Method and system for controlling power plant during network frequency fluctuations within frequency emergency dead zone

Abstract

According to one aspect of the present invention, there is provided a method of controlling a renewable energy power plant to provide frequency regulation for a power network to which the power plant is connected. The power plant includes a plurality of power units operable to provide up-regulation and / or down-regulation of the power network. The method comprises: receiving a measured frequency level of the power network, the measured frequency level indicating a frequency deviation within a frequency emergency dead zone of the power network; identifying a sub-band of the frequency deviation from a plurality of sub-bands within the frequency emergency dead zone based on the measured frequency level; identifying one or more power units authorized for at least one frequency regulation service within the identified sub-band; determining a deliverable power offset from the baseline power level for each authorized power unit, the deliverable power offset adjusting the service based in part on the at least one authorized frequency; and determining a power setpoint and assigning the power setpoint to one or more authorized power units to meet a plant power offset request for the measured frequency level. The setpoint is determined by selecting one or more of the authorized power units to provide a deliverable power offset determined for that power unit, wherein a cumulative power offset of the one or more selected power units is less than or equal to the plant power offset request; and if there is a power shortage between the plant power offset request and the accumulated power offset, determining a setpoint for a remaining authorized power unit to meet the power shortage.

Description

Field of the Invention

[0001] The present disclosure relates to methods and systems for controlling a power plant to provide frequency regulation services, particularly frequency regulation services within a frequency contingency deadband of a power network to which the power plant is connected. Aspects of the present invention relate to a method and to a power plant controller. Background Art

[0002] Regulators and operators of power networks expect connected power plants to comply with "grid codes" and provide specific services to the power network.

[0003] For example, national or international power networks have a nominal frequency, also known as the utility or mains frequency, which is typically 50 Hz or 60 Hz. Some operators require power plants to support the power network when the frequency of the power network deviates from the normal operating range near the nominal frequency (also known as the frequency contingency deadband). Such frequency variations are undesirable because the equipment supplied with power is configured to operate at a specific frequency with relatively strict tolerances. Therefore, it is important to take corrective measures quickly even when the frequency deviates from the nominal frequency by less than 1 Hz.

[0004] In some cases, power plant operators provide frequency regulation services, such as frequency containment reserves (FCR), to further improve grid stability even when the network frequency remains within the frequency contingency deadband. For example, a power plant operator may agree (contract, consent) to provide up- and / or down-regulation services to offset deviations from the nominal operating frequency of the power network in the market on an hourly, daily, or annual basis. In this context, up-regulation means increasing the power supply of the power plant or reducing the power consumption of the power plant, while down-regulation means reducing the power supply of the power plant or increasing the power consumption of the power plant.

[0005] Recently, it has become possible for individual power units, such as individual energy generators, energy consumers, and / or energy storage devices of a power plant, to provide different frequency regulation services within the frequency contingency deadband. In particular, it is possible to agree that individual power units offset frequency deviations within one or more sub-bands (sub-frequency bands) of the frequency contingency deadband. However, this range of options increases the control complexity.

[0006] The object of the present invention is to solve one or more drawbacks associated with the prior art. Summary of the Invention

[0007] According to one aspect of the present invention, there is provided a method of controlling a renewable energy power plant to provide frequency regulation to an electrical power network to which the power plant is connected. The power plant includes a plurality of power units operable to provide upward and / or downward regulation of the electrical power network. The method includes: receiving or obtaining a (measured) frequency level of the electrical power network, the (measured) frequency level indicating a frequency deviation within a frequency contingency deadband of the electrical power network; based on the (measured) frequency level, identifying a subband of the frequency deviation from among a plurality of subbands within the frequency contingency deadband; identifying one or more power units authorized for at least one frequency regulation service within the identified subband; determining a deliverable power offset (offset amount) from a baseline power level for each authorized power unit, the deliverable power offset being based in part on at least one authorized frequency regulation service; and determining a power setpoint and dispatching the power setpoint to one or more authorized power units to meet a plant power offset request for the (measured) frequency level. The setpoint is determined by: (i) selecting one or more of the authorized power units to provide the deliverable power offset determined for that power unit, wherein the cumulative power offset of the one or more selected power units is less than or equal to the plant power offset request; and (ii) if there is a power shortage between the plant power offset request and the cumulative power offset, determining the setpoints of the remaining authorized power units to meet the power shortage.

[0008] In this way, the method reduces the control complexity associated with controlling the power plant to provide frequency regulation services within the frequency contingency deadband while facilitating an agreement on the scope of frequency regulation services for the individual power units of the power plant.

[0009] The deliverable power offset can be determined, for example, as the minimum of: a specified power offset for the power unit and a possible power offset for the power unit. In this case, the specified power offset can be based on, for example, at least one authorized frequency regulation service and the measured frequency level. The possible power offset can be, for example, the difference between the baseline power level of the power unit and an upper and / or lower limit of the available power of the power unit.

[0010] Optionally, each power unit can be authorized for one or more of a plurality of frequency regulation services. Each frequency regulation service can be associated with a specified power offset for a corresponding frequency level within one or more of the plurality of subbands. In this way, the individual power units can be controlled to provide different frequency regulation services.

[0011] Multiple frequency regulation services may include, for example, one or more of the following: (i) Frequency Containment Reserve for Normal Operation (FCR-N) in response to a frequency deviation below the nominal frequency level of the power network; (ii) FCR-N in response to a frequency deviation above the nominal frequency level; (iii) Frequency Containment Reserve for Disturbance (FCR-D) in response to a frequency deviation below the nominal frequency level; (iv) FCR-D in response to a frequency deviation above the nominal frequency level; and / or (v) a combination of two or more selected from (i) to (iv).

[0012] Optionally, each frequency regulation service is associated with a corresponding power-frequency (P-f) curve. For example, the method may further include determining a specified power offset for each authorized power unit based on the P-f curve associated with at least one authorized frequency regulation service.

[0013] In an example, each frequency regulation service (e.g., each of the FCR-N frequency regulation service and the FCR-D frequency regulation service) may be associated with a corresponding P-f offset curve with respect to a baseline power level in a corresponding sub-band relative to a frequency contingency deadband.

