Capacity calculation method and device of active power filter, equipment and storage medium

Abstract

The invention discloses a capacity calculation method, device and equipment of an active power filter and a storage medium, and relates to the technical field of power harmonic compensation. Background harmonic voltage historical data, grid structure information, main equipment parameters and operation mode information of a land power grid are acquired; according to the grid structure information, the main equipment parameters and the operation mode information, calculating the equivalent impedance of the onshore power grid in offshore wind power access; according to the impedance of the offshore wind power system and the equivalent impedance, determining the harmonic frequency with the harmonic amplification risk in the background harmonic voltage historical data; calculating an equivalent harmonic current according to the equivalent impedance and the background harmonic voltage historical data corresponding to the harmonic frequency; the compensation capacity of the active power filter is calculated according to the equivalent harmonic current, accurate calculation of the APF compensation capacity is completed, and the economical efficiency of APF capacity configuration is improved.

Description

Technical Field

[0001] This application relates to the technical field of power harmonic compensation, and in particular to a method, apparatus, device and storage medium for calculating the capacity of an active power filter. Background Technology

[0002] An Active Power Filter (APF), as a highly efficient dynamic harmonic compensation device, functions by real-time detection and injection of a compensation current equal in magnitude but opposite in phase to the harmonic current, thereby purifying the power quality of the grid. For conventional industrial nonlinear loads (such as rectifiers and frequency converters), their harmonic spectra are relatively fixed and easy to measure. Therefore, the capacity design of the APF can be directly based on the effective value of the harmonic current of the object to be compensated, a straightforward and mature method. However, in the specific scenario where offshore wind power is connected to the onshore grid via AC submarine cables, determining the capacity of the APF faces unprecedented challenges. Offshore wind power systems typically include tens or even hundreds of kilometers of submarine cables, whose capacitance to ground per unit length is much greater than that of onshore overhead lines. This concentrated capacitive reactive power causes offshore wind power systems to exhibit low impedance or even resonant characteristics at specific harmonic frequencies. When the onshore grid itself has inherent background harmonic voltages (mainly from a large number of nonlinear loads in the grid), these background harmonic voltages act on the parallel circuit formed by the "offshore wind power system impedance" and the "onshore grid impedance," potentially causing severe harmonic voltage and current amplification near the resonance point. At this time, the amplitude of the harmonic current flowing into the offshore wind power access point may be several times or even tens of times that of the current generated by the original background harmonic source of the onshore power grid.

[0003] To suppress such harmonic amplification, an APF (Advanced Harmonic Filter) is typically connected in parallel at the onshore connection point of offshore wind power. The current common approach to capacity design is to directly measure the effective value of the total harmonic current at the connection point after wind power grid connection, when harmonic amplification occurs, and calculate the required compensation current for the APF accordingly. However, this method has a fundamental flaw: the current that the APF actually needs to compensate for in order to suppress amplification is essentially the "source" that triggers this amplification phenomenon, namely the equivalent background harmonic current of the onshore power grid, which is much smaller than the amplified harmonic current at the connection point. Designing based on the latter will lead to a severe overestimation of the APF capacity, resulting in huge waste of equipment investment and space. Theoretically, if the distribution, content, and changes of all harmonic sources within the onshore power grid with varying operating modes can be accurately determined, the equivalent background harmonic current can be accurately calculated. However, in actual large-scale power grids, the number of harmonic sources is enormous, their distribution is widespread, and their time-varying characteristics are extremely strong, making it virtually impossible to obtain complete information on them in engineering practice. Changes in the operation mode, grid structure, and switching status of reactive power compensation equipment can significantly alter the transmission path of harmonics from the source to the access point and the system harmonic impedance, making it difficult to directly measure and stably assess background harmonic currents.

[0004] Therefore, determining the APF capacity for suppressing harmonic amplification in offshore wind power when accurate information about harmonic sources within the power grid is unavailable is a problem that urgently needs to be solved. Summary of the Invention

[0005] The main objective of this application is to provide a method, apparatus, device, and storage medium for calculating the capacity of an active power filter (APF), aiming to solve the technical problem of determining the APF capacity for suppressing harmonic amplification in offshore wind power when it is impossible to accurately obtain information on harmonic sources within the power grid.

[0006] To achieve the above objectives, this application proposes a method for calculating the capacity of an active power filter, the method comprising:

[0007] Acquire historical data on background harmonic voltages, grid structure information, main equipment parameters, and operating mode information of the onshore power grid; The equivalent impedance of the onshore power grid at offshore wind power access is calculated based on the grid structure information, the main equipment parameters, and the operation mode information. The harmonic order with harmonic amplification risk in the historical background harmonic voltage data is determined based on the impedance of the offshore wind power system and the equivalent impedance. The equivalent harmonic current is calculated based on the historical background harmonic voltage data corresponding to the equivalent impedance and the harmonic order. The compensation capacity of the active power filter is calculated based on the equivalent harmonic current.

[0008] In one embodiment, the step of calculating the equivalent impedance of the onshore power grid for offshore wind power integration based on the grid structure information, the main equipment parameters, and the operating mode information includes: The conventional operating mode of the onshore power grid is determined based on the aforementioned operating mode information; For each of the aforementioned conventional operating modes, the short-circuit capacity of the offshore wind power access point when offshore wind power is not connected is calculated based on the grid structure information and the main equipment parameters. The corresponding current equivalent impedance is calculated based on the short-circuit capacity, and the minimum value among the current equivalent impedances is selected as the equivalent impedance of the onshore power grid.

[0009] In one embodiment, the step of determining the harmonic order with harmonic amplification risk in the historical background harmonic voltage data based on the impedance of the offshore wind power system and the equivalent impedance includes: Impedance analysis is performed based on the impedance of the offshore wind power system and the equivalent impedance to obtain the resonant frequency when there is a risk of harmonic amplification. The range of resonant frequencies in which electrical resonance occurs is determined based on the resonant frequency. Based on the resonant frequency range, the historical data of the background harmonic voltage are filtered to obtain the harmonic numbers that pose a risk of harmonic amplification.

[0010] In one embodiment, the step of performing impedance analysis based on the impedance of the offshore wind power system and the equivalent impedance to obtain the resonant frequency when there is a risk of harmonic amplification includes: Obtain submarine cable parameters characterizing the power collection system and high-voltage transmission section of an offshore wind farm; An impedance model of the offshore wind power system with the equivalent impedance as the boundary is constructed based on the submarine cable parameters. The resonant frequency at which harmonic amplification risk is determined based on the impedance model of the offshore wind power system and the total impedance frequency characteristics after the equivalent impedance is connected in parallel.

[0011] In one embodiment, the step of calculating the equivalent harmonic current based on the historical background harmonic voltage data corresponding to the equivalent impedance and the harmonic order includes: The maximum harmonic voltage value corresponding to the harmonic number is extracted from the historical background harmonic voltage data based on the harmonic number. The harmonic impedance is determined based on the minimum value of the equivalent impedance and the harmonic order. The equivalent harmonic current is calculated based on the maximum harmonic voltage and the harmonic impedance.

