Low frequency power transmission system starting method based on switch detection synchronization and storage medium

Abstract

The application provides a low-frequency power transmission system starting method based on switch synchronization detection and a storage medium. The low-frequency power transmission system comprises a plurality of frequency conversion stations, any one of the plurality of frequency conversion stations comprises a series-connected power frequency charging switch, a power frequency transformer, a matrix converter, a low-frequency transformer, a low-frequency line switch and a synchronization detection device; the starting method comprises: opening the low-frequency line switch; closing the power frequency charging switch, uncontrolled charging and controlled charging of the capacitor of the matrix converter; in response to the capacitor voltage of the matrix converter being stable, the frequency conversion station is unlocked after switching to a first running mode, and a rated low-frequency side voltage is generated; closing the low-frequency line switch of the first frequency conversion station in the plurality of frequency conversion stations, and generating a rated low-frequency voltage on the low-frequency line; controlling the first frequency conversion station to remain in the first running mode; closing the low-frequency line switch of the remaining frequency conversion stations based on the synchronization detection device; and controlling the remaining frequency conversion stations to switch to a second running mode.

Description

Technical Field

[0001] This application relates to the field of low-frequency power transmission, and more specifically, to a low-frequency power transmission system startup method and storage medium based on switch synchronization. Background Technology

[0002] Low-frequency power transmission systems based on full-bridge modular multilevel matrix converters (M3Cs) represent a novel power transmission method. By using M3C alternating current (AC) converters to transform industrial frequency AC into low-frequency AC for transmission, transmission efficiency is improved. In COSCO's offshore wind power transmission schemes, it is highly competitive because it eliminates the need for costly and complex offshore frequency conversion stations. Although low-frequency power transmission systems have enormous application potential, there are currently no reports of actual engineering projects based on M3C low-frequency power transmission technology being put into operation, both domestically and internationally. Further detailed and specific research on its application is still needed.

[0003] Current research on low-frequency transmission systems primarily focuses on steady-state operation control strategies and fault ride-through control strategies under transient operation. No relevant patent literature mentions startup strategies for complete low-frequency transmission systems. Startup strategies are essential in the engineering applications of low-frequency transmission systems; a reasonable startup strategy is crucial to ensuring system equipment safety and reducing the complexity of system startup.

[0004] For low-frequency power transmission systems, similar to the operation of DC power transmission, one frequency converter station controls and stabilizes the voltage of the low-frequency power grid, while other frequency converter stations control their respective transmitted power. Under this control strategy, low-frequency power transmission systems can achieve relatively stable power transmission. However, the startup of low-frequency power transmission systems differs from that of DC power transmission systems. The low-frequency system power after AC-AC conversion by the M3C converter is AC, and during startup, the DC-side switches cannot be directly closed to connect the two stations for power transmission. Instead, it is necessary to detect the synchronization of the line switches to connect the low-frequency lines between the two stations. Therefore, it is necessary to study a startup method for low-frequency power transmission systems based on switch synchronization to promote engineering applications.

[0005] The information disclosed in the background section is only intended to enhance the understanding of the background of this application, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0006] This application aims to provide a low-frequency power transmission system startup method and storage medium based on low-frequency line switch synchronization. A certain frequency converter station controls and stabilizes the voltage of the low-frequency power transmission network, uses a synchronization device to close the low-frequency line switch, and the remaining frequency converter stations switch their operating modes to power transmission modes, ultimately realizing the startup of the low-frequency power transmission system.

[0007] According to one aspect of this application, a startup method for a low-frequency power transmission system based on switch synchronization is proposed. The low-frequency power transmission system includes multiple frequency converter stations. The low-frequency sides of the multiple frequency converter stations are connected in parallel to the low-frequency power transmission network via low-frequency line switches, and the power frequency sides of the multiple frequency converter stations are connected to the power frequency power transmission network via power frequency charging switches. Each of the multiple frequency converter stations includes a power frequency charging switch, a power frequency transformer, a matrix converter, a low-frequency transformer, a low-frequency line switch, and a synchronization detection device connected in series. The startup method includes:

[0008] Disconnect the low-frequency line switch;

[0009] The power frequency charging switch is closed to enable both uncontrolled and controlled charging of the capacitors in the matrix converter.

