AR046164A1 - Metodo para operar una planta de energia eolica - Google Patents

Metodo para operar una planta de energia eolica

Info

Publication number
AR046164A1
AR046164A1 ARP040103428A ARP040103428A AR046164A1 AR 046164 A1 AR046164 A1 AR 046164A1 AR P040103428 A ARP040103428 A AR P040103428A AR P040103428 A ARP040103428 A AR P040103428A AR 046164 A1 AR046164 A1 AR 046164A1
Authority
AR
Argentina
Prior art keywords
wind turbines
operating
requirements
ability
faults
Prior art date
Application number
ARP040103428A
Other languages
English (en)
Inventor
Aloys Wobben
Original Assignee
Aloys Wobben
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Family has litigation
First worldwide family litigation filed litigation Critical https://patents.darts-ip.com/?family=34384557&utm_source=google_patent&utm_medium=platform_link&utm_campaign=public_patent_search&patent=AR046164(A1) "Global patent litigation dataset” by Darts-ip is licensed under a Creative Commons Attribution 4.0 International License.
Application filed by Aloys Wobben filed Critical Aloys Wobben
Publication of AR046164A1 publication Critical patent/AR046164A1/es

Links

Classifications

    • 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
    • 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
    • H02J3/001—Methods to deal with contingencies, e.g. abnormalities, faults or failures
    • 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
    • F03D7/00—Controlling wind motors 
    • F03D7/02—Controlling wind motors  the wind motors having rotation axis substantially parallel to the air flow entering the rotor
    • F03D7/028—Controlling wind motors  the wind motors having rotation axis substantially parallel to the air flow entering the rotor controlling wind motor output power
    • F03D7/0284—Controlling wind motors  the wind motors having rotation axis substantially parallel to the air flow entering the rotor controlling wind motor output power in relation to the state of the electric grid
    • 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
    • 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
    • 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
    • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
    • H02P9/00—Arrangements for controlling electric generators for the purpose of obtaining a desired output
    • H02P9/10—Control effected upon generator excitation circuit to reduce harmful effects of overloads or transients, e.g. sudden application of load, sudden removal of load, sudden change of load
    • H02P9/102—Control effected upon generator excitation circuit to reduce harmful effects of overloads or transients, e.g. sudden application of load, sudden removal of load, sudden change of load for limiting effects of transients
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
    • H02P9/00—Arrangements for controlling electric generators for the purpose of obtaining a desired output
    • H02P9/10—Control effected upon generator excitation circuit to reduce harmful effects of overloads or transients, e.g. sudden application of load, sudden removal of load, sudden change of load
    • H02P9/105—Control effected upon generator excitation circuit to reduce harmful effects of overloads or transients, e.g. sudden application of load, sudden removal of load, sudden change of load for increasing the stability
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
    • F05B—INDEXING SCHEME RELATING TO WIND, SPRING, WEIGHT, INERTIA OR LIKE MOTORS, TO MACHINES OR ENGINES FOR LIQUIDS COVERED BY SUBCLASSES F03B, F03D AND F03G
    • F05B2270/00—Control
    • F05B2270/10—Purpose of the control system
    • F05B2270/107—Purpose of the control system to cope with emergencies
    • 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

Abstract

Continuar operando significa la aptitud de unidades de generación incorporada para permanecer en línea durante las fallas del sistema y para la compensación de las fallas. Junto con el incremento de participación de las turbinas eólicas en sistemas energéticos, los requisitos para continuar operando para este tipo de generación constituyen parte de códigos de acceso a transmisión ( en algunos casos, específicos para turbinas eólicas). Las turbinas eólicas ENERCON han sido también desarrolladas para cumplir estos requisitos y proveen aptitud para continuar operando. Se describe el principio del comportamiento de las turbinas durante las fallas en sistemas balanceados y las compensaciones de las fallas, así como modelos para considerar esta conformación en el marco de estudios de fallas y de dinámica de sistemas.
ARP040103428A 2003-09-23 2004-09-23 Metodo para operar una planta de energia eolica AR046164A1 (es)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
EP03021439 2003-09-23

