A voltage control method, device, equipment and storage medium for a flexible low-frequency power transmission system

Abstract

The present invention discloses a voltage control method, device, equipment and storage medium for a flexible low-frequency power transmission system. The voltage control method for a flexible low-frequency power transmission system of the present invention determines the AC voltage control command value on the second frequency side of the AC converter according to the reactive power emitted by the reactive power control point on the second frequency side of the AC converter and the terminal voltage of the new energy power generation system to achieve voltage regulation of the AC converter; determines the reactive power command value of the new energy power generation system to achieve reactive power regulation of the new energy power generation system; and adjusts the AC voltage on the second frequency side of the AC converter and the reactive power of the new energy power generation system. The present invention realizes reactive power flow control of the power system on the second frequency side by voltage regulation of the AC converter and reactive power regulation of the new energy power generation system, which can reduce reactive current flowing through the AC converter and the transmission line, and can reduce the current capacity of key equipment.

Description

Technical Field

[0001] The present invention belongs to the technical field of power transmission and distribution of electric power systems, and specifically relates to a voltage control method, device, equipment and storage medium for a flexible low-frequency power transmission system. Background Art

[0002] In recent years, the planning and construction of new energy bases represented by wind power and photovoltaic power has been continuously expanded. Therefore, the construction of power grids urgently needs economical and efficient large-capacity long-distance transmission technology. Affected by the line capacity increase effect and transmission loss, industrial frequency AC transmission technology is difficult to apply to large-capacity long-distance transmission systems. DC transmission technology can significantly increase the transmission capacity of long lines, but it also faces problems such as immature DC transformer and circuit breaker technology, high investment costs, and difficulty in networking DC systems. Flexible low-frequency transmission technology can obtain a transmission capacity far exceeding the industrial frequency AC system by reducing the transmission frequency. At the same time, the manufacturing difficulty and cost of low-frequency transformers and circuit breakers are also significantly lower than those of DC transformers and circuit breakers. The above advantages make flexible low-frequency transmission technology have broad application prospects in scenarios such as urban power grid interconnection, new energy grid connection, and long-distance power supply.

[0003] Current carrying capacity is an important factor limiting the transmission capacity of transmission lines. The current flowing through the AC line includes both active current for transmitting active power and a large amount of reactive current. The main sources of reactive current in the line are the normal operation of other power equipment and the charging of the ground capacitance of the AC line, especially in the long-distance cable transmission scenario represented by the medium and long-distance offshore wind power transmission system. Under the condition of current carrying capacity restriction, reactive current will squeeze the living space of active current, thereby reducing the active power transmission capacity of the line. Flexible low-frequency transmission technology can reduce the reactive current of the line by reducing the operating frequency of the line, thereby increasing the active power transmission capacity of a single-circuit line and reducing the number of line construction and investment costs. On the other hand, as the core equipment of the flexible low-frequency transmission system, the selection of the switching devices and sub-module capacitors required by the AC converter will also be affected by the reactive current flowing through the AC converter. When transmitting a certain active power, the reactive power output of the AC converter increases, and the bridge arm current stress and sub-module capacitor voltage fluctuation also increase, while increasing the capacity of the switching devices and the capacitance of the sub-module will increase the investment cost of the AC converter. In summary, if the reactive current can be reduced as much as possible under a given system active transmission capacity, it will be of great significance to improving the economic efficiency of the project.

[0004] So far, most of the literature on the construction of flexible low-frequency transmission system solutions mainly considers optimizing the distribution of system reactive power flow and reducing line reactive current by installing additional reactive compensation equipment, but this method also requires additional equipment investment costs, and the economic improvement effect is limited. Considering that the AC converter itself has flexible control capability optimization, if the system reactive current can be effectively controlled through a special control system design and the current capacity of key equipment can be reduced, it will be of great significance to improve the engineering economy of flexible low-frequency transmission system. Summary of the invention

[0005] The technical problem to be solved by the present invention is to overcome the defects of the above-mentioned prior art and provide a voltage control method, device, equipment and storage medium for a flexible low-frequency power transmission system, which realizes reactive power flow control of the power system on the second frequency side through voltage regulation of the AC converter and reactive power regulation of the new energy power generation system to reduce the reactive current flowing through the AC converter and the transmission line.

[0006] To this end, the present invention adopts the following technical solution.

