Flexible sliding mode suppression method and device for circulating current of modular multilevel converter

Abstract

The invention relates to a flexible sliding mode suppression method and device for circulating current of a modular multilevel converter. The method comprises the following steps: constructing a circulating current model of the modular multilevel converter; the method comprises the following steps: based on a modular multilevel converter circulating current model, constructing a modular multilevel converter circulating current decoupling model under a two-phase rotating coordinate system through phase sequence separation and space vector coordinate transformation; and introducing a generalized proportional integral sliding mode surface and a hyperbolic tangent reaching law, and calculating a sliding mode circulating current control law to realize flexible suppression of circulating current of the modular multilevel converter. Compared with the prior art, the method has the advantages of effectively suppressing circulating current harmonic waves, improving the system reliability, being simple and easy to implement and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of modular multi-level converter circulating current control, and in particular to a method and device for suppressing the circulating current of a modular multi-level converter with flexible sliding mode. Background Art

[0002] Circulating current is an inherent current component in modular multilevel converter (MMC). Its harmonic component is introduced by the voltage fluctuation of submodule capacitors, which distorts the current waveform of each bridge arm. Existing circulating current suppression methods are mainly divided into two categories: topology adjustment method and control optimization method. Among them, the topology adjustment method uses the topological harmonic ablation capability of MMC itself to achieve circulating current suppression, and adjusts the connection mode and mixing ratio of half-bridge, full-bridge and other sub-modules to suppress harmonics. However, this type of method needs to compromise between the cost of new devices and the economic benefits of circulating current suppression, and is difficult to apply in practice. The control optimization method fully considers the strong coupling relationship between the energy of MMC bridge arm and the voltage fluctuation of submodule capacitors, and suppresses the harmonic components of circulating current by optimizing the closed-loop controller of MMC system, which is suitable for engineering practice. However, as the commutation targets of new power systems become increasingly complex, control parameter adjustment becomes more and more difficult. The sliding mode control method has the advantages of strong robustness, high flexibility and simple implementation, and has become the mainstream technology in control optimization methods. However, the high switching frequency and discontinuous control during the sliding mode control process lead to high-frequency jitter in the system, which weakens the MMC circulating current harmonic suppression effect. Therefore, it is urgent to develop flexible sliding mode control technology for MMC circulating current to suppress high-frequency jitter and improve the circulating current harmonic suppression effect of modular multilevel converters.

[0003] After searching, Chinese invention patent publication number CN116094353A discloses a modular multi-level converter control system and a sliding mode circulating current controller. A sliding mode circulating current controller with a new approaching law is introduced into the MMC control system. The sliding film circulating current controller is used to replace the PI controller to suppress the circulating current in the converter. The sliding film surface is designed according to the state equation of the circulating current. The nonlinear control characteristics are used to change purposefully and continuously according to the current state of the system in the dynamic process, forcing the system to move according to the predetermined "sliding mode" state trajectory. Therefore, the present invention designs a sliding mode circulating current controller in the MMC control system, and uses the sliding mode circulating current controller to participate in the circulating current suppression. The sliding mode circulating current controller has fewer parameters to adjust and a fast response speed. At the same time, the use of a new approaching law reduces the system jitter; it is not sensitive to disturbances and has a strong suppression ability for disturbances, which solves the problem of poor robustness of the PI converter controller for circulating current suppression. The existing patent has the problems of complex system and poor circulating current suppression effect.

[0004] How to achieve high suppression of the circulating current of modular multilevel converters by simplifying the system has become a technical problem that needs to be solved. Summary of the invention

[0005] The purpose of the present invention is to overcome the defects of the prior art and provide a method and device for suppressing the flexible sliding mode of circulating current in a modular multi-level converter.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] According to one aspect of the present invention, a method for suppressing a flexible sliding mode of a circulating current of a modular multilevel converter is provided, the method comprising the following steps:

[0008] Step S1, constructing a modular multilevel converter circulation model;

[0009] Step S2, based on the modular multilevel converter circulating current model of step S1, constructing a modular multilevel converter circulating current decoupling model in a two-phase rotating coordinate system through phase sequence separation and space vector coordinate transformation;

[0010] Step S3, introducing the generalized proportional integral sliding mode surface and the hyperbolic tangent reaching law, and substituting the calculated sliding mode circulating current control law into the modular multilevel converter circulating current decoupling model of step S2, so as to realize the flexible suppression of the modular multilevel converter circulating current.

