CN116365570A

CN116365570A - Power transmission and transformation system and wind generating set comprising same

Info

Publication number: CN116365570A
Application number: CN202111620517.7A
Authority: CN
Inventors: 岑先富; 赵志坚; 单秀清; 吴安; 刘河
Original assignee: Beijing Goldwind Science and Creation Windpower Equipment Co Ltd
Current assignee: Beijing Goldwind Science and Creation Windpower Equipment Co Ltd
Priority date: 2021-12-28
Filing date: 2021-12-28
Publication date: 2023-06-30

Abstract

The present disclosure provides a power transmission and transformation system and a wind generating set including the same, the power transmission and transformation system includes: a first converter connected to the generator at a generator side of the wind power generation unit and configured to convert alternating current output from the generator into direct current; the second converter is arranged on the power grid side; and a dc bus connected between the dc side of the first converter and the dc side of the second converter and configured to transfer dc power, wherein the second converter is configured to convert ac power received from the power grid into dc power for transfer to the dc bus or to convert dc power received through the dc bus into ac power. By adopting the wind power generation system, the voltage prototype variable flow system of the wind power generation unit can be constructed, wind storage integration can be realized, the wind power generation unit has various operation modes, and the wind power generation system has better friendliness in grid connection or off-grid operation.

Description

Power transmission and transformation system and wind generating set comprising same

Technical Field

The disclosure belongs to the technical field of wind power generation, and more particularly relates to a power transmission and transformation system for a wind generating set and the wind generating set comprising the power transmission and transformation system.

Background

In the market of wind generating sets, the current conversion scheme of the existing mainstream is a back-to-back integrated alternating current-direct current-alternating current conversion scheme, wherein a converter is arranged at the bottom of the wind generating set. In the wind turbine generator system applying the current transformation scheme, the electric energy transmission mode from the tower top to the tower bottom is an alternating current transmission mode.

However, as power increases, the number of machine side cables of a wind turbine generator set employing such a variable current scheme may increase significantly, resulting in increased costs and difficulty in cabling. In particular, as the number of cables increases, twisted cable segment reliability issues are increasingly prominent. In addition, due to the changes of the length, the number and the laying modes of the machine side cables, the design of the machine side du/dt filter of the tower bottom PWM converter becomes difficult, common mode peak value exceeding problems often occur, potential hazards are brought to motor insulation, and insulation design cost is increased.

Meanwhile, the market demand of wind and storage integration is gradually scheduled, and a voltage source type converter supporting a weak power grid becomes a research hot spot, but no mature scheme and product are introduced and applied at present.

Disclosure of Invention

The present disclosure has been made in view of the above-described problems. It is an object of the present disclosure to provide a power transmission and transformation system for a wind power generation set, which is capable of improving transmission power efficiency, reducing voltage loss, reducing the number of tower section cables, and reducing power transmission costs.

Another object of the present disclosure is to provide a power transmission and transformation system for a wind generating set, where the power transmission and transformation system can provide a standby power supply for the wind generating set, and achieve wind storage integration of the wind generating set, so as to provide power support for a voltage prototype converter and enhance adaptability to a weak power grid.

Another object of the present disclosure is to construct a voltage prototype variable current system for a wind turbine generator system.

According to a first aspect of the present disclosure, there is provided a power transmission and transformation system for a wind power generator set, the power transmission and transformation system comprising: a first converter connected to the generator at a generator side of the wind power generation unit and configured to convert alternating current output from the generator into direct current; the second converter is arranged on the power grid side; and a dc bus connected between the dc side of the first converter and the dc side of the second converter and configured to transfer dc power, wherein the second converter is configured to convert ac power received from the power grid into dc power for transfer to the dc bus or to convert dc power received through the dc bus into ac power.

Preferably, the power transmission and transformation system may further include a direct current energy storage unit connected to the direct current bus.

