MMC self-synchronization decoupling control method and device

Abstract

The invention relates to the field of novel power system frequency stability evaluation, and discloses an MMC self-synchronization decoupling control method and device, and the method comprises the steps: adjusting the reference value of the capacitor voltage of a receiving end MMC sub-module according to the frequency deviation constraint of a receiving end AC system after the load disturbance of a receiving end power grid occurs; according to the capacitor voltage of the sub-module, the frequency deviation and the reference value of the capacitor voltage of the sub-module of the receiving end MMC, adaptively adjusting the input number of the sub-modules of the upper and lower bridge arms of the receiving end MMC; and controlling the input number of the sub-modules of the sending-end MMC to be synchronous with the input number of the sub-modules of the receiving-end MMC.

Description

Technical Field

[0001] The present invention relates to the field of novel power system frequency stability assessment, and in particular to an MMC self-synchronous decoupling control method and device. Background Art

[0002] High-voltage direct current (HVDC) technology based on modular multilevel converters (MMC-HVDC) boasts fast control speed, flexible operation, and high power supply reliability. It has become an important technical means for the centralized transmission of renewable energy, asynchronous power grids, weak power grids, and the interconnection of isolated power sources. However, MMC-HVDC, which uses traditional vector control strategies, decouples the frequency of the AC system at both the sending and receiving ends and struggles to provide inertial support for the system under AC system disturbances, which is detrimental to system frequency stability. The integration of power electronics at the source, grid, and load sides has made the low-inertia characteristics of power systems increasingly prominent, and frequency stability issues have become increasingly prominent. Therefore, it is necessary to explore new control strategies for converter stations that can actively support system inertia, participate in frequency stability regulation, and maintain system safety and stability. Summary of the Invention

[0003] In view of this, the present invention provides an MMC self-synchronous decoupling control method and device to solve the problem of frequency stability caused by the low inertia characteristics of power electronic power systems.

[0004] In a first aspect, the present invention provides an MMC self-synchronous decoupling control method, wherein the power transmission system includes a receiving-end power grid and a sending-end power grid, the receiving-end power grid and the sending-end power grid are connected via a DC line, and both the receiving-end power grid and the sending-end power grid include an MMC. The method includes: after a load disturbance occurs in the receiving-end power grid, adjusting the reference value of the capacitor voltage of the receiving-end MMC submodule according to the frequency deviation constraint of the receiving-end AC system; adaptively adjusting the number of submodules put into operation in the upper and lower bridge arms of the receiving-end MMC according to the capacitor voltage, frequency deviation and reference value of the capacitor voltage of the submodule of the receiving-end MMC; and controlling the number of submodules put into operation in the sending-end MMC to be synchronized with the number of submodules put into operation in the receiving-end MMC.

[0005] When a load disturbance occurs in the receiving-end power grid, the present invention increases the control dimension from the traditional two-dimensional to three-dimensional by simultaneously adjusting the reference value of the capacitor voltage and the input amount of the sub-module, thereby achieving decoupling of the sub-module voltage and the DC voltage and providing inertial support for the AC system.

[0006] In an optional embodiment, the process of adjusting the reference value of the capacitor voltage of the receiving-end MMC sub-module includes: determining whether the rate of change of the actual output angular frequency of the receiving-end MMC exceeds a preset threshold; when the rate of change of the actual output angular frequency of the receiving-end MMC exceeds the preset threshold, calculating the reference value of the capacitor voltage of the receiving-end MMC sub-module based on the maximum deviation limit of the AC system frequency, the actual value of the receiving-end system frequency, the rated frequency, the maximum increment of the capacitor voltage reference value during the energy absorption stage, and the initial reference value of the capacitor voltage during the energy absorption stage.