[0012] In one embodiment, the step of calculating the compensation capacity of the active power filter based on the equivalent harmonic current includes: Perform a square root operation on the equivalent harmonic current to obtain the effective value of the harmonic current; The target compensation capacity is calculated based on the preset rated voltage of the offshore wind power access point and the effective value of the harmonic current. The target compensation capacity is corrected according to the preset margin coefficient to obtain the compensation capacity of the active power filter.

[0013] In one embodiment, the step of acquiring historical background harmonic voltage data, grid structure information, main equipment parameters, and operating mode information of the onshore power grid includes: The harmonic voltage content of the onshore power grid at the offshore wind power access point is obtained within a preset time period when the offshore wind power system is not connected, and the harmonic voltage content is used as historical background harmonic voltage data. Obtain the grid topology connection information and the connection relationship of networks at different voltage levels near the offshore wind power access point, and use the connection relationship as the grid structure information; Obtain the parameters of the main transformer, reactor, and rated capacity of the compensation equipment near the offshore wind power access point, and use the main transformer parameters, reactor parameters, and rated capacity as the main equipment parameters; The system acquires the switching status and routine operation mode of the main equipment near the offshore wind power access point, and uses the switching status and routine operation mode as operation mode information.

[0014] Furthermore, to achieve the above objectives, this application also proposes a capacity calculation device for an active power filter, the device comprising: The data acquisition module is used to acquire historical background harmonic voltage data, grid structure information, main equipment parameters, and operating mode information of the onshore power grid; The impedance calculation module is used to calculate the equivalent impedance of the onshore power grid when connected to offshore wind power based on the grid structure information, the main equipment parameters, and the operation mode information. The risk assessment module is used to determine the harmonic order in the historical background harmonic voltage data that has the risk of harmonic amplification based on the impedance of the offshore wind power system and the equivalent impedance. The harmonic current calculation module is used to calculate the equivalent harmonic current based on the historical data of the background harmonic voltage corresponding to the equivalent impedance and the harmonic order. The capacity calculation module is used to calculate the compensation capacity of the active power filter based on the equivalent harmonic current.

[0015] In addition, to achieve the above objectives, this application also proposes a capacity calculation device for an active power filter, the device comprising: a memory, a processor, and a computer program stored in the memory and executable on the processor, the computer program being configured to implement the steps of the capacity calculation method for the active power filter as described above.

[0016] In addition, to achieve the above objectives, this application also proposes a storage medium, which is a computer-readable storage medium, on which a computer program is stored, and when the computer program is executed by a processor, it implements the steps of the capacity calculation method for the active power filter as described above.

[0017] In addition, to achieve the above objectives, this application also provides a computer program product, which includes a computer program that, when executed by a processor, implements the steps of the active power filter capacity calculation method described above.

[0018] This application provides a method for calculating the capacity of an active power filter (APF). The method includes: acquiring historical background harmonic voltage data, grid structure information, main equipment parameters, and operating mode information of an onshore power grid; calculating the equivalent impedance of the onshore power grid at offshore wind power access based on the grid structure information, main equipment parameters, and operating mode information; determining the harmonic order with harmonic amplification risk in the historical background harmonic voltage data based on the offshore wind power system impedance and the equivalent impedance; calculating the equivalent harmonic current based on the historical background harmonic voltage data corresponding to the equivalent impedance and the harmonic order; and calculating the compensation capacity of the APF based on the equivalent harmonic current. In summary, this application indirectly calculates the equivalent harmonic current based on historical data of the onshore power grid, rather than directly using the amplified harmonic current at the offshore wind power access point. This achieves accurate calculation of the APF compensation capacity, solves the technical problem that existing methods cannot directly measure the background harmonics within the power grid, and improves the accuracy and economy of APF capacity configuration. Attached Figure Description

[0019] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0020] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 A flowchart illustrating the first embodiment of the capacity calculation method for the active power filter of this application; Figure 2 This is a schematic diagram illustrating the connection relationship between offshore wind power and onshore power grid system in one embodiment of the active power filter capacity calculation method of this application; Figure 3 This is a flowchart illustrating the second embodiment of the capacity calculation method for the active power filter of this application. Figure 4 This is an evaluation diagram of harmonic amplification at the offshore wind power access point in one embodiment of the capacity calculation method for the active power filter of this application. Figure 5 This is a schematic diagram showing the comparison of harmonic voltage compensation before and after at the offshore wind power access point in one embodiment of the active power filter capacity calculation method of this application. Figure 6 This is a harmonic voltage waveform diagram of an offshore wind power access point without APF compensation in one embodiment of the active power filter capacity calculation method of this application. Figure 7 The diagram shows the harmonic voltage waveform at the offshore wind power access point with APF compensation in one embodiment of the active power filter capacity calculation method of this application. Figure 8 This is a schematic diagram of the module structure of the capacity calculation device for the active power filter according to an embodiment of this application; Figure 9 This is a schematic diagram of the hardware operating environment involved in the capacity calculation method of the active power filter in this application embodiment.

[0022] The purpose, features, and advantages of this application will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0023] It should be understood that the specific embodiments described herein are merely illustrative of the technical solutions of this application and are not intended to limit this application.

[0024] To better understand the technical solution of this application, a detailed description will be provided below in conjunction with the accompanying drawings and specific implementation methods.

[0025] The main solution of this application embodiment is as follows: acquiring historical background harmonic voltage data, grid structure information, main equipment parameters, and operating mode information of the onshore power grid; calculating the equivalent impedance of the onshore power grid for offshore wind power access based on the grid structure information, the main equipment parameters, and the operating mode information; determining the harmonic order with harmonic amplification risk in the historical background harmonic voltage data based on the offshore wind power system impedance and the equivalent impedance; calculating the equivalent harmonic current based on the historical background harmonic voltage data corresponding to the equivalent impedance and the harmonic order; and calculating the compensation capacity of the active power filter based on the equivalent harmonic current.

[0026] An Active Power Filter (APF), as a highly efficient dynamic harmonic compensation device, functions by detecting and injecting a compensation current equal in magnitude but opposite in phase to the harmonic current in real time, thereby purifying the power quality of the grid. For conventional industrial nonlinear loads (such as rectifiers and frequency converters), their harmonic spectra are relatively fixed and easy to measure. Therefore, the capacity design of the APF can be directly based on the effective value of the harmonic current of the object to be compensated, a straightforward and mature method. However, in the specific scenario where offshore wind power is connected to the onshore grid via AC submarine cables, determining the capacity of the APF faces unprecedented challenges. Offshore wind power systems typically include tens or even hundreds of kilometers of submarine cables, whose capacitance to ground per unit length is much greater than that of onshore overhead lines. This concentrated capacitive reactive power causes offshore wind power systems to exhibit low impedance or even resonant characteristics at specific harmonic frequencies. When the onshore grid itself has inherent background harmonic voltages (mainly from a large number of nonlinear loads in the grid), these background harmonic voltages act on the parallel circuit formed by the impedance of the offshore wind power system and the impedance of the onshore grid, potentially causing severe harmonic voltage and current amplification near the resonance point. At this time, the amplitude of the harmonic current flowing into the offshore wind power access point may be several times or even tens of times that of the current generated by the original background harmonic source of the onshore power grid.

