An electromagnetic transient equivalent modeling method for offshore wind farms

Abstract

The application belongs to the technical field of power systems, and discloses a kind of offshore wind farm electromagnetic transient equivalent modeling method, comprising: obtaining the connection mode of offshore wind farm fan, the fan that is merged into offshore booster station through same AC submarine cable is divided into an equivalent area;Equivalent fan and equivalent AC submarine cable parameters are obtained according to the connection mode of fan using corresponding equivalent method;According to the equivalent fan and equivalent AC submarine cable parameters of each equivalent area obtained, an equivalent electromagnetic transient model of offshore wind farm is established.The beneficial effect is that the fan in the same AC submarine cable is divided into an equivalent area, and an equivalent area is equivalent to an equivalent fan and an equivalent AC cable, effectively coordinating the contradiction between calculation accuracy and simulation efficiency in offshore wind farm electromagnetic transient simulation, which can effectively ensure the equivalent accuracy of offshore wind farm, and can simplify several wind turbine generators to several fans for calculation, greatly improving the electromagnetic transient simulation efficiency of offshore wind farm.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power systems, in particular to a kind of offshore wind farm electromagnetic transient equivalent modeling method. BACKGROUND

[0002] Offshore wind power represents the frontier and commanding heights of wind power technology field, will become the development focus of future wind power market, also is the important content of strategic emerging industry. Large-scale grid connection of offshore wind power brings profound changes to the transient and dynamic characteristics of power system.

[0003] In order to solve the problem of grid connection of offshore wind power, it is necessary to establish simulation model to simulate and analyze the operation of offshore wind farm. The general technical means in the prior art electromagnetic transient simulation software Power Systems Computer Aaded Desagn (PSCAD) and Matrax Laboratory (MATLAB) cannot realize detailed electromagnetic transient modeling of all wind turbines in wind farm. While electromagnetic transient simulation platform Power System Model (PSModel) can establish detailed electromagnetic transient model for each wind turbine respectively, and more accurately analyze the grid operation characteristics of offshore wind farm, but the data processing and calculation amount is considerable, and the simulation efficiency of electromagnetic transient is also significantly reduced.

[0004] Therefore, it is necessary to improve the existing modeling method, and improve the operation efficiency of the model on the basis of electromagnetic transient modeling of all wind turbines. SUMMARY

[0005] The purpose of the present application is to provide a new kind of offshore wind farm electromagnetic transient equivalent modeling method, improve the efficiency of modeling simulation operation.

[0006] In order to achieve the above purpose, the present application provides a kind of offshore wind farm electromagnetic transient equivalent modeling method, comprising:

[0007] The connection mode of each wind turbine in offshore wind farm into offshore booster station is obtained, and the wind turbines into offshore booster station through the same AC submarine cable are divided into an equivalent area;

[0008] The connection mode of wind turbine in each equivalent area is determined, the equivalent method of wind turbine is determined according to the connection mode of wind turbine, the wind turbine in equivalent area is equivalent according to the determined equivalent method, and the equivalent wind turbine and equivalent AC submarine cable parameter are obtained;

[0009] According to the equivalent wind turbine and equivalent AC submarine cable parameter of each equivalent area obtained, the equivalent electromagnetic transient model of offshore wind farm is established.

[0010] Further, the connection mode of the fan in each equivalent area is determined, the equivalent method of the fan is determined according to the connection mode of the fan, the fan in the equivalent area is equivalent according to the determined equivalent method, and equivalent fan and equivalent AC sea cable parameters are obtained, specifically as follows:

[0011] If the fan in the a-th equivalent area is in series connection mode, the a-th equivalent fan and the a-th equivalent AC sea cable parameters of the a-th equivalent area are obtained by using fan series connection equivalent method;

[0012] If the fan in the b-th equivalent area is in parallel connection mode, the b-th equivalent fan and the b-th equivalent AC sea cable parameters of the b-th equivalent area are obtained by using fan parallel connection equivalent method;

[0013] If the fan in the c-th equivalent area is in mixed connection mode, the c-th equivalent fan and the c-th equivalent AC sea cable parameters of the c-th equivalent area are obtained by using fan mixed connection equivalent method; a, b, and c are serial numbers of the equivalent areas.

