A fan power conversion system and a fan power conversion system control method

Abstract

This application discloses a wind turbine power conversion system and a control method for the wind turbine power conversion system, relating to the field of wind power technology. The wind turbine power conversion system includes: at least one wind turbine cluster, which is composed of several DC wind turbines connected in series, used to output electrical energy converted from wind energy in DC form; each DC wind turbine is equipped with a corresponding DC converter, and each DC converter is used to adjust its corresponding single-unit output voltage to maintain a balance among the single-unit output voltages formed by the DC wind turbines within the wind turbine cluster. By combining the DC wind turbine series structure with the voltage regulation capability of the DC converter, the problem of unbalanced output voltages of the wind turbines caused by wind power fluctuations is effectively solved, reducing the wind curtailment rate and improving the overall efficiency and stability of the wind power system.

Description

Technical Field

[0001] This application relates to the field of wind power technology, and in particular to a wind turbine power conversion system and a control method for the wind turbine power conversion system. Background Technology

[0002] With the rapid development of offshore wind power, traditional AC transmission systems face problems such as large capacitive charging current of submarine cables, limited transmission distance, and significant reactive power loss. All-DC transmission systems, due to their advantages of high transmission efficiency, low loss, and no need for reactive power compensation, are gradually becoming the mainstream solution for transmitting offshore wind power.

[0003] However, due to the uneven distribution of wind power in space and time, the voltage imbalance between the wind turbines in the system leads to an increase in wind curtailment rate, making the all-DC power transmission scheme fail to achieve the expected results. Summary of the Invention

[0004] The main objective of this application is to provide a wind turbine power supply system and a control method for the wind turbine power supply system, aiming to solve the technical problem of how to reduce the wind curtailment rate of the wind turbine power supply system.

[0005] To achieve the above objectives, embodiments of this application provide a wind turbine power supply system, which includes:

[0006] At least one wind turbine cluster, which consists of several DC wind turbines connected in series, is used to output the electrical energy converted from wind energy in DC form in series. Each DC fan is equipped with a corresponding DC converter, which is used to adjust its own single-unit output voltage so that the single-unit output voltage generated by each DC fan in the fan cluster is kept balanced.

[0007] In one embodiment, the wind turbine power distribution system includes: a plurality of wind turbine clusters; Each wind turbine cluster is connected in parallel to the converter station.

[0008] In one embodiment, each DC converter is further configured to regulate and maintain the overall output voltage generated by each DC fan at a target voltage.

[0009] In one embodiment, the DC-DC converter includes: A multi-branch transformer, whose primary side is connected to the generator of a DC wind turbine, and whose secondary side is equipped with multiple secondary windings; Several AC / DC rectifiers, each AC / DC rectifier's AC side is connected to a corresponding secondary winding; Several step-down circuits are used. The input of each step-down circuit is connected to the DC side of a corresponding AC / DC rectifier. The outputs of each step-down circuit are cascaded together to serve as the output of a DC-DC converter.

[0010] In one embodiment, the secondary windings are mutually insulated.

[0011] In one embodiment, the AC / DC rectifier is also equipped with a protection circuit; The protection circuit is configured on the DC side of the AC / DC rectifier; The protection circuit is used to stabilize the bus voltage when it detects that the bus voltage of the DC bus of the AC / DC rectifier exceeds the preset safe voltage, so that the bus voltage does not exceed the preset safe voltage.

[0012] In one embodiment, the step-down circuit is a half-bridge BUCK circuit.

[0013] Furthermore, to achieve the above objectives, this application also proposes a wind turbine substation system control method, applied to the wind turbine substation system described above. The method includes the following steps: Obtain the operating status information of each stage cascade module in each DC-DC converter; Based on the operating status information, generate the drive control signals for each DC converter; Based on the drive control signals, the output voltage of each DC converter is adjusted to keep the output voltage of each DC fan in the fan cluster balanced.

