Onshore wind power transmission system

Abstract

An onshore wind power transmission system, used for solving the problems in the related art of AC integration and transmission such as harmonic resonance and reactive power transmission. The onshore wind power transmission system uses a bipolar topology structure, and each pole comprises a wind power sending-end unit and a wind power receiving-end unit. The wind power sending-end unit comprises a DC transformer and two or more wind turbines. A machine-side converter is arranged inside each wind turbine and each wind turbine corresponds to a low-voltage circuit breaker. The DC transformer is provided with a sending-end DC circuit breaker. For each wind turbine, electric energy generated thereby is rectified by the machine-side converter into first DC power, the first DC power is connected in parallel to the DC transformer via the low-voltage circuit breaker and is boosted into second DC power, and the second DC power is transmitted into the wind power receiving-end unit via the sending-end DC circuit breaker of the DC transformer. The wind power receiving-end unit comprises a receiving-end converter station, a coupling transformer, and a startup circuit. The second DC power is, after being converted by the receiving-end converter station, connected to an AC grid via the coupling transformer and the startup circuit.

Description

An onshore wind power transmission system

[0001] This application claims priority to Chinese Patent Application No. 202411692535.X, filed on November 25, 2024, entitled "An Onshore Wind Power Transmission System", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of wind power transmission technology, and more particularly to an onshore wind power transmission system. Background Technology

[0003] Wind power bases, by concentrating advantageous resources, can fully leverage economies of scale and reduce power generation costs, making them an important direction for the large-scale development of wind power. Currently, wind power systems mainly employ two methods: AC collection-AC transmission and AC collection-DC transmission. However, large-scale wind power bases involve long collection distances, and using the AC collection-AC transmission method would lead to significant problems such as harmonic resonance and reactive power transmission. On the other hand, using the AC collection-DC transmission method presents the issues of multiple power conversion stages and high system costs. Summary of the Invention

[0004] This application provides an onshore wind power transmission system to solve or partially solve the problems of AC collection and transmission such as harmonic resonance and reactive power transmission in existing related technologies.

[0005] This application provides an onshore wind power transmission system. The onshore wind power transmission system adopts a bipolar topology and includes a first pole transmission unit and a second pole transmission unit. Each pole transmission unit includes a wind power sending-end unit and a wind power receiving-end unit.

[0006] Each of the wind power sending-end units includes a DC transformer and two or more wind turbine units; each wind turbine unit is equipped with an organic side converter, and each wind turbine unit corresponds to a low-voltage circuit breaker; a sending-end DC circuit breaker is installed at the output end of the DC transformer.

[0007] For each of the wind turbine generators, the electrical energy generated by the wind turbine generator is rectified into first DC power by the turbine-side converter and then connected in parallel to the DC transformer via the low-voltage circuit breaker.

[0008] The first DC power is stepped up to the second DC power through the DC transformer, and the second DC power is sent to the wind power receiving unit through the sending-end DC circuit breaker.

[0009] Each wind power receiving-end unit includes a receiving-end converter station, a connecting transformer, and a starting circuit;

[0010] After the second DC power is converted by the receiving-end converter station, it first passes through the connecting transformer for voltage calibration, then through the starting circuit, and finally connects to the AC power grid.

[0011] Optionally, the mechanical parts of each wind turbine are 690V AC; the electrical energy generated by the wind turbine is rectified into ±550V DC by the turbine-side converter.

[0012] Optionally, the ±550V first DC power obtained after rectification by the machine-side converter is connected in parallel to the input terminal of the DC transformer via the low-voltage circuit breaker; the input terminal of the DC transformer corresponds to the low-voltage side, and the output terminal corresponds to the high-voltage side.

[0013] The low-voltage side of the DC transformer boosts the first DC power of ±550V to a second DC power of a higher voltage level, and outputs it through the high-voltage side of the DC transformer; the higher voltage level refers to a voltage capacity of ±100kV and above.

[0014] Optionally, the DC transformer is composed of multiple DC converter units, which are connected and combined in series and parallel.

[0015] The ±550V first DC power is boosted and rectified by each of the DC-DC converter units to output medium-voltage DC power.

[0016] The voltages of each medium-voltage DC power supply are summed to obtain a second DC power supply with a high voltage level.

[0017] Optionally, each of the DC transformer units consists of an IGBT module, a high-frequency transformer, and a rectifier and filter output;

[0018] In each of the DC transformer units, the ±550V first DC power is first inverted by the IGBT module, then stepped up by the high-frequency transformer, and then rectified and filtered by the rectifier and filter output to output medium-voltage DC power.

[0019] Optionally, the receiving-end converter station includes a full-bridge / half-bridge hybrid MMC converter with DC fault clearing capability;

[0020] The high-voltage second DC power is commutated by the full-bridge and half-bridge hybrid MMC converter, then undergoes voltage calibration by the connecting transformer to obtain calibrated high-voltage AC power, which then passes through the starting circuit and is finally connected to the AC power grid via power frequency AC transmission.

