WO2021091386A1 - Hydraulic system comprising active devices and method for controlling such a hydraulic system - Google Patents

Hydraulic system comprising active devices and method for controlling such a hydraulic system Download PDF

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Publication number
WO2021091386A1
WO2021091386A1 PCT/NL2020/050699 NL2020050699W WO2021091386A1 WO 2021091386 A1 WO2021091386 A1 WO 2021091386A1 NL 2020050699 W NL2020050699 W NL 2020050699W WO 2021091386 A1 WO2021091386 A1 WO 2021091386A1
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WO
WIPO (PCT)
Prior art keywords
fluid
hydraulic system
active device
pressure
active devices
Prior art date
Application number
PCT/NL2020/050699
Other languages
French (fr)
Inventor
Jan Henk Cnossen
Denis Alexandrovích BURAKOV
Martinus Johannes Gerardus HEIJLEN
Original Assignee
Flamco B.V.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Flamco B.V. filed Critical Flamco B.V.
Priority to EP20808533.2A priority Critical patent/EP4055327A1/en
Publication of WO2021091386A1 publication Critical patent/WO2021091386A1/en

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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24D—DOMESTIC- OR SPACE-HEATING SYSTEMS, e.g. CENTRAL HEATING SYSTEMS; DOMESTIC HOT-WATER SUPPLY SYSTEMS; ELEMENTS OR COMPONENTS THEREFOR
    • F24D3/00—Hot-water central heating systems
    • F24D3/10—Feed-line arrangements, e.g. providing for heat-accumulator tanks, expansion tanks ; Hydraulic components of a central heating system
    • F24D3/1008—Feed-line arrangements, e.g. providing for heat-accumulator tanks, expansion tanks ; Hydraulic components of a central heating system expansion tanks
    • F24D3/1025—Compressor controlled pressure heads
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24D—DOMESTIC- OR SPACE-HEATING SYSTEMS, e.g. CENTRAL HEATING SYSTEMS; DOMESTIC HOT-WATER SUPPLY SYSTEMS; ELEMENTS OR COMPONENTS THEREFOR
    • F24D19/00—Details
    • F24D19/10—Arrangement or mounting of control or safety devices
    • F24D19/1006—Arrangement or mounting of control or safety devices for water heating systems
    • F24D19/1009—Arrangement or mounting of control or safety devices for water heating systems for central heating
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B13/00—Transmission systems characterised by the medium used for transmission, not provided for in groups H04B3/00 - H04B11/00
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24D—DOMESTIC- OR SPACE-HEATING SYSTEMS, e.g. CENTRAL HEATING SYSTEMS; DOMESTIC HOT-WATER SUPPLY SYSTEMS; ELEMENTS OR COMPONENTS THEREFOR
    • F24D2220/00—Components of central heating installations excluding heat sources
    • F24D2220/04—Sensors
    • F24D2220/046—Pressure sensors

Definitions

  • the invention disclosed herein relates to a hydraulic system comprising fluid conduits and a plurality of active devices to adjust an operational parameter of said hydraulic system.
  • Hydraulic systems of this type commonly form part of a central heating system or hot water system in which heated fluid is transferred through the conduits towards and from radiators located in spaces to be heated.
  • Hydraulic systems of the aforementioned type are closed systems to avoid the introduction of in particular oxygen into the conduits, where it may cause corrosion.
  • a consequence of being a closed system is that such hydraulic systems are continuously subjected to variations in fluid pressure and fluid volume stemming from temporal and spatial variations in temperature of fluid located therein. This poses the risk that a pressure of fluid within the hydraulic system rises to excessive levels, which may damage the hydraulic system and/or interrupt a proper functioning thereof.
  • hydraulic systems comprise one or more active devices designed to diminish exuberant pressures of fluid to acceptable levels.
  • active devices typically comprise a hollow tank or vessel bisected by a flexible diaphragm.
  • the section of the hollow vessel beneath this flexible diaphragm is fluidly connected to the fluid conduits of the hydraulic system and therefore contains fluid, whereas the section above the flexible diaphragm contains gas and is fluidly connected to a compressor and/or a pump.
  • a buildup of excess pressure of fluid in the hydraulic system is offset by allowing fluid from the fluid conduits to enter the lower section of the hollow vessel, thereby displacing the flexible diaphragm, in conjunction with an operation by the compressor or pump.
  • active devices may likewise raise pressure of fluid by injecting fluid into the fluid conduits of hydraulic system, and periodically degas the hydraulic system be venting off gasses trapped therein.
  • Larger hydraulic systems typically comprise a plurality of active devices, each of which comprises a finite expansion volume and remaining expansion capacity; and therefore a finite capability of adjusting pressure of fluid in the hydraulic system. Moreover, when pressure of fluid in the hydraulic system is adjusted by an active device as described above, the expansion volume and remaining expansion capacity of said active device are changed. This in turn affects the ability of said active device to react to subsequent deviations in pressure of fluid, as doing so requires an appropriate amount of expansion volume or expansion capacity.
  • said active devices are often located at different height levels relative to one another. Due to static fluid pressure stemming from a height distance between the highest point of the hydraulic system and the height level at which a given active device is placed, each of the active devices experiences a different pressure of fluid in the hydraulic system even under normal operating conditions.
  • each active device exhibits a tendency to retain its initial shape when displaced while said active device injects fluid into the hydraulic system or withdraws fluid therefrom.
  • thermostatic control valves are controlled by means of acoustic signals that are transmitted and received by, respectively, acoustic transmitters and acoustic transmitters comprised by the zone heat control system.
  • An objective of the present invention is to provide a hydraulic system that is improved relative to the state of the art in that at least one or some of the above described drawbacks is obviated or abated.
  • This objective is achieved with a hydraulic system comprising fluid conduits, a plurality of active devices, such as expansion pumps or compressor devices, each of which comprising a vessel fluidly connected to with fluid conduits, wherein each vessel is configured for injection of fluid into, and/or extraction of fluid from, the hydraulic system for controlling pressure; wherein the hydraulic system moreover comprises a controller configured to select, for injection and/or extraction of fluid, at least one active device among the plurality of active devices based on a group of selection criteria, said group comprising: an injection capacity of the vessel of the selected active device; and an extraction capacity of the vessel of the selected active device.
  • the above objective is furthermore achieved with a controller of or for such a hydraulic system.
