DE20000146U1 - Device for regulating a size in a heating system - Google Patents

Description

Patent attorneys *&iacgr; ^.·| . · · J. &Sgr;&iacgr;&iacgr;&idigr;

BEETZ'& PARTNER .:.·..· *..' .;. \.*\.*

"Strndnsdorfslc. 10, D-80538 Munich

G 200 00 146.9 18.01.2000

New description Device for controlling a variable in a heating system

The invention relates to a device for controlling a variable in a heating system and for preparing an input variable for a control system.

In a heating system, fluctuations in the temperature of the boiler water can be caused, for example, by a two-point operation of the burner that heats the boiler water. This in turn has a disruptive effect on the temperature of the heating circuit flow water, which should be kept as constant as possible at a specified target temperature. For this purpose, a mixer controller can be used, for example, which regulates the disturbances caused by fluctuations in the boiler water temperature so that the heating circuit flow water temperature remains within a narrow tolerance band around its target value.

Three- and four-way mixers are used as actuators, for example, whereby the corresponding valves are opened and closed incrementally and can move through an angle range of 90°, for example. By adjusting the mixer valve, colder heating circuit return water is mixed with the heated water coming from the boiler, thus setting the desired heating circuit flow temperature. The transfer behavior of a mixer can depend on the difference between the boiler flow and heating circuit return temperatures, the volume flows, the mixer type and the mixer design. Since most of these influencing factors are unknown and dependent on the operating point, it is difficult to achieve precise control of the heating circuit flow temperature at every operating point. However, good control behavior under normal operating conditions must be guaranteed on the one hand, and stable behavior in borderline situations, i.e. e.g. when the boiler temperature fluctuates greatly, on the other.

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Furthermore, very simple AD converters and controllers are used in heating technology for cost reasons. This results in problems due to the value quantization of the measured variables used. The setpoint for the heating circuit flow temperature is also a value derived from such measured variables and is therefore subject to interference such as quantization noise. This can lead to unwanted setpoint jumps due to the quantization effects, particularly when the measured values contribute multiplicatively to the formation of the setpoint or a difference between the measured values is required to form the setpoint. Such setpoint jumps are small in magnitude but can interfere with a connected controller. In the case of flow temperature control, these effects trigger actuating movements, which unnecessarily increases the number of actuating signals for the mixer motor or for the relay(s) controlling it, which means an unnecessary load on the relays or the motor.

An object of the invention is to provide a device for controlling a variable in a heating system which has a high control quality.

Another object of the invention is to provide a device for processing an input variable for a control system, with which the influence of disturbances in the input variable is reduced.

These objects are achieved with the features of the independent claims. Dependent claims are directed to preferred embodiments of the invention.

According to the invention, in order to control a variable in a heating system, a manipulated variable for controlling an actuator is determined by a multi-point controller. A feedback device connected to the multi-point controller determines a feedback variable depending on the manipulated variable supplied to it as an input variable. The multi-point controller in turn determines the

Control variable depending on a setpoint for the variable to be controlled and on an actual value of the variable to be controlled and the feedback variable.

The variable to be controlled is preferably the heating circuit flow or return temperature of the heating system. The actuator can, for example, have a motor that controls one or more valves. Such a valve can, for example, be a mixing valve for mixing boiler water with heating circuit return water. The multi-point controller can, for example, be a three-point controller that can output three different control variables to control the actuator depending on its input variable. The control variables can, for example, cause a valve to open or close or lead to the valve position being held. Accordingly, a motor controlling the valve can rotate in the "open valve" or "close valve" direction or remain in its position, i.e. be switched off, for example. The feedback device can have a delaying transmission behavior. This can preferably be a proportional transmission behavior with a first or higher order delay, such as a PT1 or PT2 behavior and/or a low-pass behavior.

Furthermore, according to the invention, a change threshold value is determined by a threshold determination device for preparing an input variable for a control. A change determination device determines the change over time of a received variable, whereby it can receive the variable e.g. from a variable determination device. A comparison device compares the change over time with the change threshold value, whereby an input variable determination device determines the input variable for the control by calculating the received variable with previously received variables if the amount of the change over time is smaller than the change threshold value, and otherwise from the received variable.

Preferably, the input variable for the control and/or the received variable are setpoint values for the heating circuit flow temperature. Such a setpoint value can change in intentional larger jumps, which can be clearly distinguished from unwanted disturbances, for example.

