Fault ride-through control method and system for wind power transmission system based on power angle response modal adjustment

Abstract

The application provides a wind power transmission system fault ride-through control method and system based on power angle response mode adjustment, comprising: establishing a reduced dimension equivalent model of a fault power grid, calculating a power angle of a grid-connected converter station in normal operation and a phase shift of a power angle curve of the grid-connected converter station under a power grid fault; if the sum of the power angle in normal operation and the phase shift under the power grid fault is greater than 90 degrees, power outer loop control reference values of the grid-connected converter station under the power grid fault are set as maximum active power reference values and corresponding alternating current bus voltage reference values in a first decrease and then increase mode; otherwise, an active power reference value of the grid-connected converter station is set as a larger one of maximum active power reference values in a first increase and then decrease mode and the first decrease and then increase mode, and a corresponding alternating current bus voltage reference value of the grid-connected converter station is set; the method can maximize the transmission of wind farm active power on the basis of ensuring uninterrupted operation of the wind power transmission system through the grid-connected flexible DC transmission system.

Description

Technical Field

[0001] This invention relates to the field of power system safety and stability control, specifically to a fault ride-through control method and system for a wind power-structured flexible DC transmission system based on power angle response mode adjustment. Background Technology

[0002] As the grid short-circuit ratio decreases and rotational inertia weakens, grid-connected converter stations relying on phase-locked loop synchronization may experience small-disturbance instability. Grid-connected converter stations can simulate the operating characteristics of synchronous motors and effectively support grid voltage and frequency, thus becoming a key technology for large-scale wind power transmission. Although the probability of a three-phase short-circuit fault in the grid is low, it will cause a sharp increase in the AC current of the grid-connected converter station, even exceeding the tolerance limit of power devices. Simultaneously, during grid faults, the active power of the grid-connected converter station drops sharply, and its power angle may become unstable under the action of the power outer loop controller. To prevent wind power from being blocked through the grid-connected flexible DC transmission system and thus threatening grid security and stability, fault ride-through control has become a focus of the industry.

[0003] Existing technologies focus on avoiding steady-state current exceeding limits through AC current limiting units or virtual impedance control. Technicians switch grid-type converter stations to phase-locked loop (PLL) synchronous mode and use current limiters to bring the current loop to saturation; others introduce virtual impedance to reduce the voltage inner loop reference value, thereby preventing active and reactive current reference values ​​from exceeding limits. Compared to synchronous motors with fixed parameters and slow adjustment speeds, grid-type converter stations have more flexible control capabilities. Researchers mainly focus on two directions: adjusting control reference values ​​and optimizing grid parameters to avoid power angle instability in grid-type converter stations under grid faults. Technicians use the Lyapunov direct method to introduce frequency deviation and AC voltage deviation into the active and reactive power reference values, respectively; others characterize the power angle stability boundary of grid-type converter stations and propose a rolling optimization strategy using virtual inertia and reactive power droop coefficients. However, the above studies address AC current safety and power angle stability of grid-type converter stations in isolation. A single control objective cannot simultaneously ensure the safety of AC current and the stability of power angle in grid-type converter stations, which may lead to the failure of grid-type transmission system fault ride-through.

[0004] Technicians have already focused on the coupling between AC current and power angle in grid-connected converter stations under grid fault conditions. They have revealed that the AC current limiting unit causes the port characteristics of the grid-connected converter station to switch from a voltage source to a current source, and have proposed a saturated current phase control method to enhance the power angle stability margin. Other technicians have pointed out that virtual impedance control can ensure the virtual inertia and damping response capability of the grid-connected converter station, and that adaptive adjustment of impedance amplitude and angle balances AC current safety and power angle stability. Existing technologies address the coupling problem between AC current safety and power angle stability caused by voltage amplitude drops at the grid connection point of the grid-connected converter station. However, three-phase short-circuit faults also change the grid topology. The newly added fault transition resistance branch causes the equivalent impedance of the grid to change from inductive to resistive-inductive under normal operation, resulting in coupling between the AC bus voltage, power angle, active power, and reactive power of the grid-connected converter station through the interaction of the fault equivalent impedance. Existing technologies have not yet taken into account the changes in equivalent impedance after grid faults and their impact on the AC current and power angle response of grid-connected converter stations. The fault ride-through control reference value is set only based on the voltage amplitude, which makes it difficult to ensure the uninterrupted operation of the grid-connected transmission system under various fault scenarios.

