Operating wind turbine in microgrid

Abstract

There is described a method of operating a plurality of wind turbines (2a, 2b, 2c) connected to a local grid (4) but isolated from any utility grid (5) providing power, the method comprising: monitoring (6a, 6b, 6c) the wind turbines (2a, 2b, 2c) with respect to at least one temporary stop requirement; selecting one or more of the wind turbines (2a, 2b, 2c) on the basis of the proximity to the respective temporary stop requirements, in particular the lower the proximity, the more urgent the temporary stop; entering a non-idle state by at least one selected wind turbine (2a, 2b) or by at least one non-selected wind turbine, thereby supplying power to the local grid.

Description

Technical Field

[0001] The present invention relates to a method for operating a plurality of wind turbines, which are connected to a local power grid but isolated from any public power grid supplying power, and the present invention further relates to a corresponding arrangement device. Furthermore, the present invention relates to a system comprising at least two wind turbines and an arrangement device. Background Art

[0002] An example of an isolated local power grid can be an offshore wind farm when the electrical connection to the onshore power grid is interrupted. When the offshore power grid is started, a plurality of wind turbines will generate electrical power (active or reactive power) in order to help support consumers in a small electrical local power grid, such as other wind turbines, even though the wind speed may allow the turbines to generate electrical power. A balance between electrical power output and power consumption must always be maintained in the electrical local power grid. Otherwise, the frequency will either increase or decrease until the local power grid collapses.

[0003] There may be a need for a method for operating a plurality of wind turbines, which are connected to a local power grid but isolated from any public power grid supplying power, wherein the stability of the local power grid can be improved, and wherein the performance of the local power grid can be improved, such that in particular the local power grid can be operated efficiently, and in particular a required number of wind turbines can be started (which are even in an isolated state disconnected from any energy-supplying public power grid) and / or it is possible to also support idling wind turbines with respect to a temporary stop. Summary of the Invention

[0004] This need can be met by the subject matter of the independent claims. Advantageous embodiments of the present invention are described by the dependent claims.

[0005] According to an embodiment of the present invention, there is provided a method for operating a plurality of wind turbines, which are connected to a local power grid but isolated from any public power grid supplying power, the method comprising monitoring the wind turbines with respect to at least one temporary stop requirement; selecting one or more of the wind turbines based on the proximity to a respective temporary stop, in particular the lower the proximity, the more urgent the temporary stop; entering a non-idling state by at least one selected wind turbine or by at least one non-selected wind turbine, thereby supplying power to the local power grid.

[0006] The proximity can be determined based on at least one of the following or based on at least one of the following: the remaining duration until the next temporary stop requiring at least one part, and / or the time elapsed since the previous temporary stop of at least one part was executed.

[0007] Proximity can be expressed in different units or, for example, as a proximity level or a proximity score without any physical units. In one example, proximity is expressed in units of time. Proximity can be predicted from monitoring data, thereby also considering, for example, the expected service life or the expected operating capacity of one or more of the parts of a wind turbine. For example, when each of a plurality of wind turbines requires a next temporary stop, it can be predicted later from historical operating data. Proximity can also be based on a deterministic temporary stop period, such as caused by lubrication of a part. Determining proximity can further allow obtaining a ranking of wind turbines with respect to the urgency of the required temporary stop.

[0008] The plurality of wind turbines can include two or more wind turbines, in particular a subset of a wind farm or an entire wind farm. Each of the plurality of wind turbines is directly or indirectly connected to each other within a local power grid. The local power grid can operate, for example, in the medium voltage range, such as, for example, between 20 kV and 200 kV. The local power grid is disconnected from any power-supplying public power grid such that the local power grid does not receive any electrical power from any power-supplying public power grid. In this sense, the local power grid is isolated or standalone.

[0009] The method can be implemented in software and / or hardware and can be executed by one or more units, which, for example, relate to one or more of the plurality of wind turbines, such as a control unit or a control section having processing capabilities for performing at least one selection step. The control section can also be communicatively connected to the wind turbines in order to send corresponding operating control signals, which are used to command the wind turbines to either enter an idling state or a non-idling state.

