EP2940309A1 - Method for regulating a pump system and regulated pump system - Google Patents

Abstract

The invention relates to a method for controlling a pump system (1), which has at least two hydraulically operated parallel centrifugal pumps (2, 3) which are each driven by speed-controlled, electromotive drive units (7, 8). In this case, the determined electrical power consumption (P1) of one of the centrifugal pumps (2) is compared with the determined power consumption (P2) of another centrifugal pump (3), and depending on the result of this power comparison, the rotational speed (n_soll1, n_soll2) of at least one of these centrifugal pumps (2 , 3) adapted such that the electrical power consumptions (P1, P2) of the centrifugal pumps (2, 3) reach a predetermined ratio, in particular be aligned.

Description

The present invention relates to a method for controlling a pump system, which has at least two hydraulically operated parallel centrifugal pumps, which are each driven by speed-controlled, electromotive drive units. Furthermore, the invention relates to a pump system for the application of the method.

Pump systems with two or more hydraulically operated parallel centrifugal pumps are known. Due to the parallel operation they promote into a common pressure line. Each of these pumps usually consists of a pump unit, an electric motor driving this, which is usually preceded by a frequency converter, and a control electronics, which typically controls the speed of the centrifugal pump according to a designated control curve. There are also known as double pumps, in which two centrifugal pumps are arranged in a single pump housing, as in the European patent application EP 0 735 273 A1 is described

The German patent application DE 3918246 A1 discloses a pump system with multiple pumps in which a second or further pump is switched on and off depending on the power of a first pump. An actual control, ie a change of control dynamically during operation, does not take place here. The second or further pump has a fixed capacity and is only on or off as needed. The pump system does not consist of a double pump with common housing but independent pump units.

In the German patent application DE 102010055841 A1 The performance of two pumps are compared with each other, which are housed in a common double pump housing. The performance comparison is used here only to determine whether the single mode or synchronous operation at low speed both pumps for the double pump unit is energetically cheaper.

In the case of pump systems with several pumps whose flow rates add on the outlet side, it can be seen that even with structurally identical drives, identical impellers and synchronous, ie identical speed and direction of rotation, there are differences in the delivery rate of the pumps. This is due to the principle, since in the pumps, if they are to be connected to the same side and operated with the same direction of rotation, an adjustment of the wiring within the pump housing to the common rail is required. The Druckstutzenkanäle in the pump housings then have a different course and a different arrangement, as for example, based on the double pumps in the Figures 1 and 2 is apparent. As a result, the two centrifugal pumps of a double pump differ in their hydraulic properties, which results in differences in the delivery rates of the pumps despite the same speed and design. Promotes the one pump more than the other, also acts a kind Mittkopplungseffekt, because the capacity of the other pump on the common pressure side is affected by the additional power of a pump. This causes the delivery of the other pump is additionally reduced. The flow of the other pump is - plastically speaking - pushed away from the flow of a pump.

This phenomenon is particularly pronounced when the centrifugal pumps promote the pressure side via an uncontrolled valve in the pressure line, which has a valve flap. In the ideal case, the same flow rates, this flap assumes an approximately central position relative to the flow cross sections at the respective pump outlet, so that the same effective flow cross sections are present at the outlets of the two pumps. The case of slightly unequal flow rates means that the flap appears to be fully open for one pump, ie only forms a small hydraulic resistance. For the other pump, however, the off-center valve flap forms a partially closed valve. ie a high hydraulic resistance, against which it promotes. This resistance causes said further reduction of the capacity of this pump.

Ultimately, this other pump unnecessarily consumes energy in supposed synchronous operation, because it promotes against the partially closed valve flap.

The European patent application EP 1614903 A1 Although calls this problem of hydraulic asymmetry in double pumps, it teaches to remedy, however, only the use of a permanently adapted to the corresponding hydraulic control, without executing how to make this adjustment. There is no active, automatic adjustment during operation. Only different parameters for the regulation of the hydraulics are programmed at the factory or during the installation.

Also the international publication WO 2009/079447 A1 addresses the problem of different hydraulic properties of centrifugal pumps in a double and multi-pump system. It solves it by balancing the torque between the pumps to get equal flow rates. The tables of said publication can be seen, however, that are set at the achieved control target identical torques, different speeds in the centrifugal pumps. Furthermore, then the recorded electrical power of the centrifugal pumps are different.

It is an object of the present invention to provide an alternative method for controlling a pump system with at least two hydraulically coupled centrifugal pumps, which instead of a pure speed synchronous operation sets a predetermined ratio of the performance of the centrifugal pumps, in particular a substantially equal flow rate, so that the pump system energy efficient to operate. Furthermore, it is an object to provide a corresponding pump system for carrying out the method.

This object is achieved by the method according to claim 1 and the pump system according to claim 13. Advantageous developments are specified in the subclaims.

According to the invention, a method for controlling a pump system is proposed, which has at least two hydraulically operated parallel centrifugal pumps, which are each driven by speed-controlled, electromotive drive units, in which the determined electrical power consumption of one of the centrifugal pumps is compared with the determined power consumption of another centrifugal pump, and in Depending on the result of this performance comparison, the speed of at least one of these centrifugal pumps is adjusted such that the electrical power consumption of the centrifugal pumps reach a predetermined ratio.

The core idea of the present invention is to adapt the centrifugal pumps, starting from a speed-synchronous operation, in which the delivery capacity of one of the centrifugal pumps is impaired due to the delivery rate of the other pump, so that the impairment of a centrifugal pump is reduced. This can be done in different ways.

