Offshore wind power hybrid direct current sending-out system and offshore side and onshore side alternating current fault ride-through method thereof
By coordinating the control of onshore MMC inverter stations and offshore auxiliary MMC converters, and combining the low voltage ride-through and energy consumption modules of wind turbines, the construction difficulty and high cost of traditional offshore wind power hybrid DC transmission systems during AC faults have been solved, achieving transient energy balance and system stability.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-10
- Publication Date
- 2026-03-13
AI Technical Summary
Traditional offshore wind power hybrid DC transmission systems rely on centralized DC energy dissipation devices when AC grid failures occur, leading to high construction difficulty and cost.
By coordinating onshore MMC inverter stations, offshore auxiliary MMC converters, and offshore wind turbines, the system achieves transient surplus energy balance without relying on centralized DC energy dissipation devices. It utilizes the integral freezing unit and the maximum limit unit of the given current to control the fault current, combined with the low voltage ride-through and energy dissipation modules of the wind turbines.
In the event of an AC failure, transient surplus energy was balanced, DC blockage was avoided, and construction difficulty and cost were reduced.
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Figure CN121663497A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of power system technology, and in particular to an offshore wind power hybrid DC transmission system and its AC fault ride-through method on the offshore and onshore sides. Background Technology
[0002] In the field of power system technology, the flexible DC transmission scheme based on Modular Multilevel Converter (MMC) is currently the mainstream solution for offshore wind power transmission during the development of offshore wind power clusters.
[0003] However, as offshore wind power develops towards deeper waters and larger scales, using DRUs as the main converter and supplementing them with small-capacity MMCs to construct a hybrid DC transmission system is a common way to achieve economical and efficient transmission from offshore wind power clusters. When an AC grid fault causes a voltage drop, the reduced AC voltage leads to a decrease in the output power of the receiving-end converter station, while the power generated by the offshore wind farm remains largely unaffected. The surplus power generated by this power imbalance between the sending and receiving ends will generate overvoltage on the DC line. Currently, energy dissipation devices are often configured, using energy-dissipating resistors to dissipate the surplus power, thereby suppressing the overvoltage caused by the surplus power.
[0004] In summary, traditional offshore wind power hybrid DC transmission systems require centralized DC energy dissipation devices to balance transient surplus energy in the event of short-circuit faults at both the sending and receiving ends, which presents challenges in construction and high costs. Summary of the Invention
[0005] This application provides an offshore wind power hybrid DC transmission system, an AC fault ride-through method on the offshore and onshore sides, fault ride-through equipment, and a computer storage medium, which can achieve transient surplus energy balance without relying on DC centralized energy consumption devices, reducing construction difficulty and cost.
[0006] In a first aspect, embodiments of this application provide a method for AC fault ride-through on the marine side, including:
[0007] In the event of an AC short-circuit fault detected on the offshore side, the short-circuit current control module of the offshore auxiliary converter is activated. The integral link freezing unit and the given current maximum limiting unit in the short-circuit current control module are activated to control the fault current. The low voltage ride-through control unit in the wind turbine is activated, and the DC side energy consumption module of the wind turbine is activated to control the energy consumption resistor to be connected.
[0008] The offshore switchgear was opened to isolate the fault point;
[0009] With the AC fault cleared, the integral freezing unit and the given current maximum limiting unit are deactivated, and the marine auxiliary converter resumes AC voltage control.
[0010] Close the aforementioned marine switchgear;
[0011] The energy-consuming resistor of the wind turbine is disconnected, restoring the wind turbine to normal operation mode. The normal operation control module of the grid-side converter in the wind turbine is restarted, and the power transmission is restored.
[0012] The integral freezing unit is used to control the fault current of the offshore auxiliary converter, and the given current maximum limiting unit is used to provide a given current maximum limiting value to control the fault current flowing into the offshore auxiliary converter.
[0013] Secondly, embodiments of this application provide an AC fault ride-through method on the land side, including:
[0014] When an AC short-circuit fault is detected on the onshore side, the short-circuit current control module of the onshore inverter station is activated, and the maximum limit unit of the given current in the short-circuit current control module is activated to control the fault current.
[0015] Start the DC side energy consumption module of the wind turbine in the wind turbine unit, and control the energy consumption resistor in the wind turbine unit to be connected;
[0016] When the AC fault has been cleared, the maximum limiting unit of the given current is deactivated, the offshore auxiliary converter restores DC voltage and reactive power control, and sends an onshore AC fault clearance signal to the wind turbine.
[0017] When the wind turbine receives an onshore AC fault clearing signal, the energy-consuming resistor is disconnected, the wind turbine is restored to normal operation mode, and the grid-side converter normal operation control module in the wind turbine is restarted.
[0018] The given current maximum limiting unit is used to provide a given current maximum limiting value to control the fault current flowing into the offshore auxiliary converter.
[0019] Thirdly, embodiments of this application provide an offshore wind power hybrid DC transmission system for implementing the offshore-side AC fault ride-through method and the onshore-side AC fault ride-through method in the above embodiments, including:
[0020] Motor set;
[0021] Offshore switchgear, which is connected to the wind turbine generator;
[0022] The offshore rectifier station is equipped with a short-circuit current control module for controlling fault current. The wind turbine generators are connected to the AC busbar of the offshore rectifier station via AC collector cables and the offshore switchgear.
[0023] A conversion station is provided, wherein the offshore rectifier station is connected to the conversion station, which is used to convert the DC submarine cable into a DC overhead line and connect it to the onshore switchgear collection station via the DC overhead line.
