Patent Application
20160013653
The invention relates to a converter station for transmitting electrical power, having a converter, which has a DC-voltage connection and an AC-voltage connection, and at least one transformer, which is connected to the AC-voltage connection.
A converter station such as this is known, for example, from the article by S. Bernal-Perez et al., “Wind power plant control for the connection to multiterminal HVdc links”, IEEE, 2012, page 2873. That document discloses an installation in which a diode rectifier is connected on the DC-voltage side to a DC-voltage intermediate circuit. The DC-voltage intermediate circuit extends between two voltage source converters (VSC). The diode rectifier is connected to a wind farm via transformers and an AC-voltage grid. Furthermore, filter units, which are arranged on the AC-voltage side of the converter, are disclosed. On the DC-voltage side, a smoothing inductor is used to smooth the direct current generated by the diode rectifier.
The connection of wind farms erected in the sea to a supply grid on land is generally done with direct current in the case of large transmission paths. For this reason, in practice, a converter is at present accommodated on an open-sea platform which is erected in the vicinity of the wind farm in the sea. Said converter in the sea is connected via an AC-voltage grid to the wind farm, wherein a DC-voltage connection extends from the DC-voltage connection thereof to a converter on land. However, the erection of such converters in the sea is cost-intensive owing to the still large weight and large volume of the converters.
The problem addressed by the invention is therefore to provide a converter station of the type mentioned at the outset which is as inexpensive as possible.
Said problem is solved within the context of the invention in that the converter station is arranged in a manner distributed on at least two support structures which are erected independently of one another.
According to the invention, the converter station is no longer arranged on a single support structure; rather, the weight of the converter station is distributed on various support structures. Therefore, within the context of the invention, it is possible to dispense with the very expensive platforms which are usual today and, instead, support structures are used which, for example, are also used to support wind turbines. The distributed arrangement of the converter station according to the invention on comparatively inexpensive support structures is particularly advantageous in the case of a converter which is configured as a diode rectifier. The diode rectifier has a significantly lower weight in comparison with the self-commutated converters used up to now for connecting wind farms. This also applies in a restricted manner to a thyristor converter which is populated with current valves in the form of thyristors.
The converter station according to the invention may have, for example, a converter which is held by an individual, that is to say separate, support structure. Further components are not held on said support structure. In this case, the converter forms at least a six-pulse bridge with its current or voltage valves. One of the DC-voltage terminals of said six-pulse bridge is connected, for example, to the ground potential. The other DC-voltage terminal is then, for example, connected via a single-pole DC-voltage connection to a converter on land. It is also possible to configure the converter as a twelve-pulse bridge known from high-voltage direct-current transmission. The twelve-pulse bridge has two six-pulse bridges which are connected in series on the DC-voltage side. The connection point thereof is generally at ground potential. Each six-pulse bridge is connected, for example, via a separate transformer to an AC-voltage grid. The windings of the two transformers are connected to one another in a different manner, with the result that a different phase shift occurs at the transformers during transmission. Of course, the converter station may also have two six-pulse bridges which each have one terminal at ground potential.
The configuration of the converter is, in principle, arbitrary within the context of the invention. By way of example, the converter is a self-commutated converter, for instance a voltage source converter (VSC). The use of a modular multi-level converter is also possible within the context of the invention. Of course, the converter may also be an externally commutated converter the converter valves of which have thyristors.
According to a first variant of the invention, the converter and at least one of the transformers are held on different support structures. This separation has proven to be particularly expedient with respect to the distribution of weight.