[0005] In summary, clarifying the multimodal response mechanism of the power angle of grid-type converter stations under grid faults, in order to determine the maximum active power transmission capacity of wind power through the grid-type flexible DC transmission system under safe and stable constraints, and to adjust the active power reference value and AC bus voltage reference value of the grid-type converter station, thereby reducing the active power loss of wind farms while ensuring power angle stability, AC current safety, and DC voltage not exceeding limits, has become an urgent problem to be solved by those skilled in the art. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention proposes a fault ride-through control method for wind power grid-type flexible DC transmission systems based on power angle response mode adjustment. This method includes:

[0007] S101. Collect the AC bus voltage and complex power of the grid-type converter station during normal operation and at the moment of grid fault, respectively, and establish the fault equivalent model of the external power grid of the grid-type converter station.

[0008] S102. Calculate the power angle curve of the grid-type converter station under normal operation and the phase shift of the power angle curve of the grid-type converter station under grid fault.

[0009] S103. Calculate the maximum active power and its corresponding AC bus voltage that causes the grid-type converter station to exhibit a mode of first decreasing and then increasing power angle under grid fault conditions.

[0010] S104. Set a threshold. If the sum of the phase offsets of the power angle curves of the grid-type converter station under normal operation and the power angle curves of the grid-type converter station under grid faults is greater than the set threshold, then execute S105; otherwise, execute S106.

[0011] S105. Reactive power-voltage outer loop control of the closed-loop grid-type converter station: Set the active power and AC bus voltage reference values ​​of the grid-type converter station to the maximum active power and corresponding AC bus voltage of the first-decrease-then-increase mode, respectively, and execute S109.

[0012] S106: Calculate the maximum active power and its corresponding AC bus voltage that causes the power angle of the grid-type converter station to exhibit a mode of first increasing and then decreasing under grid fault conditions.

[0013] S107: Compare the maximum active power of the grid-type converter station in the first-increase-then-decrease mode and the first-decrease-then-increase mode. If the former is greater than the latter, execute S108; otherwise, return to S105.

[0014] S108: Closed-loop reactive power-voltage outer loop for grid-type converter stations, setting the control reference value of the grid-type converter station to the maximum active power and its corresponding AC bus voltage in the first-increase-then-decrease mode;

[0015] S109: Continuously monitor the grid connection point voltage of grid-connected converter stations, and exit fault ride-through control after the grid connection point voltage recovers.

[0016] A fault ride-through control system for a wind power grid-type flexible DC transmission system based on power angle response mode adjustment, the system includes: an acquisition and initialization module, a first calculation module, a second calculation module, a third calculation module, a judgment module, and a control module;

[0017] The acquisition and initialization module is used to acquire the AC bus voltage, active power and reactive power of the grid-type converter station under normal operation and grid fault conditions, and to establish an equivalent model of the external grid fault of the grid-type converter station.

[0018] The first calculation module is used to calculate the power angle of the grid-type converter station under normal operation and the phase shift of the power angle curve of the grid-type converter station under grid fault.

[0019] The second calculation module is used to calculate the maximum active power and its corresponding AC bus voltage that causes the power angle of the grid-type converter station to exhibit a mode of first increasing and then decreasing under grid fault conditions.

[0020] The third calculation module is used to calculate the maximum active power and its corresponding AC bus voltage that causes the power angle of the grid-type converter station to exhibit a mode of first decreasing and then increasing under grid fault conditions.

[0021] The judgment module is used to determine whether the sum of the power angle and phase offset during normal operation is greater than 90 degrees. If it is greater, the result of the second calculation module is input into the control module; if it is less, the result of the third calculation module is input into the control module.

[0022] The control module is used to lock the reactive power-voltage outer loop control of the grid-type converter station, and sets the active power and AC bus voltage reference values ​​of the grid-type converter station as the output results of the judgment module.

[0023] This invention proposes a fault ride-through control device for a wind power grid-type flexible DC transmission system based on power angle response mode adjustment, comprising: a processor, a memory, and a computer program stored in the memory and configured to be executed by the processor. When the processor executes the computer program, it implements a fault ride-through control method for a wind power grid-type flexible DC transmission system based on power angle response mode adjustment.

[0024] The beneficial effects of this invention are:

[0025] This invention calculates and compares whether the sum of the phase shifts between the power angle curve of a grid-connected converter station under normal operation and the power angle curve of a grid-connected converter station under grid fault conditions is greater than 90 degrees. This determines the maximum active power of the grid-connected transmission system under grid fault conditions and the required power angle response mode of the grid-connected converter station, quantifying the maximum active power support capability of the grid-connected transmission system to the faulty grid under the premise of safe and stable operation. By optimizing the AC bus voltage reference value and active power reference value of the grid-connected converter station, this invention guides the grid-connected converter station to enter the response mode required for the maximum active power of the wind farm under DC voltage safety constraints. This avoids power angle instability, DC voltage exceeding limits, and steady-state AC current exceeding limits, while controlling the wind farm to maximize its active power balance support for the faulty grid. Attached Figure Description