[0021] Optionally, the DC circuit breaker at the sending end of each pole is connected to the full-bridge / half-bridge hybrid MMC converter at the receiving end via a high-voltage DC overhead line.

[0022] When a fault occurs on any high-voltage DC overhead line, the full-bridge and half-bridge hybrid MMC converters on the same pole work together with the DC circuit breaker at the sending end to clear the DC line fault. The operation of the line on the pole that has not experienced a fault is not affected during this period.

[0023] Optionally, when a fault occurs on any high-voltage DC overhead line, for the faulty pole:

[0024] The line protection systems of the wind power sending-end unit and the wind power receiving-end unit at the faulty pole detect the fault and each executes a fault clearing action, thereby achieving coordinated fault clearing of the DC lines at both the sending and receiving ends of the same pole; wherein,

[0025] The line protection of the wind power sending unit of the fault pole generates a trip command and sends the trip command to the sending DC circuit breaker of the fault pole to control the tripping of the sending DC circuit breaker of the fault pole.

[0026] The line protection of the wind power receiving-end unit of the faulty pole generates a voltage control command and sends the voltage control command to the full-bridge and half-bridge hybrid MMC converter of the faulty pole, so that the full-bridge and half-bridge hybrid MMC converter of the faulty pole controls the DC side voltage of the receiving end of the pole to below 0.

[0027] Optionally, after the sending and receiving ends of the faulty pole have completed the fault clearing action, and after the deionization occurs within a preset recovery time, the full-bridge and half-bridge hybrid MMC converter of the faulty pole controls the restoration of the DC side voltage of the receiving end of the pole, the DC circuit breaker of the sending end of the faulty pole is re-closed, and the onshore wind power transmission system resumes operation.

[0028] Optionally, the receiving-end converter station includes a receiving-end DC circuit breaker and a half-bridge MMC converter; the receiving-end DC circuit breaker is located between the half-bridge MMC converter and the sending-end DC circuit breaker of the same polarity.

[0029] The high-voltage second DC power is commutated by the receiving-end DC circuit breaker and the half-bridge MMC converter. It is then calibrated by the connecting transformer to obtain calibrated high-voltage AC power, which is then transmitted through the starting circuit and finally connected to the AC power grid via power frequency AC transmission.

[0030] Optionally, the DC circuit breaker at the sending end of each pole is connected to the DC circuit breaker at the receiving end of the same pole via a high-voltage DC overhead line.

[0031] When a fault occurs on any high-voltage DC overhead line, the receiving-end DC circuit breaker and the sending-end DC circuit breaker on the same pole work together to clear the DC line fault, and the operation of the line on the pole that has not experienced a fault is not affected during this period.

[0032] Optionally, when a fault occurs on any high-voltage DC overhead line, for the faulty pole:

[0033] The line protection systems of the wind power sending-end unit and the wind power receiving-end unit at the faulty pole detect the fault and each executes a fault clearing action, thereby achieving coordinated fault clearing of the DC lines at both the sending and receiving ends of the same pole; wherein,

[0034] The line protection of the wind power sending unit of the fault pole generates a sending-end trip command and sends the sending-end trip command to the sending-end DC circuit breaker of the fault pole to control the tripping of the sending-end DC circuit breaker of the fault pole.

[0035] The line protection of the wind power receiving-end unit of the faulty pole generates a receiving-end trip command and sends the receiving-end trip command to the receiving-end DC circuit breaker of the faulty pole to control the tripping of the receiving-end DC circuit breaker of the faulty pole.

[0036] Optionally, after the sending and receiving ends of the faulty pole have completed the fault clearing action, and after the deionization occurs within a preset recovery time, both the sending and receiving DC circuit breakers of the faulty pole are re-closed, and the onshore wind power transmission system resumes operation.

[0037] Optionally, the onshore wind power transmission system further includes a positive DC overhead line and a negative DC overhead line;

[0038] The neutral line area between the positive DC overhead line and the negative DC overhead line adopts an overhead line metal neutral line and is clamped by grounding at the receiving end;

[0039] or,

[0040] For the neutral line region between the positive DC overhead line and the negative DC overhead line, grounding is achieved through grounding electrodes at both the sending and receiving ends.

