HYDRAULIC PUMP ARRANGEMENT

Abstract

Provided is a hydraulic pump arrangement including a plurality of motor-pump units connected to a common confluence, wherein each motor-pump unit of the hydraulic pump arrangement includes a pump realized provide pressurized fluid at its outlet; a motor arranged to drive the pump; a bypass valve configured to relieve pressure at the pump outlet; and wherein the hydraulic pump arrangement further includes a controller configured to receive a feedback signal from each motor-pump unit and to actuate the bypass valve of a motor-pump unit on the basis of the motor speed of that motor-pump unit. Further provided is a method of operating such a hydraulic pump arrangement, and a wind turbine including a number of such hydraulic pump arrangements.

Claims

1. A hydraulic pump arrangement comprising a plurality of motor-pump units connected to a common confluence, wherein each motor-pump unit of the hydraulic pump arrangement comprises: a pump configured to provide pressurized fluid at an outlet; a motor arranged to drive the pump; and a bypass valve configured to relieve pressure at the outlet; wherein the hydraulic pump arrangement further comprises a controller configured to receive a feedback signal from each motor-pump unit and to actuate the bypass valve of a motor-pump unit on a basis of a motor speed of the motor-pump unit.

2. The hydraulic pump arrangement according to claim 1, wherein the motor of the motor-pump unit comprises a variable-frequency drive.

3. The hydraulic pump arrangement according to claim 1, wherein a bypass valve is at least one of: a seat valve, a spool valve, and a controllable relief valve.

4. The hydraulic pump arrangement according to claim 1, wherein the pump of the motor-pump unit is as at least one: an internal gear pump, an external gear pump, and an axial piston pump.

5. The hydraulic pump arrangement according to claim 1, wherein the motor-pump unit comprises a speed sensor arranged to determine the motor speed and to provide a feedback signal to the controller.

6. The hydraulic pump arrangement according to claim 1, wherein the motor-pump unit comprises a pressure transducer arranged at the outlet and configured to provide a feedback signal to the controller.

7. The hydraulic pump arrangement according to claim 1, wherein the controller is configured to estimate a value of pressure and/or flow at the confluence from the feedback signals and to compare an estimated quantity with a reference quantity.

8. A method of operating a hydraulic pump arrangement according to claim 1, the method comprising a step of obtaining a reference quantity and determining a corresponding actual quantity at the confluence and, if the actual quantity is greater than the reference quantity, the method comprises the steps of: reducing a speed of the motor-pump unit to a minimum operating speed, opening the bypass valve of the motor-pump unit, stopping the motor-pump unit, and closing the bypass valve of the motor-pump unit; if the actual quantity is lower than the reference quantity, the method comprises the steps of: opening the bypass valve of an additional motor-pump unit, starting the motor-pump unit, increasing the speed of the motor-pump unit to reach a minimum operating speed, and subsequently closing the bypass valve of the motor-pump unit.

9. The method according to claim 8, comprising a step of decreasing the speed of a number of operational motor-pump units towards the minimum operating speed while the actual quantity is greater than the reference quantity.

10. The method according to claim 8, comprising a step of increasing the speed of a number of operational motor-pump units towards a maximum operating speed while the actual quantity is lower than the reference quantity.

11. The method according to claim 8, wherein the motor of the motor-pump unit comprises a variable-frequency drive configured to provide a speed feedback signal, and the method comprises a step of regulating the bypass valve of the motor-pump unit on a basis of the speed feedback signal.

12. The method according to claim 8, comprising a step of modelling the motor-pump unit to determine a relationship between motor speed and pump flow and/or to determine a relationship between motor torque and pump pressure and/or to determine a relationship between motor torque and pressure at the confluence.

13. A wind turbine comprising a number of hydraulic pump arrangements according to claim 1, configured to provide pressurized fluid to a hydraulic rotor blade pitching system and/or a hydraulic rotor brake system and/or a service crane system.

14. The wind turbine according to claim 13, wherein a wind turbine controller is configured to generate a reference quantity for each consumer and to forward the reference quantities to the corresponding hydraulic pump arrangements.

Description

BRIEF DESCRIPTION

[0026] Some of the embodiments will be described in detail, with reference to the following figures, wherein like designations denote like members, wherein:

[0027] FIG. 1 shows a schematic diagram of an embodiment of the hydraulic pump arrangement;

[0028] FIG. 2 shows a first flowchart to illustrate steps of a method;

[0029] FIG. 3 shows a second flowchart to illustrate steps of a method;

[0030] FIG. 4 is a schematic representation of a wind turbine with several embodiments of hydraulic pump arrangements; and

[0031] FIG. 5 shows a conventional hydraulic pump arrangement.

