Synchronous reluctance machine

A synchronous reluctance machine includes a stator and a rotor which is spaced apart from the stator by an air gap. The rotor rotatably mounted about an axis and includes laminations which are arranged axially one behind the other. Each lamination has an anisotropic magnetic structure which is formed by flux blocking sections and flux conducting sections. The flux blocking sections and flux conducting sections form poles of the rotor, with the flux blocking sections forming axially running channels and allowing an axial air flow. The laminated core of the rotor is axially subdivided into at least two component laminated cores, with radial cooling gaps being formed between the poles in the region of the q axis as viewed in a circumferential direction and between the component laminated cores as viewed axially.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is the U.S. National Stage of International Application No. PCT/EP2016/068047, filed Jul. 28, 2016, which designated the United States and has been published as International Publication No. WO 2017/032543 and which claims the priority of European Patent Application, Serial No. 15182109.7, filed Aug. 24, 2015, pursuant to 35 U.S.C. 119(a)-(d).

BACKGROUND OF THE INVENTION

The invention relates to a synchronous reluctance machine, in particular a motor or a generator of a wind power plant comprising a stator and a rotor which is spaced apart from said stator by an air gap and which is rotatably mounted about an axis, which has an anisotropic magnetic structure, which is formed by flux blocking sections essentially arranged axially one behind the other.

The invention likewise relates to a wind power plant with a generator designed in this way.

As a rule asynchronous machines with cage armatures or synchronous machines are used as dynamo-electric machines, i.e. motors or generators with a power of a few hundred kW and greater. However these machines have a rotor that is complex to manufacture, with a short-circuit cage or a pole winding.

Machines in this power class generally need a cooling of the rotor, since the losses arising there are no longer able to be dissipated solely by convection. Thus the rotor is usually cooled by cooling air, which is generated by self-ventilation or by outside ventilation. Moreover the stator of such a machine must be supplied evenly with cooling air over its entire axial length. With these machines described above a high power factor is frequently demanded, in order to minimize the proportion of reactive power that must be made available to operate the machine.

With dynamo-electric machines of this power class a distinction is essentially made between two types of primary cooling with air. On the one hand there are machines through which air flows only in an axial direction, such as is described for example in DE 2009 051 651 B4. In this invention a circulation of this type is combined with a water jacket cooling of the laminated core of the stator.

Furthermore there are dynamo-electric machines, in which the cooling air also flows radially through the machine, specifically through the stator. In order to make this possible, stator and rotor laminated cores are interrupted by radial cooling slots. This enables the surface onto which the air flows to be significantly enlarged.

Thus DE 10 2012 210 120 A1 describes a dynamo-electric machine with radial cooling slots in stator and rotor and a separate cooling circuit for the winding heads.

Disclosed in EP 2 403 115 A1 is a concept with radial cooling slots for a permanently excited synchronous machine.

A synchronous reluctance machine has the disadvantage, compared to the machines mentioned above, that the power factor is comparatively low and lies at around 0.7 to 0.75. For this reason this type of machine is hardly used at all in the power class of a few hundred kW and greater.

For example the cooling of a reluctance machine of a smaller power and size is described in EP 2 589 132 B1. In this arrangement the cooling air flows axially through flux barriers of the rotor. The stator is fully, laminated in the axial direction.

For machines of greater power this cooling is not suitable inter alia, since the ratio of volume to surface is too small and thus a sufficient cooling surface is not available.

SUMMARY OF THE INVENTION

Using this as its starting point, the underlying object of the invention is to create a synchronous reluctance machine, in particular for a higher power class of a few hundred kW and greater, which with sufficient cooling provides a comparatively high power factor. Furthermore the synchronous reluctance machine is to be suitable for use in wind power plants.

The object of the said task is successfully achieved by a synchronous reluctance machine, in particular a motor or a generator, with a power of greater than 300 kW, with a stator and a rotor spaced apart from said stator by an air gap and rotatably mounted about an axis, of which the laminations arranged axially one behind the other each have an anisotropic magnetic structure, which is formed by flux blocking sections and flux conducting sections and wherein the flux blocking sections and flux conducting sections form poles of the rotor, wherein these flux blocking sections form channels running axially and make an axial air flow possible, wherein the laminated core of the rotor is subdivided axially into at least two component laminated cores, wherein radial cooling gaps are present in each case between the poles in the region of the q axis viewed in the circumferential direction, and viewed axially, are present between the component laminated cores.

