Method and device for evaluating voltage sags of an ac bus

Abstract

The disclosure provides a voltage dip evaluation method and evaluation device for an AC bus. The voltage dip evaluation method comprises: extracting impedance parameters of a first wind turbine and a second wind turbine, wherein the first wind turbine and the second wind turbine are connected in parallel to the AC bus, and the first wind turbine and the second wind turbine are both direct start wind turbines, the first wind turbine is in a stable operation state, and the second wind turbine is in a direct start state; calculating a rated working current of the first wind turbine and a starting transient current of the second wind turbine; and determining a voltage dip amplitude of the AC bus based on the inductance of the first wind turbine, the rated working current of the first wind turbine, and the starting transient current of the second wind turbine.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to the field of wind power generation, and more particularly, to a voltage dip evaluation method and evaluation device for an AC bus of parallel wind generators. BACKGROUND

[0002] In recent years, parallel wind power generation systems have developed rapidly, and a large number of wind generators are connected in parallel to the grid, which leads to increasingly intensified interaction between wind generators and between wind generators and the grid. Grid connection guidelines require wind generators to strictly meet relevant grid connection and networking standards for power quality and robustness, especially the ability of wind generators to remain connected to the grid and to pass through faults when the grid experiences short-time faults. However, the direct starting method used for transient starting of high-power wind generators will cause the transient current of the starting wind generator to increase, thereby causing transient voltage dip of the AC bus to which the wind generator is connected, which is likely to cause excessive current stress on switch devices of the wind generator's variable current system and reduce the overall operating life of power electronic devices and the wind power system.

[0003] At present, relevant research has been conducted on the starting transient control evaluation of parallel direct-start wind generators at home and abroad. However, the existing evaluation methods all have certain deficiencies, for example, some evaluation methods do not consider the influence of actual wind turbine capacity on voltage dip, some evaluation methods are too complex to be practical, and some evaluation methods do not consider the performance evaluation of wind power systems when multiple parallel wind generators are directly started. SUMMARY

[0004] Therefore, an object of embodiments of the present disclosure is to provide a voltage dip evaluation method and evaluation device for an AC bus, so as to guarantee the reliability and stability of grid connection of each wind generator in a wind power system.

[0005] In one general aspect, there is provided a voltage dip evaluation method for an AC bus, the voltage dip evaluation method comprising: extracting impedance parameters of a first wind generator and a second wind generator, wherein the first wind generator and the second wind generator are connected in parallel to the AC bus, and the first wind generator and the second wind generator are both direct-start wind generators, the first wind generator is in a stable operating state, and the second wind generator is in a direct starting state; calculating a rated operating current of the first wind generator and a starting transient current of the second wind generator; and determining a voltage dip amplitude of the AC bus based on a reactance of the first wind generator, the rated operating current of the first wind generator, and the starting transient current of the second wind generator.

[0006] Optionally, the step of calculating the rated operating current of the first wind generator and the starting transient current of the second wind generator comprises: calculating the rated operating current of the first wind generator based on a power capacity, an operating voltage and a power factor of the first wind generator; and calculating the starting transient current of the second wind generator based on a starting reference coefficient, a power capacity, an operating voltage and a power factor of the second wind generator.

[0007] Optionally, the inductive reactance of the first wind generator is determined based on the transient impedance and the sub-transient impedance of the first wind generator.

[0008] Optionally, the step of determining the voltage dip magnitude of the AC bus comprises: determining the average of the transient impedance and the sub-transient impedance of the first wind generator as the inductive reactance of the first wind generator; and determining the voltage dip magnitude of the AC bus based on the product of the inductive reactance of the first wind generator and the starting transient current of the second wind generator and the rated operating current of the first wind generator.

[0009] Optionally, the voltage dip assessment method further comprises: determining a post-dip voltage of the AC bus based on the voltage dip magnitude of the AC bus; and determining the maximum allowable capacity of the second wind generator based on a relationship between the post-dip voltage of the AC bus and the minimum limit voltage of the AC bus, or based on the relationship between the post-dip voltage of the AC bus and the minimum limit voltage of the AC bus and the minimum value of the three-phase voltage of the AC bus.