[0007] In an optional implementation manner, the reference value calculation formula of the receiving-end MMC sub-module capacitor voltage is:

[0008]

[0009] Among them, U' SM0 is the reference value of the submodule capacitor voltage during the energy absorption phase; a is the control coefficient; f is the actual value of the receiving system frequency; f0 is the rated frequency; Δf max is the maximum deviation limit of the AC system frequency; ΔU SM0max Indicates the maximum increase in the capacitor voltage reference value during the energy absorption phase; U SM0 is the initial reference value of the capacitor voltage during the energy absorption phase.

[0010] In an optional implementation, the formula for calculating the number of submodules put into use in the upper and lower bridge arms of the receiving-end MMC is:

[0011]

[0012] Among them, N new is the total number of submodules put into the upper and lower bridge arms of the converter station during the energy absorption phase; N is the number of submodules put into the upper and lower bridge arms of the receiving end MMC during stable operation; U' SM0 is the reference value of the submodule capacitor voltage during the energy absorption phase; f is the actual value of the receiving system frequency; f0 is the rated frequency; Δf max is the maximum deviation limit of the AC system frequency; b and c are control coefficients; the numerator 0.05 in b represents the per-unit value of the maximum allowable deviation of the DC bus voltage; J v is the effective moment of inertia of the MMC; U SM0 is the initial reference value of the capacitor voltage during the energy absorption phase; C SM is the submodule capacitance value.

[0013] In an optional implementation, the sending-end MMC adopts constant active power and constant reactive power control.

[0014] In a second aspect, the present invention provides an MMC self-synchronous decoupling control device, comprising: a reference value adjustment module, used to adjust the reference value of the capacitor voltage of the receiving-end MMC sub-module according to the frequency deviation constraint of the receiving-end AC system after a load disturbance occurs in the receiving-end power grid; a receiving-end MMC sub-module quantity adjustment module, used to adaptively adjust the number of sub-modules put into operation in the upper and lower bridge arms of the receiving-end MMC according to the capacitor voltage, frequency deviation and reference value of the receiving-end MMC sub-module capacitor voltage of the sub-module; a sending-end MMC sub-module quantity adjustment module, controlling the synchronization of the number of sub-modules put into operation in the sending-end MMC with the number of sub-modules put into operation in the receiving-end MMC.

[0015] In an optional embodiment, the receiving-end MMC sub-module quantity adjustment module includes: a judgment unit, used to judge whether the change rate of the actual output angular frequency of the receiving-end MMC exceeds a preset threshold; a calculation unit, used to calculate the reference value of the capacitor voltage of the receiving-end MMC sub-module based on the maximum deviation limit of the AC system frequency, the actual value of the receiving-end system frequency, the rated frequency, the maximum increment of the capacitor voltage reference value during the energy absorption stage, and the initial reference value of the capacitor voltage during the energy absorption stage when the change rate of the actual output angular frequency of the receiving-end MMC exceeds the preset threshold.

[0016] In an optional implementation, the calculation unit calculates the reference value of the capacitor voltage of the receiving-end MMC sub-module by the following formula:

[0017]

[0018] Among them, U' SM0 is the reference value of the submodule capacitor voltage during the energy absorption phase; a is the control coefficient; f is the actual value of the receiving system frequency; f0 is the rated frequency; Δf max is the maximum deviation limit of the AC system frequency; ΔU SM0max Indicates the maximum increase in the capacitor voltage reference value during the energy absorption phase; U SM0 is the initial reference value of the capacitor voltage during the energy absorption phase.

[0019] In an optional implementation manner, the receiving-end MMC submodule quantity adjustment module calculates the number of submodules put into use in the upper and lower bridge arms of the receiving-end MMC using the following formula:

[0020]

[0021] Among them, N new is the total number of submodules put into the upper and lower bridge arms of the converter station during the energy absorption phase; N is the number of submodules put into the upper and lower bridge arms of the receiving end MMC during stable operation; U' SM0 is the reference value of the submodule capacitor voltage during the energy absorption phase; f is the actual value of the receiving system frequency; f0 is the rated frequency; Δfmax is the maximum deviation limit of the AC system frequency; b and c are control coefficients; the numerator 0.05 in b represents the per-unit value of the maximum allowable deviation of the DC bus voltage; J v is the effective moment of inertia of the MMC; U SM0 is the initial reference value of the capacitor voltage during the energy absorption phase; C SM is the submodule capacitance value.

