Advanced function of an intermediate monitoring-control layer for a virtual power plant

Abstract

The invention proposes a method for controlling a virtual power plant and a corresponding computer program and control device. A first frequency regulation setpoint power, corrected by a decrease of a magnitude corresponding to a corrective value, is provided to the local controllers of renewable sources. A second frequency regulation setpoint power, corrected by an increase of a magnitude corresponding to the corrective value, is provided to the local controllers of the system able to be controlled with energy storage. The sum of the corrected frequency regulation setpoint powers is substantially equal to the sum of the expected setpoint powers, not counting contribution to a frequency regulation service. The corrective value is determined on the basis of an adjustment power error.

Description

French Description Description Title: Advanced function of an intermediate control-command layer of a virtual power plant Technical domain

[0001] This disclosure relates to the field of controlling a virtual power plant, or VPP, which combines variable renewable energies, such as wind or photovoltaic, and a controllable system with energy storage.

[0002] More particularly, the present disclosure relates to a method for controlling a virtual power plant, a corresponding computer program and a corresponding control device.

[0003] The massive development and integration of variable renewable energies, or RES, such as wind and photovoltaic energy into the electricity system makes it more complex to adapt electricity production to consumption. Today, renewable energies always inject their maximum power into the grid and contribute very little to "system services," such as frequency regulation and voltage regulation, which are essential to ensure the security and safety of the electricity system. This type of operation will not be able to persist when the penetration rate of variable RES is no longer marginal in the electricity system.

[0004] One possible and promising solution is to pool the operation of several variable resources with a controllable system with integrated energy storage, in the form of an aggregated production plant, in order to make its production more "controllable" and more flexible. This involves continuous management of several distributed resources in an intelligent and coordinated manner, as if these resources were at a single injection point seen by the electrical system, hence the concept of a so-called "virtual" power plant. French Description

[0005] Currently, frequency control services are allocated to renewable energy sources based on estimates of their maximum available active power.

[0006] The maximum available active power, or AAP, of a power plant or farm composed of variable renewable energies is the maximum power that it could have produced without contributing to a frequency control reserve, i.e. without capping its power. This is not "measurable" once the reserve is placed on the renewable energy farm, and can only be "estimated" by a mathematical calculation process based on the measurements and physical parameters of the farm. This estimation is, for example, implemented by an AAP power estimator provided locally at the renewable energy farm. There are necessarily differences between the actual instantaneous values ​​of the maximum available active power and the corresponding estimates.

[0007] In the state of the art, several solutions exist to enable a variable renewable energy plant to contribute to a frequency control service despite these differences between the estimated value and the actual value of the maximum active power available. Two of these solutions are presented here.

[0008] According to a first solution, the renewable energy plant is controlled so that it permanently produces below its maximum power (AAP) with a constant margin in addition to the reserve power upwards if the plant must provide it, in order to partially cover the errors induced by the AAP power estimator. This first solution is presented in [3]. The main disadvantage of this first solution is a significant loss of renewable energy production, therefore an economic loss for the renewable energy producer (unsold energy).

[0009] According to a second solution in the context of a VPP composed of renewable energy and storage, part or all of the reserve placed on renewable energy producers is moved to storage, if a frequency control gap between what is realized and what is expected is detected, because the frequency control service provided by storage is generally more efficient than that provided by variable renewable energy. French Description thanks to its better "controllability". This voluntary "transfer" of reserve capacity makes it possible to make the overall frequency adjustment of the VPP more precise. The biggest drawback of this second solution is that it does not allow compliance with an operating schedule and reserve allocation previously calculated by an upstream optimizer. This second solution therefore presents a high risk of deoptimization from a global point of view, that is to say on a time scale longer than a single optimization step.

[0010] There is therefore a need for more efficient control of a virtual power plant aggregating variable renewable energies and a controllable system with energy storage and contributing to a frequency control service. Abstract

[0011] This disclosure improves the situation.

[0012] A method is proposed for controlling a virtual power plant, connected to the electricity network, aggregating a plurality of installations capable of contributing to a frequency regulation service, the plurality of installations comprising at least one controllable system with energy storage and a set of renewable sources having a maximum available active power varying over time, the method being implemented by a control device connected to an optimizer and to local controllers of the sources and of the controllable system with energy storage, the method comprising: a) obtaining from the optimizer sets of parameters respectively associated with respective time intervals, a set of parameters comprising a first setpoint power provided for the set of sources and a second setpoint power provided for the controllable system with energy storage,during the associated time interval and excluding contribution to the frequency regulation service, the optimizer being further configured to provide upward and / or downward reserve capacity instructions on all the installations for the associated time interval, b) determine, for a sub-interval of a current time interval, an error, Description of control power of the virtual power plant based on a difference between power measurements produced by each installation of the virtual power plant and an expected effective theoretical value based on a real-time estimation of a maximum active power available from all the renewable sources and on a current frequency measurement of the electrical network, c) determining, for the sub-interval, a corrective value based on the control power error, d1) providing the local controllers of the renewable sources, for the sub-interval, with a first frequency regulation setpoint power corrected by a reduction of a magnitude corresponding to the corrective value, and d2) providing the local controllers of the controllable system with energy storage, for the sub-interval,a second frequency regulation setpoint power corrected by an increase of a magnitude corresponding to the corrective value, the sum of the corrected frequency regulation setpoint powers being substantially equal to the sum of the setpoint powers provided excluding contribution to the frequency regulation service.

