Control of hydraulic pressure in a diaphragm compressor

Abstract

A diaphragm compressor (2) comprises: a compression chamber (3) separated from a hydraulic fluid chamber (4) by a multi-layered metal diaphragm (5), a hydraulic fluid pressure sensor (6a) configured for measuring a hydraulic peak pressure inside said hydraulic fluid chamber (4), a hydraulic fluid adjustment assembly (13), and a controller (7), wherein said controller (7) is configured to compare said hydraulic peak pressure value with a target pressure value, wherein said target pressure value is higher than a discharge pressure from said compression chamber (3). The controller (7) is further configured to, via said hydraulic fluid adjustment assembly (13), control the injection of hydraulic fluid into said hydraulic fluid chamber (4) if said target pressure value is higher than said hydraulic peak pressure value, and to control the removal of hydraulic fluid from said hydraulic fluid chamber (13) if said target pressure value is below said hydraulic peak pressure value.

Description

CONTROL OF HYDRAULIC PRESSURE IN A DIAPHRAGM COMPRESSOR Field of the invention

[0001] The invention relates to a diaphragm compressor and a method of controlling the hydraulic pressure of such diaphragm compressor. Background of the invention

[0002] It is known in the art of gas diaphragm compressors to adjust the volume of oil in the oil chamber of a diaphragm compressor.

[0003] One example is applicants own publication WO2019011386 disclosing an injection assembly which together with a pressure sensor is controlling injection of oil into the chamber. The amount of injected oil is limited to the oil needed thus in principle only the needed volume of oil is injected into the oil chamber. It is mentioned that during normal operation there is no need for removal of oil from the chamber, only in emergency situations a return path guides oil back to an oil reservoir.

[0004] Another example is WO2022 / 099219 where oil is introduced into the oil chamber and excess oil exits the oil chamber via a valve when the pressure of the oil in the oil chamber is above a certain pressure.

[0005] Accordingly, in the art, during normal operation, excess oil from an oil chamber is removed at high pressure leading to a reduction in efficiency of the compressor.Summary of the invention

[0006] The inventors have identified the above-mentioned problem and challenge related to the control of a diaphragm compressor and solved the problem by the present invention as described below.

[0007] In an aspect, the invention relates to a diaphragm compressor comprising: ^ a compression chamber separated from a hydraulic fluid chamber by a multi- layered metal diaphragm, ^ a hydraulic fluid pressure sensor configured for measuring a hydraulic peak pressure inside said hydraulic fluid chamber, ^ a hydraulic fluid adjustment assembly, and ^ a controller, wherein said controller is configured to compare said hydraulic peak pressure value with a target pressure value wherein said target pressure value is higher than a discharge pressure from said compression chamber, and wherein said controller is further configured to, via said hydraulic fluid adjustment assembly, control: - injection of hydraulic fluid into said hydraulic fluid chamber if said target pressure value is higher than said hydraulic peak pressure value, and - removal of hydraulic fluid from said hydraulic fluid chamber if said target pressure value is below said hydraulic peak pressure value.

[0008] This is advantageous in that it has the effect that only the hydraulic fluid needed to establish a desired target pressure is introduced into the hydraulic chamber.

[0009] Further, this is advantageous in that removal of hydraulic fluid can be made without pressurizing the hydraulic fluid. Thus, without using energy to pressurize it prior to removing it and thereby increase efficiency of the compressor.

[0010] Further, this is advantageous in that it has the effect, that injecting and removing of hydraulic fluid can be made by controlling one and the same assembly i.e. both in terms of control and implementation, this inventive control is advantageous.

[0011] Measuring pressure of hydraulic fluid inside the hydraulic fluid chamber is advantageous in that direct real-time measurement tents to be more precise and faster than measurements made by external devices. Such external devices may include mechanical valves which are adjusted to open if needed based on sensed pressure. Measuring inside the hydraulic fluid chamber enable faster response than the known simpler mechanical valves and thereby a new level of adjustability which is based on real-time pressure measurements. Real-time response should here be understood at least as fast as to enable one measurement and an adjustment based hereon within the same compression cycle.

[0012] In an exemplary embodiment of the invention, said controller is configured to establish a delta pressure value between said target pressure value and said hydraulic peak pressure value, and to compare said delta pressure value with a threshold value, preferably one of a plurality of threshold values.

[0013] Establishing the delta value is advantageous in that it has the effect, that a measure for remaining gas in the compression chamber is established. Hence, if the delta pressure value zero i.e. the target pressure is equal to the hydraulic peak pressure the diaphragm leaves no volume left in the compression chamber and thus it is empty.

[0014] If the hydraulic peak pressure is above the target pressure, hydraulic fluid should be removed to not waste energy (to unnecessary compression) and reduce wear of the compressor component.

[0015] If the hydraulic peak pressure is below the target pressure, hydraulic fluid should be injected to ensure complete emptying of the compression chamber.Complete empty should be understood as, as empty for gas as possible / required, preferably with no gas pockets or a determined size of any remaining gas pockets.

[0016] If the delta value is between a removal threshold and an injection threshold (i.e. above the injection and below the removal threshold), the hydraulic peak pressure is considered sufficiently high and no control signal is established by the controller.

[0017] If the delta value is between a removal threshold and a upper error threshold, hydraulic fluid should be removed from the hydraulic chamber. If the delta valued is above the upper error threshold emergency stop should be initiated. Alternatively, emergency stop should be initiated if the hydraulic peak pressure is above an upper emergency stop threshold.

[0018] If the delta value is between an injection threshold and a lower error threshold, hydraulic fluid should be injected into the hydraulic chamber. If the delta valued is below the lower error threshold emergency stop should be initiated. Alternatively, emergency stop should be initiated if the hydraulic peak pressure is below a lower emergency stop threshold.

[0019] If injection or removal is required, the controller is controlling this via control of the adjustment assembly.

[0020] Hence, the delta pressure could be considered a pressure error between the high pressure peak and the target pressure. The sized of the delta pressure is used as input to and thus as one control parameter for a PID regulator that in an embodiment is controlling the flow (injection or removal) of the hydraulic fluid i.e. the size of the delta pressure would be considered proportional to the injection flow of hydraulic fluid. Hence, a small delta pressure lead to a small flow and vice versa.

[0021] In an exemplary embodiment of the invention said hydraulic fluid sensor is mounted on said diaphragm compressor so that it is in fluid communication with the hydraulic fluid in said hydraulic fluid chamber.

[0022] Such fluid communication may be established by drilling a sensor mounting hole in the compressor into the hydraulic fluid chamber. If the hydraulic fluid chamberis provided in an oilplate, the hole may be provided therein and at the outer side, the pressure sensor may be fastened e.g. by a thread so that no leakage is possible. In this way, even though the sensor is not physically inside the chamber, since it is in touch with the hydraulic fluid the pressure in the sensor mounting hole is the same as in the chamber due to the fluid characteristics.

[0023] In an exemplary embodiment of the invention said diaphragm compressor further comprises: ^ a gas pressure sensor located in a gas inlet, ^ a gas pressure sensor located in a gas discharge, and ^ a crank shaft position sensor.

[0024] This is advantageous in that it has the effect, that additional information related to the operation of the compressor may be obtained.

[0025] In an exemplary embodiment of the invention said diaphragm compressor further comprises a gas pressure sensor mounted on said diaphragm compressor so that it is in fluid communication with the gas in said gas compression chamber.

[0026] As a hydraulic fluid pressure sensor inside the hydraulic fluid chamber, a temperature sensor inside the gas compression chamber is advantageous in that it has the effect, that more precise and faster than measurements can be made compared to similar measurements made by external devices such as those that may be positioned in the gas inlet or gas discharge. Accordingly faster response to changes in pressure of the gas can be made by the controller.

[0027] In an exemplary embodiment of the invention said compressor is configured to establish a pressure of at least 50MPa, preferably at least 75Mpa and most preferably up to at least 100MPA.

[0028] This is advantageous in that it has the effect, that the compressor is able to work in a hydrogen refueling station where it is able to perform pressure consolidation and direct fill of receiving vessels of a fuel cell vehicle.

[0029] In an exemplary embodiment of the invention said compressor is configured to operate at an operation speed of at least 300rpm, preferably at least 500rmp and most preferably up to 800rpm

[0030] High operation speed is advantageous in that it increases the performance of the compressor in that a higher mass flow is provided. However, a high operation speed also increases wear of components (including the diaphragm). With this said an operation speed up to 1000 rpm has been proven to be possible.

[0031] In an exemplary embodiment of the invention said adjustment assembly comprising a member movable between a first end and a second end of a pressure booster vessel and wherein said controller is configured to control said movable member towards said first end if hydraulic fluid is to be injected into the hydraulic fluid chamber and towards said second end if hydraulic fluid is to be removed from the hydraulic fluid chamber.

[0032] This is advantageous in that it has the effect, that the adjustment assembly is able to take hydraulic fluid from the hydraulic fluid reservoir (or another source), pressurize it and inject it to the hydraulic chamber. At the same time the adjustment assembly is able to take hydraulic fluid from the hydraulic chamber and conduct it to the hydraulic fluid reservoir (or another vessel).

[0033] With this said, if only minor amounts are to be injected or removed, the mere displacement of the movable member is sufficient to establish the injection / removal.

[0034] The adjustment assembly may be fluidly connecting the hydraulic fluid chamber with the hydraulic fluid reservoir. A control valve may be fluidly connecting the hydraulic fluid chamber and a hydraulic fluid reservoir. With this said, it should be noted, that two hydraulic fluid reservoirs may exist. One for lubrication of the crank shaft and one acting as source for the injection of the hydraulic fluid.

[0035] In an exemplary embodiment of the invention said hydraulic fluid adjustment assembly comprises a pump controlled by said compressor control signal to inject hydraulic fluid into said hydraulic fluid chamber.

[0036] In an exemplary embodiment of the invention injection of said hydraulic fluid is provided by a mix of hydraulic fluid from said pump and from said pressure booster vessel.

[0037] In an exemplary embodiment of the invention said multi-layered diaphragm comprises a gas diaphragm, a hydraulic fluid diaphragm and a leakage diaphragm.

[0038] Having a multi-layered diaphragm comprising the three mentioned layers is advantageous in that they can be manufactured according to individual purposes. Hence, the gas diaphragm can be coated to meet requirements of an aggressive gas such as a hydrogen gas. The hydraulic fluid diaphragm can be coated to meet requirements of the hydraulic fluid and the leakage diaphragm is designed to ensure that gas and hydraulic fluid do not mix in case of a leakage of one of the gas or hydraulic fluid diaphragms.