[0024] The onshore switchgear collection station is used to collect DC overhead lines and connect them to the onshore inverter station;
[0025] The onshore inverter station is used to convert direct current into alternating current and transmit electrical energy to the onshore AC power grid.
[0026] In another aspect, this application provides a fault-crossing device, which includes at least one connected processor and a memory, wherein the memory is used to store program code, and the processor is used to call the program code in the memory to execute the methods described in the above aspects.
[0027] In another aspect, this application provides a computer storage medium including instructions that, when executed on a computer, cause the computer to perform the methods described in the above aspects.
[0028] In another aspect, this application provides a computer program product containing instructions that, when run on a computer, cause the computer to perform the methods described in the above aspects.
[0029] The technical solution of this application embodiment, through the coordinated operation of onshore MMC inverter station, offshore auxiliary MMC converter and offshore wind turbine, achieves transient surplus energy balance without relying on DC centralized energy consumption device in the case of AC short circuit fault in offshore wind power hybrid DC transmission system. During fault ride-through, DC blocking is not caused by transient surplus energy impact, thereby reducing construction difficulty and cost. Attached Figure Description
[0030] Figure 1 This is a topology diagram of an offshore wind power hybrid DC transmission system in one embodiment;
[0031] Figure 2 This is a schematic diagram illustrating the control and protection process of the auxiliary MMC in one embodiment;
[0032] Figure 3 This is a schematic diagram illustrating the control and protection process of an onshore MMC inverter station in one embodiment.
[0033] Figure 4 This is a schematic diagram illustrating the principle of wind turbine control and protection process in an offshore wind farm according to one embodiment.
[0034] Figure 5 This is a schematic diagram of the grid-side converter control and protection module in one embodiment;
[0035] Figure 6 This is a schematic diagram illustrating the principle of the DC-side energy consumption control logic for a wind turbine in one embodiment.
[0036] Figure 7 This is a flowchart illustrating an AC fault-crossing method on the sea side in one embodiment.
[0037] Figure 8 This is a timing information diagram illustrating a method for oversea-side AC fault crossing in one embodiment;
[0038] Figure 9 This is a flowchart illustrating an AC fault-crossing method on the land side in one embodiment.
[0039] Figure 10 This is a timing information diagram illustrating the onshore AC fault-crossing method in one embodiment;
[0040] Figure 11 This is a steady-state operating waveform diagram of the offshore wind power hybrid DC transmission system in one embodiment;
[0041] Figure 12 This is a steady-state operating waveform diagram of the onshore side of an offshore wind power hybrid DC transmission system in one embodiment;
[0042] Figure 13 This is a schematic diagram of a three-phase AC short-circuit fault in an offshore wind power hybrid DC transmission system in one embodiment.
[0043] Figure 14 This is a schematic diagram of a three-phase AC short-circuit fault on land in an offshore wind power hybrid DC transmission system in one embodiment.
[0044] Figure 15 This is an internal structural diagram of a fault-crossing device in one embodiment;
[0045] Figure 16 This is an internal structural diagram of the fault-crossing device in another embodiment. Detailed Implementation
[0046] The terms "first," "second," etc., in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments described herein can be implemented in a sequence other than that illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or modules is not necessarily limited to those explicitly listed, but may include other steps or modules not explicitly listed or inherent to these processes, methods, products, or devices. The division of modules in the embodiments of this application is merely a logical division; in actual applications, there may be other division methods. For example, multiple modules may be combined into or integrated into another system, or some features may be ignored or not performed. Additionally, the shown or discussed mutual coupling or direct coupling or communication connection may be through some interface, and the indirect coupling or communication connection between modules may be electrical or other similar forms, none of which are limited in the embodiments of this application. Furthermore, the modules or sub-modules described as separate components may or may not be physically separated, may or may not be physical modules, or may be distributed among multiple circuit modules. Some or all of the modules may be selected according to actual needs to achieve the purpose of the embodiments of this application.
[0047] Figure 1 This is a topology diagram of an offshore wind power hybrid DC transmission system in one embodiment, also known as an offshore wind power hybrid DC transmission topology diagram based on weak AC interconnection. See below for reference. Figure 1 The offshore wind power hybrid DC transmission system provided in this application includes: an offshore wind farm, offshore switchgear, an offshore rectifier station, an onshore switchgear collection station, and an onshore inverter station.
[0048] Offshore wind farms include at least one wind turbine unit, which is equipped with a grid-side converter normal operation control module, a low voltage ride-through control unit, and a DC-side energy consumption module.
[0049] Among them, the offshore switchgear is connected to the wind turbine, and the offshore switchgear is also known as the offshore 66kV gas-insulated switchgear (GIS).
[0050] Among them, the offshore rectifier station is also known as the offshore DRU-MMC rectifier station. The wind turbine units are collected to the AC bus of the offshore rectifier station through AC collector submarine cables and offshore switchgear.
[0051] The offshore rectifier station includes a diode rectifier unit and an offshore auxiliary converter. The diode rectifier unit (DRU) and the offshore auxiliary converter are connected in parallel on the AC side and operate independently on the DC side. The offshore auxiliary converter is also known as an offshore auxiliary MMC converter or auxiliary MMC converter. The offshore auxiliary converter is equipped with a short-circuit current control module.
[0052] The offshore rectifier station is connected to the conversion station via a high-voltage DC submarine cable. The conversion station is used to convert the DC submarine cable into a DC overhead line and then connect it to the onshore switchgear collection station via the DC overhead line.