[0013] The proposed method enables efficient frequency control provision by means of corrected frequency control setpoint powers. It is based on an estimation, possibly in real time, of the maximum active power available from renewable sources combined with a network frequency measurement and power measurements produced by the virtual power plant installations and thus enables effective correction of any control power error.

[0014] It allows to respect a value of sum of the setpoint powers which has been previously planned for example by the optimizer, given that the sum of the corrected setpoint powers is substantially equal to the sum of the planned setpoint powers. Thus, the general optimization of the production French Description over a period of time of the order of, for example, a day is only very little affected.

[0015] Also provided is a computer program comprising instructions for implementing the above method when this program is executed by a processor.

[0016] Also provided is a non-transitory computer-readable recording medium on which is recorded a program for implementing the above method when this program is executed by a processor.

[0017] There is also provided a device for controlling a virtual power plant, connected to the electricity network, aggregating a plurality of installations capable of contributing to a frequency regulation service, the plurality of installations comprising at least one controllable system with energy storage and a set of renewable sources having a maximum available active power varying over time, the control device being connected to an optimizer and to local controllers of the sources and of the controllable system with energy storage, the control device being configured to: a) obtain from the optimizer sets of parameters respectively associated with respective time intervals, a set of parameters comprising a first setpoint power provided for all the sources and a second setpoint power provided for the controllable system with energy storage,during the associated time interval and excluding contribution to the frequency regulation service, the optimizer being further configured to provide upward and / or downward reserve capacity instructions on all the installations for the associated time interval, b) determining, for a sub-interval of a current time interval, a control power error of the virtual power plant on the basis of a difference between power measurements produced by each installation of the virtual power plant and an expected effective theoretical value based on a real-time estimate of a maximum active power available from all the renewable sources and on a current frequency measurement of the electrical network, French Description c) determining, for the sub-interval, a corrective value on the basis of the control power error, d1) providing the local controllers of the renewable sources, for the sub-interval, with a first frequency regulation setpoint power corrected by a reduction of a magnitude corresponding to the corrective value, and d2) providing the local controllers of the controllable system with energy storage, for the sub-interval, with a second frequency regulation setpoint power corrected by an increase of a magnitude corresponding to the corrective value, the sum of the corrected frequency regulation setpoint powers being substantially equal to the sum of the setpoint powers provided excluding contribution to the frequency regulation service.

[0018] In one example, when the estimation error value is greater than a low threshold and less than a high threshold, the corrective value is zero.

[0019] This makes it possible, in particular when the low threshold has a negative value and the high threshold has a positive value, to limit the frequency of corrective actions which are then only carried out when the estimate of the maximum active power available is considered to deviate too much from its actual value.

[0020] In one example, when the estimation error value is below a low threshold, the corrective value is proportional to the estimation error.

[0021] In one example, when the estimation error value is greater than a high threshold, the corrective value is proportional to the estimation error.

[0022] This proportionality is not essential, nor is it necessary that the mathematical expression linking the corrective value to the estimation error be identical whether the estimation error is positive or negative.

[0023] In one example, the corrective value is saturated between limit values ​​indicative of a minimum value between: - a maximum power of the controllable system with energy storage in French Description charge, - a maximum power of the controllable system with energy storage in discharge, - the estimated maximum available active power of renewable sources, - the reserve capacities placed on all the installations, - minimum technical powers of renewable sources.

[0024] In one example, the time intervals have a duration greater than 10 minutes and less than 1 hour.

[0025] In one example, the current subinterval has a duration less than 30 seconds.

[0026] In one example, b), c), d1) and d2) are repeated periodically. Brief description of the drawings

[0027] Other features, details and advantages will become apparent upon reading the detailed description below, and upon analyzing the attached drawings, in which: Fig.1

[0028] [Fig. 1] represents an example of aggregating variable renewable energy sources with a controllable system with storage, thus forming a virtual power plant. Fig.2

[0029] [Fig. 2] illustrates an example of the architecture of a three-layer control system for controlling a virtual power plant. Fig.3

[0030] [Fig.3] illustrates the impact, in an electrical network, of the production-consumption balance on the frequency Fig.4

[0031] [Fig. 4] represents the dynamics of release of the different reserves constituting the frequency adjustment. French Description Fig.5

[0032] [Fig. 5] illustrates the constitution and release of a reserve provided by a virtual power plant comprising a variable renewable energy source and contributing to a frequency control service. Fig.6

[0033] [Fig.6] illustrates the impact of errors in the estimation of available power on the performance of frequency control, through the result of a primary frequency control test in a 12 MW wind farm. Fig.7

[0034] [Fig.7] shows a comparison of the measured and expected responses of the primary frequency control provided by a 12 MW wind farm in a test. Fig.8 Fig.9 Fig.10

[0035] [Fig. 8], [Fig. 9] and [Fig. 10] represent SIMULINK diagrams relating to a general algorithm for controlling a virtual power plant aggregating variable renewable energy sources with a controllable system with storage and contributing to a frequency control service, in exemplary embodiments. Description of the embodiments

[0036] A particular example of a virtual power plant (VPP) is now described with reference to Figure 1. Different installations (102, 104, 106) are aggregated therein, namely in this example photovoltaic (102) and wind (104) energy sources as well as a controllable system with energy storage (106), for example using batteries. These installations make it possible to supply a network Electrical description (108) in energy. The joint management of VPP installations makes it possible to provide additional services.

