Method and system for improving control of a renewable energy power plant

Abstract

According to one aspect of the invention, a control system for a renewable energy generator in a renewable energy power plant is provided, the renewable energy power plant including a plurality of renewable energy generators. The control system includes one or more controllers configured to execute machine-readable instructions to: determine a first power reference value for the renewable energy generators using droop control techniques, the first power reference value being determined based on a frequency signal indicating a frequency level of the renewable energy generators; receive a second power reference value from a power plant controller associated with the plurality of renewable energy generators; and control the power level of the renewable energy generators based at least in part on the first power reference value and the second power reference value.

Description

Technical Field

[0001] This disclosure relates to methods and systems for improving the control of renewable energy power plants connected to power grids. Background Technology

[0002] Regulators and operators of power grids expect connected power plants to comply with "grid specifications" and provide specific services to the power grid. For example, some operators require power plants to support the power grid when the measured power grid frequency deviates from the normal operating range or permissible range (also known as the frequency emergency dead zone).

[0003] To support the power grid, in normal operating mode (i.e., under fault-free conditions), the individual energy generators of a power plant are controlled by a central power plant controller. For example, the power plant controller may provide reference values ​​(i.e., target values ​​or “setpoints”) for one or more generation parameters (such as active power, reactive power, and / or voltage) to be produced by the individual renewable energy generators in the power plant. These reference values ​​or setpoints can be assigned to local controllers associated with the individual renewable energy generators, which operate to implement the setpoints received from the power plant controller. In this way, the power plant controller provides effective steady-state control of the power plant to support the frequency of the power grid.

[0004] However, when the power grid experiences transient conditions (such as sudden frequency drift), data communication between the central power plant controller and individual generator controllers may be too slow, and the central control system may not be able to meet the response time requirements. Therefore, drift may not be adequately mitigated, leading to grid failures and instability.

[0005] The purpose of this invention is to overcome one or more shortcomings of the prior art. Summary of the Invention

[0006] According to one aspect of the invention, a control system for a renewable energy generator in a renewable energy power plant is provided, the renewable energy power plant including a plurality of renewable energy generators. The control system includes one or more controllers configured to execute machine-readable instructions to: determine a first power reference value for the renewable energy generators using droop control techniques, the first power reference value being determined based on a frequency signal indicating a frequency level of the renewable energy generators; receive a second power reference value from a power plant controller associated with the plurality of renewable energy generators; and control the power level of the renewable energy generators based at least in part on the first power reference value and the second power reference value. For example, the second power reference value may be determined based on a frequency signal indicating a frequency level of a power grid.

[0007] For example, the control system can be configured to control the active power level of a renewable energy generator based at least in part on a first power reference value and a second power reference value, wherein such power reference values ​​take the form of active power reference values.

[0008] It should be understood that the control system can take the form of a single controller with multiple modules controlling a renewable energy generator, or it can take the form of a system comprising multiple controllers performing the same function.

[0009] In each case, the control system determines a first power reference value for a corresponding generator among the plurality of renewable energy generators based on the local frequency level of the generator. In this context, the frequency level of the renewable energy generator refers to the frequency of the current and / or voltage measured at the output of the renewable energy generator (e.g., at the corresponding terminal of the renewable energy generator). The control system also receives a second power reference value from a central power plant controller, which can determine such a power reference value for each of the plurality of renewable energy generators. Advantageously, the control system then combines the first and second power reference values ​​to control the renewable energy generators. By doing so, the control system effectively combines centralized and decentralized approaches to control the active power output of the renewable energy generators.

[0010] The second power reference value incorporates centralized control, which is well-suited for steady-state conditions, while the first power reference value incorporates local control at the generator to adapt to transient conditions. In particular, the first power reference value can be updated more frequently than the second power reference value (which is delayed due to transmission from the power plant controller to the local controller), thereby allowing for more frequent adjustments to control signals and providing faster response times (as is typically required to mitigate drift under transient grid conditions).

[0011] Therefore, embodiments of the present invention will provide improved control during transient grid conditions and enhance control reliability in the event of loss or impairment of communication between the central power plant controller and the local control system of the renewable energy generator.

[0012] For example, the second power reference value can be determined based on a frequency signal indicating the frequency level of the power network to which the power plant is connected. Exemplarily, the frequency signal can indicate the frequency level at the interconnection point between the power plant and the power network. For example, the frequency signal can be based on measurements obtained at a measurement point (e.g., a power meter), which is appropriately positioned to monitor the power supply to the power network and / or the frequency level of the power network. If the power plant is temporarily disconnected from the power network (e.g., in islanded operation mode), the second power reference value can be determined based on a predetermined frequency level (e.g., the frequency level of the power network before disconnection). Therefore, when the power plant is disconnected, the first power reference value is repeatedly updated by the control system to adjust the control signal to adapt to transient conditions with an appropriately fast response time.

[0013] In one example, the control system can be configured to control the power level of a renewable energy generator by determining the output power value for renewable energy based at least in part on a first power reference value and a second power reference value. For example, the first power reference value and the second power reference value can be added together.

