Static control loop for an inverter interfacing an intermittent power source and an AC power grid

Abstract

Static control loop for an inverter interfacing an intermittent power source and an AC power grid. The invention relates to a primary control method for an inverter interfacing an intermittent power source and an AC power grid. Through each of the different aspects of the invention, a new static control loop, or droop control loop 5, is proposed that adapts to variations in the available active power of the inverter 1.This loop can be advantageously implemented on each inverter that, among a plurality of generators connected to the grid, interfaces with an intermittent energy source, while ensuring: correct allocation of active power among the generators, and correct signaling, via the frequency at the point of connection of each generator to the grid, of when each generator reaches its active power limits, thus enabling the activation of protective measures so that each generator in the plurality returns to its active power range. Figure for the abbreviation: Fig. 4.

Description

Title of the invention: Static control loop for an inverter interfacing an intermittent power source and an AC electrical network. Technical field

[0001] The present invention relates to a primary control method for an inverter that interfaces a power source and an AC electrical grid, the power source being potentially intermittent. More specifically, the present invention relates to a droop control loop, hereinafter referred to as a "droop control loop," which allows generators connected to an AC electrical grid to contribute to maintaining balance or sharing active power on the AC electrical grid, in particular by regulating the frequency at an output point of each generator to the balance frequency of the AC electrical grid. PRIOR TECHNIQUE

[0002] Initially, the droop control loop strategy, hereinafter referred to as the "droop strategy," was created to control synchronous machines that interface with non-intermittent energy sources, such as fossil fuels. Later, the strategy was adapted for implementation on inverters, as generators, also interfacing with non-intermittent energy sources. However, this initial adaptation is partly dysfunctional, especially if the droop strategy is implemented on inverters that interface primarily, or even exclusively, with intermittent energy sources, such as solar, wind, etc.These malfunctions can even cause inverters to disconnect, which can jeopardize the stability of the AC power grid if the available active power from other generators connected to the AC grid is insufficient to meet the grid's electricity demand. The following paragraphs explain in more detail how the conventional droop strategy works and its potential malfunctions.

[0003] Figure 1 represents an inverter 1 that interfaces a non-intermittent power source 2 with the control scheme 5 corresponding to the conventional droop strategy. This strategy considers, as input, a measurement of the active power P(t) that the inverter 1 supplies to the AC power grid and uses it to calculate the setpoint value j of the frequency. The internal control loops 10 are responsible for ensuring that the frequency at the connection point 4 of Inverter 1 to the AC electrical network 3 follows the setpoint calculated by the Droop control loop 5. It is assumed that network 3 potentially contains loads and other generators that interface with non-intermittent power sources, and that conventional droop strategies are also implemented on these generators.

[0004] More precisely, the function used by the conventional droop strategy to calculate the frequency value as a function of the active power P(t) of The inverter takes the form of a linear function: [MATH 1] pref(t) = fmax - mp x (P0 - P"") with a fixed slope "mP", such that This function can be represented by a profile fp tc' VTp pmaxass pirlin ass [ ' JJ as illustrated in [Fig. 2]. It should be noted that, for a given droop strategy implemented on a generator, what is designated as the "|p* profile" is the set of steady-state operating points defined in the ^p plane and on which the generator can stabilize; this set of operating points is defined by the implemented droop strategy. During transients, the generator's operating point may be outside this profile. As shown below, this representation helps to understand, in particular, how the conventional droop strategy allows for a correct allocation of active power when implemented on inverters interfacing with non-intermittent energy sources.

[0005] Figure 2 shows, on the same plane / p fref\, the profiles corresponding to two inverters connected to the same AC electrical network and controlled with the conventional droop strategy. Sub-indices 1 and 2 identify the parameters of the droop strategy which relates to the first inverter and the second inverter, respectively. The available active power (p^sP, p^P) at the output of each The inverter coincides with the maximum assigned active power. the inverter, since the energy source that each inverter interfaces with is non-intermittent.

[0006] The key to the conventional droop strategy is that the frequency f(t) is, in steady state, a single quantity in each AC electrical network 3. Transiently, two points in the same AC electrical network may have different frequencies, but the electrical laws governing the behavior of the AC electrical network 3 cause all points in the network to have the same frequency f(t) in order to reach steady state. This implies that, once the Once steady state is reached, all generators in the network will converge to the same frequency setpoint 0, and this setpoint will coincide with the frequency f(t) at every point in the network. 3. If the generators converge to the same frequency setpoint, and more specifically, with reference to [Fig. 2], if the The first inverter reaches operating point A and the second inverter reaches operating point A', corresponding to the same setpoint frequency. The proportion between the active power P(t) produced and the assigned active power range ass j will be the same for all generators, i.e., for the two inverters considered: [MATH 2] pmitwss pmavtJM

[0007] This explains that the first attribute of the conventional droop strategy is that it allows a correct allocation of active power in the case of non-intermittent energy sources.

[0008] Furthermore, the generators of network 3 will converge to the setpoint frequency < fmin s' ct only if all the generators each supply an

[0009]

[0010] active power greater than or equal to their available active power > p^isP yi j. Consequently, crossing the minimum frequency threshold fmln can be used as a signal to activate protection measures, for example implemented using frequency-metric relays which allow loads to be disconnected from the AC electrical network 3. Conversely, the generators of network 3 will converge to the setpoint frequency f”™* if and only if all the generators each supply an active power less than or equal to their minimum rated active power (P^t) P^m ass~ ij • As a result, crossing the maximum frequency threshold fmux can be used as a signal to activate protection measures, for example implemented by frequency-metric relays which allow generators to be disconnected from the AC electrical network 3. We can then conclude that the conventional droop strategy has a second attribute: it signals, for example via the setpoint frequency value ^'00, whether the generators are reaching their active power limits. And this signal can to be used to activate alternative power grid protection measures, in order to ensure that all generators return to their active power ranges.

[0011] As we will develop below, this conventional droop strategy is not portable to the control of inverters 1 associated with intermittent energy sources, or at the very least does not allow the control of such inverters with the same attributes as those acquired for an inverter 1 associated with a non-intermittent energy source 2, and therefore does not allow us to benefit from it.

[0012] The traditional way of controlling inverters 1 which interface intermittent energy sources 2, such as photovoltaic panel inverters, is to control them so that the active power P(t) which they supply to the network 3 is always equal to the available active power p^P^- Traditionally, therefore, droop control loops were not implemented for this type of inverter.

[0013] Active power sharing systems based on droop strategies and active power sharing systems not based on droop strategies have since been developed to control inverters 1 that interface intermittent power sources 2.

[0014] Systems based on droop strategies are described, for example, in the following articles: has. H. Liu, Y. Yang, X. Wang, PC Loh, F. Blaabjerg, W. Wang, and D. Xu, “An enhanced dual drop control scheme for resilient active power sharing among paralleled two-stage converters,” IEEE Transactions on Power Electronics, vol. 32, no. 8, pp. 6091-6104, Aug. 2017; b. H. Mahmood and J. Jiang, “Decentralized power management of multiple PV, battery, and droop units in an islanded microgrid,” IEEE Transactions on Smart Grid, vol. 10, no. 2, pp. 1898-1906, Mar. 2019; c. Z. Chen, RH Lasseter, and TM Jahns, “Active power reserve control for grid-forming PV sources in microgrids using model-based maximum power point estimation,” in 2019 IEEE Energy Conversion Congress and Exposition (ECCE), Sep. 2019, p. 41-48; d. Z. Li, K. W. Chan, J. Hu, and J. M. Guerrero, “Adaptive droop control using adaptive virtual impedance for microgrids with variable pv outputs and load demands,” IEEE Transactions on Industrial Electronics, vol. 68, no. 10, pp. 9630-9640, Oct. 2021; And e. NL Diaz, JC Vasquez, and JM Guerrero, “A communication-less dis-tributed control architecture for islanded microgrids with renewable generation and storage,” IEEE Transactions on Power Electronics, vol. 33, no. 3, pp. 1922-1939, Mar. 2018.

[0015] With an intermittent energy source 2, the power available in the source Energy is variable. Consequently, the active power available exit of inverter 1 is variable. It is to adapt the conventional droop strategy to these variations in available active power pdtsP^ that the droop control loops

[0016] described in the articles listed above have been proposed. The droop control loops described in the first three articles cited above are based on different principles, but they give rise to equivalent profiles composed of a fixed and stationary slope profile, to which is added a vertical profile that passes through as illustrated in Figure 9 by the profile | p associated with the first inverter (identified by the index "1"), the vertical profile moving along the P-axis as pdixP^ varies. The The main problem with this type of profile is that it does not guarantee a correct allocation of active power. For example, with reference to Figure 9, if we consider the point of steady-state operation, denoted A, of the first inverter, this inverter provides an active power equal to its available active power, while the second inverter whose operating point in the same steady state is rated A' would work well below its active power available

[0017] The droop control loops described in the last two articles cited above correspond to a droop profile with a slope that changes as the available active power p^P^ varies, so that the profile always passes through the points pmn j and p^P^ as illustrated in Figure 10 by the Profile FP1 associated with the first inverter (identified by the index "1"). The The main problem with this type of droop profile is that its slope is strongly linked to the dynamic behavior of the generators. More specifically, steep slopes can cause oscillations in electrical quantities that can destabilize the network 3 (See N. Pogaku, M. Prodanovic, and TC Green, “Modeling, analysis and testing of autonomous operation of an inverter-based microgrid,” IEEE Transactions on Power Electronics, vol. 22, no. 2, pp. 613-625, Mar. 2007; A. Firdaus and S. Mishra, “Mitigation of Power and Frequency Instability to Improve Load Sharing Among Distributed Inverters in Microgrid Systems,” IEEE Systems Journal, vol. 14, no. 1, pp. 1024-1033, 2020.).

