Offshore wind power plant unit short-circuit current calculation method and device

Abstract

The invention provides an offshore wind power plant unit short-circuit current calculation method and device. The method comprises the steps of determining first current and first voltage of each unit; obtaining a second voltage output by each unit and a second current output by the offshore converter module after the offshore wind plant has a short-circuit fault; determining a reference current of each unit and determining a third voltage output by the offshore commutation module; a current contribution of the second voltage, the reference current, and the third voltage to the short circuit fault is determined. A passive network assembly is composed of an offshore wind power plant unit section filter, an offshore boost module, an electric energy transmission module, an offshore commutation module and a land commutation module, a second voltage and a second current are obtained by analyzing transient response characteristics of the passive network assembly, and a reference current and a third voltage are obtained by combining a fault ride-through strategy. And according to the contribution of the second point voltage, the reference current and the third voltage to the current of the short-circuit fault, the short-circuit current of the fault point of the offshore wind power plant unit is determined, and the accuracy of short-circuit current calculation is greatly improved.

Description

Technical Field

[0001] This application relates to the field of new energy power generation technology, and in particular to a method and apparatus for calculating the short-circuit current of offshore wind farm units. Background Technology

[0002] Offshore wind farms can be connected to the grid via methods such as high-voltage AC grid connection and flexible DC grid connection. Due to the capacitive effect of the power transmission modules on the seabed, high-voltage AC grid connection is mostly used for near-shore grid connection operations. For large-scale wind farms far from the coast, flexible DC grid connection is currently more commonly used. Flexible DC grid connection typically employs a unipolar symmetrical structure. When a short-circuit current fault occurs within the wind farm, the current suppression effect of the offshore wind farm units increases the complexity of the short-circuit current calculation process. On the other hand, short-circuit current calculation relies too heavily on electromagnetic transient solutions, considering only the changes in fundamental frequency amplitude and phase angle while ignoring information from other frequencies. Furthermore, the relatively short electromagnetic transient time further increases the complexity of the short-circuit current calculation process.

[0003] It should be noted that the above introduction to the technical background is only for the purpose of providing a clear and complete explanation of the technical solutions of this application and facilitating understanding by those skilled in the art. It should not be assumed that these technical solutions are known to those skilled in the art simply because they have been described in the background section of this application. Summary of the Invention

[0004] This application provides a method and apparatus for calculating the short-circuit current of offshore wind farm turbines.

[0005] The first aspect of this application proposes a method for calculating the short-circuit current of offshore wind farm turbines, applicable to offshore wind power transmission systems. The offshore wind power transmission system includes: at least one turbine, an offshore booster module, an offshore converter module, a power transmission module, a land-based converter module, and a land-based power grid. The offshore booster module is connected to the turbine; the offshore converter module is connected to the offshore booster module; the power transmission module is connected to the offshore converter module; the land-based converter module is connected to the power transmission module; and the land-based power grid is connected to the land-based converter module. The method for calculating the short-circuit current of the offshore wind farm turbines includes:

[0006] Based on the power flow status before a short-circuit fault occurs in an offshore wind farm, determine the first current and first voltage of each unit;

[0007] After a short-circuit fault occurs in an offshore wind farm, the second voltage output by each unit and the second current output by the offshore converter module are obtained.

[0008] Based on the unit fault ride-through control strategy, the first current and the second voltage, determine the reference current of each unit after a short-circuit fault occurs; based on the offshore converter module fault ride-through control strategy, the first voltage and the second current, determine the third voltage output by the offshore converter module.

[0009] The short-circuit current at the fault point of the offshore wind farm unit is determined based on the current contribution of the second voltage, reference current, and third voltage to the short-circuit fault.

[0010] A second aspect of this application provides a short-circuit current calculation device for offshore wind farm turbines, characterized in that it is applicable to offshore wind power transmission systems. The offshore wind power transmission system includes: at least one turbine, an offshore booster module, an offshore converter module, a power transmission module, a land-based converter module, and a land-based power grid. The offshore booster module is connected to the turbine; the offshore converter module is connected to the offshore booster module; the power transmission module is connected to the offshore converter module; the land-based converter module is connected to the power transmission module; and the land-based power grid is connected to the land-based converter module. The offshore wind farm turbine short-circuit current calculation device includes:

[0011] The first acquisition module is used to determine the first current and first voltage of each unit based on the power flow state before a short-circuit fault occurs in the offshore wind farm.

[0012] The second acquisition module is used to acquire the second voltage output by each unit and the second current output by the offshore converter module after a short circuit fault occurs in the offshore wind farm.

[0013] The third acquisition module determines the reference current of each unit after a short-circuit fault occurs based on the unit fault ride-through control strategy, the first current, and the second voltage; and determines the third voltage output by the offshore converter module based on the offshore converter module fault ride-through control strategy, the first voltage, and the second current.

[0014] The fourth acquisition module is used to determine the short-circuit current at the fault point of the offshore wind farm unit based on the current contribution of the second voltage, the reference current, and the third voltage to the short-circuit fault.

