Classifications

• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
  • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
  • H02J3/36—Arrangements for transfer of electric power between ac networks via a high-tension dc link
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F03—MACHINES OR ENGINES FOR LIQUIDS; WIND, SPRING, OR WEIGHT MOTORS; PRODUCING MECHANICAL POWER OR A REACTIVE PROPULSIVE THRUST, NOT OTHERWISE PROVIDED FOR
  • F03D—WIND MOTORS
  • F03D15/00—Transmission of mechanical power
  • F03D15/20—Gearless transmission, i.e. direct-drive
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F03—MACHINES OR ENGINES FOR LIQUIDS; WIND, SPRING, OR WEIGHT MOTORS; PRODUCING MECHANICAL POWER OR A REACTIVE PROPULSIVE THRUST, NOT OTHERWISE PROVIDED FOR
  • F03D—WIND MOTORS
  • F03D9/00—Adaptations of wind motors for special use; Combinations of wind motors with apparatus driven thereby; Wind motors specially adapted for installation in particular locations
  • F03D9/20—Wind motors characterised by the driven apparatus
  • F03D9/25—Wind motors characterised by the driven apparatus the apparatus being an electrical generator
  • F03D9/255—Wind motors characterised by the driven apparatus the apparatus being an electrical generator connected to electrical distribution networks; Arrangements therefor
  • F03D9/257—Wind motors characterised by the driven apparatus the apparatus being an electrical generator connected to electrical distribution networks; Arrangements therefor the wind motor being part of a wind farm
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
  • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
  • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
  • H02J3/381—Dispersed generators
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
  • H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
  • H02J2300/20—The dispersed energy generation being of renewable origin
  • H02J2300/28—The renewable source being wind energy
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E10/00—Energy generation through renewable energy sources
  • Y02E10/70—Wind energy
  • Y02E10/72—Wind turbines with rotation axis in wind direction
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E10/00—Energy generation through renewable energy sources
  • Y02E10/70—Wind energy
  • Y02E10/76—Power conversion electric or electronic aspects

Definitions

• This invention relates to a wind power plant comprising at least one wind power station, which comprises a wind turbine, an electric generator driven by this wind turbine and a rectifier, and an electric direct voltage connection between the rectifier arranged at the wind power station and an inverter, the alternating voltage side of which is connected to a transmission or distribution network, the inverter being arranged on the network side of the plant.
• the invention is preferably intended to be used in such cases where the connection between the generator and the transmission or distribution network includes a cable intended to be submerged into water. Consequently, expressed in other words, it primarily relates to such applications where one or several wind turbines with associated generators are intended to be placed in seas or lakes, wherein the cable connection extends to the transmission or distribution network placed on land.
• the invention can, however, also imply advantages in cases where the wind turbines and the generators are located on land and the connection, which in that case not nec- essarily has to consist of a cable but instead can be realized in the form of aerial lines or cables, connects several such wind turbines/generators with the transmission or distribution network.
• the voltage variation may not be more than 4%. Different countries have different regulations and as a rule the regulations are mitigated in case of a lower voltage level on the transmission line. Voltage variations could also have to be treated differently depending on time intervals. Rapid voltage variations causes "flicker", i.e. light variations in glow lamps, which is regulated in rules.
• a solution to the problem above with long cable distances is to transmit the power with high-voltage direct voltage.
• the cable can then be drawn right up to a strong network.
• Another advan- tage is that DC-transmissions have lower losses than AC-trans- missions. From a technical point of view the cable distance can then be of unlimited length.
• a HVDC-link consists of a rectifier station, a transmission line (cable or aerial line), an inverter station and filters for removing overtones generated during the conversion.
• thyristors are used for rectification and inversion.
• Thyristors can be switched on but not switched off; the commutation takes place at the zero- crossing of the voltage, which is determined by the alternating voltage, and the converters are therefore called line commu- fating.
• a disadvantage with this technique is that the converters consume reactive power and cause current overtones, which are sent out in the network.
