WO2020095137A1

WO2020095137A1 - Fluid pump drive device, more particularly a compressor device and pump device

Info

Publication number: WO2020095137A1
Application number: PCT/IB2019/059036
Authority: WO
Inventors: Bart Maria M. RAES; Yassine BENÔMAR; Peter Jozef Heirman; Stijn Johan E. BROUCKE
Original assignee: Atlas Copco Airpower, Naamloze Vennootschap; Vrije Universiteit Brussel
Priority date: 2018-11-07
Filing date: 2019-10-23
Publication date: 2020-05-14
Also published as: FR3088091B3; FR3088091A3; BE1026762A1; BE1026762B1

Abstract

Fluid pump device provided with a fluid pump element with a drive (3) and further provided with a control unit (18) that is connected to a pressure sensor (17) configured to measure the pressure of the fluid, downstream from the fluid pump element, characterised in that the drive (3) comprises a brushless, double-feed synchronous reluctance motor with a rotor (10) and at least one stator (11), whereby the rotor (10) is configured to drive or form a driven shaft (9), whereby the drive is further provided with at least two windings (12 and 13), at least one winding (12) of which is connected to a fixed frequency power supply (14) and at least one other winding (13) is connected to a frequency converter (15), and that said control unit (18) is also connected to said frequency converter (15) and is provided with an algorithm to control the drive (3) based on a reading from said pressure sensor (17), such that the pressure of the fluid, downstream from the fluid pump element: - is set to a desired value; or - is kept within a certain pressure range, this pressure range being defined by an upper and lower limit of the pressure of the fluid, downstream from the fluid pump element.

Description

Fluid pump device, more particularly a compressor device and pump device.

The present invention relates to a fluid pump device such as a compressor device or a pump device.

Traditionally, such fluid pump devices are driven by a drive, either fixed speed or variable speed.

A fixed speed drive is cheaper and simpler to implement than a variable speed drive.

However, a variable speed drive has a number of specific advantages.

In particular such variable speed drive will be able to reduce the energy consumption of, for example, the compressor device, as it allows the speed to be adapted to the varying demand for compressed gas. In this way, a reduction in the consumption of up to 35% and even more can be realised, depending on the type of compressor device.

Although a variable speed drive has big advantages, it involves extra costs and complexity due to the presence of a frequency converter that can cause a certain power loss.

This is why a fixed speed drive is often chosen. The purpose of the present invention is to provide a solution to at least one of the aforementioned and other disadvantages by providing a fluid pump device, whereby the power losses and the cost price of the frequency converter can be drastically reduced.

To this end the present invention relates to a fluid pump device as described in claim 1.

Such fluid pump device according to the invention comprises as it were a combination of a fixed speed motor and a variable speed motor.

Preferably, the winding that is directly connected to the fixed frequency power supply will feed a certain power P_grid to the rotor of the drive, while the winding that is connected to the frequency converter will feed a variable power Pcontroi to the rotor, where primarily Pcontroi is equal to P_grid multiplied by the ratio of the variable frequency of the frequency converter and the fixed frequency.

Both aforementioned powers Pcontroi and P_grid are added up and form the total power.

The rotor's maximum speed of rotation will depend on this eventual total power, whereby the ratio of the torques delivered by the different windings remains constant.

The rotor can be coupled with or serve as the drive shaft of said fluid pump. As the winding connected to the fixed frequency power supply will always feed a constant frequency to the rotor and thus provide a constant part of the total speed, this can be considered as a fixed speed motor.

The fixed frequency power supply is for example, but not necessarily, an electrical grid.

The winding connected to the frequency converter, on the other hand, shall provide a variable part of the total speed, such that this can be considered as a variable speed motor .

In this way a fluid pump device according to the invention allows the principle of the combination of a fixed speed motor with a variable speed motor to be applied to drive a fluid pump such as a compressor or a pump.

