Fault ride-through method and apparatus for new energy transmission system, and electronic apparatus

Abstract

A fault ride-through method and apparatus for a new energy transmission system, and an electronic apparatus, relating to the technical field of new energy grid connection and flexible direct-current power transmission. The method comprises: acquiring a voltage parameter of a grid-connected inverter and a voltage of an alternating-current system, the voltage parameter comprising at least one of the following: an alternating-current voltage of the grid-connected inverter, a direct-current voltage of the grid-connected inverter, and a direct-current voltage change rate; on the basis of at least one of the voltage parameter and the voltage of the alternating-current system, determining whether a low-voltage fault has occurred in a new energy transmission system; and when a low-voltage fault has occurred in the new energy transmission system, adjusting the new energy transmission system at least according to a preset adjustment method, so that the new energy transmission system carries out fault ride-through within a preset duration, the preset adjustment method comprising at least one of the following: adjusting the active current of the grid-connected inverter and adjusting the integral element of a flexible direct-current system. The problem of lack of a fault ride-through method suitable for a large-scale new energy flexible direct-current transmission system is solved.

Description

Fault ride-through method and device and electronic device for new energy transmission system

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on July 31, 2023, with application number 202310958261.3 and invention name “Fault ride-through method for new energy transmission system, its device and electronic device”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the technical field of new energy grid connection and flexible direct current transmission, and more specifically, to a fault ride-through method, a fault ride-through device, a computer-readable storage medium, and an electronic device for a new energy transmission system. Background Art

[0003] Deserts, Gobi deserts, and other areas are rich in wind and solar resources. Large-scale renewable energy power generation bases are primarily located in the "Three Norths" and Tibet, and are located at the end of the main grid. Due to the weak local power grids, insufficient absorption capacity, lack of large-scale grid support, and thousands of kilometers from load centers in the east, large-scale renewable energy power stations in these scenarios typically need to transmit power to load centers via flexible DC transmission systems.

[0004] When connected to the grid, both renewable energy power plants and flexible DC transmission systems must possess low-voltage fault ride-through capabilities. This means that if the voltage at the grid connection point of a renewable energy power plant or flexible DC transmission system drops, the power plant and flexible DC transmission system can continue to operate for a period of time. Off-grid operation is permitted only when a grid fault cannot be quickly restored, while providing reactive power support to the grid to support voltage recovery. For large-scale renewable energy power plants, when transmitting via flexible DC, the sending-end grid system is a power electronics system that primarily relies on flexible DC to provide stable AC voltage support. Because the fault characteristics of the sending-end grid system differ from those of traditional AC grids, different fault ride-through strategies are required for renewable energy power plants and flexible DC. Currently, there is a lack of mature fault ride-through strategies suitable for large-scale transmission scenarios for flexible DC.

[0005] Existing standards for fault ride-through strategies for renewable energy power plants are primarily designed for applications involving access to large AC power grids. In scenarios where 100% renewable energy flexible DC transmission is used, the existing fault ride-through strategies present two major challenges:

[0006] 1) During a low voltage fault, the grid-connected inverter of a remote renewable energy source may have difficulty sensing the low voltage characteristics, resulting in the inverter being unable to enter the low voltage ride-through state;

[0007] 2) During the fault recovery period, the new energy transmission system has AC overvoltage problems and the recovery time is long.

[0008] In addition, in terms of the flexible DC fault ride-through characteristics: after a fault occurs, the flexible DC transmission system may enter a new low-voltage steady-state point and cannot recover to the rated voltage.

[0009] Therefore, there is an urgent need for a fault ride-through strategy that can be applied to the flexible DC transmission system of large-scale renewable energy power stations, so as to quickly detect low-voltage faults in the renewable energy transmission system and achieve smooth low-voltage ride-through of the transmission system.

[0010] Summary of the Invention

[0011] The main purpose of this application is to provide a fault ride-through method, a fault ride-through device, a computer-readable storage medium and an electronic device for a new energy transmission system, so as to at least solve the problem in the prior art of the lack of a fault ride-through method suitable for a flexible direct current transmission system of a large-scale new energy power station.

[0012] To achieve the above-mentioned objectives, according to one aspect of the present application, a fault ride-through method for a new energy transmission system is provided, comprising: obtaining voltage parameters of a grid-connected inverter and a voltage of an AC system, the voltage parameters comprising at least one of the following: the AC voltage of the grid-connected inverter, the DC voltage of the grid-connected inverter, and a DC voltage change rate, the DC voltage change rate being determined based on the DC voltage of the grid-connected inverter, and the new energy transmission system comprising the grid-connected inverter, the AC system, and a flexible DC system; determining whether a low voltage fault occurs in the new energy transmission system based on at least one of the voltage parameters and the voltage of the AC system; in the event that a low voltage fault occurs in the new energy transmission system, adjusting the new energy transmission system at least according to a preset adjustment method so that the new energy transmission system performs fault ride-through within a predetermined time period, the preset adjustment method comprising at least one of the following: adjusting the active current of the grid-connected inverter and adjusting the integral link of the flexible DC system.

[0013] Optionally, based on at least one of the voltage parameters and the voltage of the AC system, determining whether a low voltage fault occurs in the new energy transmission system includes: determining whether the voltage parameters of the grid-connected inverter meet preset conditions, the preset conditions including one of the following: within a first delay period, the AC voltage of the grid-connected inverter is less than or equal to an AC low voltage threshold, within a second delay period, the DC voltage is greater than or equal to a DC overvoltage threshold, and the DC voltage change rate is greater than or equal to a DC voltage slope threshold; when the voltage parameters meet the preset conditions, determining that a low voltage fault occurs in the new energy transmission system.

[0014] Optionally, based on at least one of the voltage parameters and the voltage of the AC system, determining whether a low voltage fault occurs in the new energy transmission system includes: when the voltage of the AC system is less than or equal to the AC low voltage threshold within a third delay period, determining that a low voltage fault occurs in the new energy transmission system.

[0015] Optionally, the new energy transmission system is adjusted at least according to a preset adjustment method, including: switching the active power control mode of the grid-connected inverter from a constant DC voltage control mode to an active current control mode; based on a preset climbing rate, restoring the active current reference value of the grid-connected inverter from a first current value to a target active current value, and the target active current value is the active current reference value of the transmission system before a low voltage fault occurs; and limiting the active current reference value of the grid-connected inverter to obtain the active current control loop reference value of the grid-connected inverter.

[0016] Optionally, the active current reference value of the grid-connected inverter is subjected to a limiting process to obtain the active current control loop reference value of the grid-connected inverter, including: Determine the maximum limit of the active current reference value of the grid-connected inverter, I drefmax is the maximum limit of the active current reference value of the grid-connected inverter, I max is the maximum withstand current value of the grid-connected inverter, is the reactive current reference value of the grid-connected inverter; when the current active current reference value of the grid-connected inverter is less than the maximum limit of the active current reference value, the current active current reference value is determined as the active current control loop reference value of the grid-connected inverter; when the current active current reference value of the grid-connected inverter is greater than or equal to the maximum limit of the active current reference value, the maximum limit of the active current reference value is determined as the active current control loop reference value of the grid-connected inverter.

[0017] Optionally, in the event of a low voltage fault in the renewable energy transmission system, the fault ride-through method further comprises: freezing the integral link of the proportional-integral controller of the grid-connected inverter so that the output of the integral link in the proportional-integral controller remains unchanged during the occurrence of the low voltage fault in the renewable energy transmission system; switching the reactive power control mode of the grid-connected inverter from the target control mode to the constant reactive current control mode, wherein the target control mode includes one of the following: constant reactive power control mode and AC side voltage control mode; and adopting the method of controlling the reactive power control mode when the AC voltage drop depth of the grid-connected inverter is within the target voltage drop depth range. Determine a reactive current reference value of the grid-connected inverter, wherein the target voltage sag depth range is composed of a voltage sag depth lower limit value and a voltage sag depth upper limit value, detU1 is the voltage sag depth lower limit value, detU2 is the voltage sag depth upper limit value, and ΔU is the AC voltage sag depth of the grid-connected inverter. is the reactive current reference value of the grid-connected inverter, is the maximum reactive output current of the grid-connected inverter; when the AC voltage drop depth of the grid-connected inverter is greater than the upper limit value of the voltage drop depth, the maximum reactive output current of the grid-connected inverter is determined as the reactive current reference value of the grid-connected inverter; when the AC voltage drop depth of the grid-connected inverter is less than the lower limit value of the voltage drop depth, the reactive current reference value of the grid-connected inverter is determined to be 0.

[0018] Optionally, the fault ride-through method also includes: when the voltage parameter of the grid-connected inverter no longer meets the preset conditions and the current active current value of the grid-connected inverter recovers to the target active current value, switching the reactive control mode of the grid-connected inverter from the fixed reactive current control mode to the target control mode, and switching the active control mode of the grid-connected inverter from the active current control mode to the fixed DC voltage control mode, wherein the preset conditions include one of the following: within the first delay period, the AC voltage of the grid-connected inverter is less than or equal to the AC low voltage threshold, within the second delay period, the DC voltage is greater than or equal to the DC overvoltage threshold and the DC voltage change rate is greater than or equal to the DC voltage slope threshold, the target active current value is the active current value of the new energy transmission system before a low voltage fault occurs, and the target control mode includes one of the following: fixed reactive power control mode and AC side voltage control mode.

[0019] Optionally, the new energy transmission system is adjusted at least according to a preset adjustment method, including: reducing the integral coefficient of the AC voltage loop of the flexible DC system in the proportional-integral controller, so that during a low voltage fault of the new energy transmission system, the integral speed of the proportional-integral controller of the flexible DC system is slowed down.

[0020] Optionally, in the event of a low voltage fault in the new energy transmission system, the fault ride-through method further comprises: adjusting the AC voltage outer loop reference value of the flexible DC system according to the voltage drop degree of the AC system; Determine a reference value of the positive-sequence d-axis voltage component of the AC voltage of the flexible DC system, wherein: is the reference value of the positive-sequence d-axis voltage component of the AC voltage of the flexible DC system, is the reference value of the positive-sequence d-axis voltage component of the AC voltage of the flexible DC system before a low-voltage fault occurs in the new energy transmission system, is the negative-sequence voltage amplitude of the AC voltage of the flexible DC system; the positive-sequence q-axis voltage component reference value, the negative-sequence d-axis voltage component reference value and the negative-sequence q-axis voltage component reference value of the AC voltage of the flexible DC system are all set to 0; the current of the flexible DC system is limited so that the positive-sequence d-axis current reference value of the current of the flexible DC system is less than or equal to the positive-sequence d-axis current limit value, the positive-sequence q-axis current reference value is less than or equal to the positive-sequence q-axis current limit value, the negative-sequence d-axis current reference value is less than or equal to the negative-sequence d-axis current limit value, the negative-sequence q-axis current reference value is less than or equal to the negative-sequence q-axis current limit value, and the positive and negative sequence dq-axis total current reference value is less than or equal to the total current reference threshold.