[0026] To make the purpose, technical solution, and advantages of the invention clearer, the invention will be further described below with reference to the accompanying drawings, wherein:

[0027] Figure 1 This is a flowchart of the fault ride-through control method for a wind power grid-type flexible DC transmission system based on power angle response mode adjustment in the embodiments of this application;

[0028] Figure 2 This is a schematic diagram of the fault ride-through control device for a wind power grid-type flexible DC transmission system based on power angle response mode adjustment in the embodiments of this application;

[0029] Figure 3 This is a schematic diagram of the fault ride-through control device for a wind power grid-type flexible DC transmission system based on power angle response mode adjustment in the embodiments of this application;

[0030] Figure 4 A schematic diagram of a flexible DC transmission system for wind power via a grid under grid fault conditions;

[0031] Figure 5These are effect diagrams under the embodiments of the present invention, wherein Figure (a) is a graph showing the relationship between time and active power of the grid-type converter station, Figure (b) is a graph showing the relationship between time and reactive power of the grid-type converter station, Figure (c) is a graph showing the relationship between time and power angle of the grid-type converter station, Figure (d) is a graph showing the relationship between time and AC bus voltage of the grid-type converter station, Figure (e) is a graph showing the relationship between time and DC voltage of flexible DC transmission, and Figure (f) is a graph showing the relationship between time and active power of the wind farm. 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 application establishes a reduced-dimensional equivalent model of a faulted power grid, calculates the power angle of a grid-type converter station under normal operation and the phase shift of the power angle curve under power grid faults; if the sum of the power angle under normal operation and the phase shift under power grid faults is greater than 90 degrees, the power outer loop control reference value of the grid-type converter station under power grid faults is set to the maximum active power reference value in the first-decreasing-then-increasing mode and its corresponding AC bus voltage reference value, respectively; otherwise, the active power reference value of the grid-type converter station is set to the larger of the maximum active power reference value in the first-increasing-then-decreasing mode and the first-decreasing-then-increasing mode, and the AC bus voltage reference value of the grid-type converter station is set accordingly.

[0034] Specifically, in the first aspect of this application, the present invention proposes a fault ride-through control method for wind power transmission systems via grid-connected flexible DC transmission based on power angle response mode adjustment. A reduced-dimensional equivalent model of the faulted power grid is established, and the power angle of the grid-connected converter station under normal operation and the phase shift of the power angle curve under power grid fault are calculated. If the sum of the power angle under normal operation and the phase shift under power grid fault is greater than 90 degrees, the outer loop control reference value of the power of the grid-connected converter station under power grid fault is set to the maximum active power reference value in the first-decreasing-then-increasing mode and its corresponding AC bus voltage reference value, respectively. Otherwise, the active power reference value of the grid-connected converter station is set to the larger of the maximum active power reference value in the first-increasing-then-decreasing mode and the first-decreasing-then-increasing mode, and the AC bus voltage reference value of the grid-connected converter station is set accordingly. This invention maximizes the transmission of active power from the wind farm while ensuring uninterrupted operation of the wind power transmission system via the grid-connected flexible DC transmission system.

[0035] like Figure 1 As shown, this invention proposes a fault ride-through control method for wind power grid-type flexible DC transmission systems based on power angle response mode adjustment, comprising the following steps:

[0036] S101: Collect the AC bus voltage and complex power of the grid-type converter station during normal operation and at the moment of grid fault, and establish the fault equivalent model of the external power grid of the grid-type converter station;

[0037] S102: Calculate the power angle of a grid-type converter station under normal operation and the phase shift of the power angle curve of a grid-type converter station under grid fault conditions;

[0038] S103: Calculate the maximum active power and its corresponding AC bus voltage that causes the power angle of the grid-type converter station to exhibit a mode of first decreasing and then increasing under grid fault conditions.

[0039] S104: If the sum of the phase offsets between the power angle curve of the grid-type converter station under normal operation and the power angle curve of the grid-type converter station under grid fault is greater than 90 degrees, execute S105; otherwise execute S106.

[0040] S105: Reactive power-voltage outer loop control of the closed-loop grid-type converter station. Set the active power and AC bus voltage reference values ​​of the grid-type converter station to the maximum active power and corresponding AC bus voltage of the first-decrease-then-increase mode, respectively, and execute S109.

[0041] S106: Calculate the maximum active power and its corresponding AC bus voltage that causes the power angle of the grid-type converter station to exhibit a mode of first increasing and then decreasing under grid fault conditions.

[0042] S107: Compare the maximum active power of the grid-type converter station in the first-increase-then-decrease mode and the first-decrease-then-increase mode. If the former is greater than the latter, execute S108; otherwise, execute S105.

