WO2012175952A1 - Improved regulation of underwater turbines - Google Patents

Improved regulation of underwater turbines Download PDF

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Publication number
WO2012175952A1
WO2012175952A1 PCT/GB2012/051415 GB2012051415W WO2012175952A1 WO 2012175952 A1 WO2012175952 A1 WO 2012175952A1 GB 2012051415 W GB2012051415 W GB 2012051415W WO 2012175952 A1 WO2012175952 A1 WO 2012175952A1
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WO
WIPO (PCT)
Prior art keywords
generators
output
resistor
generator
array
Prior art date
Application number
PCT/GB2012/051415
Other languages
French (fr)
Inventor
Michael Torr Todman
John Richard Carew Armstrong
Original Assignee
Tidalstream Limited
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
Application filed by Tidalstream Limited filed Critical Tidalstream Limited
Publication of WO2012175952A1 publication Critical patent/WO2012175952A1/en

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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
    • F03B—MACHINES OR ENGINES FOR LIQUIDS
    • F03B15/00—Controlling
    • 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
    • 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
    • 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
    • H02J3/40—Synchronising a generator for connection to a network or to another generator
    • 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
    • H02J3/46—Controlling of the sharing of output between the generators, converters, or transformers
    • 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
    • F05B2220/00—Application
    • F05B2220/70—Application in combination with
    • F05B2220/706—Application in combination with an electrical generator
    • F05B2220/7064—Application in combination with an electrical generator of the alternating current (A.C.) type
    • F05B2220/70642—Application in combination with an electrical generator of the alternating current (A.C.) type of the synchronous type
    • 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
    • F05B2240/00—Components
    • F05B2240/40—Use of a multiplicity of similar components
    • 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
    • F05B2270/101—Purpose of the control system to control rotational speed (n)
    • 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
    • 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
    • Y02E10/20—Hydro 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
    • Y02E10/30—Energy from the sea, e.g. using wave energy or salinity gradient
    • 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
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/60—Arrangements for transfer of electric power between AC networks or generators via a high voltage DC link [HVCD]