[0021] Optionally, the fault ride-through method also includes: when the new energy transmission system no longer has a low voltage fault within the fourth delay period, restoring the integral coefficient of the AC voltage loop of the flexible DC system in the proportional-integral controller to a target value, and the target value is the integral coefficient of the AC voltage loop of the flexible DC system in the proportional-integral controller before the new energy transmission system has a low voltage fault.

[0022] According to another aspect of the present application, a fault ride-through device for a new energy transmission system is provided, comprising: an acquisition unit, configured to acquire voltage parameters of a grid-connected inverter and a voltage of an AC system, the voltage parameters comprising at least one of the following: the AC voltage of the grid-connected inverter, the DC voltage of the grid-connected inverter, and a DC voltage change rate, the DC voltage change rate being determined based on the DC voltage of the grid-connected inverter, and the new energy transmission system comprising the grid-connected inverter, the AC system, and a flexible DC system; a first determination unit, configured to determine whether a low voltage fault occurs in the new energy transmission system based on at least one of the voltage parameters and the voltage of the AC system; and a first adjustment unit, configured to adjust the new energy transmission system, at least according to a preset adjustment method, in the event that a low voltage fault occurs in the new energy transmission system, so that the new energy transmission system performs fault ride-through within a predetermined time period, the preset adjustment method comprising at least one of the following: adjusting the active current of the grid-connected inverter and adjusting the integral link of the flexible DC system.

[0023] According to another aspect of the present application, a computer-readable storage medium is provided, which includes a stored program, wherein when the program is running, the device where the computer-readable storage medium is located is controlled to execute any one of the fault-crossing methods of the new energy transmission system.

[0024] According to another aspect of the present application, an electronic device is provided, comprising a memory and a processor, wherein the memory stores a computer program, and the processor is configured to execute any one of the fault ride-through methods of the new energy transmission system through the computer program.

[0025] Applying the technical solution of the present application, first, the AC voltage and DC voltage of the grid-connected inverter are obtained, and based on the DC voltage of the grid-connected inverter, the DC voltage change rate is determined, and the voltage of the AC system is obtained. Then, based on the DC voltage change rate and the voltage parameters of the AC voltage and DC voltage of the grid-connected inverter, or the voltage of the AC system, or the voltage of the AC system, it is determined whether a low voltage fault has occurred in the renewable energy transmission system. Finally, if a low voltage fault has occurred in the renewable energy transmission system, at least the active current of the grid-connected inverter is adjusted, or at least the integral component of the flexible DC system is adjusted, or at least the active current of the grid-connected inverter and the integral component of the flexible DC system are adjusted. This solution detects whether a low voltage fault has occurred in the renewable energy transmission system by using the voltage parameters of the grid-connected inverter, or the voltage of the AC system, or the voltage parameters of the grid-connected inverter and the voltage of the AC system. This allows timely sensing of the low voltage fault in the renewable energy transmission system, allowing the grid-connected inverter and the flexible DC system to promptly enter a low voltage fault ride-through state. In addition, when it is determined that a low voltage fault occurs in the new energy transmission system, this scheme at least adjusts the active current of the grid-connected inverter, or at least adjusts the integral link of the flexible DC system, or at least adjusts the active current of the grid-connected inverter and the integral link of the flexible DC system. In this way, the new energy transmission system can be restored to the rated voltage before the fault more quickly, thereby achieving smooth ride-through of the low voltage fault of the new energy transmission system, thereby greatly improving the recovery speed of the new energy transmission system fault ride-through without overvoltage problems, and thus solving the problem in the existing technology of the lack of a fault ride-through method suitable for the flexible DC transmission system of large-scale new energy power stations. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The drawings that constitute part of this application are used to provide a further understanding of this application. The illustrative embodiments of this application and their descriptions are used to explain this application and do not constitute an improper limitation on this application. In the drawings:

[0027] FIG1 shows a hardware structure block diagram of a mobile terminal for executing a fault ride-through method of a new energy transmission system provided in an embodiment of the present application;

[0028] FIG2 is a schematic flow chart showing a fault ride-through method for a new energy transmission system according to an embodiment of the present application;

[0029] FIG3 shows a schematic diagram of a grid-connected inverter connected to an AC system according to an embodiment of the present application;

[0030] FIG4 shows a schematic diagram of determining whether a low voltage fault occurs in a new energy transmission system according to an embodiment of the present application;

[0031] FIG5 shows another schematic diagram of determining whether a low voltage fault occurs in a new energy transmission system according to an embodiment of the present application;

[0032] FIG6 shows a schematic diagram of restoring a target active current value by a preset ramp rate according to an embodiment of the present application;

[0033] FIG7 shows a schematic diagram of freezing an integral link in a proportional-integral controller of a grid-connected inverter according to an embodiment of the present application;

[0034] FIG8 shows a schematic diagram of determining a reactive current reference value according to an AC voltage drop degree provided by an embodiment of the present application;

[0035] FIG9 shows a schematic structural diagram of a fault ride-through device of a new energy transmission system provided according to an embodiment of the present application.

[0036] Among them, the above-mentioned drawings include the following figure marks: 102, processor; 104, memory; 106, transmission equipment; 108, input and output equipment; 100, grid-connected inverter; 200, AC grid connection point; 300, OR gate; 400, AND gate; 500, comparator; 600, proportional-integral controller; 10, acquisition unit; 20, first determination unit; 30, first adjustment unit. DETAILED DESCRIPTION

[0037] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0038] In order to enable those skilled in the art to better understand the present invention, the following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of this application.

[0039] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequential order. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present application described here. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0040] As introduced in the background technology, the existing technology lacks a fault ride-through method suitable for flexible DC transmission systems of large-scale new energy power stations. To solve the above problems, the embodiments of the present application provide a fault ride-through method, a fault ride-through device, a computer-readable storage medium and an electronic device for a new energy transmission system.

[0041] The technical solutions in the embodiments of the present invention will be described clearly and completely below with reference to the accompanying drawings in the embodiments of the present invention.

[0042] The method embodiments provided in the embodiments of the present application can be executed in a mobile terminal, a computer terminal or a similar computing device. Taking operation on a mobile terminal as an example, FIG1 is a hardware structure block diagram of a mobile terminal of a fault-crossing method for a new energy transmission system according to an embodiment of the present invention. As shown in FIG1 , the mobile terminal may include one or more (only one is shown in FIG1 ) processors 102 (the processor 102 may include but is not limited to a processing device such as a microprocessor MCU or a programmable logic device FPGA) and a memory 104 for storing data, wherein the mobile terminal may also include a transmission device 106 and an input and output device 108 for communication functions. It will be understood by those skilled in the art that the structure shown in FIG1 is only for illustration and does not limit the structure of the mobile terminal. For example, the mobile terminal may also include more or fewer components than those shown in FIG1 , or have a configuration different from that shown in FIG1 .

[0043] Memory 104 can be used to store computer programs, such as application software programs and modules, such as the computer program corresponding to the fault ride-through method for the new energy transmission system in the embodiments of the present invention. Processor 102 executes the computer programs stored in memory 104 to execute various functional applications and data processing, thereby implementing the aforementioned method. Memory 104 may include high-speed random access memory (RAM) and may also include non-volatile memory, such as one or more magnetic storage devices, flash memory, or other non-volatile solid-state memory. In some examples, memory 104 may further include memory remote from processor 102, which can be connected to the mobile terminal via a network. Examples of such networks include, but are not limited to, the Internet, an intranet, a local area network, a mobile communication network, and combinations thereof. Transmission device 106 is used to receive or transmit data via a network. Specific examples of such networks may include a wireless network provided by the mobile terminal's telecommunications provider. In one example, transmission device 106 includes a network interface controller (NIC), which can be connected to other network devices via a base station to enable communication with the Internet. In one example, the transmission device 106 may be a radio frequency (RF) module, which is used to communicate with the Internet wirelessly.

[0044] In this embodiment, a fault-crossing method for a new energy delivery system running on a mobile terminal, a computer terminal, or a similar computing device is provided. It should be noted that the steps shown in the flowchart of the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and although a logical order is shown in the flowchart, in some cases, the steps shown or described can be executed in an order different from that shown here.

[0045] FIG2 is a flow chart of a fault ride-through method for a new energy transmission system according to an embodiment of the present application. As shown in FIG2 , the fault ride-through method includes the following steps:

[0046] Step S201: Acquire voltage parameters of a grid-connected inverter and a voltage of an AC system, wherein the voltage parameters include at least one of the following: the AC voltage of the grid-connected inverter, the DC voltage of the grid-connected inverter, and a DC voltage change rate, wherein the DC voltage change rate is determined based on the DC voltage of the grid-connected inverter, and the new energy transmission system includes the grid-connected inverter, the AC system, and the flexible DC system.

[0047] 3 , the AC voltage of the grid-connected inverter 100 may be the voltage of the grid-connected inverter 100 at the AC grid connection point 200. The AC grid connection point 200 is the point where the grid-connected inverter 100 is connected to the AC system (not shown in FIG3 ).

[0048] In the above step S201 , the DC voltage of the above grid-connected inverter may be the voltage of the DC side of the grid-connected inverter.

[0049] In actual application, the specific process of determining the DC voltage change rate of the above-mentioned grid-connected inverter can be: calculating the difference between the DC voltages of the grid-connected inverter at two different times; then calculating the ratio of the difference to the difference at the two different times, and then the DC voltage change rate of the above-mentioned grid-connected inverter can be obtained.

[0050] Step S202, determining whether a low voltage fault occurs in the new energy transmission system based on at least one of the voltage parameter and the voltage of the AC system;

[0051] In step S202, whether the new energy transmission system has a low voltage fault can be determined based on the voltage parameters of the grid-connected inverter; or based on the voltage of the AC system. Of course, whether the new energy transmission system has a low voltage fault can also be determined based on the voltage parameters of the grid-connected inverter and the voltage of the AC system.

