Regulation of heat supply to consumers. Method of regulation of heating turbines Coupled and uncoupled regulation

2. Classification of ACP. Management principles.

Control- this is a targeted impact on an object, which ensures its optimal (in a certain sense) functioning and is quantitatively assessed by the value of the quality criterion (indicator). The criteria may be of a technological or economic nature (productivity of a process plant, cost of production, etc.).

During operation, output values ​​deviate from specified values ​​due to disturbances z V and a discrepancy appears between the current at T and given and 3 values ​​of the output quantities of the object. If available disturbances z V the object independently ensures normal functioning, i.e., it independently eliminates any discrepancies that arise y T -i 3, then it does not need management. If the object does not ensure the fulfillment of normal operating conditions, then in order to neutralize the influence of disturbances, control action x P, changing the material or heat flows of the object using an actuator. Thus, during the control process, impacts are applied to the object that compensate for disturbances and ensure the maintenance of its normal operating mode.

Regulationcalled maintaining the output values ​​of an object near the required constant or variable values ​​in order to ensure the normal mode of its operation by applying control actions to the object.

An automatic device that ensures that the output values ​​of an object are maintained near the required values ​​is called automatic regulator.

According to the principle of regulation ASRs are divided into those operating by deviation, by disturbance and by a combined principle.

By deviation. In systems that operate by deviation of the controlled variable from the set value (Fig. 1-2, A), indignation z causes deviation of the current value of the controlled variable at from its set value And. The automatic regulator AR compares the values u and and, when they mismatch, it generates a regulatory effect X the corresponding sign, which through the actuator (not shown in the figure) is supplied to the control object OR, and eliminates this mismatch. In deviation control systems, mismatch is necessary to form regulatory influences; this is their drawback, since the regulator’s task is precisely to prevent mismatch. However, in practice, such systems have become predominantly widespread, since the regulatory influence in them is carried out regardless of the number, type and location of the appearance of disturbing influences. Deviation control systems are closed.

Out of outrage. When regulating by disturbance (Fig. 1-2, b) regulator AR B receives information about the current value of the main disturbance z 1. When measuring it and not matching with nominal meaning and B the regulator forms the regulatory impact X, directed to the object. In systems operating on a disturbance, the control signal travels along the circuit faster than in systems built on the principle of deviation, as a result of which the disturbing influence can be eliminated even before a mismatch occurs. However, it is practically impossible to implement disturbance-based control for most chemical technology objects, since this requires taking into account the influence of all disturbances of the object ( z 1, z 2, ...) the number of which is usually large; in addition, some of them cannot be quantified. For example, measuring such disturbances as changes in the activity of the catalyst, the hydrodynamic situation in the apparatus, the conditions of heat transfer through the wall of the heat exchanger and many others encounters fundamental difficulties and is often impracticable. Usually the main disturbance is taken into account, for example, by the load of the object.

In addition, signals about the current value of the controlled variable are sent to the system control loop by disturbances at do not arrive, therefore, over time, the deviation of the controlled value from the nominal value may exceed the permissible limits. Disturbance control systems are open.

According to the combined principle. With such regulation, i.e., with the joint use of the principles of regulation by deviation and disturbance (Fig. 1-6, V), it is possible to obtain high-quality systems . In them the influence of the main disturbance z 1 is neutralized by the AR B regulator, which operates on the principle of disturbance, and the influence of other disturbances (for example, z 2 etc.) - an AR regulator that responds to the deviation of the current value of the reacted quantity from the set value.

According to the number of controlled quantities ASRs are divided into one-dimensional and multidimensional. One-dimensional systems have one adjustable variable, the latter have several adjustable quantities.

In its turn multidimensional systems can be divided into unrelated and coupled control systems. In the first of them, the regulators are not directly related to each other and act separately on the common object of regulation. Systems unrelated controls are usually used when the mutual influence of the controlled quantities of the object is small or practically absent. Otherwise, systems are used related regulation, in which regulators of various quantities of one technological object are interconnected by external connections (outside the object) in order to weaken the mutual influence of the controlled quantities. If in this case it is possible to completely eliminate the influence of the controlled quantities on one another, then such a system of coupled regulation is called autonomous.

