DE3230058A1 - Method and device for circulating the heat carrier in a radiator system - Google Patents

Abstract

The circulating pump of a radiator system is operated at a speed which is dependent on the heating power in order to avoid consuming unnecessary energy when the radiators are turned down. The pump drive contains a converter which is supplied from the supply network and has a pulse-controlled invertor supplying an asynchronous machine. A constant, frequency-independent binary curve shape which is pulse-width modulated with a high-frequency sampling voltage is specified for the pulse-controlled invertor output voltage. In the case of the selected curve shapes (Fig. 3), the harmonics which are caused by the binary curve shape are in a region where they have no significant influence either on the losses in the invertor and the machine which are caused by harmonics or on the development of noise in the radiator system. A sampling frequency of over 5 kHz is required for the pulse-width modulation, which is possible as a result of the use of power transistors as the invertor switches. <IMAGE>

Description

Method and device for circulating the heat transfer medium

in a heating pipe system The invention relates to a method for Circulation of the heat transfer medium in a heating pipe system by means of a circulation pump and a drive device for a circulation pump for carrying out the method.

Heating systems for buildings usually contain a closed one Pipe system in which a heat transfer medium, e.g. hot water, passes through a first heat exchanger (such as a boiler or a solar collector) is conducted and thereby heat picks up, which he then subsequently when flowing through a second heat exchanger (Radiator) releases into the environment. The transport of the heated water to the Radiators are carried out by circulation pumps and the heat is released into the environment (heating power) the system is regulated by valves on the radiators that increase the flow rate or throttle less. The circulation pump must be designed so that it can operate in cold ambient temperatures, where all radiator valves have to be fully opened, another sufficient one Allow delivery pressure or flow of hot water. Such extreme ambient temperatures however, are only available on a few days of the year. During the rest of the operating time the heating system, the radiators are partially or completely closed and one Unregulated or uncontrolled circulation pump delivers too much. This creates disruptive Flow noises, in addition, the pumps work with an unfavorable degree of efficiency, because the pump curve the system characteristic for this changed Loads is not adjusted. Too much energy is then used.

In the face of rising energy costs, people are increasingly willing to do that Additional costs for a heat output-dependent change in the pump output in purchase gain weight. The pump could be equipped with a speed-controlled DC motor are driven, but the invention is intended to open up the possibility of To use commercially available three-phase machines economically, but several times Pole-changing drives that adjust the speed of the pump in stages because of the required relay circuits, which are currently relatively expensive and appear prone to failure.

Variable-speed drives have already been developed for other purposes, which do not work according to the pole-changing principle. Such a drive contains a three-phase machine whose supply voltage is supplied by an inverter and is changed proportionally to the desired speed, inverters are preferred used where each AC voltage output has an inverter switch alternating in a high-frequency cycle on the positive and negative DC voltage input are switched and the duration of each switching state is selected so that results in a pulse-width-modulated output voltage of the desired curve shape.

With regard to a low harmonic torque and an optimal The converter and machine are used for the AC output voltage in these Commercially available drives should aim for a curve that is as sinusoidal as possible. In addition will be for everyone AC voltage output a corresponding sinusoidal Control voltage generated whose intersection points with a high-frequency triangular voltage the switching pulses for the one working on the respective inverter output Inverter switch supplies and thus the length of each, to the modulated Output voltage to be assembled voltage pulses determined.

The DC input voltage to the inverter is almost constant impressed, e.g. by the inverter input via a voltage intermediate circuit with the DC voltage output of one connected to an AC supply voltage Rectifier is connected. When using an asynchronous machine, in general an amplitude of the supply voltage that decreases proportionally with decreasing speed required, with a disproportionate rate only towards the lowest speeds Decrease in the voltage amplitude is provided. The corresponding amplitude control the AC output voltage can be achieved by the ratio of Sinus amplitude changed to the amplitude of the triangular voltage used as the probe voltage will. The frequency ratio between triangular voltage and output voltage is determined the number of switching operations of each switch within a voltage period and thus the approximation to the sinusoidal shape.