[0052] In actual application, the new energy transmission system in step S202 may be a transmission end that transmits electricity to a load center (ie, a receiving system). The receiving system (ie, a load center) may be a terminal that receives electricity.

[0053] Step S203: When a low voltage fault occurs in the new energy transmission system, the new energy transmission system is adjusted at least according to a preset adjustment method so that the new energy transmission system can ride through the fault within a predetermined time period. The preset adjustment method includes at least one of the following: adjusting the active current of the grid-connected inverter and adjusting the integral link of the flexible DC system.

[0054] In a specific embodiment, adjusting the integral link of the flexible DC system may further include: adjusting the integral link of the AC voltage loop of the flexible DC system in a proportional-integral controller.

[0055] In the above-mentioned fault ride-through method for the renewable energy transmission system, first, the AC voltage and DC voltage of the grid-connected inverter are obtained, and the DC voltage change rate is determined based on the DC voltage of the grid-connected inverter, and the voltage of the AC system is obtained; then, based on the voltage parameters including the DC voltage change rate and the AC voltage and DC voltage of the grid-connected inverter, or the voltage of the AC system, or the voltage including the DC voltage change rate and the AC voltage and DC voltage of the grid-connected inverter and the voltage of the AC system, it is determined whether a low voltage fault has occurred in the renewable energy transmission system; finally, when it is determined that a low voltage fault has occurred in the renewable energy transmission system, at least the active current of the grid-connected inverter is adjusted, or at least the integral link of the flexible DC system is adjusted, or at least the active current of the grid-connected inverter is adjusted and the integral link of the flexible DC system is adjusted. This solution detects whether a low voltage fault has occurred in the renewable energy transmission system by using the voltage parameters of the grid-connected inverter, or the voltage of the AC system, or the voltage parameters of the grid-connected inverter and the voltage of the AC system. In this way, the low voltage fault of the renewable energy transmission system can be sensed in a timely manner, so that the grid-connected inverter and the flexible DC system can enter a low voltage fault ride-through state in a timely manner. In addition, when it is determined that a low voltage fault occurs in the new energy transmission system, this scheme at least adjusts the active current of the grid-connected inverter, or at least adjusts the integral link of the flexible DC system, or at least adjusts the active current of the grid-connected inverter and the integral link of the flexible DC system. In this way, the new energy transmission system can be restored to the rated voltage before the fault more quickly, thereby achieving smooth ride-through of the low voltage fault of the new energy transmission system, thereby greatly improving the recovery speed of the new energy transmission system fault ride-through without overvoltage problems, and thus solving the problem in the existing technology of the lack of a fault ride-through method suitable for the flexible DC transmission system of large-scale new energy power stations.

[0056] It should be noted that the steps shown in the flowcharts of the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and that, although a logical order is shown in the flowcharts, in some cases, the steps shown or described can be executed in an order different from that shown here.

[0057] In order to further detect whether a low voltage fault occurs in the new energy transmission system more quickly and accurately, in the specific implementation process, the above-mentioned step S202 can be implemented through steps S2021 and S2022. Specifically, step S2021: determine whether the above-mentioned voltage parameters of the above-mentioned grid-connected inverter meet preset conditions, and the above-mentioned preset conditions include one of the following: within the first delay time, the AC voltage of the above-mentioned grid-connected inverter is less than or equal to the AC low voltage threshold, and within the second delay time, the above-mentioned DC voltage is greater than or equal to the DC overvoltage threshold, and the above-mentioned DC voltage change rate is greater than or equal to the DC voltage slope threshold; step S2022, if the above-mentioned voltage parameters meet the above-mentioned preset conditions, determine that a low voltage fault occurs in the above-mentioned new energy transmission system.

[0058] In a specific embodiment, when the voltage parameter does not satisfy the preset condition, it is determined that no voltage fault occurs in the new energy transmission system.

[0059] In a specific embodiment of the present application, the first delay duration and the second delay duration can both be 10ms. Of course, the first delay duration and the second delay duration are not limited to 10ms, and can also be other suitable values. That is to say, in the present application, there is no restriction on the size of the first delay duration and the second delay duration, and the specific values ​​can be flexibly adjusted according to the actual application scenario.

[0060] In the actual application process, as shown in FIG4 , the first situation: the comparator 500 can be used to determine the AC voltage U of the grid-connected inverter within the first delay time t1. pcc Is it less than or equal to the AC low voltage threshold U ac_low The second case: The comparator 500 can be used to determine the DC voltage U of the grid-connected inverter within the second delay time t2. dc Is it greater than or equal to the DC overvoltage threshold U dc_low The third case: by the comparator 500, determine the DC voltage change rate detU dc Is it less than or equal to the DC voltage slope threshold U dc_det When the first condition is met, the first signal may be sent to the OR gate 300; when the second condition is met, the second signal may be sent to the AND gate 400; when the third condition is met, the third signal may be sent to the AND gate 400. When the AND gate 400 receives the second signal and the third signal at the same time, the fourth signal may be sent to the OR gate 300. When the OR gate 300 receives either the first signal or the fourth signal, the OR gate 300 may issue a first low voltage fault signal S Low , which means that a low voltage fault has occurred in the new energy transmission system.

[0061] The above-mentioned step S202 of the present application can be implemented through step S2024: when the voltage of the above-mentioned AC system is less than or equal to the AC low voltage threshold within the third delay period, it is determined that a low voltage fault occurs in the above-mentioned new energy transmission system, thereby further realizing a relatively simple and rapid determination of whether a low voltage fault occurs in the transmission system.

[0062] In a specific embodiment of the present application, the third delay duration may be 10ms. Of course, the third delay duration is not limited to 10ms, and may also be other appropriate values. In other words, in the present application, there is no restriction on the size of the third delay duration, and the specific value may be flexibly adjusted according to the actual application scenario.

[0063] In a specific embodiment of the present application, as shown in FIG5 , the comparator 500 detects that the voltage U pcc_hvdc Less than or equal to the AC low voltage threshold U ac_low2 In the case of a low voltage fault, the second low voltage fault signal S is output. Low2 , which means that a low voltage fault has occurred in the new energy transmission system.

[0064] The above-mentioned step S203 can also be implemented through steps S2031, S2032, and S2033. Specifically, step S2031: switching the active power control mode of the above-mentioned grid-connected inverter from the constant DC voltage control mode to the active current control mode; step S2032: based on a preset ramp rate, restoring the active current reference value of the above-mentioned grid-connected inverter from the first current value to the target active current value, wherein the target active current value is the active current reference value of the above-mentioned transmission system before the low voltage fault occurs; step S2033: limiting the active current reference value of the above-mentioned grid-connected inverter to obtain the active current control loop reference value of the above-mentioned grid-connected inverter.

[0065] In the actual application process, as shown in FIG6 , when a low voltage fault of the above-mentioned new energy transmission system is detected, the current active current reference value of the grid-connected inverter will quickly drop to a first current value (for example, 0 as shown in FIG6 ), that is, the target active current value I d_ref1 Rapidly decrease to the first current value (for example, 0 as shown in FIG6 ). In order to make the current active current reference value of the grid-connected inverter recover to the target active current value I more quickly d_ref1 In this solution, a preset ramp rate is set to restore the active current reference value of the grid-connected inverter from the first current value to the target active current value I d_ref1, that is, restoring the grid-connected inverter's active current reference value to the target active current value before the low-voltage fault occurred. Simultaneously, this solution also limits the grid-connected inverter's active current reference value, ensuring that the grid-connected inverter's active current reference value is less than or equal to the maximum active current reference value limit.

[0066] In a specific embodiment of the present application, the preset climbing rate can be 2 p.u. / s. Of course, the preset climbing rate is not limited to 2 p.u. / s and can also be other appropriate values. In other words, in the present application, there is no restriction on the magnitude of the preset climbing rate, and the specific value can be flexibly adjusted according to the actual application scenario.

[0067] In order to further reasonably determine the active current control loop reference value of the new energy grid-connected inverter, in one embodiment of the present application, the above step S2033 can also be implemented by the following steps: based on Determine the maximum limit of the active current reference value of the above grid-connected inverter, I drefmax is the maximum limit of the active current reference value of the above-mentioned grid-connected inverter, I max is the maximum withstand current value of the above grid-connected inverter, is the reactive current reference value of the above-mentioned grid-connected inverter; when the current active current reference value of the above-mentioned grid-connected inverter is less than the maximum limit value I of the above-mentioned active current reference value drefmax In the case of the above-mentioned current active current reference value, the current active current reference value is determined as the active current control loop reference value of the above-mentioned grid-connected inverter; in the case that the current active current reference value of the above-mentioned grid-connected inverter is greater than or equal to the maximum limit of the above-mentioned active current reference value, the maximum limit of the above-mentioned active current reference value I drefmax , determined as the reference value of the above-mentioned active current control loop of the above-mentioned grid-connected inverter.

[0068] In some embodiments, the fault ride-through method of the present application further includes at least one of step S204, step S205, step S206, step S207, and step S208. Specifically, step S204: freezing the integral link of the proportional-integral controller of the above-mentioned grid-connected inverter so that during the occurrence of the low-voltage fault of the above-mentioned new energy transmission system, the output of the integral link in the above-mentioned proportional-integral controller remains unchanged; step S205: switching the reactive power control mode of the above-mentioned grid-connected inverter from the target control mode to the constant reactive current control mode, and the above-mentioned target control mode includes one of the following: constant reactive power control mode, AC side voltage control mode; step S206: when the AC voltage drop depth of the above-mentioned grid-connected inverter is within the target voltage drop depth range, adopt Determine a reactive current reference value of the grid-connected inverter, wherein the target voltage sag depth range is composed of a voltage sag depth lower limit value and a voltage sag depth upper limit value, detU1 is the voltage sag depth lower limit value, detU2 is the voltage sag depth upper limit value, and ΔU is the AC voltage sag depth of the grid-connected inverter. is the reactive current reference value of the above-mentioned grid-connected inverter, is the maximum reactive output current of the above-mentioned grid-connected inverter; in step S207, when the AC voltage drop depth of the above-mentioned grid-connected inverter is greater than the above-mentioned voltage drop depth upper limit, the maximum reactive output current of the above-mentioned grid-connected inverter is determined as the above-mentioned reactive current reference value of the above-mentioned grid-connected inverter; in step S208, when the AC voltage drop depth of the above-mentioned grid-connected inverter is less than the above-mentioned voltage drop depth lower limit, the above-mentioned reactive current reference value of the above-mentioned grid-connected inverter is determined to be 0.

