Starting control method and system for actively reducing low-frequency line closing current

Abstract

The application provides a low-frequency power transmission network, a starting control method and system for reducing low-frequency line closing current, and is used for a low-frequency power transmission network comprising at least two frequency conversion stations, and comprises a low-frequency line switch of the frequency conversion station; a power frequency network connection switch of the frequency conversion station is closed, and the capacitor of the full-bridge submodule is charged from the power frequency side; after the capacitor voltage is stabilized, the modular multi-level matrix converter of the frequency conversion station is unlocked and operated in an independent operation mode; after the low-frequency voltage of the frequency conversion station drops to zero, the low-frequency line switch is closed; one of the frequency conversion stations is switched to a low-frequency voltage control mode, and the low-frequency voltage thereof is restored to a rated value, so that the low-frequency voltage is kept stable; the other frequency conversion stations are switched to a power control mode, and the low-frequency side zero power is controlled, and when the low-frequency voltage is restored to the rated value, the power is raised or lowered to the instructed value according to the power instruction. According to the embodiments, the low-frequency line closing current can be reduced, and the low-frequency power transmission system can be started quickly, safely and smoothly.

Description

Technical Field

[0001] This application relates to a method for actively reducing the closing current of low-frequency lines. More specifically, it relates to a starting control method and system for actively reducing the closing current of low-frequency lines in a low-frequency transmission network. Background Technology

[0002] With the rapid development of offshore wind power, long-distance transmission and grid connection technologies for large-capacity offshore wind power have become a major focus. Low-frequency transmission technology based on Modular Multilevel Matrix Converter (M3C), through AC / AC conversion, offers advantages over power frequency AC and DC transmission in medium- to long-distance offshore wind power transmission, including better economic efficiency and operational stability, thus attracting significant attention and competitiveness.

[0003] Low-frequency power transmission networks built using low-frequency power transmission technology are mainly used in scenarios such as onshore new energy aggregation and transmission, multi-island interconnection, and long-distance power transmission in remote areas. They have good application prospects for the grid connection and transmission of distributed new energy in the future.

[0004] Low-frequency transmission networks contain two or more frequency converters. Since both sides of each frequency converter are AC systems, the operation of the low-frequency transmission network requires each frequency converter to have a consistent and stable low-frequency voltage during normal operation. Therefore, it is necessary to select one frequency converter to control and establish the low-frequency voltage, while the other frequency converters control the active and reactive power they transmit, thereby achieving stable power transmission and stable system operation.

[0005] During the startup phase of a low-frequency transmission network, each frequency converter station needs to charge and unlock its respective M3C converter. At this time, the low-frequency side voltages of each station are not consistent. To avoid large voltage and current fluctuations and system stability issues when closing low-frequency line switches, synchronization can be monitored to complete the closing process. However, this method requires additional switch synchronization devices, increasing control complexity and potentially causing overvoltage and overcurrent problems, which can negatively impact equipment operation.

[0006] Therefore, researching a low-frequency network start-up control method that can reduce the closing current of low-frequency lines is of great significance for the engineering application of low-frequency power transmission technology. Summary of the Invention

[0007] This application provides a startup control method and system for low-frequency transmission networks that actively reduces the closing current of low-frequency lines, in order to solve problems such as large voltage and current fluctuations and system stability during the closing of low-frequency line switches.

[0008] According to one aspect of this application, a low-frequency power transmission network is proposed, the low-frequency power transmission network comprising at least two frequency converter stations, each frequency converter station comprising a modular multilevel matrix converter; a power frequency connection transformer connected to the power frequency side of the modular multilevel matrix converter; a power frequency network connection switch connected between the power frequency grid and the power frequency connection transformer; a low-frequency connection transformer connected to the low-frequency side of the modular multilevel matrix converter; and a low-frequency line switch connected between the low-frequency power transmission network and the low-frequency connection transformer.

[0009] According to some embodiments, the modular multilevel matrix converter includes multiple bridge arms, each bridge arm including a bridge arm reactor and at least one full-bridge submodule, the bridge arm reactor and the at least one full-bridge submodule being connected in series, and the full-bridge submodule including a switching device H-bridge and a capacitor.