[0011] Preferably, in step S1, the modular multilevel converter circulation model is specifically:

[0012]

[0013]

[0014] Among them, i cirj is the j-phase circulation, i jp 、i jl are the upper and lower arm currents of phase j, respectively, j = {a, b, c}, representing the three phases a, b, and c in the modular multilevel converter; u cirj is the j-phase circulating current voltage drop; L0 is the bridge arm inductance; R0 is the bridge arm resistance; U dc is the DC side voltage; u jp 、u jl are the upper and lower bridge arm voltages of phase j respectively.

[0015] Preferably, the construction process of the modular multilevel converter circulating current decoupling model includes: using a synchronous rotating coordinate transformation method to convert the three-phase coordinates of the current into positive and negative sequence two-phase rotating coordinates, decoupling the positive, negative and zero characteristic sequences in the DC and harmonics in the circulating current, and constructing a modular multilevel converter circulating current decoupling model;

[0016] The modular multilevel converter circulating current decoupling model is specifically as follows:

[0017]

[0018] in, They are respectively the MMC three-phase circulating current voltage drop and the d-axis and q-axis components of the three-phase circulating current in the negative-sequence and positive-sequence two-phase rotating coordinate systems; L0 is the bridge arm inductance; R0 is the bridge arm resistance; ω0 is the fundamental angular frequency.

[0019] Preferably, the step S3 comprises:

[0020] Step S3-1, defining a circulating current tracking error of a modular multilevel converter;

[0021] Step S3-2, selecting a generalized proportional integral sliding surface based on the tracking error of step S3-1;

[0022] Step S3-3, introducing the hyperbolic tangent function into the sliding mode reaching law to achieve flexible control of the circulation;

[0023] Step S3-4, obtaining the system control law based on the generalized proportional integral sliding mode surface and the sliding mode reaching law, and calculating the module circulation control law;

[0024] Step S3-5, substituting the modular circulating current control law into the modular multilevel converter circulating current decoupling model to obtain the flexible suppression of the modular multilevel converter circulating current.

[0025] More preferably, the modular multilevel converter circulating current tracking error is defined as:

[0026]

[0027]

[0028] in, They are the tracking errors of the d-axis and q-axis circulating current components in the negative-sequence and positive-sequence two-phase rotating coordinate systems, respectively; They are the d-axis and q-axis components of the three-phase circulating current of the modular multilevel converter in the negative-sequence and positive-sequence two-phase rotating coordinate systems respectively; They are the reference values ​​of d-axis and q-axis circulating current components of the modular multilevel converter in the negative-sequence and positive-sequence two-phase rotating coordinate systems, respectively.

[0029] Preferably, the generalized proportional integral sliding surface is specifically:

[0030]

[0031] Among them, s1 and s2 are the sliding surfaces of d and q axes in the negative and positive sequence two-phase rotating coordinate systems, respectively, and c 11 、c21 is the proportionality coefficient; c 12 、c 22 is the generalized integral coefficient; They are the tracking errors of the d-axis and q-axis circulating current components in the negative-sequence and positive-sequence two-phase rotating coordinate systems respectively.

[0032] Preferably, the sliding mode reaching law is specifically:

[0033]

[0034] in, and They are the sliding mode reaching laws of d-axis and q-axis in the negative-sequence and positive-sequence two-phase rotating coordinate systems respectively, c1 and c2 are the reaching law coefficients, s1 and s2 are the sliding surfaces, and λ1 and λ2 are the boundary layer thickness parameters.

[0035] Preferably, the computing module circulation control law is specifically:

[0036]

[0037] in, are the control laws of the d-axis and q-axis circulation components in the negative-sequence and positive-sequence two-phase rotating coordinate systems, respectively; c1 and c2 are the reaching law coefficients, λ1 and λ2 are the boundary layer thickness parameters, and c 11 、c 21 is the proportionality coefficient; c 12 、c 22 is the generalized integral coefficient; They are the tracking errors of the d-axis and q-axis circulating current components in the negative-sequence and positive-sequence two-phase rotating coordinate systems respectively.

