DE102008029377A1 - Device for a wind or hydroelectric power plant for generating electrical energy - Google Patents

Abstract

The invention relates to a homopolar generator for a device for generating electrical energy. The generator is in particular part of a wind or hydroelectric power plant and is directly, i. without intermediate transmission, driven by the wings of the wind or hydropower plant. A superconducting coil mechanically decoupled from the rotor, i. not co-rotated with the rotor, generates a magnetic flux, which is guided by the rotor so that it passes through the stator winding of a stator in the radial direction. The rotor has for this purpose the stator claw-shaped surrounding rotor sections, which conduct the magnetic flux. At the rotor portions, conductive poles are provided to the magnetic flux, causing the magnetic flux to vary in the circumferential direction of the stator. With constant magnetic field and rotating rotor, a voltage is thus induced in the stator windings. The rotor preferably rotates at a constant frequency. By an appropriate choice of the number of poles, the output frequency of the generator can be adapted to the mains frequency.

Description

The Invention relates to a generator, in particular a homopolar generator, for a device for generating electrical energy. The generator is in particular part of a wind or hydroelectric power plant.

The Impeller of a large wind turbine usually turns at less than one revolution per second. The impeller is coupled in many wind turbines to a transmission that is a conventional Synchronous or asynchronous generator drives at high speed. The Connection to a power grid can be direct or via Frequency converter. Often are fed twice Asynchronous generators used in which the rotor over Slip rings is fed by a frequency converter.

It is advantageous to couple the generator directly, ie without expensive and trouble-prone intermediate gear to the impeller. For example. in US 7 154 191 B2 a wind energy plant is described in which the impeller is directly connected to the rotor. The rotor carries permanent magnets, with the help of which a varying magnetic flux is generated, which passes through the stator windings of a stator. However, a generator driven by the impeller must provide a frequency of 50 Hz or 60 Hz for connection to the power supply network. The low output frequency of the generator due to the low rotational frequency of the impeller must therefore be brought back via frequency converter to 50 Hz or 60 Hz. An alternative is to couple the synchronous generator directly to the impeller and equip the generator with a rotor of such a high number of poles that a frequency corresponding to the mains frequency can be provided. In this case, he can feed directly into the grid.

high-position directly driven wind generators with permanently excited rotors realized. A disadvantage of direct network connection is that the reactive power requirement the network does not have a variable excitation of the rotor can be adjusted. Especially in offshore wind turbines can this can be detrimental to the network stability. Direct drive generators with network connection via frequency converter are also known.

By Windings via slip rings excited high-pole synchronous generators have not prevailed. The disadvantage is the high cost of materials for the large number of rotor coils and the high power requirement for the excitement, which worsens the efficiency. Superconducting excitation coils have been proposed to reduce them the excitation power considerably. The high cost of superconducting material and cryogenic cooling and insulation leave this version also appear to be not economical.

For example. in US Pat. No. 7,049,724 B2 An electric machine or a generator with a disk-shaped rotor and a disk-shaped stator is described, in which a superconducting, mechanically decoupled from the rotor coil is used. The coil generates a magnetic flux which is conducted by means of poles of the rotor in the axial direction through the stator. The disadvantage of this machine is that it reacts very vulnerable to axial forces. This vulnerability increases with increasing rotor diameter. It is therefore necessary to set correspondingly large tolerances, for example for the air gap between the poles of the rotor and the stator, whereby the efficiency of the machine is worse.

The previously known methods have in common that expensive, susceptible to interference Gearbox, frequency converter and / or slip rings needed and that high material, maintenance and operating costs are incurred.

By the elimination of gearbox, frequency converter and slip rings would both a higher reliability and less Maintenance effort achieved. This is particularly advantageous for the Use in offshore wind turbines, whose importance in the future will increase significantly.

moreover could be when using a fixed, non-rotating superconducting coil considerable effort for material and Operation can be saved, while maintaining the complexity the system or the generator decreases.

It It is therefore the object of the invention to provide a cost-effective, robust and less prone to failure device for Specify generation of electrical energy.

