Wind turbine generator set box transformer substation, wind turbine generator set and wind power plant

Abstract

The utility model relates to the technical field of new energy power generation, and discloses a wind turbine generator set box transformer substation, a wind turbine generator set and a wind power plant, which can restrain 5 / 7 harmonic waves. The high-voltage side and the low-voltage side of the wind turbine generator box transformer are in magnetic induction, the low-voltage side comprises at least one first low-voltage winding and at least one second low-voltage winding, the first low-voltage winding and the second low-voltage winding are connected in parallel, and the wiring modes of the first low-voltage winding and the second low-voltage winding are different. The high-voltage side comprises at least one high-voltage winding, and the magnetic field of the high-voltage winding is ahead of the magnetic field of any low-voltage winding in time.

Description

Technical Field

[0001] The present disclosure relates to the technical field of new energy power generation, and in particular, to a wind turbine transformer, a wind turbine and a wind farm. Background Art

[0002] During the grid connection process of a wind turbine, it is impossible to suppress the 5 / 7th harmonics with a relatively high content at the grid connection point of the wind turbine, and it is necessary to additionally configure a passive or active filter bank, resulting in an increase in the operating cost of the wind farm. Summary of the Utility Model

[0003] The purpose of the present disclosure is to provide a wind turbine transformer, a wind turbine and a wind farm that can suppress the 5 / 7th harmonics.

[0004] To achieve the above purpose, in a first aspect, the present disclosure provides a wind turbine transformer, where the high-voltage side and the low-voltage side of the wind turbine transformer are magnetically induced. The low-voltage side includes at least one first low-voltage winding and at least one second low-voltage winding. The first low-voltage winding and the second low-voltage winding are connected in parallel, and the wiring methods of the first low-voltage winding and the second low-voltage winding are different;

[0005] The high-voltage side includes at least one high-voltage winding, and the magnetic field of the high-voltage winding leads the magnetic field of any low-voltage winding in time.

[0006] In a second aspect, the present disclosure provides a wind turbine, including: an inverter, a filtering device, and the wind turbine transformer according to the first aspect. The inverter, the filtering device, and the wind turbine transformer are connected in series in sequence.

[0007] In a third aspect, the present disclosure provides a wind farm, including the wind turbine according to the fourth aspect.

[0008] Through the above technical solution, the high-voltage side and the low-voltage side of the wind turbine transformer are magnetically induced. The low-voltage side includes a first low-voltage winding and a second low-voltage winding connected in parallel, and the wiring methods of the first low-voltage winding and the second low-voltage winding are different. The high-voltage side includes at least one high-voltage winding, and the magnetic field of the high-voltage winding leads the magnetic field of any low-voltage winding in time. The two low-voltage windings are connected in parallel, and the magnetic field of the high-voltage winding leads the magnetic field of any low-voltage winding in time, which can ensure that the phase currents flowing through the two low-voltage windings are in the same direction. Therefore, by adjusting the turn ratio of the windings, the 5 / 7th harmonics can be suppressed.

[0009] Other features and advantages of the present disclosure will be described in detail in the subsequent specific implementation part. Brief Description of the Drawings

[0010] The accompanying drawings are used to provide a further understanding of the present disclosure, and constitute a part of the specification. Together with the following detailed description, they are used to explain the present disclosure, but do not constitute a limitation to the present disclosure. In the accompanying drawings:

[0011] Figure 1 is a circuit diagram of an existing grid-connected topology of a wind turbine generator set.

[0012] Figure 2 is a circuit diagram of a wind turbine generator set box transformer shown according to an exemplary embodiment of the present disclosure.

[0013] Figure 3 is another circuit diagram of a wind turbine generator set box transformer shown according to an exemplary embodiment of the present disclosure.

[0014] Figure 4a and Figure 4b is a current vector diagram of a wind turbine generator set box transformer under fundamental wave shown according to an exemplary embodiment of the present disclosure.

[0015] Figure 5a and Figure 5b is a current vector diagram of a wind turbine generator set box transformer under 5th harmonic shown according to an exemplary embodiment of the present disclosure.