[0007] In a first aspect, the present invention provides a voltage control method for a flexible low-frequency power transmission system, wherein the flexible low-frequency power transmission system comprises a first frequency AC power grid, an AC switching station, and a second frequency AC power grid connected in series in sequence, wherein the AC switching station comprises a first frequency side transformer, an AC converter, and a second frequency side transformer connected in series in sequence, wherein the first frequency side transformer is connected to the first frequency AC power grid, and the second frequency AC power grid comprises a new energy power generation system and a transmission line, wherein the new energy power generation system is connected to the second frequency side transformer via the transmission line;

[0008] The voltage control method comprises:

[0009] Collect the reactive power emitted by the reactive power control point on the second frequency side of the AC converter and the terminal voltage of the new energy power generation system;

[0010] By comparing the reactive power emitted by the reactive power control point on the second frequency side of the AC converter with the preset set reactive power, an AC voltage control command value on the second frequency side of the AC converter is determined to achieve voltage regulation of the AC converter, which is used to reduce the reactive current flowing through the second frequency side of the AC converter;

[0011] By comparing the terminal voltage and rated voltage of the renewable energy power generation system, the reactive power command value of the renewable energy power generation system is determined, and the reactive power regulation of the renewable energy power generation system is realized, which is used to reduce the reactive current flowing through the transmission line.

[0012] Furthermore, the second frequency side regulation system is used to regulate the voltage of the AC converter and the reactive power of the new energy power generation system.

[0013] Furthermore, the second frequency side regulation system has two control modes: an AC converter reactive minimum mode and a line reactive minimum mode. When the AC converter is in the reactive minimum mode, the reactive current on the second frequency side of the AC converter is minimized; when the AC converter is in the reactive minimum mode, the reactive current flowing through the transmission line is minimized.

[0014] Furthermore, the position of the reactive power control point on the second frequency side of the AC-commutator is determined by the control mode of the second frequency side regulation system. When the second frequency side regulation system adopts the AC-commutator reactive minimum mode, the reactive power control point on the second frequency side of the AC-commutator is located between the AC-commutator and the second frequency side transformer; when the second frequency side regulation system adopts the line reactive minimum mode, the reactive power control point on the second frequency side of the AC-commutator is located between the second frequency side transformer and the transmission line.

[0015] Furthermore, the operating frequency of the first-frequency AC power grid is higher than that of the second-frequency AC power grid.

[0016] Furthermore, the AC voltage control command value at the second frequency side of the AC converter is obtained by the following method:

[0017] 1) When the reactive power generated by the reactive power control point on the second frequency side of the AC converter In the dead zone range , ], the AC voltage control command value at the second frequency side of the AC converter is U 1ref Equal to the AC voltage rating on the second frequency side of the AC converter U 1n ;

[0018] 2) When the reactive power generated by the reactive power control point on the second frequency side of the AC converter Out of dead zone range [ , ], the AC voltage control command value at the second frequency side of the AC converter is U 1ref Obtained by the proportional-integral controller, the control equation corresponding to the proportional-integral controller is as follows:

[0019] ,

[0020] in, K 1 and T 1 are the proportional coefficient and the integral time constant, s represents the Laplace operator; and The actual value and the set value of the reactive power are respectively sent for the reactive power control point at the second frequency side of the AC converter.

[0021] Furthermore, the reactive power command value of the new energy power generation system is obtained by the following method:

[0022] 1) When the actual value of the terminal voltage of the new energy power generation system U 2 When in the dead zone, the reactive power command value of the new energy power generation system is equal to 0;

[0023] 2) When the actual value of the terminal voltage of the new energy power generation system U 2 When the dead zone is exceeded, the reactive power command value of the new energy power generation system It is obtained by the proportional controller, and the control equation corresponding to the proportional controller is as follows:

[0024] ,

[0025] in, K 2 is the proportionality factor, U 2n It is the rated value of the terminal voltage of the renewable energy power generation system.

[0026] In a second aspect, the present invention provides a voltage control device for a flexible low-frequency power transmission system, the voltage control device comprising:

[0027] Data acquisition module: used to collect the reactive power emitted by the reactive power control point on the second frequency side of the AC converter and the terminal voltage of the new energy power generation system;

[0028] Voltage regulation module: by comparing the reactive power emitted by the reactive power control point on the second frequency side of the AC converter with the preset set reactive power, the AC voltage control command value on the second frequency side of the AC converter is determined to achieve voltage regulation of the AC converter and reduce the reactive current flowing through the second frequency side of the AC converter;

[0029] Reactive power regulation module: By comparing the terminal voltage and rated voltage of the renewable energy power generation system, the reactive power command value of the renewable energy power generation system is determined, the reactive power regulation of the renewable energy power generation system is realized, and the reactive current flowing through the transmission line is reduced.