[0014] Further, if the fan in the a-th equivalent area is in series connection mode, the a-th equivalent fan and the a-th equivalent AC sea cable parameters of the a-th equivalent area are obtained by using fan series connection equivalent method, specifically as follows:

[0015] PA type line equivalent parameters of the AC sea cable of the a-th equivalent area, AC outlet voltage of each fan, and average value and reactive power consumption of voltage drop of the AC sea cable are obtained;

[0016] Equivalent fan and equivalent AC sea cable parameters are obtained according to the PA type line equivalent parameters, the AC outlet voltage of each fan, and the average value and the reactive power consumption of the voltage drop of each AC sea cable.

[0017] Further, the AC outlet voltage of each fan is obtained, specifically as follows:

[0018] The fans are sequentially numbered from 1 to n according to transmission distance of the fan to the offshore booster station, the transmission distance of the n-th fan to the offshore booster station is the farthest, the outlet AC voltage of each fan is recorded as to The active power output of each fan is recorded as to ;

[0019] A middle fan in the several fans is selected as a reference fan, the middle fan is the x-th fan, x = n / 2; and the AC voltage at the outlet of the x-th fan is set as the first reference voltage; the outlet AC voltage of each series fan is calculated according to the first reference voltage.

[0020] ​Further, the outlet AC voltage of each serial fan is calculated according to the first reference voltage, specifically:

[0021] The outlet AC voltage of the first fan to the xth fan is calculated according to the first formula, specifically:

[0022] ;

[0023] wherein the jth fan in the serial type outputs active power according to the rated capacity , represents the equivalent resistance value of the AC cable between the jth fan and the (j-1)th fan, represents the equivalent reactance value of the AC cable between the jth fan and the (j-1)th fan; j is the number of the fan;

[0024] The outlet AC voltage of the x+1th fan to the nth fan is calculated according to the second formula, specifically:

[0025] .

[0026] Further, the reactive power consumption of the AC submarine cable is obtained, specifically:

[0027] The reactive power consumption of the AC submarine cable is obtained according to the third formula, specifically:

[0028] ;

[0029] is the reactive power consumption of the AC submarine cable, represents the equivalent susceptance value of the AC cable between the jth fan and the (j-1)th fan.

[0030] Further, if the fans in the bth equivalent area are in parallel connection mode, the bth equivalent fan and the bth equivalent AC submarine cable parameters of the bth equivalent area are obtained by using the fan parallel connection equivalent method, specifically:

[0031] The PA type line equivalent parameters of the AC submarine cable of the bth equivalent area, the AC outlet voltage of each fan and the average value of the voltage drop and the reactive power consumption of the AC submarine cable are obtained;

[0032] The equivalent fan and the equivalent AC submarine cable parameters are obtained according to the PA type line equivalent parameters, the AC outlet voltage of each fan and the average value of the voltage drop and the reactive power consumption of each AC submarine cable.

[0033] Further, the AC processing voltage of each fan is obtained, specifically:

[0034] The number of the fans in the bth equivalent area is numbered from 1 to n, and the outlet AC voltage of each fan numbered in turn is denoted as arrive The AC voltage at the outlet of the offshore booster station is denoted as The active power output of each wind turbine, numbered sequentially, is recorded as follows: arrive .

[0035] The AC voltage of the offshore substation is selected as the second reference voltage; the AC voltage at the outlet of each parallel fan is calculated based on the second reference voltage.

[0036] Furthermore, the calculation of the AC outlet voltage of each parallel fan based on the second reference voltage specifically involves:

[0037] The outlet AC voltage of each parallel fan is calculated according to the fourth formula, which is as follows:

[0038] ;

[0039] Among them, the rated active power of each wind turbine ; Indicates wind turbine j The equivalent resistance value of the AC cable between the substation and the offshore substation. Indicates wind turbine j The equivalent reactance value of the AC cable between the substation and the offshore substation.

[0040] Furthermore, if the wind turbines in the c-th equivalent region are connected in a mixed configuration, then the c-th equivalent wind turbine and c-th equivalent AC submarine cable parameters in the c-th equivalent region are obtained using the wind turbine mixed connection equivalent method, specifically as follows:

[0041] The c-th equivalent region includes several series-connected wind turbines and several parallel-connected wind turbines. If the wind turbines are connected to the offshore substation in a series-first and then parallel manner, the equivalent method of wind turbine series connection is used first, and then the equivalent method of wind turbine parallel connection is used for equivalence.

[0042] If the wind turbines are connected to the offshore substation in parallel first and then in series, then the equivalent method of wind turbine parallel connection should be used first, followed by the equivalent method of wind turbine series connection.

