Data processing: generic control systems or specific application – Generic control system – apparatus or process – Optimization or adaptive control
Reexamination Certificate
2000-05-31
2003-09-09
Follansbee, John (Department: 2121)
Data processing: generic control systems or specific application
Generic control system, apparatus or process
Optimization or adaptive control
C700S029000, C700S030000, C700S031000, C700S032000, C700S047000, C700S048000, C700S173000, C701S058000, C701S059000, C701S060000, C701S063000, C701S068000
Reexamination Certificate
active
06618631
ABSTRACT:
FIELD OF THE INVENTION
The invention is directed to an adaptive control system and related method. More particularly, the invention is directed to an adaptive control system with the capability to prevent or reduce undesired adaptation of a control system due to selected characteristic(s) of the plant or control system.
BACKGROUND OF THE INVENTION
Adaptive control systems have the capability to adapt control response to changing conditions within the plant being controlled or the plant's operating environment. Adaptation to changing plant or environmental conditions provides enhanced control response for many kinds of plants, and may be required for certain types of plants that cannot be controlled with static control systems. However, conventional adaptive control systems have a tendency to adapt to plant or control system characteristics to which they should not. The control response of adaptive control systems can be greatly diminished when subjected to certain characteristic(s) of the plant or system, and can be rendered unstable in attempting to adapt to these characteristics. An example of a characteristic that could adversely affect an adaptive control system is a control or authority limit imposed on the control elements of an adaptive control system. If an operator generates a command signal that exceeds the ability of the control system or plant to respond, adaptation of the control system can render the control system unstable. It is desirable to reduce or prevent the impact of such characteristic(s) from adversely affecting the adaptive control system's performance.
SUMMARY OF THE INVENTION
The methods, apparatus, and system, of the invention overcome the disadvantages noted above.
A first method of the invention comprises generating a hedge signal to avoid adaptation to a characteristic of at least one of an adaptive control system and a plant controlled by such system. The first method can comprise modifying a commanded state signal with the hedge signal. The first method can also comprise generating a reference model state signal using the commanded state signal modified by the hedge signal. The first method also can comprise generating a tracking error signal based on the reference model state signal and a plant state signal, and generating an adaptive control signal to adapt control response of the adaptive control system. Through compensation for the characteristic in the tracking error signal, the adaptive control signal can be generated so as not to significantly adapt to the characteristic. Hence a characteristic of the plant or control system that would impair or be detrimental to control system's performance and/or stability can be hedged out of the adaptive portion of the control system to prevent adverse impact on control of the plant. The hedge signal can be generated based on a difference between a first signal derived from a plant model not having the characteristic to be hedged, and a second signal derived from a plant model having the characteristic. The first signal can generated based on an input control signal and a plant state signal in addition to the plant model not having the characteristic. The second signal can be generated using a command control signal and a plant state signal, in addition to the plant models with the characteristic. The input control signal can be generated based on a commanded state signal, a plant state signal, and an adaptive control signal, and the command control signal can be generated using the input command signal modified by a control allocation and a control characteristic imposed by a controller. The input control signal and command control signal can be used to hedge a characteristic of the control system to which adaptation is not to be performed. The method can also include generating a display based on the input control signal. An operator can use the display to generate a command control signal. In this aspect of the invention, the operator's control and response can be hedged.
A second method of the invention is executed by an adaptive control system. The second method comprises generating an input control signal based on a commanded state signal, a plant state signal, and an adaptive control signal. The second method also comprises generating a command control signal based on a commanded state signal, a plant state signal, an adaptive control signal, and further based on control allocation and a control characteristic of a controller used to generate the command control signal. The second method further comprises supplying the command control signal to an actuator, controlling a state of the plant based on the command control signal, sensing a state of the plant, and generating a plant state signal based on the sensing of the plant. The second method comprises generating a first signal based on the input control signal, the plant state signal, and a plant model without a plant characteristic to which the adaptive control system is not to adapt. The second method also comprises generating a second signal based on the command control signal, the plant state signal, and a plant model with the plant characteristic to which the adaptive control system is to adapt. The second method further comprises generating a hedge signal by differencing the first and second signals, and generating a reference model state signal by modifying the commanded state signal with the hedge signal to include the effect of the control allocation and control characteristic on plant state from the reference model state signal. The second method further comprises comparing the plant state signal and the reference model state signal, generating a tracking error signal based on the comparing step, and generating the adaptive control signal based on the tracking error signal. The second method can comprise generating a reference model signal based on the commanded state signal, the hedge signal, and a reference model signal derived from a reference model representing the target response of the plant, the reference model signal to generate the input control signal. The second method can also comprise generating a reference model signal based on the commanded state signal, the hedge signal and a reference model signal derived from a reference model representing the target response of the plant, the reference model signal, to generate the command control signal. The second method can also comprise generating a linear control signal based on the tracking error signal, generating a reference model signal based on the commanded state signal, the hedge signal, and a reference model, and generating a pseudo- control signal based on the linear control signal, the reference model signal, and the adaptive control signal, and the pseudo-control signal. The adaptive control signal can be generated with the plant state signal. The adaptive control signal can be generated with a neural network having connection weights adjusted based on the tracking error signal and the pseudo-control signal. The neural network maps the plant state signal to the adaptive control signal. The plant state signal can also be used to generate the adaptive control signal. The second method can comprise generating the commanded state signal based on a control action from an operator. The operator can be human, and the method can comprise generating a display based on the plant state signal. The display can be used by the operator to generate the commanded state signal. The second method can comprise generating the commanded state signal based on a signal generated by an operator that is a computer. The second method can also comprise generating a display for an operator based on the input control signal so that the operator can generate the command control signal based on the display.
An apparatus of the invention can be used in an adaptive control system for controlling a plant. The apparatus is a hedge unit coupled to receive at least one control signal and a plant state signal. The hedge unit generates a hedge signal based on the control signal, the
Calise Anthony J.
Johnson Eric Norman
Follansbee John
Georgia Tech Research Corporation
Pham Thomas
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