Land wind power transmission system

Abstract

The invention discloses an onshore wind power transmission system which is used for solving the problems of alternating current collection and transmission such as harmonic resonance and reactive power transmission in the prior art. The land wind power transmission system adopts a bipolar topological 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 direct current transformer and more than two wind turbine generators; a generator-side converter is arranged in each wind generator set and corresponds to one low-voltage circuit breaker; the direct-current transformer is provided with a sending-end direct-current circuit breaker; for each wind power set, electric energy generated by the wind power set is rectified into first direct current through a machine-side converter, and the first direct current is connected into a direct-current transformer in parallel through a low-voltage circuit breaker to be boosted into second direct current which is sent into a wind power receiving end unit through a sending end direct-current circuit breaker of the direct-current transformer; the wind power receiving end unit comprises a receiving end converter station, a connection transformer and a starting loop; the second direct current is converted by the receiving end converter station and then is connected to the alternating current power grid through the connection transformer and the starting loop.

Description

Technical Field

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

[0002] Wind power generation bases gather advantageous resources, which can give full play to the scale effect and reduce the cost of power generation. It is an important direction for the large-scale development of wind power generation. At present, there are two main types of wind power generation systems: AC collection-AC transmission and AC collection-DC transmission. However, large wind power generation bases have long collection distances. 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 will be many power conversion links and high system costs. Summary of the invention

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

[0004] The present invention provides an onshore wind power transmission system, wherein the onshore wind power transmission system adopts a bipolar topology structure, and the onshore wind power transmission system comprises a first-pole transmission unit and a second-pole transmission unit, and each of the transmission units comprises a wind power sending-end unit and a wind power receiving-end unit; wherein,

[0005] Each wind power sending-end unit comprises a DC transformer and two or more wind turbines; an organic 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 generator set, the electric energy generated by the wind turbine generator set is rectified into a first direct current through the machine-side converter, and connected in parallel to the direct current transformer through the low-voltage circuit breaker;

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

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

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

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

[0011] Optionally, the ±550V first direct current obtained after rectification by the machine-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;

[0012] 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.

[0013] Optionally, 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;

[0014] The first direct current of ±550V is boosted and rectified by each of the direct current converter units to output medium voltage direct current;

[0015] The voltages of the medium voltage direct currents are summed to obtain a second direct current of a high voltage level.

[0016] Optionally, each of the DC transformer units is composed of an IGBT module, a high-frequency transformer, and a rectifier filter output;

[0017] In each of the DC transformer units, the first ±550V DC power is first converted into AC power through the IGBT module, then boosted through the high-frequency transformer, and then rectified and filtered through the rectifier and filter output to output medium-voltage DC power.

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

[0019] After the high-voltage second direct current is converted by the full-bridge and half-bridge hybrid MMC converter, it is first calibrated by the connecting transformer to obtain calibrated high-voltage alternating current, then passes through the starting circuit, and finally is connected to the AC power grid via industrial frequency AC transmission.

[0020] Optionally, 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 DC overhead line of a high voltage level;

[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 the joint coordination of fault clearing of the DC lines at the sending end and the receiving end 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 half-bridge hybrid MMC converter at the fault pole, so that the full-bridge half-bridge hybrid MMC converter at the fault pole controls 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 have completed 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 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.

[0027] Optionally, the receiving-end converter station comprises 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 second direct current of high voltage level passes through the receiving end DC circuit breaker, is converted by the half-bridge MMC converter, and then is voltage calibrated by the connecting transformer to obtain the calibrated high voltage level alternating current, and then passes through the starting circuit, and finally is connected to the AC power grid through industrial frequency AC transmission.

[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 high-voltage DC overhead line, the receiving-end DC circuit breaker and the sending-end DC circuit breaker at the same pole cooperate 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.

[0031] Optionally, when a fault occurs on any high voltage DC overhead line, for the faulty pole:

[0032] 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 the joint coordination of fault clearing of the DC lines at the sending end and the receiving end of the same pole; wherein,

[0033] 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;

[0034] The line protection of the wind power receiving-end 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.

[0035] 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 sending end DC circuit breaker and the receiving end DC circuit breaker of the fault 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] The neutral line region 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;

[0038] or,

[0039] The 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.

