An onshore wind power transmission system

Abstract

The present invention discloses an onshore wind power transmission system, which is used to solve the problems of AC collection and transmission such as harmonic resonance and reactive power transmission existing in the related art. The onshore wind power transmission system adopts a bipolar topology structure, and each pole includes a wind power sending end unit and a wind power receiving end unit; the wind power sending end unit includes a DC transformer and more than two wind turbines; an in-machine side converter is arranged inside each wind turbine and corresponds to a low-voltage circuit breaker; a sending end DC circuit breaker is installed on the DC transformer; for each wind turbine, the electric energy generated by it is rectified into a first direct current by the in-machine side converter and is connected in parallel to the DC transformer through the low-voltage circuit breaker to be boosted into a second direct current, and is sent into the wind power receiving end unit through the sending end DC circuit breaker of the DC transformer; the wind power receiving end unit includes a receiving end converter station, a coupling transformer and a starting circuit; after the second direct current is converted by the receiving end converter station, it is connected to the AC power grid through the coupling transformer and the starting circuit.

Description

Technical Field

[0001] The present invention relates to the technical field of wind power transmission, and particularly to an onshore wind power transmission system. Background Art

[0002] Wind power generation bases gather superior resources, can give full play to the scale effect, and reduce the power generation cost, which is an important direction for the scale development of wind power generation. At present, there are mainly two ways for wind power generation systems: AC collection - AC transmission and AC collection - DC transmission. However, for large - scale wind power generation bases with a long collection distance, if the AC collection - AC transmission method is adopted, problems such as harmonic resonance and reactive power transmission will be prominent. And if the AC collection - DC transmission method is adopted, there are problems such as many power conversion links and high system cost. Summary of the Invention

[0003] The present invention provides an onshore wind power transmission system for solving or partially solving problems such as harmonic resonance and reactive power transmission in AC collection and transmission in the existing related technologies.

[0004] The present invention provides an onshore wind power transmission system. The onshore wind power transmission system adopts a bipolar topology structure 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; wherein,

[0005] Each of the wind power sending - end units includes a DC transformer and more than two wind turbines; an in - machine side converter is arranged inside each wind turbine, and each wind turbine corresponds to a low - voltage circuit breaker; a sending - end DC circuit breaker is installed at the output end of the DC transformer;

[0006] For each wind turbine, the electric energy generated by the wind turbine is rectified into a first direct current by the in - machine side converter and is connected in parallel to the DC transformer through the low - voltage circuit breaker;

[0007] The first direct current is boosted to a second direct current by the DC transformer, and the second direct current is sent into the wind power receiving - end unit through the sending - end DC circuit breaker;

[0008] Each of the wind power receiving - end units includes a receiving - end converter station, a coupling transformer, and a starting circuit;

[0009] After the second direct current is converted by the receiving - end converter station, it is first voltage - calibrated by the coupling transformer, then passes through the starting circuit, and finally is connected to the AC power grid.

[0010] Optionally, the mechanical part of each wind turbine is 690V AC; the electric energy generated by the wind turbine is rectified by the machine-side converter into the first direct current of ±550V.

[0011] Optionally, the first direct current of ±550V obtained after rectification by the machine-side converter is connected in parallel to the input end of the DC transformer through the low-voltage circuit breaker; the input end of the DC transformer corresponds to the low-voltage side, and the output end corresponds to the high-voltage side;

[0012] The low-voltage side of the DC transformer boosts the first direct current of ±550V to the second direct current of a high voltage level and outputs it through the high-voltage side of the DC transformer; the high voltage level represents a voltage with a voltage capacity of ±100kV or more.

[0013] Optionally, the DC transformer is composed of multiple DC converter units, and the multiple DC converter units are connected and combined in a series-parallel manner;

[0014] The first direct current of ±550V is respectively subjected to boost rectification processing by each DC converter unit, and medium-voltage direct current is output;

[0015] According to the medium-voltage direct currents, voltage summation is performed to obtain the second direct current of a high voltage level.

[0016] Optionally, each DC transformer unit consists of an IGBT module, a high-frequency transformer, and a rectifier filter output;

[0017] In each DC transformer unit, the first direct current of ±550V first undergoes AC inversion through the IGBT module, then is boosted through the high-frequency transformer, and then undergoes rectification and filtering through the rectifier filter output to output medium-voltage direct current.

[0018] Optionally, the receiving-end converter station includes a full-bridge half-bridge hybrid MMC converter with DC fault clearing capability;

[0019] After the second direct current of the high voltage level undergoes commutation through the full-bridge half-bridge hybrid MMC converter, it first undergoes voltage calibration through the connecting transformer to obtain the calibrated alternating current of the high voltage level, then passes through the startup circuit, and finally is connected to the AC power grid.