[0014] Optionally, the control system is configured to control the power level of the renewable energy generator by comparing the determined output power value with a power feedback value indicating the power output of the renewable energy generator obtained by the control system. In this way, the control system is able to operate in a feedback operating mode to enhance the control of the renewable energy generator.

[0015] For example, the control system can be configured to determine a first power reference value at a first frequency and receive a second power reference value at a second frequency. For example, the second frequency may be lower than the first frequency. Therefore, the first power reference value is updated more frequently to adjust the control signal accordingly to adapt to transient conditions.

[0016] For example, the control system can be configured to use a droop reference frequency to determine a first power reference value for the renewable energy generator. The droop reference frequency can be based on one or more of the following: a predetermined reference frequency; and / or a frequency signal that indicates the frequency level of the renewable energy generator.

[0017] Optionally, the control system is configured to select a droop reference frequency from a predetermined reference frequency and corresponding inputs of a frequency signal based on control inputs.

[0018] In one example, the control system can be configured to apply a low-pass filter to a frequency signal indicating the frequency level of a renewable energy generator; and to compare the low-pass filtered signal with a drooping reference frequency.

[0019] Optionally, the control system can be further configured to determine a first power reference value based on one or more active power limits associated with the renewable energy generator. In this way, the first power reference value is limited to permissible active power levels both above and below.

[0020] Optionally, the control system may be further configured to: determine the available power level of the renewable energy generator; and determine at least one of the one or more active power limits based on the determined available power level.

[0021] In one example, the control system may be further configured to determine a first power reference value based on one or more rate-of-change limits associated with the power output of the renewable energy generator.

[0022] Optionally, the control system may be configured to determine at least one of the one or more rate of change limits based on the maximum permissible rate of change of the active power of the renewable energy generator.

[0023] In one example, the control system can be configured to use a droop gain to determine a first power reference value. For instance, the droop gain can be determined based on a frequency signal that indicates the frequency level of a renewable energy generator. In this way, the droop gain can be tuned and operate across a frequency range.

[0024] For example, the one or more controllers may be configured to determine the droop gain based on a curve that correlates a corresponding value of the droop gain with the indicated frequency level of the renewable energy generator. Therefore, the droop may include an (adjustable) frequency dead zone. Alternatively, the control system may be configured to select, from multiple curves that correlate a corresponding value of the droop gain with the indicated frequency level, the curve that correlates the corresponding value of the droop gain with the indicated frequency level.

[0025] Optionally, the first power reference value is output to the power plant controller to determine the second power reference value. For example, the first power reference value can be output to the power plant controller to determine the second power reference value in subsequent iterations.

[0026] According to another aspect of the invention, a power plant control system for a renewable energy power plant is provided, the renewable energy power plant comprising a plurality of renewable energy generators. The power plant control system includes one or more control systems as described in the preceding aspect of the invention for controlling respective generators among the plurality of renewable energy generators. In one example, the power plant control system may further include a power plant controller configured to determine a second power reference value and assign it to each of the one or more control systems.

[0027] According to another aspect of the invention, a method for operating a renewable energy power plant including a renewable energy generator is also provided. The method includes: determining a first power reference value for the renewable energy generator, the first power reference value being determined by a local controller associated with the renewable energy generator using droop control technology, the first power reference value being determined based on a frequency signal indicating a frequency level of the renewable energy generator; determining a second power reference value for the renewable energy generator, the second power reference value being determined by a power plant controller; allocating the second power reference value from the power plant controller to a local controller; receiving the second power reference value at the local controller; and controlling the power level of the renewable energy generator via the local controller based at least in part on the first power reference value and the second power reference value.

[0028] Within the scope of this invention, it is expressly intended that the various aspects, embodiments, examples, and alternatives set forth in the foregoing paragraphs, claims, and / or the following description and drawings, particularly the various features therein, may be adopted 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. The applicant reserves the right to accordingly amend any initially filed claim or to file any new claim, including the right to amend any initially filed claim to subordinate to and / or incorporate any feature of any other claim, even if not originally claimed in this manner. Attached Figure Description

[0029] One or more embodiments of the invention will now be described by way of example only with reference to the accompanying drawings, in which: Figure 1 The diagram schematically illustrates a power network connected to a renewable energy power plant, which includes a power plant controller. Figure 2 It shows Figure 1 An exemplary control structure for a power plant; Figure 3 It shows Figure 2 Exemplary submodules of the control structure shown; and Figure 4 The operation according to an embodiment of the present invention is shown. Figure 1 An exemplary method for renewable energy power plants. Detailed Implementation

[0030] Embodiments of the present invention relate to methods and systems for improving the control of renewable energy power plants, particularly with respect to sudden frequency drift.

[0031] This is achieved by coordinating centralized and decentralized approaches to control the active power output of renewable energy generators, which supports the frequency of the connected power grid. Specifically, as in conventional systems, a central power plant controller is configured to determine reference values ​​(i.e., target values ​​or “setpoints”) for one or more generation parameters (e.g., active power, reactive power, and / or voltage) to be produced by the individual renewable energy generators in the power plant. These reference values ​​or setpoints are assigned to local controllers associated with the individual renewable energy generators, which operate the generators to implement the setpoints received from the power plant controller. In this way, the power plant controller provides centralized control of the renewable energy generators, resulting in effective steady-state control that supports the frequency and voltage of the connected power grid.

