Method and system for improving control of a regenerative energy field

Abstract

According to one aspect of the present invention, there is provided a power plant controller for a renewable energy power plant including a plurality of renewable energy generators. The renewable energy farm is connected to a power network. The farm controller is configured to execute machine-readable instructions to: receive a signal indicative of a voltage level of a power network to which the farm is connected; receiving a plurality of signals from the plurality of renewable energy generators, the Good signal indicating a voltage level of the respective renewable energy generator; and for each of the plurality of renewable energy generators, determining a respective reactive power setpoint based on: an indicated voltage level of the power network; an indicated voltage level of the renewable energy generator; and a reference voltage level based on the indicated voltage levels of the plurality of renewable energy generators; and scheduling each determined reactive power setpoint to a respective local controller associated with a respective renewable energy generator for controlling the renewable energy generator.

Description

Technical Field

[0001] The present disclosure relates to methods and systems for improving the control of renewable energy plants connected to a power network. Background Art

[0002] Regulators and operators of power grids expect connected power plants to comply with a 'grid code' and provide specific services to the power grid. For example, some operators require power plants to support the power grid when the voltage level of the power grid deviates from the normal operating range or the allowed range around the nominal voltage value.

[0003] For example, the lower threshold value may be, for example, in the range from about -5% to about -20% of the nominal voltage, and the upper threshold value may be, for example, in the range from about +5% to about +20% of the nominal voltage. For example, in a 110 kV network, the normal operating range may be between 96 and 123 kV, in a 220 kV network, it may be between 193 and 245 kV, and in a 380 kV network, it may be between 350 and 420 kV.

[0004] To support the power grid, the farm controller may provide reference values (i.e., target values or "set points") for one or more electrical production parameters (such as active power and / or reactive power) to be generated by the individual renewable energy generators (renewable energy generators) of the farm. These reference values or set points may be dispatched to local controllers associated with respective ones of the renewable energy generators, which operate the generators to achieve the set points received from the farm controller. For example, the farm controller may provide reactive power reference values for use by the individual renewable energy generators to support the power grid by consuming or injecting reactive power accordingly.

[0005] Conventional dispatch strategies balance the reactive power demand of the power network between the renewable energy generators to provide equal currents in the feeder cables connecting the generators in the power plant.

[0006] However, such a dispatching strategy may result in voltage deviations between different generators and significant voltage distortion.It is an object of the present invention to address one or more disadvantages associated with the prior art. Summary of the Invention

[0007] According to one aspect of the present invention, a farm controller is provided for a renewable energy farm comprising a plurality of renewable energy generators. The renewable energy farm is connected to a power network, and the farm controller is configured to execute machine-readable instructions to: receive a signal indicating a voltage level of the power network to which the farm is connected; determine a reactive power reference value for each renewable energy generator based on the indicated voltage level of the power network; receive a plurality of signals from the plurality of renewable energy generators, each signal indicating a voltage level of a corresponding renewable energy generator; and for each of the plurality of renewable energy generators: determine a reactive power regulation based on a difference between the indicated voltage level of the renewable energy generator and a reference voltage level based on the indicated voltage levels of the plurality of renewable energy generators; determine a reactive power setpoint based on the reactive power reference value and the reactive power regulation determined for the renewable energy generator; and dispatch the determined reactive power setpoint to a local controller associated with the renewable energy generator for controlling the renewable energy generator.

[0008] According to another aspect of the present invention, a farm controller for a renewable energy farm comprising a plurality of renewable energy generators is provided. The renewable energy farm is connected to a power network, and the farm controller is configured to execute machine-readable instructions to: receive a signal indicating a voltage level of the power network to which the farm is connected; receive a plurality of signals from the plurality of renewable energy generators, each signal indicating a voltage level of a respective renewable energy generator; for each of the plurality of renewable energy generators, determine a respective reactive power set point, the reactive power set point being determined based on: an indicated voltage level of the power network; an indicated voltage level of the renewable energy generator; and a reference voltage level, the reference voltage level being based on the indicated voltage levels of the plurality of renewable energy generators; and dispatch each determined reactive power set point to a respective local controller associated with the respective renewable energy generator for controlling the renewable energy generator.

[0009] In this way, the farm controller is advantageously configured to determine reactive power setpoints that take into account the voltage level of the power network, while also taking into account the individual local voltage levels of the generators and how these voltage levels vary between farms. The farm controller is thus able to improve the balance of voltage levels across the farm, providing improved voltage margin in addition to reducing voltage distortion and feeder system losses.

[0010] In an example, a power plant controller is configured to determine a reactive power set point by: determining a reactive power reference value for each renewable energy generator based on an indicated voltage level of a power network; and for each of a plurality of renewable energy generators: determining a reactive power regulation based on a difference between the indicated voltage level of the renewable energy generator and a reference voltage level; and determining a reactive power set point based on the reactive power reference value and the reactive power regulation determined for the renewable energy generator.

[0011] In this way, the farm controller is advantageously configured to determine a reactive power setpoint that collectively meets the total reactive power demand of the farm, while also appropriately setting the individual reactive power setpoints of the individual renewable energy generators to account for relative local voltage levels between the generators.

[0012] In one example, a droop control technique is used to determine reactive power regulation for each renewable energy generator. The droop control technique provides a reliable relationship between input and output parameters. That is, the droop control technique can define reactive power regulation based on the difference between the indicated voltage level of the renewable energy generator and a reference voltage level. For example, the droop control technique can define the relationship as a linear function, where a droop coefficient of the function defines the slope of the linear relationship. In one example, the droop coefficient can be a fixed value or a variable value that can be updated in real time based on fluctuations in the indicated local voltage level of the renewable energy generator.