[0020] Optionally, the sending-end DC circuit breaker at each pole of the sending end is connected to the full-bridge half-bridge hybrid MMC converter at the same pole of the receiving end through a high-voltage level DC overhead line;

[0021] When a fault occurs in any high-voltage DC overhead line, the full-bridge and half-bridge hybrid MMC converters at the same pole cooperate with the sending-end DC circuit breaker to clear the DC line fault, and the line operation of the pole where the fault does not occur is not affected during this period.

[0022] Optionally, when a fault occurs on any high-voltage DC overhead line, for the faulty pole:

[0023] The line protection of the wind power sending end unit of the fault pole and the line protection of the wind power receiving end unit of the fault pole detect the fault and respectively perform fault clearing actions to achieve joint coordination of fault clearing of the sending end and receiving end DC lines of the same pole; wherein,

[0024] The line protection of the wind power sending-end unit of the fault pole generates a tripping instruction, and sends the tripping instruction 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;

[0025] The line protection of the wind power receiving unit at the fault pole generates a voltage control instruction, and sends the voltage control instruction to the full-bridge and half-bridge hybrid MMC converters at the fault pole, so that the full-bridge and half-bridge hybrid MMC converters at the fault pole control the DC side voltage of the receiving end of the pole to below 0.

[0026] Optionally, when the sending end and the receiving end of the fault pole complete the fault clearing action, after de-ionization for a preset recovery time, the full-bridge and half-bridge hybrid MMC converters of the fault pole control to restore the DC side voltage of the receiving end of the pole, the sending end DC circuit breaker of the fault pole is reclosed, and the onshore wind power transmission system resumes operation.

[0027] 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 pole;

[0028] The high-voltage second DC power passes through the receiving-end DC circuit breaker and the half-bridge MMC converter for conversion, and then passes through the connecting transformer for voltage calibration to obtain the calibrated high-voltage AC power, and then passes through the starting circuit and is finally connected to the AC power grid.

[0029] Optionally, the sending-end DC circuit breaker of each pole of the sending end is connected to the receiving-end DC circuit breaker of the same pole of the receiving end through a high-voltage DC overhead line;

[0030] When a fault occurs in any DC overhead line of an extremely high voltage level, the receiving-end DC breaker and the sending-end DC breaker of the same pole cooperate to clear the DC line fault, and the line operation of the pole without fault is not affected during this period.

[0031] Optionally, when a fault occurs in any DC overhead line of an extremely high voltage level, for the faulty pole where the fault occurs:

[0032] The line protection of the wind power sending-end unit of the faulty pole and the line protection of the wind power receiving-end unit of the faulty pole detect the fault and each execute a fault clearing action to achieve the joint cooperation of fault clearing for the sending-end and receiving-end DC lines of the same pole; among which,

[0033] The line protection of the wind power sending-end unit of the faulty pole generates a sending-end trip command and issues the sending-end trip command to the sending-end DC breaker of the faulty pole to control the opening of the sending-end DC breaker of the faulty pole;

[0034] The line protection of the wind power receiving-end unit of the faulty pole generates a receiving-end trip command and issues the receiving-end trip command to the receiving-end DC breaker of the faulty pole to control the opening of the receiving-end DC breaker of the faulty pole.

[0035] Optionally, when the sending-end and receiving-end of the faulty pole complete the fault clearing action, after the deionization in the preset recovery time, the sending-end DC breaker and the receiving-end DC breaker of the faulty pole are both reclosed, and the onshore wind power transmission system resumes operation.

[0036] Optionally, the onshore wind power transmission system further includes a positive DC overhead line and a negative DC overhead line;

[0037] For the neutral line area between the positive DC overhead line and the negative DC overhead line, an overhead line metal neutral line is adopted and clamped by grounding at the receiving end;

[0038] Or,

[0039] For the neutral line area between the positive DC overhead line and the negative DC overhead line, it is grounded through a grounding electrode at the sending end and the receiving end respectively.