[0010] The control section can also be communicatively connected to the wind turbines in order to receive monitoring data regarding the corresponding temporary stop requirements of the respective wind turbines. Thus, monitoring the wind turbines can involve receiving measurement data and / or configuration data and / or operating state data from one or more (in particular all) of the plurality of wind turbines. The monitoring data can include sensor data and / or historical operating data and / or operating state data of the respective wind turbines. The monitoring data can further include one or more thresholds, which define operating limits regarding remaining operating time, elapsed operating time, elapsed operating capacity, remaining operating capacity, etc.

[0011] The control unit can process the monitoring data in order to obtain a proximity, in particular a proximity level (explained in detail below), which indicates how close the respective wind turbine is to the respective temporary stop requirement (“distance”). The proximity can be expressed in different units or, for example, as a proximity level or a proximity score without any physical unit. In one example, the proximity is expressed in units of time. The proximity can be predicted from the monitoring data, thus also taking into account, for example, the expected service life or the expected operating energy of one or more of the parts of the wind turbine. For example, when each of a plurality of wind turbines requires the next temporary stop, it can be predicted later from historical operating data. The proximity can also be based on a deterministic temporary stop period, for example caused by the lubrication of parts. Determining the proximity can further allow obtaining a ranking of the wind turbines with respect to the urgency of the required temporary stop.

[0012] For example, a temporary stop can be required due to a regular or conditional maintenance service to be performed at at least one part of the wind turbine.

[0013] The selection step can either select those wind turbines that are to enter a non-idling state or those wind turbines that are to enter an idling state based on the proximity. In one embodiment, those wind turbines are selected based on the proximity to the respective temporary stop requirement to enter a non-idling state in order to provide or supply electrical power to the local power grid. In particular, those wind turbines can be selected to enter a non-idling state for which the temporary stop is the furthest away in the future or at least is expected to be the furthest away in the future. Thus, those selected wind turbines are expected not to require a temporary stop in the future at least within a pre-determined time range, such that they can supply electrical energy to the local power grid. In this embodiment, the non-selected wind turbines are to enter an idling state or remain or stay in an idling state because for those non-selected wind turbines, the temporary stop can be more urgent or can be required in the near future. When the selected wind turbine or a plurality of the selected wind turbines enter a non-idling state, it can involve starting those wind turbines in order to, for example, direct the rotor into the wind in order to generate electrical energy output to the local power grid. The idling wind turbines can then consume or receive some of the power provided by the non-idling wind turbines. Due to the reasonable selection of the wind turbines, it can ensure that the local power grid has a relatively stable voltage and / or frequency, such that a local power grid collapse can be avoided.

[0014] Accordingly, embodiments of the present invention address the selection of wind turbines for providing electrical power to a microgrid or a local grid. A local grid or a microgrid may be characterized by being supplied by several energy sources, and it always needs to maintain a balance between energy production and consumption. If that balance is not achieved, the local grid or the microgrid may collapse due to frequency runaway, which can be avoided according to embodiments of the present invention.

[0015] A wind turbine may periodically need to stop (e.g., for lubrication of the pitch system (providing lubricant)) or untwist the tower cables. Pitch lubrication is an example of an operation where the wind turbine stops to take action to prevent unnecessary wear of the pitch bearings, and untwisting of the power cables is an example of an operation where the turbine stops in order to perform an action to prevent mechanical parts from exceeding their operating range. Those types of stops are also referred to as periodic service stops.

[0016] The proximity to the corresponding temporary stop requirements can comply with the periodic service stops that need to be performed by different wind turbines. For example, if the next service stop of a particular wind turbine is relatively soon, the proximity will have a low value, for example. In other cases, when the periodic stop is at a point relatively far in the future, the proximity can have a relatively high value for this wind turbine. In other embodiments, the proximity can comply with one or more other temporary stop requirements, which can be measured in different physical quantities. The proximity can combine the different temporary stop requirements of different parts or portions of the wind turbine into one quantity (in particular, a proximity score or a proximity level).

[0017] According to embodiments of the present invention, when a wind turbine stops for a periodic service stop, which requires stopping the electrical power supply to the local grid, the conventionally observed risks can be avoided. In this conventional scenario, the balance between power production and power consumption within the microgrid and the local grid can no longer be maintained by the remaining power-generating wind turbines in the island.

[0018] According to embodiments of the present invention. The method further includes at least one of the following: operating non-selected wind turbines (if any) in an idle state so as not to supply power to the local grid; and receiving power from the local grid at at least one of the idle wind turbines.