[0022] In a third aspect, the present invention provides a computer device comprising: a memory and a processor, the memory and the processor being communicatively connected to each other, the memory storing computer instructions, and the processor executing the computer instructions to thereby execute the MMC self-synchronous decoupling control method of the first aspect or any corresponding embodiment thereof.

[0023] In a fourth aspect, the present invention provides a computer-readable storage medium having computer instructions stored thereon, the computer instructions being used to enable a computer to execute the MMC self-synchronizing decoupling control method of the first aspect or any corresponding embodiment thereof. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0025] Figure 1 This is a schematic diagram of the MMC-HVDC transmission system.

[0026] Figure 2 is a flow chart of an MMC self-synchronization decoupling control method according to an embodiment of the present invention;

[0027] Figure 3 : is a structural block diagram of an MMC self-synchronous decoupling control device according to an embodiment of the present invention

[0028] Figure 4 Schematic diagram of the hardware structure of a computer device according to an embodiment of the present invention. DETAILED DESCRIPTION

[0029] To make the purpose, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative efforts shall fall within the scope of protection of the present invention.

[0030] According to an embodiment of the present invention, an embodiment of an MMC self-synchronizing decoupling control method is provided. It should be noted that the steps shown in the flowchart of the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and although a logical order is shown in the flowchart, in some cases, the steps shown or described can be executed in an order different from that shown here.

[0031] To address frequency stability issues caused by the low inertia characteristics of power electronic power systems, this embodiment proposes a self-synchronous decoupling control strategy to improve the inertial support capability of flexible direct current transmission systems, thereby actively supporting system inertia. By analyzing the available energy supporting the inertia of the MMC-HVDC transmission system, the feasibility of utilizing its energy margin to improve the inertia level of the receiving-end power grid is quantitatively analyzed. Similar to the rotor motion equation of a synchronous machine, a converter station self-synchronization control strategy that considers the energy margin of energy storage elements in the MMC-HVDC transmission system is proposed to actively support the power grid inertia at the receiving end while achieving self-synchronization without a phase-locked loop. On this basis, considering the impact of DC voltage safety constraints on capacitor energy margin utilization, a decoupling control strategy for the system DC voltage and submodule capacitor voltage is proposed. By adaptively adjusting the number of submodule inputs and the capacitor voltage reference value, the energy margin of the energy storage elements in the MMC-HVDC transmission system is fully utilized, effectively improving the inertia level and frequency stability of the receiving-end power grid.

[0032] The inertia response process of the synchronous machine can be described as follows:

[0033]

[0034] Where J is the moment of inertia of the synchronous machine, ω is the angular velocity of the synchronous machine, and P M is the mechanical power, P E is the electromagnetic power.

[0035] The characteristic equations of each physical quantity in the MMC-HVDC transmission system that varies with power are shown in Equation (1-2), which can be used to characterize the dynamic characteristics of capacitor voltage and DC current caused by power imbalance.

[0036]

[0037] Where, P in is the input power of the MMC-HVDC transmission system, P out is the output power of the receiving converter station, N is the number of bridge arm submodules, C SM is the submodule capacitance value, U SM is the submodule voltage value, L eq is the bridge arm inductance, I dc is the DC current value.

[0038] In order to make the receiving-end converter station have the inertial response characteristics of the synchronous machine, by analogy with the rotor motion equation of the synchronous machine and equation (1-2), equation (1-3) can be obtained:

[0039]

[0040] Integrating both ends of equation (1-3), we can get:

[0041]

[0042] Where, ω v and ω v0 are the actual output angular frequency and rated angular frequency of the converter station, J v is the effective moment of inertia of the converter station.