The triangle frequency, however, cannot be chosen arbitrarily high, otherwise too many switching operations with high switching losses and a thermal one Destruction of the converter switch occur. As a converter switch are usually Thyristors are used, which additionally have a certain minimum duration for each Switching process must be adhered to, so that the key frequency is practically 400 Hz can not exceed significantly.

For the operation of a circulation pump described above, e.g. a three-phase asynchronous machine suitable that with a symmetrical system from three pulsed phase voltages which are practically sinusoidal at a high modulation frequency is fed. The generation of the sinusoidal voltage system by means of a pulse inverter However, it is relatively expensive, since three around 1200 egg. offset against each other Control voltages must be generated in the inverter control. It is take into account that the inverter is at full load (nominal operation) of the drive is to be interpreted, but the fundamental oscillation amplitude with conventional control methods to generate sinusoidal output voltages does not reach the values for full voltage utilization of the converter are possible. The energy saving Due to the heat output-dependent speed control of the circulation pump, the higher manufacturing costs.

It should also be noted that the torque of the drive is even greater Has harmonics, the more the voltage deviates from the sinusoidal shape of the feed will.

This increases the risk of structure-borne sound vibrations in the heating pipe system occur which can lead to unbearable noise pollution of the environment.

The invention now enables the economical use of an asynchronous machine, while also avoiding increased noise pollution. The effort can be like this be kept small that the pump drive compared to the market Circulation pumps necessary additional costs are offset by the energy savings that e.g. in a temperate climate with a building heating in three heating periods is achieved.

This is achieved according to the invention by a method with the Features of claim 1.

Accordingly, the circulation pump is driven by an asynchronous machine, via an inverter with a DC voltage intermediate circuit containing a Pls inverter is fed from an alternating voltage network. The frequency of the inverter output voltage is specified proportionally to a desired speed and also its amplitude is - at least in the upper speed range - also proportional to the desired Rotational speed. There is one reference voltage for each inverter output Setpoint voltage with the same for all frequencies and all inverter outputs Curve shape specified. Only two voltage values are required for this nominal voltage, e.g. "positive" and "negative", permitted ("binary curve"). Compared to a full block control, in the first half period (i.e. between phases Oo and 1800 of the fundamental oscillation at the corresponding inverter output) a positive voltage and during the second half period (between 1800 and 3600) a negative voltage is generated, are to certain phase positions that are specified independently of the speed, Gaps are provided in which the voltage is in each case the opposite binary state having. The gaps are in the vicinity of the zero crossings of the output voltage fundamental oscillation and are arranged with quarter-period symmetry, i.e. they are symmetrical with regard to the zero crossings and the maxima of the fundamental oscillation. The sum of the gap widths within each half period is much smaller than the width of the gap-free Area in the middle of each half-period.

The target voltage is therefore due to the width of the gap-free area essentially represents a full block control, which only pieces on the block flanks having. This enables almost the maximum voltage utilization that can be achieved with full block control of the converter. The disadvantage of full block control, however, is a high harmonic content the output currents that lead to energy losses in the converter and machine as well as to Excitation of resonance frequencies in the heating pipe system and thus noise pollution could lead. Both are avoided by the provided gaps, which a certain Represent the approach of the full block control to the sinusoidal shape. Although can through the gaps in the harmonic spectrum with full block control existing harmonics are amplified and also the harmonic frequencies change to the extent that by shifting the basic frequency with the desired speed. Through the Choice of the gaps can however be achieved that the harmonics at all Load states lie in an area in which there is no structure-borne noise excitation in the pipe system occurs.

From the respective target voltage for the relevant inverter output a pulse-width-modulated control signal is generated by means of a high-frequency sensing voltage to switch over the inverter switch working on the relevant inverter output formed, with the pulse width ratio corresponding to the desired amplitude is given. E.g.

the binary nominal voltage with a high-frequency triangular voltage, whose amplitude is proportional to the alternating voltage amplitude specified as a function of the speed is to be compared to the switching commands of the inverter switch from the intersection points to build.