[0032] Advantageously, to handle transient grid fluctuations (such as sudden frequency drift), the local controller of the renewable energy generator is further configured to determine another power reference value using droop control techniques. For example, the droop control technique can determine a first power reference value based on the associated frequency level of the renewable energy generator (e.g., a frequency level determined from measurements at the generator terminals), and the local controller can receive a second power reference value assigned from the power plant controller. The local controller is configured to control the power level of the renewable energy generator based on the first and second power reference values. For example, the first and second power reference values ​​can be combined to determine a control signal for controlling one or more generation parameters of the renewable energy generator. For example, the control signal can be determined by comparing it with feedback measurements of the power output from the renewable energy generator.

[0033] Therefore, the power plant controller assigns a second power reference value to local controllers to provide centralized control, which is well-suited for steady-state conditions, while each local controller further determines a first power reference value to provide decentralized control to adapt to transient grid conditions. Specifically, by determining the first power reference value locally, transmission delays are mitigated, and the first power reference value can be updated more frequently than the second power reference value to adjust control signals with a fast response time. This fast response time is typically required to mitigate drift under transient grid conditions.

[0034] In this way, it is conceivable that embodiments of the present invention will provide improved control during transient grid conditions and enhance control reliability in the event of loss or impairment of communication between the central power plant controller and the local controllers of renewable energy generators. For example, when a power plant disconnects, a first power reference value can be repeatedly updated to adjust the control signal with a fast response time to adapt to transient conditions.

[0035] Figure 1This illustrates a typical architecture where renewable energy power plants are connected to the main grid or a wider power network. Figure 1 In the example shown, the renewable energy power plant is a wind power plant (WPP). As the skilled reader will understand, a WPP comprises multiple wind turbine generators (WTGs). WTGs are commonly referred to as "wind turbines." The example shown is merely representative, and the skilled reader will understand that other specific architectures are possible. In other examples, the power plant may include other renewable energy sources, such as solar power plants, biomass power plants, ocean / wave / tidal power plants, or hybrid power plants combining different types of renewable energy power plants. Therefore, the present invention relates generally to renewable energy power plants and renewable energy generators, and not specifically to wind power plants and generators as shown in the figures. The components of wind power plants and power grids are conventional, and therefore the skilled reader will be familiar with them. In addition to... Figure 1 In addition to the components shown and described herein, other known components may be additionally or alternatively incorporated. Such modifications will be within the capabilities of those skilled in the art.

[0036] Figure 1 An electric power system 10 comprising a wind power generation project (WPP) 12 is shown. In this example, the WPP 12 includes a plurality of wind power generation projects (WTGs) 14. Each of the plurality of WTGs 14 converts wind energy into electrical energy, which is transmitted from the WPP 12 as active power and / or current to the main power grid or “main grid” 16 for distribution.

[0037] Despite Figure 1 As not shown, WPP 12 may also include compensation devices, such as a static synchronous compensator (STATCOM) or another type of synchronous compensator, configured to provide reactive power or reactive current support as needed.

[0038] WPP 12 also includes a connection network 18 for connecting WPP 12 to the main grid 16. In this example, WPP 12 and the main grid 16 are connected at an interconnection point (PoI) 20, which is the interface between WPP 12 and the main grid 16. PoI 20 may also be referred to as a common coupling point, which may be abbreviated as "PCC" or "PoCC".

[0039] WPP 12 further includes a power plant controller 22 (hereinafter referred to as PPC 22) for centralized control of WTG 14, and in this example, each WTG 14 is associated with a corresponding local WTG controller 15. In this example, the WTG controller 15 acts as a local controller for the renewable energy generator. As the skilled reader will understand, the WTG controller 15 can be considered as a local control system capable of operating the WTG 14 in the manner specified herein, and may include multiple controller modules controlling the various components of the WTG, or may include only a single controller with multiple sub-modules (as will be described in the examples below). The computer system of the WTG controller 15 may operate based on software downloaded via a communication network or programmed thereon from a computer-readable storage medium.

[0040] A bidirectional control network can be deployed between PPC 22 and WTG controller 15 to enable bidirectional communication. For example, the uplink direction (i.e., 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 PPC 22 to the local WTG controller 15. The downlink direction can be used by WTG 15 to return information about its current operating status (e.g., the amount of currently generated active power and / or a locally determined power reference) to the central PPC 22. Such a control network can be implemented, for example, as a bus system, i.e., a CAN bus (ISO 11898) or an Ethernet bus (IEEE 802.3).

[0041] The role of PPC 22 is to provide centralized control of WTG 14 and to act as the command and control interface between WPP 12 and the grid 16 (more specifically, grid operator 26). For example, grid operator 26 may be a transmission system operator (TSO) or a distribution system operator (DSO).

[0042] PPC 22 is configured to generate and send distribution signals to WTG controller 15. The distribution signals contain setpoints for active and reactive current and / or power determined by PPC 22 to provide frequency and voltage support to main grid 16 based on measurements of power supply from WPP 12 to main grid 16 and / or the frequency level of main grid 16.