[0043] S108: Closed-loop reactive power-voltage outer loop for grid-type converter stations, setting the control reference value of the grid-type converter station to the maximum active power and its corresponding AC bus voltage in the first-increase-then-decrease mode;

[0044] S109: Continuously monitor the grid connection point voltage of grid-connected converter stations, and exit fault ride-through control after the grid connection point voltage recovers.

[0045] In the embodiments of this application, in step S101, the equivalent model of external power grid faults of the grid-type converter station consists of the equivalent power grid model under normal operation and the equivalent fault transition resistance and reactance connected in parallel at the grid connection point. The equivalent power grid model under normal operation is a reactance series voltage source, and the calculation method for the model parameters is as follows:

[0046]

[0047]

[0048] in, This is the equivalent reactance of the power grid during normal operation. This is the equivalent reactance of the converter transformer; , and These are the active power, reactive power, and AC bus voltage of a grid-type converter station during normal operation. This is the equivalent electromotive force of the power grid under normal operation, which is equal to the rated voltage of the power grid. and These are the equivalent fault transition resistance and reactance, respectively; and These represent the active and reactive power of grid-type converter stations under grid fault conditions. This refers to the AC bus voltage of a grid-type converter station under power grid fault conditions; parameters and Calculate according to the following formulas:

[0049]

[0050] in, This refers to the AC bus voltage phase of a grid-type converter station under power grid fault conditions.

[0051] In the embodiments of this application, in step S102, the power angle of the grid-type converter station during normal operation is calculated using the following formula:

[0052]

[0053] in, The power angle of a grid-type converter station during normal operation.

[0054] In the embodiments of this application, in step S102, the phase shift of the power angle curve of the grid-type converter station under grid fault is calculated by the following formula:

[0055]

[0056] in, This refers to the phase shift of the power angle curve of a grid-type converter station under grid fault conditions.

[0057] In the embodiments of this application, in step S103, the maximum active power and its corresponding AC bus voltage that cause the power angle of the grid-type converter station to exhibit a mode of first decreasing and then increasing under grid fault conditions are determined by solving the following formula:

[0058]

[0059] in, and These represent the maximum active power and corresponding AC bus voltage of a grid-type converter station exhibiting a mode of first decreasing and then increasing power angle under grid fault conditions. The parameters of the Lagrange multiplier equation for the mode of decreasing followed by increasing; To establish the power angle stability boundary of the feasible region for fault crossing under the first-decreasing-then-increasing mode, This is the AC current safety boundary for the fault traversal feasible region under the first-decrease-then-increase mode.

[0060] The calculation in step S103 is the value required to achieve the control target (i.e., maximum active power) (i.e., maximum active power and its corresponding AC bus voltage). In step S105, the control reference value is adjusted according to the calculated value to achieve the control target.

[0061] The reactive power-voltage outer loop controller of a grid-type converter station is the control architecture during normal operation, generating a voltage reference value based on reactive power and its deviation. This invention addresses fault conditions, thus blocking the control architecture used during normal operation. The voltage reference value is no longer generated from reactive power and its deviation, but is determined by the maximum active power exhibiting a decreasing-then-increasing mode in the power angle of the grid-type converter station and its corresponding AC bus voltage.

[0062] In the embodiments of this application, the power angle stability boundary and AC current safety boundary of the fault crossover feasible region under the first-decreasing-then-increasing mode are determined by the following formula:

[0063]

[0064]

[0065] In the formula, This refers to the point where the active power of a grid-type converter station crosses zero under grid fault conditions. The power angle of the grid-type converter station corresponding to the stable equilibrium point under grid fault conditions; The maximum allowable AC current for a grid-type converter station; parameters Calculate using the following formula:

[0066]

[0067]

[0068]

[0069] In the embodiments of this application, in step S106, the maximum active power and its corresponding AC bus voltage that cause the power angle of the grid-type converter station to exhibit a mode of first increasing and then decreasing under grid fault conditions are determined by solving the following formula:

[0070]

[0071] In the formula, and These represent the maximum active power and corresponding AC bus voltage of a grid-type converter station exhibiting a power angle that first increases and then decreases under grid fault conditions. The parameters of the Lagrange multiplier equation for the first increasing and then decreasing modes; For the power angle stability boundary of the feasible region for fault crossing under the first-increase-then-decrease mode, This is the AC current safety boundary for the fault traversal feasible region under the first-increase-then-decrease mode.