[0039] In an exemplary embodiment of the invention a control valve is connecting said hydraulic fluid chamber with a fluid reservoir.

[0040] Preferably the control valve may be implemented as a pneumatic or electrically controllable valve. The control valve may also be referred to or implemented e.g. as a relief valve or an unloading valve.

[0041] A controllable valve is advantageous in that it has the effect, that removal of hydraulic fluid can be made fast and flexible. Fast should be understood as faster than by moving the piston one compression cycle. Flexible should be understood as at any time during a compression cycle.

[0042] Having a controllable closed fluid circuit between chamber and reservoir is advantageous in that if for some reason, the excess volume should be removed immediately e.g. within a few compression cycles such as within one or twocompression cycles. An example hereof could be emergency stop which preferably instantly should bring the compressor operation to stop.

[0043] Fast removal of hydraulic fluid may be needed to adapt to changes in inlet or discharge pressures occurring e,g, from changed of inlet pressure or vessel connected to the inlet of the compressor, from an end of a refueling of a receiving vessel e.g. of a fuel cell vehicle leading to an almost instantly stop of gas flow, etc.

[0044] In an exemplary embodiment of the invention hydraulic fluid is removed from said hydraulic fluid chamber via said control valve when said hydraulic peak pressure is above said target pressure.

[0045] This is advantageous in that it has the effect, that hydraulic fluid can be removed from the hydraulic chamber / pressure can be reduces faster by guiding hydraulic fluid out of the hydraulic chamber via the control valve than by waiting for the piston to move away from the diaphragm. Control of hydraulic fluid volume i.e. the removal or injection is sometimes referred to as modulating.

[0046] In an exemplary embodiment of the invention removal from said hydraulic fluid chamber is done by controlling said movable member.

[0047] In an exemplary embodiment of the invention a bleed valve is connecting said hydraulic fluid chamber with a fluid reservoir.

[0048] This is advantageous in that prior to starting up the compressor, the bleed valve may be opened. By opening the bleed valve e.g. in one second oil will be drained from the oil chamber and thereby a well-defined oil volume in the hydraulic chamber is established. More specific, in this way the gas pressure will force the diaphragm towards the inner wall of the oil chamber and a well-defined start position of the system is achieved. Such pre-start use of the bleed valve may be referred to as a reset of the hydraulic system. Such reset is useful when preparing for starting the compressor in that it will improve reliability of the compressor and ensure that start-up can be made quickly.

[0049] The fluid reservoir may be an independent vessel or it may be the hydraulic fluid reservoir.

[0050] Further, the bleed valve may be used to reset the volume of hydraulic fluid in the chamber if that is unknown during startup up of the compressor or simply to vent hydraulic fluid from the chamber.

[0051] In an exemplary embodiment of the invention removal from said hydraulic fluid chamber is done by controlling said movable member and said bleed valve.

[0052] It should be mentioned that preferably the removal of hydraulic fluid is based on active control i.e. a control signal from a controller that is controlling a valve, movable member, motor, pump or the like. It is not, as in the prior art, controlled simply be once adjusting a spring of a check valve or similar.

[0053] In an exemplary embodiment, said diaphragm compressor is controlled according to the method specified in the paragraphs

[0054] –

[0152]

[0054] In an aspect, the invention relates to a method of establishing and analysing a part of a hydraulic fluid pressure waveform of a diaphragm compressor, the diaphragm compressor comprises: ^ a compression chamber separated from a hydraulic fluid chamber by a diaphragm, and ^ a hydraulic fluid pressure representation unit communicatively connected to a controller, wherein said controller establishes said hydraulic fluid pressure waveform by control of said diaphragm compressor (2) and wherein said controller (7) establishes a delta pressure value between a determined target peak pressure value and a hydraulic peak pressure value at a discharge part of said hydraulic fluid pressure waveform, wherein said hydraulic peak pressure value is established by said hydraulic fluid pressure representation unit,wherein said controller establishes a compressor control signal based on said delta pressure value, and wherein said compressor control signal is used to control the operation of said compressor.

[0055] This method is advantageous in that it has the effect, that the behaviour of the diaphragm is controlled i.e. in a controlled manner it is possible to determine size of gas pocket in the gas chamber and to empty such gas pockets in a controlled manner. Controlled manner should be understood as contact may be established between diaphragm and gas chamber wall and thereby optimal control in terms of pressurize gas with a minimum of wear of the diaphragm is achieved. This is ultimately achieved with the delta pressure is zero i.e. the hydraulic peak pressure equals the target pressure.

[0056] As indicated above, it may only be necessary to establish part of a hydraulic fluid pressure waveform (the hydraulic fluid pressure waveform may also sometimes simply be referred to as a waveform) to perform an analysis of the waveform according to the invention. As an example of such analysis could be mentioned comparing pressure values from two discrete pressure measurements. From such comparison, it may be possible to determine if the compression cycle is at the inlet pressure (same value, around expected value), towards the discharge pressure (second higher than the first), at the discharge pressure (same value around expected value) or towards the inlet pressure again (first higher than the second). Note that the expected values are known e.g. from inlet pressure, outlet pressure, etc.

[0057] The waveform is generated by a compressor piston physically moving in a cylinder so as to facilitate movement of hydraulic fluid towards and away from the diaphragm in successive compression cycles. One compression cycle of the piston is defined by one revolution of the crankshaft i.e. a 360degree rotation thereof. In one compression cycle the waveform starts at an inlet pressure and increases towards a discharge pressure. According to the present invention the discharge part ends in a hydraulic peak pressure generated by injection of hydraulic fluid into the hydraulicchamber. Hence, as the skilled person would know (and therefore not disclosed in further details) the pressure of the waveform is linked to the distance between the piston and the diaphragm and thus indirectly also to the crankshaft position. Accordingly, the hydraulic fluid pressure waveform is established by control of the compressor e.g. based on a compressor control signal determining an amount of hydraulic fluid to be injected (or removed) from the hydraulic fluid chamber. Specifically, the method concerns analysing a hydraulic fluid pressure waveform established as consequence of e.g. a specific input to the compressor controller resulting in a change of the hydraulic fluid pressure waveform. This change is then analysed by the above-described method and based on this analysis a compressor control signal is established, which is used in the control the compressor i.e. in a feed- back control loop.

[0058] The analysis of the waveform or part hereof is advantageous in that it has the effect that control of performance of the compressor can be optimized and error detection can be implemented. Performance can be optimized in that injection and removal of hydraulic fluid can be regulated and an error can be detected if the established waveform or part hereof deviates from the expected.

[0059] A comparison between the target pressure and the hydraulic peak pressure resulting in a delta pressure value of zero is advantageous in that the operation of the compressor is sufficiently optimized. Meaning that all gas possible to leave the compression chamber has left the compression chamber.

[0060] In an exemplary embodiment of the invention said controller is identifying said part as a gas discharge part based on input from said hydraulic fluid pressure representation unit.

[0061] In an exemplary embodiment of the invention said hydraulic fluid pressure representation unit is a pressure sensor measuring the pressure of the hydraulic fluid inside said hydraulic fluid chamber.

[0062] Measuring pressure by a pressure sensor located inside the hydraulic fluid chamber (or in a channel directly fluidly connected to the inside of the hydraulic fluidchamber) is advantageous in that a precise and fast measurement of hydraulic fluid pressure can be established directly in the chamber. Such sensor may be mounted in a sensor hole or channel and measurements may be obtained directly i.e. not indirectly via valves and / or other equipment located outside the chamber.

[0063] In an exemplary embodiment of the invention said hydraulic fluid pressure representation unit is a sensing unit measuring the pressure of the hydraulic fluid in a conduit fluidly connected to said hydraulic fluid chamber.

[0064] Such sensing unit may be located in the conduit connecting the hydraulic fluid chamber to the hydraulic fluid reservoir, either at the inlet side or at the outlet side (if any) of the hydraulic fluid chamber.

[0065] In general, a sensor according to the present invention should be understood as a transmitter i.e. providing continuous feedback or alternatively providing discrete sensor data. A pressure sensor may e.g. provide analogue, electrical or visual data to the controller. In addition, external sensors may be implemented as a pressure regulating valve, check valve or similar.

[0066] In an exemplary embodiment of the invention said hydraulic fluid pressure representation unit is a gas sensor measuring a gas inlet pressure and wherein the pressure of the hydraulic fluid in said hydraulic fluid chamber is derived from said discharge gas pressure.

[0067] This is especially advantageous for determining the minimum pressure of the hydraulic fluid.

[0068] In an exemplary embodiment of the invention said hydraulic fluid pressure representation unit is a gas sensor measuring a gas discharge pressure and wherein the pressure of the hydraulic fluid in said hydraulic fluid chamber is derived from said discharge gas pressure.

[0069] At least during the discharge part of the wave form, the pressure is typically constant for two or more successive pressure readings. Accordingly, from this information, and as long as gas is leaving the compression chamber, the pressure ofthe hydraulic fluid may be the same as the pressure of the discharged gas. Hence, the hydraulic fluid pressure representation unit is typically implemented as a sensor measuring the pressure of hydraulic fluid directly or indirectly.

[0070] In an exemplary embodiment of the invention said part of said hydraulic fluid pressure waveform is established based on two or more datapoints received from said hydraulic fluid pressure representation unit.

[0071] Data points should be understood as values measured e.g. pressure values measured by a pressure sensor.

[0072] In an exemplary embodiment of the invention said compressor comprises a crank shaft position sensor and wherein at least part of said hydraulic fluid pressure waveform is established based in input from said hydraulic fluid pressure representation unit and said crank shaft position sensor.

[0073] Using e.g. a pressure sensor, such as the pressure sensor positioned inside the hydraulic fluid chamber, in combination with a crank position sensor enables predicting when e.g. the various parts of the waveform start and terminates. Hence, it is possible to determine with greater certainty e.g. when the pressure of the hydraulic fluid in the hydraulic fluid chamber is starting to increase toward the end of the gas discharge part (when the hydraulic pressure raise begins) and when to read the value of the hydraulic peak pressure.

[0074] Put in another way, this is advantageous in that based on the position of the crank in a compression cycle, a data point (measured pressure value) can be associated with a specific location of the waveform and thereby the hydraulic peak pressure can be established. Thus, information of a single point together with the location of the crank may be sufficient to derive where on the waveform a pressure measurement is established.

