FIELD OF THE INVENTION

The present invention relates to a floating power supply system.

BACKGROUND OF THE INVENTION

In traditional offshore energy farms, a series of power sources are connected to an offshore substation, that collects this power, transforms it to a higher voltage to reduce power loss during transport and supplies it to a power consumer.

Offshore power farms generate electricity in bodies of water, usually at sea. They can for example use tidal, wind and deep-sea current energy. These offshore power farms are also less controversial than those on land, as they have less impact on people and the landscape.

Offshore power farms usually consist in a series of power sources coupled to an offshore substation, and the power is supplied to the power consumer, either on land or offshore from the offshore substation via one or a few high voltage transmission cables.

The power sources can be coupled in parallel or in series to the substation. If using DC power, the voltage can be increase by serial coupling of several individual DC power sources in an array, hence potentially omitting the need for a voltage transformer on the offshore substation. However, a series coupling of an array of wind turbines in an offshore wind farm has the disadvantage that if one cable or a power source fails then the whole array of wind turbines fails.

Substations transform voltage from high to low, or the reverse, or may transform AC voltage to DC, or the reverse, or perform any of several other important functions. A substation also normally has the function of connecting the cables from several individual power sources, such as offshore wind turbines, before sending the power in one or a few cables to shore. Between the power source(s) and power consumer, electric power may flow through several substations at different voltage levels. Each substation is quite expensive.

One objective of the present invention is to provide a floating power supply system, that will reduce the risk of malfunctioning and the overall cost of an energy farm, amongst other things by removing the need for one or more separate offshore substation(s). SUMMARY OF THE INVENTION

In a first aspect, the present invention relates to a floating power supply system comprising: an offshore floating foundation, comprising at least one buoyancy member; a first power source, installed on or inside the offshore floating foundation, a first cable terminal for exporting power to a power consumer; a second cable terminal for receiving power from at least a second power source; and a first power converter for converting power produced by the first power source and power received via the second cable terminal to power supplied to the first cable terminal.

As used herein, the term “buoyancy member” is used to denote a hull or other type of housing, which contains a material having a density lower than the density of water. The material having a density lower than the density of water will typically contain a gas, such as air.

The first power source may be located on this hull, for example on top of or on the side (i.e. somewhere on the outside of this hull) or the first power source may be located inside this hull, i.e. together with the material having a density lower than the density of water.

In an embodiment, the power consumer is an offshore hydrocarbon producing installation.

In an embodiment, the power consumer is a power consumer on land or on an island electrical grid connected to the first cable terminal via a subsea cable.

An advantage of the inventive floating power supply is that the floating power supply removes the need for a substation between the power sources and power consumer.

In an embodiment, the first power converter is located on or inside the at least one buoyancy member.

In an embodiment, the offshore floating foundation, comprises a plurality of buoyancy members.

In an embodiment, the offshore floating foundation, comprises a framework for mechanically connecting the buoyancy members to each other. In an embodiment, the first power converter is located on or between the framework.

By placing the first power converter on or inside the at least one buoyancy member, or on or between the framework, multiple effects are obtained. Firstly, the weight of the first power converter may be used as part of the ballast of the offshore floating foundation. Secondly, in case the first power source comprises a wind turbine with a tower, and if the first power converter is connected directly or indirectly to the tower of such wind turbine , e.g. by welding, weak points will be created that increases the fatigue on the wind turbine tower which is normally already highly utilized with respect to structural stresses in the steel weldments. Additionally, the weight of the first power converter would also increase fatigue on the wind turbine tower. When fatigue increases on the wind turbine tower or the foundation, the risk of failure and damage over time increases and the lifetime of the floating power supply system is reduced. The disclosed placement of the power converter therefore avoids this problem.

In an embodiment, the first power converter comprises a voltage transformer for converting power produced by the first power source or received via the second cable terminal to power having a higher voltage supplied to the first cable terminal.

In an embodiment, the power supplied to the first cable terminal is between 66 kV and 320 kV.

In an embodiment, the power produced by the first power source or received via the second cable terminal is AC power.

In an embodiment, the power produced by the first power source or received via the second cable terminal is DC power.

In an embodiment, the first power converter comprises a voltage transformer for converting power produced by the first power source or received via the second cable terminal to power having a lower voltage supplied to the first cable terminal.

In an embodiment, the first power converter comprises a power converter for converting AC power produced by the first power source, e.g. a wind turbine, or received via the second cable terminal to DC power supplied to the first cable terminal.

In an embodiment, the first power converter comprises a power converter for converting DC power produced by the first power source, e.g. a wind turbine, or received via the second cable terminal to AC power supplied to the first cable terminal.

