WO2009153187A2

WO2009153187A2 - Device for a wind or water power system for generating electrical energy

Info

Publication number: WO2009153187A2
Application number: PCT/EP2009/057067
Authority: WO
Inventors: Günter RIES
Original assignee: Siemens Aktiengesellschaft
Priority date: 2008-06-20
Filing date: 2009-06-09
Publication date: 2009-12-23
Also published as: DE102008029377A1; DE102008029377B4; WO2009153187A3

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 water power generating system and is driven directly, i.e. without intermediately connected gear mechanisms, by the blades of the wind or water power system. A superconducting coil, which is mechanically decoupled from the rotor, i.e. does not rotate along with the rotor, generates a magnetic flux which is conducted by the rotor in such a way that it penetrates the stator winding of a stator in the radial direction. For this purpose, the rotor has rotor sections which surround the stator in the form of a claw and which conduct the magnetic flux. Poles which conduct the magnetic flux and which cause the magnetic flux to vary, viewed in the circumferential direction of the stator, are provided on the rotor sections. When the magnetic field is constant and the rotor is rotating, a voltage is therefore induced in the stator windings. The rotor preferably rotates at a constant frequency. By correspondingly selecting the pole numbers it is possible to adapt the output frequency of the generator to the mains frequency.

Description

description

Device for a wind or hydroelectric power plant for generating electrical energy

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 rotates at less than one revolution per second. In many wind turbines, the impeller is coupled to a gearbox which drives a conventional synchronous or asynchronous generator at high speed. The connection to a power supply network can be made directly or via frequency converter. Often double-fed asynchronous generators are used in which the rotor is fed via slip rings from a frequency converter.

It is advantageous to couple the generator directly, ie without expensive and trouble-prone intermediate gear to the impeller. For example. US Pat. No. 7 154 191 B2 describes a wind energy plant in which the impeller is connected directly to the rotor. The rotor carries permanent magnets, which generate a varying magnetic flux that passes through the stator windings of a stator. However, an impeller-driven generator must provide a frequency of 50Hz or 60Hz to connect to the power grid. 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 50Hz or 60Hz. 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-pole direct-drive wind generators with permanently excited rotors are realized. A disadvantage of direct network connection is that the reactive power demand of the network can not be adjusted via a variable excitation of the rotor. This can be detrimental to grid stability, especially in offshore wind farms. Direct-drive generators with grid connection via frequency inverters are also known.

By winding over slip rings excited high-pole synchronous generators have not prevailed. A disadvantage is the high cost of materials for the large number of rotor coils and the high power requirement for the excitation, which worsens the efficiency. Superconducting excitation coils have been proposed, they significantly reduce the excitation power. The high cost of superconducting material and cryogenic cooling and insulation also make this version seem not economical.

For example. US Pat. No. 7,049,724 B2 describes an electric machine or a generator with a disk-shaped rotor and a disk-shaped stator, in which a superconducting coil mechanically decoupled from the rotor 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, interference-prone transmission, frequency converter and / or slip rings are required and that high material, maintenance and operating costs incurred. The elimination of gearbox, frequency converter and slip rings would result in both higher reliability and less maintenance. This is particularly advantageous for use in offshore wind turbines, the importance of which will increase significantly in the future.

In addition, considerable expense for material and operation could be saved when using a fixed, non-rotating superconducting coil, at the same time the complexity of the system or of the generator decreases.

It is therefore an object of the invention to provide an inexpensive, robust and less susceptible to interference device for generating electrical energy.

This object is achieved by the inventions specified in the independent claims. Advantageous embodiments emerge from the dependent claims.

In the device according to the invention, the special advantages of a homopolar machine are exploited, as described, for example, in DE 10 2004 014 123 A1. In the homopolar machine, in contrast to synchronous or asynchronous machines, a mag- netic flux Φ generated by an exciter 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 sliding 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 homopolar machine is very simple and robust and can generally be used as a motor or as a generator.