[0043] Subsequently, the WTG controller 15 controls the WTG 14 according to the setpoint contained in the distribution signal, and in this way, the WPP 12 can change its power or current output in response to the setpoint received from the PPC 22.

[0044] For this purpose, the power plant controller (PPC) 22 is connected to the main grid 16 at a point of measurement (PoM) 24 (e.g., a power meter). For example, the PPC 22 can be configured to receive one or more measurement signals from the PoM 24, including measurements of the power supply from the WPP 12 to the main grid 16 and / or measurements of the frequency level of the main grid 16.

[0045] PPC 22 is a suitable computer system for executing the control and commands described herein, and therefore may include a processing module 28, a connection module 30, a storage module 32, and a sensing module 34, etc. Figure 1 As shown.

[0046] The connection module 30, storage module 32 and / or sensing module 34 are configured to provide the processing module 28 with information indicating the frequency level of the main power grid 16 and the power level, current level and / or voltage level of WTG 14 and / or WPP 12.

[0047] For example, sensing module 34 may receive such information directly from one or more connected sensors or power meters (e.g., at PoM 24) and transmit it to processing module 28. Alternatively or additionally, the information may be determined by one or more systems (e.g., WTG controller 15) connected to connection module 30, and this information may then be transmitted to processing module 28 via connection module 30. In each case, the determined information may be permanently or temporarily stored in storage module 32, and processing module 28 may recall the information from storage module 32 as needed. PPC 22 may also receive information about power grid 16 and / or local buses, substations, and networks from energy management system (not shown).

[0048] Compared to conventional arrangements, the local WTG controller 15 is additionally configured to use droop control technology to determine a further power reference or setpoint for controlling the respective WTG 14. For example, each WTG controller 15 can be configured to determine a further power reference for controlling the respective WTG 14 based on the frequency level of the power output from that WTG 14.

[0049] In this way, the local WTG controller 15 is thus configured to control the power level of the corresponding WTG 14 by determining a control signal based on a combination of a power reference value received from the PPC 22 and a power reference value locally determined by the WTG controller 15. It should be understood that the locally determined power reference value can be updated at a higher frequency than the power reference value determined by the PPC, for example, due to the relatively slow data communication between the PPC and the WTG controller 15. Therefore, the power reference value determined by the WTG controller 15 is more responsive to transient grid conditions, providing effective control of the WTG 14. Furthermore, in the event of a missing power reference value from the PPC 22 (e.g., after communication loss), the WTG controller 15 is able to provide distributed control of the corresponding WTG 14, thereby improving the stability of the WPP 12. It should be understood that this control arrangement can also provide effective control during a fault in the main grid 16, where the centralized control of the PPC 22 can be replaced by autonomous control performed by the local WTG controller 15.

[0050] Therefore, the PPC 22 and the local WTG controller 15 can 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 measurement input) and generate a control signal or reference based on the difference between the two input values.

[0051] Now refer to Figure 2 An exemplary control structure according to embodiments of the present invention will be described in more detail.

[0052] like Figure 2 As shown, the overall controller architecture of WPP 12 includes a central PPC 22 and a local WTG controller 15. For simplicity, Figure 2 A single WTG controller 15 is shown, but it should be understood that the PPC 22 is connected to each local WTG controller 15 in essentially the same way.

[0053] The central PPC 22 and the local WTG controller 15 each include reactive power and active power controllers; however, to avoid obscuring the invention, the following description is limited to the active power control aspect. Figure 2 Only the active power controller is shown in the image.

[0054] In this example, PPC 22 is primarily configured to regulate the frequency of the connected power network using frequency feedback measurements and is shown receiving (among other inputs) a frequency signal f_WPP (e.g., the frequency level at PoI 20) indicating the frequency level of the main power grid 16. For example, PPC 22 may receive a sequence of time-varying measurements indicating one or more power characteristics at PoM 24, which can be used to derive the frequency signal according to one or more known methods. Such measurements may include, for example, voltage and / or current measurements.

[0055] The frequency signal f_WPP is provided to the active power controller 37 (i.e., P controller 37) of PPC 22 and can be used to regulate the grid frequency in one or more of its active power control loops.

[0056] Therefore, the P controller 37 can receive various signals related to active power control, such as the frequency signal f_WPP and the feedback signal Pmeas_WPP indicating the active power output from WPP 12 to the grid 16. In this example, the P controller 37 can also receive the feedback signal Pmeas_WTG indicating the active power output from each WTG 14, such as... Figure 2 As shown.

[0057] Despite Figure 2 Not shown, but it should be understood that the P controller 37 can also receive signals from each local WTG controller 15 indicating available active power, i.e., the amount of active power currently maximum producible by each WTG 14. For example, a function called "Pavail" of the local WTG controller 15 can also determine the amount of maximum producible active power. For example, each WTG controller 15 can measure and / or determine the currently prevailing wind speed, and calculate, for example, the amount of active power that can be produced under the current prevailing wind conditions based on the power curve of the WTG 14. Each WTG controller 15 generates a Pavail signal, which can be fed back to the PPC 22.