[0014] In one embodiment, the operating status information includes voltage status information; The steps for generating the drive control signals for each DC-DC converter based on the operating status information include: Based on the level modulation strategy, the target working module is selected from each cascade module according to the voltage state information; Generate the corresponding drive control signals for each target working module.

[0015] In one embodiment, the operating status information includes power status information; The steps for generating the drive control signals for each DC-DC converter based on the operating status information include: Based on the power status information, obtain the target duty cycle of each stage module; Based on the duty cycle of each target, generate the corresponding drive control signals for each stage of the interconnected module.

[0016] This application provides a wind turbine power conversion system and a control method for the wind turbine power conversion system. The wind turbine power conversion system includes: at least one wind turbine cluster, which is composed of several DC wind turbines connected in series, used to output the electrical energy converted from wind energy in DC form in series; each DC wind turbine is equipped with a corresponding DC converter, and each DC converter is used to adjust its corresponding single-unit output voltage to keep the single-unit output voltage of each DC wind turbine in the wind turbine cluster balanced. By combining the DC wind turbine series structure with the voltage regulation capability of the DC converter, the problem of unbalanced output voltage of each wind turbine caused by wind power fluctuations is effectively solved, the wind curtailment rate is reduced, and the overall efficiency and stability of the wind power system are improved. Attached Figure Description

[0017] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0018] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a structural schematic diagram of the wind turbine substation system provided in Embodiment 1 of this application; Figure 2 This is a structural schematic diagram of Embodiment 2 of the wind turbine substation system of this application; Figure 3 This is a schematic diagram of a DC-DC converter. Figure 4 This is a schematic diagram of a step-down circuit; Figure 5 This is a flowchart illustrating an embodiment of the wind turbine substation control method of this application. Figure 6 This is a schematic flowchart of a second embodiment of the wind turbine substation control method of this application; Figure 7 This is another flowchart provided for Embodiment 2 of the wind turbine substation control method of this application.

[0020] The purpose, features, and advantages of this application will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0021] It should be understood that the specific embodiments described herein are merely illustrative of the technical solutions of this application and are not intended to limit this application.

[0022] To better understand the technical solution of this application, a detailed description will be provided below in conjunction with the accompanying drawings and specific implementation methods.

[0023] This application presents a wind turbine power distribution system according to a first embodiment, such as... Figure 1 As shown, the wind turbine power supply system includes: At least one wind turbine cluster 100, which is composed of several DC wind turbines 10 connected in series, is used to output the electrical energy converted from wind energy in DC form in series. Each DC fan 10 is equipped with a corresponding DC converter 12. Each DC converter 12 is used to adjust its corresponding single-unit output voltage so that the single-unit output voltage formed by each DC fan 10 in the fan cluster 100 is kept balanced.

[0024] It should be noted that in this embodiment, the DC wind turbine 10 is a power generation device that can convert wind energy into DC electrical energy and output it. It mainly consists of a generator 11 and a DC converter 12. The wind turbine cluster 100 refers to an energy collection unit formed by connecting several DC wind turbines 10 in series, and its output is also in DC form.

[0025] As is easily understood, the single-unit output voltage refers to the DC voltage value output by the corresponding DC fan 10 after adjustment by the corresponding DC converter 12 when a single DC fan 10 is operating. In this embodiment, each DC fan 10 is equipped with a DC converter 12, which has voltage conversion and regulation functions and is mainly used to regulate the single-unit output voltage of the corresponding DC fan 10. The DC converter 12 can adopt various topologies according to actual needs, such as buck-boost circuits, isolated converters, etc., to achieve wide-range voltage regulation and adapt to DC fans 10 of different power levels.