[0072] In the embodiments of this application, the power angle stability boundary and AC current safety boundary of the fault crossover feasible region under the first-increase-then-decrease mode are determined by the following formula:

[0073]

[0074]

[0075] In the formula, The power angle of the grid-type converter station corresponding to the unstable equilibrium point under grid fault conditions is calculated using the following formula:

[0076]

[0077] In this embodiment, the present invention proposes a fault ride-through control system for a wind power grid-type flexible DC transmission system based on power angle response mode adjustment, such as... Figure 2 As shown, the system includes: an acquisition and initialization module, a first calculation module, a second calculation module, a third calculation module, a judgment module, and a control module;

[0078] The acquisition and initialization module is used to acquire the AC bus voltage, active power and reactive power of the grid-type converter station under normal operation and grid fault conditions, and to establish an equivalent model of the external grid fault of the grid-type converter station.

[0079] The first calculation module is used to calculate the power angle of the grid-type converter station under normal operation and the phase shift of the power angle curve of the grid-type converter station under grid fault.

[0080] The second calculation module is used to calculate the maximum active power and its corresponding AC bus voltage that causes the power angle of the grid-type converter station to exhibit a mode of first increasing and then decreasing under grid fault conditions.

[0081] The third calculation module is used to calculate the maximum active power and its corresponding AC bus voltage that causes the power angle of the grid-type converter station to exhibit a mode of first decreasing and then increasing under grid fault conditions.

[0082] The judgment module is used to determine whether the sum of the power angle and phase offset during normal operation is greater than 90 degrees. If it is greater, the result of the second calculation module is input into the control module; if it is less, the result of the third calculation module is input into the control module.

[0083] The control module is used to lock the reactive power-voltage outer loop control of the grid-type converter station, and sets the active power and AC bus voltage reference values ​​of the grid-type converter station as the output results of the judgment module.

[0084] In this embodiment, the specific implementation of the system is the same as that of the method.

[0085] In the embodiments of this application, such as Figure 3 As shown, the fault ride-through control device for a wind power grid-type flexible DC transmission system based on power angle response mode adjustment of this application includes a processor, a memory, and a computer program stored in the memory and configured to be executed by the processor. When the processor executes the computer program, it implements the fault ride-through control method for a wind power grid-type flexible DC transmission system based on power angle response mode adjustment.

[0086] This disclosure can be a system, method, and / or computer program product. A computer program product may include a computer medium having computer-readable program instructions loaded thereon for causing a processor to implement various aspects of this disclosure.

[0087] Computer-readable storage media can be tangible devices capable of holding and storing instructions for use by an instruction execution device. Computer-readable storage media can be, for example—but not limited to—electrical storage devices, magnetic storage devices, optical storage devices, electromagnetic storage devices, semiconductor storage devices, or any suitable combination of the foregoing. More specific examples (a non-exhaustive list) of computer-readable storage media include: portable computer disks, hard disks, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), static random access memory (SRAM), portable compact disc read-only memory (CD-ROM), digital multifunction disc (DVD), memory sticks, floppy disks, mechanical encoding devices, such as punch cards or recessed protrusions storing instructions thereon, and any suitable combination of the foregoing. The computer-readable storage media used herein are not to be construed as transient signals themselves, such as radio waves or other freely propagating electromagnetic waves, electromagnetic waves propagating through waveguides or other transmission media (e.g., light pulses through fiber optic cables), or electrical signals transmitted through wires.

[0088] The computer-readable program instructions described herein can be downloaded from computer-readable storage media to various computing / processing devices, or downloaded via a network, such as the Internet, local area network, wide area network, and / or wireless network, to an external computer or external storage device. The network may include copper transmission cables, fiber optic transmission, wireless transmission, routers, firewalls, switches, gateway computers, and / or edge servers. A network adapter card or network interface in each computing / processing device receives the computer-readable program instructions from the network and forwards them to the computer-readable storage media in the respective computing / processing device.

[0089] Computer program instructions used to perform the operations of this disclosure may be assembly instructions, instruction set architecture (ISA) instructions, machine instructions, machine-dependent instructions, microcode, firmware instructions, status setting data, or source code or object code written in any combination of one or more programming languages, including object-oriented programming languages ​​such as Smalltalk, C++, etc., and conventional procedural programming languages ​​such as the "C" language or similar programming languages. The computer-readable program instructions may execute entirely on the user's computer, partially on the user's computer, as a standalone software package, partially on the user's computer and partially on a remote computer, or entirely on a remote computer or server. In cases involving a remote computer, the remote computer may be connected to the user's computer via any type of network—including a local area network (LAN) or a wide area network (WAN)—or may be connected to an external computer (e.g., via the Internet using an Internet service provider). In some embodiments, electronic circuitry, such as programmable logic circuitry, field-programmable gate arrays (FPGAs), or programmable logic arrays (PLAs), is personalized by utilizing the status information of the computer-readable program instructions to implement various aspects of this disclosure.