[0016] Figure 6a and Figure 6b is a current vector diagram of a wind turbine generator set box transformer under 7th harmonic shown according to an exemplary embodiment of the present disclosure.

[0017] Figure 7 is a flowchart of a control method for a wind turbine generator set box transformer shown according to an exemplary embodiment of the present disclosure.

[0018] Figure 8 is a block diagram of a control device for a wind turbine generator set box transformer shown according to an exemplary embodiment of the present disclosure.

[0019] Figure 9 is a circuit diagram of a wind turbine generator set shown according to an exemplary embodiment of the present disclosure.

[0020] Description of Reference Numerals

[0021] 10 Converter, 20 Filter Device, 30 Existing Wind Turbine Generator Set Box Transformer, 40 Collector Line, 50 Wind Turbine Generator Set Box Transformer, 1 Low Voltage Side, 2 High Voltage Side, 11 First Low Voltage Winding, 12 Second Low Voltage Winding, 21 First High Voltage Winding, 22 Second High Voltage Winding, Wind Turbine Phase Change Control Device 80, Determination Module 81, Adjustment Module 82 Detailed Description

[0022] The following is a detailed description of the specific embodiments of the present disclosure in conjunction with the accompanying drawings. It should be understood that the specific embodiments described herein are only for the purpose of illustrating and explaining the present disclosure, and are not intended to limit the present disclosure.

[0023] As the proportion of wind power generation in wind turbines continues to increase, various harmonics will be generated, thus affecting the power quality of the grid connection point. Therefore, effectively reducing the harmonic current of the wind farm connected to the grid is of great significance for the safe and stable grid connection of wind power.

[0024] The conventional grid connection topology of wind turbines is as Figure 1 shown. The three-phase voltage output by the converter 10 in the wind turbine is input to the existing wind turbine box transformer 30 through the LCL filtering device 20, is increased to 35 kV by the existing wind turbine box transformer 30, and then is transmitted to the 35 kV side of the 110 kV or 220 kV step-up substation of the wind farm booster station through the collector line 40 (such as underground cable, overhead line, etc.), and is connected to the grid after being stepped up by the 110 kV / 220 kV transformer.

[0025] The links with filtering functions in the whole grid connection process include the LCL filtering device 20 and the existing wind turbine box transformer 30. Among them, the LCL filtering device 20 can filter out high-order harmonics; the existing wind turbine box transformer 30 adopts the Dy11 wiring method, and the high-order harmonics above the third and its integer multiples can form a circulating current on the primary side (i.e., the high-voltage side) of the transformer, which is beneficial to restricting the 3Nth harmonic. That is, the wiring characteristics of the existing wind turbine box transformer 30 can restrict the 3Nth harmonic on the 35 kV collector line side, but cannot suppress the 5 / 7th harmonics with relatively high content at the current grid connection point of the wind farm. The wind farm also needs to be additionally equipped with a passive or active filter bank, resulting in an increase in the operating cost of the wind farm. And the actual measurement results at the grid connection point of the wind farm show that the content of the 5 / 7th harmonics at the grid connection point is still at a relatively high level. Therefore, the existing wind turbine grid connection topology does not have the ability to suppress the 5 / 7th harmonics.

[0026] In view of this, the present disclosure provides a wind turbine box transformer, a wind turbine and a wind farm, which can ensure that the phase currents flowing through the two low-voltage windings are in the same direction, so that by adjusting the turn ratio of the windings, the 5 / 7th harmonics can be suppressed.

[0027] Figure 2 is a block diagram of a wind turbine box transformer shown according to an exemplary embodiment of the present disclosure, as Figure 2 shown. The high-voltage side 2 of the wind turbine box transformer is magnetically coupled with the low-voltage side 1. The low-voltage side 1 includes at least one first low-voltage winding 11 and at least one second low-voltage winding 12. The first low-voltage winding 11 and the second low-voltage winding 12 are connected in parallel, and the wiring methods of the first low-voltage winding 11 and the second low-voltage winding 12 are different;

[0028] The high-voltage side 2 includes at least one high-voltage winding, and the magnetic field of the high-voltage winding leads the magnetic field of any low-voltage winding in time.