[0014] Optionally, a combination of frequency regulation services is associated with a corresponding P-f curve (e.g., a combination of the FCR-N frequency regulation service and / or the FCR-D frequency regulation service may be associated with a corresponding P-f curve). For example, the corresponding P-f curve may be determined by summing the corresponding P-f offset curves of the combined FCR-N frequency regulation service and / or FCR-D frequency regulation service.

[0015] Each power unit may be authorized for one or more frequency regulation services, for example, within a corresponding service period. In this way, different frequency regulation services may be agreed upon for different periods, providing more flexible operation.

[0016] Optionally, the method further includes determining a specified power offset for each authorized power unit based on the corresponding agreed maximum contribution to at least one authorized frequency regulation service. The maximum contribution to at least one authorized frequency regulation service may be agreed upon (reached an agreement) for a specified service period, for example. For example, the maximum contribution may be set or determined according to various factors, including, for example, the fatigue life or age of the power unit.

[0017] Optionally, the method further includes determining a possible power offset for the power unit based on the baseline power level of the power unit and the upper and / or lower limits of the available power of the power unit.

[0018] In an example, one or more authorized power units can be selected by ranking one or more authorized power units in a priority list based on the deliverable power offset determined for each authorized power unit; and selecting the top 1 to M power units, where M is a positive integer. In this way, the method can ensure that the power units authorized to provide the greatest contribution are prioritized in the response.

[0019] Optionally, M is the largest positive integer used to ensure that the cumulative power offset of the one or more selected power units is less than or equal to the plant power offset request.

[0020] In an example, the plurality of power units can include: one or more renewable energy generators, such as wind turbine generators; one or more energy storage devices, such as battery units; and / or one or more energy consumers, such as electrolyzers and / or chemical plants.

[0021] According to another aspect of the present invention, there is provided a computer-readable storage medium including instructions that, when executed by a computer, cause the computer to perform the above method.

[0022] According to yet another aspect of the present invention, there is provided a power plant controller configured to perform the method described in the previous aspects of the present invention.

[0023] Within the scope of the present invention, it is expressly intended that the various aspects, embodiments, examples, and alternatives set forth in the preceding paragraphs, claims, and / or the following description and drawings, particularly their respective features, can be implemented independently or in any combination. That is, all embodiments and / or features of any embodiment can be combined in any way and / or combination, unless these features are incompatible. The applicant reserves the right to change any originally filed claim or to file any new claim accordingly, including the right to modify any originally filed claim to be subordinate to any other claim and / or to incorporate any feature of any other claim, even though originally not claimed in such a manner. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] One or more embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings, in which:

[0025] Figure 1 A power network connected to a renewable energy power plant including a power plant controller is schematically shown;

[0026] Figure 2 Shows a Figure 1 system diagram of the control module of the power plant controller according to an embodiment of the present invention;

[0027] Figure 3shows Figure 2 an exemplary P-f curve of the control module;

[0028] Figure 4 shows an exemplary method of controlling a power plant according to an embodiment of the present invention; and Figure 1 as shown; and

[0029] Figure 5 shows Figure 1 exemplary functional components of the power plant controller as shown. DETAILED DESCRIPTION

[0030] Generally, the present invention relates to methods and systems for controlling a renewable energy power plant to provide frequency regulation for a connected power network while the frequency level is maintained within a frequency contingency dead band of the power network.

[0031] The renewable energy power plant includes a plurality of power units, which may include one or more power generators, power consumers, and / or power storages, operable to provide up-regulation and / or down-regulation of the power network. Thus, each power unit is operable to counteract a frequency deviation within the frequency contingency dead band.

[0032] However, the power units may be authorized, configured, or controlled to provide different frequency regulation services within the frequency contingency dead band. In particular, each power unit may be authorized, configured, or controlled to provide one or more frequency regulation services, where each frequency regulation service defines a corresponding power offset from a baseline power level for an authorized power unit when the frequency level deviates within one or more corresponding sub-bands of the frequency contingency dead band. By way of example, when the frequency level decreases from a nominal operating frequency into a corresponding sub-band of the frequency contingency dead band, a battery unit of the power plant may be authorized to provide frequency containment reserve for normal operation (FCR-N). Accordingly, the power level of the battery unit may thus be adjusted or offset from the baseline power level to counteract the frequency deviation within the corresponding frequency sub-band.

[0033] Since the individual power units are authorized to provide corresponding frequency regulation services within the frequency contingency dead band, the individual power units are configured to provide different power offsets based on the frequency level of the power network.

[0034] Advantageously, the method and system of the present invention are configured to receive a measured frequency level of a power network, which indicates a frequency deviation within a frequency contingency deadband, identify to which sub-band the frequency level has deviated, and thereby identify one or more power units authorized to provide frequency regulation services within that frequency sub-band. Based on that identification, the method and system further determine the corresponding power offsets that can be delivered from each authorized power unit to counteract the frequency deviation. In particular, the deliverable power offset from each power unit is an offset from the corresponding baseline power level of that power unit, which may correspond to a prescribed frequency-related offset for the frequency regulation service or the maximum possible offset that the power unit can provide given its primary operating conditions.

[0035] To counteract the frequency deviation, the system receives or otherwise determines a power plant power offset request that specifies the total power offset from the power plant baseline power level for counteracting the frequency deviation. Accordingly, the method and system of the present invention determine a setpoint and dispatch it to the authorized power units to cumulatively satisfy the power plant power offset request. In this regard, the setpoint is determined and dispatched to ensure: (i) the selection of authorized power units delivers the corresponding power offsets, and (ii) the remaining authorized power units reduce or resolve any unresolved shortfall between the power plant power delivery offset request and the cumulative power offsets provided by the selected power units.

[0036] Thus, the authorized power units can be operated to provide the agreed frequency regulation service, and the frequency deviation can be counteracted by the cumulative power offsets. In this way, it is expected that the method and system of the present invention will provide enhanced grid stability and improved operational flexibility, thereby allowing for a wider adoption of frequency regulation services within the frequency contingency deadband.