[0030] In a third aspect, the present invention provides a computer device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the steps of the method when executing the computer program.

[0031] In a fourth aspect, the present invention provides a computer-readable storage medium having a computer program stored thereon, wherein the computer program implements the steps of the method when executed by a processor.

[0032] Based on the above technical scheme, the present invention has the following beneficial technical effects: the present invention realizes reactive power flow control of the power system on the second frequency side through voltage regulation of the AC converter and reactive power regulation of the new energy power generation system, which can reduce the reactive current flowing through the AC converter and the transmission line, and can reduce the current capacity of key equipment.

[0033] The present invention does not require additional reactive power compensation equipment, has good economic efficiency, and has important application value in practical engineering design. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 A schematic diagram of the topological structure of a flexible low-frequency power transmission system in a specific implementation manner of the present invention;

[0035] Figure 2 This is a flow chart of a voltage control method for a flexible low-frequency power transmission system of the present invention;

[0036] Figure 3 It is a topological structure diagram of the offshore wind power low-frequency transmission system in a specific implementation manner of the present invention;

[0037] Figure 4 This is a structural diagram of a voltage control device for a flexible low-frequency power transmission system of the present invention;

[0038] Figure 5 A schematic diagram of the logical structure of a computer device provided in Example 4 of the present invention. DETAILED DESCRIPTION

[0039] In order to facilitate the understanding of the present invention, the present invention is described in more detail below in conjunction with the accompanying drawings and specific embodiments. Preferred embodiments of the present invention are provided in the accompanying drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described in this specification. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present invention more thorough and comprehensive.

[0040] It should be noted that, unless otherwise defined, all technical and scientific terms used in this specification have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0041] Example 1

[0042] This embodiment provides a voltage control method for a flexible low-frequency power transmission system. Figure 2 shown.

[0043] The flexible low-frequency power transmission system, such as Figure 1As shown, it includes a first frequency AC grid, an AC switching station, and a second frequency AC grid connected in series, wherein the operating frequency of the first frequency AC grid is higher than that of the second frequency AC grid. The AC switching station includes a first frequency side transformer, an AC converter, and a second frequency side transformer connected in series, wherein the first frequency side transformer is connected to the first frequency AC grid, and the second frequency AC grid includes a new energy power generation system and a transmission line, wherein the new energy power generation system is connected to the second frequency side transformer via the transmission line.

[0044] A second frequency side regulation system is provided between the AC switching station and the second frequency AC power grid. The voltage regulation of the AC converter and the reactive power regulation of the new energy power generation system are performed through the second frequency side regulation system to reduce the reactive current flowing through the AC converter and the transmission line.

[0045] The steps of the voltage control method are as follows:

[0046] First, determining a control mode of the second frequency side regulation system;

[0047] The second frequency side regulation system has two control modes: the AC converter reactive minimum mode (i.e. Figure 1 Mode 1) and line reactive power minimum mode (i.e. Figure 1 When the AC converter is in the minimum reactive mode, the reactive current on the second frequency side of the AC converter is minimum; when the line is in the minimum reactive mode, the reactive current flowing through the transmission line is minimum.

[0048] Secondly, the reactive power emitted by the reactive power control point on the second frequency side of the AC converter and the terminal voltage of the new energy power generation system are collected;

[0049] The position of the reactive power control point on the second frequency side of the AC converter is determined by the control mode of the second frequency side regulation system. When the second frequency side regulation system adopts the AC converter minimum reactive mode (i.e., mode 1), the reactive power control point on the second frequency side of the AC converter is located between the AC converter and the second frequency side transformer; when the second frequency side regulation system adopts the line reactive minimum mode (i.e., mode 2), the reactive power control point on the second frequency side of the AC converter is located between the second frequency side transformer and the transmission line.

[0050] Then, by comparing the reactive power emitted by the reactive power control point on the second frequency side of the AC converter with the preset set reactive power, the AC voltage control command value on the second frequency side of the AC converter is determined, and the voltage regulation of the AC converter is implemented through the second frequency side regulation system to reduce the reactive current flowing through the second frequency side of the AC converter; by comparing the machine-end voltage and the rated voltage of the new energy power generation system, the reactive power command value of the new energy power generation system is determined, and the reactive power regulation of the new energy power generation system is implemented through the second frequency side regulation system to reduce the reactive current flowing through the transmission line.

