Method and system for damping power oscillations during frequency fluctuations

Abstract

Aspects of the invention relate to a method (200) for controlling a renewable energy power plant (12), such as a wind power plant (12). In particular, aspects of the invention relate to a method (200) for controlling a renewable energy power plant (12) when a frequency level of an electrical power network (16) to which the power plant (12) is connected is outside a frequency deadband. The method (200) comprises: receiving a measured frequency level (40) of the electrical power network (16); determining and dispatching a setpoint for controlling a power characteristic of the power plant (12) based on the measured frequency level; monitoring changes in the measured frequency level (40) to detect an inflection point in the measured frequency level (40); and when an inflection point is detected, applying a damping control scheme until one or more damping control conditions are met, the damping control scheme comprising determining and dispatching a setpoint for controlling the power characteristic based on the inflection point. Aspects of the invention can be used to control the active power output of a wind power plant (22) and damp oscillations in a controlled power characteristic when the frequency level of a connected electrical power network (16) fluctuates outside a frequency deadband.

Description

Technical Field

[0001] This disclosure relates to methods and systems for suppressing power oscillations that occur on power networks during frequency fluctuations. Background Technology

[0002] Electricity grid regulators and operators expect connected power plants to comply with "grid specifications" and provide specific services to the electricity grid.

[0003] For example, some operators require power plants to support the power grid when its frequency deviates from the normal operating range or allowable range (also known as the frequency dead zone). A range of control strategies have been developed for wind power plants to provide support during such frequency deviations. For instance, power plant controllers and wind turbine controllers typically achieve frequency support by adjusting active power output levels to offset the frequency deviation. In underfrequency events, active power output levels increase to support the grid when the frequency level deviates below the lower limit of the frequency dead zone. In overfrequency events, active power output levels decrease to provide support when the frequency level rises above the upper limit of the frequency dead zone.

[0004] However, in this situation, frequency fluctuations in the power grid outside the frequency dead zone can lead to oscillating active power output, resulting in insufficient support for the power grid and damage to power plants.

[0005] The purpose of this invention is to address one or more of the drawbacks associated with the prior art. Summary of the Invention

[0006] According to one aspect of the invention, a method is provided for controlling a renewable energy power plant when the frequency level of the power network to which the power plant is connected is outside a frequency dead zone. The renewable energy power plant may be a wind power plant, for example, comprising one or more wind turbine generators. The method includes: receiving a measured frequency level of the power network; determining and assigning a setpoint for controlling the power characteristics of the power plant based on the measured frequency level; monitoring changes in the measured frequency level to detect an inflection point in the measured frequency level; and when an inflection point is detected, applying a damping control scheme until one or more damping control conditions are met, the damping control scheme including determining and assigning a setpoint for controlling the power characteristics based on the inflection point.

[0007] In this manner, during frequency events (i.e., when the frequency level is outside the permissible range / frequency dead zone), this method provides frequency-dependent control of power characteristics that are effectively frozen or suspended when a frequency inflection point in the connected power network is detected. The controlled power characteristics can take various suitable forms, such as, for example, the active power output of a power plant. This control has the effect of suppressing oscillations in the controlled power characteristics, which would otherwise oscillate with fluctuations in the frequency level of the connected power network during frequency events. Therefore, this method mitigates oscillations in the controlled power characteristics, protects the power plant, and supports a rapid return of the power network frequency to the dead zone.

[0008] Optionally, the damping control scheme includes determining and assigning setpoints for controlling the power characteristics according to a target value (at which the target value is located). For example, the target value may be determined based on the frequency level at a detected inflection point. In one example, the target value may be determined based on a measurement of the controlled power characteristic at the detected inflection point. In this way, the target value is fixed according to the detected inflection point and may have the effect of freezing the power characteristic level or otherwise freezing the desired level that the power characteristic will reach.

[0009] Optionally, the damping control scheme includes determining and assigning setpoints for ramping up or down toward a target value of the determined controlled power characteristic. For example, the damping control scheme may determine ramping or ramping rates, respectively, for increasing or decreasing the determined setpoint at a constant rate. For example, such ramping or ramping rates (slopes) may be predetermined.

[0010] In one example, the damping control scheme includes assigning setpoints to target values ​​until one or more damping control conditions are met. For example, the damping control scheme may begin assigning setpoints to target values ​​in response to detecting an inflection point, or the damping control scheme may begin assigning setpoints to target values ​​after the target value has been reached, for example, after the setpoint has risen or fallen to the target value.

[0011] Optionally, the damping control scheme includes using a lookup table to determine target values ​​for the controlled power characteristics, the lookup table including multiple target values ​​for the controlled power characteristics, each target value corresponding to a specific frequency of the power network.

[0012] In one example, a damping control scheme may include determining the rate of rise or fall for raising or lowering the setpoint toward a target value of the controlled power characteristic, the rate of rise or fall being determined using a lookup table that includes multiple rate of rise or fall for the setpoint. For example, each rate of rise or fall in the lookup table may correspond to at least one of the following: a corresponding frequency of the power network; a corresponding target value of the controlled power characteristic; and / or a corresponding difference between a measured value of the controlled power characteristic and the target value of the controlled power characteristic.

[0013] Optionally, the one or more damping control conditions may include conditions that are met at the end of the application period. For example, the damping control scheme may be configured to start the application period once the controlled power characteristics reach a target value.

