Field of the disclosure

The disclosure relates to an electric turbomachine that comprises an electric machine and at least one turbomachine stage comprising an impeller attached to a shaft of the electric machine. The electric turbomachine can be for example a turbocompressor, a pump, a blower, or a turbogenerator.

Background

In many cases, an electric turbomachine is a high-speed electric turbomachine that is provided with contactless bearings. The contactless bearings comprise typically axial magnetic bearings for axially supporting a rotating part of the electric turbomachine and radial bearings for radially supporting the rotating part. The rotating part comprises typically a rotor of an electric machine and one or more impellers attached to a shaft of the rotor. The radial bearings can be radial magnetic bearings, radial gas bearings, or radial liquid bearings. The axial magnetic bearings must be able to absorb axial forces acting on the rotating part. Correspondingly, the radial bearings must be able to absorb radial forces acting on the rotating part. The axial forces comprise a net effect of axial forces directed to one or more impellers of the turbomachine. In many cases, these axial forces which are caused by a pressure difference between different sides of each impeller can be significant. Furthermore, the axial forces comprise the gravitation force directed to the rotating part in cases where the electric turbomachine has a non-horizontal shaft, e.g. a vertical shaft.

The capacity of an axial magnetic bearing to carry axial force is dependent on areas of bearing surfaces of the axial magnetic bearing, on the magnetic permeability of material of the bearing surfaces, and on magnetic flux density on the bearing surfaces. As there are natural upper limits for the magnetic permeability and the magnetic flux density, the areas of the bearing surfaces determine the capacity of the axial magnetic bearing. In a case of a conical magnetic bearing which can generate both radial and axial forces, the areas of the bearing surfaces from the viewpoint of axial bearing capacity are the areas of axial projections of conical bearing surfaces. The axial projections are projections on a geometric plane that is perpendicular to the axial direction.

There are different alternatives to implement axial magnetic bearings of an electric turbomachine. In a first alternative, the electric turbomachine comprises conical bearings which can generate both radial and axial forces. In a second alternative, end surfaces of an electromagnetically active part of a rotor of an electric machine are configured to act as bearing surfaces of the axial magnetic bearings. In a third alternative, the axial magnetic bearing comprises a bearing disc attached to a shaft of the electrical machine and having axially facing bearing surfaces on opposite sides of the bearing disc. In conjunction with the above-mentioned first and second alternatives, it may in some cases be challenging to provide sufficiently large bearing surfaces to carry an axial load. On the other hand, the bearing disc in the third alternative may need an attachment mechanism which increases the length of the rotating part. The length of the rotating part is wanted to be minimized to maximize natural frequencies, such as bending mode natural frequencies, of the rotating part because, when a rotation speed approaches a speed that excites a natural frequency of the rotating part, the rotating part may begin to resonate. This can be a challenging phenomenon since it may be difficult to the bearings to generate sufficient support forces with a sufficient bandwidth.

Summary

The following presents a simplified summary in order to provide a basic understanding of some aspects of various invention embodiments. The summary is not an extensive overview of the invention. It is neither intended to identify key or critical elements of the invention nor to delineate the scope of the invention. The following summary merely presents some concepts of the invention in a simplified form as a prelude to a more detailed description of exemplifying embodiments of the invention.

In this document, the word “geometric” when used as a prefix means a geometric concept that is not necessarily a part of any physical object. The geometric concept can be for example a geometric point, a straight or curved geometric line, a geometric plane, a non-planar geometric surface, a geometric space, or any other geometric entity that is zero, one, two, or three dimensional.

In accordance with the invention, there is provided a new electric turbomachine that can be for example a high-speed electric turbomachine. The electric turbomachine can be for example a turbo-compressor, a pump, a blower, or a turbogenerator.

An electric turbomachine according to the invention comprises:

- an electric machine comprising a stator and a rotor configured to electromagnetically interact with each other,

- at least one turbomachine stage comprising an impeller attached to a shaft of the rotor, and

- at least one axial magnetic bearing comprising a magnetic actuator.

The above-mentioned impeller is a radial impeller comprising a backplate and vanes connected to the backplate. The backplate comprises ferromagnetic material and is configured to act as a part of the axial magnetic bearing so that the magnetic actuator of the axial magnetic bearing is configured to direct a magnetic force to the backplate. The impeller can be made of ferromagnetic material or, alternatively, a disc of ferromagnetic material can be at least a part of a backplate of an impeller that is otherwise made of non-ferromagnetic material.

