Enhanced reactive power control for offshore wind farms

Abstract

A method of dynamically controlling reactive power compensation in a wind power generation system, the method comprising: obtaining one or more predetermined functions for determining values of a plurality of control parameters based on values of a plurality of input parameters; obtaining values for the plurality of input parameters; based on the obtained values of the input parameters, using the one or more predetermined functions to determine values of the control parameters; and, based on the determined values of the control parameters, controlling a plurality of wind turbine generators to supply or consume a first amount of reactive power and controlling reactive power compensation equipment external to the wind turbine generators to supply or consume a second amount of reactive power.

Description

[0001] ENHANCED REACTIVE POWER CONTROL FOR OFFSHORE WIND FARMS

[0002] Technical field

[0003] The present invention relates to a method of dynamically controlling reactive power compensation in a wind power generation system, and to a method of configuring a wind power generation system.

[0004] Background

[0005] In an alternating current (AC) circuit, phase differences between current and voltage produce reactive power. Whilst reactive power cannot be used to perform work, it is required by power grids in order to maintain correct voltage levels and to allow loads such as household devices and industrial plants to operate. Power grid operators therefore specify minimum requirements for the reactive power capabilities of power plants such as wind farms. Dedicated reactive power compensation equipment, such as switched reactors and static synchronous compensators (STATCOM), can be installed to supply or consume reactive power according to the requirements of the grid. However, these components are expensive, and meeting reactive power requirements can increase the cost of an offshore wind farm by 1 -3%.

[0006] Summary

[0007] According to a first aspect of the present invention, there is provided a method of dynamically controlling reactive power compensation in a wind power generation system, the wind power generation system comprising a plurality of wind turbine generators and reactive power equipment external to the plurality of wind turbine generators, wherein said plurality of wind turbine generators and reactive power equipment are connected via an export cable to a power transmission grid, and wherein the method comprises: obtaining one or more predetermined functions for determining values of a plurality of control parameters based on values of a plurality of input parameters, wherein the plurality of input parameters includes (i) an active power output of the plurality of wind turbine generators and (ii) a reactive power set point for the wind power generation system, and wherein the plurality of control parameters includes at least (i) a parameter indicative of a first amount of reactive power to be supplied or consumed by the wind turbine generators and (ii) a parameter indicative of a second amount of reactive power to be supplied or consumed by the reactive power compensation equipment external to the wind turbine generators; during operation of the wind power generation system, obtaining values for the plurality of input parameters; based on the obtained values of the input parameters, using the one or more predetermined functions to determine values of the control parameters.

[0008] In an embodiment, the method further comprises, based on the determined values of the control parameters, controlling the plurality of wind turbine generators to supply or consume the first amount of reactive power and controlling the reactive power compensation equipment external to the wind turbine generators to supply or consume the second amount of reactive power.

[0009] In an embodiment, the method comprises controlling the plurality of wind turbine generators to supply or consume the first amount of reactive power by sending a control signal based on the determined values of the control parameters to a wind turbine control system, to cause the wind turbine control system to determine set points for individual wind turbine generators such that the plurality of wind turbine generators supplies or consumes the first amount of reactive power.

[0010] In an embodiment, the one or more predetermined functions comprise a look-up table mapping values of the plurality of input parameters to values of the plurality of control parameters.

[0011] In an embodiment, the input parameters further include any one or more of: a system configuration of the wind power generation system; one or more temperature measurements of the export cable; and a voltage of the power transmission grid.

[0012] In an embodiment, obtaining the values of the input parameters comprises, for one or more of the input parameters, performing measurements on the wind power generation system in operation. In an embodiment, the second amount of reactive power comprises: an amount of reactive power to be supplied or consumed by dynamic reactive power compensation equipment that is able to supply or consume a variable amount of reactive power over a continuous range of values; an amount of reactive power to be supplied or consumed by fixed reactive power compensation equipment that is able to supply or consume a substantially fixed amount of reactive power, or is able to provide a variable amount of reactive power only in discrete steps.