Definitions

  • This invention relates to the regulation of an array of underwater turbines mounted on a common structure, such as a semi-submersible platform.
  • Most underwater turbines are single units driving either a generator for feeding a local load or a variable speed conversion unit/generator connected to the electrical grid of a geographical region.
  • each turbine drives an AC asynchronous induction generator with all the outputs connected to a common AC bus which then drives a single rectifier-inverter converter unit feeding an electrical grid.
  • This system allows the speed of turbines in the array to rise and fall with variations of the stream flow, allowing turbine rotors to run at optimum tip speed and improving the output of the array relative to fixed speed operation.
  • One advantage of this system is that failure of the electrical grid removes excitation from each turbine generator so that it is electrically inert and safe, generating no voltage even though it may still be rotating in the stream flow.
  • this is also a disadvantage, since there is then no means of electrically loading the rotor and by this means preventing a potentially damaging overspeed condition.
  • a further disadvantage of this system is that individual electrical control of each turbine is not possible - all turbines must rotate at the frequency demanded by the common converter, generating the power and thrust relevant to the local flow conditions. This may be a considerable disadvantage where a turbine array consists of turbines higher and lower in the stream flow, and thus experience different flow rates due to depth shear. It would be desirable to provide an improved underwater turbine/generator which can better regulate rotor speed in varying stream flow.
  • an array of underwater turbines provided on a platform, each turbine being directly connected to a respective synchronous alternating current generator, the electrical outputs of the generators being coupled to a common bus for connection to an electrical grid.
  • the bus is preferably provided on the platform, and in one embodiment the array further includes in series a rectifier and an inverter for coupling said generators to an electrical grid.
  • the bus is an a.c. bus and the rectifier and inverter are provided on the platform.
  • Each generator may include a respective rectifier at the output thereof, and in one such arrangement the bus is a d.c. bus and the rectifiers and inverter are provided on the platform.
  • a sub-set of generators may be linked on the platform to a common rectifier.
  • the rectifier associated with each generator may be continually controlled by adjusting the loading on the respective generator, so that the turbine rotor stays at or near a desired characteristic, for example a characteristic corresponding to optimum tip speed ratio.
  • a single inverter is provided on the platform.
  • a controller is provided, and the or each rectifier is controlled with reference to a look-up table of power output and turbine speed.
  • the controller loads the generator(s) associated with the rectifier so as to increase power output to meet the desired characteristic. If output power is too high, the controller may unload the generator(s) allowing speed to increase to meet the desired characteristic.
  • the controller may be operated by reference to a suitable algorithm or other means of matching rotor speed and power output to a desired characteristic.
  • the controller may be on the platform. In one embodiment the controller is adapted to follow a rotor speed/output power characteristic corresponding to optimum rotor tip speed ratio.
  • the array may further include a resistor on the platform said resistor being connected to the output of one or more generators in order to regulate the output thereof.
  • a plurality of such resistors may be provided, and one or more resistors may be associated with an individual generator or with a sub-set of generators.
  • This aspect of the invention provides a means of regulating one or more turbines in the event that the power-handling capacity of the bus is exceeded, or in the event that the bus fails. Either of the foregoing could lead to potential run-away of the turbines, and accordingly the provision of one or more resistors provides an additional safety factor.
  • One or more resistors are provided on the platform so as to be close to the generators, thereby to minimize heat build-up in the electrical connections thereof. Heat absorbed by the resistors is radiated directly to the surrounding water, which provides for effective cooling thereof.
  • the array may comprise one or more resistors connected to a respective generator or sub-set of generators, or one or more resistors adapted for connection in turn to a sequence of generators, or a means of coupling of resistors to suit the control demand of one or more generators.
  • the invention provides a method of regulating an array of synchronous alternating current generators on an underwater platform, the outputs of the generators being connected by an electrical bus, the method comprising providing a rectifier for the output of each generator and controlling each rectifier to regulate the output current of a respective generator.
  • the method further comprises electrically connecting a resistor on the platform to the output of one or more of said generators to regulate the output thereof.
  • the method may comprise connecting a resistor or group of resistors to one or more generators in turn.
  • a method is useful where the available resistor capacity is insufficient to bring all generators to a speed where a brake may be engaged, but is sufficient to hold all generators with an acceptable speed range, thereby to prevent overspeeding of any generator.
  • the invention provides a method of regulating an underwater array of synchronous alternating current generators, comprising the steps of detecting loss of control frequency and immediately connecting one or more resistors to the output of said generators to limit or reduce the speed thereof.
  • the loading provided by the bus is used to regulate generator speed, and the loading is lost by failure of the bus or an external connection thereof.
  • the control frequency of the bus or the electrical current thereof may be used to load the generator.
  • Figure 1 is a schematic showing two out of a plurality of tidal turbines connected by an AC bus.
  • Fig. 2 shows an arrangement similar to Fig. 1, but connected by a DC bus.
  • each individual turbine rotor 1 drives a synchronous generator 3 with a self-excited permanent magnet or wound field.
  • the generator is directly driven by via a step-up gearbox 2. Connection by endless belt or chain is also envisaged along with direct 1 : 1 shaft drive.
  • the AC output from each generator is fed into an AC bus 4 collecting same- frequency power, which in turn is fed into a single converter consisting of a rectifier 5 feeding an inverter 6.
  • the frequency - and therefore speed - of the generators 3 is controlled by regulating the loading of the single rectifier 5.
  • the role of the inverter 6 is to supply grid-compatible power to the grid 9 via a step-up transformer 7.
  • the turbine/generators are mounted as an array on a platform, which is in use submerged in the stream flow.
  • the rectifier 5, inverter 6 and transformer 7 are also be located on the platform, and the transformer output is connected to the shore by a suitable underwater cable.
  • the load on the generators can be determined by control of the rectifier by reference to, for example, a look-up table relating rotor speed and generator output.
  • a dump resistor 8 located locally to each turbine may be switched into the output of generator 3 to provide a means of slowing or stopping the rotor 1. This arrangement obviates overspeeding of the turbine rotor in a strong stream flow in the event say of a failure of the electrical supply from the grid, or of the converter 5-6.
  • the resistor may be automatically connected in the event that turbine blades reach a pre-determined speed.
  • the resistor 8 may comprise a plurality of individual resistor units connectable as required to give the required resistive loading.
  • a single dump resistor or resistor group may serve a group of generators. This latter solution may provide a lower cost alternative, or be better suited to installation on a platform provided that the risk associated with failure of the resistor or resistor group is acceptable.
  • a single group dump load could in one alternative be made small enough to serve just one turbine, and used sequentially to slow down in turn each turbine in an array. Individual turbines of an array can be slowed or stopped by connection to the dump resistor(s). In one embodiment it is sufficient to slow the or each turbine to a speed at which it is safe to engage a mechanical brake, by which the rotor may be halted and parked.
  • the invention may be used to reduce speed of any turbine which is damaged or becomes defective, or where for any reason a turbine or generator is no longer required to rotate at the rated speed. Where speed reduction is required for one or more of a group of turbines having common control, it may be necessary to reduce the speed of all turbines in the group.
  • the configuration of Figure 2 is an alternative that allows individual control of speed and/or load of each turbine of an array.
  • a rectifier 15 is provided at the output of each generator and is connected to a DC bus 14.
  • the bus 14 feeds as in the first embodiment into a single inverter 6, again delivering power to the grid in a transformer 7.
  • Both embodiments address control of turbines of a multiple turbine array on a single platform where different stream flows may be encountered at different locations.
  • speed control of individual turbines is provided in the embodiment of Fig. 2, and may also allow trimming of the attitude of a platform by adjusting the speed and thereby thrust of one or more turbines.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Control Of Eletrric Generators (AREA)
  • Other Liquid Machine Or Engine Such As Wave Power Use (AREA)
  • Hydraulic Turbines (AREA)
  • Control Of Water Turbines (AREA)

