RU2494433C2 - Energy-saving automatic control system - Google Patents

Abstract

FIELD: power industry.

SUBSTANCE: structure of multi-circuit ACS with frequency separation of control channels includes an input channel of a demand, algebraic adders, on which comparison of a demand signal is made to a feedback signal, and a block of controls with the corresponding control channels. The specific feature of the proposed structure is determined by available band-pass filters in each of the control channels. In the proposed structure for separation of frequencies in control channels there used are ideal band-pass filters that do not add any additional delay to the system and contribute to the fact that the closed system remains stable under condition that individual control circuits are initially stable. Therefore, according to the proposed structure of multi-circuit ACS with frequency separation of control channels due to use of ideal band-pass filters the alternating operation of each of the control circuits takes place, thus allowing to achieve the required dynamic and energy efficiency of the energy-saving ACS as a whole.

EFFECT: improvement of control quality and energy efficiency of control of a process object due to choosing a dynamically effective and energy efficient control channels and their actuation depending on frequency characteristics of disturbing actions and response to them of individual control circuits; simpler calculation of settings of the corresponding controls.

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Description

The invention relates to the field of automatic control systems. It can be used to automate the operation of various industrial facilities (chemical reactors, heat exchangers, etc.) that have in their structure several control channels of one technological quantity (temperature, pressure, etc.) by using one or more control loops connected depending on the dynamic and energy characteristics of the object and the characteristics of the disturbing effect.

Known regulatory systems that use two control actions to maintain the value of the technological quantity (see, for example, EG Dudnikov and others. “Automatic control in the chemical industry.” M .: Chemistry, 1987. - 368 p.), Where one of control channels, the best in terms of the quality of transients, is uneconomical, while the other control channel, on the contrary, is economical, but inferior in quality of transients. As a result, in the best quality control position, a P-controller is used to improve performance, and in the economical control channel, a PI or PID controller is used to eliminate static error. When constructing such a system, difficulties arise associated with the calculation of the control system and the connection of other control channels, the best from the position of maximum suppression of the current disturbance (interference).

The purpose of the invention is to improve the quality of regulation and energy efficiency of controlling a technological object by selecting dynamically effective (best in relation to the quality of the transition process) and energy efficient (best in terms of energy saving) control channels and turning them into operation depending on the frequency characteristics of disturbing influences ( interference signals) and the response to them of individual control loops. In addition, due to the separation of the frequency spectra of the control loops, the calculation of the settings of the corresponding controllers is simplified.

Chemical-technological system (CTS) is intended for the targeted processing of a certain raw material stream of a substance into a necessary product with energy effects on the starting material and the occurrence of chemical transformations. CTS can be characterized by an appropriate structure that defines the relationship between its elements, and a set of variables (coordinates) that determine its current state. For controlled CTS, the most characteristic are three types of coordinates: controlled coordinates, control coordinates, and coordinates corresponding to external perturbations.

In general, in the steady state, the relationship between these coordinates can be represented by a set of algebraic equations in an implicit form.

$$f_i(\overline{y},\overline{u},\overline{\omega },k,v,\eta )=0,i\in I,(\mathrm{one})$$

, $$\overline{u}$$

, $$\overline{\omega }$$

- соответственно векторы управляемых, управляющих и возмущающих координат ХТС;Where $$\overline{y}$$

, $$\overline{u}$$

, $$\overline{\omega }$$

- respectively, vectors of controlled, controlling, and disturbing coordinates of the XTS;

k is a set of design parameters;

v - stoichiometric coordinates and physicochemical constants;

η - the efficiency of the elements of the CTS.

The structure of the vector P also includes various energy flows used to conduct the process in the considered CTS.

The effectiveness of the functioning of the CTS is usually assessed using any performance criterion, the expression of which almost always includes controlled and controlling coordinates:

$$J=\Phi (\overline{y},\overline{u},D)(2)$$

D - parameters affecting the performance of the CTS.

, который минимизирует (или максимизирует) критерий эффективности при соблюдении необходимых технологических и организационных ограничений вида:The task of optimizing the operating mode of the CTS is to select such a vector of control coordinates $$\overline{u}*$$

, which minimizes (or maximizes) the performance criterion while observing the necessary technological and organizational limitations of the form:

; $${\overline{S}}_Q=\left\{S_Q|S_Q\in E^h;{\varphi }_i(S_Q)=0,i=\overline{\mathrm{one},p};{\varphi }_j(S_Q)\le 0,j=\overline{\mathrm{one},q}\right\}(3)$$

;

- обобщенное обозначение варьируемых переменных;Where $${\overline{S}}_Q$$

- generalized designation of variable variables;

