UA57871C2 - Heating installation and method of its operation - Google Patents

Abstract

The invention relates to a heating installation, comprising a supply vessel (6) with an inlet and an outlet (4, 5) for a heated fluid; and a feed system (9, 10) for a heat transfer fluid with a feed line in which a valve (11) is situated, a temperature probe (4) which detects the temperature of the heated fluid and a control circuit (18) which activates the valve in dependence on a deviation of the temperature from a predetermined value. The invention also relates to a method for operating this installation. The aim of the invention is to obtain a rapid reaction from the installation while exerting a minimal mechanical load on the parts that are moved. To this end, the control circuit (18) has a limit frequency detector (19) which determines fluctuations in the temperature (Tist) and reduces or increases the loop amplification (V) of the control circuit (18) when the frequency is too high or too low, respectively.

Description

fluctuations of any frequency are acceptable. Such oscillations do not load the executive organs, because they cause very small movements. In addition, when the user draws warm water, fluctuations within this range are barely noticeable and therefore acceptable.

The advantage of the method is that the frequency determination is carried out in an indirect way by means of gate movements and/or gate control signals. The valve control signals and corresponding valve movements are directly determined by the temperature deviation from the set value.

The deviation information remains in the system and is used to generate signals that are easily recognized. This function can be implemented without extra costs.

The method involves counting the number of changes in the direction of movement of the valve during a predetermined time interval and reducing the circuit gain if this count exceeds the maximum value.

The frequency can be determined by simple counting in a predetermined time interval. If this interval is about 5 minutes, the specified number of changes in the direction of movement of the valve can be set equal, for example, from 3 to 10, without considering this as instability. If the number of such changes exceeds this set value, the system state is considered unstable and the loop gain is reduced.

At each such excess, the countdown stops and a new time interval begins. This accelerates the achievement of a stable state. The greater the instability of the system, the higher the frequency, i.e., the valve's direction of movement changes more often. If the correction is to be carried out only when the conditions of the criterion are met, then this correction should not be carried out in the common interval. Thanks to this, the load on the mechanical elements is reduced and the achievement of a stable state is accelerated.

If the frequency becomes low enough, the loop gain increases and the setpoint changes.

A simultaneous loop rise and setpoint change are performed to determine if the system is entering an oscillation mode. In the absence of such a mode, increasing the gain of the circuit does not automatically lead to the appearance of oscillations and does not give confidence in the suitability of such gain. Changing the setpoint creates a perturbation that provides the desired information.

If the frequency becomes too high after the loop gain is increased, the loop gain is changed back to what it was before the increase. This is the search for the "boundary". Such a load allows you to determine the gain of the circuit at which the control circuit loses stability, and thus to find that with further increase the control circuit will no longer be stable. This allows you to return to the previous loop gain without additional iterations.

In the most preferred embodiment, the gain of the circuit is set depending on the load of the installation. This creates an opportunity to protect the control system and, accordingly, moving parts from loads caused by too frequent movements. When the needs of the installation are small, for example, when the water intake is small, you can be satisfied with small circuit reinforcements. Reaction speed is also not mandatory. This gives the advantage that, for example, when the consumption is reduced at night, most of the valves of the batteries of the heating system are throttled and, according to the small need, only a small amount of heat is supplied to them. When the demand increases, for example due to water withdrawal or excessive opening of the valve, a quick reaction of the installation becomes necessary. In this case, the circuit is switched to high gain. When using the appropriate criterion for determining the need, it is possible to partially avoid the previous multi-step iterations.

An important feature is that the load of the installation is determined by the temperature of the hot liquid.

This method of preliminary determination is fast enough and does not require additional structural elements. The load of the installation, for example, by the selection of warm water, causes a relatively rapid decrease in the temperature in the collector due to the arrival of a corresponding amount of cold water. Accordingly, it is possible to raise the gain of the circuit quite quickly without creating the danger of immediate oscillations. When, after some time, oscillations occur, it can be assumed that the load of the installation has stopped and go back to the gain of the circuit, which corresponds to "idling".

Next, on the examples of preferred embodiments, a description of the invention is provided with references to the drawings, in which: Fig. 1 - a schematic representation of a heating installation for the preparation of warm water, Fig. 2 - a diagram of the control device, Fig. 3 - curves corresponding to a decrease in circuit gain, Fig. .4 - curves corresponding to the increase in circuit gain, Fig. 5 - diagrams explaining the operation of the protection system.

Fig. 1 schematically illustrates the heating installation 1 for the preparation of warm technical water, which can be selected through taps 2 or other means of selection. Faucets 2 are installed on the annular pipeline 3, which has a supply channel 4 and an outflow channel 5, connected to a collector b, for example, a boiler. The circulation pump 7 installed in the ring pipeline C ensures the supply of warm water to the faucets 2 in the appropriate amount without significant delay.

