Wind farm controllers, systems and methods

Abstract

The present disclosure relates to wind farm controllers (99), wind farms (105), systems (100) and methods (120). A wind farm controller (99) is configured to: determine setpoints for a plurality of wind turbines (10) of a wind farm (105) based on an active power required by a variable load (111) connected to the wind farm (105), and to send the determined setpoints to the wind turbine controllers (36) of the plurality of wind turbines (10).

Description

GENERAL ELECTRIC RE OVABLES ESPANA S.L. DECEMBER 20, 2024 700832-WO-1 P5457PC00WIND FARM CONTROLLERS, SYSTEMS AND METHODS

[0001] The present disclosure relates to systems, and to methods for operating these systems. More in particular, the present disclosure relates to systems comprising a wind farm, a diode rectifier unit (DRU) and a variable load, particularly in the absence of a utility grid. The present disclosure further relates to wind farm controllers and operation of the wind farm controllers.BACKGROUND

[0002] Modern wind turbines are commonly used to supply electricity into the electrical grid. Wind turbines of this kind generally comprise a tower and a rotor arranged on the tower. The rotor, which typically comprises a hub and a plurality of blades, is set into rotation under the influence of the wind on the blades. Said rotation generates a torque that is normally transmitted through a rotor shaft to a generator, either directly (“directly driven” or “gearless”) or through the use of a gearbox. This way, the generator produces electricity which can be supplied to the electrical grid.

[0003] The wind turbine hub may be rotatably coupled to a front of the nacelle. The wind turbine hub may be connected to a rotor shaft, and the rotor shaft may then be rotatably mounted in the nacelle using one or more rotor shaft bearings arranged in a frame inside the nacelle. The nacelle is a housing arranged on top of a wind turbine tower that may contain and protect the gearbox (if present) and the generator (if not placed outside the nacelle) and, depending on the wind turbine, further components such as a power converter, and auxiliary systems.

[0004] A wind farm may comprise a plurality of wind turbines, which may be organized in groups or clusters. For example, wind turbines may be organized in strings. The AC power of fixed frequency supplied by the wind turbines may be delivered at a point of common coupling (PCC) of the wind farm. At the PCC, a HVDC (High Voltage Direct Current) transmission line may connect the wind farm to a utility grid or a load.

[0005] The use of an HVDC transmission line can minimize power losses during longdistance transmission compared to AC systems. This is especially beneficial for offshore windfarms far from the main grid. Also, subsea cables for HVDC have been reported to be less intrusive and more environmentally friendly than AC cables.

[0006] In order to rectify the wind farm’s voltage / power output, the AC power provided by the wind farm may be delivered to a DRU. A DRU passively converts the high voltage AC voltage / power into high voltage DC voltage / power. The high voltage DC power may then be transferred through high voltage lines (known as HVDC link) towards a utility grid or variable load.

[0007] Since the DRU is passive, an AC input voltage of the DRU will have a single DC output voltage. In other words, a DRU provides a DC fixed output voltage for a given AC input voltage. Also, power through the DRU can only flow from the wind farm towards the utility grid or variable load. But power cannot flow from the utility grid or the load to the wind farm.

[0008] It has been proposed to use wind farms for a dedicated power supply to an electrolysis plant for hydrogen production. In operation, the electrolysis plant may require a varying electrical power output. Although herein a reference is generally made to an electrolysis plant, it should be clear that other variable loads e.g. industrial or other plants may be used as well.

[0009] Using a DRU and an HVDC transmission may have some advantages over using a unit which allows providing a plurality of output DC voltages for a same input AC voltage (for example by including IGBTs) and a HVAC transmission. For example, a DRU unit has a relatively simple structure, a robust and reliable operation due to the presence of diodes, low losses, and it may be easy to transport and install.

[0010] However, having a DRU as an interface between an AC transmission system and a DC transmission system may cause that only two of the following may simultaneously be controlled: AC voltage at the input side of the DRU, AC frequency at the input side of the DRU and DC voltage at the output side of the DRU.

[0011] In the absence of an electrical power grid, and a suitable power converter, the varying electrical power output has to be adjusted for by the wind farm itself, i.e. by adjusting the electrical power output of the wind farm. Both the wind farm and the load may be seen as “disconnected” since power can flow in a single direction and thus the DRU “decouples” the wind farm and the variable load.

[0012] In such a situation, the controllers of the wind turbines have to cope with maintaining a power, frequency and voltage balance in the wind farm as part of a system formed by the wind farm, the DRU and the (onshore) variable load. The larger the number of wind turbines in the wind farm, the more complicated it will be to provide optimal power (both active andreactive) and voltage setpoints for the individual wind turbines, maintaining the stability of the wind farm and ensuring that a suitable active power is transferred through the DRU and the variable load.

[0013] The present disclosure aims at solving at least some of the above disadvantages.SUMMARY

[0014] In an aspect of the present disclosure, a system is provided. The system comprises a variable load and a wind farm to power the variable load. The wind farm comprises a plurality of wind turbines, a wind farm controller and a common output line to deliver AC power from the wind farm. The system further comprises a diode regulator unit, DRU, electrically connected to the common output line to rectify the delivered AC power, a high-voltage direct current, HVDC, transmission electrically connecting the DRU to a converter of the variable load. The wind farm controller is configured to determine individual setpoints for the plurality of wind turbines of the wind farm based on an active power required by the variable load, and to send the determined individual setpoints to wind turbine controllers of the corresponding wind turbines.