[0013] In the example, the following equation is used to determine reactive power regulation:

[0014] ΔQ i =(V REF_WTG –V_WTG i )×Droop

[0015] where ΔQ i is the reactive power regulation of the i-th renewable energy generator, i=1 to N, where N is a positive integer corresponding to the number of renewable energy generators in the power plant, V REF_WTG is the reference voltage level, V_WTG i is the indicated voltage level of the i-th renewable energy generator, and Droop is the droop coefficient of the droop control technique (relating the determined voltage difference to the corresponding reactive power regulation, e.g. with the unit VAR / V). The droop coefficient Droop may be the same for each renewable energy generator in order to ensure that the sum of the reactive power regulation Equal to zero.

[0016] In an example, a farm controller is configured to determine droop factors (Droop) for a plurality of renewable energy generators based on a power parameter of the renewable energy farm. For example, the farm controller may determine the droop factor (Droop) using a lookup table storing predetermined values of the droop factor (Droop) for corresponding values of the farm's power parameter. In this manner, the droop factor is advantageously adapted to farm conditions to improve reactive power regulation.

[0017] In an example, the farm controller is configured to limit each determined reactive power regulation using an upper power limit and / or a lower power limit. In this way, the farm controller reduces the load demand on the renewable energy generators, reducing the risk of damage.

[0018] In an example, the farm controller is configured to limit the determined rate of change of the reactive power regulation using a rate of change limit.

[0019] In an example, the reactive power reference value is determined for each renewable energy generator by: determining a reactive power reference value for the renewable energy farm based on an indicated voltage level of the power network; and

[0020] The reactive power reference value is divided among the plurality of renewable energy generators to determine an individual reactive power reference value for each renewable energy generator.

[0021] In an example, the reference voltage level is determined as an average voltage level of indicative voltage levels of a plurality of renewable energy generators.

[0022] In an example, the farm controller is configured to limit the reference voltage level using an upper voltage threshold and / or a lower voltage threshold.

[0023] In this way, the farm controller mitigates the effects of abnormal voltage levels and reduces the risk of damage to the renewable energy generators.

[0024] In an example, the farm controller is configured to limit the rate of change of the reference voltage level using a rate of change limit.

[0025] In an example, multiple signals received from multiple renewable energy generators each indicate a voltage level of the corresponding renewable energy generator at one or more of: a low voltage side of a transformer of the renewable energy generator, which connects the renewable energy generator to a power plant; a high voltage side of the transformer; and / or at corresponding terminals of a power converter of the renewable energy generator.

[0026] In an example, the farm controller is configured to determine respective reactive power setpoints based, at least in part, on detecting one of a plurality of farm operating conditions based on a reference voltage level and an indicated voltage level of a corresponding renewable energy generator.

[0027] In an example, the multiple field operating conditions include: the active power output or reactive power output of the power plant is greater than or equal to an upper power threshold; the active power output or reactive power output of the power plant is less than or equal to a lower power threshold; the indicated voltage level of the power network is greater than or equal to an upper voltage threshold; and / or the indicated voltage level of the power network is less than or equal to a lower voltage threshold.

[0028] According to another aspect of the present invention, a method of operating a renewable energy farm connected to a power network is provided. The renewable energy farm includes a plurality of renewable energy generators, and the method includes: obtaining a signal indicating a voltage level of a power network to which the farm is connected; obtaining a plurality of signals from the plurality of renewable energy generators, each signal indicating a voltage level of a respective renewable energy generator; determining, for each of the plurality of renewable energy generators, a respective reactive power set point based on: an indicated voltage level of the power network; an indicated voltage level of the renewable energy generator; and a reference voltage level based on the indicated voltage levels of the plurality of renewable energy generators; and dispatching the determined reactive power set point from a farm controller to a local controller associated with the renewable energy generator for controlling the renewable energy generator.

[0029] According to another aspect of the present invention, a method for operating a renewable energy farm connected to a power network is provided. The renewable energy farm includes a plurality of renewable energy generators, and the method includes: obtaining a signal indicating a voltage level of a power network to which the farm is connected; determining a reactive power reference value for each renewable energy generator based on the indicated voltage level of the power network; obtaining a plurality of signals from the plurality of renewable energy generators, each signal indicating a voltage level of a corresponding renewable energy generator; and for each of the plurality of renewable energy generators: determining a reactive power regulation based on a difference between the indicated voltage level of the renewable energy generator and a reference voltage level based on the indicated voltage levels of the plurality of renewable energy generators; determining a reactive power setpoint based on the reactive power reference value and the reactive power regulation determined for the renewable energy generator; and dispatching the determined reactive power setpoint from a farm controller to a local controller associated with the renewable energy generator for controlling the renewable energy generator.

[0030] It is expressly intended that within the scope of the present invention, the individual aspects, embodiments, examples, and alternatives set forth in the preceding paragraphs, in the claims, and / or in the following description and drawings, and in particular individual features thereof, may be taken independently or in any combination. That is, all embodiments and / or features of any embodiment may be combined in any manner and / or combination, unless such features are incompatible. Applicants reserve the right to change any originally filed claims or documents accordingly, including the right to amend any originally filed claim to rely on and / or combine any feature of any other claim, even though protection was not originally claimed in that manner. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] One or more embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0032] Figure 1 schematically illustrates a power network connected to a renewable energy farm including a farm controller;

[0033] Figure 2 Show Figure 1 An exemplary control structure of a power plant;

[0034] Figure 3 Shows the operation according to the embodiment of the present invention Figure 1 An exemplary method for a renewable energy power plant; and

[0035] Figure 4 According to an embodiment of the present invention, Figure 3 Exemplary sub-steps of the method shown. DETAILED DESCRIPTION

[0036] Embodiments of the present invention relate to methods and systems for improving the control of renewable energy plants, particularly in connection with providing voltage support to a power network.