[0018] Furthermore, the droop control loops described in the last three articles cited above require an estimation / measurement of the available power p^PiA But This measurement / estimate may be inaccurate and differ from the available active power. real p!l'P real / A This is dangerous in the case where p^PÏÿ y p4^p real / A because the inverter can then converge towards an operating point with > pdisp real^ outside its active power range, and, given that then ^ref y ^min, no protection measure would be activated.

[0019] Thus, the droop strategies proposed in the aforementioned articles: a. do not allow for a correct allocation of active power between generators, and / or b. cause oscillations in electrical quantities that can destabilize the alternating current electrical network, and / or c. do not allow correct activation signaling of protection measures, in particular through the value of the frequency f(t) at an output point of each generator (or equivalently at a connection point of each generator to the network), when the generators reach, or even exceed, their active power limits.

[0020] Active power sharing systems not based on droop strategies give results comparable to those of droop strategies, including maintaining the balance of active power to which several generators contribute, the correct allocation of active power between generators, and compliance with the operating ranges of each generator connected to the AC power grid. For example, the following articles describing such systems not based on droop strategies can be found in the scientific literature: has. E. Espina, J. Llanos, C. Burgos-Mellado, R. Cârdenas-Dobson, M. Martinez-Gômez, and D. Sâez, “Distributed Control Strategies for Microgrids: An OverView,” IEEE Access, vol. 8, pp. 193412-193448, 2020, doi: 10.1109 / ACCESS.2020.3032378, and b. DE Olivares et al., “Trends in Microgrid Control,” IEEE Transactions on Smart Grid, vol. 5, no. 4, pp. 1905-1919, July 2014.

[0021] The demonstrator described in “The Interflex consortium, 'D9.3 Demonstration results based on the KPI measurements and lessons learned from the demonstrations', Tech. Rep., 2019” and the industrial solution described in “C. Mahieux and A. Oudalov, 'Balancing act', ABB, 2015” also fall under such systems not based on droop strategies.

[0022] However, these systems require communication links between the different generators and / or with a network server. The most significant disadvantages associated with this requirement are the cost of building these links and the potential reduction in system reliability in the event of a communication failure. In contrast, droop control loops have the major advantage of not requiring, by their very nature, communication links, particularly between the different generators. generators, because they are implemented independently on each generator.

[0023] It follows from the above that there is a need for control of inverters that interface intermittent energy sources with an alternative electrical grid. Alternatives to existing systems, whether or not based on droop strategies, would be appreciated, in particular: a. if they did not necessarily implement communication links between the different generators and / or with a network server, and / or b. if they made it possible to guarantee a correct allocation of active power between generators, and / or c. if they made it possible to avoid the appearance of oscillations in electrical quantities likely to destabilize the alternating electrical network.

[0024] More specifically, with respect to existing systems based on droop strategies, a new control strategy that allows adaptation to the variations in available active power p^isp^ typical of intermittent energy sources is desirable, which should be able to guarantee: a. a correct allocation of active power between the generators, and / or b. Correct activation signaling of protective measures when the generators reach, or even exceed, their active power limits. SUMMARY

[0025] To achieve this objective, according to a first aspect of the invention, a droop control method, or "droop" method according to Anglo-Saxon terminology, is provided for an inverter intended to interface an intermittent energy source and an alternating current electrical network by regulating the frequency f(t) at a connection point of the inverter to the network, the method comprising, as a function of: i. a constant fmax defining the maximum frequency limit of the network, ii. a constant fmm defining the minimum frequency limit of the network, iii. a constant pmax asx defining the maximum active power assigned to the inverter, iv. a constant p™'" ax defining the minimum active power assigned to the inverter, v. a measure of active power P(t) that the inverter supplies to the grid at time t, and vi. a measurement or estimation of the available active power pc^sp^^ in the inverter at time z, a. a step consisting of implementing: i. A first control branch, denoted a, configured to calculate a first frequency setpoint satisfying, or being a solution of, a first control function defined in a plane j by the following equation: [MATH 3] = fux (t) -mpx (P(t) -P”™ ass) where f"" (f) =f™ +mpX (p^t) -p™ and _[jjnax y (pmax ass pmin «ysj gj A second control branch, denoted / ?, comprising the implementation of a first proportional-integral regulator, referenced PI-1, and a first saturation function, and configured to calculate a second frequency setpoint satisfying, or being a solution of, a second function of control-command defined in the plane p by the equation next: [MATH 4] max ( aux 1 ( t ), 0 ), with auxl(j) = KPppl^ , where Kppi_p, the proportional gain of the first proportional-integral regulator, and r, the integral gain of the first proportional-integral regulator, are parameters greater than zero and predetermined according to the inverter concerned, and b. a step consisting of imposing a frequency setpoint value on the The inverter's connection point to the grid is determined as the sum of the first and second frequency setpoints.

[0026] A second aspect of the invention relates to a computer program product comprising instructions which, when executed by at least one processor, carry out the steps of the static control method according to the first aspect of the invention.

[0027] A third aspect of the invention relates to a control unit or computer for an inverter intended to interface an intermittent energy source and an alternating current electrical network by regulating the frequency (fit) at the inverter connection point. to the network, the control unit comprising electronic and / or microelectronic components configured to implement the static control method according to the first aspect of the invention.

[0028] A fourth aspect of the invention relates to an inverter for interfacing an intermittent energy source and an alternating current electrical network by regulating the frequency f(t) at the point of connection of the generator to the network and comprising at least one of the following: a. a non-transient readable medium comprising instructions, which when executed by at least one processor, carry out the steps of the static control method according to the first aspect of the invention, and b. a control unit according to the third aspect of the invention.

[0029] The inverter according to the fourth aspect of the invention may advantageously be free of a communication link with another generator or a server connected to the AC power grid, in order to ensure at least one, preferably both, of a correct allocation of active power between the generators and correct activation signaling of protection measures when the generators reach, or even exceed, their active power limits. Alternatively or in addition, the voltage at the point of connection of the generator to the grid may be single-phase or polyphase.

[0030] Through each of the different aspects of the invention, a new droop control loop is proposed that adapts to variations in the available active power of the inverter. Consequently, it can be implemented for an inverter interfacing an intermittent energy source, and advantageously on each inverter that, among a plurality of generators, interfaces with an intermittent energy source, while ensuring: a. a correct allocation of active power among the generators, and b. a correct signaling, by means of the frequency at the point of connection of each generator to the network, of the attainment by each generator of its active power limits, which allows the activation, possibly in a known way, of protection measures, possibly known, so that each generator of the plurality returns to its active power range. BRIEF DESCRIPTION OF THE FIGURES

[0031] The aims, objects, features and advantages of the invention will become clearer from the detailed description of an embodiment thereof, which is illustrated by the following accompanying drawings in which:

[0032] [Fig. 1] Fig. 1 represents a functional diagram of a control system for an inverter interfacing a non-intermittent energy source with a alternative electrical network and illustrates the control-command type diagram of a control loop corresponding to a conventional droop strategy.

[0033] [Fig.2] Figure 2 graphically represents, in the plane p fre^, profiles of operation of two inverters each interfacing a non-intermittent energy source with the same alternating current electrical network, the inverters being controlled according to a conventional droop strategy.

[0034] [Fig. 3] Figure 3 graphically represents, in the plane p freJ j, profiles of operation of two inverters interfacing, one with an intermittent energy source and the other with a non-intermittent energy source, with the same alternating electrical network, the inverters being controlled according to a conventional droop strategy.

[0035] [Fig.4] Fig.4 represents a functional diagram of a control system- control of an inverter interfacing an intermittent power source with an alternating electrical network and illustrates a control-command type diagram of a control loop according to a first embodiment of the present invention.

[0036] [Fig. 5] Figure 5 graphically represents, in the p fre / j plane, profiles of operation of two inverters interfacing, for one, an intermittent energy source, and, for the other, a non-intermittent energy source, with the same alternating electrical network, the inverter interfacing the non-intermittent energy source being controlled according to a conventional droop strategy and the inverter interfacing the intermittent energy source being controlled by a control loop as illustrated in [Fig.4].

[0037] [Fig.6] Fig.6 represents a functional diagram of a control system- control of an inverter interfacing an intermittent power source with an alternating electrical network and illustrates a control-command type diagram of a control loop according to a second embodiment of the present invention.

[0038] [Fig.7] Fig.7 represents a functional diagram of a control system- The diagram illustrates the control of an inverter interfacing an intermittent power source with an AC electrical network and shows a control-command type diagram of a control loop according to a third embodiment of the present invention. It should be noted that branch 12 shown corresponds to the first embodiment, but it could also correspond to the third embodiment.

[0039] [Fig. 8] Figure 8 graphically represents, in the plane p), the operating profiles of two inverters interfacing, for one, an intermittent energy source, and, for the other, a non-intermittent energy source, with the same alternating current electrical network, the inverter interfacing the non-intermittent energy source being controlled according to a conventional droop strategy and the inverter interfacing the intermittent power source being controlled by a control loop as illustrated in [Fig.7].

[0040] [Fig. 9] Figure 9 graphically represents, in the plane p^re f), profiles of operation of two inverters interfacing, for one, an intermittent energy source, and, for the other, a non-intermittent energy source, with the same alternating electrical network, the inverter interfacing the non-intermittent energy source being controlled according to a conventional droop strategy and the inverter interfacing the intermittent energy source being controlled by a droop strategy adapted, according to a known prior art, to an intermittent energy source.