[0027] To suppress such harmonic amplification, an APF (Advanced Harmonic Filter) is typically connected in parallel at the onshore connection point of offshore wind power. The current common approach to capacity design is to directly measure the effective value of the total harmonic current at the connection point after wind power grid connection, when harmonic amplification occurs, and calculate the required compensation current for the APF accordingly. However, this method has a fundamental flaw: the current that the APF actually needs to compensate for in order to suppress amplification is essentially the "source" that triggers this amplification phenomenon, namely the equivalent background harmonic current of the onshore power grid, which is much smaller than the amplified harmonic current at the connection point. Designing based on the latter will lead to a severe overestimation of the APF capacity, resulting in huge waste of equipment investment and space. Theoretically, if the distribution, content, and changes of all harmonic sources within the onshore power grid with varying operating modes can be accurately determined, the equivalent background harmonic current can be accurately calculated. However, in actual large-scale power grids, the number of harmonic sources is enormous, their distribution is widespread, and their time-varying characteristics are extremely strong, making it virtually impossible to obtain complete information on them in engineering practice. Changes in the power grid's operation mode, grid structure, and the switching status of reactive power compensation equipment can significantly alter the transmission path of harmonics from their sources to the connection point and the system's harmonic impedance, making it difficult to directly measure and stably assess background harmonic currents. Therefore, determining the APF capacity for suppressing harmonic amplification from offshore wind power, without accurately obtaining information on harmonic sources within the power grid, is a pressing issue that needs to be addressed.

[0028] It should be noted that the executing entity in this embodiment can be an active power filter capacity calculation system, a computing service device with data processing, network communication, and program execution functions, or an electronic device capable of realizing the aforementioned active power filter capacity calculation function, etc. This embodiment does not specifically limit it in this way. The following uses an active power filter capacity calculation system as an example to describe this embodiment and the following embodiments.

[0029] Based on this, embodiments of this application provide a method for calculating the capacity of an active power filter, referring to... Figure 1 , Figure 1 This is a flowchart illustrating the first embodiment of the active power filter capacity calculation method of this application.

[0030] In this embodiment, the capacity calculation method for the active power filter includes steps S10 to S50: Step S10: Obtain historical data of background harmonic voltage, grid structure information, main equipment parameters, and operating mode information of the onshore power grid.

[0031] It should be noted that, as Figure 2 As shown, the overall structure of offshore wind power integration into the onshore power grid includes the offshore wind farm, the onshore power grid, and a parallel-connected APF (Automatic Power Filter) for suppressing harmonics at the connection point. For the onshore power grid to which the offshore wind power system is to be integrated, the system will acquire basic data for subsequent harmonic amplification assessment and APF capacity calculation through data acquisition and monitoring. This includes historical background harmonic voltage data reflecting the harmonic characteristics of the power grid, grid structure information reflecting the grid topology, main equipment parameters reflecting the characteristics of major electrical equipment, and operating mode information reflecting the grid's operating status.

[0032] In one feasible implementation, step S10 specifically includes: Step S101: Obtain the harmonic voltage content of the onshore power grid at the offshore wind power access point within a preset time period when the offshore wind power system is not connected, and use the harmonic voltage content as historical background harmonic voltage data.

[0033] It should be noted that the harmonic voltage content refers to the effective value or content rate of each harmonic (usually referring to the 2nd to 50th harmonics) obtained through Fourier transform decomposition. It is typically expressed as a percentage of the fundamental voltage's effective value, reflecting the degree of harmonic pollution in the power grid. Background harmonic voltage historical data refers to the historical data of harmonic voltage content measured at the offshore wind power connection point by the onshore power grid when the offshore wind power system is not yet connected. For onshore power grids awaiting connection to offshore wind power systems, harmonic voltage data is collected within a preset time period (preferably one year or several years) using power quality monitoring devices installed at the offshore wind power connection point. Monitoring records of the harmonic voltage content within this preset time period are extracted and stored as historical background harmonic voltage data. By collecting historical data over a longer period, the harmonic voltage characteristics of the onshore power grid under different seasons, load levels, and operating conditions can be covered.

[0034] Step S102: Obtain the grid topology connection structure information and the connection relationship of networks at different voltage levels near the offshore wind power access point, and use the connection relationship as the grid structure information.

[0035] It should be noted that for onshore power grid areas near offshore wind power access points, the system will extract the power grid topology connection structure information of the area from the power grid dispatch management system or power grid planning database. This topology connection structure information includes the physical connection relationship of transmission lines, the electrical main wiring method of substations, the connection relationship of busbars, etc. At the same time, it will extract the transformer connection relationship and electromagnetic coupling relationship between networks of different voltage levels, and integrate the above information as the grid structure information.

[0036] Additionally, it should be noted that power grid topology connection information refers to structured data describing the physical connection relationships between various electrical components (such as buses, lines, transformers, circuit breakers, etc.) in the power grid. It is usually represented in the form of node-branch, reflecting the physical structure and electrical connection relationships of the power grid. The connection relationship between networks of different voltage levels refers to the electrical connection established between power grids of different voltage levels through transformers, including parameters such as transformer connection group, turns ratio, and impedance voltage. This connection relationship determines the transmission and transformation characteristics of harmonics between different voltage levels.

[0037] Step S103: Obtain the parameters of the main transformer, reactor, and rated capacity of the compensation equipment near the offshore wind power access point, and use the main transformer parameters, reactor parameters, and rated capacity as the main equipment parameters.

[0038] It should be noted that for onshore power grid areas near offshore wind power access points, the system will extract the parameters of the main transformers (including rated capacity, rated voltage, short-circuit impedance percentage, no-load loss, load loss, connection group, etc.), reactor parameters (including rated capacity, rated voltage, rated reactance, reactance rate, quality factor, etc.), and the rated capacity and compensation characteristic parameters of compensation equipment (such as parallel capacitors, static var compensators, etc.) from the power grid equipment management system or power grid planning data, and integrate the above parameters as the main equipment parameters.

[0039] Step S104: Obtain the switching status and routine operation mode of the main equipment near the offshore wind power access point, and use the switching status and routine operation mode as operation mode information.

[0040] It should be noted that the switching status refers to the opening and closing status of switching equipment (such as circuit breakers and disconnectors), which determines whether electrical equipment is put into operation or taken out of operation. Different switching combinations of equipment form different power grid topologies. The normal operation mode refers to the equipment switching status and system operation conditions that frequently occur in the daily dispatch and operation of the power grid. It is usually divided into maximum operation mode, minimum operation mode and normal (average) operation mode according to factors such as system load level, power output, and maintenance schedule. The equivalent impedance of the power grid under different operation modes is significantly different, which has an important impact on harmonic amplification characteristics.

[0041] Specifically, for the onshore power grid area near the offshore wind power access point, the system extracts the switching status records of the main equipment (including main transformers, high-voltage reactors, low-voltage reactors, parallel capacitor banks, static var compensators, etc.) in this area from the power grid dispatch and operation management system. It analyzes and organizes the routine operating modes in daily operation, including the maximum operating mode (the operating mode with the tightest system interconnection and the largest short-circuit capacity), the minimum operating mode (the operating mode with the weakest system interconnection and the smallest short-circuit capacity), and typical operating modes in between. These switching statuses and routine operating modes are used as operating mode information. It is understandable that by obtaining multiple typical operating modes, the harmonic amplification risk under different operating conditions can be assessed, ensuring that the APF capacity design can adapt to the most unfavorable operating conditions of the power grid.