[0019] Non-selected wind turbines may be commanded to operate in an idle state because they may be known not to be reliable power-generating wind turbines, because they may require relatively urgent temporary stops (at least compared to the selected wind turbines that enter a non-idle state). The idle wind turbines may then receive power from the local grid in order to actually allow the execution of the required temporary stops and / or in order to ensure reliable and safe operation even in the idle state.

[0020] According to an embodiment of the invention, selecting one or more of the wind turbines comprises selecting one or more of the wind turbines having the greatest proximity to a corresponding temporary stop requirement or greater than a threshold, the threshold depending in particular on the wind speed and / or the total number of wind turbines.

[0021] When the proximity is relatively large or greater than the threshold, the urgency for a temporary stop can be relatively low. Thus, making the selection based on a relatively large or greater-than-threshold proximity can ensure that the selected wind turbines are actually capable of generating power for a substantial time period in order to supply power to the local grid, thereby improving the stability of the local grid.

[0022] According to an embodiment of the invention, selecting one or more of the wind turbines comprises selecting some of one or more of the wind turbines such that the electrical power output supplied by the non-idling wind turbines and the electrical power consumption by the idling wind turbines are substantially balanced within the local grid, wherein in particular the minimum number of wind turbines supplying power to the local grid may depend on the wind speed.

[0023] The above-mentioned threshold may also depend on the power requirements within the local grid in an embodiment, and may in particular depend on the total number of wind turbines, and may also depend on the wind speed. For example, a number of wind turbines may be selected to enter a non-idling state in order to generate electrical power such that the generated electrical power is sufficient, depending on the actual wind speed, to meet the power requirements of the idling wind turbines.

[0024] The selection may be updated in a regular or periodic or continuous manner. The method may also involve, for example, monitoring the total power generated and supplied to the microgrid, and also monitoring the total power consumed by the idling wind turbines and / or also the non-idling wind turbines. In this regard, the wind turbines may also provide measurement data regarding power output or power consumption to a control section which, for example, performs the selection step and also sends control signals to the wind turbines.

[0025] According to an embodiment of the invention, the method further comprises, for each of the wind turbines, determining a proximity level and / or a proximity score based on the corresponding temporary stop requirement; selecting one or more of the wind turbines based on the proximity level, wherein the proximity level is a binary quantity or is quantified with more than two values, in particular in a continuous manner.

[0026] The proximity level and / or proximity score can indicate how close the respective wind turbine is to a requirement for a temporary stop. The level or score can be provided in physical units, such as time, or can be provided as a quantity without units. In a very simple embodiment, the proximity level can have only two possible values, which can simplify the method. However, it can be advantageous to determine a proximity level with more than two possible values in order to have more flexibility and prioritization regarding the number of wind turbines that can be selected. The proximity level can allow for the determination of a ranking order of wind turbines with respect to service maintenance requirements.

[0027] According to an embodiment of the invention, the proximity score obeys the weights of multiple parts or wind turbines with respect to predictability and / or importance and / or vulnerability.

[0028] The weights can allow for prioritizing one part or the service requirements of one part over another part. Additionally, some of the temporary stops can be less important and / or less predictable than other temporary stops. This can also be captured within the proximity score or proximity level. Thus, high flexibility can be provided and multiple temporary stops of multiple parts of the wind turbine can be obeyed.

[0029] According to an embodiment of the invention, the method further comprises at least one of the following: establishing a ranking order of wind turbines based on the proximity level of the wind turbines; selecting wind turbines to enter a non-idling state based on the ranking order; selecting wind turbines to enter an idling state and / or perform maintenance based on the ranking order.

[0030] The ranking order can advantageously be used to select those wind turbines that should enter a non-idling state and / or to select those wind turbines to be put into an idling state. For example, when the ranking order is from a low proximity score to a high proximity score, the wind turbines sorted at the end part or (e.g.) the second half of the sorted list can be selected to enter a non-idling state, and the wind turbines in the start part can be selected to enter an idling state. Thus, the selection can be simplified.