[0041] [Fig. 10] Figure 10 graphically represents, in the plane p fre^, profiles operation of two inverters interfacing, for one, an intermittent energy source, and, for the other, a non-intermittent energy source, with the same alternating electrical network, the inverter interfacing the non-intermittent energy source being controlled according to a conventional droop strategy and the inverter interfacing the intermittent energy source being controlled by a droop strategy adapted, according to another prior art known relative to that considered in [Fig.9], to an intermittent energy source.

[0042] [Fig. 11] Figure 11 shows an electrical and control diagram of a embodiment of each of two droop control loops, one relating to active power, denoted P, and illustrating a droop control loop according to an embodiment of the invention, and the one relating to reactive power, denoted Q, which is not directly concerned by the present invention.

[0043] The drawings are given by way of example and are not limiting of the invention. Some constitute schematic representations of principle intended to facilitate understanding of the invention. DETAILED DESCRIPTION

[0044] Before proceeding with a detailed review of embodiments of the invention, optional features that may be used in combination or alternatively are listed below:

[0045] According to an example of the first aspect of the invention, the implementation of the second control branch is further dependent on: a. a measurement of the DC voltage at the inverter input, and b. a setpoint value for the DC voltage at the input of the inverter, and This also includes the implementation of a first proportional regulator, referenced P-1, the first proportional-integral regulator, the first saturation function and the first proportional regulator being configured to impose, on the second frequency setpoint fre^~^( t), a value defined by a variant of the second control function, said variant taking the form of the following equation: [MATH 5] max ( aux 1 ( t ) 0 ), with auxl(t) = aux 1 ( t) + KPp[ 1 * aux2(f) + Kipi ](t)dr with aux2(t) = Kp ]*((t) -vderef (t) ), where Kp, the proportional gain of the first proportional regulator, is a parameter strictly greater than zero and predetermined according to the inverter in question. The method according to this example of the first aspect of the invention prevents the second frequency setpoint from stabilizing while the input voltage (f) of the inverter is not equal to its setpoint value rei(t) ■

[0046] According to an example of the first aspect of the invention, the step of implementing the first and second branches further comprises, depending on: a. a measurement of the DC voltage at the inverter input, and b. a setpoint value of the DC voltage \dc ref(t^ at the input of the inverter, the implementation of a third control branch, denoted T, comprising the implementation of a second proportional-integral controller, referenced Pi - 2, a second saturation function and a second proportional controller, referenced P - 2, and configured to calculate a third frequency setpoint satisfying, or being a solution of, a third function of control-command defined in the plane by the following equation: [MATH 6] min(aux3(t), 0), with artU) = Kf^P^ ) +K.pll «J(F^ ^-P[t) ) *df with bis^iSp+ aux^ and auxA( t) = KPp2*( ( t) - (t ) ), where KPpi^, the proportional gain of the second proportional-integral regulator, and Kipp?, the integral gain of the second proportional-integral regulator, are greater than zero parameters predetermined according to the inverter in question, and Kpp^, the gain The proportional value of the second proportional regulator is a parameter strictly greater than zero and predetermined according to the inverter in question, and: The frequency setpoint value fte^j at the inverter's connection point to the grid is determined as the sum of the first, second, and third frequency setpoints, ' ref-a x s-ref-yf Y The method according to this / (0= / (0+ / (0+ / y) An example of the first aspect of the invention allows for managing the conceivable eventuality that the measurement or estimation of the available active power p^'P^ of an inverter 1 interfacing an intermittent energy source 2 may be erroneous and differ from the actual available active power, which is denoted pdisp real^

[0047] According to an example of the first aspect of the invention, at least one, preferably each, of said parameters can be predetermined by an analysis of the time response of the inverter and / or by an analysis of the frequency response of the inverter and / or by implementation of a pole placement method.

[0048] According to an example of the first aspect of the invention, for a given inverter, each of the aforementioned parameters is substantially constant over time.

[0049] According to an example of the first aspect of the invention, at least one of the second and third control branches further includes the implementation of at least one subtractor and at least one adder.

[0050] According to another example of the first aspect of the invention, the implementation of the first control branch may include the implementation of: a. two multipliers by a constant, this constant being defined by mP for one and by "mP" for the other, b. two subtractors, one to calculate p(t) - P''1 and the other to calculate p^P pmin ass, and c. two adders, one to calculate f™* ( / ) and the other to calculate rA,(o-

[0051] According to another example, the generator may be associated with, or include, one or more so-called internal control loops (as opposed in particular to the droop control loop proposed here, which is an external control loop). And the internal control loops of each generator are configured to control the frequency of the generator's connection point to the AC power grid; such internal control loops may be said to be configured in 'voltage source' (or 'grid-forming') mode.

[0052] According to another example of the first aspect of the invention, the step of imposing the setpoint value freJ(A of frequency at the point of connection of the inverter to network includes the supply of said value to at least one internal control loop of the inverter.

[0053] It is specified that, within the framework of the present invention, the following notations are adopted: a. fit) is the frequency at a point in an alternating electrical network, and more specifically the frequency of the sinusoidal voltage at a point of connection of an inverter to an alternating electrical network; b. / r ^0 is a frequency setpoint for an inverter, calculated by its droop control loop and varies over time; c. fmax is a constant defining the maximum frequency limit used to define the droop strategy; d cs( a constant defining the minimum frequency limit used to define the drop strategy; e. P(t) is a measure of active power that an inverter provides to the AC electrical network to which it is connected, and varies over time; fp / max an is a conS(an(C) defining the maximum rated (or "nominal") active power of an inverter; g pmin ass csl a constant defining the minimum rated (or "nominal") active power of an inverter; h. pdtsp csj is a measure or estimate of the available active power in an inverter, and depends on the energy source interfaced by the inverter. More specifically, p^P can be a constant if the inverter interfaces a non-intermittent energy source, or can be time-variable, pdlsp^, if the inverter interfaces an intermittent energy source with the AC electrical grid; i. v^ft) is a measure of the DC voltage at the input of an inverter and varies over time; and j. ref is a setpoint value for the DC input voltage of a inverter, and can be constant or variable over time, c ref(f), depending on the constitution of the DC circuit located upstream of the inverter and the way in which this circuit is controlled; it is preferable, if not necessary, that v“c( t) does not deviate excessively from its setpoint value to ensure the proper functioning of the inverter and the power source.

[0054] Furthermore, the following are understood to mean: a. “Generator” means any element capable of supplying a network with the power produced by an energy source by interfacing the energy source with itself and the grid. For example, a generator can be a synchronous machine that interfaces with a gas (or hydraulic) turbine, or an inverter that interfaces with a photovoltaic panel or a wind turbine. As is clear from the detailed description that follows, the generators primarily discussed here not only interface with the grid and an intermittent energy source, but also actively control the amplitude and frequency of the sinusoidal voltage at the point of connection between the generator and the grid. Such generators operate in 'voltage source' mode (or "grid-forming" in English), as opposed to the 'current source' mode (or "grid-feeding", or "grid-following", in English). Therefore, each generator implemented within the framework of the present invention can be considered a generator in 'voltage source' mode or equivalently a 'grid-forming' type generator; b. “load” means any electrical element connected to the alternating electrical network to subtract active power from it, and more particularly that required for its operation; c. “active power balance” means the state of the network in which the sum of the active power supplied to the network (by generators, for example) is equal to the sum of the active power drawn from the network (by loads, for example), less losses; and d. “Droop control loop” or equivalently “droop control loop” is a set of functions, typically digital and therefore implemented by a (micro)processor, but potentially analog and then implemented by electronic components, that enable the implementation of a droop strategy (or equivalently “droop control loop strategy”) aimed at allowing a generator to participate in maintaining the active power balance of the AC electrical grid to which it is connected. Normally, and this is the case here, two droop control loops are implemented on each generator: one that allows it to contribute to the active power balance and another to the reactive power balance. As is well known, the distinction between active and reactive power applies only to the case of an AC electrical grid, as opposed to a DC electrical grid.Active power is the "useful" power (typically, the power produced by an energy source becomes active power once it passes through the AC electrical grid). Reactive power is necessary for the operation of the AC electrical grid, but it is not useful; it simply "travels back and forth" within the grid. (See figures.) The attached functional diagrams, namely Figures 1, 4, 6, and 7, represent only one of the two droop control loops: the control loop contributing to the balance of active power, which is the one concerned by the droop strategy proposed here. However, the droop control loop contributing to the balance of reactive power is also present, although not shown in the aforementioned figures. In contrast to these figures, Figure 11 illustrates an electrical and control diagram in which, for example, one embodiment of each of the two droop control loops—namely, the active power loop, denoted P, and the reactive power loop, denoted Q—is represented. Each of the two loops is identifiable in Figure 11 by its interaction with either the active power (P) or the reactive power (Q). e. “Droop profile”, a profile defined in the fre^ plane as a set of steady-state operating points on which a given generator can stabilize, this set of operating points being defined by the implemented droop strategy. During transients, i.e., outside the steady state, the operating point of each generator may be outside this profile; f. "frequency at a point in a network", the frequency of the sinusoidal voltage at that point in the network.

[0055] As indicated, malfunctions of the conventional droop strategy appear if it is implemented on a generator that interfaces an intermittent energy source with the AC electrical grid. These malfunctions are notably due to the fact that the available active power p^P, which is then time-varying, may be less than the maximum active power assigned f^nux ass to the generator.