[0041] As can be seen from the above technical solutions, this application has the following advantages:

[0042] An onshore wind power transmission system is provided. The onshore wind power transmission system adopts a bipolar topology, with each pole including a wind power sending-end unit and a wind power receiving-end unit. The wind power sending-end unit includes a DC transformer and two or more wind turbine generators. Each wind turbine generator has an internal turbine-side converter and a corresponding low-voltage circuit breaker. The DC transformer is equipped with a sending-end DC circuit breaker. For each wind turbine generator, the generated electricity is rectified into a first DC current by the turbine-side converter and then connected in parallel to the DC transformer via the low-voltage circuit breaker to be stepped up into a second DC current. This second DC current is then sent to the wind power receiving-end unit via the sending-end DC circuit breaker of the DC transformer. The wind power receiving-end unit includes a receiving-end converter station, a connecting transformer, and a starting circuit. After the second DC current is commutated at the receiving-end converter station, it is connected to the AC power grid via the connecting transformer and the starting circuit. The wind turbine outputs DC, which is then boosted to a medium-to-high voltage level before being transmitted over long-distance overhead lines. This not only reduces intermediate AC-to-DC conversion stages, effectively solving traditional AC collection and transmission problems such as harmonic resonance and reactive power transmission, but also lowers power generation costs. Furthermore, the all-DC transmission method offers higher transmission efficiency and reliability. Simultaneously, the bipolar system enables high-capacity power transmission, and compared to a symmetrical monopolar system, the bipolar system employed in this application avoids bipolar outages in the event of a monopolar fault, resulting in higher system reliability. Attached Figure Description

[0043] 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, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0044] Figure 1 is a schematic diagram of the circuit principle structure of an onshore wind power transmission system;

[0045] Figure 2 is a schematic diagram of the circuit principle structure of a wind turbine side rectifier;

[0046] Figure 3 is a schematic diagram of the circuit principle structure of a DC transformer unit for step-up rectification;

[0047] Figure 4 is a schematic diagram of the circuit principle structure of one of the receiving-end commutation units;

[0048] Figure 5 is a schematic diagram of the circuit principle structure of another onshore wind power transmission system;

[0049] Figure 6 is a schematic diagram of the circuit principle structure of another onshore wind power transmission system;

[0050] Figure 7 is a schematic diagram of the basic topology of a converter station containing only one type of half-bridge submodule. Detailed Implementation

[0051] This application provides an onshore wind power transmission system to solve or partially solve the problems of AC collection and transmission such as harmonic resonance and reactive power transmission in existing related technologies.

[0052] To make the inventive objectives, features, and advantages of this application more apparent and understandable, the technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described below are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0053] As an example, wind power bases, by concentrating advantageous resources, can fully leverage economies of scale and reduce power generation costs, making them an important direction for the large-scale development of wind power. Currently, wind power systems mainly employ two methods: AC collection-AC transmission and AC collection-DC transmission. However, large-scale wind power bases involve long collection distances, and using the AC collection-AC transmission method would lead to prominent issues such as harmonic resonance and reactive power transmission. On the other hand, using the AC collection-DC transmission method results in more power conversion stages and higher system costs.

[0054] To effectively address the current issues of harmonic resonance and reactive power transmission in onshore wind power transmission, and to achieve efficient grid connection, a novel onshore wind power transmission topology needs to be proposed to reduce the overall cost of the onshore wind power transmission system while ensuring stable transmission of onshore wind power.

[0055] Further analysis of this application shows that adopting an all-DC transmission method can reduce intermediate conversion stages. However, if a system architecture based on symmetrical single poles is used, the operational flexibility and reliability will be lower, and it will not be able to meet the demand for large-capacity power transmission.

[0056] Therefore, one of the core inventive points of this application is to organically combine DC power transmission technology with DC-type wind turbines to propose a bipolar topology onshore wind power all-DC power transmission system. Each pole of the onshore wind power transmission system can include multiple wind turbines and turbine-side converters. The low-voltage DC output from the DC-type wind turbines is boosted and collected by a DC converter, and then connected to the receiving-end flexible DC converter station via a long-distance overhead line equipped with a DC circuit breaker. The receiving-end flexible DC converter station adopts a full-bridge and half-bridge hybrid MMC (Modular Multilevel Converter) converter with DC fault clearing capability, or a combined architecture of receiving-end DC circuit breaker and half-bridge MMC converter. The wind turbine output is DC, which is boosted to a medium-to-high-level DC voltage and finally transmitted via a long-distance overhead line. This not only reduces intermediate AC-DC conversion links and effectively solves traditional AC collection and transmission problems such as harmonic resonance and reactive power transmission, but also reduces power generation costs. The all-DC transmission method offers higher transmission efficiency and reliability. Furthermore, the bipolar system enables high-capacity power transmission, and compared to a symmetrical unipolar system, the bipolar system employed in this application avoids bipolar outages in the event of a unipolar fault, resulting in higher system reliability.

[0057] Referring to Figure 1, a schematic diagram of the circuit principle structure of an onshore wind power transmission system provided in an embodiment of this application is shown.

[0058] The onshore wind power transmission system in this embodiment adopts a bipolar topology. To better distinguish the bipolar structure, the onshore wind power transmission system is specifically defined as including a first pole transmission unit (corresponding to the upper half of Figure 1) and a second pole transmission unit (corresponding to the lower half of Figure 1). Each pole transmission unit includes a wind power sending-end unit (corresponding to the sending end) and a wind power receiving-end unit (corresponding to the receiving end).