[0026] It should be noted that, in this embodiment, since the fan cluster 100 is composed of several DC fans 10 connected in series, the current flowing through each DC fan 10 is equal in the series structure, and the single-unit output voltage of each fan is determined by the output power of each DC fan 10. The static characteristics of a single fan cluster 100 are as follows: ; in, , ... These are the individual output voltages of the first to the nth DC fans connected in series; The overall output voltage provided for a single wind turbine cluster; , ... These represent the currents flowing through the first to the nth DC fans connected in series; The current flowing through a single wind turbine cluster; Let be the output power of the i-th series-connected DC fan. The single-unit output voltage provided for the i-th series-connected DC fan. The current flowing through the i-th series-connected DC fan (i can be a positive integer from 1 to n, where n is the total number of DC fans 10 connected in series within the fan cluster 100).

[0027] However, the output power of each DC fan 10 mainly depends on the amount of wind energy converted. Due to the fluctuation and uneven spatial and temporal distribution of wind energy, the theoretical output voltage of each DC fan 10 is inconsistent, which affects the system stability and power output quality.

[0028] It is easy to understand that, in this embodiment, the individual output voltage of each DC-DC converter 12 can be kept balanced, ensuring the overall output voltage stability of the series-connected wind turbine cluster 100, which facilitates subsequent grid connection or transmission. Furthermore, the above-mentioned balance control strategy does not require changing the power output of the wind turbines themselves; it can be achieved simply by adjusting the DC-DC converter 12, exhibiting characteristics of fast response and flexible control.

[0029] Alternatively, only a portion of the DC fans 10 can be selected to provide power output to the fan cluster 100. By controlling the DC converters 12 of the selected DC fans 10 to output the same voltage, the effect of voltage balance can be achieved.

[0030] This application provides a wind turbine power conversion system, comprising: at least one wind turbine cluster, which is composed of several DC wind turbines connected in series, used to output the electrical energy converted from wind energy in DC form; each DC wind turbine is equipped with a corresponding DC converter, and each DC converter is used to adjust its corresponding single-unit output voltage to maintain the balance of the single-unit output voltages formed by the DC wind turbines in the wind turbine cluster. By combining the DC wind turbine series structure with the voltage regulation capability of the DC converter, the problem of unbalanced output voltage of each wind turbine caused by wind power fluctuations is effectively solved, reducing the wind curtailment rate and improving the overall efficiency and stability of the wind power system.

[0031] Based on the first embodiment of the wind turbine power substation system of this application, a second embodiment of the wind turbine power substation system of this application is proposed. In the second embodiment of the wind turbine power substation system of this application, the content that is the same as or similar to that in the first embodiment can be referred to the above description, and will not be repeated hereafter. Based on this, please refer to... Figure 2 , Figure 3 as well as Figure 4 In this embodiment, the wind turbine power supply system includes: multiple wind turbine clusters 100; Each wind turbine cluster of 100 units is connected in parallel to the converter station of 200 units.

[0032] It should be understood that converter station 200 is a dedicated station in the power system used to convert between AC and DC power. In this embodiment, the wind turbine cluster 100 can ultimately transmit electrical energy to the power grid through converter station 200.

[0033] It should be noted that in this embodiment, multiple wind turbine clusters 100 can be connected in parallel to the converter station 200. This allows for more flexible expansion of the wind farm capacity, enabling each wind turbine cluster 100 to operate independently without affecting each other, thus improving the reliability and maintainability of the system.

[0034] It is worth noting that the above parallel structure ensures that the overall output voltage of each wind turbine cluster 100 is the same, which is the DC bus voltage of the converter station 200. In this embodiment, power coordination among the wind turbine clusters 100 can be achieved by adjusting the output voltage of each DC converter 12 within each wind turbine cluster 100.

[0035] Furthermore, in this embodiment, each DC converter 12 is also used to regulate and maintain the overall output voltage formed by each DC fan 10 at the target voltage.

[0036] It should be noted that the target voltage is the DC bus voltage of the converter station 200 or the rated voltage of the system design. In this embodiment, the overall output voltage of each DC fan 10 connected in series within each fan cluster 100 needs to match the DC bus voltage of the converter station 200. Therefore, each DC converter 12 can also adjust and maintain the overall output voltage formed by each DC fan 10 at the target voltage.