[0053] Among them, the onshore switchgear collection station is used to collect DC overhead lines and connect them to the onshore inverter station.
[0054] Among them, the onshore inverter station is also known as the onshore MMC inverter station. The onshore inverter station is used to convert DC power into AC power and transmit electrical energy to the onshore AC power grid.
[0055] The offshore wind power hybrid DC transmission system in this embodiment is used to implement an AC fault ride-through method on the offshore side and an AC fault ride-through method on the onshore side. It should be noted that the specific steps and implementation principles of the above two methods are described in subsequent embodiments.
[0056] Compared to traditional systems in conventional technologies, the technical solution of this application embodiment, through the coordinated operation of onshore MMC inverter stations, offshore auxiliary MMC converters, and offshore wind turbines, achieves transient surplus energy balance without relying on centralized DC energy consumption devices in the event of an AC short-circuit fault in the offshore wind power hybrid DC transmission system. During fault ride-through, DC blocking is not caused by transient surplus energy impact, thereby reducing construction difficulty and cost.
[0057] For example, this application constructs as follows Figure 1 A hybrid DC transmission topology for offshore wind power based on weak AC interconnection is proposed, and corresponding control and protection methods for the auxiliary MMC of the offshore rectifier station are put forward.
[0058] Specifically, the offshore wind farm consists entirely of grid-connected wind turbines. The electrical energy output from the wind turbines is collected by the offshore 66kV gas-insulated switchgear (GIS) and AC collector submarine cable to the AC bus of the offshore DRU-MMC rectifier station. It is then transmitted to the onshore AC power grid via the offshore DRU-MMC rectifier station, long-distance high-voltage DC submarine cable, onshore switchgear collection station, DC overhead line, and onshore MMC inverter station.
[0059] The AC bus of the offshore rectifier station is denoted as the point of common coupling (PCC). The offshore rectifier station adopts a hybrid DC transmission topology in which the DRU and auxiliary MMC converters are connected in parallel on the AC side and operate independently on the DC side. The DC side of the auxiliary MMC is connected to the 66kV AC bus output from the nearby offshore wind farm through a small uncontrolled rectifier, a transformer, and an AC weak tie line.
[0060] In one embodiment, the offshore auxiliary converter includes a first normal operation control module; wherein the first normal operation control module includes an active power control unit, an AC voltage control unit, an output current control unit, and a pulse generation unit; the active power control unit is connected to the AC voltage control unit, the AC voltage control unit is connected to the output current control unit, and the output current control unit is connected to the pulse generation unit.
[0061] In one embodiment, the offshore auxiliary converter includes a first short-circuit current control module; wherein the first short-circuit current control module includes an active power control unit, an AC voltage control unit, an output current control unit, a pulse generation unit, an integrator freezing unit, and a given current maximum limiting unit; the active power control unit is connected to the AC voltage control unit, the AC voltage control unit is connected to the output current control unit, the output current control unit is connected to the pulse generation unit, the integrator freezing unit is connected to the AC voltage control unit, and the given current maximum limiting unit is connected to the output current control unit.
[0062] Based on the above embodiments, the offshore auxiliary converter includes a first normal operation control module and a first short-circuit current control module that are interconnected.
[0063] The first normal operation control module and the first short-circuit current control module include an active power control unit, an AC voltage control unit, an output current control unit, and a pulse generation unit; the first short-circuit current control module includes an integral freezing unit and a given current maximum limiting unit.
[0064] Among them, the first normal operation control module refers to the auxiliary MMC normal operation control module, and the first short-circuit current control module refers to the auxiliary MMC short-circuit current control module.
[0065] For example, the auxiliary MMC of the offshore rectifier station adopts a half-bridge topology and operates in voltage / frequency (V / f) control mode to support the amplitude and frequency of the offshore AC voltage, while dynamically compensating for the reactive power required by the DRU and the offshore wind farm, and controlling the active power of the offshore wind farm to be completely transmitted by the DRU.
[0066] Figure 2 This is a schematic diagram illustrating the principle of the control and protection process of the auxiliary MMC in one embodiment, such as... Figure 2As shown, the control and protection process of the auxiliary MMC of the marine rectifier station is as follows.
[0067] The modules that implement the above control and protection processes mainly include an auxiliary MMC normal operation control module and an auxiliary MMC short-circuit current control module, covering an active power control unit, an AC voltage control unit, an integral link freezing unit, a given current maximum limiting unit, an output current control unit, and a pulse generation unit.
[0068] The system includes: an active power control unit (APU) to control active power so that all active power in the offshore wind farm is transmitted by the DRU; an AC voltage control unit to establish AC voltage on the offshore side, providing commutation voltage to the DRU and supporting the normal operation of the DRU and grid-connected wind turbines; a current control unit to perform closed-loop control of the auxiliary MMC's output current and output three-phase voltage reference values to the auxiliary MMC pulse generation unit; and an auxiliary MMC pulse generation unit to generate control pulse signals for the auxiliary MMC.
[0069] Among them, the given current maximum limiting unit is used to provide a given current maximum limiting value to the current control unit when an AC fault is detected, so as to control the fault current flowing into the marine auxiliary MMC.
[0070] The function of the integral freezing unit is to control the fault current of the marine auxiliary MMC when an AC short-circuit fault is detected on the marine side. This prevents the fault current from being too large and causing damage to the auxiliary MMC, thereby ensuring the stable operation of the auxiliary MMC during the fault and laying the foundation for subsequent fault recovery and normal system operation.