[0037] This is achieved by determining an individual reactive power set point for each renewable energy generator based on an indicated voltage level of the power network and a local voltage level at each generator. In particular, the central farm controller is configured to receive signals indicative of the voltage level of the power network and the local voltage levels of the individual renewable energy generators, and to determine a respective reactive power set point for each renewable energy generator based on:

[0038] (i) the indicated voltage level of the power network,

[0039] (ii) the indicated voltage level of the renewable energy generator, and

[0040] (iii) a reference voltage level based on indicative voltage levels of the plurality of renewable energy generators.

[0041] For example, a farm controller can determine a total reactive power demand (or reference value) for the renewable energy farm to support the power network based on an indicated voltage level of the power network. For example, the farm controller can include a closed-loop controller for determining the reactive power demand based on a feedback measurement of the reactive power output of the farm and an indicated voltage level of the power network, for comparison with corresponding reference values, e.g., receivable as external input from a network operator. The total reactive power demand can then be divided into individual reactive power reference values (or set points) for the individual renewable energy generators. For example, the individual reactive power reference values can be determined by equally distributing the overall reactive power reference demand among the generators or by otherwise distributing the reactive power reference demand among the generators (e.g., based on the capabilities or available power of the individual generators). Advantageously, to minimize power losses in the farm, the central farm controller can further adjust each of the initial reactive power reference values based on the local voltage level of the respective generator. In particular, the central farm controller can determine, for each renewable energy generator, a respective reactive power setpoint by adjusting an initially determined reactive power reference value based on the local voltage level. For example, the farm controller can be configured to adjust each initial reactive power reference value based on, in each case, a deviation of the respective local voltage level from a reference voltage level for the generator, wherein the reference voltage level is advantageously based on the local voltage level itself. For example, the reference voltage level can be an average voltage level of the renewable energy generators.

[0042] The determined reactive power setpoints are then dispatched to the respective local controllers, which control the respective renewable energy generators accordingly to support the network voltage.

[0043] In this way, it is contemplated that embodiments of the present invention will provide a more balanced voltage output from the generators, reduce losses in the feed system, and provide more voltage margin or capacity for improved control reliability in the event of a network fault.

[0044] Figure 1 A typical architecture is shown in which a renewable energy farm is connected to a main or wider power network. Figure 1In the example shown, the renewable energy power plant is a wind power plant (WPP). As will be understood by those skilled in the art, a WPP comprises a plurality of wind turbine generators (WTGs). WTGs are often referred to as 'wind turbines'. The examples shown are representative only, and those skilled in the art will understand that other specific architectures are possible. In other examples, the power plant may comprise other renewable energy sources, such as a solar power plant, a biomass power plant, an ocean / wave / tidal power plant, or a hybrid power plant having a combination of different types of renewable energy power plants. Therefore, the present invention relates generally to renewable energy power plants and renewable energy generators, rather than being specific to wind power plants and generators as shown in the accompanying drawings. The components of the wind power plant and the power network are conventional, and will therefore be familiar to the technical reader. It is expected that, except for Figure 1 Other known components may be incorporated in addition to or in place of the components shown and described herein. Such changes will be within the capabilities of those skilled in the art.

[0045] Figure 1 The power system 10 is shown incorporating a WPP 12. In this example, the WPP 12 comprises a plurality of WTGs 14. Each of the plurality of WTGs 14 converts wind energy into electrical energy, which is passed from the WPP 12 to a main power network, or 'main' 16, for distribution as real power and / or current.

[0046] Although not in Figure 1 As shown in FIG, the WPP 12 also includes compensation equipment, such as a static synchronous compensator (STATCOM) or other type of synchronous compensator, configured to provide reactive power or reactive current support as needed.

[0047] The WPP 12 also includes a connection network 18 for connecting the WPP 12 to the main network 16. Figure 1 Not shown in the figures, the WTGs 14 may be connected together in the WPP 12 via respective feeder lines / systems connected to one or more substations or collection points of the WPP 12. Such substations or collection points may thus be part of a connecting network 18 in which the power outputs from the WTGs 14 are combined, and the connecting network 18 may further include one or more transmission lines connecting the substations / collection points to the main network 16. The power generated by each WTG 14 may thus be transmitted to a respective one of the substation(s) or collection point(s) via a respective feeder system, and in turn, via the transmission line(s), to the main network 16.

[0048] In this example, the WPP 12 and the main network 16 are connected at a point of interconnection (PoI) 20, which is the interface between the WPP 12 (or its transmission line(s)) and the main network 16. The PoI 20 may also be referred to as a point of common coupling, which may be abbreviated as 'PCC' or 'PoCC'.

[0049] The WPP 12 also includes a power plant controller 22, hereinafter referred to as PPC 22, for centralized control of the WTGs 14, and each of the WTGs 14 is associated with a corresponding local WTG controller 15. As will be understood by those skilled in the art, the WTG controller 15 can be considered to be a local control system capable of operating the WTG 14 in the manner specified herein, and can include multiple control modules that control individual components of the WTG or simply a single controller with multiple sub-modules (as will be described in the examples below). The computer system of the WTG controller 15 can operate according to software downloaded via a communication network or programmed onto it from a computer-readable storage medium.

[0050] Although in this example each WTG 14 is associated with a respective local WTG controller 15, this arrangement is not intended to limit the scope of the invention. In other implementations, groups of WTGs may share a single, semi-centralized WTG controller, eg, such that there are fewer WTG controllers than WTGs.

[0051] In any case, a bidirectional control network may be arranged between the PPC 22 and the WTG controller 15, enabling bidirectional communication. For example, the uplink direction (i.e., the direction from the central PPC 22 to the local WTG controller 15) is used to send reference values (e.g., for voltage and / or reactive power) from the PPC 22 to the local WTG controller 15. The downlink direction may be used for the WTG 15 to return information about its current operating state (e.g., about the amount of reactive power currently being generated and / or the local voltage level) to the central PPC 22. Such a control network may, for example, be implemented as a bus system, i.e., a CAN bus (ISO 11898) or an Ethernet bus (IEEE 802.3).

