Method and device for determining model parameters to control modules of a steam power plant

A technology of model parameters and steam generators, which is applied in the direction of steam engine devices, steam generation, control systems, etc., which can solve the unavoidable, inaccurate estimated values ​​of boiler time constants stored in time constants, and the inability to rule out the decline of control quality over time, etc. problems to achieve high flexibility

Active Publication Date: 2016-08-03
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AI-Extracted Technical Summary

Problems solved by technology

The disadvantage of this approach, however, is that the value of the storage time constant must always also be specified in advance
The overhead for measuring and storing the time constant cannot thus be avoided
In addition, the inaccuracy of the stored time constant directly contributes to the in...
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The invention relates to a method and to a corresponding device for determining at least one model parameter of a control engineering model of a steam generator, wherein a control engineering model structure having the at least one characteristic model parameter is predetermined for the steam generator. Measurement signals of the steam generation process are recorded online. According to the invention, the at least one model parameter is estimated online. For this purpose the same input signal is applied to both the real process and the model of the steam generator. Next, an estimability analysis is carried out, wherein at least one output signal of the respective process and/or model, or at least one input signal, are processed by a comparative evaluation on the basis of a gradient analysis. Estimation ranges within which a valid parameter estimation is possible are defined in a further step on the basis of the gradient analysis. If the estimability is positively assessed, the current estimated value of the at least one model parameter is improved and furthermore the model is adapted by means of the estimated values in an iterative process. The invention further relates to a control unit for a steam generator and to a computer program product.

Application Domain

Simulator controlBoiler control +2

Technology Topic

Comparative evaluationSteam-electric power station +8


  • Method and device for determining model parameters to control modules of a steam power plant
  • Method and device for determining model parameters to control modules of a steam power plant
  • Method and device for determining model parameters to control modules of a steam power plant


  • Experimental program(1)