[0043] The above equation represents the coupling relationship between the output angular frequency of the receiving-end converter station of an MMC-HVDC transmission system and the state variables of the energy storage element. Therefore, in the event of power imbalance, the output angular frequency of the receiving-end converter station can be directly changed based on changes in the capacitor voltage and inductor current. This can then be used to adjust the output power of the receiving-end converter station to achieve inertial response characteristics similar to those of a synchronous machine. Therefore, based on the coupling relationship established by equations (1-4), this embodiment designs a self-synchronization control method for the receiving-end converter station of an MMC-HVDC transmission system.

[0044] The structure and control scheme of the MMC-HVDC transmission system are shown in the attached Figure 1 As shown, the transmission system includes a receiving-end power grid and a sending-end power grid, which are connected by a DC line. Both the receiving-end power grid and the sending-end power grid include MMCs. The system adopts symmetrical monopole connection, wherein the sending-end converter station adopts constant active power and constant reactive power control; the receiving-end converter station adopts the self-synchronous control proposed in this embodiment. From the perspective of energy saving, by analogy with the rotor equation of the synchronous generator set, a phase-locked loop is not required to achieve the self-synchronous grid connection of the converter station, that is, it presents the characteristics of a voltage source and can actively support the frequency and voltage of the receiving-end AC system. In this embodiment, an MMC self-synchronous decoupling control method is provided. Figure 2 FIG. 1 is a flow chart of the MMC self-synchronous decoupling control method according to the present embodiment. Figure 2 As shown, the process includes the following steps:

[0045] Step S1: After a load disturbance occurs in the receiving-end power grid, the reference value of the capacitor voltage of the receiving-end MMC submodule is adjusted according to the frequency deviation constraint of the receiving-end AC system.

[0046] Optionally, the process of adjusting the reference value of the capacitor voltage of the receiving-end MMC sub-module includes: determining whether the rate of change of the actual output angular frequency of the receiving-end MMC exceeds a preset threshold; when the rate of change of the actual output angular frequency of the receiving-end MMC exceeds the preset threshold, calculating the reference value of the capacitor voltage of the receiving-end MMC sub-module based on the maximum deviation limit of the AC system frequency, the actual value of the receiving-end system frequency, the rated frequency, the maximum increment of the capacitor voltage reference value during the energy absorption stage, and the initial reference value of the capacitor voltage during the energy absorption stage.

[0047] Specifically, after a high-power load is removed from the receiving AC system, the AC system frequency rises, and the AC frequency output by the MMC also rises. When the frequency reaches the maximum frequency deviation threshold, the MMC activates frequency protection. The relationship between the MMC output angular velocity is shown in Equation (1-4).

[0048] Specifically, when the load at the receiving end of the AC network is cut off, the system frequency rises, the output power of the receiving converter station decreases, and the capacitor voltage of the submodule increases. Under the action of self-synchronization control, ω v Gradually increase to track the changes in system frequency. Since the energy stored in the capacitor in the MMC-HVDC transmission system accounts for a large proportion of the total energy, and there is a strong coupling relationship between the output angular frequency deviation of the receiving end converter station and the capacitor voltage of the submodule, in order to make full use of the energy margin of the capacitor, that is, when ω v When the rate of change exceeds its starting threshold, the capacitor voltage of the submodule can reach 1.5U SMN ,Under the constraint of system frequency deviation, the reference value of the sub-module capacitor ,voltage can be adjusted according to the frequency deviation, as shown in ,Equation (1-5).

[0049]

[0050] Among them, U' SM0 is the reference value of the submodule capacitor voltage during the energy absorption phase; a is the control coefficient; f is the actual value of the receiving system frequency; f0 is the rated frequency; Δf max is the maximum deviation limit of the AC system frequency; ΔU SM0max Indicates the maximum increase in the capacitor voltage reference value during the energy absorption phase; U SM0 is the initial reference value of the capacitor voltage during the energy absorption phase.