[0037] An example of a control-command mechanism (200) of a VPP is now described with reference to FIG. 2.

[0038] In general, three functional layers (210, 220, 230) acting at different time scales make it possible to operate a VPP made up of several physical assets (controlled resources):

[0039] A first optimization layer (230), sometimes called "operational planning scheduler" in English, or in the context of this document "optimizer", makes it possible to determine the operating programs of all the controlled resources and allocates the service capacities by taking into account the renewable energy production forecasts, the operational constraints and the available market information (e.g.: forecast of SPOT prices and system service prices). In general, this layer optimizes the operation of the VPP from D-1 to the horizon 15 - 30 minutes before real time, on each step of 30 minutes (or 15 minutes at the most precise).

[0040] A second intermediate control-command layer (220), sometimes called "short-term control" or STC, intervenes between each optimization step (e.g.: 30 min) and real time, and makes it possible to monitor the performance of the VPP and to take necessary actions to manage hazards or unforeseen events within each optimal programming step. This management may in particular relate to the management of the storage charge state, to the compensation of the short-term variability of renewable energy, to a fortuitous malfunction of a component or a communication system intended for the transmission of measured data and / or instructions, to the correction of the performance of a service, etc.

[0041] A third control-command layer (210) acts as close as possible to real time and includes the functions or algorithms corresponding to the services to be provided and adapted to the technologies controlled. This layer is physically implemented at the local level by local controllers (202, 204, 206) of the French Description installations (102, 104, 106). Its role is to execute the programs defined by the upper layer upstream of real time and to provide the various services to the electrical system based on local measurements (voltage, frequency, etc.), while respecting the physical laws specified in the network codes for each service.

[0042] In the absence of the intermediate control-command layer (STC), the local controllers directly take into account the values ​​calculated by the optimizer as execution instructions (e.g.: reference powers of each resource, volume of reserve to be placed, etc.). These values ​​are mathematically constant over each optimization step (i.e. over a period of 15 or 30 minutes). This can work more or less correctly when the VPP is composed only of resources that vary little over time (e.g.: battery, hydroelectric power plant with dam, etc.), but could cause performance problems when the VPP includes variable producers.

[0043] The invention differs from the prior art and aims to improve the performance of a VPP contributing to a frequency control service not by optimizing or re-optimizing the use of the installations within a VPP, but by a control-command function which minimizes the loss of producible without imposing a transfer of reserve from renewable sources to energy storage. Such a control-command function can be integrated for example at the level of the aforementioned intermediate control-command layer. By way of illustration, an example of implementation focused on primary frequency control or "FCR service" is described in this document. In general, there is no requirement to limit the scope of application of the invention to primary frequency control alone.

[0044] In an electrical system and as shown in Figure 3, frequency is the image of the supply-demand balance. When electricity production is higher than consumption at a given time, the network frequency tends to increase (302). Conversely, when electricity production is lower than consumption at a given time, the network frequency tends to decrease (306). In order to ensure the proper functioning of the system Electrical description as well as the safety of equipment and people, the frequency must be set around its nominal value (304), for example 50 Hz in Europe.

[0045] Currently, the services required for frequency regulation or adjustment are mainly carried out by conventional producers, in charge of production such as hydropower, nuclear power, etc. Producers of variable renewable energy are currently exempt from this, but there is no technical obstacle to variable renewable energy sources being controlled in such a way as to contribute to the frequency adjustment service.

[0046] In continental Europe, Transmission System Operators (TSOs) have at their disposal three levels of reserves, i.e. complementary means either of production or, to a lesser extent, of consumption reduction, which are used with different activation times [2]. For example, in France, these three reserve levels, respectively called primary, secondary and tertiary reserves, are illustrated in Figure 4 in a scenario illustrated by a representation (402) relating to the power injected into the electricity network (108) as a function of time and, equivalently, in a representation (404) relating to the frequency of the electricity network (108) as a function of time.

[0047] In this scenario, the occurrence of a network incident at a time T causes, around T+15 seconds, a frequency excursion beyond an acceptable limit. The primary reserve is triggered to stabilize the frequency. Then, around T+30 seconds, the secondary reserve is triggered to bring the frequency closer to its nominal value. Finally, around T+15 minutes, the tertiary reserve is triggered in case the secondary reserve tends to be exhausted without having been able to restore the nominal frequency.

[0048] Producers participating in the frequency adjustment service must be able to modulate their produced power according to the variation in frequency on the network, i.e. increase their production when the Description frequency is below the nominal value and decrease their output when the frequency is beyond the nominal value.

[0049] Unlike conventional generators and storage, which operate under a constant or quasi-constant active power setpoint at each dispatching step, building up the frequency control reserve on wind and PV generators is more complex. Indeed, when no reserve is allocated to them, these generators are operated to produce the maximum available power at any time, depending on wind or sunshine conditions.