According to the number of signal paths ASRs are divided into single-circuit and multi-circuit. Single-circuit are called systems containing one closed loop, and multi-circuit- having several closed circuits

By purpose(the nature of the change in the reference influence) ASRs are divided into automatic stabilization systems, program control systems and tracking systems.

Automatic stabilization systems are designed to maintain the controlled variable at a given value, which is set constant ( u=const). These are the most common systems.

Program control systems constructed in such a way that the specified value of the controlled variable is a function of time known in advance u=f(t). They are equipped with software sensors that form the value And in time. Such systems are used to automate batch chemical processes or processes operating in a specific cycle.

In tracking systems the set value of the controlled variable is not known in advance and is a function of an external independent technological variable u=f(y 1). These systems serve to regulate one technological quantity ( slave), which is in a certain dependence on the values ​​of another ( leading) technological value. A type of tracking systems are systems for regulating the ratio of two quantities, for example, the costs of two products. Such systems reproduce at the output a change in the driven quantity in a certain ratio with the change in the leading one. These systems seek to eliminate the mismatch between the value of the leading quantity, multiplied by a constant factor, and the value of the driven quantity.

By the nature of regulatory influences There are continuous ASR, relay and pulse.

Continuous ACPare constructed in such a way that a continuous change in the input value of the system corresponds to a continuous change in the output value of each link.

Relay (positional) ACP contain a relay link that converts a continuous input value into a discrete relay value that takes only two fixed values: the minimum and maximum possible. Relay links make it possible to create systems with very high gain factors. However, in a closed control loop, the presence of relay links leads to self-oscillations of the controlled quantity with a certain period and amplitude. Systems with position controllers are relay-based.

Pulse ASRcontain a pulse element that converts a continuous input quantity into a discrete pulse value, i.e., into a sequence of pulses with a certain period of their alternation. The period of occurrence of pulses is set forcibly. The input value is proportional to the amplitude or duration of the output pulses. The introduction of a pulse link frees the system's measuring device from the load and allows the use of a low-power, but more sensitive measuring device at the output that responds to small deviations of the controlled value, which leads to an increase in the quality of system operation.

In the pulse mode, it is possible to construct multi-channel circuits, which reduces the energy consumption for actuating the actuator.

Systems with a digital computing device in a closed control loop also operate in a pulsed mode, since the digital device produces the calculation result in the form of pulses following certain time intervals necessary for the calculations. This device is used when the deviation of a controlled variable from a set value must be calculated from the readings of several measuring instruments or when, in accordance with the criteria for the best quality of system operation, it is necessary to calculate a program for changing the controlled variable.

Connecting the installations according to an unrelated control scheme ensures the independence of the operation of both installations, i.e., changing the water flow for hot water supply within a wide range from zero (at night) to maximum has virtually no effect on the operation of the heating system.

To do this, the water flow in the supply line must be equal to the total water flow for heating - ventilation and hot water supply. Moreover, the water consumption for DHW should be taken according to the maximum load of hot water supply and the minimum temperature of water in the supply line, i.e. in the mode when the DHW load is completely covered from the supply line (if the consumer does not have storage tanks installed).

Water consumption for heating, ventilation, hot water supply and total water consumption by each network subscriber does not depend on the network configuration. The calculated flow rate by the subscriber is set using a throttle diaphragm, the diameter of the hole of which is determined by the formula (clause 4.17 SP 41-101-95)

where G is the estimated water flow in the pipeline, equal to Gtotal t/hour

DN - pressure damped by the diaphragm, m

The minimum size of the aperture opening is 3 mm

Automation of the make-up system

Automated make-up devices maintain a constant or varying water pressure at the network make-up point.

For heating networks with relatively small pressure losses in the mains and a favorable terrain profile, the pressure at the recharge point in all modes (including the mode when the network pumps are stopped) is maintained constant. It is planned to maintain constant pressure in the return manifold in front of the network pumps using a downstream pressure regulator (make-up regulator) installed on the make-up water pipeline.