• IGBT Insulated Gate Bipolar Transistor
• An IGBT Insulated Gate Bipolar Transistor
• the converters can be produced ac- cording to a completely different principle, so called self-com- mutating converters.
• a self-commutating converter is characterized in that the voltage is built up by a rapid pulse pattern , which is generated by the converter.
• the voltage differ- ence between the pulse pattern and the sinusoidal network voltage will lie above the inductances on the network side.
• inverters There are two types of self-commutating inverters; a voltage stiff, VSI (Voltage Source Inverter) and a current stiff, CSI (Current Source I nverter), with somewhat different characteristics.
• VSI Voltage Source Inverter
• CSI Current Source I nverter
• a synchronous generator is not to any disadvantage, but rather to an advantage, since the asynchronous generator requires a more expensive and more complicated rectifier. If it is desired to have a direct driven generator and consequently eliminate the need of a gear unit between the turbine and the generator, the generator must be synchronous since it will be provided with so many poles. In other words, a direct driven generator requires a DC-intermediate link. In the concept it is also possible to actively regulate the moment by changing the trigger angle, if a controlled rectifier is used. In most concepts having a variable rotational speed, an external active rotational speed control is furthermore provided by so called pitch control, which implies that the blade angle is changed on the turbine. A disadvantage with a variable rotational speed according to the related concepts is the price of the required power electronics and furthermore that the maintenance of such power electronics out at sea will be difficult and costly.
• the purpose of the invention is to achieve, with a more simple and cheap system for variable rotational speed, the same good power transmission from a sea-based wind park to the land- based network as offered by a modern HVDC-system, with the possibility to eliminate the necessity of transformers and controlled power electronics in the wind power stations. This is very valuable since all maintenance carried out at sea is costly and difficult to perform.
• a further purpose of the invention is to be able to have such a high voltage on the DC-transmission that low losses are obtained also for a large wind park, for instance on 50-1 00 MW.
• the purpose of the invention is achieved primarily through the features defined in the characterizing part of the subsequent claim 1 .
• the unsolved problem of prior technique that the DC- voltage will be too low is consequently solved by connecting the DC/DC-converter out at sea with its low-voltage side electrically connected to the rectifier and its high-voltage side electrically connected to the inverter.
• Such a DC/DC-converter functions in about the same way as a transformer for DC; it steps up the direct voltage a factor n: 1 and steps down the direct current as 1 :n, where n is the conversion. This implies that the inverter and the rectifier are no longer connected in series.
• the rectifier is formed as a passive diode rectifier in series with a local step-up direct voltage converter.
• the local step-up direct voltage converter suitably consists of a choke, a series connected IGBT-valve and a series connected diode. This can also be the basic design of a DC/DC- converter.
• the inverter is constituted by a voltage stiff, self-commutated system, the characteristics of which are superior to a line commutated system from a power regulating point of view.
• a voltage stiff, self-commutated system the characteristics of which are superior to a line commutated system from a power regulating point of view.
• Such a system is characterized, in an embodiment of the invention, in that at least one capacitor is connected in parallel over the inverter on the DC-link and that inductances are connected in series with each phase on the network side.
• the valves are constituted by series connected IGBT.s.
• thermore the conventional insulation technology for stator windings is sensitive to temperature variations, humidity and salt, which a wind turbine generator is exposed to.
• a solid insulation is used for at least one winding in the generator, which insulation preferably is performed according to the subsequent claim 14.
• the winding has more specifically the character of a high-voltage cable.
• a generator manufactured in this way creates the prerequisites of achieving considerably higher voltages than conventional generators. Up to 400 kV can be achieved.
• such an insulation system in the winding implies insensibility to salt, humidity and temperature variations.
• the high output voltage implies that transformers can be completely excluded, which implies avoidance of the already mentioned disadvantages such as increase in costs, reduction in effectivity, risks of fire and risks for the environment. The latter are due to the fact that conventional transformers contains oil.