[0037] Figure 1 An example architecture is illustrated where a renewable energy power plant (PP) is connected to the main grid or power network. The PP includes a plurality of power units for providing frequency regulation services to the connected power network when the frequency level of the power network remains within the normal operating range near the nominal frequency. Each power unit is capable of providing upregulation and / or downregulation to counteract the frequency deviation and acts as a power generator or supplier, a power consumer or receiver, or a power storage. The PP may include a single type of power unit, or the PP may take the form of a hybrid power plant (HPP), as in this example, which includes at least two different types of power units, in particular electrolyzers of an electrolysis system, wind turbine generators (WTGs) of a wind power generation system, and battery units of an energy storage system.

[0038] The examples shown in the figures are merely representative, and the skilled reader will understand that other specific architectures of renewable energy power plants are possible. For example, it is possible that the PP can be characterized by any one type of power unit, or that the renewable energy power plant can be configured as a hybrid power plant having two or more types of power units, the two or more types of power units being incorporated as respective power generation, power consumption, or power storage systems.

[0039] In addition, the skilled reader will understand that each such system of the PP can be formed by a single power unit. Thus, since each power system can include a single power unit and a hybrid power plant requires two or more power systems, a hybrid power plant can be defined as a power plant incorporating at least two power units that generate power from different renewable energy sources, consume power for different applications, and / or store power in different forms. In addition, while electrolysis systems, wind power systems, and battery energy storage systems are discussed herein, it should also be understood that other forms of power units can also be appropriately included in a renewable energy power plant. For example, it is contemplated that the power generation system can include a wind power system and / or a photovoltaic system; the power consumption system can include an electrolysis system, a chemical plant, and / or a thermal energy system; and the energy storage system can include a battery energy storage system and other forms of energy storage.

[0040] The skilled reader will understand that the methods, systems, and techniques also described below can be applied to many different configurations of power networks. In addition, the components of renewable energy power plants and power networks are conventional and are thus familiar to the skilled reader. It is contemplated that other known components can be incorporated in addition to or in place of the components shown and described in Figure 1 Such changes will be within the capabilities of a person skilled in the art.

[0041] Consider in more detail Figure 1, the power system 10 incorporates (includes) the PP 12. The PP 12 includes a wind power generation system 16, a battery energy storage system 18, an electrolysis system 20, and a power plant controller 34 (hereinafter referred to as PPC 34). The wind power generation system 16 includes a plurality of wind turbine generators (WTG) 22 configured to convert wind energy into electrical energy. The battery energy storage system 18 includes one or more battery units 24 that provide centralized or semi-centralized energy storage for the PP 12, particularly rechargeable batteries. For example, the battery energy storage system 18 may include a plurality of electrochemical batteries, such as lithium-ion batteries and / or solid-state batteries, which are operable to store and release electrical energy as needed. The electrolysis system 20 includes one or more electrolyzers 25 configured to generate hydrogen using electrical energy. For example, the electrolysis system 20 may form part of a broader hydrogen generation system for producing hydrogen. In each of these systems 16, 18, 20, it is also possible to have a single WTG 22, battery unit 24, and / or electrolyzer 25.

[0042] The PP 12 is connected to the main power grid 26 (also referred to as the main electrical network) via a connection network 28. The PP 12 and the main power grid 26 are connected at an interconnection point (PoI) 30, which is the interface between the PP 12 and the main power grid 26. It should be assumed that, unless otherwise stated, references to connected components or connections between components include appropriate feeder lines or transmission lines.

[0043] Electrical energy supplied from the wind power generation system 16 and / or the energy storage system 18 can be transferred to the electrolysis system 20 for hydrogen production and / or transferred as active current via the connection network 28 to the main transmission network or the main power grid 26 for distribution. Electrical energy can also be transferred from the wind power generation system 16 and / or the main power grid 26 to the electrolysis system 20 and / or the energy storage system 18 for storage. In this way, each system 16, 18, 20 is operable to provide upregulation and downregulation in response to frequency deviations, particularly by offsetting the active power level (either positively or negatively) from the baseline power level at the nominal frequency.

[0044] Figure 1Each of the WTGs 22, battery units 24, and / or electrolyzers 25 within the systems 16, 18, 20 is associated with a respective controller generally labeled 32. In some embodiments, a subset of the WTGs 22, battery units 24, and / or electrolyzers 25 may share a single semi - centralized controller such that the number of controllers is less than the number of power units (where a power unit in this context is a reference to a single WTG 22, battery unit 24, or electrolyzer 25). As will be apparent to those skilled in the art, the controller 32 can be considered a computer system capable of operating the WTG 22, battery unit 24, and / or electrolyzer 25 in the manner prescribed herein and may include multiple modules that control the respective components of each power unit 22, 24, 25.

[0045] During normal operation of the PP 12, the controller 32 operates the WTG 22 and / or the battery unit 24 to achieve the active and reactive current and / or power set - points received from the PPC 34. In this way, the WTG 22 and / or the battery unit 24 provide frequency and voltage support to the main power grid 26. The controller 32 may also operate the electrolyzer 25 to achieve the active current and / or power set - points received from the power plant controller PPC 34 to draw power from the WTG 22 and / or the battery unit 24 to produce hydrogen.

[0046] To this end, the PPC 34 is connected to the power network 10 at a measurement point (PoM) 36 and is also connected to each of the systems 16, 18, 20 of the PP 12, for example via the controller 32. For example, the PPC 34 may be configured to receive from the PoM 36 one or more measurement signals including measurements of the power supply from the PP 12 to the main power grid 26 and / or the frequency level of the main power grid 26, and determine the corresponding set - points and dispatch them to the controller 32. The PPC 34 may also receive information about the power grid 26 and / or the connection network 28 from an energy management system (not shown) or by direct measurement.

[0047] In this regard, the role of the PPC 34 is to act as a command and control interface between the PP 12 and the power grid 26, and more specifically, as a command and control interface between the systems 16, 18, 20 and the grid operator or transmission system operator (TSO) 38.