Various embodiments of the invention will now be explained in more detail by way of example with reference to the accompanying schematic drawings.

Fig. 1 is a block diagram of an embodiment according to the invention for heating circuit flow temperature control,

Fig. 2 is a representation of the output variable of a three-point controller versus the input variable according to the state of the art,

Fig. 3 is a flow chart of an embodiment of the invention for controlling a variable,

Fig. 4 is a block diagram of an embodiment of the device according to the invention for preparing an input variable for a control
and

Fig. 5 is a flow chart of an embodiment according to the invention for preparing an input variable for a control system.

In Fig. 1, a controller 101 outputs a control variable S to control a mixer motor (actuator) 102. The mixer motor 102 can be controlled, for example, via two relays for the opening and closing movement of a valve. This also makes it possible to hold the valve position. The motor 102 sets a mixer position, i.e. the degree of opening of a valve, depending on the control variable S and/or the duration of the control variable S. The transmission behavior (step response) of the motor can have the course shown in box 102. An integrating characteristic curve with a final value is shown there, at which the motor or the

Valve can have reached an end position such as "fully open" or "fully closed". Depending on the mixer position, a mixing ratio is established between the boiler flow water and the heating circuit return water, so that an actual temperature HVist* of the heating circuit flow water can be established at the outlet of the mixer 104, which corresponds to a specified target value HVsoll within a narrow tolerance range. The transfer behavior (step response) of the mixer 104 can be described by a gain factor (proportionality factor), which can be dependent on the difference between the boiler flow and heating circuit return temperatures, the volume flows, the mixer type and the mixer design.

The heating circuit flow temperature HVist* can be measured by a temperature sensor 106, which is advantageously mounted as close as possible behind the mixer 104. The effect of the distance between the mixer 104 and the sensor 106 can be described in terms of time, for example, by a dead time Tt, which depends not only on the distance but also on the volume flow in the heating circuit and is not known. Box 105 shows such a transfer behavior (step response). The closer the sensor 106 is placed behind the mixer 104, the shorter this undesirable dead time Tt becomes. The transfer behavior (step response) of the sensor 106 can be described by a PTl element (first order delay element). The heat transfer from the heating water to the pipe wall on which the sensor 106 is arranged and from there to the sensor 106 results in an approximate PT2 transfer behavior (second order delay element) shown in box 106. The sensor 106 outputs an actual value HVist of the variable to be controlled to a summation point 107. Due to the transfer behavior of the sensor 106 and the dead time Tt, this actual value HVist does not exactly match the actual temperature HVist* of the water at the outlet of the mixer.

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The target value HV for the control can be output by a size determination device 110. It can be determined, for example, as a function of a desired room temperature change using a characteristic field or a table, which can be permanently stored and can take into account other influencing factors such as the outside temperature. The target value HV can be passed on directly to the control, in this case the summation point 107, or it can be processed using a device 109 according to the invention for processing a value for a control and then passed on to the summation point 107 as the target value HVsoll. In the latter case, for example, interference can be reduced by digitization, which would lead to an unwanted disruption of the control.

In the summation point 107, the actual value HVist is subtracted from the setpoint value HVsoll, and the summation point 107 accordingly passes on a control difference e to a second summation point 108. In another embodiment, it is conceivable that the setpoint value HVsoll is subtracted from the actual value HVist in the summation point 107 in order to obtain the control difference e. The summation point 108 receives a feedback variable HVrück as a further input variable, which it subtracts from the control difference e. Accordingly, the summation point 108 outputs a controller input variable HVein to the controller 101. In another embodiment, the control difference e can be subtracted from the feedback variable HVrück in order to obtain the controller input variable HVein. In other embodiments, the two summation points 107 and 108 can be interchanged with each other and/or the feedback variable HVrück can be interchanged with the actual value HVist.

In this embodiment, the controller 101 is a three-point controller, with the curve of the manipulated variable S as a function of the controller input variable HVein being shown in box 101. A three-point controller will be described in more detail later with reference to Fig. 2. The output from the controller 101

Manipulated variable S is fed to a feedback device 103, which in the case shown here exhibits a PTI behavior (step response). It outputs the feedback variable HVrück depending on the manipulated variable S. In another embodiment, instead of one feedback device 103, two feedback devices can be provided, which can have different temporal behavior. Both feedback devices can thus exhibit a PTI behavior, although the time constants can differ from one another. The feedback devices can then each be operated depending on the sign of the manipulated variable S. For example, a switch can be provided in front of the two feedback devices, which is actuated by the manipulated variable S and switches one or the other feedback device accordingly. The outputs of the two feedback devices can then be fed to the summation point 108 accordingly.