Ideally, the speed of at least one of the centrifugal pumps can be adjusted so that the electrical power consumption of the centrifugal pumps are equalized. This means that the regulation takes place so that the power consumption reaches a predetermined ratio of 1. It should be noted at this point that as a "ratio" within the meaning of the invention can not only be a geometric relationship that describes the quotients of power consumption, but also an arithmetic ratio that describes the difference in power consumption. Thus, an equalization of the electric power consumption of the centrifugal pumps to each other means that is controlled to a distance of the power consumption to each other by zero.

Matching the electrical power inputs to each other means that they receive substantially, at least on average, the same electrical power. This causes the two centrifugal pumps regardless of their different Hydraulic properties or the wiring to the common pressure line have substantially the same flow. This ensures that none of these centrifugal pumps has more hydraulic losses than the other centrifugal pump in operation of both considered centrifugal pumps. In the case of a valve flap at the outlet of the centrifugal pumps, a middle position of this valve cap is achieved. Overall, this improves the efficiency of the pump system.

It has been found, however, that in order to improve the efficiency, it is not absolutely necessary in every application to regulate the centrifugal pumps to a power ratio of 1 (i.e., symmetrical power consumption). Also, a power ratio in which the power inputs have a small distance to each other, for example, differ by 1% to 10% or between 1 W and 20W, may be sufficient to reduce the hydraulic impairment of a centrifugal pump by the other centrifugal pump. The ratio between the power consumption can thus for example be between 0.85 and 1.

The ratio can basically be fixed. However, it is advantageous to select the ratio operating point-dependent, so that the ratio is defined, for example, as a function of the volume flow delivered by the pump system or the differential pressure. In this case, the ratio can become smaller with increasing volume flow, i. be smaller at low flow rates than at larger flow rates, because the hydraulic differences of the centrifugal pumps at low flow rates make more noticeable than at high flow rates.

In the case of a valve flap at the output of the centrifugal pumps, although no center position of this valve cap is achieved by the regulation to a power difference. However, this creates an open position of the valve flap, thereby improving the overall efficiency of the pump system.

In one embodiment variant of the pump system, the centrifugal pumps convey into a common pressure line, with which they are connected via an uncontrolled valve, which at least has an adjusting means are connected to each other. The adjusting means may be a valve flap or a ball valve. The position of the actuating means is dependent on the delivery pressure or flow of both centrifugal pumps. This means that the flow rate of a centrifugal pump determines or at least co-determines the degree of opening of the valve for the other centrifugal pump. In particular, in this type of pump systems, as they are for example in the case of a double pump, the proposed method allows a balancing of the flow rates and balancing the power consumption, provided that is regulated to a ratio of 1.

The regulation according to the invention takes place dynamically during operation of the pump system. The method can be downstream of a characteristic control of the pump system, which ideally outputs a synchronous speed setpoint for all centrifugal pumps, control technology. As a result, the method can be used universally in any pump system with two or more centrifugal pumps.

The two centrifugal pumps can be housed in a common pump housing. This means that their wheels rotate in each case in a pump chamber, which structurally share a single housing. If a valve of the type described above is present, this can then be part of the pump housing or be arranged in this. However, it is also possible that the two centrifugal pumps have their own pump housing, which are mounted in parallel. Their outlets can open directly into the pressure line or can be combined via the valve to the common pressure line. The valve can therefore also be present outside of the pump housing.

The two drive units can be structurally identical. This means that they do not differ significantly in their electro-mechanical properties, in particular with regard to rotational speed and torque with identical current supply. However, it is also possible and conceivable for individual applications that different drive units, in particular different power and / or size, are used for the pump system. Thus, in a double pump unit, for example, one of the two drive units can be more powerful than the other drive unit. Also the centrifugal pumps need not necessarily identical. Rather, they can have different wheels.

Especially in such an application, it is necessary not to regulate a symmetrical power consumption, but to set a power ratio in the unequal drive units and / or wheels, which takes into account the inequality. Thus, with a corresponding ratio of the power consumption of the centrifugal pumps can still be achieved that they achieve at least on average substantially the same flow rates. This also improves the hydraulic efficiency of the overall system. The ratio can be significantly smaller for such a case, depending on the difference of the drive units or centrifugal pumps, as in identical drive units or centrifugal pumps, for example, between 0.5 and 0.85 are.

According to an advantageous embodiment of the method according to the invention, the centrifugal pumps can be speed-controlled with a characteristic control, which outputs a synchronous speed setpoint for all centrifugal pumps. This makes it possible to adapt the operating point of the pump system to the current operating state of the hydraulic system supplied by the pump system. Preferably, then a subsequent adjustment of the speed setpoint for at least one of the centrifugal pumps depending on the result of the power comparison.

If a ratio of 1 is regulated, the rotational speed is suitably adjusted only when the power difference between the drive units exceeds a predetermined limit value. This has the advantage that small fluctuations in the power consumption of a centrifugal pump, which can be further enhanced by the subtraction, are disregarded for the regulation according to the invention. By using a limit value, a hysteresis is formed, which suppresses constant regulation with small power differences. The limit may be between 1% and 10%, for example 2% of the maximum power of the drive units. According to a further development, different limit values can be used for positive and negative power differences. This means that in case of a positive power difference between the one and the other centrifugal pump unit, a first threshold and in the case of a negative power difference between the one and the other centrifugal pump unit, a second threshold can be used. If these limit values are the same, a symmetrical hysteresis window results, with unbalanced limit values an asymmetrical hysteresis window. For example, both limits can be between 1% and 10%, preferably about 2% of the maximum power of the drive units.