[0010] In response to the stabilization of the capacitor voltage of the matrix converter, the frequency conversion station switches to the first operating mode and unlocks, generating the rated low-frequency side voltage.

[0011] The low-frequency line switch of the first frequency conversion station among the multiple frequency conversion stations is closed, and the low-frequency line generates the rated low-frequency voltage.

[0012] Control the first frequency converter to maintain the first operating mode;

[0013] Based on the aforementioned synchronization detection device, the remaining low-frequency line switch of the frequency converter station is closed.

[0014] Control the remaining frequency converters to switch to the second operating mode.

[0015] According to some embodiments, the matrix converter includes nine bridge arms, with three bridge arms per group; one end of each of the three bridge arms in the same group is connected to a three-phase power frequency side port, and the other end of each of the three bridge arms is connected to one phase of a low-frequency side port; the three groups of bridge arms are respectively connected to different phases of the low-frequency side port; each bridge arm includes a series-connected reactor and a full-bridge submodule.

[0016] According to some embodiments, the full-bridge submodule includes switching devices and the capacitor.

[0017] According to some embodiments, the conditions for stable capacitor voltage of the matrix converter include:

[0018] The average value of the capacitor voltage of each of the full-bridge submodules of the bridge arm is greater than or equal to the first capacitor voltage threshold.

[0019] The first capacitor voltage threshold is the rated voltage value of the converter submodule.

[0020] According to some embodiments, the remaining low-frequency line switch of the frequency converter station after closing includes:

[0021] By fixing the frequency difference on both sides of the low-frequency line switch, the control strategy shortens the synchronous closing cycle.

[0022] The actual delay of the synchronization device is checked and time compensation is performed.

[0023] According to some embodiments, controlling the remaining frequency converters to switch to the second operating mode includes:

[0024] Control the power of the low-frequency power transmission network to zero.

[0025] According to some embodiments, it further includes: controlling the power increase of the frequency converter station in the second operating mode;

[0026] The voltage amplitude and frequency of the low-frequency transmission network of the frequency converter station, which is in the first operating mode, are controlled to be at the rated voltage value.

[0027] According to some embodiments, controlling the first frequency converter to maintain the first operating mode includes:

[0028] The matrix converter is controlled to generate its own low-frequency side voltage, which includes adjustable frequency and amplitude.

[0029] According to some embodiments, controlling the remaining frequency converters to switch to the second operating mode includes:

[0030] The active and reactive power of the remaining low-frequency side of the frequency converter station are controlled, and the active and reactive power of the low-frequency side are adjustable within the rated range.

[0031] According to another aspect of this application, a computer-readable storage medium is provided, comprising:

[0032] The computer-readable storage medium stores a computer program;

[0033] When the computer program is executed by the processor, it implements the low-frequency power transmission system startup method based on switch synchronization as described in any of the preceding descriptions.

[0034] The technical solutions according to some embodiments of this application may have one or more of the following beneficial effects:

[0035] 1. During the startup process, the frequency converter station does not add any new operating modes, there are few switching of operating modes, the startup process is simple and reliable, and the user experience is strong;

[0036] 2. By adopting a fixed frequency difference and a synchronization device delay compensation control method, the impact of synchronous closing overcurrent can be reduced, ensuring the equipment safety of the low-frequency power transmission system.

[0037] 3. Only the control strategy during the startup of the low-frequency transmission system is changed, without adding any new hardware structure, making it highly usable on-site.

[0038] 4. It is suitable for low-frequency or frequency-division transmission projects, and is also suitable for two-terminal and multi-terminal projects, with strong adaptability.

[0039] It should be understood that the above general description and the following detailed description are merely exemplary and do not limit this application. Attached Figure Description

[0040] The above and other objects, features, and advantages of this application will become more apparent from the detailed description of exemplary embodiments with reference to the accompanying drawings. The drawings described below are merely some embodiments of this application and are not intended to limit the scope of this application.

