DEVICE FOR CONTROLLING A TERMINAL DEVICE TO COMPENSATE FOR A VOLTAGE DISTURBANCE

Description

Arrière-plan de l'invention

[0001] The present invention relates to the technical field of multi-terminal high voltage direct current (HVDC) transmission installations and more particularly to a device for controlling a terminal of such an installation.

[0002] Such HVDC installations allow the transmission of electricity over long distances using direct current lines several hundred kilometers long, these direct current lines forming a continuous part of said installations. These installations therefore allow the transmission of direct current, rather than alternating current as is the case in traditional installations. They are particularly used for the transmission of electricity to or from offshore wind farms.

[0003] The terminals of these installations generally allow the conversion of an alternating voltage into a direct voltage and vice versa, these terminals being connected between an alternating power supply network and the direct part of said installation. Each of these terminals supplies or draws power from the direct part of the installation.

[0004] An example of such an HVDC installation 14 is shown on the figure 1 . In this example, first 100, second 200, third 300 and fourth 400 terminals are connected respectively to first 102, second 202, third 302 and fourth 402 AC power supply networks. These four terminals are also connected to a continuous part 16 of the installation via direct current lines. In this example, the fourth terminal 400is connected to a wind farm and transfers to the continuous part 16 of the installation a constant power.

[0005] In practice, the voltage of the DC part of this type of installation is likely to vary. For example, a terminal may break down or be disconnected from the DC part of the installation, or from one of the alternative power supply networks, for maintenance operations. In this case, the terminal no longer supplies or draws power from the DC part of the installation, so that an overall imbalance appears between the power drawn and the power supplied to the DC part of the installation. The power supplied or drawn and the voltage of the DC part increase or decrease together. For example, the fourth terminal 400 may fail, so that the power supplied to the DC part and therefore the voltage of the DC part of the installation decreases.

[0006] Control devices are known according to the prior art for controlling the terminals of an installation in order to compensate for the loss of power of the continuous part, by increasing the power contribution of each of the terminals. 100,200,300 remaining (see for example publications CN105281356 A, CN104821595 A, US2013 / 285460 A1, GB2537684 A, WO2012 / 000548 A1).

[0007] An example of such compensation carried out by a device according to the prior art is given in figure 2 . The graph of the figure 2 represents the evolution of the voltage of the continuous part 16 of the installation 14 of the figure 1 , depending on the power supplied or taken by each of the terminals controlled by the device according to the prior art, on said continuous part. P 5 is a characteristic curve representing the voltage variation of the continuous part 16of the installation in the event of an imbalance between the power supplied and the power taken from the continuous part of the installation, for example following a breakdown of the fourth terminal 400. A power deficit ΔP dis , equivalent to 500MW, appears due to the loss of the fourth terminal which initially supplied a power of 500MW to the continuous part of the installation. This power deficit suffered by the installation leads to a reduction in the voltage of the continuous part, by a voltage ΔV dc . The voltage of the DC part, which was initially equal to V dc 0 is now equal to the modified voltage V' dc .

[0008] To compensate for this power deficit in the continuous part of the installation and this drop in voltage in the continuous part, the control device according to the prior art proposes to vary the power supplied or taken by the first 100, second200 and third 300 terminals depending on the voltage drop of the DC part 16 of the installation. These power variations are linear, they are represented respectively by the curves P 1 , P 2 , P 3 and P 4. The curves P 1 , P 2 and P 3 allow compensation powers to be defined respectively ΔP 1 , ΔP 2 and ΔP 3 which can be provided by the first 100, second 200 and third 300 terminals to compensate for voltage drop ΔV dc of the continuous part of the installation. We note that the evolution of the curves P 1 , P 2 and P 3 is identical so that the compensation powers ΔP 1 , ΔP 2 and ΔP 3 are equal and verify: ΔP 1 = ΔP 2 = ΔP 3 = − ΔP dis 3

[0009] In practice, the power supplied or drawn by each of the terminals on the continuous part of HVDC installations is however limited by an upper power limit and a lower power limit. These upper and lower power limits are set by the manufacturer. When the power supplied or drawn by a terminal reaches one of these power limits, the terminal risks being damaged. The said upper and lower power limits define a nominal operating range of the converter. figure 3 illustrates the evolution of the power supplied or taken by the terminals of the figure 1 , controlled by a device according to the prior art, taking into account these limits. In this example, the second terminal 200,which was drawing power from the DC part of the installation, breaks down, its curve being marked with a cross. A power disturbance appears and the voltage of the DC part 16 undergoes an unwanted increase. The upper power limits P max and lower P min terminals are respectively equal to 1000MW and -1000MW.

[0010] When the power supplied or taken by one of the terminals reaches the upper or lower power limit, this terminal must be placed in saturation to avoid damage. The power it supplies or takes from the continuous part is then kept constant. In the example of the figure 3 , the second terminal fails, resulting in a drop in the power drawn from the continuous part of the installation, which must be compensated by the first and third terminals. The power drawn by the first terminal 100reached the lower power limit P min , before the voltage changed V ' dc of the continuous part is not reached. Also, this first terminal 100 is placed in saturation so that the power it draws can no longer vary. From then on, the terminal 100 cannot draw more power to interrupt or compensate for the voltage increase. It therefore no longer contributes to compensating for the voltage increase on the DC part. Compensation is then continued by the other terminals whose power supplied or drawn may still vary, in this case by the third terminal, which is still not sufficient to compensate for the voltage increase on the DC part 16 and also risks causing a further increase in the voltage of the DC part of the installation, which is not desirable. Objet et résumé de l'invention

[0011] An aim of the present invention is to propose a device for controlling a terminal of an HVDC installation which overcomes the aforementioned problems.