[0031] According to an embodiment of the invention, the proximity level of the temporary stop requirement is determined based on at least one of the following or based on at least one of the following: the remaining duration until the next temporary stop that requires at least one part; the time elapsed since the previous temporary stop of at least one part was performed; the remaining load level that at least one part will be able to experience in the future; the cumulative load level that at least one part has experienced (in the past); the number of degrees of rotation of the nacelle rotation since the previous cable-unwinding operation; the number of degrees of rotation that the nacelle will be able to rotate in the future until the next cable-unwinding operation is required, wherein the proximity level in particular obeys at least one operating threshold, in particular an operating time threshold and / or a wear level threshold.

[0032] Thus, high flexibility is provided for determining the proximity level. Other criteria may also be adhered to.

[0033] Monitoring a wind turbine with respect to at least one temporary stop requirement according to an embodiment of the invention comprises at least one of the following; receiving measurement data regarding the operating state and / or performance and / or service life of at least one wind turbine part; receiving at least one operating threshold regarding the operation of the part; determining a proximity level based on the measurement data and / or the operating threshold.

[0034] The measurement data may be provided, for example, by wind turbine sensors mounted at one or more locations at one or more parts of the wind turbine. The operating threshold may be obtained, for example, from an electronic storage (which is included in the wind turbine), or may be obtained from a central storage which holds configuration and design data for the wind turbine. Thus, the specific configuration of the wind turbine can be adhered to, and in particular the operating threshold can be met.

[0035] A temporary stop according to an embodiment of the invention comprises at least one of the following: lubricating at least one part of the wind turbine, at least one part being in particular a gear system and / or a pitch system and / or a yaw system; untwisting a power cable, in particular a power cable arranged in the wind turbine tower; stopping the wind turbine; performing a temporary stop on at least one part of the wind turbine.

[0036] A temporary stop according to an embodiment of the invention comprises at least a temperature measurement of a part or a fluid in the turbine, in particular the hydraulic oil temperature, which needs to be within an operating range defined by a higher temperature value and a lower temperature value. The distance is the minimum absolute difference between the measured or estimated temperature and the boundary of the operating range.

[0037] The method according to an embodiment of the invention further comprises at least one of the following, in particular if the local power grid is electrically stable: performing a temporary stop on at least one idling wind turbine, in particular giving priority to those idling wind turbines with the lowest proximity level according to a ranking order; updating the proximity level of the idling wind turbines after a temporary stop has been performed, in particular updating the ranking of the wind turbines in a sorted list, wherein performing a temporary stop on a wind turbine in particular increases the proximity level, thus reducing the urgency level of the temporary stop for the corresponding wind turbine.

[0038] Accordingly, the temporary stops carried out conventionally are supported by embodiments of the present invention. When a temporary stop is actually carried out for one or more of the idling wind turbines, it can be prepared to supply power to the local power grid after having been started. For example, the selection step can be updated when any temporary stop of any of the idling wind turbines is carried out. As a result, after the temporary stop is completed, the previous idling wind turbine will now be selected as the wind turbine that should enter the non-idling state in order to supply electrical power to the local power grid. At the same time, one of the previously selected wind turbines (which has actually supplied electrical power to the local power grid) can have a proximity score or level that is lower than previously, and this (these) wind turbine(s) can be selected to enter the idling state afterwards.

[0039] Accordingly, the wind turbines that are commanded to generate electrical power and supply it to the local power grid can be determined dynamically, such that the electrical stability of the local power grid can be ensured.

[0040] According to an embodiment of the present invention, the method further comprises at least one of the following, in particular in a periodic manner: updating the proximity level of the wind turbines; updating the selection of the wind turbines to enter the non-idling state; supplying power to the local power grid by the wind turbines according to the updated selection and / or the updated proximity level; performing a temporary stop of the idling wind turbines based on the updated proximity level.

[0041] Accordingly, the ability of the wind turbines to supply reliable power to the local power grid can be monitored or observed or detected.

[0042] Entering the non-idling state can involve operating the yaw system and / or the pitch system in order to direct the wind turbine towards the wind, and also appropriately adjusting the pitch angle of the rotor blades in order to effectively capture the wind power. The local power grid to which the wind turbine is connected can be in an idling state in the initial state (for example) or some wind turbines can already be in the non-idling state of supplying power to the grid. Afterwards, a dynamic selection of the wind turbines based on the proximity obtained from the temporary stop requirements can be carried out.