[0029] In the embodiments of the present disclosure, two low-voltage side windings are connected in parallel, and the magnetic field of the high-voltage winding leads the magnetic field of any low-voltage winding in time. By increasing the number of windings on the low-voltage side of the wind turbine transformer and changing the wiring method, the fundamental wave line currents induced by the two low-voltage side windings on the high-voltage side winding can be made in the same direction and the 5 / 7th harmonics in the opposite direction through the phase-shifting method, thereby eliminating the 5 / 7th harmonics on the high-voltage side. The cancellation of the 5 / 7th harmonic current in the line current on the 35 kV side can be achieved, so that the content of the 5 / 7th harmonics at the grid connection point is greatly reduced.

[0030] To facilitate those skilled in the art to better understand the wind turbine transformer provided by the present disclosure, a detailed description thereof is given below.

[0031] In a feasible embodiment, the structure of the first low-voltage winding 11 includes an axial structure or a radial structure, and the structure of the second low-voltage winding 12 is the same as that of the first low-voltage winding 11.

[0032] It should be understood that the low-voltage windings on the low-voltage side may also have other structures, and the present disclosure does not limit this.

[0033] In a feasible embodiment, the magnetic field of the high-voltage winding 21 leads the magnetic field of any low-voltage winding by 30° electrical angle in time.

[0034] It is worth noting that the magnetic field of the high-voltage winding leads the magnetic field of the low-voltage winding by 30° electrical angle in time, which is convenient for making the line currents of different frequencies induced by the two low-voltage side windings on the high-voltage side winding in the same direction or in the opposite direction through the phase-shifting method subsequently.

[0035] It is worth noting that according to the number of high-voltage windings on the high-voltage side in the wind turbine transformer, there are two magnetic induction methods between the high-voltage side and the low-voltage side. The first method is that when the high-voltage side includes one high-voltage winding, all the low-voltage windings on the low-voltage side are magnetically induced with this high-voltage winding; the second method is that when the high-voltage side includes multiple high-voltage windings, the first low-voltage winding and the second low-voltage winding on the low-voltage side are magnetically induced with different high-voltage windings respectively.

[0036] For the first method: when the high-voltage side includes one high-voltage winding, all the low-voltage windings on the low-voltage side are magnetically induced with this high-voltage winding.

[0037] In a feasible embodiment, as Figure 2As shown, the low-voltage side 1 includes the first low-voltage winding 11 and the second low-voltage winding 12, the high-voltage side includes a high-voltage winding, and both the first low-voltage winding 11 and the second low-voltage winding 12 are electrically connected to the high-voltage winding.

[0038] In the embodiments of the present disclosure, the 5 / 7th harmonics induced by the low-voltage side windings in the high-voltage side can be cancelled out, achieving a significant suppression of the 5 / 7th harmonics by the in-situ box transformer, and thus greatly reducing the 5 / 7th harmonic content at the grid connection point of the wind farm.

[0039] For the second method: As Figure 3 shown, when the high-voltage side includes two high-voltage windings, the first low-voltage winding and the second low-voltage winding in the low-voltage side are respectively magnetically induced with different high-voltage windings.

[0040] In a feasible embodiment, the low-voltage side 1 includes the first low-voltage winding 11 and the second low-voltage winding 12, and the high-voltage side 2 includes a first high-voltage winding 21 and a second high-voltage winding 22;

[0041] The first low-voltage winding 11 is electrically connected to the first high-voltage winding 21, and the second low-voltage winding 12 is electrically connected to the second high-voltage winding 22.

[0042] In the embodiments of the present disclosure, the 5 / 7th harmonics induced by the low-voltage side windings in the high-voltage side can be cancelled out, achieving a significant suppression of the 5 / 7th harmonics by the in-situ box transformer, and thus greatly reducing the 5 / 7th harmonic content at the grid connection point of the wind farm.

