EPE Association: EPE 2007 - Subtopic 13-1 - LS: Power electronics for wind energy (Joint EPE and IEEE Wind Day)

EPE 2007 - Subtopic 13-1 - LS: Power electronics for wind energy (Joint EPE and IEEE Wind Day)
You are here: EPE Documents > 01 - EPE & EPE ECCE Conference Proceedings > EPE 2007 - Conference > EPE 2007 - Topic 13: 'Electrical energy generating systems, renewable energy systems' > EPE 2007 - Subtopic 13-1 - LS: Power electronics for wind energy (Joint EPE and IEEE Wind Day)

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   A high power density converter system for the Gamesa G10x 4,5 MW turbine
By BIRK Jens; ANDRESEN Björn [View]
[Download]

Abstract: One of the main points in the design of a Multi-MW-class turbine is the size and weight of the total turbine. Gamesa has developed a converter system with a very high power density and low weight. The system is designed and tested to withstand very high short circuit currents, high vibrations and other wind turbine typical environmental aspects.

   A New Architecture for Offshore Wind Farms
By PRASAI Anish; KREIKEBAUM Frank; BENDRE Ashish; DIVAN Deepak; YIM Jung-Sik; SUL Seung-Ki [View]
[Download]

Abstract: Offshore wind farms using HVDC links can be positioned a large distance from shore, opening up new opportunities for wind generation. Conventional approaches using 60 hertz generators and transformers are not appropriate in such applications, as they are heavy and result in expensive and complex installation and maintenance issues. This paper proposes an alternative architecture for such wind farms, using PM generators, medium frequency transformers and simple power converters to realize a compact and light system. It is possible that in the long term, the proposed approach may prove attractive for land-based wind farms as well.

   Control of Back-to-Back-Connected Neutral-Point-Clamped Converters in Wind Mill Applications
By POU Josep; ROBLES Eider; ZARAGOZA Jordi; IBANEZ Pedro; ARIAS Antoni; CEBALLOS Salvador [View]
[Download]

Abstract: This paper analyzes back-to-back-connected neutral-point-clamped converters in wind turbine applications. A control strategy for the grid-connected converter is proposed that is able to operate under unfavorable voltage conditions. The positive-sequence voltage detector is able to provide an accurate position of the grid voltage vector so that the controller is always synchronized. The wind generator, which is a permanent magnet machine with an external rotor, operates properly throughout a voltage-dip process. The task of balancing voltages on the dc-link capacitors of the back-to-back connection is performed by the modulation strategies. Simulation and experimental results are provided.

   Control of Doubly-fed Induction Generators under Asymmetrical Grid Conditions
By RICHTER Marlies; NAVARRO Daniel [View]
[Download]

Abstract: In the presented study a control scheme for the control of doubly-fed induction generators in wind power plants during slight and long lasting asymmetries is developed. The proposed strategy is based on the field-oriented control. The machine side as well as the grid side control are considered. Additional controllers are deployed for the negative sequence currents. This allows achieving additional control targets during asymmetrical grid voltages, e.g. the reduction of electrical torque oscillations. The suggested control scheme was tested by simulations using the program PSCAD/EMTDC. Some simulations results are given to show the potencial performance improvement of the DFIG-control-system with the proposed control strategy.

   Design and Comparison of Full-size Converters for Large Variable-Speed Wind Turbines
By ZENG Xiangjun; BLAABJERG Frede; CHEN Zhe [View]
[Download]

Abstract: The full-size converters for wind turbine systems can flexibly realize variable-speed control and meet power system operational requirements. The designs of Two-Level, Three-Level Neutral Point Clamped and Three-Level Flying Capacitor converter as full-size back-to-back converters for large wind turbine system are discussed in this paper. The harmonic standard and power system operation requirements for the converters are considered. And SVPWM with the on-off control is proposed to suppress the neutral point potential or fly-capacitor voltage deviation and drift for the three-level converters. The simulation models made by Simulink and Matlab are used to verify the designs and analyze power losses of the converters. And the performance and costs of three types of the converters are compared.