These The object is achieved by that in the independent claims solved inventions. Advantageous embodiments result from the dependent claims.

In the apparatus according to the invention, the particular advantages of a homopolar machine are exploited, as they are, for example, in DE 10 2004 014 123 A1 is described. In the homopolar machine, in contrast to synchronous or asynchronous machines, a mag- netic flux Φ generated by an exciting coil varies in amplitude between a minimum and a maximum value, but its direction does not reverse, so that its polarity remains constant. The rotor of a homopolar machine has neither windings nor grinding contacts. The excitation coil is mechanically decoupled from the rotor completely and does not rotate with the rotor. The homopolar machine is therefore particularly suitable for applications in which an electrical machine to work with a superconducting exciter coil, since the cooling of the excitation coil is much easier to handle than mitmitierender coil.

A Homopolarmaschine is very simple and robust and can generally be used as a motor or as a generator.

The inventive system for generating electrical Energy includes a generator that advantageously serves as a homopolar generator is trained. This includes a fixed annular Stator with stator winding, a rotatable annular Rotor made of ferromagnetic material such as iron and a fixed annular exciting coil, wherein the stator and the exciting coil in the radial direction between a first and a second rotor section are arranged. A magnetic flux Φ generated by the exciting coil becomes guided by the rotor and passes through the stator in the radial direction, perpendicular to the stator winding. Both rotor sections have a Variety of poles on the radial direction of the stator are directed towards and guide the magnetic flux Φ. Between the poles of a rotor section are interpolar spaces. The poles of the two rotor sections are in the radial direction opposite, the same applies to the pole interspaces.

at current-carrying exciter coil is the magnetic flux between opposite poles considerably larger as between opposite pole spaces, so that the magnetic flux Φ with the rotor in Circumferential direction of the rotor is seen depending on the location. at on the other hand, the magnetic flux Φ varies a certain location in the circumferential direction of the rotor, d. H. for example in the Area of a specific section of the stator winding, depending on from time, so that induces a voltage in the stator winding becomes.

There the excitation coil is fixed, d. H. not co-rotated, it can be beneficial as a superconducting coil, in particular as a high-temperature superconductor (HTSC) be educated. This affects the fact that the exciter coil does not cause any excitation power, so that the efficiency increases.

The System works with a fixed, known number of revolutions of the rotor, d. H. in the case of a wind turbine with a fixed number of revolutions of the Impeller. Depending on the grid frequency is a certain, of provided the number of revolutions of the rotor dependent number of poles, so that the generator always has the correct frequency available provides. Frequency converters are therefore not necessary, a gearbox its unneccessary.

There unlike synchronous generators, only a single one, though larger excitation coil is provided, reduce the material and operating costs for generating the magnetic River Φ.

about a variation of the exciter current can also be the changing reactive power demand covered by the network to be supplied.

There the excitation coil is not co-rotated and on the rotating rotor No electrical components are present on slip rings be completely dispensed with.

Of the Generator can be used, for example, in wind or hydroelectric plants come, with the rotor of the generator directly to the impeller is coupled.

Further Advantages, features and details of the invention will become apparent the embodiment described below as well based on the drawings.

there shows:

1 a wind energy plant in back and cross-sectional view,

2 a section of a longitudinal section through rotor and stator,

3 a section of a cross section through parts of the generator,

4 a plan view of a stator winding in a schematic view.

The 1 shows a wind turbine 10 in a rear view and a cross-sectional view with a device according to the invention, the directly driven generator 20 for generating electrical energy. The wind turbine 10 includes in the illustrated embodiment, an impeller 30 with three wings 31 , wherein more or less wings may be provided. The impeller 30 is fixed with a rotor 40 of the generator 20 connected so that when wind the rotor 40 together with the wings 31 and the impeller 30 is set in rotation. The rotor 40 is this with its axis of rotation 50 in suitable stores 60 stored in a housing 70 are housed. Also indicated is a fastening device 71 holding a stator 80 (in 1 not shown) of the generator 20 includes. The stator 80 is concentrated to the rotor 40 arranged and over the fastening device 71 with the housing 70 firmly, ie non-rotatably connected. Furthermore, a cryocooler 90 for cooling for one to the rotor 40 and to the stator 80 concentric exciter coil 100 (in 1 not shown) of the generator 20 intended. The entire construction is on a mast 110 attached.

