Method for supplying power to a wind farm under low wind conditions

Abstract

A method for supplying power to an electrically isolated wind farm comprising multiple wind turbines (A1, A2, ..., An) and a generator (G) is described. Under low-wind conditions where wind speeds fall below a threshold, active power (P) and reactive power (Q) are supplied from the generator (G) to a first wind turbine (A1) and passive components of the wind farm. In a second operating mode following the first operating mode, active power (P) is supplied from the generator (G) to the first wind turbine (A1) and the second wind turbine (A2), and reactive power (Q) is supplied / consumed by the first wind turbine (A1) to the cables and transformers connecting it to the second wind turbine (A2).

Description

Technical Field

[0001] The present invention relates to a method for supplying electricity to an islanded wind farm under low wind conditions, and to such a wind farm.

[0002] A conventional wind farm comprises multiple wind turbines connected in parallel to each other in multiple strings, which may also be referred to as an array. When no grid connection is available, generators are connected to the wind farm to supply power to the wind turbines in the strings. A control device is provided, configured to operate the wind farm in several operating modes.

[0003] In low-wind conditions where wind speeds fall below a threshold, electrically isolated wind farms can perform what is known as a black start (or self-excitation mode) on their own, or maintain excitation with the help of a relatively small auxiliary power source. Such an auxiliary power source can take the form of a diesel or other fuel-powered generator, photovoltaic or energy storage equipment, or a combination of some or all of the above.

[0004] When isolated from or islanded by the power grid, wind turbines can maintain AC frequency and voltage within the island by exchanging active and reactive power via passive components such as cables and transformers. However, when wind conditions are low, wind turbines cannot supply active power, and an additional power source is necessary.

[0005] By maintaining excitation in this scenario, the wind turbine power converter operates in voltage-supported mode (Vmode), also known as reactive power support mode, where the entire current capability of the wind turbine converter can be used to derive and / or introduce reactive power. This gives the wind farm the ability to maintain excitation and thus enables climate control within the turbine, which also allows them to be used to excite components in the grid. The latter scenario allows wind farms to become key future contributors to the black start of the wider grid, where large transformers and transmission lines can use the full capacity of the wind turbine power converter to back-excite from the wind farm. Summary of the Invention

[0006] The objective is to provide a method for supplying electricity to a wind farm under low wind conditions, and a wind farm where the additional energy source required under low wind conditions is only large enough to supply the auxiliary and electrical losses of the wind farm and its grid components, which typically total less than 1% of the wind farm's rated power, but large enough, excluding wind turbine converters, to handle both the reactive and active power loads of the wind farm. The reactive load of a wind farm is typically significantly greater than 1% and depends on the length of the cables between the wind turbines.

[0007] This objective is achieved by means of the subject matter of the independent claims. The invention is further developed as set forth in the dependent claims.

[0008] According to a first aspect of the invention, a method for supplying electricity to a wind farm is provided. The wind farm includes a plurality of wind turbines connected in parallel to each other in a first string, wherein corresponding cable segment circuit breakers are arranged between adjacent wind turbines in the first string; and a generator connected to a first wind turbine in the first string, wherein a first string circuit breaker is arranged in the line between the generator and the first wind turbine. The method includes the following operating modes under low-wind conditions where wind speeds fall below a threshold: a first operating mode in which a first series of circuit breakers is closed to supply active power from a generator to a first wind turbine, and to supply or consume reactive power from the generator to a passive cable and / or transformer between the generator and the first wind turbine, while the remaining cable segments in the first series are open; and a second operating mode following the first operating mode in which a cable segment circuit breaker between the first wind turbine and an adjacent second wind turbine is closed to supply active power from the generator to both the first and second wind turbines, and to supply or consume reactive power from the first wind turbine to a passive cable and / or transformer between the first and second wind turbines, while the remaining cable segments in the first series are open.

[0009] The passive components of the cables and transformers between the generator and the first wind turbine need to exchange reactive power with the generator. The term "exchange" is used because cables tend to generate reactive power, and transformers tend to consume reactive power. The production and consumption of each component do not tend to be balanced, and therefore the generator is useful in compensating for the differences through consumption or supply. In a wind farm, the reactive power generation of the cables tends to dominate the consumption of the transformers, and therefore the generator must consume reactive power to achieve balance.

[0010] As more cables are connected, wind turbines will also need to consume reactive power to help maintain this balance, as generators will not be sized to do so. When wind speeds are low, the reactive power flow in the wind farm will dominate the active power flow supplied to wind turbine auxiliary equipment to compensate for power losses.

[0011] In addition to the first and second wind turbines, the second operating mode is also used to sequentially excite the first string of wind turbines.