• a generator having such a winding formed by a cable can be produced by threading the cable in slots performed for this purpose in the stator, whereupon the flexibility of the winding cable implies that the threading work can be easily performed.
• the two semiconducting layers of the insulation system have a potential compensating function and consequently reduce the risk of surface glow.
• the inner semiconducting layer is to be in electrically conducting contact with the electrical conductor, or a part thereof, located inwardly of the layer, in order to obtain the same potential as this.
• the inner layer is intimately fastened to the solid insulation located outwardly thereof and this also applies to the fastening of the outer semiconducting layer to the solid insulation.
• the outer semiconducting layer tends to contain the electrical field within the solid insulation. In order to guarantee a maintained adherence between the semiconducting layers and the solid insulation also during temperature variations, the semiconducting layers and the solid insulation have essentially the same thermal coefficient of expan- sion.
• the outer semiconducting layer in the insulation system is connected to ground potential or otherwise a relatively low potential.
• the generator has a number of features which have already been mentioned above and which distinctly differ from conventional technology. Further features are defined in the dependent claims and are discussed in the following :
• the winding in the magnetic circuit is produced of a cable having one or several permanently insulated electrical conductors with a semiconducting layer at the conductor and outwardly of the solid insulation.
• Typical cables of this kind are cables having an insulation of cross-linked polyethylene or ethylene-propene, which for the purpose here in question are further developed concerning stands of the electrical conductor and also the character of the insulation system.
• Cables having a circular cross section are preferred, but cables having another cross section can also be used, for instance in order to achieve a better packing density.
• Such a cable makes it possible to design a laminated core of the magnetic circuit in a new and optimal way as concerns slots and teeth.
• the winding is produced with a stepwise increasing insulation or the best utilization of the laminated core.
• the winding is produced as a concentric ca- ble winding, which makes it possible to reduce the number of coil end crossings.
• the shape of the slots is adapted to the cross section of the winding cable so that the slots are in the form of a number of cylindrical openings extending axially and/or radially outwardly of each other and having constrictions running between the layers of the stator winding.
• the shape of the slots is adapted to the cable cross section in question and to the stepwise changing thickness of the insulation of the winding.
• the stepwise insulation makes it possible for the magnetic core to have an essentially constant tooth width independent of the radial extension .
• winding conductor consisting of a number of layers brought together, i.e. insulated strands, does not necessarily have to be correctly transposed, and non-insulated and/or insulated from each other.
• the cable can have an outer diameter in the order of 10- 40 mm and a conductor area in the order of 1 0-200 mm 2 .
• a transformer with variable transmission is arranged on the high voltage side of the inverter.
• Fig 1 is a schematic axial end view of a sector of the stator in an electric generator in the wind power plant according to the invention.
• Fig 2 is an end view, partly cut, of a cable used in the stator winding according to Fig 1
• Fig 3 is a schematic view, partly in section, of an embodiment of a wind power generator according to the invention
• Fig 4 is a schematic view showing the embodiment of the wind power plant according to the invention.
• Fig 5 is a schematic perspective view showing an embodiment of a transformer with variable transformation.
• Fig 1 shows a schematic axial view through a sector of the stator 2.
• the rotor of the generator is denoted as 3.
• the stator 2 is in a conventional way formed of a laminated core.
• Fig 1 shows a sector of the generator corresponding to a pole pitch. From a yoke section of the core, located furthest out in radial direction, a number of teeth 5 extend radially inwards towards the rotor 3 and these teeth are separated by a slot 6, in which the stator winding is arranged.
• PEX cross-linked polyethylene
• the cables 7 are schematically illustrated in Fig 1 , wherein only the electrically conducting central part of each cable section or coil side is shown. It appears that each slot 6 has a varying cross section with alternating broad parts 8 and narrow parts 9.
• the broad parts 8 are essentially circular and surround the cable, waist sections between the broad parts forming the narrow parts 9. The waist sections serve to radially fix the position of each cable.
• the cross section of the slot 6 be- I
• Fig 2 shows a stepwise cut end view of a high-voltage cable for use in the generator.