The 2 shows a longitudinal section, inter alia, by the rotor 40 and the stator 80 in detail. The attachment of the impeller 30 on the rotor 40 is not shown, but takes place in a known per se such that the set by wind moving wings 31 the rotor 40 over the impeller 30 set in rotation.

The generator 20 is designed as a homopolar generator. The rotor 40 of the generator 20 includes three rotor sections 41 . 42 . 43 and has an approximately U-shaped profile. The first 41 and the second rotor section 42 are arranged spaced in the radial direction, wherein the radially outer first 41 and the radially inner second rotor section 42 forming the U-legs of the profile, while the third rotor section 43 the sections 41 . 42 combines. In particular, the profile of the rotor 40 shaped as a horizontal U, ie the U-legs are oriented in the axial or in the z-direction.

In the radial direction between the rotor sections 41 . 42 or between the U-legs is in the region of the third rotor section 43 the fixed exciter coil 100 arranged. Especially due to the fact that the exciter coil 100 is fixed, it makes sense, a superconducting exciter coil 100 to use, since the cooling is much easier to accomplish than with a co-rotating coil.

The exciter coil 100 is preferably a high-temperature superconductor. It is in a cryostat 101 and is through a cooling line 102 maintained at operating temperature. The cooling line 102 is by the in the 1 illustrated cryocooler 90 provided. The cooling can be done, for example, indirectly with liquid neon or hydrogen in a thermosyphone. The superconducting exciter coil 100 can be operated with DC and unlike conventional, normal temperature, no excitation power, whereby the efficiency of the entire system increases.

alternative The annular exciter coil can also be used with a normal conductor such as a copper or aluminum conductor at ambient temperature operate. Although this requires excitation, but that far below the power cost for the rotor one high-pole conventional synchronous machine remains. Of the Efficiency of Homopolarmaschine is correspondingly higher. Maybe such a normal conductor coil, for example. With air over a fan or with a water circuit forcibly cooled become.

The exciter coil 100 generates a magnetic flux Φ coming from the rotor 40 or from the rotor sections 41 . 42 . 43 as is symbolized by the arrows. At the rotor sections 41 respectively. 42 are first for directing the magnetic flux Φ in the radial direction 44 or second pole 45 formed in the radial direction of the rotor sections 41 . 42 protrude. Between two first poles 44 (or between two second poles 45 ) is a first pole gap 46 (or a second pole gap 47 ). The poles 44 . 45 extend in the axial direction preferably over the entire area, which is determined by the depth of the stator, ie its extent in the axial direction. Opposite first and second poles 44 . 45 form a pair of poles 48 , In the circumferential direction of the rotor 40 seen have the first poles 44 and the first pole interspaces 46 of the first rotor section 41 the same width w _R. The same applies to the second pole 45 and the second pole gaps 47 of the second rotor section 42 , Preferably, the entire rotor 40 comprising the rotor sections 41 . 42 . 43 and the poles 44 . 45 formed integrally of solid iron to best guide the magnetic flux Φ.

The stationary stator 80 includes two three-phase stator windings 81 . 82 and a stator core 83 made of laminated iron for conducting the magnetic flux Φ, wherein the stator 80 and thus the stator windings 81 . 82 in the radial direction between the rotor sections 41 . 42 or between the U-legs are arranged. In the axial direction are the stator 80 and the exciter coil 100 arranged side by side. Because of that, two windings 81 . 82 used, the output power of the generator doubles 20 opposite to a single winding. In general, two-, four- or multi-phase stator windings can be used. It is also conceivable to provide more or fewer than two windings.

The stator 80 is using a fastening device 71 at one part 72 of the housing 70 attached. The fastening device 71 also fixes the cryostat 101 with the exciter coil 100 and the cooling line 102 , For example. can the fastening device 71 be formed as a double-walled cylinder, wherein the stator 80 and the cryostat 101 are arranged and fixed between the cylinder walls.

