A design method and system for virtual transient reactance of wind turbine generator

Abstract

The present invention provides a design method and system for a virtual transient reactance of a wind turbine. The method first establishes a relationship between the current-limiting reactance and the equivalent reactance of the wind turbine based on the short-circuit capacity of the grid connection point and the rated capacity of the wind turbine. Secondly, based on the short-circuit capacity of the wind power grid connection point and the transmission capacity of the wind turbine under different voltage drops, the short-circuit ratio requirement under voltage drop conditions is obtained. Finally, based on the short-circuit ratio requirement model under voltage drop constraints, the transient reactance parameter values ​​of the wind turbine are coordinated and designed to obtain the optimal transient impedance value for fully utilizing the voltage support potential of the wind turbine. By obtaining the optimal transient reactance value, the present invention fully utilizes the voltage support potential of the wind turbine and can significantly improve the voltage stability of the wind turbine system.

Description

Technical Field

[0001] The present invention relates to the technical field of active voltage support for a novel power system with high penetration of new energy, and in particular to a design method and system for a virtual transient reactance of a wind turbine generator set. Background Art

[0002] With the continuous increase in the penetration rate of renewable energy power generation, the short-circuit capacity of systems with a high proportion of new energy has decreased, resulting in insufficient system short-circuit ratio, which has seriously threatened voltage stability. The traditional short-circuit ratio calculation model only considers the short-circuit capacity of synchronous generators, and does not take into account the voltage support capacity of new energy units. Quantifying the active voltage support capacity of wind turbines and ensuring the short-circuit ratio requirements of the system under voltage drop safety constraints are necessary requirements for achieving high penetration of new energy. Therefore, how to give full play to the voltage support capacity of wind turbines, coordinate the transient impedance parameters of wind turbines, and effectively ensure the voltage stability of new power systems with high penetration of new energy is a technical bottleneck that needs to be broken through to achieve large-scale and safe access to the grid for new energy. Therefore, it is very necessary to design a design method and system for virtual transient reactance of wind turbines. Summary of the Invention

[0003] In order to overcome the deficiencies of the prior art, the present invention aims to provide a method and system for designing a virtual transient reactance of a wind turbine generator system.

[0004] To achieve the above object, the present invention provides the following solutions:

[0005] The present invention provides a design method for a virtual transient reactance of a wind turbine generator system, comprising:

[0006] Calculating an initial short-circuit ratio based on wind turbine system parameters, and calculating an initial value of a wind turbine virtual transient reactance based on the initial short-circuit ratio;

[0007] Determine whether the voltage drops. If not, no action is taken.

[0008] If a drop occurs, the relationship between the current-limiting reactance and the equivalent reactance of the wind turbine is established based on the short-circuit capacity of the grid connection point and the capacity requirements of the rated capacity of the wind turbine;

[0009] Based on the short-circuit capacity of the wind power grid connection point and the transmission capacity of the wind turbine under different voltage drops, the short-circuit ratio requirement under the voltage drop safety constraint is obtained;

[0010] Design the virtual transient reactance value of the wind turbine according to the short-circuit ratio requirements under different voltage drop depths;

[0011] Determine whether the initial short-circuit ratio requirement is greater than the short-circuit ratio. If so, determine the fan rotor current I r Is it greater than the rotor current limit I rmaxIf it is less than, no processing is done; if it is greater than or equal to, the dynamic voltage is adjusted to ensure that the wind turbine rotor current I r Do not exceed the limit and maintain the initial value of the wind turbine virtual transient reactance;

[0012] If the initial short-circuit ratio requirement is less than or equal to the short-circuit ratio, the initial value of the wind turbine virtual transient reactance is replaced by the wind turbine virtual transient reactance value calculated at this time, and the wind turbine rotor current I is determined. r Is it greater than the rotor current limit I rmax If it is less than, no processing is done; if it is greater than or equal to, the dynamic voltage is adjusted to ensure that the wind turbine rotor current I r Do not exceed the limit.

[0013] Preferably, based on the short-circuit capacity of the grid connection point and the capacity requirements of the rated capacity of the wind turbine, a relationship between the current-limiting reactance and the equivalent reactance of the wind turbine is established, specifically:

[0014] The short-circuit capacity of the busbar at the grid connection point is obtained as:

[0015]

[0016] Where S TP is the short-circuit capacity of the grid connection point, E is the equivalent potential of the system, X sr is the current limiting reactance;

[0017] According to industry standards, the short-circuit capacity S of the busbar at the grid connection point TP is the rated capacity S of the wind turbine WTN 3 times, and the current limiting reactance X is obtained. sr About the equivalent reactance X of wind turbines WT The relationship is:

[0018]

[0019] Convert it to get the current limiting reactance X sr About the equivalent reactance X of wind turbines WT The relationship is:

[0020] X sr =K set X WT (3)

[0021] Where K set The value range is (0,1 / 3].