[0069] Regarding the above step S204, as shown in FIG7 , the DC voltage U dc The DC voltage reference value U of the grid-connected inverter dc_ref The target value is then input into the proportional-integral controller 600 of the grid-connected inverter. The proportional-integral controller 600 of the grid-connected inverter receives the first low voltage fault signal S Low In the case of the grid-connected inverter, the integral link of the proportional integral controller 600 (i.e., the integral link of the proportional integral controller 600 of the grid-connected inverter) i / s) is frozen so that during the occurrence of the low voltage fault, the output of the integral link in the proportional integral controller remains unchanged. dc_ref Usually output by MPPT controller (Maximum Power Point Tracking controller, MPPT for short) or set according to modulation requirements, k p is the proportional coefficient of the proportional-integral controller of the grid-connected inverter, k i is the integral coefficient of the proportional-integral controller of the grid-connected inverter, and S is the Laplace operator.

[0070] In the above step S205, the reactive power control mode of the grid-connected inverter is switched from the target control mode to the constant reactive current control mode, so that the grid-connected inverter can provide dynamic reactive power support for the transmission system.

[0071] In actual application, during low voltage fault, priority is given to controlling the reactive current of the grid-connected inverter. As shown in Figure 8, the reactive current reference value of the grid-connected inverter can be determined according to the AC voltage drop depth ΔU of the grid-connected inverter. Specifically, when the AC voltage drop depth ΔU of the grid-connected inverter is within the target voltage drop depth range (i.e., detU1≤ΔU≤detU2), the Determine the reactive current reference value of the grid-connected inverter When the AC voltage drop depth ΔU is greater than the upper limit of the voltage drop depth (ie ΔU>detU2), the maximum reactive output current is determined as the reactive current reference value (ie When the AC voltage drop depth is less than the voltage drop depth lower limit (ΔU>detU1), the reactive current reference value is determined to be 0 (i.e. ).

[0072] In actual application, the above-mentioned fault ride-through method also includes step S209. When the above-mentioned voltage parameters of the above-mentioned grid-connected inverter no longer meet the preset conditions and the current active current value of the above-mentioned grid-connected inverter is restored to the target active current value, the reactive control mode of the above-mentioned grid-connected inverter is switched from the fixed reactive current control mode to the target control mode, and the active control mode of the above-mentioned grid-connected inverter is switched from the active current control mode to the fixed DC voltage control mode, wherein the above-mentioned preset conditions include one of the following: within the first delay period, the AC voltage of the above-mentioned grid-connected inverter is less than or equal to the AC low voltage threshold, within the second delay period, the above-mentioned DC voltage is greater than or equal to the DC overvoltage threshold and the above-mentioned DC voltage change rate is greater than or equal to the DC voltage slope threshold, the above-mentioned target active current value is the active current value of the above-mentioned new energy transmission system before the low voltage fault occurs, and the above-mentioned target control mode includes one of the following: fixed reactive power control mode and AC side voltage control mode.

[0073] Specifically, the expression of the proportional-integral controller of the AC voltage loop of the flexible DC system is G(s)=K up +K ui / s. In the event of a low voltage fault in the renewable energy transmission system, in order to slow down the integration speed of the proportional-integral controller, in some implementations, the above step S203 further includes step S2034, which reduces the integral coefficient K of the AC voltage loop of the above flexible DC system in the proportional-integral controller. ui , so that during a low voltage fault of the above-mentioned new energy transmission system, the integral speed of the above-mentioned proportional-integral controller of the above-mentioned flexible DC system is slowed down and reduced.

[0074] In one embodiment of the present application, the fault ride-through method further includes at least one of step S210, step S211, step S212, and step S213. Step S210: adjusting the AC voltage outer loop reference value of the flexible DC system according to the voltage drop of the AC system; step S211: using Determine the reference value of the positive-sequence d-axis voltage component of the AC voltage of the flexible DC system, where: is the reference value of the positive-sequence d-axis voltage component of the AC voltage of the above flexible DC system, is the reference value of the positive-sequence d-axis voltage component of the AC voltage of the flexible DC system before a low-voltage fault occurs in the renewable energy transmission system, is the negative-sequence voltage amplitude of the AC voltage of the flexible DC system; step S212, setting the positive-sequence q-axis voltage component reference value, the negative-sequence d-axis voltage component reference value, and the negative-sequence q-axis voltage component reference value of the AC voltage of the flexible DC system to 0; step S213, limiting the current of the flexible DC system so that the positive-sequence d-axis current reference value of the current of the flexible DC system is less than or equal to the positive-sequence d-axis current limiting value I dP_max , the positive sequence q axis current reference value is less than or equal to the positive sequence q axis current limit value I qP_max , the negative sequence d axis current reference value is less than or equal to the negative sequence d axis current limit value I dN_max , the negative sequence q axis current reference value is less than or equal to the negative sequence q axis current limit value I dN_max And the total current reference value of the positive and negative sequence dq axis is less than or equal to the total current reference threshold I max2 .

[0075] Specifically, by considering the asymmetric fault scenario, in the above step S210, the AC voltage outer loop reference value of the flexible DC system can be adjusted according to the voltage drop degree of the AC system. The size of the positive sequence d-axis voltage component is continuously reduced, which can ensure that the non-fault phase does not generate overvoltage during an asymmetric short circuit fault.

[0076] In some implementations, the fault ride-through method further includes step S214: if the new energy transmission system no longer has a low voltage fault within the fourth delay time t4, the AC voltage loop of the flexible DC system is adjusted to the integral coefficient K in the proportional integral controller. ui Restore to the target value, where the target value is the integral coefficient of the AC voltage loop of the flexible DC system in the proportional-integral controller before a low voltage fault occurs in the new energy transmission system.

[0077] In order to enable those skilled in the art to more clearly understand the technical solution of the present application, the implementation process of the fault ride-through method of the new energy transmission system of the present application will be described in detail below with reference to specific embodiments.

[0078] This embodiment relates to a specific fault ride-through method for a new energy transmission system, including the following steps:

[0079] Step S1: obtaining voltage parameters of the grid-connected inverter and the voltage of the AC system, wherein the voltage parameters of the grid-connected inverter include at least one of the AC voltage of the grid-connected inverter, the DC voltage of the grid-connected inverter, and the DC voltage change rate;

[0080] Step S2:

[0081] The first judgment scenario: within the first delay period, the AC voltage of the grid-connected inverter is less than or equal to the AC low voltage threshold, or within the second delay period, the DC voltage is greater than or equal to the DC overvoltage threshold and the DC voltage change rate is less than or equal to the DC voltage slope threshold, determining that a low voltage fault has occurred in the new energy transmission system;

[0082] The second judgment scenario: when the voltage of the AC system is less than or equal to the AC low voltage threshold within the third delay time, it is determined that a low voltage fault occurs in the new energy transmission system.

[0083] Step S3: When a low voltage fault occurs in the new energy transmission system, the grid-connected inverter is adjusted as follows:

[0084] Step S31: Method for adjusting the active current side of the grid-connected inverter:

[0085] (1) Switch the active power control mode of the grid-connected inverter from the constant DC voltage control mode to the active current control mode;

[0086] (2) Based on the preset ramp rate, the active current reference value of the grid-connected inverter is restored from the first current value 0 to the target active current value I d_ref1 ;

[0087] (3) Limit the active current reference value of the grid-connected inverter and Determine a maximum limit of the active current reference value of the grid-connected inverter. If the current active current reference value of the grid-connected inverter is less than the maximum limit of the active current reference value, the current active current reference value is determined as the reference value of the active current control loop. If the current active current reference value of the grid-connected inverter (e.g., a photovoltaic inverter) is greater than or equal to the maximum limit of the active current reference value, the maximum limit of the active current reference value is determined as the reference value of the active current control loop.

[0088] Step S32: Method for adjusting the DC voltage side of the grid-connected inverter:

[0089] The integral component of the proportional-integral controller of the grid-connected inverter is frozen so that the output of the integral component in the proportional-integral controller remains unchanged during the occurrence of a low voltage fault.

[0090] Step S33: Adjustment method of reactive current side of grid-connected inverter:

[0091] Switch the reactive power control mode of the grid-connected inverter from the constant reactive power control mode or the AC side voltage control mode to the constant reactive current control mode;

[0092] When the AC voltage drop depth of the grid-connected inverter is within the target voltage drop depth range, use Determine the reactive current reference value of the new energy grid-connected inverter; when the AC voltage dip depth is greater than the voltage dip depth upper limit, determine the maximum reactive output current as the reactive current reference value; when the AC voltage dip depth is less than the voltage dip depth lower limit, determine the reactive current reference value as 0;

[0093] Step S4: When the voltage parameters on the grid-connected inverter side no longer meet the preset conditions and the current active current value of the grid-connected inverter is restored to the target active current value, the reactive power control mode of the grid-connected inverter is switched from the fixed reactive current control mode to the target control mode, and the active power control mode of the grid-connected inverter is switched from the active current control mode to the fixed DC voltage control mode.

[0094] Step S5: When a low voltage fault occurs in the renewable energy transmission system, the flexible DC system is adjusted as follows:

[0095] Step S51: Adjusting the AC voltage of the flexible DC system:

[0096] Reduce the integral coefficient of the proportional-integral controller of the AC voltage loop of the flexible DC system so that the integral speed of the proportional-integral controller of the flexible DC system is slowed down during low-voltage faults in the renewable energy transmission system.

[0097] Step S52: Adjust the AC voltage outer loop side of the flexible DC system:

[0098] (1) According to the AC voltage drop degree of the flexible DC system, adjust the AC voltage outer loop reference value of the flexible DC system;

[0099] (2) Adoption A positive-sequence d-axis voltage component reference value of the AC voltage of the flexible DC system is determined, and a positive-sequence q-axis voltage component reference value, a negative-sequence d-axis voltage component reference value, and a negative-sequence q-axis voltage component reference value of the AC voltage of the flexible DC system are all set to 0.

[0100] Step S53: Adjust the current of the flexible DC system:

[0101] The current of the flexible DC system is limited so that the positive-sequence d-axis current reference value of the flexible DC system is less than or equal to the positive-sequence d-axis current limit value, the positive-sequence q-axis current reference value is less than or equal to the positive-sequence q-axis current limit value, the negative-sequence d-axis current reference value is less than or equal to the negative-sequence d-axis current limit value, the negative-sequence q-axis current reference value is less than or equal to the negative-sequence q-axis current limit value, and the total current reference value of the positive and negative sequence dq axes is less than or equal to the total current reference threshold.