  • each active device comprises a vessel fluidly connected with the fluid conduits, and each vessel is configured for injection of fluid into, and/or extraction of fluid from, the hydraulic system for controlling pressure
  • said method comprising selecting, for injection and/or extraction of fluid, at least one active device among the plurality of active devices based on a group of selection criteria, said group comprising: an injection capacity of the vessel of the active device; and an extraction capacity of the vessel of the active device.
  • a computer program comprising instructions to cause a controller comprised by a hydraulic system to execute the steps of the aforementioned method, as well as a non-transitory computer-readable medium storing such a computer program.
  • Figure 1 depicts an exemplary embodiment of a hydraulic system in accordance with the present invention
  • Figure 2 depicts an exemplary embodiment of an active device comprised by the hydraulic system of Figure 1 ;
  • Figure 3 depicts a graph illustrating at least part of a scheme for determining that at least two of the active devices depicted in figure 1 are fluidly connected to one another.
  • a hydraulic system 1 comprises fluid conduits 2 carrying fluid towards and from various components or devices comprised by the system.
  • Hydraulic system 1 is a closed off system with no substantial amount of fluid being exchanged with its surroundings.
  • Hydraulic system 1 may comprise any number of devices or components fluidly connected with fluid conduits 2 including boilers or other heating elements and radiators and other types of heat exchangers (not shown).
  • hydraulic system 1 During operation of hydraulic system 1 fluid within conduits 2 is subjected to temporal and spatial temperature variations. As this fluid expands when its temperature increases and compresses when its temperature decreases, hydraulic system 1 is consequently subjected to variations in pressure of fluid therein. The variations in pressure of fluid in hydraulic system 1 may result in a pressure of fluid that is either excessively high or excessively low, which may hamper the operational functionality of hydraulic system 1 or cause damage to hydraulic system 1.
  • hydraulic system 1 comprises a plurality of active devices 3a, 3b, 3c, 3d configured to, if deemed to be necessary, adjust a pressure of fluid within hydraulic system 1 to a safe or acceptable level.
  • each of the active devices 3a, 3b, 3c, 3d is fluidly connected to fluid conduits 2 and configured to adjust an operational parameter of hydraulic system 1.
  • each one of active devices 3a, 3b, 3c, 3d comprises a vessel fluidly connected to the fluid conduits for injection of fluid from the vessel of the active devices 3a, 3b, 3c, 3d into hydraulic system 1 and/or extraction of fluid from said vessel into hydraulic system 1.
  • the term “operational parameter” may constitute any parameter related to an operation of hydraulic system 1; and may comprise, for example, pressure of fluid, flow speed of fluid, temperature of fluid or the like.
  • said operational parameter constitutes a pressure of fluid within hydraulic system 1 that is adjustable by an action of a pump or a compressor comprised by active devices 3a, 3b, 3c, 3d.
  • each of the plurality of active devices 3a, 3b, 3c, 3d is additionally connected to a communication network 4 schematically represented by the dashed lines connecting each of said active devices 3a, 3b, 3c, 3d.
  • the communication network 4 may be embodied by a wired communication network or by a wireless communication network.
  • said wireless communication network may be based on any suitable technology, such as wireless fidelity (Wi-Fi), cellular technology, Bluetooth or ZigBee.
  • Communication network 4 may furthermore be connected to an external server or client or cloud-based computing platform (not shown).
  • FIG 2 depicts an exemplary embodiment of an active device 3 comprised by hydraulic system 1 as depicted in Figure 1 with reference signs 3a, 3b, 3c, 3d.
  • Active device 3 comprises a fluid based transmitter 5 configured to transmit a signal through fluid conduits 2 with the fluid therein as a transmission medium.
  • Active device 3 furthermore comprises a fluid based receiver 6 configured to receive a signal through fluid 2 with the fluid therein as a transmission medium.
  • Fluid based transmitter 5 and fluid based receiver 6 of active device 3 are respectively configured to transmit and receive signals to and from other active devices 3, which likewise comprise a similar or identical fluid based transmitter 5 and/or fluid based receiver 6.
  • fluid based transmitter 5 and fluid based receiver 6 are embodied by distinct, separate components.
  • a transducer (not shown) having the combined functionality of fluid based transmitter 5 and fluid based receiver
  • Active device 3 furthermore comprises a controller 8.
  • controller 8 is comprised by active device 3.
  • controller 8 may embodied by a distinct entity located within hydraulic network 1 that does not form part of any one of active devices 3a, 3b, 3c, 3d in particular.
  • controller 8 may alternatively be located outside of the physical boundaries of hydraulic network 1 ; being embodied by a an external server, client or cloud-based computer platform connected to any one or more of devices 3a, 3b, 3c, 3d via communication network 4.
  • hydraulic system 1 may comprise a plurality of controllers 8, each of which exhibiting at least some of the functionality that will be described here below.
  • each of the active devices 3a, 3b, 3c and 3d may comprise a controller 8.
  • a natural inclination of the artisan may consist of implementing a master-slave principle, wherein controller 8 of one of the active devices 3a, 3b, 3c and 3d is designated to act as a master controller and controllers 8 of other active devices are designated to act as a slave controller.
  • controllers 8 in a number or all of the active devices 3a, 3b, 3c and 3d, a floating-master principle may be implemented.
  • controllers 8 of active devices are equal, in that each controller 8 is configured to practically autonomously decide on injection and/or extraction of fluid by the active device 3 to which the controller 8 belongs, based on a selection criterion for deciding to activate this active device, for example a local pressure in the system at a location where this active device is connected to the system.
  • the controller 8 of the thus activated active device 3 may communicate information about the action initiated by the local active device 3 to the other (controllers 8 of the other) active devices via communication network 4 or though the fluid 2 in the system, for these other active devices to locally determine their response or contribution, and maintain coordination of the responses.
  • the one of the active devices initiating action is temporarily a master, but then the other active devices may not receive master-like instructions, but information to enable these other active devices to autonomously determine their coordinated responses. This way, the controller 8 of any active device may initiate an action, for the others to follow suit, or refrain from responding.
  • the floating master principle may allow the system to keep running, when for example the fluid 2 is used to communicate information to the other active devices about initiated actions.
  • the controller 8 is in communication with, for example, active device 3a comprising fluid based transmitter 5 and, for example, active device 3b comprising fluid based receiver 6.