[0075] Hence, by mapping or reading pressure signals, from e.g. the pressure sensor inside the hydraulic fluid chamber, and correlated these with position information from a crank shaft position sensor, a waveform, part hereof or a single value can beestablished. Based on such relationship the control of the compressor, at least volume of hydraulic fluid in the hydraulic fluid chamber, can be optimized compared to known methods.

[0076] Further, analysis of a waveform or part hereof established as described above may be used to predict errors in the gas or hydraulic system associated with the compressor. Such error prediction may be optimized by information from gas inlet and / or gas outlet sensors. As an example of an error that is possible to predict could be mentioned a faulty gas check valve. An indication hereof is a change in the form of the pressure waveform (parts of the curve may shift) while the minimum and maximum pressures may remain unchanged.

[0077] It should be mentioned that the analysis, data acquisition and control mentioned in this document is preferably handled by the compressor controller but may in part or as a whole be handled by a dedicated controller different from the compressor controller. Any such controller may be a standard industrial programmable logic controller.

[0078] In an exemplary embodiment of the invention a volume of gas inside said compression chamber is determined based on knowledge of geometry of said compression chamber and position of said crank shaft.

[0079] The volume of the compression chamber and of the hydraulic chamber is defined by design and therefore known. The position of the diaphragm is related to the position of the crank shaft, hence from this knowledge, the volume occupied by the hydraulic fluid can be established. Thus, this volume subtracted the total volume of the two chambers equals the gas volume.

[0080] It should be mentioned that two or more methods of establishing the gas volume may be combined or one method may be used to verify the result of another method.

[0081] Information of the volume of gas in the compression chamber is advantageous in that movement of the diaphragm can be controlled based on this information.

[0082] In an exemplary embodiment of the invention a volume of gas inside said compression chamber is determined based on pressure readings from said hydraulic fluid pressure representation unit and on temperature readings from a hydraulic fluid temperature sensor.

[0083] The viscosity of a hydraulic fluid may change with temperature and thus the volume of the hydraulic fluid in the hydraulic chamber may change with its temperature. Accordingly, input from a temperature sensor together with input from a pressure sensor may be used to determine the volume of hydraulic fluid in the hydraulic chamber. This volume subtracted the total volume of the two chambers equals the gas volume.

[0084] In an exemplary embodiment of the invention a volume of gas inside said compression chamber is determined based on measurement of gas flow passing through a gas inlet into said compression chamber and out through a gas discharge out of said compression chamber.

[0085] Based on measurement of e.g. mass flow of gas into and out of the compression chamber may be used to determine the gas volume inside the compression chamber.

[0086] In an exemplary embodiment of the invention a volume of remaining gas inside the compression chamber is determined at least once during said discharge part of said hydraulic fluid pressure waveform.

[0087] Preferably, the volume of remaining gas is determined when the hydraulic peak pressure is reached i.e. at the point in time where pressure measured by the pressure representation unit such as the pressure sensor inside the hydraulic chamber is measuring its highest value. But in principle, any given time during the compression cycle, the gas volume remaining inside the compression chamber can be established.

[0088] The exact volume of remaining gas is unknown and thus it is estimated or derived from knowledge that mass flow increases with an increasing hydraulic peak pressure. This is true at least up to a pressure difference up to around 150bar between the discharge pressure and hydraulic peak pressure. Hence, from experience it known that at such pressure difference the compression chamber is emptied.

[0089] The compression chamber should at least in this context be understood as the volume between the diaphragm and the inner wall of the compression chamber in which gas which is able to be discharged via movement said membrane can be trapped. This volume may be referred to as dynamic in that it changes size with movement of the diaphragm.

[0090] In an exemplary embodiment of the invention said determined target peak pressure value is established based on information of said volume of remaining gas inside the compression chamber is.

[0091] This is advantageous in that it has the effect, that depending on the volume of remaining gas inside the compression chamber the target peak pressure value can be determined.

[0092] In an exemplary embodiment of the invention said determined target peak pressure value is calculated as the sum of a gas pressure associated with the compression chamber and an empty pressure value.

[0093] In an exemplary embodiment of the invention said determined target peak pressure value is calculated as the sum of said gas discharge pressure and said empty pressure value.

[0094] The determined target peak pressure value may also sometimes be referred to simply as the target pressure.

[0095] Accordingly, the target pressure is preferably combined by the empty pressure value and a pressure measurable in relation to the compression chamber such as the inlet pressure or discharge pressure. Thus, the empty pressure value is anadditional pressure that is added to the discharge pressure to ensure emptying of the gas chamber.

[0096] In an exemplary embodiment of the invention said empty pressure value is determine prior to operation of said diaphragm compressor.

[0097] The empty pressure value may be a fixed pressure determined based on tests and / or simulations.

[0098] The empty pressure value may vary in dependency of the e.g. the gas discharge or inlet pressure. Accordingly, the target peak pressure value may vary in dependency of e.g. the gas discharge or inlet pressure.

[0099] In an exemplary embodiment of the invention said empty pressure value is determined to be between 10bar and 200bar, such as between 75bar and 175bar such as 150bar.

[0100] The empty pressure value is determined as a trade-off between energy consumption, discharged gas, wear of compressor parts (mainly diaphragm).

[0101] In an exemplary embodiment of the invention said determined target peak pressure value is determined by said controller based on mode of operation of the diaphragm compressor.

[0102] The empty pressure value and thus the target pressure may be different depending on mode of operation of the compressor. The target pressure may be lower in a slow running / low discharge pressure mode of operation than in a high speed / high discharge pressure mode of operation.

[0103] Thus, the target pressure may in a slow / low-speed mode of operation be determined as a compromise between the time it takes to reach a target pressure in a receive vessel and the cost of energy, OPEX i.e. cost of wear of the compressor parts, cost of servicing, keeping noise below a threshold value, or the like.

[0104] In an exemplary embodiment of the invention said determined target peak pressure value is determined by said controller based on a change in one of said inlet pressure and said discharge pressure.

[0105] A change in inlet pressure may be initiated by a supply bank shift. A bank shift may result in a change of inlet pressure of several hundred bars.

[0106] A change in discharge pressure may be initiated by end of refueling i.e. flow through the gas chamber is stopped from one point in time to another. This timing in stopping may be predicted by the controller knowing the current pressure in the receiving vessel and the determined target pressure of the receiving vessel.

[0107] In an exemplary embodiment of the invention said delta pressure value is an average delta pressure value of delta pressure values established in two or more compression cycles.

[0108] Averaging the delta values i.e. establishing a moving average is advantageous in that it has the effect, that hysteresis is achieved. Hence, the effect of one single incorrect measurement is reduced and may not alone lead to change in the control of the compressor. On the other hand, the number of compression cycles over which the delta values are averaged should not be too high. If too many cycles are averaged, then fast response to e.g. a need of hydraulic fluid may be compromised. As an example, delta values between 2 and 15, such as between of 5-10 compression cycles may be averaged and still maintaining the fast response.

[0109] In an exemplary embodiment of the invention said delta pressure value is compared to two or more delta pressure value thresholds and when crossing one of said delta pressure value thresholds, said control signal is established.

[0110] It should be mentioned that a single delta value may be compared to the target pressure as well as an averaged delta value may be compared to the target pressure. If the delta value is zero i.e. if the hydraulic peak pressure is equal to the target pressure, no change of volume hydraulic fluid in the hydraulic chamber is needed. If below,hydraulic fluid should be injected and if above, hydraulic fluid should be removed. This may lead to a huge number of minor adjustments in the adjustment assembly.

[0111] Therefore, it is advantageous to establish delta value thresholds such as a upper threshold which may equal the target pressure and a lower threshold which may be in the range of ±25 bar from the target pressure.

[0112] Alternatively, or in addition, an averaged delta pressure value may be compared to the delta pressure value threshold.

[0113] The delta pressure value may as mentioned be compared to several threshold values. These threshold values may define ranges in which hydraulic fluid are to be removed, injected or maintained at current level.

[0114] Further, these threshold values may define error limits. Hence, if a delta pressure value is above or below one of these error limits, this may indicate a component is failing or is going to fail in a predicted future.

[0115] It should be mentioned that a single or two successive reading (data points) from e.g. a pressure sensor may also or in addition be compared to the threshold values. This is especially relevant to see if such data points are out of the expected range, if so, immediately stop of operation of the compressor may be required.

[0116] In an exemplary embodiment of the invention one of said two or more delta pressure value thresholds is a removal threshold value and wherein hydraulic fluid is removed from said compression chamber when said delta pressure value exceed said removal threshold value.

[0117] This is advantageous in that it at least has the effect, that energy used to turn the crank shaft around is saved and the discharge pressure can be reduced.

[0118] Accordingly, if the delta pressure value is above the removal threshold value (which may be equal to or just below the target pressure, preferably not above the target pressure), the volume of hydraulic fluid in the hydraulic fluid chamber is too high and hydraulic fluid have to be removed. Hydraulic fluid may be removed instantlyby opening the control valve (also sometimes referred to as unloading valve or relief valve) i.e. without waiting for the piston to move away from the diaphragm and without opening a control valve.

[0119] Instantly should be understood as within the same compression cycle as the operation cycle in which the delta pressure value exceeded the removal threshold. There is a relationship between the size of the delta pressure and the injection of the hydraulic fluid. This relationship is so that if the delta pressure is small only a small amount of hydraulic fluid is injected and if the delta pressure is high, large amount of hydraulic fluid is injected.

[0120] The control valve may be opened for as long time as the pressure, e.g. measured by the pressure sensor, is above the removal threshold.

[0121] If, after the removal, the delta pressure value is still, at the next comparison with the threshold value, above the removal threshold, hydraulic fluid is again removed, preferably in the same compression cycle. This may continue until the delta pressure value is below the removal threshold value.

[0122] In an exemplary embodiment of the invention one of said two or more delta pressure threshold is an upper error threshold value.

[0123] An upper error threshold value is advantageous in that if the delta pressure value is above such threshold, this may indicate an error which need appropriate action. Such action may be to derate or stop the operation of the compressor such as turning off the compressor motor.

[0124] In an exemplary embodiment of the invention one of said two or more delta pressure value thresholds is an injection threshold value.