[0015] A third aspect of this application provides an electronic device, comprising: a processor; and a memory for storing executable instructions of the processor; wherein the processor is configured to execute the instructions to implement the short-circuit current calculation method for offshore wind farm turbines proposed in the first aspect of this application.

[0016] A fourth aspect of this application provides a non-transitory computer-readable storage medium that, when instructions in the storage medium are executed by a processor of an electronic device, enables the electronic device to perform the method proposed in the first aspect of this application.

[0017] A fifth aspect of this application provides a computer program product including a computer program that, when executed by a processor in a communication device, implements the method proposed in the first aspect of this application.

[0018] The technical solutions provided by the embodiments of this application bring at least the following beneficial effects:

[0019] A passive network component consisting of offshore wind farm turbine section filters, offshore booster modules, power transmission modules, offshore converter modules, and onshore converter modules is used to obtain a second voltage and a second current by analyzing the transient response characteristics of the passive network component. Combined with a fault ride-through strategy, a reference current and a third voltage are obtained. Then, based on the current contribution of the second point voltage, reference current, and third voltage to the short-circuit fault, the short-circuit current at the fault point of the offshore wind farm turbine is determined, which greatly improves the accuracy of short-circuit current calculation.

[0020] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and do not limit this application. Attached Figure Description

[0021] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings, wherein:

[0022] Figure 1 This is a schematic flowchart of a method for calculating the short-circuit current of an offshore wind farm turbine provided in an embodiment of this application.

[0023] Figure 2 This is a schematic flowchart of another method for calculating the short-circuit current of an offshore wind farm turbine provided in an embodiment of this application;

[0024] Figure 3 This is a schematic diagram of the structure of an offshore wind power transmission system provided in an embodiment of this application;

[0025] Figure 4 This is a schematic diagram of the structure of an equivalent multi-port network for an offshore wind farm provided in an embodiment of this application;

[0026] Figure 5 A schematic diagram of the structure of a short-circuit current calculation device for an offshore wind farm unit provided in an embodiment of this application;

[0027] Figure 6 This is a schematic diagram of the structure of an electronic device according to an embodiment of this application;

[0028] Figure 7 This is a schematic diagram of the structure of another electronic device provided according to an embodiment of this application. Detailed Implementation

[0029] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with those of this application. Rather, they are merely examples of apparatuses and methods consistent with some aspects of the embodiments of this application as detailed in the appended claims.

[0030] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to limit the embodiments of this application. The singular forms “a” and “the” as used in the embodiments of this application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any or all possible combinations of one or more of the associated listed items.

[0031] It should be understood that although the terms first, second, third, etc., may be used to describe various information in the embodiments of this application, such information should not be limited to these terms. These terms are only used to distinguish information of the same type from each other. For example, without departing from the scope of the embodiments of this application, first information may also be referred to as second information, and similarly, second information may also be referred to as first information. Depending on the context, the words "if" and "suppose" as used herein can be interpreted as "when," "when," or "in response to a determination."

[0032] Embodiments of this application are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application.

[0033] It should be noted that the method for calculating the short-circuit current of offshore wind farm units provided in any embodiment of this application can be executed alone, or it can be executed together with possible implementation methods in other embodiments, or it can be executed together with any technical solution in related technologies.

[0034] The following describes, with reference to the accompanying drawings, a method and apparatus for calculating the short-circuit current of offshore wind farm turbines according to embodiments of this application.

[0035] Figure 1 This is a schematic flowchart illustrating a method for calculating the short-circuit current of an offshore wind farm turbine, provided in an embodiment of this application. Figure 3 This is a schematic diagram of the structure of an offshore wind power transmission system provided in an embodiment of this application. Figure 1 As shown, this method is applicable to, for example Figure 3 The offshore wind power transmission system shown includes: at least one turbine generator, an offshore booster module, an offshore converter module, a power transmission module, a land-based converter module, and a land-based power grid. The offshore booster module is connected to the turbine generator; the offshore converter module is connected to the offshore booster module; the power transmission module is connected to the offshore converter module; the land-based converter module is connected to the power transmission module; and the land-based power grid is connected to the land-based converter module. The method for calculating the short-circuit current of the offshore wind farm turbine generator includes, but is not limited to, the following steps:

[0036] S101, based on the power flow status before a short-circuit fault occurs in the offshore wind farm, determine the first current and first voltage of each unit.