  • controller 8 is configured to - upon transmission of a signal by fluid based transmitter 5 of active device 3a and reception of said signal by fluid based receiver 6 of active device 3b - determine that active device 3a and active device 3b are fluidly connected to one another via fluid conduits 2.
  • existence of a fluid connection between two or more of the active devices 3a, 3b, 3c, 3d can be determined quickly and reliably, which is considered advantageous when designing or installing hydraulic system 1 or expanding an existing hydraulic system 1 with additional fluid conduits 2 and/or active devices 3a, 3b, 3c, 3d.
  • a determination scheme may be applicable for diagnosing a malfunctioning of hydraulic system 1 , for example when detecting leaks in fluid conduits 2.
  • knowledge of an existent fluid connection between two or more of active devices 3a, 3b, 3c, 3d may be applied to adjust an operational parameter of hydraulic system 1 in a manner wherein fluidly connected active 3a, 3b, 3c. 3d work together in a coordinated manner, thereby enhancing a degree efficiency with which said adjustment of the operational parameter is performed.
  • fluid based transmitter 5 is configured to transmit a signal by manipulating a pressure of fluid in conduits 2, thereby emitting a predetermined pressure coded signal through fluid conduits 2.
  • a pressure coded signal may be embodied by one or more pressure pulses with a predetermined duration, amplitude and/or time intervals between them.
  • the signal may constitute at least one of a flow speed coded signal, an acoustic signal, an optical signal, an electrical signal and an electromagnetic signal that propagates through fluid in fluid conduits 2.
  • fluid based transmitter 5 and fluid based receiver 6 comprise appropriate means to respectively transmit and receive the fluid based signal that is used, such as respectively an acoustic transmitter and acoustic receiver in embodiments wherein an acoustic signal is applied.
  • fluid based transmitter 5 may be embodied by a pump and/or a compressor comprised by active device 3a, 3b, 3c, 3d that is additionally configured perform adjustment of pressure of fluid in hydraulic system 1.
  • controller 8 may be configured to select at least one active device 3a, 3b, 3c, 3d fluidly connected with to least one other active device 3a, 3b, 3c, 3d and to drive said at least one selected active device 3a, 3b, 3c, 3d to adjust the operational parameter. Controller 8 may drive active device 3 to withdraw fluid from hydraulic system 1 or inject fluid therein, thereby adjusting pressure of fluid in hydraulic system.
  • controller 8 may select one or more of fluidly mutually connected active devices 3a, 3b, 3c, 3d based on an operational characteristic of one or more of these active devices 3a, 3b, 3c, 3d. For example, controller 8 may select one or more of active devices 3a, 3b, 3c, 3d based on an available expansion volume, thereby ensuring that the at least one selected active device 3a, 3b, 3c, 3d contains a sufficient volume of fluid to be injected into hydraulic system 1 to adjust a pressure of fluid therein.
  • An alternative or additional operational characteristic on the basis of which a fluidly connected active device 3a, 3b, 3c, 3d may be selected by controller 8, is a remaining expansion capacity in said active device 3a, 3b, 3c, 3d required for withdrawing liquid from hydraulic system 1 , to thereby lower a pressure of fluid in hydraulic system 1.
  • each active device 3a, 3b, 3c, 3d exhibits hysteretic behaviour due to the presence of a flexible diaphragm therein. Consequently, each of active devices 3a, 3b, 3c, 3d comprises a hysteresis characteristic with a certain hysteresis or bandwidth, which likewise constitutes an operational characteristic of said respective active devices 3a, 3b, 3c, 3d.
  • the active device comprising the widest bandwidth or hysteresis may dictate; the bandwidth of other active devices being recalculated based thereon and the newly found bandwidth for an individual hysteresis being normative for a specific active device 3a, 3b, 3c, 3d to all actions.
  • controller 8 is configured to select at least one of active devices 3a, 3b, 3c, 3d for controlling an operational parameter of hydraulic network 1 based on a selection criterion.
  • Said selection criterion may be one from a group of selection criteria comprising an injection capacity (of the vessel) of the selected active device and an extraction capacity (of the vessel) of the selected active device. Both the injection capacity and the extraction capacity are dependent on the physical dimensions of the vessel of a given active device and the amount of liquid present therein.
  • said group of selection criteria moreover comprises a hysteresis characteristic of the selected active device and/or a static pressure at or near the selected active device, said static pressure resulting from a difference in height level at which the selected active device is disposed relative to the other active devices among the plurality of active devices.
  • Controller 8 may furthermore be configured to drive the at least one selected active device 3a, 3b, 3c, 3d by transmitting thereto a control signal.
  • the control signal is preferably transmitted using wired or wireless communication network 4.
  • control signal may be transmitted by controller 8 using fluid based transmitter 5 comprised by a selected active devices 3a, 3b, 3c or 3d to a fluid based receiver 6 comprised by an other active device 3a, 3b, 3c or 3d through fluid conduits 2, thereby using the fluid located therein as a transmission medium.
  • controller 8 is preferably configured to be capable of transmitting control signals through both fluid conduits 2 and communication network 4 to achieve an increased degree of flexibility and reliability.
  • fluid based transmission of control signals through fluid conduits 2 may be used in the event that communication by means of communication network 4 is not available, for example due to a technical malfunction or a power failure.
  • transmission of control signals may occur exclusively through communication network 4 in the event that fluid based transmission of control signals is not possible in a reliable manner, for example due to a leak in somewhere in fluid conduits 2 of hydraulic system 1.
  • active device 3a, 3b, 3c, 3d may comprise a sensor 7 configured to sense an operational parameter of hydraulic system 1.
  • the operational parameter of hydraulic system 1 may be a pressure of fluid within hydraulic system 1 , wherein sensor 7 comprises a pressure sensor.
  • controller 8 may be configured to determine a need to adjust an operational parameter of hydraulic system 1. Determination of this need may be based on the operational parameter exceeding a predetermined range as measured by sensor 7 by exceeding a lower or upper threshold. Correction of said operational parameter may subsequently be performed as described above.
  • FIG. 3 there is depicted a total of four graphs, with reference to which an exemplary scheme for determining that at least two of active devices 3, 3a, 3b, 3c, 3d are fluidly connected to one another will be further elucidated.
  • the top two graphs respectively represent an expansion volume V a of a given active device 3, for example active device 3a, as a function of time; and a pressure of fluid P a in hydraulic system 1 as a function of time, at or near a location at which active device 3a is fluidly connected to fluid conduits 2.