[0051] Step S2: Adaptively adjust the number of submodules put into operation in the upper and lower bridge arms of the receiving-end MMC according to the capacitor voltage of the submodule, the frequency deviation and the reference value of the capacitor voltage of the receiving-end MMC submodule.

[0052] Specifically, according to the capacitor voltage and frequency deviation of the sub-module, the number of sub-modules put into the upper and lower bridge arms of the converter station can be adaptively adjusted, as shown in equation (1-6), to achieve decoupling control of the sub-module capacitor voltage and DC voltage.

[0053]

[0054] Among them, N new is the total number of submodules put into the upper and lower bridge arms of the converter station during the energy absorption phase; N is the number of submodules put into the upper and lower bridge arms of the receiving end MMC during stable operation; U' SM0 is the reference value of the submodule capacitor voltage during the energy absorption phase; f is the actual value of the receiving system frequency; f0 is the rated frequency; Δf max is the maximum deviation limit of the AC system frequency; b and c are control coefficients; the numerator 0.05 in b represents the per-unit value of the maximum allowable deviation of the DC bus voltage; J v is the effective moment of inertia of the MMC; U SM0 is the initial reference value of the capacitor voltage during the energy absorption phase; C SM is the submodule capacitance value.

[0055] Step S3: Control the number of submodules put into the sending-end MMC to be synchronized with the number of submodules put into the receiving-end MMC.

[0056] Specifically, the input level of the submodules at the sending-end converter station is synchronized with that at the receiving-end converter station via communication, thereby fully utilizing the energy margin of the submodule capacitors. It can be seen that by changing the number of submodules input at the converter station, the capacitor voltage can be increased while the DC voltage is reduced. Without changing the input power at the sending end, the DC current will also increase with increasing frequency, causing the operating mode of the inductor in the MMC-HVDC transmission system to shift from energy release under traditional modulation strategies to energy storage in the MMC-HV DC transmission system. This fully utilizes the role of energy storage elements in the system and improves their inertial support capacity.

[0057] This embodiment also provides an MMC self-synchronizing decoupling control device, which is used to implement the above-mentioned embodiments and preferred embodiments. Details already described will not be repeated here. As used below, the term "module" may refer to a combination of software and / or hardware that implements a predetermined function. Although the devices described in the following embodiments are preferably implemented in software, implementation using hardware, or a combination of software and hardware, is also possible and contemplated.

[0058] This embodiment provides an MMC self-synchronous decoupling control device, such as Figure 3 Shown, including:

[0059] A reference value adjustment module is used to adjust the reference value of the capacitor voltage of the receiving-end MMC submodule according to the frequency deviation constraint of the receiving-end AC system after a load disturbance occurs in the receiving-end power grid;

[0060] The receiving-end MMC submodule quantity adjustment module is used to adaptively adjust the number of submodules put into use in the upper and lower bridge arms of the receiving-end MMC according to the capacitor voltage, frequency deviation and reference value of the capacitor voltage of the submodule;

[0061] The sending-end MMC submodule quantity adjustment module controls the synchronization of the submodule quantity of the sending-end MMC and the submodule quantity of the receiving-end MMC.

[0062] In some optional implementations, the receiving-end MMC sub-module quantity adjustment module includes:

[0063] A judging unit, configured to judge whether a rate of change of an actual output angular frequency of the receiving-end MMC exceeds a preset threshold;

[0064] The calculation unit is used to calculate the reference value of the capacitor voltage of the receiving-end MMC submodule based on the maximum deviation limit of the AC system frequency, the actual value of the receiving-end system frequency, the rated frequency, the maximum increment of the capacitor voltage reference value during the energy absorption phase, and the initial reference value of the capacitor voltage during the energy absorption phase when the rate of change of the actual output angular frequency of the receiving-end MMC exceeds a preset threshold.

