On-line adaptive model predictive control in a process control system
First Claim
1. An adaptive process controller for controlling one or more devices within a process plant, the adaptive process controller comprising:
- a controller having a prediction unit that uses a prediction model to determine a prediction signal for a set of one or more process variables, a prediction error unit that combines the prediction signal with a set point signal to produce a prediction error signal, and a combiner that multiplies the prediction error signal by a controller gain signal to produce a change in a control signal and that uses the change in the control signal to develop a control signal for controlling one of the set of process variables;
a process model estimation unit communicatively coupled to one or more devices within the process plant to collect process data during the on-line operation of the process plant and that determines a new process model representing the operation of a portion of the process plant from the collected process data, the new process model including a set of model parameters defining characteristics of the portion of the process plant; and
a controller adaptation unit that uses a closed form equation that expresses a new controller gain signal as a function of at least one of the set of process model parameters of the new process model to calculate the new controller gain signal and that adapts the controller to use the new controller gain signal while the controller is operating on-line to control the portion of the process plant.
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Abstract
A method of creating and using an adaptive DMC type or other MPC controller includes using a model switching technique to periodically determine a process model, such as a parameterized process model, for a process loop on-line during operation of the process. The method then uses the process model to generate an MPC control model and creates and downloads an MPC controller algorithm to an MPC controller based on the new control model while the MPC controller is operating on-line. This technique, which is generally applicable to single-loop MPC controllers and is particularly useful in MPC controllers with a control horizon of one or two, enables an MPC controller to be adapted during the normal operation of the process, so as to change the process model on which the MPC controller is based to thereby account for process changes. The adaptive MPC controller is not computationally expensive and can therefore be easily implemented within a distributed controller of a process control system, while providing the same or in some cases better control than a PID controller, especially in dead time dominant process loops, and in process loops that are subject to process model mismatch within the process time to steady state.
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Citations
31 Claims
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1. An adaptive process controller for controlling one or more devices within a process plant, the adaptive process controller comprising:
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a controller having a prediction unit that uses a prediction model to determine a prediction signal for a set of one or more process variables, a prediction error unit that combines the prediction signal with a set point signal to produce a prediction error signal, and a combiner that multiplies the prediction error signal by a controller gain signal to produce a change in a control signal and that uses the change in the control signal to develop a control signal for controlling one of the set of process variables; a process model estimation unit communicatively coupled to one or more devices within the process plant to collect process data during the on-line operation of the process plant and that determines a new process model representing the operation of a portion of the process plant from the collected process data, the new process model including a set of model parameters defining characteristics of the portion of the process plant; and a controller adaptation unit that uses a closed form equation that expresses a new controller gain signal as a function of at least one of the set of process model parameters of the new process model to calculate the new controller gain signal and that adapts the controller to use the new controller gain signal while the controller is operating on-line to control the portion of the process plant. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)
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16. A method of adapting a process controller that controls one or more devices to implement a process within a process plant using a prediction unit that uses a prediction model to determine a prediction signal for a set of one or more process variables, a prediction error unit that combines the prediction signal with a set point signal to produce a prediction error signal, and a combiner that multiplies the prediction error signal with a controller gain signal to produce a change in a control signal, and that uses the change in the control signal to develop a control signal for controlling the one or more devices, the method comprising:
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collecting process data during on-line operation of the process plant; determining, from the collected process data, a new process model including a set of model parameters that characterize the process; using a closed form equation that expresses a new controller gain signal as a function of at least one of the set of model parameters to calculate the new controller gain signal; and providing the new controller gain signal to the process controller for use as the controller gain signal in controlling a portion of the process plant during subsequent operation of the process controller. - View Dependent Claims (17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31)
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Specification