[0052] The function of PPC 22 is to provide centralized control of WTG 14 and act as a command and control interface between WPP 12 and network 16, more specifically, network operator 26. For example, network operator 26 may be a transmission system operator (TSO) or a distribution system operator (DSO).

[0053] The PPC 22 is configured to generate and send dispatch signals to the WTG controller 15. The dispatched signals include active and reactive current and / or power, set points determined by the PPC 22 to provide frequency and voltage support to the primary network 16 based on measurements of power characteristics of the WTG 14, WPP 12, and / or the primary network 16.

[0054] In turn, the WTG controller 15 controls the WTG 14 according to the setpoint contained within the dispatch signal, and in this way, the WPP 12 is able to vary its power or current output in response to the setpoint received from the PPC 22 .

[0055] To this end, a power plant controller (PPC) 22 is connected to the main grid 16 at a point of measurement (PoM) 24 (such as a power meter). For example, the PPC 22 may be configured to receive one or more measurement signals from the PoM 24, the one or more measurements incorporating or including measurements of power supplied from the WPP 12 to the main grid 16 and / or a frequency level of the main grid 16.

[0056] The PPC 22 is a suitable computer system for executing the controls and commands as described herein, and thus may integrate a processing module 28, a connectivity module 30, a memory module 32, a sensing module 34, and the like, as shown. Figure 1 shown.

[0057] Connectivity module 30 , memory module 32 , and / or sensing module 34 are configured to provide information indicative of frequency levels of primary network 16 and power levels, current levels, and / or voltage levels of WTG 14 and / or WPP 12 to processing module 28 .

[0058] For example, the sensing module 34 may receive such information directly from one or more connected sensors or power meters (e.g., at the PoM 24) and communicate the information to the processing module 28. Alternatively or additionally, information may be determined by one or more systems connected to the connectivity module 30 (such as the WTG controller 15), and the information may in turn be communicated to the processing module 28 via the connectivity module 30. In each case, the determined information may be permanently or temporarily stored in the memory module 32, from which it may be recalled by the processing module 28. The PPC 22 may also receive information about the network 16 and / or local buses, substations, and networks from an energy management system (not shown).

[0059] The PPC 22 and local WTG controller 15 may therefore each be arranged to operate in a feedback mode in which they compare a reference value (e.g. from a reference input) with a measured value (e.g. from a measured input) and generate a control signal or reference based on the difference between the respective input values.

[0060] However, in contrast to conventional arrangements, the PPC 22 is configured to determine and dispatch reactive power setpoints to the WTG controllers 15 based on both the voltage level of the main grid 16 and the local voltage levels of the individual WTGs 14. In this way, the PPC 22 is configured to use the local voltage levels to determine individualized reactive power setpoints for controlling each WTG 14, better distributing the voltage levels among the WTGs 14 while meeting the reactive power requirements of the main grid 16.

[0061] References will now be attached Figure 2 An exemplary control structure according to an embodiment of the present invention is described in more detail.

[0062] like Figure 2 As shown in FIG, the overall controller structure of the WPP 12 includes a central PPC 22 and local WTG controllers 15. For simplicity, Figure 2 A single WTG controller 15 is shown in FIG, but it should be understood that the PPC 22 is connected to each local WTG controller 15 in substantially the same manner.

[0063] The central PPC 22 and the local WTG controller 15 each include both reactive power controllers and active power controllers, however, the following description is limited to the aspects of reactive power control to avoid obscuring the present invention, thus Figure 2 Only the reactive power controller is shown in FIG.

[0064] PPC 22 is shown receiving, among other inputs, a voltage signal V_PoC indicative of the voltage level of primary network 16. For example, PPC 22 may receive a sequence of time-varying measurements indicative of the voltage level at PoM 24, which may be used to derive voltage signal V_PoC.

[0065] The voltage signal V_PoC is provided as an input to a reactive power controller 37 (ie, Q controller 37 ) of the PPC 22 , where the voltage signal V_PoC is used to regulate the reactive power of the network 16 .

[0066] To this end, the Q controller 37 receives signals related to reactive power control, such as a voltage signal V_PoC, and a feedback signal Q_WPP indicating reactive power output from the WPP 12 to the main grid 16. The Q controller 37 also receives WTG feedback signals from individual WTGs. For example, the WTG feedback signals may include signals indicating reactive power output and voltage of each WTG 14. That is, the WTG feedback signals may include:

[0067] (i) Local power signal Qmeas_WTG i , which indicates each WTG iReactive power output; and

[0068] (ii) Local voltage signal V_WTG i , which indicates each WTG i voltage level;

[0069] Where i=1 to N and N is a positive integer corresponding to the number of WTGs 14 in the WPP 12 .

[0070] The Q controller 37 is configured to determine an individual reactive power set point for dispatching to the corresponding WTG controller 15. That is, the Q controller 37 is configured to determine a reactive power set point Qset_WTG for each WTG 14. i To this end, the Q controller 37 may include one or more reactive power control loops for determining a reactive power set point Qset_WTG based on such inputs. i , as will be described in more detail.

[0071] In an example, the Q controller 37 may also receive external control inputs for reactive power Qref and / or voltage Vref control to be obtained at the PoM 24, and / or one or more parameters of a droop function used in the Q controller 37. Such parameters may include a slope or droop factor that defines a mapping of the measured voltage to the reactive power to be generated, for example in units of VAR / V.

[0072] As indicated at the outset, the concept of "reactive power" includes other related parameters such as reactive current, power factor, etc. Therefore, the reactive power setpoint Qset_WTG i It may also indicate the amount of reactive current to be generated by the respective WTG 14. Thus, the WTG 14 and / or STATCOM may also be commanded with a reactive current set point rather than a reactive power (and optionally active power) set point.