[0043] According to an embodiment of the present invention, the plurality of wind turbines comprises one of the following: two or more wind turbines, a subset of the wind farm wind turbines, all the wind turbines of a wind farm; and / or wherein the idling state of the wind turbine comprises at least one of the following: the wind turbine is stopped, the rotor rotates slowly, the wind turbine does not supply power to the local power grid; and / or the proximity level indicates at least one of the following: the "distance" to the next temporary stop, the emergency level for performing a temporary stop. Accordingly, the method can be flexibly applied to any group of wind turbines.

[0044] It should be understood that features disclosed, explained, provided or employed independently or in any combination in a method of operating a plurality of wind turbines connected to a local power grid but isolated from any public power grid supplying power can also be employed or provided independently or in any combination in an arrangement device for operating a plurality of wind turbines according to an embodiment of the present invention, and vice versa.

[0045] According to an embodiment of the present invention, there is provided an arrangement device for operating a plurality of wind turbines, which is connected to a local power grid but disconnected from the public power grid. The arrangement device includes: an input port for receiving monitoring data of the wind turbines regarding at least one temporary stop requirement; a processor adapted to select one or more of the wind turbines based on the proximity to the corresponding temporary stop requirement; and an output port for supplying a control signal to at least one selected wind turbine or to at least one non - selected wind turbine to enter a non - idling state so as to supply power to the local power grid.

[0046] The arrangement device can be implemented in software and / or hardware. The arrangement device can in particular be part of a control unit, in particular an electric field controller or a controller for at least controlling a subset of the wind turbines of a wind farm. The monitoring data can be received from the wind turbines, and the control signal can also be supplied to the wind turbines. The wind turbines can either be capable of calculating the proximity or proximity level by themselves or can provide raw data to the control unit, which by itself can calculate the corresponding proximity, in particular the proximity level, from the monitoring data and potentially from other configuration data or operating limit data.

[0047] According to an embodiment, there is provided a system including: at least two wind turbines connected to a local isolated power grid (in particular a wind farm); and an arrangement device according to the previous embodiment communicatively connected to the wind turbines.

[0048] The aspects defined above and further aspects of the present invention are apparent from and will be elucidated with reference to the examples of embodiments to be described hereinafter. The invention will be described in more detail hereinafter with reference to the examples of embodiments, but the invention is not limited to the examples of embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Embodiments of the present invention are now described with reference to the accompanying drawings. The present invention is not limited to the embodiments shown or described.

[0050] Figure 1 A system according to an embodiment of the present invention is schematically shown.

[0051] Figure 2 An example of a method schematic diagram according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0052] In Figure 1 The system 1 schematically shown in includes at least two wind turbines 2a, 2b, 2c, which can potentially form a wind farm or a subset of the wind turbines of a wind farm with other wind turbines. In addition, the system 1 includes an arrangement device 3 according to an embodiment of the present invention for operating a plurality of wind turbines 2a, 2b, 2c, which are connected to each other in a local power grid 4 but disconnected from the public power grid 5. Thus, the wind turbines 2a, 2b, 2c are isolated from the public power grid 5 and thus form an isolated body. The local power grid 4 may include one or more circuit breakers (which may allow different wind turbines 2a, 2b, 2c to be connected to each other), and may include electronic components such as cables, capacitors, resistors, circuit breakers, transformers, and the like.

[0053] The arrangement device 3 includes input / output ports 5a, 5b, 5c for receiving monitoring data 6a, 6b, 6c regarding at least one temporary stop requirement from the respective wind turbines 2a, 2b, 3c.

[0054] In addition, the arrangement device 3 includes a processor not shown in detail, which is adapted to select one or more of the wind turbines based on the proximity to the respective temporary stop requirements.

[0055] Via the input / output ports 5a, 5b, 5c, the arrangement device 3 supplies the respective control signals 7a, 7b, 7c to the respective wind turbines to command the wind turbines to enter a non-idling state or an idling state. The arrangement device selects one or more wind turbines to enter a non-idling state and sends the respective control signals to enter a non-idling state. For the other wind turbines, the arrangement device 3 may provide the respective control signals to enter or remain in an idling state.