• the high-voltage cable 7 comprises one or several electrical conductors 14, each of which comprises a number of strands 15, which together give a circular cross section.
• the conductors can for instance be of copper.
• These con- ductors 14 are arranged in the middle of the high-voltage cable 7 and in the shown embodiment each of the conductors is surrounded by a partial insulation 16. It is however possible to omit the partial insulation 16 on one of the conductors 14.
• the conductors 14 are surrounded by a first semiconducting layer 17. Around this first semiconducting layer 17 there is an insulation layer 1 8, e.g.
• a wind power station is shown with a magnetic circuit of the type described with reference to Figs 1 and 2.
• the generator 1 is driven by a wind turbine 20 via a shaft 21 .
• the generator 1 can be direct driven by the turbine 20, i.e. that the rotor of the generator is coupled fixed in rotation to the shaft of the turbine 20, there can be a gearing 22 between the turbine 20 and the generator 1 .
• This can for instance be constituted by a single-step planetary gearing, the purpose of which is to change up the rotational speed of the generator in relation to the rota- tional speed of the turbine.
• the stator 2 of the generator carries the stator windings 23, which are built up of the cable 7 described above.
• the cable 7 can be unsheathed and pass on into a sheathed cable 24 via a cable joint 25.
• Fig 4 which in a schematic form broadly illustrates the wind power plant, two wind power stations 29 connected in parallel are illustrated, each having a generator 1 .
• the number of wind power stations can of course be larger than two.
• a rectifier 27 is comprised in each wind power station 26.
• the parallel connection of the wind power stations takes place at the point indicated with 28.
• An electric direct voltage connection is present between the rectifiers 27 arranged at the wind power stations 26 and an inverter 30, the alternating voltage side of which is connected to a transmission or distribution network.
• the inverter 30 is arranged on the network side of the plant. This normally implies that the inverter 30 is located on land relatively close to the transmission or distribution network 31 .
• the wind power stations 26 including the generators and the rectifiers 27 are located at sea on suitable foundations .
• the direct voltage connection 29 comprises a section denoted as 32 in Fig 4, which section in practice can be very long. Along this section there is, consequently, a connection part 33, which is critical in regard of losses.
• this connection part 33 is considered to be formed of an underwater cable, namely in the case that the wind power stations 26 are situated out at sea or in a lake.
• the connection part 33 can also be formed of one or several aerial lines or cables.
• the plant comprises a DC/DC-converter 34 having a low-voltage side electrically connected to the rectifiers 27 and a high-voltage side electrically connected to the inverter 30.
• the DC/DC- converter 34 is arranged on the wind power station side of the plant. Expressed in other words, this implies that the previously discussed connection part 33 is situated between the DC/DC- converter 34 and the inverter 30.
• the converter 34 is considered to be placed on one of the foundations that are carrying one of the wind power stations 26 or alternatively there can be a particular foundation for the converter 34. Independent of which type of foundation the converter 34 is placed on, the foundation in question is also provided with bus-bars in order to parallel connect the occurring wind power stations.
• the converter 34 is arranged in such a way that it operates as a direct voltage increaser, i.e. that the direct voltage in the connection part 33 between the converter 34 and the inverter 30 is intended to be, through the converter, higher and suitably substantially higher than the voltage on the input side of the con- verter 34.
• the inverter 30 is a voltage stiff self-commutated inverter.
• a capacitor 35 is parallel connected over the DC- link of the inverter 30.
• the inverter 30 suitably has network inductances 36 connected in series with each phase on its network side, it is preferred that the inverter comprises series connected IGBT:s.
• the generators are synchronous generators with permanent magnetized rotors.
• the rectifiers 27 are passive rectifiers. This eliminates the necessity of active power control electronics out at sea. As passive rectifiers, diode rectifiers are preferred. These diode rectifiers 27 are in series with a local step-up direct voltage converter 37. In a preferred embodiment, each separate converter 37 comprises a choke, a series connected IGBT-valve 39 and a series connected diode 40. The converter 34 could be formed like such a step-up direct voltage converter. 1 D
• a preferred embodiment according to the invention of a transformer with variable transmission is illustrated.