[0041] Figure 1 A schematic diagram of a matrix converter structure is shown in an exemplary embodiment;

[0042] Figure 2 A flowchart illustrating an exemplary embodiment of a low-frequency transmission system startup method based on switch synchronization is shown.

[0043] Figure 3 A schematic diagram of a low-frequency power transmission system consisting of three frequency conversion stations is shown in an exemplary embodiment. Detailed Implementation

[0044] Exemplary embodiments will now be described more fully with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many forms and should not be construed as limited to the embodiments set forth herein; rather, they are provided so that this application will be thorough and complete, and will fully convey the concept of the exemplary embodiments to those skilled in the art. The same reference numerals in the drawings denote the same or similar parts, and therefore repeated descriptions of them will be omitted.

[0045] The described features, structures, or characteristics can be combined in any suitable manner in one or more embodiments. Numerous specific details are provided in the following description to give a full understanding of embodiments of this disclosure. However, those skilled in the art will recognize that the technical solutions of this disclosure can be practiced without one or more of these specific details, or other methods, components, materials, devices, etc. In these cases, well-known structures, methods, devices, implementations, materials, or operations will not be shown or described in detail.

[0046] The flowcharts shown in the accompanying drawings are merely illustrative and do not necessarily include all content and operations / steps, nor do they necessarily have to be performed in the described order. For example, some operations / steps can be broken down, while others can be combined or partially combined; therefore, the actual execution order may change depending on the specific circumstances.

[0047] The terms "first," "second," etc., in the specification, claims, and accompanying drawings of this application are used to distinguish different objects, not to describe a specific order. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to these processes, methods, products, or apparatuses.

[0048] Those skilled in the art will understand that the accompanying drawings are merely schematic diagrams of exemplary embodiments, and the modules or processes in the drawings are not necessarily essential for implementing this application, and therefore cannot be used to limit the scope of protection of this application.

[0049] This application applies to low-frequency or frequency-division transmission projects, and is applicable to both two-terminal and multi-terminal projects. The low-frequency transmission system includes N frequency converter stations, where N is an integer greater than or equal to 2, and n is the frequency converter station number (n = 1, 2, ..., N). The low-frequency side of the nth frequency converter station is connected to a low-frequency line switch QL. n The frequency converter is connected in parallel to a common low-frequency transmission network, and the power frequency side of the frequency converter station is connected via a power frequency charging switch (QC). n Each is connected to its respective power frequency transmission network; the frequency conversion station includes power frequency charging switches (QC) connected in series. n Power frequency transformer TG n M3C Matrix Converter n Low-frequency transformer TL n Low-frequency circuit switch QL n Synchronous detection device.

[0050] Figure 1 A schematic diagram of a matrix converter structure of an exemplary embodiment is shown.

[0051] like Figure 1 As shown, the matrix converter M3C n It includes 9 bridge arms; three bridge arms are divided into three groups; one end of each of the three bridge arms in the same group is connected to the three-phase power frequency side port, and the other end of the three bridge arms is connected to one phase of the low frequency side port. The three groups of bridge arms are connected to different phases of the low frequency side port respectively; each bridge arm includes a series reactor and multiple full-bridge sub-modules, and each full-bridge sub-module includes four switching devices and one capacitor.

[0052] According to an example embodiment, the matrix converter M3C n Including 9 bridge arms, SM au SM bu SM cu SM av SM bv SM cvSM aw SM bw SM cw Among them, SM au SM bu SM cu As one phase, SM au SM bu SM cu One end of each of the three bridge arms is connected to ports a, b, and c on the three-phase power frequency side, and the other end of each bridge arm is connected to one phase u on the low-frequency side port; SM av SM bv SM cv As one phase, SM av SM bv SM cv One end of each of the three bridge arms is connected to ports a, b, and c on the three-phase power frequency side, and the other end of each bridge arm is connected to one phase v of the low-frequency side port; SM aw SM bw SM cw As one phase, SM aw SM bw SM cw One end of each of the three bridge arms is connected to the three-phase power frequency side ports a, b, and c, respectively, and the other end of each of the three bridge arms is connected to one phase w of the low frequency side port.