Example Embodiment

[0023] Figure 1 is used to illustrate the dynamic process of steam generation and explain two model parameters: the boiler time constant TDE and the storage time constant TSP.
[0024] in Figure 1A A block diagram of the steam generator is shown in simplified form. The combustion chamber of the boiler K is fed with fuel BR at its entrance, where the fuel may be, for example, coal that is pulverized into pulverized coal in a coal pulverizer. Fuel can be measured here The material flow rate. The corresponding thermal power of the fuel Corresponds to the material flow rate corrected for the heating value HW of the fuel. The fuel is burned inside the boiler K. In order to generate steam, the water supplied in the pipe in the wall of the steam generator is heated and vaporized. Through the superheater The piping system delivers the steam to the turbine valve TV. Steam generation DE ges The whole process is ideally divided into two parts: the actual steam generation DE and the steam storage (Dampfspeicherung) SP, where the previously generated steam is collected and stored in the steam storage. Here, the steam storage SP shown is only used to illustrate the conceptual model, and the steam storage corresponds to the total volume of all pipes of the steam generator. In the steam generator DE ges Get the fresh steam material flow rate at the output end (Frischdampfmassenstrom) And measure the steam pressure p D. Turbine material flow m T Equal to the adjusted fresh steam material flow rate after the steam generator
[0025] Figure 1B The possible deformation of the structural model of the control technology of the steam generator is shown. The time-varying parameters and functional relationships are illustrated by appropriate graphic symbols and combined into a structural diagram.
[0026] As an input parameter, the fuel material flow Supplied to the steam generator, which is shown in the figure through the control system DE ges To represent. In the structural model, the different heating value of the fuel is taken into account by the amplification element HW.
[0027] In addition, each combustion and the resulting steam generation also have different efficiency, which is Figure 1B As a separate module η DE Is shown. From the point of view of control technology, these factors are considered to be related to fuel material flow The factor by which the input parameters are multiplied.
[0028] Taking this model into consideration, the dynamics of the steam generation process are divided into two partial systems: actual steam generation and steam storage. According to experience, part of the process of the steam generator can be described by an ideal three-order system model with three identical time constants TDE[s]. This means that in the case of a jump change in the fuel material flow and in the case of a constant pressure, a delay in the turbine material flow occurs, which corresponds to the response of the system with respect to the pT3 element. Thus, the boiler time constant TDE describes the flow of fuel And the steam flow rate on the boiler output The delay between and thus characterizes the dynamic characteristics of coal pulverization, combustion and actual steam generation.
[0029] Part of the process of the steam storage is based on the conceptual model of a locally concentrated storage, where the mass storage distributed throughout the steam generator (for example in a pipeline) is classified into the steam volume. The parameters of the existing steam storage are collected by storing the time constant TSP.
[0030] DE in total steam ges Obtain the turbine steam material flow m at the output end T And send it to the turbine. in Figure 1B The steam volume acquisition is shown by means of a subtractor SUB connected before the steam storage SP. At two material flows And m T The difference between the integral and the steam pressure p in the steam storage SP D Proportional, and, with the steam generator material flow In contrast, it is a measurable parameter. The integral element is shown in the structural model specified here for the purpose of integration. The integral time constant of the steam boiler corresponds to the storage time constant TSP.
[0031] The part of the system that generates the flow (which contains the turbine and the generator) is not part of the control system and is not shown here. However, the valve position y of the turbine input valve T The control parameter (through which the steam flow of the turbine is controlled) is an important parameter because it is used to control the steam flow of the turbine. In the fuel material flow Constant and the flow of material from which steam is generated Also under the constant condition, the jump change of the turbine valve is also at the steam pressure p D Play a role. Increasing the turbine steam material flow mT by opening the turbine valve TV results in a decrease in steam pressure. Material flow in steam generation The storage time constant TSP[%/bars] can be calculated from the change of steam pressure when the position of the turbine valve yT is constant.
[0032] The estimation method according to the present invention is further described below. In this regard, for the sake of clarity, the Figure 1B The model shown in and as an example estimates the model parameters of the boiler time constant TDE and the storage time constant TSP. However, the method can also be applied to a single model parameter or to more than two model parameters through corresponding modifications. Other model parameters (such as the magnification factor) can also be determined in this way.
[0033] according to figure 2 , Clarified the main operation mode in online parameter estimation. In parallel with the actual steam generation process P, a comparison model or simulation model M needs to be compared in order to determine one or more unknown model parameters (time constants in the considered embodiment). If the same input signal ES is connected to both the real process P and the model of the steam generator M, the time constant can be explained according to the output signal of the process ASP (process measurement data) and the simulation model ASM (simulation result) proportion. As a result, the evaluation of the SBA is performed in the first step through the evaluation of the comparison of the signals. Here, at least one output signal or at least one input signal ES of each process ASP and/or model ASM is processed according to gradient analysis. The estimation range is defined according to gradient analysis, and effective parameter estimation is possible within the estimation range. If the estimability is assessed as positive, then in the next step the current estimate for the time constant is improved and fed back to the model. This is figure 2 It is clarified by the estimated value generator SWG in, which also outputs the estimated value SW to the model M. Thus, the iterative approximation of the time constant of the model and the real process is realized.
