Method for operating a circulation pump in a twin pump construction

Description

[0001] The invention relates to a method for operating a twin-configuration circulation pump.

[0002] A twin pump, or twin-type circulation pump, consists of at least two separate individual pumps, particularly centrifugal pumps, housed in a common casing. The discharge ports of the individual pumps converge at a common discharge port of the twin pump. This design offers two advantages: firstly, redundancy, where the redundant pump takes over if the running pump fails due to a defect (single-pump operation); and secondly, both pumps can be operated synchronously in dual-pump mode, which, under certain conditions, allows for more energy-efficient operation and increased flow rates from both individual pumps.

[0003] To prevent backflow through the non-running pump during single-pump operation, a diverter valve is installed at the point on the discharge port where the individual ports of the two pumps converge. During single-pump operation, this valve closes the discharge port of the deactivated pump due to pressure. During dual-pump operation, the diverter valve should ideally be positioned centrally so that the pumped medium from both pumps can flow as freely as possible into the common discharge port.

[0004] The function of the diverter valve is shown schematically in Figure 1 indicated, where the left illustration 1a shows a single-pump operation in which the pressure port of the stationary pump 2 is closed by means of the flap 3, and illustration 1b shows the two-pump operation with the switching flap 3 in the most exact possible center position.

[0005] Conventional control of the twin pump is achieved by the system controller; in the case of a heating circulation pump, by the heating system's control unit. This controls both pumps based on a target pressure (target head) to be achieved by the twin pump. To reach this target head, both pumps receive a common control signal in the form of the target speed of their drive units. The corresponding block diagram can be found in the Figure 2 remove.

[0006] Conventional control assumes that both individual pumps deliver the same output pressure at the same target speed, which then corresponds to the total head of the system. In reality, due to different flow paths dictated by the installation space, the two individual pumps deliver slightly different output pressures at the same target speed. Because both pumps rotate in the same direction, for example, only the flow of one pump can be ideally guided. The second pump then has a longer flow path, particularly with a higher curve component. Manufacturing tolerances can also exacerbate these differences. This deviation in head results in the diverter valve being subjected to different force vectors, causing it to pivot from its neutral position. Under certain circumstances, the valve position becomes unstable, similar to an inverted pendulum.Even the slightest deflections of the flap from its central position, which can be caused, for example, by turbulence balls, lead to the flap flipping to one side.

[0007] Without suitable countermeasures, one of the two pumps will always be hydraulically blocked in this case, and parallel pumping with both pumps will no longer be possible. Mechanical solutions are known from the prior art. One approach involves modifying the flap with a spoiler, which, through the resulting back pressure, is intended to stabilize the flap position. An alternative solution is based on a butterfly-type switching flap that includes a spring element between the two vanes.

[0008] However, these solutions require design modifications to the switching valve, which not only results in higher production costs but can also lead to disadvantages regarding wear and tear on the valve.

[0009] EP 2 940 309 A1 discloses a method for controlling a pump system with electrical power balancing. EP 0 735 273 A1 discloses a twin pump with higher-level control.

[0010] Therefore, a solution is being sought that can overcome the problems mentioned above.

[0011] This problem is solved by a method according to the features of claim 1. Advantageous embodiments of the method are the subject of the dependent claims.

[0012] According to the invention, a method for operating a twin-configuration circulating pump is proposed. The method is based on a circulating pump with at least two separate individual pumps whose discharge ports converge into a common discharge port. Although the invention explicitly refers to a twin-configuration, theoretically more than two individual pumps can operate together within the pump. For the sake of simplicity, the following will refer to a twin-configuration or two individual pumps. However, the embodiments of the invention also apply without limitation to a configuration with more than two individual pumps.

[0013] The individual pumps used can each be designed as centrifugal pumps and arranged within a common housing of the circulation pump. Each individual pump includes its own variable-speed drive unit, preferably in the form of an electric motor.

[0014] Furthermore, at least one pivotable changeover valve is provided in the pressure port, enabling switching between single- and multi-pump operation. In single-pump operation, the valve is pivoted from its central position, so that one pressure outlet port of a single pump is closed. In two-pump operation, the valve should ideally be in a central position in which the pressure ports of the individual pumps are open and the opening diameter of the pressure ports of both individual pumps is either not affected at all or at least affected equally by the valve.