[0043] It should be noted that in the above two methods, the wiring methods of the first low-voltage side winding, the second low-voltage side winding, and each high-voltage side winding are the same.

[0044] In a feasible embodiment, as Figure 2 shown, the first low-voltage winding 11 includes a first coil l1, a second coil l2, and a third coil l3. The first end a1 of the first coil l1, the first end b1 of the second coil l2, and the first end c1 of the third coil l3 are connected to the second low-voltage winding 12, and the second end x1 of the first coil l1 is respectively connected to the second end y1 of the second coil l2 and the second end z1 of the third coil l3.

[0045] In a feasible embodiment, as Figure 2As shown, the second low-voltage winding 12 includes a fourth coil l4, a fifth coil l5, and a sixth coil l6. The first end a2 of the fourth coil l4 is respectively connected to the first end a1 of the first coil l1 and the second end y2 of the fifth coil l5. The first end b2 of the fifth coil l5 is respectively connected to the first end b1 of the second coil l2 and the second end z2 of the sixth coil l6. The first end c2 of the sixth coil l6 is respectively connected to the first end c1 of the third coil l3 and the second end x2 of the fourth coil l4.

[0046] In a feasible embodiment, as Figure 2 shown, the high-voltage winding includes a seventh coil L1, an eighth coil L2, and a ninth coil L3. The first end A of the seventh coil L1 is connected to the second end Y of the eighth coil L2. The first end B of the eighth coil L2 is connected to the second end Z of the ninth coil L3. The first end C of the ninth coil L3 is connected to the second end X of the seventh coil L1.

[0047] It should be noted that the first low-voltage winding adopts a star connection method (i.e., Y connection method), the second low-voltage winding adopts a delta connection method (i.e., △ connection method), and the high-voltage winding adopts a delta connection method (i.e., the connection method of the wind turbine transformer is Dy11d connection). On the basis of retaining the harmonic suppression characteristics of the wind turbine transformer for 3N harmonics, the phase-shifting method can be used to make the fundamental line currents induced by the two low-voltage windings on the high-voltage winding in the same direction, and the 5 / 7 harmonics in the opposite direction, so as to eliminate the 5 / 7 harmonics on the high-voltage side.

[0048] The low-voltage side of the wind turbine transformer is the secondary side of the wind turbine transformer, and the high-voltage side of the wind turbine transformer is the primary side of the wind turbine transformer. The two low-voltage windings are connected in parallel, and the phase currents flowing through the windings are in the same direction. The current flow directions of the wind turbine transformer at different frequencies are as follows:

[0049] For the fundamental wave, refer to Figure 4a and Figure 4b , in the Dy11 connection method, the high-voltage side I AB-11 lags behind the secondary side I ab-11 by 30°; in the Dd connection method, the high-voltage side I AB-21 is in the same direction as the secondary side I ab-21 . However, since the secondary side I ab-21 itself leads I ab-11 by 30°, the line currents I AB-11 induced by the two low-voltage windings on the primary side are in the same direction as I AB-21 , and the high-voltage side output current is the sum of the two.

[0050] For the 5th harmonic, refer to Figure 5a and Figure 5b, in the Dy11 connection mode, the high-voltage side I AB-15 leads the secondary side I ab- 25 by 30°; in the Dd connection mode, the high-voltage side I AB-21 is in the same direction as the secondary side I ab-21 . Since the 5th harmonic is a negative sequence, when the secondary side is equivalent to the primary side, I ab-15 leads I ab-25 by 150°. Therefore, the line currents I AB-11 induced by the two low-voltage side windings on the primary side are AB-21 in the opposite direction to I. By adjusting the winding turns ratio, the 5th harmonic output on the high-voltage side can be further made zero.