The biggest advantage is that the frequency converter will be smaller scale and therefore cheaper than when all the power were to be supplied solely by the frequency converter .

Indeed, in a conventional variable speed drive with a rotor and stator, the stator will only contain one winding which is connected to the electrical grid via the frequency converter. The frequency converter will have to be able to convert the power over the entire power range of the drive to control the rotor over the entire speed range. In a fluid pump device according to the invention the frequency converter only needs to be adjustable over a range of 50% of the total power, for example, to be able to reach the full speed range if it concerns a bi-directional frequency converter.

The winding that is directly connected to the electrical grid will supply a constant power of 50% of the total maximum power, for example. The other winding will have a variable or adjustable power up to 50% of the total maximum power. The frequency converter therefore only needs to have half the range of the conventional frequency converter.

If the frequency converter is also a regenerative frequency converter, it can supply a 'negative power' or take up power and feed it back into the electrical grid.

Said other winding shall thus be able to supply variable or adjustable power from -50% to +50%, such that the sum of the power of both windings will therefore vary from 0 to 100% of the total power.

By halving the control range of the frequency converter, for example, its cost price will also be greatly reduced. This also means the power losses will be smaller.

But it will also be possible to realise a drive whereby the power of the rotor can vary in a more limited control range, for example between 30% and 100%. This means, whereas a traditional variable speed drive is always adjustable from 0 to the maximum power or speed, in this embodiment the drive according to the invention will possess an adjustable power or speed from a certain minimum to the maximum power or speed, whereby this minimum is greater than zero, such that for example a range, within which the power or speed is adjustable, is possible from 30% to 100%.

According to the invention this can be realised, for example, by having the winding that is directly connected to the fixed frequency power supply, deliver a constant power of 65% of the total maximum power and by varying the power of the other winding that is connected to the frequency converter from -35% to +35% of the total maximum power by controlling the frequency. The combination of both windings then results in a possible variation in power, and therefore speed, from 30% to 100% of the total maximum power or speed.

In this case the frequency converter will have to make a variation of only 35% possible.

This more limited range has no disadvantages compared with a control range between 0% and 100%.

Indeed, consumers often do not need variable speed over the whole operational range. Under a certain minimum speed, a compressor device with a variable speed drive, for example, will behave as a load/unload controlled compressor due to decreasing efficiency of the compressor installation at low speeds. In this case, the compressor installation will be in operation between two pressure set points.

As a result, there is no need for an adjustable speed lower than 30% of the maximum speed and in practice, an adjustable speed in the range between 30% and 100% is sufficient .

According to the invention, the fluid pump device is provided with a control unit that is connected to a sensor and with said frequency converter; and said control unit comprises an algorithm to control the compressor element based on a reading from said sensor.

According to the invention, said sensor is formed by a pressure sensor that is configured to measure the pressure of the fluid, downstream from the fluid pump element, downstream from the outlet of the fluid pump element.

Said algorithm is configured to:

- control said pressure of the fluid downstream from the fluid pump element to a desired value:

or

- keep it within a certain pressure range, said pressure range being defined by an upper and lower limit of the fluid pressure in question, for example the pressure in a pressure vessel that is connected to the outlet of said fluid pump element.

With the intention of better showing the characteristics of the invention a few embodiments of a variable speed fluid pump device according to the invention are described hereinafter, by way of an example without any limiting nature, with reference to the accompanying drawings, wherein : figure 1 schematically shows a fluid pump according to the invention;

figure 2 schematically shows a drive of a fluid pump device according to the invention.

The fluid pump schematically shown in figure 1 in this case relates to a compressor device 1, which essentially comprises a compressor element 2 that is driven by a drive

3.

In this case this compressor element 2 is a screw compressor element, but this is not necessary for the invention. It can for example also concern a piston compressor or a scroll compressor.

The compressor element 2 is provided with a housing 4 with an inlet 5 to suck in gas and an outlet 6 for compressed gas . In this case two screw rotors 7 are rotatably mounted in the housing 4, whereby, in this example, each screw rotor 7 comprises a shaft 8, and whereby the shafts 8 are mounted with bearings in the housing 4.