In the case when the static pressure of the heating network exceeds the pressure in the return manifold of the boiler room when the network pumps are operating, adjustment to static pressure is carried out manually. Water pressure is measured in the pressure pipes of the feed pumps with local indicating and signaling pressure gauges, which give an impulse to turn on the backup pump, and in the return manifold - with indicating, recording and signaling pressure gauges on the local switchboard. At the local switchboard, they also provide for the installation of a secondary device indicating, recording and signaling flow meter for measuring the flow rate of make-up water and a secondary device of recording and signaling oxygen meter for measuring the oxygen content in the make-up water. The resistance thermometer on the make-up line is connected to a common recording device, which simultaneously records the temperature of the supply water.

In open heating networks, when installing central storage tanks, the pressure in the return pipeline is automatically regulated by two control valves, the first of which is installed on the bypass pipeline of excess network water to the storage tanks, and the second on the pipeline from the storage tanks after the transfer pumps. During hours when the hot water supply load is below the daily average, the transfer pumps are turned off and the pressure in the return pipeline is regulated by the first valve. During hours when the hot water load is higher than the daily average, the transfer pumps are automatically turned on, the first control valve is closed, and the pressure regulator switches to the control valve installed after the transfer pumps.

To ensure constant flow of make-up water in an open heating network, a flow regulator is installed on the pressure pipeline of the make-up pumps.

The water level in the deaerator make-up tank is maintained by a control valve on the chemically purified water line. If instead of a vacuum deaerator operating on sliding pressure, an atmospheric one is used, then an additional regulator is installed that maintains constant pressure in the deaerator column. The scheme provides for an emergency stop of the working: make-up and transfer pumps and automatic activation of the reserve ones, as well as signaling the pressure in the return pipeline of the level in the make-up deaerator tank and the network water storage tanks and the oxygen content in the make-up water.

The basis for building connected regulation systems is principle of autonomy. In relation to an object with two inputs and outputs, the concept of autonomy means the mutual independence of output coordinates y 1 And y 2 when two closed control systems operate.

Essentially, the autonomy condition consists of two invariance conditions: invariance of the first output y 1 in relation to the signal of the second regulator X p2 and invariance of the second output y2. in relation to the signal of the first regulator X p1:

In this case the signal X p1 can be considered as a disturbance for y2, and the signal X p2 - how outrage for y 1. Then the cross channels play the role of disturbance channels (Fig. 1.35). To compensate for these disturbances, dynamic devices with transfer functions are introduced into the control system R 12 (p) And R 21 (r), the signals from which are sent to the corresponding control channels or to the inputs of the regulators.

By analogy with invariant ASRs, the transfer functions of compensators R 12 (p) And R 21 (r), determined from the autonomy condition, will depend on the transfer functions of the direct and cross channels of the object and, in accordance with expressions (1.20) and (1.20,a), will be equal to:

Just as in invariant ASRs, for the construction of autonomous control systems, an important role is played by physical feasibility and technical implementation approximate autonomy.

The condition of approximate autonomy is written for real compensators, taking into account the operating frequencies of the corresponding regulators:

In chemical technology, one of the most complex multi-connected objects is the rectification process. Even in the simplest cases - when separating binary mixtures - several interconnected coordinates can be identified in a distillation column (Fig. 1.36). For example, to regulate the process in the lower part of the column, it is necessary to stabilize at least two technological parameters that characterize the material balance in the liquid phase and in one of the components. For this purpose, the liquid level in the still and the temperature under the first plate are usually selected, and the flow of heating steam and the selection of the still product are used as control input signals. However, each of the regulatory influences affects both outputs: when the heating steam flow rate changes, the intensity of evaporation of the bottom product changes, and as a result, the liquid level and steam composition change. Similarly, a change in the bottoms product selection affects not only the level in the bottoms, but also the reflux ratio, which leads to a change in the composition of the steam at the bottom of the column.