[0022] Preferably, based on the short-circuit capacity of the wind power grid connection point and the transmission capacity of the wind turbine generator set under different voltage drops, the short-circuit ratio requirement under the voltage drop safety constraint is obtained, specifically:

[0023] When a ground short circuit fault occurs, the grid connection point voltage U N =ME, where M is the voltage drop, ranging from [0,1], E is the equivalent potential of the AC system, and U N is the voltage at the grid connection point of the wind turbine;

[0024] When the voltage drops, the short-circuit capacity of the grid connection point and the transmission capacity of the wind turbine are obtained as follows:

[0025]

[0026] Where S WT Transmission capacity for wind turbines;

[0027] The ratio of the short-circuit capacity at the grid connection point to the transmission capacity of the wind turbine is the system short-circuit ratio (SCR). M ,for:

[0028]

[0029] The system short-circuit ratio is improved by taking the voltage support of the wind turbine into account in the form of a synchronous generator. The short-circuit ratio requirement that meets the voltage sag safety constraint is obtained and expressed as:

[0030]

[0031] Where, X d ′ is the unit transient reactance value of the generator set, X T is the per-unit reactance of the line transformer, X n is the per-unit value of the equivalent reactance on the AC system side, E′ is the virtual electromotive force after the transient reactance of the virtual synchronous machine, and SCR M In order to meet the short-circuit ratio requirement of voltage drop safety constraint, U N is the voltage at the grid connection point of the wind turbine, P WF It is the active power output by the wind turbine.

[0032] Preferably, the virtual transient reactance value of the wind turbine is designed according to the short-circuit ratio requirements under different voltage drop depths, specifically:

[0033] According to the short-circuit ratio requirement that meets the voltage drop safety constraint, the virtual transient reactance value of the wind turbine is calculated as:

[0034]

[0035] The present invention also provides a design system for virtual transient reactance of a wind turbine generator set, comprising:

[0036] A current limiting reactance acquisition module is used to establish a relationship between the current limiting reactance and the equivalent reactance of the wind turbine generator set based on the short-circuit capacity of the grid connection point and the rated capacity of the wind turbine generator set;

[0037] A fault test model construction module is used to obtain the short-circuit ratio requirement under voltage drop safety constraints based on the short-circuit capacity of the wind power grid connection point and the transmission capacity of the wind turbine unit under different voltage drops;

[0038] The wind turbine transient reactance parameter design module is used to design the wind turbine virtual transient reactance value according to the short-circuit ratio requirements under different voltage drop depths.

[0039] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0040] The present invention provides a design method and system for a wind turbine virtual transient reactance. Compared with traditional methods, first, based on the short-circuit capacity of the grid connection point and the capacity requirements of the wind turbine rated capacity, a relationship between the current-limiting reactance and the equivalent reactance of the wind turbine is established. Second, based on the short-circuit capacity of the wind power grid connection point and the transmission capacity of the wind turbine under different voltage drops, the short-circuit ratio requirement under voltage drop conditions is obtained. Finally, based on the short-circuit ratio requirement model under voltage drop constraints, the transient reactance parameter values ​​of the wind turbine are coordinated and designed to obtain the optimal transient impedance value, which is used to fully utilize the voltage support potential of the wind turbine. By obtaining the optimal transient reactance value, the present invention fully utilizes the voltage support potential of the wind turbine and can significantly improve the voltage stability of the wind turbine system. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0042] Figure 1 A schematic flow chart of a design method for a wind turbine virtual transient reactance according to an embodiment of the present invention;

[0043] Figure 2 This is a circuit diagram for testing the fault of the grid-connected system of a doubly-fed wind turbine generator set implemented in the present invention;

[0044] Figure 3 A flowchart of a design method for virtual transient reactance of a wind turbine generator system according to an embodiment of the present invention;

[0045] Figure 4 This is a topology diagram of the simulation system according to an embodiment of the present invention;

[0046] Figure 5 This is a system dynamic response curve diagram when the voltage drop depth is 80% according to an embodiment of the present invention;

[0047] Figure 6 This is a system dynamic response curve diagram when the voltage drop depth is 40% according to an embodiment of the present invention;

[0048] Figure 7 This is a system dynamic response curve diagram when the voltage drop depth is 30% according to an embodiment of the present invention. DETAILED DESCRIPTION

[0049] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0050] The purpose of the present invention is to provide a design method and system for the virtual transient reactance of a wind turbine generator set. By obtaining the short-circuit ratio requirements under different voltage drop depths, the virtual transient reactance value of the wind turbine generator set that meets the voltage drop safety constraints is solved, thereby fully unleashing the voltage support potential of the wind turbine generator set and significantly improving the voltage stability of the wind power transmission system.

