GB2615758A

GB2615758A - A vacuum pump assembly

Info

Publication number: GB2615758A
Application number: GB2202037.4A
Authority: GB
Inventors: Spenkuch Dirk
Original assignee: Leybold GmbH
Current assignee: Leybold GmbH
Priority date: 2022-02-16
Filing date: 2022-02-16
Publication date: 2023-08-23
Also published as: GB202202037D0

Abstract

A vacuum pump assembly 2 comprising a first vacuum pump 4; a first motor 6 driving the first vacuum pump; a first converter 8 supplying electrical power to the first motor; a second vacuum pump 10; a second motor 12 driving the second vacuum pump; and a second converter 14 supplying electrical power to the second motor; and an electrical coupling 16 directly electrically connecting the first converter to the second converter such that electrical power can flow directly from the first converter to the second converter. Preferably the first motor is able to operate in a generator or braking mode, such that the first motor generates electrical power. The electrical power generated by the first motor may be supplied to the second motor via the second converter and the electrical coupling. A method of operating a vacuum pump assembly is also claimed.

Description

A VACUUM PUMP ASSEMBLY

FIELD OF THE INVENTION

The present invention relates to accommodating for the energy generated 5 in braking a vacuum pump.

BACKGROUND

Conventionally, Roots vacuum pumps are driven by motors. The motors typically receive electrical power from a grid via a frequency converter. A Roots pump may operate at different frequencies during normal operation. In other words, during normal operations of the Roots pump, the rotational frequency of its rotors may vary. To decrease the rotational frequency of the rotors, braking is applied to the motor that is driving the Roots pump. For example, an electric motor brake may be operated to brake, i.e. slow, the motor. The braking of the motor may be achieved by using dynamic braking. In dynamic braking, the frequency converter does not supply any electrical power from the grid to the motor, e.g. the frequency converter is disconnected from the grid. In this case, the motor acts as a generator. The generator action converts the mechanical energy of rotation to electrical energy which is dissipated as heat.

SUMMARY OF THE INVENTION

In a first aspect, there is provided a vacuum pump assembly comprising: a first vacuum pump; a first motor configured to drive the first vacuum pump; a first converter configured to supply electrical power to the first motor; a second vacuum pump; a second motor configured to drive the second vacuum pump; and a second converter configured to supply electrical power to the second motor; and an electrical coupling directly electrically connecting the first converter to the second converter such that electrical power can flow directly from the first converter to the second converter. -2 -

The converters may be, for example, frequency converters or power converters.

The first motor may be further configured to operate in a generator or braking mode, thereby to reduce the frequency at which the first vacuum pump is operating. When operating in the generator or braking mode, the first motor may generate electrical power. The second converter may be further configured to, using the generated electrical power received via the electrical coupling, supply electrical power to the second motor.

The electrical coupling may be a conductive wire, wires or cable attached to the first converter at a first end and attached to the second converter at a second end opposite to the first end.

The first converter may comprise a first rectifier electrically coupled to a first inverter via a first DC link. The second converter may comprise a second rectifier electrically coupled to a second inverter via a second DC link. The electrical coupling may directly connect the first DC link to the second DC link.

One or more of the first converter, the second converter, and the electrical coupling may comprise one or more energy storage devices.

The first vacuum pump may be a Roots vacuum pump. The second vacuum pump may be a screw pump.

The vacuum pump assembly may further comprise: one or more further vacuum pumps configured to operate at a constant frequency; one or more further motors, each of the one or more further motors being arranged to drive a respective further pump of the one or more further pumps; one or more further converters, each of the one or more further converters being arranged to supply electrical power to a respective further motor of the one or more further motors; and one or more further electrical couplings, each further electrical coupling of the one or more further electrical couplings electrically coupling a respective further converter to the first converter such that electrical power can flow from the first converter to that respective further converter. Each of the one or more further converters may comprise a further rectifier coupled to a further inverter via a further DC link. Each of the further electrical couplings electrically may connect -3 -the further DC link of a respective further converter to the first and/or second DC links.