[0073] like Figure 2As shown, in this non-limiting example, the Q controller 37 includes a VQ-PF controller 42 and a Q setpoint scheduler 41. The VQ-PF controller 42 generates an internal overall reference value, Qref_WPP, for reactive power to be generated by the WPP 12 based on inputs to the Q controller 37. "V" stands for voltage, "Q" stands for reactive power, and "PF" stands for power factor; "VQ-PF" thus indicates that the VQ-PF controller 42 is capable of receiving V, Q, and / or PF as external references and generating the internal reference value, Qref_WPP, based on such external references. For example, when the voltage signal, V_PoC, is above a voltage threshold, the VQ-PF controller 42 may generate a reduced Qref_WPP value. To this end, the VQ-PF 42 may also include one or more droop functions or lookup tables for determining a prescribed reactive power level for the WPP 12, for a respective network voltage level, and / or a predetermined ramp rate for increasing or decreasing the reactive power level. In particular, the lookup table may contain a reactive power voltage (QV) curve relating network voltage levels to corresponding reactive power demands of the WPP 12, which may then be used in the power control loop to determine the internal reference value Qref_WPP.

[0074] The Q set point scheduler 41 uses the overall reactive power reference Qref_WPP to determine the individual reactive power set points Qset_WTG for each local WTG controller 15 and STATCOM controller 33 (if applicable). i .

[0075] For simplicity, the subsequent description only refers to the individual reactive power setpoint Qset_WTG for each local WTG controller 15 i However, it will be appreciated that further reactive power set points may be determined in substantially the same manner for the STATCOM controller 33 , which in effect is considered to be an additional local WTG controller 15 , if applicable.

[0076] The Q setpoint scheduler 41 is configured to set the Q setpoint according to the local voltage level V_WTG of the WTG 14. i Splitting the overall reactive power reference Qref_WPP into individual reactive power set points Qset_WTG i In this way, the overall reactive power reference Qref_WPP is met while balancing the voltage levels between the WTGs 14 .

[0077] For this purpose, the Q setpoint scheduler 41 is also configured to receive the local voltage signal V_WTG i , where each voltage signal V_WTG iIndicates the local voltage level of a corresponding one of the WTGs 14. For example, each voltage signal V_WTG i It may be derived from a time-varying sequence of voltage measurements obtained at the respective WTG 14. Such voltage measurements may, for example, be determined at respective terminals of a power converter of the WTG 14 and / or at the low or high voltage side of a transformer connecting the WTG 14 to the wider WPP 12.

[0078] The Q setpoint scheduler 41 is configured to use a single voltage level V_WTG i To determine the appropriate share or distribution of the overall reactive power reference Qref_WPP among the WTGs 14. This is done at least in part by determining the appropriate share or distribution of the overall reactive power reference Qref_WPP among the WTGs 14. i The set of local voltage levels V_WTG i This is achieved by comparing with a reference voltage level Vref_WTG (such as an average voltage level).

[0079] The Q setpoint scheduler 41 may be configured to initially determine a reactive power reference value Qref_WTG for each WTG 14 by nominally dividing or apportioning the total reactive power demand Qref_WPP of the WPP 12 among the WTGs 14. i .

[0080] The present invention is not intended to be particularly concerned with a nominal division of the total reactive power demand Qref_WPP, which may be determined according to a predetermined function and may or may not provide a uniform distribution.

[0081] To give an example, the Q setpoint scheduler 41 may be configured to divide the total reactive power demand Qref_WPP equally among the WTGs 14 according to the following equation:

[0082] Qref_WTG i =Qref_WPP / N

[0083] Where N is equal to the number of WTGs 14 between which the reactive power demand is shared.

[0084] In other examples, the initial partitioning may take into account the available reactive power Qavail at each WTG 14 i , and Q setpoint scheduler 41 may therefore also receive a signal Qavail from the local WTG controller 15 i , in order to determine the nominal share of the total Qref_WPP, where Qavail i indicates the available reactive power, ie the amount of reactive power that can currently be produced maximally by an individual WTG 14. In this way, the total Qref_WPP can be apportioned according to the capabilities of the individual WTGs 14.

[0085] Thereafter, the Q setpoint scheduler 41 may be configured to be based on the local voltage level V_WTG of the corresponding WTG 14 i Determine the initial reactive power reference value Qref_WTG i For example, the Q set point scheduler 41 may be configured to be based on the local voltage level V_WTG obtained from the WTG 14. i The deviation from the reference voltage level Vref_WTG determines the adjustment for each WTG 14. The reference voltage level Vref_WTG used for this comparison is advantageously based on the local voltage level V_WTG of the group of WTGs 14. i The Q setpoint scheduler 41 may therefore receive a local voltage signal V_WTG for each WTG 14 i , and based on this determine an average voltage level, which is used as a reference voltage level Vref_WTG.

[0086] To determine the corresponding reactive power regulation, the Q setpoint scheduler 41 may include a droop controller (not shown) that includes one or more schemes, rules, or algorithms for droop control of reactive power output of each WTG 14. The droop controller may, for example, include a droop coefficient Droop that relates the change in reactive power to the local voltage level V_WTG. i The deviation from the reference voltage level Vref_WTG is associated with Vref_WTG. In particular, the reactive power regulation can thus be determined according to the following equation:

[0087] ΔQ i =(V ref_WTG –V_WTG i )×Droop

[0088] Where ΔQ i is the reactive power regulation for the i-th WTG 14, where i=1 to N and is a positive integer corresponding to the number of WTGs 14, V REF_WTG is the reference voltage level, V_WTG i is the indicated voltage level of the ith WTG 14 , and Droop is the droop coefficient of the droop control technique, eg, having units of VAR / V.