[0071] In one embodiment, the onshore inverter station includes a second normal operation control module; wherein the second normal operation control module includes a reactive power control unit, a DC voltage control unit, an output current control unit, and a pulse generation unit; wherein the reactive power control unit and the DC voltage control unit are respectively connected to the output current control unit, and the output current control unit is connected to the pulse generation unit.
[0072] In one embodiment, the onshore inverter station includes a second short-circuit current control module; wherein the second short-circuit current control module includes a reactive power control unit, a DC voltage control unit, an output current control unit, a pulse generation unit, and a given current maximum limiting unit; wherein the reactive power control unit and the DC voltage control unit are respectively connected to the output current control unit, the output current control unit is connected to the pulse generation unit, and the given current maximum limiting unit is connected to the output current control unit.
[0073] Based on the above embodiments, the onshore inverter station includes a second normal operation control module and a second short-circuit current control module that are interconnected.
[0074] The second normal operation control module and the second short-circuit current control module include a reactive power control unit, a DC voltage control unit, an output current control unit, and a pulse generation unit; the second short-circuit current control module includes a given current maximum limiting unit.
[0075] Among them, the second normal operation control module refers to the normal operation control module of the onshore MMC inverter station, and the second short-circuit current control module refers to the short-circuit current control module of the onshore MMC inverter station.
[0076] For example, the onshore MMC inverter station adopts a full-bridge-half-bridge hybrid topology and operates in constant DC voltage and constant reactive power control mode. It is used to control the DC voltage of the high-voltage DC transmission system to remain constant, while providing reactive power or AC voltage support to the onshore power grid.
[0077] Figure 3 This is a schematic diagram illustrating the control and protection process of an onshore MMC inverter station in one embodiment, as shown below. Figure 3 As shown, the control and protection process of the auxiliary MMC of the marine rectifier station is as follows.
[0078] The modules implementing the above control and protection processes mainly include the onshore MMC inverter station normal operation control module and the onshore MMC inverter station short-circuit current control module, encompassing the DC voltage control unit, reactive power control unit, given current maximum limiting unit, output current control unit, and pulse generation unit. Their specific division and connection relationships are as follows: Figure 3 As shown, the functions of each unit are similar to those of the marine auxiliary MMC, and will not be described again in this embodiment.
[0079] Optionally, in some embodiments of this application, the wind turbines in the offshore wind farm operate in a grid-connected control mode, and the wind power main control module of the wind turbine includes a turbine-side converter control module, a grid-side converter control and protection module, and a wind turbine DC-side energy consumption module.
[0080] The control and protection module of the grid-side converter includes the third normal operation control module and the AC fault control module of the grid-side converter; the third normal operation control module refers to the normal operation control module of the grid-side converter and the AC fault control module of the grid-side converter.
[0081] The DC-side energy consumption module of the wind turbine includes a switch and an energy-consuming resistor. The control logic of the DC-side energy consumption module of the wind turbine includes a DC bus voltage detection circuit, a hysteresis comparison circuit, an energy-consuming resistor input control circuit, and an energy-consuming resistor cut-off control circuit.
[0082] Figure 4 This is a schematic diagram illustrating the principle of wind turbine control and protection in an offshore wind farm according to one embodiment, such as... Figure 4 As shown, this application proposes a control and protection method for wind turbine units in an offshore wind farm. In the offshore AC system transmitted through the DRU-MMC rectifier station, the wind turbine units in the offshore wind farm operate in a grid-following control mode. The wind power main control module includes a turbine-side converter control module, a grid-side converter control and protection module, and a wind turbine DC-side energy consumption module.
[0083] The turbine-side converter control module is used to control the electromagnetic torque applied to the permanent magnet synchronous motor by the turbine-side converter in the wind power converter based on the torque reference value issued by the wind turbine main control module; wherein the turbine-side converter adopts the same control strategy as the full-power conversion wind turbine.
[0084] Figure 5 This is a schematic diagram of the grid-side converter control and protection module in one embodiment, as shown below. Figure 5 As shown, the grid-side converter control and protection module is used for DC voltage and reactive power control during the normal power generation phase of the wind turbine. When an AC short-circuit fault occurs on the offshore or onshore side, it is used to activate the low voltage ride-through logic, so that the wind turbine can operate continuously without disconnecting from the grid within a certain voltage drop range and time interval, thus avoiding the expansion of AC faults.
[0085] The grid-side converter control and protection module includes a grid-side converter normal operation control module and a grid-side converter AC fault control module, covering a DC voltage control unit, a reactive power control unit, a grid-side converter output current control unit, a grid-side converter pulse generation unit, and a low voltage ride-through control unit.
[0086] The low-voltage ride-through control unit of the grid-side converter AC fault control module is used to provide a current command value to the grid-side converter output current control unit according to the voltage drop depth when a voltage drop is detected on the offshore side, thereby providing a certain amount of reactive power and AC voltage support to the system. The setting principles of other units can be referred to in other embodiments of this application, and their principles are similar, so they will not be described again here.
[0087] Figure 6 This is a schematic diagram illustrating the principle of the DC-side energy consumption control logic for a wind turbine in one embodiment, as shown below. Figure 6 As shown, the DC-side energy dissipation module of the wind turbine consists of a switch and an energy dissipation resistor, which is used to provide a transient energy dissipation path on the wind turbine side for AC fault ride-through of the offshore wind power hybrid DC transmission system.
[0088] When the wind turbine is running normally, the switch is open. When the DC bus voltage is overvoltage, the switch closes, the energy-consuming resistor is activated, and the transient energy is dissipated. Its control logic includes DC bus voltage detection, hysteresis comparison, energy-consuming resistor activation control, and energy-consuming resistor deactivation control.