[0037] It should be noted that, as Figure 3 As shown, offshore wind farms need to consider their grid connection issues. Currently, many factors are considered when connecting offshore wind power to the grid, mainly including: the scale of wind power development, the transmission capacity and distance of the transmission line, the economic efficiency and reliability of offshore wind power operation, the grid connection voltage level, the operation mode of the coastal power grid, the grid structure, and the operation mode of grid connection. Different transmission methods are adopted according to the distance of the offshore wind farm from the project and the scale of the installed units. They are broadly divided into high-voltage AC transmission and high-voltage DC transmission. According to the technological development in recent years, transmission methods also include ship-borne battery transmission and fractional frequency wind power system (FFWPS, which refers to reducing the transmission frequency without increasing the voltage level, thereby reducing the electrical distance of AC transmission lines, thereby increasing the transmission power capacity of the transmission lines and reducing the number of transmission circuits and outgoing corridors). Among them, high-voltage AC transmission first converts the AC power with fluctuating voltage amplitude and frequency output from each wind turbine into constant voltage industrial frequency AC power through a converter, and then into submarine cable after being stepped up by an offshore step-up transformer, and then transmitted to the land and connected to the grid. Due to the influence of capacitor charging in cable lines, this type of power transmission has a large reactive power loss and a low effective load rate of the cable. Therefore, it can only transmit electrical energy over short distances and with small capacity. Generally, reactive power compensators are also required, and direct connection to the power grid will also increase the safety risks of the power grid and power plants.

[0038] There are two main topologies for high-voltage direct current (HVDC) transmission: one is the traditional HVDC based on line commutated converters (LCC) (LCC-HVDC); the other is the flexible HVDC based on voltage source converters (VSC) (VSC-HVDC). Both operate on similar principles: the AC power output from wind turbines is converted to DC by an offshore converter, then transmitted to land via submarine DC cables, and finally converted back to AC at the onshore converter station before being fed into the grid. LCC-HVDC offers advantages such as large single-converter capacity, low cost, high reliability, and mature technology, but it also suffers from problems such as susceptibility to harmonics, the need for reactive power compensation, and susceptibility to commutation failures due to AC system interference, limiting its wider application. With the development of power electronics technology, more mature power electronic devices and technologies have entered the field of high-power power transmission. VSC-HVDC has advantages such as being less prone to commutation failure, strong stability, and the ability to control active and reactive power separately. It also has advantages such as black start capability and the ability to connect to passive network power supply. After overcoming the problems of high harmonic content and large losses caused by the early use of two-level and three-level converters, the use of modular multilevel converter technology has greatly improved the performance.

[0039] Furthermore, offshore wind farm units mainly consist of wind turbine generators, infrastructure, power transmission systems, and monitoring systems. Among these, the wind turbine generator is the core component of an offshore wind farm, typically composed of three parts: the tower, the nacelle, and the blades. The tower supports the entire wind turbine generator, the nacelle contains the generator and gearbox, and the blades are responsible for capturing wind energy and converting it into mechanical energy. Offshore wind turbine generators are usually installed on wind turbine towers, which are fixed to the seabed or floating platforms on the sea surface by infrastructure. When wind blows across the blades, the blades rotate, converting kinetic energy into mechanical energy, which is transmitted to the generator through a gear system. The generator converts the mechanical energy into electrical energy and transmits it to the onshore power grid through a grid connection device. The control system is responsible for monitoring wind speed and direction, the turbine's operating status, and automatically adjusting the blade angle and rotation speed to maximize the capture and conversion of wind energy.

[0040] Because of the constant tidal currents in the waters surrounding offshore wind farms, these currents affect the condition of infrastructure. For example, they can impact the connection status of power collection lines. Poor contact, short circuits between different lines, and improper construction and maintenance can all lead to changes in the transmission voltage and output current of each turbine. Short-circuit faults have a significant impact on wind farms. They can not only cause wind turbines to shut down, affecting power supply, but also affect the grid's relay protection system, causing it to malfunction or malfunction. The inherent disadvantages of wind power generation, such as uneven power generation frequency and large voltage peak-to-valley differences, can cause voltage fluctuations after connection to the power grid, potentially affecting the normal operation of power transmission equipment such as transformers. Therefore, a series of measures are needed to prevent and address short-circuit problems within offshore wind farms. First, it is essential to strengthen equipment maintenance and management, regularly inspect the condition of lines and connections, and promptly identify and address potential safety hazards. Second, it is crucial to improve the skills and safety awareness of operators to avoid malfunctions caused by improper operation. Furthermore, advanced monitoring and diagnostic technologies can be employed to monitor and provide early warnings of the wind farm's operational status in real time, enabling timely detection and handling of faults such as short circuits. Moreover, through the monitoring system of the offshore wind farm turbines, the first current of each turbine can be determined based on the power flow state before a short circuit fault occurs (wherein the first current includes the d-axis component). and q-axis components Where i represents the i-th generator unit (1≤i≤n), n represents the number of generator units (n is a positive integer) and the first voltage.

[0041] S102, acquire the second voltage output by each unit and the second current output by the offshore converter module after a short circuit fault occurs in the offshore wind farm.