[0042] Step S20: Calculate the equivalent impedance of the onshore power grid when connected to offshore wind power based on the grid structure information, the main equipment parameters, and the operation mode information.

[0043] It should be noted that, based on the acquired grid structure information, main equipment parameters, and operating mode information, the system will use power system analysis software to establish a mathematical model of the onshore power grid, calculate the short-circuit capacity of the offshore wind power access point under different operating modes, and convert the short-circuit capacity to obtain the corresponding equivalent impedance. Finally, the minimum value of the equivalent impedance under each operating mode will be selected as the basis for subsequent APF capacity calculation.

[0044] Additionally, it should be noted that the equivalent impedance of the onshore power grid at the offshore wind power connection point refers to the part of the onshore power grid outside the offshore wind power connection point being equivalent to a series resistor and reactance (usually mainly reactance). This equivalent impedance reflects the impedance characteristics of the onshore power grid under a specific operating mode and is a key parameter for calculating harmonic voltage distribution and assessing the risk of harmonic amplification. The smaller the equivalent impedance, the larger the system short-circuit capacity, and the easier it is for harmonic current to flow into the system.

[0045] In one feasible implementation, step S20 specifically includes: Step S201: Determine the conventional operation mode of the onshore power grid based on the operation mode information.

[0046] It should be noted that in this step, the system performs statistical analysis on the acquired operating mode information, identifies frequently occurring typical operating conditions, and selects representative conventional operating modes. Preferably, the maximum operating mode (corresponding to the condition with the strongest system connectivity and the largest short-circuit capacity), the minimum operating mode (corresponding to the condition with the weakest system connectivity and the smallest short-circuit capacity), and the average operating mode (corresponding to the general operating condition of the system under normal operation) are selected as the conventional operating modes for subsequent calculations. By selecting multiple typical operating modes, the harmonic amplification characteristics under different system intensities can be comprehensively evaluated, ensuring that the APF capacity design can still meet the requirements for suppressing harmonic amplification under the most unfavorable operating conditions.

[0047] Additionally, it should be noted that the maximum operating mode (i.e., operating mode 1) refers to the operating mode in which the short-circuit capacity at the offshore wind power access point is the largest and the equivalent impedance of the system is the smallest. It typically corresponds to the operating condition where all main transformers are operating in parallel, all interconnecting lines are in operation, and the system is most interconnected. The minimum operating mode (operating mode 2) refers to the operating mode in which the short-circuit capacity at the offshore wind power access point is the smallest and the equivalent impedance of the system is the largest. It typically corresponds to the operating condition in which some main transformers are out of operation, some interconnecting lines are under maintenance, and the system is least interconnected. The average operating mode (operating mode 3) refers to the typical operating condition between the maximum and minimum operating modes, reflecting the average characteristics of the power grid under normal operating conditions.

[0048] Step S202: For each of the conventional operating modes, calculate the short-circuit capacity of the offshore wind power access point when the offshore wind power is not connected, based on the grid structure information and the main equipment parameters.

[0049] It should be noted that for each defined conventional operating mode, based on the equipment switching status corresponding to that operating mode, combined with the grid structure information and main equipment parameters, a power grid model under that operating mode is established using power system analysis software. A short-circuit fault (three-phase short circuit) is set at the offshore wind power access point, the short-circuit current at that point is calculated, and the short-circuit capacity of the offshore wind power access point is calculated based on the short-circuit current and rated voltage.

[0050] Step S203: Calculate the corresponding current equivalent impedance based on the short-circuit capacity, and select the minimum value among the current equivalent impedances as the equivalent impedance of the onshore power grid.

[0051] It should be noted that in this step, for each calculated short-circuit capacity under normal operating conditions, the system calculates the corresponding current equivalent impedance, as shown in Formula 1: (Formula 1) in, This refers to the rated voltage (line voltage) at the offshore wind power connection point. This represents the short-circuit capacity. The current equivalent impedance under various conventional operating modes is compared, and the minimum value is selected as the equivalent impedance of the onshore power grid for subsequent calculations. It can be understood that the minimum equivalent impedance refers to the smallest among the current equivalent impedances calculated under multiple conventional operating modes. This corresponds to the operating mode with the strongest system interconnection and the largest short-circuit capacity. Under this mode, the equivalent harmonic current generated by the same harmonic voltage is the largest, representing the most unfavorable operating condition for designing the APF capacity. Under this condition, the equivalent harmonic source current of the onshore power grid is the largest, and it is necessary to ensure that the APF capacity designed according to this condition has sufficient compensation capability.

[0052] Step S30: Determine the harmonic order in the historical background harmonic voltage data that has the risk of harmonic amplification based on the impedance of the offshore wind power system and the equivalent impedance.

[0053] It should be noted that the impedance of an offshore wind power system refers to the equivalent impedance from the offshore wind power access point to the offshore wind farm side, including the impedance of the offshore wind farm's collection system and the high-voltage transmission system. In this step, the system establishes an impedance analysis model of the offshore wind power system. This model considers the impedance characteristics of the offshore wind farm's collection system and the high-voltage transmission system, especially the distributed capacitance effect of long-distance AC submarine cables. The impedance of the offshore wind power system is connected in series with the equivalent impedance of the onshore power grid. The frequency response characteristics of this series impedance are analyzed to identify the frequency points where series resonance may occur and to determine the harmonic orders that pose a risk of harmonic amplification.

[0054] Understandably, the harmonic order that poses a risk of harmonic amplification refers to the harmonic order at which electrical resonance may occur at certain frequencies when an offshore wind power system is connected to the onshore power grid. This is due to the interaction between the capacitive impedance of the offshore wind power system and the inductive impedance of the onshore power grid, resulting in a significant amplification of the harmonic voltage or harmonic current at that frequency and in the vicinity. It usually corresponds to the characteristic harmonics in the mid-to-high frequency band.

[0055] Step S40: Calculate the equivalent harmonic current based on the historical background harmonic voltage data corresponding to the equivalent impedance and the harmonic order.

[0056] It should be noted that for each harmonic identified as having a harmonic amplification risk, the system extracts the historical maximum value of each harmonic voltage from the historical background harmonic voltage data, combines it with the minimum equivalent impedance, calculates the corresponding equivalent harmonic current for each harmonic, and synthesizes the equivalent harmonic currents of each harmonic into a total effective value of the equivalent harmonic current. The equivalent harmonic current refers to the effective value of the harmonic current output by the harmonic current source when the background harmonic source in the onshore power grid is equivalently represented as a harmonic current source connected at the offshore wind power access point. Physically, it represents the harmonic current injected into the offshore wind power access point by the onshore power grid under the most unfavorable operating conditions. This current differs from the harmonic current actually amplified after the offshore wind power is connected; the former is the source of harmonic amplification, while the latter is the result of harmonic amplification. The APF can effectively suppress harmonic amplification by compensating for this equivalent harmonic current.

[0057] In one feasible implementation, step S40 specifically includes: Step S401: Extract the maximum value of the harmonic voltage corresponding to the harmonic number from the historical background harmonic voltage data according to the harmonic number.