[0040] It can be seen from the above technical solutions that the present invention has the following advantages:

[0041] Provided is an onshore wind power transmission system. 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 two or more wind turbines; a 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 DC power by the machine-side converter, and connected to the DC transformer in parallel through the low-voltage circuit breaker to be stepped up into a second DC power, which is sent to 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 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 fan output is DC, which is boosted to medium and high-level DC voltage and finally sent out through long-distance overhead lines. This can not only reduce the intermediate AC-DC conversion link, effectively solve the traditional AC collection and transmission problems such as harmonic resonance and reactive power transmission, but also reduce the cost of power generation. The full DC transmission method has higher transmission efficiency and reliability. At the same time, the bipolar system can realize large-capacity power transmission, and compared with the symmetrical monopolar system, the bipolar system adopted by the present invention can avoid bipolar shutdown after a monopolar fault occurs, and the system operation reliability is higher. 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 drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. 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 creative work.

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

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

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

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

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

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

[0049] Figure 7 The figure is a schematic diagram of the basic topology structure of a converter station including only one half-bridge submodule. DETAILED DESCRIPTION

[0050] The embodiment of the present invention provides an onshore wind power transmission system for solving or partially solving the problems of AC collection and transmission such as harmonic resonance and reactive power transmission existing in the prior art.

[0051] In order to make the purpose, features and advantages of the present invention more obvious and easy to understand, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described below are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0052] As an example, wind power bases gather advantageous resources, which can give full play to the scale effect and reduce the cost of power generation. It is an important direction for the large-scale development of wind power generation. At present, there are two main types of wind power generation systems: AC collection-AC transmission and AC collection-DC transmission. However, large wind power bases have long collection distances. 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 will be many power conversion links and high system costs.

[0053] In order to effectively solve the current AC collection and transmission problems such as harmonic resonance and reactive power transmission in onshore wind power transmission, and to achieve efficient grid connection, it is necessary to propose a new onshore wind power transmission topology to reduce the overall cost of the onshore wind power transmission system on the basis of stable onshore wind power transmission.

[0054] After further analysis, the present invention adopts a full DC transmission mode, which can reduce the intermediate conversion link. However, if a system architecture based on symmetrical monopole is adopted, the operation flexibility and reliability are low, and it cannot meet the demand for large-capacity power transmission.

[0055] Therefore, one of the core invention points of the embodiment of the present invention is to organically combine the DC transmission technology with the DC wind turbine, and propose an onshore wind power full DC transmission system with a bipolar topology structure. 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 by the DC wind turbine is boosted and collected by the 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 combined with a half-bridge MMC converter. The wind turbine output is DC, which is boosted to a medium-to-high-level DC voltage and finally sent out through a long-distance overhead line. It can not only reduce the intermediate AC-DC conversion link, effectively solve the traditional AC collection and transmission problems such as harmonic resonance and reactive power transmission, but also reduce the cost of power generation. The full DC transmission mode has higher transmission efficiency and reliability. At the same time, the bipolar system can realize large-capacity power transmission, and compared with the symmetrical monopolar system, the bipolar system adopted by the present invention can avoid bipolar shutdown after a monopolar fault occurs, and the system operation reliability is higher.

[0056] Reference Figure 1 , showing 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 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, the electric energy generated by the wind turbine is rectified into the first direct current by the machine-side converter, and connected in parallel to the DC transformer through the low-voltage circuit breaker. The first direct current is boosted into the second direct current by the DC transformer, and the second direct current is sent to the wind power receiving unit through the sending-end DC circuit breaker.

[0060] Combination Figure 1 , Figure 2 The figure shows a schematic diagram of the circuit principle structure of a wind turbine side rectification. Figure 1 Taking the permanent magnet direct drive generator 1 of one pole as an example, the mechanical part of each wind turbine set is 690V AC, and the electric energy generated by the wind turbine set is rectified into a first DC of ±550V by the machine-side converter.

[0061] Next, the ±550V first DC power obtained after rectification by multiple machine-side converters in multiple application scenarios is connected in parallel to the input end of the DC transformer through a low-voltage circuit breaker, which corresponds to the low-voltage side. The low-voltage side of the DC transformer boosts the ±550V first DC power to a second DC power of a high voltage level, and outputs it through the high-voltage side of the DC transformer (which can also be understood as the second DC power boosted to a high-voltage level on the high-voltage side). Among them, the high voltage level means a voltage capacity of ±100kV and above. A sending-end DC circuit breaker is installed at the output end (i.e., corresponding to the high-voltage side) of each DC transformer. Then it is connected to the receiving-end converter station of the wind power receiving unit via 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~module n), and the multiple DC converter units are connected in series and parallel.