[0056] The arrangement device 3 is capable of performing a method of operating a plurality of wind turbines according to an embodiment of the present invention together with the wind turbines 2a, 2b, 2c. Thus, the method includes monitoring the wind turbines 2a, 2b, 2c regarding at least one temporary stop requirement, wherein in the illustrated embodiment, the monitoring data 6a, 6b, 6c is obtained at the arrangement device 3 from the respective wind turbines 2a, 2b, 2c. Thereafter, the arrangement device 3 selects one or more of the wind turbines based on the proximity to the respective temporary stop requirements (in particular based on the monitoring data 6a, 6b, 6c obtained). When receiving the control signals 7a, 7b, 7c supplied from the arrangement device 3, the selected wind turbines or the non-selected wind turbines then enter a non-idling state, thereby supplying power to the local power grid. Supplying power can be understood as (either or) both the active power for frequency support and / or the reactive power for boosting the voltage or supporting the existing voltage in the local power grid.

[0057] According to one embodiment, for example, wind turbines 2a and 2b are selected to enter a non-idling state in order to supply power 8a, 8b to a microgrid or a local grid 4. Wind turbine 2c is not selected and instead remains in an idling state. In order to remain in the idling state, however, wind turbine 2c also requires electrical power 9c, which it receives from the local grid 4 that is powered by wind turbines 2a, 2b.

[0058] In the example 2 shown, the number of wind turbines is selected such that the electrical power output supplied by the non-idling wind turbines 2a, 2b and the electrical power consumption of the idling wind turbine 2c are substantially balanced within the local grid 4.

[0059] The arrangement device 3 can determine a proximity level or a proximity score for different wind turbines 2a, 2b, 2c based on the received monitoring data 6a, 6b, 6c. Using the proximity level, the wind turbines 2a, 2b, 2c can be set in a ranking order, and the selection can be based on the ranking order. The wind turbine 2c in the idling state can then receive a temporary stop, such as lubrication of the gear system or the pitch system or the yaw system or a cable uncoiling operation of the power cable

[0060] After that, the monitoring data is updated, and additionally the selection of the wind turbines can be updated to define and command those wind turbines with a relatively high proximity score to enter or remain in a non-idling state in order to supply electrical energy and power to the local grid 4.

[0061] According to an embodiment of the present invention, the wind turbines calculate how "far" they are from needing to stop for one of the reasons mentioned above, i.e., to perform a temporary stop (especially involving a periodic service stop). The measurement of how far they are from needing to stop can depend on a threshold of an operating limit that needs to be avoided. Such a threshold can be, for example, an estimated value in terms of time (hours, minutes) or an estimated value in terms of the number of rotations before cable uncoiling is required.

[0062] At the site level, the electric field controller (an example of an embodiment of the arrangement device 3) can select the wind turbines that are farthest from having to undergo periodic service stops (to reduce the risk of one of them impacting the operation of the small grid). Additionally, when the operation of the small grid is stable (electrically), the electric field controller or the arrangement device 3 can instruct the idling turbines to increase their distance to the service stop condition. Thus, these wind turbines can actually perform a temporary stop action. If one of the wind turbines that is not idling (i.e., generating power and supplying it to the local grid 4) is approaching the stop condition, the electric field controller or the arrangement device 3 can start the idling turbine that has the maximum distance to its stop condition. Once that turbine has started, the turbines with a shorter distance to the stop condition can stop and thus enter the idling state. The active power used to increase the distance of the idling turbines to the service stop is free because it is provided by the operating wind turbines, i.e., the non-idling wind turbines. Increasing the distance to the service stop when in the isolated mode can tend to have a positive effect on the energy generated when connected to the grid. The reason may be that when connected to the local grid 4 that allows it to generate more active power, the distance to the service stop can reduce the number of service stops that the turbine has to make.

[0063] The number of turbines required to maintain power isolation (especially those in the non-idling state) can likely depend on the wind speed at the site, and the number of turbines that can increase the distance to the service stop will also likely be wind speed-dependent.

[0064] Embodiments of the present invention provide a positive effect in continuously monitoring the distance of the operating turbines to the service stop, and when they are approaching, the idling turbine with the maximum distance to the service stop can be started. Additionally, it can increase / optimize the distance of the idling turbines to the service stop. Thus, the risk of the operating turbines performing unwanted service stops can be reduced or even avoided.