[0050] Various notations used in the remainder of this document are now explained. Among these notations, the powers are all considered, unless otherwise indicated, to be electrical powers expressed in MW. The use of the acronym "ESS" in a notation indicates that this notation relates to the controllable system with energy storage. The use of "RES" in a notation indicates that this notation relates to renewable energy sources with time-varying power. Finally, the use of the acronym "VPP" in a notation indicates that this notation relates to all the installations of the virtual power plant.

[0051] denotes the frequency of the electrical network (108). This frequency is measurable in real time and is expressed in Hz.

[0052] and designate reserve capacities, respectively upward and downward, placed on the controllable system with storage (106). and designate reserve capacities, respectively upward and downward, placed on the renewable energy sources (102, 104). These reserve capacities are similar to powers and can be programmed in advance, for example by the optimizer (230).

[0053] The total power of the controllable system with energy storage is noted and is the sum of two quantities which are: - the power of the controllable system with energy storage allocated to another French Description service than that of the frequency adjustment, noted , which can be programmed in advance, for example by the optimizer (230), and - the power of the controllable system with energy storage allocated to the frequency adjustment, noted and which can be given, for example, by the formula: valid for a frequency included in a frequency range extending from 49.8 Hz to 50.2 Hz. Outside this frequency range, the value of is saturated respectively by and .

[0054] Similarly, the total power of the VPP, noted , is the sum of two quantities which are: - the power of the VPP allocated to a service other than that of the frequency adjustment, noted , which can be programmed in advance, for example by the optimizer (230), and - the power of the VPP allocated to the frequency adjustment, noted and which can be given, for example, by the formula: . This formula is also valid for a frequency included in a frequency range extending from 49.8 Hz to 50.2 Hz. Outside this frequency range, the value of is saturated respectively by and . Similarly, the total power of renewable energy sources, denoted , is the sum of the power of renewable energy sources not allocated to the frequency control service, denoted , and the power of renewable energy sources allocated to the frequency control service, denoted . French Description

[0055] These formulas result in an injection or absorption of the entire primary reserve placed for an absolute frequency variation of 200 mHz or 0.2 Hz in the electrical network around a nominal frequency of 50 Hz. This corresponds to the current requirement of RTE for the management of the French electrical network and more generally to the requirement applicable to all electricity transmission network operators in Europe. It is recalled in this regard that the scope of application of the invention cannot be strictly limited either to a particular territory or to the particular case of the release of the primary reserve.The person skilled in the art will understand that the formulas provided in this document are to be considered solely as an illustrative example and will be able to easily adapt them according to the reserve level(s) concerned, as well as according to local requirements defining in particular the nominal frequency of the electrical network (which is for example 60 Hz in the United States) and the rules relating to the release of the reserve level(s) concerned.

[0056] denotes the maximum active power available from renewable energy sources (102, 104). As already indicated, this quantity is not measurable but only estimated.

[0057] Assuming that the renewable power plant is programmed by the optimizer (230) to provide base power, apart from the release of reserves associated with frequency adjustment, it is then assumed that .

[0058] denotes the maximum power of the controllable system with energy storage (106) in discharge, as returned for example by a storage monitoring system. Thus defined, its value must always be of a positive sign. For example, on a battery, the BMS, for “Battery Management System” in English, returns power limits according to its state of charge: the maximum power in discharge will be reduced near 0% state of charge and the maximum power in charge will be reduced near 100% state of charge. French Description

[0059] denotes the maximum power of the controllable system with energy storage (108) under load, as returned by the storage monitoring system. Thus defined, its value must always be of negative sign.

[0060] designates the minimum technical power of non-renewable energy sources (102, 104). For example, for a wind farm, this power corresponds to the value below which all or part of the turbines in the farm can no longer remain in starting condition.

[0061] denotes an additional correction power to be applied to the renewable power plant. The determination of this additional correction power is detailed in this document. In other words, using the technique proposed in this document, the setpoint power of the renewable energy sources (102, 104) can be determined according to the formula .

[0062] In order to guarantee the term, in return this correction power can also be applied to the setpoint of the controllable system with energy storage according to the formula.

[0063] Some previous patented works aim at designing AAP power estimators for wind and photovoltaic farms [3][4][5]. That being said, the AAP power estimation process of a variable renewable energy farm can still induce estimation errors, i.e. the difference between the estimated available power and its actual value ^ ^ ^ ^ ^ ^ ^ , ^^^ , the latter being unmeasurable as already explained.

[0064] Two possible strategies for controlling an EnR farm participating in the frequency control service are now described, with reference to Figure 5. Once the available power of the EnR farm is estimated, this farm can be operated below its maximum available production to constitute symmetrical reserve (502), by drawing the volume of upward reserve ( ) to be allocated on this farm. Note that if only the downward reserve must French Description to be provided by the farm, it can be operated at its available power without necessarily being clipped, it is a control implementing the constitution of an asymmetric reserve (504).

[0065] In general, when an renewable energy plant only provides the downward reserve, its base production corresponding to a frequency equal to the nominal frequency of the electricity network is maintained at its estimated available production to avoid any loss of energy linked to voluntary clipping. In this case, . When it also provides an upward reserve, its production must be voluntarily clipped to constitute the corresponding reserve volume. In this case, .

[0066] Estimating AAP power in real time is essential to enable a variable renewable energy farm to provide reserve. When the farm is controlled to contribute to the frequency control service, the total power of . In the same way as previously specified, this formula is valid for a frequency between 49.8 and 50.2 Hz and does not include saturations by the allocated reserve capacities.