[0043] Compared with existing technologies, the electromagnetic transient equivalent modeling method for offshore wind farms proposed in this invention has the following advantages: This invention divides the wind turbines in the same AC submarine cable into an equivalent region, and equates an equivalent region to an equivalent wind turbine and an equivalent AC cable. This effectively coordinates the contradiction between calculation accuracy and simulation efficiency in the electromagnetic transient simulation of offshore wind farms. It can effectively ensure the external equivalent accuracy of offshore wind farms, and can simplify dozens or even hundreds of wind turbine units into a few wind turbines for calculation, greatly improving the electromagnetic transient simulation efficiency of offshore wind farms. Attached Figure Description

[0044] Figure 1 is a first flowchart of a method for electromagnetic transient equivalent modeling of an offshore wind farm according to the present application;

[0045] Figure 2 is a second flowchart of a method for electromagnetic transient equivalent modeling of an offshore wind farm according to the present application;

[0046] Figure 3 is a schematic diagram of a series connection mode of wind turbines in an equivalent region and an equivalent transient model in a method for electromagnetic transient equivalent modeling of an offshore wind farm according to the present application;

[0047] Figure 4 is a schematic diagram of a parallel connection mode of wind turbines in an equivalent region and an equivalent transient model in a method for electromagnetic transient equivalent modeling of an offshore wind farm according to the present application;

[0048] Figure 5 is a schematic diagram of a mixed connection mode of wind turbines in an equivalent region and an equivalent transient model in a method for electromagnetic transient equivalent modeling of an offshore wind farm according to the present application;

[0049] Figure 6 is a schematic diagram of a wind farm modeling of an equivalent region including only a series connection mode in a method for electromagnetic transient equivalent modeling of an offshore wind farm according to the present application;

[0050] Figure 7 is a schematic diagram of a wind farm modeling of an equivalent region including only a parallel connection mode in a method for electromagnetic transient equivalent modeling of an offshore wind farm according to the present application. DETAILED DESCRIPTION

[0051] The specific embodiments of the present application will be further described in detail below with reference to the accompanying drawings and examples. The following examples are used to illustrate the present application, but are not used to limit the scope of the present application.

[0052] To help the public better understand the technical solutions of the present application, the electromagnetic transient simulation technology is further described. The electromagnetic transient simulation technology is an important basis for power system research, planning and operation, and is a key technology for fully understanding and understanding the characteristics of the power system. As the most accurate simulation method in simulation at present, electromagnetic transient simulation is mainly used for detailed simulation of the mutual conversion of electricity and magnetism in the power system and the transient process of the circuit, and has the ability to accurately simulate a large number of power electronic devices such as DC systems and new energy. Therefore, based on electromagnetic transient simulation, the study of the influence of offshore wind farms on the transient characteristics of offshore wind power, the selection of access modes and the stability of large power grids is of great significance, and it is urgent to study the electromagnetic transient simulation method of offshore wind farms. Currently, a large offshore wind farm generally includes dozens or even hundreds of wind turbine generators, and in the modeling process, accuracy and efficiency cannot be considered, and improvement is needed.

[0053] For example, Figure 1 and Figure 2As shown, the application discloses a kind of offshore wind farm electromagnetic transient equivalent modeling method, mainly includes the following steps:

[0054] Step S1, obtain the connection mode of each wind turbine in offshore wind farm into offshore booster station, wind turbine into offshore booster station through the same AC submarine cable is divided into an equivalent area;

[0055] Step S2, determine the connection mode of the wind turbine in each equivalent area, determine the equivalent method of wind turbine according to the connection mode of wind turbine, the wind turbine in equivalent area is equivalent according to the equivalent method determined, and the equivalent wind turbine and equivalent AC submarine cable parameters are obtained;

[0056] Step S3, according to the equivalent wind turbine and equivalent AC submarine cable parameters of each equivalent area obtained, an equivalent electromagnetic transient model of offshore wind farm is established.

[0057] In step S1, obtain the connection mode of each wind turbine in offshore wind farm into offshore booster station, wind turbine into offshore booster station through the same AC submarine cable is divided into an equivalent area.

[0058] In this embodiment, offshore wind farm includes several wind turbines and several offshore booster stations, offshore booster station connects several AC submarine cables, and offshore booster station connects several wind turbines through AC submarine cable. Multiple wind turbines on the same AC submarine cable are divided into an equivalent area, and all wind turbines in an equivalent area are equivalent to an equivalent wind turbine, and the number of wind turbines in simulation modeling is reduced by equivalent wind turbine.