[0040] From the above technical solutions, it can be seen that the present invention has the following advantages:

[0041] An onshore wind power transmission system is provided. The onshore wind power transmission system adopts a bipolar topology, with each pole comprising a wind power sending unit and a wind power receiving unit. The wind power sending unit comprises a DC transformer and two or more wind turbines. Each wind turbine is internally provided with a machine-side converter corresponding to a low-voltage circuit breaker. The DC transformer is equipped with a sending-end DC circuit breaker. For each wind turbine, the electric energy generated by the wind turbine is rectified into a first DC power by the machine-side converter, and then connected in parallel to the DC transformer through a low-voltage circuit breaker to be boosted to a second DC power. The second DC power is then transmitted to the wind power receiving unit through the sending-end DC circuit breaker of the DC transformer. The wind power receiving unit comprises 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 is connected to the AC power grid through the connecting transformer and the starting circuit. The wind turbine output is DC, which is then boosted to medium- to high-level DC voltages before being transmitted via long-distance overhead lines. This not only reduces the intermediate AC-DC conversion process, effectively solving traditional AC collection and transmission issues 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. Compared to symmetrical unipolar systems, the bipolar system employed in this invention avoids bipolar outages in the event of a unipolar fault, resulting in higher system reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0043] Figure 1 This is a schematic diagram of the circuit principle structure of an onshore wind power transmission system;

[0044] Figure 2 This is a schematic diagram of the circuit principle structure of a wind turbine side rectification;

[0045] Figure 3 This is a schematic diagram of the circuit principle structure of a DC transformer unit step-up rectification;

[0046] Figure 4 This is a schematic diagram of the circuit principle structure of one of the receiving-end commutation units;

[0047] Figure 5 This is a schematic diagram of the circuit principle structure of another onshore wind power transmission system;

[0048] Figure 6 This is a schematic diagram of the circuit principle structure of another onshore wind power transmission system;

[0049] Figure 7 It is a schematic diagram of the basic topology structure of a converter station that only contains one half-bridge sub-module. Specific implementation manners

[0050] An embodiment of the present invention provides an onshore wind power transmission system, which is used to solve or partially solve problems such as harmonic resonance and reactive power transmission in AC collection and transmission in the existing related technologies.

[0051] To make the object, features, and advantages of the present invention more obvious and understandable, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the embodiments described below are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0052] As an example, a wind power generation base aggregates advantageous resources, can give full play to the scale effect, reduce the power generation cost, and is an important direction for the large-scale development of wind power generation. At present, there are mainly two ways for a wind power generation system: AC collection - AC transmission and AC collection - DC transmission. However, for a large wind power generation base with a long collection distance, if the AC collection - AC transmission method is adopted, problems such as harmonic resonance and reactive power transmission will be prominent. If the AC collection - DC transmission method is adopted, there are problems such as many power conversion links and high system costs.

[0053] To effectively solve the problems of AC collection and transmission such as harmonic resonance and reactive power transmission in current onshore wind power transmission, and at the same time achieve efficient grid connection, a new onshore wind power transmission topology structure needs to be proposed to reduce the overall cost of the onshore wind power transmission system on the basis of the stable transmission of onshore wind power.

[0054] After further analysis of the present invention, adopting the full DC transmission method can reduce the intermediate conversion links. However, if a system architecture mainly based on a symmetric monopole is adopted, the operation flexibility and reliability are relatively low, and it cannot meet the large-capacity power transmission requirements.

[0055] Therefore, one of the core inventive points of the embodiment of the present invention is to organically combine DC transmission technology with DC wind turbines to propose an onshore wind power full DC transmission system with a bipolar topology. Each pole sending end of the onshore wind power transmission system can include multiple wind turbines and machine-side converters. The low-voltage DC output of the DC wind turbine is boosted and collected by a DC converter, and then connected to the flexible DC converter station at the receiving end through a long-distance overhead line equipped with a DC circuit breaker. The flexible DC converter station at the receiving end adopts a full-bridge and half-bridge hybrid MMC (Modular Multilevel Converter) converter with DC fault clearing capability, or a combined architecture of a receiving-end DC circuit breaker and a half-bridge MMC converter. The wind turbine output is DC, which is boosted to a medium-to-high-level DC voltage and finally transmitted through a long-distance overhead line. This not only reduces the intermediate AC-DC conversion link, 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 has higher transmission efficiency and reliability. At the same time, the bipolar system can achieve large-capacity power transmission. Compared with the symmetrical monopole system, the bipolar system adopted by the present invention can avoid bipolar shutdown after a monopole fault occurs, and the system operation reliability is higher.

[0056] Reference Figure 1 , shows a schematic diagram of the circuit principle structure of an onshore wind power transmission system provided by an embodiment of the present invention.

[0057] The onshore wind power transmission system in the embodiment of the present invention adopts a bipolar topology. In order to better distinguish the bipolar, the onshore wind power transmission system is set to specifically include a first-pole transmission unit (corresponding to Figure 1 The upper part of the) and the second pole transmission unit (corresponding to Figure 1 Each transmission unit includes a wind power sending unit (corresponding to the sending end) and a wind power receiving unit (corresponding to the receiving end).