[0089] The DC voltage detection unit is used to detect the DC voltage in real time and output the voltage signal to the hysteresis comparison circuit. The hysteresis comparison circuit compares the DC voltage with the hysteresis range and outputs the signal to the energy-consuming resistor connection and disconnection control circuit. If the voltage is lower than the hysteresis range, the energy-consuming resistor is disconnected; if the voltage is higher than the hysteresis range, the energy-consuming resistor is connected.
[0090] In addition, in some embodiments, this application proposes an AC fault ride-through method for offshore wind power hybrid DC transmission systems, specifically including an AC fault ride-through method on the offshore side and an AC fault ride-through method on the onshore side. Based on the distributed energy consumption of offshore wind turbines, this application achieves transient surplus energy balance without relying on centralized DC energy consumption devices in the event of an AC short-circuit fault in the offshore wind power hybrid DC transmission system through the coordinated cooperation of onshore MMC inverter stations, offshore auxiliary MMC converters, and offshore wind turbines. During fault ride-through, DC blocking is not caused by transient surplus energy impact.
[0091] Figure 7 This is a flowchart illustrating an AC fault ride-through method on the offshore side in one embodiment. This application provides an AC fault ride-through method on the offshore side, applied to an offshore wind power hybrid DC transmission system as described in any of the above embodiments. The AC fault ride-through method on the offshore side includes:
[0092] S701, when an AC short-circuit fault is detected on the offshore side, the short-circuit current control module of the offshore auxiliary converter is activated. The integral link freezing unit and the maximum limit unit of the given current in the short-circuit current control module are activated to control the fault current. The low voltage ride-through control unit in the wind turbine is activated. The DC side energy consumption module of the wind turbine is activated to control the energy consumption resistor to be connected.
[0093] Among them, the marine auxiliary converter is the marine auxiliary MMC.
[0094] For example, after an AC short-circuit fault is detected on the offshore side, the offshore auxiliary MMC short-circuit current control module is activated, the integral circuit freezing circuit and the given current maximum limiting unit are both activated to control the fault current, the low voltage ride-through control unit of the wind turbine is activated, the DC side energy consumption module of the wind turbine is activated, and the control energy consumption resistor is put into operation.
[0095] The integral freezing unit is used to control the fault current of the offshore auxiliary converter, and the given current maximum limiting unit is used to provide a given current maximum limiting value to control the fault current flowing into the offshore auxiliary converter.
[0096] S702, the offshore switchgear is opened to isolate the fault point.
[0097] Among them, the offshore switchgear is a 66kV offshore switch. For example, the offshore 66kV switch is opened to isolate the fault point.
[0098] S703, when the AC fault has been cleared, the integral circuit freeze unit and the given current maximum limit unit are deactivated, and the offshore auxiliary converter resumes AC voltage control.
[0099] For example, after the AC fault is cleared, the integral circuit freeze circuit and the maximum limit unit of the given current both exit, and the marine auxiliary MMC resumes AC voltage control.
[0100] S704, also known as Shanghai switchgear.
[0101] For example, the 66kV offshore switch is closed. The closing of the offshore AC side switch must be completed before the wind turbine power transmission is restored.
[0102] S705 controls the disconnection of the energy-consuming resistor, restoring the wind turbine to normal operating mode. The normal operating control module of the grid-side converter in the wind turbine restarts, and the transmission power is restored.
[0103] For example, when the energy-consuming resistor is disconnected, the wind turbine returns to normal operation mode, the normal operation control module of the grid-side converter of the wind turbine restarts, and the transmission power is restored.
[0104] More specifically, upon detecting a fault in the sending-end AC grid, the offshore sending-end auxiliary MMC controls the fault current flowing into it through a preset current-limiting mechanism. Simultaneously, the offshore wind turbine enters low-voltage ride-through logic, limiting the fault current to reduce output and activating distributed energy dissipation devices within the turbine to absorb surplus power. After clearing the AC fault by disconnecting the 66kV switch of the offshore AC system, the auxiliary MMC resumes AC voltage control.
[0105] in addition, Figure 8 This is a timing information diagram illustrating a method for oversea-side AC fault ride-through in one embodiment. The timing information of the oversea-side AC fault ride-through method is as follows: Figure 8 As shown. In Figure 8 In the process of switching on the 66kV switch in Shanghai, the operation needs to be completed before the energy consumption is withdrawn, in order to avoid the risk of system instability that may result from "the power of the wind turbine in front of the gate has been restored but there is nowhere to transfer this part of the energy".
[0106] Figure 9 This is a flowchart illustrating an onshore AC fault ride-through method in one embodiment, applied to an offshore wind power hybrid DC transmission system as described in any of the above embodiments. The onshore AC fault ride-through method includes:
[0107] S901: When an AC short-circuit fault is detected on the land side, the short-circuit current control module of the land inverter station is activated, and the maximum limit unit of the given current in the short-circuit current control module is activated to control the fault current.
[0108] The given current maximum limiting unit is used to provide a given maximum current limit value to control the fault current flowing into the offshore auxiliary converter.
[0109] For example, after an AC short-circuit fault is detected on the onshore side, the short-circuit current control module of the onshore MMC inverter station is activated, and the maximum current limiting unit is activated to control the fault current, providing dynamic reactive power support to the onshore AC grid during the fault and recovery period.
[0110] S902, start the DC side energy consumption module of the wind turbine in the wind turbine unit, and control the energy consumption resistor in the wind turbine unit to be connected.