[0010] According to one aspect of this application, a startup control method for actively reducing the closing current of low-frequency lines is provided for a low-frequency transmission network as described above. The startup control method includes disconnecting the low-frequency line switch of the frequency converter station; closing the power frequency network connection switch of the frequency converter station, thereby charging the capacitor of the full-bridge submodule from the power frequency side; after the capacitor voltage stabilizes, unlocking and operating the modular multilevel matrix converter of the frequency converter station in an independent operation mode; closing the low-frequency line switch after the low-frequency voltage of the frequency converter station drops to zero; switching one of the frequency converter stations to a low-frequency voltage control mode and restoring its low-frequency voltage to the rated value, and controlling its low-frequency voltage to remain stable; switching the other frequency converter stations to a power control mode, controlling their low-frequency side to zero power, and when their low-frequency voltage recovers to the rated value, adjusting the power to the command value according to the active power and reactive power commands.

[0011] According to some embodiments, the criteria for determining that the capacitor voltage is stable are as follows:

[0012] U c_mean ×2N>U F_L

[0013] Among them, U c _ mean It is the average capacitor voltage of multiple arms of the modular multilevel matrix converter of the frequency converter station, where N is the number of full-bridge submodules in each arm, and U is the average capacitor voltage of the multiple arms of the modular multilevel matrix converter of the frequency converter station. F_L It is the power frequency line voltage of the modular multilevel matrix converter of the frequency converter station.

[0014] According to some embodiments, the step of unlocking the frequency converter to operate in an independent mode includes unlocking the modular multilevel matrix converter of the frequency converter to operate, establishing a rated low-frequency voltage, and increasing the capacitor voltage of each bridge arm to the rated value by controlling the circulating current in the bridge arm, and maintaining stability.

[0015] According to some embodiments, switching one of the frequency converters to a low-frequency voltage control mode includes controlling the circulating current in the bridge arm of the one frequency converter to maintain the capacitor voltage of each bridge arm of the one frequency converter stable; and controlling the low-frequency voltage output by the modular multilevel matrix converter in the one frequency converter to have an adjustable low-frequency frequency and low-frequency voltage amplitude, wherein the low-frequency frequency varies between zero and the power frequency, and the low-frequency voltage amplitude varies between zero and the rated value.

[0016] According to some embodiments, switching other frequency converters to power control mode includes controlling the circulating current in the bridge arms of the other frequency converters to maintain the stability of the capacitor voltage of each bridge arm submodule of the other frequency converters; and controlling the low-frequency active power and reactive power output of the modular multilevel matrix converter of the other frequency converters to reach the commanded value, wherein the commanded value is between zero and the rated value.

[0017] According to one aspect of this application, a startup control system for actively reducing the closing current of low-frequency lines is proposed for use in the low-frequency transmission network as described above. The startup control system comprises: a signal acquisition module for acquiring electrical analog and switching quantities of the frequency converter and the low-frequency transmission network; a bridge arm submodule capacitor charging control module for controlling the capacitor charging operation of the frequency converter and determining whether the capacitor voltage is stable; an independent operation control module for controlling the unlocked operation of the modular multilevel matrix converter of the frequency converter and increasing the capacitor voltage to a rated value and maintaining stability by controlling the circulating current in each bridge arm of the frequency converter; a low-frequency voltage control module for controlling the circulating current in the bridge arms of the frequency converter to maintain the capacitor voltage of each bridge arm stable and controlling the output frequency and amplitude of the modular multilevel matrix converter of the frequency converter to achieve an adjustable low-frequency voltage; and a power control module for controlling the circulating current in the bridge arms of the frequency converter to maintain the capacitor voltage of each bridge arm stable and controlling the low-frequency active and reactive power output of the modular multilevel matrix converter of the frequency converter to reach the commanded values.

[0018] According to some embodiments, the electrical analog quantities and switching quantities include the capacitor voltage of the bridge arm, low-frequency voltage, bridge arm current, active power, reactive power, power frequency network connection switch opening and closing signals and / or low-frequency line switch opening and closing signals.

[0019] According to some embodiments, after receiving a capacitor charging command, the bridge arm submodule capacitor charging control module closes the power frequency network connection switch of the frequency converter station to charge the bridge arm submodule capacitor from the power frequency side, and determines whether the submodule capacitor voltage is stable. The criteria for determining whether the capacitor voltage is stable are as follows:

[0020] U c_mean ×2N>U F_L

[0021] Among them, U c_mean It is the average capacitor voltage of multiple arms of the modular multilevel matrix converter of the frequency converter station, where N is the number of full-bridge submodules in each arm, and U is the average capacitor voltage of the multiple arms of the modular multilevel matrix converter of the frequency converter station. F_L It is the power frequency line voltage of the modular multilevel matrix converter of the frequency converter station.