[0012] In one embodiment, the wind farm comprises n wind turbines in a first string, wherein the first wind turbine is the upstream wind turbine in the first string, and the nth wind turbine is the downstream wind turbine in the first string. The method includes sequentially closing cable segment circuit breakers, starting from a cable segment circuit breaker between the first and second wind turbines and continuing to a cable segment circuit breaker between the nth and (n-1)th wind turbines, thereby sequentially supplying active power from a generator to the first through nth wind turbines, and sequentially supplying or consuming reactive power from the wind turbines to corresponding downstream passive cables and / or transformers.

[0013] In the third operating mode, the n wind turbines in the first string can be used to excite the m wind turbines in the second string. In the fourth operating mode, a minimum number of energized wind turbines can operate in conjunction with a generator to excite the power grid, which includes grid transformers and transmission lines. The generator will supply active power to the wind turbines and the power grid, while the wind turbines will supply reactive power to or consume reactive power from the power grid to control voltage.

[0014] In an embodiment, the wind farm further includes at least one additional plurality of wind turbines connected in parallel to each other in at least one additional string, wherein corresponding cable segment circuit breakers are arranged between adjacent wind turbines in the at least one additional string; wherein a generator is connected to a first wind turbine in the at least one additional string, and wherein at least one additional string circuit breaker is arranged in the line between the generator and the first wind turbine in the at least one additional string. The method further includes, after closing the wind turbine circuit breaker between the nth and (n-1th)th wind turbines in the first string, performing first and second operating modes in the at least one additional string in the same manner as described above for the first string, and / or sequentially closing the cable segment circuit breakers in the at least one additional string in the same manner as described above for the first string; wherein reactive power is also supplied from the wind turbines of the first string to the passive cables and / or transformers of the additional strings, or consumed from the passive cables and / or transformers of the additional strings to the wind turbines of the first string.

[0015] In this embodiment, the wind farm further includes a grid supply line connected to a bus between the first wind turbine and the generator via a grid supply line circuit breaker. The grid supply line circuit breaker closes to supply active power if a minimum number of wind turbines in the wind farm are being supplied with active power, and reactive power is consumed from the bus between the first wind turbine and the generator to the grid supply line or from the grid supply line to the bus between the first wind turbine and the generator. The generator can be connected to any point in the wind farm and will be located based on site conditions, depending on where available connection points are located.

[0016] In one embodiment, the power grid supply line is connected to the power grid at its far end via a power grid circuit breaker, wherein the power grid supply line includes a power grid transformer and / or transmission line between the power grid supply line circuit breaker and the power grid circuit breaker, wherein the power grid circuit breaker is disconnected when the above steps are performed.

[0017] In an embodiment, the wind farm includes at least one of the following: each wind turbine in a first string includes a corresponding wind turbine connection circuit breaker to connect the corresponding wind turbine to or disconnect it from the first string; each wind turbine in the at least one additional string includes a corresponding wind turbine circuit breaker to connect the corresponding wind turbine to or disconnect it from at least one other string; and a generator is connected to the first string via a generator circuit breaker, wherein the generator circuit breaker closes under low wind conditions and opens under conditions other than low wind conditions.

[0018] According to a second aspect of the invention, a wind farm is provided. The wind farm includes a plurality of wind turbines connected in parallel to each other in a first string, wherein corresponding cable segment circuit breakers are arranged between adjacent wind turbines in the first string; a generator connected to a first wind turbine in the first string, wherein a first string circuit breaker is arranged in the line between the generator and the first wind turbine; and control equipment configured to operate the wind farm in the following operating modes under low wind conditions where wind speeds fall below a threshold: a first operating mode in which the first string circuit breaker closes to supply active power from the generator to the first wind turbine, and to supply active power from the generator to the passive cable and / or transformer between the generator and the first wind turbine, or from the generator and the first... A passive cable and / or transformer between wind turbines consumes reactive power to a generator, while the remaining cable segment circuit breaker in the first string is open; and a second operating mode following the first operating mode, wherein the cable segment circuit breaker between the first wind turbine and the adjacent second wind turbine is closed to supply active power from the generator to the first and second wind turbines, and to supply or consume reactive power from the first wind turbine to the passive cable and / or transformer between the first and second wind turbines, while the remaining cable segment circuit breaker in the first string is open.

[0019] Different control devices can be used to close these circuit breakers because they may be owned by a grid operator rather than a wind farm operator's regime.