   Estimation of the costs due to renewable energies for a transmission system operator
By SCHULZ Woldemar; HORENKAMP Willi; REHTANZ Christian; HÄGER Ulf; WANIEK Daniel; HANDSCHIN Edmund [View]
[Download]

Abstract: By nature the generation from renewable energies sources is not performed on demand, but on offer. This yields the need of converting the energy to the actual demand. In Germany the execution of this process is obliged to the four transmission system operators. In this paper the occurring costs of the process of purchasing and transmitting renewable energies in Germany are analyzed for sample control areas. These costs include the expenses for additive required control power as well as the expenses caused by the special balancing group for renewable energies. During the operation of this balancing group accrue costs for balancing energy and as a result of trading transactions at electricity markets. Through this paper, the main question of the sensitivity of these costs from parameters in the observed control area is addressed.

   Performance Comparison of a Left Shunt UPQC and a Right Shunt UPQC applied to Enhance Fault-Ride-Through Capability of a Fixed Speed Wind Generator
By CONLON Michael; GAUGHAN Kevin; BASU Malabika; JAYANTI N. G. [View]
[Download]

Abstract: The enhancement of voltage-ride through capability of a Fixed Speed Induction Generator (FSIG) with the help of a Unified Power Quality Conditioner (UPQC) is examined. The performance of the Left-Shunt (LS) and Right-Shunt (RS) UPQC are compared under both full and partial voltage restoration. From the comparative study, the rating of the UPQCs is determined.

   Reactive Power Generation by DFIG based Wind Farms with AC Grid Connection
By WILCH Michael; FELTES Christian; ERLICH Istvan [View]
[Download]

Abstract: Balancing reactive power within a grid is one of the fundamental tasks of transmission system operators. With increasing portion of wind power, wind turbines have to contribute to reactive power generation during steady state as well as during transient conditions. First, this paper provides an overview about the available options to supply reactive power by wind farms typically connected to the grid by AC cables. Then the Fault-ride Through (FRT) sequence of the Doubly-Fed Induction Generators (DFIG) is discussed in order to explain the reactive power generation capability of this type of wind turbines during low voltage periods. Under steady state conditions the utilization of var sources represents an optimization task. It is shown in the paper that generation of reactive power by WT may be a favorable option under economic aspects. FRT with DFIG is possible even if the grid voltage drops to zero. To protect the converter against overcurrent and overvoltage DFIG are equipped with crowbar and sometimes with chopper. When the crowbar is switched on the machine is a var consumer. However the Line Side Converter (LSC) can be controlled to supply up to 50\% of the required reactive current. When the crowbar is not activated the DFIG can supply reactive power from the rotor side through the machine as well as through the LSC. For illustration, simulation results for an exemplary fault are shown and elucidated.

   Storage of fluctuating wind energy
By LERCH Edwin [View]
[Download]

Abstract: Over the last 15 years wind energy becomes more and more important in Germany. The total installed capacity of wind generation was 19300 MW (June 2006) with new installation of about 900 MW in the first 3 months in 2006. In 2010 the contribution of renewable energy to the gross electricity consumption shall be 12.5 per cent (renewable energy sources act EEG) and in 2020 20 per cent. The acceptance of utilisation of wind power in Germany is very high. Wind energy supply varies over day time, over the year and regional. In addition demand of electrical power varies over daytime and over the year but not correlated with the variation of wind. The average full load hours of the German wind generation is about 1600 h/a and will increase 2010 to about 1960 h/a based on increasing off-shore wind parks in Germany. In 2010 24 GW wind plants are planned on-shore, in the North Sea additional 4.4 GW off-shore wind parks and in the Baltic Sea about 1 GW off-shore wind generation. This will increase 2015 to 8.4 GW (North Sea) and 1.4 GW (Baltic Sea). The load centers in Germany are in the central and southern parts of Germany far away from the main wind park locations at the coasts or off-shore. To transport this high power to the load centers some hundred kilometre of new AC and DC lines have to be built together with new compensation and control equipment to strengthen and operate the system securely. 4 main corridors each with a capacity of 2000-4000 MW are necessary to bring the power to the load centers. In the last years there is a discussion about the necessity of such a large improvement of the system and the possibilities to solve the transportation targets closer related to the average available wind power and not related to the size of installed wind power capacity. A possible alternative is the installation of energy storage systems based on compressed air (so called compressed air energy storage CAES) stored in large underground caverns. The paper will show the available technology and the possibilities to combine this storage equipment with wind parks to use wind parks in a way of quasi conventional power plants.