In this example one of the shafts 8 extends through the housing 4 to the drive 3. In this case this shaft 8 is the driven shaft 9 of the compressor element 2.

The drive 3 essentially comprises a rotor 10 and at least one stator 11; as shown in figure 2.

In this case the rotor 10 serves as the driven shaft 9, this means: an extended section of the rotor 10 forms the driven shaft 9, but it is also possible that the rotor 10 or an extended section thereof is directly or indirectly coupled to the driven shaft 9, via gearwheels or another form of mechanical coupling.

Apart from the rotor 10 and at least one stator 11, the drive 6 comprises two windings 12 and 13 in this case.

In this case, but not necessarily, the two windings 12 and 13 are mounted on one stator 11 and the rotor 10 is free from windings.

It is not excluded that two stators 11 are present and that every stator 11 is provided with one or at least one winding 12 or 13. Also, the rotor 10 in this example is made of a material with a low magnetic reluctance, such as for example iron.

It is also possible that one or at least one winding 12 or 13 is mounted on the rotor 10 and one or at least one winding is mounted on the stator 11.

It is also possible that in such a set-up, the rotor 10 is provided with permanent magnets or is partly made of copper, aluminium or another electrically conductive material .

According to the invention, one winding 12 is directly connected to a fixed frequency power supply, for example an electrical grid 14 and one winding 13 is connected to a frequency converter 15 which in turn can be connected to the electrical grid 14.

The frequency converter 15 will ensure that the power supplied to the rotor 10 by the winding 13 in question can be varied.

Preferably, but not necessarily, the frequency converter 15 is a regenerative frequency converter 15, this means it will also allow power to be fed back into the grid 14.

Preferably, the drive 3 is also a brushless drive, without carbon brushes or slip rings. This has the advantage that the drive 3 is very reliable and only requires minimal maintenance . In addition to the compressor element 2 and the drive 3, the compressor device 1 can also be provided with an oil circuit for injecting oil or another liquid in the compressor element 2 or the drive 3 for cooling and/or lubricating.

The compressor device 1 can also be provided with a liquid separator, a pressure vessel, one or more sensors, such as for example pressure or temperature sensors and/or other peripheral equipment.

In this case the compressor device 1 is provided with a pressure vessel 16 on which the outlet 6 ends, and a pressure sensor 17 configured to measure the pressure p of the fluid, downstream from the fluid pump element, in this case the pressure in the pressure vessel.

It is not excluded that the pressure sensor 17 is mounted at the outlet 6 of the compressor element 2.

The pressure sensor 17 is connected to a control unit 18, which in turn is connected to said drive 3, all this such that the signal of the pressure sensor 17 goes to the control unit 18, which based on this can control the drive

3.

The control unit 18 is for example, but not necessarily, a PID controller. The operation of the fluid pump device 1 according to the invention is very simple and as follows.

During operation of the fluid pump device, so in this case the compressor device 1, the drive 3 will drive the fluid pump element (here in the form of the compressor element 2), whereby the screw rotors 7 will rotate and will compress the gas, sucked in via the inlet 5, in the known way. The compressed gas will leave the compressor element 2 via the outlet 6.

The rotation of the rotor 10 of the drive 3 is transmitted to the compressor element 2 via the driven shaft 9.

The speed of the rotor 10 is determined by the power which is delivered to the rotor 10 by the two windings 12 and 13.

The winding 12 will supply a power P_grid to the rotor 10. This power P_grid is constant, to the extent that the load of the compressor element is constant.

The winding 13 will supply a variable power P_COntroi to the rotor 10, which is controlled by the frequency converter 15.

In this case, but not necessarily according to the invention, the winding 13 will also be able to supply a 'negative' power, this means that power can be fed back to the electrical grid 14. The sum of both powers P_grid + Pcontroi shows the total power P of the rotor 10, which in turn will be a measure for the speed of the rotor 10.

