DEVICE FOR GENERATING ELECTRICAL ENERGY

Abstract

A device for generating electrical energy, in particular a wind turbine, having at least one generator is disclosed. The generator provides electrical energy by means of multi-phase, machine-side connection means and is connected to at least one converter having a DC link via the multi-phase, machine-side connection means. A method for operating a device for generating electrical energy, in particular a wind turbine, is also disclosed. The object of providing a device for generating electrical energy, in particular a wind turbine, which reliably avoids the development of surges despite parasitic inductances and capacitances by means of the machine-side multi-phase connection means is achieved in that means for attenuating at least one series resonance in the zero sequence of the machine-side connection means are provided between generator and converter.

Claims

1. A device for generating electrical energy, in particular a wind turbine, comprising: at least one generator, wherein the generator provides electrical energy via multi-phase, machine-side connection means and is connected to at least one converter having a DC link via the multi-phase, machine-side connection means, wherein means for attenuating at least one series resonance in the zero sequence of the machine-side connection means are provided between generator and converter.

2. The device according to claim 1, wherein the means for attenuating the series resonance in the zero sequence have at least one magnetically coupled series resistance effective for the zero sequence of the machine-side connection means.

3. The device according to claim 1, wherein the at least one magnetically coupled series resistance in the zero sequence has an electrical resistance R for which the following applies: $\begin{array}{cc}R=d*\sqrt{\frac{L}{C}}& \end{array}$ wherein L is the inductance and C is the capacitance of the machine-side connection means between generator and converter and d is the proportionality factor of the attenuation, and the following applies for d:
0.25d1.8.

4. The device according to claim 1, wherein the at least one magnetically coupled series resistance in the zero sequence of the machine-side connection means is coupled by means of at least one magnetic core.

5. The device according to claim 4, wherein the at least one magnetic core surrounds the neutral conductor of the machine-side connection means between converter and generator for the magnetic coupling of the series resistance.

6. The device according to claim 5, wherein the neutral conductor of the machine-side connection means is designed at least in some areas as cables and/or busbars and wherein the at least one magnetic core is arranged in at least one of these areas.

7. The device according to claim 4, wherein the at least one magnetic core is made of electrical sheet, wherein an air gap is optionally provided to provide a specific magnetic resistance of the magnetic core.

8. The device according to claim 4, wherein the at least one magnetic core is made of soft magnetic full material, preferably ferrite, wherein the at least one magnetic core has at least one coil, the winding connections of which are connected to one another by means of at least one series resistance.

9. The device according to claim 1, wherein the at least one series resistance is arranged on cooling means and can optionally be variably adjusted in terms of its resistance value.

10. The device according to claim 1, wherein the machine-side connection means are dimensioned such that the series resonance of the connection means in the zero sequence occurs below 500 kHz, preferably below 150 kHz.

11. The device according to claim 1, wherein the device is a wind turbine, wherein the wind turbine as a generator has a double-fed asynchronous machine or a synchronous generator.

12. A method for operating a device for generating electrical energy, in particular a wind turbine according to claim 1, comprising the step of: determining at least one series resonance in the zero sequence of the machine-side connection means between generator and converter, determining a series resistance for attenuating this series resonance depending on the series resonance determined, and magnetically coupling this series resistance into the zero sequence.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The invention shall be described in greater detail below using embodiments in combination with the figures, in which:

[0028] FIG. 1 is a schematic representation of a device for generating electrical energy in the form of a wind turbine,

[0029] FIG. 2 is a simulation of the excess voltage caused by a series resonance in a voltage time diagram of a phase against the zero potential on the machine-side input of the converter,

[0030] FIG. 3 is an embodiment of a circuit diagram of the connection means from the generator to the converter,

[0031] FIGS. 4, 5 are an embodiment of a magnetically coupled series resistance in a sectional view and a plan view and

[0032] FIG. 6 is a further embodiment of a magnetically coupled series resistance with a sheet metal magnetic core.

DETAILED DESCRIPTION

[0033] FIG. 1 shows a device for generating electrical energy in the form of a wind turbine 1 having at least one generator 2, wherein the generator provides electrical energy to at least one converter 4 with a DC link via multi-phase, machine-side connection means 3. The connection means 3 shown in FIG. 1 are provided on the machine-side, in other words provided between the generator 2 and the converter 4, and are generally designed to be three-phase. In the present embodiment, the connection means 3 are divided into three sections A, B and C. In areas A and C, the connection means 3 are designed as a cable. In area B, the connection means 3 provided on the machine side are designed as busbars. Busbars differ from cables in that they generally do not have a round cross-sections, but rather square and in particular rectangular cross-sections in order to achieve the advantages of the busbars, i.e. to be easily premountable. Due to the flat extension of the cross-section, they can carry very high currents in a very small space. For example, busbars can easily guide the current at a right angle while cables cannot achieve this due to their high level of rigidity. Pre-assembly, for example in the tower of the wind turbines, is also difficult to achieve with cables. In addition, where the outputs to be carried are high, busbars are also significantly cheaper than cables. A disadvantage of busbars, however, is that due to the geometric cross-sectional shape of the busbars and their arrangement in the tower higher parasitic inductances and capacitances can occur.