[0063] When boosting, the first DC power of ±550V 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 the second DC power of a high voltage level (such as ±100kV or ±110kV).

[0064] More specifically, Figure 3 A schematic diagram of the circuit principle structure of a DC transformer unit step-up rectification is shown.

[0065] Combination Figure 3 It can be seen that each DC transformer unit is mainly composed of an IGBT (Insulated Gate Bipolar Transistor) module, a high-frequency transformer and a rectifier and filter output.

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

[0067] More specifically, the DC transformer unit input is ±550V DC, and the input end is composed of an IGBT module. The ±550V first DC is first inverted into a high-frequency low-voltage AC by the IGBT module, and then boosted to a high-frequency high-voltage AC by a high-frequency transformer, and then output through a rectifier and filter (diode rectifier), and after rectification and filtering, a ±2.5kV medium-voltage DC is formed.

[0068] Each DC transformer unit can obtain a boosted medium voltage DC power of ±2.5kV. The n DC / DC converter units are connected in series and parallel to finally output a second DC power of a corresponding high voltage level. For example, for a second DC power of ±110kV, 44 DC / DC converter units are connected in series and parallel to form a DC transformer.

[0069] It is understandable that for the second direct current of ±110kV, the number of direct current transformer units is not necessarily 44, as long as the final output direct current voltage is ±110kV. 44 is used here because the high-voltage side output of a single direct current transformer unit is ±2.5kV, which is accumulated to ±110kV. For example, for a direct current of ±550V, assuming that a single direct current converter unit can output a direct current of 5kV, the direct current transformer only needs 22 direct current converter units to obtain a total direct current of ±110kV. It is understandable that the present invention is not limited to this.

[0070] Figure 4 A schematic diagram of the circuit principle structure of one of the receiving-end converter units provided in an embodiment of the present invention is shown.

[0071] Combination Figure 4 Each wind power receiving unit can include a receiving converter station, a connecting transformer and a starting circuit. After the high-voltage second DC power is converted by the receiving converter station, it first passes through the connecting transformer for voltage calibration, then passes through the starting circuit, and finally connects to the AC 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 capability, that is, a full-bridge half-bridge hybrid MMC converter.

[0073] Among them, MMC consists of multiple sub-modules (SM). Each sub-module usually 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 the A, B, and C phases in a three-phase AC system.

[0074] The full-bridge half-bridge hybrid MMC converter provided in the embodiment of the present invention is mainly composed of two submodules: HBSM (Half-Bridge Submodule) and FBSM (Full-Bridge Submodule). Among them, HBSM is composed of two IGBTs and an energy storage capacitor. FBSM is composed 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 can mainly include two sub-modules: full-bridge sub-module and half-bridge sub-module. Therefore, when a fault occurs, the full-bridge sub-module can output a negative level and cooperate with the half-bridge sub-module to control the DC side voltage below 0. The topological structure of the full-bridge and half-bridge hybrid MMC converter partially adopts the half-bridge sub-module. Compared with the full-bridge sub-module, it can reduce the number of power devices and reduce the investment cost of the equipment while realizing the DC side fault ride-through.

[0076] The DC side of the full-bridge and half-bridge hybrid MMC converter is connected to the DC breaker at the same-pole sending end, receiving the second DC power of ±110kV, and the AC side is connected to the connection transformer and the starting circuit, and then connected to the large power grid through the 110kV power frequency AC transmission. That is, after the high-voltage level ±110kV second DC power is converted by the full-bridge and half-bridge hybrid MMC converter, it is first calibrated by the connection transformer to obtain the calibrated high-voltage level AC power (that is, AC power that meets the standard voltage level), and then passes through the starting circuit, and finally connected to the AC grid through the 110kV power frequency AC transmission.

[0077] The connecting transformer (also called connecting transformer or coupling transformer) can further boost the voltage transmitted at the sending end to achieve voltage conversion, thereby reducing line losses during long-distance power transmission.

[0078] The Start-Up Circuit enables the system to start smoothly and reliably after power-on or reset.

[0079] Among them, the voltage level of the grid-side AC power is 110kV and above. Here, the voltage level of ±110kV DC power obtained after boosting at the receiving end is used as an example for explanation. In actual applications, the voltage level of the grid-side AC power 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.