[0015] According to this aspect, the wind farm controller is in charge of determining the setpoints for the wind turbines of the wind farm for regulating the output of the wind farm, and therefore a DC output of the DRU to which the wind farm is electrically connected. In this way, suitable setpoints for the individual wind turbines may be determined to keep a power, voltage and frequency balance in the wind farm which supplies the DRU.

[0016] Throughout this disclosure, a variable load is a load (usually an onshore load) which is electrically connected to the output of the DRU and therefore capable of receiving active power from the DRU. The load may be connected to the DRU through an HVDC transmission line and a converter (for converting DC to AC). The size of the variable load in terms of power use is comparable to the size of the wind farm, meaning that the wind farm is capable of affecting the active power supplied to the variable load in a noticeable manner. The variable load is therefore smaller than a usual utility grid.

[0017] In a further aspect of the present disclosure, a method for operating a wind farm comprising a plurality of wind turbines is provided. The method comprises a wind farm controller sending individual setpoints to the plurality of wind turbines, operating the plurality of wind turbines in accordance with the setpoints to generate an AC voltage power output to a common output line of the wind farm. The method comprises rectifying the AC power output using a diode regulator unit, DRU, and delivering the rectified power output to an HVDCtransmission line to power a variable load. The wind farm controller determines the active power required by the variable load, and the wind farm controller determines the individual setpoints based on the active power required by the variable load.

[0018] In yet a further aspect of the present disclosure, a wind farm controller is provided. The wind farm controller is configured to: determine power required by a variable load by monitoring a voltage of an HVDC transmission line connecting a diode rectifier unit, DRU, to the variable load, to determine individual setpoints for a plurality of wind turbines in the wind farm based on the determined power required by the variable load and to send the determined individual setpoints to wind turbine controllers of the plurality of wind turbines. The individual setpoints include wind turbine output voltage, wind turbine output active power and wind turbine output reactive power.BRIEF DESCRIPTION OF THE DRAWINGS

[0001] Figure 1 illustrates a perspective view of one example of a wind turbine;

[0002] Figure 2 illustrates a simplified, internal view of one example of the nacelle of the wind turbine of the figure 1 ;

[0003] Figure 3 schematically illustrates an example of a system including an offshore wind farm, an offshore DRU and an onshore variable load;

[0004] Figure 4 schematically shows an example of a control loop scheme for determining wind turbine setpoints; and

[0005] Figure 5 shows a flow chart of an example of a method for operating a wind farm.DETAILED DESCRIPTION OF EXAMPLES

[0006] Reference now will be made in detail to embodiments of the present disclosure, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation only, not as a limitation. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present disclosure. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present disclosure covers such modifications and variations as come within the scope of the appended claims and their equivalents.

[0007] Figure 1 is a perspective view of an example of a wind turbine 10. In the example, the wind turbine 10 is a horizontal-axis wind turbine. Alternatively, the wind turbine 10 may be a vertical-axis wind turbine. In the example, the wind turbine 10 includes a tower 15 that extends from a support system 14 on a ground 12, a nacelle 16 mounted on tower 15, and a rotor 18 that is coupled to nacelle 16. The rotor 18 includes a rotatable hub 20 and at least one rotor blade 22 coupled to and extending outward from the hub 20. In the example, the rotor 18 has three rotor blades 22. In an alternative embodiment, the rotor 18 includes more or less than three rotor blades 22. The tower 15 may be fabricated from tubular steel to define a cavity (not shown in figure 1) between a support system 14 and the nacelle 16. In an alternative embodiment, the tower 15 is any suitable type of a tower having any suitable height. According to an alternative, the tower can be a hybrid tower comprising a portion made of concrete and a tubular steel portion. Also, the tower can be a partial or full lattice tower.

[0008] The rotor blades 22 are spaced about the hub 20 to facilitate rotating the rotor 18 to enable kinetic energy to be transferred from the wind into usable mechanical energy, and subsequently, electrical energy. The rotor blades 22 are mated to the hub 20 by coupling a blade root region 24 to the hub 20 at a plurality of load transfer regions 26. The load transfer regions 26 may have a hub load transfer region and a blade load transfer region (both not shown in figure 1). Loads induced to the rotor blades 22 are transferred to the hub 20 via the load transfer regions 26.

[0009] In examples, the rotor blades 22 may have a length ranging from about 15 meters (m) to about 90 m or more. Rotor blades 22 may have any suitable length that enables the wind turbine 10 to function as described herein. For example, non-limiting examples of blade lengths include 20 m or less, 37 m, 48.7 m, 50.2m, 52.2 m or a length that is greater than 91 m. As wind strikes the rotor blades 22 from a wind direction 28, the rotor 18 is rotated about a rotor axis 30. As the rotor blades 22 are rotated and subjected to centrifugal forces, the rotor blades 22 are also subjected to various forces and moments. As such, the rotor blades 22 may deflect and / or rotate from a neutral, or non-deflected, position to a deflected position.

[0010] Moreover, a pitch angle of the rotor blades 22, e.g. an angle that determines an orientation of the rotor blades 22 with respect to the wind direction, may be changed by a pitch system 32 to control the load and power generated by the wind turbine 10 by adjusting an angular position of at least one rotor blade 22 relative to wind vectors. Pitch axes 34 of rotor blades 22 are shown. During operation of the wind turbine 10, the pitch system 32 may particularly change a pitch angle of the rotor blades 22 such that the angle of attack of (portions of) the rotor blades are reduced, which facilitates reducing a rotational speed and / or facilitates a stall of the rotor 18.

[0011] In the example, a blade pitch of each rotor blade 22 is controlled individually by a wind turbine controller 36 or by a pitch control system 80. Alternatively, the blade pitch for all rotor blades 22 may be controlled simultaneously by said control systems.