The regulation of the pump system can be effected such that the rotational speed of one drive unit is reduced relative to the rotational speed of the other drive unit and / or the rotational speed of the other drive unit is increased relative to the rotational speed of the one drive unit if the power consumed by the one drive unit is higher, in particular higher the first limit is higher than the power absorbed by the other drive unit.

Alternatively or additionally, the rotational speed of one drive unit can be increased relative to the rotational speed of the other drive unit and / or the rotational speed of the other drive unit can be reduced relative to the rotational speed of the one drive unit if the power consumed by one drive unit is lower, in particular by the second limit value , as the absorbed power of the other drive unit.

The speed adjustment can thus be done in three different ways. It can be done either only with one centrifugal pump, only with the other centrifugal pump or with both centrifugal pumps simultaneously, in the latter case, the adjustment takes place in the opposite direction.

Furthermore, it can be provided that the adaptation of the rotational speed takes place only up to a maximum value. This maximum value can be specified relative or absolute. Thus, the adjustment of the speed in the case of a relative indication, for example, by a maximum of 2% to 6% of the rated speed of the centrifugal pumps. 2% means that for centrifugal pumps with a rated speed of approx. 3000 rpm, the speed is adjusted between 60 rpm and 180 rpm. The speeds The two centrifugal pumps then differ a maximum between 60U / min and 180U / min. Alternatively, the maximum speed difference can also be specified in absolute speed values. For example, the speed adjustment can be a maximum of 40rpm to 60rpm.

Said adaptation of the speed of at least one of the centrifugal pumps is here understood to refer to the original speed reference, i. to the synchronous speed which the centrifugal pump is preset by the speed controller. In one embodiment of the method according to the invention, in which the rotational speed of both centrifugal pumps is adjusted in opposite directions, this means that the maximum value for each centrifugal pump is based on this synchronous nominal rotational speed, so that the rotational speed difference of the centrifugal pumps corresponds to two times the maximum value.

The change of the speed can be done in discrete steps or continuously. Discrete steps have the advantage that the method can be carried out iteratively and checked after each step, whether the speed change reaches the desired goal. Thus, the power comparison and the adjustment of the speed depending on the result of this power comparison can be repeated after each speed change.

The step size of the steps may, for example, be between 1 rpm and 10 rpm. This comparatively small increment ensures that the method moves slowly in the direction of symmetrical power consumption and does not affect the higher-level speed control, in particular their stability is not affected.

The step size can be fixed so that the same step size is used in every operating state. Alternatively, the step size may be variable in particular depending on the amount of the difference of the recorded services. This has the advantage that the respective operating state of the pump system can be taken into account. The higher the power difference, the higher the step size can be. With a power difference of up to 2W, for example, a step size of 1 rpm, with power differences of 2W to 5W, a step size of 2U / min and with power differences between 5W and 10W a step size of 5U / min can be used. This causes the power balancing to be faster.

The method described is repeated over and over again in order to be able to determine dynamically in operation whether a speed change is required, in which direction it should be undertaken and whether a previous speed change had the correct effect. It is particularly advantageous if the power comparison and the adaptation of the rotational speed are repeated as a function of the result of this power comparison only after a waiting time has elapsed. This waiting time can be, for example, between 0.1s and 20s. The waiting time causes the method according to the invention to be carried out at low frequencies, so that it does not affect the higher-level speed control.

• Mittel zur Ermittlung der elektrischen Leistungsaufnahme einer der Kreiselpumpe,
• Mittel zur Ermittlung der elektrischen Leistungsaufnahme einer anderen Kreiselpumpe,
• eine Auswerteeinheit, die eingerichtet ist, die ermittelten Leistungsaufnahmen miteinander zu vergleichen, und
• eine Pumpensteuerung, die dazu eingerichtet ist, in Abhängigkeit des Ergebnisses dieses Leistungsvergleichs die Drehzahl zumindest einer der Kreiselpumpen derart anzupassen, dass die elektrischen Leistungsaufnahmen ein vorbestimmtes Verhältnis erreichen, insbesondere einander angeglichen werden.

The invention further relates to a pump system comprising at least two hydraulically operated parallel centrifugal pumps, which are each driven by variable speed electromotive drive units, and further comprising

• Means for determining the electrical power consumption of one of the centrifugal pumps,
• Means for determining the electrical power consumption of another centrifugal pump,
• an evaluation unit which is set up to compare the determined power consumption with one another, and
• a pump control, which is adapted to adjust the speed of at least one of the centrifugal pumps depending on the result of this power comparison such that the electrical power consumption reaches a predetermined ratio, in particular, be aligned with each other.

Preferably, the pump system is a double pump, in which the two centrifugal pumps are arranged in a common pump housing. Furthermore, the pump system can be set up to carry out the method according to the invention.