In a further aspect, there is provided a method of operating a vacuum pump assembly, the method comprising: supplying electrical power, by a first converter, to a first motor; driving, by the first motor, a first vacuum pump at a first frequency; braking the first motor to reduce the frequency at which the first pump is driven from the first frequency to a lower frequency, thereby generating electrical power by the first motor; transferring the generated electrical power from the first motor to the first converter; and transferring the generated electrical power directly from the first converter to the second converter.

Braking the first motor may comprise operating the first motor in a generator mode.

The method may further comprise storing at least some of the generated electrical power in one or more electrical energy storage devices located in one or more of the first converter, the second converter, and the electrical coupling.

The method may further comprise: using the electrical power transferred from the first converter, supplying electrical power by the second converter to a second motor; and driving, by the second motor, a second pump.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic illustration (not to scale) of a pump assembly; Figure 2 is a schematic illustration (not to scale) showing the coupled together frequency converters of the pump assembly; Figure 3 is a flowchart of a method of using a pump assembly; and Figure 4 is a schematic illustration (not to scale) of a further pump assembly.

DETAILED DESCRIPTION -4 -

Figure 1 is a schematic illustration (not to scale) of a vacuum pump assembly 2.

The pump assembly 2 comprises a Roots pump 4, a first motor 6, a first frequency converter 8, a screw pump 10, a second motor 12, a second frequency converter 14, a DC coupling 16, and an electrical power grid 18.

The Roots pump 4 is configured to operate at a range of frequencies. The Roots pump 4 comprises one or more rotors configured to rotate at the range of frequencies. During normal operation, the Roots pump 4 may be periodically controlled, e.g. by a controller, to increase its operational frequency, i.e. to periodically increase the rotational speed/frequency of its one or more rotors.

During normal operations, the Roots pump 4 may also be periodically controlled, e.g. by a controller, to decrease its operational frequency, i.e. to periodically decrease the rotational speed/frequency of its one or more rotors.

The first motor 6 is operatively coupled to the Roots pump 4. The first motor 6 is configured to drive the Roots pump 4. The controlling of the operational frequency of the Roots pump 4 may be done by braking or accelerating the first motor 6.

The first frequency converter 8 is electrically coupled to the first motor 6. The first frequency converter 8 is configured to supply electrical power to the first motor 6. The first frequency converter 8 is electrically coupled to the grid 18 such that it may receive electrical power from the grid 18. The first frequency converter 8 is configured to convert the electrical power received at its input, i.e. from the grid 18, into electrical power that is used by the first motor 6 to drive the Roots pump 4.

The screw pump 10 may be controlled, e.g. by a controller, to operate at a constant frequency. The screw pump 10 comprises one or more rotors. During normal operation, the frequency at which the screw pump 10 operates tends not to change, i.e. the rotational speed/frequency of the one or more rotors of the screw pump is constant.

The second motor 12 is operatively coupled to the screw pump 10. The second motor 12 is configured to drive the screw pump 10. -5 -

The second frequency converter 14 is electrically coupled to the second motor 12. The second frequency converter 14 is configured to supply electrical power to the second motor 12. The second frequency converter 14 is electrically coupled to the grid 18 such that it may receive electrical power from the grid 18.

The second frequency converter 14 is configured to convert the electrical power received at its input, i.e. from the grid 18, into electrical power that is used by the second motor 12 to drive the screw pump 10.

The first frequency converter 8 is electrically coupled to the second frequency converter 14 via the DC coupling 16. The DC coupling 16 allows to electrical power in the form of a direct current to flow directly from the first frequency converter 8 to the second frequency converter 14 and vice versa. In this embodiment, the DC coupling 16 bypasses the grid 18 such that electrical power, in the form of DC current, passes between the first and second frequency converters 8, 14 without passing via the grid 18. The DC coupling 16 can be a conductive wire, wires, or cable attached to the first frequency converter 8 at one end and attached to the second frequency converter 14 at an opposite end, thereby allowing electric power to flow directly from the first frequency converter 8 to the second frequency converter 14. The coupling 100 between the first and second frequency converters 8, 14 is described in more detail later below with reference to Figure 2.