[0013] In an embodiment, the static reactive power compensation equipment comprises one or more capacitors and / or one or more switched reactors, and wherein the dynamic reactive power compensation equipment comprises one or more static synchronous compensators.

[0014] In an embodiment, the control parameters further include one or more tap changer set points for respective transformers of the wind power generation system.

[0015] In an embodiment, the method further comprises: based on the active power output of the plurality of wind turbine generators, and optionally a system configuration of the wind power generation system, determining a maximum and / or minimum reactive power output of the wind turbine generators, and wherein the determined values of the control parameters are determined based on said maximum and / or minimum reactive power output.

[0016] In an embodiment, the plurality of input parameters includes one or more temperature measurements of the export cable, and wherein the method further comprises: in response to determining that a temperature measurement at a portion of the export cable exceeds a predetermined threshold, increasing the first amount of reactive power to be supplied or consumed by the wind turbine generators.

[0017] In an embodiment, the plurality of wind turbine generators are located offshore, and one or more components of the reactive power compensation equipment external to the wind turbine generators is located onshore, optionally at an interconnect between the wind power generation system and the power transmission grid. According to a second aspect, there is provided a reactive power control system for dynamically controlling reactive power compensation in a wind power generation system, the wind power generation system comprising a plurality of wind turbine generators and reactive power equipment external to the plurality of wind turbine generators, wherein said plurality of wind turbine generators and reactive power equipment are connected via an export cable to a power transmission grid, and wherein the reactive power control system is configured to: obtain one or more predetermined functions for determining values of a plurality of control parameters based on values of a plurality of input parameters, wherein the plurality of input parameters includes (i) an active power output of the plurality of wind turbine generators and (ii) a reactive power set point for the wind power generation system, and wherein the plurality of control parameters includes at least (i) a parameter indicative of a first amount of reactive power to be supplied or consumed by the wind turbine generators and (ii) a parameter indicative of a second amount of reactive power to be supplied or consumed by the reactive power compensation equipment external to the wind turbine generators; during operation of the wind power generation system, obtain values for the plurality of input parameters; and based on the obtained values of the input parameters, use the one or more predetermined functions to determine values of the control parameters.

[0018] In an embodiment, the reactive power control system is further configured to, based on the determined values of the control parameters, control the plurality of wind turbine generators to supply or consume the first amount of reactive power and control the reactive power compensation equipment external to the wind turbine generators to supply or consume the second amount of reactive power.

[0019] In an embodiment, the reactive power control system is configured to control the plurality of wind turbine generators to supply or consume the first amount of reactive power by sending a control signal based on the determined values of the control parameters to a wind turbine control system, to cause the wind turbine control system to determine set points for individual wind turbine generators such that the plurality of wind turbine generators supplies or consumes the first amount of reactive power. In an embodiment, the reactive power control system is located onshore and the wind turbine control system is located offshore.

[0020] According to a third aspect, there is provided a method of configuring a wind power generation system, the wind power generation system comprising a plurality of wind turbine generators and reactive power equipment external to the plurality of wind turbine generators, wherein said plurality of wind turbine generators and reactive power equipment are connected via an export cable to a power transmission grid, and wherein the method comprises: modelling the wind power generation system, wherein the modelling is based on at least (i) a predicted capability of the plurality of the wind turbine generators and the export cable to supply and / or consume reactive power and (ii) one or more possible reactive power set points for the wind power generation system; based on the modelling, determining a minimum amount of additional reactive power required to be supplied and / or consumed by the wind power generation system; and configuring the wind power generation system, wherein said configuring comprises installing or removing reactive power compensation equipment external to the wind turbine generators, such that the wind power generation system comprises sufficient reactive power compensation equipment external to the wind turbine generators to supply and / or consume at least the determined minimum amount of additional reactive power.

[0021] In an embodiment, the method further comprises: based on the modelling and the reactive power compensation equipment external to the wind turbine generators, determining one or more functions for determining values of a plurality of control parameters based on values of a plurality of input parameters, wherein the plurality of input parameters includes (i) an active power output of the plurality of wind turbine generators and (ii) a reactive power set point for the wind power generation system, and wherein the plurality of control parameters includes at least (i) a parameter indicative of a first amount of reactive power to be supplied or consumed by the wind turbine generators and (ii) a parameter indicative of a second amount of reactive power to be supplied or consumed by the reactive power compensation equipment external to the wind turbine generators. Brief description of the drawings

[0022] Fig. 1 shows schematically a wind power generation system.