The only moving part of the generator 20 is therefore the rotor 40 comprising the rotor slice 41 . 42 . 43 and the poles 44 . 45 , The stator 80 and - unlike synchronous generators - the exciter coil 100 are stuck to the case 70 therefore they can not rotate. Alternatively, the stator could 80 and / or the exciter coil 100 with another fixed part of the wind turbine 10 firmly, ie not rotatable or displaceable, be connected. For this purpose, for example, the mast 110 in question.

Because the rotor 40 no electrical components such as coils o. Ä. Wears, can advantageously be dispensed slip rings, etc.

The 3 shows a section through the rotor 40 , the stator 80 and the stator windings 81 . 82 according to the in the 2 indicated line AA. The poles 44 . 45 of the rotor 40 are on the the stator 80 facing sides of the rotor sections 41 . 42 arranged and cause the magnetic flux Φ as indicated by the arrows the stator 80 and the stator windings 81 . 82 in the radial direction, ie perpendicular to the stator windings 81 . 82 interspersed. The stator windings 81 . 82 each have three phases u, v, w. Between the first poles 44 and the stator 80 as well as between the second poles 45 and the stator 80 In each case there is an air gap, which ideally is as small as possible, that is to say of the order of 5-15 mm. The the stator 80 permeating magnetic flux Φ is in the region between two opposite poles 44 . 45 ie in the area of a pole pair 48 greater than in the area between two opposite pole spaces 46 . 47 lies. During a rotation of the rotor 40 triggered by a movement of the wings 31 therefore varies in the range of the stator windings 81 . 82 the magnetic flux Φ as a function of time, so that in the stator windings 81 . 82 a voltage is induced, which can be tapped at a position not shown.

Because the surfaces of the poles 44 . 45 on (imaginary) cylinder surfaces lie and the magnetic flux Φ the stator 80 penetrated in the radial direction, it is comparatively easy, by structural means such as spokes and / or discs, the radial distances from the axis of rotation of the rotor 40 adjust and thus the air gaps between rotor 40 and stator 80 regardless of magnetic, wind or other forces to comply exactly. This is advantageous - especially for machines with large diameters such as wind turbines - eg. In relation to in US Pat. No. 7,049,724 B2 described generator with disc-like arrangement of rotor and stator with axially directed magnetic flux. Other disadvantages of in US Pat. No. 7,049,724 B2 have already been mentioned.

The in the 2 and 3 shown generator 20 can in a specific execution a 5 MW generator 20 be, directly, ie without additional gear driven rotor 40 regardless of the wind conditions with a fixed rotation frequency of 15 revolutions / minute rotates. Depending on the frequency of the network in which the generator 20 generated electrical energy is to be fed, a certain number of first 44 or second poles 45 needed. For example. for a frequency of 50 Hz will be 200 pole pairs 48 ie 200 first and second poles each 44 . 45 needed. Accordingly, for a frequency of 60 Hz, 240 pole pairs are used. The excitation coil generates a magnetic flux of 1 T in the air gaps. The air gaps can be, for example, 7 mm or 12 mm wide, the width of the air gaps being based on the ampere-turn number of the superconducting exciter coil 100 in such a way that with larger air gap a larger ampere-turn number is needed to produce the magnetic flux of 1T. Since this increases the cost of the system, the narrowest possible air gap is advantageous. The width of the air gaps depends in turn essentially on the mechanical tolerances of the rotor 40 and stator 80 from.

Due to the fixed rotational speed and the matched number of pole pairs is advantageously achieved that the electrical energy generated can be fed directly into the network, so that no frequency converter o. Ä. Are required. Typically, the rotor has 40 of such a generator 20 a diameter of the order of 10 m. The excitation of the generator 20 is done by a fixed, ie non-co-rotating HTSC excitation coil 100 , which is cooled to 27 K using liquid neon and generates a magnetic flux density of 1 T in the air gaps.