[0012] To this end, the invention relates to a device for controlling a terminal connected in a multi-terminal high-voltage direct current transmission installation, the terminal being connected between a first alternating current power supply network and a continuous part of said installation, the terminal being able to supply or draw power from the continuous part of the installation between an upper power limit and a lower power limit, the device further comprising at least one regulation module configured to vary the power supplied or drawn by the terminal on the continuous part of the installation, as a function of a voltage variation on the continuous part of the installation, the device further comprising a limitation module configured to limit the variation of the power supplied or drawn by the terminal, for a given voltage variation,when the power difference between the power supplied or taken by said terminal and the upper power limit or the lower power limit becomes less than a determined value.,

[0013] The installation may comprise from two to several dozen terminals, including the terminal controlled by the control device according to the invention. Said terminal constitutes an interface between the continuous part of the installation and the first alternating electricity supply network.

[0014] The continuous part of the installation allows the transport of direct current between the terminals of said installation. It may include one or more direct current transmission lines connecting said terminals.

[0015] Furthermore, the AC power supply network may include one or more AC transmission lines. These lines may be connected to an AC source, for example from a wind farm.

[0016] Preferably, the terminal comprises at least one voltage converter for converting an alternating voltage into a direct voltage and vice versa. In a non-limiting manner, this converter may be a modular multi-level converter (MMC) in half-bridge, called Half-Bridge (HB), a full-bridge converter, called Full-Bridge (FB) or a converter having an Alternate Arm Converter (AAC) structure. These structures are well known to those skilled in the art.

[0017] The power supplied or taken by the terminal from the DC part of the installation represents the contribution of said terminal to the DC part of the installation. When the terminal supplies power, denoted by a positive sign, the terminal operates in rectifier mode and behaves like a generator. When the terminal takes power, denoted by a negative sign, from the DC part, the terminal operates in inverter mode and behaves like a load. HVDC installations generally include these two types of terminals.

[0018] The upper and lower power limits are terminal operating limits beyond which the terminal risks being damaged and is no longer able to supply or draw power from the continuous part of the installation. When the power drawn or supplied by a terminal reaches one of these limits, it must be placed in saturation.

[0019] The voltage variation of the DC part of the installation can be caused by a breakdown, for example by one of the other terminals of the installation, or by maintenance operations. The breakdown of a terminal causes a power disturbance of the installation, and therefore a variation in the power of the DC part of the installation, positive or negative, which is not desirable. This power disturbance causes a proportional increase or decrease in the voltage of the DC part.

[0020] The regulation module is configured to increase or decrease the power supplied or drawn by the terminal on the DC part in order to compensate for this power disturbance and therefore limit the voltage variation of the associated DC part. More preferably, the regulation module makes it possible to interrupt the voltage variation and more preferably to compensate for said voltage variation. The terminal is therefore capable of providing positive or negative compensation power to limit, interrupt or at least partially compensate for such a voltage variation on the DC part of the installation. The regulation module is preferably, but not limited to, installed locally, close to the terminal.

[0021] The limitation module makes it possible to limit the variation in the power supplied or drawn by the terminal, in response to a given voltage variation, when this power is close to the upper or lower power limit. One advantage is to prevent the power drawn or supplied by the terminal from reaching this limit and thus avoid having to deactivate the voltage variation compensation action, by placing the terminal in saturation. Consequently, thanks to the invention, the compensation carried out by the terminal is reduced when approaching its lower or upper power limit and the power supplied or drawn by the terminal is maintained between the lower and upper power limits. The behavior of the terminal is therefore anticipated and better controlled, which improves the stability of the entire installation.

[0022] Unlike the solutions of the prior art in which the power supplied or taken by a terminal, to limit a voltage variation on the DC part, varies in an identical and linear manner for all the terminals, the device according to the invention makes it possible to take into consideration the initial contribution of the terminal, that is to say the power that it initially supplies or takes from the DC part, and to adapt the variation of the power supplied or taken by this terminal to its operating limits, so as not to reach these limits. The behavior of the terminal is adapted when the power that it supplies or takes approaches the power limits.

[0023] The power difference between the power supplied or taken by said terminal and the upper power limit or the lower power limit is preferably calculated in real time.

[0024] The determined value of the power deviation below which the limitation module is configured to limit the variation of the power supplied or taken by the terminal can be chosen arbitrarily by an operator or can be a function of the state of the terminal or the installation.

[0025] In a non-limiting manner, the limitation module can limit the variation in power supplied or taken by the terminal by providing the regulation module with limitation data or by sending a limitation signal to the regulation module. The regulation module adapts the variation in power supplied or taken, for a given voltage variation, according to the limitation data or the limitation signal provided by the limitation module.

[0026] Preferably, the regulation module is configured to increase the power supplied or decrease the power drawn by the terminal on the DC part of the installation in the event of a voltage drop on the DC part of the installation. Subsequently, the expression "increase the power supplied" corresponds to a variation in power in the positive direction. Also, an increase in power supplied tends to move the power supplied away from zero power. Similarly, a "decrease in power drawn" corresponds to a positive variation in the power drawn.

[0027] A decrease in the power supplied or an increase in the power drawn from the DC part of the installation leads to a drop in the voltage of the DC part, which must be compensated. For example, the failure of another terminal in the installation initially supplying power to the DC part of the installation results in a power deficit in the DC part. In this case, the regulation module allows the power supplied to be increased or the power drawn by the terminal to be reduced in order to increase the power of the DC part. The terminal then provides positive compensation power.

[0028] Advantageously, the limitation module is configured to limit the increase in the power supplied or the decrease in the power taken by the terminal on the continuous part of the installation, for a given voltage drop, when the power difference between said power supplied or taken by the terminal and the upper power limit becomes less than the determined value. In this way, when approaching the upper power limit, the compensation power supplied by the terminal is reduced, for a given voltage drop. The risk that the power supplied or taken by the terminal reaches the upper power limit is therefore reduced.

[0029] For example, when the terminal operates in rectifier mode, it initially supplies a significant amount of power to the DC part of the installation, close to its upper power limit, so that the difference between the power supplied by the terminal and the upper limit is less than the determined value. If a voltage drop occurs on the DC part of the installation, said terminal can then only supply a small amount of compensating power. The power it supplies to the DC part can only increase slightly before reaching the upper power limit. Thanks to the invention, the increase in the power it supplies, for a given voltage drop, and therefore the compensating power supplied, are limited and the power supplied by the terminal is kept below said upper power limit.