[0058] In some embodiments, the P controller 37 may also receive external control inputs, such as a power curtailment signal from a grid provider, which can specify the extent to which the active power production of WPP 12 should be limited. The power curtailment provision can be expressed in absolute terms (e.g., in MW) or in relative terms (e.g., as a percentage of the power plant's rated active power or the active power that WPP 12 can currently produce (i.e., the sum of Pavail)).

[0059] like Figure 2As shown, in this example, the P controller 37 includes a frequency (f) and active power (P) controller 42, and a P setpoint distributor 43. The f and P controllers 42 generate an internal overall reference value, Pref_WPP, for the active power to be produced by WPP 12 based on inputs to the P controller 37, such as the frequency signal and the active power output from WPP 12 to the grid 16. For example, when the frequency signal is above a frequency threshold, the f and P controllers 42 can generate a reduced Pref_WPP value.

[0060] If WPP 12 operates in power-limiting mode, the f and P controllers 42 can also generate an increased Pref_WPP value when the frequency signal is below the frequency threshold to aid in grid frequency control. In embodiments with external power-limiting functionality, the external power-limiting signal also affects the evaluation of Pref_WPP. For example, if the signal requires the generated active power to be x% of the active power currently available to WPP 12, then Pref_WPP will be set to x% of the sum of all Pavail values.

[0061] The P setpoint allocator 43, for example, uses Pavail information to divide the overall Pref_WPP (determined by the f and P controllers 42) into individual active power setpoints or reference values ​​Pref2_WTG for the local WTG controller 15. This allocation does not need to be uniform; for example, WTG 14 in the first row, which bears a higher load, may be more power-limited than those with lower loads. Each power reference value Pref2_WTG is assigned to the corresponding WTG controller 15.

[0062] The local WTG controller 15 includes a local P controller 45. The local P controller 45 receives the corresponding Pref2_WTG value allocated from the PPC 22 as input. In a normal system, the local WTG controller 15 will control the WTG 14 based on such input, for example, in feedback operation mode.

[0063] Advantageously, the local P controller 45 further includes a droop controller 46 in the control structure. The droop controller 46 receives a signal f_WTG indicating the frequency level of the power output from the corresponding WTG 14 and a droop reference frequency F_droop as inputs, and determines another reference value Pref1_WTG for the active power to be produced by the corresponding WTG 14. The droop reference frequency F_droop can be the nominal frequency level of the WTG 14, or the droop reference frequency F_droop can be based on the signal f_WTG.

[0064] The droop controller 46 includes one or more schemes, rules, or algorithms for droop control. That is, the droop controller 46 implements one or more droop control techniques to determine an active power reference value Pref1_WTG based on the droop reference frequency input F_droop and the frequency level f_WTG of the power output from WTG 14. For example, when the frequency level f_WTG is above a frequency threshold, the f and P controller 42 can generate a decreased Pref1_WTG value. If WPP 12 is operating in power-limiting mode, the f and P controller 42 can also generate an increased Pref1_WTG value when the frequency signal f_WTG is below the frequency threshold to facilitate frequency control of the power grid. The active power reference value Pref1_WTG determined by the droop controller 46 can be further limited according to one or more active power limits, which can be determined, for example, based on the available power level of WTG 14, and / or according to one or more rate-of-change limits associated with the power output of WTG 14 (e.g., the maximum permissible rate of change of active power of WTG 14), as will be described in more detail below.

[0065] P controllers 45 each determine control signals for controlling the corresponding WTG 14 based on the power reference value Pref2_WTG received from PPC 22 and the power reference value Pref1_WTG determined by the droop controller 46. In the following description, the power reference value Pref1_WTG determined by the droop controller 46 can therefore be referred to as the "first power reference value" provided to the P controller 45, while the power reference value Pref2_WTG received from PPC 22 can be referred to as the "second power reference value" provided to the P controller 45. Another input to the P controller 45 is a signal indicating the active power measured at the output of the corresponding WTG 14. Figure 2 This is referred to as "Pmeas_WTG". Therefore, the P controller 45 combines the first power reference value and the second power reference values ​​Pref1_WTG and Pref2_WTG with the measured active power output Pmeas_WTG, and generates a control signal C based on the difference between the input values. The determined control signal C controls WTG 14 to generate the corresponding amount of active power.

[0066] Now refer to Figure 3 Exemplary details of the control structure are discussed.

[0067] exist Figure 3In the example shown, the f and P controller 42 of PPC 22 includes a first control module and a second control module. Specifically, the f and P controller 42 includes a frequency droop controller 100 and an active power loop 102 for determining the active power reference Pref_WPP of WPP 12. However, PPC 22 is not particularly limited in this respect, and in other examples, the f and P controller 42 may include additional or alternative modules for determining the active power reference value Pref_WPP.

[0068] In this example, a frequency signal f_WPP indicating the frequency level of the main grid 16 (e.g., determined at PoI 20) is provided as input to the frequency droop controller 100. The frequency droop controller 100 includes one or more droop control techniques for determining a droop power reference Pctrl_PoC_ref, which is provided as input to the active power loop 102. For this purpose, the frequency droop controller 100 may further receive a reference frequency for comparison with the frequency signal. For example, the reference frequency may correspond to the nominal frequency of the main grid 16 (typically 50Hz or 60Hz).