[0051] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0052] Figure 1 A schematic flow chart of a design method for a wind turbine virtual transient reactance according to an embodiment of the present invention is provided. Figure 3 The flowchart of the design method of the virtual transient reactance of the wind turbine provided by the embodiment of the present invention is as follows: Figure 1 and Figure 3 As shown, the present invention provides a design method for virtual transient reactance of a wind turbine generator set, comprising:

[0053] Calculating an initial short-circuit ratio based on wind turbine system parameters, and calculating an initial value of a wind turbine virtual transient reactance based on the initial short-circuit ratio;

[0054] Determine whether the voltage drops. If not, no action is taken.

[0055] If a drop occurs, the relationship between the current-limiting reactance and the equivalent reactance of the wind turbine is established based on the short-circuit capacity of the grid connection point and the capacity requirements of the rated capacity of the wind turbine;

[0056] Based on the short-circuit capacity of the wind power grid connection point and the transmission capacity of the wind turbine under different voltage drops, the short-circuit ratio requirement under the voltage drop safety constraint is obtained;

[0057] Design the virtual transient reactance value of the wind turbine according to the short-circuit ratio requirements under different voltage drop depths;

[0058] Determine whether the initial short-circuit ratio requirement is greater than the short-circuit ratio. If so, determine the fan rotor current I r Is it greater than the rotor current limit I rmax If it is less than, no processing is done; if it is greater than or equal to, the dynamic voltage is adjusted to ensure that the wind turbine rotor current I r Do not exceed the limit and maintain the initial value of the wind turbine virtual transient reactance;

[0059] If the initial short-circuit ratio requirement is less than or equal to the short-circuit ratio, the initial value of the wind turbine virtual transient reactance is replaced by the wind turbine virtual transient reactance value calculated at this time, and the wind turbine rotor current I is determined. r Is it greater than the rotor current limit I rmax If it is less than, no processing is done; if it is greater than or equal to, the dynamic voltage is adjusted to ensure that the wind turbine rotor current I r Do not exceed the limit.

[0060] The initial short-circuit ratio is calculated based on the wind turbine system parameters, and the initial value of the wind turbine virtual transient reactance is calculated based on the initial short-circuit ratio, specifically:

[0061] Calculation of initial short-circuit ratio (SCR) based on wind turbine system parameters NM , is the ratio of the initial system short-circuit capacity to the initial equipment capacity, and the initial value of the wind turbine virtual transient reactance X is calculated based on the initial short-circuit ratio. d ′=F(SCR NM ).

[0062] Determine whether the voltage drops, specifically:

[0063] If the grid voltage U<0.9U n , it is determined that a voltage drop occurs, otherwise it is determined that no voltage drop occurs.

[0064] The present invention builds a double-fed wind turbine grid-connected system fault test circuit, the circuit diagram is as follows Figure 2 As shown in the figure, based on the short-circuit capacity of the grid connection point and the rated capacity requirements of the wind turbine, the relationship between the current-limiting reactance and the equivalent reactance of the wind turbine is established, specifically:

[0065] Depend on Figure 2 It can be seen that, ignoring the influence of system impedance, the short-circuit capacity of the bus at the grid connection point is:

[0066]

[0067] Where S TP is the short-circuit capacity of the grid connection point, E is the equivalent potential of the system, X sr is the current limiting reactance;

[0068] In order to ensure the stability of the system voltage, according to industry standards, the short-circuit capacity S of the grid connection point is set. TP There are certain requirements, and its value should be greater than the rated capacity S of the wind turbine WTN 3 times, and the current limiting reactance X is obtained. sr About the equivalent reactance X of wind turbines WT The relationship is:

[0069]

[0070] Convert it to get the current limiting reactance X sr About the equivalent reactance X of wind turbines WT The relationship is:

[0071] X sr =K set X WT (3)

[0072] Where K set The value range is (0,1 / 3].

