This invention relates to the control of a plurality of fluid-driven turbines via a single fully integrated and submersible control unit. Continual drive to lower the cost of tidal energy has seen all aspects of tidal turbines and ancillary assets targeted to realise these reductions. A major development has been to resolve challenges surrounding reliability and expense of bespoke large single rotor devices. This has led to several developers exploring the potential of devices consisting of multiple rotors mounted to the seafloor.

Any tidal device generating electricity requires sophisticated control to ensure optimised generation, power to network injection requirements and to ensure safety procedures are executed to a certain standard. Seafloor mounted devices have to date been unable to achieve this with turbine controls remaining an integral part of the individual turbine nacelles owing, in a large part, to issues of space available on seafloor mounted structures and also flow characteristics. Therefore, controls have been continued to be placed in individual nacelles, which naturally requires recovery of all nacelles to maintain all failure prone assets. This necessitates the dismantling of each turbine to access and perform necessary maintenance, which is a labour intensive and time costly process and is carried out ashore to ensure the other units housed in the nacelle are kept in a satisfactory condition resulting in large operational and maintenance costs over a 20- 25 year lifetime of the turbine devices. In addition, there are also problems with nacelle-mounted control. Owing to the rotation of devices, the nacelles are prone to water ingress through seals thereby causing humidity which has been seen to impact and cause faults in nacelle-mounted control systems.

It is this area that the present invention targets. It has been identified that accessibility of controls for a plethora of turbines will contribute significantly to cost reductions in relation to capital expenditure but more extensively operational expenditure of submersible tidal devices. The invention provides a highly advantageous commercial position over other existing submersible multi-rotor devices providing lower levelized cost of energy to be realised and pushing technology closer to commercialisation and inter-technological competitiveness.

This intensive nature of repairs associated with submersed, nacelle integrated control units is not a new problem within the sector. One solution has involved a control module which enables the module to be replaced in a simple switch-in switch-out procedure. Although an improvement such a solution still requires the dismantling of each turbine which cannot be carried out in the field and hence is still a time costly procedure.

The present invention eliminates issues with labour intensive accessibility as well as inability to perform routine maintenance in the field. Ability to easily access control units will enable rapid response in-the-field maintenance enabling reduced down time. According to a first aspect of the present invention, there is provided apparatus comprising a submersible control hub connectable to a plurality of power generating devices, the control hub including power control equipment, the power control equipment having a plurality of power input interfaces and a single power output interface.

According to a second aspect of the present invention, there is provided a method of controlling a plurality of submerged power generating devices, the method comprising a control hub receiving the power generated by way of a plurality of power input interfaces corresponding to the plurality of power generating devices, and transforming the power received by the plurality of power input interfaces to a single power output interface.

Owing to these aspects, the control hub enables the independent and simultaneous control of a plurality of fluid-driven turbines to reduce the cost, weight and size of the turbines as well as enabling significant operational expenditure reductions compared with controls located within individual turbines. According to a third aspect of the invention, there is provided apparatus comprising a submersed support structure including a plurality of power generating devices with the control hub connected thereto. According to a fourth aspect of the invention, there is provided a method of readily removing and/or replacing, from an offshore location, the control hub through a column of water from a submersed support structure including a plurality of power generating devices A submersed support structure with a plurality of power generating devices enables removal of control equipment from induvial turbine nacelles and put into the surrounding device structure. This allows reductions in cost, weight and size of the power generating devices whilst enabling all power generation controls to be maintained from a single location eliminating the costly and time-consuming requirement to open individual turbine nacelles.

The control hub is, preferably, integrated into a multi-turbine device and is independent of the multi-turbine device so that it can be utilised on any semi-submersible or bottom mounted multi-turbine platform. Alternatively, it can be its own induvial self-contained unit enabling multiple turbines/devices/structures to be controlled from a submersed location preventing interaction with highly dynamic forcing at the sea surface. Advantageously, a power connection bridle is mounted to the multi-turbine device and is used to transmit power and data to/from the control hub and on to shore via a single export cable. The power connection bridle contains one half of a wet mate connector and switch gear to isolate the control hub when required.

Multiple control hub units can be connected to a single power connection bridle enabling many turbines to be connected to a single export cable. In order that the present invention can be clearly and completely disclosed, reference will now be made, by way of example only, to the accompanying drawings, in which:-

Figure 1 is a perspective view of a power-generating assembly comprising a plurality of power generating devices having a control hub mounted thereto, Figure 2 is a view similar to Figure 1, but with the control hub shown disconnected from the assembly,

Figure 3 shows a high-level system architecture of the assembly of Figure 1,

Figure 4 shows a more detailed system architecture for the assembly of Figure 1. Figure 5 shows the system architecture for a deck/shore connection of the control hub, Figure 6 shows an alternative high-level system architecture of the assembly of Figure 1, and

Figure 7 shows a more detailed system architecture for the assembly of Figure 6. Referring to Figures 1 and 2, a submersible control hub 2 is mountable to an assembly 4 comprising a plurality of power generating devices in the form of water-driven rotary turbine devices 6. The assembly 4 is fixed to the seafloor or other ground surface of a body of water. The control hub 2 is advantageously mounted to a wing-like structure of the assembly 4 as this location enables all power control equipment (drives, inverters etc.) that would, conventionally, be included in each nacelle 8 of each turbine device 6 to be removed and placed in a single location on the assembly 4. Logistically, this enables each turbine 6 to have maintenance performed on it at the same time. It also enables use of mutual electrical components to control multiple turbines reducing cost. In addition, the arrangement shown in Figures 1 and 2 reduces the size and weight of the turbines 6 thus providing further cost savings in relation to turbine manufacture and, in the event of turbine replacement, less components are required to be swapped out.