[0067] Two main sources of error mean that the frequency control provided by a variable renewable energy farm cannot always be as efficient as that provided by a conventional power plant.

[0068] The first main source of error concerns the natural variability of wind or photovoltaic production depending on meteorological conditions, such as wind speed and direction for wind production, or sunshine and cloud cover for photovoltaic production, which can vary at any time. The variation trend of renewable energy production is not always in the direction favorable to frequency control. For example, a sharp increase in wind production following a gust of wind can be Description concomitant with a situation where the frequency is above 50 Hz, in which the network manager seeks instead to reduce production.

[0069] The second main source of error concerns the estimation of the maximum available power. Errors relating to this estimation can lead to unintentional adjustments that do not necessarily correspond to the responses expected by the network manager, particularly in the case of overestimation of renewable energy production. This problem was observed and analyzed within the framework of the VPP demonstrator of the European project EU-SysFlex [6]. Figure 6 illustrates the impact of estimation errors on the response of the frequency control of a variable renewable energy farm and represents on the same time scale the evolution of the AAP, actual, and expected powers of the farm (602) as well as the evolution of the frequency (604) of the network.We can see that due to overestimation of production between 16:09-16:10, the actual power of the rated farm is limited by the effective AAP and decreases unintentionally without any correspondence with the evolution of the network frequency at the same time. This therefore leads to a deviation of the actual and measured power of the farm from the expected rated power.

[0070] For these two main reasons, there is a gap between the expected response and the measured response when a variable renewable energy farm participates in frequency control. This gap is, for example, quantified during tests of the EU-SysFlex demonstrator for a 12 MW wind farm providing primary reserve. Figure 7 represents for this purpose on the same time scale: the evolution of the actual power of the wind farm (702), the evolution of the supply of primary reserve by the wind farm (704), i.e. the evolution of the primary reserve actually provided by the wind farm, noted and that of the primary reserve supposed to be provided in theory by the wind farm, noted the evolution of the difference between these two quantities and (706). French Description

[0071] If adjustment errors are not corrected, this leads to underperformance of frequency control and risks resulting in a reduction in remuneration or even a penalty for the participating generator. From an electricity system perspective, incorrect frequency control also poses a risk to the safety of the electricity network and users.

[0072] The proposed technique can be incorporated as a function of the STC (220) and aims to correct, within an optimization step, the underperformance of the frequency adjustment due to the variability of production and to the estimation errors of the renewable energy producible, while mobilizing the flexibility available on the time step concerned. This flexibility can include in particular the storage power of the system with controllable storage (106) and the modulation margin available on the production sources (102, 104).

[0073] The value of a so-called “corrective” power setpoint is calculated for a given time interval whose duration corresponds to the STC control time step.

[0074] This value can be transmitted to local renewable energy source controllers to correct, almost in real time, the performance of the VPP plant frequency control.

[0075] In parallel, a value equal or substantially equal to that of the corrective power setpoint, and of opposite sign, can also be transmitted to the local controller of the controllable system with energy storage, in order to compensate for the correction applied to the level of the renewable energy sources and thus maintain constant or substantially constant the reference power of the VPP plant outside system services, noted .

[0076] Indeed, a change in an optimization step can have significant consequences, often in the unfavorable direction, on the overall optimality of VPP management. It is therefore essential to guarantee this reference power at the VPP plant level when correcting the underperformance in frequency control of one or more installations of this plant. French Description

[0077] An example of an algorithm that may be suitable for determining the value of the corrective power setpoint within the framework of a VPP plant control and command process is now described.

[0078] Here we assume that the VPP plant participates in the primary frequency adjustment. We are at a given moment where a adjustment error is present, that is to say, as a reminder, a difference between the expected response of the renewable energy sources and that measured. The adjustment error noted corresponds to the difference in electrical power allocated to frequency adjustment between a theoretical value noted and an estimated value noted . In other words, .

[0079] The estimated value can be obtained by the following general formula: .

[0080] There are different ways to make a theoretical estimate of the control power of the renewable power plant. For example, it is possible to take into account the dynamics of the renewable power plant by modeling its response time noted via a first order, according to the following known mathematical formula: . In the same way as previously specified, this formula is valid for a frequency between 49.8 and 50.2 Hz and does not include saturations by the allocated reserve capacities.

[0081] Such modeling is generally sufficient for the purposes of determining the adjustment error.

[0082] Determining the adjustment error allows for the implementation of corrective actions for the frequency adjustment performance. A corrective action is an application of a correction instruction noted at a local controller level. French Description

[0083] An example of a possible correction instruction is a proportional instruction via a gain G, according to the formula .

[0084] The correction instruction is not necessarily proportional. Among other possible forms, the correction instruction can be linear or not, proportional integral, proportional integral derivative, etc.

[0085] For example, a dead band can be applied to the term to filter out smaller amplitude errors and avoid over-stressing of resources within the VPP due to frequency adjustment performance correction actions.

[0086] According to one example, the correction setpoint may be saturated. For this, a noted minimum value and / or a noted maximum value may be defined as limits of the correction setpoint. When these two limits are defined, the correction setpoint is saturated according to the formula: .

