Offshore boost converter control method and device

Abstract

The invention provides an offshore boost converter control method and device, and relates to the technical field of fault ride-through, and the method comprises the steps: determining the current output positive sequence current and fault depth of an MMC; according to the positive sequence current and the fault depth, determining a mode feature corresponding to the MMC; under the condition that the mode characteristic is a full modulation mode, reducing the positive sequence voltage of the MMC; determining an amplitude limiting value of the MMC positive sequence voltage according to the negative sequence modulation voltage; and controlling the positive sequence voltage based on the amplitude limiting value. Therefore, under the condition that the system is influenced by the negative-sequence current, the system can be prevented from generating large transient overcurrent and overvoltage.

Description

Technical Field

[0001] The present disclosure relates to the technical field of fault ride-through, and in particular to an offshore boost converter control method and device. Background Art

[0002] In traditional MMC control, there is no effective solution to the transient overcurrent and overvoltage problems caused by negative sequence current, which may lead to system instability and equipment damage. In the prior art, a constant positive sequence voltage is usually used to control the MMC, but no regulation and limiting is performed on the negative sequence current. Summary of the invention

[0003] The present disclosure aims to solve one of the technical problems in the related art at least to some extent.

[0004] The first aspect of the present disclosure provides a method for controlling an offshore boost converter, including:

[0005] Determine the positive sequence current and fault depth currently output by the MMC;

[0006] Determining a mode feature corresponding to the MMC according to the positive sequence current and the fault depth;

[0007] When the mode characteristic is a full modulation mode, reducing the positive sequence voltage of the MMC;

[0008] Determining the amplitude limit value of the MMC positive sequence voltage according to the negative sequence modulation voltage;

[0009] Based on the amplitude limiting value, the positive sequence voltage is controlled.

[0010] The second aspect of the present disclosure provides a control device for an offshore boost converter, comprising:

[0011] The first determination module is used to determine the positive sequence current currently output by the MMC and the fault depth;

[0012] A second determination module is used to determine a mode feature corresponding to the MMC according to the positive sequence current and the fault depth;

[0013] A first regulating module, configured to reduce the positive sequence voltage of the MMC when the mode characteristic is a full modulation mode;

[0014] A third determination module, used to determine the amplitude limit value of the MMC positive sequence voltage according to the negative sequence modulation voltage;

[0015] A control module is used to control the positive sequence voltage based on the limit value.

[0016] The third aspect embodiment of the present disclosure proposes an electronic device, including: a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the program, the offshore boost converter control method proposed in the first aspect embodiment of the present disclosure is implemented.

[0017] The fourth aspect embodiment of the present disclosure proposes a non-temporary computer-readable storage medium storing a computer program, which, when executed by a processor, implements the offshore boost converter control method proposed in the first aspect embodiment of the present disclosure.

[0018] The offshore boost converter control method, device, equipment and storage medium provided by the present disclosure have the following beneficial effects:

[0019] In the disclosed embodiment, the positive sequence current and fault depth currently output by the MMC are first determined, and then the mode characteristics corresponding to the MMC are determined according to the positive sequence current and the fault depth, and then the positive sequence voltage of the MMC is reduced when the mode characteristics are in full modulation mode, and then the amplitude limit value of the positive sequence voltage of the MMC is determined according to the negative sequence modulation voltage, and finally the positive sequence voltage is controlled based on the amplitude limit value. Thus, when the system is affected by the negative sequence current, it is possible to avoid the system from generating large transient overcurrent and overvoltage. The transient overcurrent and overvoltage problems caused by the multilevel converter (MMC) when it is affected by the negative sequence current are solved. By determining the positive sequence current and fault depth currently output by the MMC, and determining the mode characteristics of the MMC based on them, and then reducing the positive sequence voltage of the MMC in the full modulation mode, the amplitude limit value of the positive sequence voltage of the MMC is determined by the negative sequence modulation voltage, and finally the positive sequence voltage of the MMC is controlled based on the amplitude limit value. The transient overcurrent and overvoltage generated by the negative sequence current of the MMC are reduced, and the stability and reliability of the system are improved. By reducing the positive sequence voltage of the MMC and determining the limit value, the output of the MMC can be better controlled, and the power consumption and loss of the system can be reduced. By determining the mode characteristics of the MMC for specific fault depths and positive sequence currents, the operating efficiency of the MMC under different fault conditions can be improved.