[0111] For example, through communication between the onshore MMC inverter station, the offshore auxiliary MMC, and the wind turbine, the DC-side energy dissipation module of the wind turbine is activated, and the energy dissipation resistor is activated to dissipate the surplus power output by the offshore wind farm.
[0112] S903, when the AC fault has been cleared, the maximum current limiting unit is deactivated, the offshore auxiliary converter resumes DC voltage and reactive power control, and sends an onshore AC fault clearing signal to the wind turbine.
[0113] For example, after the AC fault is cleared, the maximum current limiting unit exits, the offshore auxiliary MMC restores DC voltage and reactive power control, and sends an AC fault clearing signal to the wind turbine.
[0114] S904: When the wind turbine receives an onshore AC fault clearing signal, the control energy-consuming resistor is disconnected, the wind turbine is restored to normal operation mode, and the grid-side converter normal operation control module in the wind turbine is restarted.
[0115] For example, upon receiving an onshore AC fault clearing signal, the control energy-consuming resistor is disconnected, the wind turbine returns to normal operation mode, and the grid-side converter normal operation control module is restarted.
[0116] in addition, Figure 10 This is a timing information illustration of an onshore AC fault ride-through method in one embodiment. The timing information of the onshore AC fault ride-through method is as follows: Figure 10 As shown.
[0117] Specifically, after a fault is detected in the onshore receiving-end AC grid, the onshore receiving-end flexible DC converter station controls the fault current through a preset current limiting mechanism, providing dynamic reactive power support to the AC grid during the fault and recovery period; during this period, transient energy balance is achieved by calling the distributed energy consumption of the wind turbine through rapid communication between DC and wind turbine (5ms+9ms+0.4ms+0.4ms, totaling about 15ms).
[0118] The technical research process and other technical details of this application are described below with reference to a specific embodiment.
[0119] In traditional technologies, the flexible DC transmission scheme based on modular multilevel converters is currently the mainstream solution for offshore wind power transmission during the development of offshore wind power clusters. The transmission system mainly consists of an offshore MMC rectifier station, a high-voltage DC submarine cable, and an onshore MMC inverter station. This solution has been adopted in some offshore wind power projects.
[0120] However, as offshore wind power develops towards deeper waters and larger scales, MMC-based offshore converter equipment faces challenges such as high cost, heavy weight, and difficult construction. Diode rectifier units (DRUs) offer advantages such as simple structure, low cost, and light weight; however, DRUs lack AC voltage generation capabilities and have high harmonic and reactive power requirements. Adopting a hybrid DC transmission system using DRUs as the main converter and supplemented by small-capacity MMCs is the preferred approach for achieving economical and efficient transmission from offshore wind power clusters.
[0121] Depending on their installation location, energy-consuming devices can be divided into two categories: AC energy-consuming devices and DC energy-consuming devices. AC energy-consuming devices are generally installed on the AC side of offshore converter stations, which is limited by the space of the offshore converter platform.
[0122] One technology proposes a series-connected centralized resistor scheme for the Insulated Gate Bipolar Transistor (IGBT) valve section, which has been widely used in offshore wind power DC transmission projects. Another technology proposes replacing the IGBT valve section with half-bridge and full-bridge submodules in an MMC (Multi-Level Controller), enabling multi-level output capability and better control. However, the aforementioned centralized power consumption methods utilize a large number of fully controlled devices and require the construction of dedicated unloading stations, resulting in high costs.
[0123] Based on this, this patent proposes an AC fault ride-through method for an offshore wind power hybrid DC transmission system and its offshore and onshore sides, also known as the AC fault ride-through method for an offshore wind power hybrid DC transmission system. Through the coordinated operation of the onshore receiving-end MMC inverter station, the offshore sending-end auxiliary MMC converter, and the offshore wind turbine, the operational stability of the offshore wind power hybrid DC transmission system is improved. In the event of a short-circuit fault at the sending and receiving ends of the offshore wind power hybrid DC transmission system, transient surplus energy balance is achieved without relying on centralized DC energy dissipation devices. During fault ride-through, DC blocking is not caused by transient surplus energy impact, thus reducing construction difficulty and cost.
[0124] In terms of numerical verification, this application utilizes the PSCAD / EMTDC simulation platform to build a ±500kV / 2000MW offshore wind power hybrid DC transmission system. The system topology is as follows: Figure 1 As shown, at 5 seconds, three-phase AC short-circuit faults were set at sea and onshore, with a fault duration of 100 milliseconds. The steady-state operation and AC ride-through waveforms are shown below. It can be seen that, in the event of AC short-circuit faults at sea and onshore in the offshore wind power hybrid DC transmission system, the method proposed in this application can achieve transient surplus energy balance without relying on centralized DC energy dissipation devices, and no DC blocking occurs due to transient surplus energy impact during fault ride-through.
[0125] Figure 11 This is a waveform diagram of the offshore steady-state operation of an offshore wind power hybrid DC transmission system in one embodiment. Figure 11 In the middle, from top to bottom, are the effective value of the line voltage of the PCC point, the active power output of the auxiliary MMC, the reactive power output of the auxiliary MMC, and the waveform of the AC current output by the offshore wind farm.
[0126] Figure 12 In one embodiment, the onshore steady-state operation waveform diagram of the offshore wind power hybrid DC transmission system is shown. Figure 12 In the middle, from top to bottom, are the waveforms of DC voltage, active power received by the onshore MMC inverter station, reactive power received by the onshore MMC inverter station, and AC current on the onshore grid side.