[0090] Various aspects of this disclosure are described herein with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this disclosure. It should be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer-readable program instructions.

[0091] These computer-readable program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, or other programmable data processing apparatus to produce a machine such that, when executed by the processor of the computer or other programmable data processing apparatus, they create means for implementing the functions / actions specified in one or more blocks of the flowchart and / or block diagram. These computer-readable program instructions can also be stored in a computer-readable storage medium that causes a computer, programmable data processing apparatus, and / or other device to operate in a particular manner; thus, the computer-readable medium storing the instructions comprises an article of manufacture that includes instructions for implementing aspects of the functions / actions specified in one or more blocks of the flowchart and / or block diagram.

[0092] Computer-readable program instructions may also be loaded onto a computer, other programmable data processing apparatus, or other device to cause a series of operational steps to be performed on the computer, other programmable data processing apparatus, or other device to produce a computer-implemented process, thereby causing the instructions executed on the computer, other programmable data processing apparatus, or other device to perform the functions / actions specified in one or more boxes of a flowchart and / or block diagram.

[0093] The flowcharts and block diagrams in the accompanying drawings illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to various embodiments of the present disclosure. In this regard, each block in a flowchart or block diagram may represent a module, segment, or portion of an instruction containing one or more executable instructions for implementing a specified logical function. In some alternative implementations, the functions marked in the blocks may occur in a different order than those shown in the drawings. For example, two consecutive blocks may actually be executed substantially in parallel, and they may sometimes be executed in reverse order, depending on the functions involved. It should also be noted that each block in the block diagrams and / or flowcharts, and combinations of blocks in the block diagrams and / or flowcharts, may be implemented using a dedicated hardware-based system that performs the specified function or action, or using a combination of dedicated hardware and computer instructions.

[0094] To verify the effectiveness of the present invention, as follows Figure 4 The following analysis uses a schematic diagram of a wind power transmission system via a grid-connected flexible DC transmission line under grid fault conditions as an example. Figure 4 As shown, the grid-type flexible DC transmission has a rated DC voltage of ±800 kV and a rated transmission capacity of 900 MW. The wind farm consists of 180 direct-drive wind turbines with a rated capacity of 5 MW each. The power grid is an improved 2-unit, 4-zone network with a rated voltage of 220 kV and a unit reactance of 0.94 × 10⁻³ H / km for the transmission lines. The virtual inertia and damping coefficient of the grid-type converter station are 5 and 0.18, respectively. The reactive power-AC voltage droop coefficient of the grid-type converter station is 0.06, the maximum allowable DC voltage is 1.1 pu, and the maximum allowable AC current is 1.2 pu. A three-phase short-circuit fault occurs in the power grid at 0.25 s and is cleared after 100 ms.

[0095] To verify the effectiveness of the fault ride-through control method for wind power transmission via a grid-type flexible DC transmission system based on power angle response mode adjustment proposed in this invention, a comparative group was established using a constant power angle control method for grid-type converter stations based on the AC bus voltage drop. The active power, reactive power, power angle, AC bus voltage, DC voltage of the flexible DC transmission system, and active power of the wind farm at the grid-type converter station were recorded and analyzed.

[0096] According to the aforementioned step S102, the power angle of the grid-type converter station is 4.8 degrees during normal operation, and the phase shift of the power angle curve of the grid-type converter station under grid fault is 21.3 degrees.

[0097] According to the aforementioned step S103, the maximum active power and its corresponding AC bus voltage of the grid-type converter station exhibiting a mode of first decreasing and then increasing power angle under grid fault conditions are 0.55 pu and 0.69 pu, respectively.

[0098] According to the aforementioned step S104, the sum of the phase offsets between the power angle curve of the grid-type converter station under normal operation and the power angle curve of the grid-type converter station under grid fault is less than 90 degrees, and step S106 is executed.

[0099] According to the aforementioned step S106, the maximum active power and its corresponding AC bus voltage that make the power angle of the grid-type converter station exhibit a mode of first increasing and then decreasing under grid fault conditions are 0.74 pu and 0.63 pu, respectively.

[0100] According to the aforementioned step S107, the maximum active power of the grid-type converter station in the first-increase-then-decrease mode is greater than that in the first-decrease-then-increase mode, so execute S108;

[0101] According to the aforementioned step S108: the reactive power-voltage outer loop of the grid-type converter station is closed, and the active power reference value and AC bus voltage of the grid-type converter station are set to 0.74 pu and 0.63 pu, respectively.