[0080] Voltage calibration is set because the voltage at the input end of the connection transformer is generally not a standard voltage level. That is, although the 110kV high voltage level is used in the embodiment of the present invention, there may be deviations in actual applications. The high voltage level voltage received by the receiving end needs to be converted to a standard voltage level after conversion before it can be connected to the external power grid.

[0081] 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 DC overhead line of a high voltage level (such as ±110kV).

[0082] When a high voltage DC overhead line (±110kV) at any pole fails, the full-bridge and half-bridge hybrid MMC converters at the same pole work together with the DC circuit breaker at the sending end to clear the DC line fault. The line operation of the pole where the fault does not occur is not affected during this period.

[0083] In the specific implementation, when a fault occurs in any high-voltage DC overhead line (±110kV), for the faulty pole: the line protection of the wind power sending unit at the faulty pole and the line protection of the wind power receiving unit at the faulty pole detect the fault and each performs a fault clearing action to achieve joint coordination of fault clearing of the sending and receiving DC lines at the same pole.

[0084] The line protection of the wind power sending-end unit at the fault pole generates a tripping instruction, and sends the tripping instruction to the sending-end DC circuit breaker at the fault pole to control the tripping of the sending-end DC circuit breaker at the fault pole.

[0085] 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 half-bridge hybrid MMC converter at the fault pole, so that the full-bridge half-bridge hybrid MMC converter at the fault pole controls the DC side voltage of the receiving end of the pole to below 0.

[0086] Furthermore, when the sending end and the receiving end of the fault pole complete the fault clearing action, after the preset recovery time (such as hundreds of milliseconds) of de-ionization, the full-bridge and half-bridge hybrid MMC converter of the fault pole controls to restore the DC side voltage of the receiving end of the pole. The DC circuit breaker at the sending end of the fault pole is reclosed. 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 in the figure, and is grounded at the receiving end for clamping (DC isolation).

[0089] Alternatively, for the (low voltage) neutral area between the positive DC overhead line and the negative DC overhead line, the following 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 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 the 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 converter with DC fault clearing capability. The wind turbine output is DC, which is boosted to a medium- and high-level DC voltage by DC, and finally sent out through a long-distance overhead line, which can not only reduce the intermediate AC-DC conversion link, effectively solve the traditional AC collection and sending problems such as harmonic resonance and reactive power transmission, but also reduce the cost of power generation. The all-DC transmission method has higher transmission efficiency and reliability. At the same time, the bipolar system can realize large-capacity power transmission, and compared with the symmetrical monopolar system, the bipolar system adopted in the present invention can avoid bipolar shutdown after a monopolar fault occurs, and the system operation reliability is higher.

[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 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 elaborated here.

[0094] Each wind power receiving unit may include a receiving converter station, a connecting transformer and a starting circuit. After the high-voltage second DC power is converted by the receiving 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 grid.

[0095] Specifically, in the embodiment 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. Figure 6 It can be seen 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 topology of the half-bridge MMC converter for each pole is as follows: Figure 7 As shown. Figure 7 It can be seen that the half-bridge MMC converter only includes a half-bridge sub-module, and no full-bridge sub-module is provided.

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

[0098] 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 level (±110kV) DC overhead line.

[0099] When a fault occurs in any high-voltage DC overhead line (±110kV), 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 will not be affected during this period.

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

[0101] The line protection of the wind power sending-end unit at the fault pole generates a sending-end tripping instruction, and sends the sending-end tripping instruction to the sending-end DC circuit breaker at the fault pole to control the tripping of the sending-end DC circuit breaker at the fault pole.

[0102] The line protection of the wind power receiving-end 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.

[0103] Furthermore, when the sending end and the receiving end of the fault pole complete the fault clearing action, after a preset recovery time (such as hundreds of milliseconds) of de-ionization, the sending end DC circuit breaker and the receiving end DC circuit breaker of the fault pole are both re-closed. 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 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 in the figure, and is grounded at the receiving end for clamping (DC isolation).