Preferably, the power transmission and transformation system may further include: the breaker switch is connected between the second converter and the power grid transformer; the first switch is connected between the alternating-current side of the second converter and the self-used transformer of the wind generating set; and a second switch connected between the grid transformer and the utility transformer.

Preferably, the power transmission and transformation system may further comprise a controller configured to perform the following operations in response to the grid being fault-free and the wind power generator set meeting grid-connected conditions: switching on the first converter and the second converter and closing the circuit breaker switch to incorporate the wind power unit into the grid; closing the first switch or the second switch, and supplying power to an auxiliary system of the wind generating set by the generator or the power grid; the direct current energy storage unit is simultaneously turned on to store a portion of the direct current converted via the first converter in the direct current energy storage unit.

Preferably, the controller may be further configured to, in response to a grid fault and the wind turbine meeting a power generation condition: switching on the first converter and switching off the breaker switch so as to enable the wind generating set to run off-grid; switching on the dc energy storage unit to store at least a portion of the dc power converted via the first converter in the dc energy storage unit; the second switch is opened, the second converter is closed and the first switch is closed to power the auxiliary system with the generator.

Preferably, the controller may be further configured to, in response to a grid fault and the wind turbine not meeting the power generation condition: and stopping the generator, opening the first converter, the breaker switch and the second switch, switching on the second converter and closing the first switch to supply power to the auxiliary system by using the direct current energy storage unit.

Preferably, the controller may be further configured to, in response to the grid being fault-free and the wind turbine not meeting the power generation condition: opening the first converter, closing the second converter and the dc energy storage unit, and closing the breaker switch to store the dc converted via the second converter in the dc energy storage unit; the first switch is opened and the second switch is closed to power the auxiliary system with the grid.

Preferably, the controller may be further configured to, in response to the grid being fault-free and the wind turbine meeting the power generation but not the grid-tie condition: switching on the first converter and switching off the second converter and the breaker switch, switching on the dc energy storage unit to store the dc converted via the first converter in the dc energy storage unit; the first switch is opened and the second switch is closed to power the auxiliary system with the grid.

Preferably, the dc energy storage unit may be a dc energy storage inverter unit and may be arranged inside or outside a tower of the wind power generation set.

Preferably, the power transmission and transformation system may further include a cable twisting prevention device disposed between the first converter and the dc bus.

According to a second aspect of the present disclosure, there is provided a wind power plant comprising a power transmission and transformation system as described above.

Preferably, the first converter may be arranged within a nacelle of the wind power plant, the direct current bus may be arranged within a tower of the wind power plant, and the second converter may be arranged at a tower bottom of the wind power plant.

According to the power transmission and transformation system for the wind generating set, the first converter for rectification is arranged at the cabin of the tower top, the second converter for inversion is arranged at the tower bottom, and the power is transmitted in a direct current transmission mode at the tower barrel part, so that the direct current transmission power efficiency is improved, the energy consumption and the voltage loss of the wind generating set side are reduced, the number of cables of the tower barrel section is reduced, and the power transmission cost of the wind generating set side is reduced.

The power transmission and transformation system for the wind generating set according to the exemplary embodiment of the present disclosure is provided with a direct current transmission part, which improves transmission power efficiency, reduces voltage loss, reduces the number of tower section cables, and reduces power transmission costs.

The power transmission and transformation system for a wind generating set according to the exemplary embodiment of the present disclosure is provided with a direct current energy storage inversion unit such that both the first converter (i.e., the machine side converter) and the second converter (i.e., the grid side converter) can be independently operated, and is advantageous in constructing a voltage prototype conversion system.

In addition, the wind generating set comprising the power transmission and transformation system according to the exemplary embodiment of the disclosure realizes the integration of power generation, energy storage and set power generation, has various operation modes, and has better friendliness in grid connection or off-grid operation.