[0030] One advantage is improved terminal control and installation stability in the event of a voltage drop.

[0031] Advantageously, the regulation module is configured to decrease the power supplied or increase the power drawn by the terminal on the DC part of the installation in the event of an increase in voltage on the DC part of the installation. Subsequently, the expression "decrease in the power supplied" designates a variation in the power supplied in the negative direction. Also, a decrease in the power supplied causes the power supplied to tend towards zero power. Similarly, an increase in the power drawn moves the power drawn away from zero power. A terminal whose power drawn from the DC part increases therefore tends to draw more power.

[0032] An increase in the power supplied or a decrease in the power drawn from the DC part of the installation leads to an increase in the voltage of the DC part, which must be compensated. For example, the failure of another terminal in the installation drawing power from the DC part of the installation results in excess power from the DC part. In this case, the regulation module can reduce the power supplied or increase the power drawn by the terminal, in order to reduce the power of the DC part. The terminal then provides negative compensation power.

[0033] Preferably, the limitation module is configured to limit the reduction in the power supplied or the increase in power taken by the terminal on the continuous part of the installation, for a given increase in voltage, when the power difference between said power supplied or taken by the terminal and the lower power limit is less than the determined value.

[0034] In this way, as the lower power limit is approached, the negative compensation power supplied by the terminal is reduced, for a given voltage variation. The risk that the power supplied or drawn by the terminal reaches the lower power limit is therefore reduced.

[0035] For example, when the terminal operates in inverter mode, it initially draws a significant amount of power from the DC part of the installation, close to its lower power limit. If a voltage increase occurs on the DC part of the installation, said terminal can then draw only a small amount of additional compensation power. The power it draws from the DC part can only increase slightly before reaching the lower power limit. Thanks to the invention, the increase in the power it draws and therefore the compensation power drawn are limited and the power drawn by the terminal is maintained above said lower power limit.

[0036] Another advantage is to improve terminal control and installation stability in the event of an increase in the voltage of the DC part.

[0037] Advantageously, the limitation module is configured to increase the variation in the power supplied or taken by the terminal on the DC part of the installation, for a given voltage variation, when the power difference between said power supplied or taken by the terminal and the upper power limit or the lower power limit is greater than an additional determined value. One advantage is to allow the terminal to contribute more to the compensation of the voltage variation on the DC part when the power that it supplies or takes from the DC part is far from its upper power limit or its lower power limit.

[0038] For example, the terminal may initially supply low power to the DC part of the installation, well below its upper power limit, so that the difference between the power supplied by the terminal and the upper limit is greater than the additional determined value. If a voltage drop occurs on the DC part of the installation, the terminal is then able to supply significant compensating power. The power it supplies to the DC part may increase significantly.

[0039] The additional determined value is preferably greater than the determined value. Without departing from the scope of the invention, the additional determined value may be equal to the determined value.

[0040] Preferably, the limitation module comprises a management module configured to allocate to the terminal a higher power compensation limit. P sup and a lower power compensation limit P inf from maximum and minimum power values ​​supplied by the first alternative power supply network and terminal operating power settings.

[0041] The said maximum and minimum power values ​​correspond to upper and lower power limits that the first alternative power supply network is capable of supplying.

[0042] Upper compensation limits P sup and lower P inf respectively define an upper power range and a lower power range, allocated to the terminal, within which the power supplied or drawn by the terminal can vary. This upper power range is also called UVCR (“Under Voltage Containment Reserve” in English) and this lower power range is also called OVCR (“Over Voltage Containment Reserve” in English).

[0043] UVCR corresponds to a power range in which the power supplied or drawn by the terminal can vary in order to compensate for a drop in voltage in the DC part. It can be calculated using the following expression: UVCR = P sup − P 0 P 0 being the power supplied or taken by the terminal in the absence of disturbance.

[0044] OVCR corresponds to a power range in which the power supplied or drawn by the terminal can vary in order to compensate for an increase in voltage of the DC part. It can be calculated using the following expression: OVCR = P inf − P 0

[0045] The terminal can therefore provide compensation power within the upper or lower power range. These limits depend on the terminal's operating data, so that terminal control is better controlled. They can be chosen so as not to damage the terminal and to respect its operating constraints.

[0046] Preferably, the lower power range OVCR is determined to satisfy the equation: POVCR ≤ OVCR ≤ 0

[0047] POVCR (Procurable Over Voltage Containment Reserve) corresponds to the maximum lower power range that can be secured by the terminal to compensate for an increase in voltage of the DC part of the installation.

[0048] POVCR is preferably determined from the following equation: POVCR = max P min − P 0 , POVCR AC

[0049] POVCR AC< is the maximum lower power reserve that can be supplied by the first AC power supply network to the terminal. P min is the lower power limit of the terminal.

[0050] The following equation is verified: POVCR AC = P ACmin − P 0 Or P ACmin< is a minimum power value that can be supplied by the AC power supply network to the terminal.

[0051] Preferably, the UVCR upper power range is determined to satisfy the equation: 0 ≤ UVCR ≤ PUVCR

[0052] PUVCR (Procurable Under Voltage Containment Reserve) corresponds to the maximum upper power range that can be secured by the terminal to interrupt or compensate for a voltage drop in the continuous part of the installation.

[0053] PUVCR is preferably determined from the following equation: PUVCR = min P max − P 0 , PUVCR AC

[0054] PUVCR AC< is the maximum upper power range that can be supplied by the first AC power supply network to the terminal.

[0055] The following equation is verified: PUVCR AC = P ACmax − P 0 Or P ACmax< is a maximum power value that can be supplied by the AC power supply network to the terminal.

[0056] In the event of a failure of a terminal referenced "k", the management module is preferably configured to regulate the upper UVCR power range and the lower OVCR power range in order to respect the following inequalities at all times: ∑ m = 1 , m ≠ k N UVCR m ≥ P k * si P k * ≥ 0 ∑ m = 1 , m ≠ k N OVCR m ≤ P k * si P k * ≤ 0

[0057] In these equations, N is the number of terminals in the installation, UVCR m and OVCR m are the upper and lower power ranges allocated to each of the terminals m in the installation, P k * is the power supplied or taken by terminal “k” in the absence of disturbance.