[0102] Step S6: When the new energy transmission system no longer has a low voltage fault within the fourth delay period, the integral coefficient of the AC voltage loop of the flexible DC system in the proportional-integral controller is restored to the target value (i.e., restored to the integral coefficient before the low voltage fault occurs).

[0103] In a specific embodiment, in the scenario of flexible direct current transmission from a 10 million kilowatt photovoltaic power station:

[0104] If the existing fault ride-through method is used, the renewable energy transmission system operates at the full power of 10 GW from the photovoltaic power station. At 9.1 seconds, a three-phase short circuit occurs on the long AC line at the exit of the flexible DC converter station, lasting 100 milliseconds. After the fault is cleared, the faulty line is disconnected. It takes 700 milliseconds for the flexible DC converter station to restore AC voltage and active power. Furthermore, severe overvoltage occurs, with the maximum AC line voltage reaching 850 kV.

[0105] Using the fault ride-through method in this solution, the renewable energy transmission system operates at full power of 10 GW of flexible direct current (DC) from the photovoltaic power station. At 10 seconds, a three-phase short circuit is established on the long AC line at the DC converter station's exit, lasting 100 milliseconds. After the fault, the faulty line is disconnected. During the fault, reactive power is output by adjusting the q-axis current reference value based on the AC undervoltage. Based on the AC undervoltage and DC overvoltage criteria, the d-axis current is reduced to zero and then slowly increased at a preset ramp rate of 2 p.u. / s, gradually restoring active power. As can be seen, after the fault is cleared, the AC voltage at the DC converter station is restored within 40 milliseconds, and the transmission system restores active power within 400 milliseconds, with no overvoltage.

[0106] The embodiment of the present application also provides a fault ride-through device for a new energy transmission system. It should be noted that the fault ride-through device for a new energy transmission system of the embodiment of the present application can be used to execute the fault ride-through method for a new energy transmission system provided by the embodiment of the present application. The device is used to implement the above-mentioned embodiments and preferred implementation methods, and the details that have been explained will not be repeated. As used below, the term "module" can implement a combination of software and / or hardware that implements a predetermined function. Although the devices described in the following embodiments are preferably implemented in software, implementation in hardware, or a combination of software and hardware, is also possible and conceivable.

[0107] The following introduces the fault ride-through device of the new energy transmission system provided in the embodiment of the present application.

[0108] FIG9 is a schematic diagram of the structure of a fault ride-through device of a new energy transmission system according to an embodiment of the present application. As shown in FIG9 , the fault ride-through device includes:

[0109] an acquisition unit 10 configured to acquire voltage parameters of the grid-connected inverter and the voltage of the AC system, the voltage parameters including at least one of the following: the AC voltage of the grid-connected inverter, the DC voltage of the grid-connected inverter, and a DC voltage change rate, the DC voltage change rate being determined based on the DC voltage of the grid-connected inverter, the new energy transmission system including the grid-connected inverter, the AC system, and the flexible DC system;

[0110] 3 , the AC voltage of the grid-connected inverter 100 may be the voltage of the grid-connected inverter 100 at the AC grid connection point 200. The AC grid connection point 200 is the point where the grid-connected inverter 100 is connected to the AC system (not shown in FIG3 ).

[0111] In the acquisition unit, the DC voltage of the grid-connected inverter may be a voltage on a DC side of the grid-connected inverter.

[0112] In actual application, the specific process of determining the DC voltage change rate of the above-mentioned grid-connected inverter can be: calculating the difference between the DC voltages of the grid-connected inverter at two different times; then calculating the ratio of the difference to the difference at the two different times, and then the DC voltage change rate of the above-mentioned grid-connected inverter can be obtained.

[0113] A first determining unit 20 is configured to determine whether a low voltage fault occurs in the new energy transmission system based on at least one of the voltage parameter and the voltage of the AC system;

[0114] In the first determining unit, whether a low voltage fault has occurred in the new energy transmission system can be determined based on the voltage parameters of the grid-connected inverter; or based on the voltage of the AC system. Of course, whether a low voltage fault has occurred in the new energy transmission system can also be determined based on the voltage parameters of the grid-connected inverter and the voltage of the AC system.

[0115] In actual application, the new energy transmission system in step S202 may be a transmission end that transmits electricity to a load center (ie, a receiving system). The receiving system (ie, a load center) may be a terminal that receives electricity.

[0116] The first adjustment unit 30 is used to adjust the above-mentioned new energy transmission system in the event of a low voltage fault in the above-mentioned new energy transmission system, at least according to a preset adjustment method, so that the above-mentioned new energy transmission system can perform fault ride-through within a predetermined time period. The above-mentioned preset adjustment method includes at least one of the following: adjusting the active current of the above-mentioned grid-connected inverter and adjusting the integral link of the above-mentioned flexible DC system.

[0117] In a specific embodiment, adjusting the integral link of the flexible DC system may further include: adjusting the integral link of the AC voltage loop of the flexible DC system in a proportional-integral controller.

[0118] In the fault ride-through device of the above-mentioned new energy transmission system, the acquisition unit is used to obtain the AC voltage and DC voltage of the grid-connected inverter, and determine the DC voltage change rate according to the DC voltage of the grid-connected inverter, and obtain the voltage of the AC system; the first determination unit is used to determine whether a low voltage fault occurs in the new energy transmission system based on the voltage parameters including the DC voltage change rate and the AC voltage and DC voltage of the grid-connected inverter, or the voltage of the AC system, or the voltage parameters including the DC voltage change rate and the AC voltage and DC voltage of the grid-connected inverter and the voltage of the AC system; the first adjustment unit is used to adjust at least the active current of the grid-connected inverter, or at least the integral link of the flexible DC system, or at least the active current of the grid-connected inverter and the integral link of the flexible DC system when it is determined that a low voltage fault occurs in the new energy transmission system. This solution detects whether a low voltage fault occurs in the renewable energy transmission system by using the voltage parameters of the grid-connected inverter, or the voltage of the AC system, or the voltage parameters of the grid-connected inverter and the voltage of the AC system. This allows the renewable energy transmission system to be detected in a timely manner, allowing the grid-connected inverter and the flexible DC system to timely enter a low voltage fault ride-through state. In addition, when determining that a low voltage fault occurs in the renewable energy transmission system, this solution adjusts at least the active current of the grid-connected inverter, or at least the integral link of the flexible DC system, or at least the active current of the grid-connected inverter and the integral link of the flexible DC system. This allows the renewable energy transmission system to recover to the rated voltage before the fault relatively quickly, thereby achieving smooth ride-through of the low voltage fault in the renewable energy transmission system, thereby greatly improving the recovery speed of the renewable energy transmission system fault ride-through without overvoltage problems, thereby solving the problem in the prior art of the lack of a fault ride-through method suitable for flexible DC transmission systems of large-scale renewable energy power stations.

[0119] In order to further detect whether a low voltage fault occurs in the transmission system more quickly and accurately, in the specific implementation process, the above-mentioned first determination unit also includes a first determination module and a second determination module, wherein the above-mentioned first determination module is used to determine whether the above-mentioned voltage parameters of the above-mentioned grid-connected inverter meet preset conditions, and the above-mentioned preset conditions include one of the following: within the first delay period, the AC voltage of the above-mentioned grid-connected inverter is less than or equal to the AC low voltage threshold, within the second delay period, the above-mentioned DC voltage is greater than or equal to the DC overvoltage threshold, and the above-mentioned DC voltage change rate is greater than or equal to the DC voltage slope threshold; the above-mentioned second determination module is used to determine that a low voltage fault occurs in the above-mentioned new energy transmission system when the above-mentioned voltage parameters meet the above-mentioned preset conditions.

[0120] In a specific embodiment, when the voltage parameter does not satisfy the preset condition, it is determined that no voltage fault occurs in the new energy transmission system.

[0121] In a specific embodiment of the present application, the first delay duration and the second delay duration can both be 10ms. Of course, the first delay duration and the second delay duration are not limited to 10ms, and can also be other suitable values. That is to say, in the present application, there is no restriction on the size of the first delay duration and the second delay duration, and the specific values ​​can be flexibly adjusted according to the actual application scenario.

[0122] In the actual application process, as shown in FIG4 , the first situation: the comparator 500 can be used to determine the AC voltage U of the grid-connected inverter within the first delay time t1. pcc Is it less than or equal to the AC low voltage threshold U ac_low The second case: The comparator 500 can be used to determine the DC voltage U of the grid-connected inverter within the second delay time t2. dc Is it greater than or equal to the DC overvoltage threshold U dc_low The third case: by the comparator 500, determine the DC voltage change rate detU dc Is it less than or equal to the DC voltage slope threshold U dc_det When the first condition is met, the first signal may be sent to the OR gate 300; when the second condition is met, the second signal may be sent to the AND gate 400; when the third condition is met, the third signal may be sent to the AND gate 400. When the AND gate 400 receives the second signal and the third signal at the same time, the fourth signal may be sent to the OR gate 300. When the OR gate 300 receives either the first signal or the fourth signal, the OR gate 300 may issue a first low voltage fault signal S Low , which means that a low voltage fault has occurred in the new energy transmission system.

[0123] The above-mentioned first determination unit of the present application also includes a third determination module, which is used to determine that a low voltage fault occurs in the above-mentioned new energy transmission system when the voltage of the above-mentioned AC system is less than or equal to the AC low voltage threshold within a third delay period. This further realizes a relatively simple and rapid determination of whether a low voltage fault occurs in the transmission system.

[0124] In a specific embodiment of the present application, the third delay duration may be 10ms. Of course, the third delay duration is not limited to 10ms, and may also be other appropriate values. In other words, in the present application, there is no restriction on the size of the third delay duration, and the specific value may be flexibly adjusted according to the actual application scenario.

[0125] In a specific embodiment of the present application, as shown in FIG5 , the comparator 500 detects that the voltage U pcc_hvdc Less than or equal to the AC low voltage threshold U ac_low2 In the case of a low voltage fault, the second low voltage fault signal S is output. Low2 , which means that a low voltage fault has occurred in the new energy transmission system.

[0126] The above-mentioned first adjustment unit also includes a first switching module, a first execution module and a first processing module, wherein the above-mentioned first switching module is used to switch the active control mode of the above-mentioned grid-connected inverter from a constant DC voltage control mode to an active current control mode; the above-mentioned first execution module is used to restore the active current reference value of the above-mentioned grid-connected inverter from a first current value to a target active current value based on a preset climbing rate, and the above-mentioned target active current value is the active current reference value of the above-mentioned transmission system before a low voltage fault occurs; the above-mentioned first processing module is used to perform limiting processing on the active current reference value of the above-mentioned grid-connected inverter to obtain the active current control loop reference value of the above-mentioned grid-connected inverter.