[0073] Based on the short-circuit capacity of the wind power grid connection point and the transmission capacity of the wind turbine under different voltage drops, the short-circuit ratio requirement under the voltage drop safety constraint is obtained, specifically:

[0074] When a ground short circuit fault occurs, the grid connection point voltage U N =ME, where M is the voltage drop, ranging from [0,1], E is the equivalent potential of the AC system, and U N is the voltage at the grid connection point of the wind turbine;

[0075] When the voltage drops, the short-circuit capacity of the grid connection point and the transmission capacity of the wind turbine are obtained as follows:

[0076]

[0077] Where S WT Transmission capacity for wind turbines;

[0078] The ratio of the short-circuit capacity at the grid connection point to the transmission capacity of the wind turbine is the system short-circuit ratio (SCR). M ,for:

[0079]

[0080] The system short circuit ratio is constrained by the voltage drop depth and the current limiting reactance. The greater the voltage drop after the system fault, that is, the smaller the M value, the greater the SCR M The larger it is, the higher the short-circuit ratio requirement for the grid connection point;

[0081] The system short-circuit ratio is improved by taking the voltage support of the wind turbine into account in the form of a synchronous generator. The short-circuit ratio requirement that meets the voltage sag safety constraint is obtained and expressed as:

[0082]

[0083] Where, X d ′ is the unit transient reactance value of the generator set, X T is the per-unit reactance of the line transformer, X n is the per-unit value of the equivalent reactance on the AC system side, E′ is the virtual electromotive force after the transient reactance of the virtual synchronous machine, and SCR M In order to meet the short-circuit ratio requirement of voltage drop safety constraint, U N is the voltage at the grid connection point of the wind turbine, P WF It is the active power output by the wind turbine.

[0084] According to the short-circuit ratio requirements under different voltage drop depths, the virtual transient reactance value of the wind turbine is designed, specifically:

[0085] According to the short-circuit ratio requirement that meets the voltage drop safety constraint, the virtual transient reactance value of the wind turbine is calculated as:

[0086]

[0087] Wind turbines can improve the short-circuit ratio of the grid connection point by reducing transient reactance. According to the short-circuit ratio requirement, the required equivalent impedance is calculated to obtain the optimal value of the transient reactance of the wind turbine.

[0088] The present invention also provides a design system for virtual transient reactance of a wind turbine generator set, comprising:

[0089] A current limiting reactance acquisition module is used to establish a relationship between the current limiting reactance and the equivalent reactance of the wind turbine generator set based on the short-circuit capacity of the grid connection point and the rated capacity of the wind turbine generator set;

[0090] A fault test model construction module is used to obtain the short-circuit ratio requirement under voltage drop safety constraints based on the short-circuit capacity of the wind power grid connection point and the transmission capacity of the wind turbine unit under different voltage drops;

[0091] The wind turbine transient reactance parameter design module is used to design the wind turbine virtual transient reactance value according to the short-circuit ratio requirements under different voltage drop depths.

[0092] The present invention is based on the DigSILENT PowerFactory 15.2 simulation environment to build the following Figure 4 The basic parameters of the 3-machine 9-node grid-connected simulation system with high wind power penetration are shown in Table 1.

[0093] Table 1 System impedance parameters

[0094]

[0095] Table 2 Parameters of 2MW doubly-fed wind turbine DFIG

[0096]

[0097]

[0098] The simulation uses the following three control methods to compare the effects of different control methods on system voltage support, namely: Example 1, Scheme 1: Voltage drop control in the grid connection standard; Scheme 2: Voltage stability support control proposed by the present invention. Example 2, Scheme 1: Low voltage ride-through control (reactive current coefficient is 1.5); Scheme 2: Voltage stability support control (X d ′=1.1,SCR=2); Option 3: Voltage Stability Support Control (X d ′=0.8,SCR=1.5)system dynamic response. Example 3, Scheme 1: Low voltage ride-through control (reactive current coefficient is 1.5); Scheme 2: Improved low voltage ride-through control (dynamic reactive current coefficient); Scheme 3: Proposed voltage stability support control;

[0099] Example 1: To verify the supporting effect of wind turbines on system voltage using the proposed parameter design method, a three-phase ground short circuit fault with a duration of 0.625s is set at bus B7. The system dynamic response is as follows: Figure 5 shown.