In an embodiment, the second cable terminal may connect from 1 to 20 cables, from 1 to 10 or from 1 to 5 cables, each electrically connecting a second power source to the first cable terminal.

In an embodiment, the first power source is a wind turbine. The wind turbine is typically located on foundations separate from the power consumer.

In an embodiment, the first power source is a wind turbine and the wind turbine is located on at least one buoyancy member of the floating foundation.

In an embodiment, the first power source may be a solar power source or a wave power source.

In an embodiment, the at least a second power source may be a wind turbine, a solar power source or a wave power source.

In an embodiment, the solar power source may be a solar panel.

In an embodiment, the wave power source may be a wave energy converter.

In an embodiment, the ballast of the floating foundation is at least provided by the weight of the first power converter.

In an embodiment the power consumer are consumers on land or on an island electrical grid connected to a cable terminal on the floating foundation via a subsea cable.

In an embodiment, at least 5 %, preferably at least 10 %, of the ballast of the floating foundation is provided by the weight of the first power converter.

In an embodiment, the floating foundation comprises at least three buoyancy members; wherein the first power converter is located on or inside a first buoyancy member and/or on or inside a second buoyancy member.

In an embodiment, the floating foundation further comprises an energy storage located on or inside the offshore foundation.

In an embodiment, the floating foundation comprises at least one additional unit. The at least one additional unit may be a heliport, a control unit, a crane, a working deck etc. In an embodiment, the floating power supply system further comprises a second power converter.

In an embodiment, the second power converter is a bidirectional power converter for converting AC power produced by the first power source or received from the first power converter to a DC power supplied to the battery and for converting DC power stored in the battery to an AC power supplied to the first power converter.

In an embodiment, the second power converter is a bidirectional power converter for converting AC power produced by the first power source and/or for converting AC power received via the second cable terminal to a DC power supplied to the battery and for converting DC power stored in the battery to an AC power supplied to the first power converter.

In an embodiment, the energy storage is a rechargeable battery or a plurality of rechargeable batteries.

In an embodiment, the energy storage comprises a hydrogen system further comprising an electrolysis system converting electricity to hydrogen or a hydrogen compound, a hydrogen storage unit and a hydrogen energy conversion unit converting the stored hydrogen to usable electrical energy.

In an embodiment, the floating power supply comprises a cooling system for cooling the energy storage, wherein the cooling system comprises:

- a cooling fluid circulation pump for circulation of cooling fluid through a cooling fluid circuit;

- a heat exchanger connected to the cooling fluid circuit, wherein the heat exchanger is submerged in ballast water.

In an embodiment, the cooling system further comprises a valve for controlling the flow of the fluid in the cooling fluid circuit.

In an embodiment, the heat exchanger is submerged in the ballast water in one of the buoyancy members.

In an embodiment, the cooling system may additionally, or alternatively, cool the first power converter and/or the second power converter.

During periods of high winds, the power produced by the wind turbine will be sufficient to recharge the energy storage and to supply power to the power consumer. During periods with low wind or no wind, the energy storage is preferably also dimensioned to supply sufficient electric power to the hydrocarbon power consumer.

Periods with low wind or no wind may be predicted, for example based on a weather forecast and gas turbines may be safely started to take over the power generation. However, the wind turbine may suffer a sudden technical fault and shut down within seconds, or at least within one minute. Also, other interruptions of the power supply may be sudden, for example a sudden reduction in the power generating equipment supplying power to said installation due to a failure etc. The floating power supply system will be able to supply power to the power consumer in all of the above situations.

In an embodiment, the buoyancy member on or in which the first power source is located is different from the buoyancy member on or in which the first power converter is located.

In an embodiment, the buoyancy member on or in which the first power source is located is different from the buoyancy member on or in which the second power converter and/or the energy storage is located.

In an embodiment, the buoyancy member on or in which the first power converter is located is different from the buoyancy member on which the additional unit is located.

In an embodiment, the buoyancy member on or in which the first power converter is located is different from the buoyancy member on or in which the second power converter and/or the energy storage is located.

An advantage of arranging the power converter(s), additional unit(s) and/or energy storage on or in different buoyancy elements is that the ballast of the floating foundation is more evenly distributed. In the case where the at least one additional unit is a helipad, such distribution is also important to provide a ballasting effect against the helipad.

In an embodiment, the buoyancy member on which the wind turbine is located is different from the buoyancy member on or in which the energy storage is located.

In an embodiment, the floating foundation comprises three buoyancy members in a triangular configuration.