[0015] Unlike the prior art, the present invention proposes generating individual control variables for the pump drives of the at least two individual pumps of the circulation pumps by means of a control system for the circulation pump and controlling them accordingly. The individual control variables are to be set in such a way that a diverter valve is stabilized in its neutral position during two-pump operation, according to the invention. In particular, the problematic deviation between the resulting delivery heads at identical rotational speeds of the individual pumps is to be reduced to zero by means of individual control of the individual drives, thereby effectively stabilizing the valve position.

[0016] One possibility, which is not part of the claimed invention, is to control the individual pumps in a so-called master-slave mode. In this case, an individual pump operating as a slave is regulated to the actual flow rate of an individual pump operating as a master. For example, a flow controller can be used for this purpose, to which the actual flow rate of the master pump is supplied as the setpoint and the current flow rate of the individual pump operating as a slave as the actual value. Based on these input values, the flow controller outputs a correction value for the setpoint speed of the pump operating as a slave. Consequently, the pump operating as a slave can be operated at a setpoint speed that differs from that of the master pump. This measure allows for the targeted compensation of design-related differences in the geometric structure of the individual pumps and ensures a sufficiently stable position of the diverter valve.

[0017] According to the invention, an alternative solution to the master-slave concept involves considering the twin pump as a multi-variable system with at least two inputs and outputs. In this example, the input variables are the respective rotational speeds of the individual pumps, while their controlled variables are the individual delivery heads and / or flow rates of the individual pumps. Here, too, the delivery head / flow rates of both individual pumps are controlled separately, thus generating suitable manipulated variables individually.

[0018] Due to the hydraulic coupling between the individual pumps, the set speed of one pump also affects the other. Mathematically, the control loop of the circulation pump can be described using so-called transfer elements and coupling elements, where a transfer element characterizes the influence of the manipulated variable on the associated individual pump, and a coupling element describes the influence of the manipulated variable on the other individual pump. Consequently, the hydraulic coupling can lead to interactions between at least two individual pumps, which can potentially cause oscillations of disturbance signals. Possible consequences include increased energy consumption, increased noise, increased wear, or even pressure surges within the piping system.

[0019] To avoid these interactions, the invention proposes a decoupling control system between the individual pumps. A so-called P-canonical structure is considered a suitable variant. By introducing decoupling blocks that behave inversely to the coupling blocks described above, the mutual influence of the individual pumps can be compensated. Ideally, the individual controlled variables can then be stabilized with independent single-variable controllers. Each individual pump of the circulation pump can be controlled by an independent single-variable controller, which receives the target head as the setpoint and the actual head of the corresponding individual pump as the controlled variable. Based on this, a suitable rotational speed is output.

[0020] In addition to the method according to the invention, the present invention also relates to a control unit, in particular a system controller for a heating system, for controlling at least one twin-configuration circulation pump according to the method according to the invention or an advantageous embodiment of the method. Accordingly, the control unit offers the same advantages and properties as those already discussed in detail above with reference to the method according to the invention. Therefore, a repetitive description is omitted.

[0021] The invention also relates to a circulation pump, in particular a heating circulation pump, in a twin design. The circulation pump is suitable for receiving individual control parameters via an external interface for controlling its at least two electric pump drives.

[0022] Finally, the present invention relates to a hydraulic system, in particular a heating system, with at least one control unit according to the invention.

[0023] Further advantages and features of the invention will be explained in more detail below with reference to the exemplary embodiments shown in the figures. The figures show: Figure 1: a sketch to illustrate the flap position in single and dual-pump operation; Figure 2: a block diagram of a conventional heating system in dual-pump operation; Figure 3: a block diagram of an embodiment not covered by the invention; and Figure 4: a block diagram of an embodiment of the invention.

[0024] As already described in detail in the introductory part of the description, the individual drives of conventional twin pumps are currently controlled with identical target speeds, which are determined by a suitable controller depending on the target delivery head (see Figure 2 ).

[0025] The solution according to the invention deviates from this practice and instead provides for individual control of the individual pumps, thereby enabling different control variables, i.e., target speeds, to be generated for each pump depending on the target delivery head of the circulation pump. This allows design-related differences in flow characteristics as well as any manufacturing tolerances between the individual pumps of a twin pump to be compensated for, so that ideally both can be operated with the same delivery head. This allows the diverter valve to be stabilized in its neutral position.