[0056] To illustrate these malfunctions, consider Figure 3, which, like Figure 2, represents the lp profiles of two inverters controlled with the strategy of conventional droop, but this time, unlike the case discussed in Introduction, a first inverter that interfaces an intermittent energy source the second inverter being associated with a non-intermittent energy source. According to the scenario illustrated according to which p^ls:P^ < p™ax the electrical network al The alternating current can stabilize, that is, reach a steady state, at operating point A of the first inverter and at operating point A' of the second inverter. The first inverter then provides an active power very close to its active power available p^P, while the active power of the second inverter is well below its available active power pf^P. Consequently, the second inverter will have a improved dynamic response to disturbances in the alternative electrical grid, such as in the event of increased demand. Furthermore, if the network alternating electrical current stabilized at operating point B of the first inverter and at operating point B' of the second inverter, the first inverter should then provide a active power greater than its available active power p^isP, which should

[0057]

[0058] causing its disconnection from the grid. It is therefore clear from this example that the conventional droop strategy does not guarantee a correct allocation of active power between grid-connected generators, regardless of the steady-state operating conditions to be achieved, when at least one of the generators interfaces an intermittent energy source with the AC grid. Furthermore, even if the first inverter were 'over-utilized', allowing the grid to reach steady state, the frequency at operating point B would be greater than / , and consequently, no protective measures could be activated solely on the basis of the frequency value (fit). It can then be concluded that, in this case, the frequency value / ( / ) does not accurately signal whether the generators are reaching their active power limits. The invention described below proposes a control strategy that allows an inverter to contribute to maintaining the active power balance of the AC electrical grid to which it is connected, by regulating the frequency at an output point of the inverter. This strategy can therefore be called a droop strategy. And like the droop strategies known in the prior art, the strategy proposed herein has the major advantage of requiring, in order to contribute to maintaining the active power balance of the AC electrical grid, no communication link, particularly between the different generators and / or loads connected to the AC electrical grid and / or with a server connected to the grid. Unlike prior art droop strategies, in the case where one of the generators connected to the network is an inverter interfacing an intermittent energy source, the droop strategy proposed here makes it possible to guarantee a correct allocation of active powers among the different generators connected to the AC electrical network and to guarantee correct signaling, through a measurement of the frequency f(t\ of the reaching of their active power limits by each generator, which allows the activation of protection measures in particular configured so that, if a generator goes out of its active power range, located by definition between its minimum assigned power pmln ass and its available power pdi^pi A it returns to its active power range.

[0059] As already announced above, the droop strategy proposed here is, like the droop strategies known in the prior art, "decentralized", that is to say, it can be implemented independently on each generator connected to the alternative electrical network.

[0060] Not only does its implementation therefore not require communication links, as already indicated above, but also the possible activation of protection measures by implementation of the droop strategy proposed here does not require communication links either, in particular between the different generators and loads connected to the alternative electrical network or with a network server.

[0061] It should also be noted that the droop strategy proposed here, whatever its embodiments which are described below, is suitable for any alternating electrical network, regardless in particular of its number of phases (these networks are most often single-phase or three-phase, but can, alternatively, include two phases or more than three phases).

[0062] With reference to Figures 4 and 5, a first embodiment of the droop control loop 5 according to the first aspect of the invention is described below.

[0063] Figure 4 shows an inverter 1 which, as a generator, interfaces an intermittent energy source 2, and the control scheme corresponding to the first embodiment mentioned above of the droop loop 5 proposed herein. This scheme is composed of the first and second "branches", referenced 11 and 12 and denoted a, which are described below.

[0064] The droop control loop 5 illustrated in Figure 4 allows, like the other embodiments described below, the implementation of a droop control method for an inverter 1 intended to interface an intermittent energy source 2 with an AC power grid 3 by regulating the frequency f(t) of the connection point 4 of the inverter 1 to the grid 3. The grid 3 potentially contains, in a non-imitative manner, loads and / or other generators that interface with intermittent energy sources and / or generators that interface with non-intermittent energy sources. It is assumed that all generators operate in 'voltage source' (or 'grid-forming') mode, and that functional droop control loops are implemented on each of these generators.For example, the conventional droop control loop can be implemented on inverters that interface with non-intermittent energy sources, and the proposed droop control loop 5 can be implemented on inverters that interface with intermittent energy sources. If there are generators operating in 'current source' mode (or 'grid-feeding' or 'grid-following' mode), their operation can be likened to that of loads drawing negative active power from the grid.

[0065] In order to understand the operation of the droop control loop 5 illustrated in Figure 4, Figure 5 shows the profiles of a first inverter and a second inverter connected to the same AC power grid: the first inverter interfaces with an intermittent power source and is controlled with the droop control loop 5 illustrated in [Fig.4]; the second inverter interfaces with a non-intermittent power source and is controlled with a conventional droop control loop.

[0066] It should be noted here that the droop control loop 5 illustrated in [Fig. 4], as well as those illustrated in Figures 6 and 7, are preferably each implemented in the form of a computer program product comprising instructions which, when executed by at least one processor, carry out the steps of the corresponding static control method. The hardware on which each of the computer program products can be executed more particularly comprises a microprocessor and / or an analog card and / or a computer. Furthermore, the three blocks illustrated at the top of each of Figures 4, 6, and 7, entitled respectively "electrical conditioning circuit and intermittent power source," "inverter," and "electrical filters," are preferably hardware components or comprise such components, and for example, switches, capacitors, resistors, etc. According to the illustration in [Fig.4], this also being true for the illustrations given by figures 6 and 7, the conditioning circuit of the intermittent power source 2 transmits a direct current to the inverter 1, and the inverter 1 transforms this direct current into an alternating current, to transmit the latter to electrical filters 100, configured to filter the alternating current produced by the inverter 1 before transmitting it to the alternating electrical network 3, so that the alternating current produced by the inverter 1 can be distributed to the various loads connected to the network 3. .

[0067] The method is implemented according to a plurality of input parameters, including: a. a constant fmax defining the maximum frequency limit of network 3, b. a constant fmm defining the minimum frequency limit of network 3, c. a constant p^'^ defining the maximum active power assigned to Inverter 1, d. a constant p™'" ass defining the minimum active power assigned to the inverter 1, e. a measure of active power P(t) that inverter 1 supplies to network 3 at time t, and f. a measurement or estimation of the available active power p^^PN j in Inverter 1 at this moment

[0068] The various measurements mentioned above are preferably all carried out locally, that is to say at or around the inverter 1, in particular to justify the "decentralized" aspect of the process according to the first aspect of the invention. These measurements may involve one or more measurement processing units. These units may themselves implement, or even include, measuring devices, and in particular for measuring alternating or direct current and / or alternating or direct voltage, as shown in Figures 4, 6 and 7 by the "measurement processing" blocks and the long dashed lines that connect said blocks to the locations in system 0 where the measurements can be carried out, typically on either side of the inverter 1 and at the output of the electrical filters 100.The various means of carrying out the measures necessary for implementing the process according to the first aspect of the invention are not described herein either, as they are presumed to be known to a person skilled in the art.

[0069] Based on the aforementioned input parameters of the process according to the first aspect of the invention, the latter first comprises a step consisting of implementing: a. A first control branch 11, denoted a, which is configured to calculate a first frequency setpoint y''A'). and b. A second control branch 12, denoted , which is configured to calculate a second frequency setpoint j

[0070] A second step of the process consists of adding the first and second frequency setpoints to obtain the final frequency setpoint, ^rei y, which is sent to the internal control loops 10 illustrated in [Fig. 4]. The mathematical expression corresponding to this step is: [MATH 7]

[0071] As illustrated in [Fig. 4], the first control branch 11 can be implemented through several control functions, and it can include: a. two multipliers by a constant, this constant being defined by mP for one and by "mP" for the other, b. two subtractors, one to calculate P(t) - Pnm ass and the other to calculate c. two adders, one to calculate false(t) and the other to calculate

[0072] The mathematical expression that defines the first frequency setpoint given by the first branch 11 is: [MATH 8] (t) -mp* (P(t) -P1^ where y— +mpX^P^ .p^ and _çjjnax J-min'} / {jÿitax ass jpnm «svj

[0073] The second control branch 12 can be implemented through several control functions, and it can include: a. a subtractor for calculating ass _ b. a proportional-integral regulator 121, denoted PLI in [Fig. 4], and c. a saturation function 122.

[0074] The mathematical expression that defines the second frequency setpoint given by the second branch 12 is: [MATH 9] f(t) = max(aux 1(t), 0)'or: auxl(t) = KPpj *(pminai^ ) +Kipi ^pm^-p( t) ydr where Kp is the proportional gain of the first proportional-integral regulator 121 and Kipi r the integral gain of the first proportional-integral regulator 121, are pa Ramers greater than zero and predetermined according to the inverter 1 concerned. It It should be noted that the first term of the function aux 1 ( t ) (i.e., -A4)' is called the "proportional term of the regulator 121", and the second term of the function auxl(t) (i.e., is aPPe^ * integral term of the regulator 121.

[0075] The function amT(t) is a proportional-integral controller equation with a so-called "parallel" architecture. Other PI 121 controller architectures, for example a "series" architecture, would also be valid. A person skilled in the art is presumed to know how to adapt the function "M.ïl(t)" to said other architectures, for an identical technical effect and a result of the same nature.

