Adaptive fault ride-through method and device for wind power through flexible transmission system

Abstract

The present application belongs to the field of power system protection and control, and discloses a wind power through flexible transmission system adaptive fault ride-through method and device. After the failure of the receiving end power grid, the grid side converter station calculates the critical active power of the wind power side converter station and the critical voltage of the grid connection point of the wind power through flexible transmission system when the wind power through flexible transmission system is controlled by the priority of alternating voltage and the priority of direct current voltage, respectively, calculates and compares the relative gain of the grid connection point voltage and the relative gain of the active power of the wind power side converter station, and then determines the priority of the wind power through flexible transmission system fault ride-through, adjusts the active and reactive current reference value of the grid side converter station, and implements control. The present application can control the direct current voltage of the wind power through flexible transmission system and the alternating voltage of the fault power grid, support the voltage of the fault power grid and reduce the active power loss of the wind farm while ensuring the uninterrupted operation of the wind power through flexible transmission system.

Description

Technical Field

[0001] This invention relates to the field of power system protection and control, specifically to an adaptive fault ride-through method and apparatus for wind power transmission via flexible direct current systems. Background Technology

[0002] During grid short-circuit faults, wind power transmitted via flexible DC transmission systems must support the faulty grid voltage while ensuring DC voltage safety. DC voltage control methods for wind power transmitted via flexible DC transmission systems under grid fault conditions fall into two categories: those utilizing energy dissipation or storage devices, and those using wind farm-side converter station regulation. Existing engineers have improved the devices, topology, and switching algorithms of centralized DC energy dissipation devices, enhancing DC voltage control accuracy and reducing electromagnetic interference. Other engineers have connected flywheel energy storage devices in parallel on the DC side of flexible DC transmission lines, or used submodule capacitors to temporarily store surplus power. However, energy dissipation or storage devices increase hardware costs and cannot be used continuously due to capacity limitations. Therefore, DC voltage control methods based on wind farm-side converter station regulation have received more attention. For wind farm-side converter stations where AC voltage is the control object, engineers have proposed a precise voltage reduction and harmonic injection DC voltage control method; for wind farm-side converter stations where active power is the control object, engineers have incorporated the DC voltage deviation into the active power reference value of the wind farm-side converter station and adjusted the droop coefficient based on the surplus power and the wind farm converter station capacity. Wind farm converter stations with constant DC voltage control can autonomously adjust active power to ensure that the DC voltage equals the rated value during fault steady-state conditions. However, DC voltage control methods based on wind power-side converter station regulation reduce the active power fed into the flexible DC transmission line from the wind farm, and most existing studies have neglected the active power loss of the wind farm caused by DC voltage control.

[0003] The transition impedance during a grid short-circuit fault is often resistive, causing the grid impedance to abruptly change from purely inductive during normal operation to resistive-inductive during the fault. Therefore, the grid connection voltage of the transmitting 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 resistive component of the equivalent impedance of the faulted grid. The active power of the grid-side converter station equals the product of the AC voltage and the active current. Under constant DC voltage control, the active power of the wind power-side converter station ultimately equals 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 simultaneous changes in the grid connection voltage of the transmitting system and the active power of the wind power-side converter station under constant DC voltage control. The AC voltage control effect and DC voltage control cost of the wind power transmission system via flexible DC transmission are coupled under the influence of the equivalent impedance of the faulted grid. Existing technologies assume that the faulted grid remains inductive, neglecting the abrupt change in grid impedance before and after the fault caused by the fault transition impedance and its impact on fault ride-through of wind power via flexible DC transmission. The active power of the grid-side converter station, which sacrifices AC voltage support, will significantly reduce the active power of the wind power-side converter station under constant DC voltage control, resulting in active power loss in the wind farm.