[0058] By maintaining these conditions, the power and voltage disturbance induced by the loss of the "k" terminal of the installation can always be interrupted or compensated by the other terminals of the installation.

[0059] Advantageously, the management module implements a calculation based on the following optimization functions: min ∑ m = 1 N − φ m OVCR OVCR m min ∑ m = 1 N φ m UVCR UVCR m Or φ m OVCR And φ m UVCR are weighting coefficients dependent on the cost of energy supply to each of the installation's terminals.

[0060] Preferably, the upper power compensation limit P sup is less than the upper power limit, so the power supplied by the terminal is limited by this upper power limit. Similarly, the lower power compensation limit P inf is preferably greater than the lower power limit, so that the power drawn by the terminal is limited by this lower power limit.

[0061] According to a particularly advantageous aspect of the invention, the limitation module is configured to determine a boost constant g +< and an undervoltage constant g-< , different from the overvoltage constant, associated with the terminal, and the regulation module is configured to vary the power supplied or taken by the terminal on the continuous part of the installation by applying the linear relationship: ΔP = − g + Δv dc si Δv dc > 0 And ΔP = − g − Δv dc si Δv dc < 0 Or ΔP is the variation in the power supplied or taken by the terminal, induced by the regulation module, Δv dc is the voltage variation on the DC part of the installation. One advantage is that it is easy to adjust the power contribution of a terminal by adjusting the undervoltage constant or the overvoltage constant.

[0062] It is understood that the limitation module limits the variation in power taken or supplied by the terminal by providing the regulation module with the undervoltage constants g -< and overvoltage g +< .

[0063] The skilled person understands that the boost constant may also be referred to as the overvoltage constant and the undervoltage constant may also be referred to as the undervoltage constant. The undervoltage and boost constants are also referred to as "droop" parameters.

[0064] The variation in power supplied or taken by the terminal as a function of the variation in voltage on the continuous part of the installation is therefore linear and can be modeled by an affine function, whose undervoltage constants g -< and overvoltage g +< are the slope coefficients.

[0065] The higher the undervoltage constant g -< is low, the less the increase in power supplied or the decrease in power drawn, for a given drop in voltage. Similarly, the higher the boost constant gThe lower the +<, the less the drop in power supplied and the lower the increase in power taken, for a given increase in voltage.

[0066] The variation ΔP of power supplied or taken can be adapted by modifying the undervoltage and overvoltage constants. In particular, the limitation module makes it possible to determine the undervoltage constants and the overvoltage constants independently. Thanks to the device according to the invention, it is therefore possible to define a variation in power supplied or taken by the terminal that is different for a voltage drop and for a voltage increase of the DC part. One advantage is being able to adapt this variation to the needs of the installation and according to the upper and lower power limits of the different terminals.

[0067] The limiting module can determine the undervoltage and overvoltage constants centrally. These constants can be predetermined and updated periodically.

[0068] Without limitation, the limitation module can centrally determine a plurality of undervoltage and overvoltage constants specific to a plurality of terminals.

[0069] Preferably, the limiting module is configured to determine an undervoltage constant g -< less than the boost constant g+< when the power difference between the power supplied or taken by the terminal on the continuous part of the installation and the upper power limit is less than the determined value. One advantage is to reduce the terminal's contribution to compensate for a voltage drop, when its power supplied or taken is close to the upper power limit, while allowing its contribution to compensate for a voltage increase on the continuous part.

[0070] Without limitation, for a terminal whose initially supplied power is close to the upper power limit, the limitation module determines a low undervoltage constant, so as to reduce the increase in supplied power, for a given voltage drop. On the other hand, the limitation module determines a boost constant greater than the undervoltage constant so that the decrease in supplied power for a given voltage increase is not limited as much.

[0071] Advantageously, the limiting module is configured to determine a boost constant g +< less than the undervoltage constant g-< when the power difference between the power supplied or taken by the terminal on the continuous part of the installation and the lower power limit is less than the determined value. One advantage is to reduce the terminal's contribution to compensate for an increase in voltage, when its power supplied or taken is close to the lower power limit, while allowing its contribution to compensate for a drop in voltage on the continuous part.

[0072] In a non-limiting manner, for a terminal initially drawing power close to the lower power limit, the limitation module determines a low boost constant, so as to limit the increase in power drawn, for a given increase in voltage. On the other hand, the limitation module determines an undervoltage constant greater than the boost constant so that the decrease in power drawn, for a given drop in voltage, is not limited as much.

[0073] Advantageously, the limitation module comprises a calculator configured to determine an undervoltage constant g -< verifying the relationship: g − = − P sup − P 0 V dc lim − − V dc 0 = − UVCR V dc lim − − V dc 0 Or V dc lim − is the lower voltage limit set for the continuous part of the installation, V dc 0 is the nominal voltage of the DC part of the installation in the absence of disturbance and P0 is the power supplied or taken by the terminal in the absence of disturbance.

[0074] One interest is to adapt the variation of the power supplied or taken by the terminal to the limits imposed by the terminal and by the installation. The limitation module makes it possible in particular to jointly maintain the power supplied or taken by the terminal on the continuous part below the upper power compensation limit and the voltage of the continuous part above the lower voltage limit.

[0075] P 0 is the power supplied or taken by the terminal when the voltage of the DC part does not vary.

[0076] More preferably, the limiting module includes a calculator configured to determine a boost constant g +< verifying the relation: g + = − P 0 − P inf V dc 0 − V dc lim + = OVCR V dc 0 − V dc lim + Or V dc lim + is the upper limit of the fixed voltage of the continuous part of the installation,V dc 0 is the nominal voltage of the DC part of the installation in the absence of disturbance and P 0 is the power supplied or taken by the terminal in the absence of disturbance.

[0077] The limitation module makes it possible in particular to jointly maintain the power supplied or taken by the terminal on the continuous part above the lower power compensation limit and the voltage of the continuous part below the upper voltage limit.