[0089] In an example, the droop coefficient Droop can be such that every 1 unit (pu) of local voltage level deviation produces 0.05 pu of reactive power regulation. The droop coefficient Droop can be selected to be positive or negative. In other examples, the droop coefficient Droop can be linked to operating conditions, and the droop controller can be configured to determine the droop coefficient Droop as a function of an electrical power parameter (such as the reactive power output Q_WPP of the WPP 12 or the voltage level V_PoC of the main network 16). For example, the droop controller can include one or more control modules (not shown) configured to determine the droop coefficient based on a curve that relates corresponding values of the droop coefficient to the electrical power parameter (such as the voltage level V_PoC of the main network 16). For example, the curve can be selected from a plurality of such curves based on a control input (such as can be provided from a network or field operator). In this way, the droop coefficient is tunable according to operating conditions.

[0090] In each case, the droop controller is configured to use the same droop coefficient Droop for all WTGs 14 in order to ensure that the sum of the outputs is zero.

[0091] The output of the droop controller is the reactive power regulation ΔQ for each WTG 14 i , which can be compared with the initial reactive power reference value Qref_WTG i The combination is passed to the power limit block and / or rate limiter block (not shown) before. That is, additional logic (such as a limiter or rate limiter) may also be implemented to define the determined variables, such as reactive power regulation ΔQ i The power limit block applies upper and lower power limits to the reactive power regulation. The rate limiter block may also apply one or more rate of change limits to the determined reactive power regulation ΔQ i Again, the WTG controller 15 may determine the rate of change limit based on a maximum allowed rate of change of reactive power of the WTG 14 (such as may be specified for a particular type of WTG).

[0092] The Q setpoint scheduler 41 may therefore determine the reactive power setpoint Qset_WTG for each WTG 14 by: i : Divide the overall reactive power reference value Qref_WPP among the WTGs 14 to determine the initial reference value Qref_WTG i , reactive power regulation ΔQ i Added to the initial reference value Qref_WTG i For example, each reactive power set point Qset_WTG i It can therefore be determined according to the following equation:

[0093] Qset_WTGi =(Qref_WPP / N)+ΔQi=(Qref_WTG i )+ΔQi.

[0094] It should be understood here that the calculation is performed with the capacitive reactive power having a positive sign, so that the WTG 14 with a higher voltage will operate in a more inductive manner with a positive droop coefficient.

[0095] In this way, the Q setpoint scheduler 41 is configured to adjust the Q setpoint according to the local voltage level V_WTG of the individual WTG 14. i To adjust the nominal division of the overall Qref_WPP and the output individual reactive power set point Qset_WTG i , to produce a more balanced voltage level in each WTG 14. In this way, the individual reactive power setpoints Qset_WTG i Collectively, it is ensured that the WTG 14 meets the reactive power demand Qref_WPP of the WPP 12 .

[0096] The local WTG controller 15 includes a local Q controller 45. The local Q controller 45 receives the corresponding Qset_WTG scheduled from the PPC 22. i The value is used as input and the WTG 14 is controlled accordingly to generate a corresponding amount of reactive power, for example in a feedback operating mode.

[0097] In this way, the WTGs 14 are controlled to meet the reactive power demand Qref_WPP of the WPP 12 while producing balanced voltage levels between the WTGs 14 , which reduces power losses in the feed system and provides greater capability for responding to low / high voltage network faults.

[0098] Reference will now be made additionally to Figure 3 and Figure 4 The method 300 of operating the WPP 12 according to an embodiment of the present invention is described in more detail.

[0099] In step 302, PPC 22 obtains a voltage signal indicative of a voltage level V_PoC of primary network 16. For example, PPC 22 may receive or otherwise obtain a series of measurements, such as voltage measurements at PoM 24, and derive voltage signal V_PoC based thereon.

[0100] In parallel, in step 304, the PPC 22 receives a set of voltage signals indicative of the local voltage levels of the WTGs 14. That is, the PPC 22 receives a respective voltage signal V_WTG for each WTG 14. i , collectively forming a group of local voltage signals. For example, each local voltage signal V_WTG iThe local voltage level at a respective one of the WTGs 14 is indicated and may be received from the respective WTG controller 15 .

[0101] In step 306 , the PPC 22 determines the voltage level V_PoC of the primary network 16 and the indicated local voltage level V_WTG of each WTG 14 based primarily on the indicated voltage level V_PoC of the primary network 16 and the indicated local voltage level V_WTG of each WTG 14 . i To determine the reactive power set point Qset_WTG for each WTG 14 i In this context, the indicated voltage level V_PoC of the main network 16 is comparable to a reference voltage level (such as a nominal voltage level) of the main network 16. The difference or error can be used to determine a corresponding amount of reactive power to be supplied by the WPP 12 in order to mitigate this difference and thus support the power network to return to the nominal voltage level. For example, this may involve using a droop function or a lookup table, which is stored in the PPC 22, relating values of the indicated network voltage to corresponding reactive power values to support the network 16. At the same time, the indicated local voltage level V_WTG of the WTG 14 i are comparable to each other for the PPC 22 to determine how to determine the individualized reactive power setpoint Qset_WTG for the WTG 14 i , which will balance the loads while collectively consuming / injecting the required amount of reactive power to support the power network back towards nominal voltage levels.

[0102] Individual reactive power set point Qset_WTG i Thus, the PPC 22 may determine in step 306 according to one or more schemes, rules, or methods. As an example, Figure 4 The reactive power set point Qset_WTG for each WTG 14 is determined in step 306. i Exemplary sub-steps of the method.

