Assembly comprising a floating structure, a wind turbine and drive means therefor

Abstract

The invention relates to a floating assembly (1) for generating electrical power, the assembly comprising a floating structure (10) connected to a buoy (20) by at least one flexible connection (30), a wind turbine (100) comprising a bearing structure (110) supporting a propeller (120) that rotates about an axis of rotation, such that it further comprises means (128) for driving the propeller (120) in order to rotate its rotor (126), means (50) for measuring the distance of separation between the floating structure (10) and a vertical axis of rotation of the buoy (20), and means (80) for activating the drive means (128) to rotate its rotor (126) in order to move the floating structure (10) away from the buoy when the distance of separation measured by the distance sensor (50) is below a given threshold.

Description

Description Title of the invention: Assembly comprising a floating structure, a wind turbine and means for motorizing the latter Technical field of the invention

[0001] The present invention relates to a floating assembly comprising at least one floating structure connected to a submerged buoy using at least one flexible connection, means connected to the submerged buoy for anchoring said floating structure to a seabed and a wind turbine mounted on the floating structure and comprising a propeller connected to a rotor rotating on itself around an axis of rotation. Prior art

[0002] Faced with global warming and the increasingly pressing scarcity of fossil fuels, the majority of the world's major powers have decided to introduce a growing share of renewable energy into their energy policies as an alternative. As a result, wind power is among the two energy sources experiencing the strongest growth in terms of installed capacity annually.

[0003] As is known, a wind turbine consists of a mast attached to a base (concrete foundations) and raised upwards on which is mounted a turbine nacelle equipped with a hub and a propeller with several blades (generally three arranged at 120° from each other). This mechanical system is completed by a unit for transforming the rotational movement of the propeller into an electric current, including in particular a brake, a multiplier, a generator / alternator, a transformer and cables for coupling it to the electricity network. Wind turbines are generally installed in fields (cultivated or not) or in dedicated spaces, and are most often grouped together in the form of wind farms.

[0004] However, living near these wind farms presents many disadvantages for local residents. First of all, the wind turbines generate noise during their operation. This noise is particularly disturbing when wind turbines operate at night while local residents want to sleep. Furthermore, although efforts have been made to make them aesthetically pleasing, wind turbines form a significant mass that can spoil the landscape and scare away nearby wildlife. In addition, the space required for the installation of an onshore wind turbine can be significant. Thus, it may be impossible to install an onshore wind turbine in certain locations, or a limit on the number of onshore wind turbines installed may be imposed to the detriment of electricity production capacity.

[0005] To limit noise and visual nuisance for local residents and improve electricity production capacity, the construction of offshore wind farms is booming around the world following the implementation of public policies promoting renewable energy. This interest in offshore installations is explained in particular, but not only, by the greater strength and greater regularity of the wind at sea (offshore), which allows for a higher total theoretical yield (much higher load factor, around 40%, whereas it generally reaches around 30% for onshore wind) and potentially a better return on investment.

[0006] There are few technological differences between an onshore wind turbine and an offshore wind turbine. Indeed, the components that make up the wind turbine itself (without its support) remain essentially identical, only increased resistance to corrosion in a marine environment is required for offshore wind turbines. This is achieved in particular through more effective protection of the internal components and the coating applied to the external components. Increasing the thickness of the materials making up the mast is also a way to combat the regular attacks of waves and currents. In addition, while an onshore wind turbine is most often limited to 3.5-5 MW, an offshore wind turbine can easily provide 8-10 MW, or even 12-15 MW for very recent models.Indeed, this is possible due to the quality of the wind that offshore allows us to achieve, that is to say a stronger, more regular wind, with a laminar flow that is not disturbed by possible reliefs. It is even considered to go further, still in the. aim of increasing the competitiveness of offshore wind power in the energy market. There are currently three main types of offshore wind turbines.

[0007] The first type concerns so-called conventional or fixed offshore wind turbines, i.e. wind turbines such as those installed on land, but which are slightly modified to be able to be installed at sea. The best known of these consist of a fixed mast several tens of meters long (up to 150 m or even more) connected to the seabed and supporting three blades driven by offshore or coastal winds, each of which can measure more than 100 m in length. As the wind direction can change, this first type of offshore wind turbine comprises a turbine generally mounted mobile on a mast so as to adapt to the wind direction. However, the turbine constitutes a significant weight at the top of the wind turbine, which generates a considerable lever arm and can cause significant tilting stresses.It is therefore necessary to provide an anchoring structure for the wind turbine that must withstand the constraints linked to both the force of the wind and the weight of the turbine. To date, the majority of offshore wind turbines are placed on the seabed. The mast of this first type of offshore wind turbine therefore most often rests either on a metal tube deeply embedded in the underwater subsoil (single-pile wind turbine), or on a base (gravity concrete) consisting of a large structure placed on the seabed or (more rarely) on a metal lattice structure called a "jacket" resting on the ground. Offshore wind turbines of this first type are generally very heavy and their installation, particularly that of the anchoring structure, can be long, expensive and tedious, especially depending on weather conditions.Indeed, for an 8MW wind turbine the penetration length of the monopile into the seabed can exceed 30 meters for a pile diameter of approximately 8-10 m. As for the gravity foundation, it may be necessary to pour more than 2000 tons of concrete, several tens of meters deep, with a ground footprint of several tens of meters in diameter (approximately 50-60 meters for an 8 MW wind turbine).