As the backplate of the impeller is used as the part of the axial magnetic bearing, the rotating part of the electric turbomachine can be shorter and thereby natural frequencies, such as bending mode natural frequencies of the rotating part can be higher than in a case where there is an axial bearing disc separate from the impeller. Therefore, critical speeds of the rotating part can be higher. Furthermore, the surface of the backplate acting as a bearing surface can in many cases be greater than an end surface of an electromagnetically active part of the rotor or an axial projection of a bearing surface of a conical magnetic bearing. Thus, a sufficient axial bearing capacity can be achieved without a need for an axial bearing disc. Exemplifying and non-limiting embodiments are described in accompanied dependent claims.

Various exemplifying and non-limiting embodiments both as to constructions and to methods of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific exemplifying and nonlimiting embodiments when read in connection with the accompanying drawings.

The verbs “to comprise” and “to include” are used in this document as open limitations that neither exclude nor require the existence of unrecited features.

The features recited in dependent claims are mutually freely combinable unless otherwise explicitly stated.

Furthermore, it is to be understood that the use of “a” or “an”, i.e. a singular form, throughout this document does not exclude a plurality.

Brief description of the figures

Exemplifying and non-limiting embodiments of the invention and their advantages are explained in greater detail below in the sense of examples and with reference to the accompanying drawings, in which: figure 1 illustrates an electric turbomachine according to an exemplifying and nonlimiting embodiment, figure 2 illustrates an electric turbomachine according to an exemplifying and nonlimiting embodiment, figure 3 illustrates an electric turbomachine according to an exemplifying and nonlimiting embodiment, and figures 4a and 4b illustrate a part of an electric turbomachine according to an exemplifying and non-limiting embodiment. Description of exemplifying and non-limiting embodiments

The specific examples provided in the description below should not be construed as limiting the scope and/or the applicability of the accompanied claims. Lists and groups of examples provided in the description are not exhaustive unless otherwise explicitly stated.

Figure 1 illustrates an electric turbomachine according to an exemplifying and nonlimiting embodiment. Stationary elements of the electric turbomachine are presented as sections taken along a geometric section plane that is parallel with the yz-plane of a coordinate system 199. The electric turbomachine comprises an electric machine 101 that comprises a stator 102 and a rotor 103. The stator 102 comprises a ferromagnetic core structure and a multiphase winding, e.g. a three- phase winding, installed in slots of the ferromagnetic core structure. The rotor 103 comprises a shaft 106 and an electromagnetically active part for producing torque in co-operation with the stator 102. In this exemplifying case, the electric machine 101 is an induction machine and the electromagnetically active part of the rotor 103 comprises a cage winding. It is also possible that the electromagnetically active part of the rotor 103 comprises for example permanent magnets, wound windings, and/or ferromagnetic structures providing saliency. Thus, the electric machine 101 can be as well an electrically excited synchronous machine, a permanent magnet machine, or a reluctance machine. It is also possible that the electric machine 101 is an induction machine where the rotor comprises other electrically conductive structures instead of a cage winding.

The electric turbomachine comprises turbomachine stages 104 and 112. The turbomachine stage 104 comprises an impeller 105 that is attached to a first end of the shaft 106 of the rotor 103. The impeller 105 is a radial impeller that comprises a backplate 109 and vanes connected to the backplate 109. In figure 1 , one of the vanes is denoted with a reference 110. The turbomachine stage 104 comprises a casing 122. The casing 122 comprises typically a volute which surrounds the impeller 105. The casing 122 may further constitute a diffuser that converts kinetic energy of fluid into pressure by gradually slowing down a velocity of the fluid. The turbomachine stage 112 comprises an impeller 113 that is attached to a second end of the shaft 106 of the rotor 103. The impeller 113 is a radial impeller that comprises a backplate 115 and vanes connected to the backplate 1 15. In figure 1 , one of the vanes is denoted with a reference 114. The turbomachine stage 112 comprises a casing 123.

