Self-adaptive fault ride-through method and device of wind power flexible direct output system

Abstract

The invention belongs to the field of power system protection and control, and discloses a self-adaptive fault ride-through method and device for a wind power flexible direct output system. After a receiving-end power grid breaks down, a power grid side converter station calculates the critical active power of a wind power side converter station and the critical voltage of a sending-out system grid-connected point when wind power is preferentially controlled by alternating current voltage and direct current voltage through a flexible direct current sending-out system; and calculating and comparing the relative gain of the grid-connected point voltage of the sending-out system with the relative gain of the active power of the converter station at the wind power side, further determining the priority of the wind power in fault ride-through of the flexible direct sending-out system, adjusting the active and reactive current reference values of the converter station at the power grid side, and implementing control. According to the invention, control of the DC voltage of the wind power flexible direct-current output system and the AC voltage of the fault power grid can be considered, and the fault power grid voltage is supported and the active power loss of the wind power plant is reduced while uninterrupted operation of the wind power flexible direct-current output system is ensured.

Description

Technical Field

[0001] The present invention relates to the field of power system protection and control, and in particular to a method and device for adaptive fault ride-through of a wind power flexible direct current transmission system. Background Art

[0002] During a short-circuit fault in the power grid, the wind power transmission system through the flexible direct current transmission system needs to support the faulty power grid voltage on the basis of ensuring the safety of the direct current voltage. The direct current voltage control methods of the wind power transmission system through the flexible direct current transmission system under power grid faults are divided into two categories: using energy consumption or energy storage devices, and adjusting the wind power side converter station. Existing technicians have improved the devices, topologies and switching algorithms based on centralized direct current energy consumption devices, improving the control accuracy of direct current voltage and reducing electromagnetic interference. Some technicians also connect flywheel energy storage devices in parallel on the direct current side of flexible direct current transmission, or use submodule capacitors to temporarily store surplus power. However, energy consumption or energy storage devices increase hardware costs and cannot be used continuously due to capacity limitations. Therefore, direct current voltage control methods based on wind power side converter station adjustment have received more attention. For wind power side converter stations with AC voltage as the control object, technicians have proposed a direct current voltage control method with precise voltage reduction and harmonic injection; for wind power side converter stations with active power as the control object, technicians introduce direct current voltage deviation into the active power reference value of the wind power side converter station, and adjust the droop coefficient according to the surplus power and the capacity of the wind farm converter station. The wind farm converter station with constant DC voltage control can autonomously adjust the active power to ensure that the DC voltage is equal to the rated value in the fault steady state. However, the DC voltage control method based on the regulation of the wind farm converter station will reduce the active power fed into the flexible DC transmission by the wind farm, and most of the existing studies have ignored the active power loss of the wind farm caused by DC voltage control.

[0003] The transition impedance of a grid short-circuit fault is often resistive, causing the grid impedance to suddenly change from pure inductive during normal operation to resistive inductive during the fault period. Therefore, the voltage at the grid connection point of the transmission system under a grid fault depends not only on the reactive current of the grid-side converter station, but also on the product of the active current of the grid-side converter station and the resistance component of the equivalent impedance of the faulty grid. The active power of the grid-side converter station is equal to the product of the AC voltage and the active current. Under the control of the fixed DC voltage, the active power of the wind power converter station is ultimately equal to the active power of the grid-side converter station. Therefore, changing the active or reactive current of the grid-side converter station under a grid fault will cause the grid connection point voltage of the transmission system and the active power of the wind power converter station under the control of the fixed DC voltage to change simultaneously. The AC voltage control effect and the DC voltage control cost of the wind power transmission system through the flexible DC transmission system under the influence of the equivalent impedance of the faulty grid are coupled. The existing technology assumes that the faulty grid remains inductive, ignoring the sudden change of the grid impedance before and after the fault caused by the fault transition impedance and the impact on the fault crossing of the wind power transmission system through the flexible DC transmission system. The active power of the grid-side converter station sacrificed to provide AC voltage support will significantly reduce the active power of the wind power-side converter station under the action of fixed DC voltage control, resulting in active power loss of the wind farm.

[0004] In summary, how to establish a coupling function between the active power of the wind power side converter station and the active and reactive currents of the grid side converter station under the control of the grid connection point voltage and the fixed DC voltage of the transmission system, so as to determine the control priority during the fault ride-through of the wind power through the flexible DC transmission system, adjust the active and reactive power reference values ​​of the grid side converter station, and coordinate with the fixed DC voltage control of the wind power side converter station to reduce the active power loss of the wind farm while ensuring the DC voltage safety of the transmission system, has become a problem that technicians in this field need to solve urgently. Summary of the invention

[0005] In view of the deficiencies of the above-mentioned prior art, the present invention believes that the transition impedance of a power grid short-circuit fault is often resistive, so that the grid impedance suddenly changes from pure inductive during normal operation to resistive inductive during the fault period. Therefore, the voltage at the grid connection point of the transmission system under a power grid fault depends not only on the reactive current of the grid-side converter station, but also on the product of the active current of the grid-side converter station and the resistive component of the equivalent impedance of the faulty grid. The active power of the grid-side converter station is equal to the product of the AC voltage and the active current, and the active power of the wind power side converter station under the constant DC voltage control is ultimately equal to the active power of the grid-side converter station. Therefore, changing the active or reactive current of the grid-side converter station under a power grid fault will cause the voltage at the grid connection point of the transmission system and the active power of the wind power side converter station under the constant DC voltage control to change simultaneously, and the AC voltage control effect and the DC voltage control cost of the wind power transmission system through the flexible direct current transmission are coupled under the influence of the equivalent impedance of the faulty grid. The fault ride-through of wind power transmitted through the flexible direct current transmission system should take into account the AC / DC voltage control coupling caused by the equivalent impedance of the faulty grid, taking into account both the AC voltage control effect and the DC voltage control cost, thereby facilitating the increase of the faulty grid voltage and reducing the active power loss of the wind farm.

[0006] The present invention discloses a method and device for adaptive fault ride-through of a wind power transmission system via a flexible direct current. After a power grid fault is detected, the grid-side converter station pre-calculates the critical active power of the wind power side converter station and the critical voltage of the transmission system grid connection point when the wind power transmission system via a flexible direct current is given priority in AC voltage control and DC voltage control, calculates and compares the relative gain of the grid connection point voltage of the transmission system and the relative gain of the active power of the wind power side converter station, determines the priority of the wind power transmission system via a flexible direct current when the fault is ridden, adjusts the active and reactive current reference values ​​of the grid-side converter station, and implements control.