[0022] According to one aspect of this application, a startup control system for actively reducing the closing current of low-frequency lines is proposed. The startup control system includes one or more processors; a storage device for storing one or more programs; when the one or more programs are executed by the one or more processors, the one or more processors implement the method as described above.

[0023] According to some example embodiments of this application, the startup process of a low-frequency power transmission system can be completed without adding a low-frequency switching synchronizing device, and the voltage of the low-frequency power transmission network can be established quickly. At the same time, the impact of the startup process on the system is reduced, the safety of the system equipment is ensured, and it has the conditions for engineering application. It can be applied to low-frequency and frequency-division power transmission projects and is suitable for two-end and multi-end system applications. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below.

[0025] Figure 1 A diagram of a low-frequency power transmission network structure according to an example embodiment of this application is shown.

[0026] Figure 2 A schematic diagram of a modular multilevel matrix converter structure according to an example embodiment of this application is shown.

[0027] Figure 3 The flowchart illustrates a startup control method for actively reducing the closing current of a low-frequency line according to an example embodiment of this application.

[0028] Figure 4 A flowchart of a startup control method for actively reducing the closing current of a low-frequency line according to an example embodiment of this application is shown.

[0029] Figure 5 A block diagram of a startup control system for actively reducing low-frequency line closing current is shown according to an example embodiment of this application.

[0030] Figure 6 This diagram illustrates a startup control system for actively reducing low-frequency line closing current according to an example embodiment of this application.

[0031] Figure 7This diagram illustrates another active low-frequency line closing current reduction start-up control system block diagram according to an example embodiment of this application. Detailed Implementation

[0032] 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.

[0033] 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, apparatus, or operations may be employed. In these cases, well-known structures, methods, apparatuses, implementations, materials, or operations will not be shown or described in detail.

[0034] The flowcharts shown in the accompanying drawings are merely illustrative and do not necessarily include all content and operations / steps, nor do they necessarily need 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.

[0035] 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.

[0036] Figure 1 A diagram of a low-frequency power transmission network structure according to an example embodiment of this application is shown. The following is in conjunction with… Figure 1 Taking a low-frequency power transmission network containing three frequency converter stations as an example, a low-frequency power transmission network according to an example embodiment of this application will be described in detail.

[0037] like Figure 1 The low-frequency power transmission network shown includes frequency converter 1, frequency converter 2, and frequency converter 3. Frequency converter 1 is connected to the power frequency grid S1, frequency converter 2 is connected to the power frequency grid S2, and frequency converter 3 is connected to the power frequency grid S3. Figure 1 As shown, frequency converter 1 includes a power frequency network connection switch QF1, a power frequency connection transformer TF1, a modular multilevel matrix converter M3C1, a low-frequency connection transformer TL1, and a low-frequency line switch QL1; frequency converter 2 includes a power frequency network connection switch QF2, a power frequency connection transformer TF2, a modular multilevel matrix converter M3C2, a low-frequency connection transformer TL2, and a low-frequency line switch QL2; frequency converter 3 includes a power frequency network connection switch QF3, a power frequency connection transformer TF3, a modular multilevel matrix converter M3C3, a low-frequency connection transformer TL3, and a low-frequency line switch QL3.

[0038] Figure 2 A schematic diagram of a modular multilevel matrix converter structure according to an example embodiment of this application is shown. Figure 2 As shown, the modular multilevel matrix converter consists of nine bridge arms connected in parallel. Each bridge arm comprises a bridge arm reactor and N full-bridge submodules connected in series. Each full-bridge submodule consists of a switching device (H-bridge) and a capacitor, and its connection method is as follows: Figure 2 As shown.

[0039] Figure 3 A flowchart illustrating a method for actively reducing the closing current of a low-frequency line according to an example embodiment of this application is shown below. Figure 3 Taking an example, a method for actively reducing the closing current of a low-frequency line according to an example embodiment of this application will be described in detail.

[0040] According to some example embodiments of this application, such as Figure 3 The method shown is applicable to low-frequency transmission networks, which include at least two such networks. Figure 1 The frequency converter station is shown. According to some embodiments, the modular multilevel matrix converter in the frequency converter station includes, as shown... Figure 2 The circuit structure shown is shown.

[0041] like Figure 3 As shown, in step S301, the low-frequency line switch of the frequency converter station is disconnected, and the low-frequency power transmission system network is shut down.