The electric turbomachine comprises axial magnetic bearings 107 and 116. The axial magnetic bearing 107 comprises a magnetic actuator 108 that has a ringshaped ferromagnetic core structure and a ring-shaped winding which surround the shaft 106 of the rotor 103. The backplate 109 of the impeller 105 comprises ferromagnetic material and it is configured to act as a part of the axial magnetic bearing 107 so that the magnetic actuator 108 of the axial magnetic bearing 107 is configured to direct a magnetic force to the backplate 109 in the negative y-direction of the coordinate system 199. The axial magnetic bearing 116 comprises a magnetic actuator 117 that has a ring-shaped ferromagnetic core structure and a ring-shaped winding which surround the shaft 106 of the rotor 103. The backplate 115 of the impeller 113 comprises ferromagnetic material and it is configured to act as a part of the axial magnetic bearing 116 so that the magnetic actuator 117 of the axial magnetic bearing 116 is configured to direct a magnetic force to the backplate 115 in the positive y-direction of the coordinate system 199.

In the exemplifying electric turbomachine illustrated in figure 1 , the electric machine 101 is a bearingless electric machine which does not comprise separate radial bearings but in which the stator 102 is used not only for producing torque in cooperation with the rotor 103 but also for magnetically levitating the rotor in radial directions i.e. in directions perpendicular to the y-axis of the coordinate system 199. In this exemplifying case, the electric turbomachine comprises position sensors 121 and 124 for producing position signals which are indicative of the position of the rotor 103 with respect to reference positions in axial and radial directions. In the exemplifying electric turbomachine illustrated in figure 1 , the position sensors 121 and 124 are integrated with the casings 122 and 123 of the turbomachine stages 104 and 112. It is also possible that the position of the rotor 103 is detected by supplying high-frequency measurement voltages to the windings of the axial magnetic bearings 107 and 116 and to the multiphase winding of the stator 102. Thereafter, the radial and axial positions of the rotor 103 can be determined based on impedances of different ones of the above-mentioned windings at the frequency of the measurement voltages. In this exemplifying case, there is no need for position sensors such as the above-mentioned position sensors 121 and 124.

In an electric turbomachine according to an exemplifying and non-limiting embodiment, each phase-winding of the multiphase winding of the stator 102 comprises an intermediate point and a controller 125 is configured to determine first current components and second current components so that torque is generated in accordance with electric machine control and magnetic levitation force is radially directed to the rotor 103 in accordance with levitation control when the first current components are supplied to terminals of the multiphase winding and the second current components are supplied to the intermediate points of the multiphase winding. The controller 125 is configured to carry out the levitation control in accordance with the position signals produced by the position sensors 121 and 124. The electric machine control can be for example scalar control or vector control. The electric turbomachine comprises a converter 111 configured to supply the above- mentioned first and second current components to the terminals and the intermediate points of the multiphase winding.

The implementation of the controller 125 can be based on one or more analogue circuits, one or more digital processing circuits, or a combination thereof. Each digital processing circuit can be a programmable processor circuit provided with appropriate software, a dedicated hardware processor such as for example an application specific integrated circuit “ASIC”, or a configurable hardware processor such as for example a field programmable gate array “FPGA”. Furthermore, the controller 125 may comprise one or more memory circuits each of which can be for example a Random-Access Memory “RAM” circuit.

In the exemplifying electric turbomachine illustrated in figure 1 , labyrinth seals are attached to the ring-shaped ferromagnetic core structures of the axial magnetic bearings 107 and 116 so that the labyrinth seals are between the ring-shaped ferromagnetic core structures and the shaft 106 of the rotor. In figure 1 , one of the labyrinth seals is denoted with a reference 127. The labyrinth seals reduce leakage of working fluid from the turbomachine stages to a gas-space of the electric machine 101 down to an acceptable level. In some cases, the working fluid that has leaked to the gas-space of the electric machine 101 can be utilized for cooling the rotor 103 and/or end-windings of the multiphase winding of the stator 102. In the exemplifying electric turbomachine illustrated in figure 1 , the ends of the electromagnetically active part of the rotor 103 are provided with winglets to enhance the cooling of the end-windings and the rotor 103. In figure 1 , one of the winglets is denoted with a reference 126. In the exemplifying electric turbomachine illustrated in figure 1 , the stator frame comprises cavities for liquid or gaseous cooling fluid, e.g. water, to cool the stator 102. In figure 1 , one of the cavities is denoted with a reference 126. A phase change of the cooling fluid can be used for enhancing the cooling.

Figure 1 illustrates a situation in which the electric turbomachine is operating as a turbo-compressor so that the turbomachine stages 104 and 112 are series connected. An outlet 118 of the turbomachine stage 104 is coupled with a fluid transfer connection to an inlet 119 of the turbomachine stage 112. In this exemplifying case, the electric turbomachine comprises a temperature control element 120 that is between the turbomachine stages 104 and 112 and is configured to change temperature of working fluid flowing from the outlet 118 of the turbomachine stage 104 to the inlet 119 the turbomachine stage 112. The temperature control element 120 can be for example an intercooler configured to cool the working fluid. In an exemplifying case in which the turbomachine stages are turbine stages configured to produce mechanical power, the temperature control element can be a heater.