[0065] In some optional implementations, the calculation unit calculates the reference value of the capacitor voltage of the receiving-end MMC sub-module by the following formula:

[0066]

[0067] Among them, U' SM0 is the reference value of the submodule capacitor voltage during the energy absorption phase; a is the control coefficient; f is the actual value of the receiving system frequency; f0 is the rated frequency; Δf max is the maximum deviation limit of the AC system frequency; ΔU SM0max Indicates the maximum increase in the capacitor voltage reference value during the energy absorption phase; U SM0 is the initial reference value of the capacitor voltage during the energy absorption phase.

[0068] In some optional implementations, the receiving-end MMC submodule quantity adjustment module calculates the number of submodules put into use in the upper and lower bridge arms of the receiving-end MMC using the following formula:

[0069]

[0070] Among them, N new is the total number of submodules put into the upper and lower bridge arms of the converter station during the energy absorption phase; N is the number of submodules put into the upper and lower bridge arms of the receiving end MMC during stable operation; U' SM0 is the reference value of the submodule capacitor voltage during the energy absorption phase; f is the actual value of the receiving system frequency; f0 is the rated frequency; Δf max is the maximum deviation limit of the AC system frequency; b and c are control coefficients; the numerator 0.05 in b represents the per-unit value of the maximum allowable deviation of the DC bus voltage; J v is the effective moment of inertia of the MMC; U SM0 is the initial reference value of the capacitor voltage during the energy absorption phase; C SM is the submodule capacitance value.

[0071] The MMC self-synchronizing decoupling control device in this embodiment is presented in the form of a functional unit, where the unit refers to an ASIC circuit, a processor and memory that executes one or more software or fixed programs, and / or other devices that can provide the above functions.

[0072] The further functional description of each of the above modules and units is the same as that of the above corresponding embodiments and will not be repeated here.

[0073] The embodiment of the present invention also provides a computer device having the above Figure 3 The MMC self-synchronous decoupling control device shown.

[0074] See also Figure 4 , Figure 4 is a structural diagram of a computer device provided by an optional embodiment of the present invention, such as Figure 4 As shown, the computer device includes: one or more processors 10, memory 20, and interfaces for connecting various components, including high-speed interfaces and low-speed interfaces. Various components utilize different buses to communicate with each other and can be installed on a common mainboard or installed in other ways as needed. The processor can process the instructions executed in the computer device, including instructions stored in the memory or on the memory to display the graphical information of the GUI on an external input / output device (such as, a display device coupled to the interface). In some optional embodiments, if necessary, multiple processors and / or multiple buses can be used together with multiple memories and multiple memories. Equally, multiple computer devices can be connected, and each device provides part of the necessary operations (for example, as a server array, a group of blade servers, or a multi-processor system). Figure 4 A processor 10 is taken as an example.

[0075] The processor 10 may be a central processing unit, a network processor, or a combination thereof. The processor 10 may further include a hardware chip. The hardware chip may be an application-specific integrated circuit, a programmable logic device, or a combination thereof. The programmable logic device may be a complex programmable logic device, a field programmable gate array, a general purpose array logic, or any combination thereof.

[0076] The memory 20 stores instructions that can be executed by at least one processor 10, so as to enable at least one processor 10 to execute the method shown in the above embodiment.

[0077] The memory 20 may include a program storage area and a data storage area, wherein the program storage area may store an operating system, an application required for at least one function; the data storage area may store data created based on the use of a computer device for displaying a small program landing page, etc. In addition, the memory 20 may include a high-speed random access memory, and may also include a non-transient memory, such as at least one disk storage device, a flash memory device, or other non-transient solid-state storage device. In some optional embodiments, the memory 20 may optionally include a memory remotely located relative to the processor 10, and these remote memories may be connected to the computer device via a network. Examples of the above-mentioned network include, but are not limited to, the Internet, an intranet, a local area network, a mobile communication network, and a combination thereof.