[0014] In one example, the method may further include comparing a measured frequency level to a frequency dead zone to determine an overclocking event or an underclocking event. In an overclocking event, the measured frequency level is above the upper limit of the frequency dead zone. In an underclocking event, the measured frequency level is below the lower limit of the frequency dead zone.

[0015] Optionally, if an overclocking event is identified, changes in the measured frequency level can be monitored to detect inflection points in the form of peaks (peak values) of the measured frequency level. Optionally, if an underclocking event is identified, changes in the measured frequency level can be monitored to detect inflection points in the form of troughs (valley values) of the measured frequency level.

[0016] In one example, the one or more damping control conditions may include conditions that are satisfied when a further inflection point is detected. In particular, the further inflection point may take the form of, for example, a further peak in the frequency level measured during an overclocking event, the further peak being at an increased frequency level; or a further trough in the frequency level measured during an underclocking event, the further trough being at a decreased frequency level.

[0017] Optionally, upon detecting a further inflection point, the current damping control scheme is canceled, and another damping control scheme is applied to determine and assign a setpoint for controlling the power characteristics based on the further inflection point.

[0018] In one example, the one or more damping control conditions may include conditions that are satisfied when the measured frequency level rises above a lower threshold frequency. Optionally, the condition may be satisfied when the measured frequency level rises above the lower threshold frequency during a determined underfrequency event.

[0019] In one example, the one or more damping control conditions may include conditions that are satisfied when the measured frequency level drops below an upper threshold frequency. Optionally, the condition may be satisfied when the measured frequency level drops below the upper threshold frequency during a determined overclocking event.

[0020] Optionally, the method may further include determining an upper threshold frequency and / or a lower threshold frequency based on the measured frequency level at the detected inflection point.

[0021] In one example, the method may further include receiving one or more user inputs and determining one or more parameters of the damping control conditions based on the one or more user inputs. For example, at least one of an upper threshold frequency, a lower threshold frequency, and / or an application period can be determined through one or more user inputs.

[0022] Optionally, the one or more damping control conditions include conditions that must be met upon receiving an override command. For example, the override command may be provided by one or more user inputs.

[0023] In the example, the method may also include canceling the damping control scheme based on one or more damping control conditions being met.

[0024] For example, after the damping control scheme is removed, the setpoint can be determined and assigned, for example, based on the frequency level measured when or after the damping control scheme is removed.

[0025] Optionally, after canceling the damping control scheme, the method may further include determining a target value for the controlled power characteristic based on a measured frequency level, and determining and assigning setpoints based on the target value. For example, setpoints for rising or falling toward the target value may be determined and assigned. For example, the method may include determining an upward or downward rate for increasing or decreasing the determined setpoints toward the target value at a constant rate.

[0026] For example, controlled power characteristics may include at least one of the following: the active power output of the power plant; the voltage level of the power plant; and / or the reactive power output of the power plant.

[0027] According to another aspect of the present invention, a power plant controller is provided, the power plant controller being configured to perform the method described in the preceding aspect of the present invention.

[0028] According to one aspect of the present invention, a computer-readable storage medium is provided, the computer-readable storage medium including instructions that, when executed by a computer, cause the computer to perform the methods described above.

[0029] Within the scope of this invention, all aspects, embodiments, examples, and alternatives listed in the foregoing paragraphs, claims, and / or the following description and drawings, especially their individual features, may be used 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 amend any originally filed claim or accordingly file any new claim, including the right to amend any originally filed claim to make it subordinate to any other claim and / or incorporate any feature of any other claim, even though the original claims were not filed in this manner. Attached Figure Description

[0030] One or more embodiments of the present invention will now be described by way of example only, with reference to the accompanying drawings, wherein:

[0031] Figure 1 The diagram schematically illustrates the power network connected to the wind power plant, which includes the power plant controller.

[0032] Figure 2 An embodiment of the present invention is shown. Figure 1 System diagram of the control module of the power plant controller;

[0033] Figure 3 Showing Figure 2 Example Pf curve of the control module;

[0034] Figure 4 The operation according to an embodiment of the present invention is shown. Figure 2 The method of controlling the module;

[0035] Figure 5 A pair of charts are displayed, illustrating the relationship between... Figure 1 The frequency level of the power grid connected to the wind farm, and according to Figure 4 The method shown determines the corresponding active power setpoint, which is used for control during frequency events. Figure 1 The active power output of the wind power plant; and

[0036] Figure 6 An embodiment of the present invention is shown. Figure 4 Example sub-steps of the method. Detailed Implementation

[0037] Generally, the present invention relates to methods and systems for controlling the power characteristics of renewable energy power plants (such as wind power plants), the term "power characteristics" encompassing characteristics including, for example, active power output, reactive power output, and / or voltage levels. In particular, the present invention relates to methods and systems for providing such control when the frequency level of the connected power network is outside an acceptable or permissible frequency range (referred to as a frequency dead zone). In the following description, the period during which the frequency level deviates outside the frequency dead zone may be referred to as a "frequency event".

[0038] During such frequency events, the methods and systems of the present invention are configured to determine and assign setpoints for controlling the power characteristics of one or more generators at a power plant based on the frequency level of the connected power network. However, during such frequency events, the frequency level may fluctuate rapidly; therefore, the methods and systems of the present invention are advantageously configured to suppress oscillating behavior in the power characteristics by monitoring the frequency level of the power network and effectively freezing the power characteristics when a frequency inflection point is detected. For example, when a frequency peak is detected during an overfrequency event, a damping control scheme is applied, wherein a setpoint for controlling the power characteristics of a renewable generator is determined and assigned based on the detected inflection point until one or more damping control conditions are met. These damping control conditions effectively provide one or more conditions that allow the power characteristics to increase or decrease again to further support the connected power network, and may include conditions met upon the expiration of a threshold time period, or, for example, based on a frequency level falling below a threshold frequency. The benefits of doing so are reduced oscillations in the controlled power characteristics, less damage to the power plant, and a faster return of the connected power network to the frequency dead zone.