[0053] According to the example embodiment, the full-bridge submodule includes four switching devices: two upper transistors and two lower transistors. The upper and lower transistors are connected in series and then in parallel with a capacitor. The midpoint of the series branch is led out and connected in series with the next submodule.

[0054] Figure 2 A flowchart illustrating an exemplary embodiment of a low-frequency transmission system startup method based on switch synchronization is provided.

[0055] S100: Disconnect the low-frequency line switches QL at each frequency converter station. n .

[0056] According to the example embodiment, the low-frequency line switch QL of each frequency converter station is disconnected. n Each frequency converter station is disconnected from the low-frequency power transmission network and electrically isolated from each other.

[0057] S200: QC switch for closing power frequency charging at each frequency converter station n .

[0058] According to the example embodiment, the power frequency charging switch QC of each frequency conversion station is closed. n Uncontrolled charging of the bridge arm capacitors is performed. After the uncontrolled charging of the module ends, it automatically switches to controlled charging of the module. The module includes all full-bridge sub-modules.

[0059] S300: Determine whether the average voltage of each bridge arm capacitor is stable.

[0060] According to some embodiments, the method for determining the stability of the bridge arm capacitor voltage of a frequency converter station is as follows: when the average value of the capacitor voltage of each bridge arm submodule is greater than or equal to a first capacitor voltage threshold, the bridge arm capacitor voltage of the frequency converter station is considered stable. Here, the first capacitor voltage threshold is the rated voltage value of the converter submodule.

[0061] According to the example embodiment, after the bridge arm capacitor voltage of all the frequency converter stations stabilizes, each frequency converter station switches to the first operating mode and is then unlocked.

[0062] According to some embodiments, the first operating mode is set as follows: control matrix converter M3C n Self-generated low-frequency side voltage, which includes adjustable frequency and amplitude.

[0063] S400: Determine whether the low-frequency side voltage of each frequency converter station has reached the rated value.

[0064] Once the average voltage of each bridge arm capacitor reaches the rated voltage of the converter submodule, the first operating mode is used to control the low-frequency side voltage of each frequency converter station.

[0065] S500: Close any low-frequency line switch QL at any frequency converter station n .

[0066] According to the example embodiment, after the low-frequency side voltage of each frequency converter station reaches the first rated voltage value, the low-frequency line switch QL of any frequency converter station is closed. n The low-frequency line generates the first rated voltage, and the frequency converter station maintains the first operating mode.

[0067] According to an example embodiment, the first rated voltage value can be automatically set based on the low-frequency transmission system based on switch synchronization.

[0068] S600: Close the low-frequency line switches QL of the remaining frequency converter stations. n .

[0069] According to an example embodiment, based on a low-frequency line switch synchronization device, based on the low-frequency line switch QL... n The voltage phase and amplitude on both sides, and the remaining low-frequency line switch QL at the frequency converter station after closing. n The synchronous closing cycle can be shortened by using a fixed frequency difference control strategy on both sides; considering the problem of synchronous closing overcurrent, the actual delay of the synchronizing device should be checked and time compensation should be performed to reduce the problem of synchronous closing overcurrent.

[0070] S700: The remaining frequency converters switch to the second operating mode to control the power on the low-frequency side.

[0071] According to the example embodiment, the remaining frequency converters will automatically switch to the second operating mode after the low-frequency line switch is closed, and control the low-frequency side to zero power.

[0072] According to some embodiments, the second operating mode is set to control the active power and reactive power of the remaining frequency converter on the low-frequency side, wherein the active power and reactive power on the low-frequency side are adjustable within the rated range.

[0073] After all frequency converters are interconnected, the frequency converters in the second operating mode will increase their power according to the instructions and then start up. Specifically, the frequency converters in the first operating mode control the voltage amplitude of the low-frequency transmission network to the rated amplitude value and the frequency to the rated frequency value, and control the active power and reactive power of the low-frequency transmission network to the commanded values.

