Data processing: generic control systems or specific application – Generic control system – apparatus or process – Optimization or adaptive control
Reexamination Certificate
2001-04-09
2003-05-27
Patel, Ramesh (Department: 2121)
Data processing: generic control systems or specific application
Generic control system, apparatus or process
Optimization or adaptive control
C700S019000, C700S034000, C700S041000, C700S067000, C700S073000, C700S074000, C318S609000, C318S610000
Reexamination Certificate
active
06571135
ABSTRACT:
FIELD OF AND BACKGROUND OF THE INVENTION
The invention relates to a control unit for controlling a system with several coupled variables.
The paper by W. Engel entitled “Grundlegende Untersuchungen über die Entkopplung von Mehrfachregelkreisen” [Basic Investigations on the Decoupling of Multiple Control Loops] published in “Regelungstechnik,” 1966, Number 12, pp. 562 to 568 already discloses a control system for a process in which several variables that reciprocally influence one another are controlled. The P-canonical and V-canonical structures are indicated as possible ways to describe a process with several coupled control variables of a so-called multivariable system. If nothing is known about the relationships and the signal shape within a multiple control system it is proposed to select the P-canonical structure for simplicity's sake. In a P-canonical structure of a transmission system, each output variable depends on the input variables but not on other output variables.
FIG. 1
shows a block diagram of a 2×2 multivariable system in P-canonical structure. The input variables are labeled y
1
and y
2
and the output variables x
1
and x
2
. In a controlled system, the input variables y
1
and y
2
represent manipulated variables provided to actuators, while the output variables x
1
and x
2
represent metrologically recorded control variables of the controlled system. The structure shown may be readily expanded for a different number of inputs and outputs as discussed in the aforementioned paper by Engel for an n×n system. The two transfer functions g
11
and g
22
between the input variable y
1
and the output variable x
1
, or between the input variable y
2
and the output variable x
2
, are referred to as main systems, the transfer functions g
12
and g
21
between y
2
and x
1
or between y
1
and x
2
are referred to as coupling systems.
The P-canonical structure has the advantages both that it is clear for the user and that conventional methods may be used to identify the transfer functions in the main systems and the coupling systems. A suitable identification method is described, for instance, in German reference DE 41 20 796 A1. The identification of the transfer functions g
11
and g
21
may be carried out in accordance with the conventional method by keeping input variable y
2
constant and using input variable y
1
to apply an excitation function to the transfer elements, i.e., to the system to be controlled. From the responses of the output variables x
1
and x
2
, a suitable transfer function g
11
or g
21
can be calculated. Analogously, the transfer functions g
12
and g
22
should also be determined with a constant input variable y
1
.
The aforementioned paper by Engel, which is incorporated into the present application by reference, further states that such a multivariable system may be controlled by a device depicted in FIG.
2
. The principal structure is again described by means of a 2×2 multivariable system, which is provided with identical reference numbers as those used in
FIG. 1. A
decoupling network
2
in P-canonical structure is connected upstream from the multivariable system
1
. Decoupling members
3
and
4
realize transfer functions k
21
and k
12
, respectively, which may be determined, for instance, by the method described in the paper by Engel. The task of the decoupling members k
21
and k
12
is to reduce the extent of coupling within the multivariable system
1
, which in the control loop shown represents the system, so that the precompensated system
5
, formed by system
1
and the decoupling network
2
that precedes it, is approximately decoupled. In this case, approximately decoupled means that the effective paths from an output signal u
1
of a controller
6
with a transfer function r
11
to the control variable x
2
and from an output signal u
2
of a controller
7
with a transfer function r
22
to the control variable x
1
are without significance for the configuration of the control transfer functions r
11
and r
22
. In the ideal case, there is no longer any effective connection between the output variable u
1
and the control variable x
2
or between the output variable u
2
and the control variable x
1
. The precompensated system
5
is thus separated into two single-variable systems with the input variable u
1
and the output variable x
1
, or with the input variable u
2
and the output variable x
2
, for which a single variable controller
6
or
7
may be configured. A suitable configuration method for PI or PID controllers in single variable systems is, for instance, the magnitude optimum known from European Patent EP 0 707 718 B1.
The control unit shown in
FIG. 2
may be readily implemented in a process control system. Various controller types and summation points are usually available as function modules. Thus, only the decoupling members must be newly implemented.
The described control unit exhibits good control response in linear operation. No strategy is known, however, which may be used to deal advantageously with non-linear cases, which occur in practice, e.g., if the manipulated variable y
1
runs into its limit or if the controllers
6
or
7
are switched between manual and automatic operation.
OBJECTS OF THE INVENTION
One object of the present invention is to provide a control unit to control a system with several coupled control variables, which is characterized by an improved control response.
SUMMARY OF THE INVENTION
To attain this and other objects, the novel control unit of the aforementioned type has controllers each of which is associated and has a control variable with a decoupling network connected upstream from the system. The decoupling network has at least a first decoupling member to which the output variable of a first controller is routed and which generates a first correcting quantity for the output variable of a second controller, to reduce the coupling between the control variables. The second controller has a PI or PID controller core and is configured such that the value of the integral action component and the output variable of the second controller are kept constant when the output variable of the controller core of the second controller corrected with the first correcting quantity reaches a manipulated variable limit. Additional embodiments are also described below.
The invention has an advantage that the control variable, even if the associated manipulated variable was previously at the manipulated variable limit, quickly responds to a sign change in the corresponding control deviation at the input of the controller. The reason for this is that the manipulated variable change performs a change in its sign immediately after a sign change in the control deviation, since the so-called integrator windup, i.e., the runaway of the integrator of a PI or PID controller, is eliminated while the manipulated variable is at its limit. If only one decoupling member is used in a multivariable control, it is sufficient to detect a manipulated variable limit merely by means of the output variable of the corresponding controller, which is corrected by the correcting quantity of the decoupling member, and to use a suitable strategy to eliminate integrator windup.
Various strategies are possible to eliminate integrator windup. One option is to keep constant the state, i.e., the value of the integral action component and the output of the controller when the controlled variable limit is reached. Another option for eliminating integrator windup is to switch a determined quantity instead of the control deviation to the controller core, as long as the corrected output variable would reach or would exceed the manipulated variable limit if the control deviation were applied to the controller core, so that the corrected output variable of the controller corresponds to the value of the manipulated variable limit. This option is described in detail in the European Patent EP 0 707 718 B1, to which reference is made for further details, and which is incorporated by refer
Bergold Stefan
Pandit Madhukar
Pfeiffer Bernd-Markus
Patel Ramesh
Siemens Aktiengesellschaft
Sughrue & Mion, PLLC
LandOfFree
Control unit for controlling a system with several coupled... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Control unit for controlling a system with several coupled..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Control unit for controlling a system with several coupled... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3093582