[0065] Figure 2 Figure 10 shows a schematic diagram of a method according to an embodiment of the present invention. The method starts at start block 11. In method step 12, N turbines (N is an integer) are selected that have the maximum distance to the service stop. In method step 13, there is a waiting period to allow the local grid 4 to be stable electrically. During this waiting period, the selected N turbines (or at least one turbine) supply power to the local grid 4.

[0066] From method step 13, the method branches into two branches 14 and 15. In branch 14, in evaluation block 16, it checks whether a running turbine (i.e., a non-idling wind turbine) is too close to a service stop. If the check is confirmed, it transitions to method step 17, where a wind turbine in idling with the maximum distance to the service stop is started in method step 17. In the next method step 18, once the turbine is started, the turbine with the shortest distance stops and it is instructed to increase the distance to the service stop (e.g., by performing a temporary stop action). From method step 18, it transitions back to evaluation block 16.

[0067] In the second branch 15, evaluation block 19 evaluates whether an idling wind turbine is close to a service stop. If this is the case, it transitions to method block 20. In method step 20, x (where x is an integer) wind turbines with the minimum distance to the service stop are instructed to increase the distance to the service stop, e.g., by performing one or more temporary stop operations. In method step 20, it transitions back to evaluation block 19.

[0068] Figure 2 The method schematic diagram 10 shown is only an example of a specific embodiment of the present invention. According to other embodiments, Figure 2 One or more of the method steps shown may be omitted.

[0069] It should be noted that the term "comprising" does not exclude other elements or steps, and "a" or "an" does not exclude a plurality. Additionally, elements described in connection with different embodiments may be combined. It should also be noted that the reference signs in the claims should not be construed as limiting the scope of the claims.

[0070] It should be noted that the term "comprising" does not exclude other elements or steps, and "a" or "an" does not exclude a plurality. Additionally, elements described in connection with different embodiments may be combined. It should also be noted that the reference signs in the claims should not be construed as limiting the scope of the claims.

Claims

1. A method of operating a plurality of wind turbines (2a, 2b, 2c), the plurality of wind turbines (2a, 2b, 2c) being connected to a local power grid (4) but isolated from any power - supplying public power grid (5), the method comprising: monitoring (6a, 6b, 6c) the wind turbines (2a, 2b, 2c) with respect to at least one temporary stop requirement; selecting one or more of the wind turbines (2a, 2b, 2c) based on proximity to a respective temporary stop requirement, in particular the lower the proximity, the more urgent the temporary stop, wherein the proximity is determined based on at least one of the following or based on at least one of the following: the remaining duration until the next temporary stop requiring at least one part, and / or the time elapsed since the previous temporary stop of at least one part; entering a non - idling state by at least one selected wind turbine (2a, 2b) or by at least one non - selected wind turbine so as to supply power to the local power grid.

2. The method according to the preceding claim, further comprising at least one of the following: establishing a ranking order of the wind turbines (2a, 2b, 2c) based on the proximity of the wind turbines, in particular the proximity level; selecting wind turbines (2a, 2b) based on the ranking order to enter the non - idling state; selecting wind turbine (2c) based on the ranking order to enter an idling state and / or perform maintenance.

3. The method according to any one of the preceding claims, further comprising at least one of the following: if there is a non - selected wind turbine (2c), operating the non - selected wind turbine (2c) in an idling state so as not to supply power to the local power grid; and receiving power (9c) from the local power grid (4) at at least one of the idling wind turbines (2c).

4. The method according to any one of the preceding claims, wherein selecting one or more of the wind turbines (2a, 2b, 2c) comprises: selecting one or more of the wind turbines (2a, 2b) having the greatest proximity to a respective temporary stop requirement or greater than a threshold value, the threshold value depending in particular on the wind speed and / or the total number of wind turbines.

5. The method according to any one of the preceding claims, wherein selecting one or more of the wind turbines (2a, 2b, 2c) comprises: selecting some of one or more of the wind turbines (2a, 2b, 2c) such that the electrical power output supplied by the non - idling wind turbines (2a, 2b) and the electrical power consumption of the idling wind turbines (2c) are substantially balanced within the local power grid (4), wherein, in particular, the number of wind turbines supplying power to the local power grid depends on the wind speed.