[0100] like Figure 5 As shown in the figure, when the voltage drop depth is 80%, after taking the voltage support capacity of renewable energy to the grid connection point into account in the short-circuit ratio, the wind turbine can improve the short-circuit ratio of the grid connection point by reducing the transient reactance and adjusting the system parameters to obtain the optimal value of the transient reactance.

[0101] When the DFIG employed Option 1, the wind turbine generated approximately 70 Mvar of reactive power, with a low rotor current. The grid-connection voltage during the voltage dip was approximately 0.16 pu, below the system stability requirement for a voltage dip, forcing the wind turbine to operate offline. When the DFIG employed Option 2, the turbine's rotor current was approximately 1.2 pu, and the turbine generated approximately 130 Mvar of reactive power during the fault. The grid-connection voltage during the voltage dip was approximately 0.23 pu. Under the same fault conditions, Option 2 increased the grid-connection voltage by 0.07 pu, meeting the system stability requirement for a voltage dip, reducing the risk of wind turbine offline operation and improving system voltage safety.

[0102] Example 2: To verify the supporting effect of wind turbines on system voltage using the proposed parameter design method, a three-phase ground short circuit fault with a duration of 0.625s occurs at bus B2 at 10s. The system dynamic response is as follows: Figure 6 shown.

[0103] like Figure 6 As shown in the figure, when the voltage dip depth is 40%, when the DFIG adopts Scheme 1 control strategy, the wind turbine generates approximately 140Mvar of reactive power during the fault, the grid connection voltage is approximately 0.6pu during the dip, and the transient overvoltage is approximately 1.16pu after the fault is cleared. When the DFIG adopts Scheme 2 control strategy, the unit rotor current is approximately 1.12pu, the wind turbine generates approximately 390Mvar of reactive power, the grid connection voltage is approximately 0.75pu during the dip, and the transient overvoltage is approximately 1.12pu after the fault is cleared. When the DFIG adopts Scheme 3 control strategy, the unit rotor current is approximately 1.18pu, the wind turbine generates approximately 450Mvar of reactive power, the grid connection voltage is approximately 0.8pu during the dip, and the transient overvoltage is approximately 1.07pu after the fault is cleared. Under the same fault conditions, Scheme 2 increased wind turbine reactive power by 250 Mvar compared to Scheme 1, raising the grid connection point voltage by 0.15 pu. After the fault was cleared, the system absorbed a significant amount of excess reactive power, reducing transient overvoltage by 0.05 pu. Scheme 3, while maintaining rotor current overload, increased the system short-circuit ratio above the required value by reducing transient reactance. Compared to Scheme 2, the wind turbine generated an additional 60 Mvar of reactive power, raising the grid connection point voltage by 0.05 pu. After the fault was cleared, the system absorbed even more excess reactive power, reducing transient overvoltage by 0.05 pu. This fully exploited the voltage support capability of the DFIG and significantly improved system voltage stability.

[0104] Example 3: To verify the supporting effect of wind turbines on system voltage using the proposed parameter design method, a three-phase ground short circuit fault with a duration of 0.625s occurs at bus B2 at 10s. The system dynamic response is as follows: Figure 7shown.

[0105] Figure 7 The dynamic responses of the system under three control schemes were compared. When the voltage sag depth was 30%, when using Scheme 1, the DFIG unit generated approximately 120 Mvar of reactive power, the rotor current was relatively small, and the grid connection voltage during the voltage sag was approximately 0.68 pu. When using Schemes 2 and 3, the unit rotor current was approximately 1.1 pu. Due to the less severe voltage sag, the wind turbine generated more reactive power during the fault, approximately 320 Mvar, and the grid connection voltage during the sag was approximately 0.85 pu. Compared to Scheme 1, the wind turbine significantly increased its reactive power under both control schemes to support the system voltage, reducing the magnitude of the voltage sag. However, the voltage sag control method, which only increases reactive power by increasing reactive current, not only fails to accurately assess system voltage safety, but also easily causes transient overvoltage problems during the voltage recovery process after the fault is cleared.

[0106] After the fault is cleared, Scheme 2 increases the maximum transient overvoltage from 1.12 pu to 1.27 pu compared to Scheme 1. However, under Scheme 3, the maximum transient overvoltage at the grid connection point decreases from 1.12 pu to 1.07 pu. While generating the same reactive power as in Scheme 2 during the fault, absorbing excess reactive power after the fault is cleared avoids transient overvoltages. Test results demonstrate that the proposed voltage stability support control not only addresses wind turbine voltage sag but also significantly reduces system transient overvoltages, further contributing to voltage stability.