[0012] Further, in the example, as the wind direction 28 changes, a yaw direction of the nacelle 16 may be rotated about a yaw axis 38 to position the rotor blades 22 with respect to wind direction 28.

[0013] In the example, the wind turbine controller 36 is shown as being centralized within the nacelle 16, however, the wind turbine controller 36 may be a distributed control system throughout the wind turbine 10, on the support system 14, within a wind farm, and / or at a remote-control center. The wind turbine controller 36 may include one or more processors configured to perform one or more of the steps of the methods described herein. Further, many of the other components described herein include one or more processors. The wind turbine controller 36 may also include a memory, e.g. one or more memory devices. As used herein, a memory may comprise memory element(s) including, but not limited to, a computer readable medium (e.g., random access memory (RAM)), a computer readable non-volatile medium (e.g., a flash memory), a floppy disk, a compact disc-read only memory (CD-ROM), a magnetooptical disk (MOD), a digital versatile disc (DVD) and / or other suitable memory elements.

[0014] Figure 2 is an enlarged sectional view of a portion of the wind turbine 10. In the example, the wind turbine 10 includes the nacelle 16 and the rotor 18 that is rotatably coupled to the nacelle 16. More specifically, the hub 20 of the rotor 18 is rotatably coupled to an electric generator 42 positioned within the nacelle 16 by the main shaft 44, a gearbox 46, a high-speed shaft 48, and a coupling 50. In the example, the main shaft 44 is disposed at least partially coaxial to a longitudinal axis (not shown) of the nacelle 16. A rotation of the main shaft 44 drives the gearbox 46 that subsequently drives the high-speed shaft 48 by translating the relatively slow rotational movement of the rotor 18 and of the main shaft 44 into a relatively fast rotational movement of the high-speed shaft 48. The latter is connected to the generator 42 for generating electrical energy with the help of a coupling 50. Furthermore, a transformer 90 and / or suitable electronics, switches, and / or inverters may be arranged in the nacelle 16 in order to transform electrical energy generated by the generator 42 having a voltage between e.g. 400V to 1000 V into electrical energy having medium voltage (e.g. 10 - 35 kV). Offshore wind turbines may have for example generator voltages between 650 V and 3500 V, and transformer voltages may for instance be between 30 kV and 70 kV. Said electrical energy is conducted via power cables from the nacelle 16 into the tower 15.

[0015] In some examples, the wind turbine 10 may include one or more shaft sensors 51. The shaft sensors may be configured to monitor at least one of torque loads acting on the mainshaft 44 and / or the high-speed shaft 48, and a rotational speed of the shaft 44, 48. In some examples, the wind turbine 10 may include one or more generator sensors 53. The generator sensors may be configured to monitor at least one of a rotational speed of the generator 42 and a generator torque. Shaft sensors 51 and / or generator sensors 53 may include, for instance, one or more torque sensors (e.g., strain gauges or pressure sensors), optical sensors, accelerometers, magnetic sensors, speed sensors and Micro-Inertial Measurement Units (MIMUs).

[0016] The gearbox 46, generator 42 and transformer 90 may be supported by a main support structure frame of the nacelle 16, optionally embodied as a main frame 52. The gearbox 46 may include a gearbox housing that is connected to the main frame 52 by one or more torque arms 103. In the example, the nacelle 16 also includes a main forward support bearing 60 and a main aft support bearing 62. Furthermore, the generator 42 can be mounted to the main frame 52 by decoupling support means 54, in particular in order to prevent vibrations of the generator 42 to be introduced into the main frame 52 and thereby causing a noise emission source.

[0017] Optionally, the main frame 52 is configured to carry the entire load caused by the weight of the rotor 18 and components of the nacelle 16 and by the wind and rotational loads, and furthermore, to introduce these loads into the tower 15 of the wind turbine 10. The rotor shaft 44, generator 42, gearbox 46, high speed shaft 48, coupling 50, and any associated fastening, support, and / or securing device including, but not limited to, support 52, and forward support bearing 60 and aft support bearing 62, are sometimes referred to as a drive train 64.

[0018] In some examples, the wind turbine may be a direct drive wind turbine without gearbox 46. Generator 42 operates at the same rotational speed as the rotor 18 in direct drive wind turbines. They therefore generally have a much larger diameter than generators used in wind turbines having a gearbox 46 for providing a similar amount of power than a wind turbine with a gearbox.

[0019] The nacelle 16 may also include a yaw drive mechanism 56 that may be used to rotate the nacelle 16 and thereby also the rotor 18 about the yaw axis 38 to control the perspective of the rotor blades 22 with respect to the wind direction 28.

[0020] For positioning the nacelle 16 appropriately with respect to the wind direction 28, the nacelle 16 may also include at least one meteorological measurement system which may include a wind vane and an anemometer. The meteorological measurement system 58 can provide information to the wind turbine controller 36 that may include wind direction 28 and / or wind speed.

[0021] In the example, the pitch system 32 is at least partially arranged as a pitch assembly 66 in the hub 20. The pitch assembly 66 includes one or more pitch drive systems 68 and at least one sensor 70. Each pitch drive system 68 is coupled to a respective rotor blade 22 (shown in figure 1) for modulating the pitch angle of a rotor blade 22 along the pitch axis 34. Only one of three pitch drive systems 68 is shown in figure 2.