Drawings

The above and other aspects, features and other advantages of the present invention will become apparent and more readily appreciated from the following detailed description of the exemplary embodiments, taken in conjunction with the accompanying drawings, in which:

fig. 1 is a schematic diagram showing a power transmission and transformation system and an arrangement thereof in a wind turbine generator system according to an exemplary embodiment of the present disclosure.

Reference numerals illustrate: 10-a power transmission and transformation system; 110-a first current transformer; 120-a second current transformer; 130-a direct current bus; 132-a capacitor; 140-a direct current energy storage unit; 20-an impeller; 30-a self-use transformer; 40-grid transformer; 150-a cable twisting prevention device; s0-a breaker switch; s1-a first switch; s2-a second switch; g-generator.

Detailed Description

The following description of specific embodiments is provided in connection with the accompanying drawings to assist the reader in a comprehensive understanding of the methods, apparatus, and/or systems described herein. However, various changes, modifications, and equivalents of the methods, devices, and/or systems described herein will be apparent after an understanding of the present disclosure. For example, the order of operations described herein is merely an example and is not limited to those set forth herein, but may be altered as will be apparent after an understanding of the disclosure of the present application, except for operations that must occur in a particular order. Furthermore, descriptions of features known in the art may be omitted for clarity and conciseness.

The features described herein may be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, the embodiments described herein have been provided to illustrate only some of the many possible ways to implement the methods, devices, and/or systems described herein, which will be clear after an understanding of the present disclosure.

The terminology used herein is for the purpose of describing various embodiments only and is not intended to be limiting of the disclosure. Singular forms also are intended to include plural forms unless the context clearly indicates otherwise. The terms "comprises," "comprising," and "having" specify the presence of stated features, amounts, operations, components, elements, and/or combinations thereof, but do not preclude the presence or addition of one or more other features, amounts, operations, components, elements, and/or combinations thereof.

Unless defined otherwise, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs after understanding this disclosure. Unless explicitly so defined herein, terms (such as those defined in a general dictionary) should be construed to have meanings consistent with their meanings in the context of the relevant art and the present disclosure, and should not be interpreted idealized or overly formal. In addition, in the description of the examples, when it is considered that detailed descriptions of well-known related structures or functions will cause a ambiguous explanation of the present disclosure, such detailed descriptions will be omitted.

In the following description, an arrangement in which a power transmission and transformation system is applied to a wind turbine generator set is described in detail as an exemplary embodiment with reference to fig. 1.

As shown in fig. 1, the power transmission and transformation system 10 may include a first current transformer 110, a second current transformer 120, and a dc bus 130. The first current transformer 110 may be arranged in a nacelle of the wind power plant located at the top of the tower, the direct current bus 130 may be arranged in a tower of the wind power plant, and the second current transformer 120 may be arranged at the bottom of the wind power plant.

The first converter 110 may be connected to the generator G at a generator side of the wind generating set, and configured to convert Alternating Current (AC) output by the generator into Direct Current (DC). Specifically, the first converter 110 may be used to actively rectify the ac power from the generator G into dc power having positive and negative polarities after the generator G is driven to output ac power. Although not shown, a switch may be provided on the dc side of the first converter 110, which may be installed in the cabin. The first converter 110 may be connected to the dc bus 130 or disconnected from the dc bus 130 via the switch.

The dc bus 130 may be connected between the dc side of the first converter 110 and the dc side of the second converter 120 and used to transmit dc power. In other words, a direct current bus transmission line is adopted from the top of the tower to the bottom of the wind generating set. As an example, the dc bus 130 may be a copper cable, an aluminum alloy cable, or a pipe bus, but is not limited thereto, as long as it has excellent dc transmission characteristics. In addition, a capacitor 132 may be connected between the positive electrode p+ and the negative electrode P-of the dc bus 130 to improve the system voltage from the point of compensating reactance, thereby reducing power loss and improving the stability of the system.