[0103] In sub-step 308, the PPC 22 may determine an overall reactive power reference value, Qref_WPP, for the WPP 12 based on the voltage signal V_PoC. For example, the PPC 22 may use the deviation of the network voltage signal V_PoC from a reference voltage (such as the nominal network voltage) to determine a corresponding reactive power demand to be consumed / injected by the WPP 12 (to support the network 16), and input the reactive power value into a control loop for determining the overall reactive power reference value, Qref_WPP, by comparison with one or more feedback measurements of the reactive power output, Qmeas_WPP, from the PPC 22 to the WPP 12. For example, the PPC 22 may use a droop function, a lookup table, or a QV curve to relate the deviation of the network voltage signal V_PoC from the reference voltage to a corresponding reactive power demand, and compare the reactive power demand with the measured reactive power output, Qmeas_WPP, to determine the overall reactive power reference value, Qref_WPP, for the WPP 12. Optionally, the control loop of the PPC 22 may also use the reactive power output Qmeas_WTG from each of the WTGs 14 i Furthermore, the reactive power loop may receive a reactive power reference Qref or a voltage reference Vref from other Q-related control aspects.

[0104] The reactive power loop includes one or more schemes, rules or algorithms for combining the various inputs and comparing the reactive power to the reactive power feedback measurement. Based on this, the reactive power loop determines an overall reactive power reference Qref_WPP for the WPP 12, which can be provided to the Q setpoint scheduler 41.

[0105] In sub-step 310, the PPC 22 may divide the overall reactive power reference value Qref_WPP into the initial reactive power reference value Qref_WTG for each WTG 14. i .

[0106] For example, the Q setpoint scheduler 41 may determine the individual reactive power reference values Qref_WTG by dividing the overall reactive power reference value Qref_WPP among the WTGs 14. i .

[0107] As previously discussed, the division may be achieved in a uniform manner by simply dividing the overall reactive power reference Qref_WPP equally among the WTGs 14 according to the following equation:

[0108] Qref_WTG i =Qref_WPP / N.

[0109] In other examples, although not shown, the Q setpoint scheduler 41 may receive Qavail from the WTG controller 15. i The signal Qref_WPP is then divided among the WTGs 14 , taking into account the available reactive power at each WTG 14 .

[0110] In sub-step 312, the PPC 22 may calculate the voltage based on the corresponding local voltage signal V_WTG. i To determine the reactive power regulation ΔQ for each WTG 14 i For each WTG 14, the indicated voltage level V_WTG may be determined in part by i Comparison with the reference voltage level Vref_WTG determines the reactive power regulation ΔQ i .

[0111] As previously mentioned, the reference voltage level Vref_WTG itself may be based on the set of voltage signals received in step 304. For example, the PPC 22 may be configured to determine the local voltage level V_WTG based on the indicated local voltage level Vref_WTG in the received set of voltage signals. i The reference voltage level Vref_WTG is determined by the average value or another function.

[0112] Each reactive power regulation ΔQ i can then be based on the corresponding local voltage level V_WTG i The comparison with the reference voltage level Vref_WTG determines the corresponding reactive power regulation. The PPC 22 may use one or more functions, lookup tables and / or QV curves for this purpose to compare the local voltage deviation (from the average voltage level) with the corresponding reactive power regulation ΔQ i associated.

[0113] To give an advantageous example, the PPC 22 may use a droop control function for this purpose and determine the respective reactive power adjustments ΔQ according to the following equations i :

[0114] ΔQi=(V REF_WTG –V_WTG i )×Droop

[0115] Where ΔQ i is the reactive power regulation of the i-th WTG 14, where I=1 to N and is a positive integer corresponding to the number of WTGs 14, V REF_WTG is the reference voltage level, V_WTG iis the indicated voltage level of the ith WTG 14 , and Droop is the droop coefficient of the droop control technique. It should be understood here that the droop coefficient Droop may define a linear relationship between the local voltage deviation and the corresponding reactive power regulation for each WTG 14 .

[0116] In sub-step 314, the PPC may be based on the initial reactive power reference value Qref_WTG i and reactive power regulation ΔQ determined for each WTG 14 i , determining the reactive power set point Qset_WTG for each WTG 14 i .

[0117] For example, each reactive power set point Qset_WTG i It can be determined by the following: i and the reactive power regulation value ΔQ determined for each WTG 14 i Added together.

[0118] Back to Figure 3 Once the PPC 22 has determined the reactive power set point Qset_WTG for each WTG 14 i , PPC22 sets the determined reactive power set point Qset_WTG i In step 316 , dispatch is made to the corresponding WTG controller 15 for the WTG 14 .

[0119] In step 318, the WTG controller 15 receives a data packet containing the reactive power setpoint Qset_WTG i The WTG 14 is controlled accordingly to generate a corresponding amount of reactive power.

[0120] In this way, a more balanced voltage output is provided from the WTGs 14, reducing losses in the feed system, and providing more voltage margin or capacity in the event of a network fault to improve control reliability.

[0121] It will be appreciated that various changes and modifications may be made to the examples described above without departing from the scope of the present invention.

[0122] For example, the PPC 22 may be configured to determine the voltage level V_PoC based on the indicated voltage level of the main network 16, individually, or additionally based on the indicated local voltage level V_WTG of each of the WTGs 14. i (which is based on detecting one of a plurality of operating conditions of the WPP 12), selectively determining a reactive power set point Qset_WTG for each WTG 14 iFor example, the PPC 22 may often be configured to determine an overall reactive power reference value Qref_WPP based on an indicated voltage level V_PoC of the main network 16 and to determine an individual reactive power set point Qset_WTG for each WTG 14 by apportioning the overall reactive power reference value Qref_WPP equally or in some other manner among the WTGs 14. i However, when detecting one of the selected operating conditions of the WPP 12, the PPC may be configured to additionally be based on the local voltage level V_WTG i To determine the reactive power set point Qset_WTG of each WTG 14 i , as described above. For example, such field operating conditions may include: the active power output or reactive power output of the WPP 12 is greater than or equal to an upper power threshold; the active power output or reactive power output of the WPP 12 is less than or equal to a lower power threshold; the indicated voltage level V_PoC of the power network 16 is greater than or equal to an upper voltage threshold; and / or the indicated voltage level V_PoC of the power network 16 is less than or equal to a lower voltage threshold.