[0010] Optionally, the relationship between the post-dip voltage of the AC bus and the minimum limit voltage of the AC bus is that the post-dip voltage of the AC bus is greater than or equal to the minimum limit voltage of the AC bus.

[0011] Optionally, the voltage dip assessment method further comprises: determining an average effective dip voltage of the AC bus; and verifying the determined voltage dip magnitude of the AC bus based on the average effective dip voltage of the AC bus.

[0012] Optionally, the step of determining the average effective dip voltage of the AC bus comprises: dividing the total area of the voltage curve of the AC bus into multiple intervals according to the starting duration of the second wind generator to perform Riemann summation calculation, thereby determining the average effective dip voltage of the AC bus.

[0013] In another general aspect, there is provided a voltage dip evaluation device for an AC bus, the voltage dip evaluation device comprising: a parameter extraction unit configured to extract impedance parameters of a first wind power generator and a second wind power generator, wherein the first wind power generator and the second wind power generator are connected in parallel to the AC bus, and the first wind power generator and the second wind power generator are both direct start-up wind power generators, the first wind power generator is in a stable operation state, and the second wind power generator is in a direct start-up state; a current calculation unit configured to calculate a rated operating current of the first wind power generator and a start-up transient current of the second wind power generator; and a voltage dip amplitude determination unit configured to determine a voltage dip amplitude of the AC bus based on a reactance of the first wind power generator, the rated operating current of the first wind power generator, and the start-up transient current of the second wind power generator.

[0014] In another general aspect, there is provided a computer-readable storage medium storing a computer program which, when executed by a processor, implements the voltage dip evaluation method for an AC bus as described above.

[0015] In another general aspect, there is provided a computing device comprising: a processor; and a memory storing a computer program which, when executed by the processor, implements the voltage dip evaluation method for an AC bus as described above.

[0016] The voltage dip evaluation method and the evaluation device for an AC bus according to embodiments of the present disclosure can effectively establish an evaluation model of wind power generator power capacity and AC bus voltage dip, guarantee the safe start-up of wind power generators in a wind power generation system, ensure that the grid-connected current of the wind power generation system always remains in a safe operating zone, avoid the occurrence of overcurrent problems, and improve the fault ride-through capability of the wind power generation system. In addition, the voltage dip evaluation method and the evaluation device for an AC bus according to embodiments of the present disclosure are easy to implement in engineering and are convenient for popularization and application. BRIEF DESCRIPTION OF DRAWINGS

[0017] The above and other objects and features of the present disclosure will become more apparent from the following description of the embodiments taken in conjunction with the accompanying drawings.

[0018] Figure 1 FIG. 1 is a circuit structure diagram illustrating parallel direct start-up wind power generators.

[0019] Figure 2 FIG. 2 is a flowchart illustrating a voltage dip evaluation method for an AC bus according to an embodiment of the present disclosure.

[0020] Figure 3 FIG. 3 is a diagram illustrating an example of verifying a voltage dip amplitude of an AC bus according to an embodiment of the present disclosure.

[0021] Figure 4 is a graph showing an example of a relationship between a maximum allowable capacity of a wind power generator and a voltage dip of an AC bus according to an embodiment of the disclosure.

[0022] Figure 5 is a block diagram of a voltage dip evaluation device of an AC bus according to an embodiment of the disclosure.

[0023] Figure 6 is a block diagram of a computing device according to an embodiment of the disclosure. DETAILED DESCRIPTION

[0024] The following detailed description is provided to help the reader obtain a thorough understanding of the methods, devices, and / or systems described herein. However, the various changes, modifications, and equivalents thereof will be clear to those skilled in the art after an understanding of the disclosure provided herein. For example, the order of the operations described herein is merely an example and is not limited to those set forth herein, but can be changed as will be apparent after an understanding of the disclosure provided herein, except for operations that must occur in a particular order. Also, descriptions of features known to those skilled in the art can be omitted for the sake of clarity and conciseness.

[0025] The features described herein can be implemented in different forms and should not be construed as limited to the examples described herein. Rather, these examples have been provided so that this disclosure will be thorough and complete, and will fully convey the scope of the methods, devices, and / or systems described herein to those skilled in the art after an understanding of the disclosure provided herein.

