Generator with compact single turn wave winding and wind turbine

A generator is provided that includes at least one pole set representing one phase. Each pole set includes a plurality of poles. Only one conductor is turned about the poles of a particular pole set such that only half a single turn is associated to each pole of the particular pole set.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority of European Patent Office application No. 10163306.3 EP filed May 19, 2010, which is incorporated by reference herein in its entirety.

FIELD OF INVENTION

The present invention relates to a generator and to a wind turbine.

BACKGROUND OF INVENTION

Based on today's technology in direct drive generators, each coil is composed of more than one series turn while a chosen number of coils may also be connected in series. The two aforementioned selectable numbers, i.e. the number of series in turn and the number of coils connected in series, may be chosen to obtain the terminal voltage of the generator which itself may have already been chosen based on power electronics/grid requirements. In the described conventional type of winding, the series turns in each slot need to be electrically insulated from each other due to the voltage difference between the turns in series. Furthermore, the whole conductors in the slot need to be insulated from the neighbouring lamination via so called slot insulation due to the voltage difference between the turns and the lamination which is grounded through the coupling with shaft and wind tower.

The aforementioned type of insulation used in the slot of the machines with conventional windings, results in different disadvantages: Poor heat transfer coefficient of the insulation makes it very difficult for the main source of heat in the generator, i.e. the windings to get cooled down through the neighbouring laminations. Using the required insulation in the slots decreases the slot space for the active material, which is usually copper, and thereby the so called fill factor. This in turn reduces the out put torque for the same current density or decreases the efficiency for the same torque. A typical value of fill factor for conventional type of winding is in the range of 70-80%.

SUMMARY OF INVENTION

It is a first objective of the present invention to provide a generator with an increased slot fill factor and with decreased manufacturing costs. It is a second objective of the present invention to provide an advantageous wind turbine.

The above objectives are solved by the features of the independent claims. The depending claims define further developments of the present invention.

The inventive generator comprises at least one pole set representing one phase. Each pole set comprises a number of poles. Only one conductor is turned about the poles of a particular pole set such that only half a single turn is associated to each pole. The only one conductor, which may preferably a single turn solid or compact winding, can replace the conventional windings giving the advantage of having less insulation in the slot. This reduces the insulation between the conductor and a neighboring lamination of the pole, so called slot insulation. Moreover, the conventional turn-turn insulation between the conductors within a slot becomes unnecessary. Furthermore, a better cooling of the windings and a higher slot fill factor can be achieved. Another advantage is that the manufacturing of the coils and the winding process becomes significantly easier and less costly than for multi-turn conventional windings. Furthermore, using only one solid or compact large conductor with the proposed suitable slot shape results in low skin effect loss.

The inventive generator may be a three phase or a multi-phase generator. In the inventive generator each phase may have a single Go or Return path, also designated as half a single turn, in each pole. The single Go or Return paths or half a single turns are arranged in a wave-like configuration. For example, the half a single turn itself can be a solid or compact conductor. It may return in the next pole and may continue this way of wave-like distribution along the whole circumference of the stator or rotor.

The inventive generator may comprise a stator comprising the at least one pole set. Additionally or alternatively, the generator may comprise a rotor comprising the at least one pole set. Preferably, the generator may comprise a stator, a rotor and a rotation axis. The stator may be located radially inside of the rotor (inner stator machine).

Advantageously the conductor comprises a number of, preferably solid or compact, conductor elements. The conductor elements can be conductively connected to each other. The conductor elements can be connected to each other by welding or by a mechanical fixation, for example.

Generally, the generator can comprise at least one slot between the poles. Preferably, the conductor elements may have the shape of straight bars or arcs. For example, a first straight bar can be placed in a slot and can be connected to a second straight bar in another slot by means of an arc. In this way the conductor elements can be connected to each other forming a wave-like configuration.

Generally, the conductor may at least partly be located in at least one slot between the poles. The generator may comprise a rotation axis. The slot may be closed or partly closed at a radial position related to the rotation axis. Advantageously, the slot may have a rectangular or trapezoidal or triangular shape in a plane perpendicular to the rotation axis. Preferably, the slot may have an incremental opening in radial direction related to the rotation axis.

Moreover, the slot can comprise at least one bridge which partially or fully closes the slot at a radial position. The bridge can be integral part of an element forming the slot, for example of a lamination of the pole. Alternatively, the bridge can be a separate element. In this case, the bridge can mechanically be fixed to the element forming the slot, for example to the pole lamination. For instance, the slot may comprise the side face. The element or lamination forming the slot can comprise a cavity in the side face of the slot. The cavity can be used for mechanical fixing the bridge. The mentioned bridges can be simply built by re-designing the tooth shape of the poles, especially of the lamination.