[0102] Figure 5 (a) to (f) are waveform diagrams of the active power, reactive power, power angle, AC bus voltage of the grid-type converter station, DC voltage of the flexible DC transmission, and active power of the wind farm under grid fault conditions, respectively. Figure 5 The horizontal axis represents time, and the vertical axis represents the active power, reactive power, power angle, AC bus voltage, DC voltage of flexible DC transmission, and active power of wind farm, respectively. The solid line represents the curve of the fault ride-through control method of wind power through the grid-type flexible DC transmission system based on power angle response mode adjustment proposed in this invention, and the dashed line represents the curve of the comparison group.

[0103] like Figure 5(a)~(b) This invention, by comprehensively considering power angle stability and AC current constraints, derives the feasible domain of reference values ​​for AC bus voltage and active power in grid-type converter stations. During grid faults, the grid-type converter station controlled by the proposed method outputs 0.74 pu of active power and 0.05 pu of reactive power, with the combined apparent power being 0.75 pu, which is exactly equal to the limit corresponding to the maximum allowable AC current. This indicates that the method fully utilizes the AC current margin of the grid-type converter station. The comparative method only determines the reference values ​​for active and reactive power based on grid-side operating requirements and AC current limitations, failing to fully account for the equivalent impedance changes in the faulty grid. Although this method does not induce power angle instability, its output active power is lower than that of this invention. To suppress DC voltage exceeding limits, the active power of the wind farm controlled by the comparative method is significantly reduced during faults. Figure 5 As shown in (c)~(f), the proposed method improves the active power output of the wind farm by 64.3% compared to the comparison method.

[0104] The above-described embodiments further illustrate the purpose, technical solution, and advantages of the present invention. It should be understood that the above-described embodiments are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made to the present invention within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A fault ride-through control method for a wind power grid-type flexible DC transmission system based on power angle response mode adjustment, characterized in that, include: S101. Collect the AC bus voltage and complex power of the grid-type converter station during normal operation and at the moment of grid fault, respectively, and establish the fault equivalent model of the external power grid of the grid-type converter station. S102. Calculate the power angle curve of the grid-type converter station under normal operation and the phase shift of the power angle curve of the grid-type converter station under grid fault. S103. Calculate the maximum active power and its corresponding AC bus voltage that causes the grid-type converter station to exhibit a mode of first decreasing and then increasing power angle under grid fault conditions. S104. Set a threshold. If the sum of the phase offsets of the power angle curves of the grid-type converter station under normal operation and the power angle curves of the grid-type converter station under grid faults is greater than the set threshold, then execute S105; otherwise, execute S106. S105. Reactive power-voltage outer loop control of the closed-loop grid-type converter station: Set the active power and AC bus voltage reference values ​​of the grid-type converter station to the maximum active power and corresponding AC bus voltage of the first-decrease-then-increase mode, respectively, and execute S109. S106: Calculate the maximum active power and its corresponding AC bus voltage that causes the power angle of the grid-type converter station to exhibit a mode of first increasing and then decreasing under grid fault conditions. S107: Compare the maximum active power of the grid-type converter station in the first-increase-then-decrease mode and the first-decrease-then-increase mode. If the former is greater than the latter, execute S108; otherwise, return to S105. S108: Closed-loop reactive power-voltage outer loop for grid-type converter stations, setting the control reference value of the grid-type converter station to the maximum active power and its corresponding AC bus voltage in the first-increase-then-decrease mode; S109: Continuously monitor the grid connection point voltage of grid-connected converter stations, and exit fault ride-through control after the grid connection point voltage recovers.

2. The fault ride-through control method for a wind power grid-type flexible DC transmission system based on power angle response mode adjustment according to claim 1, characterized in that, The fault equivalent model of the external power grid for a grid-type converter station is as follows: ； in, This is the equivalent reactance of the power grid during normal operation. This is the equivalent reactance of the converter transformer; , and These are the active power, reactive power, and AC bus voltage of a grid-type converter station during normal operation. This represents the equivalent electromotive force of the power grid during normal operation. and These represent the active and reactive power of grid-type converter stations under grid fault conditions. This refers to the AC bus voltage of a grid-type converter station under power grid fault conditions.

3. The fault ride-through control method for a wind power grid-type flexible DC transmission system based on power angle response mode adjustment according to claim 1, characterized in that, The power angle of a grid-type converter station during normal operation is calculated as follows: ； in, The power angle of a grid-type converter station during normal operation; This is the equivalent reactance of the power grid during normal operation. This is the equivalent reactance of the converter transformer; This refers to the active power of a grid-type converter station during normal operation. These are the AC bus voltages of a grid-type converter station during normal operation; This represents the equivalent electromotive force of the power grid during normal operation.