[0059] The following explanation uses one pole in Figure 1 as an example. Each wind power transmission unit includes a DC / DC (Direct Current to Direct Current Converter) transformer and two or more wind turbines (for simplicity, only turbine 1 and turbine n, two permanent magnet direct-drive generators, are shown in Figure 1). Each wind turbine has an internal organic-side converter (for clarity, it is shown separately from the wind turbine in Figure 1). Each wind turbine corresponds to a low-voltage circuit breaker.

[0060] For each wind turbine, the electrical energy generated by the turbine is rectified into first DC power by the turbine-side converter and then connected in parallel to a DC transformer via a low-voltage circuit breaker. The first DC power is then stepped up to second DC power by the DC transformer, and the second DC power is sent to the wind power receiving unit via the sending-end DC circuit breaker.

[0061] Referring to Figure 1, Figure 2 shows a schematic diagram of the circuit principle structure of a wind turbine side rectifier. Taking the permanent magnet direct-drive generator 1 with one pole in Figure 1 as an example, the mechanical part of each wind turbine is 690V AC, and the electrical energy generated by the wind turbine is rectified into ±550V DC by the turbine-side converter.

[0062] Next, the ±550V first DC power, rectified by multiple generator-side converters in multiple application scenarios, is connected in parallel to the input terminal of the DC transformer (corresponding to the low-voltage side) via a low-voltage circuit breaker. The low-voltage side of the DC transformer steps up the ±550V first DC power to a higher voltage level second DC power, which is then output via the high-voltage side of the DC transformer (or, in other words, stepped up to a higher voltage level second DC power). Here, "high voltage level" refers to a voltage capacity of ±100kV and above. A sending-end DC circuit breaker is installed at the output terminal (corresponding to the high-voltage side) of each pole of the DC transformer. Then, it is connected to the receiving-end converter station of the wind power receiving unit via a long-distance overhead line.

[0063] As can be seen from Figure 1, the DC transformer is composed of multiple DC converter units (such as module 1 to module n), which are connected and combined in series and parallel.

[0064] During the boost process, the ±550V first DC power is first boosted and rectified by each DC converter unit to output medium-voltage DC power. Then, the voltages of each medium-voltage DC power are summed to obtain a second DC power of a high voltage level (such as ±100kV or ±110kV).

[0065] More specifically, Figure 3 shows a schematic diagram of the circuit principle structure of a DC transformer unit for boost rectification.

[0066] As can be seen from Figure 3, each DC transformer unit mainly consists of an IGBT (Insulated Gate Bipolar Transistor) module, a high-frequency transformer, and a rectifier and filter output.

[0067] In each DC transformer unit, the ±550V DC power is first inverted by the IGBT module, then stepped up by the high-frequency transformer, and then rectified and filtered to output medium-voltage DC power.

[0068] More specifically, the DC transformer unit has a ±550V DC input, and the input terminal consists of IGBT modules. First, the ±550V DC is inverted into high-frequency low-voltage AC by the IGBT modules, and then stepped up to high-frequency high-voltage AC by the high-frequency transformer. After rectification and filtering (diode rectifier), the output is formed as ±2.5kV medium-voltage DC.

[0069] Each DC transformer unit can provide a stepped-up medium-voltage DC power of ±2.5kV. By connecting n DC / DC converter units in series and parallel, a second DC power of a corresponding high voltage level can be output. For example, for a second DC power of ±110kV, 44 DC / DC converter units need to be connected in series and parallel to form a DC transformer.

[0070] It is understandable that the number of DC transformer units for the ±110kV second DC voltage does not necessarily have to be 44, as long as the final output DC voltage is ±110kV. 44 units are used here because the high-voltage side output of a single DC transformer unit is ±2.5kV, which, when accumulated, equals ±110kV. For example, assuming that ±550V DC voltage can be processed by a single DC converter unit to output 5kV DC voltage, only 22 DC converter units are needed to obtain the total ±110kV DC voltage. It is understood that this application does not impose any limitations on this.

[0071] Figure 4 shows a schematic diagram of the circuit principle structure of one of the receiving-end commutation units provided in an embodiment of this application.

[0072] Referring to Figure 4, each wind power receiving-end unit may include a receiving-end converter station, a connecting transformer, and a starting circuit. The high-voltage second DC power is converted at the receiving-end converter station, then undergoes voltage calibration through the connecting transformer, then passes through the starting circuit, and finally connects to the AC grid.

[0073] Specifically, in the embodiments of this application, the receiving-end converter station of each pole adopts a full-bridge and half-bridge hybrid MMC topology with DC fault clearing capability, that is, a full-bridge and half-bridge hybrid MMC converter.