[0037] It is worth noting that in this embodiment, during the above process, each DC converter 12 can also adjust the single-unit output voltage balance of each DC fan 10, thereby achieving overall and local coordinated control.

[0038] Furthermore, in this embodiment, the DC-DC converter 12 includes: The multi-split winding transformer 121 has its primary side connected to the generator 11 of the DC fan 10, and its secondary side is equipped with multiple secondary windings. Several AC / DC rectifiers 122, each AC / DC rectifier 122 having its AC side connected to a corresponding secondary winding; Several step-down circuits 123 are provided. The input terminal of each step-down circuit 123 is connected to the DC side of a corresponding AC / DC rectifier. The output terminals of each step-down circuit 123 are cascaded together to serve as the output terminal of the DC-DC converter 12.

[0039] It should be noted that in this embodiment, the generator 11 is the wind power generation structure configured inside the DC wind turbine 10, which is the core of converting wind energy into electrical energy, and its output electrical energy is in the form of alternating current; the multi-split winding transformer 121 refers to a transformer with a special structure in which there are multiple windings on the secondary side. Its primary side is connected to the generator 11 to receive the alternating current provided by the generator 11, and its secondary side is connected to multiple AC / DC rectifiers 122 through multiple secondary windings.

[0040] It is easy to understand that in this embodiment, by means of the multi-split winding transformer 121, all the power output by the generator 11 can be diverted to multiple independent secondary windings, thereby reducing the voltage and current stress on each subsequent AC / DC rectifier 122 and step-down circuit 123, and thus using power devices with lower withstand voltage ratings to process high-power electrical energy.

[0041] It should be noted that in this embodiment, the AC / DC rectifier 122 can mainly convert the alternating current generated by the generator 11, whose voltage and frequency vary with the wind speed, into stable direct current; the step-down circuit 123 can mainly step down the high-voltage direct current obtained by the AC / DC rectifier 122 to a low-voltage direct current that is easy to adjust flexibly, and can realize a wide range of voltage adjustment functions.

[0042] Furthermore, in this embodiment, the secondary windings are mutually insulated.

[0043] It is easy to understand that in this embodiment, the multiple secondary windings of the multi-split winding transformer 121 are designed to be mutually insulated, thus achieving electrical isolation and improving system safety.

[0044] Furthermore, in this embodiment, the AC / DC rectifier 122 is also equipped with a protection circuit 1221; The protection circuit 1221 is configured on the DC side of the AC / DC rectifier 122; The protection circuit 1221 is used to stabilize the bus voltage when the bus voltage of the DC bus of the AC / DC rectifier 122 exceeds the preset safe voltage, so that the bus voltage does not exceed the preset safe voltage.

[0045] It should be noted that, in this embodiment, the DC side of the AC / DC rectifier 122 can also be configured with a protection circuit 1221, which can absorb the DC bus overvoltage of the AC / DC rectifier 122 caused by power fluctuations or faults when the AC / DC rectifier 122 is working.

[0046] It is easy to understand that the preset safety voltage is a voltage threshold used to characterize the overvoltage of the DC bus of the AC / DC rectifier 122. In this embodiment, when a sudden power change in the DC fan 10 or a system disturbance causes the DC bus voltage of the AC / DC rectifier 122 to exceed the preset safety voltage, the protection circuit 1221 responds quickly to stabilize the DC bus voltage, thereby preventing damage to the AC / DC rectifier 122. Specifically, the DC bus voltage can be limited to a safe range by dissipating or transferring energy.

[0047] As a specific approach, the AC / DC rectifier 122 can adopt a mature two-level or three-level converter solution.

[0048] Furthermore, in this embodiment, the step-down circuit 123 is a half-bridge BUCK circuit.

[0049] It should be noted that, in this embodiment, the half-bridge BUCK circuit can adjust the output voltage by changing the switch duty cycle. Cascading its outputs can increase the total output voltage, meeting the high voltage requirements of the series cluster. Each half-bridge BUCK circuit can be controlled independently, facilitating modular voltage equalization control.