Rice. 1.35. Block diagrams of autonomous automated control systems: A– compensation of the impact from the second regulator in the first control loop; b– compensation of the impact from the first regulator in the second control loop; c – autonomous two-coordinate control system

Rice. 1.36. An example of a control system for an object with several inputs and outputs:

1 - distillation column; 2 – boiler; 3 – reflux condenser; 4 – reflux tank; 5 - Temperature regulator; 6,9 – level regulators; 7 – flow regulator; 8 – pressure regulator

To regulate the process in the upper part, you can select steam pressure and temperature as output coordinates, and the supply of refrigerant to the reflux condenser and reflux to reflux the column as regulating input parameters. Obviously, both input coordinates affect the pressure and temperature in the column during thermal and mass transfer processes.

Finally, considering the temperature control system simultaneously in the upper and lower parts of the column by supplying reflux and heating steam, respectively, we also obtain a system of unrelated control of an object with internal cross-links.

When analyzing complex automatic control systems, their structural diagrams, showing the points of application of influences and possible paths of propagation of signals that interact between system elements, become of particular importance.

Structural diagrams consist of the following structural elements:

dynamic, carrying out some functional or operator connection between their input and output signals;

transformative, serving to transform the nature or structure of signals;

comparisons in which signals are subtracted or added;

branching points, at which the signal propagation path branches into several paths leading to different points in the system;

connections or lines of a block diagram indicating the directions of signal propagation;

points of application of influences;

logical, performing logical operations.

We indicated above that any automatic control system, according to the very principle of its operation, always

has at least one feedback that serves to compare the actual and required value of the controlled variable. We agreed to call this kind of feedback the main one.

It should, however, be noted that modern automatic control systems, in addition to the main feedback loops, the number of which is equal to the number of controlled quantities, often have several more auxiliary or local feedback loops. Automatic control systems with one controlled variable, having only one main feedback and no local feedback, are called single-circuit. In single-loop systems, a force applied to any point can bypass the system and return to the original point, following only one bypass path (see Fig. II.8). Automatic control systems that, in addition to one main feedback, have one or more main or local feedbacks are called multi-circuit. Multi-circuit systems are characterized by the fact that in them an impact applied to any point can bypass the system and return to the original point, following several different bypass paths.

As an example of a multi-circuit (double-circuit) automatic control system with one controlled variable, we can cite a servo system in which, in addition to the main feedback, which serves to generate an error signal and is carried out using a selsyn sensor and a selsyn receiver, there is also local feedback; the latter is carried out using a tachogenerator and an RC circuit connected to it, the voltage from the output of which is subtracted from the error signal.

An example of a multi-circuit automatic control system with several controlled variables is an aircraft engine control system, in which the controlled variables can be engine speed, boost pressure, ignition timing, oil temperature, coolant temperature and other variables.

The reasons for introducing local feedback into an automatic control system are very different. For example, they are used in correcting elements to convert a signal in accordance with the required control law, in amplifying elements - for linearization, lowering the noise level, lowering the output resistance, in actuating elements - to increase power.

Feedbacks covering several series-connected system elements can be introduced to give them the required dynamic properties.

Multidimensional automatic control systems, i.e. systems with several controlled quantities, are divided into

into systems of unrelated and connected regulation.

Unrelated control systems are those in which regulators designed to regulate various quantities are not connected to each other and can only interact through a common object of regulation. Systems of unrelated regulation, in turn, can be divided into dependent and independent.

Dependent systems of unrelated regulation are characterized by the fact that in them a change in one of the controlled quantities depends on a change in the others. As a result, in such systems the processes of regulation of various controlled quantities cannot be considered independently, in isolation from each other.

An example of a dependent system of unrelated control is an airplane with an autopilot that has independent rudder control channels. Suppose, for example, that an airplane deviates from its intended course. This will cause, thanks to the presence of the autopilot, a deflection of the rudder. When returning to a given course, the angular velocities of both bearing surfaces of the aircraft, and therefore the lifting forces acting on them, will become unequal, which will cause the aircraft to roll. The autopilot will then deflect the ailerons. As a result of rudder and aileron deflections, the aircraft's drag will increase. Therefore, it will begin to lose height, and its longitudinal axis will deviate from the horizontal. In this case, the autopilot will deflect the elevator.

Thus, in the considered example, the processes of regulation of three controlled quantities - course, lateral roll and longitudinal roll - strictly speaking, cannot be considered independent of each other, despite the presence of independent control channels.