[0022] In the example, the pitch assembly 66 includes at least one pitch bearing 72 coupled to hub 20 and to a respective rotor blade 22 (shown in figure 1) for rotating the respective rotor blade 22 about the pitch axis 34. The pitch drive system 68 includes a pitch drive motor 74, a pitch drive gearbox 76, and a pitch drive pinion 78. The pitch drive motor 74 is coupled to the pitch drive gearbox 76 such that the pitch drive motor 74 imparts mechanical force to the pitch drive gearbox 76. The pitch drive gearbox 76 is coupled to the pitch drive pinion 78 such that the pitch drive pinion 78 is rotated by the pitch drive gearbox 76. The pitch bearing 72 is coupled to pitch drive pinion 78 such that the rotation of the pitch drive pinion 78 causes a rotation of the pitch bearing 72.

[0023] Pitch drive system 68 is coupled to the wind turbine controller 36 for adjusting the pitch angle of a rotor blade 22 upon receipt of one or more signals from the wind turbine controller 36. In the example, the pitch drive motor 74 is any suitable motor driven by electric power and / or a hydraulic system that enables pitch assembly 66 to function as described herein. Alternatively, the pitch assembly 66 may include any suitable structure, configuration, arrangement, and / or components such as, but not limited to, hydraulic cylinders, springs, and / or servomechanisms. In certain embodiments, the pitch drive motor 74 is driven by energy extracted from a rotational inertia of hub 20 and / or a stored energy source (not shown) that supplies energy to components of the wind turbine 10.

[0024] The pitch assembly 66 may also include one or more pitch control systems 80 for controlling the pitch drive system 68 according to control signals from the wind turbine controller 36, in case of specific prioritized situations and / or during rotor 18 overspeed. In the example, the pitch assembly 66 includes at least one pitch control system 80 communicatively coupled to a respective pitch drive system 68 for controlling pitch drive system 68 independently from the wind turbine controller 36. In the example, the pitch control system 80 is coupled to the pitch drive system 68 and to a sensor 70. During normal operation of the wind turbine 10, the wind turbine controller 36 may control the pitch drive system 68 to adjust a pitch angle of rotor blades 22.

[0025] According to an embodiment, a power generator 84, for example comprising a battery and electric capacitors, is arranged at or within the hub 20 and is coupled to the sensor 70, the pitch control system 80, and to the pitch drive system 68 to provide a source of powerto these components. In the example, the power generator 84 provides a continuing source of power to the pitch assembly 66 during operation of the wind turbine 10. In an alternative embodiment, power source 84 provides power to the pitch assembly 66 only during an electric power loss event of the wind turbine 10. The electric power loss event may include power grid loss or dip, malfunctioning of an electrical system of the wind turbine 10, and / or failure of the wind turbine controller 36. During the electric power loss event, the power generator 84 operates to provide electric power to the pitch assembly 66 such that pitch assembly 66 can operate during the electric power loss event.

[0026] In the example, the pitch drive system 68, the sensor 70, the pitch control system 80, cables, and the power source 84 are each positioned in a cavity 86 defined by an inner surface 88 of hub 20. In an alternative embodiment, said components are positioned with respect to an outer surface of hub 20 and may be coupled, directly or indirectly, to the outer surface.

[0027] As used herein, the term “processor” is not limited to integrated circuits referred to in the art as a computer, but broadly refers to a controller, a microcontroller, a microcomputer, a programmable logic controller (PLC), an application specific integrated circuit, and other programmable circuits, and these terms are used interchangeably herein.

[0028] Figure 3 schematically illustrates an example of a system 100. The system 100 comprises a variable load 111, a high voltage direct current (HVDC) transmission line 102, a DRU 104 and a wind farm 105, specifically an offshore wind farm. The DRU 104 is electrically connected to the wind farm 105, the HVDC line 102 is electrically connected to the DRU 104, and the variable load 111 is electrically connected to the HVDC line 102 through a converter 109 (in this case an onshore HVDC converter). HVDC transmission, HVDC transmission line and HVDC line are used interchangeably herein.

[0029] The wind farm 105 comprises a plurality of wind turbines 10. The number of wind turbines in the wind farm may in some examples be over 100 or 200 wind turbines. The wind turbines may be arranged in clusters. In the current example, the wind turbines are arranged in strings. Each wind turbine 10 may be connected to or disconnected from a corresponding string via one or more switches or circuit breakers. A wind farm controller 99 may be communicatively coupled to the wind turbine controllers of the individual wind turbines 10.

[0030] The generator 42 of a corresponding wind turbine 10 produces AC (alternating current) power of variable frequency due to varying wind conditions. A power converter may be provided for adjusting the power output from the generator 42 to one suitable for the utility grid 101, e.g. to an AC power having fixed frequency. The power converter may comprise amachine-side converter, a line-side converter and a DC (direct current) link connecting the machine-side and the line-side converter (not shown).

[0031] The generator 42 of the wind turbines 10 may be a permanent magnet generator comprising a generator rotor carrying a plurality of permanent magnets and a stator in some examples. The permanent magnet generator may be directly driven by the wind turbine rotor 18. The stator of the generator may be connected to the machine-side converter, which may be configured to convert the received AC voltage to DC voltage, the DC voltage then being delivered to the DC-link. The line-side converter may be configured to convert the DC voltage from the DC-link into a fixed frequency AC voltage. In some examples, the power converter of individual wind turbines may include a dynamic brake.

[0032] The wind farm controller can send suitable setpoints to the individual wind turbine controllers 36 (see figure 2). The individual wind turbine controllers can convert the received setpoints in setpoints for the converter, or the converter controller. E.g. power and reactive power setpoints received by the wind turbine controller may be converted into torque and reactive power setpoints for the converter.