As discussed above, during normal operation of the Roots pump 4, the operating frequency of the Roots pump 4 may be decreased. To achieve the reduction in the operating frequency of the Roots pump 4, braking is applied to the first motor 6 to reduce the operating speed of the first motor 6. The reduction in the operating speed of the first motor 6 results in a decrease in the operating frequency at which Roots pump 4 is being driven. This braking action is done by the first motor 6 operating in a generator mode in which the first motor 6 converts the mechanical energy of the rotating first motor 6 into electrical energy. Thus, the first motor 6 generates AC power when performing the braking action. The generated AC power is then transferred to the first frequency converter 8 via an electrical coupling electrically connecting the first frequency converter 8 to the first motor 6. The generated AC power is converted into DC power by the first -6 -frequency converter 8, e.g. by an inverter in the first frequency converter 8 operating in reverse (explained in more detail below with reference to Figure 2). The DC power converted from the generated AC power is then transferred from the first frequency converter 8 to the second frequency converter 14 by the DC coupling 16. Some or all of the DC power can be stored in at least one of the first frequency converter 8, second frequency converter 14, and/or the DC coupling 16, e.g. by a capacitor positioned on the DC coupling 16 or in the first or second frequency converter 8, 14. Furthermore, some or all of the DC power can be converted by the second frequency converter 14, e.g. by an inverter in the second to frequency converter 14, into electrical power that can be used to power the second motor 12. In other words, the second frequency converter 14 may convert the DC power back to AC power, and supply that AC power to the second motor 12 thereby to drive the screw pump 10. Thus, the electrical energy generated from the braking of the first motor 6 may be used to drive the screw pump 10. In this way, the power taken from the grid 18 by the second frequency converter 14 can be reduced or eliminated.

Figure 2 is a schematic illustration (not to scale) of the first frequency converter 8 coupled with the second frequency converter 14.

The first frequency converter 8 comprises a first rectifier 20, a first DC link 22, and a first inverter 24.

The first rectifier 20 is configured to convert AC electrical power to DC electrical power. The first rectifier 20 is configured to receive, as an input, AC power from the grid 18. The first rectifier 20 is configured to output the DC power to the first DC link 22.

The first DC link 22 is configured to transfer the DC power output from the first rectifier 20 to the first inverter 24. Also, in this embodiment, the first DC circuit 22 comprises a first capacitor 23 configured to store power for the first inverter 24. The first capacitor 23 can store the converted DC power discussed above.

The first inverter 24 is configured to convert DC electrical power, received at its input, i.e. from the first DC link 22, to AC electrical power. The first inverter 24 is configured to output AC electrical power to the first motor 6. The first inverter 24 is electrically coupled to the first motor 6 such that the output AC electrical power can be supplied to the first motor 6.

The first inverter 24 is also configured to operate in reverse. In this operating mode, the first inverter 24 operates essentially as a rectifier. In particular, the first inverter 24 is further configured to receive AC power from the first motor 6, e.g. via the same electrical coupling that is used by the first frequency converter 8 to supply power to the first motor 6. The first inverter 24 is further configured to convert the AC power received from the first motor 6 into DC power. The first inverter 24 is further configured to output the DC power converted from the received AC power to the first DC link 22.

The second frequency converter 14 has the same construction as the first frequency converter 8. The second frequency converter 14 comprises a second rectifier 26, a second DC link 28, and a second inverter 30.

The second rectifier 26 is configured to convert AC electrical power to DC electrical power. The second rectifier 26 is configured to receive, as an input, AC power from the grid 18. The second rectifier 26 is configured to output the DC power to the second DC link 28.

The second DC link 28 is configured to transfer the DC power output from the second rectifier 26 to the second inverter 30.

The DC coupling 16 directly electrically couples the first DC link 22 of the first frequency converter 8 to the second DC link 28 of the second frequency converter 14. The DC coupling 16 may be a conductive wire, wires, or cable attached to the first DC link 22 at one end and attached to the second DC link 28 at an opposite end, thereby allowing electrical power to flow directly from the first DC link 22 to the second DC link 28.

The second DC link 28 comprises a second capacitor 29 configured to store power for the second inverter 30. The second capacitor 29, when the second DC link 28 receives the converted DC power from the first DC link 22, can store at least some of the converted DC power. -8 -

The second inverter 30 is configured to convert DC electrical power to AC electrical power. The second inverter 30 is configured to output AC electrical power to the second motor 12. The second inverter 30 is electrically coupled to the second motor 12 such that the output AC electrical power can be supplied to the second motor 12.