[0058] It should be noted that, as shown in Table 1, for each harmonic order with a identified risk of harmonic amplification (such as the 5th, 7th, 11th, and 13th harmonics), the system will retrieve the effective values ​​of the harmonic voltage at all measurement times within a preset time period from the acquired historical background harmonic voltage data, and then select the maximum harmonic voltage value for that harmonic order. This maximum harmonic voltage value represents the voltage level of that harmonic in the onshore power grid under the most severe harmonic pollution conditions. It serves as the basis for calculating the equivalent harmonic current under the most unfavorable conditions, ensuring that the APF capacity design can cope with the worst harmonic conditions in the power grid.

[0059] Table 1

[0060] Step S402: Determine the harmonic impedance based on the minimum value of the equivalent impedance and the harmonic order.

[0061] It should be noted that in this step, as shown in Table 2, the system uses the minimum equivalent impedance as the equivalent reactance at the fundamental frequency. Based on the relationship between the harmonic order n and the fundamental frequency, the system calculates the harmonic impedance corresponding to that harmonic order. Since the equivalent reactance at the harmonic frequency is proportional to the harmonic order, i.e. ,in Here, n is the equivalent reactance at the fundamental frequency, and n is the harmonic order. Let be the harmonic impedance at the nth harmonic frequency.

[0062] Table 2

[0063] Step S403: Calculate the equivalent harmonic current based on the maximum value of the harmonic voltage and the harmonic impedance.

[0064] It should be noted that, as shown in Table 3, for each harmonic order with a risk of harmonic amplification, the system uses the maximum value of the harmonic voltage and the impedance of that harmonic to calculate the equivalent harmonic current using Ohm's law. The calculation formula is as follows: ,in, For the nth harmonic current, It represents the maximum value of the nth harmonic voltage.

[0065] Table 3

[0066] Step S50: Calculate the compensation capacity of the active power filter based on the equivalent harmonic current.

[0067] It should be noted that in this step, the system will combine the calculated equivalent harmonic currents into a total effective value of harmonic current, and combine it with the rated voltage of the system at the offshore wind power access point to calculate the theoretical compensation capacity that the parallel APF needs to provide, and after considering a certain engineering margin (such as 20%), the final design capacity is obtained.

[0068] In one feasible implementation, step S50 specifically includes: Step S501: Perform a square root operation on the equivalent harmonic current to obtain the effective value of the harmonic current.

[0069] It should be noted that, as shown in Table 4, in this step, the system will perform square root calculations on the sum of squares of each equivalent harmonic current to calculate the effective value of the synthesized equivalent harmonic current. ,in, This represents the effective value of the harmonic current.

[0070] Table 4

[0071] Step S502: Calculate the target compensation capacity based on the preset rated voltage of the offshore wind power access point and the effective value of the harmonic current.

[0072] It should be noted that in this step, the system will calculate the target compensation capacity of the APF according to the capacity calculation formula for parallel APF. : (Formula 2) in, The preset rated voltage is 220kV in this embodiment.

[0073] Step S503: Correct the target compensation capacity according to the preset margin coefficient to obtain the compensation capacity of the active power filter.

[0074] It should be noted that in actual engineering design, to account for calculation errors, component aging, and possible slight changes in future operating conditions, a certain margin is usually reserved based on the theoretical value. (e.g., 10%~20%), thereby determining the final design value of the APF compensation capacity. Understandably, this approach avoids the capacity waste caused by directly using amplified harmonic currents, while also solving the problem of not being able to directly measure harmonic sources within the power grid, thus achieving an optimal balance between accuracy and economy.

[0075] This embodiment provides a method for calculating the capacity of an active power filter (APF). The method includes: acquiring historical background harmonic voltage data, grid structure information, main equipment parameters, and operating mode information of an onshore power grid; calculating the equivalent impedance of the onshore power grid at offshore wind power access based on the grid structure information, main equipment parameters, and operating mode information; determining the harmonic order with harmonic amplification risk in the historical background harmonic voltage data based on the offshore wind power system impedance and the equivalent impedance; calculating the equivalent harmonic current based on the historical background harmonic voltage data corresponding to the equivalent impedance and the harmonic order; and calculating the compensation capacity of the APF based on the equivalent harmonic current. In summary, this embodiment indirectly calculates the equivalent harmonic current based on historical data of the onshore power grid, rather than directly using the amplified harmonic current at the offshore wind power access point. This achieves accurate calculation of the APF compensation capacity, solves the technical problem of existing methods being unable to directly measure the background harmonics within the power grid, and improves the accuracy and economy of APF capacity configuration.

[0076] Based on the first embodiment of this application, in the second embodiment of this application, the content that is the same as or similar to that in Embodiment 1 above can be referred to the above description, and will not be repeated hereafter. Based on this, please refer to... Figure 3 , Figure 3This is a flowchart illustrating the second embodiment of the active power filter capacity calculation method of this application. Step S30 specifically includes: Step S301: Perform impedance analysis based on the impedance of the offshore wind power system and the equivalent impedance to obtain the resonant frequency when there is a risk of harmonic amplification.

[0077] It should be noted that in this step, the system will utilize the equivalent impedance of the onshore power grid, combined with the submarine cable parameters (including distributed parameters such as resistance, inductance, and capacitance of the submarine cable) of the offshore wind farm's collection system and high-voltage transmission system, to... Type equivalent circuit or multiple An impedance model of an offshore wind power system is established using an equivalent circuit. By analyzing the impedance frequency characteristic curve of this impedance model through frequency scanning, resonant frequencies with harmonic amplification risks are identified.

[0078] Understandably, the resonant frequency refers to the frequency at which, when an offshore wind power system is connected in parallel with an onshore power grid, the imaginary parts of their impedances are equal in magnitude but opposite in sign, resulting in a zero imaginary part of the total impedance. At this frequency, the system's equivalent impedance reaches its maximum value, and even a small harmonic current excitation can generate a large harmonic voltage, leading to severe harmonic amplification.

[0079] In one feasible implementation, step S301 specifically includes: Step A10: Obtain submarine cable parameters characterizing the offshore wind farm's collection system and high-voltage transmission section.

[0080] It should be noted that the main submarine cable model parameters used are shown in Table 5, including the submarine cable parameters for the offshore wind farm power collection system and the submarine cable parameters for the high-voltage transmission system. Specifically, the submarine cable parameters include the cable model specifications, length, resistance per unit length, inductance per unit length, and capacitance per unit length.

[0081] Table 5

[0082] Step A20: Construct an impedance model of the offshore wind power system with the equivalent impedance as the boundary based on the submarine cable parameters.

[0083] It should be noted that, considering the impact of wind turbines in the harmonic frequency band is far less than that of submarine cable capacitance, all wind turbines are usually ignored in the modeling, and only the submarine cable network is considered. For long-distance submarine cables, the distributed parameter effect is significant, and one or more parameters are typically used. Equivalent circuits are cascaded to approximate its impedance-frequency characteristics. Based on the topological connection relationship between the collector network and the transmitting cable, all submarine cables are... By appropriately combining equivalent circuits in parallel, the overall equivalent impedance of the offshore wind power system as viewed from the onshore access point can be obtained.

[0084] Step A30: Determine the resonant frequency at which there is a risk of harmonic amplification based on the impedance model of the offshore wind power system and the total impedance frequency characteristics after the equivalent impedance is connected in parallel.