[0033] The line-side converter may be connected to a corresponding busbar through a main transformer. The main transformer may be configured to step-up the voltage delivered by the power converter, e.g. to 33 kV. The main transformer may be installed within the nacelle 16 or the tower 15 of the wind turbine in some examples. The main transformer may be arranged at other suitable places in other examples.

[0034] The active power output provided by each wind turbine and received in the corresponding string busbar is delivered to a wind farm bus, i.e. a common output line, and a point of common coupling (PCC) of the wind farm.

[0035] The wind farm 105 may comprise an offshore substation 106. The DRU 104 may be arranged at the substation 106 in some examples. The DRU may comprise a plurality of diode bridges connected to the PCC of the wind farm. A transformer 107 and a passive AC filter 108 may be arranged between the PCC of the wind farm and the DRU 104. The system 100 may further comprise an onshore voltage source converter (VSC) HVDC platform 109. One or more HVDC lines 102 may connect the DRU 104 and the VSC-H CD platform 109.

[0036] In the current example, an onshore transformer 110 steps down the voltage for feeding it to a variable load 111, specifically a hydrogen electrolysis plant. The wind farm 105 and the DRU 104 are electrically disconnected from the public utility grid 101. Therefore, the active power produced by the wind farm 105 can be transferred to and received by the variable load 111, but not to the utility grid 101.

[0037] As shown in the example of figure 3, the power generation and transmission system 100 may include a utility grid 101. The HVDC line(s) 102 may connect to another (onshore) VSC-HVCD platform 112, which, through a corresponding transformer 113, leads to the utility grid 101. The present disclosure is particularly aimed at situations in which there is no utility grid 101, i.e. wherein the electrical connection between the wind farm 105 and the utility grid 101 is missing.

[0038] In an aspect of the present disclosure, a system 100 is provided. The system comprises: a variable load 111 and a wind farm 105 to power the variable load 111. The wind farm comprises a plurality of wind turbines 10, a wind farm controller 99 and a common output line configured to deliver AC power from the wind farm. The system further comprises a diode regulator unit (DRU) 104 electrically connected to the common output line to rectify the delivered AC power, and a high-voltage direct current (HVDC) transmission 102 electrically connecting the DRU 104 to a converter 109 of the variable load 111.

[0039] The wind farm controller 99 is configured to: determine individual setpoints for the plurality of wind turbines 10 of the wind farm 105 based on an active power required by the variable load 111, and to send the determined individual setpoints to the wind turbine controllers 36 of the corresponding wind turbines.

[0040] In this manner, the wind farm controller is in charge of determining the setpoints for the plurality of wind turbines. The setpoints may be determined for each individual wind turbine. I.e., each wind turbine may receive its own setpoints. The output of the wind farm 105 is adapted to the requirements of the variable load 111, and the voltage in the DC transmission 102 is regulated by the offshore wind farm 105.

[0041] The variable load 111 may be a hydrogen electrolysis plant in some examples. The active power from the wind farm 105 may therefore be used to split water into hydrogen and oxygen. The plant may for example comprise a plurality of electrolyzers. Producing hydrogen using the active power produced by the wind farm may result in practically zero greenhouse gas and pollutant emissions.

[0042] In some examples, neither the variable load 111, nor the HVDC transmission, are connected to a utility grid 101.

[0043] In some examples, the wind farm controller 99 may be configured to determine the individual setpoints based on a voltage in the HVDC transmission 102. I.e., the wind farm controller may have access to the voltage in the HVDC transmission and may use its value to determine the individual setpoints. Some examples in which the voltage in the HVDC transmission 102 is used to determine the individual setpoints are mentioned below.

[0044] The setpoints may specifically include a wind turbine output voltage, a wind turbine active power output and / or a wind turbine reactive power output. These setpoints may be calculated for each of the wind turbines. Depending for example on wind turbine location, turbine power generation capability and others, one or more of the setpoints received by a wind turbine may differ from the setpoints received by another wind turbine.

[0045] The wind farm 105 regulates the voltage in the DC transmission 102 and the voltage and frequency at the point of common coupling of the wind farm. I.e., both the AC and DC sides of the DRU 104 are regulated by the wind farm 105.

[0046] The individual setpoints may depend on local wind conditions of the individual wind turbines, but can also depend on the overall configuration of the wind farm, and the location of individual wind turbines within the wind farm. I.e. depending on impedances of power cables, transformer(s) and other components, the wind farm controller may send suitable setpoints to the individual wind turbines.

[0047] Setpoints may be determined in several manners. In some examples, a model or simulation of the wind farm may be used. In some of these examples, the wind farm controller 99 may be configured to determine the individual setpoints based on online power flow analysis in the wind farm 105. For example, a power flow or load flow algorithm may be used in real time. Wind turbine location and power generation capability, network topology (location, length, etc. of the power cables) and others may allow to obtain a model of the wind farm. Measured electrical values (e.g. voltage, active power output, frequency and others) may be used as input for the algorithm based on the network model of the wind farm. In real time, setpoints may be determined based on the current electrical values and the network model of the wind farm. For example, the wind farm controller 99 may be configured to determine the individual setpoints based on a location of the wind turbines within the wind farm.

[0048] Determining the setpoints may comprise: based on the network model of the wind farm 105, determining how much individual active power has to be generated by the plurality of wind turbines to feed the active power required by the variable load 111. And based on the individual active power, determining the individual voltage and optionally the individual reactive power to generate the previously determined individual active power.