[0038] Preferably, the process of realizing flexible suppression of circulating current of a modular multilevel converter comprises:

[0039] Substitute the modular circulating current control law into the modular multilevel converter circulating current decoupling model to obtain the suppressed MMC system circulating current:

[0040]

[0041] in, They are the d-axis and q-axis components of the MMC three-phase circulating current voltage drop in the negative-sequence and positive-sequence two-phase rotating coordinate systems respectively; are the d-axis and q-axis components of the MMC three-phase circulating current in the negative-sequence and positive-sequence two-phase rotating coordinate systems respectively; L0 is the bridge arm inductance; R0 is the bridge arm resistance; ω0 is the fundamental angular frequency; They are the control laws of the d-axis and q-axis circulating current components in the negative-sequence and positive-sequence two-phase rotating coordinate systems respectively.

[0042] According to another aspect of the present invention, an electronic device is provided, including a memory and a processor, wherein a computer program is stored in the memory, and the method described above is implemented when the processor executes the program.

[0043] Compared with the prior art, the present invention has the following beneficial effects:

[0044] 1) The method of the present invention models the complex circulating current of the modular multilevel converter, performs negative-sequence and positive-sequence two-phase rotating coordinate transformation and model decoupling, and then introduces the generalized proportional integral sliding mode surface and the hyperbolic tangent sliding mode reaching law respectively to construct a sliding mode circulating current suppression method, thereby achieving effective and flexible suppression of the circulating current of the modular multilevel converter and improving the reliability of the modular multilevel converter system.

[0045] 2) The method provided by the present invention fully considers the three-phase unbalanced circulating current situation, selects the generalized proportional integral sliding mode surface based on the tracking error, introduces the hyperbolic tangent function into the sliding mode reaching law to reduce high-frequency jitter, thereby achieving the improvement of the harmonic suppression effect of the modular multilevel converter circulating current under the condition of three-phase unbalance, and provides a new control method for the increasingly complex commutation targets such as new power systems and source-grid-load-storage interaction.

[0046] 3) The present invention performs negative-sequence and positive-sequence two-phase rotating coordinate transformation on the circulation model of the modular multilevel converter, and then decouples the model. The decoupling separates the positive, negative, and zero-sequence harmonic components in the circulation under the three-phase unbalanced state, thereby improving the targeted suppression and reducing the complexity of the model, making the synovial suppression effect better and easier to implement. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 It is a schematic flow chart of the flexible sliding mode suppression method of the modular multi-level converter circulation in the present invention.

[0048] Figure 2 Schematic diagram of the circulating current suppression effect of the modular multi-level converter in an embodiment of the present invention. DETAILED DESCRIPTION

[0049] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions 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 ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0050] Example 1

[0051] This embodiment relates to a flexible sliding mode suppression method for circulating current of a modular multilevel converter. Taking the voltage imbalance state of the power grid in a flexible direct current transmission scenario as an example, the complex circulating current of the modular multilevel converter is firstly modeled, and the negative-sequence and positive-sequence two-phase rotating coordinate transformation and model decoupling are performed. Then, the generalized proportional integral sliding mode surface and the hyperbolic tangent sliding mode reaching law are introduced respectively to construct a sliding mode circulating current suppression method, so as to realize the flexible suppression of circulating current of the modular multilevel converter. Figure 1 , specifically including the following steps:

[0052] Step S1, constructing the MMC circulation model:

[0053]

[0054]

[0055] Among them, i cirj is the j-phase circulation, i jp 、i jl are the upper and lower arm currents of phase j, respectively, j = a, b, c, representing the three phases a, b, and c in MMC; u cirj is the j-phase circulating current voltage drop; L0 is the bridge arm inductance; R0 is the bridge arm resistance; U dc is the DC side voltage; u jp 、u jl are the upper and lower bridge arm voltages of phase j respectively.

[0056] Step S2: Based on the MMC circulation model described in step S1, a MMC circulation decoupling model in a two-phase rotating coordinate system is constructed through phase sequence separation and space vector coordinate transformation:

[0057]

[0058] in, They are respectively the MMC three-phase circulating current voltage drop and the d-axis and q-axis components of the three-phase circulating current in the negative-sequence and positive-sequence two-phase rotating coordinate systems; L0 is the bridge arm inductance; R0 is the bridge arm resistance; ω0 is the fundamental angular frequency.