[0058] by Figure 1 Each wind power sending end unit includes a DC / DC (Direct Current to Direct Current Converter) DC transformer, two or more wind turbines (for simplicity, Figure 1 Only two permanent magnet direct drive generators, wind turbine 1 and wind turbine n, are shown in the figure. Each wind turbine is equipped with an organic side converter (for ease of explanation, Figure 1 Each wind turbine corresponds to a low-voltage circuit breaker.

[0059] For each wind turbine generator, the electric energy generated by the wind turbine generator is rectified into first direct current by the machine-side converter and is connected in parallel to the DC transformer through a low-voltage circuit breaker. The first direct current is boosted to second direct current by the DC transformer, and the second direct current is sent into the wind power receiving end unit through the sending-end DC circuit breaker.

[0060] Combined with Figure 1 , Figure 2 Figure 1 shows a schematic diagram of the circuit principle structure of rectification on the wind turbine generator side. Taking Figure 1 wind turbine 1 of one pole as an example, the mechanical part of each wind turbine generator is 690V alternating current, and the electric energy generated by the wind turbine generator is rectified into first direct current of ±550V by the machine-side converter.

[0061] Then, the first direct current of ±550V obtained after rectification by the machine-side converters in multiple application scenarios is connected in parallel to the input end of the DC transformer, that is, the corresponding low-voltage side, through the low-voltage circuit breaker. The low-voltage side of the DC transformer boosts the first direct current of ±550V to second direct current of a high voltage level and outputs it through the high-voltage side of the DC transformer (it can also be understood as boosting to second direct current of a high voltage level on the high-voltage side). Among them, the high voltage level means a voltage with a voltage capacity of ±100kV or above. A sending-end DC circuit breaker is installed at the output end of each pole of the DC transformer (that is, the corresponding high-voltage side). Then it is connected to the receiving-end converter station of the wind power receiving end unit through a long-distance overhead line.

[0062] From Figure 1 it can be seen that the DC transformer is composed of multiple DC converter units (such as module 1 to module n), and the multiple DC converter units are connected and combined in a series-parallel manner.

[0063] When boosting, first, each DC converter unit separately performs boosting and rectification processing on the first direct current of ±550V and outputs medium-voltage direct current. Then, according to each medium-voltage direct current, voltage summation is performed to obtain second direct current of a high voltage level (such as ±100kV or ±110kV).

[0064] More specifically, Figure 3 Figure 2 shows a schematic diagram of the circuit principle structure of boosting and rectification of a DC transformer unit.

[0065] Combined with Figure 3 it can be seen that each DC transformer unit mainly consists of an IGBT (Insulated Gate Bipolar Transistor) module, a high-frequency transformer, and a rectification and filtering output.

[0066] In each DC transformer unit, the first DC power of ±550V is first inverted into AC power through an IGBT module, then stepped up through a high-frequency transformer, and then rectified and filtered through a rectifier and filter to output medium-voltage DC power.

[0067] More specifically, the input of the DC transformer unit is ±550V DC, and the input terminal is composed of an IGBT module. First, the IGBT module inverts the first DC power of ±550V into high-frequency low-voltage AC power, and steps it up to high-frequency high-voltage AC power through a high-frequency transformer. Then, it passes through a rectifier and filter output (diode rectifier), and after rectification and filtering, it forms medium-voltage DC power of ±2.5kV.

[0068] The medium-voltage DC power of ±2.5kV after stepping up can be obtained through each DC transformer unit. Composed of n DC / DC DC converter units connected in series and parallel, finally, the second DC power corresponding to a high voltage level can be output. For example, for the second DC power of ±110kV, 44 DC / DC DC converter units need to be connected in series and parallel to form a DC transformer.

[0069] It can be understood that for the second DC power of ±110kV, the number of DC transformer units is not necessarily 44, as long as the finally output DC voltage is ±110kV. Here, 44 are used because the high-voltage side output of a single DC transformer unit is ±2.5kV, and the accumulation is ±110kV. For example, for DC power of ±550V, assuming that after being processed by a single DC converter unit, DC power of 5kV can be output. At this time, only 22 DC converter units are needed for the DC transformer to obtain a total DC power of ±110kV. It can be understood that the present invention does not limit this.

[0070] Figure 4 The circuit principle structure diagram of one of the receiving end converter units provided by the embodiment of the present invention is shown.

[0071] Combined with Figure 4 , each wind power receiving end unit can include a receiving end converter station, a coupling transformer, and a starting circuit. After the second DC power of a high voltage level is converted through the receiving end converter station, it first passes through the coupling transformer for voltage calibration, then passes through the starting circuit, and finally accesses the AC power grid.

[0072] Specifically, in the embodiment of the present invention, the receiving end converter station of each pole adopts a full-bridge half-bridge hybrid MMC topology structure with DC fault clearing ability, that is, a full-bridge half-bridge hybrid MMC converter.