[0023] Fig. 2 is a flow diagram illustrating a method of dynamically controlling reactive power compensation in a wind power generation system as shown in Fig. 1 .

[0024] Fig. 3 shows schematically a set of predetermined functions for use in a method as shown in Fig. 2.

[0025] Fig. 4 shows schematically the effect of increasing reactive power output from wind turbine generators on the temperature profile of an export cable.

[0026] Fig. 5 is a flow diagram illustrating a method of configuring a wind power generation system as shown in Fig. 1 .

[0027] Fig. 6 shows plots of active power output as a function of reactive power output, for four different configurations of wind power generation system.

[0028] Detailed description

[0029] The present disclosure provides methods and systems which leverage the reactive power capability of wind turbine generators more effectively. When implemented during operation of a wind power generation system, the present technology allows for improved dynamic control of reactive power output, as well as improved cable temperature management. The present technology can also be applied at the design phase, or during the configuration of the wind power generation system, where it allows for the amount of reactive power compensation equipment to be reduced, thus saving resources and costs.

[0030] Fig. 1 shows schematically a wind power generation system 100 according to the present disclosure. The wind power generation system 100 comprises a plurality of wind turbine generators (WTGs) 101 and a step-up transformer (not shown) connected via an export cable 102 to a power transmission grid 103. The wind power generation system 100 also comprises reactive power compensation equipment 104. The reactive power compensation equipment 104 is configured to supply or consume an amount of reactive power such that the wind power generation system 100 supplies a desired total amount of reactive power to the grid 103. For example, the reactive power compensation equipment 104 may be configured to supply or consume an amount of reactive power such that the wind power generation system 100 complies with reactive power constraints or set points specified by a grid operator 105.

[0031] WTGs also have the ability to supply and consume reactive power, for example using power factor correction capacitors provided therein. It will therefore be appreciated that the reactive power compensation equipment 104 is provided in addition to (e.g. external to, or remote from) the WTGs 101 , and in addition to the transformer and the export cable 102. For example, the WTGs 101 may be located offshore, and one or more components of the reactive power compensation equipment 104 may be located onshore.

[0032] The reactive power compensation equipment 104 may comprise one or more static or “fixed” reactive power compensation components and / or one or more dynamic reactive power compensation components. Dynamic reactive power compensation components, such as static VAr compensators and static synchronous compensators (STATCOM), are able to supply or consume a variable amount of reactive power over a continuous range of values, for example in response to receiving a reactive power set point. In comparison, fixed reactive power compensation components, such as capacitor banks and switched reactors, are able to supply or consume a substantially fixed amount of reactive power, for example in response to receiving an off / on signal, or are able to provide a variable amount of reactive power only in discrete (non- continuous) steps (e.g. by switching different numbers of reactors). In one example, the reactive power compensation equipment 104 comprises one or more first fixed reactive power compensation components located onshore, one or more second fixed reactive power compensation components located offshore, and / or one or more dynamic reactive power compensation components located onshore (e.g. in the form of STATCOM).

[0033] A reactive power control system 106 is configured to control the reactive power equipment 104 to supply or consume a specified amount of reactive power at a given time point. The reactive power control system 106 is also configured to control the reactive power output of the plurality of WTGs 101 by sending commands or reference values to a wind turbine control system 107. The wind turbine control system 107 is, in turn, configured to send commands and reference values to individual WTGs 101 in order to control their operation. In particular, the wind turbine control system 107 is configured to determine set points for individual WTGs 101 and to send the determined set points to the WTGs 101 , such that the plurality of WTGs supplies or consumes the total amount of reactive power specified by the reactive power control system 106. The wind turbine control system 107 thus allows the reactive power control system 106 to control the reactive power output of the WTGs 101 by sending a single command or set point to the wind turbine control system 107. That is, the reactive power control system 106 is able to view the plurality of WTGs 101 as a single unit for the purposes of reactive power control.