DETAILED DESCRIPTION

[0032] FIG. 1 shows a schematic diagram of an embodiment of the hydraulic pump arrangement 1. In this exemplary embodiment, the hydraulic pump arrangement 1 comprises n motor pump units MP1, . . . , MPn. Each motor pump unit MP1, . . . , MPn comprises a pump such as an internal gear pump or similar, and a motor such as a variable speed motor. The outlets of the motor pump units MP1, . . . , MPn converge at a common confluence 10. The outlet of each motor pump unit MP1, . . . , MPn is also connected to a return line 12 via a bypass valve V1, . . . , Vn. A consumer may be assumed to be connected between the confluence 10 and the return line 12, and these points of connection are indicated by the x symbols. The diagram also shows various other elements with which the skilled person will be familiar, such as a filter 13 in a return line 12, a supply line 15 to deliver the pressurized working fluid to the consumer, and a fluid reservoir or tank 14.

[0033] In this exemplary embodiment, a bypass valve V1, . . . , Vn is realised as a spool valve, but can equally be realised as a seat valve or a controlled pressure relief valve, as will be known to the skilled person. Each valve V1, . . . , Vn can be actuatedi.e. opened or closedin response to a signal C_V1, . . . , C_Vn from a controller 11.

[0034] The inventive hydraulic pump arrangement 1 measures or estimates the pressure and/or flow at the confluence 10, and compares the actual quantity Q.sub.10 with a reference quantity R. The reference quantity R can comprise a reference pressure and/or a reference flow, so that the actual quantity Q.sub.10 may be understood to comprise a value of pressure and/or a value of flow. The actual quantity Q.sub.10 at the confluence 10 can be measured directly using an appropriate sensor, for example. Alternatively, a known relationship may be used to estimate the momentary pressure and/or flow Q.sub.10 at the confluence 10. For example, the actual flow at the confluence 10 can be determined from a known relationship between pump flow and motor speed. Knowing the motor speed of each motor pump unit MP1, . . . , MPn as reported by feedback signals FB1, . . . , FBn, the combined flow at the confluence 10 can be determined to a relatively high degree of accuracy. The motor speed of a motor pump unit MP1, . . . , MPn can easily be obtained, for example as an rpm feedback signal FB1, . . . , FBn from a variable speed drive. Alternatively, the motor speed may be deduced from a pressure measured at each pump outlet and reported as a feedback signals FB1, . . . , FBn.

[0035] The controller 11 can compare the measured or estimated quantity Q.sub.10 with the reference quantity R for the consumer of that hydraulic pump arrangement 1. If the pressure/flow Q.sub.10 at the confluence 10 needs to be adjusted, the controller 11 can initially issue control signals C_MP1, . . . , C_MPn to one or more motors of the hydraulic pump arrangement 1 to increase or decrease motor speed as appropriate. In this drawing, it is assumed that motor pump units MP1, MP2 are running, and the measured or estimated pressure/flow Q.sub.10 at the confluence 10 is lower than the reference pressure/flow R. If the controller 11 establishes that the motors of those motor pump units MP1, MP2 are already running at maximum speed (using feedback signals FB1, FB2), the controller 11 opens the bypass valve V3 of an additional motor pump unit MP3, starts its motor and monitors its speed by means of its feedback signal FB3 until the speed of that additional motor pump unit MP3 has reached the minimum operating speed (at which the pump lubrication level is deemed to be satisfactory). At this point, the controller 11 issues a signal C_V3 to close the bypass valve V3 of the additional motor pump unit MP3. The speed of this motor pump unit MP3 can then be gradually increased (with an appropriate control signal C_MP3) while monitoring the pressure/flow Q.sub.10 at the confluence 10. If the actual quantity Q.sub.10 meets the target requirement R, the controller 11 will maintain this configuration of the hydraulic pump arrangement 1. Otherwise, the steps can be repeated to start a further motor pump unit.

[0036] In an alternative scenario, again using FIG. 1, it is assumed that motor pump units MP1, MP2, MP3 are running, and that at some point, the pressure/flow Q.sub.10 at the confluence 10 is higher than the reference pressure/flow R. To respond to the lower requirement R, the controller 11 lowers the speed of one or more motor pump units while monitoring the actual pressure/flow Q.sub.10. If the pressure/flow Q.sub.10 at the confluence 10 cannot be lowered sufficiently in this way, even if all active motor pump units MP1, MP2, MP3 are running at their lowest speeds (monitored by the feedback signals FB1, FB2, FB3), the controller 11 selects a motor pump unit to shut down, for example the second motor pump unit MP2. It issues a signal C_V2 to open the bypass valve V2 of that motor pump unit MP2, turns off the motor, and issues a signal C_V2 to close the bypass valve V2. If the actual pressure/flow Q.sub.10 at the confluence 10 can be reduced to meet the lowered reference R by these steps, the controller 11 will maintain this configuration. Otherwise, the steps can be repeated to shut down a further motor pump unit.