But you can also advantageously use a triangular voltage more constant Compare amplitude with an amplitude voltage and the comparison result, the a binary equal voltage signal pulse-width-modulated according to the desired amplitude to feed together with the binary nominal voltage to a vXtLUSIV-OR gate, at its output then the pulse-width-modulated nominal voltage as a control signal for the inverter switch is pending.

Pulse width modulation, like the binary nominal voltage curve, can also be lead to excitations of sound frequencies in the pipe system. However, this is avoided if the sampling frequency is always higher than 5 kz.

The control of the pulse inverter is particularly easy if the scanning voltage is specified independently of the speed, e.g. at around 6 kHz. The pulse inverter can be operated with such high sampling frequencies without difficulty, if an inverter with switches made of power transistors is used as an inverter will. Such a transistor inverter is, for example, in the German patent application P 30 30 485.9 (VPA 80 P 3149).

According to this method, the circulation pump can be driven at one speed which are specified as a function of the heating output of the heating pipe system will. The speed can e.g. depend on the temperature difference at the input and output of the radiators, i.e. in the flow and return of the heat transfer medium, controlled or controlled, but in particular the speed can also be a function of the delivery rate and / or the delivery pressure of the circulation pump can be changed.

The invention is based on an exemplary embodiment and 5 figures explained in more detail.

Fig. 1 shows a heating pipe system with a circulation pump, which with a drive device is provided according to the invention, Fig. 2 shows a drive device for the circulation pump and serves to illustrate a preferred exemplary embodiment, Fig. 3 shows different pulse patterns for the control voltage of the inverter, Fig. 4 illustrates the keying of the predetermined according to the pulse pattern Control voltage for generating the pulse width modulated output voltage and Fig. 5 shows the corresponding control of the pulse-controlled inverter.

According to Fig. 1 is in the coming from a mixing valve 1 flow pipe a closed heating pipe system, a circulation pump 3 arranged through the the heated heat transfer medium to the inlet valves 4 of several heat exchangers 5 (radiators space heating). A return system leads from the heat exchangers 5 6 back to the mixing valve 1, which is designed as a four-way valve and allows part of the heat transfer medium cooled in the heat exchangers 5 into another To conduct heat exchanger 7 (boiler) and replace it with heated water. With 8, the expansion tank of the heating pipe system is referred to.

The circulation pump 3 is driven by an asynchronous machine 10, which is fed by the output AC voltage of a pulse-controlled inverter 11. Of the Inverter is part of a converter via a DC voltage intermediate circuit 12 connected to a rectifier 14 fed by a supply network 13.

The inverter switches of the inverter 11 are controlled by means of control lines 15u, 15v, 15W controlled with corresponding switching impulses from the inverter control 16 can be delivered. The inverter control can use the flow rate as a reference variable JM of the heat transfer medium are supplied, which is arranged in the flow system 2 by means of a Flow meter 17 is detected. In addition or as an alternative, it is provided the delivery pressure of the circulation pump by means of a differential pressure meter arranged in parallel 18 to capture.

The drive device for the circulation pump preferably contains -the Asynchronous machine 10, the converter fed from the AC voltage network 13 with the pulse-controlled inverter 20, which is connected to the rectifier via the voltage intermediate circuit 21 22 is connected, a speed sensor 23 and the converter control 24, as shown in Fig. 2 is shown.

The rectifier 22 is designed as an uncontrolled rectifier bridge, via fuses 25 and converter switch 26 to phases R, S, T of the network 13 is connected. A power supply part 27 supplies the supply voltage for control.

The intermediate circuit 21 contains the intermediate circuit capacitor 28, the charged via a series resistor 29 which can be short-circuited after a delay time will.

Furthermore, two measuring shunts are provided in order to use the contactor 31 Short-circuiting the series resistor 29 and switching the inverter on and off 20 to make. This also means that the inverter can be switched off in the event of a fault possible.