[0051] Specifically, the AC voltage control instruction value at the second frequency side of the AC converter is obtained by the following method:

[0052] 1) When the reactive power generated by the reactive power control point on the second frequency side of the AC converter In the dead zone range , ], the AC voltage control command value at the second frequency side of the AC converter is U 1ref Equal to the AC voltage rating on the second frequency side of the AC converter U 1n ;

[0053] 2) When the reactive power generated by the reactive power control point on the second frequency side of the AC converter Out of dead zone range [ , ], the AC voltage control command value at the second frequency side of the AC converter is U 1ref Obtained by the proportional-integral controller, the control equation corresponding to the proportional-integral controller is as follows:

[0054] (1)

[0055] in, K 1 and T 1 are the proportional coefficient and the integral time constant, s represents the Laplace operator; and The actual value and the set value of the reactive power are respectively sent for the reactive power control point at the second frequency side of the AC converter.

[0056] Specifically, the reactive power command value of the new energy power generation system is obtained by the following method:

[0057] 1) When the actual value of the terminal voltage of the new energy power generation system U 2 When in the dead zone, the reactive power command value of the new energy power generation system is equal to 0;

[0058] 2) When the actual value of the terminal voltage of the new energy power generation system U 2 When the dead zone is exceeded, the reactive power command value of the new energy power generation system It is obtained by the proportional controller, and the control equation corresponding to the proportional controller is as follows:

[0059] (2)

[0060] in, is the reactive power command value of the new energy power generation system, K 2 is the proportionality factor, U 2 and U 2n They are the actual value and rated value of the terminal voltage of the new energy power generation system respectively.

[0061] Application Examples

[0062] The method described in Example 1 is applied to an offshore wind power low-frequency transmission system, and the specific contents are as follows:

[0063] The topology of the offshore wind power low-frequency transmission system is as follows: Figure 3 As shown in Table 1, the AC voltage proportional integral controller on the second frequency side of the AC converter shown in formula (1) and the reactive power proportional controller shown in formula (2) are used, and Figure 2 control flow.

[0064] Table 1 is the equipment parameter table of offshore wind power low-frequency transmission system

[0065]

[0066] When the proportional coefficient in formula (2) is 500, the results of using the two control modes of the present invention and the control mode not using the present invention are shown in Table 2.

[0067] Table 2 Data comparison table of using the control method of the present invention and not using the control method of the present invention

[0068]

[0069] It can be seen from Table 2 that when the two control modes of the present invention are adopted, compared with the control mode not adopting the present invention, the system reactive power flow distribution can be optimized, the reactive power of the converter, the line head end and the line end can be significantly reduced, the equipment design requirements are reduced, the system loss is reduced, and a beneficial economic effect can be achieved.

[0070] Example 2

[0071] This embodiment provides a voltage control device for a flexible low-frequency power transmission system, such as Figure 4 As shown, the method for implementing the method described in Example 1 includes:

[0072] Data acquisition module: used to collect the reactive power emitted by the reactive power control point on the second frequency side of the AC converter and the terminal voltage of the new energy power generation system;

[0073] Voltage regulation module: by comparing the reactive power emitted by the reactive power control point on the second frequency side of the AC converter with the preset set reactive power, the AC voltage control command value on the second frequency side of the AC converter is determined to achieve voltage regulation of the AC converter and reduce the reactive current flowing through the second frequency side of the AC converter;

[0074] Reactive power regulation module: By comparing the terminal voltage and rated voltage of the renewable energy power generation system, the reactive power command value of the renewable energy power generation system is determined, the reactive power regulation of the renewable energy power generation system is realized, and the reactive current flowing through the transmission line is reduced.

[0075] It should be noted that each module in the voltage control device of the above-mentioned flexible low-frequency power transmission system can be fully or partially implemented by software, hardware and a combination thereof. The above-mentioned modules can be embedded in or independent of the processor in the computer device in the form of hardware, or can be stored in the memory of the computer device in the form of software, so that the processor can call and execute the operations corresponding to the above modules. For the specific definition of the voltage control device of a flexible low-frequency power transmission system, please refer to the definition of the voltage control method of a flexible low-frequency power transmission system above. The two have the same functions and effects, which will not be repeated here.