[0034] Dynamic control of reactive power compensation during operation of the wind power generation system

[0035] Fig. 2 is a flow diagram illustrating a method 200 of dynamically controlling reactive power compensation in a wind power generation system as shown in Fig. 1 .

[0036] In step 201 , one or more predetermined functions are obtained by the reactive power control system 106 and stored for use during operation of the wind power generation system 100. The predetermined functions map values of a plurality of input parameters to values of a plurality of control parameters.

[0037] The input parameters include: a system configuration (SysCon) of the wind power generation system 100; an active power output of the plurality of WTGs 101 (Pwind); a voltage of the power transmission grid 103 (Vgrid); one or more temperature measurements of the export cable 102; and a reactive power set point for the wind power generation system 100 (QREF). In one example, the system configuration parameter indicates one or more properties of the plurality of WTGs 101 that affect the capability of the WTGs 101 to supply or consume reactive power. For example, the system configuration parameter may indicate the number of WTGs 101 that are present, connected, and functioning, and / or the status of one or more circuit breakers. The active power output of the plurality of WTGs 101 is a continuous and measurable parameter (in units of MW), and is variable according to factors such as wind speed. The voltage of the power transmission grid (Vgrid) may, for example, be a voltage measurement at the point of interconnection between the wind power generation system 100 and the power transmission grid 103 (illustrated by vertical dashed line in Fig. 1). The reactive power set point (QREF) is an amount of reactive power (in units of MVAr) to be supplied by the wind power generation system 100 to the grid 103, and is set by the grid operator 105. QREF may be provided in the form of a specific target value, or a range of values within which the wind power generation system 100 must operate.

[0038] The control parameters indicate amounts of reactive power (Q, in MVAr) to be supplied or consumed by different components of the wind power generation system 100. In particular, the control parameters indicate an amount of reactive power to be supplied by each of: the plurality of WTGs 101 (QWTG) ; the fixed reactive power compensation equipment (Qs, fixed); and the dynamic reactive power compensation equipment (Qs,dyn). The control parameters may also include a tap changer set point (Vtrafo) for the step-up transformer.

[0039] It will be appreciated that different implementations of the functions are possible, provided that a predetermined relationship or mapping is specified between different values of the input parameters and different values of the control parameters. In one example, the predetermined functions may comprise one or more look-up tables mapping values of the plurality of input parameters to values of the plurality of control parameters. In this way, the computational demand of determining the values of the control parameters may be reduced. In another example, the predetermined function may comprise a neural network which has been trained to output values of the control parameters based on the values of the input parameters. The predetermined functions may be determined by modelling the wind power generation system 100 (e.g. during the design phase) as described below.

[0040] In step 202, during the operation of the wind power generation system 100, values for the plurality of input parameters are obtained. Obtaining the values of the input parameters may comprise, for one or more of the input parameters, performing measurements on the wind power generation system 100 in operation. Examples of measureable parameters are the active power output of the WTGs 101 , the one or more temperature values of the export cable 102, and the voltage of the power transmission grid 103. Other input parameters, such as the reactive power set point QREF may simply be provided to the reactive power control system 106, for example by the grid operator 105. In step 203, based on the obtained values of the input parameters, the one or more predetermined functions are used to determine values of the control parameters. The operation of an example set of functions is shown schematically in Fig. 3. The functions may be implemented with a suitable controller 304, e.g. comprising a processor, memory, input and output ports etc.

[0041] In box 301 of Fig. 3, a set of four predetermined functions (fSd, fss, fwtg, and ftrafo) are provided for determining values of the control parameters Qs,dyn, Qs, fixed, Qwtg, and Vtrafo respectively, based on values of the input parameters Pwind, Vgrid, SysCon, and QREF.