[0051] For the 7th harmonic, see Figure 6a and Figure 6b . In the Dy11 connection mode, the high-voltage side I AB-11 lags behind the secondary side I ab- 11 by 30°; in the Dd connection mode, the high-voltage side I AB-21 is in the same direction as the secondary side I ab-21 . Since the 7th harmonic is a positive sequence, when the secondary side is equivalent to the primary side, I ab-17 lags behind I AB-27 by 210°. Therefore, the line currents I AB-11 induced by the two low-voltage side windings on the primary side are AB-21 in the opposite direction to I. By adjusting the winding turns ratio, the 7th harmonic output on the high-voltage side can be further made zero.

[0052] In summary, the wind turbine transformer in the embodiments of the present disclosure can make the 5th / 7th harmonics induced by the secondary side windings on the primary side cancel each other out, achieving a significant suppression of the 5th / 7th harmonics by the wind turbine transformer, and thus greatly reducing the 5th / 7th harmonic content at the grid connection point of the wind farm.

[0053] In the wind turbine provided by the present disclosure, the two low-voltage side windings in the wind turbine transformer can be connected in parallel to the same wind turbine, or the two low-voltage side windings can be respectively connected to two or an integer multiple of wind turbines. Only by making the output signals of two or more wind turbines the same through the control system can it be ensured that the 5th / 7th harmonic line currents on the primary side of the two low-voltage side windings are opposite in phase. It is also possible to eliminate the 5th / 7th harmonics on the high-voltage side of the step-up transformer by changing the structure and connection mode of the substation step-up transformer. And the high-voltage side voltage level is generally 35 kV, and it can also be applied to other voltage levels, which is not limited in the present disclosure.

[0054] Based on the same concept, the present disclosure also provides a control method for a wind turbine transformer, including the above-mentioned wind turbine transformer, as Figure 7 shown, the method may include the following steps:

[0055] In step S11, determine the measured harmonic value of the harmonic to be suppressed on the high-voltage side of the box-type transformer of the wind turbine generator set, and the box-type transformer of the wind turbine generator set adopts the target wiring method;

[0056] In step S12, according to the harmonic limit value corresponding to the harmonic to be suppressed and the measured harmonic value, adjust the turns ratio of the first low-voltage winding and the second low-voltage winding on the low-voltage side of the box-type transformer of the wind turbine generator set to suppress the harmonic on the high-voltage side of the box-type transformer of the wind turbine generator set.

[0057] In the embodiment of the present disclosure, the two low-voltage side windings are connected in parallel, and the magnetic field of the high-voltage winding leads the magnetic field of any low-voltage winding in time. Increase the number of windings on the low-voltage side of the box-type transformer of the wind turbine generator set and change the wiring method. Adjust the turns ratio of the first low-voltage winding and the second low-voltage winding on the low-voltage side of the box-type transformer of the wind turbine generator set. Through the phase-shifting method, the fundamental wave line currents induced by the two low-voltage side windings on the high-voltage side winding are in the same direction, and the 5 / 7th harmonics are in the opposite direction, so as to eliminate the 5 / 7th harmonics on the high-voltage side. It is possible to cancel the 5 / 7th harmonic current in the line current on the 35 kV side, so as to greatly reduce the 5 / 7th harmonic content at the grid connection point.

[0058] In a feasible embodiment, the determining the measured harmonic value of the harmonic to be suppressed on the high-voltage side of the box-type transformer of the wind turbine generator set may include:

[0059] Determine the first measured harmonic value of the 5th harmonic and / or the second measured harmonic value of the 7th harmonic on the high-voltage side of the box-type transformer of the wind turbine generator set.

[0060] In a feasible embodiment, the target wiring method may be determined by the following method:

[0061] According to the theoretical harmonic value of the harmonic to be suppressed, determine the number of low-voltage windings on the low-voltage side and the wiring method of each low-voltage winding.

[0062] In a feasible embodiment, the determining the number of low-voltage windings on the low-voltage side and the wiring method of each low-voltage winding according to the theoretical harmonic value of the harmonic to be suppressed may include:

[0063] According to the theoretical harmonic value, determine the number of the first low-voltage winding and the second low-voltage winding on the low-voltage side, and the target wiring method of the first low-voltage winding and the second low-voltage winding.