[0034] The geometric design of the busbars in area B in connection with the cable routing in areas A and C of the machine-side connection means 3 cannot prevent parasitic inductances and capacitances, so that resonances and thus undesirable voltage fluctuations occur in particular in the zero sequence, i.e. the voltage of all phases relative to the zero potential or earth.

[0035] FIG. 2 shows a simulation of the time progression of the voltage in a phase of the converter 4 relative to the zero potential during two switching operations of a circuit breaker of the converter 4. The first and second switch switching operations are ideally carried out in steps. The diagram further shows the unattenuated progression of the voltage U.sub.ug as a dashed line and the time progression of the voltage with attenuation of the series resonance U.sub.ug as a continuous line.

[0036] It can be seen that the unattenuated voltage U.sub.ug shows significant overshooting relative to the zero potential during the first switching operation and takes on values of between approximately 1300 V and 2500 V in the case shown. The voltage peaks can, however, be problematic with regard to the components of the converter. Voltage flashovers can cause damage to the converter or to the connection means to the generator.

[0037] As already mentioned, the inventor identified that series resonances, in particular the first series resonance in the zero sequence of the multi-phase connection means 3 are the cause of the voltage peaks. If this at least one, preferably the first series resonance in the zero sequence of the machine-side connection means 3 between generator 2 and converter 4 is attenuated via means for attenuating the resonance, there is a significant reduction in the voltage peaks. The correspondly simulated voltage progression U.sub.g in FIG. 2 shows that the minimum voltage peak value of U.sub.g is only around 1700 V and the maximum peak value is +750 V. The overshooting behavior could be reduced by +900 V or 750 V for this switching operation. If this attenuation is not sufficient, greater attenuation of the voltage overshooting can be achieved by selecting a higher proportionality factor d. The attenuation is preferably selected so that the voltage U.sub.g takes on values for which the inputs of the converter and also the connection means are designed, so that no voltage flashovers can occur and damage is prevented. The attenuation of the series resonance is also clearly visible in the second switching operation and shows even smaller voltage peak values. The desired reduction effect on the voltage peak value is set by selecting the magnet material of the core and/or selecting the resistance value and thus via the proportionality factor d; the reduction effect can be seen in FIG. 2 as an example. At the same time, despite the attenuation, the power loss to be accepted is low. It is a maximum of about 2 kW.

[0038] FIG. 3 shows a circuit diagram of the connection means 3 of an embodiment of a device for generating electrical energy, in particular a wind turbine, having a generator 2 and a converter 4 or 4. The connection means 3 between generator 2 and converter 4 or 4 are designed to be three-phase L1, L2, L3 or L1, L2, L3. At the same time, the generator 3 is also connected to the converter 4 or 4 by means of a neutral conductor N or N. The neutral conductor N, N is part of the machine-side connection means 3.

[0039] Furthermore, in FIG. 3 the connection means 3 are divided into three areas A, B and C, wherein area B is for example designed as a busbar, for example in the tower of a wind turbine. Areas A and C should for example be designed as cables. Means for attenuating the series resonance of the connection means 3 in the zero sequence 5, 6, 7, 8 and 9 are also shown in FIG. 3, wherein the means shown for attenuating the series resonance 5, 6, 7, 8 and 9 in particular aim to illustrate the various possible positions of the attenuating means. In the present embodiment, the means for attenuating the series resonance in the zero sequence 5, 6, 7, 8 and 9 are designed as series resistances magnetically coupled into the neutral conductor N and symbolized by the annular magnetic core in FIG. 3.

[0040] The means for attenuating the series resonance 5, 6, 7, 8 and 9 can be provided in the areas A, B and C of the connection means. If, for example, the neutral conductor N is realized by the metallic tower wall of a wind turbine in area B, the magnetic coupling of the means for attenuating the series resonance cannot occur in this area. In this case, however, another position for the magnetic coupling of a series resistance 5, 7, 8 or 9 can be used for attenuating the series resonance, for example in the cable routing areas A and C. In principle, the cable routing areas A and C of the connection means 3 are preferably selected for the magnetic coupling of the series resistance as the magnetic coupling of the series resistance is easily possible in these areas with relatively small magnetic cores.

[0041] As shown in FIG. 3, the generator 3 can also be connected to a further converter 4 via multi-phase connection means 3, wherein three further phases L1, L2 and L3 and a further neutral conductor N provide the electrical connection between the converter 4 and the generator 3. A means for attenuating the series resonance 9 can additionally be provided in the neutral conductor N of the connection means to the converter 4. In principle, where converters 4 and 4 are operated in parallel, it is also sufficient to provide a magnetically coupled series resistance 7, 6 or 5 before the branch of the parallel neutral conductor N for the converter 4.

[0042] The generator in FIG. 3 is merely shown schematically. This generator 3 can be a synchronous generator, the stator of which is connected to the converters 4 and 4. The generator 3 can, however, also be designed as a double-fed asynchronous machine so that the generator 2 is connected to the converter 4 or 4 on the rotor side via multi-phase connection means 3. In order to indicate this, the phases L1, L2 and L3 at the generator 3 are dashed lines to the rotor.