[0004] In summary, how to establish a coupling function between the active power of the wind turbine-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 constant DC voltage of the transmission system, in order to determine the control priority during the fault ride-through of wind power through the flexible DC transmission system, adjust the reference values ​​of active and reactive power of the grid-side converter station, and coordinate with the constant DC voltage control of the wind turbine-side converter station to reduce the active power loss of the wind farm while ensuring the safety of the DC voltage of the transmission system, has become an urgent problem to be solved by those skilled in the art. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention argues that the transition impedance during a grid short-circuit fault is often resistive, causing the grid impedance to abruptly change from purely inductive during normal operation to resistive-inductive during the fault. Therefore, the grid connection voltage of the transmitting system under grid fault conditions 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 faulted grid. The active power of the grid-side converter station equals the product of the AC voltage and the active current. Under constant DC voltage control, the active power of the wind power-side converter station ultimately equals the active power of the grid-side converter station. Therefore, changing the active or reactive current of the grid-side converter station under grid fault conditions leads to simultaneous changes in the grid connection voltage of the transmitting system and the active power of the wind power-side converter station under constant DC voltage control. This results in a coupling of the AC voltage control effect and DC voltage control cost of the wind power transmission system via flexible DC transmission under the influence of the equivalent impedance of the faulted grid. The fault crossing of wind power through the flexible direct transmission system should take into account the AC / DC voltage control coupling caused by the equivalent impedance of the fault grid, and balance the AC voltage control effect and DC voltage control cost, so as to help raise the voltage of the fault grid and reduce the active power loss of the wind farm.

[0006] This invention discloses an adaptive fault ride-through method and apparatus for wind power transmitted via a flexible direct current transmission system. Upon detecting a grid fault, 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's grid connection point when AC voltage control and DC voltage control are prioritized. It calculates and compares the relative gain of the transmission system's grid connection point voltage and the relative gain of the wind power-side converter station's active power to determine the priority for fault ride-through of wind power via the flexible direct current transmission system. The reference values ​​of active and reactive currents at the grid-side converter station are then adjusted, and control is implemented.

[0007] In a first aspect, the present invention provides an adaptive fault ride-through method applicable to a wind power transmission system via flexible DC transmission; the wind power transmission system via flexible DC transmission includes 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. Detect the AC bus voltage of the converter station on the grid side;

[0009] S102. Compare the AC bus voltage with a preset voltage threshold.

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

[0011] S104. Calculate the relative voltage gain at the grid connection point of the wind power transmission system via flexible direct current transmission and the relative active power gain of the wind power-side converter station.

[0012] S105. Compare the relative voltage gain at the grid connection point of wind power transmitted through the flexible direct transmission system and the relative active power gain of the wind power-side converter station.

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

[0014] S107. If the relative gain of the voltage at the grid connection point of the wind power transmission system is less than or equal to the relative gain of the active power of the wind power-side converter station, then DC voltage control shall take priority, and the reference values ​​of the active and reactive currents of the grid-side converter station shall be adjusted 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 its maximum active power.

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

[0016] The detection module is used to detect the AC bus voltage of the grid-side converter station;

[0017] The first comparison module is used to compare 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 transmission system and the corresponding critical active power of the wind power-side converter station when AC voltage control takes priority; and the critical voltage of the wind power grid connection point of the flexible direct transmission system and the corresponding critical active power of the wind power-side converter station when DC voltage control takes priority.

[0019] The second calculation module is used to calculate the relative voltage gain at the grid connection point of the wind power transmission system and the relative active power gain of the wind power-side converter station.

[0020] The second comparison module is used to compare the relative voltage gain at the grid connection point of the wind power transmission system and the relative active power gain of the wind power-side converter station.

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

[0022] The second control module is used to prioritize DC voltage control and adjust the reference values ​​of active and reactive currents 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 converter station to reach its maximum active power when the relative gain of the voltage at the grid connection point of the wind power transmission system is less than or equal to the relative gain of the active power of the wind power converter station.