  • the bottom two graphs of Figure 3 respectively represent an expansion volume V b of an other active device 3, for example active device 3b, as a function of time; and a pressure of fluid P b in hydraulic system 1 at or near a location at which active device 3b is fluidly connected to fluid conduits 2 of hydraulic system 1.
  • a fluid based transmitter 5 comprised by active device 3b transmits a pressure coded signal to a fluid based receiver 6 comprised by active device 3a.
  • Transmission of the pressure coded signal comprises, in this exemplary embodiment, injection of fluid into hydraulic system 1 from an expansion volume V b of active device 3b, for example by means of a pump or compressor comprised by active device 3b.
  • the initial injection of fluid into hydraulic system 1 occurs over the time period from t 0 to t 2 , during which time pressure P b of fluid in hydraulic system 1, as measured near active device 3b, increases while an expansion volume V b of active device 3b decreases.
  • the increase in pressure P b dissipates throughout fluid conduits 2 of hydraulic system 1 with a finite speed, therefore experiencing a “delay” before reaching active device 3a at t l where it is detected as pressure P a by a fluid based receiver 6 comprised by the active device 3a.
  • the injection of fluid into hydraulic system 1 by active device 3b is subsequently followed by withdrawal of fluid therefrom starting at t 2 , during which the expansion volume V b of active device 3b increases.
  • controller 8 may determine that active devices 3a and 3b are fluidly connected to one another via fluid conduits 2.
  • the determination scheme depicted in Figure 3 may furthermore comprise transmission and reception of a signal in a reverse direction to determine that active devices 3a, 3b are fluidly mutually connected.
  • said determination scheme may furthermore comprise transmitting, by fluid based transmitter 5 comprised by active device 3a, a subsequent pressure coded signal to fluid based receiver 6 comprised by active device 3b.
  • the manipulation of pressure P a , P b of fluid in hydraulic system 1 may be repeated a predetermined number of times as represented by the exemplary sawtooth wave in the graphs of Figure 3.
  • the predetermined number of increases and decreases in pressure P a , P b of fluid in hydraulic system 1 constitute an example of a pressure coded signal in the context of the present disclosure and invention.
  • two (or more) active devices for example expansion devices
  • at least one is set in a degassing mode.
  • an amount of fluid is extracted from the system, degassed under a lower pressure in the expansion space, and degassed fluid is returned to the system.
  • Another of the at least two active devices may then be adjusted by means of the invention to operate asynchronously, relative to the at least one in the degassing mode, i.e. to inject fluid into the system.
  • the goal may be pursued that no or hardly any pressure change occurs in the system during the degassing process, or at least a pressure drop due to the extraction of fluid to be degassed is as small as possible.
  • the injecting active device may then be adjusted to operate so as not to raise pressure in the system, and merely compensate for the extracted fluid as accurately as possible.
  • the active devices may be specific degassing devices, such as pressure step degassers, wherein the fluid is brought to vacuum during such a cyclic degassing mode. Active devices may operate semi-continuously in complementary modes, as disclosed above, in particular during a start-up phase, where new fluid is inserted into a system, which may require degassing over a considerable start-up period.

Abstract

The invention disclosed herein relates to a hydraulic system comprising fluid conduits and a plurality of active devices, each of which comprising a vessel fluidly connected with the fluid conduits, wherein each vessel is configured for injection of fluid into, and/or extraction fluid from, the hydraulic system for controlling pressure. The herein hydraulic network moreover comprises a controller configured to select, for injection and/or extraction of fluid, at least one active device among the plurality of active devices based on at least one of an injection capacity of the vessel of the selected active device; and an extraction capacity of the vessel of the selected active device.

Description

HYDRAULIC SYSTEM COMPRISING ACTIVE DEVICES AND METHOD FOR CONTROLLING SUCH A HYDRAULIC SYSTEM
The invention disclosed herein relates to a hydraulic system comprising fluid conduits and a plurality of active devices to adjust an operational parameter of said hydraulic system. Hydraulic systems of this type commonly form part of a central heating system or hot water system in which heated fluid is transferred through the conduits towards and from radiators located in spaces to be heated.
Hydraulic systems of the aforementioned type are closed systems to avoid the introduction of in particular oxygen into the conduits, where it may cause corrosion. A consequence of being a closed system is that such hydraulic systems are continuously subjected to variations in fluid pressure and fluid volume stemming from temporal and spatial variations in temperature of fluid located therein. This poses the risk that a pressure of fluid within the hydraulic system rises to excessive levels, which may damage the hydraulic system and/or interrupt a proper functioning thereof.
To prevent damage to or malfunctioning of the hydraulic system, hydraulic systems comprise one or more active devices designed to diminish exuberant pressures of fluid to acceptable levels. For this purpose, such active devices typically comprise a hollow tank or vessel bisected by a flexible diaphragm. The section of the hollow vessel beneath this flexible diaphragm is fluidly connected to the fluid conduits of the hydraulic system and therefore contains fluid, whereas the section above the flexible diaphragm contains gas and is fluidly connected to a compressor and/or a pump. A buildup of excess pressure of fluid in the hydraulic system is offset by allowing fluid from the fluid conduits to enter the lower section of the hollow vessel, thereby displacing the flexible diaphragm, in conjunction with an operation by the compressor or pump. Moreover, active devices may likewise raise pressure of fluid by injecting fluid into the fluid conduits of hydraulic system, and periodically degas the hydraulic system be venting off gasses trapped therein.
Larger hydraulic systems typically comprise a plurality of active devices, each of which comprises a finite expansion volume and remaining expansion capacity; and therefore a finite capability of adjusting pressure of fluid in the hydraulic system. Moreover, when pressure of fluid in the hydraulic system is adjusted by an active device as described above, the expansion volume and remaining expansion capacity of said active device are changed. This in turn affects the ability of said active device to react to subsequent deviations in pressure of fluid, as doing so requires an appropriate amount of expansion volume or expansion capacity.
Furthermore, in hydraulic systems comprising a plurality of active devices, for example due to space limitations, said active devices are often located at different height levels relative to one another. Due to static fluid pressure stemming from a height distance between the highest point of the hydraulic system and the height level at which a given active device is placed, each of the active devices experiences a different pressure of fluid in the hydraulic system even under normal operating conditions.