According to a preferred variant of the invention, the support structures can be arranged in the sea or in a lake, wherein at least one support structure is a wind-turbine support structure which is dimensioned to hold a wind turbine. In other words, according to this variant of the invention, support structures which also serve or can also serve to hold wind turbines are used. With respect to their dimensioning, the materials used and the material strengths thereof, they are designed to hold masses which correspond to the mass of a wind turbine which is customary on the market. Such usual support structures for holding wind turbines, that is to say wind-turbine support structures, are known to a person skilled in the art under the terms mono-pile, tri-pile, tripod, jacket, gravity foundation, floating support structure, or the like. Exemplary embodiments thereof are specified below with reference to the drawing. Wind-turbine support structures are expedient in production in comparison with open-sea platforms. In this case, within the context of the invention, it is not ruled out that other components which are not components of the converter station are also held by the respective support structure. According to the invention, parts of the converter station may thus also be arranged on a support structure which additionally supports or holds a wind turbine. Within the context of the invention, the components of the converter station may also be directly mounted on a tower of the support frame of the wind turbine.
Expediently, the converter has a plurality of DC-voltage side series-connected or parallel-connected partial converters. Using said partial converters, the converter can be easily scaled and can thus easily be adapted to the respectively present current or voltage requirements. In this case, each partial converter may be arranged on a separate support structure which is assigned to said partial converter alone, for example a mono-pile. Of course, a plurality of partial converters may also be held on a support structure.
According to a further development which is expedient in relation hereto, each partial converter is connected on the AC-voltage side to a partial transformer, wherein said partial converter and said partial transformer are arranged in a common partial encapsulation housing. According to said advantageous further development, components which are assigned, for example, to a string of a wind farm may be generated, wherein the string is connected to a number of wind turbines. The encapsulation housing may be arranged in the sea in a simple manner, for example on the support structure of a wind turbine.
Expediently, each partial converter has two DC-voltage terminals which can be bypassed by means of a bypass switch. According to said advantageous further development, a partial converter station, which comprises by way of example a partial converter and a partial transformer, may be bypassed, for example in the event of a fault. If the partial converter station is connected to a section of a wind farm, for example to a string of a wind farm, said section may also be bypassed in this way. This is advantageous since the faults may be present both in the respective component and the string or branch of the AC-voltage grid connected to the component.
Expediently, each partial converter forms a six-pulse bridge or a twelve-pulse bridge.
Expediently, a filter unit is provided on the AC-voltage side of the converter. The filter unit is used to compensate reactive power and to filter out harmonics of the fundamental harmonic, which may occur during normal operation of the converter. The filter unit may also comprise wind turbines or consist exclusively of wind turbines.
Expediently, each partial converter is connected on the DC-voltage side to a partial smoothing inductor. The partial smoothing inductor is used to smooth the direct current. This is particularly expedient if the partial converters are at least partially configured as partial diode rectifiers.
In the case of a preferred configuration of the invention, the partial converters are at least partially partial diode rectifiers or thyristor partial converters, the current valves of which have a series circuit composed of diodes or of thyristors. The partial diode rectifier, which again may form a six-pulse or twelve-pulse bridge, is particularly light in comparison to the self-commutated partial converter and causes fewer losses. The thyristor partial converter forms current valves, which are actively switched on, therefore, during an ignition impulse but may not be switched off. However, thyristor current valves are robust and inexpensive.
Advantageously, the converter is a diode rectifier. As has already been mentioned, the diode rectifier with its passive power semiconductors which are not actuable is light and has low losses in comparison with a converter with converters that can be switched on and off. However, within the context of the invention, the converter may also be a self-commutated converter, for example a voltage source converter (VSC) and, in particular, a modular multi-level converter. Such converters have power semiconductor switches which can be switched on and off, such as IGBTs, GTOs, IGCTs, or the like.
If the converter is a diode rectifier, it is expedient that the diode rectifier is connected on the DC-voltage side to a smoothing inductor.
Expediently, power supply means for supplying an AC-voltage grid connected to the converter station are provided. The power supply means cater to the circumstances in which a diode rectifier allows a power transmission in only one direction. In the case of a wind-farm connection, to which the converter station according to the invention is particularly suited, it is often necessary, however, to supply the AC-voltage grid connected to the converter station with electrical power. By way of example, the wind turbines of the wind farm can be set up using said electrical energy and the rotor blades can be adjusted to the respectively required angle. The power supply means comprise, for example, a diesel engine which drives a generator, wherein the generator generates the required electrical power which is fed into the AC-voltage grid connected to the wind farm.