[0074] In the startup method of this embodiment, each frequency converter station is charged and unlocked from the power frequency side, establishing a first rated voltage. The low-frequency line switch of any one frequency converter station is closed, generating the first rated voltage on the low-frequency line, and that frequency converter station maintains its first operating mode. Based on the low-frequency line switch synchronization device, the low-frequency line switches of the remaining frequency converter stations are closed. After the low-frequency line switches are closed, they automatically switch to a second operating mode and control zero power on the low-frequency side. After all frequency converter stations are interconnected, the frequency converter stations in the second operating mode increase their power according to instructions to complete the startup process.

[0075] Figure 3 A schematic diagram of a low-frequency power transmission system consisting of three frequency conversion stations is shown in an exemplary embodiment.

[0076] Figure 3 The diagram shows a low-frequency power transmission system consisting of three frequency converter stations. Frequency converter station 1 includes a power frequency charging switch QC1, a power frequency transformer TG1, a matrix converter M3C1, a low-frequency transformer TL1, and a low-frequency line switch QL1 connected in series. The low-frequency side of frequency converter station 1 is connected in parallel to a common low-frequency power transmission network via the low-frequency line switch QL1, and the power frequency side of frequency converter station 1 is connected to the power frequency transmission network S1 via the power frequency charging switch QC1. Frequency converter station 2 includes a power frequency charging switch QC2, a power frequency transformer TG2, a matrix converter M3C2, a low-frequency transformer TL2, and a low-frequency line switch QL2 connected in series. The low-frequency side of frequency converter station 2 is connected in parallel to a common low-frequency power transmission network via the low-frequency line switch QL2, and the power frequency side of frequency converter station 2 is connected to the power frequency transmission network S2 via the power frequency charging switch QC2. Frequency converter station 3 includes a power frequency charging switch QC3, a power frequency transformer TG3, a matrix converter M3C3, a low frequency transformer TL3, and a low frequency line switch QL3 connected in series. The low frequency side of frequency converter station 3 is connected in parallel to a common low frequency transmission network through the low frequency line switch QL3, and the power frequency side of frequency converter station 3 is connected to the power frequency transmission network S3 through the power frequency charging switch QC3.

[0077] The startup steps are as follows:

[0078] Disconnect the low-frequency line switches QL1, QL2 and QL3 of each frequency converter station; disconnect each frequency converter station from the low-frequency power transmission network and electrically isolate them from each other;

[0079] Close the power frequency charging switches QC1, QC2 and QC3 of each frequency conversion station to perform uncontrolled charging of the bridge arm capacitors. After the uncontrolled charging of the module is completed, it will automatically switch to controlled charging of the module.

[0080] After the capacitor voltage stabilizes, each frequency converter station switches to the first operating mode and then unlocks. The first operating mode is set to: control the capacitor voltage of each bridge arm at the rated voltage value of the converter submodule; control the matrix converter M3C. n The self-generated low-frequency side voltage includes adjustable frequency and amplitude. The capacitors of each bridge arm of M3C1 in control station 1 are charged to the rated voltage value of the converter submodule; the capacitors of each bridge arm of M3C2 in control station 2 are charged to the rated voltage value of the converter submodule; the capacitors of each bridge arm of M3C3 in control station 3 are charged to the rated voltage value of the converter submodule.

[0081] Once the low-frequency voltage of each frequency converter station reaches the first rated voltage, close the low-frequency line switch QL1 of any frequency converter station (taking frequency converter station 1 as an example). The low-frequency line will generate the first rated voltage, and the frequency converter station will maintain the first operating mode.

[0082] Based on the low-frequency line switch synchronization device, the low-frequency line switches QL2 and QL3 of frequency converter stations 2 and 3 are closed. After the low-frequency line switches are closed, frequency converter stations 2 and 3 automatically switch to the second operating mode and control the low-frequency side to zero power. The second operating mode is set as follows: controlling the active and reactive power of the remaining low-frequency side of the frequency converter stations, wherein the active and reactive power of the low-frequency side are adjustable within the rated range; and controlling the power of the low-frequency side according to the target command, wherein the power command is zero, including both active and reactive power.

[0083] After all frequency switching stations are interconnected, the frequency switching stations in the second operating mode will increase their power according to the instructions and then start up.

[0084] This application also provides a computer-readable storage medium storing a computer program, which, when executed by a processor, implements the steps of the above-described soft-start method for low-frequency power transmission systems.