An independent system of unrelated regulation is characterized by the fact that in it the change in each of the controlled quantities does not depend on the change in the others, due to which the processes of regulation of various quantities can be considered in isolation from each other. As an example of independent uncoupled control systems, one can often consider the speed control system of a hydraulic turbine and the voltage control system of the synchronous generator it rotates. The regulation processes in these systems are independent, due to the fact that the voltage regulation process usually proceeds many times faster than the speed regulation process.

Systems of coupled regulation are those systems in which regulators of various controlled quantities have mutual connections with each other, interacting between them outside the object of regulation.

A system of coupled regulation is called autonomous if the connections between its constituent regulators

are such that a change in one of the regulated quantities during the regulation process does not cause changes in the remaining regulated quantities.

IZVESTIYA

GOMSK ORDER OF THE RED BANNER OF LABOR POLYTECHNIC

INSTITUTE NAMED AFTER S. M. KIROV

RESEARCH OF THE SYSTEM OF CONNECTED REGULATION OF ONE CLASS OF OBJECTS WITH DISTRIBUTED

PARAMETERS

V. I. KARNACHUK, V. Y. DURNOVTSEV

(Presented by the scientific seminar of the Department of Physics and Technology)

Multiply connected control systems (MCC) are currently finding increasing use in the automation of complex objects. This is due to the fact that complex automation of production processes requires a transition from the regulation of one parameter to the associated regulation of several quantities that influence each other. Among such systems, a large place is occupied by similar SMRs, consisting of several identical, identically configured regulators operating from a common source of raw materials or a common load. Multi-channel ACS of objects with distributed parameters, the task of which is to automatically optimize the parameter distribution, can be classified as the same type of SMR. This problem cannot be solved correctly if the mutual influence of the controlled parameters is not taken into account. Taking into account mutual influence significantly complicates the analysis of the system, since in a coupled system the dynamics of each parameter is described by a high-order differential equation.

The founder of the theory of regulation of several parameters is I. N. Voznesensky. He showed that in order to eliminate the influence of parameters on each other, it is necessary to introduce artificial connections into the system to compensate for the influence of natural connections. In this case, the connected system turns into an unconnected one, i.e., autonomous. The problem of autonomy is a specific problem that is absent in the theory of one-dimensional ATS. I. N. Voznesensky solved this problem for a first-order plant controlled by an ideal controller. Later, physically and technically feasible conditions for autonomy were found for more complex systems. In these works, the range of objects considered is, as a rule, limited to first-order objects. However, in practice, when researching in the field of control of objects with distributed parameters such as a distillation column, oil and gas reservoir, vulcanization chambers, various types of reactors, etc., a more complex approximation is often required.

This paper discusses some issues of synthesizing two-dimensional SMR of an astatic object with phase advance.

when the object for each controlled quantity is described by a second-order differential equation:

t dH dx 2 dt2 dt

koTi -U- +kou. dt

The block diagram of the coupled regulation system is shown in Fig. 1. The system is designed to maintain a given value of the X parameter in two different areas of a large object.

2 regulator w

Rice. 1. Block diagram of two-dimensional construction and installation work

The object of regulation is a multiply connected system with a ^-structure according to the accepted classification. The transfer functions of objects for each direct channel are equal:

K0(T,p+1) ■

SR) - ^02 (P)

P(T2P+> 1)

The relationship between the adjustable parameters is presented in the block diagram through constant coefficients Li2 = ¿2b, although in the general case it is not time invariant. Integrated regulators with a transfer function are considered:

The regulators receive control signals from inertial sensors (thermocouples) located near the corresponding regulators. Transfer functions of sensors:

Wn(p) = WT2(p) =

Analysis of a coupled system using equations of motion, written even in operator form, is inconvenient due to the high order of the equations. The matrix method of writing equations has much greater convenience, especially for structural synthesis.

In a matrix form of notation, the equation for an object with a Y-structure has the form:

■ WciWcalia^i 1 - W 01^02^12^21

1 - 1^0] 1 - 12^21

a ^ and the column matrices of the controlled and regulating quantities, respectively.

For the controller you can write:

^^(¿y-X). (6)

u%(p)=G 0 [o

5 - transforming matrix of control actions; y is a matrix-column of control actions.