[0087] For example, the maximum value of the correction setpoint can be defined by the minimum between the maximum power of the landfill storage and the maximum volume of possible shaving power on the renewable power plant. So that the correction setpoint does not induce a reduction in the volume of reserve available on the storage, this value can be deduced from the maximum power of the landfill storage, according to the following formula: .

[0088] For example, the minimum value of the correction setpoint can be defined by the minimum between the maximum power of the storage system under load and, in the event of additional capping on the renewable power plant, the maximum volume of additional power thus made accessible. In the remainder of this document, it is considered that no additional capping is planned on the renewable power plant and that this volume of additional power is zero. So that the correction setpoint does not induce a reduction in the reserve volume at Description the available drop, this value can be deduced from the maximum power of the storage under load, according to the formula.

[0089] The correction setpoint is applied, for the control of renewable energy sources, as an additional power modulation setpoint, i.e. in addition to the setpoint associated with the frequency adjustment. In the mathematical formulas provided in this document, the correction setpoint is conventionally constructed as a positive value.

[0090] In order to guarantee the power for the performance control carried out by the transmission system operator, the correction setpoint is also applied in parallel to the controllable system with energy storage. In the same way as for renewable energy sources, this correction setpoint must be understood as an additional power modulation setpoint.

[0091] The correction instruction applied to renewable sources and that applied to the controllable system with energy storage have a substantially equal absolute value, with a relative or absolute tolerance chosen according to a criterion linked to the performance control carried out by the transmission system manager, and an opposite sign.

[0092] By convention, when the correction instruction applied to renewable sources has a positive sign, it corresponds to a value of increase in power supplied by renewable sources.

[0093] Similarly, by convention, when the correction instruction applied to the controllable system with energy storage has a positive sign, it corresponds to a discharge instruction.

[0094] Figure 8 is a block diagram (800) describing a set of mathematical operations that can be used in the control of renewable energy sources (e.g., a wind farm) and a controllable system with energy storage (e.g., a battery storage system). The Description frequency and reserve capacities placed respectively upwards and downwards on the wind farm are used to determine a control setpoint defined to control the wind farm so that it participates in the primary frequency control service. In parallel, the frequency and reserve capacities placed respectively upwards and downwards on the controllable system with energy storage are used to determine a control setpoint defined to control the energy storage so that it participates in the primary frequency control service. The same corrective value is then taken into account as the absolute value of correction instructions applied to renewable energy sources and to the controllable system with energy storage. Thus, the instruction actually transmitted to the wind farm controller integrates and . Similarly, the setpoint actually transmitted to the controller of the controllable system with energy storage integrates and . It should be noted that, in Figure 8, the corrective value is applied negatively to the wind farm and positively to the battery storage system. A possible algorithm for calculating the corrective value is explained in Figure 9, which is another block diagram (900) following that of Figure 8. According to this algorithm, the corrective value is a function of the amplitude of the power adjustment error, but with a dead band, i.e. an interval of adjustment error for which the corresponding corrective value is zero, as well as a maximum limit and a minimum limit saturating the corrective value.

[0095] The proposed technique was tested in simulation on the case of a VPP consisting of a controllable system with battery energy storage and a wind farm, aggregated to provide primary frequency control.

[0096] The simulation platform used comprises four models, namely: a wind farm model (204) which represents a 12 MW wind farm composed of 6 2 MW turbines associated with a local controller allowing in particular the provision of frequency adjustment, a controllable system model with energy storage (206) which represents a Description of a battery storage system with 3 MWh of energy and 2 MW of power, an FCR controller model which represents a control system associated with a frequency regulation service and exploiting the controllable system with energy storage and an STC controller model, i.e. an intermediate control-command system.

[0097] The simulation platform is represented in Figure 10 in the form of a block diagram (1000) where each block represents a model. Each model is configured to receive as input and return as output time series composed of samples associated with a given instant or a given elementary time period. For the sake of simplicity and pedagogy, reference is made, for the explanation of the operation of the models, to input and output signals, each signal representing a sample. Unless otherwise specified, a signal supplied to a model representing an entity relates to this entity.So for example when a signal representing an upward or downward reserve capacity is supplied to the wind farm model, it is considered that this upward or downward reserve capacity is placed on the wind farm, in other words that it defines, for the wind farm, the share of the active power allocated to the upward or downward frequency adjustment.

[0098] The wind farm model is configured to receive as input five signals representing respectively: a real maximum power, from a history, indicative of a historical value of AAP power, a volume, or a capacity, of upward reserve, a volume, or a capacity, of downward reserve, the frequency of the electrical network and a corrective value calculated algorithmically and corresponding to a real-time modulation of the power of the wind farm to contribute to a primary frequency control service, or "FCR, Frequency Containment Reserve" in English. French Description

[0099] Based on the five input signals, the wind farm model is configured to output an estimated AAP power signal and a signal representing actual measurable power. Thus, the wind farm model integrates an AAP power estimator as well as a frequency adjustment service controller.

[0100] The controllable system model with energy storage is configured to receive as input a signal representing a setpoint power and a signal representing the corrective value and to return as output, on the basis of these signals received as input, three signals representing respectively: a state of charge (SOC), a maximum power and a minimum power acceptable by the controllable system with energy storage.

[0101] The maximum power is associated with a maximum discharge speed and the minimum power is associated with a maximum charge speed acceptable by the controllable system with energy storage.