Figur 1

eine erste Ausführungsvariante einer Doppelpumpe im Querschnitt

Figur 2

eine zweite Ausführungsvariante einer Doppelpumpe im Querschnitt

Figur 3

Leistungskurven der Doppelpumpe gemäß Figur 1 ohne Leistungssymmetrierung

Figur 4

Drehzahlkurven der Doppelpumpe gemäß Figur 1 ohne Leistungssymmetrierung

Figur 5

Blockschaltbild der Struktur der erfindungsgemäßen Regelung

Figur 6

Ablaufdiagramm des erfindungsgemäßen Verfahrens

Figur 7

Leistungskurven der Doppelpumpe gemäß Figur 1 mit Leistungssymmetrierung

Figur 8

Drehzahlkurven der Doppelpumpe gemäß Figur 1 mit Leistungssymmetrierung

Further features and advantages of the method and the pump system according to the invention are explained in more detail below with reference to embodiments and the accompanying drawings. Show it:

FIG. 1

a first embodiment of a double pump in cross section

FIG. 2

a second embodiment of a double pump in cross section

FIG. 3

Performance curves of the double pump according to FIG. 1 without power balancing

FIG. 4

Speed curves of the double pump according to FIG. 1 without power balancing

FIG. 5

Block diagram of the structure of the control according to the invention

FIG. 6

Flowchart of the method according to the invention

FIG. 7

Performance curves of the double pump according to FIG. 1 with power balancing

FIG. 8

Speed curves of the double pump according to FIG. 1 with power balancing

FIG. 1 shows a pump system 1 with two hydraulically operated in parallel centrifugal pumps 2, 3, each by a drive unit 7, 8 (not shown) (see FIG. 3 ) are driven. These drive units 7, 8 are speed-controlled electric motor drives, which are structurally identical. They are also driven in rotation in the same direction. The two centrifugal pumps 2, 3 are housed in a common pump housing 4. This means that the respective impellers of the centrifugal pumps 2, 3, which are also structurally the same, each lie in a pump housing, but these two pump housings are integrally formed. It follows that the outlet channels of the two centrifugal pumps 2, 3 are arranged differently and shaped to be able to promote in a common pressure line 6 in the same direction of rotation of the drive units 7, 8 can. The pump system according to FIG. 1 is commonly referred to as a double pump or twin pump.

In the transition of the pump outlets of the two centrifugal pumps 2, 3 is an uncontrolled valve 9 in the common pump housing 4, which has two valve flaps 5a, 5b. Each of these valve flaps can each close an outlet of one of the two centrifugal pumps 2, 3. The valve 9 avoids that one of the centrifugal pumps 2, 3 promotes into the outlet channel and the pump chamber of the other centrifugal pump when this other centrifugal pump is switched off and only one centrifugal pump is operated. This would create a hydraulic short circuit. In the common ideal operation of both centrifugal pumps, the two valve flaps 5 a, 5 b are held in a central position in which they rest against each other back to back. The delivery flow of the respective centrifugal pump 2, 3 is then conveyed past the respective valve flap 5a, 5b, the same effective flow cross section being established.

However, small flow rate differences of the two centrifugal pumps 2, 3 lead to an off-center position of the two valve flaps 5a, 5b. Such asymmetries in the flow rates arise in principle due to the different arrangement and shape of the outlet channels of the centrifugal pumps 2, 3, even if the drive units 7, 8 are operated at the same speed and the wheels are identical. The eccentric position of the valve flap 5a, 5b has the consequence that the centrifugal pump 2, 3 with a lower flow rate sees a higher hydraulic resistance at the output. In addition to the design-related asymmetry in the flow rate, this is consequently enhanced during operation. The hydraulic asymmetry is also noticeable in an asymmetrical electrical power consumption, wherein the centrifugal pump 2, 3, which promotes against a partially closed valve 9, wastes power.

FIG. 2 shows an alternative variant of a double pump 1 in cross section, which is constructed substantially identical in construction to the first variant. There are only the formation of the pump housing of the respective centrifugal pumps 2, 3 and the design of the valve 9 of those in FIG. 1 , The valve 9 is formed by a single pivotable flap 5. This flap 5 has two end stops, wherein it closes the outlet of a centrifugal pump 2, when it occupies the first end stop, and closes the outlet of the other centrifugal pump 3 when it assumes the second end stop. The position of the valve flap 5 is dependent on the delivery pressure of both centrifugal pumps 2, 3.

The double pump 1 according to FIG. 2 shows the same problem of asymmetry in the flow rates and an electrical Leistungsunsymmetrie as the double pump according to FIG. 1 although the drive units and the impellers are identical and operating at synchronous speed.

FIG. 3 illustrates the course of the electrical power consumption P1, P2 of the two centrifugal pumps 2, 3 FIG. 1 or their drive units 7, 8 in the speed-synchronous operation at 3400 U / min in each case above the total delivery rate Q of the double pump 1. The total delivery rate Q was measured here.

In the lower flow range, in particular up to about 11 m ³ / h, only the electrical power consumption P1 of the first centrifugal pump 2 increases. This is done linearly. The power consumption P2 of the second centrifugal pump 3, however, remains constant in this lower flow range. This means that the second centrifugal pump 3 promotes against a closed or at least substantially closed valve flap 5b.