[0048] Those skilled in the art should understand that the PPC 34 is thus a suitable computer system for performing the control and commands as described herein and may thus include a processor 40, a connection module 42, a storage module 44, and a sensing module 46.

[0049] During normal operation, the frequency level of the connected main power grid 26 may deviate from the nominal operating frequency of the power grid 26 within the normal operating range or the frequency emergency dead band. The frequency emergency dead band is typically a small area around the operating frequency. For example, the nominal operating frequency is typically 50 Hz, or in some examples 60 Hz, as measured at the PoI 30 or PoM 36, and the upper and lower frequency limits of the frequency emergency dead band can be + / - 0.5 Hz.

[0050] For example, the deviation typically occurs due to an imbalance between power generation and power consumption in the power grid 26 or in response to a power grid fault, and the PP 12 can provide primary frequency regulation services, including frequency containment reserve (FCR) services, to counteract the deviation from the nominal operating frequency within the frequency emergency dead band.

[0051] Typically, operable power plants can provide such frequency regulation services within a limited service period. For example, a power plant operator can offer capacity and meet reserve requirements for an annual, daily, and / or hourly market. Thus, a power plant operator can agree to provide such frequency regulation services within a 24-hour period (although this example is not intended to limit the scope of the present invention).

[0052] Thus, even if the network frequency remains within the frequency emergency dead band, a power plant operator can support the network by ramping up or down based on the deviation of the current frequency from the nominal operating frequency of the network.

[0053] In the method and system of the present invention, the individual power units 22, 24, 25 can be operated to provide corresponding frequency regulation services within the frequency emergency dead band. For example, the individual power units 22, 24, 25 can offer capacity within their respective service periods and agree to perform the corresponding frequency regulation services.

[0054] In particular, the individual power units 22, 24, 25 can be authorized to provide corresponding frequency regulation services that define how the power level of the power unit should be adjusted or offset from the corresponding baseline power level to counteract frequency deviations within one or more sub-bands of the frequency emergency dead band.

[0055] Thus, the PPC 34 is configured to manage the power units 22, 24, 25 according to the agreed frequency regulation services and determine and dispatch corresponding set points to cumulatively counteract the frequency deviations.

[0056] For this purpose, Figure 2 a frequency regulation control scheme, algorithm, or "controller" 100 is illustrated, which forms part of the processing module 40 of the PPC 34 for determining set points and dispatching them to the power units 22, 24, 25 during a frequency regulation service period.

[0057] The controller 100 is configured to receive a measured frequency level of the connected main power grid 26, which indicates a frequency deviation within a frequency contingency deadband of the power grid 26, and identify to which sub-band the frequency level has deviated.

[0058] Once the controller 100 has identified the sub-band into which the frequency deviation has fallen, the controller 100 further identifies one or more power units 22, 24, 25 that have been authorized to provide corresponding frequency regulation services in that sub-band. For example, the controller 100 may receive a list of participants or instructions for each service period from a power plant operator, where the instructions indicate the agreed frequency regulation services for each of the power units 22, 24, 25. Thus, the controller 100 can compare the corresponding sub-bands of those frequency regulation services with the frequency deviation in order to identify the power units 22, 24, 25 authorized to counteract the frequency deviation.

[0059] Thus, the authorized power units 22, 24, 25 are controllable to counteract the frequency deviation by increasing or decreasing the power level of each power unit 22, 24, 25 from a corresponding baseline power level at a nominal operating frequency. For example, in response to a frequency deviation above the nominal operating frequency, the power level of each authorized power unit 22, 24, 25 can be reduced, for example, by curtailing the power supply of the WTG 22, increasing the power consumption of the electrolyzer 25, and / or reducing the power supply to / increasing the power supply from the battery unit 24. Conversely, in response to a frequency deviation below the nominal operating frequency, the power level of each authorized power unit 22, 24, 25 can be increased, for example, by using the spinning reserve of the WTG 22, reducing the power consumption of the electrolyzer 25, and / or increasing the power supply to / reducing the power supply from the battery unit 24.

[0060] Each frequency regulation service is associated with a specified power offset for a corresponding frequency level within a corresponding one or more sub-bands. Thus, the controller 100 may include one or more look-up tables 102, as Figure 2 shown, for determining the specified power offset for each authorized power unit for a corresponding frequency level measurement result, and / or for a predetermined ramp rate for increasing or decreasing the power level.

[0061] In particular, the look-up table 102 may include a plurality of power-frequency (P-f) curves associated with corresponding frequency regulation services within the frequency contingency deadband. For example, the look-up table 102 may include corresponding P-f curves for the following frequency regulation services:

[0062] (i) Frequency Containment Reserve for Normal Operation (FCR-N) in response to a frequency deviation below the nominal frequency level;

[0063] (ii) FCR-N in response to a frequency deviation above the nominal frequency level;

[0064] (iii) Frequency Containment Reserve for Disturbance (FCR-D) in response to a frequency deviation below the nominal frequency level;

[0065] (iv) FCR-D in response to a frequency deviation above the nominal frequency level; and / or

[0066] (v) Any combination of these services.

[0067] Each P-f curve can define a power offset from a baseline frequency curve for the measured frequency level, such that the frequency level measurement result (f) can be matched with the corresponding active power target value P(f) or active power offset.

[0068] By way of illustration, a P-f curve of a type familiar to those skilled in the art is shown in Figure 3 .

[0069] The first P-f curve 110 shows the baseline frequency curve of a power plant for the nominal frequency level. The second P-f curve 112 shows an example P-f curve generated by the FCR-D service in response to a frequency deviation below the nominal frequency level. The third P-f curve 114 shows an example P-f curve generated by the FCR-D service in response to a frequency deviation above the nominal frequency level. The fourth P-f curve 116 shows an example P-f curve generated by a combination of the FCR-N service and the FCR-D service in response to a frequency deviation below the nominal frequency level. The fifth P-f curve 118 shows an example P-f curve generated by a combination of the FCR-N service and the FCR-D service in response to a frequency deviation above the nominal frequency level.

