Controller, vacuum pump and method for pumping hydrogen gas

Abstract

A method (500) of controlling a vacuum pump to pump hydrogen gas with minimal or no supplementary purge gas, the method (500) comprising controlling (501) a rotor of the vacuum pump to operate in a first mode for pumping hydrogen gas, wherein a first rotation frequency of the rotor in the first mode is controlled to be greater than or equal to 120Hz.

Description

[0001] CONTROLLER, VACUUM PUMP AND METHOD FOR PUMPING HYDROGEN GAS

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to vacuum pumps and in particular to vacuum pumps for pumping hydrogen gas.

[0004] BACKGROUND

[0005] Conventionally, vacuum pumps are driven by motors. The motors typically receive electrical input power from an alternating current (AC) power supply. An electrical circuit tends to be used to rectify the received AC input power in order to generate DC power that can then be inverted to an AC output power suitable for driving the motor of the vacuum pump. Historically the frequency of the AC input power determined the operating frequency of the vacuum pump (i.e., the rotation frequency of the rotor of the vacuum pump). Resultantly, conventional vacuum pumps tend to operate with operational / rotation frequencies of 50-100Hz.

[0006] Multi-stage vacuum pumps such as dry pumps comprise a stator and rotor combination that define a plurality of pump stages (i.e., pump chambers) between an inlet of the vacuum pump and an outlet. Conventional multi-stage vacuum pumps tend to readily pump air or relatively heavy gases with good performance. For instance, pressures of 0.005mbar with pump speeds of 50m3 / h to 500m3 / h tend to be achievable with power consumptions in the range of 1 kWto 7kW.

[0007] However, semiconductor fabrication applications such as EUV lithography can use lighter gases, particularly hydrogen. Large quantities of hydrogen tend to be required to prevent contaminant deposition on fabrication critical components. The consumption of hydrogen in such applications also tends to be increasing as a result of performance upgrades and additional tooling. Conventional multi-stage vacuum pumps tend not to be able to pump hydrogen gas with the same level of performance as other heavier gases. Indeed pressures of only 20mbar may be achieved with negligible pump speed even when consuming power in excess of 10kW. This tends to be because hydrogen is a light gas with energetic (high velocity) molecules that can leak easily between components (and against the pumping direction), and even out of, a vacuum pump system. It is has become well established in the art that in order to pump a light gas such as hydrogen, large quantities of a heavier supplementary purge gas such as nitrogen must be injected into the pump chambers (i.e. , at the inlet or an interstage of the plurality of pump chambers) to improve pumping efficiency.

[0008] SUMMARY OF THE INVENTION

[0009] In an aspect, there is provided a controller for controlling a vacuum pump to pump hydrogen gas with minimal or no supplementary purge gas, wherein the controller is configured to: control a rotor of the vacuum pump to operate in a first mode for pumping hydrogen gas, wherein a first rotation frequency of the rotor in the first mode is controlled to be greater than or equal to 120Hz.

[0010] It is well established in the art that vacuum pumps are operated at frequencies below 100Hz, typically in the range of 50-100Hz. This has been established owing to the historical availability of AC input power frequencies to controllers (i.e., motor drive electronics). In addition when attempting to pump lighter gases, it is convention to use a relatively heaver supplementary purge gas injected into the pump chambers of the vacuum pump (i.e., at the inlet stage or an interstage) to improve pumping efficiencies. Such purge gases include nitrogen, for example. Indeed, such a convention in the art is evident from the long standing use of purge gases in applications requiring the pumping of hydrogen gas.

[0011] The inventor has found that, contrary to prior art approaches, a vacuum pump can in fact be configured to pump hydrogen gas without the need for large quantities of supplementary purge gas. Specifically, by increasing the rotation frequency of the rotor of the vacuum pump to or beyond 120Hz, a surprising effect of increased pump speed and overall pumping efficiency has been observed when supplementary purge gases are not used. This tends to allow hydrogen gas to be pumped without the vast quantities of supplementary purge gas that conventionally are required. Even more specifically, the rate of change of volumetric efficiency of a vacuum pump tends to increase at 120Hz. The term volumetric efficiency as used herein refers to the peak pumping speed of the vacuum pump divided by the geometric volume of the first or inlet stage of the vacuum pump over time. The peak pumping speed is measured according to ISO21360 titled “Vacuum technology - Standard methods for measuring vacuum pump performance”, which is herein incorporated in its entirety by reference The geometric volume over time is the geometrical volume per unit time.