[0026] As used herein, the term "and / or" includes any one of the associated listed items, as well as any combination of any two or more of the associated listed items.

[0027] Although terms such as "first", "second", and "third" can be used herein to describe various components, assemblies, regions, layers, or portions, these components, assemblies, regions, layers, or portions should not be limited by these terms. Rather, these terms are used only to distinguish one component, assembly, region, layer, or portion from another component, assembly, region, layer, or portion. Thus, a component, assembly, region, layer, or portion referred to as a first component, a first assembly, a first region, a first layer, or a first portion in the examples described herein can also be referred to as a second component, a second assembly, a second region, a second layer, or a second portion without departing from the teachings of the examples.

[0028] In the description, when an element (such as a layer, region or substrate) is referred to as being "on" another element, "connected to" or "coupled to" another element, it can be directly on the other element or directly connected or coupled to the other element, or one or more other elements can be interposed therebetween. In contrast, when an element is referred to as being "directly on" another element, "directly connected to" or "directly coupled to" another element, there are no other elements interposed therebetween.

[0029] The terminology used herein is for the purpose of describing various examples only and is not intended to be limiting of the disclosure. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms "comprises", "comprising", "includes", "including" and "has", "having" as used herein, specify the presence of stated features, numbers, operations, components, elements, and / or groups thereof, but do not preclude the presence or addition of one or more other features, numbers, operations, components, elements, and / or groups thereof.

[0030] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs when read in light of the present disclosure. Unless otherwise explicitly defined herein, the terms (such as those defined in commonly used dictionaries) should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the disclosure, and should not be interpreted in an idealized or overly formal sense.

[0031] Further, in the description of examples, detailed descriptions of well-known related structures or functions are omitted when it is deemed that such detailed description will cause ambiguous interpretation of the present disclosure.

[0032] Figure 1 is a circuit configuration diagram showing parallelly connected direct-start wind power generators.

[0033] Referring to Figure 1 , a first wind power generator 1 and a second wind power generator 2 are connected in parallel to an AC bus, and the first wind power generator and the second wind power generator are both direct-start wind power generators. In general, a wind power generator uses auxiliary equipment for soft start protection in order to avoid excessive starting current or interference during starting, and a direct-start wind power generator does not consider other equipment, but only considers the starting of the wind power generator itself, i.e., directly starts, which is also referred to as hard start, and is distinguished from soft start of the wind power generator. Impedance parameters of the first wind power generator 1 are represented as Z1=R g1 +X g1 , and impedance parameters of the second wind power generator 2 are represented as Z2=R g2 +X g2 , where R g1 and R g2respectively represent the impedance of the first wind power generator 1 and the impedance of the second wind power generator 2, X g1 and X g2 respectively represent the reactance of the first wind power generator 1 and the reactance of the second wind power generator 2. When the first wind power generator 1 is in a stable operation state, at the moment of direct start-up of the second wind power generator 2, an AC bus voltage dip occurs.

[0034] Here, it should be noted that the number of wind power generators connected in parallel to the AC bus can be greater than 2. However, the impact on the AC bus voltage is the greatest when one wind power generator directly starts up in the case of two wind power generators connected in parallel to the AC bus, and the impact on the AC bus voltage is not obvious when one wind power generator directly starts up in the case of multiple wind power generators connected in parallel to the AC bus. Therefore, the present disclosure is described taking the case of two wind power generators connected in parallel to the AC bus as an example, however, the number of wind power generators connected in parallel to the AC bus is not limited to 2.

[0035] Reference will be made below to Figure 2 The voltage dip evaluation method of the AC bus is specifically described.

[0036] Figure 2 is a flow chart illustrating the voltage dip evaluation method of the AC bus according to an embodiment of the present disclosure.

[0037] Reference is made to Figure 2 In step S201, the impedance parameters of the first wind power generator and the second wind power generator can be extracted. As described above, the first wind power generator and the second wind power generator are connected in parallel to the AC bus, and the first wind power generator and the second wind power generator are both direct start-up type wind power generators, the first wind power generator is in a stable operation state, and the second wind power generator is in a direct start-up state. Here, the impedance parameters of the wind power generators can be extracted through a wind power generator user data manual.