[0059] In this embodiment, one offshore wind farm can include several equivalent areas, and the connection mode of wind turbine in different equivalent areas can be the same or different, and according to the connection mode of wind turbine in equivalent area, it can be divided into series connection mode, parallel connection mode and mixed connection mode.

[0060] Referring to Figure 3 , Figure 4 and Figure 5 , it can be seen that the connection mode between wind turbines in the same equivalent area can be divided into three kinds. Figure 3 It is series connection mode, and the series connection mode is specifically: multiple wind turbines are connected in series through the same AC submarine cable to the same offshore booster station. Figure 4 It is parallel connection mode, and the parallel connection mode is specifically: multiple wind turbines are connected in parallel through the same AC submarine cable to the same offshore booster station. Figure 5 It is mixed connection mode, and the mixed connection mode is specifically: mixed connection includes two connection modes, one is that multiple wind turbines are connected in series to form a first branch, and multiple first branches are connected in parallel on the same AC submarine cable; the other is that multiple wind turbines are connected in parallel to form a second branch, and multiple second branches are connected in series on the same AC submarine cable. Because the connection mode of wind turbine is different, different equivalent methods are needed to equivalent equivalent area.

[0061] In step S2, the connection method of the wind turbines in each equivalent region is determined, and the equivalent method of the wind turbines is determined according to the connection method. The wind turbines in the equivalent region are then equivalent according to the determined equivalent method to obtain the equivalent wind turbines and equivalent AC submarine cable parameters. Specifically:

[0062] If the wind turbines in the a-th equivalent region are connected in series, then the wind turbine series equivalent method is used to obtain the parameters of the a-th equivalent wind turbine and the a-th equivalent AC submarine cable in the a-th equivalent region.

[0063] If the wind turbines in the b-th equivalent region are connected in parallel, then the b-th equivalent wind turbine and b-th equivalent AC submarine cable parameters in the b-th equivalent region are obtained by using the wind turbine parallel connection equivalent method.

[0064] If the wind turbines in the c-th equivalent region are in a mixed connection mode, then the c-th equivalent wind turbine and c-th equivalent AC submarine cable parameters in the c-th equivalent region are obtained by using the wind turbine mixed connection equivalent method; a, b, and c are the serial numbers of each equivalent region.

[0065] In this embodiment, if the wind turbines in the a-th equivalent region are connected in series, the wind turbine series equivalent method is used to obtain the parameters of the a-th equivalent wind turbine and the a-th equivalent AC submarine cable in the a-th equivalent region, specifically:

[0066] Obtain the equivalent parameters of the PA type line of the AC submarine cable in the a-th equivalent region, obtain the AC outlet voltage of each wind turbine, and obtain the average voltage drop and reactive power consumption of the AC submarine cable.

[0067] The equivalent wind turbine and equivalent AC submarine cable parameters are obtained based on the equivalent parameters of the PA type line, the AC outlet voltage of each wind turbine, the average voltage drop of each AC submarine cable segment, and the reactive power consumption.

[0068] In this real-time example, the equivalent parameters of the PA type line of the AC submarine cable in the a-th equivalent region are obtained by: calculating the equivalent parameters of the PI type line of all AC submarine cables in the region based on the specifications and length of the AC submarine cable.

[0069] In this embodiment, obtaining the AC outlet voltage of each wind turbine specifically involves:

[0070] Based on the transmission distance from the wind turbine to the offshore substation, the wind turbines are numbered sequentially from 1 to n, with the nth wind turbine having the longest transmission distance. The outlet AC voltage of each sequentially numbered wind turbine is denoted as... arrive The active power output of each sequentially numbered wind turbine is recorded as follows: arrive ;

[0071] Select several middle fans in the wind turbine as the reference fan, the middle fan is the xth fan, x=n / 2; and set the alternating voltage of the xth fan outlet is the first reference voltage; the outlet alternating voltage of each series fan is calculated according to the first reference voltage.

[0072] In this embodiment, the outlet alternating voltage of each series fan is calculated according to the first reference voltage, specifically:

[0073] The outlet alternating voltage of the first fan to the xth fan is calculated according to the first formula, and the first formula is specifically:

[0074] ;

[0075] Wherein, the jth series fan outputs active power according to the rated capacity , represents the equivalent resistance value of the alternating cable between the jth fan and the (j-1)th fan, represents the equivalent reactance value of the alternating cable between the jth fan and the (j-1)th fan; j is the number of the fan;

[0076] The outlet alternating voltage of the x+1th fan to the nth fan is calculated according to the second formula, and the second formula is specifically:

[0077] .