[0049] The variable load 111 may require a certain amount of active power. That amount of active power corresponds to a certain DC voltage on the DC transmission 102, and thus a certain output DC voltage of the DRU 104. Since the DRU 104 is passive, that output DC voltage univocally corresponds to a certain input AC voltage for the DRU 104 and thus a certain AC voltage which the wind farm 105 has to provide.

[0050] The wind farm controller 99 can therefore determine, based on the active power required by the variable load 111 , the amount of active power that the wind farm has to provide. The wind farm controller may also know the actual active power output of the individual wind turbines 10. Based on the active power output desired for the wind farm 105 and the actual active power of the individual wind turbines 10, the wind farm controller may determine active power setpoints for the individual wind turbines.

[0051] l.e., the wind farm controller 99 may know how much active power the wind farm 105 should produce, and how much active power is actually being produced. The difference between these values is indicative of how much the total power production of the wind turbines should be varied. Based on the model of the wind farm, the wind farm controller may determine the individual active power setpoints.

[0052] In these and in other examples, the wind turbines of the wind farm may be producing less power than the theoretically available power according to wind conditions, i.e. the maximum power for a given wind speed. In this manner, power production may be increased if needed in response to variations of the variable load.

[0053] The wind farm controller 99 may further determine voltage and reactive power setpoints for the individual wind turbines. In this regard, active power and voltage are related (through the electrical current). And voltage and reactive power are also related. Accordingly, the three power setpoints (active power, reactive power and voltage) may be determined for individual wind turbines.

[0054] In some other examples, the determination of active power setpoints may be omitted. Rather, the voltage setpoints for the individual wind turbines may be determined. As already mentioned, a DC voltage on the DC transmission 102 may correspond to a certain output DC voltage of the DRU 104, to a certain input AC voltage for the DRU 104 and to a certain AC voltage which the wind farm 105 has to provide. By knowing the AC voltage the wind farm has to provide, the wind farm controller 99 may determine the voltage setpoints for the individual wind turbines. Additionally, reactive power setpoints for the individual wind turbines may optionally be determined in these examples.

[0055] Once the setpoints have been determined, the wind farm controller 99 may communicate them to the corresponding wind turbines.

[0056] In examples where this way of determining the setpoints is used, it may be assumed that no active power is lost between its production site and consumption site, e.g. between the wind farm 105 and the variable load 111. In some other examples, losses of active power during active power transport may be considered. Such losses may for example be estimatedin advance with simulations of the entire system 100. Therefore, if the variable load 111 requires X megawatts of active power, the wind farm 105 will have to provide more than X megawatts. The wind farm controller may know and use this information for determining the setpoints for the individual wind turbines more precisely. Alternatively, a model for the HVDC link could be used to calculate the losses based on the resistance on the line.

[0057] The wind farm controller 99 may be configured to determine the setpoints and send the determined setpoints periodically. For example, the setpoint determination may be performed each 2 to 10 minutes, e.g. each 5 minutes.

[0058] Alternatively, if the wind farm controller 99 determines that there has been a change which requires re-determining the setpoints, then the setpoints may be determined again. A change may for example include a substation circuit breaker status change, a change in the capability of a wind turbine 10 of generating a certain amount of active power, a change in the number of wind turbines able to generate active power, and others.

[0059] Another manner to determine the setpoints for the individual wind turbines is explained in the following. In this example, the wind farm controller 99 may be configured to: monitor the actual voltage output of the DRU 104, and if the monitored actual voltage output is different from the expected output voltage of the DRU 104, determine a reactive power setpoint such that the difference between the actual and the expected voltage output of the DRU is reduced.

[0060] An example of this way of proceeding is schematically illustrated at the top of figure 4. The voltage output of the DRU 104 may be monitored. A suitable sensor, e.g. a voltage sensor may be used. For example, DC voltage may be measured at the DC transmission 102. This value is represented as Vdc_act in figure 4. A feedback control loop for controlling the output voltage is provided in this example, more particularly a PID control loop. The Vdc_act may be compared to a desired or expected DC voltage output of the DRU, Vdc_ref. The difference between these values may be indicative of a DC voltage drop or increase which should be implemented to achieve the Vdc_ref value. Since there is a relationship between voltage and reactive power Q, reactive power references (i.e. reactive power setpoints) for the wind turbines may be determined by the wind farm controller.

[0061] The wind farm controller 99 may further be configured to convert the actual voltage output Vdc_act of the DRU 104 into an actual voltage output of the wind farm 104, and to compare the actual voltage output of the wind farm 105 with a desired or expected voltage output of the wind farm. As previously indicated, the output DC voltage of the DRU corresponds to a specific input AC value of the DRU. Therefore, the wind farm controller may know andcompare a current AC voltage of the wind farm with a desired or expected AC voltage of the wind farm. And based on the difference, it may determine a reactive power output for the wind farm and individual reactive power setpoints for the wind turbines.

[0062] The above type of steps may also be performed to determine active power setpoints for the wind turbines. In this regard, the wind farm controller 99 may be configured to monitor the actual frequency output of the wind farm 105. And if the monitored actual frequency output is different from the desired or expected frequency output of the wind farm 105, the wind farm controller 99 may determine active power setpoints such that the difference between the actual and expected frequency output of the wind farm 105 is reduced.

[0063] An example of these steps is illustrated in the middle scheme of figure 4. Similarly to the previous explanation, the actual frequency output of the wind farm Freq_act may be monitored. If the frequency is not the desired or expected frequency Freq_ref, an active power output of the wind farm may be determined for achieving the desired or expected frequency. The wind farm controller 99 may then determine active power setpoints for the individual wind turbines such that the desired active power output of the wind farm is achieved.