[0012] By using a rotation frequency greater than or equal to 120Hz, the size of the vacuum pump also tends to be able to be manufactured smaller. This tends to be a result of an increased volume of hydrogen gas being pumped per unit time.

[0013] By avoiding the requirement for a supplementary purge gas, the use of vast volumes of, for instance, nitrogen gas tends to be avoided. This tends to offer efficiencies such as reduced cost and energy consumption (both in terms of use of the vacuum pump and production of the nitrogen gas itself), whilst also achieving a less complex vacuum pump system.

[0014] The controller may be used to retrofit pre-existing vacuum pumps with capabilities to pump hydrogen gas without supplementary purge gas.

[0015] The first rotation frequency may be greater than or equal to 120Hz and less than or equal to 180Hz. The inventor has found that whilst rotation frequencies greater than or equal to 120Hz tend to enable the use of supplementary purge gas to be avoided when pumping hydrogen gas, a further preferred range of rotation frequencies exists. More specifically, the inventor has identified that the improvement in pumping speed and volumetric efficiency continues to increase continuously to 180Hz. Beyond 180Hz the inventor has found that the rate of change of improvement with increasing rotation frequency tends to be lower. As a result, the preferred range of 120Hz-180Hz has been identified for improving the pumping of hydrogen gas. In addition, the use of frequencies greater than 180Hz tends to add little performance improvement at the expense of a more complex / expensive drive train, increased motor wear, excessive power draw, and worse motor efficiency.

[0016] The first rotation frequency may be greater than or equal to 140Hz and less than or equal to 180Hz. The inventor has found in particular that a broad peak in volumetric efficiency tends to be approached and substantially maintained for rotation frequencies in this range when pumping hydrogen gas with minimal or no supplementary purge gas.

[0017] The first rotation frequency may be is greater than or equal to 140Hz and less than or equal to 160Hz. The inventor has found that the peak in volumetric efficiency tends to be achieved within this particular range of rotation frequencies.

[0018] The controller may be configured to control the rotor of the vacuum pump to operate in a second mode for pumping a gas other than hydrogen gas, wherein a second rotation frequency of the rotor in the second mode is controlled to be less than 120Hz. This tends to enable a vacuum pump to be operated according to the type of gas being pumped. More specifically, a vacuum pump may operate at conventional rotation frequencies for pumped gases such as air where relatively good pump speeds and efficiencies can be achieved at lower frequencies. The same vacuum pumps may have the rotation frequency increased specifically for the pumping of hydrogen gas. The second rotation frequency may be less than or equal to 100Hz, more preferably less than or equal to 100Hz and greater than or equal to 50Hz.

[0019] The controller may be configured to control a motor of the vacuum pump to control the rotor. The motor may, for instance, comprise an induction motor. The controller may comprise a circuit for driving the motor. The circuit may be referred to as a drive unit or drive electronics for the motor. The circuit may comprise a rectifier and an inverter. The circuit may comprise analogue electronics. The circuit may use pulse width modulation to control the motor. The circuit may comprise digital electronics.

[0020] The controller referred to herein may comprise at least one memory and at least one processor coupled with the at least one memory. The at least one memory may comprise instructions which when executed by the at least one processor cause the controller to control the rotation frequency of the rotor in accordance with the disclosure herein.

[0021] In a second aspect, there is provided a vacuum pump for pumping hydrogen gas with minimal or no supplementary purge gas, comprising: a stator and a rotor defining a plurality of pump stages; a motor for rotating the rotor; and the controller of the first aspect.

[0022] According to a third aspect, there is provided a vacuum pump apparatus comprising: the vacuum pump of the second aspect; and a hydrogen recovery system arranged to recover the hydrogen gas pumped by the vacuum pump.

[0023] The hydrogen gas pumped by the vacuum pump tends to be purer owing to the lack of a requirement for a supplementary purge gas such as nitrogen. Accordingly, the hydrogen recovery system tends to operate more efficiently in respect of hydrogen recovered, costs, and power consumption. Commercially supplied hydrogen tends to be produced by steam reformation of natural gas - a process that consumes large amounts of energy and emits carbon dioxide (both from the reformation process directly and originating from the production of power required for the process). Improving hydrogen recovery therefore tends to further enable a reduction in carbon footprint of processes using the vacuum pump described herein. This is particularly relevant to semiconductor manufacturing processes such as EUV processes that typically consume large quantities of hydrogen.