[0078] In this embodiment, the reactive power consumption of the alternating sea cable is obtained, specifically:

[0079] The reactive power consumption of the alternating cable is obtained according to the third formula, and the third formula is specifically:

[0080] ;

[0081] is the reactive power consumption of the alternating sea cable, represents the equivalent susceptance value of the alternating cable between the jth fan and the (j-1)th fan.

[0082] In this embodiment, referring to Figure 6 , if the wind farm only contains one equivalent area, and the fan of the equivalent area is series, the step of establishing the electromagnetic transient model includes:

[0083] Step 101: according to the specifications and length of the alternating sea cable, the PI type line equivalent parameters of all alternating sea cables in the area are calculated, specifically including PI type line resistance R , reactance X and ground capacitance B .

[0084] Step 102: forn The wind turbines are connected in series, and according to the distance between the wind turbines and the offshore booster station, the wind turbines are numbered from 1 to n The outlet AC voltage of each wind turbine is numbered, and the outlet AC voltage of each wind turbine is The outlet AC voltage of the offshore booster station is The active power output of each wind turbine is .

[0085] Step 103: Selecting the middle wind turbine of the series-connected wind turbines as the reference wind turbine, and setting the outlet AC voltage of the first wind turbine as the reference voltage. n x x n Step 104: Calculating the outlet AC voltage of the offshore booster station and each wind turbine. x According to the rated capacity, the active power output of the series-connected wind turbine is set as

[0086] Step 105: Calculating the voltage drop between the wind turbine and the offshore booster station and the reactive power consumption of the AC submarine cable.

[0087] The equivalent resistance value of the AC cable between the wind turbine and the wind turbine-1 is represented as j The equivalent reactance value of the AC cable between the wind turbine and the wind turbine-1 is represented as j According to the first formula, the outlet AC voltage of the wind turbine 1 to the wind turbine j j j According to the second formula, the outlet AC voltage of the wind turbine x

[0088] ;

[0089] x n

[0090]

[0091] Step 105: Calculating the voltage drop between the wind turbine n and the offshore booster station and the reactive power consumption of the AC submarine cable.

[0092] The voltage drop between the wind turbine n and the offshore booster station is determined as .

[0093] According to the third formula, the reactive power consumption of the entire AC submarine cable is calculated according to the outlet voltage of each wind turbine and the ground admittance of each section of the AC submarine cable. ​​​​​​​​​​​​​​​​​Representing the fan j With the fan j The equivalent susceptance value of the AC cable between the -1.

[0094] ;

[0095] Step 106: Calculate the equivalent fan active power output.

[0096] According to n The rated active power of the fan, the active power output of the equivalent fan is calculated according to the following formula.

[0097] ;

[0098] Step 107: Calculate the equivalent AC cable parameters.

[0099] According to the principle of keeping the voltage drop of the equivalent AC cable unchanged before and after, the following complex equation is obtained, according to the principle of keeping the real part and imaginary part of the left and right ends of the complex equation equal, the equivalent resistance of the equivalent AC cable is solved And the equivalent reactance According to the principle of keeping the reactive loss of the ground admittance branch unchanged before and after, as shown in the following formula, the ground admittance .

[0100] ;

[0101] ;

[0102] Step 108: Establish the electromagnetic transient model of the equivalent fan and the equivalent AC cable in a single equivalent area.

[0103] Finally, the electromagnetic transient equivalent model of the wind farm is obtained as shown in Figure 2 .

[0104] In this embodiment, if the fan in the bth equivalent area is in parallel connection mode, the fan parallel equivalent method is used to obtain the bth equivalent fan and the bth equivalent AC cable parameters of the bth equivalent area, which are as follows:

[0105] Obtain the PA type line equivalent parameters of the AC cable in the bth equivalent area, the AC outlet voltage of each fan, and the average value and reactive power consumption of the voltage drop of the AC cable;

[0106] According to the PA type line equivalent parameters, the AC outlet voltage of each fan, and the average value and reactive power consumption of the voltage drop of each AC cable, the equivalent fan and the equivalent AC cable parameters are obtained.