[0125] Accordingly, if the delta pressure value is below the injection threshold value, the volume of hydraulic fluid in the hydraulic fluid chamber is too low and hydraulic fluid have to be injected in a subsequent compression cycle to ensure optimal operation of the compressor including faster pressurizing gas to a desired pressure in a receiving vessel. Injection of hydraulic fluid may be required to be able to establish sufficientpressure by the diaphragm into the compression chamber to ensure emptying it complete. If, after the injection, the delta pressure value is still, at the next comparison with the threshold value, below the injection threshold, hydraulic fluid is again in a subsequent compression cycle injected. This continuous until the delta pressure value is above the injection threshold value i.e. between the removal (target pressure) and injection thresholds.

[0126] In an exemplary embodiment of the invention one of said two or more delta pressure threshold is a lower error threshold value.

[0127] A lower error threshold value is advantageous in that if the delta pressure value is below, this may indicate an error which need appropriate action. Such action may be to derate or stop the operation of the compressor such as of the compressor motor.

[0128] It should be noted that the comparison of delta pressure values / hydraulic peak pressure values and threshold values may result in a compressor control signal and that this compressor control signal may be used to control the mode of operation of the compressor, compressor motor, control valve, bleed valve, etc.

[0129] In an exemplary embodiment of the invention said compressor control signal is controlling a hydraulic fluid adjustment assembly and thereby injection of hydraulic fluid into said hydraulic fluid chamber.

[0130] In an exemplary embodiment of the invention said compressor control signal is controlling said hydraulic fluid adjustment assembly and thereby removal of hydraulic fluid from said hydraulic fluid chamber.

[0131] This is advantageous in that it has the effect, that the same adjustment assembly is able to adjust the volume of hydraulic fluid inside the compression chamber by injecting hydraulic fluid into and removing hydraulic fluid from the compression chamber.

[0132] In an exemplary embodiment of the invention said hydraulic fluid adjustment assembly comprising a member movable between a first end and a second end of apressure booster vessel and wherein said controller is controlling said movable member towards said first end if hydraulic fluid is injected into the hydraulic fluid chamber and towards said second end if hydraulic fluid is removed from the hydraulic fluid chamber.

[0133] An adjustment assembly with a movable member in a fixed volume, is advantageous in that only the amount of hydraulic fluid needed to ensure correct volume of hydraulic fluid in the hydraulic fluid chamber can be obtained. The volume is controlled by controlling the position of the movable member between the first and second ends. Injection or removal of hydraulic fluid as a result of the comparison of the delta pressure value with the delta value pressure thresholds (in other words comparing the hydraulic peak pressure with the target pressure). A correct volume of hydraulic fluid is advantageous in that hydraulic peak pressure is controlled which minimize load on the diaphragm contrary to known systems where the same amount of hydraulic fluid is added to the chamber after each compression cycle. In such known systems the excessive hydraulic fluid is simply pushed out of the hydraulic chamber by the diaphragm. The energy needed to pressurize and subsequently push the pressurized hydraulic fluid out of the hydraulic fluid chamber is not used by the inventive volume control of the hydraulic fluid according to the present invention.

[0134] As mentioned, control of the hydraulic peak pressure should be understood as ensuring it is high enough to empty the compression chamber. Emptying or completely emptying the compression chamber should be understood as reached when the diaphragm is in contact with the inner wall of the compression chamber from edge to edge of the compression chamber both along the length and the width of the compression chamber.

[0135] In an exemplary embodiment of the invention said hydraulic fluid adjustment assembly is controlled asynchronously with the compression cycles.

[0136] This should be understood as during one compression cycle, the adjustment assembly does not necessarily need to both inject and remove hydraulic fluid from thehydraulic chamber. In fact in a plurality of successive compression cycles, the adjustment assembly may inject hydraulic fluid without removing and vice versa.

[0137] Such asynchronous control is advantageous in that the specifications of the adjustment assembly does not need to comply with high-speed requirements for being able to follow compression cycles. This reduces the costs of the components of the adjustment assembly.

[0138] In an exemplary embodiment of the invention a time period passes from said compressor control signal is established to said adjustment assembly is activated.

[0139] Typically, the compressor control signal is established by the compressor in the same clock period as the delta pressure is compared to the target pressure. Alternatively in the following 1-10 clock periods.

[0140] However, injection is preferably performed at inlet pressure and removal may be performed whenever suitable i.e. a time period after the compressor control signal is established. Thus, waiting e.g. until the inlet pressure part with injecting hydraulic fluid is advantage in that the pressure established in the adjustment assembly for being able to inject hydraulic fluid is reduced.

[0141] The main reason for introducing hydraulic fluid according to the present invention is to establish the hydraulic peak pressure. The discharge pressure is typically possible to establish simply be driving the piston up and down the cylinder. Injection may be needed to compensate for leakage e.g. between piston and cylinder.

[0142] However, movement of the diaphragm towards the inner wall of the compression chamber does not always follow a predictable path. The diaphragm may flex, perform a non-uniform bend or bend in an undesired / unpredictable profile and when such movement of the diaphragm occur, gas may be trapped in a gas pocket in the compression chamber. The gas pocket may occur in the area from the edge of the compression chamber to the gas discharge e.g. between the gas inlet and gas outlet because of the diaphragm covering the gas discharge before all gas has escaped thecompression chamber. Such gas pocket is undesirable in that it lead to a reduced efficiency of the compressor.

[0143] As mentioned, the normal discharge pressure established by the reciprocating piston is not sufficient to empty such gas pocket. Therefore, injection of an excess of hydraulic fluid is needed to establish the hydraulic peak pressure. As mentioned, the volume of injected hydraulic fluid is controlled to equal the volume of the gas pocket and therefore the compression chamber is emptied. As mentioned, a pressure between e.g. 130bar and 170bar above the discharge pressure has been proven to be sufficient at empty the gas pockets.

[0144] In an exemplary embodiment of the invention said hydraulic fluid adjustment assembly is injecting hydraulic fluid into said hydraulic chamber in a number of compression cycles not interrupted by a compression cycle in which hydraulic fluid is removed from said hydraulic chamber.

[0145] This is advantageous in that it has the effect, that the hydraulic peak pressure can be built up cycle by cycle. Not necessarily over successive cycles, a cycle with injection may be follow by a cycle with no injection which again may be followed by a cycle with injection. Thereby, compressor efficiency is increased as describe elsewhere in this document.

[0146] . As mentioned to optimize operation of the compressor including behaviour of the diaphragm, it may be necessary to remove hydraulic fluid. During normal operation, the piston establishes a pressure in the hydraulic chamber corresponding to the discharge pressure when moving towards the diaphragm. Thus, when the piston is moving away from the diaphragm, it is able to reduce the pressure correspondingly.

[0147] It should be mentioned, that a change of a process parameter may influence the needed oil volume and lead to the need of removal of hydraulic fluid. Such process parameters may include temperature, gas pressure variation, operation speed, etc.

[0148] In an exemplary embodiment of the invention said hydraulic fluid adjustment assembly is removing hydraulic fluid with a frequency that is lower than the compression cycle frequency.

[0149] This is advantageous in that it has the effect, that the correct pressure is reached within an acceptable time with adjustment assembly components that does not have to comply with requirements for the frequencies with the compressor is operating. As an example, a compression cycle frequency may e.g. be 13Hz and the changes to injection / draining (removal) flow of hydraulic fluid can be made at lower frequency, so that the desired flow may be updated e.g. 1, 2, 3, 4 or 5 times per second.

[0150] In an exemplary embodiment of the invention said hydraulic fluid adjustment assembly is initiating removing hydraulic fluid from said hydraulic fluid chamber when a piston of said compressor (2) is traveling away from said diaphragm.

[0151] The removal may be initiated after the piston has left the top dead center i.e. after the piston has travelled away from the diaphragm during a measurable time period. This is an effect of the asynchronous control of the removal leading to a flexible control of the adjustment assembly so that injection / removal of hydraulic fluid may be facilitated over several compression cycles. It should be mentioned that both injection and removing is actively controlled e.g. based on the established compressor control signal. Based on that signal, the controller is controlling the hydraulic fluid adjustment assembly actively to either inject hydraulic fluid, remove hydraulic fluid or maintain level of hydraulic fluid in the hydraulic fluid chamber. This is in contrast to known systems where e.g. a flexible member such as a spring is passively controlling the removal of hydraulic fluid.

[0152] In an exemplary embodiment of the invention the method is implemented in a diaphragm compressor according to any of the paragraphs

[0006] –

[0053] The drawings

[0153] For a more complete understanding of this disclosure, reference is now made to the following brief description, taken in connection with the accompanyingdrawings and detailed description, wherein like reference numerals represent like parts. The drawings illustrate embodiment of the invention and elements of different drawings can be combined within the scope of the invention: Fig. 1 disclose a principle illustration of a compressor according to the present invention, Fig. 2a disclose a detailed illustrated of a compressor according to the present invention, Fig. 2b illustrates examples of gas pockets in a compression chamber Fig. 3 illustrates a control flow chart, Fig. 4 illustrates a pressure waveform, Fig. 5 illustrates a hydraulic fluid adjustment assembly, and Fig. 6 illsutrates two waveforms with different target pressures.Detailed description

[0154] The present invention is described in view of exemplary embodiments only intended to illustrate the principles and implementation of the present invention. The skilled person will be able to provide several embodiments within the scope of the claims.

[0155] Fig. 1 illustrates an example of a diaphragm compressor 2 according to the present invention. The diaphragm compressor 2 is illustrated in a side view. The stipulated lines are defining the plates in which the cavity is provided. These plates may be referred to as oil platen and gas plate. In the oil plate a cavity referred to as hydraulic fluid chamber 4 or simply fluid or oil chamber is made and in the gas plate a cavity referred to as gas chamber 3 is made. The inner walls of these chambers 3, 4 may be equipped with tracks or recesses which are used to guide hydraulic fluid (also referred to simply as oil) and gas respectively in predetermined path / direction. The two chambers 3, 4 are separated by a diaphragm 5 which is made of several sheets of a metal or alloy. Alternatively, the diaphragm is made of a composite material.

[0156] The design of the oil and gas chambers 3, 4 and of channels leading oil and gas to and from these chambers 3, 4 together with the bending profile of the diaphragm 5 may in some situations allow gas pockets in the gas chamber 3. Such gas pockets are undesired in that it lead to a reduced efficiency of the compressor.

[0157] Accordingly, in addition to increase efficiency be removing these gas pockets efficiency may also be increase by reducing the discharge pressure PD. Hence, if a discharge pressure of e.g. 500bar is chosen, then less hydraulic fluid is needed in the hydraulic chamber 4 compared to a discharge pressure of e.g. 800bar. Thus, the volume of the compression chamber is a bit larger thereby allowing a bit more gas per cycle leading to an increased efficiency.