[0042] As illustrated by box 302, values (Qmax and Qmin) may also be calculated for the maximum and minimum reactive power output of the WTGs 101 , based on the current active power output of the WTGs 101 and the system configuration (e.g. the number of WTGs 101 currently available for the supply of reactive power). As shown in the figure, the values of Qmaxand Qminmay be included as inputs to the functions shown in box 301 , for example where Qmaxand Qminare determined by and received from the wind turbine control system 107 or another entity outside of the reactive power control system 106. Alternatively, the calculated values of Qmaxand Qminmay be used to modify one or more of the control parameters determined by the functions, to ensure that the control parameter value Qwtg does not exceed the reactive power capability of the WTGs 101.

[0043] As illustrated by box 303, an additional reactive power term, AQ, may also be determined, based on one or more temperature measurements of the export cable 102. In particular, AQ may be an additional amount of reactive power to be supplied by the WTGs 101 , in response to determining that a temperature measurement at a portion of the export cable 102 exceeds a predetermined threshold. The additional term AQ may be added to the value of Qwtg determined by the function fwtg, or may be included as an input parameter to said function as shown in the figure. In one example, where the input parameters include values of Qminand Qmaxas described above, the value of Qwtg may only be modified to the extent that the constraints of Qminand Qmaxare not violated.

[0044] Fig. 4 (panels A and B) show example plots of temperature profiles along the length of an export cable 102. As shown in the panel A, the temperature (TL) at one end of the cable (e.g. at a land side, furthest from the WTGs 101 ) is significantly higher than the temperature (To) at the other end of the cable (e.g. at an offshore side, closest to the WTGs), and the temperature T exceeds a predetermined threshold of 85eC. The conventional approach for reducing temperature in a subsea power cable is to reduce active power output. However, as shown in panel B, by shifting the current profile of the cable, an increase in the reactive power output of the WTGs 101 is able to modify the temperature profile of the cable 102, such that the peak temperature in the cable 102 is reduced. In this way, a reduction in the active power output of the wind power generation system 100 may be reduced or avoided, thereby reducing or avoiding revenue losses. An example implementation is shown schematically in panel C. Here, it is first determined whether or not a maximum temperature value of the cable exceeds the predetermined threshold value (box 400). In response to determining that the maximum temperature of the cable does exceed the threshold, an additional reactive power term AQ is calculated by multiplying the difference between To and TL by a predetermined constant, k. The optimal value for k will be depend on properties of the wind power generation system, such as the available range of reactive power flexibility of the cable, as will be appreciated by the skilled person.

[0045] In step 204, based on the determined values of the control parameters, the reactive power control system 106 controls the different components of the wind power generation system 100 to supply or consume the amount of reactive power specified by the respective control parameters. In particular, the reactive power control system 106 controls the WTGs 101 via the wind turbine control system 107 as described above in relation to Fig. 1.

[0046] System configuration

[0047] As described above, the present technology may also be applied at the design phase, or during the configuration of the wind power generation system 100. Fig. 5 is a flow diagram illustrating a method 500 of configuring a wind power generation system 100 as shown in Fig. 1 .

[0048] In step 501 , the wind power generation system 100 is modelled, based on at least: a predicted capability of the plurality of the WTGs 101 (and optionally of the transformer and the cables 102) to supply and / or consume reactive power; and one or more possible reactive power set points for the wind power generation system 100 provided by the grid operator 105.

[0049] In step 502, based on the modelling, a minimum amount of additional reactive power required to be supplied and / or consumed by the wind power generation system 100 is then determined. In one example, determining the minimum amount of additional reactive power required includes determining a minimum amount of additional reactive power to be supplied by dynamic reactive power compensation equipment.

[0050] In step 503, the wind power generation system 100 is configured by installing an amount of reactive power compensation equipment 104 which is sufficient to supply and / or consume at least the determined minimum amount of additional reactive power. Alternatively, the method may be implemented during or after the construction of the wind power generation system 100. In this case, where the capability of the reactive power compensation equipment 104 exceeds the determined minimum amount, surplus equipment may be removed and redeployed to other projects.

[0051] In optional step 504, one or more functions as described above, which map input parameter values to control parameter values, may be determined based on the modelling in step 501 and the configuration of the wind power generation system in step 503. The controller 304 for implementing the functions and generating the control parameter values is configured appropriately and installed.