[0020] In one embodiment, the wind farm comprises n wind turbines in a first string, wherein the first wind turbine is the upstream wind turbine in the first string, and the nth wind turbine is the downstream wind turbine in the first string. The control equipment is configured to sequentially close cable segment circuit breakers, starting from the cable segment circuit breaker between the first and second wind turbines and continuing up to the cable segment circuit breaker between the nth and (n-1)th wind turbines, thereby sequentially supplying active power from the generator to the first through nth wind turbines, and sequentially supplying or consuming reactive power from the wind turbines to the corresponding downstream passive cables and / or transformers.

[0021] In an embodiment, the wind farm further includes at least one additional plurality of wind turbines connected in parallel to each other in at least one additional string, wherein corresponding cable segment circuit breakers are arranged between adjacent wind turbines in the at least one additional string; wherein a generator is connected to a first wind turbine in the at least one additional string, wherein at least one additional string circuit breaker is arranged in the line between the generator and the first wind turbine in the at least one additional string, wherein after closing the wind turbine circuit breaker between the nth and (n-1th)th wind turbines in the first string, the control device is further configured to perform first and second operating modes in the at least one additional string in the same manner as in the first string as described above, and / or to sequentially close the cable segment circuit breakers in the at least one additional string in the same manner as in the first string as described above; wherein reactive power is also supplied from the wind turbines of the first string to the passive cables and / or transformers of the additional strings, or consumed from the passive cables and / or transformers of the additional strings to the wind turbines of the first string.

[0022] In an embodiment, the wind farm further includes a grid power supply line connected to a bus between the first wind turbine and the generator via a grid power supply line circuit breaker, wherein if a minimum number of wind turbines in the first string are energized, the control device is configured to close the grid power supply line circuit breaker to supply active power and to supply or consume reactive power from the bus between the first wind turbine and the generator to the grid power supply line.

[0023] In one embodiment, the power grid supply line is connected to the power grid via a power grid circuit breaker, wherein the power grid supply line includes a power grid transformer and / or transmission line between the power grid supply line circuit breaker and the power grid circuit breaker, and wherein the control device is configured to disconnect the power grid circuit breaker when the above steps are performed.

[0024] In an embodiment, the wind farm includes at least one of the following: each wind turbine in a first string includes a corresponding wind turbine circuit breaker to connect or disconnect the corresponding wind turbine from the first string; each wind turbine in the at least one additional string includes a corresponding wind turbine circuit breaker to connect or disconnect the corresponding wind turbine from the at least one additional string; and a generator is connected to the first string via a generator circuit breaker, wherein control equipment is configured to close the generator circuit breaker under low wind conditions and open the generator circuit breaker under conditions other than low wind conditions.

[0025] Advantageously, using a small auxiliary power source to excite and supply the active power demand of the wind turbine power converter allows the reactive power balancing and transient current capabilities of the wind turbine power converter to be used to further excite wind farms and large transmission system components. The full-capacity availability of the wind turbine power converter allows for a significant reduction in the size of the auxiliary energy source, so that it only needs to supply active power losses / loads.

[0026] There are two applications that can use this capability:

[0027] 1) The national power system itself has experienced a power outage and requires re-stimulation. Regardless of available wind speed, wind farms can self-stimulate and contribute to re-stimulation through the following:

[0028] a) Reverse excitation components within the power transmission system, such as transformers and transmission lines. These components present a reactive power load to the power system, and their excitation can introduce large transients that reach and exceed the steady-state ratings of the wind farm, and far exceed the ratings of additional energy sources. Therefore, the total reactive power capability of the wind turbine power converters can support their excitation and steady-state operation; a separate additional energy source cannot do this. The excitation of such components can then facilitate the connection of additional generators or the connection of interconnectors to other already excited parts of the system.

[0029] (b) Synchronize with the voltage of the already energized transmission system and connect the wind farm without introducing large transients, utilizing the voltage / reactive power support capabilities of the wind turbine power converters to immediately support further power system recovery processes. In this case, the connection of the wind farm to the transmission system, which has been energized by another generator, allows it to provide voltage support and reactive power balancing, can be crucial for energizing other parts of the transmission system.

[0030] 2) Due to power outages in grid components (due to maintenance or failure), wind farms are isolated from the transmission system but are required to self-excite or maintain excitation to maintain climate and / or other auxiliary systems. Periods of low wind speeds for power generation are typically short in duration (a few hours, possibly up to 1-2 days). Therefore, by using additional power sources, the wind farm's ability to maintain excitation eliminates the need for repeated de-excitation and re-excitation as wind speeds decrease and recover.