[0158] A reciprocating movement of a piston 8 in a cylinder 9 is facilitated by a crankshaft 10 mechanically connected to the piston 8. The piston 8 then forces oil from the cylinder and into the oil chamber 4. As the piston continuous towards its top dead center, it increases the pressure of the oil in the chamber. Thereby, the diaphragm 5 ispushed towards the gas chamber 3 and thereby compresses the gas comprised therein to a certain pressure until a discharge valve in the gas discharge 18 opens. The position of the piston may be derived from crankshaft position which may be measured or derived from information provided by a crankshaft position sensor 12.

[0159] It should be mentioned that by using a timer of a controller 7, the position of the crank shaft may be derived. This way of determining the position of the crank shaft obviously would require at least one correlation between timer and crank shaft position. Further, it would be preferred that the relationship therebetween is updated continuously to avoid drifting of e.g. time to position or vice versa.

[0160] The oil is comprised in a close circuit which could be said to start in a hydraulic fluid reservoir 23. If oil is needed in the oil chamber 4, oil from this reservoir 23 may be guide to the oil chamber 4 via a first conduit path 11a. A hydraulic fluid adjustment assembly 13 is controlling the oil flow to and preferably also from the oil chamber 4. The oil flow is controlled based on input from one or more sensors such as one or more hydraulic fluid pressure representation units 6.

[0161] Oil may be provided to the oil chamber from a not illustrated reservoir that is different from the reservoir 23. In this case, the main purpose of the reservoir 23 is lubrication of the crank shaft.

[0162] In case of an anomaly, oil may be guide from the oil chamber 4 to the reservoir 23 via a second conduit 11b.

[0163] A gas inlet 17 is fluidly connected to a not illustrate gas supply vessel e.g., of a supply storage, comprising gas. Gas is supplied to the compression chamber 3 with a pressure that is referred to as a gas inlet pressure. Accordingly, gas with an inlet pressure is allowed access to the gas chamber 3 via the gas inlet when a not illustrated valve hereof is opened. Similarly, a gas discharge 18 is fluidly connected to a not illustrate receiving vessel. Accordingly, gas discharged from the gas chamber is used to increase pressure in a not illustrated receiving vessel via a not illustrated valve of the gas discharge 18.

[0164] The oil pressure is typically equal to the gas discharge pressure when the gas discharge valve opens in the gas discharge 18. Hence, the oil pressure regulated according to a required discharge pressure of the compressor and thus, the oil level (pressure and / or volume) can be reduced when requirements to gas discharge pressure are low to reduce wear of diaphragm, and elevated when discharge pressure needs to be higher.

[0165] The flow of gas and oil is controlled by a controller 7 which is communicatively connected to the valves and sensors required for controlling gas and oil flow according to the present invention. Just to mention a few, the sensor 6a-6n, 12 and the adjustment assembly 13 may be communicating with the controller 7.

[0166] It should be mentioned that a temperature sensor may provide temperature information of gas temperature inside the compression chamber. Such temperature sensor may be implemented as the pressure sensor 6a in or with access to the hydraulic chamber.

[0167] A hydraulic fluid temperature sensor (not illustrated) may be provided. Such temperature sensor may be mounted and located as the hydraulic fluid pressure sensor 6a.

[0168] A bleed valve 22 may be implemented either as illustrated connected to the conduit 11a or with a separate conduit to the chamber 4. The bleed valve may be used in case of emergency, for venting or preferably before / during start up if the volume in the chamber 4 is unknown.

[0169] The bleed valve may be manual or automatic. An automatic bleed valve 22 may be during a start up routine where the chamber 4 is emptied by opening the bleed valve and letting the gas pressure push the diaphragm to contact the inner wall of the chamber 4. In this way a known position of the diaphragm and a known volume of oil is provided which is advantageous during start up of the compressor. Especially if also the position of the crankshaft and thereby piston 23 is also known e.g. from a crankshaft position sensor 12.

[0170] The pressure of the oil is measured by a hydraulic fluid pressure representation unit 6 such as a hydraulic fluid pressure sensor 6a positioned so as to be able to measure the oil pressure inside the oil chamber 4. Alternatively, the hydraulic fluid pressure representation unit 6 may be implemented as a sensing unit 6b located in fluid connection 11a between the oil chamber 3 and oil reservoir 23. In yet another alternative, the hydraulic fluid pressure representation unit 6 is implemented as a sensing unit 6c in the second conduit 11b. In yet another alternative, the hydraulic fluid pressure representation unit 6 may be implemented as a gas sensor 6d, 6e which may be located to measure gas inlet pressure or gas discharge pressure. In yet another alternative, the hydraulic fluid pressure representation unit 6 may be implemented as a gas sensor 6n located inside or fluidly connected to the compression chamber 3. Such sensor 6n may be provided in the chamber 3 as the sensor 6a in the hydraulic chamber 4. Various types of pressure sensors may be used such as piezoelectric sensors.

[0171] Fig. 2a illustrate a diaphragm compressor 2 in an embodiment where the piston 8 is not reciprocating perpendicular to the rest position of the diaphragm 5. Such design is especially advantageous if the chambers 3, 4 are non-circular such as having an oblong shape when seen in a top view (such top view is not illustrated). In this way it may be possible to push gas from the gas inlet 17 towards the gas discharge 18 by pressurizing the end (of an oblong shaped chamber) of the chamber 4 closest to the gas inlet 17 first. Then continue pressurizing towards the discharge 18 thereby establish a wavelike movement of the diaphragm 5. It should however be mentioned that it is possible to implement the present invention in other types of compressors e.g. where the piston is moving perpendicular to the rest position of the diaphragm.

[0172] A pressure sensor 6a is connected to the oil plate. The pressure sensor 6a is illustrated as being able to be in contact with the oil in the chamber 4. The sensor 6a does not need to extend all the way to the interior of the chamber 4. It may be sufficient that the sensing part is located inside a passage in fluid communication with the chamber 4 as illustrated in Fig. 2a.

[0173] The pressure sensor 6a is communicating with the controller 7 which may be an industrial controller such as a programmable logic controller typically referred toas a PLC. Such PLC communicate via I / O modules with valves, sensors, pumps, etc. Such communication may be via electric wires or wirelessly. Thereby providing the PLC with measurements of the oil pressure preferably real-time.

[0174] The oil chamber 4 may be connected to the oil reservoir 23 via a control valve 19 in the second conduit path 11b. According to the present invention, if present, it is mainly for use in emergency to protect e.g. the diaphragm in case the compressor is acting unexpected / uncontrollable in one way or the other. Hence the control valve 19 ensure the pressure inside the oil chamber 4 does not exceed a predetermined value. This predetermined value may be a threshold / opening pressure of a control valve 19.

[0175] It should be noted that in theory, the bleed valve 22 (together with other components such as the controller, pressure sensor and air for controlling status of the valve) may be controlled to have the same functionality as the control valve 19. It should however be noted, that using the control valve which is opening at a threshold pressure is more reliable e.g. in an emergency situation.

[0176] As the skilled person would recognize such control valve 19 in a second conduit path 11b is how the oil pressure is controlled in most systems for controlling the hydraulic pressure in prior art diaphragm compressor. Not only in emergency situations but also during normal operation.

[0177] The oil chamber 4 may be connected to the oil reservoir 23 via a bleed valve 22. The bleed valve 22 may be used during start up if the volume of hydraulic fluid in the hydraulic chamber is unknown. In this situation, the compression chamber is pressurized while the bleed valve 22 is opened. In this way the hydraulic chamber 4 is emptied. Then a minor / known volume of hydraulic fluid may be injected, and the compressor can be started up with knowledge of volume in the chamber 4. Further, the bleed valve 22 may be used for venting the hydraulic chamber 4 in case this is necessary.

[0178] The injection and removal of hydraulic fluid may according to the present invention be made via the same conduit namely the conduit 11a connecting the hydraulic chamber 4 with the hydraulic adjustment assembly 13. This adjustmentassembly 13 comprise an intensifier / pressure booster 21 which in an embodiment comprises a movable member 14. Further, the adjustment assembly 13 comprises a first, second and third valve 8a, 8b, 8c and a pump 9. These valves, pump, booster, etc. may together be referred to as the adjustment assembly 13. The adjustment assembly 13 is explained in further details with respect to fig. 5.

[0179] As would be known by the skilled person, that the diaphragm 5 does not always behave as expected especially not at high speed such as above or between 500- 800rpm. The diaphragm may flex i.e. move towards the inner wall of the compression chamber in a wavelike manner where the “wave” may close the gas discharge 18 before all gas escape the chamber 3. It may move in a non-uniform profile also resulting in a risk of closing the gas discharge 18 before all gas escapes chamber 3. It may move in a uniform profile where gas is trapped in a gas pocket between the inlet and discharge also preventing gas from escaping the compression chamber 3

[0180] Two such possible gas pockets GP1 and GP2 are illustrated in fig.2b. Fig.2b illustrates part of the compression chamber 3, the diaphragm 5, gas inlet 17 and gas outlet 18. As note, part of the two gas pockets are overlapping.

[0181] It has been found from test and simulations that a pressure between 75bar and 225bar in the hydraulic chamber above discharge pressure is sufficient to empty the compression chamber independent of the behaviour / profile of the diaphragm. More specifically pressures between 100bar and 200bar, such as between 125bar and 175bar has turned out to be sufficient to empty gas pockets such as GP1 and GP2. In a particular embodiment, a pressure of 150bar above discharge pressure has been determined as target pressure for the hydraulic peak during a discharge part of a pressure waveform such as the one illustrated in fig.3.

[0182] The compression ratio of the compressor 2 is known by design and may e.g. be 1:2, 1:2,5, 1:3 and so on. Hence, in an embodiment where the compressor 2 has a compression ratio of 1:2, if the inlet pressure is 400bar, the discharge pressure can be up to 800bar. The 800bar pressure, of this example, provided by the piston at its top center point may not (at least not at high speed i.e. above e.g. 800rpm) be sufficient toforce the diaphragm to shape long the inner wall of the compression chamber i.e. to push the remaining gas towards a closed discharge outlet with sufficient pressure to force the diaphragm to open a passage from the gas pocket to the discharge.