[0069] The active power loop 102 may further receive feedback measurements of the power output from PPC 22 to WPP 12 (such as those measured at PoM 24) and optionally the power output Pmeas_WTG from each WTG 14 as inputs. Additionally, the active power loop 102 may receive a locally determined reference value Pref1_WTG for each WTG and / or an active power reference value Pref from other P-related control aspects, which may be provided as an addition to or alternative to the droop power reference Pctrl_PoC_ref (e.g., when operating in islanded mode).

[0070] The active power loop 102 includes one or more schemes, rules, or algorithms for combining various active power reference values ​​and comparing the power with active power feedback measurements. Based on this, the active power loop 102 determines an active power reference Pref_WPP for WPP 12, which is provided to the P setpoint distributor 43. As previously described, although not shown, the P setpoint distributor 43 may receive Pavail signals from the WTG controller 15 and determine a corresponding second power reference value Pref2_WTG for each WTG controller 15 based on these inputs.

[0071] Turning now to WTG controller 15, droop controller 46 is shown as determining a first power reference value Pref1_WTG for WTG 14 based on the droop reference frequency F_droop and the signal f_WTG indicating the frequency level of the corresponding WTG 14.

[0072] The droop reference frequency F_droop can be determined by one or more parameters that can be controlled by the grid or power plant operator. Specifically, in Figure 3 In the example shown, the droop controller 46 can receive the measured frequency level f_WTG of WTG 14 and determine the droop reference frequency F_droop as a constant setpoint / nominal frequency fSet_WTG or a low-pass filtered value of the measured frequency f_WTG based on the configurable parameter "UseFiltRef". In this way, an operator (e.g., a power plant operator) can selectively configure the droop reference frequency F_droop by setting the configurable parameter UseFiltRef to use a constant setpoint fSet_WTG (e.g., UseFiltRef = 1), or a low-pass filtered value of the measured frequency f_WTG (e.g., UseFiltRef = 0), or a combination thereof.

[0073] In parallel, the droop controller 46 applies a low-pass filter individually to the indicated frequency level f_WTG of WTG 14 at block 103 and compares the droop frequency F_droop with the output low-pass filtered frequency level. The error is then provided to the droop gain block 104 of the droop controller 46.

[0074] The droop gain value of droop gain block 104 can be determined by control input itself, or the droop gain value can be configured to vary with and be determined based on the indicated frequency level f_WTG of the droop reference frequency F_droop or WTG 14. For example, droop controller 46 may include one or more control modules (not shown) configured to determine the droop gain based on a curve that correlates a corresponding value of the droop gain with the droop reference frequency F_droop or WTG frequency level f_WTG. For example, this curve may be selected from multiple such curves based on control input from a grid or power plant operator. In this way, the droop gain can be tuned according to the operating frequency range.

[0075] The output of droop gain box 104 is the power reference value of WTG 14, such as... Figure 3 As shown, before the first power reference value Pref1_WTG is output to the P controller 45, the power reference value is passed to the power limit box 108 and the rate limiter box 110.

[0076] Power limit block 108 applies upper and lower active power limits to the power reference value, wherein the WTG controller 15 can determine the upper and / or lower limits based on feedback from the available power level Pavail of the WTG 14. Rate limiter block 110 can further apply one or more rate-of-change limits to the power reference value. Similarly, the WTG controller 15 can determine the rate-of-change limit based on the maximum permissible rate of change of the active power of the WTG 14 (e.g., possibly specified for a particular type of WTG). In this way, the WTG 14 can adjust its active power production during transient and semi-steady-state conditions if frequency deviations occur.

[0077] The output of power limit block 108 is a first active power reference value, Pref1_WTG, which is provided to the P controller 45 of WTG controller 15. The P controller 45 of WTG controller 15 is configured to determine the control signal C of WTG 14 by combining the first and second active power reference values, Pref1_WTG and Pref2_WTG, received from droop controller 46 and PPC 22, and comparing the combined reference value with the feedback active power measurement value, Pmeas_WTG, from WTG 14. For example, the P controller 45 of WTG controller 15 can be configured to combine the first and second active power reference values, Pref1_WTG and Pref2_WTG, received from droop controller 46 and PPC 22 by summing the reference values, and the P controller 45 can be calibrated accordingly. The output control signal C can take the form of an active power reference that WTG 14 follows by adjusting one or more control parameters of WTG 14. In other words, the power output of WTG 14 can be controlled according to the control signal C to minimize the error between the combined power reference value and the power measurement feedback. To this end, WTG 14 and / or WTG controller 15 may therefore include one or more additional control modules or instructions for converting the control signal C into one or more corresponding commands for controlling the WTG 14 for corresponding parameters (e.g., pitch, yaw, etc.) and / or its converters.

[0078] It should also be understood that the locally determined first power reference value Pref1_WTG can be updated at a higher frequency than the second power reference value Pref2_WTG received from PPC 22, for example, because data communication between PPC 22 and WTG controller 15 is relatively slow. Therefore, the first power reference value Pref1_WTG determined by WTG controller 15 is more responsive to transient conditions, thereby providing effective control of WTG 14.

[0079] Now refer to Figure 4 The method 400 for running WPP 12 according to an embodiment of the present invention will be described in more detail.