In an embodiment, the floating foundation comprises four buoyancy members, the fourth buoyancy member placed between the 3 buoyancy members which are positioned in a triangular configuration.

In an embodiment, the first power source may be arranged on the fourth buoyancy member. In an embodiment, the floating foundation is a semi-submersible platform.

Alternatively, the floating foundation may be a spar type of platform.

In an embodiment, the floating power supply system is configured to supply electric power to the power consumer simultaneously from the wind turbine and the energy storage.

In an embodiment the first power source produces AC power.

In an embodiment the first power source produces DC power.

In an embodiment the at least a second power source supplies AC power.

In an embodiment the at least a second power source supplies DC power. In an embodiment, the at least a second power source produces AC power, and comprises a power converter to transform AC to DC power supplied to the second cable terminal.

In an embodiment the at least a second power source is a plurality of second power sources.

In an embodiment the plurality of second power sources are coupled in series to the second cable terminal.

In an embodiment the plurality of second power sources are coupled in parallel to the second cable terminal.

In an embodiment the plurality of second power sources are coupled in a ring configuration to the second cable terminal.

In a second aspect, the present invention relates to an offshore power farm comprising a floating power supply system according to the first aspect of the invention; and at least a second power source.

In an embodiment of the second aspect of the invention, the offshore power farm is an offshore wind farm. In other words, the first power source and the at least a second power source are wind turbines. DETAILED DESCRIPTION

Embodiments of the invention will now be described in detail with reference to the enclosed drawings, wherein:

Fig. 1 illustrates a perspective view of a first embodiment of the floating power supply system;

Fig. 2 illustrates a schematical perspective view of a first embodiment of the floating power supply system;

Fig. 3 is a diagram of the first embodiment of the floating power supply system coupled to second power sources in series;

Fig. 4 is a diagram of the first embodiment of the floating power supply system coupled to second power sources in parallel;

Fig. 5 illustrates a schematical perspective view of a second embodiment of the floating power supply system;

Fig. 6 is a diagram of the second embodiment of the floating power supply system coupled to second power sources in series;

Fig. 7 is a diagram of the second embodiment of the floating power supply system coupled to second power sources in parallel;

Fig. 8 illustrates the content of the second power converter;

Fig. 9 illustrates the cooling system schematically.

Fig.10 illustrates an embodiment of the power farm.

First embodiment

Initially, it is referred to fig. 1, wherein a floating power supply system 1 is shown. The floating power supply system 1 is connected to a power consumer 14 via a power cable connected to a first cable terminal 13. The power consumer 14 may be an offshore hydrocarbon producing installation, such as a drilling platform type of installation (floating types, seabed fixed types), a FPSO (a floating production, storage and offloading) type of installation, an oil and/or gas production platform or any other type of offshore installation involved with production of hydrocarbons. The power consumer 14 may also be any type of power consumer on land or on an island.

It is now referred to fig. 1 to 4. Here it is shown that the floating power supply system 1 comprises a floating offshore foundation 10 comprising three buoyancy members I la, 11b, 11c in a triangular configuration. The floating offshore foundation 10 also comprises a framework 12 for mechanically connecting the buoyancy members I la, 11b, 11c to each other. As shown in fig. 2, the floating power supply system 1 comprises a first power source 20 installed on the offshore floating foundation 10, and a first power converter 25 located inside the first buoyancy member I la. The first power converter 25 receives power from the first power source 20 and from at least a second power source 16 electrically connected via a power cable to a second cable terminal 15. The first power converter 25 supplies power to a power consumer 14 electrically connected via a power cable to a first cable terminal 13. In this embodiment, the first power source 20 is a wind turbine located on the third buoyancy member 11c. The weight of the first power converter 25 is used as part of the ballast of the floating foundation 10.

As shown in fig. 1, the floating power supply system 1 is separated from the power consumer by a distance D. This distance D may be from 150m and up to several hundred kilometres.

The first power converter 25 comprises a voltage transformer for converting power produced by the first power source 20 or received via the second cable terminal 15 to power having a higher, or lower voltage (respectively) supplied to the first cable terminal 13, and/or a frequency transformer (or frequency inverter) for converting AC power produced by the wind turbine 20 or received via the second cable terminal 15 to AC power with a different frequency supplied to the first cable terminal 13, and/or a rectifierfor converting AC power produced by the wind turbine 20 or received via the second cable terminal 15 to DC power supplied to the first cable terminal 13. It should be noted that there may be many alternative embodiments of the first power converter 25. Typically, increasing the voltage is realised when the power consumer 14 is a land- or island based power consumer, while reducing the voltage is realised when the power consumer is an offshore power consumer, such as an offshore hydrocarbon producing installation (HCPI).