[0031] When stimulating a wind farm under low wind conditions, an initial stimulation sequence is advantageous to avoid overloading additional power sources. In the initial phase, only the connection between the power source and the first wind turbine needs to be stimulated. Once the first wind turbine is stimulated, it becomes the dominant contributor to reactive power, allowing subsequent wind turbines to be sequentially stimulated by directly closing the corresponding circuit breakers (wind turbine medium voltage (MV) circuit breakers) online. Once a minimum number of wind turbines are connected, they can then stimulate larger electrical components, such as larger portions of the wind farm or components of the local transmission system.

[0032] Until now, it has been impossible to conventionally excite isolated wind farms and / or transmission system components using wind turbines under low wind conditions. In previous cases where isolated wind farms have been excited without grid access, careful switching of much larger auxiliary power sources and inductive reactive power compensation devices has been used. When combined, these are able to support active power loads within the wind farm and provide reactive power balancing and voltage support. Excitation of wind farms using such devices is highly sensitive to accidental connection or disconnection of cable segments, which can lead to equipment overload due to reactive power imbalance. Using such a combination of generator and reactive power compensation device according to the invention to excite transmission system components offers the many advantages described above.

[0033] It should be noted that embodiments of the invention have been described with reference to different subjects. In particular, some embodiments have been described with reference to apparatus-type claims, while others have been described with reference to method-type claims. However, those skilled in the art will understand from the above and below that, unless otherwise notified, any combination of features related to different subjects, in particular any combination of features between apparatus-type claims and method-type claims, is also considered to be disclosed in this application, except for any combination of features belonging to one type of subject matter. Attached Figure Description

[0034] The above-defined aspects and other aspects of the invention will become apparent from the examples of embodiments described below, and will be explained with reference to the examples of embodiments. The invention will be described in more detail below with reference to examples of embodiments, but the invention is not limited to the examples of those embodiments.

[0035] Figure 1 This shows a wind farm in its first operating mode under low wind conditions.

[0036] Figure 2 This shows a wind farm in its second operating mode under low wind conditions;

[0037] Figure 3This shows a wind farm in another operating mode after the second operating mode;

[0038] Figure 4 The image shows a wind farm in another operating mode after the second operating mode. Detailed Implementation

[0039] The illustrations in the accompanying drawings are schematic. Note that similar or identical elements are provided with the same reference numerals in different figures.

[0040] The figures below are intended to illustrate the continuous excitation process of a wind farm by a small auxiliary power source.

[0041] Figure 1 A wind farm is shown that is controlled by a control device (not shown) in several operating modes, wherein a generator G supplies active power P to a first wind turbine A1 and balances the reactive power Q of the passive cables and transformers therebetween when the first wind turbine A1 is energized. Figure 1 The diagram illustrates a wind farm in a first operating mode under low wind conditions, where the wind speed falls below a threshold. The wind farm comprises multiple wind turbines A1, A2, ..., An, which are connected in parallel to each other in a first string A, which may be a string of cables, wherein corresponding cable segment circuit breakers 21, 22, ..., 27 are arranged between adjacent wind turbines in the first string A.

[0042] Each wind turbine A, A2, ..., An in the first string A further includes a corresponding wind turbine circuit breaker 11, 12, ..., 18 to connect the corresponding wind turbine A, A2, ..., An to the first string A or to disconnect the corresponding wind turbine A, A2, ..., An from the first string A.

[0043] The wind farm includes a generator G—such as a diesel generator or any other type of power source—connected to a first wind turbine A1 in a first string A, wherein, among other things, a first string circuit breaker 20 is arranged in the line between the generator G and the first wind turbine A1. The generator G is connected to the first string A via a generator circuit breaker 50.

[0044] Under low-wind conditions where wind speeds fall below a threshold, the wind farm operates in various modes. The generator circuit breaker 50 closes under low-wind conditions and can be disconnected under other conditions. Figure 1In the first operating mode, the first series circuit breaker 20 is closed to supply active power P from generator G to the first wind turbine A1, and to supply / consume reactive power Q from generator G to the cable and transformer between generator G and the first wind turbine A1, while the remaining cable segments in the first series A are disconnected by circuit breakers 21, 22, ..., 27.

[0045] exist Figure 1 In the process, generator G excites the first part, namely the first wind turbine A1 of the first string A, thereby supplying active power to the first wind turbine A1 and balancing the reactive power of the cables and transformers between them.

[0046] Figure 2 The diagram illustrates a wind farm operating in a second mode under low wind conditions following a first operating mode. Generator G supplies active power P to first and second wind turbines A1 and A2, and the circuit breaker between the first and second wind turbines A1 and A2 is closed. When the second wind turbine A2 is energized, the reactive power Q of the balancing cable and transformer of the first wind turbine A1 is supplied. The cable segment circuit breaker 21 between the first wind turbine A1 and the adjacent second wind turbine A2 closes to supply active power P from generator G to the first and second wind turbines A1 and A2, and reactive power Q from the first wind turbine A1 to the second wind turbine A2, while the remaining cable segment circuit breakers 22, 23, ..., 27 in the first string A are open.