[0074] An MMC consists of multiple sub-modules (SMs). Each sub-module typically contains a half-bridge or full-bridge inverter and an energy storage capacitor. These sub-modules are connected in series to form a phase arm. A typical MMC includes three phase arms, corresponding to phases A, B, and C in a three-phase AC system.

[0075] The hybrid MMC converter provided in this application mainly consists of two types of submodules: HBSM (Half-Bridge Submodule) and FBSM (Full-Bridge Submodule). The HBSM consists of two IGBTs and one energy storage capacitor. The FBSM consists of four IGBTs and one energy storage capacitor.

[0076] In other words, the basic topology of a hybrid MMC converter at the receiving end mainly includes two types of submodules: full-bridge submodules and half-bridge submodules. Thus, in the event of a fault, the full-bridge submodule can output a negative level, working in conjunction with the half-bridge submodule to control the DC-side voltage below 0. By using half-bridge submodules in the topology of the hybrid MMC converter, compared to using only full-bridge submodules, the number of power devices can be reduced while achieving DC-side fault ride-through, thus lowering the equipment's investment cost.

[0077] The DC side of the full-bridge / half-bridge hybrid MMC converter is connected to the output DC interrupter at the same pole, receiving ±110kV second DC power. The AC side is connected to the connecting transformer and the starting circuit, and then connected to the main power grid via 110kV power frequency AC transmission. That is, after the high-voltage ±110kV second DC power is converted by the full-bridge / half-bridge hybrid MMC converter, it first undergoes voltage calibration through the connecting transformer to obtain calibrated high-voltage AC power (i.e., AC power conforming to the standard voltage level), then passes through the starting circuit, and finally is connected to the AC power grid via 110kV power frequency AC transmission.

[0078] A connecting transformer (also known as a coupling transformer or a linking transformer) can further boost the voltage transmitted at the sending end to achieve voltage transformation, thereby reducing line losses during long-distance power transmission.

[0079] A start-up circuit enables the system to start smoothly and reliably after power-on or reset.

[0080] The voltage level of the grid-side AC power is 110kV and above. This example uses the same voltage level as the ±110kV DC power obtained after boosting at the receiving end. In practical applications, the grid-side AC voltage level can be 220kV / 500kV / 750kV / 1000kV. Similarly, the high voltage level obtained after boosting at the sending end can also be 220kV / 500kV / 750kV / 1000kV.

[0081] Voltage calibration is required because the voltage on the input side of the transformer is generally not a standard voltage level. That is, although this embodiment uses a high voltage level of 110kV, there may be deviations in actual applications. The high voltage level received at the receiving end needs to be converted to a standard voltage level after conversion before it can be connected to the external power grid.

[0082] The sending-end DC circuit breaker of each pole is connected to the receiving-end full-bridge and half-bridge hybrid MMC converter of the same pole via a high-voltage DC overhead line (e.g., ±110kV).

[0083] When a fault occurs on any high-voltage (±110kV) DC overhead line, the full-bridge / half-bridge hybrid MMC converter on the same pole works in conjunction with the sending-end DC circuit breaker to clear the DC line fault. During this period, the operation of the line on the pole that has not experienced a fault remains unaffected.

[0084] In the specific implementation, when a fault occurs in any high-voltage (±110kV) DC overhead line, for the faulty pole: the line protection of the wind power sending unit of the faulty pole and the line protection of the wind power receiving unit of the faulty pole detect the fault and each executes the fault clearing action, so as to achieve the joint coordination of fault clearing of DC lines at the sending and receiving ends of the same pole.

[0085] Among them, the line protection of the wind power sending unit of the fault pole generates a trip command and sends the trip command to the sending DC circuit breaker of the fault pole to control the tripping of the sending DC circuit breaker of the fault pole.

[0086] The line protection of the wind power receiving-end unit at the faulty pole generates a voltage control command and sends the voltage control command to the full-bridge and half-bridge hybrid MMC converter at the faulty pole, so that the full-bridge and half-bridge hybrid MMC converter at the faulty pole controls the DC side voltage of the receiving end to below 0.

[0087] Furthermore, after the fault-clearing actions are completed at both the sending and receiving ends of the faulty pole, and after a preset recovery time (e.g., several hundred milliseconds) of deionization, the full-bridge / half-bridge hybrid MMC converter of the faulty pole controls the restoration of the DC side voltage at the receiving end of that pole. The DC circuit breaker at the sending end of the faulty pole is then reclosed. The onshore wind power transmission system resumes operation.

[0088] As shown in Figure 1, the onshore wind power transmission system also includes high-voltage positive DC overhead lines and negative DC overhead lines.

[0089] The (low-voltage) neutral line area between the positive and negative DC overhead lines can use the overhead line metal neutral line as shown in Figure 1, and be connected by clamping (DC disconnector) at the receiving end grounding.