The linear increase in the power consumption P1 of the first centrifugal pump 2 ends when a maximum power consumption is reached, which is approximately 1.24 kW here. Only in this operating state, the valve flap 5b opens increasingly, which can be seen by the now present linear increase in the electrical power consumption P2 of the second centrifugal pump 3. However, the power consumption P2 of the second centrifugal pump 3 initially does not rise to the value of the first centrifugal pump. Rather, a power slump is recorded, after which the power consumption P2 increases again with increasing flow rate Q. This brings the knowledge that even in the range of average flow rates, in particular in the range between 20 m ³ / h to 40 m ³ / h, the valve 9 assumes a position in which the total volume flow Q is not symmetrical, ie not half each, by the Partial volume flows of the two centrifugal pumps 2, 3 is formed. The first centrifugal pump 2 carries more to the total flow Q of the double pump. 1 At the same rotational speed n_set of the two centrifugal pumps 2, 3, this means that the second centrifugal pump 3 operates in the middle volume flow range against a partially closed valve flap 5b, whereby hydraulic losses occur.

In FIG. 4 the course of the speeds n_1, n_2 of the two centrifugal pumps 2, 3 of the double pump 1 is shown in each case over the total delivery rate Q of the double pump 1 for a target speed of 3400 U / min, but here in the pump control of the double pump 1, a power limitation acts, the Speed down regulates. It can be seen that the setpoint speed in the region of low delivery flow is maintained by both centrifugal pumps 2, 3. From about 17 m ³ / h, the power is limited and the synchronous speed n_soll down regulated. Nonetheless, the speeds n_1, n2_ of the centrifugal pumps 2, 3 are substantially the same.

A block diagram of the regulation of the pump system 1 according to the invention is shown in FIG FIG. 5 displayed. The block diagram schematically shows the two hydraulically operated parallel centrifugal pumps 2, 3, which promote via the valve 9 in the common pressure line 6. Further, the electric motor drive units 7, 8 of the two centrifugal pumps 2, 3, are shown, which are each fed by a separate frequency converter 14, 15. The frequency converters 14, 15 include a power electronic part (hardware) and a control part (software) that controls the power electronic part.

The frequency converter 14, 15 act on the drive units 7, 8 (electric motors M1 and M2) with a voltage U of a certain frequency f. This voltage U and frequency f are dependent on a speed setpoint input n_soll1, n_soll2, which receives each of the two frequency converters 14, 15. The electrical power P1, P2 received by the respective drive unit 7, 8 is detected in the frequency converter 14, 15 by suitable means 16, 17, for example by measurement using appropriate sensors. The determined actual values of the power consumptions P1, P2 are made available to the control.

In addition, the actual rotational speeds n_act1, n_act2 of the two centrifugal pumps 2, 3 are determined from electrical converter variables. In principle, this determination can also be carried out by measurement on the respective drive unit 7, 8. However, this requires sensors that lead to additional cost and installation costs. It is therefore advantageous to determine the actual speeds sensorless. This can be done in a known manner due to an electrical and electromechanical model of frequency converter and drive motor, which also takes into account in particular the centrifugal pump, such a model in each case in the control units (software) of the frequency converter 14, 15 are implemented to control them anyway.

The control consists of a conventional speed control by means of hydraulic controller 10, which outputs a synchronous speed n_soll for both centrifugal pumps 2, 3. The hydraulic controller 10 can regulate in a known manner according to a predefinable characteristic control, for example a Δp-constant or Δp-variable control. However, other types of rules can also be used. The Regelart can be specified to the hydraulic controller 10. Also, other external requirements that affect the speed control, such as the specification of a minimum and a maximum speed. The hydraulic controller 10, the power consumption P1, P2 and the determined actual speeds n_ist1, n_ist2 are supplied.

The synchronous rotational speed n_soll output by the hydraulic controller 10 is supplied to a power balancing 12 downstream of this control technology, which constitutes the core of the control according to the invention. The power balancing 12 adapts the synchronous speed n_soll individually for the respective centrifugal pump 2, 3 with the aim of achieving the same power consumption P1, P2. For this purpose, it determines in dependence on the result of a performance comparison of the current power consumption P1, P2 with each other a target speed n_soll1 for the one centrifugal pump 2 and a target speed n_soll2 for the other centrifugal pump 3. These individual target speeds n_soll1, n_soll2 then the inverters 14, 15, more precisely said their control units supplied, which then control the respective frequency converter 14, 15 accordingly.

It should be noted that the inverter control units, the hydraulic controller 10 and the power balancer 12 each in their own hardware or in a shared hardware, for example comprising a dedicated or common microprocessor, application-specific integrated circuit (DSIC) and DSP (digital signal processor) and own or shared memory (ROM, RAM, EEPROM) can be realized. The sharing of these components means that the software implementing the speed control 10, the power balancing 12 and the inverter control units each have their own processes, but run on the same hardware using the same resources.

FIG. 6 shows an exemplary sequence of the method according to the invention. It illustrates in a flowchart an exemplary course of power balancing. In this method example, it is provided that the two centrifugal pumps 2, 3 are always adjusted in opposite directions in their rotational speed n_soll1, n_soll2. In addition, in this example, a hysteresis is considered, and the process is repeated again and again at intervals of 3 seconds. This waiting time is realized by polling a timer.

Prior to the actual procedure, the parameters necessary for the method are initialized, see step 20. The initialization can be carried out during the commissioning of the pump system and / or during operation, for example by making a reset, i. a reset of the pump settings to the factory settings.

Initialization 20 involves zeroing a variable n_offset. This variable describes the distance, ie the difference of the individual centrifugal pump rotational speeds n_soll1, n_soll2 to the synchronous nominal rotational speed n_soll, which is specified by the hydraulic controller 10. In addition, a hysteresis descriptive parameter value P_hyst is defined. This is exemplified here as 2% of the maximum power. However, it can also be different, for example between 1% and 5%. Furthermore, it can alternatively be expressed as an absolute value or as relative value relative to a different reference size than the maximum power defined. Furthermore, the initialization of further parameters and variables can take place in step 20, for example a parameter n_limit, which defines a maximum adaptation of the nominal rotational speed n_setpoint and / or absolute rotational speed limit values n_min, n_max for the centrifugal pumps 2, 3.