[0080] In step 402, PPC 22 determines the power reference value Pref_WPP for WPP 12. The method used to determine the WPP power reference value Pref_WPP is not intended to impose a particular limitation on the scope of the invention, and may be based on the frequency level of the main grid 16 and / or use other active power reference values ​​(e.g., Pref) determined by other P-related control aspects of PPC 22.

[0081] For example, in step 402, PPC 22 can obtain a frequency signal indicating the frequency level f_WPP of the main power grid 16. For example, PPC 22 can receive or otherwise obtain a series of measurements, such as current and / or voltage measurements at PoM 24, and derive the frequency signal f_WPP based on these measurements.

[0082] Then, PPC 22 can determine the power reference value Pref_WPP of WPP 12 based on the frequency signal. For example, PPC 22 can use the droop controller 100 of PPC 102 to determine the droop power reference Pctrl_PoC_ref based on the frequency signal f_WPP. The determined droop power reference Pctrl_PoC_ref is then used to determine the power reference value Pref_WPP of WPP 12 using the active power loop 102. In particular, the droop power reference Pctrl_PoC_ref can be compared with the measured power level Pmeas_WPP of WPP 12 and the measured power level Pmeas_WTG of WTG 14, as provided by WTG controller 15. The active power loop 102 can also consider other power reference values, such as the first power reference value Pref1_WTG determined in a previous iteration, and / or power reference values ​​Pref from other P-related control aspects, as will be described in more detail.

[0083] In step 406, the P setpoint allocator 43 receives the power reference value Pref_WPP of WPP 12 and determines and allocates each second power reference value Pref2_WTG or setpoint to the WTG controller 15. For example, the active power reference value Pref_WPP of WPP 12 is passed to the P setpoint allocator 43, which receives feedback on the available power Pavail of WTG 14 (and the active power output of WTG 14). Based on such input, the P setpoint allocator 43 uses one or more rules, schemes, or algorithms to determine the respective active power reference values ​​Pref2_WTG for each WTG 14, and these reference values ​​are then allocated to the associated WTG controller 15 in the allocation signal.

[0084] In parallel, in step 408, each WTG controller 15 receives a frequency signal f_WTG indicating the frequency level of the power output of the corresponding WTG 14, and uses a droop controller 46 to determine another power reference value Pref1_WTG for controlling the WTG 14. Exemplarily, the droop controller 46 of the WTG controller 15 may receive the frequency signal f_WTG, apply a low-pass filter to the frequency signal, and compare the frequency signal with a droop frequency F_droop (which corresponds to the nominal frequency or low-pass filter value of the frequency signal f_WTG). The droop controller 46 determines a frequency error, which is provided to the droop gain block 104. The droop gain block 104 applies a droop gain to the error signal and generates a corresponding power reference. The power reference signal is further limited by upper and lower active power limits of limit block 106, and the rate of change of the power reference signal is limited by rate limiter block 108. The power reference value Pref1_WTG is output from the rate limiter block and provided to the P controller 45 of the WTG controller 15.

[0085] In step 410, the WTG controller 15 receives the allocated active power reference value Pref2_WTG from the PPC 22.

[0086] In step 412, the WTG controller 15 combines the active power reference values ​​Pref1_WTG and Pref2_WTG received from the PPC 22 and determined by the droop controller 46, and determines the control signal C for controlling the corresponding WTG 14. For example, the P controller of the WTG controller can combine the first active power reference value and the second active power reference values ​​Pref1_WTG and Pref2_WTG by adding them together, and use one or more active power control loops to compare the sum with the feedback signal Pmeas_WTG from the measured power output of the corresponding WTG 14 to determine the active power control signal. Since the locally determined power reference value Pref1_WTG can be updated at a higher frequency than the power reference value Pref2_WTG received from PPC 22, the control signal can be updated at a first frequency based on the changes in the power reference value Pref1_WTG determined by WTG controller 15, and at a second frequency (i.e., a lower frequency) based on the changes in the power reference value Pref2_WTG received from PPC 22.

[0087] In step 414, the determined control signal C is output from the WTG controller 15 to the corresponding WTG 14, or otherwise used to control one or more parameters of the WTG 14 to reduce the error between the combined active power reference value and the active power output of the WTG 14.

[0088] In this way, the local WTG controller 15 quickly updates the first power reference value Pref1_WTG and subsequently updates the control signal C, so that WTG 14 is controlled to respond quickly to frequency deviations, while the slower communication of the power reference value Pref2_WTG from PPC 22 provides effective steady-state control of WTG 14.

[0089] Furthermore, it should be understood that if communication loss occurs, causing the WTG controller 15 to fail to receive the second active power reference value Pref2_WTG from the PPC 22 (in step 410), the WTG controller 15 continues to determine the local active power reference value Pref1_WTG based on the droop control function. Therefore, the WTG controller 15 determines the appropriate control signal C for the continued operation of the WTG 14, thereby improving the operation of the WTG 14 and the overall stability of the WPP 12.

[0090] It is anticipated that this invention will thus improve grid stability and strength, thereby contributing to increased power generation capacity of WPP 12.

[0091] It should be understood that various changes and modifications can be made to the above examples without departing from the scope of the present invention.