[0106] Alternatively, for the (low voltage) neutral area between the positive DC overhead line and the negative DC overhead line, the following 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 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 the 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 combined architecture of a receiving-end DC circuit breaker combined with a half-bridge MMC converter. The wind turbine output is DC, which is boosted to a medium- and high-level DC voltage by DC, and finally sent out through a long-distance overhead line, which can not only reduce the intermediate AC-DC conversion link, effectively solve the traditional AC collection and sending problems such as harmonic resonance and reactive power transmission, but also reduce the cost of power generation. The all-DC transmission method has higher transmission efficiency and reliability. At the same time, the bipolar system can realize large-capacity power transmission, and compared with the symmetrical monopolar system, the bipolar system adopted in the present invention can avoid bipolar shutdown after a monopolar fault occurs, and the system operation reliability is higher.

[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 the second in the embodiments of the present invention. The first and the second are only used for data distinction and have no other special meanings. It can be understood that the present invention is not limited to 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 only schematic, for example, the division of the units is only a logical function division, and there may be other division methods in actual implementation, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point, the mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, indirect coupling or communication connection of devices or units, which can be electrical, mechanical or other forms.

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

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

[0112] If the 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 the technical solution can be embodied in the form of a software product. The computer software product is stored in a storage medium, including several instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the method described in each embodiment of the present invention. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM), random access memory (RAM), disk or optical disk, etc., various media 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 the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features thereof may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments 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 comprises a first-pole transmission unit and a second-pole transmission unit, each of which comprises a wind power sending-end unit and a wind power receiving-end unit; wherein, Each wind power sending-end unit comprises a DC transformer and two or more wind turbines; an organic 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; 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 machine-side converter, and connected in parallel to the direct current transformer through the low-voltage circuit breaker; The first direct current is boosted into a second direct current by the direct current transformer, and the second direct current is sent to the wind power receiving unit through the sending-end direct current circuit breaker; Each of the wind power receiving end units comprises a receiving end converter station, a connecting transformer and a starting circuit; After the second direct current is converted by the receiving-end converter station, it first passes through the connection transformer for voltage calibration, then passes through the starting circuit, and finally is connected to the AC power grid.

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 first direct current of ±550V obtained after rectification by the machine-side converter is connected in parallel to the input end of the direct current transformer through 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 direct current of ±550V is boosted by each of the direct current converter units to output medium voltage direct current; 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 filter output; In each of the DC transformer units, the first ±550V DC power is first converted into AC power through the IGBT module, then boosted through the high-frequency transformer, and then rectified and filtered through 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 full-bridge and half-bridge hybrid MMC converter with DC fault clearing capability; After the high-voltage second direct current is converted by the full-bridge and half-bridge hybrid MMC converter, it is first calibrated by the connecting transformer to obtain calibrated high-voltage alternating current, then passes through the starting circuit, and finally is connected to the AC power grid via industrial frequency AC transmission.

7. The onshore wind power transmission system according to claim 6, characterized in that: 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 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 a DC overhead line with a high voltage level at any pole fails, 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 the joint coordination of fault clearing of the DC lines at the sending end and the receiving end 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 half-bridge hybrid MMC converter at the fault pole, so that the full-bridge half-bridge hybrid MMC converter at the fault 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: When the sending end and the receiving end of the fault pole complete the fault clearing action, after the preset recovery time, the full-bridge and half-bridge hybrid MMC converter of the fault pole controls 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.

10. The onshore wind power transmission system according to any one of claims 3 to 5, characterized in that: The receiving-end converter station comprises 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 second direct current of high voltage level passes through the receiving end DC circuit breaker, is converted by the half-bridge MMC converter, and then is voltage calibrated by the connecting transformer to obtain the calibrated high voltage level alternating current, and then passes through the starting circuit, and finally is connected to the AC power grid through industrial frequency AC transmission.

11. The onshore wind power transmission system according to claim 10, 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 cooperate 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.

12. The onshore wind power transmission system according to claim 11, characterized in that: When a DC overhead line with a high voltage level at any pole fails, 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 the joint coordination of fault clearing of the DC lines at the sending end and the receiving end 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-end 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.

13. The onshore wind power transmission system according to claim 12, characterized in that: When the sending end and the receiving end of the fault pole complete the fault clearing action, after the preset recovery time, the sending end DC circuit breaker and the receiving end DC circuit breaker of the fault pole are both reclosed, and the onshore wind power transmission system resumes operation.

14. The onshore wind power transmission system according to claim 1, characterized in that: The onshore wind power transmission system further includes a positive DC overhead line and a negative DC overhead line; The neutral line region 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, The 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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