The AC voltage outputs U, V, W of the inverter 20 are respectively alternately to the DC voltage outputs of the Intermediate circuit 21 connected. Each inverter switch is via a binary Control signal (lines 15u, 15v, 15W) controlled and each contains two power field effect transistors, as they e.g.

under the registered trademark SIPMOS of the company Siemens are. The inverter output U is e.g. via the FET 31, the one with the "1" status the signal line 15U is controlled, with the positive DC voltage pole and via the FET 32, which is activated with the state, to the negative DC voltage pole tied together. Such a power FET has the opposite direction of current flow a diode characteristic, as shown by the corresponding arrow in the circuit symbol is. With such a transistor switch, a switched-on current can in contrast to thyristors can also be switched off.

Anti-parallel diodes and relief networks are not required. The control is simple and low-loss. In conjunction with an uncontrolled Input rectifier results in a cost-effective solution with little Expenditure on power components and assembly as well as a high power factor for the mains current.

As a speed sensor to generate a heating output dependent Speed setpoint, for example, a controller 23 can be used to which the control deviation between the differential pressure actual value / -p and the differential pressure setpoint ß p * the circulation pump is supplied. A flow regulator can also be provided, which can replace or superimpose the differential pressure regulator 23.

The pulse inverter generates in the method according to the invention a supply voltage for the asynchronous machine, for the various possibilities shown in FIG. 3 of the curve are specified.

With UO, the fundamental oscillation is in the top line of FIG Output voltage shown, the zero point of which has all of the following phase specifications relate.

While this is the case with the usual pulse change control mentioned at the beginning Curve UO already represents the target curve, which by means of a higher-frequency sampling frequency is sampled in order to obtain an approximately sinusoidal output voltage the curve shapes U1 to U5 shown in FIG. 3 are basically already pulsed Voltage'dar and are used in the control according to the invention as a target curve for the The output voltage, for its part, is still pulse width modulated by the high-frequency sampling frequency. A of the setpoint curves U1 to U5, which for ç = O ... 1800 are essentially positive and is essentially negative for t = 1800 ... 3600.

Pulse gaps are symmetrical around ç = 00, 900, 1800 and 2700 provided, the pulse widths of which are 30 or 60. Begins at curves U1 and U3 every half period with a gap, the sum of the gap widths in each quarter period (i.e. between 0 ° and 900) is 60. Curve shapes with more than 3 gaps and one Total gap widths over 120 per quarter period are possible, but will be less considered advantageous. With regard to a good voltage utilization as well as low Current harmonics and sound resonance excitations have the curves U1, U2 and U3 proven.

The pulse widths of 30 or 60 result from the fact that for the target curve a temporal resolving power is sufficient that of a division corresponds to a solo period in 120 time steps.

Fig. 4 explains how by scanning a target voltage, e.g. U1, with the high-frequency touch voltage UT when both voltages are equal the switching pulses for the inverter switch can be generated. At the exit a corresponding comparator results in a modulated, binary nominal voltage UmOd, which in the case shown is used as the control voltage for the inverter switch 31, 72 (Fig. 2) of the inverter output U during the times AT1 to the positive DC voltage input and during the times ß T2 to the negative DC voltage input lays.

The modulated setpoint voltage Umod thus doubles as it were modulated "voltage with a first modulation frequency corresponding to 2 A T0 and a second, higher modulation frequency UT (corresponding to j T1 + t T2) these "Second" modulation is required to keep the amplitude of the output voltage proportional to set the modulation ratio (t T1 - & T2) / (A T1 + ß ru2), the is given by the amplitude ratio of the keying voltage and the nominal voltage.