[0043] The at least one magnetically coupled series resistance in the zero sequence of the circuit diagram in FIG. 3 with reference signs 5, 6, 7, 8 or 9 has an electrical resistance for which the following is defined:

[00003]$\begin{array}{cc}R=d*\sqrt{\frac{L}{C}}& \left(1\right)\end{array}$

[0044] wherein L is the inductances and C is the capacitance of the machine-side connection means between generator and converter, d is the proportionality factor of the attenuation. For values of d in the range of 0.25 to 1.8, the magnetically coupled series resistance value is high enough for the series resonance in the zero sequence of the connection means designed to be multi-phase to be able to be attenuated very well. As already mentioned, resistance values of less than 10, preferably 1 to 5, are preferably used.

[0045] The position of the means for attenuating the series resonance, for example the position of the magnetic core for coupling the series resistance, can be arranged in the various areas A, B or C of the multi-phase connection means 3 depending on the circumstances. Since the neutral conductor N or N is not designed for the transmission of large amounts of energy, it has smaller geometric dimensions than the remaining power phases. The arrangement of a magnetic core on the neutral conductor can therefore be achieved in a simple manner. In areas B and C this occurs, as mentioned, in a particularly simple manner as the neutral conductor N or N is designed as a cable. However, it is also conceivable for attenuation means to be provided in several areas A, B and C.

[0046] FIG. 4 and FIG. 5 show a magnetic core of soft magnetic full material 10, preferably ferrite, which surrounds a neutral conductor N and has at least one coil 11 which is connected or short-circuited via at least one series resistance 12. While FIG. 4 shows a sectional view perpendicular to the longitudinal axis of the neutral conductor N, FIG. 5 is a planar view of the neutral conductor N. The soft magnetic ring 10 surrounds the neutral conductor N perpendicular to its longitudinal extension. The alternating magnetic field induced in the magnetic core generates a voltage in the coil 11 which leads to a current flow via the series resistance 12. The magnetic core 10 made of soft magnetic full material, in particular ferrite, only has very low heat losses caused by the induction of magnetic alternating fields in the magnetic core so that the heat loss in the soft magnetic, for example ferrite, ring remains low. In the series resistance 12, the heat loss is substantially released due to the attenuation of the series resonance.

[0047] The series resistance 12 is therefore preferably arranged on cooling means not shown, which ensure the safe release of heat in a simple manner. The use of a ferrite core 10 has the advantage that the heat loss resulting from the attenuation of the series resonance can be transferred to cooling means in a targeted manner. Furthermore, an optimized attenuation behavior relative to the series resonance to be attenuated can be set by selecting the series resistance in the resistance value as well as by means of the number of windings of the coil on the magnetic core. The number of windings is preferably fewer than 10, particularly preferably 2 to 6 windings.

[0048] The series resistance shown in FIG. 4 and FIG. 5 can preferably be adjusted in a variable manner in its resistance value. This has the advantage that, for example, at the site of installation of a wind turbine, an optimized attenuation of the series resonance can still be set after the installation. The same applies in the case of a retrofitting of an existing device for generating electrical energy.

[0049] A further, simple option for coupling a series resistance magnetically into the zero sequence is shown in a schematic sectional view in FIG. 6. Here, a magnetic core 10 consisting of electrical sheet is shown. The magnetic core has a defined gap so that a defined magnetic resistance can be set. The neutral conductor which is surrounded by the magnetic core 10 is also shown.

[0050] The magnetic core 10 itself constructed in this way already provides the series resistance in which the magnetic resistance leads to heat loss and therefore to an attenuation of the series resonance during the change of the magnetization direction due to the series resonance. The resulting heat loss is released in the entire magnetic core 10 and in this case must be sufficiently well dissipated. The advantage of the sheet metal magnetic core 10 is that it is cost-effective and its geometric shape can be relatively freely selected.

[0051] The device shown in FIG. 3 can be used particularly effectively if the series resonance of the connection means in the zero sequence is below 500 kHz, preferably below 150 kHz. These frequency ranges are not attenuated by the network filters (dU/dt filters) usually provided in wind turbines. The device shown in FIG. 3 provides very good attenuation of the series resonance in the zero sequence of the connection means 3.

[0052] The device for generating electrical energy, particularly the wind turbine, is preferably operated such that initially at least one series resonance in the zero sequence of the machine-side connection means 3 between generator 2 and converter 4, 4 is determined, for example after their assembly or even in advance by means of a simulation, and a series resistance 5, 6, 7, 8, 9 is magnetically coupled into the zero sequence of the connection means 3 depending on the series resonance determined. Surges induced on the machine side by the switching behavior of the converters in the zero sequence are significantly suppressed in this way and an improved switching behavior of the converters is achieved.

[0053] All references, including publications, patent applications, and patents cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.

[0054] The use of the terms a and an and the and similar referents in the context of describing the invention (especially in the context of the following claims) is to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms comprising, having, including, and containing are to be construed as open-ended terms (i.e., meaning including, but not limited to,) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., such as) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.

[0055] Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.