[0042] It should be noted that, Figure 4 This is a schematic diagram of the structure of an equivalent multi-port network for an offshore wind farm, provided as an embodiment of this application. Figure 4 As shown, the passive network components consist of offshore wind farm turbine section filters, offshore booster modules, power transmission modules (as an example, power transmission modules include submarine cables, collector lines, etc.), offshore converter modules, and onshore converter modules. Furthermore, the offshore converter module can be equivalent to a voltage source (wherein, this voltage source is not located on...). Figure 4(As shown in the diagram), each turbine in an offshore wind farm is equivalent to a current source. Therefore, multiple current sources, one voltage source, and a passive network constitute a multi-port network. If a short-circuit fault occurs in an offshore wind farm turbine, the fault node f is characterized through the multi-port network. Specifically, the grounding impedance Zf of the fault node f is obtained, along with the corresponding output voltage Uf and output current If. Since each turbine in an offshore wind farm can be equivalent to an array, the output voltage Uf is the array output voltage during a short-circuit fault. For each turbine, Ug,1, Ug,2, ..., Ug,n are the terminal voltages of each turbine, and Zg,1, Zg,2, ..., Zg,n are the equivalent impedances of each turbine. As an example, if a flexible DC high-voltage transmission topology is used, the equivalent impedance Zm and output voltage Em of the offshore converter module are obtained through the multi-port network.

[0043] It should be further explained that the terminal voltages Ug,1, Ug,2, ..., Ug,n can be represented as the second voltage output by each unit after a short-circuit fault, i.e., the second voltage Ug,i (where i represents the i-th unit, 1≤i≤n, n represents the number of units, and n is a positive integer); while the second current output at the fault location... Typically, the current at the output of the offshore converter module can be used to characterize it.

[0044] S103, based on the unit fault ride-through control strategy, the first current and the second voltage, determine the reference current of each unit after a short-circuit fault occurs; based on the offshore converter module fault ride-through control strategy, the first voltage and the second current, determine the third voltage output by the offshore converter module.

[0045] It is important to note that fault ride-through control strategy is a crucial methodology for addressing complex system faults such as short circuits within wind farms. Its core lies in immediate response and flexible adaptation. Through in-depth understanding and prediction of the system, reasonable decisions and measures are taken to mitigate the impact of faults and reduce losses. In wind farms, the application of fault ride-through control strategy is primarily reflected in the response of wind turbine generators to grid faults during grid-connected operation. When a grid fault occurs, wind turbine generators need to maintain grid connection for a certain period, and even provide some power support to the grid to help it recover from the fault. This requires wind turbine generators to have low-voltage ride-through capability, meaning they can continue to operate and output power when the grid voltage drops to maintain grid stability. To implement fault ride-through control strategy, advanced control algorithms and protection devices are required. For example, model-based control algorithms such as sliding mode control and fuzzy control can be used to achieve rapid system response and stable control. These algorithms can precisely adjust the system based on real-time data, ensuring that wind turbine generators can react quickly when a fault occurs. Simultaneously, advanced protection devices such as current protection and voltage protection are also necessary to ensure the safe operation of the system. These protective devices can quickly disconnect faulty lines when a fault occurs, preventing the fault from escalating and ensuring the normal operation of other non-faulty lines. In addition to hardware and algorithm support, fault ride-through control strategies also need to comprehensively consider the operating environment and actual conditions of the wind farm. For example, offshore wind farms, due to their unique geographical location and environmental conditions, may require special protective measures and coping strategies to address issues such as severe weather and corrosion at sea. Furthermore, as the scale of wind farms expands and technology advances, fault ride-through control strategies also need continuous updating and improvement to adapt to new operating scenarios and control modes.

[0046] Furthermore, such as Figure 3 As shown, the offshore booster module connected to the generator unit can adopt a delta-star connection, ensuring that each generator unit only outputs positive-sequence current; the generator-side converter can adopt a dual-loop control architecture. Based on the negative-sequence current suppression strategy provided by the delta-star connection and the dual-loop control architecture, the reference current of each generator unit after a short-circuit fault can be obtained.

[0047] Furthermore, during fault ride-through, the unit's q-axis reference current and d-axis reference current usually change. The transfer function of the unit-side control loop can be obtained first, and then the frequency domain value of the unit's q-axis current can be obtained by multiplying the transfer function with the frequency domain value of the q-axis current through frequency domain transformation. The q-axis current can be obtained by performing an inverse transformation on the frequency domain value of the q-axis current. The d-axis current can be obtained in the same way.

[0048] Furthermore, since offshore converter modules can employ AC voltage-frequency control, the outer loop of the offshore converter module is a voltage control loop, and the inner loop is a current control loop. Normally, offshore wind farm turbines output a stable AC voltage. When a short-circuit fault occurs, the voltage control loop reduces the voltage transmitting power, which can suppress the current to some extent. Therefore, the offshore converter module outputs a third voltage during fault ride-through.

[0049] S104. Determine the short-circuit current at the fault point of the offshore wind farm unit based on the current contribution of the second voltage, reference current, and third voltage to the short-circuit fault.

[0050] It should be noted that, as Figure 3 and Figure 4 As shown, since each generator unit can be equivalent to a current source (the current source is considered an open circuit when calculating the current contribution) and the offshore converter module can be equivalent to a voltage source (the voltage source is considered a short circuit when calculating the current contribution), the transfer function between the generator unit and the offshore converter module is obtained based on the passive network components. The third voltage can be characterized as the voltage of the fault node f. Furthermore, the frequency domain value of the third voltage is obtained. By multiplying the frequency domain value with the transfer function between the generator unit and the offshore converter module, the third contribution current of the third voltage to the short circuit fault is obtained (where the third contribution current is a frequency domain value, and the time domain value is obtained by inverse transformation of the frequency domain value).