или $$\overline{u}$$

).Q is an index denoting the form of variable variables ( $$\overline{y}$$

or $$\overline{u}$$

)

In the vast majority of cases, in the CTS, various sources of energy are used for the thermal or chemical effect on the ongoing processes: electricity, combustible gases, steam, etc. Similarly, it is possible to use “on the side” of various types of secondary energy resources (VER) obtained in the process of functioning of the specific CTS under consideration. Separate technological nodes of the CTS, using external energy and (or) producing VER, are usually constructed as shown in the figure (see figure 1), where Q _i is the flow of the i-th type of energy supplied to the CTS node; H _j is the flux of the jth type of energy diverted from the node; y is a controlled variable characterizing the operation of a technological unit.

In general terms, the relationship between the variable y and the flows Q _i and H _{j is} non-linear:

f (y, Q ₁ , ..., Q _n , H ₁ , ..., H _m ) = 0

However, for technological processes, which are based on energy transformations, in steady-state conditions, this dependence can be represented with a sufficient degree of accuracy in a linearized form

$$y={\displaystyle \sum _{i=\mathrm{one}}^n{k}_i{Q}_i+{\displaystyle \sum _{j=\mathrm{one}}^m{c}_j{H}_j}}(\mathrm{four})$$

where k _i , c _j are coefficients reflecting balance and kinetic dependencies. An efficiency criterion of type (2) for such an XTS node, reflecting the conditions of energy transformations, I _e = Φ (Q _i , H _j ), i∈I, j∈J will be called the energy saving criterion. Often it can be represented as an additive function:

$$I_{\mathrm{uh}}={\displaystyle \sum _{i=\mathrm{one}}^n{a}_i{Q}_i+{\displaystyle \sum _{j=\mathrm{one}}^m{b}_j{H}_j}}(5)$$

и $$\overline{1,m}$$

.where a _i , b _j - weight coefficients; I and J are sets of integers respectively from the series $$\overline{\mathrm{one},n}$$

and $$\overline{\mathrm{one},m}$$

.

Moreover, it must be borne in mind that individual input and output flows from (4) are external perturbations and are not included in criterion (5).

, i∈I, j∈J при ограничениях на эти же потоки с точки зрения производственных и технических возможностей.The task of optimizing the process of energy transformations in the considered node may look, for example, as $$\underset{Q,H}{min}\Phi (Q_i,H_j)$$

, i∈I, j∈J under restrictions on the same flows in terms of production and technical capabilities.

The specificity of such nodes is that in chemical technology it is often possible to find not one, but several control coordinates acting on the same controlled variable. This gives the opportunity to choose one or another control coordinate for the organization of the CAP. But in any case, in the typical CAP structure, only one regulating coordinate is used to control any variable (usually the best in terms of dynamic indicators), and the structure of the object with CAP looks like, for example, shown in Figure 2, where P is the regulator. The control coordinates Q _l and H _q can be conditionally called dynamically effective, i.e. allowing to build dynamically effective CAPs on their basis. However, the control coordinates Q _l and H _q used in the CAP may not be the best from the point of view of the efficiency criterion (5), i.e. in terms of energy conservation.

It is proposed to solve the problem of energy saving and the simultaneous achievement of effective control under conditions of real-life disturbances by using multi-loop CAPs that use several control coordinates at the same time to stabilize one variable y (t). A typical block diagram of such a CAP is shown in FIG. 3, where Q _ℓ , Q _k , H _f are control coordinates; P _Qℓ , P _Qk , P _Hf - controllers in the circuits with the corresponding control coordinates. Similarly to the concept of a dynamically effective control coordinate (in this case, Q _l ), we introduce the concept of energy-efficient coordinates that can significantly affect the criterion of energy conservation (Q _k , H _f , etc.).

CAPs constructed in accordance with the block diagram shown in Figure 3 and minimizing the performance criterion (5) will be called energy-saving CAPs (ESAPs).

необходимо выполнить следующее условие в статике:Indeed, to stabilize the variable y with stochastic change $$\overline{\omega }(t)$$

It is necessary to fulfill the following condition in statics:

$$M\left\{y\right\}=K_{\mathrm{about}bl}\cdot M\left\{u_{\mathrm{one}}\right\}+...+K_{\mathrm{about}bn}\cdot M\left\{u_n\right\}+{\displaystyle \sum _{j=\mathrm{one}}^m{K}_{\mathrm{about}b{\omega }_o}}\cdot M\left\{{\omega }_j\right\}(6)$$

or, given that in the statics M {y} = y _ass should take place:

$${\displaystyle \sum _{i=\mathrm{one}}^n{K}_{\mathrm{about}bi}}\cdot M\left\{u_i\right\}=y_{s\mathrm{but}d}-{\displaystyle \sum _{j=\mathrm{one}}^m{K}_{\mathrm{about}b{\omega }_o}\cdot M\left\{{\omega }_j\right\}}(7)$$

where K _obi are the gains on the corresponding control channels of the ESAU;

K _obωj are the gains along the perturbation channels ω _j ;

y _ass is the set value of the stabilized variable.