Moreover, the flexible diaphragm comprised by each active device exhibits a tendency to retain its initial shape when displaced while said active device injects fluid into the hydraulic system or withdraws fluid therefrom. As such, there exists no linear relationship between pressure of fluid in the hydraulic system and an expansion volume of a given active device; the active devices in such a hydraulic network instead exhibiting hysteretic behaviour.
The above described properties of active devices contribute to overall complexity of designing, installing, maintaining and efficiently operating hydraulic systems in which a plurality of such active devices is applied.
Reference is made here to US 4382543 A, which is acknowledged here to constitute the known closest prior-art for the present invention and discloses a zone heat control system. In said zone heat control system, thermostatic control valves are controlled by means of acoustic signals that are transmitted and received by, respectively, acoustic transmitters and acoustic transmitters comprised by the zone heat control system.
Moreover, DE 29 38734 Al, US 2002/189362 Al, DE 20 12547 Al, DE 3209 189 A1 and DE 92 10894 U1 are acknowledged here to constitute further prior-art bearing at least some relevance to the present invention.
An objective of the present invention is to provide a hydraulic system that is improved relative to the state of the art in that at least one or some of the above described drawbacks is obviated or abated. This objective is achieved with a hydraulic system comprising fluid conduits, a plurality of active devices, such as expansion pumps or compressor devices, each of which comprising a vessel fluidly connected to with fluid conduits, wherein each vessel is configured for injection of fluid into, and/or extraction of fluid from, the hydraulic system for controlling pressure; wherein the hydraulic system moreover comprises a controller configured to select, for injection and/or extraction of fluid, at least one active device among the plurality of active devices based on a group of selection criteria, said group comprising: an injection capacity of the vessel of the selected active device; and an extraction capacity of the vessel of the selected active device.
Preferred embodiments of a hydraulic system in accordance with the present invention are subject of the appended dependent apparatus claims.
The above objective is furthermore achieved with a controller of or for such a hydraulic system.
The objective stated above is furthermore achieved with a method in accordance with the present invention for controlling an hydraulic system comprising fluid conduits and a plurality of active devices, such as expansion pumps or compressor devices, wherein each active device comprises a vessel fluidly connected with the fluid conduits, and each vessel is configured for injection of fluid into, and/or extraction of fluid from, the hydraulic system for controlling pressure, said method comprising selecting, for injection and/or extraction of fluid, at least one active device among the plurality of active devices based on a group of selection criteria, said group comprising: an injection capacity of the vessel of the active device; and an extraction capacity of the vessel of the active device.
Preferred embodiments of a method for controlling a hydraulic system are subject of the appended dependent method claims.
Lastly, the above objective is achieved with a computer program comprising instructions to cause a controller comprised by a hydraulic system to execute the steps of the aforementioned method, as well as a non-transitory computer-readable medium storing such a computer program.
Herein above, general concepts of a hydraulic system and corresponding control method in accordance with the present invention are referred to on the basis of relatively generic indications of the features thereof, which correspond to the definitions in the appended independent claims. Herein below, preferred exemplary embodiments of the present invention are elucidated with reference to the appended drawing. It is emphasised here that these embodiments are merely of an exemplary nature and that the same or similar functionalities may be achieved with the basic principles of the present invention.
Throughout the below description of the exemplary embodiments of the present invention, identical or similar entities, components, functional units or concepts and the like may be referred to using similar or identical reference signs when referring to the appended drawing, in which:
Figure 1 depicts an exemplary embodiment of a hydraulic system in accordance with the present invention;
Figure 2 depicts an exemplary embodiment of an active device comprised by the hydraulic system of Figure 1 ; and
Figure 3 depicts a graph illustrating at least part of a scheme for determining that at least two of the active devices depicted in figure 1 are fluidly connected to one another.
With reference to Figure 1 a hydraulic system 1 comprises fluid conduits 2 carrying fluid towards and from various components or devices comprised by the system. Hydraulic system 1 is a closed off system with no substantial amount of fluid being exchanged with its surroundings. Hydraulic system 1 may comprise any number of devices or components fluidly connected with fluid conduits 2 including boilers or other heating elements and radiators and other types of heat exchangers (not shown).
During operation of hydraulic system 1 fluid within conduits 2 is subjected to temporal and spatial temperature variations. As this fluid expands when its temperature increases and compresses when its temperature decreases, hydraulic system 1 is consequently subjected to variations in pressure of fluid therein. The variations in pressure of fluid in hydraulic system 1 may result in a pressure of fluid that is either excessively high or excessively low, which may hamper the operational functionality of hydraulic system 1 or cause damage to hydraulic system 1.
To prevent such issues from occurring hydraulic system 1 comprises a plurality of active devices 3a, 3b, 3c, 3d configured to, if deemed to be necessary, adjust a pressure of fluid within hydraulic system 1 to a safe or acceptable level.
In hydraulic system 1 each of the active devices 3a, 3b, 3c, 3d is fluidly connected to fluid conduits 2 and configured to adjust an operational parameter of hydraulic system 1. In particular, each one of active devices 3a, 3b, 3c, 3d comprises a vessel fluidly connected to the fluid conduits for injection of fluid from the vessel of the active devices 3a, 3b, 3c, 3d into hydraulic system 1 and/or extraction of fluid from said vessel into hydraulic system 1. In the context of the present disclosure, the term “operational parameter” may constitute any parameter related to an operation of hydraulic system 1; and may comprise, for example, pressure of fluid, flow speed of fluid, temperature of fluid or the like. In accordance with the present exemplary embodiments, said operational parameter constitutes a pressure of fluid within hydraulic system 1 that is adjustable by an action of a pump or a compressor comprised by active devices 3a, 3b, 3c, 3d.
In Figure 1 each of the plurality of active devices 3a, 3b, 3c, 3d is additionally connected to a communication network 4 schematically represented by the dashed lines connecting each of said active devices 3a, 3b, 3c, 3d. The communication network 4 may be embodied by a wired communication network or by a wireless communication network. In embodiments of hydraulic system 1 wherein communication network 4 is embodied by a wireless communication network, said wireless communication network may be based on any suitable technology, such as wireless fidelity (Wi-Fi), cellular technology, Bluetooth or ZigBee. Communication network 4 may furthermore be connected to an external server or client or cloud-based computing platform (not shown).