Figure 3 depicts a flowchart of a method of operating the pump assembly 2.

At step s2, the first frequency converter 8 supplies electrical power to the first motor 6.

At step s4, the first motor 6 drives the Roots pump 4. The first motor 6 drives the Roots pump 4 using the electrical power supplied by the first frequency converter 8.

At step s6, the second frequency converter 14 supplies electrical power to the second motor 12.

At step s8, the second motor 12 drives the screw pump 10. The second motor 12 drives the screw pump 10 using the electrical power supplied by the second frequency converter 14.

At step sl 0, the first motor 6 brakes to reduce the operating frequency of the Roots pump 4. The braking of the first motor 6 generates AC power. The first 20 motor 6 may brake by operating in a generator or braking mode where the mechanical energy of the first motor 6 is converted into electrical energy.

At step sl 1, the AC power generated by the first motor 6 is transferred to the first frequency converter 8 via an electrical coupling that electrically connects the first frequency converter 8 to the first motor 6. The generated AC power is then converted by the first frequency converter 8, e.g. by using the first inverter 24 operating in reverse, into DC power.

At step s12, the DC power converted from the generated AC power is transferred from the first frequency converter 8 to the second frequency converter 14 via the DC coupling 16. -g -

At step s14, some or all of the converted DC power may be stored in the capacitor 23 in the first frequency converter 8 and/or the capacitor 29 in the second frequency converter 14.

At step s16, the second frequency converter 14 may convert the DC power received from the first frequency converter 8 into AC power, e.g. by using the second inverter 30. The second frequency converter 14 may supply electrical power to the second motor 12 using the AC power converted from the received DC power. Thus, the second motor 14 may use the electrical power derived from the braking of the first motor 6 to drive the screw pump 10.

Thus, a method of using the pump assembly 2 is provided It should be noted that certain steps of the method steps depicted in the flowchart of Figure 3 and described above may be omitted or such process steps may be performed in differing order to that presented above and shown in Figure 3. 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.

An advantage of the embodiments described above is that electrical power generated in the braking of the first motor can be stored by the first and/or second frequency converters. This is achieved in a relatively simple way. Complex modification of the system tends to be avoided.

Another advantage of the embodiments described above is that the braking energy, which is usually wasted, can be usefully used, e.g. to drive one or more additional pumps. Thus, the overall power used by the pump assembly tends to be reduced. Conventionally, the braking energy from fast braking is converted into waste heat energy by resistors. However, the embodiments described above use the braking energy to drive the screw pump and as such, the efficiency of the pump assembly tends to be improved, while simultaneously tending to provide for fast braking by the first motor.

Furthermore, conventionally the electrical power generated from the first motor braking could potentially overload the first frequency converter and/or any -10 -component electrically coupled to the first frequency converter. Overloads may force the first frequency converter to go into a safe mode and cease normal operations. The embodiments described above tend to prevent such overloads, e.g. by distributing the DC power between two frequency converters, in the pump assembly.

Figure 4 is a schematic illustration (not to scale) of a further pump assembly 32 comprising two screw pumps. Components which the further pump assembly 32 has in common with the pump assembly 2 are indicated with corresponding, i.e. the same, reference numerals as in Figure 1. The further pump assembly 32 differs from the pump assembly 2 in that the further pump assembly 32 additionally comprises a further screw pump 34, a third motor 36, and a third frequency converter 38.

In this embodiment, the further screw pump 34 is structurally the same as the screw pump 10.

The third motor 36 is operatively coupled to the further screw pump 34.

The third motor 36 is configured to drive the further screw pump 34 at a constant frequency.

The third frequency converter 38 is electrically coupled to the third motor 36. The third frequency converter 38 is configured to supply electrical power to the third motor 36. The third frequency converter 38 is electrically coupled to the grid 18 such that it may receive electrical power from the grid 18. The third frequency converter 38 is configured to convert the electrical power received at its input, i.e. from the grid 18, into electrical power that can be used by the third motor 36 to drive the further screw pump 34.