Advantageously, the power supply means are configured such that a diesel engine can be dispensed with, however, since the diesel engine requires a lot of maintenance and must be continuously supplied with diesel. In particular, in the event that the converter station according to the invention is situated in the sea, the fuel supply in the event of wind or storms is difficult. For this reason, within the context of the invention, it is expedient to provide power supply means by which the power can be supplied from a supply grid on land or an adjacent AC-voltage grid in the sea. Such power supply means comprise a power supply line which extends at least partially through the water and, for example, is an AC-voltage line with a voltage in the range from 50 to 70 kV.
According to a configuration of the invention which deviates therefrom, the power supply means comprise a partial converter which is connected in series with partial diode rectifiers of the converter on the DC-voltage side. It is possible using the partial converter to use the DC-voltage connection through which the converter station is connected to the power supply grid on land to also supply the power flow in the opposite direction, that is to say from land to the wind farm. In this connection, of course, it is expedient if the partial diode rectifiers, as mentioned above, are equipped with a bypass switch by means of which the bypassing of the partial diode rectifier in the series circuit is enabled, with the result that the power from a converter on land is provided by the DC-voltage connection and can be converted from the partial converter or converters into AC voltage. The AC voltage that is generated is then used for the power supply of a connected wind farm.
Expediently, the transformer is connected to a switchgear assembly. The switchgear assembly is, for example, a gas-insulated switchgear assembly, wherein a corresponding bushing between the switchgear assembly and the transformer which is stored, for example, in oil is provided. As has already been mentioned above, within the context of the invention, it is also possible to use a plurality of transformers. This also applies to the switchgear assembly.
The switchgear assembly is expediently connectable via an AC-voltage line to a coupling-in component which is connected to a power supply grid on land or an AC-voltage grid in the sea.
Advantageously, the transformer and the converter are arranged in an insulating material. The term insulating material is intended to comprise, within the context of the invention, all gases and liquids and solids which have improved insulation properties compared to atmospheric air.
Owing to the improved insulation properties, the individual components of the converter which are at different levels of electrical potential can be arranged at a shorter distance with respect to one another without voltage flashovers occurring. In particular, a diode rectifier with its passive and non-actuable power semiconductors can be arranged without problems in an insulating material. This also applies to an externally commutated converter equipped with thyristors. The insulating material must only be removed in the event of maintenance. For this purpose, for example, inlet and outlet means, via which the insulating material can escape or be poured in, are provided on an encapsulation housing in which the converter is arranged.
According to a preferred configuration of the invention, the converter and the transformer are each arranged in an encapsulation housing, wherein the encapsulation housings are connected to one another. In this way, said components may be electrically connected to one another without elaborate bushings having to be used which transfer a conductor at a high-voltage potential from one insulating-material environment into another insulating-material environment or into an air atmosphere. The encapsulation, which is generally at ground potential, of the components of the converter station moreover protects said components against damaging environmental influences which may cause damage, in particular when the converter station is erected in the sea or in a lake.
Advantageously, at least one encapsulation housing is provided in which at least a part of the converter and at least a part of the transformer are arranged together, wherein the encapsulation housing is filled with the insulating material. According to this advantageous further development of the invention, an encapsulation housing filled with insulating material is provided, in which the (partial) converter and the (partial) transformer are at least partially arranged together. In this way, the converter station may be configured to be even more compact. Of course, the wiring networks of the converter are also housed in the encapsulation housing or housings. The encapsulation housing or housings are expediently at ground potential.
The insulating material may, in principle, be gaseous, liquid or solid. Expediently, the protective gases, such as sulfur hexafluoride or the like, known in energy transmission and distribution are used. However, particular advantages emerge if a liquid, for instance an expedient insulating oil, is used as insulating material. In addition to insulation, the oil provides cooling.