The second converter 120 may be disposed at the grid side and may be configured to convert alternating current received from the grid into direct current to be transmitted to the direct current bus 130 or to convert direct current received through the direct current bus 130 into alternating current. Similar to the first current transformer 110, the second current transformer 120 may be provided with a switch on the dc side. The second converter 120 may be connected to the dc bus 130 or disconnected from the dc bus 130 via the switch.

As described above, the power transmission and transformation system according to the present exemplary embodiment may arrange the rectifying portion of the current transformer (i.e., the first current transformer 110) at the nacelle of the tower top of the wind power generation unit, arrange the inverting portion of the current transformer (i.e., the second current transformer 120) at the tower bottom, and transmit electric power using direct current at the tower section. The power transmission and transformation system according to the present exemplary embodiment can reduce the power consumption and voltage loss of the transmission line because the direct current transmission power efficiency is high.

In the prior art, the wind generating set adopts an alternating current transmission mode to transmit electric energy from the tower top to the tower bottom, and the number of cables can be greatly increased along with the improvement of power, so that the cost is increased. In contrast, the direct current power transmission and transformation system of the present exemplary embodiment can reduce the number of cables of the tower section, thereby reducing the cost of power transmission from the top of the tower to the bottom of the tower.

In addition, since the power transmission and transformation system according to the present exemplary embodiment arranges the rectifying portion in the nacelle of the tower top of the wind turbine and adopts a manner of direct current transmission of electric energy at the tower section, it is possible to avoid the problem of exceeding the standard of the common mode peak value occurring when the rectifying converter is provided at the tower bottom, thereby improving the reliability and stability of the wind turbine and being advantageous in reducing the insulation design cost.

As shown in fig. 1, the power transmission and transformation system 10 may further include a cable-twisting prevention device 150, where the cable-twisting prevention device 150 is disposed between the first converter 110 and the dc bus 130. Specifically, as an example, the anti-twisting device 150 may be a dc yaw slip ring that may be mounted on the yaw platform. Alternatively, the anti-twisting device 150 may be a conventional twisting scheme for wind turbines.

With continued reference to fig. 1, the power transmission and transformation system 10 may further include a dc energy storage unit 140 connected to the dc bus 130.

The dc energy storage unit 140 may be used to store dc power received from the generator G or from the grid and converted. Although three dc energy storage units are shown in fig. 1, it is not limited thereto. For example, the power transmission and transformation system 10 may include only one dc energy storage unit, or may include two or more than three dc energy storage units, depending on actual needs and capacities of the dc energy storage units. Specifically, the dc energy storage unit may be a dc energy storage inverter unit. Alternatively, the dc energy storage unit may include, but is not limited to, a battery pack. As an example, the dc energy storage unit is disposed inside a tower of the wind power generation set, but is not limited thereto, and the dc energy storage unit may be independently disposed outside the tower or other suitable location as desired.

In addition, the power transmission and transformation system 10 further includes a breaker switch S0, a first switch S1 and a second switch S2 at the bottom of the wind generating set.

Specifically, the breaker switch S0 is connected between the ac side of the second converter 120 and the grid transformer 40, the first switch S1 is connected between the ac side of the second converter 120 and the utility transformer 30 of the wind turbine, and the second switch S2 is connected between the grid transformer 40 and the utility transformer 30.

Although not shown in fig. 1, the wind turbine further comprises auxiliary systems for monitoring, protection, fault diagnosis, yaw, pitch, vortex-induced vibration resistance, etc. The auxiliary system requires a relatively low voltage and is therefore connected to the low voltage side of the utility transformer 30. As described above, the high-voltage side of the auxiliary system-use autotransformer 30 may be selectively connected to the second current transformer 120 or the power grid via the on-off of the first switch S1 and the second switch S2.

The power transmission and transformation system 10 may also include one or more controllers or computing modules (not shown) for controlling the power transmission and transformation system 10. Hereinafter, a controller will be described as an example, and a control operation of the power transmission and transformation system by the controller according to different working conditions of the wind turbine generator set and different operation conditions of the power grid will be described in detail.