[0038] Next, in step S202, the rated operating current of the first wind power generator and the start-up transient current of the second wind power generator can be calculated. Specifically, the rated operating current of the first wind power generator can be calculated based on the power capacity, operating voltage, and power factor of the first wind power generator, and the start-up transient current of the second wind power generator can be calculated based on the start-up reference coefficient, power capacity, operating voltage, and power factor of the second wind power generator.

[0039] For example, the rated operating current I g1 of the first wind power generator can be calculated based on the following formula (1), and the start-up transient current I g2 of the second wind power generator can be calculated based on the following formula (2).

[0040]

[0041]

[0042] wherein P g1 represents the power capacity of the first wind power generator, V g1 represents the operating voltage of the first wind power generator, cosφ g1 represents the power factor of the first wind power generator, K and m represent the starting reference coefficients of the second wind power generator (for example, but not limited to, K = 1, m = 6), P g2 represents the power capacity of the second wind power generator, V g2 represents the operating voltage of the second wind power generator, cosφ g2 represents the power factor of the second wind power generator.

[0043] Subsequently, in step S203, the voltage dip amplitude of the AC bus can be determined based on the inductive reactance of the first wind power generator, the rated operating current of the first wind power generator, and the starting transient current of the second wind power generator.

[0044] According to embodiments of the present disclosure, the voltage dip amplitude V dip (%) of the AC bus can be calculated based on the AC bus rated voltage minus the transient voltage drop of the starting second wind power generator, as shown in equation (3).

[0045]

[0046] Since the respective inductive reactance X g of the parallel wind power generators is obviously greater than the impedance R g , when the second wind power generator is directly started, the inductive reactance X d of the first wind power generator can be determined based on the transient impedance X' d and the sub-transient impedance X" g1 of the first wind power generator. More specifically, the average of the transient impedance X' d and the sub-transient impedance X" d of the first wind power generator can be determined as the inductive reactance X g1 of the first wind power generator, and the voltage dip amplitude V g1 (%) of the AC bus can be determined based on the product of the inductive reactance X g2 of the first wind power generator and the starting transient current I g1 of the second wind power generator, and the rated operating current I dip of the first wind power generator. That is, equation (3) can be converted into equation (4) as an evaluation model of the AC bus voltage dip to calculate the voltage dip amplitude V dip (%) of the AC bus.

[0047]

[0048] wherein,

[0049] Alternatively, the voltage dip assessment method of the AC bus according to the embodiments of the present disclosure can further include the steps of: determining the voltage of the AC bus after the dip based on the voltage dip magnitude of the AC bus; determining the maximum allowable capacity of the second wind power generator based on the relationship between the voltage of the AC bus after the dip and the minimum limit voltage of the AC bus, or based on the relationship between the voltage of the AC bus after the dip and the minimum limit voltage of the AC bus and the minimum value of the three-phase voltage of the AC bus.

[0050] Specifically, the relationship between the voltage of the AC bus after the dip and the minimum limit voltage of the AC bus is that the voltage of the AC bus after the dip is greater than or equal to the minimum limit voltage of the AC bus, as shown in the following formula (5).

[0051]

[0052] wherein, V g represents the AC bus rated voltage, V limit represents the minimum limit voltage.

[0053] Assuming that the voltage of the AC bus after the dip is equal to the minimum limit voltage of the AC bus, formula (5) is substituted into formula (4) to estimate the power capacity ratio of the wind power generator, as shown in the following formula (6).

[0054]

[0055] wherein, P g1 represents the power capacity of the first wind power generator, P g2 represents the power capacity of the second wind power generator, represents the maximum power capacity ratio of the second wind power generator to the first wind power generator. After determining the maximum power capacity ratio of the second wind power generator to the first wind power generator, the maximum allowable capacity of the second wind power generator can be easily determined.

[0056] On the other hand, in the case of AC bus load imbalance, the minimum value of the three-phase voltage of the AC bus can be used to estimate the power capacity ratio. In this way, formula (6) can be replaced by formula (7).

[0057]

[0058] wherein, V lowest represents the minimum value of the three-phase voltage of the AC bus.