The bridge may comprise soft magnetic composite material or ferromagnetic material. For example, the bridge may be made of soft magnetic composite material or may be made of ferromagnetic material, via punching the lamination with the appropriate shape.

The use of separate conductor elements, as previously described, allows it to use a modular winding structure. This modular winding structure can be used for closed and semi-closed slots. This reduces the skin effect. Furthermore, it significantly simplifies the winding manufacturing, especially compared with conventional winding. For example, the conductor elements, preferably the straight bars, can be inserted into the slot, which may be a closed or semi-closed slot.

The use of trapezoidal or triangular slots with incremental opening, especially towards an air gap in inner stator machines, reduces the skin effect loss which emerges in the rectangular conductors with large radial height or deep slots.

The shape of the conductor can be optimized regarding the reduction of skin effect losses. In the same way, the shape of the slot and the shape of neighboring lamination teeth of the pole can be optimized. Moreover, having only one solid large conductor pole instead of having parallel conductors the insulation between series turns in conventional windings does not exist and completely disappear. In this aspect, the present invention is more efficient than having parallel conductors where still some thin varnish may be needed around the parallel conductors. Furthermore, the slot insulation can be optimized in thickness.

A further possibility to reduce the skin effect in the single turn solid conductor is to reduce the radial height or depth of the conductor. For example, the at least one slot may have an average width w and a radial depth h related to the rotation axis of the generator. The average width w can be of a value of at least 90% of the value of the depth h. Preferably the average width w can be comparable or larger than the depth h. Keeping the area of the conductor fixed, the slot width then need to become larger. As a result, the number of slots versus the poles will be reduced. Therefore, a concentrated winding, for example in form of only one single turn solid or compact conductor, as previously described, can be used. Such a concentrated winding has a low slot to pole number ratio.

In combination with the previously mentioned optimised conductor shape, especially if an inner stator is used, the slots can be practically be made in a trapezoidal shape. In this case, the teeth or poles can be kept rectangular. The combination of these two parameters using shallow and trapezoidal slots reduces the skin effect effectively. Moreover, to improve the magnetic circuit and/or to reduce the skin effect even further closed or semi-closed slots or bridges in the middle of the slots may be used.

FE 2D analysis has shown that each of these suggested shapes will reduce the skin effect loss significantly. Furthermore, a combination of these suggested cases reduces the skin effect even further.

One draw back of using the previously described bridge is that the slot leakage will be increased. This is to some extent an advantage since it reduces the short circuit current and this way adds to reliability of the generator, for example the direct drive generator. However, possibly more significantly the output torque of the generator will fall due to flux leakage. Therefore, the decision on thickness of the bridges is a trade off between having lower skin effect on the one hand and not losing too much torque on the other hand.

Generally, the generator may comprise at least 3 pole sets. The generator may be a direct drive generator.

In the present invention, the conventional insulation between the conductors placed together in a slot and also the slot insulation are significantly reduced. This improves the slot fill factor and enhances the cooling of the generator, for example of a permanent magnet generator. Such a permanent magnet generator can, for example, be used in direct drive wind turbine applications. Furthermore, simple and modular windings are defined and provided by the present invention. This significantly simplifies the manufacturing and the winding process, thereby lowering the associated costs.

The requirement of having turn-turn insulation was removed by using single turn solid coil winding. Furthermore, the slot insulation (between the single conductor and the neighbouring teeth) is minimized by choosing its thickness optimally for each slot, realizing that each slot has a different/unique voltage difference with its neighbouring teeth. This optimal selection is not possible for conventional multi-turn windings as more than one voltage difference exists in each slot; thereby the selection is based on the worst case.

Taking the advantage of having less winding and slot insulation and all the following improvement of the generator performance, a drawback of having high extra AC loss due to skin effect are effectively reduced by the described conductor/slot shapes.

The inventive wind turbine comprises an inventive generator, as previously described. The inventive wind turbine has the same advantages as the inventive generator.

DETAILED DESCRIPTION OF INVENTION

FIG. 1schematically shows a wind turbine71. The wind turbine71comprises a tower72, a nacelle73and a hub74. The nacelle73is located on top of the tower72. The hub74comprises a number of wind turbine blades75. The hub74is mounted to the nacelle73. Moreover, the hub74is pivot-mounted such that it is able to rotate about a rotation axis79. A generator76is located inside the nacelle73. The wind turbine71is a direct drive wind turbine.

FIG. 2schematically shows a comparative illustration of multi-turn and single turn wave windings for one phase and four poles. The upper part ofFIG. 2shows the distributed winding with slots per pole and phase equal to 1 for a 3-phase machine, phases A, B and C. A, B and C correspond to Go direction of the phases and A′, B′ and C′ correspond to Return direction, i.e. opposite direction, of the phases.