[0051] Through network analysis, the second contribution current of the reference current to the short-circuit fault and the first contribution current of the second voltage to the short-circuit fault can be obtained. The first, second, and third contribution currents are then superimposed to obtain the short-circuit current at the fault point of the offshore wind farm unit.

[0052] In summary, the passive network components, consisting of offshore wind farm turbine section filters, offshore booster modules, power transmission modules, offshore converter modules, and onshore converter modules, can obtain the second voltage and second current by analyzing the transient response characteristics of the passive network components. Combined with the fault ride-through strategy, the reference current and third voltage are obtained. Then, based on the current contribution of the second point voltage, reference current, and third voltage to the short-circuit fault, the short-circuit current at the fault point of the offshore wind farm turbine is determined, which greatly improves the accuracy of short-circuit current calculation.

[0053] Figure 2 This is a schematic flowchart of another method for calculating the short-circuit current of offshore wind farm units provided in an embodiment of this application.

[0054] like Figure 2 As shown, the method includes, but is not limited to, the following steps:

[0055] S201 acquires the output voltage and output current of each unit in real time based on the wind conditions of the offshore wind farm and the tidal current status of the surrounding sea area.

[0056] For a detailed description of step S201, please refer to the relevant content in the above embodiments, which will not be repeated here.

[0057] S202, based on the output voltage and output current, record the first current and first voltage related to the power flow state before a short-circuit fault occurs in the offshore wind farm.

[0058] For a detailed description of step S202, please refer to the relevant content in the above embodiments, which will not be repeated here.

[0059] S203, acquire the second voltage output of each unit and the second current output of the offshore converter module after a short circuit fault occurs in the offshore wind farm.

[0060] Optionally, as an example, a multi-port network corresponding to the offshore wind power transmission system is obtained. Further, basic data of each turbine in the offshore wind power transmission system is obtained; a turbine model is established based on the electrical characteristics and basic data of each turbine; a power collection system model is established based on the electrical energy generated by each turbine and the transmission path of that electrical energy; and a multi-port network is obtained based on simplification and aggregation operations on the turbine model and the power collection system model.

[0061] Optionally, as an example, the second voltage output by each turbine and the second current output by the offshore converter module after a short-circuit fault occur in the offshore wind farm are obtained based on the multi-port network. Further, the grounding impedance corresponding to each turbine is obtained based on the multi-port network; the second voltage output by each turbine and the second current output by the offshore converter module after a short-circuit fault are determined based on the grounding impedance.

[0062] For further details on step S203, please refer to the relevant descriptions in the above embodiments, which will not be repeated here.

[0063] S204. Based on the unit fault ride-through control strategy, the first current and the second voltage, determine the reference current of each unit after a short-circuit fault occurs.

[0064] Optionally, as an example, based on the unit's fault ride-through control strategy, the unit's fault ride-through reactive current coefficient, the first current threshold of the offshore boost module during a short-circuit fault, and the voltage threshold set by the unit are determined (as an example, the voltage threshold can be set to 90% of the unit's rated voltage; it should be noted that the voltage threshold should be set according to the specific application scenario and is not limited to this embodiment); based on the comparison operation between the second voltage and the voltage threshold, the q-axis reference current of the unit during a short-circuit fault is determined, wherein if the second voltage ≥ the voltage threshold, the q-axis reference current is equal to the q-axis component of the first current;

[0065] If the second voltage is less than the voltage threshold, the first difference is obtained by subtracting the voltage threshold from the second voltage; the q-axis reference current is determined by multiplying the first difference with the fault ride-through reactive current coefficient and the rated current of the unit.

[0066] The first intermediate variable is obtained by operating on the arithmetic square root of the q-axis reference current and the first current in the d-axis component.

[0067] Based on the comparison between the first intermediate variable and the first current threshold, the d-axis reference current of the unit during a short-circuit fault is determined. Specifically, if the first intermediate variable ≤ the first current threshold, the d-axis reference current equals the d-axis component of the first current; if the first intermediate variable > the first current threshold, the d-axis reference current equals (the first current threshold) / (the first current threshold). 2 -q-axis reference current 2 ) 1 / 2 ;

[0068] Based on the superposition of the q-axis reference current and the d-axis reference current, the reference current of each unit after a short-circuit fault is determined. Furthermore, during fault ride-through, the q-axis and d-axis reference currents of the units typically change. The transfer function of the unit-side control loop can be obtained first. Then, through frequency domain transformation, the frequency domain value of the unit's q-axis current is obtained by multiplying the transfer function with the frequency domain value of the q-axis current. An inverse transformation of the frequency domain value of the q-axis current yields the q-axis current. The d-axis current is obtained in the same way.