[0059] The voltage dip evaluation method of the AC bus according to the embodiment of the present disclosure can also be applied to the evaluation model of the voltage dip of the AC bus. Specifically, the average effective dip voltage of the AC bus can be determined first, and then the determined voltage dip amplitude of the AC bus is verified based on the average effective dip voltage of the AC bus. To determine the average effective dip voltage of the AC bus, the total area of the voltage curve of the AC bus can be divided into multiple intervals according to the start-up duration of the second wind turbine, and the Riemann summation calculation is performed to determine the average effective dip voltage of the AC bus. For example, the average effective dip voltage V of the AC bus can be calculated according to formula (8) dip_mea .

[0060]

[0061] wherein M represents the number of intervals, V dip_i represents the actual voltage of the AC bus in the i-th interval.

[0062] Figure 3 is a diagram showing an example of verifying the voltage dip amplitude of the AC bus according to the embodiment of the present disclosure. Referring to Figure 3 , it can be found that the voltage dip amplitude of the AC bus calculated based on formula (4) is basically consistent with the average effective dip voltage V dip_mea of the AC bus, thereby proving that it is completely feasible to calculate the voltage dip amplitude of the AC bus based on formula (4).

[0063] Figure 4 is a diagram showing an example of the relationship between the maximum allowed capacity of the wind turbine and the voltage dip of the AC bus according to the embodiment of the present disclosure.

[0064] Referring to Figure 4 , the voltage after the dip of the AC bus must be greater than the minimum limit voltage, thereby providing correct design information of the maximum allowed capacity. For example, assuming that a 20% generator rated voltage dip is allowed, and the minimum limit voltage is 320V, if the voltage after the dip is about 360V, the maximum allowed capacity can be quickly estimated as 90kW. However, if the voltage after the dip is lower than the minimum limit voltage, the maximum allowed capacity will present a negative value, which does not meet the design requirements of the installed capacity of the wind turbine at this time.

[0065] The voltage dip evaluation method of the AC bus according to the embodiment of the present disclosure can effectively establish the evaluation model of the wind turbine power capacity and the voltage dip of the AC bus, guarantee the safe start of the wind turbine in the wind power generation system, and at the same time ensure that the grid-connected current of the wind power generation system always remains in the safe working area, avoid the generation of overcurrent problems, and improve the fault ride-through capability of the wind power generation system.

[0066] Figure 5is a block diagram of a voltage dip assessment device of an AC bus according to an embodiment of the disclosure.

[0067] Referring to Figure 5 The voltage dip assessment device 500 of the AC bus includes a parameter extraction unit 510, a current calculation unit 520, and a voltage dip magnitude determination unit 530.

[0068] The parameter extraction unit 510 can extract impedance parameters of a first wind power generator and a second wind power generator, wherein the first wind power generator and the second wind power generator are connected in parallel to the AC bus, and the first wind power generator and the second wind power generator are both direct start-up wind power generators, the first wind power generator is in a stable operation state, and the second wind power generator is in a direct start-up state.

[0069] The current calculation unit 520 can calculate a rated operating current of the first wind power generator and a start-up transient current of the second wind power generator. Specifically, the current calculation unit 520 can calculate the rated operating current of the first wind power generator based on a power capacity, an operating voltage, and a power factor of the first wind power generator, and can calculate the start-up transient current of the second wind power generator based on a start-up reference coefficient, a power capacity, an operating voltage, and a power factor of the second wind power generator.

[0070] The voltage dip magnitude determination unit 530 can determine a voltage dip magnitude of the AC bus based on a reactance of the first wind power generator, the rated operating current of the first wind power generator, and the start-up transient current of the second wind power generator. The reactance of the first wind power generator can be determined based on a transient impedance and a sub-transient impedance of the first wind power generator. In this way, the voltage dip magnitude determination unit 530 can determine an average of the transient impedance and the sub-transient impedance of the first wind power generator as the reactance of the first wind power generator, and determine the voltage dip magnitude of the AC bus based on a product of the reactance of the first wind power generator and the start-up transient current of the second wind power generator and the rated operating current of the first wind power generator.