[0102] The FCR controller model is configured to receive as input three signals representing respectively: an upward reserve volume, or capacity, a downward reserve volume, or capacity, and the frequency of the electrical network, and to return as output, on the basis of these signals received as input, a power signal to be followed to contribute to the frequency regulation service.

[0103] The STC controller model is configured to receive nine input signals representing: four volumes, or capacities, of reserve, respectively upwards and downwards on the wind resources and upwards and downwards on the controllable system with energy storage, the frequency of the electrical network, the estimated AAP power, the measured power of the wind farm and Description of the maximum and minimum power acceptable by the controllable system with energy storage.

[0104] Based on the received input signals, the STC controller model is configured to output a power correction signal.

[0105] Typically, the signals representing the upward and downward reserve volumes on each generation system are defined by an optimizer based on associated market prices that include the SPOT price of electricity supplied to the electricity grid and the contractual remuneration associated with the VPP's contribution to the primary frequency control service or "FCR service".

[0106] In practice, the behavior of the optimizer was not modeled in the simulation platform, as the simulation focused on the function of the intermediate control-command layer STC. For simplicity, reserve levels were simply fixed and distributed consistently over a simulation day.

[0107] The choice made was to arbitrarily place the entire downward reserve (i.e. 1 MW) and 600 kW of upward reserve on the wind farm, and on the controllable system with battery energy storage an upward reserve volume set at 400 kW.

[0108] There are many reasons for this choice.

[0109] In France, the supply of frequency adjustment is done symmetrically and the choice made allows this rule to be respected by placing 1 MW upwards and downwards on the virtual power station.

[0110] Unlike upward reserve, providing downward reserve on wind power does not require permanent curtailment of wind production and is therefore more attractive from an economic point of view. In addition, placing reserve on a controllable system with battery energy storage requires reserving part of the available capacity for charging / discharging, capacity which is therefore no longer available for other services or arbitrage on the market. This French Description are the reasons why the downward reserve is entirely carried by the wind farm.

[0111] According to feedback from the French VPP demonstrator of the EU-SysFlex project, this simulated scenario can correspond to the optimal planning of a typical day calculated by an industrial optimizer [6].

[0112] To evaluate the performance of the developed function compared to other solutions, two indicators were selected.

[0113] The first indicator relates to the percentage of time during which the estimated frequency control gain is less than 20% different from the contractual value. This is a performance control criterion called the "static criterion", currently applied in France, which notifies the producer of a deviation when the relative difference between the estimated frequency control gain and the contractual value is greater than 20% for more than 10% of the time. In other words, the estimated frequency control gain must be between 0.8 and 1.2 pu ("per unit" in English) for at least 90% of the time to comply with the "static criterion" in terms of performance.The method used to estimate the gain is based on a known method of estimating the least squares of the error carried out every 10 minutes from measurements at 10 second time steps, using however the AAP power signal as input data for the development of the power of the VPP allocated to a service other than that of the frequency adjustment [7].

[0114] The second indicator is the energy clipped on the wind farm due to power modulation according to the proposed technique or due to a permanent margin according to another possible technique.

[0115] The simulation was carried out over one day based on historical wind production and frequency in France.

[0116] The three cases evaluated in simulation are as follows.

[0117] The first case, or "control case", corresponds to a situation where no preventive action is taken on the aggregated plant to improve performance Description of the FCR service. In this control case, the first indicator, i.e. the percentage of time during which the estimated frequency control gain is different by less than 20% of the contractual value, amounts to 76.4%, which is lower than the 90% recommended to meet the static criterion. We can therefore see that without any corrective action, the frequency control performance of the VPP plant evaluated on the simulated day is 76.4%. In other words, for 23.6% of the time the service provided by the VPP is underperforming, which corresponds to 13.6 points more than the grid manager's requirement in terms of time spent in the required performance according to the current rules. The second indicator, i.e. the curtailed energy, is zero since no preventive action is taken.

[0118] The second case, or "case of a permanent margin of 200 kW" corresponds to a situation where the power supplied by the wind farm is permanently capped by 200 kW, in addition to the FCR service provided, so as to deviate from the AAP power and the associated estimation errors. This corresponds to the first solution described in the presentation of the state of the art. In this case of a permanent margin of 200 kW, the first indicator is worth 90.27%, the static criterion is therefore met. The service can therefore be considered "effective" or "efficient" according to the network manager's evaluation criterion under current rules. The second indicator amounts to 4.8 MWh, which corresponds to a significant loss of producible power, i.e. a significant loss of opportunity for the producer.

[0119] The third case corresponds to a situation where the power of the wind farm is modulated on the basis of a corrective value in accordance with the proposed technique. In this third case, the first indicator amounts to 90.27% and the second indicator is worth only 0.8 MWh. Thus, the performance of the frequency control service has also been raised to more than 90% and the performance criterion is therefore met, while largely avoiding the curtailment of wind production.

[0120] It has been proven by simulation that the present invention works correctly and is of technical and economic interest with a view to improving the Performance description of the frequency control service provided by a VPP composed of variable renewable energy and a controllable system with energy storage.

[0121] Bibliography

[0122] [1] Y. Wang et al., "WP8 Demonstration Specification for Field Testing: Aggregation Approaches for Multi-services Provision from a Portfolio of Distributed Resources", D8.1 report of EU-SysFlex project, 2018, available online at https: / / eu-sysflex.com / documents / .