EPE 2007 - Subtopic 13-1 - LS: Power electronics for wind energy (Joint EPE and IEEE Wind Day)
You are here: EPE Documents > 01 - EPE & EPE ECCE Conference Proceedings > EPE 2007 - Conference > EPE 2007 - Topic 13: 'Electrical energy generating systems, renewable energy systems' > EPE 2007 - Subtopic 13-1 - LS: Power electronics for wind energy (Joint EPE and IEEE Wind Day)
	[return to parent folder]

	A high power density converter system for the Gamesa G10x 4,5 MW turbine By BIRK Jens; ANDRESEN Björn	[View] [Download]
Abstract: One of the main points in the design of a Multi-MW-class turbine is the size and weight of the total turbine. Gamesa has developed a converter system with a very high power density and low weight. The system is designed and tested to withstand very high short circuit currents, high vibrations and other wind turbine typical environmental aspects.

	A New Architecture for Offshore Wind Farms By PRASAI Anish; KREIKEBAUM Frank; BENDRE Ashish; DIVAN Deepak; YIM Jung-Sik; SUL Seung-Ki	[View] [Download]
Abstract: Offshore wind farms using HVDC links can be positioned a large distance from shore, opening up new opportunities for wind generation. Conventional approaches using 60 hertz generators and transformers are not appropriate in such applications, as they are heavy and result in expensive and complex installation and maintenance issues. This paper proposes an alternative architecture for such wind farms, using PM generators, medium frequency transformers and simple power converters to realize a compact and light system. It is possible that in the long term, the proposed approach may prove attractive for land-based wind farms as well.

	Control of Back-to-Back-Connected Neutral-Point-Clamped Converters in Wind Mill Applications By POU Josep; ROBLES Eider; ZARAGOZA Jordi; IBANEZ Pedro; ARIAS Antoni; CEBALLOS Salvador	[View] [Download]
Abstract: This paper analyzes back-to-back-connected neutral-point-clamped converters in wind turbine applications. A control strategy for the grid-connected converter is proposed that is able to operate under unfavorable voltage conditions. The positive-sequence voltage detector is able to provide an accurate position of the grid voltage vector so that the controller is always synchronized. The wind generator, which is a permanent magnet machine with an external rotor, operates properly throughout a voltage-dip process. The task of balancing voltages on the dc-link capacitors of the back-to-back connection is performed by the modulation strategies. Simulation and experimental results are provided.

	Control of Doubly-fed Induction Generators under Asymmetrical Grid Conditions By RICHTER Marlies; NAVARRO Daniel	[View] [Download]
Abstract: In the presented study a control scheme for the control of doubly-fed induction generators in wind power plants during slight and long lasting asymmetries is developed. The proposed strategy is based on the field-oriented control. The machine side as well as the grid side control are considered. Additional controllers are deployed for the negative sequence currents. This allows achieving additional control targets during asymmetrical grid voltages, e.g. the reduction of electrical torque oscillations. The suggested control scheme was tested by simulations using the program PSCAD/EMTDC. Some simulations results are given to show the potencial performance improvement of the DFIG-control-system with the proposed control strategy.

	Design and Comparison of Full-size Converters for Large Variable-Speed Wind Turbines By ZENG Xiangjun; BLAABJERG Frede; CHEN Zhe	[View] [Download]
Abstract: The full-size converters for wind turbine systems can flexibly realize variable-speed control and meet power system operational requirements. The designs of Two-Level, Three-Level Neutral Point Clamped and Three-Level Flying Capacitor converter as full-size back-to-back converters for large wind turbine system are discussed in this paper. The harmonic standard and power system operation requirements for the converters are considered. And SVPWM with the on-off control is proposed to suppress the neutral point potential or fly-capacitor voltage deviation and drift for the three-level converters. The simulation models made by Simulink and Matlab are used to verify the designs and analyze power losses of the converters. And the performance and costs of three types of the converters are compared.