[0183] To ensure complete emptying of the compression chamber of such compressor, also when this operates at high speed, the pressure in the hydraulic chamber should be up towards and preferably at the target pressure. Thus, using a target pressure of 150bar as example, if the discharge pressure is 800bar, the pressure in the hydraulic chamber should be 950bar to ensure that no gas remain in the compression chamber at the end of a discharge part of the waveform.

[0184] Thus, a higher pressure is needed than can be provided with the piston and oil available in the chamber to completely empty the compression chamber. This has also been recognized in the prior art at described above. However, the inventors of the present invention have suggested an alternative way of achieving this higher pressure. More specifically, they have invented a controllable adjustment of this pressure which does not necessarily empty the compression completely at every cycle, but instead is using a number of cycles to establish this pressure required to do so as described below.

[0185] Fig. 3 illustrates a flow chart according to which the method of controlling the hydraulic peak pressure HPP of the present invention is explained.

[0186] In a first initial step, a target pressure TP is determined. The target pressure TP is determined to ensure complete emptying of the compression chamber as a trade- off between degree of emptying and wear of e.g. the diaphragm. The target pressure TP may as described above be found based on simulations, test runs of the compressor at different operation conditions, etc.

[0187] Such simulations and / or test runs may result in a target pressure algorithm. Once established a target pressure for a given operation condition of the compressor may be determined based on one or more input parameters from the list comprising gas and oil temperature, compressor RPM, gas inlet pressure and discharge pressure.

[0188] In a simple implementation the target pressure algorithm is a relationship between discharge pressure and desired target pressure. Such relationship may be provided in a table format where a discharge pressure DP specifies a certain target pressure TP. As an example, the target pressure TP may be 50bar or more (up to e.g. 150bar or 200bar) higher than the discharge pressure DP.

[0189] A more advanced target pressure algorithm is multiplying the target pressure associated with a given discharge pressure with a factor the size of which is depending on operation speed of the compressor. The higher RPM, the higher target pressure. This is because the time to empty the chamber 3 is reduced when the operation speed is increased.

[0190] The target pressure algorithm may also be based on the relationship between gas inlet pressure and discharge pressure of the gas from the chamber 3.

[0191] Accordingly, a target pressure is determined that is e.g. 125bar higher than the desired discharge pressure. This means that the target pressure is dynamic and selected / determined to match the current discharge pressure requirement to the compressor.

[0192] In fact, a whole range of target pressures may be determined one for each relevant discharge pressure. This plurality of target pressures may be stored in a look- up table used by the controller to determine target pressure during operation of the compressor. This especially relevant if the delta pressure is not the same for each discharge pressures.

[0193] As will be described below, the hydraulic peak pressure is controlled to match the running conditions and not just as in the prior art be optimized to high / nominal gas discharge. Hence, according to the present invention, in each compression cycle the hydraulic peak pressure may be adjusted as consequence of the determination of a new target pressure. A new target pressure is determined as consequence of a change in requirements to discharge pressure. In this way, the volumetric efficiency is increased especially at partial or low discharge pressures compared to prior art systems. this is because if the target pressure is too high, the compressibility of the hydraulic fluid inthe system starts to reduce the volumetric efficiency. This is because some of the stroke provided by the piston stroke is used to compress and expand the hydraulic oil, and this part of the piston stroke can therefore not be used to compress gas. Thus, a controllable target pressure according to the present invention can improve volumetric efficiency at least when operating at partial or low discharge pressure.

[0194] As mentioned, step S1 is initial hence, once determined this step S1 do not need to be included in the flow.

[0195] In the second step S2, the hydraulic peak pressure HPP is determined. In an embodiment, the hydraulic peak pressure HPP is simply determined by a pressure reading from the pressure senor 6a. Hence, the hydraulic peak pressure HPP is the highest pressure in the hydraulic chamber 4 during one revolution of the crank shaft 10. The hydraulic peak pressure HPP is the sum of the discharge pressure DP and a boost volume pressure BVP. At the discharge pressure DP, the discharge valve opens and gas with the discharge pressure leaves the compression chamber 3. To increase the likelihood that the chamber 3 is completely emptied a boost volume of hydraulic fluid is injected creating the pressure increase between the discharge pressure and the hydraulic peak pressure HPP.

[0196] The hydraulic peak pressure HPP may be established each revolution of the crank shaft 10 and provided to the controller 7 if not established by the controller 7. Alternatively, the controller 7 may establish an average hydraulic peak pressure and use this to establish the delta pressure ('P) in step S3.

[0197] In the third step S3, a delta pressure ('P) is determined as the difference between the hydraulic peak pressure HPP and the target pressure TP. Hence, the delta pressure 'P is a measure of missing pressure in the hydraulic chamber 4 in order to ensure that the diaphragm 5 is able to empty compression chamber 3 for gas.

[0198] A relationship exists between an increase of volume of hydraulic fluid in the hydraulic chamber 4 and an increase of the hydraulic peak pressure HPP. This relationship is a non-linear relationship. Accordingly, the delta pressure 'P is used asbasis for the adjustment of hydraulic fluid in the fluid chamber 4. This is adjustment is handled by the controller 7, more specifically it may be handled by a PID regulator of the controller 7 sending control signals to the adjustment assembly 13.

[0199] If the hydraulic peak pressure HPP is below the target pressure TP hydraulic fluid is injected. If the hydraulic peak pressure HPP is above the target pressure TP hydraulic fluid is removed. The injection and removal are performed in a fourth step S4 by the adjustment assembly 13. The adjustment assembly 13 is described in further details below with respect to fig. 5.

[0200] The principle of the control of the hydraulic peak pressure is that hydraulic fluid is injected and then the flow starts again from step S2 until the hydraulic peak pressure HPP is equal to the target pressure TP (or an acceptable distance from the target pressure TP).

[0201] The same principle is used when hydraulic fluid is to be removed from the hydraulic chamber 4. The possibility to control the removal of oil by the adjustment assembly is of particular relevance and is where the method of the present invention is superior to known system. Removal according to the present invention e.g. in the situation where the discharge pressure is reduced is preferably done one cycle after the other. In this way the removal is controlled an status such as positions and volumes are known. This is contrary to the state of the art systems which works much like opening the bleed valve i.e. uncontrolled removal of oil from the oil chamber.

[0202] Hence, when the hydraulic peak pressure HPP is equal to the target pressure TP (delta pressure 'P is zero or close to zero), is it then possible to regulate oil injection needed to compensate for leaking oil e.g. at the piston and thereby maintain a small size delta pressure (delta pressure 'P close to or at zero).

[0203] Hence, the target pressure TP may represent a volume of hydraulic fluid corresponding to a remaining gas volume. The volume of hydraulic fluid which is needed to discharge this remaining gas volume from the compression chamber is thus over one or more compression cycles injected into the hydraulic chamber.

[0204] Hence, the volume of hydraulic fluid in the compression chamber can be said to be controlled based on the volume of remaining gas in the compression chamber. The gas volume may be a measure for the control of injection / removal of hydraulic fluid in / from the hydraulic chamber. At the same time, efficiency of the compressor is increased in that all gas in the compression chamber is discharged. Put in another way, by the target pressure the size of gas pocket is controlled and when the hydraulic peak pressure equals the target pressure, the diaphragm ensures that there are no gas pockets in the gas chamber because contact between the diaphragm and the inner wall of the gas chamber is established. The force with which this contact is made is thereby indirectly determined by the target pressure.

[0205] In this way overshoot is avoided. Overshoot should be understood as a hydraulic pressure higher than the target pressure. Hence, if overshoot occurs contact is made between diaphragm and the wall of the cavity defining the gas chamber with a force that is larger than needed to empty the gas chamber leading to unnecessary wear of the diaphragm.

[0206] Accordingly, two type of gas pockets could be said to exist. One type, the size of which is regulated by the size of the target pressure and thus the hydraulic peak pressure. Another type which occurs if the diaphragm closes the discharge (see fig. 2b), this second type of gas pocket is, as the first type, emptied by increasing hydraulic peak pressure. If the target pressure is determined to be sufficiently high, this second type of gas pocket is emptied.

[0207] It should be noted that when referring to completely empty, there might still be gas in certain conduits or recesses in the gas chamber. Further, it should be mentioned that even though the ideal scenario is extremely hard to obtain, the present invention gets much closer thereto than conventional systems (such as the mentioned prior art above). In such systems volume of hydraulic fluid is not established and “enough” hydraulic fluid is therefore injected, leading to excess hydraulic fluid is pushed out of the hydraulic chamber in each cycle, again leading to inefficiency.

[0208] The speed with which the volume of hydraulic fluid is injected or removed is determined by design / geometry of the compressor and the hydraulic fluid adjustment assembly. As a non-limiting example, if the hydraulic fluid chamber comprises a volume of 0,1L to 3L of hydraulic fluid in contact with the diaphragm,

[0209] An example of an acceptable distance between the target pressure and the hydraulic peak pressure may be between ±50bar such as ±40 bar such as ±25bar.

[0210] Fig. 4 illustrates a pressure waveform 1 of pressure in the hydraulic chamber 4 during one revolution of 360q of the crank shaft 10. The waveform 1 may be referred to as comprising several parts including an inlet pressure 1a where the distance between piston 8 and diaphragm is, is moving towards or moving away from its bottom dead center. The pressure in the hydraulic chamber 4 is during this part of the curve determined at least partly from the pressure of the gas source which is connected to the gas inlet 17 of the compression chamber 3.

[0211] When the piston 8 is moving towards the top dead center the pressure increase toward a discharge pressure. This part of the waveform is denoted 1b. A small convex part and a small concave part at the beginning of the parts 1a and 1c is illustrated to indicate pressure drop over the gas inlet and discharge valves when these are opening. Thus, the pressure in hydraulic fluid need to drop below the inlet pressure before gas enters the compression chamber 3.

[0212] It should be mentioned that it is possible to compress the hydraulic fluid a bit. Hence, when the piston starts to move back from its top dead center, a short time will elapse before the pressure starts to decrease. This is because the compressed hydraulic fluid will first expand before pressure start to decrease. As an example, a compression of 5% of the hydraulic fluid may be seen.

[0213] When the gas discharge valve is opened the discharge pressure DP is maintained indicated by part 1c. The pressure increase provided by the piston moving towards the diaphragm is compensated by the gas leaving the gas discharge 18 leading to the substantially stabile pressure during this period.

[0214] Towards the end of the part 1c, the piston is continuing to move towards the diaphragm and its top dead center. And as there is no gas leaving the gas discharge the pressure increases towards the hydraulic peak pressure HPP as the diaphragm is forces against the inner wall of the compression chamber 3.