[0064] In this other manner of determining setpoints, the wind turbine controller may detect that the wind farm AC voltage and / or the wind farm frequency have changed. The change may specifically be related to a change caused by a change at the variable load 111. Based on the magnitude of the change, the wind turbine setpoints may be determined. For example, if it is detected that the wind farm frequency has decreased, then the setpoints may instruct the wind turbines to increase active power generation for increasing the wind farm frequency.

[0065] Monitoring the actual DC voltage at the output of the DRU 104 (or the AC voltage at the input of the DRU, e.g. at the point of common coupling of the wind farm 105) and comparing it to a desired or expected DC voltage at the output of the DRU 104 (or AC voltage at the input of the DRU, e.g. at the point of common coupling of the wind farm 105) may also be used for determining an output voltage setpoint for the individual wind turbines (see the bottom of figure 4).

[0066] The wind farm controller 99 may be configured to continuously monitor the actual voltage of the DRU and frequency output of the wind farm. I.e., the wind farm controller may be configured to implement a closed loop control system. In general, the wind farm controller 99 may include a feedback control loop for controlling an output voltage and / or an active power output and / or a reactive power output from the plurality of wind turbines.

[0067] Regardless of the way of determining the setpoints for the individual wind turbines, communication between a wind turbine and the wind farm controller may be lost. In someexamples, if the wind farm controller detects that communication with a wind turbine of the plurality of wind turbine has been lost, the wind farm controller may be configured to determine updated setpoints and send the determined updated setpoints to the wind turbine controllers 36. Accordingly, only the wind turbines which can communicate with the wind farm controller 99 and can generate the required active power may be used in the control scheme.

[0068] For example, if active power setpoints were being determined for 260 wind turbines, but the wind farm controller 99 detects that communication is currently possible with 240 of them, then individual active power setpoints may be recalculated for the available 240 wind turbines.

[0069] It is also possible that a wind turbine detects that it can no longer communicate with the wind farm controller. In some examples where the wind turbine detects that communication with the wind farm controller has been lost, the wind turbine may be configured to stop producing active power. For example, the wind turbine may start to idle or may shut down.

[0070] It may happen that an electric feature of the variable load 111 changes. Since the DRU 104 is disconnected from the utility grid 101, the effects of these changes may become relevant for the wind turbines 10 of the wind farm 105. For example, the load may vary such that the wind turbines do not have sufficient time for reducing the generated power. One or more wind turbines 10 may have a power converter including a dynamic brake. The dynamic brake, also known as dynamic braking resistor or chopper, of the individual wind turbines may be used to reduce the stress on the wind turbines in the load varies suddenly or excessively. Dissipating active power in the dynamic brake may help to protect the individual wind turbines 10 and the wind farm 105.

[0071] As previously indicated, the wind farm 105 of system 100 may be an offshore wind farm. The variable load may be located onshore or offshore.

[0072] As the wind farm controller 99 is configured to perform the steps indicated above, in a further aspect of the disclosure, a method 120 for operating a wind farm 105 comprising a plurality of wind turbines 10 is provided. A flow chart of an example of the method is shown in figure 5. The method comprises: at block 121, a wind farm controller 99 sending individual setpoints to the plurality of wind turbines. The method further comprises, at block 122, operating the plurality of wind turbines in accordance with the setpoints to generate an AC power output to a common output line of the wind farm 105. The method further comprises, at block 123, rectifying the AC power output using a diode regulator unit, DRU, 104, and at block 124, delivering the rectified power output to an HVDC transmission 102 to power a variable load 111. The wind farm controller 99 determines the active power required by the variableload 111 and determines the individual setpoints based on the active power required by the variable load 111. The wind farm controller may therefore effectively determine setpoints for the wind turbines, and the offshore wind farm 105 regulates the DC voltage of the DC transmission 102.

[0073] Still in a further aspect of the disclosure, a wind farm controller 99, in particular configured to perform the steps of blocks 121 to 124, is provided. An example of a wind farm controller 99 of a wind farm 105 is configured to: determine power required by a variable load 111 by monitoring a voltage of an HVDC transmission 102 connecting a diode rectifier unit (DRU) 104 to the variable load; determine individual setpoints for a plurality of wind turbines 10 in the wind farm 105 based on the determined power required by the variable load 111; and to send the determined individual setpoints to wind turbine controllers 36 of the plurality of wind turbines. The individual setpoints include wind turbine output voltage, wind turbine output active power and wind turbine output reactive power.

[0074] The wind farm controller 99 may also be configured to perform one or more of the steps explained before.

[0075] In this regard, previous details and explanations regarding system 100 may be combined and applied to the aspect of the wind farm controller 99 and the aspect of method 120, and vice versa.

[0076] For example with regard to the method, the individual setpoints may include an individual voltage setpoint. The individual setpoints may further include an individual active power setpoint and an individual reactive power setpoint.

[0077] The HVDC transmission 102 and the variable load 111 may not be connected to a utility grid 101.

[0078] The individual setpoints may be based on simulations of power flows and take into account positions of individual wind turbines 10 within the wind farm 105.

[0079] The wind farm controller 99 may monitor an actual voltage output of the DRU 104, and if the monitored actual voltage output is different from a desired or expected output voltage of the DRU, the wind farm controller 99 may determine a reactive power setpoint such that the difference between the actual and the desired or expected voltage output of the DRU is reduced.

[0080] The wind farm controller 99 may further convert the actual voltage output of the DRU into an actual voltage output of the wind farm, and to compare the actual voltage output of the wind farm with a desired or expected voltage output of the wind farm.