[0059] The synchronous rotating coordinate transformation method is used to transform the three-phase (positive, negative, and zero) current coordinates into positive and negative sequence two-phase rotating coordinates. The positive, negative, and zero characteristic sequences of DC and harmonics in the circulating current are decoupled, and the MMC circulating current decoupling model is constructed to reduce the complexity of the system.

[0060] Step S3, using a sliding mode circulating current suppressor that introduces a generalized proportional integral sliding mode surface and a hyperbolic tangent reaching law to achieve flexible suppression of MMC circulating current:

[0061] Step S3-1, define the MMC circulation tracking error, that is:

[0062]

[0063]

[0064] in, They are the tracking errors of the d-axis and q-axis circulating current components in the negative-sequence and positive-sequence two-phase rotating coordinate systems, respectively; They are the d-axis and q-axis components of the MMC three-phase circulating current in the negative-sequence and positive-sequence two-phase rotating coordinate systems respectively; They are the reference values ​​of the d-axis and q-axis circulating current components of the MMC circulating current in the negative-sequence and positive-sequence two-phase rotating coordinate systems, respectively.

[0065] Step S3-2: Select the generalized proportional integral sliding surface, that is:

[0066]

[0067] Among them, s1 and s2 are the sliding surfaces of d and q axes in the negative and positive sequence two-phase rotating coordinate systems, respectively, and c 11 、c 21 is the proportionality coefficient; c 12 、c 22 is the generalized integral coefficient; They are the tracking errors of the d-axis and q-axis circulating current components in the negative-sequence and positive-sequence two-phase rotating coordinate systems respectively.

[0068] Step S3-3, introduce the hyperbolic tangent function into the sliding mode reaching law to reduce high-frequency chattering and realize flexible control of circulating flow, that is:

[0069]

[0070] in, and They are the sliding mode reaching laws of d-axis and q-axis in the negative-sequence and positive-sequence two-phase rotating coordinate systems respectively, c1 and c2 are the reaching law coefficients, s1 and s2 are the sliding surfaces, and λ1 and λ2 are the boundary layer thickness parameters.

[0071] Step S3-4, obtain the system control law:

[0072]

[0073] in, are the control laws of the d-axis and q-axis circulation components in the negative-sequence and positive-sequence two-phase rotating coordinate systems, respectively; c1 and c2 are the reaching law coefficients, λ1 and λ2 are the boundary layer thickness parameters, and c 11 、c 21 is the proportionality coefficient; c 12 、c 22 is the generalized integral coefficient; They are the tracking errors of the d-axis and q-axis circulating current components in the negative-sequence and positive-sequence two-phase rotating coordinate systems respectively.

[0074] Step S3-5, obtaining the MMC system circulation after suppression:

[0075]

[0076] in, They are the d-axis and q-axis components of the MMC three-phase circulating current voltage drop in the negative-sequence and positive-sequence two-phase rotating coordinate systems respectively; are the d-axis and q-axis components of the MMC three-phase circulating current in the negative-sequence and positive-sequence two-phase rotating coordinate systems respectively; L0 is the bridge arm inductance; R0 is the bridge arm resistance; ω0 is the fundamental angular frequency; They are the control laws of the d-axis and q-axis circulating current components in the negative-sequence and positive-sequence two-phase rotating coordinate systems respectively.

[0077] Example 2

[0078] This embodiment also relates to a flexible sliding mode suppression method for circulating current of a modular multi-level converter, such as Figure 1 The process shown in the figure takes the MMC system built in MATLAB / SIMULINK as an example to illustrate the test method of the present invention:

[0079] (1) An MMC system model including an MMC, a dual closed-loop controller, a circulating current suppressor, and a capacitor voltage balancing controller was built in MATLAB / SIMULINK, wherein the system capacity was 3MW; the number of bridge arm submodules was 22; the AC frequency was 50 Hz; the AC voltage was 6.6 kV; the DC side voltage was 11 kV; the submodule IGBT model was TIM1200DDM17; and the circulating current suppressor was the flexible sliding mode circulating current suppressor involved in the present invention.

[0080] (2) The constructed MMC system model is set to a three-phase unbalanced state, where the voltage of phase A drops by 20%. The MMC circulating current waveforms are observed before and after the flexible sliding mode circulating current suppressor is put into operation. Figure 2 As shown, after the flexible sliding mode circulating current suppressor is put into operation, the circulating current of the MMC system under the three-phase unbalanced state is well suppressed, which verifies the effectiveness of the flexible sliding mode circulating current suppression method involved in the present invention.