[0008] However, these wind turbines have an energy yield that is not optimized. Indeed, the technique of the fixed offshore wind turbine is not economically viable in waters that are too deep (40m and beyond - in certain regions, this depth is reached very quickly close to the coast, which does not resolve the problem of visual or even noise pollution) particularly due to the costs of installation and handling. This represents a serious obstacle to the development of wind energy.

[0009] For this reason, the scientific community has been interested for several years in wind turbines on floating platforms (FWT for Floating Wind Turbine), i.e. fixed on floats and potentially positioned far from the coast with a bathymetry of several hundred meters (typically 100-300 meters). This technology has a construction and implementation cost that is essentially the same, regardless of the water depth. From a civil engineering point of view, FWTs are also less sensitive to the geotechnical conditions of the seabed than fixed wind turbines. In addition, their maintenance is simplified because it is easy to tow them to the port if necessary for repairs on the quayside and under shelter, even if the installation site is potentially more distant than for a fixed wind turbine.

[0010] Unlike the fixed offshore wind turbines mentioned above, floating wind turbines can therefore be installed well beyond 40-50 m depth, where the winds are even better in terms of power and regularity because there is, a priori, strictly no relief nearby, which further improves the load factor (50% and beyond). They include for this purpose a floating support structure on which a mast carrying the wind turbine is erected. The assembly between the turbine and the floating support platform can advantageously be carried out on land and not at sea where the conditions are potentially more difficult (currents, swell, meteorology) before towing the assembly to the site (with the possibility of choosing a favorable date from the point of view of navigation conditions) using an offshore tug to proceed with the anchoring. Wind turbines Floating wind turbines are generally maintained on their offshore production site using anchoring systems. These systems are designed to withstand common operating conditions and potentially more extreme conditions. They are therefore generally composed of anchors (drag anchor, suction anchor, buried plates, or even dead weight) and one or more anchor lines (chain, wire rope, synthetic materials such as polyester, high-density polyethylene, or even polyamide) connected to the floating platform. SPAR (Single Point Anchor Reservoir) type floats are stabilized by their high inertia because their bottom is ballasted, which considerably increases their mass and their moments of inertia in rolling and pitching. TLP (Tension Leg Platform) type floating wind turbines have a platform held by tensioned anchors so that it is the stiffness induced by these anchors that allows for great stability.Finally, the most widespread floating wind turbines of the semi-submersible float type (inspired by offshore oil and gas), comprise a platform most often with a flat bottom and low draft (10-20 meters in general) and non-tensioned anchors, its stability being ensured by Archimedes' thrust.

[0011] Here again, these wind turbines are not optimized in terms of energy efficiency because they do not adapt or adapt little to their environment due to their static position. Indeed, in the case of using a mast, it is necessary on the one hand to have a very stable floating platform (therefore large, heavy, and expensive) to limit the inclination of the mast (pitching and rolling) and on the other hand to limit the size of the wind turbines or their efficiency because of vibration problems and the proximity of the blades to the mast. In deep water, this technology is interesting. But the fact that the wind turbine is not embedded in the seabed very significantly increases the mechanical stresses induced by waves (pitching and / or rolling). Indeed, in production, these floating wind turbines are subject to currents and swell which can induce a yaw angle on the wind turbine, i.e. a rotation of the floating wind turbine relative to a vertical axis.These disturbances increase the movements of the float and consequently the mechanical stresses on several. of its elements, particularly the mast, reducing their durability. This sensitivity to swell could be reduced by increasing the size and weight of the float, but this solution would increase the cost of the kWh produced.

[0012] To combat yaw angle, some floating wind turbine models include an electrical adjustment system. For example, electric motors or a downwind drift system allow the turbine to rotate relative to the mast in order to (re)position the turbine propeller's rotation axis in line with the wind.

[0013] In order to improve the structural strength of floating wind turbines, the patent document filed on April 18, 2013 and published under number FR3004764 describes a third type of floating wind turbine that includes a floating structure that supports a horizontal axis wind turbine using several arms and no longer a single mast. The turbine nacelle is fixed relative to the floating structure of the floating wind turbine so that it can no longer orient itself into the wind independently of the floating structure that supports it to compensate for the yaw angle due to the forces of the sea. Thus, it is the assembly consisting of the floating platform, the support arms and the turbine of the wind turbine that orients itself into the wind, by rotating around an anchoring means such as a buoy or a reel. This third type therefore concerns marine wind turbines known as the self-orienting type.These wind turbines are generally smaller and lighter than those of the first type and the second type.

[0014] However, since the floating structure is subject to external conditions, such as meteorology and especially the state of the sea (current, swell, waves), the efficiency and overall performance of these devices are not optimized, particularly due to the constraints mentioned above. Indeed, experiments and numerical models show that a floating wind system using a single-point anchorage can present dynamic instabilities leading to a loss of electrical production as well as an increase in the fatigue of the wind turbine. Indeed, the floating wind turbine can oscillate with a fishtail movement, called fish-tailing in the state of the art.