[0081] If the wind farm controller 99 detects that communication with a wind turbine of the plurality of wind turbine has been lost, the wind farm controller 99 may determine updated setpoints without considering the wind turbine which has lost communication, and may send the determined updated setpoints to the wind turbine controllers 36. The method may further comprise stopping operation of the wind turbine which has lost communication.

[0082] And for example with regard to the wind farm controller 99, the wind farm controller may be configured to determine the individual setpoints based on real time estimation of the power flows in the wind farm 105.In some examples, the wind farm controller 99 may be configured to use a power or load flow algorithm of the wind farm and values of actual active power of individual wind turbines to determine voltage and reactive power setpoints for the individual wind turbines.

[0083] In other examples, the wind farm controller 99 may be configured to monitor AC voltage and frequency output of the wind farm to determine voltage, reactive power and active power setpoints for the individual wind turbines. The reactive power setpoints may be determined based on a relation between voltage and reactive power, and the active power setpoints may be determined based on a relation between frequency and active power.

[0084] Also, the wind farm controller 99 may be configured to remove a wind turbine from the determination of setpoints if communication with that wind turbine is lost. For example, if feedback from a wind turbine is to be used in the determination, the determination may be performed again without including that wind turbine.

[0085] This written description uses examples to disclose a teaching, including the preferred embodiments, and also to enable any person skilled in the art to put the teaching into practice, including making and using any devices or systems and performing any incorporated methods. The patentable scope is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims. Aspects from the various embodiments described, as well as other known equivalents for each such aspects, can be mixed and matched by one of ordinary skill in the art to construct additional embodiments and techniques in accordance with principles of this application. If reference signs related to drawings are placed in parentheses in a claim, they are solely for attempting to increase the intelligibility of the claim, and shall not be construed as limiting the scope of the claim.

Claims

CLAIMS1. A system (100) comprising:a variable load (111); anda wind farm (105) to power the variable load (111), whereinthe wind farm (105) comprises a plurality of wind turbines (10), a wind farm controller (99) and a common output line to deliver AC power from the wind farm (105), and wherein the system (100) further comprises:a diode regulator unit, DRU, (104) electrically connected to the common output line to rectify the delivered AC power;a high-voltage direct current, HVDC, transmission (102) electrically connecting the DRU (104) to a converter (109) of the variable load (111),wherein the wind farm controller (99) is configured to:determine individual setpoints for the plurality of wind turbines (10) of the wind farm (105) based on an active power required by the variable load (111); and send the determined individual setpoints to wind turbine controllers (36) of the corresponding wind turbines (10).

2. The system of claim 1 , wherein the variable load (111) is a hydrogen electrolysis plant.

3. The system of claim 1 or 2, wherein the setpoints are one or more of: wind turbine output voltage, wind turbine active power output and wind turbine reactive power output.

4. The system of any of claims 1 -3, wherein neither the variable load (111) nor the HVDC transmission (102) are connected to a utility grid (101).

5. The system of any of claims 1 - 4, wherein the wind farm controller (99) is configured to determine the individual setpoints based on a voltage in the HVDC transmission (102).

6. The system of any of claims 1 - 5, wherein the wind farm controller (99) is configured to determine the individual setpoints based on online power flow analysis of the wind farm (105).

7. The system of claim 6, wherein the wind farm controller (99) is configured to determine the individual setpoints based on a location of the wind turbines (10) within the wind farm (105).

8. The system of any of claims 1 - 5, wherein the wind farm controller (99) includes a feedback control loop for controlling an output voltage and / or an active power output and / or a reactive power output from the plurality of turbines (10).

9. The system of any of claims 1 -8, wherein one or more of the wind turbines (10) include a power converter, and wherein the power converter includes a dynamic brake.

10. The system of any of claims 1 -9, wherein the wind farm (105) is an offshore wind farm (105).

11. A method (120) for operating a wind farm (105) comprising a plurality of wind turbines (10), the method (120) comprising:a wind farm controller (99) sending (121) individual setpoints to the plurality of wind turbines (10),operating (122) the plurality of wind turbines (10) in accordance with the setpoints to generate an AC power output to a common output line of the wind farm (105);rectifying (123) the AC power output using a diode regulator unit, DRU (104); delivering (124) the rectified power output to an HVDC transmission (102) to power a variable load (111); whereinthe wind farm controller (99) determines the active power required by the variable load (111), and whereinthe wind farm controller (99) determines the individual setpoints based on the active power required by the variable load (111).

12. The method of claim 11, wherein the individual setpoints include an individual voltage setpoint.

13. The method of claim 12, wherein the individual setpoints include an individual active power setpoint and an individual reactive power setpoint.

14. The method of any of claims 11 - 13, wherein if the wind farm controller (99) detects that communication with a wind turbine of the plurality of wind turbines (10) has been lost, the wind farm controller (99) determines updated setpoints by disregarding the wind turbine which has lost communication and sends the determined updated setpoints to the wind turbine controllers (36), and optionally further comprising stopping operation of the wind turbine which has lost communication.

15. A wind farm controller (99) of a wind farm (105) configured to:determine power required by a variable load (111) by monitoring a voltage of an HVDC transmission (102) connecting a diode rectifier unit, DRU (104), to the variable load (111); determine individual setpoints for a plurality of wind turbines (10) in the wind farm (105) based on the determined power required by the variable load (111);send the determined individual setpoints to wind turbine controllers (36) of the plurality of wind turbines (10), whereinthe individual setpoints include wind turbine output voltage, wind turbine active power output and wind turbine reactive power output.

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