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

[0024] Existing technologies neglect the relationship between AC voltage control effectiveness and DC voltage control costs caused by fault transition impedance, which is detrimental to raising the fault grid voltage and may exacerbate active power losses in wind farms. This invention adaptively adjusts the reference values ​​of active and reactive currents at the grid-side converter station by determining the priority of wind power during fault ride-through through the flexible DC transmission system. While ensuring the safety of the DC voltage of the transmission system, this invention provides a similar fault grid voltage support effect to existing technologies when the equivalent impedance of the fault grid is small, while also reducing active power losses in wind farms; when the equivalent impedance of the fault grid is large, this invention has a superior voltage rise effect at the grid connection point of the transmission system. This invention utilizes only the electrical quantities of the grid-side converter station, is simple in principle, easy to implement, and highly practical. Attached Figure Description

[0025] To make the objectives, technical solutions, and advantages of the invention clearer, the invention will now be described in further detail with reference to the accompanying drawings, wherein:

[0026] Figure 1 This is a flowchart of the adaptive fault ride-through method for wind power transmitted via a flexible direct transmission system according to an embodiment of the present invention;

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

[0028] Figure 3 This is a schematic diagram of the adaptive fault-crossing device according to an embodiment of the present invention;

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

[0030] Figure 5 This is a schematic diagram of the wind power transmission system via flexible direct current under grid fault conditions, as used in an embodiment of the present invention.

[0031] Figure 6 Figure 1 shows the effect diagram under the embodiment of the present invention. Figure 2 shows the relationship between time and DC voltage, Figure 3 shows the relationship between time and grid connection point voltage of the transmission system, Figure 4 shows the relationship between time and active power of the grid-side converter station, Figure 5 shows the relationship between time and reactive power of the grid-side converter station, and Figure 6 shows the relationship between time and active power of the wind power-side converter station. Detailed Implementation

[0032] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] This invention discloses an adaptive fault ride-through method and apparatus for wind power transmission via a flexible direct current transmission system. By calculating 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, the method determines whether to prioritize DC voltage or AC voltage control during wind power transmission via the flexible direct current transmission system based on the relative magnitude of the two values. The method adaptively adjusts the reference values ​​of active and reactive current of the grid-side converter station to implement fault ride-through.

[0034] Figure 1 This is a flowchart of the adaptive fault ride-through method for wind power transmitted via a flexible direct transmission system according to an embodiment of the present invention, as follows: Figure 1 As shown, the method includes the following steps:

[0035] S101. Detect the AC bus voltage of the converter station on the grid side;

[0036] S102. Compare the AC bus voltage with a preset voltage threshold.

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

[0038] S104. Calculate the relative voltage gain at the grid connection point of the wind power transmission system via flexible direct current transmission and the relative active power gain of the wind power-side converter station.

[0039] S105. Compare the relative voltage gain at the grid connection point of wind power transmitted through the flexible direct transmission system and the relative active power gain of the wind power-side converter station.

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

[0041] S107. If the relative gain of the voltage at the grid connection point of the wind power transmission system is less than or equal to the relative gain of the active power of the wind power-side converter station, then DC voltage control shall take priority, and the reference values ​​of the active and reactive currents of the grid-side converter station shall be adjusted 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 its maximum active power.

[0042] In this embodiment of the invention, step S101 specifically refers to the wind power transmission system via flexible direct current, such as... Figure 2As shown, the wind power transmission system via flexible direct current 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 receiving-end grid is connected at the grid-side converter station. By detecting the AC bus voltage of the grid-side converter station, it can be determined whether a fault has occurred in the receiving-end grid. This detection method is mainly to prevent excessively high or low voltage from adversely affecting the wind power transmission system via flexible direct current.

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

[0044] One method is to install voltage sensors on the AC busbar of the converter station on the grid side to measure voltage values ​​in real time. The sensors convert the measured voltage signals into electrical or digital signals, which are then transmitted to the monitoring system for display and analysis. The monitoring system receives the voltage signals from the sensors and displays and records them in real time.