[0052] Reduction in additional reactive power compensation requirement

[0053] Each panel in Fig. 6 shows a plot of active power (in MW) against reactive power (in MVAr) as measured at the point of interconnection between an exemplary wind power generation system 100 and a power transmission grid 103. As shown in the plots, reactive power may be positive or negative, depending on the phase difference between current and voltage (i.e. whether current is “lagging” or “leading” the voltage). In each case, the perimeter 601 defines a space in which the wind power generation system 100 must be able to operate, e.g. as specified by the grid operator 105. The curves 602a, 602b, 602c, and 602d represent the net reactive power at the point of interconnection to the grid 103, resulting from the cabling 102, the transformers between the WTGs 101 , and, where applicable, the WTGs 101 and additional fixed reactive power compensation equipment. Arrows indicate a shortfall in reactive power compensation capability, to be provided by further dynamic compensation equipment.

[0054] Panel A shows a plot for a wind power generation system 100 assuming no reactive power output from the WTGs 101 and no fixed reactive power compensation equipment. As shown by the left-facing arrow, there is a shortfall of -400 MVAr of negative (i.e. inductive) reactive power capability. Therefore, in order to satisfy the requirements of the grid operator 105, dynamic reactive power capability in the region of 400 MVAr would be required, at very high cost.

[0055] Panel B shows the effect of introducing static reactive power compensation equipment, in the form of a 100 MVAr onshore reactor and a 100 MVAr offshore reactor, to the wind power generation system 100. The curve 602b is shifted, reducing the shortfall in reactive power capability to approximately 200 MVAr (both capacitive and inductive).

[0056] Panel C shows an example plot for a wind power generation system 100 configured taking into account the dynamic reactive power capability of the WTGs 101 and the present methods of dynamic reactive power control. In this case, no offshore reactor is required, and the requirement for additional dynamic reactive power compensation (e.g. from a STATCOM) is reduced to -100 MVAr. The cost associated with the provision of reactive power compensation is therefore greatly reduced.

[0057] Alternatively, as illustrated in panel D, the WTGs may be utilized to counteract the power dependency in the transformer and cable reactive power. The curved characteristic is then removed. This can be viewed as a power-dependent static compensation. By utilizing this method, the additional requirement for compensation is 150 MVAr (inductive and capacitive).

Claims

CLAIMS:1 . A method of dynamically controlling reactive power compensation in a wind power generation system, the wind power generation system comprising a plurality of wind turbine generators and reactive power equipment external to the plurality of wind turbine generators, wherein said plurality of wind turbine generators and reactive power equipment are connected via an export cable to a power transmission grid, and wherein the method comprises: obtaining one or more predetermined functions for determining values of a plurality of control parameters based on values of a plurality of input parameters, wherein the plurality of input parameters includes (i) an active power output of the plurality of wind turbine generators and (ii) a reactive power set point for the wind power generation system, and wherein the plurality of control parameters includes at least (i) a parameter indicative of a first amount of reactive power to be supplied or consumed by the wind turbine generators and (ii) a parameter indicative of a second amount of reactive power to be supplied or consumed by the reactive power compensation equipment external to the wind turbine generators; during operation of the wind power generation system, obtaining values for the plurality of input parameters; and based on the obtained values of the input parameters, using the one or more predetermined functions to determine values of the control parameters.

2. The method of claim 1 , further comprising: based on the determined values of the control parameters, controlling the plurality of wind turbine generators to supply or consume the first amount of reactive power and controlling the reactive power compensation equipment external to the wind turbine generators to supply or consume the second amount of reactive power.

3. The method of claim 2, comprising: controlling the plurality of wind turbine generators to supply or consume the first amount of reactive power by sending a control signal based on the determined values of the control parameters to a wind turbine control system, to cause the wind turbine control system to determine set points for individual wind turbine generators such that the plurality of wind turbine generators supplies or consumes the first amount of reactive power.

4. The method of any one preceding claim, wherein the one or more predetermined functions comprises a look-up table mapping values of the plurality of input parameters to values of the plurality of control parameters.