[0034] In this qualitative method, sufficiently strong incentives for the process constitute a precondition for estimability. If the steam generation process cannot be located in a static state, effective parameter estimation is completely possible. Only for momentary process data, it contains information about the dynamic time characteristics and therefore also information about the time constant of the process. For approximately constant measurement signals, no meaningful parameter estimation can be made. Because it is an online method, it is necessary to judge whether there are effective incentive conditions at each time.
[0035] Evaluate the estimability of the time constant by estimating the SBA. For this reason, in the case of steam generators, relevant system parameters, measurement signals (heat power Steam pressure p D And live steam material flow ). In order to obtain effective excitation conditions, the gradient of these related measurement signals must be determined and analyzed. The gradient analysis is performed by considering at least the first derivative of the process parameters of the real process. Use DT1 differentiator circuit to determine the derivative of system parameters. Based on the derivative generated in this way, the allowable conditions (Freigabe-Bedingungen) for estimating the time constant are then defined respectively.
[0036] in figure 2 The operation mode for online estimation of at least one model parameter shown schematically in can be implemented in different ways in control technology. The operation mode is to perform parallel online online estimation of two characteristic time constants of the steam generator. The estimated range is discussed.
[0037] Here, possible implementations should be presented as special embodiments. The embodiments shown here should not be regarded as limitations of the present invention. More precisely, numerous changes and modifications are possible within the scope of the existing disclosure.
[0038] The following special method is based on the recognition that the time constant can be qualitatively estimated by visually evaluating the response of the delay element to a sufficiently large stimulus. If, for example, the step response of different PT1 elements to the same excitation is examined, a description of the size ratio of the time constant can be obtained from the comparison of the response diagrams. If one of the time constants is known, an estimate of the other time constant can be derived from it. This method can also be extended to PT3 components, but the time characteristics of its deviation must be considered. The interpretation of the slope of the response graph thus depends on the position of the point under consideration on the curve change. What is important is the relative position of the inflection point. Therefore, a qualitative description of its time constant can be obtained by performing gradient analysis on the response graph of the transmission element.
[0039] If this special method is adopted, it holds:
[0040] a) Using the current estimated value of the boiler time constant by analyzing the fresh steam pressure p D To analyze the estimability of the storage time constant TSP.
[0041] With the described method, from the steam pressure p D And determine the derivative from the modeled steam pressure. In order to allow the estimation of TSP, the following logical conditions must be met for the process and for the model:
[0043] among them, with It is a value that can be set according to the situation.
[0044] This ensures that the process and the model are in a valid state, that is, there is sufficient excitation and the process and the model have synchronized output performance.
[0045] b) By analyzing the steam material flow at the output of the boiler To analyze the estimability of the boiler time constant TDE. For the real process, the storage time constant TSP is used aktuell The current estimated value from the real live steam pressure p D Determine the gradient in the derivative of. From the reverse calculation (zurückgerechnet) process steam material flow And inversely calculated modeled steam material flow Determine the derivative through the DT1 element again. In order to allow the estimated value TDE, the following logical conditions must be met for the process and model.
[0047] among them, with It is a value that can be set according to the situation.
[0048] If the above-mentioned estimability area is determined, then in the next step, the estimated values ​​of the required model parameters are generated. In this regard, the estimated value analysis SWA must be used to generate the correction value T var , The correction value initiates the matching of the current estimated value in the correct direction.
[0049] One conceivable possibility is to output a fixed value with a sign, such as T var =±1. What is more meaningful, however, is the weighted output, which is scaled according to the quality of the current estimate. If a good estimate already exists, the attenuation estimate characteristic should be used. Conversely, the strongly deviated estimates should be matched quickly. That is, in the case of ideal excitation, such a signal T var As a result, the estimation bias gradually tends to zero.
[0050] If the correction value is determined, the correction value is connected to the estimated value generator SWG. The estimated value generator may be configured as an idling integrator (freilaufender Intergrator). If the estimates allow as described above The estimated value can be corrected upward or downward by applying a positive or negative input to the integrator. The time constant T of a typical steam generator lies in the range of 30s
[0051] Therefore, this special estimation method realizes the approximation of the model parameters by dynamically comparing the measurement of the simulation parameters of the process and the model system connected in parallel, and the model parameters of the model system (here, the time constant) are continuously compared with the current To match the estimated value.
[0052] image 3 The configuration diagram of the control device R is shown. The reference variable w is provided to the control device. The control variable x is output at the output of the control device. The component of the control device is one or more calculation units BE in which the parameter estimates for online control of the steam generator according to the method of the invention are calculated.


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Description & Claims & Application Information

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