Figure 2 depicts an exemplary embodiment of an active device 3 comprised by hydraulic system 1 as depicted in Figure 1 with reference signs 3a, 3b, 3c, 3d. Active device 3 comprises a fluid based transmitter 5 configured to transmit a signal through fluid conduits 2 with the fluid therein as a transmission medium. Active device 3 furthermore comprises a fluid based receiver 6 configured to receive a signal through fluid 2 with the fluid therein as a transmission medium.
Fluid based transmitter 5 and fluid based receiver 6 of active device 3 are respectively configured to transmit and receive signals to and from other active devices 3, which likewise comprise a similar or identical fluid based transmitter 5 and/or fluid based receiver 6.
In the embodiment depicted in Figure 2, fluid based transmitter 5 and fluid based receiver 6 are embodied by distinct, separate components. Alternatively, there may be provided a transducer (not shown) having the combined functionality of fluid based transmitter 5 and fluid based receiver
6.
Active device 3 furthermore comprises a controller 8. The scope of the functionality of controller 8 may vary in accordance with different embodiments of the present invention, which will be elucidated here below. In the embodiment of an active device 3 depicted in Figure 2, controller 8 is comprised by active device 3. Alternatively, controller 8 may embodied by a distinct entity located within hydraulic network 1 that does not form part of any one of active devices 3a, 3b, 3c, 3d in particular. Moreover, controller 8 may alternatively be located outside of the physical boundaries of hydraulic network 1 ; being embodied by a an external server, client or cloud-based computer platform connected to any one or more of devices 3a, 3b, 3c, 3d via communication network 4. Moreover, hydraulic system 1 may comprise a plurality of controllers 8, each of which exhibiting at least some of the functionality that will be described here below.
More in detail, each of the active devices 3a, 3b, 3c and 3d (or at least more than one thereof) may comprise a controller 8. In such an embodiment, a natural inclination of the artisan may consist of implementing a master-slave principle, wherein controller 8 of one of the active devices 3a, 3b, 3c and 3d is designated to act as a master controller and controllers 8 of other active devices are designated to act as a slave controller.
However, as a noteworthy alternative embodiment having controllers 8 in a number or all of the active devices 3a, 3b, 3c and 3d, a floating-master principle may be implemented. According to such a floating-master principle, controllers 8 of active devices are equal, in that each controller 8 is configured to practically autonomously decide on injection and/or extraction of fluid by the active device 3 to which the controller 8 belongs, based on a selection criterion for deciding to activate this active device, for example a local pressure in the system at a location where this active device is connected to the system. The controller 8 of the thus activated active device 3 may communicate information about the action initiated by the local active device 3 to the other (controllers 8 of the other) active devices via communication network 4 or though the fluid 2 in the system, for these other active devices to locally determine their response or contribution, and maintain coordination of the responses. One could say that the one of the active devices initiating action is temporarily a master, but then the other active devices may not receive master-like instructions, but information to enable these other active devices to autonomously determine their coordinated responses. This way, the controller 8 of any active device may initiate an action, for the others to follow suit, or refrain from responding. Even in the absence of a communication network 4, such as “the cloud”, when the wired or wireless communication may be out of order temporarily or for a long duration, the floating master principle may allow the system to keep running, when for example the fluid 2 is used to communicate information to the other active devices about initiated actions. In certain embodiments of hydraulic system 1 , the controller 8 is in communication with, for example, active device 3a comprising fluid based transmitter 5 and, for example, active device 3b comprising fluid based receiver 6. In this embodiment, controller 8 is configured to - upon transmission of a signal by fluid based transmitter 5 of active device 3a and reception of said signal by fluid based receiver 6 of active device 3b - determine that active device 3a and active device 3b are fluidly connected to one another via fluid conduits 2.
Consequently, existence of a fluid connection between two or more of the active devices 3a, 3b, 3c, 3d can be determined quickly and reliably, which is considered advantageous when designing or installing hydraulic system 1 or expanding an existing hydraulic system 1 with additional fluid conduits 2 and/or active devices 3a, 3b, 3c, 3d. In addition, such a determination scheme may be applicable for diagnosing a malfunctioning of hydraulic system 1 , for example when detecting leaks in fluid conduits 2.
Moreover, as will be elucidated here below, knowledge of an existent fluid connection between two or more of active devices 3a, 3b, 3c, 3d may be applied to adjust an operational parameter of hydraulic system 1 in a manner wherein fluidly connected active 3a, 3b, 3c. 3d work together in a coordinated manner, thereby enhancing a degree efficiency with which said adjustment of the operational parameter is performed.
In preferred embodiments of the present invention fluid based transmitter 5 is configured to transmit a signal by manipulating a pressure of fluid in conduits 2, thereby emitting a predetermined pressure coded signal through fluid conduits 2. Such a pressure coded signal may be embodied by one or more pressure pulses with a predetermined duration, amplitude and/or time intervals between them. Alternatively, the signal may constitute at least one of a flow speed coded signal, an acoustic signal, an optical signal, an electrical signal and an electromagnetic signal that propagates through fluid in fluid conduits 2. Evidently, in these embodiments fluid based transmitter 5 and fluid based receiver 6 comprise appropriate means to respectively transmit and receive the fluid based signal that is used, such as respectively an acoustic transmitter and acoustic receiver in embodiments wherein an acoustic signal is applied.
In accordance with certain embodiments of the present invention wherein the fluid based signal is a pressure coded signal or a flow speed coded signal, fluid based transmitter 5 may be embodied by a pump and/or a compressor comprised by active device 3a, 3b, 3c, 3d that is additionally configured perform adjustment of pressure of fluid in hydraulic system 1.
During operation of hydraulic system 1 , there may arise a need to adjust an operational parameter of hydraulic system 1. For example, it may required to adjust pressure of fluid within hydraulic system 1 when said pressure exceeds a predetermined maximum value, at which pressure of fluid there exists a possibility that operation of hydraulic system 1 will be compromised or damage to hydraulic system 1 will occur. In accordance with certain embodiments of the present invention, controller 8 may be configured to select at least one active device 3a, 3b, 3c, 3d fluidly connected with to least one other active device 3a, 3b, 3c, 3d and to drive said at least one selected active device 3a, 3b, 3c, 3d to adjust the operational parameter. Controller 8 may drive active device 3 to withdraw fluid from hydraulic system 1 or inject fluid therein, thereby adjusting pressure of fluid in hydraulic system.