[0076] The two gains KPpix and K>PI} are predetermined parameters prior to implementation of the control method according to the first aspect of the invention. They are preferably predetermined individually for each inverter 1 on which the control method is to be implemented, since the dynamic response of the inverter 1 depends on its characteristics and the AC power grid 3 to which it is connected. Different tuning processes can be used, and for example, The analysis of the time response of system 0, the analysis of the frequency response of system 0, the pole placement method, or other processes considered to be known to a person skilled in the art, and which are therefore not detailed further here. These processes are considered to be known to a person skilled in the art, and are therefore not detailed further here.

[0077] For inverter 1 in Figure 4, if p”1™ ass -P(t) < 0, the second frequency setpoint ^ref~Pconverge towards a zero value.

[0078] Indeed, if pnmass-P(t) < 0: a. the proportional term of regulator 121 becomes strictly less than zero, and b. the integral term of regulator 121 decreases.

[0079] Consequently, the variable auxl(t) decreases and eventually becomes strictly negative. The second frequency setpoint is equal to auxl(t) as long as the latter is greater than or equal to 0, but the second frequency setpoint ÿrepp^ f remains equal to 0 when auxl(t ) becomes strictly negative, through the saturation function 122 illustrated on [Fig.4].

[0080] Consequently, if pn,n 0X3 - P (t) < 0, the second frequency setpoint y «77^^ will converge to a zero value and the value of yre7 (y) will depend only on the first branch 11, since fef t) =

[0081] The operation of the first branch 11 can be explained in the manner proposed below by describing two operating scenarios, it being understood that these two scenarios are given by way of illustration and not by way of limitation, others scenarios which are of course potentially observable.

[0082] In the first scenario, the network 3 of Figure 4 is initially in a steady-state condition such that the inverter 1 injects an active power P(t) with P'''' ass _ p ( < q and J^P ■ P(t) > 0 and its setpoint frequency is greater at the minimum network frequency (j'ref (j) > ^min\ Assuming that a disturbance occurs in the network, such as an increase in the active power consumed by the loads, the generators connected to network 3 then immediately increase their active power, in accordance with their 'voltage source' operating mode. On each generator, the increase in active power then causes a decrease in the setpoint frequency defined by its droop control loop. More precisely, on inverter 1 in Figure 4, and according to the first branch 11 described previously, the frequency decreases following a linear function with slope ” mP-

[0083] The electrical laws of the network force the setpoint frequencies of all generators connected to network 3 to converge to the same value. Through the droop loops implemented on each generator, if the total active power drawn from the network is, after losses, strictly less than the sum of the available active powers of all the generators, then each generator stabilizes at an operating point where: a. its setpoint frequency has a value strictly greater than and b. its active power has a value less than or equal to its active power available.

[0084] More precisely, the inverter 1 of [Fig.4] converges at an operating point where p(t) < which, according to the first branch 11 defined previously, translates as follows: fref(t) =fref-a(t) = (0 -mp* (P(t) -P"™

[0085] Using a complementary graphical explanation, after a disturbance in the network such as an increase in the active power consumed by the loads, the droop control loops force the generators to converge to steady-state operating points that belong to specific profiles in the plane (p). These profiles are constructed so that each generator increases its

[0086]

[0087] Active power is determined according to its operating margin, ensuring that no generator converges to an operating point located above its available active power, if there are other generators in the network whose active power is less than or equal to their available active power. Furthermore, if a generator converges to an operating point where it provides active power equal to its available active power, or less than its available active power but close to that limit, this necessarily implies that each of the other generators in the network also provides active power equal to its available active power, or less than its available active power but close to that limit. More precisely, for inverter 1 in Figure 4, if p''m ass - P(t) < 0 and with _ p^f) > (), this profile is defined by the action of the first branch 11, and consists of a segment of slope ~ inP which starts at point / ' According to the first branch 11 defined previously, this implies that the segment with slope “mP ends at the point ym / nj. It is important to note that if p^^P^ varies, this segment moves from right to left or from left to right in the plane jp fre^ following the point {pd^P^ and maintaining its slope mP. This is explained by the dependence of the variable / ^^) on the available active power ^^( ^) (i.e., (?) = jmin + x ( pdisp( ^ ) _ pmin j ), which translates the fact that f™* ( ? ) increases or decreases if ^) increases or decreases, respectively.

[0088] With reference to the operating profiles illustrated in Figure 5, the slope segment 'mP' is represented by the reference element 1001 associated with the first inverter. A possible steady-state for this network corresponds to operating point A for the first inverter and operating point A' for the second inverter. If a disturbance such as an increase in the active power consumed by the loads occurs, the droop control loops of the first and second inverters force them to converge to operating points on the drawn profiles, such as operating point B for the first inverter and operating point B' for the second inverter. It can be seen that, between the steady-state corresponding to operating points A and A' and the steady-state corresponding to operating points B and B', the first and second inverters have increased their active power, but neither has exceeded its available active power.Furthermore, if one of the first and second inverters supplies the network with an active power equal to or less than its available active power, but close to this limit, this necessarily implies that the other of the first and second inverters also supplies an active power equal to or less than its available active power, but close to this limit (See points B and B').

[0089] In the second scenario, which serves to explain the operation of the first branch 11, the network 3 in Figure 4 is initially in a steady-state condition such that the inverter 1 injects an active power P(?) with p™1” ass..p(jj < q and ( t) - P(1) > 0 and its setpoint frequency is strictly greater than the minimum network frequency (( / ) > 0). Assuming that a disturbance occurs in the network, such as an increase in the active power consumed by the loads, the generators connected to network 3 then immediately increase their active power, in accordance with their 'voltage source' operating mode. On each generator, the increase in active power then causes a decrease in the setpoint frequency defined by its droop control loop.More specifically, on inverter 1 in Figure 4, and according to the first branch 11 described previously, the frequency decreases following a linear function of slope “mP- .

[0090] The electrical laws of the network force the setpoint frequencies of all generators connected to network 3 to converge to the same value. Through the droop loops implemented on each generator, if the total active power drawn from the network is, excluding losses, strictly greater than the sum of the available active powers of all generators, then in each generator: a. the setpoint frequency evolves towards values ​​strictly less than f"7", and b. Active power evolves towards values ​​strictly greater than the available active power.

[0091] More precisely, the active power of the inverter 1 illustrated in [Fig.4] evolves towards operating points such that p( > p^P^, which, according to the first branch 11 defined previously, translates as follows: [MATH 10] - false (t)-mpx (Pt^-P™ ÆW)

[0092] A crossing of the minimum frequency threshold is then observed which can be used as a signal to activate protection measures, for example implemented using frequency-metric relays which allow to disconnect loads connected to the electrical network and return the network to a functional state where all generators inject into the network active powers less than or equal to their available active powers.

[0093] As explained previously, for inverter 1 in Figure 4, the variable is zero, or converges to a zero value, if pmlnass -p( t ^ < 0. Consequently, the second branch 12 only influences the setpoint frequency fref( if

[0094] The operation of the second branch 12 can be explained in the manner proposed below, by describing two operating scenarios, it being understood that these two scenarios are given for illustrative purposes and not for limiting purposes, other scenarios being of course potentially observable.

[0095] In the first scenario, network 3 of [Fig.4] is initially in a steady-state state such that inverter 1 is at the operating point corresponding to the activation limit of the second branch 12, i.e. with: [MATH 11] pminas.^p^ _ Q and rf(n= +o= r (t)-mPx (p^y -p™=rx (o

[0096] Assuming further that p^Pf j < pmax |a value of the reference setpoint is given by the following expression: ^ref _ false (' / ) < f™1*- We assume fi finally that there is at least one other generator whose active power injected into the network is strictly greater than its assigned minimum active power.

[0097] With reference to the droop profiles illustrated in [Fig.5], the initial state described above corresponds to the operating point C for the first inverter and to the operating point C' for the second inverter.

[0098] If a disturbance occurs in the network, such as a decrease in the active power consumed by the loads, then the generators connected to network 3 immediately reduce their active power output, in accordance with their 'voltage source' operating mode. On each generator, the decrease in active power then causes an increase in the setpoint frequency defined by its droop control loop. More precisely, on the inverter 1 in Figure 4, the aforementioned decrease in active power implies that pmmass > q. Consequently, and according to the second branch 12 defined previously: a. the proportional term of regulator 121 becomes strictly greater than zero, and b. The integral term of regulator 121 increases progressively.

[0099] Consequently, the variables f) and become strictly su greater than zero and gradually increase. This implies a gradual increase in the frequency setpoint value y'ef. It should be noted that the gradual increase in the frequency setpoint value yreJ ( / ] nc only stops when the input of the integral term of the regulator 121 becomes zero, that is, when pmln ass -P(t) = 0-

[0100] By the electrical laws governing the network, the gradual increase in the frequency setpoint of inverter 1 forces the other generators in the network to decrease the active power they inject. This allows inverter 1 to increase its active power P(t) and for it to become equal to its minimum rated active power. When pm1 - P(t) = 0, the integral term of the regulator 121 stabilizes; it neither increases nor decreases. Consequently, the variables t), yt, yt, and yf also stabilize.

[0101] The electrical laws of the network force the setpoint frequencies of all generators connected to network 3 to converge to the same value. Through the droop loops implemented on each generator, if the total active power drawn from the network is, after losses, strictly greater than the sum of the minimum assigned active powers of all the generators, then each generator stabilizes at an operating point where: a. its setpoint frequency has a value strictly less than fma\ and b. its active power has a value greater than or equal to its minimum assigned active power.

[0102] More specifically, on the inverter 1 of figure 4, and according to the second branch 12 described above, P( f ) becomes exactly equal to p"2'" due to the influence of the integral term of the regulator 121.