[0069] It should be noted that the expression for the reference current is as follows:

[0070]

[0071] Based on the fault ride-through control strategy of the offshore converter module, the first voltage and the second current, the third voltage output by the offshore converter module is determined.

[0072] Optionally, as an example, based on the fault ride-through control strategy of the offshore converter module, a second current threshold and a voltage regulation coefficient of the offshore converter module are determined in the case of a short-circuit fault; based on the comparison operation between the second current and the second current threshold, a third voltage output by the offshore converter module is determined, wherein if the second current ≤ the second current threshold, the third voltage is equal to the first voltage.

[0073] If the second current is greater than the second current threshold, the second difference is obtained by subtracting the second current from the second current threshold; the second intermediate variable is obtained by multiplying the second difference with the voltage regulation coefficient; and the third voltage is obtained by subtracting the first voltage from the second intermediate variable.

[0074] It should be noted that the expression for the third voltage is as follows:

[0075]

[0076] For further details on step S204, please refer to the relevant descriptions in the above embodiments, which will not be repeated here.

[0077] S205, determine the short-circuit current at the fault point of the offshore wind farm unit based on the contribution of the second voltage, reference current and third voltage to the short-circuit fault current.

[0078] Optionally, as an example, the transfer function from the turbine to the offshore converter module is determined based on the offshore wind power transmission system;

[0079] The first contribution current of the second voltage to the short-circuit fault is determined by multiplying the second voltage with the transfer function.

[0080] Based on network analysis, the second contribution current of the reference current to the short-circuit fault is determined (as can be seen from step S204, during fault ride-through, the unit's q-axis reference current and d-axis reference current usually change. The transfer function of the unit-side control loop can be obtained first, and then through frequency domain transformation, the frequency domain value of the unit's q-axis current is obtained by multiplying the transfer function with the frequency domain value of the q-axis current. The q-axis current is then obtained by inverse transformation of the frequency domain value of the q-axis current. Similarly, the d-axis current is obtained. The second contribution current is determined using the q-axis current and d-axis current; the specific operation process is not detailed here) and the third contribution current of the third voltage to the short-circuit fault are also determined.

[0081] The short-circuit current at the fault point of the offshore wind farm unit is determined by superimposing the first, second, and third contributing currents.

[0082] In summary, the passive network components, consisting of offshore wind farm turbine section filters, offshore booster modules, power transmission modules, offshore converter modules, and onshore converter modules, can obtain the second voltage and second current by analyzing the transient response characteristics of the passive network components. Combined with the fault ride-through strategy, the reference current and third voltage are obtained. Then, based on the current contribution of the second point voltage, reference current, and third voltage to the short-circuit fault, the short-circuit current at the fault point of the offshore wind farm turbine is determined, which greatly improves the accuracy of short-circuit current calculation.

[0083] Figure 5 This is a schematic diagram of a short-circuit current calculation device for an offshore wind farm turbine provided in an embodiment of this application. Figure 5 As shown, this offshore wind farm turbine short-circuit current calculation device is applicable to offshore wind power transmission systems. The offshore wind power transmission system includes: at least one turbine, an offshore booster module, an offshore converter module, a power transmission module, a land-based converter module, and a land-based power grid. The offshore booster module is connected to the turbine; the offshore converter module is connected to the offshore booster module; the power transmission module is connected to the offshore converter module; the land-based converter module is connected to the power transmission module; and the land-based power grid is connected to the land-based converter module. The offshore wind farm turbine short-circuit current calculation device includes:

[0084] The first acquisition module is used to determine the first current and first voltage of each unit based on the power flow state before a short-circuit fault occurs in the offshore wind farm.

[0085] The second acquisition module is used to acquire the second voltage output by each unit and the second current output by the offshore converter module after a short circuit fault occurs in the offshore wind farm.

[0086] The third acquisition module determines the reference current of each unit after a short-circuit fault occurs based on the unit fault ride-through control strategy, the first current, and the second voltage; and determines the third voltage output by the offshore converter module based on the offshore converter module fault ride-through control strategy, the first voltage, and the second current.

[0087] The fourth acquisition module is used to determine the short-circuit current at the fault point of the offshore wind farm unit based on the contribution of the second voltage, the reference current, and the third voltage to the short-circuit fault current.

[0088] Figure 6 This is a block diagram of an electronic device according to an exemplary embodiment. Figure 6 The electronic device shown is merely an example and should not impose any limitation on the functionality and scope of use of the embodiments of this application.

[0089] like Figure 6As shown, the electronic device 600 includes a processor 601, which can perform various appropriate actions and processes according to a program stored in a read-only memory (ROM) 602 or a program loaded from memory 606 into a random access memory (RAM) 603. The RAM 603 also stores various programs and data required for the operation of the electronic device 600. The processor 601, ROM 602, and RAM 603 are interconnected via a bus 604. An input / output (I / O) interface 605 is also connected to the bus 604.