[0015] In order to avoid these dynamic instabilities which are unfavorable to the economic balance of floating wind turbines, it is possible to use a single-point anchoring system with the following particularity: Two flexible anchor lines on the port and starboard sides called mooring lines connect the wind turbine by its bow (port and starboard) to an offset buoy, itself anchored to the seabed by means of 3 anchor lines. The geometry of such an assembly makes it possible to avoid unfavorable dynamic instabilities while minimizing the dimensions of the float and therefore its cost. Mathematically, this geometry, if the length of the lines, their elasticity and the port-starboard spacing are judiciously chosen, ensures that the real part of the eigenvalue of the mechanical system projected in the horizontal plane is negative.Generally, the wind turbine remains at a distance from the buoy because the thrust of the turbine blades generates a force opposite, in direction, to the projection in the horizontal plane of the water surface of the axis passing through the center of the wind turbine rotor and the center of the buoy. In other, rarer conditions, it is the drift forces generated by waves and / or the current that are prevalent that allow the wind turbine to remain at a distance from the single anchor point.

[0016] However, this system presents the risk that the wind turbine will approach the buoy in certain weather conditions or transitions in very calm weather with very little or no wind, current and swell. It may then happen that the sum of the aerodynamic and / or hydrodynamic forces applied to the floating platform change direction, which means that the minimum safety distance between the buoy and the wind turbine is no longer ensured.

[0017] The invention aims in particular to overcome the drawbacks of the prior art cited above. More specifically, the invention aims to propose a marine energy production assembly, making it possible to counter the forces of the sea and the wind to optimally stabilize the wind turbine in order to ensure good orientation of the turbine and guarantee a high production efficiency of the wind turbine. Presentation of the invention

[0018] The present invention aims to overcome these drawbacks with a completely innovative approach that is efficient, reliable, responsive, usable in a large number of marine / meteorological conditions, versatile, ecological and easily adaptable.

[0019] Thus, the invention relates to a floating assembly comprising a floating support structure for at least one wind turbine, said floating structure being connected to a buoy anchored to the seabed so that this anchoring has the particularity of allowing rotation of the wind turbine around a pivot point in order to orient itself facing the wind.

[0020] To this end, according to a first aspect, the present invention relates to a floating assembly in a marine environment for the production of electrical energy using the wind comprising: - a floating structure comprising at least one platform provided with a prow to which a buoy is connected using at least one flexible connection of the mooring line type, - means connected to the buoy for anchoring said floating structure to a seabed, - at least one wind turbine mounted on the floating structure and comprising a supporting structure erected substantially vertically on the floating structure and supporting a propeller with several blades connected to a common rotor rotating on itself around an axis of rotation, and - means for determining at least one of the following parameters among the wind direction, the wind speed, the direction of the sea current and the speed of the sea current, characterized in that it further comprises: - means for motorizing the wind turbine propeller in order to turn its rotor in one direction of rotation or in the opposite direction, - means for measuring the distance between the bow of the floating structure and a vertical rotation axis of the buoy, - control means for starting the propeller motorization means and turning its rotor in order to move the floating structure away from said buoy when said separation distance measured by the distance sensor is less than a determined threshold.

[0021] The invention is implemented according to the embodiments and variants set out below, which are to be considered individually or in any technically effective combination. According to an additional characteristic making it possible to improve the detection of the distance away and the precision / speed of reaction of the system for repositioning the floating platform of the wind turbine in relation to the buoy, the assembly comprises, in addition to means for evaluating the predicted azimuthal position of the floating structure in relation to the buoy and control means for starting the motorization means of the propeller and rotating its rotor in order to move the floating structure around said buoy along its axis in the clockwise or anti-clockwise direction according to said predicted azimuthal position of the floating structure.

[0022] Preferably, the blades making up the propeller have means for adjusting their pitch as a function of the azimuthal position of each blade, so as to create an axial component of rotor thrust collinear with the axis of said rotor and a lateral component of rotor thrust perpendicular to the axis of said rotor.

[0023] This solution makes it possible in particular to improve the precision and speed of orientation of the floating platform of the wind turbine once the separation distance threshold has been exceeded and the motorization means have been activated.

[0024] Advantageously, the means of motorizing the propeller are constituted by the rotor of the wind turbine operating in propulsion mode and connected to a main generator of electrical energy operating in propulsion mode thanks to the electric machine operating in motor mode, where the electric machine usually serves in generator mode to transform the energy of the wind into electricity.

[0025] This solution allows for the best possible integration of the motorization means in relation to the wind turbine, in particular to optimize their efficiency and responsiveness and reduce the overall weight.

[0026] Additionally, the assembly further comprises at least one secondary underwater bow thruster linked to the floating structure and connected to a secondary source of electrical energy.

[0027] This solution further optimizes the movements of the floating assembly once the separation distance threshold has been detected in order to reposition it in the best possible way for optimal operation of the wind turbine.

[0028] According to a particular characteristic, the main energy generator and / or the secondary energy source comprises a battery.

[0029] This solution guarantees the autonomy of the wind turbine's motorization means and the secondary thruster.

[0030] Additionally, the battery is rechargeable and is connected to a photovoltaic panel attached to the floating structure or the supporting structure of the wind turbine.

[0031] This will provide propulsion systems with an ecological, inexhaustible and easy to store source of energy.

[0032] According to an alternative embodiment, the main energy generator and / or the secondary energy source comprises(s) a fossil fuel engine such as a diesel generator.

[0033] Preferably, the main generator of electrical energy and the secondary source of energy are combined into a single device.

[0034] This solution allows for miniaturization of energy sources and simplification of the whole.