In the middle part ofFIG. 2two poles4representing the first phase are shown. Each of the poles4comprises a number of conductor windings5with multiple-turns per pole4. The strokes6indicate the more than one series turns. The conductors5are connected in series. This is indicated by the dashed line7. Due to the series turns each of the poles4or coils comprises a number of Go paths17and a number of Return paths18.

The lower part ofFIG. 2schematically shows the inventive single turn wave windings for one phase of an inventive generator. The pole set belonging to the first phase A comprises a number of poles4, from which four poles4a,4b,4cand4dare shown. Generally, the poles4may comprise a lamination.

Each pole4comprises a right side10, a left side11, a front side12and a back side13. A conductor8is wave-like turned about the poles4. The conductor8comprises a first half turn8a, a second half turn8b, a third half turn8cand a fourth half turn8d. The first half turn8arepresents a Return path A′, the second half turn8brepresents a Go path A, the third half turn8crepresents a Return path A′ and the fourth half turn8drepresents a Go path A.

The first half turn8aproceeds along the right side10of the first pole4aand proceeds further along the back side13of the first pole4a. Then it proceeds further along the left side11of the first pole4aand at the same time along the right side11of the second pole4b. This means, that the conductor passes a slot between the first pole4aand the second pole4b. Then the conductor8further proceeds along the front side11of the second pole4b, then along the left side11of the second pole4band at the same time along the right side10of the third pole4c. The conductor8further proceeds along the back side13of the third pole4cand along the left side of the third pole4cand at the same time along the right side10of the fourth pole4d.

In this wave-like configuration the first half a turn8ais associated to the first pole4a, the second half a turn8bis associated to the second pole4b, the third half a turn8cis associated to the third pole4cand the fourth half a turn8dis associated to the fourth pole4d.FIG. 3schematically shows part of the single turn wave windings of the lower part ofFIG. 2in a perspective view. The poles4are separated from each other by slots19.

A number of conductors8are connected in parallel and are turned about the poles in such a way that only half a single turn of each conductor is associated to each pole, as shown in the lower part inFIG. 2and inFIG. 3. The optimal number of parallel conductors to give a low value of proximity and skin effect loss can be chosen analytically or experimentally or by simulation. An example is shown inFIG. 4.

Generally, the generator76can comprise an inner stator, which means that the stator is located radially inside of the rotor of the generator related to the rotation axis79of the rotor. Alternatively, the generator can comprise an outer stator, which means that the stator is located radially outside of the rotor of the generator related to the rotation axis79of the rotor. In both cases the rotor and/or the stator can comprise the described single turn wave winding.

FIG. 4schematically shows a single turn wave winding arrangement of conductor elements in a perspective view. The conductor8comprises a number of conductor elements20,21. The solid or compact conductor elements20,21are connected to each other such that they form a single turn wave winding as shown in the lower part ofFIG. 2and inFIG. 3.

InFIG. 4the conductor8comprises a number of conductor elements20, which have the form of straight bars, and a number of conductor elements21, which have the form of an arc. The conductor elements20in form of a straight bar have a first end23and a second end24. The conductor elements21in form of an arc have a first end25and a second end26. A first conductor element in form of a straight bar20ais connected to a first conductor element in form of an arc21asuch that the second end24of the first conductor element20ain form of a straight bar is connected to the first end25of the first conductor element21ain form of an arc. The second end26of the first conductor element in form of an arc21ais connected to the first end23of a second conductor element20bin form of a straight bar. The second end24of the second conductor element20bin form of a straight bar is connected to the first end25of a second conductor element21bin form of an arc. The second end26of the second conductor element21bin form of an arc is connected to the first end23of a third conductor element20cin form of straight bar. By connecting a number of conductor elements20,21in the described way a single turn wave winding as shown inFIG. 3is obtained.

FIG. 5schematically shows part of the single turn wave winding arrangement of conductor elements, which is shown inFIG. 4, in a sectional view. The axial direction is designated as z-axis and is indicated by means of an arrow.FIG. 7schematically shows the second conductor element21bin form of an arc in a perspective view along z-direction. The current direction in the conductor element21bis indicated by means of arrows.

FIGS. 7 to 12schematically show different slot forms in sectional views.FIG. 7schematically shows a rectangular slot19in a sectional view. The slot19is formed by a first pole4aand a second pole4b. The poles4comprise iron. They further may comprise a lamination. The radial direction is indicated by an arrow28. The slot19comprises an opening in radial direction28.

FIG. 8schematically shows a rectangular closed slot in a sectional view. Again, the slot19is formed by a first pole40aand a second pole40b. The poles40have the same properties as the previously described poles4. At the position of the opening of the slot19in radial direction28the slot19inFIG. 8is closed by means of a bridge27. The bridge27connects the first pole40awith a second pole40b.