Specifically, the power transmission and transformation system can be controlled according to whether the power grid fails or not and the working condition of the wind generating set, wherein the working condition of the wind generating set comprises: the first working condition, namely the wind generating set meets the power generation condition, namely the grid connection condition; the second working condition, namely the wind generating set meets the power generation but does not meet the grid connection condition; and the third working condition-the wind generating set does not meet the power generation condition.

When the grid is fault-free, the breaker switch S0 and the second switch S2 may be selectively opened or closed by the controller, and in particular, the power transmission and transformation system may be controlled according to the working condition of the wind generating set as follows.

When the wind generating set is under the first working condition (i.e., the wind generating set meets the generating condition), the impeller 20 rotates and drives the generator G to output alternating current, the first converter 110 and the second converter 120 can be connected through the controller, so that the output alternating current is rectified into direct current through the first converter 110, and then the direct current is transmitted to the second converter 120 through the direct current bus 130 and is inverted into alternating current through the second converter 120. At this time, since the grid has no fault, the breaker switch S0 may also be closed by the controller to transmit the alternating current inverted from the second converter 120 to the grid transformer 40 and then to the grid, thereby incorporating the wind power generator set into the grid. In this case, according to the power supply requirement to the auxiliary system, the first switch S1 may be closed and the second switch S2 may be opened by the controller to supply power to the auxiliary system of the wind turbine generator set by using the generator G; alternatively, the second switch S2 may be closed and the first switch S1 may be opened by the controller to supply power to the auxiliary system of the wind power plant with the grid. Meanwhile, under the working condition, according to the energy storage requirement, the generator G can be driven to synchronously supply power to the direct current energy storage unit 140 on the direct current bus 130. Specifically, the dc energy storage unit 140 may be turned on by the controller to store a portion of the dc power converted via the first converter 110 in the dc energy storage unit 140. That is, when the grid is fault-free and the wind generating set is under the first working condition, the power transmission and transformation system can enable the wind generating set to run in a grid-connected mode, can utilize the grid or the generator G to supply power to the auxiliary system, and can utilize the generator G to charge the direct-current energy storage unit.

When the wind generating set is under the second working condition (i.e. the wind generating set meets the power generation but does not meet the grid-connected condition), the impeller 20 rotates and drives the generator G to output alternating current, but because the wind generating set does not meet the grid-connected condition, the breaker switch S0 can be opened by the controller so as to enable the wind generating set to run off-grid. At this time, the second converter 120 may also be turned off by the controller. Meanwhile, the first converter 110 may be turned on and the dc energy storage unit 140 may be turned on by the controller to convert the ac power output from the generator G into dc power by the first converter 110 and store at least a portion of the dc power in the dc energy storage unit 140, thereby generating electricity for the wind power generator. In this case, according to the power supply requirement of the auxiliary system, the controller may also close the second switch S2 to supply power to the auxiliary system by using the power grid, where the first switch S1 is in an open state. That is, when the grid is fault-free and the wind generating set is in the second working condition, the power transmission and transformation system can enable the wind generating set to run off-grid, can utilize the grid to supply power to the auxiliary system, and can utilize the generator G to charge the direct-current energy storage unit.

When the wind generating set is in the third operating condition (i.e., the wind generating set does not meet the power generating condition), the impeller 20 does not rotate and the generator G does not operate, so the first converter 110 may be disconnected by the controller. At this time, since the power grid has no fault, the second converter 120 and the dc energy storage unit 140 may be turned on by the controller and the breaker switch S0 may be closed to convert the alternating current from the power grid into the direct current via the second converter 120 and store the direct current in the dc energy storage unit 140. In this case, according to the power supply requirement of the auxiliary system, the controller may also close the second switch S2 to supply power to the auxiliary system by using the power grid, where the first switch S1 is in an open state. That is, when the grid is fault-free and the wind turbine generator system is in the third operating condition, the power transmission and transformation system may utilize the grid to supply power to the auxiliary system and may utilize the grid to charge the dc energy storage unit.