[0047] In other words, the wind farm comprises n wind turbines A1, A2, ..., An in a first string A, where the first wind turbine A1 is the upstream wind turbine in the first string A, and the nth wind turbine An is the downstream wind turbine in the first string A. During the first and second operating modes, cable segment circuit breakers 21, 22, ..., 27 are sequentially closed, starting from cable segment circuit breaker 21 between the first and second wind turbines A1, A2 and ending at cable segment circuit breaker 27 between the nth wind turbine An and the (n-1)th wind turbine An-1, thereby sequentially supplying active power P from the generator G to the first to the nth wind turbines A1, A2, ..., An, and sequentially supplying reactive power Q from or supplying reactive power Q to the wind turbines to balance the reactive power load on the cables and transformers.

[0048] exist Figure 2In this configuration, once the first wind turbine A1 is energized, the wind farm can then use its reactive power capacity to energize the second wind turbine A2, as well as the cables and transformers between them, while the generator G supplies active power loads to both. If required, the remaining wind turbines in the first string A can now be sequentially energized one after another, along with the remaining wind turbines in the first string A. With one or more wind turbines operating, the reactive power Q of the first string A can be primarily balanced by the wind turbines.

[0049] Figure 3 The diagram illustrates a wind farm in an additional operating mode following the second operating mode, where circuit breakers between the n wind turbines of the first string A are closed, and generator G supplies active power P to the wind turbines of the first string A, while the wind turbines balance the reactive power Q of the cables and transformers. Circuit breakers to the second string B and to the n wind turbines of the second string B are also closed, allowing generator G to supply active power P to the n wind turbines of the second string B and the n wind turbines of the first string A to balance the reactive power load of the cables and transformers of the second string, while the n wind turbines of the second string B are energized. The wind farm further includes at least one additional plurality of wind turbines B1, B2, ..., Bn, which are connected in parallel to each other in at least one additional string B, wherein corresponding cable segment circuit breakers 41, 42, ... 47 are arranged between adjacent wind turbines in at least one additional string B. The first wind turbine B1 is the upstream wind turbine in another string B, and the nth wind turbine Bn is the downstream wind turbine in another string B. Each wind turbine B, B2, ..., Bn in at least one other string B further includes a corresponding wind turbine circuit breaker 31, 32, ..., 38 to connect the corresponding wind turbine B, B2, ..., Bn to at least one other string B or to disconnect the corresponding wind turbine B, B2, ..., Bn from at least one other string B.

[0050] The generator G is also connected to at least one additional string B's first wind turbine B1, wherein at least one additional string circuit breaker 40 is arranged in the line between the generator G and the at least one additional string B's first wind turbine B1. After closing the wind turbine circuit breaker 18 between the nth wind turbine An and the (n-1)th wind turbine An-1 of the first string A, in at least one additional string B, in conjunction with, for example, in Figure 1 and Figure 2 The first and second operating modes are performed in the same manner as in the first string A. In other words, the cable segment circuit breakers 41, 42, ... 47 in at least one other string B are operated in the same manner as, for example, in... Figure 1 and Figure 2The first string A is closed sequentially in the same manner. Reactive power Q is also supplied from the wind turbine of the first string A to the cables and transformers of the other string B.

[0051] This means that in the first operating mode, the additional series circuit breaker 40 is closed to supply active power P from generator G to the first wind turbine B1, and to supply reactive power Q from the first series of wind turbines A to An to the cable and transformer between it and wind turbine B1, or from the cable and transformer between it and wind turbine B1 to the first series of wind turbines A to An, while the remaining cable segments in the other series B are disconnected by circuit breakers 41, 42, ..., 47.

[0052] In the second operating mode, the cable segment circuit breaker 41 between the first wind turbine B1 and the adjacent second wind turbine B2 is closed to supply active power P from the generator G to the first and second wind turbines B1 and B2, and reactive power Q from the first wind turbine B1 to the cable and transformer between it and the wind turbine B2, while the remaining cable segment circuit breakers 42, 43, ..., 47 in the other series B are open.

[0053] During the first and second operating modes, cable segment circuit breakers 41, 42, ..., 47 are sequentially closed, starting from cable segment circuit breaker 41 between the first and second wind turbines B1, B2 and ending at cable segment circuit breaker 47 between the nth wind turbine Bn and the (n-1)th wind turbine Bn-1, thereby sequentially supplying active power P from generator G to the first to the nth wind turbines B1, B2, ... Bn, and sequentially supplying / consuming reactive power Q to / from the wind turbines to the corresponding downstream cables and transformers.