[0103] It is important to note that, throughout the process described in the paragraphs above, the first branch 11 of the inverter 1 is active and increases or decreases the first frequency setpoint when the active power P(t) decreases or increases, respectively, but the effect of the integral term of the regulator 121 is dominant, causing the active power P(t) to converge towards pmin ass in steady state, and, according to the definition of the first branch 11 given previously, causing the first frequency setpoint to converge towards f™** ( / J.

[0104] Using a complementary graphical explanation, after a disturbance in the network such as a decrease in the active power consumed by the loads, the droop control loops force the generators to converge to steady-state operating points that belong to specific profiles in the plane {p freJy These profiles are constructed so that each generator reduces its active power according to its margin of maneuver, ensuring that no generator converges to an operating point below its assigned minimum active power, if there are other generators in the network whose active powers are greater than or equal to their assigned minimum active powers.

[0105] More precisely, for the inverter 1 of Figure 4, if ass -P(t) > 0- the droop profile fp is defined by the action of the second branch 12, and consists of a vertical segment that starts at point {pnnn} and ends at point |pmln ass^ fmarj. This profile ensures that the active power P(t) does not remain less than p>nmass if there are other generators whose active power is greater than their assigned minimum active power.

[0106] As explained previously, and according to the definition of the first branch 11, the variable f^Çt) depends on the available active power (i.e., false (?) = ^min mp x ( j _ pmin axs j )• Thus, the variable fa“x (j ) increases or decreases, if the available active power pd^P ( increases or decreases, respec tively. It is important to note that the aforementioned vertical segment corresponds to the second branch 12: has. b. lengthens when the variable decreases and contracts if (?) increases; and in this way, this vertical segment always starts at point p1™1 ) ].

[0107]

[0108]

[0109] It is also important to note that the points of intersection between the segments corresponding to the first branch 11 and the second branch 12 coincide at f nmin ass r-aux / x | With reference to the droop profiles illustrated in [Fig. 5], the aforementioned vertical segment is represented by the referenced element 1002 associated with the first inverter. A possible steady-state state for this network corresponds to operating point C for the first inverter and operating point C' for the second inverter. If a disturbance occurs, such as a decrease in the active power consumed by the loads, the droop control loops of the first and second inverters force them to converge to operating points on the drawn profiles, such as operating point D for the first inverter and operating point D' for the second inverter.It is observed that, between the steady-state state corresponding to operating points C and C' and the steady-state state corresponding to operating points D and D', the first inverter maintains the same active power, equal to its minimum rated active power, while the second inverter decreases its active power, without however falling below its minimum rated active power. In the second scenario intended to explain the operation of the second branch 12, the network 3 of figure 4 is initially in a steady state such that the inverter 1 injects an active power such that pm'n asx-P( t) = 0 and its setpoint frequency given by the expression: (0 +f My (cref-p) has a value such that ^ax. We finally assume that there is at least another generator whose active power injected into the network is strictly greater than its assigned minimum active power.

[0110] If a disturbance in the network, such as a decrease in the active power consumed by the loads, occurs, the generators connected to the network 3 immediately reduce their active power, in accordance with their 'voltage source' operating mode.

[0111] On each generator, the decrease in active power causes an increase in the setpoint frequency defined by its droop control loop.

[0112] More precisely, on inverter 1 in Figure 4, a decrease in active power results in p™™ 0™ > q. Consequently, and according to the second branch 12 defined previously: a. the proportional term of regulator 121 becomes strictly greater than zero, and b. The integral term of regulator 121 increases progressively.

[0113] Consequently, the variables t) t) become strictly su greater than zero and gradually increase. This implies that the value of the reference frequency j-ref increases gradually.

[0114] The electrical laws of the network force the setpoint frequencies of all generators connected to network 3 to converge to the same value. Through the droop loops implemented on each generator, if the total active power drawn from the network is, after losses, strictly less than the sum of the minimum assigned active powers of all the generators, then in each generator: a. the setpoint frequency evolves towards values ​​strictly greater than rmax, f, and b. the active power evolves towards values ​​strictly lower than the minimum assigned active power.

[0115] More precisely, on the inverter 1 of Figure 4, and according to the second branch 12 described above, this is done by means of the integral term of the regulator 121. If P( ? ) remains strictly less than pminass^ |c integral term of the regulator 121 continues to increase the value of and the setpoint frequency eventually becomes strictly greater than -f™0*,

[0116] It is important to note that, throughout the process described in the paragraphs above, the first branch 11 of the inverter 1 is active and increases or decreases the first frequency setpoint when the active power P(t) decreases or increases, respectively, but the effect of the integral term of the regulator 121 is dominant, and the frequency setpoint j^ref increases progressively.

[0117] Crossing the maximum frequency threshold fmaA can be used as a signal to activate protection measures, for example implemented using frequency-metric relays which allow disconnecting generators connected to the electrical network and returning the network to a state where all generators inject active powers into the network greater than or equal to their assigned minimum active powers.

[0118] It is concluded that the combination of the first and second branches 11 and 12 gives rise to a droop 5 control loop which retains the attributes that are those of the conventional droop 5 control loop when applied to a source non-intermittent energy 2. More specifically, the combination of the first and second branches 11 and 12 ensures a correct allocation of active power between the generators, because, through the first branch 11, no generator converges to an operating point located above its available active power if there are other generators in the network whose active powers are less than or equal to their available active powers.

[0119] By means of the first branch 11, if a generator converges to an operating point where it supplies an active power equal to its available power or less than its available active power, but close to this limit, this necessarily implies that each of the other generators in the network also supplies an active power equal to its available active power or less than its available active power, but close to this limit.

[0120] By means of the second branch 12, no generator converges to an operating point located below its assigned minimum active power if there are other generators in the network whose active powers are greater than or equal to their assigned minimum active powers.

[0121] Correct signaling that the inverters have reached their active power limits is achieved by measuring the frequency, because, via the first branch 11, if the total active power drawn from the network is, within losses, strictly greater than the sum of the available active powers of all the generators, then in each generator: a. the setpoint frequency evolves towards values ​​strictly less than fmin, and b. Active power evolves towards values ​​strictly greater than the available active power.

[0122] Via the second branch 12, if the total active power drawn from the network is, within losses, strictly less than the sum of the minimum rated active powers of all the generators, then in each generator: a. the setpoint frequency evolves towards values ​​strictly greater than / ' and b. the active power evolves towards values ​​strictly lower than the minimum assigned active power.

[0123] A second embodiment of the control method according to the first aspect of the invention is described below with reference to Figures 5 and 6. This second embodiment can be considered a variant of the first embodiment described above. Indeed, the second embodiment conforms to the first, except that the implementation of the second control branch Order 12: a. is also a function of: i. a measurement of the DC voltage vdc(t) at the input of inverter 1, and ii. a setpoint value of the DC voltage v^c ref(t) at the input of inverter 1, and b. further includes the implementation of a first proportional regulator 123, referenced P - 1 on the [Fig.6].

[0124] Note that the setpoint value of the DC voltage ref(t) is the setpoint value of the input voltage of the inverter 1. It can be constant or variable over time, depending on how the DC circuit located upstream of the inverter 1 is constructed and controlled. It is preferable that the measurement of the DC voltage vdc(t) does not deviate excessively from its setpoint value to ensure the proper operation of the inverter 1 and the energy source 2 with which it interfaces.

[0125] The mathematical expression that defines the second branch 12 according to the second embodiment is: [MATH 12] (t) = max(aux!(t) \ 0) where: «ial(0 = aaJ(t) +Kppl *aux2(t) +Kim *jaiix2{i')dt = KPpj as' ~ P(i] + atix2(t) ) +Klp / - P(i] + aux2( t) )dt , Or : aux!(t) - Kp *( ( t) -vdc ref (t)}, / “ 1 where Kpp_v, the proportional gain of the first proportional regulator 123, is a parameter strictly greater than zero and predetermined according to the inverter 1 concerned. It should be noted that the first term of the function û«xl(t) ' (i.e., *(P1™”'7'4 - P ( f ) + aux2( t ) p is called the “proportional term of the regulator 121”, and the second term of the function aux1( t ) ' (i.e., K'pi P 0 ) + aux2 ( 0 ) is called the * integral term of the regulator regulator 121.

[0126] The function auxi([ÿ] is a Proportional-Integral controller equation with a so-called "parallel" architecture. As already stated previously, other PI controller architectures, for example a "series" architecture, would also be valid. A person skilled in the art is presumed to know how to adapt the function awxl(t)' to these other architectures, for an identical technical effect and a result of the same nature.

[0127] The proportional gain of the first proportional controller 123 is a predetermined parameter prior to implementation of the control method according to this embodiment of the first aspect of the invention. It is preferably predetermined For each inverter 1 on which the control process is to be implemented, the dynamic response of inverter 1 depends on its characteristics and the AC power grid 3 to which it is connected. Various control processes can be used, such as time-domain response analysis, frequency-domain response analysis, pole placement methods, or other processes considered to be known to those skilled in the art, and which are therefore not described in detail here.