[0035] According to a preferred embodiment of the present invention, the means for measuring the distance comprise a GPS type geolocation system.

[0036] According to a particular embodiment of the present invention, the means for measuring the separation distance comprise at least one detector mounted on a double-axis connector of each mooring line connecting the buoy to the floating structure and measuring a difference in inclination of the mooring line considered between a first reference position in which said mooring line is completely under tension and a second position in which said mooring line is slack in order to deduce therefrom a potential reduction in the tension in said mooring line and a reduction in the separation distance.

[0037] This solution thus provides a reliable, rapid, and easy-to-interpret measurement of the distance, guaranteeing movement optimized of the floating set when this distance has reached the determined threshold.

[0038] According to a complementary aspect, the floating structure being connected to the buoy by two mooring lines arranged respectively on the port and starboard sides, and each mooring line comprising a double-axis connector, the means for measuring the separation distance D comprise a detector per connector axis, i.e. four detectors in total.

[0039] This sensor doubling solution improves the accuracy of standoff distance measurement, which can be difficult to determine, especially during large wave troughs. This sensor doubling solution improves the robustness of standoff distance measurement, which can be difficult to determine if a sensor fails.

[0040] According to a particularly interesting aspect of the present invention, the control means comprise at least one Proportional Integral Derivative type module adapting in real time the rotation speed of the rotor as a function of the measured separation distance and / or the speed of movement of the floating structure and / or the power supplied to the motorization means so that said floating structure is permanently located at a separation distance greater than or equal to the determined threshold.

[0041] This solution improves the responsiveness of the floating assembly repositioning system.

[0042] According to an additional feature, the control means comprise two PID modules, one per mooring line, collaborating with each other to control the rotation speed of the rotor and the pitch of the propeller blades.

[0043] This solution further improves the accuracy of the measurement and therefore that of the movement of the floating assembly for a smooth (without jolts) and rapid movement.

[0044] Advantageously, the buoy is statically anchored to the seabed using three flexible anchor lines angularly spaced from each other by 120° along a horizontal projection plane of said anchor lines.

[0045] This solution ensures uniform and stable anchoring of the floating assembly.

[0046] According to a particularly interesting characteristic of the present invention, the means for determining the direction of the wind comprise at least one of the following devices chosen from an anemometer or a weather vane.

[0047] Similarly, the means of determining the direction and speed of the ocean current are based on knowledge of tidal currents as a function of date and time, the use of a current meter, and knowledge of the surface area and drag coefficients of the submerged part of the floating structure.

[0048] Advantageously, the separation distance threshold is between approximately 80% and 90% of the nominal distance for which the mooring line connecting the floating structure to the buoy is taut. Brief description of the figures

[0049] Other advantages, aims and characteristics of the present invention emerge from the following description given, for explanatory and non-limiting purposes, with reference to the appended drawings, in which:

[0050] [Fig. 1] Figure 1 is a perspective view of a floating assembly in a marine environment for the production of electrical energy using wind according to the present invention,

[0051] [Fig. 2] Figure 2 is a side view of the floating assembly of Figure 1 and mainly comprising a floating structure and a wind turbine,

[0052] [Fig. 3] Figure 3 is a front view of Figure 1,

[0053] [Fig. 4] Figure 4 is a top view of Figure 1,

[0054] [Fig. 5] Figure 5 is a detail view of a portion of the floating assembly of Figures 1 to 4,

[0055] [Fig. 6] Figure 6 is a side view of the assembly in which the platform is in a different position from that of Figures 1 to 5,

[0056] [Fig. 7] Figure 7 is a detail view of Figure 6, and

[0057] [Fig. 8] Figure 8 is an alternative embodiment of Figure 5. Description of the embodiments

[0058] This description is given without limitation, each characteristic of an embodiment being able to be combined with any other characteristic of any other embodiment.

[0059] It should be noted, from now on, that the figures are not necessarily to scale, without this hindering their understanding.

[0060] Figures 1 to 5 represent a floating assembly 1 for the production of electrical energy using wind, in particular of the offshore type, comprising a floating structure 10 comprising at least one platform 11 provided with a bow 12 connected to a submerged buoy 20 using at least one flexible connection 30 of the hawser type, and preferably two hawsers 30 as shown, - wire-type means 40 connected to the buoy 20 for anchoring said floating structure 10 to a seabed 5, and - at least one wind turbine 100 mounted on the floating structure 10 and mainly comprising a supporting structure 110 erected substantially vertically on the floating structure 10 and supporting a propeller 120 with several blades 122 connected to a common rotor 124 rotating on itself around an axis of rotation XX'.

[0061] The platform 11 of the floating structure 10 is of a known type and comprises, for example, mechanically welded metal beams resistant to marine corrosion and supported, for example, by submerged flotation boxes. This platform 11 here has a basic square shape with four corners 15 and measures approximately 50 meters on each side for a height, including submerged flotation boxes, of approximately 25 to 30 meters, for a power of 5 MW. For a 20 MW wind turbine, the length of the float is of the order of 80m. Other shapes are of course conceivable, for example rectangular. The draft of the floating structure 10 is determined using the flotation boxes (ballast) and is adaptable if necessary to the offshore installation area of ​​the energy production unit 1, in particular as a function of the water depth, the distance from the coast and the wave conditions.