4. The fault ride-through control method for a wind power grid-type flexible DC transmission system based on power angle response mode adjustment according to claim 1, characterized in that, The phase shift of the power angle curve of a grid-type converter station under power grid fault conditions includes: ； in, The phase shift of the power angle curve of a grid-type converter station under grid fault conditions; and These are the equivalent fault transition resistance and reactance, respectively; This is the equivalent reactance of the power grid during normal operation. This is the equivalent reactance of the converter transformer; This is the equivalent reactance of the power grid during normal operation. This is the equivalent reactance of the converter transformer.

5. The fault ride-through control method for a wind power grid-type flexible DC transmission system based on power angle response mode adjustment according to claim 1, characterized in that, The calculation of the maximum active power and its corresponding AC bus voltage that causes the power angle of a grid-type converter station to exhibit a decreasing-then-increasing mode under grid fault conditions includes: ； in, and These represent the maximum active power and corresponding AC bus voltage of a grid-type converter station exhibiting a mode of first decreasing and then increasing power angle under grid fault conditions. The parameters of the Lagrange multiplier equation for the mode of decreasing followed by increasing; To establish the power angle stability boundary of the feasible region for fault crossing under the first-decreasing-then-increasing mode, This is the AC current safety boundary for the fault traversal feasible region under the first-decrease-then-increase mode.

6. The fault ride-through control method for a wind power grid-type flexible DC transmission system based on power angle response mode adjustment according to claim 5, characterized in that, The power angle stability boundary of the fault crossing feasible region under the first decrease then increase mode is: ； The AC current safety boundary for the fault traversal feasible region under the first-decrease-then-increase mode is: ； in, This refers to the point where the active power of a grid-type converter station crosses zero under grid fault conditions. The power angle of the grid-type converter station corresponding to the stable equilibrium point under grid fault conditions; This refers to the maximum permissible AC current for a grid-type converter station.

7. The fault ride-through control method for a wind power grid-type flexible DC transmission system based on power angle response mode adjustment according to claim 1, characterized in that, The calculation of the maximum active power and its corresponding AC bus voltage for the first-increase-then-decrease mode includes: ； in, and These represent the maximum active power and corresponding AC bus voltage of a grid-type converter station exhibiting a power angle that first increases and then decreases under grid fault conditions. The parameters of the Lagrange multiplier equation for the first increasing and then decreasing modes; For the power angle stability boundary of the feasible region for fault crossing under the first-increase-then-decrease mode, This is the AC current safety boundary for the fault traversal feasible region under the first-increase-then-decrease mode.

8. The fault ride-through control method for a wind power grid-type flexible DC transmission system based on power angle response mode adjustment according to claim 7, characterized in that, The power angle stability boundary of the fault crossing feasible region under the first-increase-then-decrease mode is: ； The AC current safety boundary for the fault crossover feasible region under the first-increase-then-decrease mode is: ； in, The power angle of the grid-type converter station is the value corresponding to the unstable equilibrium point under grid fault conditions.

9. A fault ride-through control system for a wind power grid-connected flexible DC transmission system based on power angle response mode adjustment, the system being used to execute the fault ride-through control method for a wind power grid-connected flexible DC transmission system based on power angle response mode adjustment as described in any one of claims 1 to 8, characterized in that, The system includes: an acquisition and initialization module, a first calculation module, a second calculation module, a third calculation module, a judgment module, and a control module; The acquisition and initialization module is used to acquire the AC bus voltage, active power and reactive power of the grid-type converter station under normal operation and grid fault conditions, and to establish an equivalent model of the external grid fault of the grid-type converter station. The first calculation module is used to calculate the power angle of the grid-type converter station under normal operation and the phase shift of the power angle curve of the grid-type converter station under grid fault. The second calculation module is used to calculate the maximum active power and its corresponding AC bus voltage that causes the power angle of the grid-type converter station to exhibit a mode of first increasing and then decreasing under grid fault conditions. The third calculation module is used to calculate the maximum active power and its corresponding AC bus voltage that causes the power angle of the grid-type converter station to exhibit a mode of first decreasing and then increasing under grid fault conditions. The judgment module is used to determine whether the sum of the power angle and phase offset during normal operation is greater than 90 degrees. If it is greater, the result of the second calculation module is input into the control module; if it is less, the result of the third calculation module is input into the control module. The control module is used to lock the reactive power-voltage outer loop control of the grid-type converter station, and sets the active power and AC bus voltage reference values ​​of the grid-type converter station as the output results of the judgment module.

10. A fault ride-through control device for a wind power grid-type flexible DC transmission system based on power angle response mode adjustment, characterized in that, The system includes a processor, a memory, and a computer program stored in the memory and configured to be executed by the processor, wherein the processor, when executing the computer program, implements the fault ride-through control method for a wind power grid-type flexible DC transmission system based on power angle response mode adjustment as described in any one of claims 1 to 8.

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