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

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

[0047] Unlike normal operation, grid faults alter the active or reactive current of the grid-side converter station, causing simultaneous changes in the active power of the wind farm-side converter station under the control of the grid connection voltage and constant DC voltage of the outgoing system. This leads to coupling between the AC voltage control effect and the DC voltage control cost of wind power transmitted through the flexible DC transmission system under the influence of the faulted grid's equivalent impedance. Therefore, fault ride-through of wind power through the flexible DC transmission system should consider the AC / DC voltage control coupling caused by the faulted grid's equivalent impedance, balancing the AC voltage control effect and the DC voltage control cost. By establishing a coupling function of the active power of the wind farm-side converter station with the active and reactive currents of the grid-side converter station under the control of the grid connection voltage and constant DC voltage of the outgoing system, the control priority during fault ride-through of wind power through the flexible DC transmission system can be determined. This allows for the adjustment of the reference values ​​of active and reactive power of the grid-side converter station, coordinated with the constant DC voltage control of the wind farm, to reduce active power loss in the wind farm while ensuring the safety of the DC voltage of the outgoing system. In this embodiment of the invention, the critical voltage at the grid connection point of the wind power transmission system via the flexible direct transmission system and the critical active power of the wind power-side converter station are used to determine the priority of wind power transmission system via the flexible direct transmission system when AC voltage control is prioritized and when DC voltage control is prioritized, so as to adaptively adjust the reference values ​​of active and reactive power of the grid-side converter station.

[0048] In this embodiment of the invention, in step S103, the critical voltage at the grid connection point of the wind power transmission system via flexible direct current transmission when AC voltage control takes priority is determined as follows:

[0049] If the difference between the phase of the equivalent potential of the faulty power grid and the equivalent impedance angle is less than or equal to the maximum allowable AC current phase angle of the grid-side converter station to avoid DC voltage overshoot; the first voltage parameter is calculated based on the equivalent resistance and reactance of the faulty power 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 power grid, the grid voltage and equivalent reactance during normal operation; the critical voltage at the point of grid connection of wind power through the flexible DC transmission system is calculated based on the sum of the first and second voltage parameters, with AC voltage control taking priority;

[0050] If the difference between the equivalent potential phase and the equivalent impedance angle of the faulted power grid is greater than the maximum allowable AC current phase angle of the grid-side converter station to avoid DC voltage overruns, 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 faulted power 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 DC voltage overruns. 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 faulted power grid, and the maximum allowable AC current phase angle of the grid-side converter station to avoid DC voltage overruns. The critical voltage at the grid connection point of the wind power transmission system via flexible DC transmission is calculated based on the difference between the third and fourth voltage parameters when AC voltage control takes priority.

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

[0052]

[0053] In the formula: Indicates the first voltage parameter. Indicates the second voltage parameter; Indicates the third voltage parameter; This represents the fourth voltage parameter.

[0054] in, This refers to the critical voltage at the grid connection point of the power transmission system when AC voltage control takes priority; R R.f and X R.f These are the equivalent resistance and reactance of the faulty power grid, respectively; E R.N and X R.N These represent the grid voltage and equivalent reactance during normal operation, respectively; K I and I GEC.N These are the maximum allowable AC current coefficient and rated AC current of the grid-side converter station, respectively; η DIF This is the difference between the phase of the equivalent potential of the faulty power grid and the angle of its equivalent impedance. To avoid DC voltage exceeding limits, the maximum allowable AC current phase angle of the grid-side converter station is calculated using the following formula:

[0055]

[0056] In the formula: R V.f and X V.f These are the equivalent fault transition resistance and reactance, respectively.

[0057] This embodiment helps ensure the stability and safety of the power grid under fault conditions by accurately calculating the critical voltage at the grid connection point of the sending system, and can optimize the operating parameters of the grid-side converter station.

[0058] In the specific implementation of this invention, the maximum allowable AC current phase angle of the grid-side converter station to avoid DC voltage exceeding the limit is equal to the arctangent of the ratio of the ordinate to the abscissa of the intersection point of the DC voltage limit boundary and the AC current limit boundary. 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. The AC current boundary equation is determined by the following formula:

[0059]

[0060] In the formula: I GEC.d and I GEC.q These are the active and reactive currents of the converter station on the grid side, respectively.