[0024] According to a fourth aspect, there is provided a method of controlling a vacuum pump to pump hydrogen gas with minimal or no supplementary purge gas, the method comprising: controlling a rotor of the vacuum pump to operate in a first mode for pumping hydrogen gas, wherein a first rotation frequency of the rotor in the first mode is controlled to be greater than or equal to 120Hz.

[0025] The first rotation frequency may be greater than or equal to 120Hz and less than or equal to 180Hz, more preferably greater than or equal to 140Hz and less than or equal to 180Hz, even more preferably greater than or equal to 140Hz and less than or equal to 160Hz. The method may comprise controlling the rotor of the vacuum pump to operate in a second mode for pumping a gas other than hydrogen gas, wherein a second rotation frequency of the rotor in the second mode is controlled to be less than 120Hz, more preferably less than or equal to 100Hz and greater than or equal to 50Hz.

[0026] According to a fifth aspect, there is provided a program or plurality of programs arranged such that when executed by a computer system or one or more processors it / they cause the computer system or the one or more processors to operate in accordance with the method of any of the fourth aspect.

[0027] According to a sixth aspect, there is provided a machine readable storage medium storing a program or at least one of the plurality of programs according to the fifth aspect.

[0028] BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 shows an example of a controller for a vacuum pump in accordance with aspects of the disclosure herein.

[0030] Figure 2 shows an example of a vacuum pump comprising the controller of Figure 1 in accordance with aspects of the disclosure herein.

[0031] Figure 3a shows an example of modelled data for a vacuum pump in accordance with aspects of the disclosure herein, the modelled data being normalised pumping speed against pressure for a plurality of rotation frequencies.

[0032] Figure 3b shows an example of volumetric efficiency against rotation frequency for the same vacuum pump modelled in Figure 3a.

[0033] Figure 4a shows an example of measured data for the same vacuum of Figure 3a in accordance with aspects of the disclosure herein, the measured data being pumping speed against pressure for a plurality of rotation frequencies. Figure 4b shows an example of volumetric efficiency against rotation frequency for the same vacuum pump measured in Figure 4a.

[0034] Figure 5 shows an example of a method in accordance with aspects of the disclosure herein.

[0035] DETAILED DESCRIPTION

[0036] Figure 1 is a schematic illustration (not to scale) of a controller 100 for a vacuum pump in accordance with aspects of the disclosure herein.

[0037] The controller 100 comprises at least one memory 110 and at least one processor 120 coupled with the at least one memory 110. The at least one memory 110 comprises instructions 112 which when executed by the at least one processor 120 cause the controller 100 to perform the methods described herein.

[0038] Specifically, the controller 100 may perform the method 500 of Figure 5 to control a vacuum pump for pumping hydrogen gas without a supplementary purge gas. Even more specifically the controller 100 is configured to control a rotor of a vacuum pump to operate in a first mode for pumping hydrogen gas, wherein a first rotation frequency of the rotor in the first mode is controlled to be greater than or equal to 120Hz.

[0039] Although the pumping of hydrogen gas is achieved without the use of a supplementary purge gas in the exemplary embodiments discussed above and below, in other embodiments a minimal amount of supplementary purge gas may be used without departing from the scope of the present disclosure. The minimal amount of supplementary purge gas may be supplied either continuously or intermittently to the vacuum pump as needed. For example, minimal amounts of supplementary purge gas can be supplied to protect one or more pump seals (such the inlet seal / high vacuum seal) from degradation during pump operation. A minimal amount of supplementary gas can be supplied during operation at between 0 slm and 5 slm, for example, between 1 slm to 4 slm. As the supply of supplementary purge gas is minimal, these embodiments still achieve substantially all the advantages discussed above and below with regard to the embodiments that use no supplementary purge gas. Figure 2 shows a schematic illustration (not to scale) of a vacuum pump 200 comprising the controller 100 of Figure 1 in accordance with aspects of the disclosure herein.

[0040] The vacuum pump 200 is for pumping hydrogen gas without a supplementary purge gas. The vacuum pump 200 comprises a stator 210 and a rotor 220 defining a plurality of pump stages (not visible). The vacuum pump 200 further comprises a motor 230 for rotating the rotor 220. The vacuum pump 200 comprises the controller 100 of Figure 1 .