[0107] In this embodiment, the AC processing voltage of each fan is obtained, which is as follows:

[0108] Number the fans in the equivalent region b from 1 to n, and denote the AC outlet voltage of each fan as follows: arrive The AC voltage at the outlet of the offshore booster station is denoted as The active power output of each wind turbine, numbered sequentially, is recorded as follows: arrive .

[0109] The AC voltage of the offshore substation is selected as the second reference voltage; the AC voltage at the outlet of each parallel fan is calculated based on the second reference voltage.

[0110] In this embodiment, the calculation of the AC outlet voltage of each parallel fan based on the second reference voltage specifically involves:

[0111] The outlet AC voltage of each parallel fan is calculated according to the fourth formula, which is as follows:

[0112] ;

[0113] Among them, the rated active power of each wind turbine ; Indicates wind turbine j The equivalent resistance value of the AC cable between the substation and the offshore substation. Indicates wind turbine j The equivalent reactance value of the AC cable between the substation and the offshore substation.

[0114] In this embodiment, obtaining the reactive power consumption of the submarine cable specifically involves:

[0115] The reactive power consumption of AC cables is obtained according to the fifth formula, which is as follows:

[0116] ;

[0117] in, To account for the reactive power consumption of the AC submarine cable, Indicates wind turbine j The equivalent susceptance of the AC cable between the substation and the offshore substation.

[0118] In this embodiment, refer to Figure 7 If a wind farm comprises only one equivalent region, and the wind turbines in that region are connected in parallel, then the steps for establishing an electromagnetic transient model include:

[0119] Step 201: Based on the specifications and length of the AC submarine cables, calculate the equivalent parameters of the PI-type lines for all AC submarine cables within the area, specifically including the PI-type line resistance. R Reactance X and capacitance to ground B .

[0120] Step 202: Calculate the AC voltage at the outlet of each wind turbine. n The wind turbines are connected in parallel, and the AC voltage at the outlet of each wind turbine is calculated according to the following formula: n The wind turbines are numbered, and the AC voltage at the outlet of each wind turbine is calculated according to the following formula: The AC voltage at the outlet of the offshore booster station is calculated according to the following formula: The active power output of each wind turbine is calculated according to the following formula: .

[0121] Step 203: Select the AC voltage at the outlet of the offshore booster station as the reference voltage.

[0122] Step 204: Calculate the AC voltage at the outlet of each wind turbine.

[0123] According to the rated active power of each wind turbine, the AC voltage at the outlet of each parallel wind turbine is calculated according to the following formula: wherein R represents the equivalent resistance value of the AC cable between the wind turbine and the offshore booster station, and X represents the equivalent reactance value of the AC cable between the wind turbine and the offshore booster station. The fourth formula is as follows: j j

[0124] ;

[0125] Step 205: Calculate the average value of the AC sea cable voltage drop and the reactive power consumption.

[0126] According to the obtained outlet voltage of each wind turbine and the ground admittance of each section of AC sea cable, the reactive power consumption of all AC sea cables is calculated according to the fifth formula.

[0127] wherein Y represents the equivalent admittance value of the AC cable between the wind turbine and the offshore booster station. The fifth formula is as follows: j

[0128] ;

[0129] Step 206: Calculate the active power output of the equivalent wind turbine.

[0130] According to the rated active power of the wind turbine, the active power output of the equivalent wind turbine is calculated according to the following formula: n

[0131] ; Step 207: Calculate the equivalent AC sea cable parameters.

[0132]

[0133] ​​​​​​​​​​The principle of setting the equivalent post-AC sea cable voltage drop to be consistent with the average value of the voltage drops of each AC sea cable line before the equivalent is obtained as follows: According to the principle of the real part and the imaginary part of the left and right ends being equal, the equivalent resistance of the equivalent AC sea cable is solved and the equivalent reactance . According to the principle of the reactive loss of the ground admittance branch being unchanged before and after the equivalent, the ground admittance is solved as shown in the following formula .

[0134]

[0135]

[0136] Step 208: Determine the electromagnetic transient model of the equivalent wind turbine and the equivalent AC sea cable of a single equivalent area.

[0137] In this embodiment, with reference to Figure 5 , if the wind turbine in the cth equivalent area is connected in a mixed connection mode, the cth equivalent wind turbine and the cth equivalent AC sea cable parameters of the cth equivalent area are obtained by using the wind turbine mixed connection equivalent method, specifically as follows:

[0138] If the wind turbine in the cth equivalent area includes a plurality of series-connected wind turbines and a plurality of parallel-connected wind turbines, if the wind turbine is connected to the offshore booster station in a series-parallel connection mode, the wind turbine series connection equivalent method is used first, and then the wind turbine parallel connection equivalent method is used for equivalent.