The hydraulic controller 10 initially determined according to external specifications and the set control mode, the target speed n_soll, with the two centrifugal pumps 2, 3 of the double pump 1 should be operated to achieve a certain operating point of the double pump 1. The determination of the speed setpoint n_setpoint from the hydraulic controller 10 is in step 22 in FIG FIG. 6 shown. However, unlike in the prior art, this setpoint speed n_setpoint is not supplied directly to the converters 14, 15 of the two centrifugal pumps 2, 3. Rather, in the hydraulic balancer 10 downstream power balancing 12, an individualization of this synchronous setpoint speed n_soll for the individual centrifugal pumps 2, 3 such that their power consumption, P1, P2 is approximately equal, provided that certain conditions are met.

Starting from the synchronous speed setpoint, the core of the method according to the invention begins with checking whether the timer has expired, step 24. The timer ensures that the method is repeated at intervals. The distance can be set and, as mentioned above, for example 3 seconds. Although the expiration check of the timer in the example according to FIG. 6 is performed at the beginning of power balancing, so the timer expiration can also be done elsewhere, for example, before or after step 30.

In the power balancing, a power comparison of the two power inputs P1 and P2 of the centrifugal pumps 2, 3 is performed. Due to the use of the hysteresis P_hyst, this must be done in two partial comparisons, since in the case of a positive power difference, which is greater than the positive hysteresis value P_hyst, in the case of a negative power difference, this must be less than the negative hysteresis value P_hyst. It should be noted at this point that in the example according to FIG. 6 a single hysteresis parameter P_hyst, ie the same Hysteresis value is used for both positive and negative differences, so that a symmetrical hysteresis is realized. However, it is also possible to realize an asymmetrical hysteresis by using a different hysteresis value for positive power differences than for negative power differences.

The first performance part comparison is performed in step 26. Here it is checked whether the power consumption P1 of the first centrifugal pump 2 is greater than the power consumption P2 of the second centrifugal pump 3 plus the hysteresis P_hyst. In addition, the further condition is checked in step 26 whether the speed adaptation n_offset has (already) reached a predetermined maximum value n_limit. Because only if this limit value n_limit has not yet been reached, an adaptation or further adaptation of the synchronous speed setpoint n_setpoint should take place.

If the two conditions in step 26, i. the first partial comparison of the power comparison on the one hand and the limit check for the rotational adjustment on the other hand, an adjustment of the synchronous speed n_soll, in order to balance the power consumption P1, P2 of the two centrifugal pumps 2, 3. This adaptation takes place in the form of a speed set n_offset related to the synchronous speed n_setpoint. In view of the fact that the power consumption P1 of the first centrifugal pump 2 is greater than the power consumption P2 of the second centrifugal pump 3, in particular higher by at least the amount of the hysteresis value P_hyst, the synchronous rotational speed n_setpoint is adjusted. This takes place here in such a way that both pump-individual desired rotational speeds n_soll1, n_soll2 are changed in opposite directions, as a result of which the rotational speed n_soll1 of the first centrifugal pump 2 is reduced and the rotational speed n_soll2 of the second centrifugal pump 3 is increased, see steps 27 and 30.

Due to the too high power consumption P1 of the first centrifugal pump 2 - as determined in step 26 - the speed offset n_offset is lowered to the synchronous speed n_set by a step of the step size x in step 27. This step size x can be fixed, for example between 1 U / min and 10 U / min. However, there is also the possibility of the step size x depending on the amount of difference the power consumption P1, P2 of the two centrifugal pumps 2, 3, where it is higher, the higher this difference. For the sake of simplicity, a fixed value of 1 rpm is used here by way of example.

Since the speed offset n_offset was previously set to zero, it is now -1 rpm. The method then proceeds to step 30, in which the speed offset n_offset is added to the synchronous speed setpoint n_setpoint to obtain the speed setpoint n_soll1 of the first centrifugal pump 2 and subtracted from the synchronous speed setpoint n_setpoint to obtain the speed setpoint n_soll2 of the second centrifugal pump 3. Since the speed offset n_offset is negative at this exemplary location of the method, i. -1 rpm, the rotational speed target value n_soll1 of the first centrifugal pump 2 is thus lowered and the rotational speed target value n_soll2 of the second centrifugal pump 3 is consequently increased. As a result, the first centrifugal pump 2 receives less power P1 and the second centrifugal pump 3 receives more power P2, so that the two power consumptions P1, P2 are approximated to one another.

The method will continue after step 30, i. in the specification of a new current speed setpoint n_soll continued by the hydraulic controller 10, which may optionally be changed from the previous synchronous speed setpoint n_soll.

If this is not the case, the previously calculated speed offset n_offset is subtracted again from the hydraulic speed command value n_setpoint newly specified by the hydraulic controller 10 in step 30 in order to determine the speed setpoint value n_soll2 for the to obtain the second centrifugal pump 3, or added to obtain the rotational speed target value n_soll1 for the first centrifugal pump 2.