[0039] Figure 1 The diagram illustrates a typical architecture where a renewable energy power plant connects to the main grid or the wider power network. Figure 1 In the example shown, the renewable energy power plant is a wind power plant (WPP). As will be known to the skilled reader, a WPP includes at least one wind turbine generator (WTG) and is also referred to as a wind farm or wind power park. A WTG is commonly referred to as a "wind turbine." 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 generally relates 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 familiar to the skilled reader. Except... Figure 1In addition to the components shown and described, it is anticipated that other known components may be added, or alternatives thereof. These changes are all within the capabilities of a skilled technician.

[0040] Figure 1 The power system 10 connected to WPP 12 is shown. In this example, WPP 12 includes multiple WTGs 14 and a power plant controller 22 (hereinafter referred to as PPC 22). Each of the multiple WTGs 14 converts wind energy into electrical energy, which is then transferred from WPP 12 as active power and / or current to the main power network or “main grid” 16 for distribution.

[0041] Although Figure 1 While not illustrated, WPP 12 may also include compensation devices, such as Static Synchronous Compensators (STATCOMs) or other types of synchronous compensators, configured to provide reactive power or reactive current support as needed. WPP 12 may also include battery energy storage systems.

[0042] Each of the WTGs 14 is associated with a corresponding WTG controller 15. In some examples, a group of WTGs may share a single semi-centralized WTG controller, thus reducing the number of WTG controllers to fewer than the number of WTGs. As will be understood by those skilled in the art, the WTG controller 15 can be considered as a computer system capable of operating the WTGs 14 in the manner specified herein, and may include multiple modules controlling the various components of the WTGs, or may be a single controller. The computer system of the WTG controller 15 may operate based on software downloaded via a communication network or software programmed onto a computer-readable storage medium.

[0043] During normal operation of WPP 12, WTG controller 15 operates to fulfill active and reactive current and / or power requests received from PPC 22, thereby providing frequency and voltage support to the main grid 16. Under abnormal conditions, WTG controller 15 operates to meet predetermined network requirements and takes action to protect WTG 14 from any potentially harmful conditions.

[0044] WPP 12 also includes a connection network 18 for connecting WPP 12 to the main power grid 16 (also known as the main power network). In this example, WPP 12 and the main power grid 16 are connected at an interconnection point (PoI) 20, which is the interface between WPP 12 and the main power grid 16. PoI 20 may also be referred to as a common coupling point, which can be abbreviated as "PCC" or "PoCC".

[0045] The Power Plant Controller (PPC) 22 is connected to the main grid 16 at the Point of Measurement (PoM) 24 and to the WTG controller 15. 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 the frequency level of the main grid 16. The PPC 22 acts as a command and control interface between the WPP 12 and the grid 16, and more specifically, between the WPP 12 and the grid operator 26 (such as a Transmission System Operator (TSO) or Distribution System Operator (DSO)). The WPP 12 can change its power or current output in response to commands received from the PPC 22.

[0046] like Figure 1 As shown, PPC 22 is a suitable computer system for executing the controls and commands described herein, and may therefore include processing module 28, connection module 30, memory module 32 and sensing module 34.

[0047] The connection module 30, memory 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.

[0048] For example, sensing module 34 can receive such information directly from one or more connected sensors (e.g., the sensor at PoM 24) and transmit the information to processing module 28. Alternatively or additionally, information can also be determined by one or more systems (such as WTG controller 15) connected to connection module 30 and then transmitted to processing module 28 via connection module 30. In each case, the determined information can be permanently or temporarily stored in memory module 32, and processing module 28 can retrieve this information from memory module 32 as needed. PPC 22 can also receive information about power grid 16 and / or local bus, substations, and networks from energy management system (not shown).

[0049] As part of its operation, PPC 22 generates and sends dispatch signals to WTG controller 15. WTG controller 15 controls WTG 14 based on the setpoint contained in the dispatch signals.

[0050] In frequency events, when the frequency level of the main grid 16 deviates from the frequency dead zone, PPC 22 will activate WTG 14 to provide frequency support for the grid 16. The frequency dead zone is typically a small area around the operating frequency of the grid 16 (typically 50 Hz, or 60 Hz in some examples, measured at PoI 20 or PoM 24). For example, the operating frequency could be 50 Hz, and the upper and lower frequency limits of the dead zone could be + / - 0.035 Hz.

[0051] Based on the control strategy mentioned above, in one example, PPC 22 can issue dispatch signals configured to control one or more power characteristics of WTG 14 to provide such frequency support. For example, the dispatch signals can be configured to control the active power output, reactive power output, and / or voltage level of WTG 14 to support frequency level return to dead zone.

[0052] For example, in an underfrequency event where the frequency level of grid 16 drops below the lower limit of the dead zone, PPC 22 can provide frequency support by assigning an increased active power setpoint to WTG 14 (i.e., a setpoint used to increase the active power supplied by WTG 14 to grid 16). Similarly, in an overfrequency event where the grid frequency rises above the upper limit of the dead zone, PPC 22 can provide frequency support by assigning a decreased active power setpoint to reduce the active power supply.