In these embodiments, controller 8 may select one or more of fluidly mutually connected active devices 3a, 3b, 3c, 3d based on an operational characteristic of one or more of these active devices 3a, 3b, 3c, 3d. For example, controller 8 may select one or more of active devices 3a, 3b, 3c, 3d based on an available expansion volume, thereby ensuring that the at least one selected active device 3a, 3b, 3c, 3d contains a sufficient volume of fluid to be injected into hydraulic system 1 to adjust a pressure of fluid therein. An alternative or additional operational characteristic, on the basis of which a fluidly connected active device 3a, 3b, 3c, 3d may be selected by controller 8, is a remaining expansion capacity in said active device 3a, 3b, 3c, 3d required for withdrawing liquid from hydraulic system 1 , to thereby lower a pressure of fluid in hydraulic system 1. Furthermore, as described above each active device 3a, 3b, 3c, 3d exhibits hysteretic behaviour due to the presence of a flexible diaphragm therein. Consequently, each of active devices 3a, 3b, 3c, 3d comprises a hysteresis characteristic with a certain hysteresis or bandwidth, which likewise constitutes an operational characteristic of said respective active devices 3a, 3b, 3c, 3d.
In particular during coordinated adjustments of an operation parameter by a plurality of fluidly mutually connected active devices 3a, 3b, 3c, 3d the active device comprising the widest bandwidth or hysteresis may dictate; the bandwidth of other active devices being recalculated based thereon and the newly found bandwidth for an individual hysteresis being normative for a specific active device 3a, 3b, 3c, 3d to all actions.
In exemplary embodiments, controller 8 is configured to select at least one of active devices 3a, 3b, 3c, 3d for controlling an operational parameter of hydraulic network 1 based on a selection criterion. Said selection criterion may be one from a group of selection criteria comprising an injection capacity (of the vessel) of the selected active device and an extraction capacity (of the vessel) of the selected active device. Both the injection capacity and the extraction capacity are dependent on the physical dimensions of the vessel of a given active device and the amount of liquid present therein. In addition, in certain embodiments of the present invention said group of selection criteria moreover comprises a hysteresis characteristic of the selected active device and/or a static pressure at or near the selected active device, said static pressure resulting from a difference in height level at which the selected active device is disposed relative to the other active devices among the plurality of active devices. Moreover, the operational parameters described here below and above may likewise constitute selection criteria in the sense of the present disclosure. Controller 8 may furthermore be configured to drive the at least one selected active device 3a, 3b, 3c, 3d by transmitting thereto a control signal. The control signal is preferably transmitted using wired or wireless communication network 4. Alternatively, control signal may be transmitted by controller 8 using fluid based transmitter 5 comprised by a selected active devices 3a, 3b, 3c or 3d to a fluid based receiver 6 comprised by an other active device 3a, 3b, 3c or 3d through fluid conduits 2, thereby using the fluid located therein as a transmission medium. These embodiments obviate the need for the presence of dedicated communication network 4. Nevertheless, controller 8 is preferably configured to be capable of transmitting control signals through both fluid conduits 2 and communication network 4 to achieve an increased degree of flexibility and reliability. In these embodiments, fluid based transmission of control signals through fluid conduits 2 may be used in the event that communication by means of communication network 4 is not available, for example due to a technical malfunction or a power failure. Similarly, transmission of control signals may occur exclusively through communication network 4 in the event that fluid based transmission of control signals is not possible in a reliable manner, for example due to a leak in somewhere in fluid conduits 2 of hydraulic system 1.
In accordance with certain embodiments, active device 3a, 3b, 3c, 3d may comprise a sensor 7 configured to sense an operational parameter of hydraulic system 1. The operational parameter of hydraulic system 1 may be a pressure of fluid within hydraulic system 1 , wherein sensor 7 comprises a pressure sensor.
In certain embodiments of hydraulic system 1 in accordance with the present invention controller 8 may be configured to determine a need to adjust an operational parameter of hydraulic system 1. Determination of this need may be based on the operational parameter exceeding a predetermined range as measured by sensor 7 by exceeding a lower or upper threshold. Correction of said operational parameter may subsequently be performed as described above.
Referring now to Figure 3, there is depicted a total of four graphs, with reference to which an exemplary scheme for determining that at least two of active devices 3, 3a, 3b, 3c, 3d are fluidly connected to one another will be further elucidated.
In Figure 3, the top two graphs respectively represent an expansion volume Va of a given active device 3, for example active device 3a, as a function of time; and a pressure of fluid Pa in hydraulic system 1 as a function of time, at or near a location at which active device 3a is fluidly connected to fluid conduits 2. The bottom two graphs of Figure 3 respectively represent an expansion volume Vb of an other active device 3, for example active device 3b, as a function of time; and a pressure of fluid Pb in hydraulic system 1 at or near a location at which active device 3b is fluidly connected to fluid conduits 2 of hydraulic system 1.
At time t0, as indicated on the horizontal axes in the graphs of Figure 3, a fluid based transmitter 5 comprised by active device 3b transmits a pressure coded signal to a fluid based receiver 6 comprised by active device 3a. Transmission of the pressure coded signal comprises, in this exemplary embodiment, injection of fluid into hydraulic system 1 from an expansion volume Vb of active device 3b, for example by means of a pump or compressor comprised by active device 3b.
As indicated in the bottom two graphs of Figure 3, the initial injection of fluid into hydraulic system 1 occurs over the time period from t0 to t2, during which time pressure Pb of fluid in hydraulic system 1, as measured near active device 3b, increases while an expansion volume Vb of active device 3b decreases. The increase in pressure Pb dissipates throughout fluid conduits 2 of hydraulic system 1 with a finite speed, therefore experiencing a “delay” before reaching active device 3a at tl where it is detected as pressure Pa by a fluid based receiver 6 comprised by the active device 3a. The injection of fluid into hydraulic system 1 by active device 3b is subsequently followed by withdrawal of fluid therefrom starting at t2, during which the expansion volume Vb of active device 3b increases. In the graphs of Figure 3, this withdrawal of liquid from hydraulic system 1 continues until t3, the resulting increase in pressure being detectable as pressure Pa at active device 3a at t4. Upon successful transmission and reception of this signal, controller 8 may determine that active devices 3a and 3b are fluidly connected to one another via fluid conduits 2.