The cooling is now improved by the inventive structure of the synchronous reluctance machine, as well as also the difference in the inductance being increased between the d and q axis of the rotor of the synchronous reluctance machine, which ultimately improves the power factor of the synchronous reluctance machine. In this power class of 300 kW and greater in this case a power factor of around 0.8 or greater is possible. The proportion of reactive power that must be made available for operating the machine can thus be reduced, which is of particular advantage in generators of wind power plants.

Viewed in the axial direction, the rotor has at least two component laminated cores, between which radial cooling gaps are present. Each flux blocking section thus has at least one cooling gap within its axial course in the rotor.

Advantageously the intermediate elements are embodied as magnetically conductive parts, so that in these sections too an additional magnetic flux can be conveyed in the rotor. The inductance in the d axis is also increased by this. These intermediate elements as magnetically conductive parts are advantageously manufactured with the same tools, e.g. punching tools, as the further laminations of the rotor. In this case they are also designed as metal laminations. By additional work steps on the intermediate elements, e.g. punching or cutting, additional options, larger cutouts, spacers, elements with a ventilation effect can be provided in these laminations.

The magnetically conductive parts of the intermediate elements can however be designed not just as laminations, but also as massive parts. This is especially of advantage when the magnetically conductive parts no longer extend as far as the air gap of the synchronous reluctance machine, since there are likely to be eddy current losses above all on the surface of the rotor.

The laminated core of the rotor is designed as axially continuous, at least in the area of the d axis. Flanking flux barriers of the d axis are additionally present, depending on the axial position in the laminated core of the reluctance rotor.

In further versions in this case, in the area of the cooling gap, the radial extent of the intermediate elements, i.e. the laminations of the d axis, can be designed radially reduced, in order to reduce eddy current losses. In such cases the radial reduction of the intermediate elements is oriented to the radial depth of the respective flux barrier.

Advantageously the difference in the inductances of the d axis and q axis of the rotor can be additionally increased when the laminated core of the rotor is designed axially around 10% longer than that of the stator. This makes for a further improvement in the power factor.

A flow of cooling air now conveyed axially, which enters into the rotor, depending on the flux blocking sections, is now diverted radially into radial cooling channels completely or at least partly. These bulkhead elements can for example be embodied from one or more individual laminations, which are preferably not magnetically conductive. The scatter losses are reduced by this.

As an alternative thereto these bulkhead elements can also be provided as laminations with cutouts with a closure of the flux blocking sections, which preferably consists in its turn of magnetically non-conductive material, such as e.g. plastic.

A flow of cooling air entering into the rotor axially via the respective flux blocking sections is subsequently—depending on the position of the flux blocking section—diverted radially in the direction of the air gap of the synchronous reluctance machine. Thereafter this flow of cooling air enters radial cooling slots and exits again on the rear side of the laminated stator core.

In one form of embodiment the radial cooling slots of the stator are arranged at least in part above the radial cooling slots of the rotor.

In a further form of embodiment the radial cooling slots of the stator are in any event not arranged above the radial cooling slots of the rotor. They are thus located at different axial positions.

Thus both the rotor and also the laminated core of the stator are now efficiently cooled. On the back of the laminated stator core, i.e. on the outer side of the stator—if the synchronous machine is designed as an inner armature—the cooling air can be collected and conveyed to one or both outlet-side winding heads, wherein on the way thereto and/or thereafter the heated cooling air flow is cooled back down by means of a heat exchanger.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1shows, in a part longitudinal section, a synchronous reluctance machine20with a stator1, has a winding head2which on its axial end face sides in each case, which each belong to a winding system not shown in any greater detail, which is embedded in grooves of the stator1that essentially run axially.

The stator1is spaced apart from a rotor3by an air gap19, wherein the rotor3is connected in a torsion-proof manner to a shaft4and is mounted rotatably about an axis18. The rotor3is designed as a four-pole reluctance armature, wherein, viewed in the circumferential direction, four poles are formed by flux blocking sections14,15,16and flux conducting sections8present between said sections. In this exemplary embodiment, viewed in the radial direction, three flux blocking sections14,15,16are present.