[0078] Advantageously, the installation comprises a plurality of terminals each being connected between an alternating current power supply network and the continuous part of said installation, each of the terminals being capable of supplying or drawing power from the continuous part of the installation between an upper power limit and a lower power limit specific to it, the regulation module being configured to vary the power supplied or drawn by each of the terminals on the continuous part of the installation, as a function of a voltage variation on the continuous part of the installation, the limitation module being configured to limit the variation of the power supplied or drawn by each of the terminals, for a given voltage variation,when the power difference between the power supplied or taken by said terminals and the upper power limit or the lower power limit specific to them becomes less than a determined value.,

[0079] The device according to the invention can therefore simultaneously and centrally control a plurality of terminals, independently of each other. This improves the stability of the entire installation. In addition, the failure of one terminal can be compensated for by each of the other remaining terminals.

[0080] Alternatively, the regulation module may comprise a plurality of regulation sub-modules, each being arranged locally near a terminal specific to it. Each of these regulation sub-modules is configured to vary the power supplied or drawn by the terminal specific to it.

[0081] In a non-limiting manner, the limitation module may be a centralized module configured to limit the variations in power supplied or taken by several terminals of the installation and, preferably, to limit the variation in the voltage of the DC part of the installation between the upper and lower voltage limits. In this variant, it provides each of the regulation sub-modules with undervoltage and overvoltage constants specific to the terminal associated with the regulation sub-module.

[0082] The invention also relates to a multi-terminal high-voltage direct current transmission installation, comprising at least one terminal connected between a first alternating current power supply network and a continuous part of said installation, the terminal being capable of supplying or drawing power from the continuous part of the installation between an upper power limit and a lower power limit, the installation comprising a terminal control device (for example a control device according to one of the embodiments described above) further comprising at least one regulation module configured to vary the power supplied or drawn by the terminal from the continuous part of the installation, as a function of a voltage variation on the continuous part of the installation,the regulation module comprising a limitation module configured to limit the variation in the power supplied or taken by the terminal, for a given voltage variation, when the power difference between the power supplied or taken by said terminal and the upper power limit or the lower power limit becomes less than a determined value.,

[0083] Finally, the invention relates to a method for controlling a terminal connected in a multi-terminal high-voltage direct current transmission installation, the terminal being connected between a first alternating current power supply network and a continuous part of said installation, the terminal being able to supply or draw power from the continuous part of the installation between an upper power limit and a lower power limit, the method comprising a step of varying the power supplied or drawn by the terminal from the continuous part of the installation, as a function of a voltage variation on the continuous part of the installation, and a step of limiting the variation of the power supplied or drawn by the terminal, for a given voltage variation,when the power difference between the power supplied or taken by said terminal and the upper power limit or the lower power limit becomes less than a determined value,

[0084] This method can implement steps corresponding to each of the embodiments of the control device as described above. Brève description des dessins

[0085] The invention will be better understood on reading the following description of an embodiment of the invention given by way of non-limiting example, with reference to the appended drawings, in which: there figure 1 illustrates an HVDC installation according to the prior art; the figure 2 illustrates the evolution of the voltage of the continuous part of the installation of the figure 1 , in response to the failure of the fourth terminal; the figure 3 illustrates the evolution of the power of the terminals of the figure 1 ,in response to the failure of the second terminal; the figure 4 illustrates an HVDC installation whose terminals are controlled by a control device according to the invention; the figure 5 illustrates a control device according to the invention; the figure 6 illustrates the evolution of the power of the terminals of the figure 4 depending on the voltage of the continuous part; the figure 7 illustrates the power variations of the terminals of the installation of the figure 1 , controlled by a device according to the prior art; the figure 8 illustrates the variation of the voltage of the continuous part of the installation of the figure 1 , whose terminals are controlled by a device according to the prior art; the figure 9 illustrates the power variations of the terminals of the installation of the figure 4 , controlled by a device according to the invention; and the figure 10 illustrates the variation of the voltage of the continuous part of the installation of the figure 4 , whose terminals are controlled by a device according to the invention. Description détaillée de l'invention

[0086] The invention relates to a device 10 terminal control 100 connected to an installation 14 multi-terminal high voltage direct current transmission HVDC.

[0087] There figure 4 illustrates an installation 14 including first 100, second 200, third 300 and fourth 400 terminals as well as a control device 10 according to the invention. In this example, the control device 10 is configured to control the first 100, second 200, third 300 and fourth 400 terminals.

[0088] The first 100, second 200, third 300and fourth 400 terminals are connected respectively to first 102, second 202, third 302 and fourth 402 alternative power supply networks. It can be seen that the fourth terminal 400 is connected to a wind farm. These four terminals are also connected to a continuous part 16 of the installation 14 via direct current lines. The terminals are voltage converters, configured to convert an alternating voltage to a direct voltage and vice versa

[0089] An example of a control device 10 according to the invention, to control the first 100 , second 200, third 300 and fourth terminals of the facility 14 is given in figure 5 . This control device 10 includes a regulation module 20, a power distribution module 22,a limitation module 24 and a synchronization module 23. The limitation module 24 includes a management module 26 and a calculator 28.

[0090] In this non-limiting example, the regulation module 20 is centrally arranged. Alternatively, the control module 20 may comprise a plurality of regulation sub-modules, each being arranged locally near a terminal of its own and of which it regulates the power supplied or taken from the continuous part of the installation.

[0091] The power distribution module 22 receives measured voltage values ​​as input V dc 1 ...Nst on the continuous part 16 of the installation 14 as well as measured values P 1. ..Nst and instructions P* 1 ...Nst of powers supplied or taken by the installation terminals. It delivers output instructions for powers supplied or taken P* 1 ...Nst by the terminals as well as voltage instructions v* dc 1 ...Nst of the continuous part. The power distribution module 22 is configured to restore the power of the installation following a disturbance. The management module 26 receives maximum power values ​​as input P ACmax< 1 ...Nst and minimal P ACmin< 1 ...Nst which can be supplied by alternative power supply networks to the installation terminals 14, as well as instructions for powers supplied or taken P* 1 ...Nst by the terminals, provided by the power distribution module 22.