[0123] [2] RTE, “Technical Reference Document,” 2020, available online at https: / / www.services-rte.com / fr / la-bibliotheque.html.

[0124] [3] J. Callec and Y. Wang, “Method for regulating power generated by a wind farm”, French patent FR 3074975 B1.

[0125] [4] J. Jacobsen, “Method for determining the available power of a wind park”. Chinese patent application CN 110402330 A.

[0126] [5] J A. Rossé and G. Delille, “Power control of inverters of a photovoltaic installation for participation in the frequency adjustment of the electrical distribution network”, French patent FR 3060229 B1.

[0127] [6] Y. Wang et al., "French demonstration: “multi-resources multi-services” virtual power plant", D8.4 report of EU-SysFlex project, 2022, available online at https: / / eu-sysflex.com / documents / .

[0128] [7] RTE, "System Services: RTE's experience," J3eA, vol. 5, p. 6, 2006.

Claims

French Claims Claims

1. Method for controlling a virtual power plant, connected to the electricity network, aggregating a plurality of installations capable of contributing to a frequency regulation service, the plurality of installations comprising at least one controllable system with energy storage and a set of renewable sources having a maximum available active power varying over time, the method being implemented by a control device connected to an optimizer and to local controllers of the sources and of the controllable system with energy storage, the method comprising: a) obtaining from the optimizer sets of parameters respectively associated with respective time intervals, a set of parameters comprising a first setpoint power provided for the set of sources and a second setpoint power provided for the controllable system with energy storage,during the associated time interval and excluding contribution to the frequency regulation service, the optimizer being further configured to provide upward and / or downward reserve capacity setpoints on all the installations for the associated time interval, b) determining, for a sub-interval of a current time interval, a control power error of the virtual power plant on the basis of a difference between power measurements produced by each installation of the virtual power plant and an expected effective theoretical value based on a real-time estimate of a maximum active power available from all the renewable sources and on a current frequency measurement of the electrical network, c) determining, for the sub-interval, a corrective value on the basis of the control power error, d1) providing the local controllers of renewable sources, for the sub-interval,a first frequency regulation setpoint power, French: French Claims corrected by a lowering of an amplitude corresponding to the corrective value, and d2) providing the local controllers of the controllable system with energy storage, for the sub-interval, with a second frequency regulation setpoint power corrected by an increase of an amplitude corresponding to the corrective value, the sum of the corrected frequency regulation setpoint powers being substantially equal to the sum of the setpoint powers provided excluding contribution to the frequency regulation service.

2. Method according to claim 1, in which, when the value of the estimation error is greater than a low threshold and less than a high threshold, the corrective value is zero.

3. Method according to claim 1 or 2, in which, when the value of the estimation error is less than a low threshold, the corrective value is proportional to the estimation error.

4. Method according to one of claims 1 to 3, in which, when the value of the estimation error is greater than a high threshold, the corrective value is proportional to the estimation error.

5. Method according to one of claims 1 to 4, in which the corrective value is saturated between limit values ​​indicative of a minimum value between: - a maximum power of the controllable system with energy storage in charge, - a maximum power of the controllable system with energy storage in discharge, - the estimated maximum available active power of the renewable sources, - the reserve capacities placed on all the installations, - minimum technical powers of the renewable sources.

6. Method according to one of claims 1 to 5, in which the time intervals have a duration greater than 10 minutes and less than 1 hour. French Claims

7. Method according to one of claims 1 to 6, wherein the current sub-interval has a duration of less than 30 seconds.

8. Method according to one of claims 1 to 7, wherein b), c), d1) and d2) are repeated periodically.

9. Computer program comprising instructions for implementing the method according to one of claims 1 to 8 when this program is executed by a processor.

10. Device for controlling a virtual power plant, connected to the electricity network, aggregating a plurality of installations capable of contributing to a frequency regulation service, the plurality of installations comprising at least one controllable system with energy storage and a set of renewable sources having a maximum available active power that varies over time,the control device being connected to an optimizer and to local controllers of the sources and of the controllable system with energy storage, the control device being configured to: a) obtain from the optimizer sets of parameters respectively associated with respective time intervals, a set of parameters comprising a first setpoint power forecast for all the sources and a second setpoint power forecast for the controllable system with energy storage, during the associated time interval and excluding contribution to the frequency regulation service, the optimizer being further configured to provide upward and / or downward reserve capacity setpoints on all the installations for the associated time interval, b) determine, for a sub-interval of a current time interval,a control power error of the virtual power plant based on a difference between power measurements produced by each installation of the virtual power plant and an expected effective theoretical value based on a real-time estimate of a maximum active power available from all renewable sources and on a current frequency measurement of the electricity network, c) determine, for the sub-interval, a corrective value based on the error, Control power claims, d1) provide the local controllers of renewable sources, for the sub-interval, with a first frequency regulation setpoint power corrected by a reduction of a magnitude corresponding to the corrective value, and d2) provide the local controllers of the controllable system with energy storage, for the sub-interval, with a second frequency regulation setpoint power corrected by an increase of a magnitude corresponding to the corrective value, the sum of the corrected frequency regulation setpoint powers being substantially equal to the sum of the setpoint powers provided excluding contribution to the frequency regulation service.

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