[0127] Figure 13 A schematic diagram of a three-phase AC short-circuit fault in an offshore wind power hybrid DC transmission system in one embodiment. Figure 13 middle, Figure 13 The left side refers to the offshore side, and from top to bottom are the effective value of the PCC line voltage, the active power output of the auxiliary MMC, the reactive power output of the auxiliary MMC, and the waveform of the AC current output by the offshore wind farm.
[0128] Correspondingly, Figure 13The right side refers to the onshore side, which, from top to bottom, consists of the effective value of the AC line voltage of the onshore power grid, the DC voltage, the active power received by the onshore MMC inverter station, the reactive power received by the onshore MMC inverter station, and the waveform of the AC current on the onshore power grid side.
[0129] Figure 14 This is a schematic diagram of an onshore three-phase AC short-circuit fault in an offshore wind power hybrid DC transmission system in one embodiment. Figure 14 middle, Figure 14 The left side refers to the offshore side, and from top to bottom are the effective value of the PCC line voltage, the active power output of the auxiliary MMC, the reactive power output of the auxiliary MMC, and the waveform of the AC current output by the offshore wind farm.
[0130] Correspondingly, Figure 14 The right side refers to the onshore side, which, from top to bottom, consists of the effective value of the AC line voltage of the onshore power grid, the DC voltage, the active power received by the onshore MMC inverter station, the reactive power received by the onshore MMC inverter station, and the waveform of the AC current on the onshore power grid side.
[0131] In another embodiment, a fault-traversal device is provided, which can be a computer device, such as a server, and its internal structure diagram can be as follows. Figure 15 As shown, the fault-crossing device includes a processor, memory, input / output (I / O) interfaces, and a communication interface. The processor, memory, and I / O interfaces are connected via a system bus, and the communication interface is also connected to the system bus via the I / O interfaces. The processor provides computing and control capabilities. The memory includes non-volatile storage media and internal memory. The non-volatile storage media stores the operating system, computer programs, and a database. The internal memory provides an environment for the operation of the operating system and computer programs in the non-volatile storage media. The database of the fault-crossing device stores relevant data. The I / O interfaces are used for exchanging information between the processor and external devices. The communication interface is used for communication with external terminals via a network connection. When the computer program is executed by the processor, it implements the various methods described in the above embodiments.
[0132] In yet another embodiment, a fault-traversal device is provided, which can be a computer device, such as a terminal, and its internal structure diagram can be as follows: Figure 16As shown, it includes a processor, memory, input / output interface, communication interface, display unit, and input device. The processor, memory, and input / output interface are connected via a system bus, and the communication interface, display unit, and input device are also connected to the system bus via the input / output interface. The processor provides computing and control capabilities. The memory includes a non-volatile storage medium and internal memory. The non-volatile storage medium stores the operating system and computer programs. The internal memory provides an environment for the operation of the operating system and computer programs in the non-volatile storage medium. The input / output interface is used for exchanging information between the processor and external devices. The communication interface is used for wired or wireless communication with external terminals; wireless communication can be achieved through Wi-Fi, mobile cellular networks, NFC (Near Field Communication), or other technologies. When the computer program is executed by the processor, it implements the various methods described in the above embodiments.
[0133] Those skilled in the art will understand that Figure 15 and Figure 16 The structure shown is merely a block diagram of a portion of the structure related to the present application and does not constitute a limitation on the fault-crossing device to which the present application is applied. Specifically, it may include more or fewer components than shown in the figure, or combine certain components, or have different component arrangements, in order to achieve the functions of computer devices such as terminals or servers.
[0134] In the above embodiments, the descriptions of each embodiment have different focuses. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions in other embodiments.
[0135] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working process of the systems, devices, equipment, modules or units described above can be referred to the corresponding process in the foregoing method embodiments, and will not be repeated here.
[0136] In the embodiments provided in this application, it should be understood that the disclosed systems, devices, equipment, or methods can be implemented in other ways. For example, the device embodiments described above are merely illustrative; for instance, the division of modules is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple modules or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the displayed or discussed mutual couplings, direct couplings, or communication connections may be indirect couplings or communication connections between devices or modules through some interfaces, and may be electrical, mechanical, or other forms.
[0137] The modules described as separate components may or may not be physically separate. The components shown as modules may or may not be physical modules; that is, they may be located in one place or distributed across multiple network modules. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs.
[0138] Furthermore, the functional modules in the various embodiments of this application can be integrated into one processing module, or each module can exist physically separately, or two or more modules can be integrated into one module. The integrated module can be implemented in hardware or as a software functional module. If the integrated module is implemented as a software functional module and sold or used as an independent product, it can be stored in a computer-readable storage medium.
[0139] In the above embodiments, implementation can be achieved, in whole or in part, through software, hardware, firmware, or any combination thereof. When implemented in software, it can be implemented, in whole or in part, as a computer program product.
[0140] The computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, all or part of the processes or functions described in the embodiments of this application are generated. The computer may be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions may be stored in a computer-readable storage medium or transmitted from one computer-readable storage medium to another. For example, the computer instructions may be transmitted from one website, computer, server, or data center to another website, computer, server, or data center via wired (e.g., coaxial cable, fiber optic, digital subscriber line (DSL)) or wireless (e.g., infrared, wireless, microwave, etc.) means. The computer-readable storage medium may be any available medium that a computer can store or a data storage device such as a server or data center that integrates one or more available media. The available medium may be a magnetic medium (e.g., floppy disk, hard disk, magnetic tape), an optical medium (e.g., DVD), or a semiconductor medium (e.g., a solid-state disk (SSD)).