[0073] Among them, the MMC consists of multiple sub-modules (SMs). Each sub-module usually includes 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 respectively.

[0074] The full-bridge and half-bridge hybrid MMC converter provided by the embodiments of the present invention is mainly composed of two types of sub-modules: HBSM (Half-Bridge Submodule) and FBSM (Full-Bridge Submodule). Among them, the HBSM consists of two IGBTs and an energy storage capacitor. The FBSM consists of four IGBTs and an energy storage capacitor.

[0075] In other words, the basic topology of the full-bridge and half-bridge hybrid MMC converter at the receiving end mainly includes two types of sub-modules: full-bridge sub-modules and half-bridge sub-modules. Thus, after a fault occurs, the full-bridge sub-module can output a negative level and cooperate with the half-bridge sub-module to jointly control the DC-side voltage below 0. The topology structure of the full-bridge and half-bridge hybrid MMC converter adopts half-bridge sub-modules in part. Compared with using only full-bridge sub-modules, it can achieve DC-side fault ride-through while reducing the number of power devices and the investment cost of equipment.

[0076] The DC side of the full-bridge and half-bridge hybrid MMC converter is connected to the outgoing DC disconnector at the same pole of the sending end, receives the second DC power of ±110 kV, the AC side is connected to the coupling transformer and the start-up circuit, and then is connected to the large power grid through 110 kV power-frequency AC power transmission. That is, after the second DC power of the high voltage level of ±110 kV is rectified by the full-bridge and half-bridge hybrid MMC converter, it first passes through the coupling transformer for voltage calibration to obtain the calibrated high voltage level of alternating current (i.e., alternating current that meets the standard voltage level), then passes through the start-up circuit, and finally is connected to the AC power grid through 110 kV power-frequency AC power transmission.

[0077] The coupling transformer (which can also be called the connection transformer or the coupling transformer) can further boost the voltage transmitted from the sending end to achieve voltage conversion, so as to reduce the line loss during long-distance power transmission.

[0078] The start-up circuit (Start-Up Circuit) can enable the system to start smoothly and reliably after power-on or reset.

[0079] Among them, the voltage level of the grid-side alternating current is 110 kV or above. Here, taking the same voltage level as the ±110 kV direct current obtained after boosting at the receiving end as an example for illustration, in actual applications, the grid-side alternating current voltage level can be 220 kV / 500 kV / 750 kV / 1000 kV. Similarly, the high voltage level obtained after boosting at the sending end can also be 220 kV / 500 kV / 750 kV / 1000 kV.

[0080] Voltage calibration is set because the voltage on one side of the input of the coupling transformer is generally not a standard voltage level. That is, although the 110 kV high voltage level is used for illustration in the embodiments of the present invention, there may be deviations in actual applications. After the high voltage level voltage received at the receiving end is rectified, it needs to be transformed into a standard voltage level through coupling before it can be connected to the external power grid.

[0081] The sending-end DC breaker of each pole at the sending end is connected to the full-bridge half-bridge hybrid MMC converter of the same pole at the receiving end through a DC overhead line with a high voltage level (such as ±110 kV).

[0082] When a fault occurs in the DC overhead line with a high voltage level (±110 kV) of any pole, the full-bridge half-bridge hybrid MMC converter of the same pole and the sending-end DC breaker cooperate together to clear the DC line fault. Among them, the line of the non-faulty pole operates without being affected during this period.

[0083] In a specific implementation, when a fault occurs in the DC overhead line with a high voltage level (±110 kV) of any pole, for the faulty pole: the line protection of the wind power sending-end unit of the faulty pole and the line protection of the wind power receiving-end unit of the faulty pole detect the fault and each execute a fault clearing action to achieve the common cooperation of clearing the DC line fault between the sending end and the receiving end of the same pole.

[0084] Among them, the line protection of the wind power sending-end unit of the faulty pole generates a tripping command and issues the tripping command to the sending-end DC breaker of the faulty pole to control the tripping of the sending-end DC breaker of the faulty pole.

[0085] The line protection of the wind power receiving-end unit of the faulty pole generates a voltage control command and issues the voltage control command to the full-bridge half-bridge hybrid MMC converter of the faulty pole, so that the full-bridge half-bridge hybrid MMC converter of the faulty pole controls the DC-side voltage at the receiving end of this pole to below 0.

[0086] Furthermore, when the sending end and the receiving end of the faulty pole have completed the fault clearing action, after the deionization in the preset recovery time (such as several hundred milliseconds), the full-bridge half-bridge hybrid MMC converter of the faulty pole controls to restore the DC-side voltage at the receiving end of this pole. The sending-end DC breaker of the faulty pole recloses. The onshore wind power transmission system resumes operation.