[0064] Based on the same concept, the present disclosure also provides a control device for a box-type transformer of a wind turbine generator set, which is used to control the above-mentioned box-type transformer of the wind turbine generator set. As Figure 8 shown, the control device 80 for the box-type transformer of the wind turbine generator set includes a determination module 81 and an adjustment module 82.

[0065] Among them, a determination module 81 is configured to determine an actual harmonic value of a harmonic to be suppressed on a high-voltage side in the wind turbine transformer substation, and the wind turbine transformer substation adopts a target wiring mode.

[0066] An adjustment module 82 is configured to adjust a turns ratio between a first low-voltage winding and a second low-voltage winding on a low-voltage side in the wind turbine transformer substation according to a harmonic limit value corresponding to the harmonic to be suppressed and the actual harmonic value, so as to suppress the harmonic on the high-voltage side in the wind turbine transformer substation.

[0067] In an embodiment of the present disclosure, two low-voltage side windings are connected in parallel, and a magnetic field of a high-voltage winding leads a magnetic field of any low-voltage winding in time. The number of windings on the low-voltage side in the wind turbine transformer substation is increased and the wiring mode is changed. The turns ratio between the first low-voltage winding and the second low-voltage winding on the low-voltage side in the wind turbine transformer substation is adjusted. By means of phase shift, the fundamental wave line currents induced by the two windings on the low-voltage side in the high-voltage side winding are in the same direction, and the 5 / 7th harmonics are in the opposite direction, so as to eliminate the 5 / 7th harmonics on the high-voltage side. The cancellation of the 5 / 7th harmonic current in the line current on the 35 kV side can be realized, so that the 5 / 7th harmonic content at the grid connection point is greatly reduced.

[0068] In a feasible embodiment, the determination module 81 is configured to determine a first actual harmonic value of the 5th harmonic and / or a second actual harmonic value of the 7th harmonic on the high-voltage side in the wind turbine transformer substation.

[0069] In a feasible embodiment, the determination module 81 is configured to determine the number of low-voltage windings on the low-voltage side and the wiring mode of each low-voltage winding according to a theoretical harmonic value of the harmonic to be suppressed.

[0070] In a feasible embodiment, the determination module 81 is configured to determine the number of the first low-voltage winding and the second low-voltage winding on the low-voltage side and a target wiring mode of the first low-voltage winding and the second low-voltage winding according to the theoretical harmonic value.

[0071] Based on the same concept, as Figure 9 shown, the present disclosure further provides a wind turbine, including: an inverter 10, a filtering device 20, and the above-mentioned wind turbine transformer substation 50, and the inverter 10, the filtering device 20, and the wind turbine transformer substation 30 are connected in series in sequence.

[0072] In a feasible embodiment, a primary side of the wind turbine transformer substation 50 is connected to a collector line 40, and the boosted three-phase voltage is transmitted to a wind farm step-up substation through the collector line 40.

[0073] In the embodiments of the present disclosure, by changing the structure and winding connection mode of the wind turbine transformer, the 3N - harmonic suppression characteristic of the wind turbine transformer is retained, and the suppression characteristic of the transformer for 5 / 7 - harmonics is significantly improved. As a result, the 5 / 7 - harmonic content at the grid connection point of the wind farm is reduced, the safe and reliable operation of the power grid is improved, and at the same time, the additional configuration of filters in the wind farm is avoided, reducing the operation cost of the wind farm. Moreover, the application scenarios of the wind turbine transformer can be the grid - connection scenarios of photovoltaic or energy - storage power station converters in addition to wind turbines. The present disclosure does not limit its application scenarios.

[0074] Based on the same concept, the present disclosure also provides a wind farm, including the above - mentioned wind turbines.

[0075] In the embodiments of the present disclosure, by changing the structure and winding connection mode of the wind turbine transformer, the 3N - harmonic suppression characteristic of the wind turbine transformer is retained, and the suppression characteristic of the transformer for 5 / 7 - harmonics is significantly improved. As a result, the 5 / 7 - harmonic content at the grid connection point of the wind farm is reduced, the safe and reliable operation of the power grid is improved, and at the same time, the additional configuration of filters in the wind farm is avoided, reducing the operation cost of the wind farm. Moreover, the application scenarios of the wind turbine transformer can be the grid - connection scenarios of photovoltaic or energy - storage power station converters in addition to wind turbines. The present disclosure does not limit its application scenarios.

