Partitioned control structure

Details Partitioned control structure Partitioned control structure

2000-03-20

2004-04-13

Patel, Ramesh (Department: 2121)

Data processing: generic control systems or specific application

Generic control system, apparatus or process

Optimization or adaptive control

C700S029000, C700S037000, C700S045000

Reexamination Certificate

active

06721608

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to control systems, and more particularly to process control systems in a two degree of freedom system.
BACKGROUND OF THE INVENTION
A process control system implements a controller to shape the response of a process to an input signal. The control system can add gain, time varying properties, frequency components, or a combination of these characteristics to the process signal. By properly choosing these characteristics, the control system can stabilize the response of the process, determine overshoot, on set acceptable error bounds and satisfy other performance criteria.
A two degree of freedom controller is generally implemented in a two degree of freedom system. Such a two degree of freedom system could consist of a setpoint and a disturbance. Within this system, the controller should track the setpoint and reject any disturbances. Controllers of this type, for example, include the precompensator
10
of FIG.
1
.
The precompensator
10
of
FIG. 1
includes a prefilter
12
and a load controller
14
. These two control elements
12
and
14
shape a process input
16
for a process
18
. The prefilter
12
shapes a prefilter response
20
to an input variable
22
. The load controller
14
shapes the input
16
to the process
18
based on the prefilter response
20
and a process state
30
that is feedback for the system. The process state
30
is altered by a second variable
32
and the transfer function
36
of the second variable
32
.
In the configuration of the precompensator
10
, the load controller
14
must shape the process input
16
based in part on the prefilter response
20
. Any inaccuracies from error in the prefilter
12
are propagated through the load controller
14
.
SUMMARY OF THE INVENTION
In accordance with a principal feature of the invention, a control structure comprises a first controller, a second controller, and a process model. The first controller and the process model are configured in a partitioned feedback loop to receive input from a first variable. The second controller is configured in parallel with the first controller to receive input from a partitioned feedback loop and feedback from a process. The process receives input from a second variable.
In accordance with another principal feature of the invention, the control structure comprises the first controller, the second controller, and the process model. The first controller shapes a response to the first variable. The process model predicts the output of the process. The second controller is isolated from the first input and receives its input from the predicted output and feedback from a process output. The second controller shapes a response to an error between the predicted output and the measured output.


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