[0054] exist Figure 3 Once the entire first string A (or its minimum number of wind turbines) is energized, it is possible to simultaneously energize other wind turbine units (e.g., those in at least one other string B) by closing another circuit breaker 40 of another string B. This can be repeated in any other string if required, until the entire wind farm is energized.

[0055] Figure 4 It is shown after the second operating mode or in Figure 3Following the initial operation, the wind farm enters another operating mode where the circuit breaker between generator G, n wind turbines of the first string A, and n wind turbines of the second string B is closed. The two strings A and B of the wind turbines have been energized using the active power P supplied by generator G and jointly balance the reactive power load on the cables and transformers. The wind farm further includes a grid supply line 5, which is connected via a grid supply line circuit breaker 6 to bus 7 between the first wind turbine A1 and generator G. If a minimum number of wind turbines in the first string A and / or at least one additional string B are energized and thus jointly provide sufficient reactive power balancing capacity, the grid supply line circuit breaker 6 closes, as in... Figure 4 As shown, active power P is supplied to bus 7 between generator G and first wind turbines A1 and B1 on power grid supply line 5, and reactive power Q is supplied to / from bus 7.

[0056] Power grid supply line 5 is connected to power grid 100 via power grid circuit breaker 8. Power grid supply line 5 includes a power grid transformer 9 and a transmission line 10 between power grid supply line circuit breaker 6 and power grid circuit breaker 8. When execution... Figures 1 to 3 In the operational mode of the embodiment, when the number of wind turbines in the first string A and / or at least one other string B is less than the minimum number, the grid circuit breaker 8 is disconnected.

[0057] exist Figure 4 In this context, once a minimum number of wind turbines in a wind farm are energized, they are then able to energize power system components such as grid transformers 9 and transmission lines 10.

[0058] In short, Figure 1 The excitation of the first wind turbine A1 using generator G as an energy source is shown. Figure 2 This illustrates how the combination of a first wind turbine A1 and a generator G can energize a second, third, fourth, and additional wind turbines up to the minimum required number of wind turbines in the first string A, so that additional groups in the additional strings B can be energized immediately. Figure 3 This illustrates how the first group of wind turbines in the first string A excites the second group of wind turbines in another string B, and this can be repeated if required until the entire wind farm is excited. Figure 4 This demonstrates how even the smallest wind turbine unit can incentivize other electrical system components.

[0059] Advantageously, when wind speeds are too low for the electricity production of the wind turbines themselves, the wind farm can self-excite and maintain the excitation of itself and the various parts of the transmission system.

[0060] Compared to the rated power of a wind farm, the size of the generator G or additional energy source required to excite / maintain the wind farm under low wind conditions can be relatively small.

[0061] This capability will bring another advantage, as it will allow for black starts of the grid regardless of wind speed. It will also eliminate the need for wind farm operators to install large temporary diesel generators and reactive power compensation equipment to maintain climate control for wind farms should extended grid outages be anticipated.

[0062] This invention also avoids providing separate diesel generators or energy storage devices, which must be sized to provide the same reactive power capacity for all wind turbine power converters and active power loads. Such large diesel generators or storage devices would significantly increase costs.

[0063] It should be noted that the term "comprising" does not exclude other elements or steps, and "a" or "an" does not exclude multiple. Elements described in conjunction with different embodiments may also be combined. It should also be noted that reference numerals in the claims should not be construed as limiting the scope of the claims.

Claims

1. A method for supplying electricity to a wind farm, the wind farm comprising a plurality of wind turbines (A1, A2, ..., An) connected in parallel to each other in a first string (A), wherein corresponding cable segment circuit breakers (21, 22, ..., 27) are arranged between adjacent wind turbines in the first string (A); and a generator (G) connected to a first wind turbine (A1) in the first string (A), wherein a first string circuit breaker (20) is arranged in the line between the generator (G) and the first wind turbine (A1); in, The method includes the following operating modes under low-wind conditions where the wind speed falls below a threshold: In the first operating mode, the first series of circuit breakers (20) are closed to supply active power (P) from the generator (G) to the first wind turbine (A1), and to supply or consume reactive power (Q) from the generator (G) to the passive cable and / or transformer between the generator (G) and the first wind turbine (A1), while the remaining cable segments in the first series (A) are disconnected by circuit breakers (21, 22, ..., 27). In the second operating mode following the first operating mode, the cable segment circuit breaker (21) between the first wind turbine (A1) and the adjacent second wind turbine (A2) is closed to supply active power (P) from the generator (G) to the first and second wind turbines (A1, A2) and to supply or consume reactive power (Q) from the first wind turbine (A1) to the passive cable and / or transformer between the first wind turbine (A1) and the second wind turbine (A2) to the first wind turbine (A1), while the remaining cable segment circuit breakers (22, 23, ..., 27) in the first string (A) are open.