As used herein, the term “wind turbine” refers to the entire system needed to produce electric energy from wind, i.e. a mast with a nacelle containing a shaft connected to rotor blades and a generator. The wind turbine may further comprise mechanical and/or electrical equipment such as gearboxes, brakes, frequency converter, transformer, and controllers for controlling the electrical and/or mechanical equipment etc. The wind turbine 20 is considered known for a skilled person and will not be described in detail herein.

Fig. 3 and fig. 4 illustrate two different embodiments of an offshore power farm. Both embodiments of the offshore power farm comprise the inventive floating power supply system 1 and a plurality of second power source (16a, 16b, ..., 16z), electrically connected to the inventive floating power supply system 1, via the second cable terminal 15.

In the first embodiment of the offshore power farm, illustrated on fig. 3, the plurality of second power source (16a, 16b, ..., 16z) are mounted in series. A series coupling has the advantage to be an economically advantageous solution as it reduces the necessary material, but is not ideal, as if one cable or a power source fails then the whole array of wind turbines fails.

In the second embodiment of the offshore power farm, illustrated on fig. 4, the plurality of second power source (16a, 16b, ..., 16z) are mounted in parallel. A parallel coupling requires a lot more cabling and is more expensive, as each power source needs to be coupled individually to the substation. On the other hand, this solution ensures that if one cable or a power source fails then the wind farm will be impacted as little as possible, as only the affected power source will be out of service and the rest of the offshore power farm will continue production.

In a second embodiment of the floating power supply system 1, illustrated in fig. 5, the floating power supply system 1 comprises a floating offshore foundation 10 comprising three buoyancy members I la, 11b, 11c in a triangular configuration. The floating offshore foundation 10 also comprises a framework 12 for mechanically connecting the buoyancy members I la, 11b, 11c to each other. As shown in fig. 2, the floating power supply system 1 comprises a first power source 20 installed on the offshore floating foundation 10, and a first power converter 25 located inside one of the buoyancy member 11b. The power converter 25 receives power from the first power source 20 and from at least a second power source 16 electrically connected via a power cable to a second cable terminal 15. The power converter 25 supplies power to a power consumer 14 electrically connected via a power cable to a first cable terminal 13. In this embodiment, the first power source 20 is a wind turbine located on the third buoyancy member 11c. In addition, in this embodiment, the floating power supply system 1 may also comprise an energy storage 30 in the form of rechargeable batteries inside the second buoyancy member 1 lb. The weight of the energy storage 30 is used as part of the ballast of the floating foundation 10.

In this second embodiment, the second power source 16 may be a land based power source, such as an onshore wind turbine and the power consumer 14 may be an offshore hydrocarbon producing installation

Here it is shown that the floating power supply system 1 further comprises a second power converter 40, which in the present embodiment is located together with the energy storage 30 inside the second buoyancy member 11b.

The second power converter 40 has two main purposes in the present embodiment. The first purpose is transfer power from the wind turbine 20 and/or received via the second cable terminal 15 via the first power converter 25 to the energy storage 30, i.e. to recharge the battery of the energy storage 30. The second purpose is to transfer power from the energy storage 30 to the first power converter 25 so that it can be further transferred to the power consumer 14.

The second power converter 40 may for example comprise a voltage transformer and/or a frequency transformer (or frequency inverter) and/or a rectifier. It should be noted that there may be many alternative embodiments of the second power converter 40.

In the present embodiment, the battery of the energy storage 30 has a nominal voltage of 1 kV DC, while the nominal voltage of the first cable terminal 13 is l lkV AC. Hence, the second power converter 40 has DC terminals connected to the energy storage 30 and AC terminals connected to the first power converter 25 which is connected to the first cable terminal 13.

Fig. 6 and fig. 7 illustrate two different embodiments of an offshore power farm. Both embodiments of the offshore power farm comprise the inventive floating power supply system 1, comprising an energy storage 30 and a plurality of second power source (16a, 16b, ... , 16z), electrically connected to the inventive floating power supply system 1, via the second cable terminal 15.

In the third embodiment of the offshore power farm, illustrated on fig. 6, the plurality of second power source (16a, 16b, ..., 16z) are mounted in series. A series coupling has the advantage to be an economically advantageous solution as it reduces the necessary material, but is not ideal, as if one cable or a power source fails then the whole wind farm fails.