[0127] In the actual application process, as shown in FIG6 , when a low voltage fault of the above-mentioned new energy transmission system is detected, the current active current reference value of the grid-connected inverter will quickly drop to a first current value (for example, 0 as shown in FIG6 ), that is, the target active current value I d_ref1 Rapidly decrease to the first current value (for example, 0 as shown in FIG6 ). In order to make the current active current reference value of the grid-connected inverter recover to the target active current value I more quickly d_ref1 In this solution, a preset ramp rate is set to restore the active current reference value of the grid-connected inverter from the first current value to the target active current value I d_ref1 , that is, restoring the grid-connected inverter's active current reference value to the target active current value before the low-voltage fault occurred. Simultaneously, this solution also limits the grid-connected inverter's active current reference value, ensuring that the grid-connected inverter's active current reference value is less than or equal to the maximum active current reference value limit.

[0128] In a specific embodiment of the present application, the preset climbing rate can be 2 p.u. / s. Of course, the preset climbing rate is not limited to 2 p.u. / s and can also be other appropriate values. In other words, in the present application, there is no restriction on the magnitude of the preset climbing rate, and the specific value can be flexibly adjusted according to the actual application scenario.

[0129] In order to further reasonably determine the active current control loop reference value of the new energy grid-connected inverter, in one embodiment of the present application, the first processing module includes a first determining submodule, a second determining submodule and a third determining submodule, wherein the first determining submodule is used to determine the active current control loop reference value of the new energy grid-connected inverter based on the first determining submodule. Determine the maximum limit of the active current reference value of the above grid-connected inverter, I drefmax is the maximum limit of the active current reference value of the above-mentioned grid-connected inverter, I max is the maximum withstand current value of the above grid-connected inverter, The reactive current reference value of the grid-connected inverter; the second determining submodule is used to determine the reactive current reference value of the grid-connected inverter when the current active current reference value of the grid-connected inverter is less than the maximum limit I of the active current reference value. drefmax In the case of the above-mentioned current active current reference value, the current active current reference value is determined as the active current control loop reference value of the above-mentioned grid-connected inverter; the above-mentioned third determining submodule is used to determine the maximum limit value of the above-mentioned active current reference value I when the current active current reference value of the above-mentioned grid-connected inverter is greater than or equal to the maximum limit value of the above-mentioned active current reference value. drefmax , determined as the reference value of the above-mentioned active current control loop of the above-mentioned grid-connected inverter.

[0130] In some embodiments, the fault-crossing device of the present application further includes a first execution unit, a first switching unit, a second determination unit, a third determination unit, and a fourth determination unit. The first execution unit is used to freeze the integral link of the proportional-integral controller of the grid-connected inverter, so that during the occurrence of a low-voltage fault in the new energy transmission system, the output of the integral link in the proportional-integral controller remains unchanged; the first switching unit is used to switch the reactive power control mode of the grid-connected inverter from the target control mode to the constant reactive current control mode, and the target control mode includes one of the following: constant reactive power control mode, AC side voltage control mode; the second determination unit is used to adopt the method of controlling the AC voltage drop depth of the grid-connected inverter when the AC voltage drop depth of the grid-connected inverter is within the target voltage drop depth range. Determine the reactive current reference value of the grid-connected inverter, wherein the target voltage sag depth range is composed of a voltage sag depth lower limit value and a voltage sag depth upper limit value, detU1 is the voltage sag depth lower limit value, detU2 is the voltage sag depth upper limit value, and ΔU is the AC voltage sag depth of the grid-connected inverter. is the reactive current reference value of the above-mentioned grid-connected inverter, is the maximum reactive output current of the above-mentioned grid-connected inverter; the above-mentioned third determining unit is used to determine the maximum reactive output current of the above-mentioned grid-connected inverter as the above-mentioned reactive current reference value of the above-mentioned grid-connected inverter when the AC voltage drop depth of the above-mentioned grid-connected inverter is greater than the above-mentioned voltage drop depth upper limit; the above-mentioned fourth determining unit is used to determine the above-mentioned reactive current reference value of the above-mentioned grid-connected inverter as 0 when the AC voltage drop depth of the above-mentioned grid-connected inverter is less than the above-mentioned voltage drop depth lower limit.

[0131] For the first execution unit mentioned above, as shown in FIG7 , the DC voltage U dc The DC voltage reference value U of the grid-connected inverter dc_ref The target value is then input into the proportional-integral controller 600 of the grid-connected inverter. The proportional-integral controller 600 of the grid-connected inverter receives the first low voltage fault signal S Low In the case of the grid-connected inverter, the integral link of the proportional integral controller 600 (i.e., the integral link of the proportional integral controller 600 of the grid-connected inverter) i / s) is frozen so that during the occurrence of the low voltage fault, the output of the integral link in the proportional integral controller remains unchanged. dc_ref Usually output by MPPT controller (Maximum Power Point Tracking controller, MPPT for short) or set according to modulation requirements, k p is the proportional coefficient of the proportional-integral controller of the grid-connected inverter, k i is the integral coefficient of the proportional-integral controller of the grid-connected inverter, and S is the Laplace operator.

[0132] For the first switching unit, the reactive power control mode of the grid-connected inverter is switched from the target control mode to the constant reactive current control mode, so that the grid-connected inverter can provide dynamic reactive power support for the transmission system.

[0133] In actual application, during low voltage fault, priority is given to controlling the reactive current of the grid-connected inverter. As shown in Figure 8, the reactive current reference value of the grid-connected inverter can be determined according to the AC voltage drop depth ΔU of the grid-connected inverter. Specifically, when the AC voltage drop depth ΔU of the grid-connected inverter is within the target voltage drop depth range (i.e., detU1≤ΔU≤detU2), the Determine the reactive current reference value of the grid-connected inverter When the AC voltage drop depth ΔU is greater than the upper limit of the voltage drop depth (ie ΔU>detU2), the maximum reactive output current is determined as the reactive current reference value (ie Iq _ref =Iq_ref 1). When the AC voltage drop depth is less than the voltage drop depth lower limit (ΔU>detU1), the reactive current reference value is determined to be 0 (i.e. I q_ref =0).

[0134] In actual application, the above-mentioned fault ride-through device also includes a second switching unit, which is used to switch the reactive control mode of the above-mentioned grid-connected inverter from a fixed reactive current control mode to a target control mode, and switch the active control mode of the above-mentioned grid-connected inverter from an active current control mode to a fixed DC voltage control mode when the above-mentioned voltage parameter of the above-mentioned grid-connected inverter no longer meets the preset conditions and the current active current value of the above-mentioned grid-connected inverter is restored to a target active current value. The above-mentioned preset conditions include one of the following: within the first delay period, the AC voltage of the above-mentioned grid-connected inverter is less than or equal to the AC low voltage threshold, within the second delay period, the above-mentioned DC voltage is greater than or equal to the DC overvoltage threshold and the above-mentioned DC voltage change rate is greater than or equal to the DC voltage slope threshold, the above-mentioned target active current value is the active current value of the above-mentioned new energy transmission system before a low voltage fault occurs, and the above-mentioned target control mode includes one of the following: fixed reactive power control mode and AC side voltage control mode.

[0135] Specifically, the expression of the proportional-integral controller of the AC voltage loop of the flexible DC system is G(s)=K up +K ui / s. In the event of a low voltage fault in the renewable energy transmission system, in order to slow down the integration speed of the proportional-integral controller, in some implementations, the above step S203 further includes step S2034, which reduces the integral coefficient K of the AC voltage loop of the above flexible DC system in the proportional-integral controller. ui , so that during a low voltage fault of the above-mentioned new energy transmission system, the integral speed of the above-mentioned proportional-integral controller of the above-mentioned flexible DC system is slowed down and reduced.

[0136] In one embodiment of the present application, the fault ride-through device further includes at least one of a second adjustment unit, a fifth determination unit, a first processing unit, and a second processing unit. The second adjustment unit is used to adjust the AC voltage outer loop reference value of the flexible DC system according to the voltage drop of the AC system; the fifth determination unit is used to adopt Determine the reference value of the positive-sequence d-axis voltage component of the AC voltage of the flexible DC system, where: is the reference value of the positive-sequence d-axis voltage component of the AC voltage of the above flexible DC system, is the reference value of the positive-sequence d-axis voltage component of the AC voltage of the flexible DC system before a low-voltage fault occurs in the renewable energy transmission system, is the negative-sequence voltage amplitude of the AC voltage of the flexible DC system; the first processing unit is used to set the positive-sequence q-axis voltage component reference value, the negative-sequence d-axis voltage component reference value, and the negative-sequence q-axis voltage component reference value of the AC voltage of the flexible DC system to 0; the second processing unit is used to limit the current of the flexible DC system so that the positive-sequence d-axis current reference value of the current of the flexible DC system is less than or equal to the positive-sequence d-axis current limit value I dP_max , the positive sequence q axis current reference value is less than or equal to the positive sequence q axis current limit value I qP_max , the negative sequence d axis current reference value is less than or equal to the negative sequence d axis current limit value I dN_max , the negative sequence q axis current reference value is less than or equal to the negative sequence q axis current limit value I qN_max And the total current reference value of the positive and negative sequence dq axis is less than or equal to the total current reference threshold I max2 .

[0137] Specifically, by considering the asymmetric fault scenario, in the second adjustment unit, the AC voltage outer loop reference value of the flexible DC system can be adjusted according to the voltage drop degree of the AC system. The size of the positive sequence d-axis voltage component is continuously reduced, which can ensure that the non-fault phase does not generate overvoltage during an asymmetric short circuit fault.

[0138] In some implementations, the fault ride-through device further includes a second execution unit configured to, when the new energy transmission system no longer experiences a low voltage fault within a fourth delay time t4, adjust the AC voltage loop of the flexible DC system to the integral coefficient K in the proportional-integral controller. ui Restore to the target value, where the target value is the integral coefficient of the AC voltage loop of the flexible DC system in the proportional-integral controller before a low voltage fault occurs in the new energy transmission system.

[0139] The fault ride-through device for the new energy transmission system includes a processor and a memory. The acquisition unit, first determination unit, and first adjustment unit are stored as program units in the memory. The processor executes the program units stored in the memory to implement the corresponding functions. All of the above modules are located in the same processor; alternatively, the above modules can be located in different processors in any combination.