6. The method according to any one of the preceding claims, further comprising: For each of the wind turbines (2a, 2b, 2c), a proximity level and / or a proximity score is determined based on the respective temporary stop requirement; One or more of the wind turbines (2a, 2b, 2c) are selected based on the proximity level; and / or A ranking order of the wind turbines (2a, 2b, 2c) is established based on the proximity level of the wind turbines, wherein the proximity level is a binary quantity or is quantified with more than two values, in particular in a continuous manner.

7. The method according to the preceding claim, wherein the proximity score or proximity level obeys the weights of a plurality of parts or wind turbines with respect to predictability and / or importance and / or vulnerability.

8. The method according to one of the preceding two claims, wherein the proximity level of the temporary stop requirement is determined based on at least one of the following or based on at least one of the following: The remaining duration until the next temporary stop requiring at least one part, the time elapsed since the previous temporary stop of at least one part The remaining load level that at least one part will be able to experience in the future; The cumulative load level that at least one part (has) experienced in the past; The number of degrees of rotation of the nacelle rotation since the previous cable management operation; The number of degrees of rotation that the nacelle will be able to rotate in the future until the next cable management operation is required, wherein the proximity level in particular obeys at least one operating threshold, in particular an operating time threshold and / or a wear level threshold.

9. The method according to any one of the preceding claims, wherein monitoring the wind turbines (2a, 2b, 2c) with respect to at least one temporary stop requirement includes at least one of the following: Receiving measurement data regarding the operating state and / or performance and / or service life of at least one wind turbine part; Receiving at least one operating threshold regarding the operation of the part; Determining the proximity level based on the measurement data and / or the operating threshold.

10. The method according to any one of the preceding claims, wherein the temporary stop includes at least one of the following: Lubrication of at least one part of the wind turbine, the at least one part being in particular a gear system and / or a pitch system and / or a yaw system; Uncabling power cables, in particular power cables arranged in the wind turbine tower; Stopping the wind turbine; Performing a temporary stop on at least one part of the wind turbine.

11. The method according to any one of the preceding claims, further comprising at least one of the following, in particular if the local power grid is electrically stable: Performing a temporary stop on at least one idling wind turbine (2c), in particular giving priority to those idling wind turbines with the lowest proximity level in the ranking order; After the temporary stop has been performed, updating the proximity level of the idling wind turbines (2c), in particular updating the ranking of the wind turbines in the sorted list, Performing the temporary stop of the wind turbine in particular increases the proximity level, thereby reducing the emergency level for the temporary stop of the corresponding wind turbine.

12. The method according to one of the preceding claims, further comprising at least one of the following, in particular in a regular manner: Updating the proximity level of the wind turbines (2a, 2b, 2c); Updating the selection of the wind turbines (2a, 2b, 2c) to enter a non-idling state; Supplying power (8a, 8b) to the local power grid (4) through the wind turbines according to the updated selection and / or the updated proximity level; Performing a temporary stop of at least one idling wind turbine (2c) based on the updated proximity level.

13. The method according to one of the preceding claims, wherein the plurality of wind turbines (2a, 2b, 2c) comprises one of the following: Two or more wind turbines; A subset of the wind farm wind turbines; All the wind turbines of the wind farm; And / or wherein the idling state of the wind turbine comprises at least one of the following: The wind turbine stops; The rotor rotates slowly; The wind turbine does not supply power to the local power grid; And / or The proximity level indicates at least one of the following: The "distance" to the next temporary stop; The emergency level for performing the temporary stop.

14. An arrangement for operating a plurality of wind turbines (2a, 2b, 2c), the plurality of wind turbines (2a, 2b, 2c) being connected to a local power grid (4) but disconnected from the public power grid (5), the arrangement comprises: Input ports (5a, 5b, 5c) for receiving monitoring data (6a, 6b, 6c) of the wind turbines regarding at least one temporary stop requirement; A processor adapted to select one or more of the wind turbines based on the proximity to the corresponding temporary stop requirement; Output ports (5a, 5b, 5c) for supplying control signals (7a, 7b, 7c) to at least one selected wind turbine or to at least one non-selected wind turbine to enter a non-idling state so as to supply power to the local power grid.

15. A system (1), comprises: At least two wind turbines (2a, 2b, 2c) connected to a local isolated power grid (4), the local isolated power grid (4) being in particular a wind farm; The arrangement according to the previous claim communicatively connected to the wind turbines (2a, 2b, 2c).

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