[0076] The preferred embodiments of the present disclosure have been described in detail above with reference to the accompanying drawings. However, the present disclosure is not limited to the specific details in the above - mentioned embodiments. Within the scope of the technical concept of the present disclosure, various simple modifications can be made to the technical solutions of the present disclosure, and these simple modifications all fall within the protection scope of the present disclosure.

[0077] In addition, it should be noted that, in the above - described specific embodiments, the various specific technical features can be combined in any suitable manner without conflict. To avoid unnecessary repetition, the present disclosure does not separately describe various possible combination methods.

[0078] Furthermore, any combination can be made among the various different embodiments of the present disclosure as long as it does not violate the idea of the present disclosure, and it should also be regarded as the content disclosed by the present disclosure.

Claims

1. A wind turbine box transformer, characterized in that: The high-voltage side (2) and the low-voltage side (1) of the wind turbine box transformer are magnetically induced, the low-voltage side (1) comprises at least one first low-voltage winding (11) and at least one second low-voltage winding (12), the first low-voltage winding (11) and the second low-voltage winding (12) are connected in parallel, and the first low-voltage winding (11) and the second low-voltage winding (12) are connected in different ways; The high voltage side (2) comprises at least one high voltage winding, the magnetic field of the high voltage winding being ahead of the magnetic field of any low voltage winding in time; The first low-voltage winding (11) comprises a first coil, a second coil and a third coil, the first end of the first coil, the first end of the second coil and the first end of the third coil are connected to the second low-voltage winding, and the second end of the first coil is connected to the second end of the second coil and the second end of the third coil respectively; The second low-voltage winding (12) comprises a fourth coil, a fifth coil and a sixth coil, the first end of the fourth coil is respectively connected to the first end of the first coil and the second end of the fifth coil, the first end of the fifth coil is respectively connected to the first end of the second coil and the second end of the sixth coil, and the first end of the sixth coil is respectively connected to the first end of the third coil and the second end of the fourth coil; The high-voltage winding includes a seventh coil, an eighth coil and a ninth coil, the first end of the seventh coil is connected to the second end of the eighth coil, the first end of the eighth coil is connected to the second end of the ninth coil, and the first end of the ninth coil is connected to the second end of the seventh coil.

2. The wind turbine box transformer according to claim 1 is characterized in that: The low-voltage side (1) comprises the first low-voltage winding (11) and the second low-voltage winding (12), and the high-voltage side (2) comprises a high-voltage winding, wherein the first low-voltage winding (11) and the second low-voltage winding (12) are both electrically connected to the high-voltage winding.

3. The wind turbine box transformer according to claim 1 is characterized in that: The low-voltage side (1) comprises the first low-voltage winding (11) and the second low-voltage winding (12), and the high-voltage side comprises the first high-voltage winding (21) and the second high-voltage winding (22); The first low-voltage winding (11) is electrically connected to the first high-voltage winding (21), and the second low-voltage winding (12) is electrically connected to the second high-voltage winding (22).

4. The wind turbine box transformer according to claim 1, characterized in that: The structure of the first low-voltage winding (11) comprises an axial structure or a radial structure, and the structure of the second low-voltage winding (12) is the same as that of the first low-voltage winding (11).

5. The wind turbine box transformer according to claim 1, characterized in that: The magnetic field of the high voltage winding leads the magnetic field of any low voltage winding by 30 electrical degrees in time.

6. A wind turbine generator set, characterized in that: include: A converter (10), a filter device (20), and a wind turbine box transformer (50) according to any one of claims 1 to 5, wherein the converter (10), the filter device (20), and the wind turbine box transformer (50) are connected in series in sequence.

7. A wind farm, characterized in that: Including the wind turbine set as described in claim 6.

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