[0070] Considering in more detail, the first P-f curve 110 (representing the baseline frequency curve) shows a frequency dead band DB, which defines a frequency range in which the active power target value P(f) is substantially constant. The example P-f curve also shows a prescribed increase in the active power target value P(f) when the frequency level drops below the frequency dead band DB, and a prescribed decrease in the active power target value P(f) when the frequency level rises above the frequency dead band DB.

[0071] In this example, the second, third, fourth, and fifth P-f curves 112, 114, 116, 118 each show a frequency dead band DB that is divided into first, second, third, and fourth sub-bands 120a-d. The second and third P-f curves 112, 114 are substantially constant over the first and second sub-bands 120a-b and correspond to the baseline P-f curve in such regions. However, an offset curve is applied to the baseline frequency curve in the third sub-band 120c of the second P-f curve 112 (corresponding to the FCR-D service for frequency deviations below the nominal frequency level). Thus, when the frequency level decreases to the third frequency sub-band 120c (during a frequency deviation below the nominal frequency level), there is a prescribed decrease in the active power target value P(f). Similarly, an offset curve is applied to the baseline frequency curve in the fourth sub-band 120d of the third P-f curve 116 (corresponding to the FCR-D service for frequency deviations above the nominal frequency level). Thus, when the frequency level increases to the fourth frequency sub-band 120d (during a frequency deviation above the nominal frequency level), there is a prescribed decrease in the active power target value P(f).

[0072] In the fourth P-f curve 116 (corresponding to a combination of FCR-N and FCR-D services for frequency deviations below the nominal frequency level), an offset curve is applied to the baseline frequency curve in the first sub-band 120a. Thus, when the frequency level decreases from the nominal operating frequency to the first frequency sub-band 120a (during a frequency deviation below the nominal frequency level), there is a prescribed decrease in the active power target value P(f). Additionally, in the third frequency sub-band 120c, the offset curve associated with the FCR-D service (for responding to frequency deviations below the nominal frequency level) is further applied to the active target power value P(f), thereby combining the FCR-N and FCR-D frequency responses. Thus, when the frequency level decreases from the first frequency sub-band 120a to the third frequency sub-band 120c, there is a further prescribed increase in the active target power value P(f).

[0073] Similarly, in the fifth P-f curve 118 (corresponding to the combination of FCR-N and FCR-D services for frequency deviations above the nominal frequency level), the offset curve is applied to the baseline frequency curve in the second sub-band 120b. Thus, when the frequency level increases from the nominal operating frequency into the second frequency dead band 120b (DB) (during frequency deviations above the nominal frequency level), there is a prescribed decrease in the active power target value P(f). Further, in the fourth frequency sub-band 120d, the offset curve associated with the FCR-D service (for responding to frequency deviations above the nominal frequency level) is further applied to the active target power value P(f), thereby combining the FCR-N and FCR-D frequency responses. Thus, when the frequency level increases from the second frequency sub-band 120b to the fourth frequency sub-band 120d, there is a further prescribed decrease in the active target power value P(f).

[0074] Accordingly, the controller 100 can receive the measured frequency level, identify in which of the first through fourth sub-bands 120a-d the frequency deviation lies, and thereby identify the corresponding power units 22, 24, 25 among the power units authorized to provide frequency regulation services in response. For example, the controller 100 can determine that the frequency deviation lies within the first frequency sub-band 120a, and thus identify any of the power units 22, 24, 25 authorized to provide the FCR-N service in response to the frequency deviation in the first sub-band 120a. Thus, for each authorized power unit 22, 24, 25, the controller 100 can determine the prescribed power offset from the Figure 3 fourth P-f curve 118 shown as described above.

[0075] If the measured frequency level subsequently further decreases into the third sub-band 120c, the controller 100 will re-determine the authorized power units 22, 24, 25 in response to the frequency deviation below the nominal frequency level and identify those power units 22, 24, 25 authorized to provide the FCR-N service or a combination of the FCR-N service and the FCR-D service. Accordingly, the controller 100 can determine the prescribed power offset for each authorized power unit 22, 24, 25 from one of the first P-f curve 112 and the third P-f curve 116, respectively.

[0076] Accordingly, the controller 100 can use one or more of the P-f curves to determine the prescribed power offset for each power unit 22, 24, 25.

[0077] In some examples, in addition to authorizing each of the power units 22, 24, 25 to provide corresponding frequency regulation services, the power plant operator may also negotiate to provide a maximum power contribution to such services. In an example, the specified power offset can thus be determined using a P-f curve that is limited to any particular maximum power contribution to the frequency regulation services of the power units 22, 24, 25. For example, the power plant operator may negotiate to provide a maximum power contribution of up to 2 MW to a particular frequency regulation service, and thus may determine the specified power offset with reference to one or more P-f curves for a maximum power contribution of up to 2 MW.

[0078] In addition, although the frequency regulation service may specify corresponding power offsets for the power units 22, 24, 25, the operating conditions may limit the extent of power adjustment from the baseline power level that can be provided by each of the power units 22, 24, 25.

[0079] In other words, given the operating conditions, each of the power units 22, 24, 25 is only capable of providing a corresponding maximum possible power offset from the baseline power level at the nominal operating frequency. The maximum possible power offset for each of the power units 22, 24, 25 corresponds to the difference between the baseline power level and the upper / lower limits of the available power. For example, given the current wind speed, the WTG 22 can only increase the power level from the baseline level to the available power level. Similarly, the battery unit 24 has limited energy storage and thus can apply upper / lower limits to the transfer of available power.

[0080] Taking this into account, the controller 100 is configured to determine the deliverable power offset for each of the power units 22, 24, 25 from its respective baseline power level, where the deliverable power offset corresponds to the lesser of (i) the specified frequency-related offset of the frequency regulation service and (ii) the maximum possible offset that the power unit can provide given the operating conditions.

[0081] Thus, the PPC 34 can determine the set points for each of the authorized power units 22, 24, 25 based on the deliverable power offset, which can be dispatched to the respective power unit controllers 32 to counteract the frequency deviation, as will be discussed in more detail below.