[0042] In step S303, the power frequency network connection switch of the frequency converter station is closed, and the capacitor of the bridge arm submodule is charged from the power frequency side.

[0043] In step S305, it is determined whether the capacitor voltage of the bridge arm submodule is stable. After the capacitor voltage is stable, each frequency converter station is unlocked and operated in independent operation mode.

[0044] According to some example embodiments of this application, the stability of the capacitor voltage of the bridge arm submodule is determined by formula (1).

[0045] U c_mean ×2N>UF_L (1)

[0046] Among them, U c_mean It represents the average capacitor voltage of multiple arms of the modular multilevel matrix converter in each frequency converter station, where N is the number of full-bridge submodules in each arm, and U... F_L It is the power frequency line voltage of the modular multilevel matrix converter in the frequency converter station.

[0047] According to some example embodiments of this application, unlocking and operating each frequency converter in an independent operation mode includes unlocking and operating the modular multilevel matrix converter, establishing a rated low-frequency voltage, and increasing the capacitor voltage of each bridge arm submodule to the rated value and maintaining stability by controlling the circulating current in the bridge arm.

[0048] In step S307, after the low-frequency voltage of the frequency converter station drops to zero, the low-frequency line switch is closed.

[0049] According to some embodiments, in step S307, before closing the low-frequency line switch, each frequency converter station remains unlocked and quickly reduces the low-frequency voltage to zero, and then quickly closes the switch.

[0050] In step S309, one of the frequency converters is switched to low-frequency voltage control mode, its low-frequency voltage is restored to the rated value, and its low-frequency voltage is controlled to remain stable.

[0051] According to some example embodiments of this application, switching one of the frequency converters to a low-frequency voltage control mode includes controlling the circulating current in the bridge arm of the selected frequency converter in step S309 to maintain the capacitor voltage of each bridge arm of the frequency converter stable. The low-frequency voltage output by the modular multilevel matrix converter in the frequency converter is controlled to have both an adjustable low-frequency frequency and an adjustable low-frequency voltage amplitude. The low-frequency frequency varies between zero and the power frequency, and the low-frequency voltage amplitude varies between zero and the rated voltage, i.e., the rated low-frequency voltage established in step S305.

[0052] According to some embodiments, the frequency converter that has switched to low-frequency voltage control mode can quickly restore the low-frequency voltage to the rated value in seconds and control the low-frequency voltage to remain stable.

[0053] In step S311, other frequency converters are switched to power control mode, and their low-frequency side is controlled to zero power. When their low-frequency voltage recovers to the rated value, the power is increased or decreased to the command value according to the active power and reactive power commands.

[0054] According to some example embodiments of this application, switching other frequency converters to power control mode includes controlling the circulating current in the bridge arms of the frequency converters not selected in step 309 to maintain the stability of the capacitor voltages of each bridge arm submodule. It also controls the low-frequency side active and reactive power output of their modular multilevel matrix converters to reach the commanded values.

[0055] According to some embodiments, the command value can be preset. The command value ranges from zero to the rated value, that is, the rated low-frequency voltage established in step S305.

[0056] Figure 4 A flowchart of a startup control method for actively reducing the closing current of a low-frequency line according to an example embodiment of this application is shown below. Figure 1 Taking a low-frequency power transmission network as an example, for Figure 4 A detailed description is provided of a startup control method for actively reducing the closing current of low-frequency lines.

[0057] like Figure 4 As shown, in S401, the low-frequency power transmission system network is shut down, i.e. disconnected. Figure 1 The low-frequency line switches QL1, QL2, and QL3 of each frequency converter station in the low-frequency transmission network.

[0058] In S403, the bridge arm submodule capacitor is charged, that is, closed. Figure 1 The three frequency converters, namely frequency converter 1 (QF1), frequency converter 2 (QF2), and frequency converter 3 (QF3), charge the capacitors of the bridge arm submodule from the power frequency side.

[0059] In S405, each frequency converter station operates independently.

[0060] Using the method shown in formula (1), after the bridge arm capacitor voltage is stable, the three frequency converters are unlocked and run in independent operation mode. By controlling the circulating current in the bridge arm, the capacitor voltage of each bridge arm sub-module is increased to the rated value and kept stable.

[0061] In S407, each frequency converter station reduces voltage and closes the circuit breaker.

[0062] In this step, before closing the low-frequency line switch, the three frequency converters remain unlocked and the low-frequency voltage of the three frequency converters is quickly reduced to zero, and then the switch is quickly closed.