[0139] If the wind turbine is connected to the offshore booster station in a parallel-series connection mode, the wind turbine parallel connection equivalent method is used first, and then the wind turbine series connection equivalent method is used.

[0140] In this embodiment, a person skilled in the art can first determine the specific situation of the mixed connection of the plurality of wind turbines, and then select the equivalent method according to the specific situation.

[0141] If the wind turbine is connected to the common point in a series connection mode, and each common point is connected in a parallel connection mode, the series connection equivalent method is used first to equivalent the wind turbine in a series connection mode to a single equivalent wind turbine, and then the parallel connection equivalent method is used to equivalent the wind turbine in a parallel connection mode to a single equivalent wind turbine.

[0142] If the wind turbine is connected to the common point in a parallel connection mode, and each common point is connected in a series connection mode, the parallel connection equivalent method is used first to equivalent the wind turbine in a parallel connection mode to a single equivalent wind turbine, and then the series connection equivalent method is used to equivalent the wind turbine in a series connection mode to a single equivalent wind turbine.

[0143] In step S3, according to the equivalent wind turbine and the equivalent AC sea cable parameters of each equivalent area obtained, an equivalent electromagnetic transient model of the offshore wind farm is established, specifically as follows:

[0144] According to the determined equivalent wind turbine and equivalent AC sea cable parameters, each equivalent area is simplified into a single equivalent wind turbine connected to the offshore booster station through an equivalent AC sea cable, an electromagnetic transient equivalent modeling method of the offshore wind farm is established, and finally electromagnetic transient simulation calculation is performed.

[0145] Compared with the prior art, the offshore wind farm electromagnetic transient equivalent modeling method provided by the embodiments of the present application has the beneficial effects that: the wind turbines in the same AC sea cable are divided into an equivalent area, and one equivalent area is equivalent to an equivalent wind turbine and an equivalent AC cable, the contradiction between the calculation accuracy and the simulation efficiency in the electromagnetic transient simulation of the offshore wind farm is effectively coordinated, the equivalent accuracy of the offshore wind farm to the outside world can be effectively ensured, and dozens or even hundreds of wind turbine generators can be simplified into several wind turbines for calculation, so that the electromagnetic transient simulation efficiency of the offshore wind farm is greatly improved.

[0146] The above description is only the preferred embodiments of the present application, and it should be pointed out that for ordinary skilled in the art, without departing from the technical principles of the present application, a number of improvements and substitutions can be made, and these improvements and substitutions should be considered as the protection scope of the present application.