If the energy criterion (5) is presented in the form:

$$I_{\mathrm{uh}}={\displaystyle \sum _{i=\mathrm{one}}^n{\alpha }_i{u}_i}(8)$$

where α _i are the corresponding weight coefficients,

then the optimum in the problem min I _e under typical constraints on the control u _i

$$u_i^{min}\le u_i\le u_i^{max}(9)$$

is located at one of the vertices of the hyperhedron defined by relations (7), (9).

Thus, the analysis of the organization features of typical CTS leads to the conclusion that it is possible to optimize the steady-state modes of their operation according to the criterion of energy saving using ESAR, which have structural redundancy in management. As a consequence of this, such ESARs must have a specific multi-circuit with the number of controls exceeding the number of controlled variables.

. Отметим, что реальный технологический процесс на достаточно длительном интервале времени практически не является стационарным, и, следовательно, на ограниченном интервале времени AT можно определить текущее среднееNow we consider this problem taking into account the conditions of dynamic modes. The location of the hyperplane (7) corresponding to the specific technological mode of the controlled CTS is primarily determined by the set of external disturbing factors $$K_{\mathrm{about}b{\omega }_j}\cdot M\left\{{\omega }_j\right\}$$

. Note that a real technological process for a sufficiently long time interval is practically not stationary, and therefore, for a limited time interval AT, the current average can be determined

, (t-ΔT)>0. $$M{\left\{{\omega }_j\right\}}_{t,\Delta T}=\frac{\mathrm{one}}{\Delta T}{\displaystyle \underset{t-\Delta T}{\overset{\Delta T}{\int }}{\omega }_j(t)dt}$$

, (t-ΔT)> 0.

и инфранизкочастотную $${\omega }_j^{н}(t)=M{\left\{{\omega }_j\right\}}_{t,\Delta T}-M\left\{{\omega }_j\right\}$$

, где M{ω_j} - среднее значение возмущения ω_j(t) за весь период работы ХТС. На основе теоремы суперпозиции объединим все возмущающие воздействия, что допустимо для линейных систем, и введем обозначения ω(t), ω^в(t), ω^н(t), что соответствует объединенному стохастическому возмущению и его высокочастотной и инфранизкочастотной составляющим со спектральными плотностями $$S_{\omega }^{в}(\omega )$$

и $$S_{\omega }^{н}(\omega ).$$

Причем: ω^в(t)+ω^н(t)=ω(t)-М{ω}.In accordance with this, in the stochastic disturbance ω _j (t), two components can be arbitrarily distinguished: high-frequency $${\omega }_j^{\mathrm{at}}(t)={\omega }_j(t)-M{\left\{{\omega }_j\right\}}_{t,\Delta T}$$

and infrared $${\omega }_j^n(t)=M{\left\{{\omega }_j\right\}}_{t,\Delta T}-M\left\{{\omega }_j\right\}$$

, where M {ω _j } is the average value of the perturbation ω _j (t) for the entire period of operation of the CTS. Based on the superposition theorem, we combine all the perturbing influences, which is acceptable for linear systems, and introduce the notation ω (t), ω ⁱⁿ (t), ω ^н (t), which corresponds to the combined stochastic perturbation and its high-frequency and infra-low-frequency components with spectral densities $$S_{\omega }^{\mathrm{at}}(\omega )$$

and $$S_{\omega }^n(\omega ).$$

Moreover: ω ⁱⁿ (t) + ω ⁿ (t) = ω (t) -M {ω}.

и $$\Delta u_{1max}^{н}$$

предельные амплитуды изменений управляющего воздействия u₁(t) для компенсации соответственно составляющих ω^в(t) и ω^н(t). Переходные процессы по u₁(t) в такой системе схематично будут выглядеть так, как показано на фигуре 4.Suppose that there exists a control coordinate u ₁ (t) that stabilizes the variable y (t) quite effectively in the entire frequency range of ω (t). The accepted partition of the perturbing effect on ω ⁱⁿ (t) and ω ^н (t) allows us to similarly represent the control u ₁ (t) in the region of high and infralow frequencies. Moreover, we can introduce into consideration the quantities $$\Delta u_{\mathrm{one}max}^{\mathrm{at}}$$

and $$\Delta u_{\mathrm{one}max}^n$$

the limiting amplitudes of changes in the control action u ₁ (t) to compensate for the components ω ⁱⁿ (t) and ω ⁿ (t), respectively. Transients in u ₁ (t) in such a system will look schematically as shown in figure 4.