In addition, when the power grid fails, the breaker switch S0 and the second switch S2 are opened by the controller, and the power transmission and transformation system can be controlled according to the working condition of the wind generating set in the following manner.

Specifically, when the wind generating set is under the first working condition, the wind generating set runs off-grid. At this time, the impeller 20 rotates and drives the generator G to output alternating current, and thus the first converter 110 may be turned on by the controller and the dc energy storage unit 140 may be turned on to convert the alternating current output from the generator G through the first converter 110 into direct current, and at least a portion of the direct current may be stored in the dc energy storage unit 140, thereby generating electricity for the wind power generator. In this case, depending on the power supply requirements for the auxiliary system, the second converter 120 can also be switched on by the controller and the first switch S1 can be closed in order to supply the auxiliary system with the generator G. That is, when the power grid fails and the wind generating set is under the first working condition, the power transmission and transformation system can enable the wind generating set to run off-grid, can utilize the generator G to supply power to the auxiliary system, and can utilize the generator G to charge the direct-current energy storage unit. In addition, the wind generating set runs off-grid in the mode, and when the power grid is recovered to normal running, the wind generating set is integrated into the power grid to run in a grid-connected running mode.

When the wind generating set is under the second working condition, the impeller 20 rotates and drives the generator G to output alternating current, so that the first converter 110 can be connected through the controller and the direct current energy storage unit can be connected, so that the alternating current output by the generator G is converted into direct current through the first converter 110, and at least part of the direct current is stored in the direct current energy storage unit 140, thereby powering the wind generating set. In this case, depending on the power supply requirements for the auxiliary system, the second converter 120 can also be switched on by the controller and the first switch S1 can be closed in order to supply the auxiliary system with the generator G or the dc energy storage unit. That is, when the power grid fails and the wind turbine generator system is under the second working condition, the power transmission and transformation system can enable the generator G or the direct-current energy storage unit to supply power to the auxiliary system, and the generator G can be used for charging the direct-current energy storage unit.

When the wind turbine is in the third operating mode, the first converter 110 may be turned on and off by the controller, since the impeller 20 is not rotating and the generator G is not operating. In this case, the auxiliary system still has a power supply demand, but cannot be charged with the grid or generator G. Accordingly, the second converter 120 may be turned on and the first switch S1 may be closed by the controller to power the auxiliary system using the dc energy storage unit 140. That is, when the power grid fails and the wind generating set is under the third working condition, the power transmission and transformation system can enable the available direct-current energy storage unit to supply power to the auxiliary system.

As described above, by the power transmission and transformation system according to the exemplary embodiment, integration of wind power generation, energy storage, machine set power (for example, anti-vortex-induced power backup, anti-typhoon power backup, and the like) can be achieved. In addition, the wind generating set utilizing the power transmission and transformation system according to the exemplary embodiment has various operation modes, and has better friendliness in grid connection and off-grid operation.

As set forth above, the power transmission and transformation system for a wind turbine generator set according to the exemplary embodiments of the present disclosure may improve transmission power efficiency, reduce voltage loss, reduce the number of tower section cables, and reduce power transmission costs.

The power transmission and transformation system for the wind generating set according to the exemplary embodiment of the present disclosure may be provided with a direct current energy storage inversion unit, so that both the first converter and the second converter may be independently operated, and it is advantageous to construct a voltage prototype conversion system.

In addition, the wind generating set comprising the power transmission and transformation system according to the exemplary embodiment of the disclosure can realize power generation, energy storage and set power integration, has various operation modes, and has better friendliness in grid connection or off-grid operation.