5. The method of any one preceding claim, wherein the input parameters further include one or more temperature measurements of the export cable.

6. The method of any one preceding claim, wherein the input parameters further include: a system configuration of the wind power generation system; and / or a voltage of the power transmission grid.

7. The method of any one preceding claim, wherein obtaining the values of the input parameters comprises, for one or more of the input parameters, performing measurements on the wind power generation system in operation.

8. The method of any one preceding claim, wherein the second amount of reactive power comprises: an amount of reactive power to be supplied or consumed by dynamic reactive power compensation equipment that is able to supply or consume a variable amount of reactive power over a continuous range of values; an amount of reactive power to be supplied or consumed by fixed reactive power compensation equipment that is able to supply or consume a substantially fixed amount of reactive power, or is able to provide a variable amount of reactive power only in discrete steps.

9. The method of claim 8, wherein the static reactive power compensation equipment comprises one or more capacitors and / or one or more switched reactors, and wherein the dynamic reactive power compensation equipment comprises one or more static synchronous compensators.

10. The method of any one preceding claim, wherein the control parameters further include one or more tap changer set points for respective transformers of the wind power generation system.11 . The method of any one preceding claim, further comprising: based on the active power output of the plurality of wind turbine generators, and optionally a system configuration of the wind power generation system, determining a maximum and / or minimum reactive power output of the wind turbine generators, and wherein the determined values of the control parameters are determined based on said maximum and / or minimum reactive power output.

12. The method of any one preceding claim, wherein the plurality of input parameters includes one or more temperature measurements of the export cable, and wherein the method further comprises: in response to determining that a temperature measurement at a portion of the export cable exceeds a predetermined threshold, increasing the first amount of reactive power to be supplied or consumed by the wind turbine generators.

13. The method of any one preceding claim, wherein the plurality of wind turbine generators are located offshore, and one or more components of the reactive power compensation equipment external to the wind turbine generators is located onshore, optionally at an interconnect between the wind power generation system and the power transmission grid.

14. A reactive power control system for dynamically controlling reactive power compensation in a wind power generation system, the wind power generation system comprising a plurality of wind turbine generators and reactive power equipment external to the plurality of wind turbine generators, wherein said plurality of wind turbine generators and reactive power equipment are connected via an export cable to a power transmission grid, and wherein the reactive power control system is configured to: obtain one or more predetermined functions for determining values of a plurality of control parameters based on values of a plurality of input parameters, wherein the plurality of input parameters includes (i) an active power output of the plurality of wind turbine generators and (ii) a reactive power set point for the wind power generation system, and wherein the plurality of control parameters includes at least (i) a parameter indicative of a first amount of reactive power to be supplied or consumed by the wind turbine generators and (ii) a parameter indicative of a second amount of reactive powerto be supplied or consumed by the reactive power compensation equipment external to the wind turbine generators; during operation of the wind power generation system, obtain values for the plurality of input parameters; and based on the obtained values of the input parameters, use the one or more predetermined functions to determine values of the control parameters.

15. The reactive power control system of claim 14, wherein the reactive power control system is further configured to, based on the determined values of the control parameters, control the plurality of wind turbine generators to supply or consume the first amount of reactive power and control the reactive power compensation equipment external to the wind turbine generators to supply or consume the second amount of reactive power.

16. The reactive power control system of claim 15, wherein the reactive power control system is configured to control the plurality of wind turbine generators to supply or consume the first amount of reactive power by sending a control signal based on the determined values of the control parameters to a wind turbine control system, to cause the wind turbine control system to determine set points for individual wind turbine generators such that the plurality of wind turbine generators supplies or consumes the first amount of reactive power.

17. The reactive power control system of claim 16, wherein the reactive power control system is located onshore and the wind turbine control system is located offshore.