[0128] The variant described here of the second branch 12 performs all the functions provided by the second branch 12 of the first embodiment described above. Additionally, it further ensures that, in steady state, the measurement of the DC voltage vdc(t) is equal to the setpoint value of the DC voltage ref if the inverter 1 stabilizes at a steady-state operating point with P(t) equal to p^“^,

[0129] This additional function of the variant of the second branch 12 is provided by the term aux2{t}, illustrated in Figure 6, which is added to the input of the Proportional-Integral controller 121. As explained previously, the second frequency setpoint fre^{t} does not stabilize until the input of the integral term -1 becomes equal to zero. In the variant of the second branch 12, the input of this integral term is P"™ ass _p^ + aux2 (t) = P”"" aXS - P (t)+ KPpi * ( (t) - (t)) • For If this input is equal to zero, the active power P(t) must be equal to the minimum rated power pmnass and the measured DC voltage ) must be equal to the setpoint value of the DC voltage ydc ret(t). The integral term of the regulator 121 then ensures that, in steady state, is equal to vdc reJ(t) if P(t) is equal to pmtnass.

[0130] Note that, ordinarily, a control loop (outside the droop control loop) is provided which ensures that the measured DC voltage vd(- ( t) is equal to the setpoint value of the DC voltage ref ( / ). However, this 'ordinary' control loop saturates and shuts down when cp, hence the usefulness of the present variant of the second branch 12. It is important to ensure that the DC voltage vdc{ t) is equal to or close to the setpoint value of the DC voltage ydc ref ( t), otherwise malfunctions of the inverter 1 and / or the power source 2 that it allows to interface may occur.

[0131] It is envisaged that the measurement or estimation of the available active power The power output (P^^t) of an inverter 1 interfacing an intermittent energy source 2 may be erroneous and differ from the actual available active power, which is denoted p^lsP This is problematic, even dangerous, in the case where p^^P réU,^^ < P^'1^ because inverter 1 can converge to an operating point with (actual pdisp) < p pdisP p outside its active power range. According to the definition of the first branch 11 given previously, at such an operating point, the setpoint frequency of inverter 1 would be fref (yj > fmin). Consequently, no protection measures would be activated, and this would cause the gradual discharge of the capacitors placed after inverter 1 until its disconnection.

[0132] To address this possibility, a third embodiment of the process according to the first aspect of the invention is proposed, which is described below with reference to Figures 7 and 8.

[0133] This third embodiment conforms to at least one of the first and second embodiments, except that the method according to the third embodiment further comprises a step of implementing a third control branch 13, denoted Y in Figure 7, configured to calculate a third frequency setpoint ^rePv

[0134] The implementation of this third branch 13 is further dependent on: a. a measurement of the DC voltage at the input of the inverter 1, and b. a setpoint value for the DC voltage ydc ref(^ at the input of the inverter 1.

[0135] The implementation of this third branch 13 may further include the implementation of: a. a second proportional-integral regulator 131, referenced PI-2 on the [Fig.7] b. a second saturation function 132, and c. of a second proportional regulator 133, referenced P - 2 on the [Fig.7].

[0136] The step used to calculate the final frequency setpoint consists of adding the first, second, and third frequency setpoints. The equivalent mathematical expression is: [MATH 13] rPi

[0137] The mathematical expression that defines the third branch 13 is: [MATH 14] fre&r ( t ) = min ( aux3 ( t ), 0)'ou : aux^t) = b^-PM)+K <pl2 U!{t)-P(t) )*dr +am4(ty and awx4(t) = KPp2 * (vù'(t) - ref(t)), where Kppp^, the proportional gain of the second proportional-integral regulator 131, ^iPI_2, the integral gain of the second proportional-integral regulator 131, are greater than zero parameters predetermined according to the inverter 1 concerned, and ^pp 2, the proportional gain of the second proportional regulator 133, is one of the parameter strictly greater than zero and predetermined according to the inverter 1 concerned. It should be noted that the first term of the function m / x3(t) (i.e., Kp p^P bls^ - P( t ) p is called the "proportional term of the regulator 131", and that the second term of the function aux3(t) (i.e., g(pdisp_pp)) is called the "integral term of the regulator 131". The function ÆWA:3(t) is a proportional-integral regulator equation with a so-called "parallel" architecture. As before, other PI regulator architectures, for example, a "series" architecture, would also be valid. A person skilled in the art is presumed to know how to adapt the function wx3(t) to these other architectures, for an identical technical effect and a result of the same nature.

[0138] The three gains Kppi 2- 2 and KPp ^ are predetermined parameters before im Implementation of the control method according to the first aspect of the invention. These are preferably predetermined individually for each inverter 1 on which the control method is to be implemented, since the dynamic response of the inverter 1 depends on its characteristics and the AC power grid 3 to which it is connected. Various tuning processes can be used, for example, time response analysis of the system, frequency response analysis of the system, pole placement methods, or other processes considered to be known to those skilled in the art, and which are therefore not described in further detail here.

[0139]

[0140] The role of the third branch 13 is significant only in the case where pdisp real < p < pdispQn explains below the operation of the third branch 13 in the other possible situations. If p( i ) > p^!sP , the first control branch 11 already ensures that the frequency setpoint decreases below the minimum limit of frequency fmm and thus enabling the activation of protection measures on the sole basis of the value of the frequency f(t). The third control branch 13 contributes, for its part, to the decrease of the frequency setpoint freJ by decreasing the third frequency setpoint fref'Y ( in the manner explained below).

[0141] Always if p(j} > , but also if: a. ydc ( ? ) < ydc ref (?) (sip(?) > p#isP real, because the external control loop which normally controls vdc(t) saturates) or b. vdc(t) = Vdc(?) (if P(r) < p^isPréelle / j, due to the loop of external control which, ordinarily, does not saturate), the input of the PI 131 regulator, equal to pdisp biS^ ^pdisp ^dcref^ ) _p(z), is then negative, and: c. The proportional term of PI - 2 becomes strictly less than zero, and d. The integral term of PI - 2 decreases.

[0142] Consequently, the variables auxSÇt) and become strictly in less than zero and gradually decrease.

[0143] If < ^^( ?) ct P(t) < P^isp 'a third frequency setpoint ^■ref-yç^ CS( saturated at zero and the action of the third control branch 13 disappears.

[0144] In this situation, vdc(t) = ref(t), because of the external control loop which, ordinarily, controls ydc(t), is not saturated because p(t) < p^lsP real

[0145] The input of the PI 131 regulator, equal to pdlsp bis^_p^= pdtsp *( ydc( t ) _ ydc ref (j _ p ), is then strictly greater than zero, the proportional term of PI - 2 becomes strictly greater than zero, and the integral term of PI - 2 gradually increases.

[0146] Consequently, the variable aux3(î) increases and eventually becomes strictly positive. The variable is equal to aux3(j) as long as the latter is in less than or equal to 0, but ^ref-yç^ remains equal to 0 when aux3(t) becomes strictly positive, through the saturation function 132 of [Fig.7].

[0147] We conclude that the role of the third branch 13 is important only in the case where pdùp <P^t) <Pdisp(t) On peut expliquer le fonctionnement de la third branch 13 in this situation considering the operating scenario described below, it being understood that this scenario is given for illustrative purposes and not as a limitation, other scenarios being of course potentially observable.

[0148] In this scenario, the network 3 of Figure 7 is initially in a steady-state state where the inverter 1 injects an active power P(t) with P(t) > Pm!n ass and P(t) < pdisp rée^Ie^, and its setpoint frequency is ■ We assume also that pdispréelleOn supPeste encore that there is at least one other generator whose active power injected into the network is strictly less than its available active power.

[0149] Considering that a disturbance in the network, such as an increase in the active power consumed by the loads, occurs, then the network 3 would reach, in steady state, a new state for which the active power of the inverter 1 would be such that pdisp real Çt^ < Pij} < pdisfJ Çonly the first and second branches 11 and 12 were implemented on the inverter 1. According to the definition given above of the first branch 11, the setpoint frequency would still (t) > fmin and consequently, no protective measures would be activated. The third branch 13 advantageously prevents the occurrence of such a malfunction, as explained below.

[0150] Given that pdisp is real, the capacitors located upstream of the inverter are discharge, which causes the progressive drop in voltage vdc(t).

[0151] The input of the PI 131 regulator, equal to P^ bis = pdisp + ( vclc ref ends by becoming negative, the proportional term of PI - 2 becomes strictly less than zero, and the integral term of PI - 2 gradually decreases.

[0152] Consequently, the variables aux3(t) and freP?(A become strictly in less than zero and decrease. Consequently, the freight frequency setpoint decreases. The advantage of decreasing the frequency setpoint when pdisp bis^p} -P(t) <0' is 9ue 'cs other inverters of network 3 are then pushed to increasing the active power they supply (due to the electrical laws governing the behavior of network 3). This allows the first inverter 1 to decrease its active power P(t) until it becomes equal to pdisp (i.e., pdisp bis~ P (j) = 0^ When (fj — 0' 'c integral term of PI -2 stabilizes; it neither increases nor decreases. Consequently, the variables Mix3(t) and also stabilize.

[0153] The key to the third branch of control 13 is then to know at what value the auxiliary variable p^'^P ^0 stabilizes. Two conditions define the value of pd^p; a. To stop the voltage drop vde(t), it is necessary that the active power P(t) of the first inverter 1 decreases and becomes equal to p^lisp real^ Qi b. To stabilize the integral term of the PI 131 controller and the third setpoint fref'v(X, it is necessary that P(t) becomes equal to the auxiliary variable

[0154] Consequently, the third control branch 13 will force the first inverter 1 to go to the only steady-state operating point that satisfies the two preceding conditions: p(ip _ pdisp bis _ pdisp real^

[0155] Note that, in order for pd'^P to be equal to the real prf^P, the PI 131 regulator will allow the voltage vdc(j) to stabilize slightly below the setpoint value ^lc ref VU that = ^(,) +^4(,) =^(,) +Kl,p_p(\-ift)-v*"f(t) )■ To prevent the voltage from deviating too far from the setpoint value ydc ref ( t ), it is preferable to implement a sufficiently large gain Kp. For example, if the setpoint value y* ref (?) is constant, and to prevent the voltage y^'( ) from stabilizing below a threshold called vdcmint, a gain equal to or greater than: , where is an estimate of the maximum possible difference between the actual available active power pdisp and the active power available p^PÇj} as measured or estimated.