[0076] Example 3

[0077] This embodiment provides a computer device, comprising: at least one processor; and a memory connected to the at least one processor in communication. The memory stores a computer program executable by the at least one processor, and when the at least one processor executes the computer device, the computer program is used to cause the computer device to execute the method according to Embodiment 1 of the present invention.

[0078] Example 4

[0079] This embodiment provides a non-transitory computer-readable storage medium storing a computer program, wherein the computer program, when executed by a processor of a computer, is used to cause the computer to execute the method according to Embodiment 1 of the present invention.

[0080] refer to Figure 5The structural block diagram of the electronic device 400 that can be used as the server or client of the present invention will now be described, which is an example of a hardware device that can be applied to various aspects of the present invention. The electronic device is intended to represent various forms of digital electronic computer equipment, such as laptop computers, desktop computers, workbenches, personal digital assistants, servers, blade servers, mainframe computers, and other suitable computers. The electronic device can also represent various forms of mobile devices, such as personal digital processing, cellular phones, smart phones, wearable devices and other similar computing devices. The components shown herein, their connections and relationships, and their functions are only examples, and are not intended to limit the implementation of the present invention described herein and / or required.

[0081] like Figure 5 As shown, the electronic device 400 includes a computing unit 401, which can perform various appropriate actions and processes according to a computer program stored in a read-only memory (ROM) 402 or a computer program loaded from a storage unit 408 to a random access memory (RAM) 403. In the RAM 403, various programs and data required for the operation of the electronic device 400 can also be stored. The computing unit 401, the ROM 402, and the RAM 403 are connected to each other via a bus 404. An input / output (I / O) interface 405 is also connected to the bus 404.

[0082] A plurality of components in the electronic device 400 are connected to the I / O interface 405, including: an input unit 406, an output unit 407, a storage unit 408, and a communication unit 409. The input unit 406 may be any type of device capable of inputting information to the electronic device 400, and the input unit 406 may receive input digital or character information, and generate key signal inputs related to user settings and / or function control of the electronic device. The output unit 407 may be any type of device capable of presenting information, and may include, but is not limited to, a display, a speaker, a video / audio output terminal, a vibrator, and / or a printer. The storage unit 408 may include, but is not limited to, a disk, an optical disk. The communication unit 409 allows the electronic device 400 to exchange information / data with other devices via a computer network such as the Internet and / or various telecommunication networks, and may include, but is not limited to, a modem, a network card, an infrared communication device, a wireless communication transceiver, and / or a chipset, such as a Bluetooth™ device, a WiFi device, a WiMax device, a cellular communication device, and / or the like.

[0083] The computing unit 401 may be a variety of general and / or special processing components with processing and computing capabilities. Some examples of the computing unit 401 include, but are not limited to, a central processing unit (CPU), a graphics processing unit (GPU), various dedicated artificial intelligence (AI) computing chips, various computing units running machine learning model algorithms, digital signal processors (DSPs), and any appropriate processors, controllers, microcontrollers, etc. The computing unit 401 performs the various methods and processes described above. For example, in some embodiments, the aforementioned voltage control method may be implemented as a computer software program, which is tangibly contained in a machine-readable medium, such as a storage unit 408. In some embodiments, part or all of the computer program may be loaded and / or installed on the electronic device 400 via the ROM 402 and / or the communication unit 409. In some embodiments, the computing unit 401 may be configured to perform the aforementioned voltage control method in any other appropriate manner (e.g., by means of firmware).

[0084] The program code for implementing the method of the present invention can be written in any combination of one or more programming languages. These program codes can be provided to a processor or controller of a general-purpose computer, a special-purpose computer or other programmable data processing device, so that the program code, when executed by the processor or controller, enables the functions / operations specified in the flow chart and / or block diagram to be implemented. The program code can be executed entirely on the machine, partially on the machine, partially on the machine as a stand-alone software package and partially on a remote machine, or entirely on a remote machine or server.

[0085] In the context of the present invention, a machine-readable medium may be a tangible medium that may contain or store a program for use by or in conjunction with an instruction execution system, device, or equipment. A machine-readable medium may be a machine-readable signal medium or a machine-readable storage medium. A machine-readable medium may include, but is not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, device, or equipment, or any suitable combination of the foregoing. A more specific example of a machine-readable storage medium may include an electrical connection based on one or more lines, a portable computer disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber, a portable compact disk read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing.