[0007] In a first aspect of the present invention, the present invention provides an adaptive fault ride-through method, which is applicable to a wind power flexible direct current transmission system; the wind power flexible direct current transmission system comprises a wind farm, a wind power side converter station, a grid side converter station and a DC cable connecting the two converter stations, comprising the following steps:

[0008] S101, detecting the AC bus voltage of the converter station on the grid side;

[0009] S102, comparing the AC bus voltage with a preset voltage threshold;

[0010] S103. If the AC bus voltage is lower than the preset voltage threshold, respectively calculate the critical voltage of the wind power grid connection point of the flexible direct current transmission system and its corresponding critical active power of the wind power side converter station when AC voltage control is prioritized; and the critical voltage of the wind power grid connection point of the flexible direct current transmission system and its corresponding critical active power of the wind power side converter station when DC voltage control is prioritized;

[0011] S104, calculating the relative voltage gain of the grid connection point of the wind power transmission system through flexible direct current transmission and the relative active power gain of the converter station on the wind power side;

[0012] S105, comparing the relative voltage gain of the grid connection point of the wind power transmission system through flexible direct current transmission and the relative active power gain of the converter station on the wind power side;

[0013] S106. If the relative voltage gain of the grid connection point of the wind power transmission system through the flexible direct current transmission is greater than the relative active power gain of the wind power side converter station, the AC voltage control is given priority, and the active and reactive current reference values ​​of the grid side converter station are adjusted to be equal to the active and reactive currents of the grid side converter station required for the wind power transmission system through the flexible direct current transmission system to reach the maximum voltage at the grid connection point;

[0014] S107. If the relative voltage gain at the grid connection point of the wind power transmission system via flexible direct current is less than or equal to the relative active power gain of the converter station on the wind power side, the direct current voltage control takes priority and adjusts the reference values ​​of the active and reactive currents of the converter station on the grid side to be equal to the active and reactive currents of the converter station on the grid side required for the converter station on the wind power side to reach the maximum active power.

[0015] In a second aspect of the present invention, the present invention provides an adaptive fault ride-through device for a wind power flexible direct current transmission system; comprising: a voltage transformer, a current transformer and a converter controller; wherein the converter controller comprises:

[0016] A detection module, used to detect the AC bus voltage of the power grid side converter station;

[0017] A first comparison module, used for comparing the AC bus voltage with a preset voltage threshold;

[0018] The first calculation module is used to calculate the critical voltage of the wind power grid connection point of the flexible direct current transmission system and its corresponding critical active power of the wind power side converter station when AC voltage control is prioritized; and the critical voltage of the wind power grid connection point of the flexible direct current transmission system and its corresponding critical active power of the wind power side converter station when DC voltage control is prioritized;

[0019] The second calculation module is used to calculate the relative gain of the voltage at the grid connection point of the wind power transmission system through flexible direct current transmission and the relative gain of the active power of the converter station on the wind power side;

[0020] The second comparison module is used to compare the relative gain of the voltage at the grid connection point of the wind power transmission system through flexible direct current transmission and the relative gain of the active power of the converter station on the wind power side;

[0021] The first control module is used to give priority to AC voltage control when the voltage relative gain of the grid connection point of the wind power transmission system via flexible direct current is greater than the active power relative gain of the wind power side converter station, and adjust the active and reactive current reference values ​​of the grid side converter station to be equal to the active and reactive currents of the grid side converter station required for the wind power transmission system via flexible direct current to reach the maximum voltage at the grid connection point;

[0022] The second control module is used to give priority to DC voltage control when the relative gain of the voltage at the grid connection point of the flexible direct current transmission system is less than or equal to the relative gain of the active power of the wind power side converter station, and adjust the active and reactive current reference values ​​of the grid side converter station to be equal to the active and reactive currents of the grid side converter station required for the wind power side converter station to reach the maximum active power.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] The prior art ignores the relationship between the AC voltage control effect and the DC voltage control cost caused by the fault transition impedance, which is not conducive to raising the fault grid voltage and may also aggravate the active power loss of the wind farm. The present invention adaptively adjusts the active and reactive current reference values ​​of the grid-side converter station by determining the priority of wind power when passing through the fault of the flexible direct current transmission system. Under the premise of ensuring the DC voltage safety of the transmission system, the present invention has a fault grid voltage support effect similar to that of the prior art when the equivalent impedance of the fault grid is small, and also reduces the active power loss of the wind farm; when the equivalent impedance of the fault grid is large, the present invention has a better voltage raising effect at the grid connection point of the transmission system. The present invention only uses the electrical quantity of the grid-side converter station, and has a simple principle, is easy to implement, and has strong practicality. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to make the purpose, technical solution and advantages of the invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings, in which:

[0026] Figure 1 It is a flow chart of a method for adaptive fault ride-through of a wind power flexible direct current transmission system according to an embodiment of the present invention;

[0027] Figure 2 It is a structural schematic diagram of a wind power flexible direct current transmission system according to an embodiment of the present invention;

[0028] Figure 3 A schematic diagram of the structure of an adaptive fault ride-through device according to an embodiment of the present invention;

[0029] Figure 4 A schematic diagram of the structure of a converter controller according to an embodiment of the present invention;

[0030] Figure 5 This is a structural schematic diagram of a wind power flexible direct current transmission system under a power grid fault adopted in an embodiment of the present invention;

[0031] Figure 6 It is a diagram showing the effects of an embodiment of the present invention, wherein Figure (a) is a diagram showing the relationship between time and DC voltage, Figure (b) is a diagram showing the relationship between time and the voltage at the grid-connected point of the transmission system, Figure (c) is a diagram showing the relationship between time and the active power of the grid-side converter station, Figure (d) is a diagram showing the relationship between time and the reactive power of the grid-side converter station, and Figure (e) is a diagram showing the relationship between time and the active power of the wind power side converter station. DETAILED DESCRIPTION

[0032] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. 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 creative work are within the scope of protection of the present invention.

[0033] The present invention discloses a method and device for adaptive fault ride-through of a wind power transmission system via a flexible direct current transmission system. By calculating the relative gain of the voltage at the grid connection point of the transmission system and the relative gain of the active power of a converter station on the wind power side, it is determined according to the relative sizes of the two whether to give priority to direct current voltage or alternating current voltage control when the wind power transmission system via a flexible direct current transmission system is fault ridden, and the active and reactive current reference values ​​of the converter station on the grid side are adaptively adjusted to implement fault ride-through.