Significant cost reductions are therefore accessible through the single control hub unit 2, which is able of controlling multiple turbines 6. The enablement of multiple turbines to have maintenance performed from a single location also prevents the need for specialist equipment to take apart turbines to enable such maintenance.

The control hub 2 contains all the power control equipment necessary so that, in the event of any issue, there is no requirement to open up individual turbine devices 6. Additionally, should a significant problem arise with the control hub 2 the entire unit can be changed out rapidly offshore with a single lift, which is also useful for upgrades and servicing. This gives significant advantages over individual control within each turbine. The control hub 2 is set down into the middle region of the upper surface of the wing like structure which enables unobstructed access from above. Referring specifically to Figure 2, the process of installation the control hub 2 is depicted. This operation can be performed offshore enabling rapid exchange of nearly all power control equipment for multiple turbine devices 6. This provides a significant time/cost advantage over traditional methods for accessing and entering multiple individual turbine devices.

Figures 1 and 2 show the wing-like structure of the assembly 4 in a near-connected state in order to show a wet-mate connection means comprising a male side 10 protruding from the underside of the wing-like structure and a female side 12 at the top end region of a main substantially vertical support strut of the assembly 4. The wet mate connection means enables a connection for electrical power and/or data to be transferred to a power connection bridle 14 by way of which generated power from the turbine devices 6 is transmitted to the control hub 2 and then to the power connection bridle 14 via the wet mate connection means.

Referring to Figure 3, a high-level overview of the system architecture is displayed. The item boundaries, location, comprising components and connection interface are shown for the control hub 2 and the power connection bridle 14. Each turbine device 6 is preferably a multi-axis tidal-driven turbine device and includes a generator G having an electrical connection with the control hub 2 by way of an input interface 16, there being a corresponding input interface 16 of each turbine device 6. The control hub includes power control equipment in the form of a plurality of variable frequency drives 18 connected to corresponding input interfaces 16, an active front end (AFE) variable frequency drive 20 and a three-phase transformer 22 to change the voltage from the generators G to a level suitable for onward transmission to a single output interface 24. Downstream of the output interface 24 is a power connection bridle 26 including switching devices 28 in order to be able to electrically disconnect the control hub 2. The turbine devices 6, the control hub 2 and the power connection bridle 26 are all submerged below the surface of a body of water. The single output from the power connection bridle provides for a connection to a power grid 30 on dry ground. The control hub 2 does not have predefined numbers of turbine devices 6 it can control or operate, and singular or multiple turbine devices could be controlled.

Referring to Figure 4, a more detailed system architecture is shown for the control hub 2. It can be seen that in addition to the generator G, each turbine device 6 includes a power supply unit PSU, and respective motors M for a bilge pump and an automatic braking system. These three individual components are electrically connected by way of further switching devices 32 to an output 34 which in turn is connected by way of a dry mate connection cable to one of the plurality of input interfaces 16 of the control hub 2. Downstream of the input interface 16 are additional switching devices 36. The control hub 2 has its own power supply unit 38 connected to one of the additional switching devices 36. It will also be seen that a brake chopper 40 is electrically connected to the variable frequency drives 18 and which is essentially an electrical switch that limits the DC bus voltage by switching braking energy to a brake resistor 42 where the braking energy is converted to heat. The braking chopper 40 is automatically activated when the actual DC bus voltage exceeds a specified level depending on the nominal voltage of the variable-frequency drives 18. The active front end variable frequency drive 20 is also connected to one of the additional switching devices 36. Each of the additional switching devices 36 is connected to not only the three-phase transformer 22 but also to, in parallel with the connection to the transformer 22, a deck/shore monitoring connection 37. In addition, these parallel connections include respective switches with an interlock mechanism therebetween which forms a circuit breaker, whereby if the current is interrupted both switches are activated.

Referring to Figure 5, the deck/shore connection 37 provides power for a suite of control hub sensors 44 which acquire monitoring data from a second suite of sensors

46 located in each turbine device 6. The control hub 2 is shown to include its own uninterruptable power supply UPS connected to a battery 48 and a plurality of power supply units PSU corresponding to the number of turbine devices 6.

Referring to Figures 6 and 7 an alternative system architecture from Figures 3 and 4 is shown making use of a plurality of active front end variable frequency drives 20 rather than the multi-axis variable frequency drive 20 used in Figures 3 and 4. Multi axis variable frequency drives can be cost prohibitive for lower power situations, hence a plurality of variable frequency drives 20 can be an attractive alternative. Additionally, there are a corresponding plurality of brake choppers 40 and brake resistors 42 connected to each of the plurality of active front end variable frequency drives 20.

The provision of the power control equipment within the control hub 2 leaves few electrical components to be present inside the turbine devices. Centralizing high risk electrical components into the control hub 2 makes for a more efficient accessibility as well as the actual servicing and maintenance to take place. Moreover, removal of the electrical components to the control hub with no moving parts or rotating seals provides extremely effective mitigation against the effect of humidity damage of the controls.