[0053] Figure 2 The illustration shows a program, algorithm, or "control module" 100 according to an embodiment of the present invention, which forms part of the processing module 28 of the PPC 22 for determining and assigning such setpoints during frequency events.

[0054] Specifically, when the frequency level of the connected main power grid 16 is outside the frequency dead zone, the control module 100 is configured to receive the measured frequency level of the connected main power grid 16 or information indicating the frequency level, and determine a setpoint for controlling one or more power characteristics of the WTG 14 based on the frequency level.

[0055] It is understood here that the measured frequency level provides an accurate measurement of the grid frequency, for example, with a resolution on the order of mHz or μHz. In one example, the measured frequency level can be filtered to remove noise associated with the measured value. For example, the measured frequency level can be noise-filtered to ignore negligible variations, i.e., variations between consecutive measurements below a corresponding upper or lower threshold. The control module 100 can receive such a noise-filtered measurement signal or determine such a signal itself by applying a suitable noise filter.

[0056] One or more power characteristics of the WTG 14 controlled by the control module 100 may include, for example, active power output, reactive power output, or voltage level of one or more of the WTG 14. However, for simplicity, in the following description, the example control module 100 is configured to control the active power output of the WTG 14, and the determined setpoint is an active power setpoint for controlling said active power output. However, this example is not intended to limit the scope of the invention.

[0057] Typically, the active power setpoint can be determined based on the measured frequency level of the connected main power grid 16, and varies accordingly with changes in the measured frequency level.

[0058] For example, control module 100 can be configured to determine an active power setpoint based on a reference active power level, which can start from a baseline value and increase (i.e., increase at a constant rate) or decrease (i.e., decrease at a constant rate) according to the measured frequency level. Here, the baseline value may correspond to an estimate of the available active power supplied by WPP 12 to the main grid 16, such as the maximum “rated” power that can be supplied to the main grid 16 under corresponding conditions (such as given wind speed conditions).

[0059] Therefore, the control module 100 may include one or more lookup tables 102 (e.g., Figure 2 As shown), the lookup table includes a target value of active power for the corresponding frequency level measurement and / or a predetermined rate of increase or decrease for increasing or decreasing the reference active power level.

[0060] For example, lookup table 102 may include a Pf curve for matching a frequency level measurement (f) with a corresponding active power target value P(f). As an illustration, Figure 3 An example Pf curve of a type familiar to technicians is shown.

[0061] The example Pf curve shows a frequency dead zone DB, which defines a frequency range in which the active power target value P(f) remains substantially constant. The example PF curve also shows the specified increase in the active power target value P(f) when the frequency level drops below the frequency dead zone DB (during an underfrequency event), and the specified decrease in the active power target value P(f) when the frequency level rises above the frequency dead zone DB (during an overfrequency event). As shown in this example, the specified increase and / or decrease in the active power target value P(f) as the frequency level deviates further from the frequency dead zone DB can include a step change in the active power target value P(f) and / or one or more different ramps defining the change in the active power target value P(f). For example, the Pf curve can be divided into a series of frequency bands, and the ramps of the Pf curve can increase or decrease in consecutive frequency bands as the frequency level deviates further from the frequency dead zone DB. Furthermore, in some examples, the Pf curve may also include minimum and / or maximum frequency levels, such as... Figure 3 As shown, above this frequency level, the active power target value P(f) can remain basically constant.

[0062] Lookup table 102 may additionally or alternatively include predetermined rise and fall rates in the form of one or more predetermined rise and / or fall rates for increasing or decreasing the reference active power level according to the corresponding conditions of WPP 12 and / or power grid 16. For example, lookup table 102 may include one or more predetermined rise or fall rates (corresponding to the corresponding frequency level measurement), changes in the measured frequency level, the reference active power level, and / or active power target values ​​(such as active power target values ​​corresponding to the measured frequency level).

[0063] For example, during an overclocking event, control module 100 can be configured to access lookup table 102 to determine a corresponding rate of decrease for proportionally reducing the reference active power level (and active power setpoint) based on the corresponding increase in the measured frequency level. In this way, control module 100 can support the main grid 16 returning to the frequency dead zone by controlling WTG 14 to generate less active power. Subsequently, when the measured frequency level returns to the frequency dead zone, control module 100 can be configured to compare the reference active power level with a baseline value and (based on the comparison) determine the rate of increase from lookup table 102 to restore the reference active power level to the baseline value.

[0064] Various methods are known in the art for determining the active power setpoint based on the measured frequency level of the connected power grid 16, but it should be understood that the above examples are not intended to limit the scope of the invention.

[0065] However, during frequency events, frequency levels can fluctuate and become unstable, especially in relatively sensitive power grids. If active power output is controlled based on measured frequency levels, such fluctuations can cause significant oscillations in active power output. For example, fluctuating frequency levels can cause the reference active power level to rise and fall rapidly, becoming highly oscillating. Such power oscillations can potentially damage components in WPP 12 and / or grid 16.

[0066] To mitigate such oscillations in active power output, the control module 100 of the present invention advantageously includes a damping controller 101, which incorporates alternative procedures, algorithms, or damping control schemes for providing suppression of active power output.