[0020] Additional aspects and advantages of the present disclosure will be given in part in the following description and in part will be obvious from the following description or learned through practice of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The above and / or additional aspects and advantages of the present disclosure will become apparent and easily understood from the following description of the embodiments in conjunction with the accompanying drawings, in which:

[0022] Figure 1 A schematic flow chart of a method for controlling an offshore boost converter provided by an embodiment of the present disclosure;

[0023] Figure 2 A relationship diagram between the positive sequence current limit value and the system negative sequence current provided in an embodiment of the present disclosure;

[0024] Figure 3 A relationship diagram between the amplitude limiting value of the positive sequence voltage and the negative sequence modulation voltage provided in the embodiment of the present disclosure;

[0025] Figure 4 A structural block diagram of an offshore boost converter control device provided by an embodiment of the present disclosure;

[0026] Figure 5 A block diagram of an exemplary computer device suitable for implementing embodiments of the present disclosure is shown. DETAILED DESCRIPTION

[0027] Embodiments of the present disclosure are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present disclosure, and should not be construed as limiting the present disclosure.

[0028] The offshore boost converter control method, apparatus, computer device, and storage medium according to embodiments of the present disclosure are described below with reference to the accompanying drawings.

[0029] It should be noted that the execution subject of the offshore boost converter control method in the embodiment of the present disclosure is an offshore boost converter control device, which can be implemented by software and / or hardware, and can be configured in any electronic device.

[0030] Figure 1 A schematic flow chart of a method for controlling an offshore boost converter provided in the first embodiment of the present disclosure.

[0031] like Figure 1 As shown, the offshore boost converter control method may include the following steps:

[0032] Step 101, determining the positive sequence current currently output by the MMC and the fault depth.

[0033] Specifically, the amplitude of the MMC transient overcurrent and overvoltage can be tested first, and the fault depth can be determined based on the amplitude. When the fault depth is a shallow fault, it is determined that the positive sequence current is less than the current limit value. Then, when the fault depth is a deep fault, the positive sequence current is limited to the current limit value.

[0034] It should be noted that, affected by negative sequence current, wind power systems will generate large transient overcurrent and overvoltage.

[0035] As the fault depth increases, the magnitude of transient overcurrent and overvoltage also increases. Therefore, by measuring the magnitude of transient overcurrent and overvoltage, the fault depth can be preliminarily assessed. Alternatively, the fault depth can be further determined by the phase relationship between current and voltage. In the case of shallow faults, the phase difference between voltage and current is small due to the large system impedance; while in the case of deep faults, the phase difference between voltage and current is large due to the presence of a lower impedance path. Alternatively, the output positive sequence current limit can also be used to determine the fault depth. When the output positive sequence current is less than the current limit value, it means that the fault is shallow; when the output positive sequence current is equal to the current limit, it means that the fault is deep.

[0036] Optionally, the current limit value of the converter in the wind turbine grid-side converter may be calculated according to the negative sequence current flowing into the grid-side converter (GSC).

[0037] It should be noted that since the negative sequence current on the MMC side is suppressed to zero, all negative sequence currents in the system flow into the GSC side. The GSC bridge arm current is related to the output positive sequence current amplitude. Therefore, in order to prevent the GSC bridge arm current from exceeding the protection setting value, it is necessary to limit its positive sequence current, thereby reducing the total current flowing into the GSC. The relationship between the GSC positive sequence current limit value and the system negative sequence current is as follows: Figure 2 As shown in the figure, Iwplim is the positive sequence current limit value, and Iwlim is the overall GSC limit value. First, the negative sequence control of the GSC is disabled, and then the positive sequence current limit value of the converter on the GSC side of the wind turbine is calculated according to the negative sequence current flowing into the wind turbine GSC, so as to avoid its overcurrent.

[0038] Step 102: Determine the mode characteristics corresponding to the MMC according to the positive sequence current and the fault depth.

[0039] Optionally, when the fault depth is a shallow fault and the positive sequence current is less than the current limit value, the mode characteristic is determined to be a full modulation mode; when the fault depth is a deep fault and the positive sequence current is limited to the current limit value, the mode characteristic is determined to be a current limiting mode.

[0040] Full-PWM Mode is a power mode where the output voltage is regulated to a fixed value, while the output current is adjusted by changing the switching frequency. In this mode, the switching frequency is usually kept constant and the output voltage is stable. Limited Current Mode is another power mode where the output current is regulated to a set maximum value. In this mode, the switching frequency is usually adjusted dynamically as the load demand changes to maintain the set output current limit.

[0041] In the current limiting mode, the MMC positive sequence current reaches the limiter limit, that is, the upper limit of the bridge arm overcurrent protection, and cannot continue to absorb the negative sequence current in the system.

[0042] In full modulation mode, the positive sequence voltage of MMC can also reduce the overcurrent and overvoltage levels in the system, but the MMC AC voltage has a greater impact on the synchronization stability of the system and can only be adjusted in full modulation mode. Therefore, it is not appropriate to suppress the system overvoltage and overcurrent by reducing the MMC output positive sequence voltage. Regardless of whether in full modulation mode or in current limiting mode, the system overvoltage and overcurrent are related to the GSC positive sequence current.