[0141] The technical solutions provided in the embodiments of this application have been described in detail above. Specific examples have been used in the embodiments of this application to illustrate the principles and implementation methods of the embodiments of this application. The description of the above embodiments is only for the purpose of helping to understand the methods and core ideas of the embodiments of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of the embodiments of this application. Therefore, the content of this specification should not be construed as a limitation on the embodiments of this application.
Claims
1. A method for AC fault ride-through on the marine side, characterized in that, The AC fault-crossing method on the sea side includes: In the event of an AC short-circuit fault detected on the offshore side, the short-circuit current control module of the offshore auxiliary converter is activated. The integral link freezing unit and the given current maximum limiting unit in the short-circuit current control module are activated to control the fault current. The low voltage ride-through control unit in the wind turbine is activated, and the DC side energy consumption module of the wind turbine is activated to control the energy consumption resistor to be connected. The offshore switchgear was opened to isolate the fault point; With the AC fault cleared, the integral freezing unit and the given current maximum limiting unit are deactivated, and the marine auxiliary converter resumes AC voltage control. Close the aforementioned marine switchgear; The energy-consuming resistor of the wind turbine is disconnected, restoring the wind turbine to normal operation mode. The normal operation control module of the grid-side converter in the wind turbine is restarted, and the power transmission is restored. The integral freezing unit is used to control the fault current of the offshore auxiliary converter, and the given current maximum limiting unit is used to provide a given current maximum limiting value to control the fault current flowing into the offshore auxiliary converter.
2. A method for AC fault ride-through on the land side, characterized in that, The onshore AC fault crossing method includes: When an AC short-circuit fault is detected on the onshore side, the short-circuit current control module of the onshore inverter station is activated, and the maximum limit unit of the given current in the short-circuit current control module is activated to control the fault current. Start the DC side energy consumption module of the wind turbine in the wind turbine unit, and control the energy consumption resistor in the wind turbine unit to be connected; When the AC fault has been cleared, the maximum limiting unit of the given current is deactivated, the offshore auxiliary converter restores DC voltage and reactive power control, and sends an onshore AC fault clearance signal to the wind turbine. When the wind turbine receives an onshore AC fault clearing signal, the energy-consuming resistor is disconnected, the wind turbine is restored to normal operation mode, and the grid-side converter normal operation control module in the wind turbine is restarted. The given current maximum limiting unit is used to provide a given current maximum limiting value to control the fault current flowing into the offshore auxiliary converter.
3. A hybrid DC transmission system for offshore wind power, characterized in that, For implementing the offshore AC fault ride-through method of claim 1 or the onshore AC fault ride-through method of claim 2, the offshore wind power hybrid DC transmission system comprises: Wind turbine units; Offshore switchgear, which is connected to the wind turbine generator; The offshore rectifier station is equipped with a short-circuit current control module for controlling fault current. The wind turbine generators are connected to the AC busbar of the offshore rectifier station via AC collector cables and the offshore switchgear. A conversion station is connected to the offshore rectifier station, which is used to convert the DC submarine cable into a DC overhead line and connect it to the onshore switchgear collection station via the DC overhead line. The onshore switchgear collection station is used to collect DC overhead lines and connect them to the onshore inverter station; The onshore inverter station is used to convert direct current into alternating current and transmit electrical energy to the onshore AC power grid.
4. The offshore wind power hybrid DC transmission system according to claim 3, characterized in that, The marine auxiliary converter in the marine rectifier station includes a first normal operation control module; The first normal operation control module includes an active power control unit, an AC voltage control unit, an output current control unit, and a pulse generation unit. The active power control unit is connected to the AC voltage control unit, the AC voltage control unit is connected to the output current control unit, and the output current control unit is connected to the pulse generation unit.
5. The offshore wind power hybrid DC transmission system according to claim 3, characterized in that, The marine auxiliary converter in the marine rectifier station includes a first short-circuit current control module. The first short-circuit current control module includes an active power control unit, an AC voltage control unit, an output current control unit, a pulse generation unit, an integral freezing unit, and a given current maximum limiting unit. The active power control unit is connected to the AC voltage control unit, the AC voltage control unit is connected to the output current control unit, the output current control unit is connected to the pulse generation unit, the integral freezing unit is connected to the AC voltage control unit, and the given current maximum limiting unit is connected to the output current control unit.
6. The offshore wind power hybrid DC transmission system according to claim 3, characterized in that, The onshore inverter station includes a second normal operation control module; The second normal operation control module includes a reactive power control unit, a DC voltage control unit, an output current control unit, and a pulse generation unit. The reactive power control unit and the DC voltage control unit are respectively connected to the output current control unit, and the output current control unit is connected to the pulse generation unit.
7. The offshore wind power hybrid DC transmission system according to claim 3, characterized in that, The onshore inverter station includes a second short-circuit current control module; The second short-circuit current control module includes a reactive power control unit, a DC voltage control unit, an output current control unit, a pulse generation unit, and a given current maximum limiting unit. The reactive power control unit and the DC voltage control unit are respectively connected to the output current control unit, the output current control unit is connected to the pulse generation unit, and the given current maximum limiting unit is connected to the output current control unit.
8. A fault-crossing device, characterized in that, The fault ride-through device includes: At least one processor and memory; The memory is used to store program code, and the processor is used to call the program code stored in the memory to execute the method as described in claim 1 or 2.
9. A computer storage medium, characterized in that, It includes instructions that, when run on a computer, cause the computer to perform the method as described in claim 1 or 2.