Interconnected regulatory systems. Communication control systems. Autonomous ACP. Single-circuit and multi-circuit, coupled and uncoupled automatic control systems, direct and indirect control Uncoupled control systems

Related systems In addition to the main regulators, the controls include additional dynamic compensators. Calculation and adjustment of such systems is much more complicated than single-circuit ACP, which prevents them wide application V industrial systems automation.

Let's consider methods for calculating multiply connected control systems using the example of an object with two inputs and two outputs.

3.1.1.Synthesis of unrelated regulation

The block diagram of the system is presented in Figure 3.1. The transformation of the two-coordinate control system to equivalent single-circuit ACS is given in Figure 3.2.

Figure 3.1 - Block diagram incoherent regulation with interconnected coordinates

Figure 3.2 - Conversion of a two-axis control system to equivalent single-circuit ACS

a is the equivalent object for the first controller; b - equivalent object for the second controller.

Let us derive the transfer function of the equivalent object in a single-circuit ASR with controller R1. As you can see, such an object consists of a main control channel and a complex system associated with it in parallel, including a second closed control loop and two cross channels of the object. The transfer function of the equivalent object has the form:

The second term on the right side of equation (7) reflects the influence of the second control loop on the one under consideration and is essentially a corrective amendment to the transfer function of the forward channel.

Similarly, for the second equivalent object we obtain the transfer function in the form:

Based on the formulas, it can be assumed that if at some frequency the modulus of the correction correction is negligible compared to the amplitude-frequency characteristic of the direct channel, the behavior of the equivalent object at this frequency will be determined by the direct channel.

The most important correction value is at the operating frequency of each circuit. In particular, if the operating frequencies of two control loops co p i and o p2 are significantly different, then we can expect that their mutual influence will be insignificant, provided:

|W p2 (iω pl)|<< |W 11 (iω pl)| ; (9)

Where |W p2 (iω pl)| =

The greatest danger is the case when the inertia of direct and cross channels is approximately the same. Let for example, Wn(p)=W12(p)=W21(p)=W22(p)=W(p). Then for equivalent objects, provided that R1(p)=R2(p)=R(p), we obtain the transfer functions:

frequency characteristics

(11)

At the stability boundary, according to the Nyquist criterion, we obtain:

or ; (12)

Where =l or |R(iω)|=0.5/|W(iω)|

Thus, the setting of the P-regulator, at which the system is on the stability boundary, is half that in a single-circuit ASR.

To qualitatively assess the mutual influence of control loops, a complex coupling coefficient is used:

;(13)

which is usually calculated at zero frequency (i.e. in steady-state modes) and at the operating frequencies of the controllers co p i and co P 2. In particular, at w = 0, the value of kc B is determined by the ratio of the gains across the cross and main channels:

VSWR (0)=Ri2 R21 /(R11 R22); (14) If at these frequencies ks B = 0, then the object can be considered as simply connected; at ks B > 1, it is advisable to swap direct and cross channels; 0<кс В <1 расчет одноконтурных АСР необходимо вести по передаточным функциям эквивалентных объектов (7) и (8).

Let's calculate ks B for our option:

kcв = (ki2*k2i)/(k11*k22)=(0.47*0.0085)/(0.015*3.25)~0.11

3.1.2 Linked regulatory systems

Figure 8 shows block diagrams of autonomous automated control systems

Figure 3.3 – block diagrams of autonomous automated control systems

a - compensation of influences from the second regulator in the first control loop;

b - compensation of influences from the first regulator in the second control loop;

c - autonomous two-coordinate control system. Figure Figure 8 - Block diagrams of autonomous automated control systems

Regulation is an artificial change in parameters and coolant flow in accordance with the actual needs of subscribers. Regulation improves the quality of heat supply, reduces excessive consumption of fuel and heat.

Depending on the point of implementation, there are:

1. central regulation - carried out at the heat source (CHP, boiler room);

2. group – at the central heating point or control center,

3. local – for ITP,

4. individual - directly on heat-consuming devices.

When the load is homogeneous, you can limit yourself to one central regulation. Central regulation is carried out according to the typical heat load, typical for the majority of subscribers in the area. Such a load can be either one type of load, for example heating, or two different types with a certain quantitative ratio, for example heating and hot water supply at a given ratio of the calculated values ​​of these loads.

A distinction is made between connecting heating systems and hot water supply installations according to the principle of coupled and unconnected regulation.

With unrelated regulation, the operating mode of the heating system does not depend on the selection of water for hot water supply, which is achieved by installing the regulator in front of the heating system. In this case, the total water consumption for the subscriber installation is equal to the sum of the water consumption for heating and hot water supply. Increased water consumption in the supply main of the heating network leads to an increase in capital and operating costs in heating networks, an increase in capital and operating costs in heating networks, and an increase in electricity consumption for coolant transport.

Associated regulation makes it possible to reduce the total water consumption in heating networks, which is achieved by installing a flow regulator at the input of the subscriber installation and maintaining the flow of network water at the input constant. In this case, with an increase in water withdrawal for hot water supply, the consumption of network water for the heating system will decrease. The lack of fuel during the period of maximum water withdrawal is compensated by an increase in the consumption of network water for the heating system during the hours of minimum water withdrawal.

The connection of subscriber installations according to the principle of uncoupled regulation is used with central high-quality regulation for the heating load, and according to the principle of coupled regulation - with central regulation for a combined load.

For closed heat supply systems with a predominant (more than 65%) housing and communal load and with relation (15), central qualitative regulation of closed systems is used for the combined load of heating and hot water supply. In this case, the connection of hot water supply heaters for at least 75% of subscribers must be carried out according to a two-stage sequential scheme.

The temperature schedule of the central quality control for the combined load of heating and hot water supply (Figure 4) is built on the basis of the heating and household temperature schedule (Appendix).

Before entering the heating system, the network water passes through the upper stage heater, where its temperature drops from to . The water consumption for hot water supply is changed by the RT temperature regulator. Return water from the heating system enters the lower stage heater, where it cools from to . During hours of maximum water consumption, the temperature of the water entering the heating system decreases, which leads to a decrease in heat transfer. This imbalance is compensated during hours of minimum water consumption, when water with a temperature higher than required according to the heating schedule enters the heating system.

We determine the balance load of hot water supply, Q g b, MW, using the formula.

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 according to a certain law 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 switching on 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 elements of the system, 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 be noted, however, 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 values.

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 control processes in these systems are independent, due to the fact that the voltage control process usually proceeds many times faster than the speed control process.

Coupled control systems are those systems in which regulators of various controlled quantities have mutual connections with each other that interact 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.