[0061] In the specific implementation of this invention, the DC voltage boundary equation is determined by the following formula:

[0062]

[0063] In the formula: X T The equivalent reactance of the connecting transformer; parameters A, B, C, and D are calculated according to the following formulas:

[0064]

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

[0066]

[0067] In the formula: U WEC.N The rated AC bus voltage of the wind power-side converter station; k i and k p These are the integral coefficient and proportional coefficient of the outer loop of the DC voltage control for the wind power-side converter station, respectively.

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

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

[0070] If the difference between the phase of the equivalent electromotive force of the faulted power grid and the equivalent impedance angle is greater than the maximum allowable AC current phase angle of the grid-side converter station to avoid DC voltage overruns; based on the maximum allowable AC current coefficient and rated AC current of the grid-side converter station, the equivalent resistance of the faulted power grid, and the maximum allowable AC current phase angle of the grid-side converter station to avoid DC voltage overruns, 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 faulted power 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 overruns, the fourth active power parameter is calculated. The fifth active power parameter is calculated based on the current phase angle. The sixth active power parameter is calculated based on the maximum allowable AC current coefficient and rated AC current, the equivalent resistance and 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 over-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 takes priority is calculated based on the difference between the fourth and fifth active power parameters and the sum of the sixth active power parameter.

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

[0072]

[0073] In the formula: This represents the first active power parameter. This represents the second active power parameter. This represents the third active power parameter; This represents the fourth active power parameter. This represents the fifth active power parameter. This represents the sixth active power parameter; The critical active power of the wind power-side converter station when AC voltage control takes priority.

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

[0075] In this embodiment of the invention, in step S103, the critical active power of the wind power-side converter station under DC voltage control priority is obtained by solving the extreme points of the first function using the Lagrange multiplier method; the first function is obtained by combining the first parameter, the second parameter, the third parameter, and the fourth parameter; the first parameter includes the maximum allowable AC current coefficient and 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 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 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 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 this invention, the critical active power of the wind power-side converter station under DC voltage control priority is obtained by solving the extreme points of the following first function using the Lagrange multiplier method:

[0077]

[0078] In the formula: Indicates the first parameter. Indicates the second parameter. Indicates the third parameter. Indicates the fourth parameter. The critical active power of the wind power-side converter station when DC voltage control takes priority.

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

[0080] In this embodiment of the invention, in step S103, the critical voltage at the grid connection point of the wind power transmission system via the flexible DC transmission line 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 DC voltage control is prioritized, as well as the equivalent resistance and reactance of the faulted 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 faulted grid, the equivalent fault transition resistance and reactance, the grid voltage and equivalent reactance during normal operation, the maximum allowable AC current coefficient and rated AC current of the grid-side converter station.

[0083] Based on the sum of the fifth and sixth voltage parameters, the critical voltage at the point of grid connection of wind power through the flexible DC transmission system is calculated when DC voltage control takes priority.

[0084] Wherein, 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 takes priority are calculated from the active and reactive currents of the grid-side converter station when the first derivative of the first function is 0.

[0085] In the specific implementation of this invention, the critical voltage of the system grid connection point is determined according to the following method when DC voltage control takes priority:

[0086]

[0087] In the formula: This represents the fifth voltage parameter. Indicates the sixth voltage parameter; The critical voltage at the grid connection point is to be supplied when DC voltage control is prioritized. and 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 takes priority are defined as the active and reactive currents of the grid-side converter station with the first derivative of the first function set to 0.

[0088] This embodiment helps ensure stable operation and optimized control of the power system when DC voltage control takes priority by accurately calculating the critical voltage at the grid connection point of the sending system.

[0089] In this embodiment of the invention, in step 105, the relative gain of the grid connection point voltage of the sending 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 sending system is obtained by dividing the difference between the critical voltage of the grid connection point of the sending system when AC voltage control is prioritized and the critical voltage of the grid connection point of the system when DC voltage control is prioritized by the critical voltage of the grid connection point of the system when DC voltage control is prioritized.

[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 takes priority and the critical active power of the wind power-side converter station when AC voltage control takes priority by the critical active power of the wind power-side converter station when AC voltage control takes priority.