. Видно, что в случае идеальной фильтрации инфранизкочастотной составляющей ω^н(t) величина $$\Delta u_{1max}^{н}\to 0$$

и $$M\left\{u_1(t)\right\}\to u_1{\min }^{+}\left|\Delta u_{1max}^{в}\right|.$$

Фильтрацию ω^н(t) предполагается осуществлять дополнительным управляющим воздействием u_i(t), i≠1, являющимся с точки зрения динамики более инерционным, чем u₁(t), а с точки зрения критерия (8) - более эффективным в смысле энергосбережения.Analysis of the graph (figure 4) allows us to conclude that to minimize (or maximize) the value in accordance with the requirements of the criterion of energy conservation (8) is possible by reducing the values $$\Delta u_{\mathrm{one}max}^n$$

. It can be seen that in the case of perfect filtration of the infra-low-frequency component ω ⁿ (t), the quantity $$\Delta u_{\mathrm{one}max}^n\to 0$$

and $$M\left\{u_{\mathrm{one}}(t)\right\}\to u_{\mathrm{one}}{\min }^{+}\left|\Delta u_{\mathrm{one}max}^{\mathrm{at}}\right|.$$

The filtering of ω ⁿ (t) is supposed to be carried out by an additional control action u _i (t), i ≠ 1, which is more inertial from the point of view of dynamics than u ₁ (t), and from the point of view of criterion (8) it is more efficient in terms of energy saving .

In other words, the spectral density of the disturbing effect ω (t) is broken up into high-frequency and infra-low-frequency parts (Figure 5) and a double-loop CAP is organized with control coordinates u ₁ (t), u _i (t), i ≠ 1. Moreover, the first of them has higher dynamic properties, and the second is more effective in the sense of the criterion of energy conservation.

Thus, the CAP has an excess of control coordinates (at least two control variables), each of which, depending on the frequency properties and the influence on the energy saving criterion, is configured to suppress the corresponding part of the external disturbance spectrum. It is natural to assume that if there are m control coordinates that differ in frequency properties and influence on the energy saving criterion, then the graph S _ω (ω) can be similarly represented as a set of m components, each of which is suppressed by an appropriately tuned circuit with a control coordinate u _i (t). Those. the CAP structure shown in Figure 3 reappears.

The structure of multi-loop CAP with frequency division of control channels (see figure 6) contains the input channel of task 1, algebraic adders 2, on which the signal of task 1 is compared with feedback signal 3, the control unit 4 with the corresponding control channels 5. The feature of the proposed structure is determined the presence of bandpass filters 6 in each of the control channels. In the proposed structure, for the separation of frequencies in the control channels, ideal band-pass filters are used that have frequency characteristics of the following form:

$$mod{W}_{\Phi j}(i\omega )=\{\begin{array}{ccc}0& PR\mathrm{and}& \omega <{\omega }_j\\ \mathrm{one}& PR\mathrm{and}& {\omega }_j\le \omega \le {\omega }_{j+\mathrm{one}}\\ 0& PR\mathrm{and}& \omega >{\omega }_{j+\mathrm{one}}\end{array}$$

$$arg{W}_{\Phi j}(i\omega )=0PR\mathrm{and}{\omega }_j\le \omega \le {\omega }_{j+\mathrm{one}}$$

.where ω _j is the cutoff frequency along the j-th channel; $$j=\overline{\mathrm{one},l}$$

.

The use of ideal filters does not introduce additional delay into the system and contributes to the fact that the closed system remains stable provided that individual control loops are initially stable.

Thus, according to the proposed structure of a multi-loop control system with a frequency separation of control channels due to the use of ideal band-pass filters, each of the control loops individually is alternately operated, which ultimately allows achieving the required dynamic and energy efficiency of the ESAR as a whole. In addition, the procedure for finding the optimal tuning parameters of the regulators is simplified, since the settings of one controller do not depend on the tuning parameters of the other.

Claims (1)

An energy-saving automatic control system containing the input channel of the reference, algebraic adders on which the reference signal is compared with the feedback signal, the block of controllers with the corresponding control channels (in the simplest case, two), which have different energy and dynamic characteristics, characterized in that each of the control channels, in order to increase the dynamic and energy efficiency of the control system as a whole, there are bandpass filters, with osobstvuyuschie separation and independent work included in each of the control circuits are configured, depending on their frequency properties and the impact on energy saving criterion, corresponding to an effective suppression of the spectrum of the external disturbance.

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