The further pump assembly 32 further comprises a further DC coupling 40 directly coupling the third frequency converter 38 to the second frequency converter 14. However, in other embodiments the further DC coupling 40 directly couples the third frequency converter 38 to the first frequency converter 8. As such, the first, second, and third frequency converters 8, 14, 38 are all connected electrically to each other. In this embodiment, the DC couplings 16, 40 bypass the grid 18 such that electrical power, in the form of DC current, passes between the first, second, and third frequency converters 8, 14, 38 without passing via the grid 18. The further DC coupling 40 may comprise a conductive wire, wires, or cable attached to the third frequency converter 38 at one end and attached to the second frequency converter 14 at an opposite end, thereby directly coupling the third frequency converter 38 to the second frequency converter 14.

In this embodiment, the third frequency converter 38 has the same construction as the first and second frequency converters 8, 14. The third frequency converter 38 comprises a third rectifier coupled to a third inverter via a third DC link. The further DC coupling 40 can directly couple the third DC link to the first or second DC link 22, 28.

As discussed above, during normal operations of the Roots pump 4, the first motor 6 braking to reduce the operating frequency of the Roots pump 4 results in the generation of AC power. The generated AC power is then transferred to the first frequency converter 8. The generated AC power is converted by the first frequency converter 8 into DC power and is transferred from the first frequency converter 8 to the second and third frequency converters 14, 38 by the DC couplings 16, 40. The converted DC power may be distributed evenly between the first, second, and third frequency converters. The converted DC power can be stored, e.g. in one or more capacitors, in at least one of the first, second, and third frequency converters 8, 14, 38 and/or the DC couplings 16, 40. Furthermore, some or all of the converted DC power can be used to drive the screw pump 10 and/or the further screw pump 34. For example, the converted DC power may be distributed evenly between the screw pump 10 and the further screw pump 34. As such, when the converted DC power is supplied to the screw pump 10 and/or the further screw pump 34, the power received from the grid 18 can be further reduced or eliminated.

In the above embodiments, the pump assembly comprises a Roots pump. However, in other embodiments, the pump assembly comprises a different type of vacuum pump other than a Roots pump instead of or in addition to the Roots 30 pump 4.

-12 -In the above embodiments, the pump assembly comprises only one Roots pump. However, in other embodiments, the pump assembly comprises a different number of Roots pumps, i.e. multiple Roots pumps.

In the above embodiments, the pump assembly comprises a screw pump.

However, in other embodiments, the pump assembly comprises a different type of vacuum pump other than a screw pump instead of or in addition to the screw pump. For example, in some embodiments, the pump assembly comprises a multi-stage Roots pump, rotary vane pump, or scroll pump, in place of the screw pump 10.

In the above embodiments, the pump assembly comprises only one screw pump. However, in other embodiments, the pump assembly comprises a different number of screw pumps, i.e. multiple screw pumps.

In the above embodiments, the frequency converters receive electrical power from an electrical power grid. However, in other embodiments, one or more of the frequency converters receives electrical power from a different power source instead of or in addition to receiving electrical power from the grid. For example, one or more of the frequency converters may receive power from an energy storage device, such as a battery or a capacitor, or from a generator.

In the above embodiments, the pump assembly comprises frequency converters. However, in other embodiments, the pump assembly comprises power converters of a different type other than a frequency converter. In the above embodiments, the first frequency converter is of the same type and construction as the second frequency converter. However, in other embodiments, the first frequency converter is not of the same type and construction as the second frequency converter.

In the above embodiments, the converted DC power may be stored in one or more capacitors. However, in other embodiments, the converted DC power is stored in an energy storage device other than the one or more capacitors, instead of or in addition to the one or more capacitors. For example, the converted DC power may be stored in one or more batteries.

-13 -In the above embodiments, the one or more capacitors for storing the converted DC power are located in one or more of the frequency converters. However, in other embodiments, the energy storage device(s) for storing the converted DC power, e.g. the one or more capacitors, may be located elsewhere, i.e. in a location other than in the frequency converters. For example, the one or more capacitors and/or batteries may be positioned along or coupled to the DC coupling.

In the above embodiments, the pump assembly comprises an electrical power grid. However, in other embodiments, the pump assembly comprises a power source other than an electrical power grid, e.g. a battery or generator.