2. The method according to the preceding claim, wherein: The wind farm consists of n wind turbines (A1, A2, ..., An) in the first string (A), where the first wind turbine (A1) is the upstream wind turbine in the first string (A), and the nth wind turbine (An) is the downstream wind turbine in the first string (A). The method includes: Starting from the cable segment circuit breaker (21) between the first and second wind turbines (A1, A2) up to the cable segment circuit breaker (27) between the nth wind turbine (An) and the (n-1)th wind turbine (An-1), the cable segment circuit breakers are closed sequentially, thereby sequentially supplying active power (P) from the generator (G) to the first to the nth wind turbines (A1, A2, ..., An), and sequentially supplying or consuming reactive power (Q) from the wind turbines to the corresponding downstream passive cables and / or transformers.

3. The method according to any one of the preceding claims, wherein The wind farm further includes at least one additional plurality of wind turbines (B1, B2, ..., Bn), the at least one additional plurality of wind turbines (B1, B2, ..., Bn) are connected in parallel to each other in at least one additional string (B), wherein corresponding cable segment circuit breakers (41, 42, ..., 47) are arranged between adjacent wind turbines in at least one additional string (B); wherein a generator (G) is connected to the first wind turbine (B1) of at least one additional string (B), wherein at least one additional string circuit breaker (40) is arranged in the line between the generator (G) and the first wind turbine (B1) of at least one additional string (B), The method further includes, after closing the wind turbine circuit breaker (18) between the nth wind turbine (An) and the (n-1)th wind turbine (An-1) in the first string (A), The first and second operating modes are performed in the at least one additional string (B) in the same manner as in the first string (A) according to claim 1, and / or the cable segment circuit breakers (41, 42, ..., 47) in the at least one additional string (B) are sequentially closed in the same manner as in the first string (A) according to claim 2; Reactive power (Q) is also supplied from the wind turbines of the first string (A) to the passive cables and / or transformers of the other string (B), or consumed from the passive cables and / or transformers of the other string (B) to the wind turbines of the first string (A).

4. The method according to any one of the preceding claims, wherein The wind farm further includes a power grid supply line (5), which is connected via a power grid supply line circuit breaker (6) to a busbar (7) between the first wind turbine (A1) and the generator (G), wherein, If the minimum number of wind turbines in the first string (A) is operating, the grid power supply line circuit breaker (6) closes to supply active power (P) and consumes reactive power (Q) from the bus (7) between the first wind turbine (A1) and the generator (G) to the grid power supply line (5) or from the grid power supply line (5) to the bus (7) between the first wind turbine (A1) and the generator (G).

5. The method according to the preceding claim, wherein... The power supply line (5) is connected to the power grid (100) at its far end via a power grid circuit breaker (8), wherein the power supply line (5) includes a power grid transformer (9) and / or transmission line (10) between the power supply line circuit breaker (6) and the power grid circuit breaker (8), wherein the power grid circuit breaker (8) is disconnected when at least one of the steps of the preceding claims is performed.

6. The method according to any one of the preceding claims, wherein, The wind farm includes at least one of the following: Each wind turbine (A, A2, ..., An) in the first string (A) includes a corresponding wind turbine connection circuit breaker (11, 12, ..., 18) to connect the corresponding wind turbine (A, A2, ..., An) to or disconnect from the first string (A); Each wind turbine (B, B2, ..., Bn) in at least one additional string (B) includes a corresponding wind turbine circuit breaker (31, 32, ..., 38) to connect the corresponding wind turbine (B, B2, ..., Bn) to at least one additional string (B) or to disconnect it from at least one additional string (B). The generator (G) is connected to the first string (A) via a generator circuit breaker (50), wherein the generator circuit breaker (50) closes under low wind conditions and opens under conditions other than low wind conditions.