[0034] Figure 1 FIG. 1 is a flow chart of a method for adaptive fault ride-through of a wind power flexible direct current transmission system according to an embodiment of the present invention. Figure 1 As shown, the method comprises the following steps:

[0035] S101, detecting the AC bus voltage of the converter station on the grid side;

[0036] S102, comparing the AC bus voltage with a preset voltage threshold;

[0037] S103. If the AC bus voltage is lower than the preset voltage threshold, respectively calculate the critical voltage of the wind power grid connection point of the flexible direct current transmission system and its corresponding critical active power of the wind power side converter station when AC voltage control is prioritized; and the critical voltage of the wind power grid connection point of the flexible direct current transmission system and its corresponding critical active power of the wind power side converter station when DC voltage control is prioritized;

[0038] S104, calculating the relative voltage gain of the grid connection point of the wind power transmission system through flexible direct current transmission and the relative active power gain of the converter station on the wind power side;

[0039] S105, comparing the relative voltage gain of the grid connection point of the wind power transmission system through flexible direct current transmission and the relative active power gain of the converter station on the wind power side;

[0040] S106. If the relative voltage gain of the grid connection point of the wind power transmission system through the flexible direct current transmission is greater than the relative active power gain of the wind power side converter station, the AC voltage control is given priority, and the active and reactive current reference values ​​of the grid side converter station are adjusted to be equal to the active and reactive currents of the grid side converter station required for the wind power transmission system through the flexible direct current transmission system to reach the maximum voltage at the grid connection point;

[0041] S107. If the relative voltage gain at the grid connection point of the wind power transmission system via flexible direct current is less than or equal to the relative active power gain of the converter station on the wind power side, the direct current voltage control takes priority and adjusts the reference values ​​of the active and reactive currents of the converter station on the grid side to be equal to the active and reactive currents of the converter station on the grid side required for the converter station on the wind power side to reach the maximum active power.

[0042] In the embodiment of the present invention, in step S101, specifically, in the wind power flexible direct current transmission system, Figure 2As shown, the wind power flexible direct current transmission system includes a wind farm, a wind power side converter station, a grid side converter station and a DC cable connecting the two converter stations; the grid side converter station is connected to the receiving end grid; by detecting the AC bus voltage of the grid side converter station, it can be determined whether the receiving end grid has a fault. This detection method is mainly to prevent excessively high or low voltage from causing adverse effects on the wind power flexible direct current transmission system.

[0043] In the embodiment of the present invention, in the wind power transmission system via flexible direct current, when a fault occurs in the receiving power grid, the grid-side converter station will quickly detect the drop in AC voltage. Therefore, the grid-side converter station can accurately determine whether the operating state of the receiving power grid is normal by detecting the difference between the AC bus voltage and the preset voltage threshold. The operating state may include a fault state and a normal state.

[0044] The voltage value can be measured in real time by installing a voltage sensor on the AC busbar of the grid-side converter station. The sensor converts the measured voltage signal into an electrical signal or a digital signal and transmits it to the monitoring system for display and analysis. The monitoring system receives the voltage signal from the sensor and displays and records it in real time.

[0045] In the embodiment of the present invention, in step S102, a voltage threshold may be set in the monitoring system, and when the voltage exceeds or falls below the set value, an alarm signal is issued to alert the operator. The voltage threshold here may be a preset voltage threshold, which may be set to 0.9pu. When the AC bus voltage drops below 0.9pu, it may be determined that a short circuit fault has occurred in the receiving-end power grid, and the fault ride-through of the wind power transmission system via the flexible direct current is initiated.

[0046] In an embodiment of the present invention, the grid-side converter station may be a half-bridge modular multilevel converter, a full-bridge modular multilevel converter or a half / full-bridge hybrid modular multilevel converter; this structure enables the grid-side converter station to independently control active and reactive physical quantities.

[0047] Unlike normal operation, changing the active or reactive current of the grid-side converter station under a grid fault will cause the voltage at the grid-connected point of the transmission system and the active power of the wind power side converter station under the control of the fixed DC voltage to change simultaneously, and the AC voltage control effect and DC voltage control cost of the wind power through the flexible DC transmission system under the influence of the equivalent impedance of the fault grid are coupled. Therefore, the fault ride-through of wind power through the flexible DC transmission system should take into account the AC and DC voltage control coupling caused by the equivalent impedance of the fault grid, taking into account the AC voltage control effect and DC voltage control cost; by establishing the coupling function of the active power of the wind power side converter station under the grid-connected point voltage of the transmission system and the fixed DC voltage control with the active and reactive current of the grid-side converter station, the control priority during the fault ride-through of the wind power through the flexible DC transmission system is determined, the active and reactive power reference values ​​of the grid-side converter station are adjusted, and coordinated with the fixed DC voltage control of the wind power side converter station, the active power loss of the wind farm is reduced under the premise of ensuring the DC voltage safety of the transmission system. In the embodiment of the present invention, the critical voltage of the wind power grid connection point of the flexible direct current transmission system when AC voltage control is prioritized and when DC voltage control is prioritized and the critical active power of the wind power side converter station are used to determine the priority of the wind power fault ride-through through the flexible direct current transmission system, and adaptively adjust the active and reactive power reference values ​​of the grid side converter station.

[0048] In the embodiment of the present invention, in step S103, the critical voltage of the wind power grid connection point when AC voltage control is prioritized is determined by the following method:

[0049] If the difference between the equivalent potential phase and the equivalent impedance angle of the faulty grid is less than or equal to the maximum allowable AC current phase angle of the grid-side converter station to avoid over-limit DC voltage; the first voltage parameter is calculated based on the equivalent resistance and reactance of the faulty grid, the maximum allowable AC current coefficient of the grid-side converter station and the rated AC current; the second voltage parameter is calculated based on the equivalent resistance and reactance of the faulty grid, the grid voltage and equivalent reactance during normal operation; the critical voltage of the wind power grid connection point when AC voltage control is prioritized is calculated based on the sum of the first voltage parameter and the second voltage parameter;

[0050] If the difference between the equivalent potential phase and the equivalent impedance angle of the faulty grid is greater than the maximum allowable AC current phase angle of the grid-side converter station to avoid over-limit DC voltage; the third voltage parameter is calculated based on the maximum allowable AC current coefficient and rated AC current of the grid-side converter station, the equivalent resistance and reactance of the faulty grid, the grid voltage and equivalent reactance during normal operation, the equivalent fault transition resistance and reactance, and the maximum allowable AC current phase angle of the grid-side converter station to avoid over-limit DC voltage; the fourth voltage parameter is calculated based on the maximum allowable AC current coefficient and rated AC current of the grid-side converter station, the equivalent resistance and reactance of the faulty grid, and the maximum allowable AC current phase angle of the grid-side converter station to avoid over-limit DC voltage; the critical voltage of the wind power connection point of the flexible direct current transmission system when AC voltage control is prioritized is calculated based on the difference between the third voltage parameter and the fourth voltage parameter.