[0092] The management module 26 of the limitation module 24is configured to output higher power compensation limits P sup 1 ... Nst and lower P inf 1 ...Nst allocated to each of the terminals.

[0093] The calculator 28 receives as input the power compensation limits P sup 1 ... Nst And P inf 1 ...Nst delivered by the management module 26 and is configured to determine and output boost constants g 1 … Nst + and undervoltage constants g 1 … Nst − associated with each of the terminals.

[0094] The synchronization module 23 receives as input the power instructions supplied or taken P* 1 ...Nst by the terminals as well as the voltage instructions v* dc 1 ...Nst of the continuous part, delivered by the power distribution module 22.This synchronization module 23 ensures temporal consistency between these instructions.

[0095] The regulation module 20 receives as input the power instructions supplied or taken P* 1 ...Nst by the terminals as well as the voltage instructions v* dc 1 ...Nst of the continuous part as well as the overvoltage constants g 1 … Nst + and undervoltage g 1 … Nst − provided by the synchronization module 23.

[0096] The regulation module 20 varies the power supplied or taken by the terminals 100,200,300,400of the installation according to said supplied or drawn power instructions, said voltage instructions as well as the overvoltage and undervoltage constants. In the variant where the regulation module comprises a plurality of sub-modules installed locally near the terminals, each of the sub-modules varies the power supplied or drawn by the terminal with which it is associated, according to said instructions and constants.

[0097] There figure 6 is a graph illustrating the evolution of the powers supplied and taken by the first 100, second 200, third 300 and fourth 400 terminals of the installation of the figure 4 , depending on the voltage variation of the DC part 16 of the installation 14, these terminals being controlled by a control device 10 according to the invention.

[0098] We see that, in this example, the fourth terminal 400 provides to the continuous part 16 of the installation a constant power P 4 equal to 500MW. The first and second terminals 100, 200 operate in inverter mode, so they draw power from the DC part of the installation. In this example, the power drawn P 1 by the first terminal has an initial value P 01 equals -900MW while the power taken P 2 by the second terminal has an initial value P 02 equals -400MW. The third terminal operates in rectifier mode, so that it supplies the continuous part 16 a power P 3 having an initial value P 03 equal to 800MW. In this non-limiting example, the nominal power of the terminals is 1000MW. Also, the powers taken or supplied P1,2,3 by the first, second and third terminals can vary between an upper power limit P max equal to 1000 MW and a lower power limit P min equal to -1000 MW.

[0099] The tension of the continuous part 16 of the installation 14 is initially of V dc 0 , which is equivalent in this graph to 1 unit of voltage, for reasons of simplification. The voltage variation of the continuous part 16 is limited by an upper voltage limit V dc lim + and a voltage limit V dc lim − inferior. In the example of the figure 6 , These upper and lower voltage limits represent a 10% variation from the initial voltage V dc 0 .

[0100] The curves P 1 and P2 respectively represent the evolution of the power taken by the first terminal 100 and by the second terminal 200 in response to a voltage variation on the DC part 16. The curve P 3 represents the evolution of the power supplied by the third terminal 300 to the continuous part.

[0101] First, the management module 26 of the limitation module 24 determines the upper power compensation limits P sup 1 ... Nst and lower P inf 1 ...Nst allocated to each of the terminals 100, 200, 300. These limits define upper UVCR and lower OVCR power ranges within which the power supplied or taken by each of the terminals can vary. The ranges allocated by the limitation module 24 to each of the terminals are grayed out on the figure 6 .The upper and lower ranges of the third terminal are denoted UVCR (Under Voltage Containment Reserve) and OVCR (Over Voltage Containment Reserve).

[0102] In this example, the lower compensation limit P inf 1 allocated to the first terminal 100 is set at -1000MW, so as to correspond to the lower power limit P min terminals. The power P 01 initially collected by the first terminal 100 being -900MW, we understand that the first terminal can draw up to 100MW additional on the continuous part 16 of the installation 14. The upper compensation limit P sup 1 allocated to the first terminal is set at -600MW. The lower compensation limit allocated P inf 2 at the second terminal 200 is set at -800MW and its upper compensation limit P sup 2 is set at 100MW. The lower compensation limit P inf 3 allocated to the third terminal 300 is set at 300MW. The upper compensation limit P sup 3 allocated to the third terminal 300 is set at 1000MW to correspond to the upper power limit P max terminals. The initial power P 03 provided by the third terminal 300 being 800MW, we understand that the power it provides to the continuous part can increase by a maximum of 200MW.

[0103] The limitation module calculator then determines first gi, second g 2 + and third g 3 + boost constants and the first g 1 − , second g 2 − and third g 3 − undervoltage constants associated respectively with the first 100, second 200 and third 300terminals. These constants are determined in such a way as to verify: g 1 , 2,3 − = − P sup 1 , 2,3 − P 01 , 02 , 03 V dc lim − − V dc 0 = − UVCR 1 , 2,3 V dc lim − − V dc 0 And g 1 , 2,3 + = − P 01 , 02 , 03 − P inf 1 , 2,3 V dc 0 − V dc lim + = OVCR 1 , 2,3 V dc 0 − V dc lim +

[0104] According to the invention, the limitation module 24 determines an undervoltage constant g 3 − from the third terminal 300 less than its boost constant g 3 + , as the power gap between the initial power P 03 of the third terminal and the upper power limit P max of the third terminal 300 is low, and more particularly less than a determined value, for example 300MW. Similarly, the overvoltage constant g 1 + from the first terminal 100 is less than its boost constant g 1 − , as the power gap between the initial power P 01 of the first terminal 100 and the lower power limit P inf of the first terminal is low, and more particularly lower than a determined value, for example 300MW.