[0156] Note that, ordinarily, a control loop (outside of the control loop droop 5) is provided which ensures that the measurement of the DC voltage f) is equal to the setpoint value of the DC voltage ydc ref. However, this 'ordinary' control loop saturates and shuts down when > p4™P, which is why vdc(t) can stabilize below ref(t).

[0157] Using a supplementary graphical explanation, and with reference to Figure 8, after a disturbance in the network such as an increase in active power consumed by the loads, the droop control loops force the generators to converge towards steady-state operating points that belong to specific profiles in the plane (p fre^- The proposed droop loop 5 gives rise to a profile {p that prevents inverter 1 from converging towards an operating point with pdisp real< P(j \ <pdisp(t) s’il existe d’autres générateurs dans le réseau dont les puissances actives sont inférieures ou égales à leurs disponibles. en termes, si pdisp réelle< p^< ce profil ip fref\ selon la troisième mode de réalisation l’invention est défini par l’action the third branch 13 and consists of a vertical segment 1003 which goes from the point pdisp real^ | at the point of intersection between the segment 1001 corresponding to the first branch 11 and the vertical placed at p( _ pdisp real (that is, the point {pdisp real^ ^aux _mpX {pdisp real _ pmin „)}).

[0158] It should be noted that this vertical segment 1003 moves from right to left or from left to right, when the actual pdisp varies.

[0159] It should also be noted that, when this segment 1003 is activated (i.e. when the active power enters the interval pdisp real^^ < pÇ^ < pdisple segment 1001 corresponding to the first branch 11 contracts, so that the end points of the two segments corresponding to the first and third branches 11 and 13 coincide.

[0160] Considering the lp profiles of [Fig.8], the initial state of the scenario described above- The point above could correspond, for example, to point A for the first inverter and point A' for the second inverter. After a disturbance such as an increase in the active power consumed by the network loads, and if only the first and second branches 11 and 12 were implemented on the first inverter, the network could reach a new steady-state state corresponding to point B for the first inverter and point B' for the second inverter. The action of branch 13 forces the first inverter to decrease its active power, bringing the network to a state that could correspond, for example, to point C for the first inverter and point C' for the second inverter.

[0161] The third control branch 13 functions correctly in the Systems where the energy source 2 is not directly connected to the capacitors placed upstream of the first inverter 1, that is, insofar as the voltage vdc(t) is not directly applied to the source. This is, for example, the case in two-stage photovoltaic power plants, which include a DC / DC converter placed between the photovoltaic array and the capacitors.

[0162] As already specified above, Figure 11 shows an electrical and control diagram of one embodiment of each of two droop control loops, one (referenced 5) relating to active power, denoted P, and illustrating a droop control loop according to any one of the embodiments of the invention, and the other relating to reactive power, denoted Q, which is not directly concerned by the present invention. A comparison between the diagram shown in [Fig. 11] and each of the diagrams shown in Figures 4, 6, and 7 illustrates the structure of a system 0 consisting of an inverter 1 and a power source 2. More particularly, the electrical and control diagram of [Fig. 11] illustrates the same system 0 differently than Figures 4, 6, and 7.

[0163] The invention is not limited to the embodiments previously described and extends to all embodiments covered by the invention.

[0164] In particular, if the proposed droop loop, according to any of the embodiments described above, is essentially dedicated to interfacing an intermittent energy source with the alternating electrical network, it should be noted that it can also be used for interfacing a non-intermittent energy source with the alternating electrical network.

[0165] Furthermore, the various mathematical functions used to define the different branches described above could be replaced by other functions giving equivalent results. For example, the saturation function 122, mathematically defined as max(auxl(t),0), could be written equivalently using logical functions. Similarly, if the aforementioned equations are each given in continuous form as a function of the time variable t, they could be described equivalently in continuous or discrete form, for example using the Laplace transform or the z-transform, which are known to those skilled in the art.

Claims

Demands

1. A method for controlling the static state of an inverter (1) for interfacing an intermittent power source (2) and an alternating current power grid (3) by regulating the frequency f(t) at a connection point (4) of the inverter (1) to the grid (3), the method comprising, as a function of: i. a constant defining the maximum frequency limit of the network (3), ii. a constant fmln defining the minimum frequency limit of the network (3), iii. a constant ass defining the maximum active power assigned to the inverter (1), iv. a constant pmin defining the minimum active power assigned to the inverter (1), v. a measure of active power t) that the inverter (1) supplies to the network (3) at time t and vi. a measurement or estimate of the active power available in the inverter (1) at time • a step consisting of implementing: A first control branch (11), denoted a, configured to calculate a first frequency setpoint satisfying a first control function- command (1001) defined in a plan / p fref ) by the following equation: [MATH 15] = false (t) -mpx (P(t) -P^ ass) where (t) =f™ +mpX -P1™ and fj ass _ plni» ass'} A second control branch (12), denoted / i, comprising the implementation of a first pro-proportional-integral controller (121) and a first saturation function (122) and configured to calculate a second frequency setpoint ri satisfying a second control function (1002) defined in the plane p ^ref j by the following equation: [MATH 16] feHi(t) = max(aux1(t), 0) 'with aux(t) = KPpi*P™^^ ) + Kipi where Kppi-v 8a'n proportional of the first proportional-integral regulator (121) and KiPPP the integral gain of the first pro-proportional-integral regulator (121), are greater than zero parameters and predetermined according to the inverter (1) concerned, and • a step consisting of imposing a setpoint value frequency at the connection point (4) of the inverter (1) to the network (3) determined as a sum of the first and second frequency setpoints .ru» -f'yu +r"(ty

2. A method according to the preceding claim, wherein the implementation of the second control branch (12): • is also a function of: i. a measurement of the DC voltage vdc(t) at the input of the inverter (1), and ii. a setpoint value of 1A DC voltage at the inverter input (1), and • further includes the implementation of a first proportional regulator (123), the first proportional-integral regulator (121), the first saturation function (122) and the first proportional regulator (123) being configured to impose, at the second frequency setpoint a value defined by a variant of the second function of control-command (1002), said variant taking the form of the following equation:

3. [MATH 17] = max(awxl(r)0)'with aux 1 ( f ) = aux 1 {t) + KPp} ]*aux2(t) + Kip[ {t)dr with aux2(t) = Kp *((t) -vdcref (t) ), where KPp, the proportional gain of the first proportional regulator (123), is a parameter strictly greater than zero and predetermined according to the inverter (1) concerned. A method according to any one of the preceding claims, wherein the step of implementing the first and second branches (11 and 12) further comprises, depending on: i. a measurement of the DC voltage ^'(f) at the input of the inverter (1), and ii. a setpoint value of the DC voltage ref(t) at the input of the inverter (1), the implementation of a third control branch (13), denoted Y, comprising the implementation of a second proportional-integral controller (131), a second saturation function (132), and a second proportional controller (133), and configured to calculate a third frequency setpoint satisfying a third control function (1003) defined in the plane [p fre^^ by the following equation: [MATH 18] - min ( auxi( t ), 0 ) 'with aux3(l) = KPp^[p(1^ bli(t)-P(t) ) +Kip[2 *[(P4^ ^-Ptl) ) *dt , with aux4(t) = Kp? * (vdc(t) - V10ref(t)), where ^ppi^ The proportional gain of the second proportional-integral regulator (131), Kj and the integral gain of the second proportional-integral regulator (131) are greater than zero parameters and predetermined as a function of the inverter (1) concerned, and KPp 2, the proportional gain of the second proportional regulator (133), is a parameter strictly greater than zero and predetermined according to the inverter (1) concerned, and in which: the frequency setpoint value fref0 at the connection point (4) of the inverter (1) to the network (3) is determined as the sum of the first, second and third frequency setpoints,

4. A method according to any one of the preceding claims, wherein at least one, preferably each, of said parameters can be predetermined by an analysis of the time response of the inverter and / or by an analysis of the frequency response of the inverter and / or by implementation of a pole placement method.

5. A method according to any one of the preceding claims, wherein the step of imposing the frequency setpoint value at the point of connection of the inverter to the network includes supplying said value to at least one internal control loop (10) of the inverter (1).

6. Product computer program comprising instructions, which when executed by at least one processor carries out the steps of the static control method according to any one of the preceding claims.

7. Control unit for an inverter (1) intended to interface an intermittent power source (2) and an alternating current power grid (3) by regulating the frequency f(t) at a connection point of the inverter (1) to the grid (3), the control unit comprising electronic and / or microelectronic components configured to implement the static control method according to any one of claims 1 to 5.

8. Inverter (1) for interfacing an intermittent power source (2) and an alternating current power grid (3) by regulating the frequency f(t) at a connection point of the inverter (1) to the grid (3) and comprising at least one of the following: • a readable non-transient medium comprising instructions, which, when performed by at least one processor, executes the steps of the static control method according to any one of claims 1 to 5, and • a control unit according to claim 7.

9. Inverter (1) according to the preceding claim, free from any communication link with another generator or server connected to the alternative electrical network.

10. Inverter (1) according to any one of the two preceding claims, wherein a voltage at the point of connection of the inverter to the network is single-phase or polyphase.

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