[0086] As used herein, the terms "machine-readable medium" and "computer-readable medium" refer to any computer program product, apparatus, and / or device (e.g., disk, optical disk, memory, programmable logic device (PLD)) for providing machine instructions and / or data to a programmable processor, including a machine-readable medium that receives machine instructions as a machine-readable signal. The term "machine-readable signal" refers to any signal for providing machine instructions and / or data to a programmable processor.

[0087] To provide interaction with a user, the systems and techniques described herein can be implemented on a computer having: a display device (e.g., a CRT (cathode ray tube) or LCD (liquid crystal display) monitor) for displaying information to the user; and a keyboard and pointing device (e.g., a mouse or trackball) through which the user can provide input to the computer. Other types of devices can also be used to provide interaction with the user; for example, the feedback provided to the user can be any form of sensory feedback (e.g., visual feedback, auditory feedback, or tactile feedback); and input from the user can be received in any form (including acoustic input, voice input, or tactile input).

[0088] The systems and techniques described herein may be implemented in a computing system that includes back-end components (e.g., as a data server), or a computing system that includes middleware components (e.g., an application server), or a computing system that includes front-end components (e.g., a user computer with a graphical user interface or a web browser through which a user can interact with implementations of the systems and techniques described herein), or a computing system that includes any combination of such back-end components, middleware components, or front-end components. The components of the system may be interconnected by any form or medium of digital data communication (e.g., a communication network). Examples of communication networks include: a local area network (LAN), a wide area network (WAN), and the Internet.

[0089] A computer system may include clients and servers. Clients and servers are generally remote from each other and usually interact through a communication network. The relationship of client and server is generated by computer programs running on respective computers and having a client-server relationship to each other.

[0090] It is obvious that those skilled in the art can easily make various modifications to the above embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art to the present invention based on the disclosure of the present invention should be within the protection scope of the present invention.

Claims

1. A voltage control method for a flexible low-frequency power transmission system, wherein the flexible low-frequency power transmission system comprises a first frequency AC power grid, an AC switching station, and a second frequency AC power grid connected in series in sequence, wherein the AC switching station comprises a first frequency side transformer, an AC converter, and a second frequency side transformer connected in series in sequence, wherein the first frequency side transformer is connected to the first frequency AC power grid, and the second frequency AC power grid comprises a new energy power generation system and a transmission line, wherein the new energy power generation system is connected to the second frequency side transformer via the transmission line, wherein: Collect the reactive power emitted by the reactive power control point on the second frequency side of the AC converter and the terminal voltage of the new energy power generation system; By comparing the reactive power emitted by the reactive power control point on the second frequency side of the AC converter with the preset set reactive power, an AC voltage control command value on the second frequency side of the AC converter is determined to achieve voltage regulation of the AC converter, which is used to reduce the reactive current flowing through the second frequency side of the AC converter; By comparing the terminal voltage and rated voltage of the renewable energy power generation system, the reactive power command value of the renewable energy power generation system is determined, and the reactive power regulation of the renewable energy power generation system is realized, which is used to reduce the reactive current flowing through the transmission line; The second frequency side regulation system is used to regulate the voltage of the AC converter and the reactive power of the new energy power generation system; The AC voltage control command value at the second frequency side of the AC converter is obtained by the following method: 1) When the reactive power generated by the reactive power control point on the second frequency side of the AC converter In the dead zone range , ], the AC voltage control command value at the second frequency side of the AC converter is U 1ref Equal to the AC voltage rating on the second frequency side of the AC converter U 1n ; 2) When the reactive power generated by the reactive power control point on the second frequency side of the AC converter Out of dead zone range [ , ], the AC voltage control command value at the second frequency side of the AC converter is U 1ref Obtained by the proportional-integral controller, the control equation corresponding to the proportional-integral controller is as follows: ， in, K 1 and T 1 are the proportional coefficient and the integral time constant, s represents the Laplace operator; and The actual value and the set value of reactive power are respectively sent out by the reactive power control point at the second frequency side of the AC converter; The reactive power command value of the new energy power generation system is obtained by the following method: 1) When the actual value of the terminal voltage of the new energy power generation system U 2 When in the dead zone, the reactive power command value of the new energy power generation system is equal to 0; 2) When the actual value of the terminal voltage of the new energy power generation system U 2 When the dead zone is exceeded, the reactive power command value of the new energy power generation system It is obtained by the proportional controller, and the control equation corresponding to the proportional controller is as follows: ， in, K 2 is the proportionality factor, U 2n It is the rated value of the terminal voltage of the renewable energy power generation system.