The shape of the target curve U1 is specified independently of the speed, during their period through the required fundamental oscillation period of the output voltage is determined and therefore variable with the required speed. For a machine that their full modulation (nominal speed 2850 rpm.) at a feed frequency of When it reaches 50 Hz, the gap duration of 60 corresponds to a "first" modulation frequency of about 1.5 kHz. Due to the speed-dependent change, in the partial load range longer gap durations with lower frequencies corresponding to the fundamental oscillation period. In this frequency range, however, lie also the resonance frequencies of the heating pipe system, which shows a strong resonance at around 1.8 kHz, for example it turned out, for example, that with a purely sinusoidal target curve or a the target curve corresponding to the full block control, each with a speed-proportional Sampling frequency is pulse-width modulated, not only at 1.8 kHz, but always when if the scanning frequency falls below 5 kHz, there is considerable noise pollution, which is felt to be all the more unpleasant as it depends on the heating output given speed in its frequency spectrum constantly changes.

It has been shown, however, that the specified voltage through the described form in cooperation with the pulse width modulation provided for the amplitude control with modulation frequencies above 5 kH only tolerable noise pollution occurs. The total in the harmonic spectrum of the modulated nominal voltage occurring frequencies and the resulting current harmonics lie rather in an area in which the heating pipe system is no longer essential can stimulate vibrations.

For example, in the case of the curve forms U2 and U3, the harmonics 5th, 7th and 11th order less strong compared to the mentioned full block control stimulated, while higher frequencies (e.g. 17th and 19th order) are much stronger emerge without, however, stimulating the heating pipe system to sound vibrations.

To ensure that the sampling frequency in turn is in the entire load range the heating pipe system can not stimulate, it is provided that the sampling frequency is always above a minimum value of preferably 5 kHz.

There. can easily be achieved in that the Sampling frequency is specified independently of the speed, e.g. at around 6 kHz.

The inverter control used in the device of FIG 24 is shown essentially in FIG. The speed setpoint n * is used as the speed control voltage a first function generator 5G entered, which between two binary voltage values alternating setpoint voltage with a frequency corresponding to the speed setpoint and a frequency-independent waveform is generated.

A second frequency generator 51 generates the high-frequency touch voltage UT. The speed control voltage is also input to a characteristic generator 52, the relationship between Voltage frequency and amplitude of a reference voltage (amplitude control voltage) generated, which is proportional to the speed at higher speeds and at lower speeds RPM decreases disproportionately.

Touch voltage and reference voltage are a threshold value transmitter with a binary output signal that indicates whether the instantaneous value of the triangular voltage is larger or smaller than the reference voltage. Characteristic curve generator and threshold value detector represent a modulation stage, which by comparing the key voltage with the Amplitude control voltage dependent on the speed setpoint, pulse width modulated pulses generated with which a logic circuit 54 from the generated in the first function generator 50 Control voltage for an inverter switch (control line 15u) a pulse width modulated Forms control voltage with which the relevant inverter switch is switched will.

The other control lines (15v, 15w) received Control voltages, each phase shifted by 1200 with respect to the control voltage on the control line 15U are.

The function generator 50 advantageously consists of a voltage-frequency converter 55, which is connected to the counter input C of a counter 56, e.g. a resettable 7-bit counter 56, is connected. A read-only memory 57 is addressed with the counter reading, in which the curve shape is saved. In this case, each period is in 120 counting steps subdivided, so that the time intervals of the frequency converter 55 generated counting pulses each of a 3 ° el. Advancing phase in the control voltage correspond and a new memory location is controlled in memory 57 every 3 ° in which the value of the binary control voltage belonging to the respective phase is stored. The resolution of the control voltage is therefore 30 with the 120th counting step of the counter 56 each period has ended and is in the corresponding memory location a reset pulse is stored, which is sent via line 58 to the reset input of the counter 56 is given and thus a new cycle for the next period initiates. It is advantageous in the read-only memory 57 for each of the inverter switches its own, correspondingly phase-shifted nominal voltage is stored and the read-only memory delivers these via separate outputs each time it is activated by the counter 56 Set voltages to the logic circuit 54. The logic circuit 54 can then be advantageous contain an EXCLUSIVE-OR gate for each of the inverter switches, the only the corresponding control voltage from the read-only memory 57 and the pulse-width modulated Pulses of the threshold value detector 53 need to be supplied.

The structure of this control is particularly simple, since it only has one single read-only memory and a single, simple analog / digital converter (voltage frequency converter 5) gets by.