Collector 6 is designed as a heat exchanger, on the primary side of which there is a supply line 9 and an outflow line 10 for a liquid or, in general, liquid coolant. The liquid coolant can be water preheated in a heating boiler, or another fluid heated in a separate heating device and intended for heat transfer. The specific method of heating the coolant does not matter. A valve 11 is installed in the power supply line, which can be opened or closed by a motor 12. The motor 12 can be, for example, a stepper, which makes it possible to set the valve 11 in different opening positions. In the supply channel 4, a temperature sensor 13 is installed, which measures the temperature of warm water in the channel 4 and is connected to the control device 14, which controls the motor 12. The control device 14 has an input 15 for entering a set temperature value in the collector 6. This set value is called also a setting.

Simultaneously with the outflow of warm water through the faucet 2, through the inlet pipeline 16, cold water flows into the collector 6. The non-return valve 17 diverts the outflow of water from the annular pipeline C to the pipeline 16.

The arrival of cold water lowers the temperature of the already heated water in the boiler 6. The sensor 13 detects this decrease in temperature and, based on this, the control device 14 activates the motor 12, which opens the valve

11. The specified elements together form the regulation circuit 18. The control device 14 is actually a "regulator", with a static gain of Hr. The inverse value of this static gain Хр is denoted as gain М of the loop.

Fig. 2 contains a diagram of the control device 14. The input and output of the device 14 are marked according to the designations of the elements in Fig.1.

The control device 14 has, firstly, a differential amplifier 23, to which the specified temperature value is received from the input 15 and the actual temperature value from the temperature sensor 13. Depending on the difference between these temperatures, a setting signal is formed for the motor 12. The static gain of this differential amplifier 23 is variable and to change it, the threshold frequency detector 19 is used. First, the detector 19 receives signals identical to those received by the motor 12. Next, it receives the actual and set temperatures. These signals, which correspond to certain values, are sent to the pre-processing unit 20, which, as will be explained later, generates a pulse under certain conditions, and under other conditions forms a threshold element, the pulses are sent to the counter 21, connected to the timer 22, which determines for the counter 21, the beginning and the end of a predetermined time Interval. The output of the counter 21 is connected to the reset input of the timer 22, as well as to the differential amplifier 23, namely, to its input through which its amplification factor is determined, that is, static amplification.

Fig. 3 illustrates the operation of the control circuit.

Fig. Za shows the Takt curve, i.e. the temperature course in supply channel 4. The dotted line indicates the set value Tzad, i.e. the temperature setpoint. On both sides of the Tzad setpoint, the neutral zone M is shown: It can be seen that initially the temperature fluctuations Tfas are relatively large Differential amplifier 23 in the set Time Intervals form pulses for activating the motor 12, shown in Fig. 35. As long as the actual temperature Tfat is less than the set point Tzad, the motor 12 works in the direction OM-, in the opposite case - in the other direction (OM-). These images illustrate only an example Possible and other methods of setting the position of the valve 11.

In the described heating installation, re-installation of the valve 11 is not critical as long as they occur in one direction. Obstacles arise when the direction of action of the motor 12 and the valve 11 changes too often and significantly.

Therefore, single pulses (fig. 3B) can determine the direction of installation, illustrated in fig. Figure 2a shows the output value of the counter 21, which increases by 1 with each change of direction. The timer 22 sets the time interval that determines the periods shown in Figure 2a. It is important that the time periods 21, 22, 73 are the same.

If during the period 21 it turns out that the counter 21 has exceeded the predetermined value, the gain factor Xr of the differential amplifier 23 increases, and the gain M of the circuit decreases accordingly.

At the same time, the counter 21 is again set to 0 and the timer 22 is reset. Accordingly, the second period 72 of the countdown begins, and even before the end of the period 21. At the same time, the value of the error, which can be corrected in the future, remains unknown.

Figure 3e shows that the gain M of the loop decreases each time the counter 21 reaches a predetermined value during the counting period 72, in this case 3. It can be seen that two corrections must be made before the gain M of the loop decreases so much that the actual temperature Tfak undergoes fluctuations, the amplitude of which, however, in most cases remains within the neutral zone. In this case, only two changes of direction occur during the period of 23 counts. In any case, the actual temperature Tfak satisfies the ratio.

Rear - 0.5M2 « Tefact « Rear - 0.5M2

The gain M of the circuit corresponds to the inverse static gain Xr of the differential amplifier 23.

