Velocity based control in a non-periodically updated controller
First Claim
1. A method of controlling a process, comprising:
- implementing, on a computer processing device, multiple iterations of a control routine to generate a control signal including, during each iteration of the control routine;
generating, using a computer processing device, an integral feedback contribution for use in producing the control signal, including using, during each of the multiple iterations including a current iteration, a continuously updated iterative filter to determine a current integral feedback contribution value for the current iteration of the control routine from an integral feedback contribution value of a preceding iteration of the control routine and a value of the control signal;
using, as determined by a switch coupled to the continuously updated iterative filter, the current integral feedback contribution to generate the control signal for the current iteration of the control routine during each controller iteration at which a new process response indication is received, and not using, as determined by the switch, the current integral feedback contribution to generate the control signal during controller iterations at which a new process response indication to the control signal is not received; and
using the control signal to control the process.
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Abstract
A technique for controlling a process using slow or non-periodically received process variable measurements enables more robust controller responses to setpoint changes and disturbance changes even when the process variable measurement feedback signals are reviewed at a rate on the order of the rate associated with the response time of the process dynamic or variable being controlled. The control technique implements iterations of a control routine to generate a control signal using a reset or rate contribution component that, in some sense, defines an expected process response to the control signal. When a new measurement of the process variable is unavailable to the controller, the reset or rate contribution component is maintained at zero or at some other previous level when generating the control signal. However, the reset contribution component is iteratively recalculated during each controller execution cycle, even when no new process variable measurement has been received, so that the output of the reset contribution component incorporates expected process changes that occur as a result of a setpoint or a feed-forward change that impacts the process input or control signal between the times that actual process variable measurement values are received at the controller. This technique makes the controller more robust when producing control signals in the presence of setpoint or feed-forward changes received between the times at which non-periodic process variable measurements are received at the controller and makes the controller operate better when the process variable feedback time interval is greater, equal to or on the order of the process response time.
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Citations
37 Claims
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1. A method of controlling a process, comprising:
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implementing, on a computer processing device, multiple iterations of a control routine to generate a control signal including, during each iteration of the control routine; generating, using a computer processing device, an integral feedback contribution for use in producing the control signal, including using, during each of the multiple iterations including a current iteration, a continuously updated iterative filter to determine a current integral feedback contribution value for the current iteration of the control routine from an integral feedback contribution value of a preceding iteration of the control routine and a value of the control signal; using, as determined by a switch coupled to the continuously updated iterative filter, the current integral feedback contribution to generate the control signal for the current iteration of the control routine during each controller iteration at which a new process response indication is received, and not using, as determined by the switch, the current integral feedback contribution to generate the control signal during controller iterations at which a new process response indication to the control signal is not received; and using the control signal to control the process. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A process controller that generates a control signal for controlling a process variable during each of a multiplicity of controller iterations of the process controller, comprising:
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a communications unit that receives a new value of the process variable at less than each of the multiplicity of iterations of the process controller; a proportional control component that generates a proportional control signal value during each of the iterations of the process controller including, a first summer that determines a difference between a set point value for the process variable and a received value of a process variable, and a proportional gain unit coupled to the summer; an integral control component that generates an integral control signal value during each of the iterations of the process controller including, a continuously updated iterative filter that determines a preliminary integral control component during each iteration of the process controller based on a previous value of the preliminary integral control component generated during a previous iteration of the process controller and based on the control signal for the current iteration of the process controller; a switch coupled to the continuously updated iterative filter that receives the preliminary integral control component and a further value, wherein the switch operates to provide the preliminary integral control component generated by the continuously updated iterative filter during process controller iterations associated with the receipt of a new value of the process variable at the communications unit as the integral control signal value and that provides the further value as the integral control signal value during controller iterations that are not associated with the receipt of a new value of the process variable at the communications unit; and a second summer that sums the proportional control signal value and the integral control signal value during each process controller iteration to produce the control signal. - View Dependent Claims (11, 12, 13, 14)
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- 15. The process controller of clam 10, wherein the integral control component further includes a third summer coupled to the iterative filter, wherein the third summer sums the control signal for previous controller iterations to produce a summed control signal value and wherein the third summer provides the summed control signal value as an input to the iterative filter.
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21. A method of generating a velocity based process control signal during each of a multiplicity of iterations of a control routine, comprising:
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receiving, via a computer processing device, a new value of the process variable being controlled at less than each the multiplicity of iterations of the control routine; generating, using a computer processing device, during each of the multiplicity of iterations of the control routine, a difference based integral feedback contribution for use in producing the control signal, including summing the control signal generated during each iteration of the control routine since the last iteration of the control routine at which a new process variable value was received to produce a summed control signal, providing the summed control signal to a continuously updated iterative filter, and using, during each of the multiplicity of iterations, the continuously updated iterative filter to determine a current integral feedback contribution value for the current iteration of the control routine from an integral feedback contribution value of a preceding iteration of the control routine and the summed control signal; and using, as determined by a switch coupled to the continuously updated iterative filter, the current integral feedback contribution value to generate the control signal for the current iteration of the control routine during each iteration at which a new process variable value is received, and not using, as determined by the switch, the current integral feedback contribution value to generate the control signal during iterations at which a new process variable value is not received from the process; and using the control signal to control the process variable. - View Dependent Claims (22, 23, 24, 25, 26)
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27. A velocity based process controller that generates a control signal for controlling a process variable during each of a multiplicity of controller iterations of the process controller, comprising:
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a communications unit that receives a new value of the process variable at less than each of the multiplicity of iterations of the process controller; an integral control component that generates an integral control signal value during each of the iterations of the process controller including, a continuously updated iterative filter that determines a preliminary integral control component during each iteration of the process controller based on a previous value of the preliminary integral control component generated during a previous iteration of the process controller and based on the control signal for the current iteration of the process controller; and a switch coupled to the continuously updated iterative filter that receives the preliminary integral control component and a further value, wherein the switch operates to provide the preliminary integral control component generated by the continuously updated iterative filter during process controller iterations associated with the receipt of a new value of the process variable at the communications unit as the integral control signal value and that provides the further value as the integral control signal value during controller iterations that are not associated with the receipt of a new value of the process variable at the communications unit; and a control signal generator coupled to receive the integral control signal value to generate a control signal for use in controlling the process during each of the controller iterations. - View Dependent Claims (28, 29, 30, 31, 35, 36, 37)
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- 32. The velocity based process controller of clam 27, wherein the integral control component includes a further summer coupled to the iterative filter, wherein the summer sums the control signal for previous controller iterations to produce a summed control signal value and wherein the summer provides the summed control signal value as an input to the iterative filter.
Specification