On the other hand, if the timer has expired, the first partial comparison for power balancing is performed again. If the power consumption P1 of the first centrifugal pump 2 is still greater than the power consumption P2 of the second centrifugal pump 3 plus the hysteresis value P_hyst, the rotational speed offset n_offset is lowered by a further step of the step width x, if the check of the second condition led to the result that the maximum speed offset n_limit has not yet been reached, ie the speed offset has not yet been lowered to the extent that it is less than the maximum speed offset n_limit with a negative sign.

The method then returns to step 30, in which the further reduced speed offset n_offset for the second centrifugal pump 2 is subtracted from the current synchronous setpoint speed n_setpoint and added to the first centrifugal pump 1.

The passage of the method according to this loop is repeated as long and as often as the power P1 of the first centrifugal pump 2 is higher than the power P2 of the second centrifugal pump 3 plus the hysteresis P_hyst and the speed offset n_offset the defined maximum value n_grenz not yet reached Has. This maximum value n_limit can be, for example, between 40 and 80 rpm, in particular 60 rpm.

If one of the two conditions checked in step 26 is not or no longer fulfilled, the second power unit comparison is performed in step 28. In this, it is checked whether the power consumption P1 of the first centrifugal pump 2 is smaller than the power consumption P2 of the second centrifugal pump 3 minus the hysteresis value P_hyst. If this condition and also the further condition is met, according to which the speed offset n_offset has not yet reached its maximum value n_limit, this time with a positive sign, then in step 29 the speed offset n_offset is increased by one step of the step width x. This step size x can also be between 1 rpm and 10 rpm. By way of example, 1 rpm is used here.

It should also be noted at this point that the step size x, by which the speed offset is lowered in step 27, does not necessarily have to be identical in height to the step size x by which the speed offset n_offset is increased in step 29. Rather, different step sizes for changing the speed offset n_offset can be selected.

The speed offset n_offset increased by the amount x is then added back to the synchronous speed setpoint n_setpoint in order to obtain the speed setpoint n_soll1 for the first centrifugal pump 2, and subtracted from the synchronous speed setpoint n_soll to the speed setpoint n_soll2 of the second centrifugal pump 3 receive. In this example, since the electric power consumption P1 of the first centrifugal pump 2 is smaller in comparison with the electric power consumption P2 of the second centrifugal pump 3 taking into account the hysteresis P_hyst, as determined in step 28, increasing the rotational speed offset n_offset in step 29 now becomes step 30 the rotational speed n_soll1 of the first centrifugal pump 2 is raised and the rotational speed n_soll2 of the second centrifugal pump 3 is lowered so as to approximate the two power consumptions P1, P2 to one another.

The method is then continued again in the specification of the current synchronous setpoint speed n_soll in step 22 by the hydraulic controller 10.

If the time span of three seconds has expired again, step 24, and the power consumption P2 of the second centrifugal pump 3 is still higher than the power consumption P1 of the first centrifugal pump 2 plus the hysteresis value P_hyst, the rotational speed offset n_offset is again increased by a step of the amount x, Step 29 if the maximum speed offset n_limit has not yet been reached. If this is not the case, in step 30 a further increase of the setpoint speed n_soll1 of the first centrifugal pump 2 and a further reduction of the setpoint speed n_soll2 of the second centrifugal pump 3 take place.

The method described here is repeatedly repeated during operation of the pump system 1 in order to achieve a dynamic power balancing of the centrifugal pumps 2, 3.

It should also be noted that the maximum speed offset n_limit in step 26 does not necessarily have to be identical to the maximum speed offset n_limit in step 28. Rather, different maximum speed offsets in said steps 26, 28 can be used.

The result of applying power balancing is shown in the diagrams of FIGS. 7 and 8th illustrated. FIG. 7 shows a representation of the power consumption P1 (Q), P2 (Q) of the first and second centrifugal pump 2, 3 respectively over the funded by the double pump 1 total flow Q. Although there are no exactly identical power consumption P1, P2, it is at least opposite the course in FIG. 3 a clear approximation of the performance curves to each other, especially on average, recognizable. Thus, in the lower flow range, the power consumption P1, P2 of both centrifugal pumps 1, 2 in the medium gradually increasing, the power consumption P1 of the first centrifugal pump 1 increases significantly flatter than it is in the absence of the power balancing 12 of the invention. As a result, it can be observed that the second centrifugal pump 3 no longer works against a closed or at least partially closed valve flap 5b, 5, so that less hydraulic losses occur and the efficiency of the double pump 1 is improved.

The fact that the power curves P1 (Q) and P2 (Q) fluctuate despite active power balancing shows the dynamic character of the power balancing according to the invention. Because in the hydraulic map, there may be areas where even the smallest speed changes, even if they are only 1 rev / min, can make the balance in the flow rate from one centrifugal pump to another. In this case, one of the centrifugal pumps temporarily, i. within the timer interval, significantly more power than the other centrifugal pump. Nevertheless, an approximation of the two power consumption and thus an improvement in efficiency in the pump system 1 is nevertheless achieved by the application of the power balancing according to the invention.

The fluctuations of the power consumption P1, P2 can be improved by reducing the timer waiting time, but not fully compensated. In addition, the waiting time realized with the timer should not become too small so as not to influence the superimposed fast speed control.