[0087] like Figure 1 It can be seen that the onshore wind power transmission system also includes high-voltage positive DC overhead lines and negative DC overhead lines.

[0088] The (low voltage) neutral area between the positive DC overhead line and the negative DC overhead line can be Figure 1 The metal neutral conductor of the overhead line is shown, and the connection method is clamped (DC isolation switch) at the receiving end.

[0089] Alternatively, for the (low voltage) neutral line area between the positive DC overhead line and the negative DC overhead line, the following method can be used: Figure 5 The connection method shown is grounded through grounding electrodes at the sending end and the receiving end respectively.

[0090] In an embodiment of the present invention, a bipolar topology onshore wind power all-DC transmission system is proposed. Each pole of the onshore wind power transmission system can include multiple wind turbines and generator-side converters. The low-voltage DC output of the DC wind turbines is boosted and aggregated by a DC converter, then connected to a receiving-end flexible DC converter station via long-distance overhead lines equipped with DC circuit breakers. The receiving-end flexible DC converter station utilizes a full-bridge and half-bridge hybrid MMC converter with DC fault clearing capabilities. The wind turbine output is DC, which is boosted to medium- to high-level DC voltages before being transmitted via long-distance overhead lines. This not only reduces the intermediate AC-DC conversion steps, effectively addressing traditional AC aggregation and transmission issues 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 can achieve large-capacity power transmission. Compared to symmetrical unipolar systems, the bipolar system employed in the present invention avoids bipolar outages in the event of a unipolar fault, resulting in higher system reliability.

[0091] Reference Figure 6 , shows a schematic diagram of the circuit principle structure of another onshore wind power transmission system provided by an embodiment of the present invention.

[0092] The onshore wind power transmission system in the embodiment of the present invention adopts a bipolar topology. In order to better distinguish the bipolar, the onshore wind power transmission system is set to specifically include a first-pole transmission unit (corresponding to Figure 6 The upper part of the) and the second pole transmission unit (corresponding to Figure 6 Each transmission unit includes a wind power sending unit (corresponding to the sending end) and a wind power receiving unit (corresponding to the receiving end).

[0093] The detailed introduction of the wind power sending end unit can be referred to the aforementioned embodiment and will not be repeated here.

[0094] Each wind power receiving end unit may include a receiving end converter station, a coupling transformer, and a starting circuit. After the second direct current with a high voltage level is converted by the receiving end converter station, it first undergoes voltage calibration through the coupling transformer, then passes through the starting circuit, and finally is connected to the AC power grid.

[0095] Specifically, in the embodiments of the present invention, the receiving end converter station of each pole includes a receiving end DC circuit breaker and a half-bridge MMC converter. As can be seen from Figure 6 it that 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.

[0096] The basic topological structure of the half-bridge MMC converter of each pole is as Figure 7 shown. As Figure 7 can be seen, the half-bridge MMC converter only includes half-bridge sub-modules and does not set full-bridge sub-modules.

[0097] For any pole, the second direct current with a high voltage level (such as ±110 kV) passes through the receiving end DC circuit breaker, is converted by the half-bridge MMC converter, then undergoes voltage calibration through the coupling transformer to obtain the calibrated alternating current with a high voltage level, then passes through the starting circuit, and finally is connected to the AC power grid through (110 kV) power frequency AC power transmission.

[0098] The sending end DC circuit breaker of each pole at the sending end is connected to the receiving end DC circuit breaker of the same pole at the receiving end through a DC overhead line with a high voltage level (±110 kV).

[0099] When a fault occurs in the DC overhead line with a high voltage level (±110 kV) of any pole, the receiving end DC circuit breaker and the sending end DC circuit breaker of the same pole cooperate together to clear the DC line fault, and the line operation of the non-faulty pole is not affected during this period.

[0100] In a specific implementation, when a fault occurs in the DC overhead line with a high voltage level (±110 kV) of any pole, for the faulty pole: the line protection of the wind power sending end unit of the faulty pole and the line protection of the wind power receiving end unit of the faulty pole detect the fault and each perform a fault clearing action to achieve the joint cooperation of clearing the DC line fault at the sending end and the receiving end of the same pole.

[0101] Among them, the line protection of the wind power sending end unit of the faulty pole generates a sending end tripping command and issues the sending end tripping command to the sending end DC circuit breaker of the faulty pole to control the tripping of the sending end DC circuit breaker of the faulty pole.

[0102] The line protection of the wind power receiving end unit of the faulty pole generates a receiving end tripping command and issues the receiving end tripping 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.