[0050] It is easy to understand that, in this embodiment, the circuit topology of the half-bridge BUCK circuit is as follows: Figure 4 As shown, the circuit includes at least an input capacitor C1, a first switching transistor Q1, and a second switching transistor Q2. The first terminal of the input capacitor C1 and the first terminal of the first switching transistor Q1 are connected to the positive terminal of the DC bus of the AC / DC rectifier 122. The second terminal of the input capacitor C1 and the second terminal of the second switching transistor Q2 are both connected to the negative terminal of the DC bus of the AC / DC rectifier 122. The second terminal of the first switching transistor Q1 is connected to the first terminal of the second switching transistor Q2. Therefore, it can be understood that the first switching transistor Q1 and the second switching transistor Q2 respectively constitute the upper and lower arms of the half-bridge circuit. High-frequency chopping is achieved by controlling the on / off state of the upper and lower arms at high frequency, thereby realizing a precise voltage reduction function. The input capacitor C1, positioned between the positive and negative terminals of the DC bus, serves to stabilize the input voltage (DC bus voltage) and absorb current ripples generated by the switching action.

[0051] It is worth noting that in this embodiment, both the first switch Q1 and the second switch Q2 can be connected in reverse parallel with a diode (not shown in the figure) as a freewheeling diode to provide a freewheeling path.

[0052] It should be noted that, in this embodiment, in Figure 2 , Figure 3 as well as Figure 4 The wind turbine substation system on display is equipped with Let C1 be the voltage across the i-th input capacitor in the series half-bridge BUCK circuit. This is the target reference value for the capacitor voltage. Let be the switching duty cycle of the i-th series-connected half-bridge BUCK circuit. This is the total voltage of the entire DC power grid (the overall output voltage of the wind turbine cluster 100). The output current of the entire series circuit. Let the output power of the i-th half-bridge BUCK circuit be (i can be a positive integer from 1 to n, where n is the total number of DC fans 10 connected in series within the fan cluster 100), then the following relationship exists: ; When the system reaches steady state, the voltage of each stage of the DC fan 10 (the voltage of each capacitor in each half-bridge BUCK circuit) is balanced, that is... Then the following relation exists: ; in, This represents the average output power.

[0053] Based on the above, the average duty cycle of the half-bridge BUCK circuit can be obtained. for: ; Therefore, it exists: ; It can be seen that the duty cycle of the half-bridge BUCK circuit is directly proportional to the ratio of the individual output power of a single DC fan 10 to the average output power. The greater the difference in output power among the DC fans 10, the greater the difference in the duty cycle of the corresponding half-bridge BUCK circuit.

[0054] This embodiment proposes a DC-DC converter scheme with wide voltage regulation capability based on cascaded half-bridge BUCK circuits. Combined with the application of multi-split transformers, it effectively solves the problems of insufficient capacity and excessive voltage and current stress in a single BUCK circuit, adapting to the operational requirements of large-capacity offshore wind turbines of 10MW and above. Flexible adaptation of the wind turbine output voltage is achieved through dynamic adjustment of the duty cycle of the half-bridge BUCK circuits.

[0055] In addition, it can be used in conjunction with the Nearest Level Modulation (NLM) control strategy to control the capacitor voltage in each half-bridge BUCK circuit in real time, which can significantly expand the adjustment range of the wind turbine output voltage. In view of the uneven spatial and temporal distribution and random fluctuations of offshore wind power, it can effectively balance the voltage differences of each wind turbine in the series cluster and reduce the wind curtailment rate.

[0056] Furthermore, embodiments of this application also provide a wind turbine substation system control method, applied to the wind turbine substation system described above, such as... Figure 5 As shown, the steps of the method include: Step S10: Obtain the operating status information of each stage cascade module in each DC-DC converter; Step S20: Generate each drive control signal for each DC-DC converter based on each operating status information; Step S30: Based on each drive control signal, adjust the individual output voltage of each DC converter so that the individual output voltages generated by each DC fan in the fan cluster are kept balanced.