[0082] Reference will now be made additionally to Figure 4 and Figure 5 to describe the operation of the PP 12 in providing frequency regulation within the frequency contingency deadband.

[0083] For example, a power plant operator may have agreed to meet the reserve requirements of the main power grid 26 during a specific service period, such as a 24-hour period. For this service period, the power plant operator may have authorized one or more of the power units 22, 24, 25 to provide corresponding frequency regulation services within the frequency contingency deadband. Additionally, in some cases, the power plant operator may have agreed on the maximum power contribution of such power units 22, 24, 25 to the corresponding frequency regulation services. For example, the power plant operator may have agreed to provide a maximum power contribution of 2 MW from one of the WTGs 22 for FCR-N services in response to a corresponding frequency deviation below the nominal frequency level. Such agreements and authorizations can be updated or changed for each service period, thereby generating a set of instructions for the PPC 34.

[0084] Accordingly, during the service period, the PPC 34 controls the power units 22, 24, 25 at a baseline power level to meet the plant power reference during normal operation. However, if the frequency level deviates from the nominal operating frequency within the frequency contingency deadband, the PPC 34 is configured to determine and dispatch setpoints to adjust the power levels of the power units 22, 24, 25 and provide frequency regulation services.

[0085] Figure 4 An example method 200 for controlling the PP 12 to provide such frequency regulation services during the service period is shown.

[0086] In step 202, the PPC 34 receives a measurement of the frequency level of the main power grid 26. In this case, the measured frequency level indicates a deviation from the nominal operating frequency (e.g., 50 Hz) of the main power grid 26 within the frequency contingency deadband.

[0087] In step 204, the PPC 34 identifies which of the plurality of subbands 116a-d the deviation falls into. In particular, continuing with the above example (which is not intended to limit the scope of the present invention), the PPC 34 can identify whether the frequency level of the main power grid 26 has deviated into one of the first through fourth subbands 120a-d of the frequency contingency deadband, as Figure 3 shown. As an example, the PPC 34 can identify that a frequency deviation below the nominal frequency level has occurred, specifically, that the frequency level has fallen into the first frequency subband 120a.

[0088] In step 206, the PPC 34 determines which of the power units 22, 24, 25 are authorized to provide frequency regulation services in the identified subband (in this example, 120a). To this end, the PPC 34 can, for example, call a participant list or instructions received from the power plant operator, thereby indicating the agreed frequency regulation services for each of the power units 22, 24, 25 during the service period.

[0089] As an example, the PPC 34 can thus identify any power units 22, 24, 25 that have been authorized to provide FCR-D services in response to a frequency deviation within the first frequency sub-band 120a. This can include, for example, one or more WTGs 22, battery units 24, or electrolyzers 25 that have agreed (contracted) to increase power supply and / or reduce power consumption to raise the frequency of the main power grid 26 when the frequency of the main power grid 26 falls within the first sub-band 120a.

[0090] In step 208, the PPC 34 determines the power offsets that can be delivered from each authorized power unit 22, 24, 25 to counteract the frequency deviation.

[0091] As previously described, the deliverable power offset is the offset that each authorized power unit 22, 24, 25 is capable of providing from its baseline power level and can thus correspond to: (i) the specified offset for the frequency regulation service for the measured frequency level, (ii) the agreed maximum contribution of the power units 22, 24, 25 to that service, or (iii) the maximum possible offset where the power units 22, 24, 25 cannot provide the specified offset or maximum contribution.

[0092] Specifically, the PPC 34 can thus determine the deliverable power offset of each authorized power unit 22, 24, 25 as the minimum of the following:

[0093] (i) the specified power offset of the power unit 22, 24, 25 for the frequency regulation service, including any agreed maximum power contribution of the power unit 22, 24, 25 to that frequency regulation service; and

[0094] (ii) the possible power offset of the power unit 22, 24, 25 considering the corresponding upper / lower limits of the baseline power level and available power.

[0095] For example, the PPC 34 can be configured to use one or more look-up tables 102 to determine the specified power offset. For example, the PPC 34 can use one or more P-f curves (such as Figure 3 the exemplary second, third, fourth, and fifth P-f curves 112, 114, 116, 118 shown in

[0096] Continuing with the previous example, the PPC 34 can thus use the third P-f curve 116 (corresponding to the FCR-D service for frequency deviations below the nominal frequency level) to determine the specified power offset for each authorized power unit 22, 24, 25 within the first frequency sub-band 120a. Thus, as the measured frequency level decreases from the upper limit to the lower limit of the first frequency sub-band 120a, the PPC 34 can determine the corresponding set points for ramping down the power levels of each authorized power unit 22, 24, 25 from the baseline power level to the first offset 122 from the baseline power level. However, if a maximum power contribution has been agreed upon for one or more of the authorized power units 22, 24, 25, the specified power offset can be capped or limited to a second offset from the baseline power level before reaching the first offset 122.

[0097] In the example, the PPC 34 can receive or otherwise determine the possible power offsets for each authorized power unit 22, 24, 25 according to various methods known in the art. For example, with respect to the WTG 22, the PPC 34 can receive the available power level or the maximum reduction amount of each WTG 22, and thus determine the corresponding possible power offset (to counteract the frequency deviation) by comparing it with the baseline power level of the WTG 22. Those skilled in the art should understand that similar principles apply to each power unit 22, 24, 25, and thus specific methods for determining the possible power offsets are not described in detail here to avoid obscuring the present invention.

[0098] Thus, in step 108, the PPC 34 determines the deliverable power offset for each authorized power unit 22, 24, 25 as the minimum of: (i) the specified power offset for the frequency regulation service and (ii) the possible power offset that the power units 22, 24, 25 can provide.

[0099] In step 210, the PPC 34 can receive or otherwise determine a plant power offset request that specifies the total power offset from the baseline power level of the PP 12 for counteracting the frequency deviation. The plant power offset request can be determined by one or more methods known to those skilled in the art, and will not be described in detail here to avoid obscuring the present invention. It should be understood that the PPC 34 can, for example, use the look-up table 102 or one or more of the P-f curves for the frequency regulation service defined therein, and thus determine the corresponding plant power offset for counteracting the frequency deviation based on the measured frequency level.