[0085] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product embodied on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0086] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0087] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0088] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0089] It should be clearly understood that this application describes how specific examples are formed and used, but this application is not limited to any details of these examples. Rather, based on the teachings of the disclosure of this application, these principles can be applied to many other embodiments.

[0090] Furthermore, it should be noted that the above figures are merely illustrative representations of the processes included in the method according to exemplary embodiments of this application, and are not intended to be limiting. It is readily understood that the processes shown in the above figures do not indicate or limit the temporal order of these processes. Additionally, it is readily understood that these processes may be executed synchronously or asynchronously, for example, in multiple modules.

[0091] Exemplary embodiments of this application have been specifically shown and described above. It should be understood that this application is not limited to the detailed structures, arrangements, or implementation methods described herein; rather, this application is intended to cover various modifications and equivalent arrangements contained within the spirit and scope of the appended claims.

Claims

1. A method for starting a low-frequency power transmission system based on switch synchronization detection, wherein the low-frequency power transmission system includes multiple frequency converter stations, the low-frequency sides of the multiple frequency converter stations are connected in parallel to the low-frequency power transmission network via low-frequency line switches, and the power frequency sides of the multiple frequency converter stations are connected to the power frequency power transmission network via power frequency charging switches; each of the multiple frequency converter stations includes a power frequency charging switch, a power frequency transformer, a matrix converter, a low-frequency transformer, a low-frequency line switch, and a synchronization detection device connected in series; characterized in that, The startup method includes: Disconnect the low-frequency line switch; The power frequency charging switch is closed to enable both uncontrolled and controlled charging of the capacitors in the matrix converter. In response to the stabilization of the capacitor voltage of the matrix converter, the frequency conversion station switches to the first operating mode and unlocks, generating the rated low-frequency side voltage. The low-frequency line switch of the first frequency conversion station among the multiple frequency conversion stations is closed, and the low-frequency line generates the rated low-frequency voltage. Controlling the first frequency converter to maintain the first operating mode includes: The matrix converter is controlled to generate its own low-frequency side voltage, which includes adjustable frequency and amplitude. Based on the aforementioned synchronization detection device, the remaining low-frequency line switch of the frequency converter station is closed. Controlling the remaining frequency converters to switch to the second operating mode includes: Control the power of the low-frequency power transmission network to zero; The active and reactive power of the remaining low-frequency side of the frequency converter station are controlled, and the active and reactive power of the low-frequency side are adjustable within the rated range.

2. The startup method as described in claim 1, characterized in that, The matrix converter includes nine bridge arms, with three bridge arms per group; one end of each of the three bridge arms in the same group is connected to a three-phase power frequency side port, and the other end of each of the three bridge arms is connected to one phase of a low-frequency side port. The three groups of bridge arms are connected to different phases of the low-frequency side port respectively; each bridge arm includes a series-connected reactor and a full-bridge submodule.

3. The startup method as described in claim 2, characterized in that, The full-bridge submodule includes switching devices and the capacitor.

4. The startup method as described in claim 3, characterized in that, The conditions for stable capacitor voltage of the matrix converter include: The average value of the capacitor voltage of each of the full-bridge submodules of the bridge arm is greater than or equal to the first capacitor voltage threshold. The first capacitor voltage threshold is the rated voltage value of the converter submodule.

5. The startup method as described in claim 1, characterized in that, The remaining low-frequency line switch of the frequency converter station after closing includes: By fixing the frequency difference on both sides of the low-frequency line switch, the control strategy shortens the synchronous closing cycle. The actual delay of the synchronization device is checked and time compensation is performed.

6. The startup method as described in claim 1, further comprising: Control the power increase of the frequency converter station in the second operating mode; The voltage amplitude and frequency of the low-frequency transmission network of the frequency converter station, which is in the first operating mode, are controlled to be at the rated voltage value.

7. A computer-readable storage medium, characterized in that, include: The computer-readable storage medium stores a computer program; When the computer program is executed by the processor, it implements the low-frequency power transmission system startup method based on switch synchronization as described in any one of claims 1 to 6.

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