[0057] It should be understood that, in this embodiment, the executing entity can be the aforementioned wind turbine power substation system.

[0058] It should be noted that, in this embodiment, the cascaded module can be understood as a DC-DC converter cascaded between various DC wind turbines, or as a local functional module cascaded between the DC-DC converters of various DC wind turbines. Operating status information refers to the operating parameters of each cascaded module, such as the voltage parameters of the input capacitor of the half-bridge BUCK circuit, the power parameters of the DC-DC converter, and other related information. This information can be collected in real time by the sensors built into the DC-DC converter.

[0059] As is easily understood, the drive control signal refers to the electrical signal used to drive the corresponding DC-DC converter to work and can adjust the operating parameters of the DC-DC converter. In this embodiment, the core of the control method is to dynamically adjust the drive control signal provided to each DC-DC converter according to the operating status of each cascade module, so that the single-unit output voltage of each cascade module that needs to work is equal, and the cascade modules that do not need to work do not provide single-unit output voltage (only forming a series circuit), thereby achieving the balance of the single-unit output voltage of each DC wind turbine that needs to work within the wind turbine cluster.

[0060] Compared with the prior art, the other beneficial effects of the wind turbine substation control method provided in this application embodiment are the same as the beneficial effects of the wind turbine substation system provided in the above embodiment, and will not be repeated here.

[0061] Based on the first embodiment of the wind turbine substation system control method of this application, a second embodiment of the wind turbine substation system control method of this application is proposed. In the second embodiment of the wind turbine substation system control method of this application, the content that is the same as or similar to that in the first embodiment can be referred to the above description, and will not be repeated hereafter. Based on this, please refer to... Figure 6 as well as Figure 7 In this embodiment, the operating status information includes voltage status information; the step of generating each drive control signal for each DC-DC converter based on each operating status information includes: Step S21A: Based on the level modulation strategy, select each target working module from each cascade module according to the voltage state information; Step S22A: Generate the corresponding drive control signals for each target working module.

[0062] It should be understood that specific references Figure 6 In this embodiment, the voltage status information in the operating status information can be used to control the operating status of each DC fan.

[0063] It should be noted that the level modulation strategy can specifically adopt the nearest level modulation method. This strategy can select the most suitable (i.e., the voltage closest to the target value) sub-modules to work by comparing the actual voltage with the target reference value in real time, thereby approximating the target output voltage waveform.

[0064] As is easily understood, a target working module refers to a cascaded module that needs to perform work to output electrical energy. In this embodiment, only the selected target working modules operate. The real-time voltage of each cascaded module can be obtained through the voltage state information corresponding to each DC-DC converter. Then, the actual acquired real-time voltages are compared with the theoretically required reference voltage to select the target working modules that need to operate. Subsequently, based on the voltage state information corresponding to each target working module, the operating parameters (switching frequency and switching losses, etc.) of each target working module can be set, and corresponding drive control signals can be generated. Finally, each drive control signal can be transmitted to the selected target working modules to drive them to perform their corresponding operations, outputting the required electrical energy, thereby balancing the individual output voltage of the selected DC wind turbines within the wind turbine cluster.

[0065] Furthermore, in this embodiment, the operating status information includes power status information; the step of generating each drive control signal for each DC-DC converter based on each operating status information includes: Step S21B: Obtain the target duty cycle of each stage module based on the power status information. Step S22B: Generate the corresponding drive control signals for each stage of the interconnected modules based on the duty cycle of each target.

[0066] It should be understood that specific references Figure 7 In this embodiment, the power status information in the operating status information can also be used to control the operating status of each DC fan.

[0067] It should be noted that the target duty cycle is a theoretical duty cycle calculated based on parameters such as the output power of each DC fan and the total system voltage, which allows the output voltage of each DC fan to reach equilibrium. In a series-connected fan cluster, the output current of each DC fan is the same; therefore, the output voltage of each DC fan is proportional to its output power. Based on the power differences of each DC fan, the required duty cycle for each cascaded module can be directly calculated, thereby achieving precise adjustment of the output voltage.