[0103] Furthermore, after the fault clearing action is completed at both the sending and receiving ends of the faulty pole, and after a preset recovery time (e.g., several hundred milliseconds) of de-ionization, both the sending and receiving DC circuit breakers of the faulty pole are reclosed, and the onshore wind power transmission system resumes operation.

[0104] Similar to the above-mentioned embodiment, the onshore wind power transmission system in the embodiment of the present invention also includes a high-voltage positive DC overhead line and a negative DC overhead line.

[0105] The (low voltage) neutral line area between the positive DC overhead line and the negative DC overhead line can be referred to as follows Figure 1 The metal neutral conductor of the overhead line is shown, and the connection method is clamped (DC isolation switch) at the receiving end.

[0106] Alternatively, for the (low voltage) neutral line area between the positive DC overhead line and the negative DC overhead line, the following method can be used: Figure 6 The connection method shown is grounded through grounding electrodes at the sending end and the receiving end respectively.

[0107] In an embodiment of the present invention, a bipolar topology onshore wind power all-DC transmission system is proposed. Each pole of the onshore wind power transmission system can include multiple wind turbines and generator-side converters. The low-voltage DC output of the DC wind turbines is boosted and aggregated by a DC converter, then connected to a receiving-end flexible DC converter station via long-distance overhead lines equipped with DC circuit breakers. The receiving-end flexible DC converter station utilizes a combination of a receiving-end DC circuit breaker and a half-bridge MMC converter. The wind turbine output is DC, which is boosted to medium- to high-level DC voltages before being transmitted via long-distance overhead lines. This not only reduces the intermediate AC-DC conversion steps, effectively resolving traditional AC aggregation and transmission issues 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 can achieve large-capacity power transmission. Compared to symmetrical unipolar systems, the bipolar system employed in the present invention avoids bipolar outages in the event of a unipolar fault, resulting in higher system reliability.

[0108] It should be noted that in order to enable those skilled in the art to better distinguish data of the same type but with different actual meanings, some technical features are distinguished by the first and second in the embodiments of the present invention. The first and second are only used for data distinction and have no other special meanings. It can be understood that the present invention does not impose any restrictions on this.

[0109] In the embodiments provided by the present invention, 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 example, the division of the units is only a logical function division. In actual implementation, there may be other division methods. For example, multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the displayed or discussed couplings or direct couplings or communication connections between each other can be through some interfaces. The indirect couplings or communication connections of the devices or units can be in electrical, mechanical or other forms.

[0110] The units described as separate components may or may not be physically separated. The components displayed as units may or may not be physical units, that is, they can be located in one place or distributed to multiple network units. Some or all of the units can be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0111] In addition, in each embodiment of the present invention, the functional units can be integrated in a processing unit, or each unit can exist physically alone, or two or more units can be integrated in one unit. The above-mentioned integrated units can be implemented in the form of hardware or in the form of software functional units.

[0112] If the above-mentioned integrated unit is implemented in the form of 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 the present invention, in essence, or the part that contributes to the prior art, or all or part of this 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 enable a computer device (which can be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the methods described in each embodiment of the present invention. The foregoing storage medium includes: various media such as USB flash drives, mobile hard disks, read-only memory (ROM), random access memory (RAM), magnetic disks or optical discs that can store program codes.

[0113] As described above, the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of each embodiment of the present invention.

Claims

1. An onshore wind power transmission system, characterized in that: The onshore wind power transmission system adopts a bipolar topology structure, and includes a first-pole transmission unit and a second-pole transmission unit, each of which includes a wind power sending end unit and a wind power receiving end unit; wherein, Each wind power sending end unit includes a DC transformer and two or more wind turbines; an organic side converter is provided inside each wind turbine, and each wind turbine 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 wind turbine generator set, the electric energy generated by the wind turbine generator set is rectified into a first direct current through the generator-side converter, and is connected in parallel to the direct current transformer through the low-voltage circuit breaker; The first DC power is boosted into a second DC power by the DC transformer, and the second DC power is sent to the wind power receiving unit through the sending-end DC circuit breaker; Each of the wind power receiving units includes a receiving 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 passes through the starting circuit, and finally is connected to the AC power grid; The receiving-end converter station includes a full-bridge and half-bridge hybrid MMC converter with DC fault clearing capability; the sending-end DC circuit breaker of each pole of the sending end is connected to the full-bridge and half-bridge hybrid MMC converter of the same pole of the receiving end through a high-voltage DC overhead line; When a fault occurs on any high-voltage DC overhead line, for the fault pole where the fault occurs: the line protection of the wind power sending end unit of the fault pole and the line protection of the wind power receiving end unit of the fault pole detect the fault and respectively perform fault clearing actions to achieve joint coordination of fault clearing of the sending end and receiving end DC lines of the same pole; wherein, The line protection of the wind power sending-end unit of the fault pole generates a tripping instruction, and sends the tripping instruction 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 unit at the fault pole generates a voltage control instruction, and sends the voltage control instruction to the full-bridge and half-bridge hybrid MMC converters at the fault pole, so that the full-bridge and half-bridge hybrid MMC converters at the fault pole control the DC side voltage of the receiving end of the pole to below 0.