[0051] In the specific implementation of the present invention, the critical voltage of the grid connection point of the transmission system when AC voltage control is prioritized is determined as follows:

[0052]

[0053] Where: represents the first voltage parameter, represents a second voltage parameter; represents a third voltage parameter; represents a fourth voltage parameter.

[0054] in, R is the critical voltage of the transmission system grid connection point when AC voltage control is prioritized; R.f and X R.f E are the equivalent resistance and reactance of the fault power grid respectively; R.N and X R.N They are the grid voltage and equivalent reactance during normal operation respectively; K I and I GEC.N are the maximum allowable AC current coefficient and rated AC current of the grid-side converter station respectively; η DIF It is the difference between the equivalent potential phase and the equivalent impedance angle of the fault power grid; In order to avoid the maximum allowable AC current phase angle of the grid-side converter station from exceeding the DC voltage limit, the parameter M is calculated as follows:

[0055]

[0056] Where: R V.f and X V.f are the equivalent fault transition resistance and reactance respectively.

[0057] This embodiment can help ensure the stability and safety of the power grid in the event of a fault by accurately calculating the critical voltage of the transmission system connection point, and can optimize the operating parameters of the grid-side converter station.

[0058] In the specific implementation of the present invention, the maximum allowable AC current phase angle of the grid-side converter station to avoid DC voltage over-limit is equal to the arc tangent of the ratio of the ordinate to the abscissa of the intersection of the DC voltage limit boundary and the AC current limit boundary. The ordinate and abscissa of the boundary intersection are determined by solving the DC voltage boundary equation and the AC current boundary equation simultaneously. The AC current boundary equation is determined by the following formula:

[0059]

[0060] Where: I GEC.d and I GEC.q They are the active and reactive currents of the converter station on the grid side respectively.

[0061] When the present invention is specifically implemented, the DC voltage boundary equation is determined as follows:

[0062]

[0063] Where: X T is the equivalent reactance of the connecting transformer; parameters A, B, C and D are calculated as follows:

[0064]

[0065] Where: P GEC.N is the active power of the converter station on the grid side during normal operation; ΔU DC.per is the maximum allowable DC voltage deviation; U DC.N is the rated DC voltage; C DC is the equivalent DC capacitance; parameters ω, ξ, γ and T DC.max They are:

[0066]

[0067] Where: U WEC.N k is the rated AC bus voltage of the wind power side converter station; i and k p They are the integral coefficient and proportional coefficient of the DC voltage control outer loop of the wind power side converter station respectively.

[0068] In the embodiment of the present invention, in step S103, when AC voltage control is prioritized, the critical active power of the wind power side converter station is determined by the following method:

[0069] If the difference between the equivalent potential phase and the equivalent impedance angle of the faulty power grid is less than or equal to the maximum allowable AC current phase angle of the power grid side converter station to avoid DC voltage exceeding the limit; the first active power parameter is calculated based on the maximum allowable AC current coefficient and the rated AC current of the power grid side converter station, the equivalent resistance of the faulty power grid, and the difference between the equivalent potential phase and the equivalent impedance angle of the faulty power grid; the first active power parameter is calculated based on the maximum allowable AC current coefficient and the rated AC current of the power grid side converter station, the equivalent reactance of the faulty power grid, the equivalent reactance of the connecting transformer, the equivalent potential phase and the equivalent impedance angle of the faulty power grid. The second active power parameter is calculated based on the difference between the maximum allowable AC current coefficient and the rated AC current, the equivalent resistance and equivalent reactance of the fault grid, the equivalent fault transition resistance and reactance, the difference between the equivalent potential phase and the equivalent impedance angle of the fault grid, the equivalent reactance of the connecting transformer, and the voltage and equivalent reactance of the grid during normal operation. The third active power parameter is calculated based on the difference between the first active power parameter and the second active power parameter and the sum of the third active power parameter to obtain the critical active power of the wind power side converter station when AC voltage control is prioritized;

[0070] If the difference between the equivalent potential phase and the equivalent impedance angle of the faulty grid is greater than the maximum allowable AC current phase angle of the grid-side converter station to avoid over-limit DC voltage; the fourth active power parameter is calculated based on the maximum allowable AC current coefficient and rated AC current of the grid-side converter station, the equivalent resistance of the faulty grid and the maximum allowable AC current phase angle of the grid-side converter station to avoid over-limit DC voltage; the fourth active power parameter is calculated based on the maximum allowable AC current coefficient and rated AC current of the grid-side converter station, the equivalent reactance of the faulty grid, the equivalent reactance of the connecting transformer and the maximum allowable AC current of the grid-side converter station to avoid over-limit DC voltage. The fifth active power parameter is calculated according to the current phase angle; the sixth active power parameter is calculated according to the maximum allowable AC current coefficient and the rated AC current, the equivalent resistance and equivalent reactance of the fault grid, the equivalent fault transition resistance and reactance, the maximum allowable AC current phase angle of the grid-side converter station to avoid DC voltage exceeding the limit, the equivalent reactance of the connecting transformer, and the grid voltage and equivalent reactance during normal operation; the critical active power of the wind power side converter station when AC voltage control is prioritized is calculated according to the difference between the fourth active power parameter and the fifth active power parameter and the sum of the sixth active power parameter.

[0071] In the specific implementation of the present invention, the critical active power of the wind power side converter station is determined by the following method when AC voltage control is prioritized:

[0072]

[0073] Where: represents the first active power parameter, represents the second active power parameter, Indicates the third active power parameter; represents the fourth active power parameter, Represents the fifth active power parameter, represents the sixth active power parameter; It is the critical active power of the converter station on the wind power side when AC voltage control is prioritized.

[0074] This embodiment can help ensure stable operation and optimized control of the power system when AC voltage control is prioritized by accurately calculating the critical active power of the wind power side converter station.

[0075] In an embodiment of the present invention, in step S103, the critical active power of the wind power side converter station is obtained by solving the extreme point of the first function by the Lagrange multiplier method when the DC voltage control is prioritized; the first function is obtained by compounding the first parameter, the second parameter, the third parameter and the fourth parameter; the first parameter includes the maximum allowable AC current coefficient and the rated AC current of the grid side converter station, the reactive current of the grid side converter station and the equivalent resistance of the fault grid; the second parameter includes the maximum allowable AC current coefficient and the rated AC current of the grid side converter station, the reactive current of the grid side converter station, the equivalent reactance of the fault grid and the equivalent reactance of the connecting transformer; the third parameter includes the maximum allowable AC current coefficient and the rated AC current of the grid side converter station and the reactive current of the grid side converter station; the fourth parameter includes the maximum allowable AC current coefficient and the rated AC current of the grid side converter station, the reactive current of the grid side converter station, the equivalent resistance and reactance of the fault grid, the equivalent reactance of the connecting transformer, the equivalent fault transition resistance and reactance, and the grid voltage and equivalent reactance during normal operation.