[0100] In step 212, in response to the plant power offset request, the PPC 34 determines the set points and assigns them to the authorized power units 22, 24, 25 to cumulatively satisfy the plant power offset request.

[0101] In this regard, set points are determined for each of the authorized power units 22, 24, 25 according to a specified power offset based on the measurement frequency level, so as to comply with any agreed maximum power contribution and / or limits on possible power offsets.

[0102] However, in some cases, the PPC 34 may determine that the cumulative or total power offset resulting from operating all the authorized power units 22, 24, 25 in this way will exceed the plant power offset request. As a result, the PP 12 will overcompensate for the frequency deviation, which may lead to a frequency deviation above the nominal frequency level.

[0103] Therefore, in step 212, the PPC 34 selects all or some of the authorized power units 22, 24, 25 to generate the deliverable power offset determined in step 208, and determines the set points of the remaining authorized power units 22, 24, 25 to cumulatively address (as much as possible) any unresolved shortfall between the plant power offset request and the cumulative power offset provided by the selected power units 22, 24, 25.

[0104] Depending on the corresponding objectives of the power plant operator, the selection of the power units 22, 24, 25 can be performed according to one or more suitable methods. For example, the objectives can be provided or defined by instructions sent to the PPC 34.

[0105] In an example, the selection can be performed by prioritizing those power units 22, 24, 25 that are capable of delivering the maximum power offset. Specifically, the PPC 34 can rank the authorized power units 22, 24, 25 in a priority list based on the deliverable power offset determined in step 208, and select the top 1 to M power units, where M is determined to be the largest positive integer such that the cumulative / total power offset of the selected power units 22, 24, 25 is less than or equal to the plant power offset request. In other words, the PPC 34 can be configured to select as many of the top-ranked power units 22, 24, 25 as possible to provide the corresponding deliverable power offset when the cumulative power offset does not exceed the plant offset power request, and determine the corresponding set points of the remaining authorized power units 22, 24, 25 to meet any unresolved power shortfall.

[0106] For this purpose, the controller 100 of the PPC 34 can be arranged, for example, as Figure 5 shown, as will be discussed in more detail below.

[0107] Figure 5 A functional block diagram is shown, which illustrates an additional non-limiting example of how a power plant control method can be implemented.

[0108] Figure 5An arrangement is shown in which the PPC 34 provides frequency control by means of a respective frequency support module 402, ranking module 403 and master dispatcher 404 for each power unit 22, 24, 25. As will be appreciated by the skilled person, each of the frequency support module 402, ranking module 403 and master dispatcher 404 may be implemented in software, firmware, hardware or any suitable combination thereof. Similarly, the described functionality may be distributed across any software, firmware and / or hardware modules, which may be distributed throughout the power generation network in any suitable manner.

[0109] like Figure 5 As shown, each of the frequency support modules 402 can receive the measured frequency f and the baseline power command P of the corresponding power unit 22, 24, 25. com Each frequency support module 402 may also receive one or more frequency regulation service authorizations FCR for that power unit 22, 24, 25, and any agreed maximum power contribution P thereto. cont and any available power limit P of the power units 22, 24, 25 cap .

[0110] According to steps 204 to 208, each frequency module 402 may thus determine whether the corresponding power unit 22, 24, 25 is authorized to provide frequency regulation services in the frequency sub-band of the measured frequency f. If the power unit 22, 24, 25 is not authorized to provide frequency regulation services in the identified sub-band, the corresponding frequency module 402 may determine a deliverable power offset ΔP of, for example, zero. del However, if the power unit 22, 24, 25 is authorized to provide frequency regulation services in the identified sub-band, the corresponding frequency module 402 may determine the power offset ΔP that may be delivered from the power unit 22, 24, 25 to offset the frequency deviation. del Specifically, the corresponding frequency module 402 can adjust the service FCR based on the authorized frequency, the measured frequency f and the agreed maximum power contribution P cont To determine the specified power offset ΔP serv , basically as described above. In addition, the frequency module 402 can also be based on the baseline power command P of the corresponding power unit 22, 24, 25 com and any available power limit P of the power unit 22, 24, 25 cap To determine the possible power offset ΔP of the respective power unit 22, 24, 25 poss Based on these determinations, frequency module 402 may therefore shift the deliverable power by ΔP del Determined as the specified power offset ΔP serv and possible power offset ΔP poss The minimum value in .

[0111] In step 212, the deliverable power offset ΔP determined for each of the power units 22, 24, 25 del is delivered to the ranking module 403, which continues to determine a priority list based on the deliverable power offset ΔP del to rank the power units 22, 24, 25. Thus, the ranking module 403 can output the corresponding "RANK" associated with each of the power units 22, 24, 25 to the main dispatcher 404.

[0112] The main dispatcher 404 also receives the baseline power command P for each of the power units 22, 24, 25 com and the deliverable power offset ΔP del , as well as the plant offset request ΔP for offsetting the frequency deviation ref .

[0113] Thus, in step 212, the main dispatcher 404 uses the received information to determine the corresponding setpoints for each of the power units 22, 24, 25. For example, the main dispatcher 404 can use the rank (RANK) of each of the power units 22, 24, 25 and the deliverable power offset ΔP del to select the top 1 to M ranked power units 22, 24, 25 to provide the deliverable power offset ΔP del , where the main dispatcher 404 determines the integer M as the maximum number of power units 22, 24, 25 that can be operated in this way without exceeding the plant offset power request ΔP ref . Thus, the setpoints for each of the top 1 to M ranked power units 22, 24, 25 can be determined based on the corresponding baseline power command P com and the corresponding deliverable power offset ΔP del . The main dispatcher 404 can further determine that the setpoint for each of the power units 22, 24, 25 having a zero deliverable power offset ΔP del is equal to the baseline power command P com . Finally, the main dispatcher 404 can determine the setpoints for the remaining power units 22, 24, 25 according to one or more strategies to satisfy the power shortage, if any, between the cumulative power offset of the top 1 to M ranked power units 22, 24, 25 and the plant offset power request ΔP ref . For example, such a strategy can determine setpoints that provide power offset from as many of the remaining power units 22, 24, 25 as possible, or maximize the power offset from the top ranked power units among those power units 22, 24, 25.