The inventive idea is not restricted to the four-pole synchronous reluctance machine20but is also able to be transferred to two-pole, six-pole, eight-pole machines etc.

Located in stator1, which is embodied as a laminated core, are axial and/or especially radial cooling channels5, which in accordance with this exemplary embodiment, are radially flush with radial cooling channels6or cooling gaps of the rotor3.

Component laminated cores30,31,32,34of the rotor3, which are each spaced apart from one another by intermediate elements7, at least in the region of the q axis, are created by the radial cooling channels6of the rotor.

The radial cooling channels5of the stator1and the radial cooling channels6of the rotor3differ in their number and axial positioning in the axial course of the respective laminated core of stator1and rotor3. The radial flush positioning of the cooling channels5,6either does not occur at all or occurs for all or merely for a few predetermined cooling channels5,6.

The flux blocking sections14,15,16essentially form cooling channels running axially, through which a flow of cooling air can be conveyed. Bulkhead elements11embodied accordingly, depending on the embodiment of said bulkhead elements11, now enable the topmost flux blocking section14or the middle flux blocking section15or the lowest flux blocking section16to be influenced in its course of the coolant flow and coolant throughput. In this case, either the entire cooling air flow running axially located in one of the flux blocking sections14,15,16is diverted and is conveyed radially via the air gap19if necessary into a cooling channel6of the stator1corresponding thereto, or only a part of the cooling air flow is diverted radially.

A flux barrier running axially must if necessary also “supply” two or more of its radial cooling slots6with cooling air as evenly as possible. To this end the through-openings25,26in the bulkhead elements11in accordance withFIGS. 5, 6are dimensioned accordingly for flow purposes, in that for each flux barrier11e.g. of a lamination according toFIG. 3Aa, a number of holes26or a reduced radial height or a narrowing25of the flux barrier11is provided.

Advantageously the bulkhead elements11are also embodied as metal laminations amagnetically. The intermediate elements7are provided as electromagnetically conductive parts, in order thereby to enlarge the magnetically conductive part of the rotor1, in particular in the area of the d axis, which additionally improves the power factor of the synchronous reluctance machine20.

FIG. 1shows a single-inlet synchronous reluctance machine20, wherein the cooling air flow only enters the machine, in particular the rotor3, from one side. Independently of whether the cooling air now exits radially from the stator1and/or axially from the rotor3, there can be a heat exchanger17located downstream in flow terms after the heating-up in the laminated cores of the stator1and rotor3, which cools the cooling air back down to a predetermined temperature. Advantageously in this case a frequency converter50, shown schematically inFIG. 7, is cooled back down, which can likewise be influenced by an additional or by the same heat exchanger17in its temperature behavior.

Diversion elements21shown in principle convey the cooling air, optionally driven using a fan22, through the heat exchanger17. The heat exchanger is not necessarily arranged radially above the stator1. The heat exchanger17can for example also be located axially on the end face sides of the synchronous reluctance machine20.

FIG. 2shows a synchronous reluctance machine20, which is embodied with two inlets, i.e. a flow of cooling air enters into the rotor3via the flux blocking section14,15,16from both the one and also the other axial end face side of the rotor3. As described above for the single-inlet machine in accordance withFIG. 1, the cooling air is diverted in the flux blocking sections14,15,16, as a result of the mechanical design, in a similar or in the same manner.

To separate the two cooling air flows to be moved towards each other, there can be a partition provided in the form of a continuous—preferably non-magnetic—partition wall12roughly in the middle of rotor3and/or rotor3and stator1. This is designed, as regards its cross section, like the bulkhead elements1in accordance withFIG. 3Cc or 3Dj. Thus the flows of air are decoupled from one another on both sides of the partition wall12, preferably in terms of flow, and an even distribution of the cooling air over the entire axial length of the machine is created. Scatter losses are avoided by the amagnetic design of the partition wall12.

A conventional rotor lamination is shown inFIG. 3Aa.