[0140] The processor includes a core, which retrieves the corresponding program unit from memory. One or more cores can be configured, and adjusting core parameters addresses the existing problem of a lack of fault ride-through methods suitable for large-scale flexible DC transmission systems in renewable energy power plants.

[0141] The memory may include non-permanent memory in a computer-readable medium, random access memory (RAM) and / or non-volatile memory, such as read-only memory (ROM) or flash RAM, and the memory includes at least one memory chip.

[0142] An embodiment of the present invention provides a computer-readable storage medium, which includes a stored program. When the program is run, the device where the computer-readable storage medium is located is controlled to execute the fault ride-through method of the new energy transmission system.

[0143] Specifically, the fault ride-through method of the new energy transmission system includes:

[0144] Step S201: Acquire voltage parameters of a grid-connected inverter and a voltage of an AC system, wherein the voltage parameters include at least one of the following: the AC voltage of the grid-connected inverter, the DC voltage of the grid-connected inverter, and a DC voltage change rate, wherein the DC voltage change rate is determined based on the DC voltage of the grid-connected inverter, and the new energy transmission system includes the grid-connected inverter, the AC system, and the flexible DC system.

[0145] Step S202, determining whether a low voltage fault occurs in the new energy transmission system based on at least one of the voltage parameter and the voltage of the AC system;

[0146] Step S203: When a low voltage fault occurs in the new energy transmission system, the new energy transmission system is adjusted at least according to a preset adjustment method so that the new energy transmission system can ride through the fault within a predetermined time period. The preset adjustment method includes at least one of the following: adjusting the active current of the grid-connected inverter and adjusting the integral link of the flexible DC system.

[0147] An embodiment of the present invention provides an electronic device including a memory and a processor, wherein the memory stores a computer program, and the processor is configured to execute the fault ride-through method of the new energy transmission system through the computer program.

[0148] Specifically, the fault ride-through method of the new energy transmission system includes:

[0149] Step S201: Acquire voltage parameters of a grid-connected inverter and a voltage of an AC system, wherein the voltage parameters include at least one of the following: the AC voltage of the grid-connected inverter, the DC voltage of the grid-connected inverter, and a DC voltage change rate, wherein the DC voltage change rate is determined based on the DC voltage of the grid-connected inverter, and the new energy transmission system includes the grid-connected inverter, the AC system, and the flexible DC system.

[0150] Step S202, determining whether a low voltage fault occurs in the new energy transmission system based on at least one of the voltage parameter and the voltage of the AC system;

[0151] Step S203: When a low voltage fault occurs in the new energy transmission system, the new energy transmission system is adjusted at least according to a preset adjustment method so that the new energy transmission system can ride through the fault within a predetermined time period. The preset adjustment method includes at least one of the following: adjusting the active current of the grid-connected inverter and adjusting the integral link of the flexible DC system.

[0152] An embodiment of the present invention provides a device, comprising a processor, a memory, and a program stored in the memory and executable on the processor. When the processor executes the program, at least the following steps are performed:

[0153] Step S201: Acquire voltage parameters of a grid-connected inverter and a voltage of an AC system, wherein the voltage parameters include at least one of the following: the AC voltage of the grid-connected inverter, the DC voltage of the grid-connected inverter, and a DC voltage change rate, wherein the DC voltage change rate is determined based on the DC voltage of the grid-connected inverter, and the new energy transmission system includes the grid-connected inverter, the AC system, and the flexible DC system.

[0154] Step S202, determining whether a low voltage fault occurs in the new energy transmission system based on at least one of the voltage parameter and the voltage of the AC system;

[0155] Step S203: When a low voltage fault occurs in the new energy transmission system, the new energy transmission system is adjusted at least according to a preset adjustment method so that the new energy transmission system can ride through the fault within a predetermined time period. The preset adjustment method includes at least one of the following: adjusting the active current of the grid-connected inverter and adjusting the integral link of the flexible DC system.

[0156] The devices in this article can be servers, PCs, PADs, mobile phones, etc.

[0157] The present application also provides a computer program product, which, when executed on a data processing device, is adapted to execute a program for initializing at least the following method steps:

[0158] Step S201: Acquire voltage parameters of a grid-connected inverter and a voltage of an AC system, wherein the voltage parameters include at least one of the following: the AC voltage of the grid-connected inverter, the DC voltage of the grid-connected inverter, and a DC voltage change rate, wherein the DC voltage change rate is determined based on the DC voltage of the grid-connected inverter, and the new energy transmission system includes the grid-connected inverter, the AC system, and the flexible DC system.

[0159] Step S202, determining whether a low voltage fault occurs in the new energy transmission system based on at least one of the voltage parameter and the voltage of the AC system;

[0160] Step S203: When a low voltage fault occurs in the new energy transmission system, the new energy transmission system is adjusted at least according to a preset adjustment method so that the new energy transmission system can ride through the fault within a predetermined time period. The preset adjustment method includes at least one of the following: adjusting the active current of the grid-connected inverter and adjusting the integral link of the flexible DC system.

[0161] Obviously, those skilled in the art will appreciate that the various modules or steps of the present invention described above can be implemented using a general-purpose computing device, can be centralized on a single computing device, or can be distributed across a network of multiple computing devices. They can be implemented using program code executable by the computing device, and thus, can be stored in a storage device and executed by the computing device. In some cases, the steps shown or described herein can be performed in a different order than that shown, or can be fabricated as separate integrated circuit modules, or multiple modules or steps can be fabricated as a single integrated circuit module. Thus, the present invention is not limited to any particular combination of hardware and software.

[0162] Those skilled in the art will appreciate that the embodiments of the present application can be provided as methods, systems, or computer program products. Therefore, the present application can adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application can adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to magnetic disk storage, CD-ROM, optical storage, etc.) that contain computer-usable program code.

[0163] The present application is described with reference to the flow chart and / or block diagram of the method, device (system), and computer program product according to the embodiment of the present application. It should be understood that each flow process and / or box in the flow chart and / or block diagram and the combination of the flow process and / or box in the flow chart and / or block diagram can be realized by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processing machine or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device produce a device for realizing the function specified in one flow chart flow or multiple flows and / or one box or multiple boxes of the block diagram.

[0164] These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce a product including an instruction device that implements the functions specified in one or more processes in the flowchart and / or one or more boxes in the block diagram.

[0165] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, so that the instructions executed on the computer or other programmable device provide steps for implementing the functions specified in one or more processes in the flowchart and / or one or more boxes in the block diagram.

[0166] In a typical configuration, a computing device includes one or more processors (CPUs), input / output interfaces, network interfaces, and memory.

[0167] The memory may include non-permanent memory in a computer-readable medium, random access memory (RAM) and / or non-volatile memory in the form of read-only memory (ROM) or flash RAM. The memory is an example of a computer-readable medium.

[0168] Computer-readable media include permanent and non-permanent, removable and non-removable media that can be implemented by any method or technology to store information. The information can be computer-readable instructions, data structures, program modules, or other data. Examples of computer storage media include, but are not limited to, phase-change memory (PRAM), static random access memory (SRAM), dynamic random access memory (DRAM), other types of random access memory (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), flash memory or other memory technology, compact disc read-only memory (CD-ROM), digital versatile disc (DVD) or other optical storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other non-transmission media that can be used to store information that can be accessed by a computing device. As defined herein, computer-readable media does not include transitory computer-readable media (transitory media), such as modulated data signals and carrier waves.

[0169] It should also be noted that the terms "comprises," "includes," or any other variations thereof are intended to encompass non-exclusive inclusion, such that a process, method, commodity, or apparatus that includes a series of elements includes not only those elements but also other elements not explicitly listed, or includes elements inherent to such process, method, commodity, or apparatus. In the absence of further limitations, an element defined by the phrase "comprises a ..." does not exclude the presence of other identical elements in the process, method, commodity, or apparatus that includes the element.

[0170] From the above description, it can be seen that the above embodiments of the present application achieve the following technical effects:

[0171] 1) In the fault ride-through method of the new energy transmission system of the present application, first, the AC voltage and DC voltage of the grid-connected inverter are obtained, and the DC voltage change rate is determined based on the DC voltage of the grid-connected inverter, and the voltage of the AC system is obtained; then, based on the voltage parameters including the DC voltage change rate and the AC voltage and DC voltage of the grid-connected inverter, or the voltage of the AC system, or the voltage parameters including the DC voltage change rate and the AC voltage and DC voltage of the grid-connected inverter and the voltage of the AC system, it is determined whether a low voltage fault occurs in the new energy transmission system; finally, when it is determined that a low voltage fault occurs in the new energy transmission system, at least the active current of the grid-connected inverter is adjusted, or at least the integral link of the flexible DC system is adjusted, or at least the active current of the grid-connected inverter is adjusted and the integral link of the flexible DC system is adjusted. This solution detects whether a low voltage fault occurs in the renewable energy transmission system by using the voltage parameters of the grid-connected inverter, or the voltage of the AC system, or the voltage parameters of the grid-connected inverter and the voltage of the AC system. This allows the renewable energy transmission system to be detected in a timely manner, allowing the grid-connected inverter and the flexible DC system to timely enter a low voltage fault ride-through state. In addition, when determining that a low voltage fault occurs in the renewable energy transmission system, this solution adjusts at least the active current of the grid-connected inverter, or at least the integral link of the flexible DC system, or at least the active current of the grid-connected inverter and the integral link of the flexible DC system. This allows the renewable energy transmission system to recover to the rated voltage before the fault relatively quickly, thereby achieving smooth ride-through of the low voltage fault in the renewable energy transmission system, thereby greatly improving the recovery speed of the renewable energy transmission system fault ride-through without overvoltage problems, thereby solving the problem in the prior art of the lack of a fault ride-through method suitable for flexible DC transmission systems of large-scale renewable energy power stations.