Generally, all bridges, which are shown in theFIGS. 8,10to12and14, can be integral part of the adjacent poles or can be separate elements. In the last case they can mechanically be fixed to the poles. Moreover, all shown bridges can comprise or can be made of soft magnetic composite material or ferromagnetic material, for example iron.

FIG. 9schematically shows a trapezoidal slot19in a sectional view. The slot19is formed by a first pole41aand a second pole41b. The poles41can have the same properties as the previously described poles4. InFIG. 9the slot19has an increasing width w. The width w increases in radial direction28. In a plane perpendicular to the rotation axis, which is identical with the shown sectional view, the slot19has a trapezoidal shape. The dashed line43inFIG. 9indicates a further variant, wherein the slot19has a triangular shape with an increasing width w in radial direction28.

FIG. 10schematically shows a semi-closed rectangular slot in a sectional view. The slot19is formed by a first pole42aand a second pole42b, which have the same properties as the previously described poles4. The opening of the slot in radial direction28is partly closed by means of a bridge29. The bridge29comprises a first portion29aand a second portion29b. The first portion29acan be part of the first pole42aor it can be a separate element which is connected to the first pole42a. The second portion of the bridge29bcan be part of the second pole42bor it can be a separate element which is connected to the second pole42b. Between the first portion29aand the second portion29bof the bridge an opening33of the slot19in radial direction28is formed.

FIG. 11schematically shows a variant of a rectangular semi-closed slot19in a sectional view. The slot19inFIG. 11is formed by a first pole44aand a second pole44b, which have the same properties as the previously described poles4. The slot19comprises inner side faces32. The height h of the slot19is indicated by an arrow. The slot19is semi-closed by means of a bridge30. The bridge30comprises a first portion30aand a second portion30b. The bridge30is located at about half of the height or depth h of the slot19. The first portion30aof the bridge is part of the first pole44aor is connected to the first pole44aat the side face32of the slot19. The second portion30bof the bridge is part of the second pole44bor is connected to the second pole44bat the side face32bof the slot19. The bridge30divides the slot19into an outer slot part19aand an inner slot part19b. The outer slot part19ais located radially outside of the inner slot part19b. The outer slot part19aand the inner slot part19bare connected to each other by means of an opening33between the first bridge portion30aand the second bridge portion30b.

FIG. 12schematically shows a rectangular closed slot in a sectional view. The slot19ofFIG. 13is faulted by a first pole45aand a second pole45b, which has the same properties as the previously described poles4. The poles45aand45bare connected to each other by means of a bridge31. The bridge31is located at about half of the height h or depth h of the slot19. The slot19comprises a first side face32aand a second side face32b. The bridge31connects the first side face32awith the second side face32bof the slot19. The bridge31divides the slot19into a radially outer slot part19aand a radially inner slot part19b.

The slots19ofFIGS. 7,8,10to12have a rectangular shape in a plane perpendicular to the rotation axis, which is identical with the shown sectional views.

FIG. 13schematically shows a generator76in a sectional view. The generator76comprises a rotation axis79, a stator78and a rotor77. InFIG. 13the rotor77is located radially outside of the stator78. This means, that the generator76ofFIG. 13is an inner stator generator. Close to the rotation axis79a shaft9is located. The stator78is connected to the shaft9. The stator78comprises a number of poles4which are arranged about circumference of the stator78. Between the poles4slots19, as previously described, are formed. In the sectional view shown inFIG. 13the poles46have a rectangular shape and the slots19have a nearly trapezoidal shape.

The stator78and the poles4may comprise an iron lamination. The rotor77comprises a number of permanent magnets80. The permanent magnets80are arranged about the whole circumference of the rotor77.

FIG. 14schematically shows enlarged view of part of the stator78.FIG. 14schematically shows a slot19, which is formed by a first pole46aand a second pole46b, which have the same properties as the previously described poles4. The slot19has a trapezoidal shape in a plane perpendicular to the rotation axis79. The slot19has an increasing width w in radial direction28. Advantageously, the slot19has an average width w which is larger than the depth or height h of the slot19in radial direction28.

The slot19can be partly closed by a bridge34. The bridge34can be located at about half of the height or depth h of the slot19. The bridge34can connect the first pole46awith the second pole46b. Alternatively or additionally, the slot19can be semi-closed by means of a bridge35, which comprises a first part35aand a second part35b. The first bridge part35acan be part of or can be connected to the first pole46aand the second bridge part35bcan be part of or can be connected to the second pole46b. Between the bridge parts35aand35ban opening33can be present. The bridge35is preferably located at the maximum width w of the slot19.