[0041] The motor 230 is an induction motor for rotating the rotor 220. The controller 200 is shown as interfacing with the motor 230. The controller 200 is integrated into a circuit for driving the motor 230. The controller 200 may control pulse width modulation in the circuit for a rectifier and inverter to control the motor 230 to rotate the rotor 220 at the first rotation frequency.

[0042] Figure 3a shows an example of modelled data 310 for a vacuum pump in accordance with aspects of the disclosure herein. The modelled data 310 comprises normalised pumping speed measured against pressure for a plurality of rotation frequencies when the vacuum pump is pumping hydrogen without a supplementary purge gas. The “pressure” is the pressure achieved by the vacuum pump at the pumping speed.

[0043] The vacuum pump relating to the modelled data 310 was a dry pump comprising an all-roots mechanism. The inlet gas was hydrogen. As noted herein, no supplementary purge gas was supplied. The vacuum pump was a multistage vacuum pump having 7 stages. The pumping speed is normalised on a scale of 0 to 2, shown in 0.5 increments. The normalisation is achieved by dividing the actual pumping speed by a peak speed of 120Hz. The pressure is expressed in units of mbar on a logarithmic scale of 0.001 to in excess of 100.

[0044] The modelled data 310 includes data 311 for a rotor rotation frequency of 80Hz, data 312 for a rotor rotation frequency of 100Hz, data 313 for a rotor rotation frequency of 120Hz, data 314 for a rotor rotation frequency of 140Hz, data 315 for a rotor rotation frequency of 160Hz, data 316 for a rotor rotation frequency of 180Hz, data 317 for a rotor rotation frequency of 200Hz. The data 311 , 312 shows that when pumping hydrogen gas without a supplementary purge as, at conventional rotor rotation frequencies of 80 or 100Hz, the vacuum pump performance is relatively poor. Specifically, an ultimate pressure of above 1 mbar is achieved with negligible pumping speed. Such poor performance is achieved even when power of 2.5kW is supplied to the pump. Expressed more generally, hydrogen cannot be pumped at satisfactory pressures without a supplementary purge gas at these rotation frequencies.

[0045] The data 313 shows that at a rotor rotation frequency of 120Hz, the pumping speed and ultimate pressure have improved to more acceptable standards of pump performance with pressures of approximately 1 mbar achievable at normalised pumping speeds of 1. As the rotation frequency increases further to 140Hz, the data 314 shows pressures between O.lmbar and 1mbar are achievable at normalised pumping speeds between 1 and 1.25. At the rotation frequency increases further to 160Hz, the data 315 shows pressures between 0.1 and 1 mbar tend to be achieved for normalised pumping speeds between 1.25 and 1.5. At 180Hz, the data 316 shows pressures between O.lmbar and 1 mbar are achievable at normalised pumping speeds approximating 1.5. The normalised pumping speed achievable at the same pressures tends to increase further to between 1.50 and 1.75 at rotation frequencies of 200Hz (i.e., for data 317). It is also evident from the modelled data 310 that as the rotation frequency increases from 80Hz to 140Hz the peak normalised pumping speed tends to be achieved at decreasing pressures. After 140Hz, the peak normalised pumping speed starts to shift to being achieved at increasing pressures. The modelled data 310 indicates that an optimum range of rotation frequencies can be established for a vacuum pump pumping hydrogen without a supplementary purge gas.

[0046] Figure 3b shows an example of volumetric efficiency data 320 for the vacuum pump performance modelled in Figure 3a. The volumetric efficiency data 320 shows volumetric efficiency against running frequency (also referred to herein as rotor rotation frequency). The volumetric efficiency is calculated by taking the peak speed achieved for a respective rotation frequency (such as the rotation frequencies shown in Figure 3a) and dividing that value by the geometrical volume of the first stage of the vacuum pump over time. More specifically, the peak speed determined from Figure 3a is measured in m3 / h. More specifically, the geometrical volume of the first stage over time is measured in m3 / h. The volumetric efficiency itself is unitless and is expressed as a percentage.

[0047] By way of a first example, at a running / rotation frequency of 80Hz, the data 320 shows a volumetric efficiency of 20%. This indicates that in a unit time, 20% of the volume of hydrogen gas entering the first stage of the vacuum pump (via the inlet) is pumped out of the first stage by the rotor.