While the present disclosure includes specific exemplary embodiments, it will be apparent to those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the claims and their equivalents. The examples described herein are to be considered in descriptive sense only and not for purposes of limitation. The description of features or aspects in each example will be considered to be applicable to similar features or aspects in other examples. Suitable results may be obtained if the described techniques are performed in a different order and/or if components in the described systems, architectures, devices or circuits are combined in a different manner and/or replaced or supplemented by other components or their equivalents. Thus, the scope of the disclosure is not to be limited by the specific embodiments, but by the claims and their equivalents, and all modifications within the scope of the claims and their equivalents are to be construed as being included in the disclosure.

Claims

1. A power transmission and transformation system for a wind turbine generator system, the power transmission and transformation system comprising:

a first converter connected to the generator at a generator side of the wind power generation unit and configured to convert alternating current output from the generator into direct current;

the second converter is arranged on the power grid side; and

a DC bus connected between the DC side of the first converter and the DC side of the second converter and used for transmitting DC,

wherein the second converter is configured to convert alternating current received from the grid into direct current for transmission to the direct current bus or to convert direct current received through the direct current bus into alternating current.

2. The power transmission and transformation system according to claim 1, further comprising a dc energy storage unit connected to the dc bus.

3. The power transmission and transformation system according to claim 2, further comprising:

the breaker switch is connected between the second converter and the power grid transformer;

the first switch is connected between the alternating-current side of the second converter and the self-used transformer of the wind generating set; and

and the second switch is connected between the power grid transformer and the self-use transformer.

4. A power transmission and transformation system according to claim 3, further comprising a controller configured to, in response to the grid being fault-free and the wind power generator set meeting a grid-tie condition:

switching on the first converter and the second converter and closing the circuit breaker switch to incorporate the wind power unit into the grid;

closing the first switch or the second switch, and supplying power to an auxiliary system of the wind generating set by the generator or the power grid;

the direct current energy storage unit is simultaneously turned on to store a portion of the direct current converted via the first converter in the direct current energy storage unit.

5. The power transmission and transformation system according to claim 4, wherein the controller is further configured to, in response to a grid fault and the wind turbine meeting a power generation condition:

switching on the first converter and switching off the breaker switch so as to enable the wind generating set to run off-grid;

switching on the dc energy storage unit to store at least a portion of the dc power converted via the first converter in the dc energy storage unit;

the second switch is opened, the second converter is closed and the first switch is closed to power the auxiliary system with the generator.

6. The power transmission and transformation system according to claim 4, wherein the controller is further configured to, in response to a grid fault and the wind turbine not meeting a power generation condition:

and stopping the generator, opening the first converter, the breaker switch and the second switch, switching on the second converter and closing the first switch to supply power to the auxiliary system by using the direct current energy storage unit.

7. The power transmission and transformation system according to claim 4, wherein the controller is further configured to, in response to the grid being fault-free and the wind turbine not meeting the power generation condition:

opening the first converter, closing the second converter and the dc energy storage unit, and closing the breaker switch to store the dc converted via the second converter in the dc energy storage unit;

the first switch is opened and the second switch is closed to power the auxiliary system with the grid.

8. The power transmission and transformation system according to claim 7, wherein the controller is further configured to, in response to the grid being fault-free and the wind turbine meeting the power generation but not the grid-tie condition:

switching on the first converter and switching off the second converter and the breaker switch, switching on the dc energy storage unit to store the dc converted via the first converter in the dc energy storage unit;

9. The power transmission and transformation system according to claim 2, wherein the direct current energy storage unit is a direct current energy storage inversion unit and is arranged inside or outside a tower of the wind generating set.

10. The power transmission and transformation system according to claim 1, further comprising an anti-twisting device arranged between the first converter and the dc bus.

11. A wind power plant, characterized in that it comprises a power transmission and transformation system according to any one of claims 1 to 10.

12. The wind power generator set of claim 11, wherein the first converter is disposed within a nacelle of the wind power generator set, the dc bus is disposed within a tower of the wind power generator set, and the second converter is disposed at a tower bottom of the wind power generator set.