The flux blocking sections14,15,16each run in the shape of an arc or in the shape of a bowl and symmetrically to the respective q axis.

The intermediate elements7, like the conventional rotor laminations in accordance withFIG. 3Aa, contain cutouts, which are referred to as flux blocking sections and which also convey the air in the axial direction through the rotor3. Metal lamination sheets in accordance withFIGS. 3Bb to 3bDare provided at predetermined axial intervals, which make a radial exit from the respective flux blocking section and the rotor3possible for the air in the flux blocking sections. The cutouts9shown there extend at least from a flux blocking section, which functions as axial cooling channel, up to the outer diameter of the laminated rotor core of the rotor3, i.e. as far as the air gap19. Each cutout9between two d axes in this embodiment forms a cooling channel6—so that with a four-pole reluctance armature—four cooling gaps6are present after each component laminated core.

With a six-pole or eight-pole reluctance armature there are accordingly six or eight cooling gaps after each component laminated core.

The cutout10in the conventional rotor lamination in accordance withFIG. 3Aaon the outer side of the rotor3likewise serves as a flux barrier lying on the outside of the rotor3.

The flux barrier10lying on the outside in a conventional rotor lamination in accordance withFIG. 3Aacan have air, but also amagnetic material, in order to obtain a homogeneous air gap19. This reduces the noise level, especially with high-revving machines.

Additional magnetic flux can now be conveyed in the rotor3by means of the magnetically conductive intermediate elements7. The inductance in the d axis of the rotor3is increased thereby. The comparatively better conductance now also enables the flux barriers to be selected larger in their geometrical dimensions, in particular their radial height, whereby the inductance in the q axis falls. Thus overall a greater difference in the inductances of the d and q axis is produced and the power factor of the synchronous reluctance machine20is improved.

The magnetically conductive intermediate elements7, in particular of the rotor3, can be manufactured with the same tools, e.g. with the same punch tools, as the further laminations of the rotor3. By additional processing of the sheets, e.g. additionally punching processes or cutting processes, suitable larger cutouts9or spacers can also be manufactured. The magnetically conductive intermediate elements7between two component laminated cores can be embodied not only as metal laminated sheets, but also as massive one-piece parts, in particular as sintered parts.

In order to reduce the eddy current losses in the magnetic intermediate elements7, these are likewise embodied as metal laminated sheets. The number and/or the axial thickness of the intermediate elements7arranged axially immediately behind one another produces the axial thickness of the cooling gap6.

In order to additionally increase the difference between the inductances Lqand Ldin the q axis and the d axis, the axial length of the laminated core of the rotor3is selected to be greater than the axial length of the laminated core of the stator1. In this case a 10% lengthening of the laminated rotor core in relation to the laminated stator core proves to be especially suitable.

In order to now guide a flow of cooling air explicitly into the radial cooling channels6of the rotor3, independently of the embodiment in accordance with the synchronous reluctance machine20according toFIG. 1,FIG. 2, or further conceivable versions, magnetically non-conductive bulkhead elements11according toFIGS. 3Ce to 3Cgare also located between the conventional laminations of the laminated rotor core according toFIG. 3Aaand the magnetically conductive intermediate elements7in accordance withFIGS. 3Bd to 3Bd. These bulkhead elements11have the effect of bringing about a radial diversion of at least one part air flow of a flux blocking section14,15,16into its respective radial cooling channel6.

As an alternative to the bulkhead elements11according toFIG. 3Ce to 3Cg, sheets with cutouts according toFIG. 3Aa—i.e. magnetically conductive sheets—also with a closure13in accordance withFIGS. 3Dh to 3Dj, can be provided to act as a bulkhead element. This closure13preferably consists of magnetically non-conductive material, e.g. of plastic.

The stator1with its winding system and also the rotor3are now cooled via radial cooling channels and/or cooling channels running axially and/or via the air gap19. In addition, by insertion of specific intermediate elements7in accordance withFIGS. 4ato 4c, an additional fan effect of the rotor3can also be created. This occurs in particular by the intermediate elements7in accordance withFIGS. 4ato 4cbeing designed with fan-like blades14. These blades14can advantageously also function at the same time as axial spacers between the component laminated cores30,31,32,33of the rotor3.