Fig. 2 shows the behavior of a known three-point controller. Depending on the input variable HVein, the output variable S, shown by the thick solid lines, takes on different values. Coming from the left, the output variable S is equal to a negative control value -San until the input variable HVein reaches a second threshold value SW2. After that, if the input variable HVein is increased further, the output variable S is zero until it reaches a fourth threshold value SW4, which is greater than the second threshold value SW2. When this value is reached, the output variable S changes its value to a positive control value San, which it retains even when the input variable HVein is increased further. If the input variable HVein is now reduced coming from the right, the value of the output variable S is only changed to zero when a third threshold value SW3 is reached, which is smaller than the fourth threshold value SW4 and greater than the second threshold value SW2. If the input variable HVein is further reduced, the output variable S remains

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at zero until it reaches a first threshold value SW1, which is smaller than the second threshold value SW2. Only then is the value of the output variable S changed to the negative control value -San. In this embodiment, a hysteresis-like behavior results.

The difference between the first SW1 and the fourth SW4 threshold value is referred to as the dead zone XT. The difference between the first SW1 and the third SW3 threshold value or between the second SW2 and the fourth SW4 threshold value is referred to as the zero zone XN. The dead zone XT and the zero zone XN can be set in the same way as the control value San to optimize the required control behavior. This can be done in conjunction with the setting of the parameters of the feedback device 103, such as a time constant TR and a gain VR of the PTL behavior shown. Depending on the heating system, other optimal values can result for this. In particular, the value range for the dead zone XT, as well as for the zero zone XN, can be 0 to 5 K, with the zero zone XN being smaller than the dead zone XT. The time constant TR of the feedback device 103 can be in a range between 0 and 1000 s, and the gain VR can be in a range between 0 and 50.

It is advantageous to store certain parameter sets for different heating systems, e.g. in an EEPROM, which can then be called up depending on the application. When determining the parameters XT, XN, TR and VR, it can be taken into account that there is a maximum control difference e that still causes a linear behavior of the manipulated variable S. This also applies to the maximum control range of the motor 102 or the valve with which a linear behavior can still be achieved.

Fig. 3 shows a flow chart to illustrate the process for controlling a variable of a heating system. In step 301

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First, the setpoint HVsoll of the variable to be controlled, e.g. the heating circuit flow temperature, is read in. In step 302, the actual value HVist of the variable to be controlled is determined. This can be done, for example, using the sensor 106 shown in Fig. 1. Then, in step 303, a controller input variable HVein is formed by subtracting a feedback variable HVrück and the actual value HVist from the setpoint HVsoll. This represents, for example, a summary of the functions of the two summation points 107 and 108 from Fig. 1, which can also be represented as one summation point. The feedback variable HVrück, the actual value HVist and the setpoint HVsoll can then be fed to this summation point at the same time. The "intermediate variable" e can then be dispensed with, for example.

In the next step 304, a query is made as to whether the controller input variable HVein is smaller than a first threshold value SWl. If this is the case, the current manipulated variable S(k) is set to the value -1 in step 305. The system then moves on to step 314. If the query in step 304 is answered in the negative, i.e. the controller input variable HVein is not smaller than the first threshold value SWl, a query is made in step 306 as to whether the controller input variable HVein is greater than a second threshold value SW2. If this is the case, a query is made in step 307 as to whether the manipulated variable S(k-l) output in a previous process run at time k-1 was equal to -1. If this is the case, the system moves on to step 310. However, if the query in step 307 is answered in the negative, then the system goes to step 308, just as it does if the query in step 306 is answered in the negative, i.e. the previous manipulated variable S(k-1) was not equal to -1 or the controller input variable HVein is not greater than a second threshold value SW2. There, it is queried whether the controller input variable HVein is less than a third threshold value SW3. If this is the case, it goes to step 309, where it is queried whether the previously output manipulated variable S(k-1) was equal to 1. If this is the case, it goes to step 310.

by setting the current manipulated variable S(k) to zero. The system then moves on to step 314.