7. A wind farm, comprising: Multiple wind turbines (A1, A2, ..., An) are connected in parallel to each other in a first string (A), wherein corresponding cable segment circuit breakers (21, 22, ..., 27) are arranged between adjacent wind turbines in the first string (A); A generator (G) is connected to a first wind turbine (A1) of a first string (A), wherein a first string of circuit breakers (20) is arranged in the line between the generator (G) and the first wind turbine (A1); and Control equipment, configured to operate the wind farm in the following operating modes under low wind conditions where wind speeds fall below a threshold: In the first operating mode, the first series of circuit breakers (20) are closed to supply active power (P) from the generator (G) to the first wind turbine (A1), and to supply or consume reactive power (Q) from the generator (G) to the passive cable and / or transformer between the generator (G) and the first wind turbine (A1), while the remaining cable segments in the first series (A) are disconnected by circuit breakers (21, 22, ..., 27). In the second operating mode following the first operating mode, the cable segment circuit breaker (21) between the first wind turbine (A1) and the adjacent second wind turbine (A2) is closed to supply active power (P) from the generator (G) to the first and second wind turbines (A1, A2) and to supply or consume reactive power (Q) from the first wind turbine (A1) to the passive cable and / or transformer between the first wind turbine (A1) and the second wind turbine (A2) to the first wind turbine (A1), while the remaining cable segment circuit breakers (22, 23, ..., 27) in the first string (A) are open.

8. The wind farm according to the preceding claims, wherein: The wind farm consists of n wind turbines (A1, A2, ..., An) in the first string (A), where the first wind turbine (A1) is the upstream wind turbine in the first string (A), and the nth wind turbine (An) is the downstream wind turbine in the first string (A). The control device is configured to: Starting from the cable segment circuit breaker (21) between the first and second wind turbines (A1, A2) up to the cable segment circuit breaker (27) between the nth wind turbine (An) and the (n-1)th wind turbine (An-1), the cable segment circuit breakers are closed sequentially, thereby sequentially supplying active power from the generator (G) to the first to the nth wind turbines (A1, A2, ..., An), and sequentially supplying or consuming reactive power (Q) from the wind turbines to the corresponding downstream passive cables and / or transformers.

9. The wind farm according to any one of claims 7 and 8, wherein The wind farm further includes at least one additional plurality of wind turbines (B1, B2, ..., Bn), which are connected in parallel to each other in at least one additional string (B), wherein corresponding cable segment circuit breakers (41, 42, ..., 47) are arranged between adjacent wind turbines in the at least one additional string (B); wherein a generator (G) is connected to the first wind turbine (B1) of the at least one additional string (B), and wherein at least one additional string circuit breaker (40) is arranged in the line between the generator (G) and the first wind turbine (B1) of the at least one additional string (B). in, After closing the wind turbine circuit breaker (18) between the nth wind turbine (An) and the (n-1)th wind turbine (An-1) in the first string (A), the control device is further configured to: The first and second operating modes are performed in at least one additional string (B) in the same manner as in the first string (A) according to claim 7, and / or the cable segment circuit breakers (41, 42, ..., 47) in the at least one additional string (B) are sequentially closed in the same manner as in the first string (A) according to claim 8; Reactive power (Q) is also supplied from the wind turbines of the first string (A) to the passive cables and / or transformers of the other string (B), or consumed from the passive cables and / or transformers of the other string (B) to the wind turbines of the first string (A).

10. The wind farm according to any one of claims 7 to 9, wherein The wind farm further includes a power grid supply line (5), which is connected via a power grid supply line circuit breaker (6) to a busbar (7) between the first wind turbine (A1) and the generator (G), wherein, If the minimum number of wind turbines in the first string (A) is energized, the control device is configured to close the grid power supply line circuit breaker (6) to supply active power (P) and to supply or consume reactive power (Q) from the bus (7) between the first wind turbine (A1) and the generator (G) to the grid power supply line (5) or from the grid power supply line (5) to the bus (7) between the first wind turbine (A1) and the generator (G).

11. The wind farm according to the preceding claim, wherein The power supply line (5) is connected to the power grid (100) via the power grid circuit breaker (8), wherein the power supply line (5) includes a power grid transformer (9) and / or transmission line (10) between the power supply line circuit breaker (6) and the power grid circuit breaker (8), wherein the control device is configured to disconnect the power grid circuit breaker (8) when performing the steps of at least one of the preceding claims.

12. The wind farm according to any one of claims 7 to 11, wherein, The wind farm includes at least one of the following: Each wind turbine (A, A2, ..., An) in the first string (A) includes a corresponding wind turbine circuit breaker (11, 12, ..., 18) to connect the corresponding wind turbine (A, A2, ..., An) to or disconnect from the first string (A); Each wind turbine (B, B2, ..., Bn) in the at least one additional string (B) includes a corresponding wind turbine circuit breaker (31, 32, ..., 38) to connect the corresponding wind turbine (B, B2, ..., Bn) to or disconnect from the at least one additional string (B). The generator (G) is connected to the first string (A) via a generator circuit breaker (50), wherein the control device is configured to close the generator circuit breaker (50) under low wind conditions and open the generator circuit breaker (50) under conditions other than low wind conditions.

Images