In the fourth embodiment of the offshore power farm, illustrated on fig. 7, the plurality of second power source (16a, 16b, ..., 16z) are mounted in parallel. A parallel coupling requires a lot more cabling and is more expensive, as each power source needs coupled individually to the substation. On the other hand, this solution ensures that if one cable or a power source fails then the wind farm will be impacted as little as possible, as only the affected power source will be out of service and the rest of the offshore power farm will continue production.

As shown in fig. 8, the second power converter 40 is a bidirectional converter comprising a bidirectional DC/DC, a bidirectional DC/AC converter and a transformer. It should be noted that there may be many alternative embodiments of the second power converter 40.

The cooling system 70

It is now referred to fig. 9, wherein the above floating power supply system 1 is shown to comprise a cooling system 70. In the buoyancy member 11 of the foundation 10, the weight of ballast water BW is used in addition to the weight of the first power converter 25 and/or of the energy storage 30 as ballast.

The purpose of the cooling system 70 is to cool the batteries and /or other electrical components of the first power converter 25 and/or of the energy storage 30. The cooling system 70 comprises a cooling fluid circulation pump 71 for circulation of cooling fluid through a cooling fluid circuit 72. In fig. 9, the cooling fluid circuit is illustrated as arrows, where dashed arrows indicate heated fluid heated by the energy storage 30 and solid arrows indicates cool fluid. The cooling system 70 further comprises a heat exchanger 73 connected to the cooling fluid circuit 72, wherein the heat exchanger 73 is submerged in the ballast water BW. The cooling system 70 further comprises a valve 74 for controlling the flow of the fluid in the cooling fluid circuit 72. Typically, the valve 74 will be temperature controlled. If the temperature of the heated fluid returning from the energy storage 30 is below a predetermined threshold value, the fluid is not circulated via the heat exchanger 73. However, if the temperature of the heated fluid returning from the energy storage 30 is above a predetermined threshold value, the fluid, or some of the fluid, is circulated via the heat exchanger 73 to reduce the temperature of the fluid.

As the ballast water BW typically will be fresh water, exposure of the cooling system 70 to seawater can be avoided, hence reducing corrosion and build-up of salt deposits on the heat exchanger.

Power farm

It is now referred to fig.10 which illustrates an embodiment of an offshore power farm. The offshore power farm comprises a number of power sources 16, electrically connected to inventive floating power supply systems 1. The power sources 16 here are typically floating offshore wind turbines. For each inventive floating power supply system 1, a few (as exemplified here two) floating offshore wind turbines are connected in series, in a few parallel circuits (as exemplified here six), via dynamic cables 115 to second cable terminal 15 of the inventive floating power supply system 1. Each of these few floating offshore wind turbines are connected in parallel to each other via the dynamic cables 115 to the inventive floating power supply system 1.

Each wind turbine typically delivers power at a voltage of 66 kV through a first series of dynamic power cables 115 to the inventive floating power supply system 1. The inventive floating power supply system 1, in addition to producing power, gather the power from the other power sources 16, and transform the power to a higher voltage to reduce power loss during transport and supplies power at a voltage of, for example 132 kV here, through a second series of dynamic power cable 113, connected to the inventive floating power supply system 1 via the first cable terminal 13. A dynamic cable is here defined as an electrical subsea cable able to handle dynamic bending and twisting as a result of the floating platforms moving in the waves and the forces acting on the cable itself when suspended from the floating platforms and down to the seabed. Static power cables on the other hand, are here defined as subsea cables that are suspended from a bottom fixed structure or platform down to the seabed, and protected from waves so that the cables do not move or bend. Static cables can have voltage levels up to 400kV and above with existing technology. For dynamic cables the limitation is the voltage level that the electrical insulation of the power cable can resist without being broken down over time. The electrical insulation of state of the art dynamic cables is currently 132kV which currently represents the limiting factor for how high the inventive floating power supply system 1 can transform the voltage. The first and second series of dynamic power cables 115, 113 are not intended for transport over long distance. Typical distance is 2- 10km

Further, the power may be, as exemplified here, supplied to a further substation 250, preferably a bottom fixed substation, a subsea substation or substation on an island so that the power may be transformed to a higher voltage to further reduce power loss during transport of the power via a static cable, for example to a voltage of 400 kV here. The static cable 114 supplies power to shore 300, to the power consumer, here a power grid 314. This further substation 250 must be fixedly attached to a static structure, so that it may be connected to a static cable 114. Hence, the static cable 114 allows transport of power at a higher voltage, which reduces power loss during transport. Static cables can transport power at a higher voltage than dynamic cables. This is why static cables are used to transport power over longer distances. Typical distance is 100-150km with alternating current (AC) and even longer distances when using direct current cables (DC).