[0048] By way of a further example, at 100Hz the volumetric efficiency is 35%. This indicates that in a unit time, 35% of the volume of hydrogen gas entering the first stage of the vacuum pump (via the inlet) is pumped out of the first stage by the rotor.

[0049] By way of a further example, at 120Hz the volumetric efficiency is 75%. This indicates that in a unit time, 75% of the volume of hydrogen gas entering the first stage of the vacuum pump (via the inlet) is pumped out of the first stage by the rotor.

[0050] By way of a further example, at 140Hz the volumetric efficiency is close to 80%. This indicates that in a unit time, close to 80% of the volume of hydrogen gas entering the first stage of the vacuum pump (via the inlet) is pumped out of the first stage by the rotor.

[0051] By way of a further example, at 160Hz the volumetric efficiency is approximately 80%. This indicates that in a unit time, 80% of the volume of hydrogen gas entering the first stage of the vacuum pump (via the inlet) is pumped out of the first stage by the rotor. The volumetric efficiency remains relatively stable at 180Hz, 200Hz, 220Hz, 240Hz and 260Hz. This indicates that little performance improvement is achieved as the frequency is increased beyond 180Hz. Running a vacuum pump beyond the 180Hz value thus offers little additional benefit at the expense of a more complex / expensive drive train, increased motor wear, excessive power draw, and worse motor efficiency. As shown in the data 320, there is a rapid improvement in efficiency at rotation frequencies greater than or equal to 120Hz relative to 100Hz, when a vacuum pump is pumping hydrogen gas without a supplementary purge gas. This increased efficiency tends to saturate at close to 80% at frequencies of 180Hz. Hence, when pumping hydrogen gas without a supplementary purge gas a preferred rotation frequency for a rotor has been found to be greater than or equal to 120Hz, more preferably greater than or equal to 120Hz and less than or equal to 180Hz.

[0052] As shown in the data 320, volumetric efficiencies of closer to 80% tend to be achieved for the preferred range of rotor rotation frequencies of 140Hz- 180Hz.

[0053] As shown in the data 320, the volumetric efficiency improvement beyond 160Hz is less apparent, and approximately only a few percent. Accordingly, an even more preferred range of rotor rotation frequencies of 140Hz-160Hz has been found.

[0054] The inventor has also obtained measured data for the same vacuum pump modelled in Figures 3a-3b to evaluate whether the effects observed during the modelled are evident in measured data.

[0055] Figure 4a shows an example of measured data 410 for the vacuum pump modelled for Figure 3a. The measured data 410 comprises pumping speed measured against pressure for a plurality of rotation frequencies when the vacuum pump is pumping hydrogen without a supplementary purge gas. The “pressure” is the pressure achieved by the vacuum pump at the pump inlet.

[0056] For the vacuum pump relating to the measured data 410 the inlet gas was hydrogen. As noted herein, no supplementary purge gas was supplied. The vacuum pump was a multistage vacuum pump having 7 stages. The pumping speed is expressed in units of m3 / hour on a scale of 0 to 400, shown in 100 m3 / h increments. The pressure is expressed in units of mbar on a logarithmic scale of 0.001 to 1000. The measured data 410 includes data 411 for a rotor rotation frequency of 90Hz, data 412 for a rotor rotation frequency of 120Hz, data 413 for a rotor rotation frequency of 140Hz, data 414 for a rotor rotation frequency of 160Hz.

[0057] The data 411 shows that when pumping hydrogen gas without a supplementary purge gas, at a conventional rotor rotation frequency of 90Hz, the vacuum pump performance is relatively poor. This tends to agree with the modelled data 311 , 312 in Figure 3a.

[0058] The data 412 shows that at a rotor rotation frequency of 120Hz, the pumping speed and ultimate pressure has improved to more acceptable standards of pump performance with pressures of approximately 0.1-1mbar are achievable at pumping speeds approximating 200-250 m3 / h. As the rotation frequency increases further to 140Hz, the data 413 shows pressures close to 0.1-1 mbar are achievable at pumping speeds close to 250-275m3 / h. As the rotation frequency increases further to 160Hz, the data 414 shows pressures between 0.1 and 1 mbar tend to be achieved for pumping speeds close to 275- 325 m3 / h. It is also evident from the measured data 410 that as the rotation frequency increases from 90Hz to 120Hz the peak pumping speed tends to be achieved at decreasing pressures. After 120Hz, the peak pumping speed largely is maintained at a similar achieved pressure. The modelled data 410 indicates that an optimum range of rotation frequencies can be established for a vacuum pump pumping hydrogen without a supplementary purge gas.