[0037] As explained with FIG. 1 above, a reference pressure/flow R can be provided for a consumer, and the hydraulic pump arrangement 1 that serves that consumer will regulate its motor-pump units MP1, . . . , MPn to the reference quantity R whenever this is changed. FIG. 2 shows a flowchart 20 to illustrate the steps of the inventive method when a reduced pressure is required at the confluence 10 of FIG. 1. In a first step 21, the actual quantity Q.sub.10 at the confluence 10 is compared to the reference quantity R. If the actual quantity Q.sub.10 is too high, the speed of one or more of the motor pump units MP1, . . . , MPn is reduced in step 21. In step 22, the speed of the slowest motor is compared to its minimum speed threshold. As long as there are one or more motor-pump units running above this minimum speed threshold, the speed of one or more of them can be reduced by repeating steps 21-23. If in step 23 it is seen that each motor-pump unit is running at its lowest possible speed, one of the motor pump units is selected to be switched off In step 24, the bypass valve of that motor pump unit is opened, the motor is stopped in step 25, and its bypass valve is closed again in step 26. The control flow returns to step 21, where the actual pressure/flow Q.sub.10 is again compared to the reference pressure/flow R. If necessary, the control loop 20 repeats until the target pressure/flow R is reached.

[0038] FIG. 3 shows a flowchart 30 to illustrate the steps of the inventive method when a higher reference pressure/flow R is required at the confluence 10. In a first step 31, the actual pressure/flow Q.sub.10 at the confluence is compared to the reference pressure/flow R. If the actual pressure/flow Q.sub.10 is too low, the motor speeds are checked in step 32 to see whether all are running at maximum speed. If not, the speed of one or more of the motor pump units is increased in step 33. If yes, the bypass valve of an additional motor pump unit is opened, and the additional motor pump unit is started in step 34. The speed of this pump is increased in step 35. In step 36, it is checked to see whether the additional motor pump unit has reached its minimum speed. If not, the control returns to step 35. If yes, the bypass valve of that motor pump unit is closed in step 37, and control returns to step 31. If necessary, the control loop 30 repeats until the target pressure/flow R is reached.

[0039] FIG. 4 is a schematic representation of a wind turbine 4 with a number of hydraulic systems H1, H2, H3in this case a hydraulic rotor blade pitching system H1, a hydraulic rotor brake system H2 and a hydraulic service crane system H3. Each hydraulic system H1, H2, H3 is the consumer of an embodiment of the inventive hydraulic pump arrangement 1, receiving pressurized fluid over a supply line 15 and returning fluid via a return line 12. Each hydraulic pump arrangement 1 comprises a suitable number of motor-pump units, depending on the requirements of its consumer. During operation of the wind turbine, the required hydraulic pressure of each consumer H1, H2, H3 will be subject to fluctuation, depending on what is happening at the consumer H1, H2, H3. To respond to these changing requirements, a control unitthe wind turbine controller 40 in this exemplary embodimentupdates the target or reference pressure/flow values of each consumer H1, H2, H3 and forwards the references Q1, Q2, Q3 to the controllers of the hydraulic pump arrangements 1.

[0040] FIG. 5 shows a conventional hydraulic pump arrangement 5. Here also, multiple motor-pump units 51 serve a consumer 58, and their outlets meet at a common confluence 50. A single bypass valve 52 or dump valve 52 is arranged on the far side of the confluence 50. As a result, whenever a motor-pump unit 51 must be shut down (to achieve a lower target pressure at the confluence 50) or switched on (to meet an increased target pressure at the confluence 50), a drop in pressure is seen by the consumer 58. This can lead to undesirable dynamics as explained above, for at least the duration needed to shut down or start up the motor-pump unit 51 and to restore pressure at the confluence 50.

[0041] Although the present invention has been disclosed in the form of preferred embodiments and variations thereon, it will be understood that numerous additional modifications and variations could be made thereto without departing from the scope of the invention.

[0042] For the sake of clarity, it is to be understood that the use of a or an throughout this application does not exclude a plurality, and comprising does not exclude other steps or elements.