[0107] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0108] The present invention uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only intended to help understand the method and core concept of the present invention. At the same time, those skilled in the art will find that the specific implementation methods and application scopes may vary based on the concept of the present invention. In summary, the contents of this specification should not be construed as limiting the present invention.

Claims

1. A design method for virtual transient reactance of a wind turbine generator system, characterized in that: include: Calculating an initial short-circuit ratio based on wind turbine system parameters, and calculating an initial value of a wind turbine virtual transient reactance based on the initial short-circuit ratio; Determine whether the voltage drops. If not, no action is taken. If a drop occurs, the relationship between the current-limiting reactance and the equivalent reactance of the wind turbine is established based on the short-circuit capacity of the grid connection point and the capacity requirements of the rated capacity of the wind turbine; Based on the short-circuit capacity of the wind power grid connection point and the transmission capacity of the wind turbine under different voltage drop levels, the short-circuit ratio requirement under the voltage drop safety constraint is obtained; Design the virtual transient reactance value of the wind turbine according to the short-circuit ratio requirements under different voltage drop depths; Determine whether the initial short-circuit ratio is greater than the short-circuit ratio requirement. If so, determine the fan rotor current I r Is it greater than the rotor current limit I rmax If it is less than, no processing is done; if it is greater than or equal to, the dynamic voltage is adjusted to ensure that the wind turbine rotor current I r Do not exceed the limit and maintain the initial value of the wind turbine virtual transient reactance; If the initial short-circuit ratio is less than or equal to the short-circuit ratio requirement, the initial value of the wind turbine virtual transient reactance is replaced by the wind turbine virtual transient reactance value calculated at this time, and the wind turbine rotor current I is determined. r Is it greater than the rotor current limit I rmax If it is less than, no processing is done; if it is greater than or equal to, the dynamic voltage is adjusted to ensure that the wind turbine rotor current I r Do not exceed the limit.

2. The method according to claim 1, characterized in that Based on the short-circuit capacity of the grid connection point and the rated capacity requirements of the wind turbine, the relationship between the current-limiting reactance and the equivalent reactance of the wind turbine is established, specifically: The short-circuit capacity of the busbar at the grid connection point is obtained as: Where S TP is the short-circuit capacity of the grid connection point, E is the equivalent potential of the system, X sr is the current limiting reactance; According to industry standards, the short-circuit capacity S of the busbar at the grid connection point TP is the rated capacity S of the wind turbine WTN 3 times, and the current limiting reactance X is obtained. sr About the equivalent reactance X of wind turbines WT The relationship is: Convert it to get the current limiting reactance X sr About the equivalent reactance X of wind turbines WT The relationship is: X sr =K set X WT (3) Where K set The value range is (0,1 / 3].

3. The method according to claim 2, characterized in that Based on the short-circuit capacity of the wind power grid connection point and the transmission capacity of the wind turbine under different voltage drop levels, the short-circuit ratio requirement under the voltage drop safety constraint is obtained, specifically: When a ground short circuit fault occurs, the grid connection point voltage U N =ME, where M is the voltage drop, ranging from [0,1], E is the equivalent potential of the AC system, and U N is the voltage at the grid connection point of the wind turbine; When the voltage drops, the short-circuit capacity of the grid connection point and the transmission capacity of the wind turbine are obtained as follows: Where S WT Transmission capacity for wind turbines; The ratio of the short-circuit capacity at the grid connection point to the transmission capacity of the wind turbine is the system short-circuit ratio (SCR). M ,for: The system short-circuit ratio is improved by taking the voltage support of the wind turbine into account in the form of a synchronous generator. The short-circuit ratio requirement that meets the voltage sag safety constraint is obtained and expressed as: Where, X d ′ is the per-unit value of the virtual transient reactance of the generator set, X T is the per-unit reactance of the line transformer, X n is the per-unit value of the equivalent reactance on the AC system side, E′ is the virtual electromotive force after the transient reactance of the virtual synchronous machine, and SCR M In order to meet the short-circuit ratio requirement of voltage drop safety constraint, U N is the voltage at the grid connection point of the wind turbine, P WF is the active power output of the wind turbine, U n The rated voltage of the grid connection point.

4. The method according to claim 3, characterized in that According to the short-circuit ratio requirements under different voltage drop depths, the virtual transient reactance value of the wind turbine is designed, specifically: According to the short-circuit ratio requirement that meets the voltage drop safety constraint, the virtual transient reactance value of the wind turbine is calculated as: 。

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