If the query in step 309 is answered in the negative, the system goes to step 311, just as it did if the query in step 308 was answered in the negative, i.e. the previous manipulated variable S(k-l) was not equal to 1 or the controller input variable HVein is not less than a third threshold value SW3. There it is queried whether the controller input variable HVein is greater than a fourth threshold value SW4. If this is the case, it goes to step 312, in which the current manipulated variable S(k) is set to 1. It then goes to step 314. If the query in step 311 is answered in the negative, i.e. the controller input variable HVein is not greater than a fourth threshold value SW4, the new manipulated variable S(k) is set equal to the previous manipulated variable S(k-l).

Subsequently, in step 314, the feedback variable HVrück is calculated by weighting the new manipulated variable S(k) and the previous manipulated variable S(k-l) according to the equation

HVrück = VR(T0/TR*S(k)+(1-TO/TR)*S(k-1))

determined. TO represents the time period (sampling time constant) between the output of the previous manipulated variable S(k-1) and the new manipulated variable S(k), TR represents the time constant of the feedback device 103 and VR represents the gain factor of the feedback device 103. Subsequently, in step 315, the new manipulated variable S(k) is stored so that it is available for the next run as the previous manipulated variable S(k-1).

The control shown here shows a quasi-linear PI behavior. In contrast to linear control, however, this is characterized by a rest position around the setpoint HVsoll, in which the manipulated variable S, for example, does not cause the valves to be controlled. This means that the actual value HVist in certain

Limits that can be finely adjusted (zero zone XN, dead zone XT) can fluctuate around the setpoint HVsoll without this leading to a change in the manipulated variable S. This can, for example, compensate for dead times in the system to be controlled and protect a motor and/or corresponding relays used for control, as they do not have to be switched as frequently.

Fig. 4 shows a block diagram of an embodiment of a device (109) according to the invention for preparing an input variable for a control system. A variable HV determined for the control system is fed to it from a variable determination device 110. A receiving device 401, which can be a plug or a memory, for example, receives the variable for the control system HV and passes this received variable HV on to various devices. For example, the change determination device 402 receives the received variable HV and can use it, for example by comparing it with a previously received variable stored in a memory 403, to determine the temporal change in this variable dHV and output it to a comparison device 405. The change determination device 402 can also be a differentiator that differentiates its input variable HV, in which case, for example, the memory 403 is not present.

A threshold value determination device 404 determines a change threshold value SWänd and also outputs this to the comparison device 405. The comparison device 405 compares the temporal change dHV with the change threshold value SWänd and outputs a signal to an input variable determination device 406 in accordance with the result of the comparison. This also receives the received variable HV from the receiving device 401.

One or more previously determined input variables, preferably the last determined input variable for the control HVregel, are stored in a memory 408. These are

a weighting device 407, which preferably weights this and the received variable HV supplied by the receiving device 401 differently and outputs it to the input variable determination device 406. The input variable determination device 406 determines the input variable for the control HV control from its input variables, which is then fed to a control such as a heating circuit flow temperature control.

Fig. 5 shows a flow chart to illustrate the process for preparing an input variable HVregel for a control system. In step 501, the change threshold value SWänd is determined. Then, in step 502, the current variable to be prepared for the control system HV(k) is received. The change over time dHV of the received variable is then determined. In the next step 504, a query is made as to whether the change over time dHV is greater than the change threshold value SWänd. If this is the case, in step 505 the current input variable for the control system HVregel(k) is set equal to the current received variable HV(k). If the query in step 504 is answered in the negative, in step 506 the input variable for the control system HVregel(k) is determined by weighting the current received variable HV(k) and the previous received variable HVregel(k-1) according to the equation

HV rule(k) = T0/xset*HV(k)+(1-TO/xset)*HV rule(k-1)

determined. Here, TO again denotes the time period between the time k and k-1, and tsoll represents a further time constant to be set. Following this, in step 507 the current input variable for the control HVregel (k) and in step 508 the current received variable HV(k) are stored.

In the case of a heating circuit flow temperature control, the change threshold value can be set to 3 K, for example, so that larger desired setpoint jumps can be avoided by the inventive

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nal device directly to the input of the control system, whereas disturbances of less than 3 K remain essentially without consequences. This means that their influence is small. When determining the threshold change value SWänd, the level of the disturbances can be taken into account in such a way that they are essentially smaller than the change threshold value SWänd and can therefore be regarded as disturbances.