2. The voltage control method of the flexible low-frequency power transmission system according to claim 1, characterized in that: The second frequency side regulation system has two control modes: the minimum reactive power mode of the AC converter and the minimum reactive power mode of the line. When the AC converter is in the minimum reactive power mode, the reactive current on the second frequency side of the AC converter is minimum; when the AC converter is in the minimum reactive power mode, the reactive current flowing through the transmission line is minimum.

3. The voltage control method of the flexible low-frequency power transmission system according to claim 2, characterized in that: The position of the reactive power control point on the second frequency side of the AC-commutator is determined by the control mode of the second frequency side regulation system. When the second frequency side regulation system adopts the AC-commutator reactive minimum mode, the reactive power control point on the second frequency side of the AC-commutator is located between the AC-commutator and the second frequency side transformer; when the second frequency side regulation system adopts the line reactive minimum mode, the reactive power control point on the second frequency side of the AC-commutator is located between the second frequency side transformer and the transmission line.

4. The voltage control method of the flexible low-frequency power transmission system according to claim 1, characterized in that: The operating frequency of the first-frequency AC power grid is higher than that of the second-frequency AC power grid.

5. A voltage control device for a flexible low-frequency power transmission system, wherein the flexible low-frequency power transmission system comprises a first frequency AC power grid, an AC switching station, and a second frequency AC power grid connected in series in sequence, wherein the AC switching station comprises a first frequency side transformer, an AC converter, and a second frequency side transformer connected in series in sequence, wherein the first frequency side transformer is connected to the first frequency AC power grid, and the second frequency AC power grid comprises a new energy power generation system and a transmission line, wherein the new energy power generation system is connected to the second frequency side transformer via the transmission line, wherein: The voltage control device comprises: Data acquisition module: used to collect the reactive power emitted by the reactive power control point on the second frequency side of the AC converter and the terminal voltage of the new energy power generation system; Voltage regulation module: by comparing the reactive power emitted by the reactive power control point on the second frequency side of the AC converter with the preset set reactive power, the AC voltage control command value on the second frequency side of the AC converter is determined to achieve voltage regulation of the AC converter and reduce the reactive current flowing through the second frequency side of the AC converter; Reactive power regulation module: By comparing the terminal voltage and rated voltage of the renewable energy power generation system, the reactive power command value of the renewable energy power generation system is determined, the reactive power regulation of the renewable energy power generation system is realized, and the reactive current flowing through the transmission line is reduced; The second frequency side regulation system is used to regulate the voltage of the AC converter and the reactive power of the new energy power generation system; The AC voltage control command value at the second frequency side of the AC converter is obtained by the following method: 1) When the reactive power generated by the reactive power control point on the second frequency side of the AC converter In the dead zone range , ], the AC voltage control command value at the second frequency side of the AC converter is U 1ref Equal to the AC voltage rating on the second frequency side of the AC converter U 1n ; 2) When the reactive power generated by the reactive power control point on the second frequency side of the AC converter Out of dead zone range [ , ], the AC voltage control command value at the second frequency side of the AC converter is U 1ref Obtained by the proportional-integral controller, the control equation corresponding to the proportional-integral controller is as follows: ， in, K 1 and T 1 are the proportional coefficient and the integral time constant, s represents the Laplace operator; and The actual value and the set value of reactive power are respectively sent out by the reactive power control point at the second frequency side of the AC converter; The reactive power command value of the new energy power generation system is obtained by the following method: 1) When the actual value of the terminal voltage of the new energy power generation system U 2 When in the dead zone, the reactive power command value of the new energy power generation system is equal to 0; 2) When the actual value of the terminal voltage of the new energy power generation system U 2 When the dead zone is exceeded, the reactive power command value of the new energy power generation system It is obtained by the proportional controller, and the control equation corresponding to the proportional controller is as follows: ， in, K 2 is the proportionality factor, U 2n It is the rated value of the terminal voltage of the renewable energy power generation system.

6. A computer device comprising a memory, a processor and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the computer program, the steps of the method according to any one of claims 1 to 4 are implemented.

7. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the method according to any one of claims 1 to 4 are implemented.

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