[0067] Specifically, the control module 100 is configured to monitor the measured frequency level to detect inflection points in the form of peaks or troughs within the measured frequency level. When a suitable inflection point is detected, the damping controller 101 is configured to determine and assign an active power setpoint corresponding to the measured frequency level at the inflection point until one or more so-called damping control conditions are met. In this case, a suitable inflection point can be a frequency peak during an overclocking event or a frequency trough during an underclocking event. For example, in each case, the inflection point can be a noise filtering inflection point whose peak-to-peak amplitude exceeds a corresponding inflection point detection threshold. However, this example is not intended to limit the scope of the invention.

[0068] Therefore, after the frequency inflection point occurs, the damping controller 101 effectively ignores further changes in the measured frequency level, and the active power setpoint is thus determined and assigned based on a constant reference frequency level over a longer period of time. This effectively suppresses any oscillating behavior in the active power output when the measured frequency level continues to fluctuate.

[0069] Understandably, the damping controller 101 can use the detected inflection point to determine the active power setpoint according to one or more suitable methods. For example, the damping controller 101 can be configured to determine the active power setpoint approximately as described above, for instance, by using a lookup table 102 to determine the active power target value P(f) at the frequency level (f) at the detected inflection point, and by determining an appropriate rise or fall rate based on the comparison between the two, for adjusting the reference active power level to the active power target value P(f). Once the reference active power level reaches the active power target value P(f), the control module 100 can assign an active power setpoint according to that value P(f) until one or more damping control conditions are met.

[0070] In examples of the invention, the one or more damping control conditions may take various suitable forms, as should be understood, including any of the following conditions provided by way of example.

[0071] Such a damping control condition can be satisfied when the application period (such as the minimum time period for which a damping control scheme determines and assigns active power setpoints based on detected inflection points) expires. For example, the damping controller 101 can be configured to initiate the application period when the active power output of WTG 14 reaches a determined active power target value P(f), and maintain that active power output for a predetermined time period. For example, this time period can be set by one or more user inputs.

[0072] Another damping control condition can be met when a further inflection point in the measured frequency level is detected. In this case, the damping control scheme can be effectively reset and reapplied, where the active power setpoint is determined and assigned based on the measured frequency level corresponding to the further inflection point. In other words, upon detection of a further inflection point, the current damping control scheme can be canceled, and another damping control scheme can be applied to determine and assign the active power setpoint based on the further inflection point.

[0073] To reduce the sensitivity of the damping controller 101 and thus provide additional damping, such a damping control condition is satisfied only when a subsequent inflection point further away from the frequency dead zone than the inflection point on which the current setpoint is based is detected. In other words, the damping control condition is satisfied only when a further peak is detected during an overclocking event, and the frequency level of the further peak is higher than the original peak; or when a further trough is detected during an underclocking event, and the frequency level of the further trough is lower than the original trough.

[0074] Similarly, another damping control condition can be satisfied when the measured frequency level deviates further from the frequency dead zone than the inflection point on which the current setpoint is based. In other words, the damping control condition can be satisfied if the measured frequency level exceeds the original frequency peak during an overclocking event, or if the measured frequency level drops below the original frequency trough during an underclocking event.

[0075] When the measured frequency level rises above the lower threshold frequency, a further condition can be satisfied. Preferably, this damping control condition can be limited to under-frequency events. Similarly, when the measured frequency level falls below the upper threshold frequency, another condition can be satisfied. Preferably, this further damping control condition can be limited to over-frequency events. For example, the upper and / or lower threshold frequencies can be user-defined, or the damping controller 101 can be configured to determine such thresholds, for example, based on the measured frequency level at a detected inflection point.

[0076] In one example, the damping controller 101 may be configured to receive one or more user inputs. For example, the damping controller 101 may be configured to receive one or more user inputs and determine one or more parameters of the damping control conditions based on these user inputs. For example, the damping controller 101 may determine the duration of the aforementioned application period based on one or more user inputs. Additionally or alternatively, these user inputs may be used to manually intervene in the damping control. For example, upon receiving a coverage command provided by the user through one or more of the user inputs, another damping control condition may be satisfied.

[0077] In some embodiments of the invention, control module 100 may be configured to cancel or deactivate the damping control scheme after one or more of the damping control conditions are met. Once canceled, control module 100 may be configured to instead determine and assign a setpoint based on the measured frequency level. For example, control module 100 may be configured to access lookup table 102 and determine a target active power value corresponding to the measured frequency level after canceling the damping control scheme, and determine an increase or decrease rate for adjusting the reference active power level based on a comparison between the determined target active power value and a reference active power level. For example, such increase or decrease rates may be applied until a further inflection point is detected when the measured frequency level is outside the frequency dead zone.

[0078] Now, additional references will be made. Figures 4 to 6 Describe the operation of control module 100.

[0079] Figure 4 An example method 200 for controlling the active power output of WPP 12 according to an embodiment of the present invention is shown. Figure 5 A pair of graphs are shown illustrating the measurement frequency level 40 and the reference active power level 50 of the main power grid 16, the reference active power level 50 representing the active power setpoint determined according to method 200.

[0080] like Figure 5 As shown, during the initial period, the measured frequency level 40 of the main power grid 16 may be within an acceptable frequency range (referred to as the frequency dead zone) around the normal operating frequency of the power grid 16, with its frequency falling between the upper limit f of the frequency dead zone. upper and lower limit f lower Between. For context, in this example, the normal operating frequency of grid 16 is 50 Hz, therefore the upper limit f upper The frequency can be 50.035 Hz, with a lower limit f. lower The frequency can be 49.965 Hz.