Further expedient configurations and advantages of the invention are the subject matter of the following description of exemplary embodiments of the invention with reference to the figures of the drawing, wherein identical reference signs refer to identically acting components and wherein
a schematically illustrates the diode rectifier in detail,
In the case of the diode rectifier 2 illustrated in
The diode rectifier 2 is arranged on a support structure 18, which is arranged in the sea approximately 50 to 400 km from the coast. In a particularly advantageous embodiment, the support structures and foundations used in the respective wind farm as support structure 18 or the components are fastened directly to the tower of a wind turbine. The transformer 6 is arranged on a corresponding support structure 19 and the transformer 7 on a support structure 20. The support structures 18, 19, 20 are therefore particularly inexpensive. As has already been mentioned above, the converter station arranged in the sea is used to transmit power generated by the wind farm into the DC-voltage connection 15.
Since the diode rectifier 2 is set up to transmit power in only one direction, namely from the transformer 6 to the converter 16 on land, the energy required by the wind farm in the event of no wind must be provided to the wind farm in another way. For this purpose, energy transmission means 21 which have a coupling-in component 22 which in this case consists of a coupling-in transformer 23 and a mechanical switch 24 are used. The coupling-in component 22 is connected via an AC-voltage line 25 and the switchgear assembly which is not illustrated in the figures to the strings 8 of the AC-voltage grid. In this case, the coupling-in component 22 is connected to the power supply grid 17 via the transformer 25. The transformer 25 supplies an expedient AC voltage in the order of magnitude between 50 and 70 kV. In this way, the wind farm can be supplied with energy from land.
The construction of the six-pulse bridge 3 is illustrated in more detail in
As has already been mentioned, the converter station 1 is distributed on a plurality of support structures, approximately 100 km from a coast 36 in the sea, wherein a converter 16 on land is connected via a DC-voltage connection 15 to the converter station 1. It can be seen that each partial converter station 31 is connected to a string 8 of an AC-voltage grid 7 which is used to connect a wind farm 37 to the converter station 1. The wind farm 37 consists of a multiplicity of wind turbines 38.
Even in the event of no wind, the wind farm 37 requires energy. This is provided thereto using the partial converter 32. For this purpose, for example, all of the partial diode rectifiers 31 are bypassed by closing the respective bypass switch 35, with the result that the partial converter 32 is directly connected to the converter 16 on land, which is a modular multi-level converter, for example. Said modular multi-level converter is connected to a power supply grid which is not illustrated in the figures and feeds the necessary power into the partial converter 32, which provides said power on the AC-voltage side for the wind farm 37.
The support structure 47 is a so-called floating support structure, wherein a freely floating buoyant body 55 is permanently anchored to the seafloor by an anchor 56 and rope 57. A tower or mast 58 is supported on the floating buoyant body 55 and set up to hold the wind turbine. The buoyant body 55 is adjusted in terms of its buoyancy forces to the intrinsic weight of the tower 58 and the weight of a wind turbine. The anchoring 56 on the seafloor 53 is done, for example, by driving piles into the seafloor. Provision is made of ballast bodies, departing from said driven piles, which lay freely on the seafloor and to which the ropes are fastened.
In the case of the support structure 48, only one driven pile has been driven into the seafloor 53, wherein the driven-in pile is extended by a tower or tower section 58. Again, parts of the converter station 1 can be fastened to the tower 58.
The support structure 49 differs from the support structure 48 in that three driven piles 59 have been driven into the seafloor. A space framework 60 can be seen above the surface 54 of the water on the three driven piles, said space framework being supported on all three driven piles. The tower or mast 58 projects perpendicularly from the space framework 60.
The support structure 50 differs from the support structure 49 in that the space framework 60 is tetrahedral and arranged below the surface 54 of the water.
The support structure 51 has a support framework 61 instead of a space framework, said support framework being supported on four driven piles 59 and extending both below and above the surface 54 of the water. Again, the tower or mast 58 of the wind turbine is supported on the support framework 61.
The support structure 52 has a stand foot 62 which lies on the seafloor 53. The mast or tower 58 extends directly from the stand foot 62.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2013/054070 | 2/28/2013 | WO | 00 |