[0026] For the concrete implementation of the control of the individual pumps, two different approaches are available: firstly, control according to the master-slave principle, and secondly, control according to a multi-variable system.

[0027] First, we will discuss the first variant, which is not covered by the invention. Figure 3A corresponding block diagram is shown. The system controller 10 regulates the target delivery head for the entire system. In the example shown, pump 1 acts as the master, while pump 2 operates as the slave. The target speed generated by the system controller 10 is supplied to pump 1 (the master pump) as a control variable and simultaneously to pump 2 for its feedforward control. Pump 2 is additionally controlled to match the actual flow rate of pump 1. This is achieved using the flow rate controller 20, whose setpoint is the generated flow rate Q1 of pump 1 and whose actual value is the resulting flow rate Q2 of pump 2. The flow rate controller 20 outputs a speed correction value for pump 2 as a control variable, which adjusts its speed accordingly and may, if necessary, deviate from the speed of pump 1.

[0028] Controlling pump 1 ensures that the system's target delivery head is reached. Controlling pump 2 ensures identical flow rates at the outlets of pumps 1 and 2, thus keeping the diverter valve in the neutral position.

[0029] As an alternative to the master-slave arrangement according to Figure 3 The twin pump can be considered as a multi-variable system 30 with two inputs and two outputs. The input variables are the two rotational speeds n1 and n2. The controlled variables are the delivery heads H1 and H2. The block diagram is shown in Figure 4.

[0030] Due to the hydraulic coupling, the two rotational speeds n1 and n2 each influence not only the pump driven by the respective speed, but also the adjacent single pump of the twin system. The transmission elements G11 and G22 describe the influence of the respective rotational speeds n1 and n2 on their own pump. The coupling elements G12 and G21 describe the influence of rotational speed n1 on the delivery head H2 and n2 on H1 of the other pump, respectively. The mathematical description of the system is nonlinear.

[0031] To decouple the system, decoupling blocks R11, R21, R12, and R22 are introduced. These decoupling blocks behave inversely to the coupling blocks G12 and G21 of the controlled system 30. In this way, the cross-couplings are eliminated, and the multi-variable system 30 can be described as a system with two independent single variables, each of which can be stabilized independently with a single-variable controller 40a and 40b.

[0032] The advantage of this solution over the master-slave approach of Figure 3 The possibility of decoupling the two individual pumps 1 and 2 lies in the possibility of doing so. Coupling the two pumps 1 and 2 results in interactions that can lead to an amplification of disturbance signals. Possible consequences include increased energy consumption, increased noise levels, increased wear, or potentially pressure surges induced in the piping system. This amplification is addressed by the multivariable approach of the Figure 4 avoided.

Claims

1. Method for operating a circulating pump in a twin design, wherein the circulating pump comprises at least two separate individual pumps, the pressure nozzles of which converge to form a common outlet pressure nozzle, and at least one switchover flap arranged in the pressure nozzle for changing between single and multiple pump operation is provided, wherein a closed-loop control means for the circulating pump generates individual actuating variables for the pump drives of the at least two individual pumps, in order to stabilize the flap position in multiple pump operation, wherein the individual actuating variables are defined such that the flap position is stabilized in multiple pump operation, characterized in that the individual pumps are controlled by the individual closed-loop control means in twin operation to identical flow rates and / or delivery heads in order to stabilize the switchover flap in its central position, wherein the closed-loop control means controls the circulating pump as a multi-variable system with the respective pump speeds as actuating variables and their delivery heads or flow rates as control variables, and decoupling control takes place between the respective actuating and / or control variables.

2. Method according to Claim 1, characterized in that the decoupling control is based on a structure p-canonique.

3. Method according to Claim 1 or 2, characterized in that the individual control variables of the multi-variable system are stabilized by means of individual and mutually independent single-variable closed-loop controllers.

4. Closed-loop control unit, in particular system controller for a heater, for the closed-loop control of at least one circulating pump in twin design according to the method according to any one of the preceding claims.

5. Circulating pump, in particular heating circulating pump, in a twin design, wherein the circulating pump is suitable for receiving individual actuating variables via an external interface for actuating its at least two electric pump drives, with at least one closed-loop control unit according to Claim 4.

6. Hydraulic system, in particular heating, with at least one closed-loop control unit according to Claim 4 and / or a circulating pump according to Claim 5.

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