[0071] Alternatively, the voltage dip assessment device 500 of the AC bus further includes a maximum allowable capacity determination unit (not shown). The maximum allowable capacity determination unit can determine a voltage after a dip of the AC bus based on the voltage dip magnitude of the AC bus, and can determine a maximum allowable capacity of the second wind power generator based on a relationship between the voltage after the dip of the AC bus and a minimum limit voltage of the AC bus, or the relationship between the voltage after the dip of the AC bus and the minimum limit voltage of the AC bus and a minimum value of three-phase voltages of the AC bus. Here, the relationship between the voltage after the dip of the AC bus and the minimum limit voltage of the AC bus is that the voltage after the dip of the AC bus is greater than or equal to the minimum limit voltage of the AC bus.

[0072] Alternatively, the voltage dip evaluation device 500 of the AC bus further comprises a verification unit (not shown). The verification unit can determine the average effective voltage dip of the AC bus, and verify the determined voltage dip amplitude of the AC bus based on the average effective voltage dip of the AC bus. Further, the verification unit can divide the total area of the voltage curve of the AC bus into multiple intervals according to the start-up duration of the second wind turbine, and perform Riemann summation calculation to determine the average effective voltage dip of the AC bus.

[0073] Figure 6 is a block diagram illustrating a computing device according to an embodiment of the present disclosure. The computing device can be implemented in or as a control device of a wind power generation system, but the present disclosure is not limited thereto.

[0074] Referring to Figure 6 The computing device 600 according to an embodiment of the present disclosure can include a processor 610 and a memory 620. The processor 610 can include, but is not limited to, a central processing unit (CPU), a digital signal processor (DSP), a microcomputer, a field programmable gate array (FPGA), a system on chip (SoC), a microprocessor, an application specific integrated circuit (ASIC), etc. The memory 620 stores a computer program to be executed by the processor 610. The memory 620 includes a high-speed random access memory and / or a non-volatile computer readable storage medium. When the processor 610 executes the computer program stored in the memory 620, the voltage dip evaluation method of the AC bus as described above can be implemented.

[0075] The computing device 600 can communicate with each wind turbine in the wind power generation system in a wired / wireless communication manner, and can also communicate with a device outside the wind power generation system in a wired / wireless communication manner.

[0076] The control method of the wind power converter according to the embodiments of the present disclosure can be written as a computer program and stored on a computer-readable storage medium. When the computer program is executed by a processor, the voltage dip evaluation method of the AC bus can be implemented as described above. Examples of the computer-readable storage medium include a read-only memory (ROM), a random access programmable read-only memory (PROM), an electrically erasable programmable read-only memory (EEPROM), a random access memory (RAM), a dynamic random access memory (DRAM), a static random access memory (SRAM), a flash memory, a non-volatile memory, a CD-ROM, a CD-R, a CD+R, a CD-RW, a CD+RW, a DVD-ROM, a DVD-R, a DVD+R, a DVD-RW, a DVD+RW, a DVD-RAM, a BD-ROM, a BD-R, a BD-R LTH, a BD-RE, a Blu-ray or optical disc memory, a hard disk drive (HDD), a solid state drive (SSD), a card memory such as a multimedia card, a secure digital (SD) card or an extreme digital (XD) card, a magnetic tape, a floppy disk, a magneto-optical data storage device, an optical data storage device, a hard disk, a solid state disk, and any other device configured to store a computer program and any associated data, data files and data structures in a non-transitory manner and provide the computer program and any associated data, data files and data structures to a processor or computer so that the processor or computer can execute the computer program. In one example, the computer program and any associated data, data files and data structures are distributed over a networked computer system, so that the computer program and any associated data, data files and data structures are stored, accessed and executed by one or more processors or computers in a distributed manner.

[0077] The voltage dip evaluation method and evaluation device of the AC bus according to the embodiments of the present disclosure can effectively establish an evaluation model of the wind power generator power capacity and the AC bus voltage dip, guarantee the safe start of the wind power generator in the wind power generation system, ensure the wind power generation system grid-connected current always remains in a safe working zone, avoid the generation of overcurrent problems, and improve the fault ride-through capability of the wind power generation system. In addition, the voltage dip evaluation method and evaluation device of the AC bus according to the embodiments of the present disclosure are easy to implement in engineering and are convenient for popularization and application.

[0078] Although some embodiments of the present disclosure have been shown and described, those skilled in the art should understand that modifications can be made to these embodiments without departing from the principles and spirit of the present disclosure, which are defined by the scope of the claims and their equivalents.