The inventive system for generating electrical

Energy comprises a generator, which is advantageously designed as a homopolar generator. This includes a fixed annular stator with stator winding, a rotatable annular rotor of ferromagnetic material such as iron and a fixed annular excitation coil, wherein the stator and the exciting coil are arranged in the radial direction between a first and a second rotor portion. A magnetic flux Φ generated by the excitation coil is conducted by the rotor and passes through the stator in the radial direction, perpendicular to the stator winding. Both rotor sections have a plurality of poles which are radially aligned with the stator and guide the magnetic flux Φ. Between the poles of a rotor section are interpolar spaces. The poles of the two rotor sections lie opposite each other in the radial direction, the same applies to the pole interspaces.

With a current-carrying exciter coil, the magnetic flux between opposing poles is considerably greater than between opposing pole gaps, so that the magnetic flux Φ is dependent on the location when the rotor is stationary in the circumferential direction of the rotor. On the other hand, with a rotating rotor, the magnetic flux Φ varies at a certain location in the circumferential direction of the rotor, i. For example, in the region of a certain portion of the stator winding, as a function of time, so that in the stator winding, a voltage is induced.

Since the excitation coil is fixed, ie not co-rotated, it can be advantageously designed as a superconducting coil, in particular as a high-temperature superconductor (HTSC). This affects the fact that the excitation coil causes no excitation power, so that the efficiency increases.

The system works with a fixed, known number of revolutions of the rotor, i. in the case of a wind turbine with a fixed number of revolutions of the impeller. Depending on the mains frequency, a certain number of poles dependent on the number of revolutions of the rotor is provided, so that the generator always provides the correct frequency. Frequency converters are therefore not necessary, a gear is superfluous.

Since, in contrast to synchronous generators, only a single, albeit larger exciting coil is provided, the material and operating costs for generating the magnetic flux Φ are reduced.

A variation of the excitation current can also cover the changing reactive power demand of the network to be supplied.

Since the excitation coil is not rotated and there are no electrical components on the rotating rotor, slip rings can be completely dispensed with.

The generator can be used, for example, in wind or hydroelectric plants, wherein the rotor of the generator is coupled directly to the impeller.

Further advantages, features and details of the invention will become apparent from the embodiment described below and with reference to the drawings.

Showing:

Figure 1 shows a wind turbine in back and

Cross-sectional view

FIG. 2 shows a detail of a longitudinal section through the rotor and stator, Figure 3 shows a detail of a cross section through parts of the generator, Figure 4 is a plan view of a stator winding in a schematic view.

1 shows a wind turbine 10 in a rear view and a cross-sectional view with a device according to the invention, which includes a 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 can be provided. The impeller 30 is fixedly connected to a rotor 40 of the generator 20, so that when the rotor 40 is rotated together with the blades 31 and the impeller 30 in rotation. The rotor 40 is mounted for this purpose with its axis of rotation 50 in suitable bearings 60 which are housed in a housing 70. Also indicated is a fastening device 71, which includes a stator 80 (not shown in FIG. 1) of the generator 20. The stator 80 is disposed concentrically with the rotor 40 and secured to the housing 70 via the fastener 71, i. non-rotatably connected. Furthermore, a cryocooler 90 for cooling is provided for an exciting coil 100 concentric with the rotor 40 and the stator 80 (not shown in FIG. 1) of the generator 20. The entire construction is mounted on a mast 110.

Figure 2 shows a longitudinal section u.a. through the rotor 40 and the stator 80 in detail. The attachment of the impeller 30 on the rotor 40 is not shown, but is done in a known per se such that the wind-driven wings 31 set the rotor 40 via the impeller 30 in rotation.

The generator 20 is designed as a homopolar generator. The rotor 40 of the generator 20 comprises three rotor sections 41, 42, 43 and has an approximately U-shaped profile. Of the first 41 and the second rotor portion 42 are arranged spaced apart in the radial direction, wherein the radially outer first 41 and the radially inner second rotor portion 42 form the U-legs of the profile, while the third rotor portion 43, the sections 41, 42 connects. In particular, the profile of the rotor 40 is shaped like a lying 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, the stationary excitation coil 100 is arranged in the region of the third rotor section 43. Specifically, because the exciter coil 100 is fixed, it is convenient to use a superconducting exciter coil 100 because cooling is much easier to accomplish than with a co-rotating coil.