[0063] In S409, each frequency converter station switches control modes. For example, after the low-frequency switches QL1, QL2, and QL3 of frequency converter station 1, frequency converter station 2, and frequency converter station 3 are closed, frequency converter station 1 is switched to low-frequency voltage control mode, and frequency converter station 2 and frequency converter station 3 are switched to power control mode.

[0064] In S411, establish the rated low-frequency voltage.

[0065] When a frequency converter switches to low-frequency voltage control mode, it can quickly restore the low-frequency voltage to the rated value within seconds and keep the low-frequency voltage stable.

[0066] In S413, the power of the low-frequency transmission network is increased.

[0067] For example, for frequency converter station 1, by controlling the circulating current in the bridge arm, the capacitor voltage of each bridge arm submodule is kept stable. Simultaneously, the low-frequency voltage output by M3C1, with adjustable frequency and amplitude, is controlled to establish the low-frequency transmission network voltage at a rate of seconds, quickly reaching the rated value from zero. The amplitude and frequency of the low-frequency transmission network voltage are then controlled to remain at their rated values, thus rapidly restoring the low-frequency voltage to its rated value. For frequency converter stations 2 and 3, by controlling the circulating current in the bridge arm, the capacitor voltage of each bridge arm submodule is kept stable. The active and reactive power outputs on the low-frequency side by M3C2 and M3C3 are controlled to reach the commanded values. Before the low-frequency transmission network voltage reaches its rated value, it operates under a zero-power command; after the low-frequency transmission network voltage reaches its rated value, the active and reactive power are adjusted according to the power command, completing the startup process.

[0068] Figure 5 A block diagram of a startup control system for actively reducing low-frequency line closing current is shown according to an example embodiment of this application.

[0069] According to some embodiments, such as Figure 5 The illustrated starting control system for actively reducing the closing current of low-frequency lines is used in low-frequency transmission networks, which include at least two such systems. Figure 1 The frequency converter station shown.

[0070] like Figure 5 As shown, the start-up control system includes a signal acquisition module 601, a bridge arm submodule capacitor charging control module 603, an independent operation control module 605, a low-frequency voltage control module 607, and a power control module 609. The signal acquisition module 601 acquires electrical analog and switching quantities from the frequency converter station and the low-frequency transmission network. The bridge arm submodule capacitor charging control module 603 controls the capacitor charging operation of the frequency converter station and determines whether the capacitor voltage is stable. The independent operation control module 605 controls the unlocking and operation of the modular multilevel matrix converter of the frequency converter station, and... The low-frequency voltage control module 607 controls the circulating current in each bridge arm of the frequency converter station to increase the capacitor voltage to a preset rated value and maintain stability. It also controls the output frequency and amplitude of the modular multilevel matrix converter of the frequency converter station to provide an adjustable low-frequency voltage. The power control module 609 controls the circulating current in each bridge arm of the frequency converter station to maintain the capacitor voltage of each bridge arm and controls the low-frequency active power and reactive power output of the modular multilevel matrix converter of the frequency converter station to reach the preset command values.

[0071] According to some embodiments of this application, electrical analog quantities and switching quantities include bridge arm capacitor voltage, low-frequency voltage, bridge arm current, active power, reactive power, power frequency network connection switch opening and closing signals and / or low-frequency line switch opening and closing signals.

[0072] According to some embodiments, after receiving the capacitor charging command, the bridge arm submodule capacitor charging control module closes the power frequency network connection switch of the frequency converter station and charges the bridge arm submodule capacitor from the power frequency side. The submodule capacitor voltage is determined by formula (1).

[0073] Figure 6 This diagram illustrates a startup control system for actively reducing low-frequency line closing current according to an example embodiment of this application. The following is an example... Figure 6 Taking an example, the working process of each module in a starting control system for actively reducing the closing current of a low-frequency line according to an example embodiment of this application will be described in detail.

[0074] like Figure 6 The low-frequency transmission network shown includes a signal acquisition module, a bridge arm submodule capacitor charging control module, an independent operation control module, a low-frequency voltage control module, and a power control module. Among them:

[0075] The signal acquisition module acquires various electrical analog and switching quantities from each frequency converter station and low-frequency transmission network. The signals acquired by the signal acquisition module include, but are not limited to, bridge arm submodule capacitor voltage, low-frequency voltage, bridge arm current, active power, reactive power, power frequency network connection switch opening and closing signals, and low-frequency line switch opening and closing signals.