• the advantage with this transformer is that its windings are provided with a solid insulation in a similar manner as already described with respect to the generator with reference to Figs 1 and 2. Consequently, the transformer windings are correspondingly built up with an insulation system comprising at least two semiconducting layers 17, 19, each of which constitutes essentially equipotential surfaces, and the solid insulation 1 8 is situated between these semiconducting -layers. Consequently, in the transformer according to Fig 5 the windings will also have the character of flexible cables.
• Fig 5 the transformer is illustrated in a principle form for one of the phases in question.
• cores having more limbs than two and associated yoke can entail that all the phase windings are placed on one and the same core.
• a transformer core consisting of a yoke and two limbs is illustrated in Fig 5, a main winding 43 being applied around one of the limbs and a control winding 44 being arranged around the other limb.
• the main winding can either be consti- tuted of a primary winding or a secondary winding. Consequently, the control winding 44 is used for varying the transformation of the transformer.
• the control winding 44 is arranged in the form of winding turns wound onto a drum 45, which drum is rotatable about the core limb in question.
• the drum 45 is driven by means of a suitable, not shown motor, e.g. via belt driving. Consequently, the control winding 44 is functioning as a variable coil.
• the number of winding turns on the control winding drum 45 is varied by means of a rotatable storage drum 46 for the winding 44.
• the winding drum 46 is also motor-driven in a suitable way.
• Fig 5 it is illustrated how an end section 47 of the control winding is grounded.
• This end section 47 is stationary and is in electrically conducting connection with the control winding 44 on the drum 45 via a slipring contact device of a kind known per se.
• a corresponding slipring contact device is provided in order to electrically connect the winding section 48 with the control winding section received on the winding drum.
• control winding 44 is formed of the previously described, flexible high-voltage cable having solid insulation.

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• Engineering & Computer Science (AREA)
• Power Engineering (AREA)
• Life Sciences & Earth Sciences (AREA)
• Sustainable Development (AREA)
• Sustainable Energy (AREA)
• Chemical & Material Sciences (AREA)
• Combustion & Propulsion (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Control Of Eletrric Generators (AREA)
• Supply And Distribution Of Alternating Current (AREA)
• Direct Current Feeding And Distribution (AREA)
• Installation Of Indoor Wiring (AREA)
• Windings For Motors And Generators (AREA)
• Wind Motors (AREA)

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• 1999
  • 1999-05-28 BR BR9917306-9A patent/BR9917306A/pt not_active IP Right Cessation
  • 1999-05-28 CN CN99816680A patent/CN1352819A/zh active Pending
  • 1999-05-28 WO PCT/SE1999/000943 patent/WO2000074198A1/en not_active Application Discontinuation
  • 1999-05-28 EP EP99933320A patent/EP1198872A1/de not_active Withdrawn
  • 1999-05-28 MX MXPA01011954A patent/MXPA01011954A/es not_active Application Discontinuation
  • 1999-05-28 CA CA002375125A patent/CA2375125A1/en not_active Abandoned
  • 1999-05-28 TR TR2001/03404T patent/TR200103404T2/xx unknown
  • 1999-05-28 JP JP2001500390A patent/JP2003501993A/ja active Pending
  • 1999-05-28 EE EEP200100628A patent/EE200100628A/xx unknown
  • 1999-05-28 AU AU49389/99A patent/AU759548B2/en not_active Ceased
  • 1999-05-28 RU RU2001131103/06A patent/RU2221165C2/ru not_active IP Right Cessation
• 2000
  • 2000-05-26 AR ARP000102579A patent/AR024115A1/es unknown
  • 2000-06-05 TW TW089110972A patent/TW436581B/zh active
• 2001
  • 2001-11-28 NO NO20015811A patent/NO20015811L/no not_active Application Discontinuation

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