Velocity based control in a non-periodically updated controller

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.