2. The onshore wind power transmission system according to claim 1, characterized in that: The mechanical part of each wind turbine generator set is 690V AC; the electric energy generated by the wind turbine generator set is rectified into a first direct current of ±550V by the machine-side converter.

3. The onshore wind power transmission system according to claim 2, characterized in that: The ±550V first direct current obtained after rectification by the generator-side converter is connected in parallel to the input end of the direct current transformer via the low-voltage circuit breaker; the input end of the direct current transformer corresponds to the low-voltage side, and the output end 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 high voltage level, and outputs it through the high-voltage side of the DC transformer; the high voltage level indicates 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 a plurality of DC converter units, and the plurality of DC converter units are connected in series and parallel; The first ±550V DC power is boosted by each of the DC converter units to output medium-voltage DC power; The voltages of the medium voltage direct currents are summed to obtain a second direct current of a high voltage level.

5. The onshore wind power transmission system according to claim 4, characterized in that: Each of the DC transformer units is composed of an IGBT module, a high-frequency transformer, and a rectifier and filter output; In each of the DC transformer units, the ±550V first DC power is first converted into AC power through the IGBT module, then boosted by the high-frequency transformer, and finally 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: After the high-voltage second DC power is converted by the full-bridge and half-bridge hybrid MMC converter, it is first voltage-calibrated by the connecting transformer to obtain the calibrated high-voltage AC power, and then passes through the starting circuit and is finally connected to the AC power grid.

7. The onshore wind power transmission system according to claim 6, characterized in that: When a fault occurs in any high-voltage DC overhead line, the full-bridge and half-bridge hybrid MMC converters at the same pole cooperate with the sending-end DC circuit breaker to clear the DC line fault, and the line operation of the pole where the fault does not occur is not affected during this period.

8. The onshore wind power transmission system according to claim 7, characterized in that: When the sending end and the receiving end of the fault pole complete the fault clearing action and after the preset recovery time, the full-bridge and half-bridge hybrid MMC converters of the fault pole are controlled to restore the DC side voltage of the receiving end of the pole, the sending end DC circuit breaker of the fault pole is reclosed, and the onshore wind power transmission system resumes operation.

9. 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 passes through the receiving-end DC circuit breaker and the half-bridge MMC converter for conversion, and then passes through the connecting transformer for voltage calibration to obtain the calibrated high-voltage AC power, and then passes through the starting circuit and is finally connected to the AC power grid.

10. The onshore wind power transmission system according to claim 9, characterized in that: The sending-end DC circuit breaker of each pole of the sending end is connected to the receiving-end DC circuit breaker of the same pole of the receiving end through a high-voltage DC overhead line; When a fault occurs in any high-voltage DC overhead line, the receiving-end DC circuit breaker and the sending-end DC circuit breaker at the same pole work together to clear the DC line fault, and the line operation of the pole where the fault does not occur is not affected during this period.

11. The onshore wind power transmission system according to claim 10, characterized in that: When a fault occurs on any high voltage DC overhead line, for the faulty pole: The line protection of the wind power sending end unit of the fault pole and the line protection of the wind power receiving end unit of the fault pole detect the fault and respectively perform fault clearing actions to achieve joint coordination of fault clearing of the sending end and receiving end DC lines of the same pole; wherein, The line protection of the wind power sending-end unit of the fault pole generates a sending-end tripping instruction, and sends the sending-end tripping instruction 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 unit at the fault pole generates a receiving-end tripping instruction, and sends the receiving-end tripping instruction to the receiving-end DC circuit breaker at the fault pole to control the tripping of the receiving-end DC circuit breaker at the fault pole.

12. The onshore wind power transmission system according to claim 11, characterized in that: When the sending end and the receiving end of the fault pole complete the fault clearing action and are de-ionized for a preset recovery time, the sending end DC circuit breaker and the receiving end DC circuit breaker of the fault pole are both re-closed, and the onshore wind power transmission system resumes operation.

13. The onshore wind power transmission system according to claim 1, characterized in that: The onshore wind power transmission system further comprises 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 the metal neutral line of the overhead line and is grounded at the receiving end for clamping; or, A neutral line region between the positive DC overhead line and the negative DC overhead line is grounded via grounding electrodes at the sending end and the receiving end respectively.

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