[0085] It should be noted that the equivalent impedance amplitude of the offshore wind power connection point varies depending on the onshore power grid's operating mode, as shown below. Figure 4 As shown. From the perspective of the offshore wind power access point, the equivalent impedance at the access point is equivalent to the overall impedance of the offshore wind power system and the equivalent impedance of the onshore power grid connected in parallel. When the sum of the imaginary parts of the two impedances is 0, the corresponding frequency is the resonant frequency. The harmonics corresponding to the resonant frequency at the access point will be amplified to their maximum value, and at the same time, the amplitude of the equivalent impedance at the access point will also reach its maximum value.

[0086] Step S302: Determine the resonant frequency range in which electrical resonance occurs based on the resonant frequency.

[0087] It should be noted that, considering the dispersion of component parameters, measurement errors, and variations in operating modes in actual power systems, the resonant frequency is not a single, fixed value, but rather fluctuates within a certain frequency range. Therefore, it is necessary to extend a certain bandwidth to both sides of the resonant frequency to form a resonant frequency range. Preferably, extending 100Hz to both the low-frequency and high-frequency sides from the resonant frequency as the center constitutes the resonant frequency range where electrical resonance may occur. Harmonics within this range all pose a significant risk of harmonic amplification. Figure 3 As shown, specifically, when the onshore power grid is in different operating modes, the frequency range in which harmonic amplification may occur is 201Hz~657Hz.

[0088] Step S303: Filter the historical data of the background harmonic voltage according to the resonant frequency range to obtain the harmonic order that has the risk of harmonic amplification.

[0089] It should be noted that in this step, the system compares the calculated frequency range with each harmonic in the historical background harmonic voltage data, filters out the harmonics falling within this harmonic order range, and further combines this with the content of each harmonic in the historical background harmonic voltage data to select the harmonics with higher content as those with a risk of harmonic amplification. Specifically, the onshore power grid background harmonics with higher content in this range are the 5th, 7th, 11th, and 13th harmonics.

[0090] In this embodiment, by establishing a joint impedance model of the offshore wind power system and the onshore power grid and performing frequency characteristic analysis, the resonant frequencies prone to harmonic amplification and their dangerous ranges are identified. This allows for the precise selection of target harmonic orders with actual amplification risks from background harmonic data. This achieves accurate positioning of the compensation target, solves the problem of overcapacity in the APF (Advanced Harmonic Filter) caused by blindly calculating capacity based on amplified harmonic currents, and improves the rationality and economy of APF capacity design.

[0091] Furthermore, based on the electrical model constructed from actual engineering data, and the APF capacity value calculated in the above embodiments, an APF harmonic compensation strategy is designed using simulation software to suppress harmonic currents at the offshore wind power access point.

[0092] Specifically, in the simulation experiment, the onshore power grid adopted operation mode 1. According to the aforementioned analysis results, there is a risk of harmonic amplification in the 457Hz~657Hz range, corresponding to the 11th and 13th harmonics. The experiment collected harmonic voltage and harmonic current information at the offshore wind power connection point before and after APF (Automatic Power Grid) connection. Figure 5 This represents a comparison of the harmonic voltage content at the offshore wind power connection point before and after connection to the APF. Figure 6 and Figure 7 The voltage waveforms at the offshore wind power access point before and after connection to the APF are shown respectively.

[0093] As can be understood from the experimental results shown in the figure above, after connecting the APF, the harmonic voltages at the offshore wind power connection point are effectively suppressed, and the harmonic voltage distortion rate at the connection point is reduced from 3.03% to 0.41%, which meets the national standard of the upper limit of 2%. This indicates that the APF capacity designed by the method in this application can generate sufficient compensation current to suppress harmonic amplification at the offshore wind power connection point.

[0094] In summary, the experimental results show that the APF capacity (39.1873 MVA) for harmonic amplification suppression at the offshore wind power connection point, calculated using the method of this application, is optimal based on the electrical model constructed from actual engineering data for connecting offshore wind power to the onshore power grid. In simulation software, based on this capacity value, the APF designed to suppress harmonic amplification can effectively suppress harmonic voltage and current amplification at the offshore wind power connection point without exceeding the design capacity.

[0095] This application also provides a capacity calculation device for an active power filter; please refer to [reference needed]. Figure 8 The capacity calculation device for the active power filter includes: Data acquisition module 10 is used to acquire historical data of background harmonic voltage, grid structure information, main equipment parameters and operating mode information of onshore power grid; Impedance calculation module 20 is used to calculate the equivalent impedance of the onshore power grid when connected to offshore wind power based on the grid structure information, the main equipment parameters and the operation mode information; Risk assessment module 30 is used to determine the harmonic order in the historical background harmonic voltage data that has the risk of harmonic amplification based on the impedance of the offshore wind power system and the equivalent impedance. Harmonic current calculation module 40 is used to calculate the equivalent harmonic current based on the equivalent impedance and the historical background harmonic voltage data corresponding to the harmonic order; The capacity calculation module 50 is used to calculate the compensation capacity of the active power filter based on the equivalent harmonic current.

[0096] The active power filter capacity calculation device provided in this application, employing the active power filter capacity calculation method described in the above embodiments, can solve the technical problem of determining the APF capacity for suppressing harmonic amplification from offshore wind power when accurate information about internal harmonic sources in the power grid cannot be obtained. Compared with the prior art, the beneficial effects of the active power filter capacity calculation device provided in this application are the same as those of the active power filter capacity calculation method provided in the above embodiments, and other technical features in the active power filter capacity calculation device are the same as those disclosed in the methods of the above embodiments, and will not be repeated here.

[0097] In one embodiment, the data acquisition module 10 is further configured to acquire the harmonic voltage content of the onshore power grid at the offshore wind power access point within a preset time period when the offshore wind power system is not connected, and use the harmonic voltage content as historical background harmonic voltage data; acquire the grid topology connection structure information and the connection relationship of networks at different voltage levels near the offshore wind power access point, and use the connection relationship as grid structure information; acquire the parameters of the main transformer, the parameters of the reactor, and the rated capacity of the compensation equipment near the offshore wind power access point, and use the parameters of the main transformer, the parameters of the reactor, and the rated capacity as main equipment parameters; acquire the switching status and the normal operation mode of the main equipment near the offshore wind power access point, and use the switching status and the normal operation mode as operation mode information.

[0098] In one embodiment, the impedance calculation module 20 is further configured to determine the conventional operating mode of the onshore power grid based on the operating mode information; for each conventional operating mode, calculate the short-circuit capacity of the offshore wind power access point when the offshore wind power is not connected based on the grid structure information and the main equipment parameters; calculate the corresponding current equivalent impedance based on the short-circuit capacity, and select the minimum value among the current equivalent impedances as the equivalent impedance of the onshore power grid.

[0099] In one embodiment, the risk assessment module 30 is further configured to perform impedance analysis based on the impedance of the offshore wind power system and the equivalent impedance to obtain the resonant frequency when there is a risk of harmonic amplification; determine the resonant frequency range in which electrical resonance occurs based on the resonant frequency; and filter the historical data of the background harmonic voltage based on the resonant frequency range to obtain the harmonic order in which there is a risk of harmonic amplification.

[0100] In one embodiment, the risk assessment module 30 is further configured to acquire submarine cable parameters characterizing the offshore wind farm collection system and the high-voltage transmission section; construct an offshore wind power system impedance model with the equivalent impedance as the boundary based on the submarine cable parameters; and determine the resonant frequency with harmonic amplification risk based on the total impedance frequency characteristics of the offshore wind power system impedance model and the equivalent impedance in parallel.