[0076] The bridge arm submodule capacitor charging control module is used to control the capacitor charging operation of the full bridge submodule and to use formula (1) to determine whether the submodule capacitor voltage is stable.

[0077] According to some embodiments, after receiving a capacitor charging command, the bridge arm submodule capacitor charging control module closes the inverter station power frequency network connection switch to charge the bridge arm submodule capacitor from the power frequency side, and determines whether the submodule capacitor voltage is stable based on the aforementioned criteria for stable bridge arm submodule capacitor voltage.

[0078] The independent operation control module is used to control the modular multilevel matrix converter of the frequency converter station to unlock and operate, establish the rated low-frequency voltage, and increase the capacitor voltage in each bridge arm sub-module to the rated value and maintain stability by controlling the circulating current in the bridge arm.

[0079] The low-frequency voltage control module is used to maintain the stability of the capacitor voltage in each bridge arm submodule by controlling the circulating current in the bridge arm, and to control the output low-frequency voltage of the modular multilevel matrix converter in the frequency converter station, which has adjustable frequency and amplitude.

[0080] The power control module is used to maintain the stability of the capacitor voltage of each bridge arm submodule by controlling the circulating current in the bridge arm of the frequency converter station, and to control the low-frequency active power and reactive power output of the modular multilevel matrix converter of the frequency converter station to reach the command value.

[0081] Figure 7 This diagram illustrates another active low-frequency line closing current reduction start-up control system block diagram according to an example embodiment of this application.

[0082] The following reference Figure 7 To describe a start-up control system 200 according to this embodiment of the present application. Figure 7 The start control system 200 shown is merely an example and should not impose any limitations on the functionality and scope of use of the embodiments of this application.

[0083] like Figure 7 As shown, the start control system 200 is represented in the form of a general-purpose computing device. The components of the analog device 200 may include, but are not limited to: at least one processing unit 210, at least one storage unit 220, a bus 230 connecting different system components (including storage unit 220 and processing unit 210), a display unit 240, etc.

[0084] The storage unit stores program code, which can be executed by the processing unit 210 to perform the methods described in this specification according to various exemplary embodiments of this application. For example, the processing unit 210 can perform, for example... Figure 1 The method shown.

[0085] Storage unit 220 may include readable media in the form of volatile storage units, such as random access memory (RAM) 2201 and / or cache memory 2202, and may further include read-only memory (ROM) 2203.

[0086] Storage unit 220 may also include a program / utility 2204 having a set (at least one) program module 2205, such program module 2205 including but not limited to: operating system, one or more application programs, other program modules and program data, each or some combination of these examples may include an implementation of a network environment.

[0087] Bus 230 can represent one or more of several types of bus structures, including a memory cell bus or memory cell controller, a peripheral bus, a graphics acceleration port, a processing unit, or a local bus using any of the various bus structures.

[0088] The simulation device 200 can also communicate with one or more external devices 300 (e.g., keyboard, pointing device, Bluetooth device, etc.), one or more devices that enable a user to interact with the simulation device 200, and / or any device that enables the simulation device 200 to communicate with one or more other computing devices (e.g., router, modem, etc.). This communication can be performed via input / output (I / O) interface 250. Furthermore, the simulation device 200 can also communicate with one or more networks (e.g., local area network (LAN), wide area network (WAN), and / or public networks, such as the Internet) via network adapter 260. Network adapter 260 can communicate with other modules of the simulation device 200 via bus 230. It should be understood that, although not shown in the figures, other hardware and / or software modules can be used in conjunction with the simulation device 200, including but not limited to: microcode, device drivers, redundant processing units, external disk drive arrays, RAID systems, tape drives, and data backup storage systems.

[0089] Through the above description of the embodiments, those skilled in the art will readily understand that the exemplary embodiments described herein can be implemented by software or by combining software with necessary hardware. The technical solutions according to the embodiments of this application can be embodied in the form of a software product, which can be stored in a non-volatile storage medium (such as a CD-ROM, USB flash drive, external hard drive, etc.) or on a network, including several instructions to cause a computing device (such as a personal computer, server, or network device, etc.) to execute the methods described above according to the embodiments of this application.

[0090] Software products may employ any combination of one or more readable media. A readable medium may be a readable signal medium or a readable storage medium. A readable storage medium may be, for example,, but not limited to, an electrical, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any combination thereof. More specific examples of readable storage media (a non-exhaustive list) include: electrical connections with one or more wires, portable disks, hard disks, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), optical fiber, portable compact disk read-only memory (CD-ROM), optical storage devices, magnetic storage devices, or any suitable combination thereof.