[0076] In the specific implementation of the present invention, the critical active power of the wind power side converter station when DC voltage control is prioritized is obtained by solving the extreme point of the following first function using the Lagrange multiplier method:

[0077]

[0078] Where: Represents the first parameter, Represents the second parameter, Represents the third parameter, Represents the fourth parameter, It is the critical active power of the converter station on the wind power side when DC voltage control is prioritized.

[0079] This embodiment can help ensure stable operation and optimized control of the power system when DC voltage control is prioritized by accurately calculating the critical active power of the wind power side converter station.

[0080] In the embodiment of the present invention, in step S103, when DC voltage control is prioritized, the critical voltage of the wind power grid connection point of the flexible DC transmission system is determined as follows:

[0081] The fifth voltage parameter is calculated based on the active and reactive currents of the grid-side converter station required for the critical active power of the wind-power-side converter station when the DC voltage control is prioritized, and the equivalent resistance and reactance of the fault grid;

[0082] The sixth voltage parameter is calculated based on the active and reactive currents of the grid-side converter station required for the critical active power of the wind power-side converter station when DC voltage control is prioritized, the equivalent resistance and reactance of the fault grid, the equivalent fault transition resistance and reactance, the grid voltage and equivalent reactance during normal operation, the maximum allowable AC current coefficient and the rated AC current of the grid-side converter station;

[0083] According to the sum of the fifth voltage parameter and the sixth voltage parameter, the critical voltage of the grid connection point of the wind power transmission system through the flexible direct current is calculated when the direct current voltage control is given priority;

[0084] Among them, when the DC voltage control is prioritized, the active and reactive currents of the grid-side converter station required for the critical active power of the wind power side converter station are calculated by the active and reactive currents of the grid-side converter station whose first-order derivative of the first function is 0.

[0085] In the specific implementation of the present invention, the critical voltage of the grid connection point of the transmission system when DC voltage control is prioritized is determined as follows:

[0086]

[0087] Where: represents the fifth voltage parameter, represents a sixth voltage parameter; To send the critical voltage of the system grid connection point when DC voltage control is given priority; and It is the active and reactive current of the grid side converter station required for the critical active power of the wind power side converter station when DC voltage control is prioritized, that is, the active and reactive current of the grid side converter station when the first-order derivative of the first function is set to 0.

[0088] This embodiment can help ensure stable operation and optimized control of the power system when DC voltage control is prioritized by accurately calculating the critical voltage of the transmission system grid connection point.

[0089] In the embodiment of the present invention, in step 105, the relative gain of the grid connection point voltage of the transmission system and the relative gain of the active power of the wind power side converter station are determined as follows:

[0090] The relative gain of the grid connection point voltage of the transmission system is obtained by dividing the difference between the grid connection point critical voltage of the transmission system when AC voltage control is preferred and the grid connection point critical voltage of the system when DC voltage control is preferred by the grid connection point critical voltage of the system when DC voltage control is preferred;

[0091] The relative gain of active power of the wind power side converter station is obtained by dividing the difference between the critical active power of the wind power side converter station when DC voltage control is preferred and the critical active power of the wind power side converter station when AC voltage control is preferred by the critical active power of the wind power side converter station when AC voltage control is preferred;

[0092] When the present invention is specifically implemented, the relative gain of the voltage at the grid connection point of the transmission system and the relative gain of the active power of the converter station on the wind power side are determined as follows:

[0093]

[0094] Where: and They are the relative voltage gain of the transmission system grid connection point and the relative active power gain of the converter station on the wind power side.

[0095] In the embodiment of the present invention, in step 106, the active and reactive current reference values ​​of the grid-side converter station when AC voltage control is prioritized are determined as follows:

[0096] If the difference between the equivalent potential phase and the equivalent impedance angle of the faulty power grid is less than or equal to the maximum allowable AC current phase angle of the power grid side converter station to avoid over-limit DC voltage, the active current reference value of the power grid side converter station when AC voltage control is prioritized is obtained according to the maximum allowable AC current coefficient of the power grid side converter station and the cosine value of the difference between the rated AC current and the equivalent potential phase and the equivalent impedance angle of the faulty power grid;

[0097] If the difference between the equivalent potential phase and the equivalent impedance angle of the faulty power grid is greater than the maximum allowable AC current phase angle of the power grid side converter station to avoid the DC voltage exceeding the limit, the active current reference value of the power grid side converter station when AC voltage control is prioritized is obtained according to the maximum allowable AC current coefficient of the power grid side converter station and the cosine value of the maximum allowable AC current phase angle of the power grid side converter station to avoid the DC voltage exceeding the limit;

[0098] If the difference between the equivalent potential phase and the equivalent impedance angle of the faulty power grid is less than or equal to the maximum allowable AC current phase angle of the power grid side converter station to avoid DC voltage over-limit, the reactive current reference value of the power grid side converter station when AC voltage control is prioritized is obtained according to the maximum allowable AC current coefficient of the power grid side converter station and the sine value of the difference between the rated AC current and the equivalent potential phase and the equivalent impedance angle of the faulty power grid;

[0099] If the difference between the equivalent potential phase and the equivalent impedance angle of the faulty power grid is greater than the maximum allowable AC current phase angle of the grid-side converter station to avoid DC voltage exceeding the limit, the reactive current reference value of the grid-side converter station when AC voltage control is prioritized is obtained based on the maximum allowable AC current coefficient of the grid-side converter station and the sine value of the maximum allowable AC current phase angle of the grid-side converter station to avoid DC voltage exceeding the limit.

[0100] When the present invention is specifically implemented, the active and reactive current reference values ​​of the grid-side converter station are determined as follows when AC voltage control is prioritized:

[0101]

[0102] Where: and They are respectively the reference values ​​of active and reactive current of the grid-side converter station when AC voltage control is prioritized.

[0103] In the specific implementation of the present invention, the reference values ​​of active and reactive currents of the grid-side converter station when DC voltage control is prioritized are:

[0104]

[0105] Where: and They are respectively the reference values ​​of active and reactive current of the grid-side converter station when DC voltage control is prioritized.

[0106] The embodiment of the present invention realizes adaptive adjustment of active and reactive power reference values ​​of the grid-side converter station through steps S101-S107. Under the premise of ensuring the DC voltage safety of the transmission system, when the equivalent impedance of the fault grid is small, it has a fault grid voltage support effect similar to that of the prior art, and also reduces the active power loss of the wind farm; when the equivalent impedance of the fault grid is large, the present invention has a better voltage raising effect at the grid connection point of the transmission system.