You can apply the algorithm according to which

Хре(1 ж) x Хр, where 7. » 0 and is a constant. It is desirable that 7. should be less than 1. After increasing the static gain Xr, which corresponds to the decrease in the gain M of the circuit, the limit frequency detector 19 starts working. When this detector detects instability, for example, 3 or more direction changes during the reference period 21, 272, ..., 7, the static gain Xr, as already noted, increases several times more. If the number of direction changes has not reached a critical value, it means that a steady state has been reached and the static gain remains unchanged.

Basically, this process can be divided into two phases. In the first phase, a check is made to see if there are "critical" oscillations, and at the end of this phase, the gain of the circuit is changed according to the results of this check. In the second phase, stability is monitored.

If no extreme fluctuations were detected in the first phase, the loop gain is increased until an unstable reference period is detected, and the adjustment process is not interrupted and the gain for the next reference period is determined. Fig. 4 shows the operation of increasing the gain of the circuit.

First, the static gain of the circuit is reduced, for example, according to the formula

Khry(1-o) x Khr, where o » 0 and is a constant, preferably less than 1. The constant a can be given the value 7, but, as a rule, it has a different value.

After that, there is a change in the temperature setting ad:

Tzad 2 Tzad - ler

For this, the control device provides a constant sensor 24 and an inverse amplifier 25 with switching, connected to a common point 26. After switching the inverse amplifier, it performs the conversion

Avr - -A5r

Changing the Tzad setting creates a disturbance that should cause oscillation. Without such oscillations, it is impossible to cause instability by changing the gain M of the circuit. After changing the setting and the Lee time delay, the limit frequency detector starts working. As long as this detector detects the stable operation of the control circuit 18, this process is repeated, that is, the gain M of the circuit increases.

At some point, the gain M of the circuit becomes so large that oscillations begin in the control circuit 18. In the embodiment illustrated in Fig. 4, this happens at the moment of IZ. In this case, the setting T-ad is set again to the current value, and the static gain Xr - to the value

Hr : Hr - c) and this completes the installation procedure. The gain M of the circuit is set to the value that last provided a stable state.

If a stable state is reached after the operations shown in Fig. 3, 4, no further operations are performed and the installation procedure is completed. In the event of a new instability, for example, due to a change in load, which leads to pendulum oscillations of the valve, a new installation procedure begins.

Fig. 5 illustrates another version of the process of changing the gain of the M circuit. This option involves the implementation of a system protective function that eliminates the possibility of oscillations at low loads close to idling.

Here, two loop gain values are selected - high and low, with the possibility of switching between them.

The purpose of this protective function is to stabilize and optimize the heating installation 1 depending on its load.

According to the protective function, the high gain M of the circuit, marked MI in Fig. 5, corresponds to the normal load. Such gain can be set, for example, using the automatic setting procedure described above. A means (not shown) of memorizing the gain can be provided.

The low gain U2 of the loop is used at idle.

Cutoff detector 19 is now used after normal mode is completed. In this case, the high M1 value of the circuit gain causes the appearance of oscillations of too high an amplitude and too high a frequency. After detecting such oscillations, caused by the previous increase in circuit gain, the gain is switched from a large value of M1 to a small value of Ma, after which the system stabilizes again.

The temperature drop caused by such a change is used to determine the value of the change during the transition from idling to normal mode. Time mark 12 in Fig. 5 corresponds to this operation. At the same time, there is a selection between moments 12 and ИZ. The load, in this case water withdrawal, is determined when the actual temperature from the Y7 value drops below the set temperature Tzad. In this case, the gain of the circuit increases to the value of M1. As a result, the regulator operates at the speed required for normal operation. At the moment of the IZ, the selection ends. Since the loop gain is too high, period 22 oscillates. They are detected by the detector of the limit frequency, and at the moment i4 the gain of the circuit again gains the value of M2. In turn, this value of M2 can be found through the appropriate Iterations when increasing the circuit gain. 21010 /

SCHI I le, "shu! 1

What is the drug?

What are you doing! pc di s b b 7 3

St s» schu -1/ nin

FIG.1 write write 25 Her 25 what

What

Shan Tei

Pot pl pi 027ИИ02Ш0Ш0200520-037.

FROM

FIG. 2 a) - Unit 77 V

KA-SHSHVSHY U -th iy OT tvo them

b)

OK"

ON-c) and

I) kn det stu e) m

FIG.Z a) ! M,

Y: Here 4. ptnyyarnen t t nepddlidotin--- 5)

Yizad dor

NV

b)

AND

FIG. 4 and M U

And yes

TbEt I in Still Shchi SHE that 7 T zad he pl wa i "p y N y; !! And

Io y and ih y

FIG. 5