[0059] Figure 4b shows an example of volumetric efficiency data 420 for the vacuum pump performance data measured in Figure 4a. The volumetric efficiency data 420 shows volumetric efficiency against running frequency (also referred to herein as rotor rotation frequency). The volumetric efficiency data 420 is calculated in the same manner as described for Figure 3b.

[0060] By way of a first example, the volumetric efficiency is shown as being close to 20% for the measured data when a rotor rotation frequency / running frequency of 90Hz was used. This indicates that in a unit time, approximately 20% of the volume of hydrogen gas entering the first stage of the vacuum pump (via the inlet) is pumped out of the first stage by the rotor. The volumetric efficiency increases to close to 75% for a rotor rotation frequency of 120Hz. This volumetric efficiency increases slightly for a rotor rotation frequency of 140Hz and is then largely maintained for the rotor rotation frequency of 160Hz.

[0061] The measured data 410 and volumetric efficiency data 420 indicate that a vacuum pump can pump hydrogen gas without a supplementary purge gas when the rotor rotation frequency is greater than 120Hz. The data 410, 420 also indicates that a preferred range of rotor rotation frequencies has been found. The preferred range is 120-160Hz where the volumetric efficiency begins to saturate. Even more preferably, the range of 140-160Hz has been found where, as shown in the data 420, the volumetric efficiency has saturated at a maximum value close to 75%.

[0062] Similar results have been observed by the inventor when modelling and measuring data for other vacuum pumps. In particular, whilst the disclosure herein may discuss modelled and measured performance for an all-roots mechanism pump, the performance improvements observed at the preferred frequencies are applicable to other pump types including other roots, claw and screw pumps.

[0063] The inventor has found that for a vacuum pump pumping hydrogen gas without a supplementary purge gas the efficiency of the vacuum pump tends to be limited by the leakage of the relatively light and energetic hydrogen gas. As the vacuum pump pumps from high vacuum to low vacuum, a certain amount of hydrogen gas tends to leak back from low vacuum to high vacuum. The pumping effect of the vacuum pump tends to fight against the leakage. At a lower rotation frequency for the rotor of the vacuum pump, such as the conventional frequencies below 100Hz, the performance is low owing to the leakage effect. However, at higher frequencies, above 120Hz, the vacuum pump performance improves and the leakage effect has less impact on overall performance. Increasing the rotation frequency for a vacuum pump pumping hydrogen gas has not been considered previously owing to the well established practices of rotation frequencies being below 100Hz and the prevalent use of heavier purge gases to enable the pumping of hydrogen gas. The inventor has further modelled and measured the effect described herein and characterised a preferred range of frequencies of rotation for a rotor of a vacuum pump.

[0064] Figure 5 shows an example of a method 500 in accordance with aspects of the disclosure herein. The method 500 may be performed by the vacuum pump 200 or the controller 100 of said vacuum pump 200.

[0065] The method 500 is a method 500 of controlling a vacuum pump to pump hydrogen gas without a supplementary purge gas.

[0066] The method 500 comprises controlling 501 a rotor of the vacuum pump to operate in a first mode for pumping hydrogen gas, wherein a first rotation frequency of the rotor in the first mode is controlled to be greater than or equal to 120Hz.

[0067] Apparatus, including the controller for the vacuum pump, for implementing the above arrangement, and performing the method steps to be described above, may be provided by configuring or adapting any suitable apparatus, for example one or more computers or other processing apparatus or processors, and / or providing additional modules. The apparatus may comprise a computer, a network of computers, or one or more processors, for implementing instructions and using data, including instructions and data in the form of a computer program or plurality of computer programs stored in or on a machine readable storage medium such as computer memory, a computer disk, ROM, PROM etc., or any combination of these or other storage media.

[0068] It should be noted that certain of the process steps of methods described herein may be omitted or such process steps may be performed in differing order to that presented herein. Furthermore, although all the process steps have, for convenience and ease of understanding, been depicted as discrete temporally-sequential steps, nevertheless some of the process steps may in fact be performed simultaneously or at least overlapping to some extent temporally.