[0107] The embodiment of the present invention also provides a wind power transmission system adaptive fault ride-through device, such as Figure 3 As shown, it may include a voltage transformer 111, a current transformer 112 and a converter controller 113. The voltage transformer 111 is used to detect the AC bus voltage of the grid-side converter station to determine whether a fault occurs in the receiving-end grid. The current transformer 112 is used to detect the active and reactive currents of the grid-side converter station to achieve precise regulation of the active and reactive currents of the grid-side converter station under grid faults. The converter controller 113 is the secondary part of the grid-side converter station, responsible for monitoring the operating status of the grid-side converter station, adjusting the output voltage and current of the converter valve, and achieving coordinated control with other power systems, thereby achieving adaptive fault ride-through.

[0108] In the embodiment of the present invention, Figure 4 As shown, the converter controller 113 includes:

[0109] The detection module 201 is used to detect the AC bus voltage of the power grid side converter station;

[0110] A first comparison module 202, configured to compare the AC bus voltage with a preset voltage threshold;

[0111] The first calculation module 203 is used to calculate the critical voltage of the wind power grid connection point of the flexible direct current transmission system and its corresponding critical active power of the wind power side converter station when AC voltage control is prioritized; and the critical voltage of the wind power grid connection point of the flexible direct current transmission system and its corresponding critical active power of the wind power side converter station when DC voltage control is prioritized;

[0112] The second calculation module 204 is used to calculate the relative gain of the voltage at the grid connection point of the wind power transmission system through flexible direct current transmission and the relative gain of the active power of the wind power side converter station;

[0113] The second comparison module 205 is used to compare the relative gain of the voltage at the grid connection point of the wind power transmission system through flexible direct current transmission and the relative gain of the active power of the converter station on the wind power side;

[0114] The first control module 206 is used to give priority to AC voltage control when the relative voltage gain of the grid connection point of the wind power transmission system via flexible direct current is greater than the relative active power gain of the wind power side converter station, and adjust the active and reactive current reference values ​​of the grid side converter station to be equal to the active and reactive currents of the grid side converter station required for the wind power transmission system via flexible direct current to reach the maximum voltage at the grid connection point;

[0115] The second control module 207 is used to give priority to DC voltage control when the relative gain of the voltage at the grid connection point of the flexible DC transmission system is less than or equal to the relative gain of the active power of the wind power side converter station, and adjust the active and reactive current reference values ​​of the grid side converter station to be equal to the active and reactive currents of the grid side converter station required for the wind power side converter station to reach the maximum active power.

[0116] This embodiment adds an adaptive fault ride-through device for wind power through flexible direct current transmission system in the grid-side converter station. The device adjusts the active and reactive current reference values ​​of the grid-side converter station, and cooperates with the fixed direct current voltage control of the wind power side converter station to reduce the active power loss of the wind farm while ensuring the safety of the direct current voltage of the transmission system. It can be understood that the embodiment of the present invention only utilizes the electrical quantity of the grid-side converter station, and has a simple principle, is easy to implement, and has strong practicality.

[0117] In order to verify the effectiveness of the present invention, Figure 5 The structural diagram of the wind power transmission system through flexible direct current under power grid fault is taken as an example for analysis. Figure 5 As shown, in this embodiment, flexible DC transmission adopts symmetrical monopole connection, the rated DC voltage is ±800kV, and the rated transmission capacity is 900MW. The wind farm consists of 180 direct-drive wind turbines with a rated capacity of 5MW. During normal operation, the grid-side converter station adopts fixed active power control, and the control reference value is 1.0pu; the wind power side converter station adopts fixed DC voltage control, and the control reference value is 1.0pu; the wind turbine adopts maximum power tracking control.

[0118] This embodiment takes the scenario that a three-phase short circuit fault occurs in the power grid at 2.15s and the fault is cleared after 200ms. In order to verify the effect of the adaptive fault ride-through method of the wind power transmission system disclosed in the present invention, the comparison group adopts an improved DC voltage control method based on direct power control. The DC voltage, the voltage at the grid connection point of the transmission system, the active power of the grid-side converter station, the reactive power of the grid-side converter station, and the active power of the wind power side converter station are recorded and analyzed.

[0119] In this embodiment, according to the aforementioned step S103, the critical voltage of the transmission system grid connection point and its corresponding critical active power of the wind power side converter station when AC voltage control is prioritized are 0.58 pu and 0.51 pu respectively;

[0120] In this embodiment, according to the aforementioned step S103, when DC voltage control is prioritized, the critical active power of the wind power converter station and its corresponding critical voltage of the transmission system grid connection point are 0.56pu and 0.66pu respectively.

[0121] In this embodiment, according to the aforementioned steps S104 and S105, the relative gain of the voltage at the grid connection point of the transmission system and the relative gain of the active power of the wind power side converter station are 0.04 and 0.29 respectively, and S106 is selected for execution;

[0122] In this embodiment, according to the aforementioned step S106, the active and reactive current reference values ​​of the grid-side converter station are equal to 1.18 pu and 0.21 pu.

[0123] Figure 6 (a) to (e) are waveform diagrams of DC voltage, grid-connected point voltage of the transmission system, active power of the grid-side converter station, reactive power of the grid-side converter station, and active power of the wind power side converter station under grid fault, respectively; the horizontal axis in the figure is time, and the vertical axis is DC voltage, grid-connected point voltage of the transmission system, active power of the grid-side converter station, reactive power of the grid-side converter station, and active power of the wind power side converter station, respectively; the solid line is the curve of the adaptive fault ride-through method of the wind power through the flexible direct current transmission system disclosed in the present invention, and the dotted line is the curve of the comparison group.

[0124] like Figure 6As shown in (a) to (d), although the comparison group provides greater reactive power to the faulty power grid, the effect of raising the voltage at the grid connection point of the transmission system is similar to that of the present invention, and the active power change of the grid-side converter station before and after the fault reaches 0.44pu, resulting in an active power surplus in the wind farm. The present invention pre-calculates and compares the relative gain of the grid connection point voltage of the transmission system and the active power of the wind farm-side converter station, determines that the equivalent impedance of the faulty power grid is small and the voltage increase at the grid connection point of the transmission system is not obvious when AC voltage control is prioritized, and selects DC voltage control priority to minimize the active power loss of the wind farm under the power grid fault. Compared with the comparison group, the active power loss of the wind farm-side converter station is reduced by 22.7%, as shown in FIG. Figure 6 This shows that the present invention can adaptively prioritize AC voltage or DC voltage control when the wind power is transmitted through the flexible direct current transmission system fault, reduce the active power loss of the wind farm when the faulty grid is strong, and basically do not reduce the AC voltage support effect on the faulty grid.