[0062] The buoy 20 is connected to two spaced points 13 and 14 of the bow 12 of the platform 11 using two identical mooring lines 30 so as to form an isosceles triangle.

[0063] The buoy 20 is typically positioned approximately 100-110 meters from the bow 12 of the platform 11, for example approximately 105 meters. Given the width of the platform 11 and the height of the attachment points 13 and 14 relative to the water level E, the mooring lines 30 each measure approximately 110 to 120 in length when fully energized. An electrical cable 35 also connects the submerged buoy 20 to the platform 11 in order to transmit the electricity produced by the wind turbine 100 during its operation, or its storage in gaseous or liquid form in a tank (not shown) placed on the platform 11 (which may then have a floor extending between mechanically welded beams) for later use. The buoy 20 is also equipped with a cable 36 connected to the shore to transport the electrical energy produced. Buoy 20 can be completely submerged below water level E in certain configurations.

[0064] As can be seen in Figures 1 to 4, the buoy 20 is also firmly anchored to the seabed 5 using three other hawsers 40, including for example a first frontal hawser of great length (approximately 500 to 600 meters) and two identical lateral hawsers of shorter length (approximately 140 to 150 meters). Other dimensions are perfectly conceivable depending on the topography of the seabed 5 where it is located. These three hawsers 40 are preferably arranged, when looking at the buoy 20 at its zenith (along the axis ZZ'), at 120° from each other, as illustrated in Figure 4. These three hawsers 40 thus keep the buoy 20 in position in a substantially static manner, but the latter can oscillate up and down along the vertical axis ZZ' depending on the swell. The buoy 20 therefore defines a substantially fixed point (except vertically) for the mooring of the floating structure 10 of the electrical energy production unit 1.

[0065] The wind turbine 100 comprises a supporting structure 110 which in this case takes the form of four uprights / posts connecting the four corners 15 of the platform 11 and joining at a common apex 124 to form a five-sided pyramid (a lower face formed by the base of the platform 11 and four identical side faces formed by two adjacent uprights together defining an isosceles or equilateral triangle). The height at the top of this supporting structure 110 of the wind turbine 100 relative to sea level is approximately 85 to 90 meters for a 5 MW wind turbine, and approximately 160-180 m for a 20 MW wind turbine.

[0066] The axis XX' of rotation of the rotor 124 supporting the blades 122 of the propeller 120 of the wind turbine 100 passes substantially through the top of the pyramidal supporting structure 110, this axis being moreover substantially parallel to the plane defined by the platform 11 (a plate connecting the angles 15 of the mechanically welded beams of the floating structure 10 can form a floor if necessary). Thus, in the upright and perfectly vertical position of the wind turbine 100 (horizontal platform 11), the axis XX' of rotation of the rotor 124 is itself horizontal. The blades 122 describe a circle of approximately 100 to 120 m in diameter while rotating so that the highest point of the blades 122 is approximately 150 to 160 m from the water level E for a 5 MW wind turbine and approximately 320 m for a 20 MW wind turbine.

[0067] According to the present invention, the floating energy production assembly further comprises means 60 and 70 for determining at least one of the following parameters among the wind direction, the wind speed, the direction of the sea current and the speed of the sea current. In the present case, the means 60 for determining the wind direction comprise at least one of the following accessories chosen from an anemometer, a LIDAR or a wind vane placed fixedly at the top of the wind turbine 100, that is to say at a height high enough to accurately measure the winds that can influence the movement of the supporting structure 10 by acting on the blades 122.

[0068] The means 70 for determining the direction and speed of the sea current are constituted by a submerged current meter type sensor connected to the platform 11 and connected to a control computer 80 containing for example a knowledge base of the tidal currents as a function of the date and time, and of the surface and drag coefficients of the submerged part of the floating structure 10.

[0069] Finally, the electrical energy production assembly 1 according to the present invention comprises a complex system for automatic repositioning of the floating platform 10 relative to the buoy 20 which will be explained in more detail below.

[0070] For this purpose, set 1 includes: - means 128 for motorizing the propeller 120 of the wind turbine 100 in order to turn its rotor 126 in one direction of rotation or in the opposite direction, - means 50 for measuring the separation distance D between the bow 12 of the floating structure 10 and the vertical rotation axis ZZ' of the buoy 20, and - control means 80, for example a computer) to start the means 128 for motorizing the propeller 120 and to turn its rotor 126 in order to move the floating structure 10 away from the buoy 20 when said separation distance D measured by the distance sensor 50 is less than a determined threshold.

[0071] According to a feature of the invention, the means 128 for motorizing the propeller 120 are constituted by the motor 128 of the rotor 126 of the wind turbine operating in propulsion mode and connected to a main electrical energy generator 129 of the battery or diesel generator or export electric cable type.

[0072] The means 50 for measuring the separation distance D comprise at least one detector 51 mounted on a double-axis connector of each mooring line 30 connecting the buoy 20 to the floating structure 10 and measuring a difference in inclination cr of the mooring line in question 30 between a first reference position in which said mooring line 30 is completely under tension and a second position in which said mooring line 30 is slack in order to deduce therefrom a potential reduction in the tension in said mooring line and a reduction in the separation distance D. In the present case, and in order to improve the measurements, each mooring line 30 comprises two double-axis connectors, each provided with a detector 51 per axis, i.e. four distance detectors 50 D in total.