In the above embodiments, the converted DC power may be distributed evenly and stored or used by the frequency converters. However, in other embodiments, the converted DC power may be distributed between frequency converters in a different way using a power distribution system.

-14 -Reference numeral list 2 -vacuum pump assembly 4 -Roots pump 6 -first motor 8 -first frequency converter -screw pump 12-second motor 14-second frequency converter 16-DC coupling to 18 -electrical power grid -first rectifier 22 -first DC link 23 -first capacitor 24 -first inverter 26-second rectifier 28 -second DC link 28 29 -second capacitor -second inverter s2-s16 -method steps 32 -further pump assembly 34 -further screw pump 36 -third motor 38 -third frequency converter -further DC coupling 100-coupling -1 5 -Reference numerals 2 -vacuum pump assembly

Claims

-16 -CLAIMS1. A vacuum pump assembly comprising: a first vacuum pump; a first motor configured to drive the first vacuum pump; a first converter configured to supply electrical power to the first motor; a second vacuum pump; a second motor configured to drive the second vacuum pump; and a second converter configured to supply electrical power to the second motor; and an electrical coupling directly electrically connecting the first converter to the second converter such that electrical power can flow directly from the first converter to the second converter.
2. The vacuum pump assembly of claim 1, wherein the first motor is further configured to operate in a generator or braking mode, thereby to reduce the frequency at which the first vacuum pump is operating, wherein, when operating in the generator or braking mode, the first motor generates electrical power.
3. The vacuum pump assembly of claim 2, wherein the second converter is further configured to, using the generated electrical power received via the electrical coupling, supply electrical power to the second motor.
4. The vacuum pump assembly of any preceding claim, wherein the electrical coupling is a conductive wire, wires or cable attached to the first converter at a 25 first end and attached to the second converter at a second end opposite to the first end.
5. The vacuum pump assembly of any preceding claim, wherein: -17 -the first converter comprises a first rectifier electrically coupled to a first inverter via a first DC link; and the second converter comprises a second rectifier electrically coupled to a second inverter via a second DC link.
6. The vacuum pump assembly of claim 5, wherein the electrical coupling directly connects the first DC link to the second DC link.
7. The vacuum pump assembly of any preceding claim, wherein one or more of the first converter, the second converter, and the electrical coupling comprises one or more energy storage devices.
8. The vacuum pump assembly of any preceding claim, wherein the first vacuum pump is a Roots vacuum pump.
9. The vacuum pump assembly of any preceding claim, wherein the second vacuum pump is a screw pump.
10. The vacuum pump assembly of any preceding claim, further comprising: one or more further vacuum pumps configured to operate at a constant frequency; one or more further motors, each of the one or more further motors being arranged to drive a respective further pump of the one or more further pumps, one or more further converters, each of the one or more further converters being arranged to supply electrical power to a respective further motor of the one or more further motors; and one or more further electrical couplings, each further electrical coupling of the one or more further electrical couplings electrically coupling a respective -18 -further converter to the first converter such that electrical power can flow from the first converter to that respective further converter.
11. The vacuum pump assembly of claim 10, wherein: each of the one or more further converters comprises a further rectifier coupled to a further inverter via a further DC link; and each of the further electrical couplings electrically connects the further DC link of a respective further converter to the first and/or second DC links.to
12. A method of operating a vacuum pump assembly, the method comprising: supplying electrical power, by a first converter, to a first motor; driving, by the first motor, a first vacuum pump at a first frequency; braking the first motor to reduce the frequency at which the first pump is driven from the first frequency to a lower frequency, thereby generating electrical power by the first motor; transferring the generated electrical power from the first motor to the first converter; and transferring the generated electrical power directly from the first converter to the second converter.
13. The method of claim 12, wherein braking the first motor comprises operating the first motor in a generator mode.
14. The method of claim 12 or claim 13, further comprising storing at least some of the generated electrical power in one or more electrical energy storage devices located in one or more of the first converter, the second converter, and the electrical coupling.
15. The method of claim 14, further comprising: using the electrical power transferred from the first converter, supplying electrical power by the second converter to a second motor; and driving, by the second motor, a second pump.