Modular multivariable control apparatus and method
First Claim
1. A method of controlling a process variable through at least two control efforts, comprising the steps of:
- a) measuring a disturbance of the process variable from a desired value;
b) determining the dead time interval between the change of a control effort and a change in the process variable for each such control effort;
c) changing at least one such control effort to at least partly compensate for such disturbance in the short term;
d) changing at least one such control effort to at least partly compensate for such disturbance in the long term; and
e) returning such control efforts changed to compensate in the short term to their original values after such control efforts changed to compensate in the long term have compensated for such disturbance.
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Abstract
A method of controlling a process including at least two process variables and at least two control efforts, with each control effort having an influence on at least one process variable, including the steps of modelling the influence that a change in each control effort has on each process variable; describing the desired trajectory which each process variable will follow towards its desired value in response to a system change; and, coupling the control of each process variable; whereby changing a first set of at least one control efforts so as to cause a desired change in at least one process variable can be compensated for by a change in a second set of at least one control efforts so that substantially no influence in exhibited on other process variables in the system in which no change is desired. The method may include delaying a desired change in such first set of control efforts a time equal to the maximum dead time lapse of any control effort of such second set of control efforts relative to any such process variable for which no change in desired.
45 Citations
18 Claims
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1. A method of controlling a process variable through at least two control efforts, comprising the steps of:
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a) measuring a disturbance of the process variable from a desired value; b) determining the dead time interval between the change of a control effort and a change in the process variable for each such control effort; c) changing at least one such control effort to at least partly compensate for such disturbance in the short term; d) changing at least one such control effort to at least partly compensate for such disturbance in the long term; and e) returning such control efforts changed to compensate in the short term to their original values after such control efforts changed to compensate in the long term have compensated for such disturbance. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A method of controlling a process including at least two process variables and at least two constrained control efforts, with each control effort having an influence on at least one such process variable, comprising the steps of:
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a) modelling the influence that a change in each such control effort has on each such process variable; b) describing the desired trajectory which each such process variable will follow towards its desired value in response to a system change; c) ranking each such control effort relative to each such process variable according to the priority in which it will be changed; d) coupling the control of each such process variable; e) changing an unsaturated control effort of highest rank of a first set of at least one control effort to compensate for a disturbance to a process variable until such disturbance is compensated for or until such highest ranked control effort is saturated, then changing a next highest ranked control effort of the first set until such disturbance is compensated for; and
,f) changing at least one control effort of a second set of at least one control effort so as to compensate for changes in said first set of at least one control efforts such that substantially no influence is exhibited on other process variables in the system in which no change is desired. - View Dependent Claims (9, 10, 11, 12, 13, 15, 16, 17)
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14. The method of claim wherein such ranking generally corresponds to the respective dead times for each control effort, with higher long term priority control effects generally having longer dead times than lesser long term priority control effects.
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18. An apparatus for controlling a process including at least two process variables ranked in accordance with the relative importance of their control and at least two control efforts for controlling said process variables, comprising:
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means for measuring the values of each process variable; means for effecting a change in the value of at least one control effort of a first set of control efforts to compensate for a disturbance to a first process variable; and compensating means for compensating for the effects that a change in said first set of control efforts has on other process variables by effecting a change in at least one control effort of a second set of control efforts and for delaying or prohibiting changes to said first set of control efforts until compensation for any higher ranked process variables can be initiated.
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Specification