Abstract

The invention discloses methods and apparatus of regulating underwater turbines arranged in an array on a submersible platform.In one embodiment resistive loads are switchable on demand to the generator output in order to increase the load thereon, so as to regulate turbine speed.

Description

IMPROVED REGULATION OF UNDERWATER TURBINES This invention relates to the regulation of an array of underwater turbines mounted on a common structure, such as a semi-submersible platform.
Most underwater turbines are single units driving either a generator for feeding a local load or a variable speed conversion unit/generator connected to the electrical grid of a geographical region.
The common feeding of the outputs of an array of turbines into a common AC bus has been described for example in WO 2004/027257. In this document each turbine drives an AC asynchronous induction generator with all the outputs connected to a common AC bus which then drives a single rectifier-inverter converter unit feeding an electrical grid. This system allows the speed of turbines in the array to rise and fall with variations of the stream flow, allowing turbine rotors to run at optimum tip speed and improving the output of the array relative to fixed speed operation. One advantage of this system is that failure of the electrical grid removes excitation from each turbine generator so that it is electrically inert and safe, generating no voltage even though it may still be rotating in the stream flow. However, this is also a disadvantage, since there is then no means of electrically loading the rotor and by this means preventing a potentially damaging overspeed condition.
A further disadvantage of this system is that individual electrical control of each turbine is not possible - all turbines must rotate at the frequency demanded by the common converter, generating the power and thrust relevant to the local flow conditions. This may be a considerable disadvantage where a turbine array consists of turbines higher and lower in the stream flow, and thus experience different flow rates due to depth shear. It would be desirable to provide an improved underwater turbine/generator which can better regulate rotor speed in varying stream flow.
According to a first aspect of the invention there is provided an array of underwater turbines provided on a platform, each turbine being directly connected to a respective synchronous alternating current generator, the electrical outputs of the generators being coupled to a common bus for connection to an electrical grid.
The bus is preferably provided on the platform, and in one embodiment the array further includes in series a rectifier and an inverter for coupling said generators to an electrical grid. In one such arrangement the bus is an a.c. bus and the rectifier and inverter are provided on the platform.
Each generator may include a respective rectifier at the output thereof, and in one such arrangement the bus is a d.c. bus and the rectifiers and inverter are provided on the platform. A sub-set of generators may be linked on the platform to a common rectifier.
Thus the rectifier associated with each generator may be continually controlled by adjusting the loading on the respective generator, so that the turbine rotor stays at or near a desired characteristic, for example a characteristic corresponding to optimum tip speed ratio. In one embodiment a single inverter is provided on the platform.
In one embodiment a controller is provided, and the or each rectifier is controlled with reference to a look-up table of power output and turbine speed. Thus if the power for a given rotor speed is too low, the controller loads the generator(s) associated with the rectifier so as to increase power output to meet the desired characteristic. If output power is too high, the controller may unload the generator(s) allowing speed to increase to meet the desired characteristic. In place of a look-up table, the controller may be operated by reference to a suitable algorithm or other means of matching rotor speed and power output to a desired characteristic. The controller may be on the platform. In one embodiment the controller is adapted to follow a rotor speed/output power characteristic corresponding to optimum rotor tip speed ratio.
The array may further include a resistor on the platform said resistor being connected to the output of one or more generators in order to regulate the output thereof. A plurality of such resistors may be provided, and one or more resistors may be associated with an individual generator or with a sub-set of generators.
This aspect of the invention provides a means of regulating one or more turbines in the event that the power-handling capacity of the bus is exceeded, or in the event that the bus fails. Either of the foregoing could lead to potential run-away of the turbines, and accordingly the provision of one or more resistors provides an additional safety factor. One or more resistors are provided on the platform so as to be close to the generators, thereby to minimize heat build-up in the electrical connections thereof. Heat absorbed by the resistors is radiated directly to the surrounding water, which provides for effective cooling thereof.
The array may comprise one or more resistors connected to a respective generator or sub-set of generators, or one or more resistors adapted for connection in turn to a sequence of generators, or a means of coupling of resistors to suit the control demand of one or more generators.