	Estimation of the costs due to renewable energies for a transmission system operator By SCHULZ Woldemar; HORENKAMP Willi; REHTANZ Christian; HÄGER Ulf; WANIEK Daniel; HANDSCHIN Edmund	[View] [Download]
Abstract: By nature the generation from renewable energies sources is not performed on demand, but on offer. This yields the need of converting the energy to the actual demand. In Germany the execution of this process is obliged to the four transmission system operators. In this paper the occurring costs of the process of purchasing and transmitting renewable energies in Germany are analyzed for sample control areas. These costs include the expenses for additive required control power as well as the expenses caused by the special balancing group for renewable energies. During the operation of this balancing group accrue costs for balancing energy and as a result of trading transactions at electricity markets. Through this paper, the main question of the sensitivity of these costs from parameters in the observed control area is addressed.

	Performance Comparison of a Left Shunt UPQC and a Right Shunt UPQC applied to Enhance Fault-Ride-Through Capability of a Fixed Speed Wind Generator By CONLON Michael; GAUGHAN Kevin; BASU Malabika; JAYANTI N. G.	[View] [Download]
Abstract: The enhancement of voltage-ride through capability of a Fixed Speed Induction Generator (FSIG) with the help of a Unified Power Quality Conditioner (UPQC) is examined. The performance of the Left-Shunt (LS) and Right-Shunt (RS) UPQC are compared under both full and partial voltage restoration. From the comparative study, the rating of the UPQCs is determined.

	Reactive Power Generation by DFIG based Wind Farms with AC Grid Connection By WILCH Michael; FELTES Christian; ERLICH Istvan	[View] [Download]
Abstract: Balancing reactive power within a grid is one of the fundamental tasks of transmission system operators. With increasing portion of wind power, wind turbines have to contribute to reactive power generation during steady state as well as during transient conditions. First, this paper provides an overview about the available options to supply reactive power by wind farms typically connected to the grid by AC cables. Then the Fault-ride Through (FRT) sequence of the Doubly-Fed Induction Generators (DFIG) is discussed in order to explain the reactive power generation capability of this type of wind turbines during low voltage periods. Under steady state conditions the utilization of var sources represents an optimization task. It is shown in the paper that generation of reactive power by WT may be a favorable option under economic aspects. FRT with DFIG is possible even if the grid voltage drops to zero. To protect the converter against overcurrent and overvoltage DFIG are equipped with crowbar and sometimes with chopper. When the crowbar is switched on the machine is a var consumer. However the Line Side Converter (LSC) can be controlled to supply up to 50\% of the required reactive current. When the crowbar is not activated the DFIG can supply reactive power from the rotor side through the machine as well as through the LSC. For illustration, simulation results for an exemplary fault are shown and elucidated.

	Storage of fluctuating wind energy By LERCH Edwin	[View] [Download]
Abstract: Over the last 15 years wind energy becomes more and more important in Germany. The total installed capacity of wind generation was 19300 MW (June 2006) with new installation of about 900 MW in the first 3 months in 2006. In 2010 the contribution of renewable energy to the gross electricity consumption shall be 12.5 per cent (renewable energy sources act EEG) and in 2020 20 per cent. The acceptance of utilisation of wind power in Germany is very high. Wind energy supply varies over day time, over the year and regional. In addition demand of electrical power varies over daytime and over the year but not correlated with the variation of wind. The average full load hours of the German wind generation is about 1600 h/a and will increase 2010 to about 1960 h/a based on increasing off-shore wind parks in Germany. In 2010 24 GW wind plants are planned on-shore, in the North Sea additional 4.4 GW off-shore wind parks and in the Baltic Sea about 1 GW off-shore wind generation. This will increase 2015 to 8.4 GW (North Sea) and 1.4 GW (Baltic Sea). The load centers in Germany are in the central and southern parts of Germany far away from the main wind park locations at the coasts or off-shore. To transport this high power to the load centers some hundred kilometre of new AC and DC lines have to be built together with new compensation and control equipment to strengthen and operate the system securely. 4 main corridors each with a capacity of 2000-4000 MW are necessary to bring the power to the load centers. In the last years there is a discussion about the necessity of such a large improvement of the system and the possibilities to solve the transportation targets closer related to the average available wind power and not related to the size of installed wind power capacity. A possible alternative is the installation of energy storage systems based on compressed air (so called compressed air energy storage CAES) stored in large underground caverns. The paper will show the available technology and the possibilities to combine this storage equipment with wind parks to use wind parks in a way of quasi conventional power plants.