[0092] For example, while the above examples focus on operation when WPP 12 is connected to the main grid 16 (providing frequency support), embodiments of the present invention also cover operation when WPP 12 is temporarily disconnected from the main grid 16 (e.g., in a short-term islanding situation).

[0093] Specifically, when WPP 12 is connected to the main grid 16, PPC 22 can determine the power reference value Pref_WPP of WPP 12 based on the frequency level f_WPP of the main grid, essentially as described in step 402. However, if WPP 12 is disconnected from the main grid 16 (e.g., after a circuit breaker trip of WPP 12), WPP 12 can be configured to enter islanded operation mode. During islanded operation mode, WPP 12 can be configured to operate essentially as described in method 400, except that PPC 22 is no longer able to determine the power reference value Pref_WPP of WPP 12 based on the frequency level f_WPP of the main grid 16. Instead, in islanded operation mode, PPC 22 can be configured to determine the power reference value Pref_WPP of WPP 12 based on one or more active power reference values ​​Pref(s) from one of the other P-related control aspects or based on a predetermined frequency level (e.g., the frequency level of the main grid 16 before disconnection). For example, when entering islanded operation mode, the power reference value Pref_WPP of WPP 12 can be determined using a substantially constant frequency level (in step 402) until grid connection is restored.

[0094] In this way, WPP 12 can operate under a variety of conditions, maintain operation when temporarily disconnected from the main grid 16, and provide frequency and / or voltage support when WPP 12 is reconnected to the main grid 16.

Claims

1. A control system for a renewable energy generator in a renewable energy power plant, the renewable energy power plant comprising a plurality of renewable energy generators, the control system comprising one or more controllers configured to execute machine-readable instructions to: Using droop control technology, a first power reference value for the renewable energy generator is determined, the first power reference value being determined based on a frequency signal indicating the frequency level of the renewable energy generator; Receive a second power reference value from the power plant controller associated with the plurality of renewable energy generators; and The power level of renewable energy generators is controlled at least in part based on a first power reference value and a second power reference value.

2. The control system according to claim 1, wherein, The control system is configured to control the power level of the renewable energy generator by determining the output power value for renewable energy based at least in part on a first power reference value and a second power reference value.

3. The control system according to claim 2, wherein, The control system is configured to control the power level of the renewable energy generator by comparing the determined output power value with a power feedback value obtained by the control system indicating the power output from the renewable energy generator.

4. The control system according to any one of the preceding claims, wherein, The control system is configured to determine a first power reference value at a first frequency; and to receive a second power reference value at a second frequency, the second frequency being less than the first frequency.

5. The control system according to any one of the preceding claims, wherein, The control system is configured to use a droop reference frequency to determine a first power reference value for the renewable energy generator, the droop reference frequency being based on one or more of the following: Pre-determined reference frequency; and / or Frequency signal, which indicates the frequency level of renewable energy generators.

6. The control system according to claim 5, wherein, The control system is configured to select a droop reference frequency from a predetermined reference frequency and corresponding inputs of a frequency signal based on control inputs.

7. The control system according to claim 5 or 6, wherein, The control system is configured to apply a low-pass filter to a frequency signal indicating the frequency level of a renewable energy generator; and to compare the low-pass filtered signal with a droop reference frequency.

8. The control system according to any one of the preceding claims, wherein, The control system is further configured to determine a first power reference value based on one or more active power limits associated with the renewable energy generator.

9. The control system according to claim 8, wherein, The control system is further configured as follows: Determine the available power level of renewable energy generators; and At least one of the one or more active power limits is determined based on the determined available power level.

10. The control system according to claim 8 or 9, wherein, The control system is further configured to determine a first power reference value based on one or more rate-of-change limits associated with the power output of the renewable energy generator.

11. The control system according to claim 10, wherein, The control system is configured to determine at least one of the one or more rate of change limits based on the maximum permissible rate of change of the active power of the renewable energy generator.

12. The control system according to any one of the preceding claims, wherein, The control system is configured to use a droop gain to determine a first power reference value, the droop gain being determined based on a frequency signal indicating the frequency level of the renewable energy generator.

13. The control system according to claim 12, wherein, The one or more controllers are configured to determine the droop gain based on a curve that correlates a corresponding value of the droop gain with the indicated frequency level of the renewable energy generator. Optionally, the control system is configured to select the curve that correlates the corresponding value of the droop gain with the indicated frequency level from a plurality of curves that correlate the corresponding value of the droop gain with the indicated frequency level.

14. The control system according to any one of the preceding claims, wherein, The first power reference value is output to the power plant controller to determine the second power reference value.

15. A method for operating a renewable energy power plant including a renewable energy generator, the method comprising: A first power reference value for the renewable energy generator is determined by a local controller associated with the renewable energy generator using droop control technology. The first power reference value is determined based on a frequency signal that indicates the frequency level of the renewable energy generator. A second power reference value is determined for the renewable energy generator; the second power reference value is determined by the power plant controller. Distribute the second power reference value from the power plant controller to the local controller; Receive the second power reference value at the local controller; as well as The power level of the renewable energy generator is controlled by a local controller based at least in part on a first power reference value and a second power reference value.

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