[0069] Whilst the examples described herein may refer to a controller comprising a memory and a processor, this is not intended to be limiting. The controller may in fact comprise analogue electronics. The controller may be drive electronics for a motor of a vacuum pump, for instance, configured to perform the methods described herein.

[0070] Whilst the examples described herein may refer to vacuum pumps with particular shapes, sizes, dimensions or number of pump chambers, this is not intended to the limiting. Operating a vacuum pump to rotate a rotor at the claimed frequency ranges as described herein has been found to provide the desirable effects described herein. Accordingly, the controller and methods of control described herein can be applied to a number of different vacuum pump designs depending on the application.

[0071] Reference numeral list

[0072] 100 - controller

[0073] 110 - memory

[0074] 112 - instructions

[0075] 120 - processor

[0076] 200 - vacuum pump

[0077] 210 - stator

[0078] 220 - rotor

[0079] 230 - motor

[0080] 310 - modelled data

[0081] 311 - 80Hz data

[0082] 312 - 100Hz data

[0083] 313 - 120Hz data

[0084] 314 - 140Hz data

[0085] 315 - 160Hz data

[0086] 316 - 180Hz data

[0087] 317 - 200Hz data 320 - modelled data

[0088] 410 - measured data

[0089] 411 - 90Hz data

[0090] 412 - 120Hz data 413 - 140Hz data

[0091] 414 - 160Hz data

[0092] 420 - measured data

[0093] 500 - method

[0094] 501 - step of method

Claims

CLAIMS1. A controller for controlling a vacuum pump to pump hydrogen gas with minimal or no supplementary purge gas, wherein the controller is configured to: control a rotor of the vacuum pump to operate in a first mode for pumping hydrogen gas, wherein a first rotation frequency of the rotor in the first mode is controlled to be greater than or equal to 120Hz.

2. The controller of claim 1 , wherein the first rotation frequency is greater than or equal to 120Hz and less than or equal to 180Hz.

3. The controller of claim 2, wherein the first rotation frequency is greater than or equal to 140Hz and less than or equal to 180Hz.

4. The controller of claim 3, wherein the first rotation frequency is greater than or equal to 140Hz and less than or equal to 160Hz.

5. The controller of any preceding claim, wherein the controller is configured to: control the rotor of the vacuum pump to operate in a second mode for pumping a gas other than hydrogen gas, wherein a second rotation frequency of the rotor in the second mode is controlled to be less than 120Hz.

6. The controller of claim 5, wherein the second rotation frequency is less than or equal to 100Hz, more preferably less than or equal to 100Hz and greater than or equal to 50Hz.

7. The controller of any preceding claim, wherein the controller is configured to control a motor of the vacuum pump to control the rotor.

8. The controller of claim 7, wherein the controller comprises a circuit for driving the motor.

9. A vacuum pump for pumping hydrogen gas with minimal or no supplementary purge gas, comprising: a stator and a rotor defining a plurality of pump stages; a motor for rotating the rotor; and the controller of any preceding claim.

10. A vacuum pump apparatus comprising: the vacuum pump of claim 9; and a hydrogen recovery system arranged to recover the hydrogen gas pumped by the vacuum pump.

11. A method of controlling a vacuum pump to pump hydrogen gas with minimal or no supplementary purge gas, the method comprising: controlling a rotor of the vacuum pump to operate in a first mode for pumping hydrogen gas, wherein a first rotation frequency of the rotor in the first mode is controlled to be greater than or equal to 120Hz.

12. The method of claim 11 , wherein the first rotation frequency is greater than or equal to 120Hz and less than or equal to 180Hz, more preferably greater than or equal to 140Hz and less than or equal to 180Hz, even more preferably greater than or equal to 140Hz and less than or equal to 160Hz.

13. The method of any one of claims 11-12, comprising:controlling the rotor of the vacuum pump to operate in a second mode for pumping a gas other than hydrogen gas, wherein a second rotation frequency of the rotor in the second mode is controlled to be less than 120Hz, more preferably less than or equal to 100Hz and greater than or equal to 50Hz.

14. A program or plurality of programs arranged such that when executed by a computer system or one or more processors it / they cause the computer system or the one or more processors to operate in accordance with the method of any of claims 11-13.

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