The excitation coil 100 is preferably a high-temperature superconductor. It is located in a cryostat 101 and is maintained at operating temperature by a cooling line 102. The cooling line 102 is supplied by the cryocooler 90 shown in FIG. The cooling can be done, for example, indirectly with liquid neon or hydrogen in a thermosyphone. The superconducting exciting coil 100 can be operated with DC and caused in

Difference to conventional, normal temperature conductors, no excitation power, whereby the efficiency of the entire system increases.

Alternatively, the annular excitation coil with a

Normal conductor such as a copper or aluminum conductor are operated at ambient temperature. Although this requires exciter power, it remains well below the power requirement for the rotor of a high-poled conventional synchronous machine. The efficiency of Homopolarmaschine is correspondingly higher. Eventually, such a normal conductor coil must, for example, be forcibly cooled with air via a fan or with a water circuit. The exciting coil 100 generates a magnetic flux Φ, which is guided by the rotor 40 and the rotor sections 41, 42, 43, as symbolized by the arrows. On the rotor sections 41 and 42, first 44 and second poles 45 are formed in the radial direction for guiding the magnetic flux Φ, which protrude in the radial direction from the rotor sections 41, 42. Between two first poles 44 (or between two second poles 45) there is a first pole intermediate space 46 (or a second pole gap 47). The poles 44, 45 extend in the axial direction preferably over the entire region, which is determined by the depth of the stator, that is, by its extent in the axial direction. Opposite first and second poles 44, 45 form a pole pair 48. As seen in the circumferential direction of the rotor 40, the first poles 44 and the first pole interspaces 46 of the first rotor section 41 have the same width w _R. The same applies to the second poles 45 and the second pole interstices 47 of the second rotor section 42. Preferably, the entire rotor 40 comprising the rotor sections 41, 42, 43 and the poles 44, 45 are integrally formed of solid iron to best suit the magnetic flux Φ conduct .

The fixed stator 80 comprises two three-phase stator windings 81, 82 and a stator core 83 made of iron 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 and between the U -Children are arranged. In the axial direction of the stator 80 and the exciter coil 100 are arranged side by side. By using two windings 81, 82, the output power of the generator 20 is doubled from 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 fastened to a part 72 of the housing 70 by means of a fastening device 71. In addition, the fastening device 71 also fixes the cryostat 101 with the exciter coil 100 and the cooling line 102. For example. For example, the fastening means 71 may be formed like a double-walled cylinder, with the stator 80 and the cryostat 101 being arranged and fixed between the cylinder walls.

Accordingly, the only moving part of the generator 20 is the rotor 40 comprising the rotor sections 41, 42, 43 and the poles 44, 45. The stator 80 and, unlike synchronous generators, the excitation coil 100 are fixedly connected to the housing 70, can therefore do not rotate. Alternatively, the stator 80 and / or excitation coil 100 could be fixed to another stationary part of the wind turbine 10, i. not rotatable or displaceable, be connected. For this purpose, for example, the mast 110 in question.

Because the rotor 40 does not have any electrical components such as coils or the like. carries, can advantageously be dispensed slip rings, etc.

FIG. 3 shows a section through the rotor 40, the stator 80 and the stator windings 81, 82 corresponding to the line A-A indicated in FIG. The poles 44, 45 of the rotor 40 are arranged on the stator 80 facing sides of the rotor sections 41, 42 and cause the magnetic flux Φ as indicated by the arrows, the stator 80 and the stator windings 81, 82 in the radial

Direction, that is perpendicular to the stator windings 81, 82 passes through. The stator windings 81, 82 each have three phases u, v, w. Between the first poles 44 and the stator 80 and between the second poles 45 and the stator 80 there is in each case an air gap which, ideally, is as small as possible, that is to say of the order of 5-15 mm. The magnetic flux Φ passing through the stator 80 is in the region between two opposite poles 44, 45, ie in the region of a pole pair 48, greater than in the region which lies between two opposite pole interstices 46, 47. In the case of a rotation of the rotor 40 triggered by a movement of the vanes 31, therefore, in the region of the stator windings 81, 82 the magnetic flux Φ varies as a function of time, so that a voltage is induced in the stator windings 81, 82 which is not shown can be tapped.