FIG. 8 shows analogously to FIG. 4 the setpoint speeds n_soll1, n_soll2 individually adapted as a function of the result of the two power unit comparisons The two centrifugal pumps 2, 3. It can be seen that the desired speeds n_soll1, n_soll2 are always offset by a speed offset n_offset to each other. Due to the symmetrical offset n_offset selected here with respect to the synchronous speed n_setpoint, this would be shown in the diagram of the FIG. 8 in the middle between the two speed curves for n_soll1 (Q) and n_soll2 (Q). The speed offset n_offset in the range of small flow rates Q, here exemplarily in the range smaller than 20m ³ / h, significantly smaller than in the range of medium and high flow rates Q. In addition, the speed offset n_offset increases with increasing flow rate Q, although he at high flow rates Q becomes smaller again in the direction of the maximum delivery flow.

As a result, it can be stated that precisely through the use of different desired speeds for the two centrifugal pumps 2, 3 of the double pump 1, a substantially symmetrical distribution of the flow to the centrifugal pumps 2, 3 is achieved, which results in the valve flap 5, 5a, 5b is predominantly in such a position, in which the effective flow cross sections in the outlet region of the respective centrifugal pump 2, 3 are approximately equal to the common pressure line 6 and remain approximately the same in time. As a result, the power consumption P1, P2 of the centrifugal pumps 2, 3 are matched to each other, the pump system 1 absorbs less power in total, so that the efficiency of the pump system 1 over conventional double pumps is improved according to the prior art.

Claims (15)

Method for controlling a pump system (1) which has at least two centrifugally operated pumps (2, 3) which are each driven by speed-controlled, electromotive drive units (7, 8), characterized in that the determined electrical power consumption (P1) of a the centrifugal pump (2) with the determined power consumption (P2) of another centrifugal pump (3) is compared, and that depending on the result of this power comparison, the speed (n_soll1, n_soll2) of at least one of these centrifugal pumps (2, 3) is adjusted such that the electrical power consumption (P1, P2) of the centrifugal pumps (2, 3) reach a predetermined ratio, in particular be aligned with each other. A method according to claim 1, characterized in that the centrifugal pumps (2, 3) convey into a common pressure line (6), with which they via an uncontrolled valve (9) having at least one adjusting means (5, 5a, 5b) with each other are connected, wherein the position of the actuating means (5, 5a, 5b) of the delivery pressure or flow of both centrifugal pumps (2, 3) is dependent. A method according to claim 1 or 2, characterized in that the centrifugal pumps (2, 3) with a characteristic control (10) are speed-controlled, which outputs a synchronous speed setpoint (n_soll) for all centrifugal pumps (2, 3), one of these characteristic regulation downstream adjustment This speed value (n_soll) is a function of the result of the power comparison. Method according to one of the preceding claims, characterized in that the adjustment of the rotational speed (n_soll) takes place only when the power difference between the drive units (7, 8) exceeds a predetermined limit value (P_hyst). Method according to one of the preceding claims, characterized in that the rotational speed (n_soll1) of a centrifugal pump (2) relative to the rotational speed (n_soll2) of the other centrifugal pump (3) is reduced and / or the rotational speed (n_soll2) of the other centrifugal pump (3) relative to the speed (n_soll1) of a centrifugal pump (2) is increased when the absorbed power (P1) of a centrifugal pump (2) higher, in particular by a first limit (P_hyst) is higher than the absorbed power (P2) of the other Centrifugal pump (3). Method according to one of the preceding claims, characterized in that the rotational speed (n_soll1) of a centrifugal pump (2) relative to the rotational speed (n_soll2) of the other centrifugal pump (3) is increased and / or the rotational speed (n_soll2) of the other centrifugal pump (3) relative to the speed (n_soll1) of a centrifugal pump (2) is reduced when the absorbed power (P1) of a centrifugal pump (2) is lower, in particular by a second threshold (P_hyst) is lower than the absorbed power (P2) of the other Centrifugal pump (3). Method according to one of the preceding claims, characterized in that the adaptation of the rotational speed (n_soll) to a maximum of ± 2% to ± 6% of the rated speed of the centrifugal pumps (2, 3), in particular by a maximum of 50U / min to 60U / min. Method according to one of the preceding claims, characterized in that the adaptation of the rotational speed (n_soll) takes place in discrete steps. A method according to claim 8, characterized in that the step size of the steps is between 1 U / min and 10 U / min. A method according to claim 8, characterized in that the step size of the steps is dependent on the amount of difference of the absorbed power (P1, P2). A method according to claim 10, characterized in that the higher the power difference, the higher the step size. Method according to one of the preceding claims, characterized in that the performance comparison is repeated again and again after a waiting time. Pump system (1) comprising at least two hydraulically operated parallel centrifugal pumps (2, 3) which are each driven by speed-controllable electromotive drive units (7, 8),
marked by - means (16) for determining the electrical power consumption (P1) of one of the centrifugal pump (2), - means (17) for determining the electrical power consumption (P2) of another centrifugal pump (3), an evaluation unit which is set up to compare the determined power consumptions (P1, P2) with one another, and - A pump controller (12), which is adapted to, depending on the result of this power comparison, the speed (n_soll1, n_soll2) of at least one of the centrifugal pumps (2, 3) to adjust such that the electrical power consumption (P1, P2) reach a predetermined ratio , in particular, be aligned with each other. Pump system (1) according to claim 13, characterized in that it is a double pump, in which the two centrifugal pumps (2. 3) are arranged in a common pump housing (4). Pump system (1) according to claim 13 or 14, characterized in that it is adapted to carry out the method according to one of claims 2 to 12.

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