[0090] Alternatively, for the (low-voltage) neutral line area between the positive DC overhead line and the negative DC overhead line, a connection method can be adopted as shown in Figure 5, where the grounding electrode is used at both the sending and receiving ends.

[0091] This application proposes a bipolar topology onshore wind power all-DC transmission system. Each pole of the onshore wind power transmission system can include multiple wind turbine generators and turbine-side converters. The low-voltage DC output from the DC-type wind turbine generators is boosted and collected by a DC converter, and then connected to the receiving-end flexible DC converter station via a long-distance overhead line equipped with a DC circuit breaker. The receiving-end flexible DC converter station adopts a hybrid MMC converter with full-bridge and half-bridge capabilities for DC fault clearing. The wind turbine output is DC, which is boosted to a medium-to-high-level DC voltage and finally transmitted via a long-distance overhead line. This not only reduces intermediate AC-DC conversion links and effectively solves problems such as harmonic resonance and reactive power transmission inherent in traditional AC collection and transmission, but also reduces power generation costs. The all-DC transmission method has higher transmission efficiency and reliability. Furthermore, the bipolar system can achieve large-capacity power transmission, and compared to a symmetrical monopolar system, the bipolar system used in this application can avoid bipolar outages after a monopolar fault, resulting in higher system reliability.

[0092] Referring to Figure 6, a schematic diagram of the circuit principle structure of another onshore wind power transmission system provided in an embodiment of this application is shown.

[0093] The onshore wind power transmission system in this embodiment adopts a bipolar topology. To better distinguish the bipolar structure, the onshore wind power transmission system is specifically defined as including a first pole transmission unit (corresponding to the upper half of Figure 6) and a second pole transmission unit (corresponding to the lower half of Figure 6). Each pole transmission unit includes a wind power sending-end unit (corresponding to the sending end) and a wind power receiving-end unit (corresponding to the receiving end).

[0094] For a detailed description of the wind power transmission unit, please refer to the aforementioned embodiments; it will not be repeated here.

[0095] Each wind power receiving-end unit may include a receiving-end converter station, a connecting transformer, and a starting circuit. The high-voltage second DC power is converted at the receiving-end converter station, then undergoes voltage calibration through the connecting transformer, then passes through the starting circuit, and finally connects to the AC grid.

[0096] Specifically, in the embodiments of this application, each receiving-end converter station includes a receiving-end DC circuit breaker and a half-bridge MMC converter. As can be seen from Figure 6, the receiving-end DC circuit breaker is located between the half-bridge MMC converter and the sending-end DC circuit breaker of the same pole.

[0097] The basic topology of the half-bridge MMC converter for each pole is shown in Figure 7. As can be seen from Figure 7, the half-bridge MMC converter only contains half-bridge submodules and does not include full-bridge submodules.

[0098] At any pole of the needle, the second DC power of high voltage level (such as ±110kV) passes through the DC circuit breaker at the receiving end, and after being commutated by the half-bridge MMC converter, it first passes through the connecting transformer for voltage calibration to obtain the calibrated high voltage level AC power, then passes through the starting circuit, and finally is connected to the AC power grid via (110kV) power frequency AC transmission.

[0099] The sending-end DC circuit breaker of each pole is connected to the receiving-end DC circuit breaker of the same pole via a high-voltage (±110kV) DC overhead line.

[0100] When a fault occurs on any high-voltage (±110kV) DC overhead line, the receiving-end DC circuit breaker and the sending-end DC circuit breaker on the same pole work together to clear the DC line fault. The operation of the line on the pole that has not experienced a fault is not affected during this period.

[0101] In the specific implementation, when a fault occurs in any high-voltage (±110kV) DC overhead line, for the faulty pole: the line protection of the wind power sending unit of the faulty pole and the line protection of the wind power receiving unit of the faulty pole detect the fault and each executes the fault clearing action, so as to achieve the joint coordination of fault clearing of DC lines at the sending and receiving ends of the same pole.

[0102] Among them, the line protection of the wind power sending unit of the fault pole generates a sending-end trip command and sends the sending-end trip command to the sending-end DC circuit breaker of the fault pole to control the tripping of the sending-end DC circuit breaker of the fault pole.

[0103] The line protection of the wind power receiving unit at the faulty pole generates a receiving-end trip command and sends the receiving-end trip command to the receiving-end DC circuit breaker at the faulty pole to control the tripping of the receiving-end DC circuit breaker at the faulty pole.

[0104] Furthermore, after the fault-clearing actions are completed at both the sending and receiving ends of the faulty pole, and after a preset recovery time (e.g., several hundred milliseconds) of deionization, both the sending and receiving DC circuit breakers of the faulty pole are re-closed. The onshore wind power transmission system resumes operation.

[0105] Similar to the aforementioned embodiments, the onshore wind power transmission system in this application also includes high-voltage positive DC overhead lines and negative DC overhead lines.