[0081] During this period, PPC 22 can be configured to control the active power output of WPP 12 according to the dead-time frequency operating mode. For example, the dead-time frequency operating mode can be controlled by the processor module 28 instead of the controller of the control module 100, or by another control system of PPC 22, for example.

[0082] For example, depending on the dead-zone frequency operating mode, PPC 22 can control WPP 12 to meet the power demand of grid operator 26 and protect WTG 14, applying power reduction or power boost as necessary.

[0083] At this point, control module 100 can determine the active power setpoint not assigned to WTG 14. For example, control module 100 can determine the active power setpoint at the baseline value of the corresponding condition, such as... Figure 5 The reference active power level 50 is indicated in the text.

[0084] However, sudden changes in power generation or load within the main grid 16 may lead to over-frequency or under-frequency events, in which the frequency level of the main grid 16 may cross (cross) the frequency dead zone.

[0085] For example, such as Figure 5 As shown, an overclocking event may occur, where a frequency level of 40 may cross and exceed the upper limit of the frequency dead zone at time t1. upper .

[0086] At this point, you can start such as Figure 4 The method 200 shown describes the control of the active power output of WPP 12. Specifically, when frequency level 40 crosses the frequency dead zone, i.e., at point t1, control module 100 can receive a measurement of frequency level 40 of the power grid 16 and determine in step 202 that frequency level 40 is outside the frequency dead zone. For example, control module 100 can measure the frequency level 40 relative to the upper limit f of the frequency dead zone. upper Compare and detect overclocking events, such as Figure 5 As in the example.

[0087] Based on this, the control module 100 can continue in step 204 to determine and assign an active power setpoint for controlling the active power output of WPP 12 during frequency events. In this way, under the control of the control module 100, PPC 22 effectively switches to frequency event operation mode, now additionally referring to... Figure 6 To provide a more detailed description.

[0088] Figure 6 Example sub-steps 206 to 212 of step 204 of a method 200 for controlling the active power output of WPP 12 during a frequency event, according to an embodiment of the present invention, are shown.

[0089] In sub-step 206, once the frequency dead zone is crossed, the control module 100 can be configured to determine and assign the active power setpoint based on the measured frequency level 40.

[0090] For example, control module 100 can determine the active power setpoint (as illustrated by reference active power level 50) by descending from a baseline value. Figure 5(As shown). Specifically, the control module 100 can access lookup table 102 and determine a predetermined rate of decrease rr2 based on the measured frequency level 40 (or its increment), and apply this rate of decrease to the baseline value. Figure 5 As shown, this has the effect of reducing the reference active power level 50 at a constant rate, thereby supporting the return frequency dead zone of the power grid 16.

[0091] Simultaneously, in sub-step 208, control module 100 monitors the frequency level to detect inflection points in the measured frequency level. Specifically, in this example, since the measured frequency level has exceeded the upper frequency limit of the frequency dead zone (in an overclocking event), control module 100 is configured to detect frequency peaks in the measured frequency level. It is understood that this peak effectively indicates the maximum frequency level reached by the power grid 16, which can be used to control active power output. In other examples, control module 100 may be configured to detect troughs during underclocking events, or control module 100 may be configured to detect any inflection point in the measured frequency level, regardless of whether the event is an overclocking or underclocking event.

[0092] Various mathematical and graphical methods are known to be available for determining such inflection points, which will not be described in detail here to avoid obscuring the invention.

[0093] like Figure 5 As shown, in sub-step 208, an inflection point in the form of a peak is detected at point t2. At this time, the measured frequency level is at frequency f1. In this example, the frequency peak f1 is between 51 and 52 Hz. Therefore, in sub-step 210, once the inflection point is detected, the control module 100 continues to apply the damping control scheme. Specifically, the damping controller 101 operates to determine and assign the active power setpoint for controlling WPP 12 based on the detected inflection point until one or more damping control conditions are met.

[0094] As an example only, the damping controller 101 may first determine the active power target value P(f1) corresponding to the measured frequency level f1 at the detected inflection point. Then, the damping controller 101 may compare a reference active power level 50 with the active power target value P(f1), and in this example, detect that the reference active power level 50 has reached the active power target value P(f1). Therefore, the damping controller 101 may continue to determine and assign active power setpoints according to the active power target value P(f1) until one or more damping control conditions are met.

[0095] In this example, a damping control condition can be satisfied when the measured frequency level rises to a level greater than the measured frequency level at the detected inflection point (i.e., frequency level f1).

[0096] For example, such as Figure 4 and Figure 5 As shown, during the time period after point t2, the control module 100 can determine in sub-step 212 whether one or more damping control conditions are met.

[0097] When the measured frequency level remains below frequency f1, the damping control condition is not met, and the control module 100 continues to determine and assign the active power setpoint based on the detected inflection point. Therefore, as Figure 5 As shown, the reference active power level 50 remains constant during this period, and the active power setpoint is output according to the active power target value P(f1). It is worth noting that during this period, the measured frequency level 40 will exhibit further inflection points in the form of frequency troughs. However, in this example, the damping control conditions of the control module 100 are not satisfied by the frequency troughs during the overclocking event, therefore the damping control scheme remains effective.

[0098] However, when the measurement frequency level rises to Figure 5 When the frequency f1 at the midpoint t3 is above the threshold, the control module 100 detects that the damping control condition has been met, and the damping control scheme is canceled. Therefore, after point t3, the control module 100 returns to sub-step 206 to determine the active power setpoint based on the measured frequency level.