[0123] In other examples, one or more limits may be applied to bound the determined reference voltage level Vref_WTG, including upper and / or lower voltage limits, and / or rate limits for limiting the rate of change of the reference voltage level Vref_WTG in successive iterations.

[0124] In the above example, it will be appreciated that the local voltage level V_WTG of the WTG 14 i For example, the routed mean square (RMS) voltage or a different representation of the voltage magnitude, such as the voltage in a rotating reference frame, can be used. Additionally and / or alternatively, such voltage signals can be filtered using different bandwidths and using different types of filters and signal processing techniques (e.g., dq transforms). The filters can be applied in the WTG 14, in the PPC 22, in different units in the communication channel, and / or any such combination.

Claims

1. A farm controller for a renewable energy farm comprising a plurality of renewable energy generators, the renewable energy farm being connected to a power network, the farm controller being configured to execute machine-readable instructions to: receiving a signal indicative of a voltage level of a power network to which the power farm is connected; receiving a plurality of signals from the plurality of renewable energy generators, each signal indicating a voltage level of a corresponding renewable energy generator; and For each of the plurality of renewable energy generators, a respective reactive power set point is determined based on: Indicated voltage level of the power network; the indicated voltage level of the renewable energy generator; and a reference voltage level based on indicated voltage levels of the plurality of renewable energy generators; and Each determined reactive power set point is dispatched to a respective local controller associated with the respective renewable energy generator for controlling the renewable energy generator.

2. The power plant controller according to claim 1, wherein: The farm controller is configured to determine the reactive power set point by: determining a reactive power reference value for each renewable energy generator based on an indicated voltage level of the power network; and For each of the plurality of renewable energy generators: determining reactive power regulation based on a difference between an indicated voltage level of the renewable energy generator and a reference voltage level; and A reactive power setpoint is determined based on the reactive power reference value and the reactive power regulation determined for the renewable energy generator.

3. The power plant controller according to claim 2, wherein: Reactive power regulation is determined for each renewable energy generator using droop control techniques.

4. The power plant controller according to claim 3, wherein: The reactive power regulation is determined using the following equation: ΔQ i =(V REF_WTG –V_WTG i )×Droop Where ΔQ i is the reactive power regulation for the i-th renewable energy generator, i=1 to N, where N is a positive integer corresponding to the number of renewable energy generators in the power plant, V REF_WTG is the reference voltage level, V_WTG i is the indicated voltage level of the i-th renewable energy generator, and Droop is the droop coefficient of the droop control technique.

5. The power plant controller according to claim 4, wherein: The farm controller is configured to determine a droop factor for the plurality of renewable energy generators as a function of an electrical power parameter of the renewable energy farm.

6. The power plant controller according to any one of claims 2 to 5, wherein: The farm controller is configured to limit the respective determined reactive power regulation using an upper power limit and / or a lower power limit.

7. The power plant controller according to any one of claims 2 to 6, wherein: The farm controller is configured to limit the determined rate of change of the reactive power regulation using a rate of change limit.

8. The power plant controller according to any one of claims 2 to 7, wherein: The reactive power reference value for each renewable energy generator is determined as follows: determining a reactive power reference value for the renewable energy farm based on an indicated voltage level of the power network; as well as The reactive power reference value is divided among the plurality of renewable energy generators to determine an individual reactive power reference value for each renewable energy generator.

9. A farm controller according to any one of the preceding claims, wherein: The reference voltage level is determined as an average voltage level of the indicated voltage levels of the plurality of renewable energy generators.

10. A farm controller according to any one of the preceding claims, wherein: The farm controller is configured to limit the reference voltage level using an upper voltage limit and / or a lower voltage limit.

11. A farm controller according to any one of the preceding claims, wherein: The farm controller is configured to limit the rate of change of the reference voltage level using a rate of change limit.

12. A farm controller according to any one of the preceding claims, wherein: The plurality of signals received from the plurality of renewable energy generators each indicate a voltage level of the respective renewable energy generator at one or more of: a low voltage side of a transformer of a renewable energy generator, the transformer connecting the renewable energy generator to the power plant; the high voltage side of the transformer; and / or At the corresponding terminals of the power converter of the renewable energy generator.

13. A farm controller according to any one of the preceding claims, wherein: The farm controller is configured to determine respective reactive power set points based, at least in part, on detecting one of a plurality of farm operating conditions based on a reference voltage level and an indicated voltage level of a corresponding renewable energy generator.

14. The power plant controller according to claim 13, wherein: The plurality of field operating conditions include: The active power output of the power plant is greater than or equal to the upper active power threshold; The active power output of the power plant is less than or equal to the lower active power threshold; The indicated voltage level of the power network is greater than or equal to an upper voltage threshold; and / or The indicated voltage level of the power network is less than or equal to the lower voltage threshold.

15. A method of operating a renewable energy farm connected to a power network, the renewable energy farm comprising a plurality of renewable energy generators, the method comprising: obtaining a signal indicative of a voltage level of said power network to which the power farm is connected; obtaining a plurality of signals from the plurality of renewable energy generators, each signal indicating a voltage level of a corresponding renewable energy generator; and For each of the plurality of renewable energy generators, a respective reactive power set point is determined based on: Indicated voltage level of the power network; Indicated voltage levels of renewable energy generators; and a reference voltage level based on indicated voltage levels of the plurality of renewable energy generators; as well as The determined reactive power setpoint is dispatched from a farm controller to a local controller associated with the renewable energy generator for controlling the renewable energy generator.

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