[0081] The method provided in this embodiment fully considers the influence of three-phase unbalance on the circulating current of the modular multilevel converter, designs a flexible sliding mode inhibitor to suppress the circulating current, and realizes the circulating current suppression of the modular multilevel converter system under three-phase unbalance while weakening the high-frequency jitter of the system, thereby improving the reliability of the modular multilevel converter system.

[0082] Example 3

[0083] The electronic device of the present invention includes a central processing unit (CPU), which can perform various appropriate actions and processes according to computer program instructions stored in a read-only memory (ROM) or loaded from a storage unit into a random access memory (RAM). In the RAM, various programs and data required for device operation can also be stored. The CPU, ROM and RAM are connected to each other via a bus. An input / output (I / O) interface is also connected to the bus.

[0084] Multiple components in the device are connected to the I / O interface, including: input units, such as keyboards, mice, etc.; output units, such as various types of displays, speakers, etc.; storage units, such as disks, optical disks, etc.; and communication units, such as network cards, modems, wireless communication transceivers, etc. The communication unit allows the device to exchange information / data with other devices through computer networks such as the Internet and / or various telecommunication networks.

[0085] The processing unit performs the various methods and processes described above, such as methods S1 to S3. For example, in some embodiments, methods S1 to S3 may be implemented as a computer software program, which is tangibly contained in a machine-readable medium, such as a storage unit. In some embodiments, part or all of the computer program may be loaded and / or installed on the device via a ROM and / or a communication unit. When the computer program is loaded into the RAM and executed by the CPU, one or more steps of methods S1 to S3 described above may be performed. Alternatively, in other embodiments, the CPU may be configured to execute methods S1 to S3 in any other appropriate manner (e.g., by means of firmware).

[0086] The functions described above herein may be performed at least in part by one or more hardware logic components. For example, without limitation, exemplary types of hardware logic components that may be used include: field programmable gate arrays (FPGAs), application specific integrated circuits (ASICs), application specific standard products (ASSPs), systems on chips (SOCs), complex programmable logic devices (CPLDs), and the like.

[0087] 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.

[0088] 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, electronic, magnetic, optical, electromagnetic, infrared, or semiconductor systems, devices, 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.

[0089] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed by the present invention, and these modifications or replacements should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A flexible sliding mode suppression method for circulating current of a modular multi-level converter, characterized in that: The method comprises the following steps: Step S1, constructing a modular multilevel converter circulation model; Step S2, based on the modular multilevel converter circulating current model of step S1, constructing a modular multilevel converter circulating current decoupling model in a two-phase rotating coordinate system through phase sequence separation and space vector coordinate transformation; Step S3, introducing the generalized proportional integral sliding mode surface and the hyperbolic tangent reaching law, and substituting the calculated sliding mode circulating current control law into the modular multilevel converter circulating current decoupling model of step S2, so as to realize the flexible suppression of the modular multilevel converter circulating current.

2. A flexible sliding mode suppression method for circulating current of a modular multilevel converter according to claim 1, characterized in that: In the step S1, the circulation model of the modular multilevel converter is specifically: Among them, i cirj is the j-phase circulation, i jp 、i jl are the upper and lower arm currents of phase j, respectively, j = {a, b, c}, representing the three phases a, b, and c in the modular multilevel converter; u cirj is the j-phase circulating current voltage drop; L0 is the bridge arm inductance; R0 is the bridge arm resistance; U dc is the DC side voltage; u jp 、u jl are the upper and lower bridge arm voltages of phase j respectively.

3. The flexible sliding mode suppression method of modular multilevel converter circulating current according to claim 1, characterized in that: The construction process of the modular multilevel converter circulating current decoupling model includes: using a synchronous rotating coordinate transformation method to convert the three-phase coordinates of the current into positive and negative sequence two-phase rotating coordinates, decoupling the positive, negative and zero characteristic sequences in the DC and harmonics in the circulating current, and constructing the modular multilevel converter circulating current decoupling model; The modular multilevel converter circulating current decoupling model is specifically as follows: in, They are respectively the MMC three-phase circulating current voltage drop and the d-axis and q-axis components of the three-phase circulating current in the negative-sequence and positive-sequence two-phase rotating coordinate systems; L0 is the bridge arm inductance; R0 is the bridge arm resistance; ω0 is the fundamental angular frequency.