[0099] like Figure 5 As shown, the control module 100 can thus proceed to access lookup table 102 and re-determine the rate of decrease rr2 based on the measured frequency level 40 (or its increase). Therefore, the active power setpoint represented by the reference active power level 50 begins to decrease again after point t3, further reducing the active power output of WTG 14.

[0100] As the reference active power level 50 decreases, the control module 100 continues to monitor the measured frequency level 40 in sub-step 208 to detect further inflection points (the next inflection point). Specifically, the control module 100 now monitors the measured frequency level 40 to detect frequency peaks that are further away from the frequency dead zone than the previous frequency peak f1.

[0101] This inflection point is in Figure 5 Point t4 is detected, and control module 100 proceeds to reapply the damping scheme in sub-step 210. However, in this example, control module 100 is configured to determine and assign the active power setpoint based on a further inflection point (i.e., frequency peak f2). For the context, in this example, frequency peak f2 is higher than frequency peak f1, but also between 51 and 52 Hz.

[0102] Therefore, the damping controller 101 can be run to determine another active power target value P(f2) corresponding to the measured frequency level f2 at a further inflection point. Thus, as before, the damping controller 101 can compare the reference active power level 50 with the active power target value P(f2), but in this example, the damping controller 101 will detect that the active power target value P(f2) at point t4 is lower than the reference active power level 50. Therefore, the damping controller 101 can access lookup table 102 to determine the corresponding rate of decrease for reducing the reference active power level 50 to the active power target value P(f2). In this example, the control module 100 can access lookup table 102 and find the rate of decrease (also the rate of decrease rr2) corresponding to the active power target value P(f2). Therefore, the control module 100 can continue to determine and assign the active power setpoint according to the rate of decrease rr2 until the active power setpoint reaches the active power target value P(f2). This occurs shortly after the detected inflection point, i.e. Figure 5 Point t5 is shown. Once the reference active power level reaches the active power target value P(f2), the control module 100 can continue to assign active power setpoints according to the active power target value P(f2) until one or more damping control conditions are met.

[0103] For the sake of context, Figure 5 Further damping control conditions are demonstrated, which are satisfied when WTG 14 provides active power output at the target active power value P(f2) during the predetermined application period.

[0104] For example, in sub-step 212, when the reference active power level reaches the active power target value P(f2) at point t5, the control module 100 can start the timer. When the application period expires, the control module 100 can cancel the damping control scheme.

[0105] like Figure 5 As shown, the application period continues until point t6. During the period between points t4 and t6, control module 100 continues according to sub-step 210 to determine and assign the active power setpoint based on the second active power target value P(f2). In this way, control module 100 provides a stable active power output (although the frequency level of grid 16 decreases during the application period), which supports grid 16 returning to the frequency dead zone.

[0106] The desired effect is that applying damping control throughout the application period will encourage the frequency level to return to the frequency dead zone. However, grid frequency is highly sensitive to a range of variables, and this may not be the case under certain conditions. Nevertheless, it is considered appropriate to remove the damping control scheme after the application period ends in order to adapt the active power level to the relevant conditions. For example, it may be necessary to increase the active power level at the end of the application period to prevent overshooting the frequency dead zone.

[0107] Therefore, when the application period expires at point t6, the control module 100 stops applying the damping control scheme and continues to determine and assign the active power setpoint based on the measured frequency level, as in sub-step 206.

[0108] Since the frequency level in this example has not yet exceeded the previous peak frequency (f2), it is reasonable to assume that the measured frequency level is below the previous peak frequency (f2). Accordingly, the active power target value P(f) corresponding to the measured frequency level (f) will be higher than the reference active power level 50. Therefore, after canceling the damping control scheme, i.e., at point t6, the control module 100 can initially determine a further active power target value P(f3) corresponding to the measured frequency level (f3) at that point. For context, in Figure 5 In the example shown, the frequency level f3 at the end of the application period is between 50 Hz and 51 Hz. The control module 100 can then compare the reference active power level 50 with the determined active power target value P(f3) and access lookup table 102 to determine the corresponding acceleration / deceleration rate rr1 based on this comparison. Then, as... Figure 5 As shown, the rate of increase rr1 can be applied to the reference active power level 50 so that the control module 100 can determine and assign an active power setpoint that increases continuously toward the active power target value P(f3).

[0109] like Figure 5 As shown, during the period between points t6 and t7, this action initially reduces the rate of decrease in the measured frequency level, thus creating another frequency inflection point in the form of a frequency trough in the measured frequency level 40. Subsequently, as the reference active power level 50 approaches the active power target value P(f3), the measured frequency level 40 begins to increase again.

[0110] However, before the reference active power level 50 reaches the active power target value P(f3), the measurement frequency level 40 changes direction again, thus... Figure 5Point t8, as shown, forms another inflection point in the form of a frequency peak f(4). In this example, the frequency peak f4 is between 50.5 and 51 Hz. This further peak indicates the fluctuating nature of the grid frequency during the overclocking event and is detected by the control module 100 in sub-step 208.

[0111] Therefore, in sub-step 210, control module 100 continues to redetermine and assign the active power setpoint based on the frequency peak (f4), roughly as described above. Thus, when accessing lookup table 102, damping controller 101 can determine the active power target value P(f4). Since the active power target value P(f4) is very close to the previous active power target value P(f3), in this case, damping controller 101 can continue to determine the same rate of rise rr1 based on a comparison between the reference active power level 50 and the active power target value P(f4).