18. A method of configuring a wind power generation system, the wind power generation system comprising a plurality of wind turbine generators and reactive power equipment external to the plurality of wind turbine generators, wherein said plurality of wind turbine generators and reactive power equipment are connected via an export cable to a power transmission grid, and wherein the method comprises: modelling the wind power generation system, wherein the modelling is based on at least (i) a predicted capability of the plurality of the wind turbine generators and the export cable to supply and / or consume reactive power and (ii) one or more possible reactive power set points for the wind power generation system;based on the modelling, determining a minimum amount of additional reactive power required to be supplied and / or consumed by the wind power generation system; and configuring the wind power generation system, wherein said configuring comprises installing or removing reactive power compensation equipment external to the wind turbine generators, such that the wind power generation system comprises sufficient reactive power compensation equipment external to the wind turbine generators to supply and / or consume at least the determined minimum amount of additional reactive power.

19. The method of claim 18, comprising: based on the modelling and the reactive power compensation equipment external to the wind turbine generators, determining one or more functions for determining values of a plurality of control parameters based on values of a plurality of input parameters, wherein the plurality of input parameters includes (i) an active power output of the plurality of wind turbine generators and (ii) a reactive power set point for the wind power generation system, and wherein the plurality of control parameters includes at least (i) a parameter indicative of a first amount of reactive power to be supplied or consumed by the wind turbine generators and (ii) a parameter indicative of a second amount of reactive power to be supplied or consumed by the reactive power compensation equipment external to the wind turbine generators; and configuring a controller to, during operation of the wind power generation system:(i) obtain values for the plurality of input parameters; and(ii) based on the obtained values of the input parameters, use the one or more functions to determine values of the control parameters.

20. The method of claim 19, comprising: configuring the controller to, based on the active power output of the plurality of wind turbine generators, and optionally a system configuration of the wind power generation system, determine a maximum and / or minimum reactive power output of the wind turbine generators, and wherein the determined values of the control parameters are determined based on said maximum and / or minimum reactive power output.21 . The method of claim 19 or 20, wherein the plurality of input parameters includes one or more temperature measurements of the export cable.

22. The method of claim 21 , wherein the method further comprises configuring the controller to, in response to determining that a temperature measurement at a portion of the export cable exceeds a predetermined threshold, increase the first amount of reactive power to be supplied or consumed by the wind turbine generators.

23. The method of any one of claims 19 to 21 , comprising configuring the controller to, based on the determined values of the control parameters, control the plurality of wind turbine generators during use to supply or consume the first amount of reactive power and control the reactive power compensation equipment external to the wind turbine generators to supply or consume the second amount of reactive power.

24. The method of any one of claims claim 23, comprising configuring the controller to control the plurality of wind turbine generators during use to supply or consume the first amount of reactive power by sending a control signal based on the determined values of the control parameters to a wind turbine control system, to cause the wind turbine control system to determine set points for individual wind turbine generators such that the plurality of wind turbine generators supplies or consumes the first amount of reactive power.

25. The method of any one of claims 19 to 24, wherein the one or more functions comprises a look-up table mapping values of the plurality of input parameters to values of the plurality of control parameters.

26. The method of any one of claims 19 to 25, wherein the input parameters further include: a system configuration of the wind power generation system; and / or a voltage of the power transmission grid.

27. The method of any one of claims 19 to 26, comprising configuring the controller to obtain the values of the input parameters by performing measurements on the wind power generation system in operation.

28. The method of any one of claims 19 to 27, wherein the second amount of reactive power comprises: an amount of reactive power to be supplied or consumed by dynamic reactive power compensation equipment that is able to supply or consume a variable amount of reactive power over a continuous range of values; an amount of reactive power to be supplied or consumed by fixed reactive power compensation equipment that is able to supply or consume a substantially fixed amount of reactive power, or is able to provide a variable amount of reactive power only in discrete steps.

29. The method of claim 28, wherein the static reactive power compensation equipment comprises one or more capacitors and / or one or more switched reactors, and wherein the dynamic reactive power compensation equipment comprises one or more static synchronous compensators.

30. The method of any one of claims 19 to 29, wherein the control parameters further include one or more tap changer set points for respective transformers of the wind power generation system.31 . The method of any one of claims 18 to 30 and comprising installing the plurality of wind turbine generators offshore, and installing one or more components of the reactive power compensation equipment external to the wind turbine generators onshore, optionally at an interconnect between the wind power generation system and the power transmission grid.

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