[0105] The regulation module 20 is then configured to vary the power supplied or taken by each of the terminals on the continuous part of the installation by applying the linear relationship: ΔP 1 , 2,3 = − g 1 , 2,3 + Δv dc si Δv dc > 0 And ΔP 1 , 2,3 = − g 1 , 2,3 − Δv dc si Δv dc < 0

[0106] In response to a positive or negative voltage variation on the DC part of the installation, the regulation module 20 therefore linearly varies the power supplied or taken P 1,2,3 by each of the terminals 100,200,300 on the continuous part 16, the boost constants g 1 , 2,3 + and undervoltage g 1 , 2,3 − constituting the directing coefficients of the power variation lines as a function of the voltage variations on the continuous part.

[0107] The boost constants g 1 , 2,3 + and undervoltage g 1 , 2,3 − are determined so that the powers supplied or taken P 1,2,3 by terminals reach lower power compensation limits P inf 1,2,3 when the DC part voltage reaches the upper voltage limit V dc lim + and so that the powers supplied or taken P 1,2,3 by terminals reach upper power compensation limits P sup 1,2,3 when the DC part voltage reaches the lower voltage limit V dc lim − . The operating constraints of the terminals are therefore better respected.

[0108] It is noted that, thanks to the invention, the third terminal 300, whose power initially supplied P 03 to the continuous part 16 is close to its upper power limit P max , sees its increase in power supplied to the continuous part reduced, for a given voltage drop. The undervoltage constant g 3 − which is associated with it by the limitation module 24 is low. The contribution of this third terminal 300 the compensation for the voltage drop is therefore reduced.

[0109] Likewise, the first terminal 100, whose power P 01 initially provided to the continuous part 16 is close to its lower power limit P min , sees its increase in power taken from the continuous part reduced, for a given increase in voltage. The overvoltage constant g 1 + which is associated with it by the limitation module 24 is low. The contribution of this first terminal to compensating for the voltage increase is therefore reduced.

[0110] Thanks to the invention, the power supplied P3 by the third terminal 300 reached the upper power limit P max when the lower voltage limit V dc lim − is reached. Similarly, the power taken P 1 by the first terminal 100 reached the lower power limit P min when the upper voltage limit V dc lim + is reached. Also, the tension of the continuous part 16 of the installation 14 is maintained between the chosen upper and lower voltage limits.

[0111] In the example of the figure 6 , the calculator 28 of the limitation module 24 determines the following overvoltage constants: gi = 1.563 MW / kV for the first terminal 100, g 2 + = 6.250 MW / kV for the second terminal 200, g 3 + = 7.81 3MW / kV for the third terminal 300. The calculator 28 of the limitation module 24also determines the following undervoltage constants: g 1 − = 4.688 MW / kV for the first terminal 100, g 2 − = 7.813 MW / kV for the second terminal 200, g 3 − = 3.125 MW / kV for the third terminal 300. The limiting module can implement an algorithm for calculating overvoltage and undervoltage constants.

[0112] There figure 7 illustrates the simulation results of the evolution of the power of the terminals 100,200,300,400 of the installation 14 of the figure 1 controlled by a device according to the prior art. At the moment t 0, we simulate the failure of the second terminal 200 of the installation 14, which then no longer draws power from the continuous part 16 of the installation. The power P 2 of the second terminal 200 becomes zero at the moment t 0. We note that the power P 1 of the first terminal 100reaches the lower power limit very quickly P min = -1000MW, and the first terminal 100 enters saturation. The control device according to the prior art does not take into account the upper power limits P max and lower P min terminals so that the variation in the power supplied or drawn by these terminals is not adapted to the approach of these power limits. The power supplied or drawn by these terminals risks reaching the upper power limits P max and lower P min and will then have to be placed in saturation.

[0113] From the moment the first terminal 100 enters saturation, the power P 2 that it takes can no longer increase to interrupt or compensate for the increase in voltage. It can no longer contribute to the compensation of voltage variation on the continuous part 16 of the installation 14.Only the third terminal 300 therefore contributes to the compensation of voltage variation, which is not sufficient. The voltage variation is no longer sufficiently compensated, which leads to an even greater voltage variation. Consequently, as can be seen in the figure 8 , the DC part voltage increases until it exceeds the upper voltage limit V dc lim + .

[0114] There figure 9 illustrates the simulation results of the evolution of the power of the terminals 100,200,300,400 of the installation 14 of the figure 5 controlled by a device 10 according to the invention. At the moment t 0, we also simulate the failure of the second terminal 200 of the installation 14, which then no longer draws power from the continuous part 16 of the installation. The power P 2 of the second terminal 200 becomes zero at the momentt 0. We note that the power P 1 of the first terminal 100 reached tends slowly towards the lower power limit P min = -1000MW, asymptotically. The control device according to the invention takes into account the upper power limits P max and lower P min terminals so that the variation in the power supplied or taken by these terminals is adapted to the approach of these power limits, so as to avoid saturation of the terminals.

[0115] As noted in figure 10 , the DC part voltage is kept below the upper voltage limit V dc lim + and tends towards this limit asymptotically. The terminals are not overloaded, and do not enter saturation, whatever the voltage variation. The device according to the invention allows a better distribution of the compensation powers.