Figure 2 illustrates an electric turbomachine according to an exemplifying and nonlimiting embodiment. Stationary elements of the electric turbomachine are presented as sections taken along a geometric section plane that is parallel with the yz-plane of a coordinate system 299. The electric turbomachine comprises an electric machine 201 that comprises a stator 202 and a rotor 203. The stator 202 comprises a ferromagnetic core structure and a multiphase winding installed in slots of the ferromagnetic core structure. The rotor 203 comprises a shaft 206 and an electromagnetically active part for producing torque in co-operation with the stator 202. The electric turbomachine comprises turbomachine stages 204 and 212. The turbomachine stage 204 comprises an impeller 205 that is attached to a first end of the shaft 206 of the rotor 203. The impeller 205 is a radial impeller that comprises a backplate 209 and vanes connected to the backplate 209. In figure 2, one of the vanes is denoted with a reference 210. The turbomachine stage 204 comprises a casing 222. The casing 222 comprises typically a volute which surrounds the impeller 205. The casing 222 may further constitute a diffuser. The turbomachine stage 212 comprises a casing 223 and an impeller 213 that has vanes and a backplate 215. In figure 2, one of the vanes of the impeller 213 is denoted with a reference 214. The impeller 213 is attached to the shaft 206 between the first end of the shaft and the electromagnetically active part of the rotor 203 so that the backplates 209 and 215 of the impellers 205 and 213 are facing towards each other.

The electric turbomachine comprises axial magnetic bearings 207 and 216. The axial magnetic bearing 207 comprises a magnetic actuator 208 that has a ringshaped ferromagnetic core structure and a ring-shaped winding which surround the shaft 206 of the rotor 203. The backplate 209 of the impeller 205 comprises ferromagnetic material and it is configured to act as a part of the axial magnetic bearing 207 so that the magnetic actuator 208 of the axial magnetic bearing 207 is configured to direct a magnetic force to the backplate 209 in the negative y-direction of the coordinate system 299. The axial magnetic bearing 216 comprises a magnetic actuator 217 that has a ring-shaped ferromagnetic core structure and a ring-shaped winding which surround the shaft 206 of the rotor 203. The backplate 215 of the impeller 213 comprises ferromagnetic material and it is configured to act as a part of the axial magnetic bearing 216 so that the magnetic actuator 217 of the axial magnetic bearing 216 is configured to direct a magnetic force to the backplate 209 in the positive y-direction of the coordinate system 299. As shown in figure 2, the magnetic actuators 208 and 217 of the axial magnetic bearings are between the backplates 209 and 215 of the impellers 205 and 213.

In the exemplifying electric turbomachine illustrated in figure 2, the electric machine 201 comprises radial magnetic bearings 231 and 232 configured to support the rotor 203 in radial directions of the rotor, i.e. in directions perpendicular to the y-axis of the coordinate system 299. The electric turbomachine comprises position sensors 221 for producing a position signal indicative of the axial position of the rotor 203 with respect to an axial reference position. The axial magnetic bearings 207 and 216 are controlled in accordance with the position signal produced by the position sensors 221 . As shown in figure 2, the position sensors 221 are between the axial magnetic bearings 207 and 216. From the viewpoint of thermal expansion of the shaft 206, it is advantageous that the position sensors 221 which measure the axial position of the rotor 203 are near to the axial magnetic bearings 207 and 216 which control the axial position of the rotor 203. The electric turbomachine comprises position sensors 229 and 230 for producing position signals indicative of the radial position of the rotor 203 with respect to a radial reference position. The radial magnetic bearings 231 and 232 are controlled in accordance with the position signals produced by the position sensors 229 and 230. Is also possible that an electric turbomachine according to an exemplifying and non-limiting embodiment comprises radial gas bearings or radial liquid bearings.