Elements of matrices and 5 can be obtained after simple structural transformations:

p(Tar+\)(TTr+\)

Then the closed-loop SMR equation can be written in the following form (hereinafter we will assume that the disturbances acting on the system / = 0):

X = (/ + Г0г р)"1 - W оГ р5Г, (7)

where / is the identity matrix.

From (7) we can obtain the characteristic equation of a closed SMR if we equate the determinants of the matrix (/ + WqWp) to zero:

| / + W0WP | = 0. (8)

Sufficient general criteria for checking stability have not yet been found for construction and installation work. Determining the roots of the characteristic equation (8) is also a rather cumbersome task, since it can be shown that even in the two-dimensional case it is necessary to solve a tenth order equation. Under such conditions, the use of computer technology to calculate construction and installation work is not only desirable, but also necessary. The importance of analogue models is especially great for solving problems of synthesizing construction and installation equipment that have certain specified properties, and, above all, autonomous installation and installation equipment. It is known that the implementation of the conditions of autonomy is often impossible; in any case, for each specific system, finding the conditions of autonomy that could be implemented in fairly simple steps is an independent task. From expression (7) it is clear that the conditions of autonomy are reduced to the diagonalization of the matrix

Ф, = (/ + ^р)-1" wQwps.

In this case, the SMR equations break down into independent equations. Obviously, the matrix Fu will be diagonal only if the matrix W0Wpj, which is the transfer matrix of the open-loop SMR, is diagonal. To implement these conditions, artificial compensating connections, transmission

Rice. 2. Electronic model of autonomous construction and installation work,

the functions of which can be determined from a more convenient for these purposes notation of the matrix equation SMR:

Fu= ^o Gr(5-Fu). (9)

There are a large number of options for implementing compensating connections. However, calculations carried out according to equation (9) show that the most convenient for implementation is the variant of the block diagram, when cross connections are imposed between the inputs of the regulator amplifiers. For this case, the transfer functions of the compensating connections have the form:

/Xu (/>) = - №«¿12; K2\(p) = -

Taking into account expression (2) we have: * and (P)<= К21 (р) =

To study two-dimensional SMR, an electronic model of the system was used, assembled on the basis of the EMU-8 analog installation. The diagram of the electronic model of the SMR is shown in Fig. 2. The following numerical values ​​of the parameters were adopted: a;o=10; KuK^/(r == 0.1; Tx = 10 sec; G2 = 0.1 sec; Tt = 0.3 Tg = 0.5 sec/s; I = 0.1 0.9.

Rice. 3. Curves of transient processes in the channels of non-autonomous (a) and autonomous (c) construction and installation works

Studies of the model have shown that a system without compensating connections remains stable up to the value of the relationship ¿ = 0.5. A further increase in L leads to divergent oscillations of the controlled variable. However, even with L<0,5 характер переходного процесса в системе является неудовлетворительным. Полное время успокоения составляет 25-ъЗО сек при максимальном выбросе 50%. Введение перекрестных связей, соответствующих условиям автономности, позволяет резко улучшить качество регулирования.

As can be seen from the graphs (Fig. 3), the sensitivity of each channel to changes in the setting in the adjacent channel is noticeably reduced. The duration of the transient process and the magnitude of the maximum overshoot can be reduced by reducing the gain of the amplifiers of both channels by a factor of 2 compared to the gain adopted for an uncoupled separate system.

1. Autonomy conditions have been found that are realized by simple active CN circuits for SMR of second-order objects - with phase advance.

2. Analysis of complex construction and installation work using analog computers allows you to select the optimal values ​​of construction and installation work parameters.

An electronic model of two-dimensional autonomous construction and installation work has been proposed.” The influence of the magnitude of the relationship on the stability of the system is shown.

LITERATURE

1. M. V. Meerov, Multiply connected control systems. Ed. "Science", 1965.

2. V. T. Morozovsky. “Automation and telemechanics”, 1962, No. 9.

3. M. D. Mezarovich. Multiply connected control systems. Proceedings of the I FAC Congress, Ed. USSR Academy of Sciences, 1961.