This means that a variable-speed circulation pump is available that both in terms of acquisition costs as well as energy savings and the Noise and maintenance-free all the requirements of a consumer article fulfilled for broad use in heating systems.

5 Figures 7 claims

Claims (7)

Claims method for circulating the heat carrier in an em Heating system by means of a circulation pump, g e -k e n n n z e i c h n e t the following features: a) The circulation pump is powered by an asynchronous machine driven by a speed dependent on the heating load of the heating pipe system; b) the asynchronous machine is powered by a voltage intermediate circuit converter with pulse inverter fed from an alternating voltage network with a pulsed alternating voltage, whose Frequency proportional to the desired speed and its amplitude at least in upper speed range is also proportional to the desired speed; c) for each inverter output is a nominal voltage with a binary, all Outputs a common curve shape that is fixed for all speeds, except for gaps near the fundamental zero crossings in the first half period one binary state and in the second half period the other binary state having, in each half period the width of the gap-free central area is much larger than the sum of the gap widths and the gaps are symmetrical are specified around the half-period center, and d) from the respective nominal voltage and a high-frequency sensing voltage becomes a pulse-width-modulated control signal to switch the working to the corresponding inverter output clerk desk formed, with the pulse width ratio corresponding to the desired amplitude is given. 2. The method according to claim 1, d a d u r c h g e k e n n z e i c h n e t that the speed is controlled depending on the delivery rate and / or the delivery pressure or is regulated. 3. The method according to claim 1 or 2 d a d u r c h g e k e n n z e i c h n e t that the high frequency of the probe voltage is above 5 kHz. 4. The method according to claim 3, d a d u r c h g e k e n n z e i c h n e t that the probe voltage is given independently of the speed, in particular at about 6 kHz will. 5. The method according to any one of claims 1 to 4, d a -d u r c h g e it does not indicate that a pulse-controlled inverter with inverter switches from power transistors is used. 6. Drive device for a circulation pump for carrying out the method according to one of claims 1 to 5, g e k e n n n z e i c h n e t by a) an asynchronous machine (10) and a converter connected to an AC voltage network (13) with a Voltage intermediate circuit (21) and a pulse inverter (20) for feeding the asynchronous machine, the inverter switches of which consist of power transistors (31, 32); b) a speed sensor (23) for generating a speed isolation value as a function of the heating power; c) an inverter control connected downstream of the speed sensor (24) with - a first function generator for generating a binary target voltage with a frequency corresponding to the speed setpoint and a frequency-independent one Curve shape, - a second FuSktionsgeber (51) for generating a high-frequency Touch voltage, - a modulation stage (52, 53), which is determined by comparing the touch voltage pulse-width-modulated with an amplitude control voltage that is dependent on the speed setpoint Pulses generated, and - a logic circuit, which consists of the binary nominal voltage and the pulse width modulated pulses pulse width modulated control voltages for the Switching of an inverter switch supplies, whereby - means are provided, phase-shifted pulse-width modulated for switching the other inverter switches To form control voltages. 7. Apparatus according to claim 6, d a d u r c h g e k e n n z e i c It should be noted that the first function generator (50) is fed from a speed setpoint Most binary oscillator (55) to generate counting pulses for a downstream Counter (56) and a read-only memory (57) addressed by the counter reading, with a separate binary setpoint voltage in the read-only memory for each inverter switch is stored and with each activation by the counter reading the corresponding The value of all nominal voltages is read out, that the second function generator a high-frequency triangle generator with a given constant frequency is that the modulation stage from a characteristic generator (52) that corresponds to the input speed setpoint an amplitude control voltage generated, and one of the amplitude control voltage exists as a threshold value and a threshold value detector acted upon by the triangular voltage, and that the logic circuit (54) for each nominal voltage to form the pulse-width-modulated Control voltage of the inverter switch concerned is an EXCLUSIVE-OR gate which contains the setpoint voltage and the pulse-width-modulated voltage tapped at the threshold value detector Pulses are supplied.