[0106] The (low-voltage) neutral line area between the positive and negative DC overhead lines can refer to the overhead line metal neutral line shown in Figure 1, and be connected by clamping (DC disconnector) at the receiving end grounding.

[0107] Alternatively, for the (low-voltage) neutral line area between the positive DC overhead line and the negative DC overhead line, a connection method can be adopted as shown in Figure 6, where the grounding electrode is used at both the sending and receiving ends.

[0108] This application proposes a bipolar topology onshore wind power all-DC transmission system. Each pole of the onshore wind power transmission system can include multiple wind turbine generators and turbine-side converters. The low-voltage DC output from the DC-type wind turbine generators is boosted and collected by a DC converter, and then connected to the receiving-end flexible DC converter station via a long-distance overhead line equipped with a DC circuit breaker. The receiving-end flexible DC converter station adopts a combined architecture of receiving-end DC circuit breaker and half-bridge MMC converter. The wind turbine output is DC, which is boosted to a medium-to-high-level DC voltage and finally transmitted via a long-distance overhead line. This not only reduces intermediate AC-DC conversion links and effectively solves problems such as harmonic resonance and reactive power transmission inherent in traditional AC collection and transmission, but also reduces power generation costs. The all-DC transmission method has higher transmission efficiency and reliability. At the same time, the bipolar system can achieve large-capacity power transmission, and compared with the symmetrical monopolar system, the bipolar system adopted in this application can avoid bipolar outage after a monopolar fault, resulting in higher system reliability.

[0109] It should be noted that, in order to enable those skilled in the art to better distinguish between data of the same type but with different actual meanings, some technical features in this application are distinguished by the terms "first" and "second". "First" and "second" are used only for data differentiation and have no other special meaning. It is understood that this application does not impose any restrictions on them.

[0110] In the embodiments provided in this application, it should be understood that the disclosed system can be implemented in other ways. For example, the device embodiments described above are merely illustrative. For instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces, or indirect coupling or communication connection between devices or units, and may be electrical, mechanical, or other forms.

[0111] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0112] Furthermore, the functional units in the various embodiments of this application can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0113] If the integrated unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of this application. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0114] The above-described embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. An onshore wind power transmission system, characterized in that, The onshore wind power transmission system adopts a bipolar topology, comprising a first-pole transmission unit and a second-pole transmission unit. Each pole transmission unit includes a wind power sending-end unit and a wind power receiving-end unit. Each of the wind power sending-end units includes a DC transformer and two or more wind turbine units; each wind turbine unit is equipped with an organic side converter, and each wind turbine unit corresponds to a low-voltage circuit breaker; a sending-end DC circuit breaker is installed at the output end of the DC transformer. For each of the wind turbine generators, the electrical energy generated by the wind turbine generator is rectified into first DC power by the turbine-side converter and then connected in parallel to the DC transformer via the low-voltage circuit breaker. The first DC power is stepped up to the second DC power through the DC transformer, and the second DC power is sent to the wind power receiving unit through the sending-end DC circuit breaker. Each wind power receiving-end unit includes a receiving-end converter station, a connecting transformer, and a starting circuit; After the second DC power is converted by the receiving-end converter station, it first passes through the connecting transformer for voltage calibration, then through the starting circuit, and finally connects to the AC power grid.

2. The onshore wind power transmission system according to claim 1, characterized in that, The mechanical parts of each wind turbine are 690V AC; the electrical energy generated by the wind turbine is rectified into ±550V DC by the turbine-side converter.

3. The onshore wind power transmission system according to claim 2, characterized in that, The ±550V first DC power obtained after rectification by the machine-side converter is connected in parallel to the input terminal of the DC transformer via the low-voltage circuit breaker; the input terminal of the DC transformer corresponds to the low-voltage side, and the output terminal corresponds to the high-voltage side. The low-voltage side of the DC transformer boosts the first DC power of ±550V to a second DC power of a higher voltage level, and outputs it through the high-voltage side of the DC transformer; the higher voltage level refers to a voltage capacity of ±100kV and above.

4. The onshore wind power transmission system according to claim 3, characterized in that, The DC transformer is composed of multiple DC converter units, which are connected and combined in series and parallel. The ±550V first DC power is boosted through each of the DC-DC converter units to output medium-voltage DC power. The voltages of each medium-voltage DC power supply are summed to obtain a second DC power supply with a high voltage level.

5. The onshore wind power transmission system according to claim 4, characterized in that, Each of the aforementioned DC transformer units consists of an IGBT module, a high-frequency transformer, and a rectified and filtered output; In each of the DC transformer units, the ±550V first DC power is first inverted by the IGBT module, then stepped up by the high-frequency transformer, and then rectified and filtered by the rectifier and filter output to output medium-voltage DC power.