[0078] The memory 20 may include a volatile memory, such as a random access memory; the memory may also include a non-volatile memory, such as a flash memory, a hard disk or a solid-state drive; the memory 20 may also include a combination of the above types of memory.

[0079] The computer device further includes a communication interface 30 for the computer device to communicate with other devices or a communication network.

[0080] The embodiment of the present invention also provides a computer-readable storage medium. The above-mentioned method according to the embodiment of the present invention can be implemented in hardware, firmware, or implemented as a computer code that can be recorded in a storage medium, or implemented as a computer code that is originally stored in a remote storage medium or a non-temporary machine-readable storage medium and downloaded through a network and will be stored in a local storage medium, so that the method described herein can be stored in such software processing on a storage medium using a general-purpose computer, a dedicated processor, or programmable or dedicated hardware. Among them, the storage medium can be a magnetic disk, an optical disk, a read-only storage memory, a random access memory, a flash memory, a hard disk or a solid-state drive, etc.; further, the storage medium can also include a combination of the above-mentioned types of memory. It can be understood that a computer, a processor, a microprocessor controller or programmable hardware includes a storage component that can store or receive software or computer code. When the software or computer code is accessed and executed by a computer, a processor or hardware, the method shown in the above embodiment is implemented.

[0081] Although the embodiments of the present invention have been described with reference to the accompanying drawings, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the present invention. Such modifications and variations are all within the scope defined by the appended claims.

Claims

1. A MMC self-synchronous decoupling control method, characterized in that: The power transmission system includes a receiving-end power grid and a sending-end power grid, the receiving-end power grid and the sending-end power grid are connected via a DC line, and both the receiving-end power grid and the sending-end power grid include an MMC. The method includes: When a load disturbance occurs in the receiving-end power grid, the reference value of the capacitor voltage of the receiving-end MMC submodule is adjusted according to the frequency deviation constraint of the receiving-end AC system; Adaptively adjust the number of submodules put into use in the upper and lower bridge arms of the receiving-end MMC according to the capacitor voltage and frequency deviation of the submodule and the reference value of the capacitor voltage of the receiving-end MMC submodule; The number of submodules put into control sending-end MMC is synchronized with the number of submodules put into control receiving-end MMC.

2. The method according to claim 1, characterized in that The process of adjusting the reference value of the capacitor voltage of the receiving-end MMC submodule includes: Determine whether the rate of change of the actual output angular frequency of the receiving end MMC exceeds a preset threshold; When the rate of change of the actual output angular frequency of the receiving-end MMC exceeds a preset threshold, the reference value of the capacitor voltage of the receiving-end MMC submodule is calculated based on the maximum deviation limit of the AC system frequency, the actual value of the receiving-end system frequency, the rated frequency, the maximum increment of the capacitor voltage reference value during the energy absorption phase, and the initial reference value of the capacitor voltage during the energy absorption phase.

3. The method according to claim 2, characterized in that The reference value calculation formula of the capacitor voltage of the receiving-end MMC submodule is: Among them, U ’ SM0 is the reference value of the submodule capacitor voltage during the energy absorption phase; a is the control coefficient; f is the actual value of the receiving system frequency; f0 is the rated frequency; Δf max is the maximum deviation limit of the AC system frequency; ΔU SM0max Indicates the maximum increase in the capacitor voltage reference value during the energy absorption phase; U SM0 is the initial reference value of the capacitor voltage during the energy absorption phase.