[0043] Therefore, by controlling the positive sequence current of GSC alone, overcurrent and overvoltage in the system can be suppressed at the same time. Therefore, by suppressing the negative sequence current to 0 on the MMC side and coordinating the reduction of the positive sequence current on the GSC side, asymmetric fault ride-through of different depths, types and locations that cannot be met by traditional control strategies can be achieved.

[0044] Therefore, the overvoltage and overcurrent of the DC transmission system can be controlled by adjusting the positive sequence current of the grid-side converter.

[0045] Step 103: When the mode characteristic is the full modulation mode, the positive sequence voltage of the MMC is reduced.

[0046] In full modulation mode, the MMC positive sequence voltage reaches the limit value. At this time, due to the limitation of the MMC modulation ratio, there is a risk that the MMC cannot generate negative sequence modulation voltage. Therefore, in order to suppress the negative sequence current on the MMC side to 0, it is necessary to reduce the MMC positive sequence voltage to reserve space for the modulation of the negative sequence voltage. Therefore, the relationship between the limit value of the positive sequence voltage and the negative sequence modulation voltage is as follows: Figure 3 As shown, U mcplim is the positive sequence voltage limit value, U mcn is the negative sequence modulation voltage.

[0047] Step 104: Determine the amplitude limit value of the MMC positive sequence voltage according to the negative sequence modulation voltage.

[0048] Specifically, the MMC negative sequence current can be suppressed to 0 first, the corresponding negative sequence modulation voltage can be generated, and then the MMC positive sequence voltage limit value can be calculated according to the negative sequence modulation voltage, so as to avoid MMC overvoltage. Specifically, the current limit value corresponding to the negative sequence modulation voltage can be determined according to the predetermined mapping relationship between the negative sequence modulation voltage and the limit value.

[0049] Step 105: Control the positive sequence voltage based on the limit value.

[0050] Specifically, the positive sequence voltage may be controlled to be lower than the limit value.

[0051] In the disclosed embodiment, the positive sequence current and fault depth currently output by the MMC are first determined, and then the mode characteristics corresponding to the MMC are determined according to the positive sequence current and the fault depth, and then the positive sequence voltage of the MMC is reduced when the mode characteristics are in full modulation mode, and then the amplitude limit value of the positive sequence voltage of the MMC is determined according to the negative sequence modulation voltage, and finally the positive sequence voltage is controlled based on the amplitude limit value. Thus, when the system is affected by the negative sequence current, it is possible to avoid the system from generating large transient overcurrent and overvoltage. The transient overcurrent and overvoltage problems caused by the multilevel converter (MMC) when it is affected by the negative sequence current are solved. By determining the positive sequence current and fault depth currently output by the MMC, and determining the mode characteristics of the MMC based on them, and then reducing the positive sequence voltage of the MMC in the full modulation mode, the amplitude limit value of the positive sequence voltage of the MMC is determined by the negative sequence modulation voltage, and finally the positive sequence voltage of the MMC is controlled based on the amplitude limit value. The transient overcurrent and overvoltage generated by the negative sequence current of the MMC are reduced, and the stability and reliability of the system are improved. By reducing the positive sequence voltage of the MMC and determining the limit value, the output of the MMC can be better controlled, and the power consumption and loss of the system can be reduced. By determining the mode characteristics of the MMC for specific fault depths and positive sequence currents, the operating efficiency of the MMC under different fault conditions can be improved.

[0052] In order to implement the above embodiments, the present disclosure also proposes an offshore boost converter control device.

[0053] Figure 4 This is a structural block diagram of an offshore boost converter control device provided in the second embodiment of the present disclosure.

[0054] like Figure 4 As shown, the offshore boost converter control device 400 may include:

[0055] A first determination module 410 is used to determine the positive sequence current currently output by the MMC and the fault depth;

[0056] A second determination module 420 is used to determine a mode feature corresponding to the MMC according to the positive sequence current and the fault depth;

[0057] A first regulating module 430, configured to reduce the positive sequence voltage of the MMC when the mode characteristic is a full modulation mode;

[0058] A third determination module 440 is used to determine the amplitude limit value of the MMC positive sequence voltage according to the negative sequence modulation voltage;

[0059] The control module 450 is configured to control the positive sequence voltage based on the amplitude limit value.

[0060] Optionally, the first determining module includes:

[0061] A test unit, used to test the amplitude of the MMC transient overcurrent and overvoltage, and determine the fault depth according to the amplitude;

[0062] A first determining unit, configured to determine, when the fault depth is a shallow fault, that the positive sequence current is less than a current limit value;

[0063] The limiting unit is used to limit the positive sequence current to the current limit value when the fault depth is a deep fault.