All of the devices or methods described can be implemented in analogue, digital or mixed form. In the case of a mixed analogue and digital implementation, corresponding analogue/digital converters and digital/analogue converters can be provided. The devices shown can communicate with each other via a data and/or control bus, so that they have no direct connection with each other and the connections shown in the figures are therefore entirely or partially symbolic.

Claims (19)

1. Device for controlling a variable in a heating system, characterized by : 1. a multi-point controller ( 101 ) which determines a manipulated variable (S) for controlling an actuator ( 102 ), 2. a feedback device ( 103 ) connected to the multi-point controller ( 101 ), to which the manipulated variable (S) is supplied as an input variable and which determines a feedback variable (HVrück) depending on the manipulated variable (S),
wherein the multi-point controller ( 101 ) determines the manipulated variable (S) as a function of a setpoint (HVsoll) for the variable to be controlled, an actual value (HVist) of the variable to be controlled and the feedback variable (HVrück). 2. Device according to claim 1, characterized in that the multi-point controller ( 101 ) is a three-point controller. 3. Device according to claim 1 or 2, characterized in that the variable to be controlled is the heating circuit flow or return temperature. 4. Device according to one of claims 1 to 3, characterized in that the actuator ( 102 ) has a motor controlling a valve. 5. Device according to claim 4, characterized in that the valve is a mixing valve ( 104 ) for mixing boiler water with heating circuit return water. 6. Device according to one of claims 1 to 5, characterized in that the feedback device ( 103 ) has a delaying transmission behavior. 7. Device according to claim 6, characterized in that the delaying transmission behavior of the feedback device ( 103 ) is dependent on the manipulated variable (S). 8. Device according to one of claims 1 to 7, characterized in that the multi-point controller ( 101 ) and/or the feedback device are digital devices. 9. Device according to one of claims 1 to 8, characterized by a sensor system ( 106 ) for determining the actual value (HVist). 10. Device according to one of claims 1 to 9, characterized by a setpoint determination device for determining the setpoint (HVsoll) 11. Device according to one of claims 1 to 10, characterized by a linking device ( 108 ) for linking the setpoint value (HVsoll), the actual value (HVist) and the feedback variable (HVrück) to a single controller input variable (HVein). 12. Device ( 109 ) for preparing an input variable (HV control) for a control, characterized by: 1. a threshold determination device ( 404 ) for determining a change threshold value (SWänd), 2. a change detection device ( 403 ) for determining the temporal change (dHV) of a received variable (HV) for the control, 3. a comparison device ( 405 ) connected to the threshold determination device ( 404 ) and the change detection device ( 403 ) for comparing the temporal change (dHV) with the change threshold value (SWänd), and 4. an input variable determination device ( 406 ) connected to the comparison device ( 405 ), which 1. if the amount of change over time (dHV) is less than the change threshold value (SWänd), the input variable (HVregel) for the control is determined from a value which is determined by offsetting the received variable (HV) with previously received variables, 2. otherwise the input variable (HV control) for the control is determined from the received variable (HV). 13. Device according to claim 12, characterized in that the input variable (HVregel) for the control and/or the received variable (HV) are setpoint values of the heating circuit flow or return temperature. 14. Device according to claim 12 or 13, characterized in that it is digital. 15. Device according to one of claims 12 to 14, characterized in that the change threshold value (SWänd) is determined as a function of the level of the interference components contained in the received quantity (HV). 16. Device according to one of claims 12 to 15, characterized by a memory ( 408 ) for storing the input variable (HVregel) for the control. 17. Device according to one of claims 12 to 16, characterized by a weighting device ( 407 ) which weights the received quantities to be calculated depending on their temporal occurrence. 18. Device according to one of claims 12 to 17, characterized in that the input variable determination device ( 406 ) determines the input variable (HVregel) for the control according to the following equation:


with the input variable for the control HVregel(k) at time k, the input variable for the control HVregel(k - 1) at time k - 1, the received variable HV(k) at time k, the time period T0 between times k and k - 1 and the weighting factor τsoll. 19. Device according to one of claims 1 to 11, characterized by a device according to one of claims 12 to 18, wherein the input variable (HV _control ) for the control forms the setpoint (HV _set ) for the variable to be controlled.