[0092] In the specific implementation of this invention, the relative gain of the grid connection point voltage of the sending system and the relative gain of the active power of the wind power-side converter station are determined according to the following method:

[0093]

[0094] In the formula: and These are the relative gain of the grid connection voltage of the transmission system and the relative gain of the active power of the wind power-side converter station, respectively.

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

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

[0097] If the difference between the phase of the equivalent potential 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 DC voltage overruns, the reference value of the active current of the grid-side converter station when AC voltage control takes priority is obtained based on the maximum allowable AC current coefficient of the grid-side converter station and the cosine value of the maximum allowable AC current phase angle of the grid-side converter station to avoid DC voltage overruns.

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

[0099] If the difference between the phase of the equivalent potential 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 DC voltage overruns, the reference value of the reactive current of the grid-side converter station when AC voltage control takes priority can be 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 overruns.

[0100] In the specific implementation of this invention, the reference values ​​of active and reactive currents of the grid-side converter station when AC voltage control takes priority are determined as follows:

[0101]

[0102] In the formula: and These are the reference values ​​for active and reactive currents of the grid-side converter station when AC voltage control takes priority.

[0103] In the specific implementation of this invention, when DC voltage control takes priority, the reference values ​​for the active and reactive currents of the grid-side converter station are as follows:

[0104]

[0105] In the formula: and These are the reference values ​​for active and reactive currents of the grid-side converter station when DC voltage control takes priority.

[0106] The embodiments of the present invention, through steps S101-S107, achieve adaptive adjustment of the active and reactive power reference values ​​of the grid-side converter station. Under the premise of ensuring the safety of the DC voltage of the transmission system, when the equivalent impedance of the fault grid is small, it has a similar fault grid voltage support effect as 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 rise effect at the grid connection point of the transmission system.

[0107] This invention also provides an adaptive fault ride-through device for a wind power transmission system via flexible direct current transmission, such as... Figure 3 As shown, the system may include a voltage transformer 111, a current transformer 112, and a converter controller 113. The voltage transformer 111 detects the AC bus voltage of the grid-side converter station to determine whether a fault has occurred in the receiving-end grid. The current transformer 112 detects the active and reactive currents of the grid-side converter station to achieve precise regulation of the active and reactive currents under grid fault conditions. The converter controller 113 is the secondary component 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 valves, and achieving coordinated control with other power systems, thereby enabling adaptive fault ride-through.

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

[0109] Detection module 201 is used to detect the AC bus voltage of the grid-side converter station;

[0110] The first comparison module 202 is used 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 transmission system and the corresponding critical active power of the wind power-side converter station when AC voltage control takes priority; and the critical voltage of the wind power grid connection point of the flexible direct transmission system and the corresponding critical active power of the wind power-side converter station when DC voltage control takes priority.

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

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

[0115] The second control module 207 is used to prioritize DC voltage control and adjust the reference values ​​of the active and reactive currents 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 its maximum active power when the relative gain of the voltage at the grid connection point of the wind power transmission system is less than or equal to the relative gain of the active power of the wind power-side converter station.

[0116] This embodiment adds an adaptive fault ride-through device to the wind power transmission system via flexible DC transmission in the grid-side converter station. The device adjusts the reference values ​​of active and reactive currents in the grid-side converter station and coordinates with the constant DC voltage control of the wind power-side converter station to reduce active power loss in the wind farm while ensuring the safety of the DC voltage of the transmission system. It is understood that this embodiment of the invention only utilizes the electrical quantities of the grid-side converter station; the principle is simple, easy to implement, and highly practical.

[0117] To verify the effectiveness of the present invention, as follows Figure 5 The following is an analysis using a schematic diagram of a wind power transmission system via flexible direct current transmission under grid fault conditions as an example. Figure 5 As shown, in this embodiment, the flexible DC transmission adopts a symmetrical single-pole connection, with a rated DC voltage of ±800kV and a rated transmission capacity of 900MW. The wind farm consists of 180 direct-drive wind turbine units with a rated capacity of 5MW. During normal operation, the grid-side converter station adopts constant active power control with a control reference value of 1.0pu; the wind-side converter station adopts constant DC voltage control with a control reference value of 1.0pu; and the wind turbine units adopt maximum power point tracking control.