6. The onshore wind power transmission system according to any one of claims 3 to 5, characterized in that, The receiving-end converter station includes a hybrid MMC converter with full-bridge and half-bridge capabilities for clearing DC faults. The high-voltage second DC power is commutated by the full-bridge and half-bridge hybrid MMC converter, then undergoes voltage calibration by the connecting transformer to obtain calibrated high-voltage AC power, which then passes through the starting circuit and is finally connected to the AC power grid via power frequency AC transmission.

7. The onshore wind power transmission system according to claim 6, characterized in that, The DC circuit breaker at the sending end of each pole is connected to the full-bridge / half-bridge hybrid MMC converter at the receiving end via a high-voltage DC overhead line. When a fault occurs on any high-voltage DC overhead line, the full-bridge and half-bridge hybrid MMC converters on the same pole work together with the DC circuit breaker at the sending end to clear the DC line fault. The operation of the line on the pole that has not experienced a fault is not affected during this period.

8. The onshore wind power transmission system according to claim 7, characterized in that, When a fault occurs on any high-voltage DC overhead line, for the faulty pole: The line protection systems of the wind power sending-end unit and the wind power receiving-end unit at the faulty pole detect the fault and each executes a fault clearing action, thereby achieving coordinated fault clearing of the DC lines at both the sending and receiving ends of the same pole; wherein, The line protection of the wind power sending unit of the fault pole generates a trip command and sends the trip command to the sending DC circuit breaker of the fault pole to control the tripping of the sending DC circuit breaker of the fault pole. The line protection of the wind power receiving-end unit of the faulty pole generates a voltage control command and sends the voltage control command to the full-bridge and half-bridge hybrid MMC converter of the faulty pole, so that the full-bridge and half-bridge hybrid MMC converter of the faulty pole controls the DC side voltage of the receiving end of the pole to below 0.

9. The onshore wind power transmission system according to claim 8, characterized in that, After the faulty pole's sending and receiving ends complete the fault clearing action, and after the deionization occurs within the preset recovery time, the full-bridge and half-bridge hybrid MMC converter of the faulty pole controls the restoration of the DC side voltage of the receiving end of the pole, the DC circuit breaker of the faulty pole's sending end is re-closed, and the onshore wind power transmission system resumes operation.

10. The onshore wind power transmission system according to any one of claims 3 to 5, characterized in that, The receiving-end converter station includes a receiving-end DC circuit breaker and a half-bridge MMC converter; the receiving-end DC circuit breaker is located between the half-bridge MMC converter and the sending-end DC circuit breaker of the same pole. The high-voltage second DC power is commutated by the receiving-end DC circuit breaker and the half-bridge MMC converter. It is then calibrated by the connecting transformer to obtain calibrated high-voltage AC power, which is then transmitted through the starting circuit and finally connected to the AC power grid via power frequency AC transmission.

11. The onshore wind power transmission system according to claim 10, characterized in that, The DC circuit breaker at the sending end of each pole is connected to the DC circuit breaker at the receiving end of the same pole via a high-voltage DC overhead line. When a fault occurs on any high-voltage DC overhead line, the receiving-end DC circuit breaker and the sending-end DC circuit breaker on the same pole work together to clear the DC line fault, and the operation of the line on the pole that has not experienced a fault is not affected during this period.

12. The onshore wind power transmission system according to claim 11, characterized in that, When a fault occurs on any high-voltage DC overhead line, for the faulty pole: The line protection systems of the wind power sending-end unit and the wind power receiving-end unit at the faulty pole detect the fault and each executes a fault clearing action, thereby achieving coordinated fault clearing of the DC lines at both the sending and receiving ends of the same pole; wherein, The line protection of the wind power sending unit of the fault pole generates a sending-end trip command and sends the sending-end trip command to the sending-end DC circuit breaker of the fault pole to control the tripping of the sending-end DC circuit breaker of the fault pole. The line protection of the wind power receiving-end unit of the faulty pole generates a receiving-end trip command and sends the receiving-end trip command to the receiving-end DC circuit breaker of the faulty pole to control the tripping of the receiving-end DC circuit breaker of the faulty pole.

13. The onshore wind power transmission system according to claim 12, characterized in that, After the faulty pole's sending and receiving ends have completed the fault clearing action, and after the preset recovery time for deionization, both the sending and receiving DC circuit breakers of the faulty pole will be re-closed, and the onshore wind power transmission system will resume operation.

14. The onshore wind power transmission system according to claim 1, characterized in that, The onshore wind power transmission system also includes a positive DC overhead line and a negative DC overhead line; The neutral line area between the positive DC overhead line and the negative DC overhead line adopts an overhead line metal neutral line and is clamped by grounding at the receiving end; or, For the neutral line region between the positive DC overhead line and the negative DC overhead line, grounding is achieved through grounding electrodes at both the sending and receiving ends.

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