Data processing: generic control systems or specific application – Generic control system – apparatus or process – Optimization or adaptive control
Reexamination Certificate
2001-01-08
2002-11-12
Gordon, Paul P. (Department: 2121)
Data processing: generic control systems or specific application
Generic control system, apparatus or process
Optimization or adaptive control
C700S042000, C700S289000
Reexamination Certificate
active
06480750
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a controlling system and to a method for operating a controlling system having a controller which acts on a controlled system with the aid of a manipulated variable as a function of a number of controller parameters.
A technical plant usually has a number of controlling systems whose purpose is to ensure an undisturbed operation of the plant. Such a controlling system usually acts on an associated controlled system so as to produce a closed control loop. In this case, for example, a sensor at the measuring point of the controlled system measures the controlled variable to be observed. If, due to a disturbance variable, the controlled variable deviates from a prescribed desired value, the controller of the controlling system acts with the aid of its manipulated variable on an actuator assigned to the controlled system. The manipulated variable supplied by the controller depends in this case on the deviation of the measured controlled variable from the prescribed desired value and further depends on a number of controller parameters via which it is possible, for example, to set the reaction rate and/or the setting accuracy of the controller.
Because of a lack of systematic knowledge of the real dynamic response of the controlled system, the setting of the controller parameters—the so-called parameterization—of such a controller is usually based on empirically obtained data which are determined, for example, when the plant is put into operation. These data are used to prescribe, for the respective controller, controller parameters which are retained unchanged during further operation. However, in the case of such a controlling system, a variation in the properties of the controlled system can lead to an impairment or deterioration of the control quality, in particular to impairment of the setting accuracy and/or of the rate of reaction of the controller. variations in the properties of the controlled system can occur in this case, in particular, from a change in load point or a change in the machine characteristic, for example because of aging or pollution.
The book by O. Völlinger, Regelungstechnik [Control engineering], 6th edition, Huttich Buchverlag Heidelberg, 1990, Chapter 1.6, pages 14 to 20, discloses an adaptive control method in which the variable system performance caused by fluctuating parameters of the controlled system is firstly detected in a suitable way, and the controller parameters are fixed with the aid of the information thus obtained.
Furthermore, U.S. Pat. No. 5,610,843 discloses the use of wavelet transformations for the purpose of characterizing controlled systems. The use of wavelet transformations is also discussed in Japanese Patent Application JP 09120303.
Furthermore, German Patent DE 34 45 791 discloses a steam turbine generator system in which the vapor pressure and the temperature can be controlled.
The article entitled “Self-tuning control of nonlinear systems using neural network adaptive frame wavelets”, which was published in the 1997 International Conference on systems man and cybernetics, volume 2, Oct. 12, 1997, pages 1017-1022, describes a special neural network with the aid of which a dynamically varying plant operation can be controlled. In accordance with the mathematical model presented therein, a wavelet transformation of an input function is performed for the process. This wavelet transformation is a basis for estimating an output function. The estimated output function is optimized by iteration steps by comparing the estimated output function with a measured output function, in order to be able to control the plant suitably.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a method for operating a controlling system, which maintains the control quality and control response of the control loop even in the case of a variation in the properties of the controlled system. It is a further object of the invention to provide a controlling system having an improved control quality and control response.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for operating a controlling system, the method includes the steps of:
acting, with a controller of a controlling system, on a controlled system by using a manipulated variable, the controller acting in dependence of a plurality of controller parameters;
determining a response characteristic of the controlled system during operation of the controller by comparing a wavelet transformation of a temporal response of the manipulated variable with a wavelet transformation of a temporal response of a controlled variable of the controller in a given time window;
ascertaining respective instants assigned to the wavelet transformation of the temporal response of the manipulated variable and to the wavelet transformation of the temporal response of the controlled variable; and
setting at least one of the controller parameters as a function of the response characteristic.
In other words, the object of the invention is achieved by virtue of the fact that the response characteristic of the controlled system is determined in a prescribable time window during operation of the controller by comparing a wavelet transformation of the temporal response of the manipulated variable with a wavelet transformation of the temporal response of a controlled variable of the controller of the controlled system, an instant assigned to the respective wavelet transformation being detected, and the or each controller parameter being set as a function of the response characteristic determined.
The invention is based on the consideration that in the event of a change in the properties of the controlled system, the control quality and the control response of the control loop are maintained even when the variation in the response of the controlled system is detected and used to adapt the controller parameters. The response characteristic of the controlled system is particularly suitable in this case for characterizing the controlled system. A variation in the response characteristic of the controlled system should therefore act on the controller parameters. In order to avoid impairment of the functionality of the controlled system, in this case the resetting of the controller parameter or parameters is performed as a function of the determined response characteristic of the controlled system in the manner of an online intervention during operation of the controller.
A wavelet transformation is used in this case to determine the response characteristic of the controlled system during operation of the controlling system. In this case, the temporal variation of the manipulated variable and of a controlled variable of the controller of the controlled system are analyzed in the same way in a prescribable time window with the aid of a wavelet transformation. The method of wavelet transformation is described, for example, in the journal Automatisierungstechnik [automation technique], edition 2, 1996, R. Oldenbourg publishers, pages 64 to 66.
With this analysis it can be established whether a prescribable component of the manipulated variable is included in the controlled variable. This is performed by decomposing the manipulated variable or the control variable into components of a so-called wavelet family in a prescribable time window at a specific instant or point in time. A wavelet family is a family of mathematical functions which are generated by mathematical stretching and/or displacement from a single output function. The mathematical stretching and/or displacement of the function in this case signifies adaptation to various frequency and amplitude components of a signal to be investigated. The time when the variable to be investigated has specific properties can be determined in this case on the basis of the presence of prescribable wavelet components within the framework of the prescribable time window.
The response characteristic of the controlle
Gordon Paul P.
Greenberg Laurence A.
Locher Ralph E.
Siemens Aktiengesellschaft
Stemer Werner H.
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