[0172] 2) In the fault ride-through device of the new energy transmission system of the present application, the acquisition unit is used to obtain the AC voltage and DC voltage of the grid-connected inverter, and determine the DC voltage change rate based on the DC voltage of the grid-connected inverter, and obtain the voltage of the AC system; the first determination unit is used to determine whether a low voltage fault occurs in the new energy transmission system based on the voltage parameters including the DC voltage change rate and the AC voltage and DC voltage of the grid-connected inverter, or the voltage of the AC system, or the voltage parameters including the DC voltage change rate and the AC voltage and DC voltage of the grid-connected inverter and the voltage of the AC system; the first adjustment unit is used to adjust at least the active current of the grid-connected inverter, or at least adjust the integral link of the flexible DC system, or at least adjust the active current of the grid-connected inverter and the integral link of the flexible DC system when it is determined that a low voltage fault occurs in the new energy transmission system. This solution detects whether a low voltage fault occurs in the renewable energy transmission system by using the voltage parameters of the grid-connected inverter, or the voltage of the AC system, or the voltage parameters of the grid-connected inverter and the voltage of the AC system. This allows the renewable energy transmission system to be detected in a timely manner, allowing the grid-connected inverter and the flexible DC system to timely enter a low voltage fault ride-through state. In addition, when determining that a low voltage fault occurs in the renewable energy transmission system, this solution adjusts at least the active current of the grid-connected inverter, or at least the integral link of the flexible DC system, or at least the active current of the grid-connected inverter and the integral link of the flexible DC system. This allows the renewable energy transmission system to recover to the rated voltage before the fault relatively quickly, thereby achieving smooth ride-through of the low voltage fault in the renewable energy transmission system, thereby greatly improving the recovery speed of the renewable energy transmission system fault ride-through without overvoltage problems, thereby solving the problem in the prior art of the lack of a fault ride-through method suitable for flexible DC transmission systems of large-scale renewable energy power stations.

[0173] The above description is merely a preferred embodiment of the present application and is not intended to limit the present application. Various modifications and variations are possible for those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present application shall be included within the scope of protection of the present application.

Claims

1. A fault ride-through method for a new energy transmission system, characterized in that: include: Acquire voltage parameters of the grid-connected inverter and the voltage of the AC system, wherein the voltage parameters include at least one of the following: the AC voltage of the grid-connected inverter, the DC voltage of the grid-connected inverter, and the DC voltage change rate, wherein the DC voltage change rate is determined according to the DC voltage of the grid-connected inverter, and the new energy transmission system includes the grid-connected inverter, the AC system, and the flexible DC system; Determining whether a low voltage fault occurs in the new energy delivery system according to at least one of the voltage parameter and the voltage of the AC system; In the event of a low voltage fault in the renewable energy transmission system, the renewable energy transmission system is adjusted at least in accordance with a preset adjustment method so that the renewable energy transmission system can perform fault ride-through within a predetermined time period. The preset adjustment method includes at least one of the following: adjusting the active current of the grid-connected inverter and adjusting the integral link of the flexible DC system.

2. The fault ride-through method according to claim 1, characterized in that: Determining whether a low voltage fault occurs in the new energy transmission system according to at least one of the voltage parameter and the voltage of the AC system includes: Determine whether the voltage parameter of the grid-connected inverter meets a preset condition, wherein the preset condition includes one of the following: within a first delay time, the AC voltage of the grid-connected inverter is less than or equal to an AC low voltage threshold, within a second delay time, the DC voltage is greater than or equal to a DC overvoltage threshold, and the DC voltage change rate is greater than or equal to a DC voltage slope threshold; When the voltage parameter meets the preset condition, it is determined that a low voltage fault occurs in the new energy transmission system.

3. The fault ride-through method according to claim 1, characterized in that: Determining whether a low voltage fault occurs in the new energy transmission system according to at least one of the voltage parameter and the voltage of the AC system includes: When the voltage of the AC system is less than or equal to the AC low voltage threshold within the third delay time, it is determined that a low voltage fault occurs in the new energy transmission system.

4. The fault ride-through method according to claim 1, characterized in that: At least according to a preset adjustment method, the new energy delivery system is adjusted, including: Switching the active power control mode of the grid-connected inverter from a constant DC voltage control mode to an active current control mode; Based on a preset ramp rate, the active current reference value of the grid-connected inverter is restored from a first current value to a target active current value, wherein the target active current value is an active current reference value of the transmission system before a low voltage fault occurs; The active current reference value of the grid-connected inverter is limited to obtain an active current control loop reference value of the grid-connected inverter.

5. The fault ride-through method according to claim 4, characterized in that: The active current reference value of the grid-connected inverter is limited to obtain the active current control loop reference value of the grid-connected inverter, including: based on Determine the maximum limit of the active current reference value of the grid-connected inverter, I drefmax is the maximum limit of the active current reference value of the grid-connected inverter, I max is the maximum withstand current value of the grid-connected inverter, is the reactive current reference value of the grid-connected inverter; In the case that the current active current reference value of the grid-connected inverter is less than the maximum limit of the active current reference value, determining the current active current reference value as the active current control loop reference value of the grid-connected inverter; When the current active current reference value of the grid-connected inverter is greater than or equal to the maximum limit value of the active current reference value, the maximum limit value of the active current reference value is determined as the active current control loop reference value of the grid-connected inverter.

6. The fault ride-through method according to claim 5, characterized in that: In the event of a low voltage fault in the new energy transmission system, the fault ride-through method further includes: Freezing the integral link of the proportional-integral controller of the grid-connected inverter so that the output of the integral link in the proportional-integral controller remains unchanged during the occurrence of a low voltage fault in the new energy transmission system; Switching the reactive power control mode of the grid-connected inverter from a target control mode to a constant reactive current control mode, wherein the target control mode includes one of the following: a constant reactive power control mode and an AC side voltage control mode; When the AC voltage drop depth of the grid-connected inverter is within the target voltage drop depth range, Determine whether the grid-connected inverter The target voltage drop depth range is composed of a voltage drop depth lower limit value and a voltage drop depth upper limit value, det U1 is the voltage drop depth lower limit value, det U2 is the voltage drop depth upper limit value, ΔU is the AC voltage drop depth of the grid-connected inverter, is the reactive current reference value of the grid-connected inverter, is the maximum reactive output current of the grid-connected inverter; In a case where the AC voltage drop depth of the grid-connected inverter is greater than the voltage drop depth upper limit value, determining the maximum reactive output current of the grid-connected inverter as the reactive current reference value of the grid-connected inverter; When the AC voltage drop depth of the grid-connected inverter is less than the voltage drop depth lower limit value, the reactive current reference value of the grid-connected inverter is determined to be 0.

7. The fault ride-through method according to any one of claims 4 to 6, characterized in that: The fault ride-through method further includes: When the voltage parameter of the grid-connected inverter no longer meets the preset conditions and the current active current value of the grid-connected inverter is restored to the target active current value, the reactive control mode of the grid-connected inverter is switched from the fixed reactive current control mode to the target control mode, and the active control mode of the grid-connected inverter is switched from the active current control mode to the fixed DC voltage control mode, wherein the preset conditions include one of the following: within a first delay time, the AC voltage of the grid-connected inverter is less than or equal to the AC low voltage threshold, within a second delay time, the DC voltage is greater than or equal to the DC overvoltage threshold, and the DC voltage change rate is greater than or equal to the DC voltage slope threshold, the target active current value is the active current value of the new energy transmission system before a low voltage fault occurs, and the target control mode includes one of the following: a fixed reactive power control mode and an AC side voltage control mode.

8. The fault ride-through method according to claim 1, characterized in that: At least according to a preset adjustment method, the new energy delivery system is adjusted, including: The integral coefficient of the AC voltage loop of the flexible DC system in the proportional-integral controller is reduced so that the integral speed of the proportional-integral controller of the flexible DC system is slowed down during a low voltage fault of the new energy transmission system.

9. The fault ride-through method according to claim 8, characterized in that: In the event of a low voltage fault in the new energy transmission system, the fault ride-through method further includes: According to the voltage drop degree of the AC system, adjusting the AC voltage outer loop reference value of the flexible DC system; use A positive-sequence d-axis voltage component reference value of the AC voltage of the flexible DC system is determined, wherein: is the reference value of the positive-sequence d-axis voltage component of the AC voltage of the flexible DC system, is the positive-sequence d-axis voltage component reference value of the AC voltage of the flexible DC system before a low voltage fault occurs in the renewable energy transmission system, is the negative sequence voltage amplitude of the AC voltage of the flexible DC system; The positive-sequence q-axis voltage component reference value, the negative-sequence d-axis voltage component reference value and the negative-sequence q-axis voltage component reference value of the AC voltage of the flexible DC system are all set to 0; The current of the flexible DC system is limited so that the positive-sequence d-axis current reference value of the current of the flexible DC system is less than or equal to the positive-sequence d-axis current limiting value, the positive-sequence q-axis current reference value is less than or equal to the positive-sequence q-axis current limiting value, the negative-sequence d-axis current reference value is less than or equal to the negative-sequence d-axis current limiting value, the negative-sequence q-axis current reference value is less than or equal to the negative-sequence q-axis current limiting value, and the positive and negative sequence dq-axis total current reference value is less than or equal to the total current reference threshold.

10. The fault ride-through method according to claim 8 or 9, characterized in that: The fault ride-through method further includes: When the new energy transmission system no longer has a low voltage fault within the fourth delay period, the integral coefficient of the AC voltage loop of the flexible DC system in the proportional-integral controller is restored to a target value, and the target value is the integral coefficient of the AC voltage loop of the flexible DC system in the proportional-integral controller before the new energy transmission system has a low voltage fault.

11. A fault ride-through device for a new energy transmission system, characterized in that: include: an acquisition unit, configured to acquire voltage parameters of the grid-connected inverter and the voltage of the AC system, wherein the voltage parameters include at least one of the following: the AC voltage of the grid-connected inverter, the DC voltage of the grid-connected inverter, and a DC voltage change rate, wherein the DC voltage change rate is determined according to the DC voltage of the grid-connected inverter, and the new energy transmission system includes the grid-connected inverter, the AC system, and the flexible DC system; A first determining unit, configured to determine whether a low voltage fault occurs in the new energy transmission system according to at least one of the voltage parameter and the voltage of the AC system; The first adjustment unit is used to adjust the new energy transmission system at least according to a preset adjustment method when a low voltage fault occurs in the new energy transmission system, so that the new energy transmission system can perform fault crossing within a predetermined time period. The preset adjustment method includes at least one of the following: adjusting the active current of the grid-connected inverter and adjusting the integral link of the flexible DC system.

12. A computer-readable storage medium, characterized in that: The computer-readable storage medium includes a stored program, wherein when the program is executed, the device where the computer-readable storage medium is located is controlled to execute the fault ride-through method of the new energy transmission system according to any one of claims 1 to 10.

13. An electronic device comprising a memory and a processor, characterized in that: The memory stores a computer program, and the processor is configured to execute the fault ride-through method of the new energy transmission system according to any one of claims 1 to 10 through the computer program.

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