Publications (1)

Publication Number Publication Date
AR046164A1 true AR046164A1 (es) 2005-11-30

Family

ID=34384557

Family Applications (1)

Application Number Title Priority Date Filing Date
ARP040103428A AR046164A1 (es) 2003-09-23 2004-09-23 Metodo para operar una planta de energia eolica

Country Status (22)

Country Link
US (1) US7525208B2 (es)
EP (2) EP1665495B1 (es)
JP (1) JP4160618B2 (es)
KR (1) KR100761760B1 (es)
CN (1) CN100420118C (es)
AR (1) AR046164A1 (es)
AT (1) ATE538524T1 (es)
BR (1) BRPI0414588A (es)
CA (1) CA2537999C (es)
CY (1) CY1112396T1 (es)
DK (1) DK1665495T3 (es)
ES (1) ES2376316T3 (es)
IL (1) IL174027A (es)
IS (1) IS8414A (es)
MA (1) MA28046A1 (es)
NO (1) NO20061771L (es)
NZ (1) NZ545842A (es)
PL (1) PL1665495T3 (es)
PT (1) PT1665495E (es)
SI (1) SI1665495T1 (es)
WO (1) WO2005031941A1 (es)
ZA (1) ZA200601889B (es)

Families Citing this family (32)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7233129B2 (en) * 2003-05-07 2007-06-19 Clipper Windpower Technology, Inc. Generator with utility fault ride-through capability
CN101401294B (zh) 2006-03-17 2013-04-17 英捷电力技术有限公司 具有激励器设备和不连接至电网的功率变换器的变速风机
US7425771B2 (en) 2006-03-17 2008-09-16 Ingeteam S.A. Variable speed wind turbine having an exciter machine and a power converter not connected to the grid
DE102006050077A1 (de) * 2006-10-24 2008-05-08 Repower Systems Ag Umrichter mit steuerbarem Phasenwinkel
US7514809B2 (en) 2006-11-16 2009-04-07 General Electric Company Excitation voltage supply for synchronous generator used in a wind turbine, and method of starting a wind turbine having such excitation voltage supply
US7622815B2 (en) 2006-12-29 2009-11-24 Ingeteam Energy, S.A. Low voltage ride through system for a variable speed wind turbine having an exciter machine and a power converter not connected to the grid
DE102007020423A1 (de) * 2007-04-27 2008-10-30 Daubner & Stommel GbR Bau-Werk-Planung (vertretungsberechtigter Gesellschafter: Matthias Stommel, 27777 Ganderkesee) Verfahren zum Betreiben einer Windenergieanlage und Windenergieanlage
DE102008010543A1 (de) * 2008-02-22 2009-08-27 Nordex Energy Gmbh Verfahren zum Betreiben einer Windenergieanlage und Windenergieanlage
DE102008045938A1 (de) 2008-09-04 2010-03-25 Powerwind Gmbh Verfahren zum Steuern der Einspeisung elektrischer Leistung einer Windenergieanlage in ein Wechselstromnetz
US7881888B2 (en) 2008-09-30 2011-02-01 Vestas Wind Systems A/S Logical scheme for severe fault detection
US8573937B2 (en) 2008-11-21 2013-11-05 Xzeres Corp. System for providing dynamic pitch control in a wind turbine
EP2394054A1 (de) * 2009-02-09 2011-12-14 Powerwind Gmbh Verfahren zur speisung eines mehrphasigen elektrischen netzes und zugehörige schaltungsanordnung