Claims

1. A method of voltage sag assessment for an AC bus, characterized by, The voltage dip evaluation method comprises: extracting impedance parameters of the first wind turbine and the second wind turbine, wherein the first wind turbine and the second wind turbine are connected in parallel to the AC bus, and the first wind turbine and the second wind turbine are both direct start wind turbines, the first wind turbine is in a stable operation state, and the second wind turbine is in a direct start state; calculating a rated operating current of the first wind turbine and a start transient current of the second wind turbine; determining a voltage dip amplitude of the AC bus based on the inductive reactance of the first wind turbine, the rated operating current of the first wind turbine, and the start transient current of the second wind turbine, wherein the inductive reactance of the first wind turbine is determined based on the transient impedance and the sub-transient impedance of the first wind turbine.

2. The voltage sag assessment method of claim 1, wherein, The step of calculating the rated operating current of the first wind turbine and the start transient current of the second wind turbine comprises: calculating the rated operating current of the first wind turbine based on the power capacity, operating voltage, and power factor of the first wind turbine; calculating the start transient current of the second wind turbine based on the start reference coefficient, power capacity, operating voltage, and power factor of the second wind turbine.

3. The voltage sag assessment method of claim 1, wherein, The step of determining the voltage dip amplitude of the AC bus comprises: determining the average of the transient impedance and the sub-transient impedance of the first wind turbine as the inductive reactance of the first wind turbine; determining the voltage dip amplitude of the AC bus based on the product of the inductive reactance of the first wind turbine and the start transient current of the second wind turbine, and the rated operating current of the first wind turbine.

4. The voltage sag assessment method of claim 1, wherein, The voltage dip evaluation method further comprises: determining a voltage after dip of the AC bus based on the voltage dip amplitude of the AC bus; determining a maximum allowable capacity of the second wind turbine based on a relationship between the voltage after dip of the AC bus and the minimum limit voltage of the AC bus, or based on the relationship between the voltage after dip of the AC bus and the minimum limit voltage of the AC bus and the minimum value of the three-phase voltage of the AC bus.

5. The voltage sag assessment method of claim 4 wherein, The relationship between the voltage after dip of the AC bus and the minimum limit voltage of the AC bus is that the voltage after dip of the AC bus is greater than or equal to the minimum limit voltage of the AC bus.

6. The voltage sag assessment method of claim 1, wherein, The voltage dip evaluation method further comprises: determining an average effective dip voltage of the AC bus; verifying the determined voltage dip amplitude of the AC bus based on the average effective dip voltage of the AC bus.

7. The voltage sag assessment method of claim 6 wherein, The step of determining the average effective dip voltage of the AC bus comprises: dividing the total area of the voltage curve of the AC bus into multiple intervals according to the start duration of the second wind turbine for Riemann summation calculation to determine the average effective dip voltage of the AC bus.

8. An apparatus for voltage sag assessment of an AC bus, characterized by, The voltage dip evaluation device comprises: The parameter extraction unit is configured to extract impedance parameters of a first wind power generator and a second wind power generator, wherein the first wind power generator and the second wind power generator are connected in parallel to the AC bus, and the first wind power generator and the second wind power generator are both direct start-up wind power generators, the first wind power generator is in a stable operation state, and the second wind power generator is in a direct start-up state. The current calculation unit is configured to calculate a rated working current of the first wind power generator and a start-up transient current of the second wind power generator. The voltage sag amplitude determination unit is configured to determine a voltage sag amplitude of the AC bus based on a reactance of the first wind power generator, the rated working current of the first wind power generator, and the start-up transient current of the second wind power generator, wherein the reactance of the first wind power generator is determined based on a transient impedance and a sub-transient impedance of the first wind power generator.

9. A computer readable storage medium storing a computer program, characterized in that, When the computer program is executed by the processor, the voltage sag evaluation method of the AC bus is implemented as claimed in any one of claims 1 to 7.

10. A computing device, comprising: The computing device comprises: a processor; and a memory storing a computer program, wherein the computer program is executed by the processor to implement the voltage sag evaluation method of the AC bus as claimed in any one of claims 1 to 7.

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