In a second aspect the invention provides a method of regulating an array of synchronous alternating current generators on an underwater platform, the outputs of the generators being connected by an electrical bus, the method comprising providing a rectifier for the output of each generator and controlling each rectifier to regulate the output current of a respective generator.
Preferably the method further comprises electrically connecting a resistor on the platform to the output of one or more of said generators to regulate the output thereof.
The method may comprise connecting a resistor or group of resistors to one or more generators in turn. Such a method is useful where the available resistor capacity is insufficient to bring all generators to a speed where a brake may be engaged, but is sufficient to hold all generators with an acceptable speed range, thereby to prevent overspeeding of any generator. In a third aspect, the invention provides a method of regulating an underwater array of synchronous alternating current generators, comprising the steps of detecting loss of control frequency and immediately connecting one or more resistors to the output of said generators to limit or reduce the speed thereof. Such a method is useful where the loading provided by the bus is used to regulate generator speed, and the loading is lost by failure of the bus or an external connection thereof. In particular the control frequency of the bus or the electrical current thereof may be used to load the generator. These and other features of the invention will be apparent from the following description of preferred embodiments illustrated, by way of example only, in the accompanying drawings in which:
Figure 1 is a schematic showing two out of a plurality of tidal turbines connected by an AC bus.
Fig. 2 shows an arrangement similar to Fig. 1, but connected by a DC bus.
In Figure 1, two turbines are illustrated, but the principle disclosed is applicable to more than two turbines. Each individual turbine rotor 1 drives a synchronous generator 3 with a self-excited permanent magnet or wound field. The generator is directly driven by via a step-up gearbox 2. Connection by endless belt or chain is also envisaged along with direct 1 : 1 shaft drive. The AC output from each generator is fed into an AC bus 4 collecting same- frequency power, which in turn is fed into a single converter consisting of a rectifier 5 feeding an inverter 6. The frequency - and therefore speed - of the generators 3 is controlled by regulating the loading of the single rectifier 5. The role of the inverter 6 is to supply grid-compatible power to the grid 9 via a step-up transformer 7. In a preferred embodiment the turbine/generators are mounted as an array on a platform, which is in use submerged in the stream flow. The rectifier 5, inverter 6 and transformer 7 are also be located on the platform, and the transformer output is connected to the shore by a suitable underwater cable.
In use the load on the generators can be determined by control of the rectifier by reference to, for example, a look-up table relating rotor speed and generator output. A dump resistor 8 located locally to each turbine may be switched into the output of generator 3 to provide a means of slowing or stopping the rotor 1. This arrangement obviates overspeeding of the turbine rotor in a strong stream flow in the event say of a failure of the electrical supply from the grid, or of the converter 5-6. The resistor may be automatically connected in the event that turbine blades reach a pre-determined speed. The resistor 8 may comprise a plurality of individual resistor units connectable as required to give the required resistive loading.
Alternatively, a single dump resistor or resistor group may serve a group of generators. This latter solution may provide a lower cost alternative, or be better suited to installation on a platform provided that the risk associated with failure of the resistor or resistor group is acceptable. A single group dump load could in one alternative be made small enough to serve just one turbine, and used sequentially to slow down in turn each turbine in an array. Individual turbines of an array can be slowed or stopped by connection to the dump resistor(s). In one embodiment it is sufficient to slow the or each turbine to a speed at which it is safe to engage a mechanical brake, by which the rotor may be halted and parked. The invention may be used to reduce speed of any turbine which is damaged or becomes defective, or where for any reason a turbine or generator is no longer required to rotate at the rated speed. Where speed reduction is required for one or more of a group of turbines having common control, it may be necessary to reduce the speed of all turbines in the group. The configuration of Figure 2 is an alternative that allows individual control of speed and/or load of each turbine of an array. A rectifier 15 is provided at the output of each generator and is connected to a DC bus 14. The bus 14 feeds as in the first embodiment into a single inverter 6, again delivering power to the grid in a transformer 7.
Both embodiments address control of turbines of a multiple turbine array on a single platform where different stream flows may be encountered at different locations. In the case of a floating or semi-submersible platform, speed control of individual turbines is provided in the embodiment of Fig. 2, and may also allow trimming of the attitude of a platform by adjusting the speed and thereby thrust of one or more turbines.