[0114] In this manner, power units 22, 24, 25 are operated to counteract the frequency deviation and support the main power grid to return to the nominal operating frequency. Thus, it is expected that the method and system of the present invention will provide enhanced grid stability and improved operational flexibility, thereby allowing for a wider adoption of frequency regulation services within the frequency contingency deadband.

[0115] It will be understood that various changes and modifications can be made to the above examples without departing from the scope of the present invention.

[0116] For example, the above frequency support method can be implemented within any suitable control function or module associated with one or more power units or power plants. As described above, the frequency support method as well as the PPC 34 can be executed locally by the respective controllers 32 of the power units 22, 24, 25. It can also be implemented in software, firmware, and / or hardware remote from the PPC, and the required set points are provided to the PPC for forwarding to its associated power plant.

[0117] Wherever the method is implemented, a look-up table or curve of P-f offset values can be accessed to determine the set points for controlling the power characteristics of the power plant. The look-up table or curve can be accessed via a communication network (such as a wired or wireless IP-based network). Alternatively, the table or curve of P-f offset values can be stored locally. Additionally, although the P-f curve has been described above for the respective frequency regulation services or combinations thereof, it should be understood that the respective frequency regulation services can alternatively define corresponding offset curves from the baseline frequency curve for any defined sub-band.

[0118] Those skilled in the art will understand that the references to time periods such as hours or days in the foregoing paragraphs are merely examples, and any other suitable one or more time periods can be used depending on the implementation.

Claims

1. A method for controlling a renewable energy power plant to provide frequency regulation to an electrical power network to which the power plant is connected, the power plant including a plurality of power units operable to provide upward and / or downward regulation of the electrical power network, and the method including: Receiving a measured frequency level of the electrical power network, the measured frequency level indicating a frequency deviation within a frequency contingency deadband of the electrical power network; Based on the measured frequency level, identifying a subband of the frequency deviation from among a plurality of subbands within the frequency contingency deadband; Identifying one or more power units authorized to provide at least one frequency regulation service within the identified subband; Determining a deliverable power offset of each authorized power unit from a baseline power level, the deliverable power offset being based in part on at least one authorized frequency regulation service; And Determining a power setpoint and dispatching the power setpoint to one or more authorized power units to meet a plant power offset request for the measured frequency level, the setpoint being determined by: Selecting one or more of the authorized power units to provide the deliverable power offset determined for that power unit, wherein the cumulative power offset of the one or more selected power units is less than or equal to the plant power offset request; And If there is a power shortage between the plant power offset request and the cumulative power offset, determining setpoints for remaining authorized power units to meet the power shortage.

2. The method according to claim 1, wherein, The deliverable power offset is determined as the minimum of: A specified power offset of the power unit, the specified power offset being based on the at least one authorized frequency regulation service and the measured frequency level; And A possible power offset of the power unit, the possible power offset being the difference between the baseline power level of the power unit and an upper and / or lower limit of the available power of the power unit.

3. The method according to claim 2, wherein, Each power unit is authorized for one or more of a plurality of frequency regulation services, each frequency regulation service being associated with a specified power offset for a corresponding frequency level within one or more of the plurality of subbands.

4. The method according to claim 3, wherein, The plurality of frequency regulation services includes one or more of the following: (i) Frequency Containment Reserve for Normal Operation (FCR-N) in response to a frequency deviation below the nominal frequency level of the electrical power network; (ii) FCR-N in response to a frequency deviation above the nominal frequency level; (iii) Frequency Containment Reserve for Disturbance (FCR-D) in response to a frequency deviation below the nominal frequency level; (iv) FCR-D in response to a frequency deviation above the nominal frequency level; and / or (v) A combination of two or more selected from (i) to (iv).

5. The method according to claim 3 or claim 4, wherein, Each frequency regulation service is associated with a corresponding power-frequency (P-f) curve; and wherein the method further includes determining the specified power offset of each authorized power unit based on the P-f curve associated with the at least one authorized frequency regulation service.

6. The method according to claims 4 and 5, wherein Each of the FCR-N frequency regulation service and the FCR-D frequency regulation service is associated with a respective P-f offset curve from a baseline power level in a respective sub-band relative to the frequency emergency deadband.

7. The method according to claim 6, wherein, A combination of the FCR-N frequency regulation service and / or the FCR-D frequency regulation service is associated with a respective P-f curve determined by summing the respective P-f offset curves of the combined FCR-N frequency regulation service and / or FCR-D frequency regulation service.

8. The method according to any one of claims 3 to 7, wherein, Each power unit is authorized for the one or more frequency regulation services during a respective service period.

9. The method according to any one of claims 2 to 8, further comprising determining the specified power offset of each authorized power unit based on a respective agreed maximum contribution to the at least one authorized frequency regulation service.

10. The method according to claim 9, wherein, The maximum contribution to the at least one authorized frequency regulation service is agreed for a specified service period.

11. The method according to any one of claims 2 to 10, further comprising determining a possible power offset of the power unit based on a baseline power level of the power unit and an upper and / or lower limit of available power of the power unit.

12. The method according to any one of the preceding claims, wherein, The one or more authorized power units are selected by: ranking the one or more authorized power units in a priority list based on the deliverable power offset determined for each authorized power unit; and selecting the 1 to M highest-ranked power units, where M is a positive integer.

13. The method according to claim 12, wherein, M is the largest positive integer for ensuring that the cumulative power offset of the one or more selected power units is less than or equal to the plant power offset request.

14. The method according to any one of the preceding claims, wherein, The plurality of power units includes: one or more renewable energy generators, such as wind turbine generators; one or more energy storage devices, such as battery units; and / or one or more energy consumers, such as electrolyzers and / or chemical plants.

15. A power plant controller configured to perform the method according to any one of the preceding claims.

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