[0091] Computer-readable storage media may include data signals propagated in baseband or as part of a carrier wave, carrying readable program code. Such propagated data signals may take various forms, including but not limited to electromagnetic signals, optical signals, or any suitable combination thereof. A readable storage medium may also be any readable medium other than a readable storage medium that can transmit, propagate, or transfer a program for use by or in connection with an instruction execution system, apparatus, or device. The program code contained on the readable storage medium may be transmitted using any suitable medium, including but not limited to wireless, wired, optical fiber, RF, etc., or any suitable combination thereof.

[0092] Program code for performing the operations of this application can be written in any combination of one or more programming languages, including object-oriented programming languages ​​such as Java and C++, and conventional procedural programming languages ​​such as C or similar languages. The program code can execute entirely on the user's computing device, partially on the user's computing device, as a standalone software package, partially on the user's computing device and partially on a remote computing device, or entirely on a remote computing device or server. In cases involving remote computing devices, the remote computing device can be connected to the user's computing device via any type of network, including a local area network (LAN) or a wide area network (WAN), or it can be connected to an external computing device (e.g., via the Internet using an Internet service provider).

[0093] The aforementioned computer-readable medium carries one or more programs, which, when executed by a device, cause the computer-readable medium to perform the aforementioned functions.

[0094] Those skilled in the art will understand that the above modules can be distributed in the device as described in the embodiments, or they can be modified accordingly and placed in one or more devices that are unique to this embodiment. The modules in the above embodiments can be combined into one module, or they can be further divided into multiple sub-modules.

[0095] According to some example embodiments of this application, the startup process of a low-frequency power transmission system can be completed without adding a low-frequency switching synchronizing device, and the voltage of the low-frequency power transmission network can be established quickly. At the same time, the impact of the startup process on the system is reduced, the safety of the system equipment is ensured, and it has the conditions for engineering application. It can be applied to low-frequency and frequency-division power transmission projects and is suitable for two-end and multi-end system applications.

[0096] The embodiments of this application have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the embodiments above are only for the purpose of helping to understand the method and core ideas of this application. Furthermore, any changes or modifications made by those skilled in the art based on the ideas of this application, and on the specific implementation methods and application scope of this application, are all within the scope of protection of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A starting control method for actively reducing the closing current of low-frequency lines, characterized in that, For use in low-frequency power transmission networks, the low-frequency power transmission network comprising at least two frequency converter stations, the frequency converter stations comprising: Modular multilevel matrix converter; A power frequency connection transformer is connected to the power frequency side of the modular multilevel matrix converter; A power frequency network connection switch is connected between the power frequency power grid and the power frequency connection transformer; A low-frequency connection transformer is connected to the low-frequency side of the modular multilevel matrix converter. A low-frequency line switch is connected between the low-frequency transmission network and the low-frequency connecting transformer; and... The modular multilevel matrix converter includes multiple bridge arms, each bridge arm comprising a bridge arm reactor and at least one full-bridge submodule. The bridge arm reactor and the at least one full-bridge submodule are connected in series. The full-bridge submodule includes an H-bridge switching device and a capacitor. The startup control method includes: Disconnect the low-frequency line switch of the frequency converter station; Close the power frequency network connection switch of the aforementioned frequency converter station, thereby charging the capacitor of the full-bridge submodule from the power frequency side; After the capacitor voltage stabilizes, the modular multilevel matrix converter of the frequency converter station is unlocked and operated in independent operation mode. After the low-frequency voltage at the frequency converter station drops to zero, the low-frequency line switch is closed. Switch one of the frequency converters to low-frequency voltage control mode, restore its low-frequency voltage to the rated value, and control its low-frequency voltage to remain stable; Switch other frequency converters to power control mode, control their low-frequency side to zero power, and when their low-frequency voltage recovers to the rated value, adjust the power to the command value according to the active power and reactive power commands.

2. The start-up control method according to claim 1, characterized in that, The criteria for determining that the capacitor voltage is stable are as follows: in, U c_mean It is the average capacitor voltage of multiple arms of the modular multilevel matrix converter of the frequency converter station. N The number of full-bridge submodules for each bridge arm. U F_L It is the power frequency line voltage of the modular multilevel matrix converter of the frequency converter station.