[0118] This embodiment uses a scenario where a three-phase short-circuit fault occurs in the power grid at 2.15 seconds, and the fault is cleared after 200 milliseconds. To verify the effectiveness of the adaptive fault ride-through method for wind power transmitted via a flexible DC transmission system disclosed in this invention, a comparative group uses an improved DC voltage control method based on direct power control. The DC voltage, grid connection 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 are recorded and analyzed.

[0119] According to the aforementioned step S103, the critical voltage of the grid connection point of the sending system when AC voltage control is prioritized and the corresponding critical active power of the wind power-side converter station are 0.58 pu and 0.51 pu, respectively.

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

[0121] In this embodiment, based on the aforementioned steps S104 and S105, the relative gain of the grid connection voltage of the output system and the relative gain of the active power of the wind power-side converter station are 0.04 and 0.29, respectively, and step S106 is selected to be executed.

[0122] According to the aforementioned step S106, the reference values ​​for active and reactive currents of the grid-side converter station are 1.18 pu and 0.21 pu, respectively.

[0123] Figure 6 (a) to (e) are waveforms of DC voltage, grid connection point voltage of the transmitting 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 conditions, respectively. The horizontal axis in the figure is time, and the vertical axis is DC voltage, grid connection point voltage of the transmitting 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 DC transmission system disclosed in this invention, and the dashed line is the curve of the comparison group.

[0124] like Figure 6As shown in (a) to (d), although the control group provided greater reactive power to the faulty grid, its effect on raising the voltage at the grid connection point of the transmitting system was similar to that of the present invention. It also resulted in a 0.44 pu change in the active power of the grid-side converter station before and after the fault, leading to a surplus of active power in the wind farm. The present invention, by pre-calculating and comparing the relative gains of the grid connection point voltage of the transmitting system and the active power of the wind farm's converter station, determined that the equivalent impedance of the faulty grid was small and that the voltage rise at the grid connection point of the transmitting system was not significant when AC voltage control was prioritized. Therefore, it selected DC voltage control as the priority, minimizing the active power loss of the wind farm under grid fault conditions. Compared to the control group, this reduced the active power loss of the wind farm's converter station by 22.7%. Figure 6 As shown in (e). This demonstrates that the present invention can adaptively prioritize AC or DC voltage control during wind power fault crossing through the flexible DC transmission system, reducing active power loss in the wind farm when the faulty grid is strong, and essentially not reducing the AC voltage support effect on the faulty grid.

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

Claims

1. An adaptive fault ride-through method for a wind power transmission system via flexible direct current transmission, wherein the wind power transmission system via flexible direct current transmission includes 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, Includes the following steps: S101. Detect the AC bus voltage of the converter station on the grid side; S102. Compare the AC bus voltage with a preset voltage threshold. S103. If the AC bus voltage is lower than the preset voltage threshold, calculate the critical voltage of the wind power grid connection point of the flexible DC transmission system when AC voltage control takes priority and the critical active power of the corresponding wind power converter station; and calculate the critical voltage of the wind power grid connection point of the flexible DC transmission system and the corresponding critical active power of the corresponding wind power converter station when DC voltage control takes priority. S104. Calculate the relative voltage gain at the grid connection point of the wind power transmission system via flexible direct current transmission and the relative active power gain of the wind power-side converter station. The relative gain of the grid connection point voltage of the sending system is obtained by dividing the difference between the critical voltage of the grid connection point of the sending system when AC voltage control is prioritized and the critical voltage of the grid connection point of the system when DC voltage control is prioritized by the critical voltage of the grid connection point of the system when DC voltage control is prioritized. 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 takes priority and the critical active power of the wind power-side converter station when AC voltage control takes priority by the critical active power of the wind power-side converter station when AC voltage control takes priority. S105. Compare the relative voltage gain at the grid connection point of wind power transmitted through the flexible direct transmission system and the relative active power gain of the wind power-side converter station. S106. If the relative gain of the voltage at the grid connection point of the wind power through the flexible direct transmission system is greater than the relative gain of the active power of the wind power-side converter station, then AC voltage control shall take priority, and the reference values ​​of the active and reactive currents of the grid-side converter station shall be adjusted to be equal to the active and reactive currents of the grid-side converter station required for the wind power to reach the maximum voltage at the grid connection point of the flexible direct transmission system. S107. If the relative gain of the voltage at the grid connection point of the wind power transmission system is less than or equal to the relative gain of the active power of the wind power-side converter station, then DC voltage control shall take priority, and the reference values ​​of the active and reactive currents of the grid-side converter station shall be adjusted 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 its maximum active power.