[0090] The following components are connected to I / O interface 605: memory 606 including hard disk; and communication section 607 including network interface card such as LAN (Local Area Network) card, modem, etc., which performs communication processing via a network such as the Internet; and driver 608 is also connected to I / O interface 605 as needed.

[0091] Specifically, according to embodiments of this application, the processes described above with reference to the flowcharts can be implemented as computer software programs. For example, embodiments of this application include a computer program carried on a computer-readable medium, the computer program containing program code for performing the methods shown in the flowcharts. In such embodiments, the computer program can be downloaded and installed from a network via communication section 607. When the computer program is executed by processor 601, it performs the functions defined in the methods of this application.

[0092] In an exemplary embodiment, a storage medium including instructions is also provided, such as a memory including instructions, which can be executed by a processor 601 of an electronic device 600 to perform the above-described method. Optionally, the storage medium may be a non-transitory computer-readable storage medium, such as a ROM, random access memory (RAM), CD-ROM, magnetic tape, floppy disk, and optical data storage device.

[0093] In this application, a computer-readable storage medium can be any tangible medium containing or storing a program that can be used by or in connection with an instruction execution system, apparatus, or device. In this application, a computer-readable signal medium can include a data signal propagated in baseband or as part of a carrier wave, carrying computer-readable program code. Such propagated data signals can take various forms, including but not limited to electromagnetic signals, optical signals, or any suitable combination thereof. A computer-readable signal medium can also be any computer-readable medium other than a computer-readable storage medium, which can transmit, propagate, or transmit a program for use by or in connection with an instruction execution system, apparatus, or device. The program code contained on the computer-readable medium can be transmitted using any suitable medium, including but not limited to: wireless, wireline, optical fiber, RF, etc., or any suitable combination thereof.

[0094] Figure 7 This is a structural block diagram of an electronic device according to an exemplary embodiment. Figure 7 The electronic device shown is merely an example and should not be construed as limiting the functionality and scope of the embodiments of this application. Figure 7 As shown, the electronic device 700 includes a processor 701 and a memory 702. The memory 702 is used to store program code, and the processor 701 is connected to the memory 702 to read program code from the memory 702 to implement the short-circuit current calculation method for offshore wind farm units in the above embodiments.

[0095] Alternatively, the number of processors 701 can be one or more.

[0096] Optionally, the electronic device may also include an interface 703, and there may be multiple interfaces 703. The interface 703 can be connected to an application and can receive data from external devices such as sensors.

[0097] Other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein. The specification and examples are to be considered exemplary only, and the true scope and spirit of this application are indicated by the following claims.

[0098] It should be understood that this application is not limited to the precise structure described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of this application is limited only by the appended claims.

Claims

1. A method for calculating short-circuit current of offshore wind farm units, characterized in that: Applicable to an offshore wind power transmission system, the offshore wind power transmission system comprises: at least one unit, an offshore boost module, an offshore converter module, an electric energy transmission module, a land converter module and a land power grid, wherein the offshore boost module is connected to the unit; the offshore converter module is connected to the offshore boost module; the electric energy transmission module is connected to the offshore converter module; the land converter module is connected to the electric energy transmission module; the land power grid is connected to the land converter module; the offshore wind farm unit short-circuit current calculation method comprises: Determine the first current and the first voltage of each unit according to the power flow state before the short circuit fault occurs in the offshore wind farm; Obtaining a second voltage output by each unit and a second current at the fault location after a short circuit fault occurs in the offshore wind farm; Determine a reference current of each unit after a short circuit fault occurs according to a unit fault ride-through control strategy, the first current and the second voltage; determine a third voltage output by the offshore converter module according to the offshore converter module fault ride-through control strategy, the first voltage and the second current; The short-circuit current of the fault point of the offshore wind farm unit is determined according to the current contribution of the second voltage, the reference current and the third voltage to the short-circuit fault.

2. The method according to claim 1, characterized in that The determining of the first current and the first voltage of each unit according to the current state before the short circuit fault occurs in the offshore wind farm includes: According to the wind conditions of the offshore wind farm and the tidal current status of the sea area surrounding the offshore wind farm, the output voltage and output current of each unit are obtained in real time; According to the output voltage and the output current, the first current and the first voltage related to the power flow state before a short circuit fault occurs in the offshore wind farm are recorded.

3. The method according to claim 1 or 2, characterized in that: The obtaining of the second voltage output by each unit and the second current output by the offshore converter module after a short circuit fault occurs in the offshore wind farm includes: Acquire a multi-port network corresponding to the offshore wind power transmission system; Based on the multi-port network, a second voltage output by each unit and a second current output by the offshore converter module are obtained after a short circuit fault occurs in the offshore wind farm.

4. The method according to claim 3, characterized in that The obtaining of a multi-port network corresponding to the offshore wind power transmission system comprises: Acquiring basic data of each unit in the offshore wind power transmission system; Establishing a unit model according to the electrical characteristics and basic data of each unit; Establishing a power collection system model according to the electric energy generated by each of the units and the transmission path of the electric energy; Based on the simplification and aggregation operations on the unit model and the power collection system model, the multi-port network is obtained.