Claims

Claims
1. An array of underwater turbines provided on a platform, each turbine being directly connected to a respective synchronous alternating current generator, the electrical outputs of the generators being coupled to a common bus for connection to an electrical grid.
2. An array according to claim 1, the array further including in series a rectifier and an inverter, for coupling said generators to an electrical grid.
3. An array according to claim 2, and comprising an alternating current bus intermediate said generators and said rectifier.
4. An array according to claim 2, wherein each generator has a respective rectifier at the output thereof, and said array comprises a direct current bus between the rectifiers and said inverter.
5. An array according to any of claims 2-4, wherein said bus, inverter, and one or more rectifiers are mounted on said platform.
6. An array according to any preceding claim, and further including a resistor connectable to the output of one or more of said generators for absorbing all or part of the electrical output thereof.
7. An array according to claim 6, and having a respective resistor for each of said generators.
8. An array according to claim 7, wherein each said resistor is between a respective generator and said bus.
9. An array according to claim 7 or claim 8, wherein each said resistor is independently connectable to the output of a respective generator.
10. An array according to any preceding claim, wherein said platform is provided with variable buoyancy whereby transition between a submerged and a surface condition may be effected.
11. A method of regulating an array of synchronous alternating current generators on an underwater platform, the outputs of the generators being connected by an electrical bus, the method comprising providing a rectifier for the output of each generator and controlling each rectifier to regulate the output current of a respective generator.
12. A method according to claim 11, and further comprising electrically connecting a resistor on the platform to the output of one or more of said generators to regulate the output thereof.
13. A method according to claim 12, wherein each generator is provided with a respective resistor, and the method comprises selectively connecting a resistor to a respective generator to regulate the output thereof.
14. A method according to claim 12, the method comprising connecting said resistor to a succession of generators in turn.
15. A method of regulating an array according to claim 3 or claim 4, upon failure of said bus, the method comprising the steps of detecting loss of control frequency and immediately connecting a resistor to the output of said generators to limit or reduce the speed thereof.
PCT/GB2012/051415 2011-06-22 2012-06-20 Improved regulation of underwater turbines WO2012175952A1 (en)

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GB1110596.2 2011-06-22
GBGB1110596.2A GB201110596D0 (en) 2011-06-22 2011-06-22 Improvements in power collection application

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EP3836335A1 (en) * 2019-12-12 2021-06-16 GE Renewable Technologies Method for coupling a hydroelectric power plant to the grid comprising at least two hydroelectric units

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