[0073] In order to refine the efficiency of the system, the assembly 1 also comprises means 90 for evaluating the predicted azimuthal position of the floating structure 10 relative to the buoy 20, for example an inertial unit, a magnetometer or a set of differential GPS and control means 80 for starting the motorization means 128 of the propeller 120 and rotating its rotor 126 in order to move the floating structure 10 around said buoy 20 along the axis ZZ' in the clockwise direction or in the counterclockwise direction according to said predicted azimuthal position of the floating structure.

[0074] For this purpose, the blades 122 making up the propeller 120 have means 130 for adjusting their pitch as a function of the azimuthal position of each blade 122 so as to create an axial component of thrust of the rotor 126 collinear with the axis XX' of said rotor 126 and a lateral component of thrust of the rotor 126 perpendicular to the axis XX' of said rotor 126. By varying the pitch of each of the blades as a function of their azimuthal position, for example sinusoidally with respectively 10°, 0°, -10°, 0° for azimuthal positions of 0°, 90°, 180°, 270°, the rotor generates sufficient lateral thrust to move the structure. The incidence of the blades 122 is adjusted in order to generate an axial / lateral thrust which will move the wind turbine back in relation to the buoy 20 and tighten the mooring lines 30.The axial / lateral thrust is regulated in order to maintain a sufficient distance D while minimizing the necessary electrical consumption (which remains completely tiny in comparison with the quantity of energy produced by the wind turbine in production mode, for example approximately 60W for a nominal power of 4 kW). The direction of the lateral thrust is chosen in order to minimize the energy and the length of the arc of the circle to be traveled to reach a stabilized position.

[0075] These adjustment means can be supplemented by two secondary underwater bow thrusters 95 and 96 connected to the platform 11 and connected to a secondary source of electrical energy 98 such as a battery (the same as that of the motorization means 128 of the wind turbine 100) or a diesel generator.

[0076] Finally, the control means 80 comprise at least one Proportional Integral Derivative (PI D) type module adapting in real time the rotation speed of the rotor 126 as a function of the measured separation distance D and / or the speed of movement of the floating structure 10 and / or the power supplied to the motorization means 128 so that said floating structure 10 is permanently located at a separation distance D greater than or equal to the determined threshold. It is even provided that the control means 80 comprise two PID modules, one per mooring line 30, collaborating with each other to control at least one of the parameters among the rotation speed of the rotor 126, the pitch of the blades 122 of the propeller and the power of the secondary underwater bow thrusters 95 and 96.

[0077] Figure 8 shows another type of structure called "upwind" (with a vertical facade and wind coming from the front) in which the blades 122 of the wind turbine 100 do not turn in the center of the pyramid formed by the supporting structure 110 but outside and on the front of the tubular structure 110. Nevertheless, the same means as those described in relation to figures 1 to 7 are used for the same objective.

[0078] As explained in the preamble, it happens that the floating structure 10 involuntarily approaches the buoy 20 (arrow F in figure 6), whether the blades 122 of the propeller 120 are rotating (energy production mode) or not.

[0079] This phenomenon was studied at length by the applicant according to the protocol described below.

[0080] Indeed, due to its anchoring system based on Single Point Mooring (SPM), floating offshore wind turbines are subject to potentially dangerous movements in low wind conditions. Indeed, the thrust applied to the rotor 124 when the blades 122 of the wind turbine 100 produce electrical energy is greater than the drag force induced by the current. The float 10 therefore naturally aligns with the direction of the wind. For wind speeds below 4 m / s, the blades 122 of the wind turbine 100 are stopped and the resulting thrust tends to be less than the drag of the current. The float 10 therefore tends to align with the direction of the current with an uncontrolled trajectory after the blades 122 of the wind turbine 100 have stopped rotating. This may cause one of the mooring lines 30 to become entangled with the mooring lines or the electric cable, or, in the worst case, a collision between the float 10 and the buoy 20.

[0081] In order to identify the environmental conditions in which the control means 80 (also called system in the present description) must be activated, a table of load cases including low winds and currents of opposite directions was used. Time series of results are extracted from a measurement database and used as reference environmental data to evaluate the system performance. These data come from a first measurement campaign A lasting 7 years started in 2012 and ended in 2019 with data sampled every hour, followed by a second measurement campaign B lasting 3 months conducted in 2013 with data sampling every 10 minutes. The data thus collected make it possible to draw up a graph representing the current speed in m / s, in a range from 0 to more than 1.2, and the wind speed in m / s in a range from 0 to more than 25 m / s.

[0082] With particular focus on high wind and current transients, studies based on a selection of wind / current data from campaign B (to have a smaller sampling rate and higher resolution) were conducted and a selection was made to identify cases in which the wind speed is lower than 5 m / s and the wind direction relative to the current is higher than 90°.

[0083] It was thus possible to highlight 47 different cases which can be classified into 3 categories, namely static conditions of the low wind and low current type, in which the system 80 according to the invention must be used to compensate for the residual tension of the mooring lines 30 which tend to attract the float 10 towards the buoy 20, conditions of predominance of the current over the wind in which the wind turbine 100 is in electrical energy production mode, and conditions of predominance of wind over current in which wind turbine 100 is stopped.

[0084] Following a selection, 13 of these 47 cases were studied in more detail, covering the 3 categories presented above. Most of the identified load cases include current velocities ranging from 0.05 m / s to 0.3 m / s. Only one load case presents current velocities up to 0.6 m / s.