The 4 Finally, schematically shows a section of a plan view of the stator 80 in the radial direction, for example. Viewing in the negative y-direction, to the course of the stator windings 81 . 82 to demonstrate. In the plan view, only the three phases u, v, w having stator winding 81 to recognize, which has a meandering course, wherein the longer line sections in the axial direction (z-direction) are aligned. The exciter coil 100 is in the 4 not shown.

The above description deals with a wind turbine. However, the device is readily applicable to modifications in the dimensioning, etc. in a hydropower plant, in which the wings 31 be driven by a watercourse.

In principle, the inventive electric machine can also be operated as a motor, wherein the electric machine is formed per se as the generator described above 20 ,

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• US 7154191 B2 [0003]
• US 7049724 B2 [0006, 0040, 0040]
• - DE 102004014123 A1 [0012]

Claims (15)

Device for generating electrical energy with a generator ( 20 ), in particular homopolar generator ( 20 ), comprising: - an annular stationary stator ( 80 ), - an annular, fixed exciting coil ( 100 ) and - an annular, rotatable rotor ( 40 ), which at least a first ( 41 ) and a second rotor section ( 42 ), wherein - the stator ( 80 ), the rotor ( 40 ) and the exciter coil ( 100 ) are arranged concentrically, - the stator ( 80 ) at least one stator winding ( 81 . 82 ), - the stator ( 80 ) and the exciter coil ( 100 ) seen in the radial direction between the first ( 41 ) and the second rotor section ( 42 ) are arranged, and wherein the rotor ( 40 ), the stator ( 80 ) and the exciter coil ( 100 ) are arranged such that the rotor ( 40 ) one of the exciter coil ( 100 ) and the magnetic flux Φ conducts the stator ( 80 ) in the radial direction, substantially perpendicular to the stator winding ( 81 . 82 ) interspersed. Device according to claim 1, characterized in that the first ( 41 ) and the second rotor section ( 42 ) are arranged concentrically and spaced apart in the radial direction. Device according to claim 1 or 2, characterized in that the stator ( 80 ) and the exciter coil ( 100 ) are arranged side by side in the axial direction. Device according to one of the preceding claims, characterized in that the rotor ( 40 ) has an approximately U-shaped profile, the first ( 41 ) and the second rotor section ( 42 ) form the U-legs of the profile and are aligned in the axial direction. Device according to one of the preceding claims, characterized in that the first ( 41 ) and the second rotor section ( 42 ) the stator ( 80 ) claw-shaped. Device according to one of the preceding claims, characterized in that at the first Rotorabschnit ( 41 ) a plurality of first poles ( 44 ) and at the second rotor section ( 42 ) a plurality of second poles ( 44 ), where - the poles ( 44 . 45 ) each on the stator ( 80 ) facing side of the respective rotor section ( 41 . 42 ) are arranged, 44 ) and second poles ( 45 ) are radially opposite. Device according to one of the preceding claims, characterized in that the rotor ( 40 ) at least comprising the rotor sections ( 41 . 42 . 43 ) and the poles ( 44 . 45 ) is integrally formed of solid iron and the of the exciter coil ( 100 ) generates magnetic flux Φ. Device according to one of the preceding claims, characterized in that at least two stator windings ( 81 . 82 ) are provided and / or that each stator winding ( 81 . 82 ) is at least multi-phase, in particular 3-phase (u, v, w) is formed. Device according to one of the preceding claims, characterized in that the stator ( 80 ) a laminated stator core ( 83 ) having. Device according to one of the preceding claims, characterized in that the exciting coil ( 100 ) is a superconducting coil, in particular a HTSC coil. Device according to one of claims 1 to 9, characterized in that the exciting coil ( 100 ) is an annular coil of a normal conductor. Device according to claim 11, characterized in that the exciter coil ( 100 ) is forced cooled with air or water. Device according to one of the preceding claims, characterized in that the rotor ( 40 ) is rotated at a fixed rotational frequency. Wind or hydroelectric power plant comprising a device for generating electrical energy according to one of the preceding Claims. Wind or hydroelectric power plant according to claim 14, characterized in that an impeller ( 30 ) or wings ( 31 ) of the wind or hydroelectric power plant ( 10 ) for driving the rotor ( 40 ) with the rotor ( 40 ) are connected.