The laminated core of the rotor3, in a single-inlet machine in accordance withFIG. 1, is now structured axially as follows. A first component laminated core30is constructed with conventional laminations in accordance withFIG. 3Aa. This is followed by an intermediate element in accordance withFIG. 3Bb, which has a predetermined axial thickness. It can be designed in one piece or as laminated sheets. It makes it possible for the cooling flow of this flux blocking section14to be directed radially outwards. This is followed in the further axial course by a bulkhead element11in accordance withFIG. 3Ce, 3Dh, 5aor6a, which closes off the flux blocking section14completely or only in part. The flux blocking sections15and16remain axially open in this bulkhead element11. No air exits radially outwards at this point from said flux blocking sections15and16.

This is adjoined axially by a next component laminated core31with conventional laminations in accordance withFIG. 3Aa. This is followed by an intermediate element in accordance withFIG. 3Bc, which has a predetermined axial thickness. It can be designed in one piece but also as laminations. It makes it possible for the flow of cooling air of this flux blocking section15to be directed radially outwards. A part flow of air of the flux blocking section14can also be directed outwards here. No air exits radially outwards from the flux blocking section16at this point.

This is then adjoined in its further axial course by a bulkhead element11in accordance withFIG. 3Cf, 3Di, 5bor6b, which closes off the flux blocking section14,15axially, completely or only in part. At least the flux blocking section16remains open in this bulkhead element.

This is adjoined axially by a next component laminated core32with conventional laminations in accordance withFIG. 3Aa. This is followed by an intermediate element in accordance withFIG. 3Bd, which has a predetermined axial thickness. It can be embodied in one piece or also as laminations. It makes it possible for the flow of cooling air of this flux blocking section16to be conveyed radially outwards. In its further axial course it is then adjoined by a bulkhead element11in accordance withFIG. 3Cg, 3Dj, 5cor6c, which, inter alia, closes off the flux blocking section axially, completely or only partly.

Also—where present—a part flow of air of the flux blocking sections14,15can be diverted outwards here. At this point the air of this flux blocking section16exits completely from its cooling channel6in each case or is at least conveyed axially onwards in part, ultimately axially out of the laminated core in this case.

If the bulkhead elements11divert the axial air flow only partly radially, the “residual air flow” remaining in this flux blocking section can be conveyed radially and/or axially into the bulkhead elements11of the other flux blocking sections located downstream in flow terms.

The laminated core of the rotor3of these versions is embodied as axially continuous, at least in the area of the d axis. Flux barriers14,15,16of the d axis flanking it are additionally present, depending on their axial position in the laminated core of the reluctance armature—depending on which component laminated core30,31,32,33is being considered.

With a two-inlet machine in accordance withFIG. 2the structure described above is transferrable, starting from the two end face sides of the rotor3up to the partition wall12and the cooling principle. Ideally in this case the partition wall12forms the bulkhead element, which divides the two flows of cooling air flowing towards one another and steers them radially to the air gap19.

The created flow of cooling air through the flux blocking sections14,15,16can basically be provided by the shaft fan22and/or external fans.

The inventive embodiment of the synchronous reluctance machine20with a frequency converter50, shown schematically inFIGS. 7 and 8, and the higher power factor of this dynamo-electric machine connected therewith also enables it to be used as a high-speed generator in a wind power plant, which can be optimized in its temperature behavior by arrangement of a heat exchanger17.FIG. 9shows a schematic overview of components of the wind power plant, including generator20having an electrically conductive connection to the frequency converter50, with the heat exchanger17being provided inside a gondola51of the wind power plant.

Laminated cores or component laminated cores30,31,32,33are also to be understood as one-piece massive parts, which likewise have a magnetic conductivity.

Depending on the requirements imposed on it in the industrial environment of the synchronous reluctance machine20or during generation of energy by the synchronous reluctance machine20, the reluctance armature will be equipped especially with those laminations, intermediate elements7or bulkhead elements11, which guarantee the best power factor. Thus a “mixture” of the aforementioned versions of laminations, intermediate elements7and bulkhead elements11is possible for single-inlet and dual-inlet machines, but also for other cooling concepts.