WO2011110193A1 (de) 2010-03-11 2011-09-15 Powerwind Gmbh Verfahren zum steuern der einspeisung elektrischer leistung einer windenergieanlage in ein wechselstromnetz
DE102010023038A1 (de) * 2010-06-08 2011-12-08 Repower Systems Ag Windenergieanlage und Verfahren zum Betreiben einer Windenergieanlage
EP2463979B1 (en) * 2010-12-08 2022-05-11 Siemens Aktiengesellschaft Fault-ride-through method, converter and power generating unit for a wind turbine
US20120147637A1 (en) 2010-12-13 2012-06-14 Northern Power Systems, Inc. Methods, Systems, and Software for Controlling a Power Converter During Low (Zero)-Voltage Ride-Through Conditions
US10103661B2 (en) * 2011-09-28 2018-10-16 Vestas Wind Systems A/S Wind power plant and a method for operating thereof
DE102012204220A1 (de) 2012-03-16 2013-09-19 Wobben Properties Gmbh Verfahren zum Steuern einer Anordnung zum Einspeisen elektrischen Stroms in ein Versorgungsnetz
DE102012212366A1 (de) * 2012-07-13 2014-01-30 Wobben Properties Gmbh Verfahren zum Steuern eines elektrischen Erzeugers
DE102012212777A1 (de) * 2012-07-20 2014-01-23 Wobben Properties Gmbh Verfahren zum Steuern eines Windparks
CA2896589A1 (en) 2012-12-31 2014-07-03 Volcano Corporation Devices, systems, and methods for assessment of vessels
AT515033B1 (de) * 2013-10-23 2020-02-15 Innio Jenbacher Gmbh & Co Og Verfahren zum Betreiben einer mit einem Energieversorgungsnetz verbundenen Kraftanlage
CN106489152A (zh) 2014-04-10 2017-03-08 Sync-Rx有限公司 在存在医学设备的情况下的图像分析
US9467081B2 (en) * 2014-09-29 2016-10-11 Ingeteam Power Technology, S.A. Protection system for a power converter connected to a doubly fed induction generator
WO2016055069A1 (en) * 2014-10-07 2016-04-14 Vestas Wind Systems A/S Reactive power support from wind turbine facilities
DE102016105662A1 (de) 2016-03-29 2017-10-05 Wobben Properties Gmbh Verfahren zum Einspeisen elektrischer Leistung in ein elektrisches Versorgungsnetz mit einem Windpark sowie Windpark
CN107346894B (zh) * 2016-05-05 2020-04-10 中国船舶重工集团海装风电股份有限公司 一种风电场发电量控制方法及风电场能量控制平台
DE102016125953A1 (de) 2016-12-30 2018-07-05 Wobben Properties Gmbh Verfahren zum Betreiben eines Windparks
WO2018229857A1 (ja) * 2017-06-13 2018-12-20 三菱電機株式会社 電力変換システム
EP3695504A1 (de) * 2017-11-22 2020-08-19 Siemens Aktiengesellschaft Energieübertragung über eine bipolare hochspannungs-gleichstrom-übertragungsstrecke
US11255309B2 (en) * 2018-08-28 2022-02-22 General Electric Company System and method for increasing mechanical inertia of a wind turbine rotor to support a power grid during an over-frequency or under-frequency disturbance of the grid
DE102019101048A1 (de) 2019-01-16 2020-07-16 Wobben Properties Gmbh Windenergieanlage zum Einspeisen elektrischer Leistung in ein elektrisches Versorgungsnetz