Figure 3 illustrates an electric turbomachine according to an exemplifying and nonlimiting embodiment. Stationary elements of the electric turbomachine are presented as sections taken along a geometric section plane that is parallel with the yz-plane of a coordinate system 399. The electric turbomachine comprises an electric machine 301 that comprises a stator 302 and a rotor 303. The stator 302 comprises a ferromagnetic core structure and a multiphase winding installed in slots of the ferromagnetic core structure. The rotor 303 comprises a shaft 306 and an electromagnetically active part for producing torque in co-operation with the stator 302. The electric turbomachine comprises a turbomachine stage 304 that comprises a casing 322 and an impeller 305 that is attached to a first end of the shaft 306 of the rotor 303. The impeller 305 is a radial impeller that comprises a backplate 309 and vanes connected to the backplate 309. In figure 3, one of the vanes is denoted with a reference 310.

The electric turbomachine comprises an axial magnetic bearing 307 that comprises a magnetic actuator 308 that has a ring-shaped ferromagnetic core structure and a ring-shaped winding which surround the shaft 306 of the rotor 303. The backplate 309 of the impeller 305 comprises ferromagnetic material and it is configured to act as a part of the axial magnetic bearing 307 so that the magnetic actuator 308 of the axial magnetic bearing 307 is configured to direct a magnetic force to the backplate 309 in the positive y-direction of the coordinate system 399. In this exemplifying case, the axial direction of the rotor 303 is vertical so that the gravity force tends to move the rotor 303 in the negative y-direction of the coordinate system 399. Furthermore, a pressure difference over the impeller 305 tends to move the rotor 303 in the negative y-direction of the coordinate system 399. The gravity force and the force caused by the pressure difference over the impeller 305 are balanced with the magnetic force directed to the backplate 309 of the impeller 305. The electric turbomachine can be further provided with one or more permanent magnet arrangements which partly balance the gravity force and the force caused by the above-mentioned pressure difference. The permanent magnet arrangements are not shown in figure 3.

In the exemplifying electric turbomachine illustrated in figure 3, the electric machine 301 comprises radial magnetic bearings 331 and 332 configured to support the rotor 303 in radial directions of the rotor, i.e. in directions perpendicular to the y-axis of the coordinate system 399. Is however also possible the electric machine 301 comprises radial gas bearings or radial liquid bearings.

Figure 4a illustrates a part of an electric turbomachine according to an exemplifying and non-limiting embodiment. Stationary elements are presented as sections taken along a geometric section plane that is parallel with the yz-plane of a coordinate system 499. The electric turbomachine comprises an electric machine and a turbomachine stage 404. Figure 4a shows a first end of a shaft 406 of the rotor of the electric machine. The other parts of the electric machine are not shown. The electric machine can be for example such as the electric machine 101 depicted in figure 1 or such as the electric machine 201 depicted in figure 2. The turbomachine stage 404 comprises an impeller 405 that is attached to the first end of the shaft 406. The impeller 405 is a radial impeller that comprises a backplate 409 and vanes connected to the backplate 409. In figure 4a, one of the vanes is denoted with a reference 410. Furthermore, the turbomachine stage 404 comprises a casing 422.

The electric turbomachine comprises an axial magnetic bearing 407 that comprises a magnetic actuator 408. Figure 4b shows the magnetic actuator 408 when seen along the negative y-direction of the coordinate system 499. The magnetic actuator 408 comprises a ferromagnetic core structure 443 and windings which surround the shaft 406. The backplate 409 of the impeller 405 comprises ferromagnetic material and it is configured to act as a part of the axial magnetic bearing 407 so that the magnetic actuator 408 is configured to direct an axial magnetic force to the backplate 409.

In the exemplifying turbomachine illustrated in figures 4a and 4b, the ferromagnetic core structure 443 of the magnetic actuator 408 is provided with axially directed apertures and the electric turbomachine comprises sensors arranged to protrude through the axially directed apertures towards the backplate 409 of the impeller 405. Each of the sensors is configured to detect an axial distance, i,e. an y-directional distance, from the sensor to the backplate 409. In figures 4a and 4b, two of the sensors are denoted with references 441 and 442. The sensors can be for example eddy current sensors or some other suitable sensors. In the exemplifying case illustrated in figures 4a and 4b, there are four sensors. It is however also possible that there is only one sensor, or there are two, three, or more than four sensors.

The specific examples provided in the description given above should not be construed as limiting the scope and/or the applicability of the appended claims. For example, it is to be noted that the electric machines and the radial bearings discussed above and presented in the appended figures are examples only and electric turbomachines according to different embodiments may comprise various kinds of electric machines and radial bearings. Lists and groups of examples provided in the description given above are not exhaustive unless otherwise explicitly stated.