[0085] The study of campaign A shows that the current can reach speeds of up to 1.1 m / s. This second study provides a more representative, extended sample of current speeds. The selection carried out in this second study thus allows us to extract 8 cases in which the transients have a current speed greater than 0.5 m / s and a wind orientation relative to the current greater than 90°.

[0086] All these data are collected and introduced into an Orcaflex ® simulation platform. In the absence of any system in accordance with the present invention, the simulation highlights several critical situations where the float 10 approaches more or less the buoy 20 and more or less quickly (arrow F in Figure 6). During these events, the two mooring lines 30 thus tend to relax. This can be measured by their inclination relative to the horizontal.

[0087] When the hawser 30 is correctly tensioned, the angle a is zero in Figure 6 or 7, when the hawser relaxes and releases, the angle a is then strictly greater than 0°, for example approximately 5 to 30°, and more specifically between approximately 10 and 20°, depending on the level of slack of the hawser 30, which may even come into contact with the surface E of the water. When the angle a begins to exceed 10°, this means that the bow 12 of the platform 11 has already moved several meters closer to the buoy 20 and that the system 80 must be started.

[0088] It is considered that the distance threshold D from which the system 80 starts up (preferably automatically) is between approximately 80% and 90% of the nominal distance for which the connecting line 30 of the floating structure 10 to the buoy 20 is under maximum tension (without stretching the line, i.e. a tension normal with the hawser straight). Thus, if the nominal distance D between the bow and the ZZ' axis is approximately 100m, then the triggering of system 80 will begin as soon as this distance D is 80 to 90m.

[0089] It appears from this study that the mooring lines 30 slacken mainly in cases where the current speed is less than or equal to 0.3 m / s. For cases where the current speed is higher (0.3 m / s and above), critical situations are rare. This can be explained by the fact that the float 10 easily aligns with the current direction when the current speed is high, while the mooring lines 30 tend to attract the float 10 towards the buoy 20 when the current is low. Nevertheless, a current of high amplitude and direction opposite to the wind can be problematic during the transient phase when the wind turbine 100 is stopped.

[0090] The invention thus makes it possible to maintain the float 10 at a desired distance from the buoy 20 with the two hawsers 30 taut. In certain situations, the invention also has the ability to move the float 10 to a safe location where it is not at risk of crashing by applying a longitudinal and lateral force to the latter.

[0091] This role is fulfilled by two actuator systems, namely: - the wind turbine 100 used in motor mode if the energy production device is connected to the network, and - two booster thrusters 95 and 96, one longitudinal and the other lateral, if the energy production device 1 is not connected to the network.

[0092] The 100 wind turbine used in motor mode aims to generate longitudinal and lateral forces through the combination of two controls: - Use the converter to drive the electric machine as a motor instead of a generator, and - Use Individual Pitch Control (IPC) to change the pitch of the blades 122 in a portion of the spinning disc to generate lateral movement.

[0093] More precisely, when the sum of the 2 vectors presented below at time t, or the forecast sum in the next few hours, indicates that float 10 risks approaching buoy 20: - the vector representing the wind thrust (estimated using a anemometer, a wind vane, the rotation speed of the rotor, the incidence of each of the blades, knowledge of the surface and the drag coefficients of the emerged part of the hull, the masts and the nacelle, knowledge of the wind forecasts), and - the vector representing the thrust of the current (estimated using knowledge of tidal currents as a function of date and time, a current meter, and knowledge of the surface and drag coefficients of the submerged part of the hull), - or when the redundant inclination measuring means 50 (inclinometers) placed on the mooring lines measure 30 an angle a exceeding a certain threshold (for example 5° or 10° depending on the length of the mooring lines 30 / the nominal distance D).

[0094] Then, the motor mode of the rotor 124 of the wind turbine 100 is activated, if it is connected to the network. Failing this, the prototype can activate bow thrusters 95 and 96 powered by an emergency energy source (batteries or diesel).

[0095] Software is used to integrate all the measurements in order to control the wind turbine 100 in motor mode. According to a diagram developed by the applicant, the software comprises five main blocks, namely: - an estimation block which calculates the variables which cannot be measured (e.g. thrust, hydrodynamic drag, etc.), these variables being used by a controller block, - a supervisory block which defines the operating mode of the system 80 according to the requests of a real-time control and data acquisition (SCADA) system, input data and alarm signals, and which chooses the actuator system to be used, - a detection block which allows the control strategy to be used depending on environmental conditions (wind direction and strength, current strength and direction), - a control block which calculates the longitudinal and lateral force commands to be applied, and - an actuator block converts these force commands into commands of blade pitch 122 and rotor speed 126 for engine mode, or in power for each of the propellers 95 and 96.

[0096] It should be clearly understood that the detailed description of the subject matter of the invention, given solely for the purpose of illustration, does not constitute a limitation in any way, technical equivalents also being included within the scope of the present invention.

[0097] Thus, the floating platform 10 could serve as a support for several wind turbines 100 and not just one.