4. The method according to claim 1, wherein The calculation formula for the number of submodules put into use in the upper and lower bridge arms of the receiving-end MMC is: Among them, N new is the total number of submodules put into operation in the upper and lower bridge arms of the converter station during the energy absorption phase; N is the number of submodules put into operation in the upper and lower bridge arms of the receiving end MMC during the stable operation period; U ’ SM0 is the reference value of the submodule capacitor voltage during the energy absorption phase; f is the actual value of the receiving system frequency; f0 is the rated frequency; Δf max is the maximum deviation limit of the AC system frequency; b and c are control coefficients; the numerator 0.05 in b represents the per-unit value of the maximum allowable deviation of the DC bus voltage; J v is the effective moment of inertia of the MMC; U SM0 is the initial reference value of the capacitor voltage during the energy absorption phase; C SM is the submodule capacitance value.

5. The method according to claim 1, wherein Also includes: The sending-end MMC adopts constant active power and constant reactive power control.

6. An MMC self-synchronous decoupling control device, characterized in that: include: A reference value adjustment module is used to adjust the reference value of the capacitor voltage of the receiving-end MMC submodule according to the frequency deviation constraint of the receiving-end AC system after a load disturbance occurs in the receiving-end power grid; The receiving-end MMC submodule quantity adjustment module is used to adaptively adjust the number of submodules put into use in the upper and lower bridge arms of the receiving-end MMC according to the capacitor voltage, frequency deviation and reference value of the capacitor voltage of the submodule; The sending-end MMC submodule quantity adjustment module controls the synchronization of the submodule quantity of the sending-end MMC and the submodule quantity of the receiving-end MMC.

7. The device according to claim 6, characterized in that The receiving-end MMC sub-module quantity adjustment module includes: A judging unit, configured to judge whether a rate of change of an actual output angular frequency of the receiving-end MMC exceeds a preset threshold; The calculation unit is used to calculate the reference value of the capacitor voltage of the receiving-end MMC submodule based on the maximum deviation limit of the AC system frequency, the actual value of the receiving-end system frequency, the rated frequency, the maximum increment of the capacitor voltage reference value during the energy absorption phase, and the initial reference value of the capacitor voltage during the energy absorption phase when the rate of change of the actual output angular frequency of the receiving-end MMC exceeds a preset threshold.

8. The device according to claim 6, characterized in that The calculation unit calculates the reference value of the capacitor voltage of the receiving-end MMC submodule by the following formula: Among them, U ’ SM0 is the reference value of the submodule capacitor voltage during the energy absorption phase; a is the control coefficient; f is the actual value of the receiving system frequency; f0 is the rated frequency; Δf max is the maximum deviation limit of the AC system frequency; ΔU SM0max Indicates the maximum increase in the capacitor voltage reference value during the energy absorption phase; U SM0 is the initial reference value of the capacitor voltage during the energy absorption phase.

9. The device according to claim 6, characterized in that The receiving-end MMC submodule quantity adjustment module calculates the number of submodules put into use in the upper and lower bridge arms of the receiving-end MMC using the following formula: Among them, N new is the total number of submodules put into operation in the upper and lower bridge arms of the converter station during the energy absorption phase; N is the number of submodules put into operation in the upper and lower bridge arms of the receiving end MMC during the stable operation period; U ’ SM0 is the reference value of the submodule capacitor voltage during the energy absorption phase; f is the actual value of the receiving system frequency; f0 is the rated frequency; Δf max is the maximum deviation limit of the AC system frequency; b and c are control coefficients; the numerator 0.05 in b represents the per-unit value of the maximum allowable deviation of the DC bus voltage; J v is the effective moment of inertia of the MMC; U SM0 is the initial reference value of the capacitor voltage during the energy absorption phase; C SM is the submodule capacitance value.

10. A computer device, characterized in that: include: A memory and a processor, wherein the memory and the processor are communicatively connected to each other, the memory stores computer instructions, and the processor executes the MMC self-synchronous decoupling control method according to any one of claims 1 to 5 by executing the computer instructions.

11. A computer-readable storage medium, characterized in that The computer-readable storage medium stores computer instructions, and the computer instructions are used to enable a computer to execute the MMC self-synchronous decoupling control method according to any one of claims 1 to 5.

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