5. The method according to claim 3, characterized in that: The method of obtaining, based on the multi-port network, a second voltage output by each unit and a second current output by the offshore converter module after a short circuit fault occurs in the offshore wind farm, comprises: According to the multi-port network, obtaining the ground impedance corresponding to each unit; The second voltage output by each unit and the second current output by the offshore converter module after a short circuit fault occurs are determined based on the grounding impedance.

6. The method according to claim 1, characterized in that The determining, according to the unit fault ride-through control strategy, the first current and the second voltage, a reference current of each unit after a short circuit fault occurs, comprises: According to the unit fault ride-through control strategy, determine the unit's fault ride-through reactive current coefficient, the first current threshold of the offshore boost module in a short-circuit fault, and the voltage threshold set by the unit; Based on the comparison operation between the second voltage and the voltage threshold, determining the q-axis reference current of the unit during the short-circuit fault process, wherein if the second voltage ≥ the voltage threshold, the q-axis reference current is equal to the q-axis component of the first current; If the second voltage is less than the voltage threshold, obtaining a first difference according to a subtraction operation of the voltage threshold and the second voltage; determining a q-axis reference current based on a product operation of the first difference, the fault ride-through reactive current coefficient and the rated current of the unit; Obtaining a first intermediate variable according to an arithmetic square root operation of a q-axis reference current and a d-axis component of the first current; Based on the comparison operation between the first intermediate variable and the first current threshold, the d-axis reference current of the unit during the short-circuit fault process is determined, wherein if the first intermediate variable is less than or equal to the first current threshold, the d-axis reference current is equal to the d-axis component of the first current; if the first intermediate variable is greater than or equal to the first current threshold, the d-axis reference current is equal to (the first current threshold 2 -q-axis reference current 2 ) 1 / 2 ; According to the superposition operation of the q-axis reference current and the d-axis reference current, the reference current of each unit after a short circuit fault occurs is determined.

7. The method according to claim 1, characterized in that The determining, according to the fault ride-through control strategy of the offshore converter module, the first voltage and the second current, a third voltage output by the offshore converter module comprises: According to the fault ride-through control strategy of the offshore converter module, a second current threshold of the offshore converter module in a short circuit fault and a voltage regulation coefficient of the offshore converter module are determined; based on a comparison operation between the second current and the second current threshold, a third voltage output by the offshore converter module is determined, wherein if the second current ≤ the second current threshold, the third voltage is equal to the first voltage; If the second current is greater than the second current threshold, a second difference is obtained based on a subtraction operation between the second current and the second current threshold; a second intermediate variable is obtained based on a multiplication operation between the second difference and the voltage adjustment coefficient; and the third voltage is obtained based on a subtraction operation between the first voltage and the second intermediate variable.

8. The method according to claim 1, characterized in that: include: The determining the short-circuit current of the fault point of the offshore wind farm unit according to the second voltage, the reference current and the third voltage to the current contribution of the short-circuit fault includes: According to the offshore wind power transmission system, determining a transfer function between the unit and the offshore converter module; Determine a first contribution current of the second voltage to a short circuit fault according to a multiplication operation of the second voltage and the transfer function; Based on the network analysis operation, determining a second contribution current of the reference current to the short circuit fault and a third contribution current of the third voltage to the short circuit fault; The short-circuit current of the fault point of the offshore wind farm unit is determined according to the superposition operation of the first contribution current, the second contribution current and the third contribution current.

9. A short-circuit current calculation device for offshore wind farm units, characterized in that: Applicable to an offshore wind power transmission system, the offshore wind power transmission system comprises: at least one unit, an offshore boost module, an offshore converter module, an electric energy transmission module, a land converter module and a land power grid, wherein the offshore boost module is connected to the unit; the offshore converter module is connected to the offshore boost module; the electric energy transmission module is connected to the offshore converter module; the land converter module is connected to the electric energy transmission module; the land power grid is connected to the land converter module; the offshore wind farm unit short-circuit current calculation device comprises: A first acquisition module, the first acquisition module is used to determine the first current and the first voltage of each unit according to the power flow state before the short circuit fault occurs in the offshore wind farm; A second acquisition module, the second acquisition module is used to obtain a second voltage output by each unit and a second current output by the offshore converter module after a short circuit fault occurs in the offshore wind farm; a third acquisition module, wherein the third acquisition module determines a reference current of each unit after a short circuit fault occurs according to a unit fault ride-through control strategy, the first current, and the second voltage; and determines a third voltage output by the offshore converter module according to the offshore converter module fault ride-through control strategy, the first voltage, and the second current; A fourth acquisition module, the fourth acquisition module is used to determine the short-circuit current of the fault point of the offshore wind farm unit according to the second voltage, the reference current and the third voltage's current contribution to the short-circuit fault.

10. An electronic device, characterized in that: include: processor; a memory for storing instructions executable by the processor; The processor is configured to execute the instructions to implement the method according to any one of claims 1 to 8.

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