[0068] It is easy to understand that in this embodiment, all DC-DC converters are operational. Since multiple cascaded modules are connected in series, the overall output voltage of the entire wind turbine cluster is the sum of the individual output voltages of each cascaded module. By precisely controlling the duty cycle of each cascaded module to achieve its corresponding target duty cycle, the individual output voltage of each DC wind turbine can be matched to its power, thereby ensuring that the overall output voltage meets the grid requirements while maintaining a balance in the individual output voltages of the DC wind turbines within the wind turbine cluster.

[0069] The above are merely preferred embodiments of this application and do not limit the patent scope of this application. Any equivalent structural or procedural transformations made using the content of this application's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent scope of this application.

Claims

1. A wind turbine power distribution system, characterized in that, The wind turbine power supply system includes: At least one wind turbine cluster, which is composed of several DC wind turbines connected in series, is used to output the electrical energy converted from wind energy in DC form in series. Each of the DC wind turbine configurations has a corresponding DC converter, and each DC converter is used to adjust its corresponding single-unit output voltage so that the single-unit output voltage formed by each of the DC wind turbines in the wind turbine cluster is kept in balance.

2. The wind turbine substation system as described in claim 1, characterized in that, The wind turbine power supply system includes: multiple wind turbine clusters; Each of the aforementioned wind turbine clusters is connected in parallel to the converter station.

3. The wind turbine substation system as described in claim 1, characterized in that, Each of the DC converters is also used to regulate and maintain the overall output voltage generated by each of the DC fans at the target voltage.

4. The wind turbine substation system as described in claim 1 or 2, characterized in that, The DC-DC converter includes: A multi-split winding transformer, the primary side of which is connected to the generator of the DC wind turbine, and the secondary side is equipped with multiple secondary windings; A plurality of AC / DC rectifiers, wherein the AC side of each AC / DC rectifier is connected to a corresponding secondary winding; Several step-down circuits are provided, with the input terminal of each step-down circuit connected to the DC side of a corresponding AC / DC rectifier, and the output terminals of each step-down circuit are cascaded to serve as the output terminal of the DC-DC converter.

5. The wind turbine substation system as described in claim 4, characterized in that, Each of the secondary windings is mutually insulated.

6. The wind turbine substation system as described in claim 4, characterized in that, The AC / DC rectifier is also equipped with a protection circuit. The protection circuit is configured on the DC side of the AC / DC rectifier; The protection circuit is used to stabilize the bus voltage when it detects that the bus voltage of the DC bus of the AC / DC rectifier exceeds the preset safe voltage, so that the bus voltage does not exceed the preset safe voltage.

7. The wind turbine substation system as described in claim 4, characterized in that, The step-down circuit is a half-bridge BUCK circuit.

8. A control method for a wind turbine substation system, characterized in that, Applied to the wind turbine substation system as described in any one of claims 1 to 7, the method comprises the following steps: Obtain the operating status information of each stage cascade module in each DC-DC converter; Based on the operating status information, each drive control signal of each DC-DC converter is generated; Based on the drive control signals, the individual output voltages of each DC converter are adjusted to maintain a balance among the individual output voltages generated by each DC fan in the fan cluster.

9. The wind turbine substation control method as described in claim 8, characterized in that, The operating status information includes voltage status information; The step of generating each drive control signal for each DC-DC converter based on each of the operating state information includes: Based on the level modulation strategy, each target working module is selected from each of the cascaded modules according to the voltage state information. Generate the corresponding drive control signals for each of the target working modules.

10. The wind turbine substation control method as described in claim 8, characterized in that, The operating status information includes power status information; The step of generating each drive control signal for each DC-DC converter based on each of the operating state information includes: Based on the power state information, the target duty cycle of each cascaded module is obtained; Based on the duty cycle of each target, generate the corresponding drive control signals for each cascaded module.

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