It is clear that by allowing the winding 12 to supply fifty percent of the total maximum power and making the winding 13 adjustable over a range of -50% to +50% of the total maximum power, a control range is possible from 0% to 100% of the total maximum power of the drive 3.

This means that it will be possible to vary the speed of the rotor 10 from 0% to 100% of the maximum speed.

The control of the frequency of the voltage over the winding 13 or in other words the control by the frequency converter 15 will be done using the control unit 18 which to this end is connected to said frequency converter 15.

Based on the measurement of the pressure sensor 17, the control unit 18 will control the frequency converter 15 such that the power that this winding 13 supplies to the rotor 10, and therefore the speed of the rotor 10, increases or decreases, such that a desired pressure is obtained in the pressure vessel 16.

Alternatively, it is also possible that the control unit 18 controls the frequency converter 15 in such a way that the pressure in the pressure vessel 16 remains within a certain pressure range, said pressure range being defined by an upper and lower limit of the pressure in the pressure vessel 16.

Although the examples and embodiments described above and shown in the figures, typically refer to a compressor device 1, it is not excluded that the fluid pump device relates to a pump device, for example a liquid pump device.

Indeed, the drive 3 according to the invention is also suitable to be applied in such pump devices.

The present invention is by no means limited to the embodiments described as an example and shown in the drawings, but a fluid pump device according to the invention can be realised in all kinds of forms and dimensions, without departing from the scope of the invention .

Claims

Claims .

1.- Fluid pump device provided with a fluid pump element with a drive (3) and further provided with a control unit

(18) that is connected to a pressure sensor (17) configured to measure the pressure of the fluid, downstream from the fluid pump element, characterised in that the drive (3) comprises a brushless, double-feed synchronous reluctance motor with a rotor (10) and at least one stator (11) , whereby the rotor (10) is configured to drive or form a driven shaft (9), whereby the drive is further provided with at least two windings (12 and 13), at least one winding (12) of which is connected to a fixed freguency power supply (14) and at least one other winding (13) is connected to a frequency converter (15), and that said control unit (18) is also connected to said frequency converter (15) and is provided with an algorithm to control the drive (3) based on a reading from said pressure sensor (17), such that the pressure of the fluid, downstream from the fluid pump element:

- is set to a desired value; or

- is kept within a certain pressure range, this pressure range being defined by an upper and lower limit of the pressure of the fluid, downstream from the fluid pump element .

2.- Fluid pump device according to claim 1, characterised in that it is made in the form of a compressor device and that the fluid pump element consists of a compressor element (2); and that the outlet of the compressor element (2) is connected to a pressure vessel (16) and that said pressure sensor (17) is configured to measure the pressure in this pressure vessel (16) .

3.- Fluid pump device according to claim 1 or 2, characterised in that said two or more windings (12 and 13) are mounted on the stator (11) .

4. - Fluid pump device according to any one of the previous claims, characterised in that there are two stators (11) and that every stator (11) is provided with at least one winding ( 12 , 13 ) .

5. Fluid pump device according to any one of the previous claims, characterised in that the fixed frequency power supply (14) is configured to feed a certain power Pgrid to the rotor (10) and that the winding (13) which is connected to the frequency converter (15) is configured to feed a variable power Pcontrol to the rotor (10).

6.- Fluid pump device according to any one of the previous claims, characterised in that the rotor (10) is provided with permanent magnets and/or an electrically conductive material .

7.- Fluid pump device according to any one of the previous claims, characterised in that the frequency converter (15) is a regenerative frequency converter (15).

8.- Fluid pump device according to any one of the previous claims, characterised in that the frequency converter (15) is configured to supply less than 50% of the power. 9.- Fluid pump device according to any one of the previous claims, characterised in that said fixed frequency power supply (14) is an electrical grid provided with single or multiphase AC voltage supply.