[0215] As described above in relation to fig. 2b, the diaphragm 5 may establish gas pockets GP1, GP2. These are the reason for boosting the hydraulic chamber 4 with hydraulic fluid and thereby enabling the emptying of these pockets.

[0216] The part 1n of the waveform 1 illustrates the pressure drop established when the piston moves away from the diaphragm again.

[0217] According to the present invention, injection and removal of hydraulic fluid is done asynchronously with the movement of the piston. More specifically, the frequency with which hydraulic fluid is injected is slower than the frequency with which the piston is moving up and down in its cylinder. Therefore, in one embodiment of the present invention, the adjustment of hydraulic pressure is done with a frequency that is lower than the frequency with which the piston is moving (compression cycle).

[0218] Fig. 5 illustrates an adjustment assembly 13 according to an embodiment of the invention. The adjustment assembly 13 may be controlled by a PID regulator which may be comprised by the controller 7.

[0219] The adjustment assembly 13 comprises a pressure booster 21 comprising a first low-pressure end 15 and a second high-pressure end 16. The second end 16 is a high-pressure end fluidly connected to the hydraulic chamber 4 via the conduit 11a. The first end 15 is a low-pressure end fluidly connected to a hydraulic fluid reservoir 23.

[0220] A movable member 14 comprises a high-pressure part 14a and a low-pressure part 14b. These parts may be piston like parts moving in cylinder like volumes. Hence, by knowledge of these cylinder like volumes, specifically the high-pressure part 21a, knowledge of volume of hydraulic fluid injected into the chamber 4 by a certain displacement of the movable member is available. As a nonlimiting example, adisplacement of the high-pressure end 14a with 1mm may lead to an injection of 0.1L / min of hydraulic fluid into the chamber 4.

[0221] The valves 8 of the booster 21 may be implemented as a multi-way valve or as one or more single way valves or a combination thereof. They may be implemented as proportional valves, electro-hydraulic valves and / or other suitable types of valves.

[0222] Between the booster 21 and the reservoir 23 the valve 8a referred to as first valve 8a is positioned. This valve 8a is positioned at this location to control flow from the booster 21 to the reservoir 23 in case hydraulic fluid is to be removed from the hydraulic chamber 4. Further, the first valve 8a has to control flow of hydraulic fluid from a pump 9 to the low-pressure part of the booster 21 in case hydraulic fluid has to be injected to the hydraulic chamber 4. Hence, by adding hydraulic fluid with a low pressure the movable member 14 is pushed towards the second end 16 and thereby hydraulic fluid with high-pressure is pushed towards the chamber 4.

[0223] The adjustment assembly 13 may further comprise a second valve 8b which is connected between the booster 21 and the chamber 4. The main purpose of the second valve 8b is to control flow of hydraulic fluid between the fluid reservoir 23 and the high-pressure part 21a (between a high-pressure end 14a of the movable member 14 and the second end 16) of the booster 21.

[0224] By control of the second valve 8b, additional hydraulic fluid can be injected into the high-pressure part 21a of the booster 21. This may be necessary if hydraulic fluid has been injected to the hydraulic chamber 4 and thereby the high-pressure end 14a is moved all the way up to or close to contact with second end 16.

[0225] A pump such as the pump 9 may be connected between the second valve 8b and the reservoir 23 which, when the second valve 8b is open may facilitate flow of hydraulic fluid into the high-pressure part 21a. Alternatively (or in addition), the movable member may be moved away from the second end 16 with the second valve 8b open and thereby hydraulic fluid may be sucked into the high-pressure part 21a without the pump 9.

[0226] In the same way, a volume of hydraulic fluid that is larger than the volume of the high-pressure part 21a may need to be removed from the hydraulic fluid chamber 4. In this situation, by moving the movable member 14 away from the second end 16 and thereby increasing the volume of the high-pressure part 21a, hydraulic fluid may be removed from the hydraulic fluid chamber 4. This of course may require a coordinated opening of the third valve 8c. When the movable member is not able to move further away from the second end 16, the third valve is closed, the second valve is opened and the movable member 14 is moved towards the second end pushing the hydraulic fluid into the reservoir 23.

[0227] A third valve 8c may be positioned between hydraulic fluid chamber 4 and the high-pressure end 16. Such third valve may be used to control if removal or injection is possible by allowing flow between the chamber 4 and the high-pressure part 21a or reservoir 23.

[0228] Uncontrolled removal of hydraulic fluid may be facilitated by opening the second and third valves 8b, 8c. Controlled removal of hydraulic fluid may be facilitated by opening the third valve 8c and increasing the high-pressure part 21a by displacing the movable member 14.

[0229] It should be mentioned that a stabilizer 20 may be provided. The stabilizer 20 may be considered as part of the adjustment assembly 13 or not. The purpose of the stabilizer 20 is to average the pressure at the third valve / high-pressure end 26. Therefore, the stabilizer may also be referred to as a modulating device for modulating hydraulic fluid volume and / pressure. The pressure in the hydraulic fluid chamber 4 may change between e.g.1200bar at the hydraulic peak pressure HPP and e.g.400 bar inlet pressure just to give a non-limiting example. In this example, the pressure changes 800bar per cycle in the hydraulic chamber 4 which is lead to higher wear of components than a smaller pressure change. Hence, the stabilizer 20 may facilitate an averaging of this pressure change to reduce load / wear on the third valve 8c / booster 21.

[0230] The stabilizer 20 may be implemented as a thin pipe with inner chicanes that restricts the free flow of hydraulic fluid through the pipe and thereby reduces the pressure at the end of the pipe towards the booster 21.

[0231] It should be mentioned that a non-illustrated valve may be positioned between the chamber 4 and the stabilizer 20 to be able to ensure that no hydraulic fluid enters the stabilizer 20 unless allowed to by opening such valve.

[0232] It should be noted that the fluid reservoirs 23 mentioned in this document may be the same or separate reservoirs independent of how they are illustrated in the figures.

[0233] As illustrated, between to the two ends 15, 16 of the booster 21 a movable member 14 is positioned. With the movable member 14 it is possible to push hydraulic fluid towards the hydraulic chamber 4 by displacing the movable member 14 towards the second end 16 (reducing the volume of the high-pressure part 21a). In the same way suck hydraulic fluid away from the hydraulic chamber 4 by displacing the movable member towards the first end 15 (increasing the volume of the high-pressure part 21a).

[0234] The displacement of the movable member 14 may be controlled by a hydraulic pump injecting hydraulic fluid into the low-pressure part 21b. This pump may again be controlled the controller 7. The controller 7 may also control the valves 8 and pumps 9. Position feedback of the movable member 14 may be provided to the controller 7 from a non-illustrated position sensor.

[0235] It should be mentioned that the adjustment assembly 13 alternatively may be implemented by one or more of the following components. Valves 8 designed for control and / or metering of hydraulic flow, a low-pressure oil motor coupled with a gear pump, an electric (servo)motor , radial piston pump, electrically driven hydraulic pump, a hydraulic intensifier / booster 21, etc.

[0236] Fig. 6 illustrates that by changing the target pressure TP, the pressure waveform 1 change accordingly. Hence, a first waveform 1a is controlled with a firsttarget pressure TP1 associated with a high discharge pressure DP1. This waveform is similar to the second waveform 1b controlled with a reduced target pressure TP2 associated with a lower discharge pressure DP2.

[0237] As illustrated, the size of the target pressures TP1, TP2 i.e. the pressure between the discharge pressure DP and the target pressure TP may be reduced as the discharge pressure is reduced.

[0238] This is an example of the dynamic target pressure and therefore dynamic hydraulic peak pressure the latter changing as consequence of the change of target pressure. The new hydraulic peak pressure is obtained by controlling the removal of oil from the chamber via the adjustment assembly.

[0239] It should be mentioned, that based on measurements provide by sensors providing information of e.g. gas inlet pressure, gas outlet pressure (e.g. gas pressure inside the compression chamber), etc. the controller 7 may be able to predict health status e.g. of valves. Hence, if the pressure of hydraulic fluid is stabile at the discharge pressure, this may indicate that the discharge valve is failing. In the same way if the pressure of hydraulic fluid is stabile at the inlet pressure, this may indicate that the inlet valve is failing.

[0240] From the above it is now clear that the invention relates to control of hydraulic fluid in a diaphragm compressor to empty, preferably completely emptying the compression chamber 3 and thereby increase the volumetric efficiency. This is obtained when the diaphragm is just in contact with the inner wall of the compression chamber from edge to edge of the compression chamber both along the length and the width of the compression chamber. This happens preferably in every compression cycle. By this control the volumetric efficiency is optimized by adjusting the target pressure to be high enough to establish the above-described contact between diaphragm and compression chamber wall. Hence, a method and a compressor are disclosed directed to control the hydraulic fluid volume in order to optimize the volumetric efficiency of a diaphragm compressor and thus empty the compression chamber.

[0241] The present invention has the advantage over the cited prior art, that hydraulic fluid may be removed from the hydraulic chamber in a controlled manner. This include removing hydraulic fluid during a part of the waveform where the pressure in the hydraulic chamber is at or below the discharge pressure. Hence, removal of hydraulic fluid is not, as in the prior art, made at highest pressure such as at the hydraulic peak pressure. Further, controlled manner should also be understood to include removal (and / or injection) of hydraulic fluid in two compression cycles which are not successive. Hence, contrary to known systems, the present invention does not require the removal of hydraulic fluid in every compression cycle.