Since the surfaces of the poles 44, 45 lie on (imaginary) cylinder surfaces and the magnetic flux Φ passes through the stator 80 in the radial direction, it is relatively simple, by structural means such as spokes and / or disks, the radial distances from the axis of rotation of the rotor 40th adjust and thus maintain the air gaps between the rotor 40 and stator 80 regardless of magnetic, wind or other forces exactly. This is advantageous, in particular for large-diameter machines such as wind turbines, for example, as compared with the generator described in US Pat. No. 7,049,724 B2 with disc-shaped arrangement of rotor and stator with axially directed magnetic flux. Other disadvantages of the system described in US Pat. No. 7,049,724 B2 have already been mentioned.

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

By the fixed speed and the coordinated

Number of pole pairs is advantageously achieved that the generated electrical energy can be fed directly into the network, so that no frequency converter o.a. needed. Typically, the rotor 40 of such a generator 20 has a diameter of the order of 10m. Excitation of the generator 20 is accomplished by a fixed, i. non-co-rotating HTS excitation coil 100 which is cooled to 27K using liquid neon and generates a magnetic flux density of IT in the air gaps.

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

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 are driven by a watercourse. In principle, the electric machine according to the invention can also be operated as a motor, wherein the electric machine is designed in itself as the generator 20 described above.

Claims

claims

1. A device for generating electrical energy with a generator (20), in particular homopolar generator (20), which comprises:

an annular fixed stator (80),

- An annular fixed excitation coil (100) and

- An annular, rotatable rotor (40) having at least a first (41) and a second rotor portion (42), wherein

- The stator (80), the rotor (40) and the excitation coil (100) are arranged concentrically,

the stator (80) has at least one stator winding (81, 82),

- The stator (80) and the excitation coil (100) in the radial direction between the first (41) and the second rotor portion (42) are arranged, and wherein the rotor (40), the stator (80) and the excitation coil (100 ) are arranged such that the rotor

(40) conducts a magnetic flux Φ generated by the excitation coil (100) and the magnetic flux Φ passes through the stator (80) in the radial direction, substantially perpendicular to the stator winding (81, 82).

2. Apparatus 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.

3. 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.

4. Device according to one of the preceding claims, characterized in that the rotor (40) has an approximately U-shaped profile, wherein the first (41) and the second Rotor section (42) forming the U-legs of the profile and are aligned in the axial direction.

5. Device according to one of the preceding claims, characterized in that the first (41) and the second rotor section (42) comprise the stator (80) claw-shaped.

6. Device according to one of the preceding claims, characterized in that at the first Rotorabschnit (41) a plurality of first poles (44) and the second

Rotor section (42) a plurality of second poles (44) is integrally formed, wherein

the poles (44, 45) are each arranged on the side of the respective rotor section (41, 42) facing the stator (80),

- Are first (44) and second poles (45) radially opposite.

7. 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 by the exciter coil (100 ) generates magnetic flux Φ.

8. 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) at least multi-phase, in particular 3-phase (u, v, w) formed is.

9. Device according to one of the preceding claims, characterized in that the stator (80) has a laminated stator core (83).

10. Device according to one of the preceding claims, characterized in that the exciter coil (100) is a superconducting coil, in particular a HTS coil.

11. Device according to one of claims 1 to 9, characterized in that the exciting coil (100) is an annular coil made of a normal conductor.

12. The device according to claim 11, characterized in that the exciter coil (100) is forcibly cooled with air or water.

13. Device according to one of the preceding claims, characterized in that the rotor (40) rotates at a fixed rotational frequency.

14. Wind or hydroelectric power plant comprising a device for generating electrical energy according to one of the preceding claims.

15. wind or hydroelectric power plant according to claim 14, characterized in that an impeller (30) or wings (31) of the wind or hydropower plant (10) for driving the rotor (40) to the rotor (40) are connected.