[0101] In one embodiment, the harmonic current calculation module 40 is further configured to extract the maximum value of the harmonic voltage corresponding to the harmonic number from the historical background harmonic voltage data based on the harmonic number; determine the harmonic impedance based on the minimum value of the equivalent impedance and the harmonic number; and calculate the equivalent harmonic current based on the maximum value of the harmonic voltage and the harmonic impedance.

[0102] In one embodiment, the capacity calculation module 50 is further configured to perform a square root operation on the equivalent harmonic current to obtain the effective value of the harmonic current; calculate the target compensation capacity based on the preset rated voltage of the offshore wind power access point and the effective value of the harmonic current; and correct the target compensation capacity based on a preset margin coefficient to obtain the compensation capacity of the active power filter.

[0103] This application provides a capacity calculation device for an active power filter. The active power filter capacity calculation device includes: at least one processor; and a memory communicatively connected to the at least one processor; wherein the memory stores instructions executable by the at least one processor, and the instructions are executed by the at least one processor to enable the at least one processor to perform the active power filter capacity calculation method in the above embodiment 1.

[0104] The following is for reference. Figure 9This document illustrates a structural schematic diagram of a capacity calculation device suitable for implementing the active power filter embodiments of this application. The capacity calculation device for the active power filter in these embodiments may include, but is not limited to, mobile terminals such as mobile phones, laptops, digital radio receivers, PDAs (Personal Digital Assistants), PADs (Portable Application Description), PMPs (Portable Media Players), in-vehicle terminals (e.g., in-vehicle navigation terminals), and fixed terminals such as digital TVs and desktop computers. Figure 9 The illustrated capacity calculation device for the active power filter is merely an example and should not impose any limitations on the functionality and scope of use of the embodiments of this application.

[0105] like Figure 9 As shown, the capacity calculation device for an active power filter may include a processing unit 1001 (e.g., a central processing unit, a graphics processing unit, etc.), which can perform various appropriate actions and processes according to a program stored in ROM (Read Only Memory) 1002 or a program loaded from storage device 1003 into RAM (Random Access Memory) 1004. RAM 1004 also stores various programs and data required for the operation of the active power filter capacity calculation device. The processing unit 1001, ROM 1002, and RAM 1004 are interconnected via bus 1005. Input / output (I / O) interface 1006 is also connected to the bus. Typically, the following systems can be connected to I / O interface 1006: input devices 1007 including, for example, touchscreens, touchpads, keyboards, mice, image sensors, microphones, accelerometers, gyroscopes, etc.; output devices 1008 including, for example, LCDs (Liquid Crystal Displays), speakers, vibrators, etc.; storage devices 1003 including, for example, magnetic tapes, hard disks, etc.; and communication devices 1009. Communication device 1009 allows the active power filter capacity calculation device to communicate wirelessly or wiredly with other devices to exchange data. Although the figure shows an active power filter capacity calculation device with various systems, it should be understood that it is not required to implement or possess all the systems shown. More or fewer systems can be implemented alternatively.

[0106] Specifically, according to the embodiments disclosed in this application, the processes described above with reference to the flowcharts can be implemented as computer software programs. For example, embodiments disclosed in this application include a computer program product comprising 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 a communication device, or installed from storage device 1003, or installed from ROM 1002. When the computer program is executed by processing device 1001, it performs the functions defined in the methods of the embodiments disclosed in this application.

[0107] The active power filter capacity calculation device provided in this application, employing the active power filter capacity calculation method described in the above embodiments, solves the technical problem of determining the APF capacity for suppressing harmonic amplification from offshore wind power when accurate information about internal harmonic sources in the power grid cannot be obtained. Compared with the prior art, the beneficial effects of the active power filter capacity calculation device provided in this application are the same as those of the active power filter capacity calculation method provided in the above embodiments, and other technical features of this active power filter capacity calculation device are the same as those disclosed in the previous embodiment method, and will not be repeated here.

[0108] It should be understood that the various parts disclosed in this application can be implemented using hardware, software, firmware, or a combination thereof. In the description of the above embodiments, specific features, structures, materials, or characteristics can be combined in any suitable manner in one or more embodiments or examples.

[0109] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

[0110] This application provides a computer-readable storage medium having computer-readable program instructions (i.e., a computer program) stored thereon, the computer-readable program instructions being used to execute the capacity calculation method of the active power filter in the above embodiments.

[0111] The computer-readable storage medium provided in this application may be, for example, a USB flash drive, but is not limited to, electrical, magnetic, optical, electromagnetic, infrared, or semiconductor systems, devices, or any combination thereof. More specific examples of computer-readable storage media may include, but are not limited to: electrical connections having one or more wires, portable computer disks, hard disks, RAM (Random Access Memory), ROM (Read Only Memory), EPROM (Erasable Programmable Read Only Memory or Flash Memory), optical fibers, CD-ROM (CD-Read Only Memory), optical storage devices, magnetic storage devices, or any suitable combination thereof. In this embodiment, the computer-readable storage medium may be any tangible medium containing or storing a program that can be used by or in conjunction with an instruction execution system, system, or device. The program code contained on the computer-readable storage medium may be transmitted using any suitable medium, including but not limited to: wires, optical cables, RF (Radio Frequency), etc., or any suitable combination thereof.

[0112] The aforementioned computer-readable storage medium may be included in the capacity calculation device of the active power filter; or it may exist independently and not assembled into the capacity calculation device of the active power filter.

[0113] The aforementioned computer-readable storage medium carries one or more programs. When these programs are executed by the capacity calculation device of the active power filter, the active power filter capacity calculation device performs the following actions: acquires historical background harmonic voltage data, grid structure information, main equipment parameters, and operating mode information of the onshore power grid; calculates the equivalent impedance of the onshore power grid at offshore wind power access based on the grid structure information, the main equipment parameters, and the operating mode information; determines the harmonic order with harmonic amplification risk in the historical background harmonic voltage data based on the offshore wind power system impedance and the equivalent impedance; calculates the equivalent harmonic current based on the historical background harmonic voltage data corresponding to the equivalent impedance and the harmonic order; and calculates the compensation capacity of the active power filter based on the equivalent harmonic current.

[0114] Computer program code for performing the operations of this application can be written in one or more programming languages ​​or a combination thereof, including object-oriented programming languages ​​such as Java, Smalltalk, and C++, as well as conventional procedural programming languages ​​such as the "C" language or similar programming languages. The program code can be executed entirely on the user's computer, partially on the user's computer, as a standalone software package, partially on the user's computer and partially on a remote computer, or entirely on a remote computer or server. In cases involving remote computers, the remote computer can be connected to the user's computer via any type of network—including LAN (Local Area Network) or WAN (Wide Area Network)—or can be connected to an external computer (e.g., via the Internet using an Internet service provider).