Claims

1. A control device for controlling (10) a terminal (100, 200, 300) connected in a multi-terminal high-voltage direct current transmission facility (14), the terminal being connected between a first AC power supply network (102, 202, 302) and a DC part (16) of said facility, the terminal being able to provide or draw power on the DC part of the facility comprised between an upper power limit and a lower power limit, the device further comprising at least one regulation module (20) configured to vary the power provided or drawn by the terminal on the DC part of the facility, as a function of a voltage variation on the DC part of the facility, the device further comprising a limitation module (24) configured to limit the variation of the power provided or drawn by the terminal, for a given voltage variation, when the power difference between the power provided or drawn by said terminal and the upper power limit or the lower power limit becomes smaller than a determined value, the limitation module (24) being configured to determine an overvoltage constant g+ and an under-voltage constant g-, different from the overvoltage constant, associated with the terminal (100, 200, 300), the regulation module being configured to vary the power provided or drawn by the terminal on the DC part (16) of the facility (14) by application of the linear relation: ΔP = − g + Δv dc if Δv dc > 0 ; and ΔP = − g − Δv dc if Δv dc < 0 where ΔP is the variation of the power provided or drawn by the terminal, induced by the regulation module, Δvdc is the voltage variation on the DC part of the facility (14), the limitation module (24) comprising a management module (26) configured to allocate to the terminal (100, 200, 300) an upper power compensation limit Psup and a lower power compensation limit Pinf from maximum and minimum power values provided by the first AC power supply network (102, 202, 302) and from operating power setpoints of the terminal, the limitation module (24) further comprising a calculator (26) configured to determine the under-voltage constant g- and the overvoltage constant g+ verifying the relation: g − = − P sup − P 0 V dc lim − − V dc 0 ; and g + = − P 0 − P inf V dc 0 − V dc lim + where V dc lim − is the set lower voltage limit of the DC part (16) of the facility (14), V dc lim + is the set upper voltage limit of the DC part (16) of the facility, Vdc0 is the nominal voltage of the DC part of the facility in the absence of disturbance and P0 is the power provided or drawn by the terminal in the absence of disturbance.

2. The control device according to claim 1, wherein the regulation module (20) is configured to increase the power provided or decrease the power drawn by the terminal (100, 200, 300) on the DC part (16) of the facility (14) in the event of a voltage drop on the DC part of the facility.

3. The control device according to claim 2, wherein the limitation module (24) is configured to limit the increase in the power provided or the decrease in the power drawn by the terminal (100, 200, 300) on the DC part (16) of the facility (14), for a given voltage drop, when the power difference between said power provided or drawn by the terminal and the upper power limit is smaller than the determined value.

4. The control device according to any one of claims 1 to 3, wherein the regulation module is configured to decrease the power provided or increase the power drawn by the terminal (100, 200, 300) on the DC part (16) of the facility (14) in the event of a voltage increase on the DC part of the facility.

5. The control device according to claim 4, wherein the limitation module (24) is configured to limit the decrease of the power provided or the increase of the power drawn by the terminal (100, 200, 300) on the DC part (16) of the facility (14), for a given voltage increase, when the power difference between said power provided or drawn by the terminal and the lower power limit becomes smaller than the determined value.

6. The control device according to any one of claims 1 to 5, wherein the limitation module (24) is configured to increase the variation of the power provided or drawn by the terminal (100, 200, 300) on the DC part (16) of the facility (14), for a given voltage variation, when the power difference between said power provided or drawn by the terminal and the upper power limit or the lower power limit becomes greater than an additional determined value.

7. The control device according to any one of claims 1 to 6, wherein the limitation module (24) is configured to determine an under-voltage constant g- smaller than the overvoltage constant g+ when the power difference between the power provided or drawn by the terminal (100, 200, 300) on the DC part (16) of the facility (14) and the upper power limit is smaller than the determined value.

8. The control device according to any one of claims 1 to 7, wherein the limitation module (24) is configured to determine an overvoltage constant g+ smaller than the under-voltage constant g- when the power difference between the power provided or drawn by the terminal (100, 200, 300) on the DC part (16) of the facility (14) and the lower power limit is smaller than the determined value.

9. The control device according to any one of claims 1 to 8, wherein the facility (14) comprises a plurality of terminals (100, 200, 300) each being connected between an AC power supply network and the DC part (16) of said facility, each of the terminals being able to provide or draw power on the DC part of the facility comprised between an upper power limit and a lower power limit that are specific thereto, the regulation module (20) being configured to vary the power provided or drawn by each of the terminals on the DC part of the facility, as a function of a voltage variation on the DC part of the facility, the limitation module (24) being configured to limit the variation of the power provided or drawn by each of the terminals, for a given voltage variation, when the power difference between the power provided or drawn by said terminals and the upper power limit or the lower power limit that are specific thereto is smaller than a determined value.

10. A multi-terminal high-voltage direct current transmission (100, 200, 300) facility (14), comprising at least one terminal connected between a first AC power supply network and a DC part (16) of said facility, the terminal being able to provide or draw power on the DC part of the facility comprised between an upper power limit and a lower power limit, the facility comprising a control device for controlling the terminal according to any one of claims 1 to 9.

11. A method for controlling a terminal connected in a multi-terminal high-voltage direct current transmission facility (14), the terminal being connected between a first AC power supply network (102, 202, 302) and a DC part (16) of said facility, the terminal being able to provide or draw power on the DC part of the facility comprised between an upper power limit and a lower power limit, the method comprising a step of varying the power provided or drawn by the terminal on the DC part of the facility, as a function of a voltage variation on the DC part of the facility, and a limitation step wherein the variation of the power provided or drawn by the terminal is limited, for a given voltage variation, when the power difference between the power provided or drawn by said terminal and the upper power limit or the lower power limit becomes smaller than a determined value, the limitation step comprising determining an overvoltage constant g+ and an under-voltage constant g-, different from the overvoltage constant, associated with the terminal (100, 200, 300), wherein the power provided or drawn by the terminal on the DC part (16) of the facility (14) is varied by application of the linear relation: ΔP = − g + Δv dc if Δv dc > 0 ; and ΔP = − g − Δv dc if Δv dc < 0 where ΔP is the variation of the power provided or drawn by the terminal, induced by the regulation module, Δvdc is the voltage variation on the DC part of the facility (14), the limitation step comprising allocating to the terminal (100, 200, 300) an upper power compensation limit Psup and a lower power compensation limit Pinf from maximum and minimum power values provided by the first AC power supply network (102, 202, 302) and from operating power setpoints of the terminal, the limitation step further comprising a step of calculating the under-voltage constant g- and the overvoltage constant g+ verifying the relation: g − = − P sup − P 0 V dc lim − − V dc 0 ; and g + = − P 0 − P inf V dc 0 − V dc lim + where V dc lim − is the set lower voltage limit of the DC part (16) of the facility (14), V dc lim + is the set upper voltage limit of the DC part (16) of the facility, Vdc0 is the nominal voltage of the DC part of the facility in the absence of disturbance and P0 is the power provided or drawn by the terminal in the absence of disturbance.