[0242] The invention has been exemplified above with the purpose of illustration rather than limitation with reference to specific examples. Details such as a specific method and system structure have been provided in order to understand embodiments of the invention. Note that detailed descriptions of well-known systems, devices, circuits, and methods have been omitted so as to not obscure the description of the invention with unnecessary details.List 1. Hydraulic fluid pressure waveform 1a-1n. Parts of the hydraulic fluid pressure waveform 2. Diaphragm compressor 3. Compression chamber 4. Hydraulic fluid chamber 5. Diaphragm 6. Hydraulic fluid pressure representation unit 6a. Hydraulic fluid pressure sensor 6b. Sensing unit 6n. Gas pressure sensor 7. Controller 8. Valve a. first valve b. second valve c. third valve 9. Pump 10. Crank shaft 11. Conduit 12. Crank shaft position sensor 13. Hydraulic fluid adjustment assembly 14. Movable member of pressure boost vessel 15. First low-pressure end of pressure boost vessel 16. Second high-pressure end of pressure boost vessel 17. Gas inlet 18. Gas discharge 19. Control valve 20. Stabiliser 21. Pressure booster vessel 22. Bleed valve 23. Hydraulic fluid reservoirDP. Discharge pressure HPP. Hydraulic Peak Pressure TP. Target pressure value 'P. Delta pressure value

Claims

Patent claims 1. A diaphragm compressor (2) comprising: ^ a compression chamber (3) separated from a hydraulic fluid chamber (4) by a multi-layered metal diaphragm (5), ^ a hydraulic fluid pressure sensor (6a) configured for measuring a hydraulic peak pressure (HPP) inside said hydraulic fluid chamber (4), ^ a hydraulic fluid adjustment assembly (13), and ^ a controller (7), wherein said controller (7) is configured to compare said hydraulic peak pressure value (HPP) with a target pressure value (TP) wherein said target pressure value (TP) is higher than a discharge pressure (DP) from said compression chamber (3), and wherein said controller (7) is further configured to, via said hydraulic fluid adjustment assembly (13), control: - injection of hydraulic fluid into said hydraulic fluid chamber (4) if said target pressure value is higher than said hydraulic peak pressure value, and - removal of hydraulic fluid from said hydraulic fluid chamber (4) if said target pressure value is below said hydraulic peak pressure value.

2. A diaphragm compressor according to claim 1, wherein said controller (7) is configured to establish a delta pressure value ('P) between said target pressure value (TP) and said hydraulic peak pressure value (HPP), and to compare said delta pressure value ('P) with a threshold value, preferably one of a plurality of threshold values.

3. A diaphragm compressor according to any of the preceding claims, wherein said hydraulic fluid sensor (6a) is mounted on said diaphragm compressor (2) so that it is in fluid communication with the hydraulic fluid in said hydraulic fluid chamber (4).

4. A diaphragm compressor according to any of the preceding claims, wherein said diaphragm compressor (2) further comprises: ^ a gas pressure sensor (6n) located in a gas inlet (17), ^ a gas pressure sensor (6n) located in a gas discharge (18), and ^ a crank shaft position sensor (12).

5. A diaphragm compressor according to any of the preceding claims, wherein said diaphragm compressor (2) further comprises a gas pressure sensor (6n) mounted on said diaphragm compressor (2) so that it is in fluid communication with the gas in said gas compression chamber (3).

6. A diaphragm compressor according to any of the preceding claims, wherein said compressor (2) is configured to establish a pressure of at least 50MPa, preferably at least 75Mpa and most preferably up to at least 100MPA.

7. A diaphragm compressor according to any of the preceding claims, wherein said compressor (2) is configured to operate at an operation speed of at least 300rpm, preferably at least 500rmp and most preferably up to 800rpm 8. A diaphragm compressor according to any of the preceding claims, wherein said adjustment assembly (13) comprising a member (14) movable between a first end (15) and a second end (16) of a pressure booster vessel (21) and wherein said controller (7) is configured to control a movable member (14) towards said first end (15) if hydraulic fluid is to be injected into the hydraulic fluid chamber (4) and towards said second end (16) if hydraulic fluid is to be removed from the hydraulic fluid chamber (4).

9. A diaphragm compressor according to any of the preceding claims, wherein said hydraulic fluid adjustment assembly (13) comprises a pump controlled by said compressor control signal to inject hydraulic fluid into said hydraulic fluid chamber (4).

10. A diaphragm compressor according to any of the preceding claims, wherein injection of said hydraulic fluid is provided by a mix of hydraulic fluid from said pump and from said pressure booster vessel (21).

11. A diaphragm compressor according to any of the preceding claims, wherein said multi-layered diaphragm comprises a gas diaphragm (5), a hydraulic fluid diaphragm and a leakage diaphragm.

12. A diaphragm compressor according to any of the preceding claims, wherein removal from said hydraulic fluid chamber is done by controlling said movable member (14).

13. A diaphragm compressor according to any of the preceding claims, wherein a bleed valve (22) is connecting said hydraulic fluid chamber (4) with a fluid reservoir (23).

14. A diaphragm compressor according to any of the preceding claims, wherein said diaphragm compressor is controlled according to the method specified in claims 15- 39.

15. A method of establishing and analysing a part (1a, 1b, …, 1n) of a hydraulic fluid pressure waveform (1) of a diaphragm compressor (2), the diaphragm compressor comprises: ^ a compression chamber (3) separated from a hydraulic fluid chamber (4) by a diaphragm (5), and ^ a hydraulic fluid pressure representation unit (6) communicatively connected to a controller (7), wherein said controller (7) establishes said hydraulic fluid pressure waveform by control of said diaphragm compressor (2) and wherein said controller (7) establishes a delta pressure value ('P) between a determined target peak pressure value (TP) and a hydraulic peak pressure value (HPP) at a discharge part (1d) of said hydraulic fluid pressure waveform (1),wherein said hydraulic peak pressure value (HPP) is established by said hydraulic fluid pressure representation unit (6), wherein said controller (7) establishes a compressor control signal based on said delta pressure value ('P), and wherein said compressor control signal is used to control the operation of said compressor.

16. A method according to claim 15, wherein said controller (7) is identifying said part (1a, 1b, …, 1n) as a gas discharge part (1d) based on input from said hydraulic fluid pressure representation unit (6).

17. A method according to any of the claims 15-16, wherein said hydraulic fluid pressure representation unit (6) is a pressure sensor (6a) measuring the pressure of the hydraulic fluid inside said hydraulic fluid chamber (4).

18. A method according to any of the claims 15-17, wherein said hydraulic fluid pressure representation unit (6) is a sensing unit (6b) measuring the pressure of the hydraulic fluid in a conduit (11) fluidly connected to said hydraulic fluid chamber (4) or a gas sensor (6n) measuring a gas inlet pressure and wherein the pressure of the hydraulic fluid in said hydraulic fluid chamber (4) is derived from said discharge gas pressure, or a gas sensor (6n) measuring a gas discharge pressure and wherein the pressure of the hydraulic fluid in said hydraulic fluid chamber (4) is derived from said discharge gas pressure.

19. A method according to any of the claims 15-18, wherein said part (1a, 1b, …, 1n) of said hydraulic fluid pressure waveform (1) is established based on two or more datapoints received from said hydraulic fluid pressure representation unit (6).

20. A method according to any of the claims 15-19, wherein said compressor (2) comprises a crank shaft position sensor (12) and wherein at least part (1a, 1b, …, 1n) of said hydraulic fluid pressure waveform (1) is established based in input from saidhydraulic fluid pressure representation unit (6) and said crank shaft position sensor (12).

21. A method according to any of the claims 15-20, wherein a volume of gas inside said compression chamber is determined based on knowledge of geometry of said compression chamber and position of said crank shaft, or based on pressure readings from said hydraulic fluid pressure representation unit (6) and on temperature readings from a hydraulic fluid temperature sensor or based on measurement of gas flow passing through a gas inlet (17) into said compression chamber and out through a gas discharge (18) out of said compression chamber.

22. A method according to any of the claims 15-21, wherein a volume of remaining gas inside the compression chamber is determined at least once during said discharge part of said hydraulic fluid pressure waveform.

23. A method according to any of the claims 15-22, wherein said determined target peak pressure value is established based on information of said volume of remaining gas inside the compression chamber is.

24. A method according to any of the claims 15-23, wherein said determined target peak pressure value is calculated as the sum of a gas pressure associated with the compression chamber and an empty pressure value.

25. A method according to any of the claims 15-24, wherein said determined target peak pressure value is calculated as the sum of said gas discharge pressure and said empty pressure value.

26. A method according to any of the claims 15-25, wherein said empty pressure value is determined to be between 10bar and 200bar, such as between 75bar and 175bar such as 150bar.

27. A method according to any of the claims 15-26, wherein said determined target peak pressure value is determined by said controller based on mode of operation of the diaphragm compressor.

28. A method according to any of the claims 15-27, wherein said determined target peak pressure value is determined by said controller based on a change in one of said inlet pressure and said discharge pressure.

29. A method according to any of the claims 15-28, wherein said delta pressure value ('P) is an average delta pressure value of delta pressure values ('P) established in two or more compression cycles.

30. A method according to any of the claims 15-29, wherein said delta pressure value ('P) is compared to two or more delta pressure value thresholds and when crossing one of said delta pressure value thresholds, said control signal is established.

31. A method according to any of the claims 15-30, wherein one of said two or more delta pressure value thresholds is a removal threshold value and wherein hydraulic fluid is removed from said compression chamber when said delta pressure value exceed said removal threshold value.

32. A method according to any of the claims 15-31, wherein one of said two or more delta pressure threshold is an upper error threshold value, or an injection threshold value, or a lower error threshold value.

33. A method according to any of the claims 15-32, wherein said compressor control signal is controlling a hydraulic fluid adjustment assembly (13) and thereby injection of hydraulic fluid into said hydraulic fluid chamber (4).

34. A method according to any of the claims 15-33, wherein said compressor control signal is controlling said hydraulic fluid adjustment assembly (13) and thereby removal of hydraulic fluid from said hydraulic fluid chamber (4).

35. A method according to any of the claims 15-34, wherein said hydraulic fluid adjustment assembly (13) comprising a member movable (14) between a first end (15) and a second end (16) of a pressure booster vessel (21) and wherein said controller (7) is controlling said movable member (14) towards said first end (15) if hydraulic fluidis injected into the hydraulic fluid chamber (4) and towards said second end (16) if hydraulic fluid is removed from the hydraulic fluid chamber (4).

36. A method according to any of the claims 15-35, wherein said hydraulic fluid adjustment assembly is controlled asynchronously with the compression cycles.

37. A method according to any of the claims 15-36, wherein said hydraulic fluid adjustment assembly is injecting hydraulic fluid into said hydraulic chamber in a number of compression cycles not interrupted by a compression cycle in which hydraulic fluid is removed from said hydraulic chamber.

38. A method according to any of the claims 15-37, wherein said hydraulic fluid adjustment assembly (13) is removing hydraulic fluid with a frequency that is lower than the compression cycle frequency.

39. A method according to any of the claims 15-38, wherein said hydraulic fluid adjustment assembly is initiating removing hydraulic fluid from said hydraulic fluid chamber when a piston of said compressor (2) is traveling away from said diaphragm.

40. A method according to any of the claims 15-39, wherein said method is implemented in a diaphragm compressor according to any of the claims 1-14.

Images