Family Cites Families (20)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3346291A1 (de) * 1983-12-21 1985-07-04 Siemens Ag Verfahren und vorrichtung zum schnellen ermitteln einer netzsynchronen referenzspannung fuer einen netzgefuehrten stromrichter nach einer netzstoerung
CN86108436A (zh) * 1986-12-20 1988-08-03 水利电力部电力科学研究院 大电力系统强自适应稳定控制方法及装置
US4764683A (en) * 1987-08-03 1988-08-16 Lloyd A. Smith Wind powered electric generator
JPH05300658A (ja) 1992-04-17 1993-11-12 Mitsubishi Electric Corp 送電設備及び該設備に用いられる電力貯蔵設備
JPH0946909A (ja) * 1995-07-27 1997-02-14 Nissin Electric Co Ltd 並列多重連系分散電源の単独運転検出装置
JPH09312934A (ja) 1996-05-21 1997-12-02 Hitachi Ltd 電力系統システムの電力系統安定化装置
JPH11159437A (ja) 1997-11-26 1999-06-15 Hitachi Eng & Service Co Ltd 風力発電設備
US20030007369A1 (en) 1998-04-02 2003-01-09 Gilbreth Mark G. Power controller
JP2002101559A (ja) 2000-09-26 2002-04-05 Nakatake:Kk 風力発電機用の系統連係装置
EP1199784A1 (de) * 2000-10-19 2002-04-24 Abb Research Ltd. Stromerzeugungsanlage sowie Verfahren zu deren Steuerung und Regelung
DE10105892A1 (de) * 2001-02-09 2002-09-12 Daimlerchrysler Rail Systems Windenergieanlage und Verfahren zum Betreiben einer Windenergieanlage
DE50214671D1 (de) * 2001-04-20 2010-11-04 Baw Gmbh Verfahren zum betreiben einer windenergieanlage
JP2003088190A (ja) 2001-09-13 2003-03-20 Meidensha Corp 発電設備
JP2005516577A (ja) 2002-01-29 2005-06-02 ヴェスタス，ウィンド，システムズ エー／エス 風力エネルギーの設備に使用するための回路装置
US7015595B2 (en) * 2002-02-11 2006-03-21 Vestas Wind Systems A/S Variable speed wind turbine having a passive grid side rectifier with scalar power control and dependent pitch control
WO2005025026A1 (de) 2003-09-03 2005-03-17 Repower Systems Ag Verfahren zum betrieb bzw. regelung einer windenergieanlage sowie verfahren zur bereitstellung von primärrefelleistung mit windenergieanlagen
BRPI0318500B1 (pt) 2003-09-16 2016-10-18 Gen Electric método para operar um conversor de frequência de um gerador
DE10361443B4 (de) * 2003-12-23 2005-11-10 Voith Turbo Gmbh & Co. Kg Regelung für eine Windkraftanlage mit hydrodynamischem Getriebe
US7126236B2 (en) * 2005-03-15 2006-10-24 General Electric Company Methods and apparatus for pitch control power conversion
US7227276B2 (en) * 2005-08-08 2007-06-05 Caiozza Joseph C Wind driven electric generator apparatus

Also Published As

Publication number Publication date
US20070159737A1 (en) 2007-07-12
EP1665495B1 (de) 2011-12-21
IL174027A (en) 2010-04-29
EP2290234A2 (de) 2011-03-02
PT1665495E (pt) 2012-02-03
EP1665495A1 (de) 2006-06-07
CN1856920A (zh) 2006-11-01
KR20060083980A (ko) 2006-07-21
IL174027A0 (en) 2006-08-01
BRPI0414588A (pt) 2006-11-07
ATE538524T1 (de) 2012-01-15
NO20061771L (no) 2006-06-13
US7525208B2 (en) 2009-04-28
CA2537999C (en) 2010-01-26
DK1665495T3 (da) 2012-03-26
KR100761760B1 (ko) 2007-09-28
WO2005031941A1 (de) 2005-04-07
PL1665495T3 (pl) 2012-07-31
EP2290234A3 (de) 2015-05-20
ZA200601889B (en) 2007-04-25
ES2376316T3 (es) 2012-03-12
CY1112396T1 (el) 2015-12-09
CN100420118C (zh) 2008-09-17
SI1665495T1 (sl) 2012-01-31
AU2004305903A1 (en) 2005-04-07
IS8414A (is) 2006-04-12
NZ545842A (en) 2008-03-28
CA2537999A1 (en) 2005-04-07
JP4160618B2 (ja) 2008-10-01
JP2007506400A (ja) 2007-03-15
MA28046A1 (fr) 2006-07-03

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