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

3. The adaptive fault ride-through method for wind power transmitted via a flexible direct transmission system according to claim 2, characterized in that, The maximum allowable AC current phase angle of the grid-side converter station to avoid DC voltage overshoot is equal to the arctangent 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 transmitted via a flexible direct transmission system according to claim 3, characterized in that, The ordinates and abscissas of the boundary intersection points 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 transmitted via a flexible direct transmission system according to claim 1, characterized in that, In step S103, the critical active power of the wind power-side converter station is determined as follows when AC voltage control takes priority: If the difference between the phase of the equivalent potential of the faulty power grid and the equivalent impedance angle is less than or equal to the maximum allowable AC current phase angle of the grid-side converter station to avoid DC voltage overshoot; the first 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 power grid, and the difference between the phase of the equivalent potential of the faulty power grid and the equivalent impedance angle; the first 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 power grid, the equivalent reactance of the connecting transformer, and the difference between the phase of the equivalent potential of the faulty power grid and the equivalent impedance angle. The difference between the first and second active power parameters is used to calculate the second active power parameter. Based on the maximum allowable AC current coefficient and rated AC current, the equivalent resistance and reactance of the fault grid, the equivalent fault transition resistance and reactance, the difference between the phase of the equivalent potential and the equivalent impedance angle of the fault grid, the equivalent reactance of the connecting transformer, and the grid voltage and equivalent reactance during normal operation, the third active power parameter is calculated. Based on the difference between the first and second active power parameters and the sum of the third active power parameter, the critical active power of the wind power-side converter station when AC voltage control takes priority is calculated. If the difference between the phase of the equivalent potential of the faulted power grid and the equivalent impedance angle is greater than the maximum allowable AC current phase angle of the grid-side converter station to avoid DC voltage overruns, 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 faulted power grid, and the maximum allowable AC current phase angle of the grid-side converter station to avoid DC voltage overruns. 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 phase angle of the maximum allowable AC current of the grid-side converter station to avoid DC voltage over-limit. The sixth active power parameter is calculated based on the maximum allowable AC current coefficient and rated AC current, the equivalent resistance and 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 over-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 takes priority is calculated based on the difference between the fourth and fifth active power parameters and the sum of the sixth active power parameters.

6. The adaptive fault ride-through method for wind power transmitted via a flexible direct transmission system according to claim 1, characterized in that, In step S103, the critical active power of the wind power-side converter station under DC voltage control priority is obtained by solving the extreme points of the first function using the Lagrange multiplier method. The first function is obtained by combining the first, second, third, and fourth parameters. The first parameter includes the maximum allowable AC current coefficient and 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 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 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 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 transmitted via a flexible direct transmission system according to claim 6, characterized in that, In step S103, the critical voltage at the grid connection point of the wind power transmission system via the flexible DC transmission line is determined as follows when DC voltage control takes priority: 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 DC voltage control is prioritized, as well as the equivalent resistance and reactance of the faulted 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 faulted grid, the equivalent fault transition resistance and reactance, the grid voltage and equivalent reactance during normal operation, the maximum allowable AC current coefficient and rated AC current of the grid-side converter station. Based on the sum of the fifth and sixth voltage parameters, the critical voltage at the point of grid connection of wind power through the flexible DC transmission system is calculated when DC voltage control takes priority. Wherein, 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 takes priority are calculated from the active and reactive currents of the grid-side converter station when the first derivative of the first function is 0.

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

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

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