[0125] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. An adaptive fault ride-through method for a wind power flexible direct current transmission system, wherein the wind power flexible direct current transmission system comprises a wind farm, a wind power side converter station, a grid side converter station and a DC cable connecting the two converter stations, characterized in that: The following steps are involved: S101, detecting the AC bus voltage of the converter station on the grid side; S102, comparing the AC bus voltage with a preset voltage threshold; S103. If the AC bus voltage is lower than the preset voltage threshold, respectively calculate the critical voltage of the wind power grid connection point of the flexible direct current transmission system and its corresponding critical active power of the wind power side converter station when AC voltage control is prioritized; and the critical voltage of the wind power grid connection point of the flexible direct current transmission system and its corresponding critical active power of the wind power side converter station when DC voltage control is prioritized; S104, calculating the relative voltage gain of the grid connection point of the wind power transmission system through flexible direct current transmission and the relative active power gain of the converter station on the wind power side; S105, comparing the relative voltage gain of the grid connection point of the wind power transmission system through flexible direct current transmission and the relative active power gain of the converter station on the wind power side; S106. If the relative voltage gain of the grid connection point of the wind power transmission system through the flexible direct current transmission is greater than the relative active power gain of the wind power side converter station, the AC voltage control is given priority, and the active and reactive current reference values ​​of the grid side converter station are adjusted to be equal to the active and reactive currents of the grid side converter station required for the wind power transmission system through the flexible direct current transmission system to reach the maximum voltage at the grid connection point; S107. If the relative voltage gain at the grid connection point of the wind power transmission system via flexible direct current is less than or equal to the relative active power gain of the converter station on the wind power side, the direct current voltage control takes priority and adjusts the reference values ​​of the active and reactive currents of the converter station on the grid side to be equal to the active and reactive currents of the converter station on the grid side required for the converter station on the wind power side to reach the maximum active power.

2. The adaptive fault ride-through method for wind power transmission system via flexible direct current transmission according to claim 1 is characterized in that: In step S103, the critical voltage of the wind power grid connection point when AC voltage control is prioritized is determined as follows: If the difference between the equivalent potential phase and the equivalent impedance angle of the faulty power grid is less than or equal to the maximum allowable AC current phase angle of the power grid side converter station to avoid the DC voltage exceeding the limit; the first voltage parameter is calculated according to the equivalent resistance and reactance of the faulty power grid, the maximum allowable AC current coefficient of the power grid side converter station and the rated AC current; The second voltage parameter is calculated based on the equivalent resistance and reactance of the faulty power grid, and the voltage and equivalent reactance of the power grid during normal operation; the critical voltage of the wind power grid connection point when AC voltage control is prioritized is calculated based on the sum of the first voltage parameter and the second voltage parameter; If the difference between the equivalent potential phase and the equivalent impedance angle of the faulty grid is greater than the maximum allowable AC current phase angle of the grid-side converter station to avoid over-limit DC voltage; the third voltage parameter is calculated based on the maximum allowable AC current coefficient and rated AC current of the grid-side converter station, the equivalent resistance and reactance of the faulty grid, the grid voltage and equivalent reactance during normal operation, the equivalent fault transition resistance and reactance, and the maximum allowable AC current phase angle of the grid-side converter station to avoid over-limit DC voltage; the fourth voltage parameter is calculated based on the maximum allowable AC current coefficient and rated AC current of the grid-side converter station, the equivalent resistance and reactance of the faulty grid, and the maximum allowable AC current phase angle of the grid-side converter station to avoid over-limit DC voltage; the critical voltage of the wind power connection point of the flexible direct current transmission system when DC voltage control is prioritized is calculated based on the difference between the third voltage parameter and the fourth voltage parameter.

3. The adaptive fault ride-through method for wind power flexible direct current transmission system according to claim 2 is characterized in that: The maximum allowable AC current phase angle of the grid-side converter station to avoid DC voltage exceeding the limit is equal to the arc tangent of the ratio of the ordinate to the abscissa of the intersection of the DC voltage limit boundary and the AC current limit boundary.

4. The adaptive fault ride-through method for wind power transmission system via flexible direct current transmission according to claim 3 is characterized in that: The ordinate and abscissa of the boundary intersection point are determined by simultaneously solving the DC voltage boundary equation and the AC current boundary equation.

5. The adaptive fault ride-through method for wind power transmission system via flexible direct current transmission according to claim 1 is characterized in that: In step S103, when AC voltage control is prioritized, the critical active power of the wind power converter station is determined by the following method: If the difference between the equivalent potential phase and the equivalent impedance angle of the faulty power grid is less than or equal to the maximum allowable AC current phase angle of the power grid side converter station to avoid DC voltage exceeding the limit; the first active power parameter is calculated based on the maximum allowable AC current coefficient and the rated AC current of the power grid side converter station, the equivalent resistance of the faulty power grid, and the difference between the equivalent potential phase and the equivalent impedance angle of the faulty power grid; the first active power parameter is calculated based on the maximum allowable AC current coefficient and the rated AC current of the power grid side converter station, the equivalent reactance of the faulty power grid, the equivalent reactance of the connecting transformer, the equivalent potential phase and the equivalent impedance angle of the faulty power grid. The second active power parameter is calculated based on the difference between the maximum allowable AC current coefficient and the rated AC current, the equivalent resistance and equivalent reactance of the fault grid, the equivalent fault transition resistance and reactance, the difference between the equivalent potential phase and the equivalent impedance angle of the fault grid, the equivalent reactance of the connecting transformer, and the voltage and equivalent reactance of the grid during normal operation. The third active power parameter is calculated based on the difference between the first active power parameter and the second active power parameter and the sum of the third active power parameter to obtain the critical active power of the wind power side converter station when AC voltage control is prioritized; If the difference between the equivalent potential phase of the faulty grid and the equivalent impedance angle is greater than the maximum allowable AC current phase angle of the grid-side converter station to avoid the DC voltage exceeding the limit; the fourth active power parameter is calculated according to the maximum allowable AC current coefficient and the rated AC current of the grid-side converter station, the equivalent resistance of the faulty grid and the maximum allowable AC current phase angle of the grid-side converter station to avoid the DC voltage exceeding the limit; The fifth active power parameter is calculated based on the maximum allowable AC current coefficient and rated AC current of the grid-side converter station, the equivalent reactance of the fault grid, the equivalent reactance of the connecting transformer, and the maximum allowable AC current phase angle of the grid-side converter station to avoid DC voltage exceeding the limit; The sixth active power parameter is calculated based on the maximum allowable AC current coefficient and the rated AC current, the equivalent resistance and equivalent reactance of the fault grid, the equivalent fault transition resistance and reactance, the maximum allowable AC current phase angle of the grid-side converter station to avoid DC voltage exceeding the limit, the equivalent reactance of the connecting transformer, and the grid voltage and equivalent reactance during normal operation; the critical active power of the wind power side converter station when AC voltage control is prioritized is calculated based on the difference between the fourth active power parameter and the fifth active power parameter and the sum of the sixth active power parameter.