[0115] The flowcharts and block diagrams in the accompanying drawings illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to various embodiments of this application. In this regard, each block in a flowchart or block diagram may represent a module, segment, or portion of code containing one or more executable instructions for implementing a specified logical function. It should also be noted that in some alternative implementations, the functions indicated in the blocks may occur in a different order than those indicated in the drawings. For example, two consecutively indicated blocks may actually be executed substantially in parallel, and they may sometimes be executed in reverse order, depending on the functions involved. It should also be noted that each block in the block diagrams and / or flowcharts, and combinations of blocks in the block diagrams and / or flowcharts, can be implemented using a dedicated hardware-based system that performs the specified function or operation, or using a combination of dedicated hardware and computer instructions.

[0116] The modules described in the embodiments of this application can be implemented in software or hardware. The names of the modules do not necessarily limit the functionality of the unit itself.

[0117] The readable storage medium provided in this application is a computer-readable storage medium that stores computer-readable program instructions (i.e., a computer program) for executing the above-described active power filter capacity calculation method. This solves the technical problem of determining the APF capacity for suppressing harmonic amplification from offshore wind power when accurate information about internal harmonic sources in the power grid cannot be obtained. Compared with the prior art, the beneficial effects of the computer-readable storage medium provided in this application are the same as those of the active power filter capacity calculation method provided in the above embodiments, and will not be repeated here.

[0118] This application also provides a computer program product, including a computer program that, when executed by a processor, implements the steps of the above-described method for calculating the capacity of an active power filter.

[0119] The computer program product provided in this application solves the technical problem of determining the APF capacity for suppressing harmonic amplification from offshore wind power when accurate information about harmonic sources within the power grid cannot be obtained. Compared with the prior art, the beneficial effects of the computer program product provided in this application are the same as those of the active power filter capacity calculation method provided in the above embodiments, and will not be elaborated upon here.

[0120] The above description is only a part of the embodiments of this application and does not limit the patent scope of this application. All equivalent structural transformations made under the technical concept of this application and using the contents of the specification and drawings of this application, or direct / indirect applications in other related technical fields, are included in the patent protection scope of this application.

Claims

1. A method for calculating the capacity of an active power filter, characterized in that, The method includes: Acquire historical data on background harmonic voltages, grid structure information, main equipment parameters, and operating mode information of the onshore power grid; The equivalent impedance of the onshore power grid at offshore wind power access is calculated based on the grid structure information, the main equipment parameters, and the operation mode information. The harmonic order with harmonic amplification risk in the historical background harmonic voltage data is determined based on the impedance of the offshore wind power system and the equivalent impedance. The equivalent harmonic current is calculated based on the historical background harmonic voltage data corresponding to the equivalent impedance and the harmonic order. The compensation capacity of the active power filter is calculated based on the equivalent harmonic current.

2. The method as described in claim 1, characterized in that, The step of calculating the equivalent impedance of the onshore power grid at offshore wind power access based on the grid structure information, the main equipment parameters, and the operating mode information includes: The conventional operating mode of the onshore power grid is determined based on the aforementioned operating mode information; For each of the aforementioned conventional operating modes, the short-circuit capacity of the offshore wind power access point when offshore wind power is not connected is calculated based on the grid structure information and the main equipment parameters. The corresponding current equivalent impedance is calculated based on the short-circuit capacity, and the minimum value among the current equivalent impedances is selected as the equivalent impedance of the onshore power grid.

3. The method as described in claim 1, characterized in that, The step of determining the harmonic order with harmonic amplification risk in the historical background harmonic voltage data based on the impedance of the offshore wind power system and the equivalent impedance includes: Impedance analysis is performed based on the impedance of the offshore wind power system and the equivalent impedance to obtain the resonant frequency when there is a risk of harmonic amplification. The range of resonant frequencies in which electrical resonance occurs is determined based on the resonant frequency. Based on the resonant frequency range, the historical data of the background harmonic voltage are filtered to obtain the harmonic numbers that pose a risk of harmonic amplification.

4. The method as described in claim 3, characterized in that, The step of performing impedance analysis based on the impedance of the offshore wind power system and the equivalent impedance to obtain the resonant frequency when there is a risk of harmonic amplification includes: Obtain submarine cable parameters characterizing the power collection system and high-voltage transmission section of an offshore wind farm; An impedance model of the offshore wind power system with the equivalent impedance as the boundary is constructed based on the submarine cable parameters. The resonant frequency at which harmonic amplification risk is determined based on the impedance model of the offshore wind power system and the total impedance frequency characteristics after the equivalent impedance is connected in parallel.

5. The method as described in claim 1, characterized in that, The step of calculating the equivalent harmonic current based on the historical background harmonic voltage data corresponding to the equivalent impedance and the harmonic order includes: The maximum harmonic voltage value corresponding to the harmonic number is extracted from the historical background harmonic voltage data based on the harmonic number. The harmonic impedance is determined based on the minimum value of the equivalent impedance and the harmonic order. The equivalent harmonic current is calculated based on the maximum harmonic voltage and the harmonic impedance.

6. The method as described in claim 1, characterized in that, The step of calculating the compensation capacity of the active power filter based on the equivalent harmonic current includes: Perform a square root operation on the equivalent harmonic current to obtain the effective value of the harmonic current; The target compensation capacity is calculated based on the preset rated voltage of the offshore wind power access point and the effective value of the harmonic current. The target compensation capacity is corrected according to the preset margin coefficient to obtain the compensation capacity of the active power filter.

7. The method as described in claim 1, characterized in that, The steps for obtaining historical background harmonic voltage data, grid structure information, main equipment parameters, and operating mode information of the onshore power grid include: The harmonic voltage content of the onshore power grid at the offshore wind power access point is obtained within a preset time period when the offshore wind power system is not connected, and the harmonic voltage content is used as historical background harmonic voltage data. Obtain the grid topology connection information and the connection relationship of networks at different voltage levels near the offshore wind power access point, and use the connection relationship as the grid structure information; Obtain the parameters of the main transformer, reactor, and rated capacity of the compensation equipment near the offshore wind power access point, and use the main transformer parameters, reactor parameters, and rated capacity as the main equipment parameters; The system acquires the switching status and routine operation mode of the main equipment near the offshore wind power access point, and uses the switching status and routine operation mode as operation mode information.

8. A capacity calculation device for an active power filter, characterized in that, The device includes: The data acquisition module is used to acquire historical background harmonic voltage data, grid structure information, main equipment parameters, and operating mode information of the onshore power grid; The impedance calculation module is used to calculate the equivalent impedance of the onshore power grid when connected to offshore wind power based on the grid structure information, the main equipment parameters, and the operation mode information. The risk assessment module is used to determine the harmonic order in the historical background harmonic voltage data that has the risk of harmonic amplification based on the impedance of the offshore wind power system and the equivalent impedance. The harmonic current calculation module is used to calculate the equivalent harmonic current based on the historical data of the background harmonic voltage corresponding to the equivalent impedance and the harmonic order. The capacity calculation module is used to calculate the compensation capacity of the active power filter based on the equivalent harmonic current.

9. A capacity calculation device for an active power filter, characterized in that, The device includes: a memory, a processor, and a computer program stored in the memory and executable on the processor, the computer program being configured to implement the steps of the capacity calculation method for an active power filter as described in any one of claims 1 to 7.

10. A storage medium, characterized in that, The storage medium is a computer-readable storage medium, and a computer program is stored on the storage medium. When the computer program is executed by a processor, it implements the steps of the capacity calculation method for the active power filter as described in any one of claims 1 to 7.

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