[0112] Then, when the reference active power level 50 finally reaches Figure 5 When the active power target value P(f4) at the midpoint t9 is reached, the frequency damping control module 100 can restart the timer in sub-step 212. However, in this example, as the timer progresses, a further damping control condition is met at point t10 before the application period expires. Specifically, the measured frequency level 40 drops below the lower threshold frequency (such as the upper limit of the frequency dead zone), which satisfies the further damping control condition of the control module 100. Therefore, the damping control scheme is canceled.

[0113] At point t10, method 200 supports a rapid return of the measured frequency level 40 to the frequency dead zone, allowing PPC 20 to resume dead zone frequency operation mode so that WTG 14 can continue operating. Therefore, method 200 suppresses active power output to avoid or significantly mitigate any damage to WPP 12 caused by frequency fluctuation events, and the grid frequency quickly returns to an acceptable operating range.

[0114] like Figure 5 As shown, although control module 100 can stop assigning active power setpoints after returning to the frequency dead zone, it can still cause the reference active power level 50 to rise toward the baseline value, for example, using a rise rate rr1 after point t10. Therefore, if the measured frequency level 40 subsequently moves out of the frequency dead zone again in an over-frequency or under-frequency event, method 200 can be restarted to support another return to the frequency dead zone.

[0115] Understandably, while the example chart illustrates an overclocking event where active power output is reduced to support the main grid 16, the method 200 is equally applicable to an underclocking event where active power is increased to support the main grid 16.

[0116] Furthermore, in the above examples of the present invention, the control module 100 is configured to cancel the damping control scheme once any one of the damping control conditions is met. However, in other examples of the present invention, the control module 100 may be configured to cancel the damping control scheme only after multiple damping control conditions are met; in some cases, each damping control condition must be met before the control scheme can be canceled.

[0117] It will be understood that various changes and modifications can be made to the above examples without departing from the scope of the invention.

Claims

1. A method (200) for controlling a power plant (12) when the frequency level of a power grid (16) to which the renewable energy power plant (12) is connected is outside a frequency dead zone, the method (200) comprising: Receive the measured frequency level (40) of the power network (16); Based on the measured frequency level, a setpoint for controlling the power characteristics of the power plant (12) is determined and assigned; The change in the measurement frequency level (40) is monitored to detect the inflection point of the measurement frequency level (40); as well as When an inflection point is detected, a damping control scheme is applied until one or more damping control conditions are met. This damping control scheme includes determining and assigning setpoints for controlling the power characteristics based on the inflection point. The one or more damping control conditions include conditions that are satisfied when a further inflection point is detected.

2. The method (200) according to claim 1, wherein, The damping control scheme includes determining and assigning setpoints for controlling the power characteristics according to a target value, the target value being determined based on the frequency level (40) at the detected inflection point.

3. The method (200) according to claim 2, wherein, The damping control scheme includes determining and assigning setpoints that cause the power characteristics to rise or fall toward the target value.

4. The method (200) according to claim 2, wherein, The damping control scheme includes assigning setpoints according to the target value until one or more damping control conditions are met.

5. The method (200) according to any one of claims 2 to 4, wherein, The damping control scheme includes using a lookup table (102) that includes multiple target values ​​of the power characteristic to determine the target value of the power characteristic, each target value corresponding to a corresponding frequency of the power network.

6. The method (200) according to claim 5, wherein, The damping control scheme includes determining a rise / fall rate for raising or lowering the setpoint toward a target value of the power characteristic, the rise / fall rate being determined using a lookup table (102) that includes a plurality of rise / fall rates of the setpoint.

7. The method (200) according to any one of claims 2 to 4, wherein, The one or more damping control conditions include conditions that must be met when the application period expires.

8. The method (200) according to claim 7, wherein, The damping control scheme is configured to initiate the application period once the power characteristics reach the target value.

9. The method (200) according to any one of claims 1 to 4, further comprising comparing the measured frequency level (40) with the frequency dead zone to determine an overclocking event or an underclocking event.

10. The method (200) according to claim 9, wherein: If an overclocking event is identified, the change in the measured frequency level (40) is monitored to detect the inflection point in the peak form of the measured frequency level (40); and / or If an underfrequency event is identified, the change in the measured frequency level (40) is monitored to detect the inflection point in the form of a trough in the measured frequency level (40).

11. The method (200) according to claim 10, wherein the further inflection point takes the form of: A further peak in the measured frequency level (40) during the overclocking event, the further peak being at an increased frequency level; or A further trough in the measured frequency level (40) during the underfrequency event, the further trough being at a reduced frequency level.

12. The method (200) according to any one of claims 1 to 4, wherein, Upon detecting the further inflection point, the current damping control scheme is canceled, and another damping control scheme is applied to determine and assign a setpoint for controlling the power characteristics based on the further inflection point.

13. The method (200) according to any one of claims 1 to 4, wherein, The one or more damping control conditions include conditions that are satisfied when the measured frequency level (40) rises above the lower threshold frequency.

14. The method (200) according to claim 13, wherein, The condition is satisfied when the measured frequency level (40) rises above the lower threshold frequency during a determined underfrequency event.

15. The method (200) according to any one of claims 1 to 4, wherein, The one or more damping control conditions include conditions that are satisfied when the measured frequency level (40) drops below the upper threshold frequency.

16. The method (200) according to claim 15, wherein, The condition is met when the measured frequency level (40) drops below the upper threshold frequency during a determined overclocking event.

17. A power plant controller (22) configured to perform the method (200) of any one of claims 1 to 16.

Images