6. The adaptive fault ride-through method for wind power transmission system via flexible direct current transmission according to claim 1 is characterized in that: In step S103, the critical active power of the wind power side converter station when DC voltage control is prioritized is obtained by solving the extreme point of the first function by the Lagrange multiplier method; the first function is obtained by compounding the first parameter, the second parameter, the third parameter and the fourth parameter; the first parameter includes the maximum allowable AC current coefficient and the rated AC current of the grid side converter station, the reactive current of the grid side converter station and the equivalent resistance of the fault grid; the second parameter includes the maximum allowable AC current coefficient and the rated AC current of the grid side converter station, the reactive current of the grid side converter station, the equivalent reactance of the fault grid and the equivalent reactance of the connecting transformer; the third parameter includes the maximum allowable AC current coefficient and the rated AC current of the grid side converter station and the reactive current of the grid side converter station; the fourth parameter includes the maximum allowable AC current coefficient and the rated AC current of the grid side converter station, the reactive current of the grid side converter station, the equivalent resistance and reactance of the fault grid, the equivalent reactance of the connecting transformer, the equivalent fault transition resistance and reactance, and the grid voltage and equivalent reactance during normal operation.

7. The adaptive fault ride-through method for wind power transmission system via flexible direct current transmission according to claim 6 is characterized in that: In step S103, when DC voltage control is prioritized, the critical voltage of the wind power grid connection point of the flexible DC transmission system is determined as follows: The fifth voltage parameter is calculated based on the active and reactive currents of the grid-side converter station required for the critical active power of the wind-power-side converter station when the DC voltage control is prioritized, and the equivalent resistance and reactance of the fault grid; The sixth voltage parameter is calculated based on the active and reactive currents of the grid-side converter station required for the critical active power of the wind power-side converter station when DC voltage control is prioritized, the equivalent resistance and reactance of the fault grid, the equivalent fault transition resistance and reactance, the grid voltage and equivalent reactance during normal operation, the maximum allowable AC current coefficient and the rated AC current of the grid-side converter station; According to the sum of the fifth voltage parameter and the sixth voltage parameter, the critical voltage of the grid connection point of the wind power transmission system through the flexible direct current is calculated when the direct current voltage control is given priority; Among them, when the DC voltage control is prioritized, the active and reactive currents of the grid-side converter station required for the critical active power of the wind power side converter station are calculated by the active and reactive currents of the grid-side converter station whose first-order derivative of the first function is 0.

8. The adaptive fault ride-through method for wind power transmission system via flexible direct current transmission according to claim 1 is characterized in that: In step S106, when AC voltage control is prioritized, the active and reactive current reference values ​​of the grid-side converter station are determined as follows: If the difference between the equivalent potential phase and the equivalent impedance angle of the faulty power grid is less than or equal to the maximum allowable AC current phase angle of the power grid side converter station to avoid over-limit DC voltage, the active current reference value of the power grid side converter station when AC voltage control is prioritized is obtained according to the maximum allowable AC current coefficient of the power grid side converter station and the cosine value of the difference between the rated AC current and the equivalent potential phase and the equivalent impedance angle of the faulty power grid; If the difference between the equivalent potential phase and the equivalent impedance angle of the faulty power grid is greater than the maximum allowable AC current phase angle of the power grid side converter station to avoid the DC voltage exceeding the limit, the active current reference value of the power grid side converter station when AC voltage control is prioritized is obtained according to the maximum allowable AC current coefficient of the power grid side converter station, the rated AC current and the cosine value of the maximum allowable AC current phase angle of the power grid side converter station to avoid the DC voltage exceeding the limit; If the difference between the equivalent potential phase and the equivalent impedance angle of the faulty power grid is less than or equal to the maximum allowable AC current phase angle of the power grid side converter station to avoid DC voltage over-limit, the reactive current reference value of the power grid side converter station when AC voltage control is prioritized is obtained according to the maximum allowable AC current coefficient of the power grid side converter station and the sine value of the difference between the rated AC current and the equivalent potential phase and the equivalent impedance angle of the faulty power grid; If the difference between the equivalent potential phase and the equivalent impedance angle of the faulty power grid is greater than the maximum allowable AC current phase angle of the grid-side converter station to avoid DC voltage exceeding the limit, the reactive current reference value of the grid-side converter station when AC voltage control is prioritized is obtained based on the maximum allowable AC current coefficient of the grid-side converter station, the rated AC current and the sine value of the maximum allowable AC current phase angle of the grid-side converter station to avoid DC voltage exceeding the limit.

9. An adaptive fault ride-through device for a wind power flexible direct current transmission system, characterized in that: include: A voltage transformer, a current transformer and a converter controller; wherein the converter controller comprises: A detection module, used to detect the AC bus voltage of the power grid side converter station; A first comparison module, used for comparing the AC bus voltage with a preset voltage threshold; The first calculation module is used to calculate the critical voltage of the wind power grid connection point of the flexible direct current transmission system and its corresponding critical active power of the wind power side converter station when AC voltage control is prioritized; and the critical voltage of the wind power grid connection point of the flexible direct current transmission system and its corresponding critical active power of the wind power side converter station when DC voltage control is prioritized; The second calculation module is used to calculate the relative gain of the voltage at the grid connection point of the wind power transmission system through flexible direct current transmission and the relative gain of the active power of the converter station on the wind power side; The second comparison module is used to compare the relative gain of the voltage at the grid connection point of the wind power transmission system through flexible direct current transmission and the relative gain of the active power of the converter station on the wind power side; The first control module is used to give priority to AC voltage control when the voltage relative gain of the grid connection point of the wind power transmission system via flexible direct current is greater than the active power relative gain of the wind power side converter station, and adjust the active and reactive current reference values ​​of the grid side converter station to be equal to the active and reactive currents of the grid side converter station required for the wind power transmission system via flexible direct current to reach the maximum voltage at the grid connection point; The second control module is used to give priority to DC voltage control when the relative gain of the voltage at the grid connection point of the flexible direct current transmission system is less than or equal to the relative gain of the active power of the wind power side converter station, and adjust the active and reactive current reference values ​​of the grid side converter station to be equal to the active and reactive currents of the grid side converter station required for the wind power side converter station to reach the maximum active power.

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