3. The start-up control method according to claim 1, characterized in that, The step of unlocking the frequency converter station to operate in independent mode includes: Unlock and operate the modular multilevel matrix converter of the frequency converter station to establish the rated low-frequency voltage. By controlling the circulating current in the bridge arms, the capacitor voltage of each bridge arm is increased to the rated value and kept stable.

4. The start-up control method according to claim 1, characterized in that, The step of switching one of the frequency converter stations to low-frequency voltage control mode includes: Control the circulating current in one of the bridge arms of the frequency converter station to keep the capacitor voltage of each bridge arm of the frequency converter station stable; The low-frequency voltage output by the modular multilevel matrix converter in one of the frequency converter stations is adjustable in both frequency and amplitude, wherein the low-frequency frequency varies between zero and the power frequency, and the low-frequency voltage amplitude varies between zero and the rated value.

5. The start-up control method according to claim 1, characterized in that, Switching other frequency converter stations to power control mode includes: Control the circulating current in the bridge arms of the other frequency converter stations to keep the capacitor voltage of each bridge arm submodule of the other frequency converter stations stable; The active and reactive power output of the modular multilevel matrix converter of the other frequency conversion station is controlled to reach the commanded value, which is between zero and the rated value.

6. A starting control system for actively reducing the closing current of low-frequency lines, characterized in that, For use in low-frequency power transmission networks, the low-frequency power transmission network comprising at least two frequency converter stations, the frequency converter stations comprising: Modular multilevel matrix converter; A power frequency connection transformer is connected to the power frequency side of the modular multilevel matrix converter; A power frequency network connection switch is connected between the power frequency power grid and the power frequency connection transformer; A low-frequency connection transformer is connected to the low-frequency side of the modular multilevel matrix converter. A low-frequency line switch is connected between the low-frequency transmission network and the low-frequency connecting transformer; and... The modular multilevel matrix converter includes multiple bridge arms, each bridge arm comprising a bridge arm reactor and at least one full-bridge submodule. The bridge arm reactor and the at least one full-bridge submodule are connected in series. The full-bridge submodule includes an H-bridge switching device and a capacitor. The start-up control system includes: The signal acquisition module is used to acquire electrical analog quantities and switching quantities of the frequency converter and the low-frequency transmission network; The bridge arm submodule capacitor charging control module is used to close the power frequency network connection switch of the frequency converter station after receiving the capacitor charging command, charge the bridge arm submodule capacitor from the power frequency side, and determine whether the submodule capacitor voltage is stable based on the aforementioned criteria for stable bridge arm submodule capacitor voltage. An independent operation control module is used to control the modular multilevel matrix converter of the frequency converter station to unlock and operate, and to increase the capacitor voltage to the rated value and maintain stability by controlling the circulating current in each bridge arm of the frequency converter station; The low-frequency voltage control module is used to control the circulating current in the bridge arm of the frequency converter station, maintain the stability of the capacitor voltage of each bridge arm, and control the low-frequency voltage of the modular multilevel matrix converter of the frequency converter station, which has adjustable output frequency and amplitude. The power control module is used to control the circulating current in the bridge arms of the frequency converter station, maintain the stability of the capacitor voltage of each bridge arm, and control the low-frequency active power and reactive power output of the modular multilevel matrix converter of the frequency converter station to reach the command value.

7. The start-up control system according to claim 6, characterized in that: The electrical analog and switching quantities include the capacitor voltage of the bridge arm, low-frequency voltage, bridge arm current, active power, reactive power, power frequency network connection switch opening and closing signals and / or low-frequency line switch opening and closing signals.

8. The start-up control system according to claim 6, characterized in that: After receiving a capacitor charging command, the bridge arm submodule capacitor charging control module closes the power frequency network connection switch of the frequency converter station, charging the bridge arm submodule capacitor from the power frequency side, and determines whether the submodule capacitor voltage is stable. The criteria for determining whether the capacitor voltage is stable are as follows: in, U c_mean It is the average capacitor voltage of multiple arms of the modular multilevel matrix converter of the frequency converter station. N The number of full-bridge submodules for each bridge arm. U F_L It is the power frequency line voltage of the modular multilevel matrix converter of the frequency converter station.

9. A starting control system for actively reducing the closing current of low-frequency lines, characterized in that, The start-up control system includes: One or more processors; Storage device for storing one or more programs; When the one or more programs are executed by the one or more processors, the one or more processors implement the method as described in any one of claims 1-5.

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