4. The flexible sliding mode suppression method of modular multilevel converter circulating current according to claim 1, characterized in that: The step S3 comprises: Step S3-1, defining a circulating current tracking error of a modular multilevel converter; Step S3-2, selecting a generalized proportional integral sliding surface based on the tracking error of step S3-1; Step S3-3, introducing the hyperbolic tangent function into the sliding mode reaching law to achieve flexible control of the circulation; Step S3-4, obtaining the system control law based on the generalized proportional integral sliding mode surface and the sliding mode reaching law, and calculating the module circulation control law; Step S3-5, substituting the modular circulating current control law into the modular multilevel converter circulating current decoupling model to obtain the flexible suppression of the modular multilevel converter circulating current.

5. A method for suppressing the flexible sliding mode of circulating current in a modular multilevel converter according to claim 4, characterized in that: The modular multilevel converter circulating current tracking error is defined as: in, They are the tracking errors of the d-axis and q-axis circulating current components in the negative-sequence and positive-sequence two-phase rotating coordinate systems, respectively; They are the d-axis and q-axis components of the three-phase circulating current of the modular multilevel converter in the negative-sequence and positive-sequence two-phase rotating coordinate systems respectively; They are the reference values ​​of d-axis and q-axis circulating current components of the modular multilevel converter in the negative-sequence and positive-sequence two-phase rotating coordinate systems, respectively.

6. The method for suppressing the flexible sliding mode of circulating current of a modular multilevel converter according to claim 1, characterized in that: The generalized proportional integral sliding surface is specifically: Among them, s1 and s2 are the sliding surfaces of d and q axes in the negative and positive sequence two-phase rotating coordinate systems, respectively, and c 11 、c 21 is the proportionality coefficient; c 12 、c 22 is the generalized integral coefficient; They are the tracking errors of the d-axis and q-axis circulating current components in the negative-sequence and positive-sequence two-phase rotating coordinate systems respectively.

7. The flexible sliding mode suppression method of modular multilevel converter circulating current according to claim 1, characterized in that: The sliding mode reaching law is specifically: in, and They are the sliding mode reaching laws of d-axis and q-axis in the negative-sequence and positive-sequence two-phase rotating coordinate systems respectively, c1 and c2 are the reaching law coefficients, s1 and s2 are the sliding surfaces, and λ1 and λ2 are the boundary layer thickness parameters.

8. The method for suppressing the flexible sliding mode of circulating current in a modular multilevel converter according to claim 1, characterized in that: The calculation model circulation control law is specifically: in, are the control laws of the d-axis and q-axis circulation components in the negative-sequence and positive-sequence two-phase rotating coordinate systems, respectively; c1 and c2 are the reaching law coefficients, λ1 and λ2 are the boundary layer thickness parameters, and c 11 、c 21 is the proportionality coefficient; c 12 、c 22 is the generalized integral coefficient; They are the tracking errors of the d-axis and q-axis circulating current components in the negative-sequence and positive-sequence two-phase rotating coordinate systems respectively.

9. The method for suppressing the flexible sliding mode of circulating current in a modular multilevel converter according to claim 1, characterized in that: The process of realizing flexible suppression of circulating current of modular multilevel converter comprises: Substitute the modular circulating current control law into the modular multilevel converter circulating current decoupling model to obtain the suppressed MMC system circulating current: in, They are the d-axis and q-axis components of the MMC three-phase circulating current voltage drop in the negative-sequence and positive-sequence two-phase rotating coordinate systems respectively; are the d-axis and q-axis components of the MMC three-phase circulating current in the negative-sequence and positive-sequence two-phase rotating coordinate systems respectively; L0 is the bridge arm inductance; R0 is the bridge arm resistance; ω0 is the fundamental angular frequency; They are the control laws of the d-axis and q-axis circulating current components in the negative-sequence and positive-sequence two-phase rotating coordinate systems respectively.

10. An electronic device comprising a memory and a processor, wherein a computer program is stored in the memory, wherein: When the processor executes the program, the method according to any one of claims 1 to 9 is implemented.

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