The determination scheme depicted in Figure 3 may furthermore comprise transmission and reception of a signal in a reverse direction to determine that active devices 3a, 3b are fluidly mutually connected. In other words, said determination scheme may furthermore comprise transmitting, by fluid based transmitter 5 comprised by active device 3a, a subsequent pressure coded signal to fluid based receiver 6 comprised by active device 3b.
The manipulation of pressure Pa, Pb of fluid in hydraulic system 1 , that is to say the rise and decline thereof, may be repeated a predetermined number of times as represented by the exemplary sawtooth wave in the graphs of Figure 3. The predetermined number of increases and decreases in pressure Pa, Pb of fluid in hydraulic system 1 constitute an example of a pressure coded signal in the context of the present disclosure and invention.
The person skilled in the art will understand that, in embodiments of the present invention wherein a signal other than a pressure coded signal is applied, determination schemes similar or otherwise comparable to the one illustrated in Figure 3 may be applied.
While the exemplary embodiments described thus far concerned a hydraulic system 1 forming part of a heating system, the scope of the present disclosure is not limited thereto. The skilled person will acknowledge that the merits of the present invention may equally be beneficial in comparable hydraulic systems serving alternative purposes with nevertheless similar or otherwise comparable underlying techniques.
Yet another special application of the invention can be mentioned, in which two (or more) active devices, for example expansion devices, are provided, of which at least one is set in a degassing mode. In such a degassing mode, an amount of fluid is extracted from the system, degassed under a lower pressure in the expansion space, and degassed fluid is returned to the system. Another of the at least two active devices may then be adjusted by means of the invention to operate asynchronously, relative to the at least one in the degassing mode, i.e. to inject fluid into the system. Thereby, the goal may be pursued that no or hardly any pressure change occurs in the system during the degassing process, or at least a pressure drop due to the extraction of fluid to be degassed is as small as possible. Likewise, the injecting active device may then be adjusted to operate so as not to raise pressure in the system, and merely compensate for the extracted fluid as accurately as possible. The active devices may be specific degassing devices, such as pressure step degassers, wherein the fluid is brought to vacuum during such a cyclic degassing mode. Active devices may operate semi-continuously in complementary modes, as disclosed above, in particular during a start-up phase, where new fluid is inserted into a system, which may require degassing over a considerable start-up period.
It is noted here that the scope of protection for the developments described in the present disclosure are by no means limited to any particular feature of the embodiments described above and illustrated in the appended drawing. The scope of protection is exclusively determined based on the limitations of the appended independent claims, but may, in some jurisdictions, even encompass obvious alternatives for features in the independent claims. Other variations for specifically described elements, components and functionalities, that may also be embodied within the scope of the appended claims of the present disclosure, have been at least hinted at in the above embodiment description or the skilled person may be considered to be able to contemplate these variations within the range of this skilled person’s general knowledge. This exemplary reference to alternative embodiments substantiates that any limitation to any specific feature, that is not defined as a limitation in the independent claims, is unwarranted.

Claims

1. A hydraulic system comprising: fluid conduits; a plurality of active devices, such as expansion pumps or compressor devices, each comprising a vessel fluidly connected with the fluid conduits, wherein each vessel is configured for injection of fluid into, and/or extraction of fluid from the hydraulic system for controlling pressure; and a controller configured to select, for injection and/or extraction of fluid, at least one active device among the plurality of active devices based on one or more than one selection criterion from a group of selection criteria, said group comprising:
- an injection capacity of the vessel of the selected active device; and
- an extraction capacity of the vessel of the selected active device.
2. Hydraulic system according to claim 1 , wherein at least one of the active devices comprises a fluid based transmitter and at least one other of the active devices comprises a fluid based receiver to, respectively, transmit and receive a pressure coded signal for driving the selected active device through the fluid conduits, with the fluid therein acting as a transmission medium.
3. Hydraulic system according to claim 2, wherein the pressure coded signal is a control signal for driving the selected active device.
4. Hydraulic system according to any one of the foregoing claims, wherein the group of selection criteria moreover comprises at least one of:
- a hysteresis characteristic of the selected active device; and
- a static pressure at or near the selected active device, said static pressure resulting from a difference in height level at which the selected active device is disposed relative to the other active devices among the plurality of active devices.
5. Hydraulic system according to any one of the foregoing claims, further comprising a wired or wireless communication network, wherein the controller is configured to transmit a control signal to the at least one selected active device via the communication network.
6. Hydraulic system according to any one of the foregoing claims, wherein the hydraulic system comprises a pressure sensor, wherein the hydraulic system is configured to determine a need to control pressure based on an output value of the pressure sensor.
7. Hydraulic system according to any one of the foregoing claims, wherein the controller is comprised by one of the active devices among the plurality of active devices.
8. A controller of or for a hydraulic system according as defined in any one of the foregoing claims.
9. A method for controlling an hydraulic system comprising fluid conduits and a plurality of active devices, such as expansion pumps or compressor devices, wherein each active device comprises a vessel fluidly connected with the fluid conduits and wherein each vessel is configured for injection of fluid into, and/or extraction of fluid from, the hydraulic system for controlling pressure, the method comprising: selecting, for injection and/or extraction of fluid, at least one active device among the plurality of active devices based on a selection criterion from a group of selection criteria, said group comprising:
- an injection capacity of the vessel of the active device; and
- an extraction capacity of the vessel of the active device.
10. Method according to claim 9, further comprising: transmitting a pressure coded signal at an active device via a fluid based transmitter; and receiving said pressure coded signal at an active device via a fluid based receiver, wherein the pressure coded signal is transmitted through the fluid conduits with the fluid therein acting as a transmission medium.
11. Method according to claim 10, wherein the pressure coded signal is a control signal for driving the selected active device.
12. Method according to any one of the foregoing claims 9 - 11, wherein the group of selection criteria moreover comprises at least one of:
- a hysteresis characteristic of the selected active device; and
- a static pressure at or near the selected active device, said static pressure resulting from a difference in height level at which the selected active device is disposed relative to the other active devices among the plurality of active devices.
13. Method according to any one of the foregoing claims 9 - 12, further comprising driving the active devices in opposite but complementary modes.
14. A computer program comprising instructions to cause a controller as defined in any one of claims 1 - 7 to execute the method as defined in any one of claims 9 - 13.
15. A non-transitory computer-readable medium storing the computer program according to claim 14.
PCT/NL2020/050699 2019-11-08 2020-11-06 Hydraulic system comprising active devices and method for controlling such a hydraulic system WO2021091386A1 (en)

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