating point using the interpolation function.

20. The method of adaptively tuning a process controller of claim 19, wherein the interpolation function is associated with a linear interpolation technique.

21. The method of adaptively tuning a process controller of claim 19, wherein the interpolation function is associated with a non-linear interpolation technique.

22. The method of adaptively tuning a process controller of claim 18, wherein updating the stored set of model parameter values includes determining a new model parameter value for a specific process operating point and changing the stored set of model parameter values based on the new model parameter value for the specific process operating point.

23. The method of adaptively tuning a process controller of claim 22, including storing an interpolation function for determining model parameter values at process operating points between two or more of the different process operating points associated with the stored set of model parameter values, and including updating the stored set of model parameter values by changing the interpolation function based on the new process model parameter value for the specific process operating point.

24. The method of adaptively tuning a process controller of claim 22, including storing an interpolation function for determining process model parameter values at process operating points between two or more of the different process operating points associated with the stored set of model parameter values, and including updating the stored set of model parameter values by changing one or more of the stored model parameter values for the different process operating points based on the interpolation function and based on the new process model parameter value for the specific process operating point.

25. The method of adaptively tuning a process controller of claim 22, wherein updating the stored set of model parameter values with the new model parameter value includes storing the new model parameter value for the specific process operating point as one of the stored set of model parameter values, and culling the stored set of model parameter values if the number of model parameter values within the stored set of model parameters values reaches a threshold.

26. The method of adaptively tuning a process controller of claim 22, wherein updating the stored set of model parameter values with the new model parameter value includes changing two or more of the stored set of model parameter values without changing their associated process operating points, based on the new model parameter value at the specific process operating point.

27. The method of adaptively tuning a process controller of claim 26, wherein using the determined current model parameter value and a process model based tuning rule to define a set of controller tuning parameter values includes defining a set of feedforward and feedback controller tuning parameters.

28. An adaptive process controller system, for implementation on a computer processor to control a process, comprising:

a computer memory;

a process controller routine stored on the computer memory and executable on the computer processor to implement a control algorithm that determines a process control signal for use in controlling the process based on a process variable input from the process and a set of controller tuning parameters; and

a tuning routine stored on the computer memory and executable on the computer processor to determine new values for the set of controller tuning parameters during operation of the process using a set of stored process model parameter values and a process state variable, wherein the set of stored process model parameter values includes a process model parameter value for a particular process model parameter for each of a plurality of different process operating points defined by the process state variable;

the tuning routine including;

a model adaptation routine that determines the stored process model parameter value for the process model parameter at each of the plurality of different process operating points,

a model parameter determination routine that determines a particular process model parameter value for a particular process operating point based on the process state variable value and the set of stored process model parameter values; and

a controller tuning parameter routine that determines the set of controller tuning parameters for the particular process operating point from the determined process model parameter value and a stored tuning rule.

29. The adaptive process controller system of claim 28, wherein the model adaptation routine stores an interpolation function parameter for determining a process model parameter value at process operating points between two or more of the plurality of different process operating points associated with the set of stored process model parameter values, and wherein the model parameter determination routine further determines the particular process model parameter value for the particular process operating point using the interpolation function parameter.

30. The adaptive process controller system of claim 29, wherein the model adaptation routine updates the set of stored process model parameter values by determining a new process model parameter value for a specific process operating point and changing the set of stored process model parameter values based on the new process model parameter value for the specific process operating point.

31. The adaptive process controller system of claim 30, wherein the model adaptation routine updates the set of stored process model parameter values by changing the interpolation function parameter based on the new process model parameter value for the specific process operating point.

32. The adaptive process controller system of claim 30, wherein the model adaptation routine updates the set of stored process model parameter values based on the new process model parameter value for the specific process operating point by storing the new process model parameter value for the specific process operating point as one of the set of stored process model parameter values, and culling the set of stored process model parameter values if the number of process model parameter values within the set of stored process model parameters values reaches a threshold.

33. The adaptive process controller system of claim 30, wherein the model adaptation routine changes the set of stored process model parameter values based on the new process model parameter value for the specific process operating point by changing two or more of the set of stored process model parameter values without changing their associated process operating points, based on the new process model parameter value at the specific process operating point.

34. The adaptive process controller system of claim 30, wherein the process controller routine implements a feedforward/feedback controller technique.