Claims

Claims Claim 1. Assembly (1) floating in a marine environment for the production of electrical energy using wind comprising: - a floating structure (10) comprising at least one platform (11) provided with a prow (12) to which a buoy (20) is connected using at least one flexible connection of the hawser type (30), - means (40) connected to the buoy (20) for anchoring said floating structure (10) to a seabed (5), - at least one wind turbine (100) mounted on the floating structure (10) and comprising a supporting structure (110) erected substantially vertically on the floating structure (10) and supporting a propeller (120) with several blades (122) connected to a common rotor (126) rotating on itself around an axis of rotation (XX'), and - means (60; 70) for determining at least one of the following parameters among the wind direction, the wind speed, the direction of the sea current and the speed of the sea current, characterized in that it further comprises: - means (128) for motorizing the propeller (120) of the wind turbine (100) in order to rotate its rotor (126) in one direction of rotation or in the opposite direction, - means (50) for measuring the separation distance D between the bow (12) of the floating structure (10) and a vertical rotation axis (ZZ') of the buoy (20), - control means (80) for starting the means (128) for motorizing the propeller (120) and rotating its rotor (126) in order to move the floating structure (10) away from said buoy (20) when said separation distance D measured by the distance sensor (50) is less than a determined threshold. Claim 2. Assembly (1) according to claim 1, characterized in that it further comprises: - means (90) for evaluating the azimuthal position prediction of the floating structure (10) relative to the buoy (20), - control means (80) for starting the motorization means (128) of the propeller (120) and rotating its rotor (126) in order to move the floating structure (10) around said buoy (20) along the axis ZZ' clockwise or counterclockwise according to said azimuthal position prediction of the floating structure (10). Claim 3. Assembly (1) according to claim 2, characterized in that the blades (122) making up the propeller (120) have means (130) for adjusting their pitch as a function of the azimuthal position of each blade (122), so as to create an axial component of thrust of the rotor (126) collinear with the axis (XX') of said rotor (126) and a lateral component of thrust of the rotor (126) perpendicular to the axis (XX') of said rotor (126). Claim 4. Assembly (1) according to any one of the preceding claims, characterized in that the means (128) for motorizing the propeller (120) consist of the motor (128) of the rotor (126) of the wind turbine operating in propulsion mode and connected to a main electrical energy generator (129). Claim 5. Assembly (1) according to any one of the preceding claims, characterized in that it further comprises at least one secondary underwater bow thruster (95; 96) linked to the floating structure (10) and connected to a secondary source of electrical energy (98). Claim 6. Assembly (1) according to claims 4 and 5, characterized in that the main generator of electrical energy (129) and / or the secondary source of electrical energy (98) comprises(s) a battery. Claim 7. Assembly (1) according to claims 4 and 5, characterized in that the main generator of electrical energy (129) and / or the secondary source of energy (98) comprises(s) a fossil fuel engine such as a diesel generator. Claim 8. Assembly (1) according to claim 6 or claim 7, characterized in that the main generator of electrical energy (129) and the secondary source of electrical energy (98) are combined into a single element. Claim 9. Assembly (1) according to any one of the preceding claims, characterized in that the means (50) for measuring the separation distance D comprise a GPS type geolocation system. Claim 10. Assembly (1) according to any one of claims 1 to 8, characterized in that the means (50) for measuring the separation distance D comprise at least one detector (51) mounted on a double-axis connector of each hawser (30) connecting the buoy (20) to the floating structure (10) and measuring a difference in inclination (a) of the hawser considered (30) between a first reference position in which said hawser (30) is completely under tension and a second position in which said hawser (30) is relaxed in order to deduce therefrom a potential reduction in the tension in said hawser and a reduction in the separation distance D. Claim 11. Assembly (1) according to claim 10, characterized in that, the floating structure (10) being connected to the buoy (20) by two mooring lines (30) arranged respectively to port and starboard, and each mooring line (30) comprising two double-axis connectors, the means (50) for measuring the separation distance D comprise a detector (51) per connector axis, i.e. four detectors in total. Claim 12. Assembly (1) according to any one of the preceding claims, characterized in that the control means (80) comprise at least one Proportional Integral Derivative (PID) type module adapting in real time the speed of rotation of the rotor (126) as a function of the measured separation distance D and / or the speed of movement of the floating structure (10) and / or the power supplied to the motorization means (128) so that said floating structure (10) is permanently located at a separation distance D greater than or equal to the determined threshold. Claim 13. Assembly (1) according to claims 11 and 12, characterized in that the control means (80) comprise two PID modules, one per mooring line (30), collaborating with each other to control the speed of rotation of the rotor (126) and the pitch of the blades (122) of the propeller (120). Claim 14. Assembly (1) according to any one of the preceding claims, characterized in that the buoy (20) is statically anchored to the seabed (5) using three flexible anchoring lines (40) angularly spaced from each other by 120° along a horizontal projection plane of said anchoring lines. Claim 15. Assembly (1) according to any one of the preceding claims, characterized in that the means (60) for determining the direction of the wind comprise at least one of the following devices chosen from an anemometer or a weather vane. Claim 16. Assembly (1) according to any one of the preceding claims, characterized in that the means (70) for determining the direction and speed of the sea current are based on knowledge of the tidal currents as a function of the date and time, the use of a current meter, and knowledge of the surface and drag coefficients of the submerged part of the floating structure. Claim 17. Assembly (1) according to any one of the preceding claims, characterized in that the separation distance threshold D is between approximately 80% and 90% of the nominal distance for which the connecting line (30) of the floating structure (10) to the buoy (20) is taut.

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