Claims

1. A method of electromagnetic transient equivalent modeling of an offshore wind farm, characterized in that, The method comprises the following steps: The connection mode of each wind turbine in the offshore wind farm to the offshore booster station is obtained, and wind turbines connected to the offshore booster station through the same AC submarine cable are divided into an equivalent area; If the wind turbines in the a-th equivalent area are connected in series, the a-th equivalent wind turbine and the a-th equivalent AC submarine cable parameters of the a-th equivalent area are obtained by using a wind turbine series connection equivalent method; If the wind turbines in the b-th equivalent area are connected in parallel, the b-th equivalent wind turbine and the b-th equivalent AC submarine cable parameters of the b-th equivalent area are obtained by using a wind turbine parallel connection equivalent method; If the wind turbines in the c-th equivalent area are connected in mixed mode, the c-th equivalent wind turbine and the c-th equivalent AC submarine cable parameters of the c-th equivalent area are obtained by using a wind turbine mixed connection equivalent method; a, b, and c are serial numbers of the equivalent areas; An equivalent electromagnetic transient model of the offshore wind farm is established according to the equivalent wind turbine and equivalent AC submarine cable parameters of each equivalent area obtained; If the wind turbines in the a-th equivalent area are connected in series, the a-th equivalent wind turbine and the a-th equivalent AC submarine cable parameters of the a-th equivalent area are obtained by using a wind turbine series connection equivalent method, specifically as follows: PA type line equivalent parameters of the AC submarine cable of the a-th equivalent area are obtained, the AC outlet voltage of each wind turbine is obtained, and the average value of voltage drop and reactive power consumption of the AC submarine cable are obtained; The equivalent wind turbine and equivalent AC submarine cable parameters are obtained according to the PA type line equivalent parameters, the AC outlet voltage of each wind turbine, and the average value of voltage drop and reactive power consumption of each section of the AC submarine cable; The AC outlet voltage of each wind turbine is obtained, specifically as follows: According to the transmission distance of the wind turbine to the offshore booster station, the wind turbines are numbered from 1 to n in sequence, the transmission distance of the nth wind turbine to the offshore booster station is the farthest, the outlet alternating voltage of each wind turbine numbered in sequence is recorded as to , the active power output of each wind turbine numbered in sequence is recorded as to ; Selecting several middle fans in the fans as reference fans, the middle fan is the xth fan, x = n / 2; and setting the alternating voltage of the outlet of the xth fan as the first reference voltage is the first reference voltage; calculating the alternating voltage of the outlet of each series fan according to the first reference voltage; If the wind turbines in the b-th equivalent area are connected in parallel, the b-th equivalent wind turbine and the b-th equivalent AC submarine cable parameters of the b-th equivalent area are obtained by using a wind turbine parallel connection equivalent method, specifically as follows: PA type line equivalent parameters of the AC submarine cable of the b-th equivalent area are obtained, the AC outlet voltage of each wind turbine is obtained, and the average value of voltage drop and reactive power consumption of the AC submarine cable are obtained; The equivalent wind turbine and equivalent AC submarine cable parameters are obtained according to the PA type line equivalent parameters, the AC outlet voltage of each wind turbine, and the average value of voltage drop and reactive power consumption of each section of the AC submarine cable; The AC outlet voltage of each wind turbine is obtained, specifically as follows: The several wind turbines in the b equivalent area are numbered from 1 to n, and the outlet alternating voltage of each wind turbine numbered in turn is recorded as to , the outlet alternating voltage of the offshore booster station is recorded as , and the active power output of each wind turbine numbered in turn is recorded as to ; The AC voltage of the offshore booster station is selected as a second reference voltage; and the AC outlet voltage of each parallel wind turbine is calculated according to the second reference voltage.

2. A method of electromagnetic transient equivalent modeling of an offshore wind farm according to claim 1, characterized in that, The AC outlet voltage of each series wind turbine is calculated according to the first reference voltage, specifically as follows: The AC outlet voltage of the first wind turbine to the x-th wind turbine is calculated according to a first formula, and the first formula is specifically as follows: ； Among them, the j-th wind turbine in the series configuration is set to output active power according to its rated capacity. , This represents the equivalent resistance value of the AC cable between fan j and fan j-1. This represents the equivalent reactance value of the AC cable between fan j and fan j-1; j is the fan number. The AC outlet voltage of the x+1-th wind turbine to the n-th wind turbine is calculated according to a second formula, and the second formula is specifically as follows: 。 3. A method of electromagnetic transient equivalent modeling of an offshore wind farm according to claim 2, characterized in that, The reactive power consumption of the AC submarine cable is obtained, specifically as follows: The reactive power consumption of the AC submarine cable is obtained according to a third formula, and the third formula is specifically as follows: ； to compensate for the reactive consumption of the AC sea cable, represents the equivalent susceptance value of the AC cable between fan j and fan j-1.

4. A method of electromagnetic transient equivalent modeling of an offshore wind farm according to claim 3, characterized in that, The AC outlet voltage of each parallel wind turbine is calculated according to the second reference voltage, specifically as follows: The AC outlet voltage of each parallel wind turbine is calculated according to a fourth formula, and the fourth formula is specifically as follows: ； wherein the rated active power of each wind turbine ; represents the equivalent resistance value of the AC cable between the wind farm j and the offshore substation, represents the equivalent resistance value of the AC cable between the wind farm j and the offshore substation.

5. The electromagnetic transient equivalent modeling method of an offshore wind farm according to claim 1, characterized in that, If the wind turbines in the c-th equivalent area are connected in mixed mode, the c-th equivalent wind turbine and the c-th equivalent AC submarine cable parameters of the c-th equivalent area are obtained by using a wind turbine mixed connection equivalent method, specifically as follows: The wind turbine in the C equivalent area includes several series-connected wind turbines and several parallel-connected wind turbines, and if the wind turbine is connected to the offshore booster station in the mode of first series connection and then parallel connection, the wind turbine series connection equivalent method is used first, and then the wind turbine parallel connection equivalent method is used for equivalence; If the wind turbine is connected to the offshore booster station in the mode of first parallel connection and then series connection, the wind turbine parallel connection equivalent method is used first, and then the wind turbine series connection equivalent method is used.

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