[0064] Optionally, the second determining module is specifically configured to:

[0065] When the fault depth is a shallow fault and the positive sequence current is less than the current limit value, determining that the mode characteristic is a full modulation mode;

[0066] When the fault depth is a deep fault and the positive sequence current is limited to the current amplitude limit value, the mode characteristic is determined to be a current limiting mode.

[0067] Optionally, the second regulation module is used to regulate the positive sequence current of the grid-side converter to control overvoltage and overcurrent of the DC transmission system.

[0068] Optionally, the first determining unit is further configured to:

[0069] The current limiting value of the converter in the grid-side converter side of the wind turbine is calculated according to the negative sequence current flowing into the grid-side converter.

[0070] In the disclosed embodiment, the positive sequence current and fault depth currently output by the MMC are first determined, and then the mode characteristics corresponding to the MMC are determined according to the positive sequence current and fault depth, and then the positive sequence voltage of the MMC is reduced when the mode characteristics are in full modulation mode, and then the amplitude limit value of the positive sequence voltage of the MMC is determined according to the negative sequence modulation voltage, and finally the positive sequence voltage is controlled based on the amplitude limit value. In this way, when the system is affected by the negative sequence current, it is possible to avoid the system from generating large transient overcurrent and overvoltage.

[0071] In order to implement the above embodiments, the present disclosure further proposes a computer device, including: a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the program, the offshore boost converter control method proposed in the above embodiments of the present disclosure is implemented.

[0072] In order to implement the above embodiments, the present disclosure further proposes a non-temporary computer-readable storage medium storing a computer program, which, when executed by a processor, implements the offshore boost converter control method proposed in the above embodiments of the present disclosure.

[0073] In order to implement the above embodiments, the present disclosure further proposes a computer program product. When an instruction processor in the computer program product executes, the offshore boost converter control method proposed in the above embodiments of the present disclosure is executed.

[0074] Figure 5 A block diagram of an exemplary computer device suitable for implementing embodiments of the present disclosure is shown. Figure 5 The computer device 12 shown is only an example and should not bring any limitation to the functions and scope of use of the embodiments of the present disclosure.

[0075] like Figure 5 As shown, the computer device 12 is in the form of a general-purpose computing device. The components of the computer device 12 may include, but are not limited to: one or more processors or processing units 16, a system memory 28, and a bus 18 that connects various system components (including the system memory 28 and the processing unit 16).

[0076] The bus 18 represents one or more of several types of bus structures, including a memory bus or memory controller, a peripheral bus, a graphics acceleration port, a processor or a local bus using any of a variety of bus structures. For example, these architectures include but are not limited to Industry Standard Architecture (ISA) bus, Micro Channel Architecture (MAC) bus, Enhanced ISA bus, Video Electronics Standards Association (VESA) local bus and Peripheral Component Interconnection (PCI) bus.

[0077] The computer device 12 typically includes a variety of computer system readable media. These media can be any available media that can be accessed by the computer device 12, including volatile and non-volatile media, removable and non-removable media.

[0078] The memory 28 may include computer system readable media in the form of volatile memory, such as random access memory (RAM) 30 and / or cache memory 32. The computer device 12 may further include other removable / non-removable, volatile / non-volatile computer system storage media. By way of example only, the storage system 34 may be used to read and write non-removable, non-volatile magnetic media ( Figure 5not shown, usually called a "hard drive"). Although Figure 5 Not shown in the figure, a disk drive for reading and writing a removable non-volatile disk (e.g., a "floppy disk"), and an optical disk drive for reading and writing a removable non-volatile optical disk (e.g., a compact disc read only memory (CD-ROM), a digital versatile disc read only memory (DVD-ROM), or other optical media) may be provided. In these cases, each drive may be connected to the bus 18 via one or more data medium interfaces. The memory 28 may include at least one program product having a set (e.g., at least one) of program modules configured to perform the functions of the various embodiments of the present disclosure.

[0079] A program / utility 40 having a set (at least one) of program modules 42 may be stored, for example, in the memory 28, such program modules 42 including but not limited to an operating system, one or more application programs, other program modules, and program data, each of which or some combination may include an implementation of a network environment. The program modules 42 generally perform the functions and / or methods of the embodiments described in the present disclosure.

[0080] The computer device 12 may also communicate with one or more external devices 14 (e.g., keyboard, pointing device, display 24, etc.), one or more devices that enable a user to interact with the computer device 12, and / or any device that enables the computer device 12 to communicate with one or more other computing devices (e.g., network card, modem, etc.). Such communication may be performed via an input / output (I / O) interface 22. In addition, the computer device 12 may also communicate with one or more networks (e.g., a local area network (LAN), a wide area network (WAN), and / or a public network, such as the Internet) via a network adapter 20. As shown, the network adapter 20 communicates with other modules of the computer device 12 via a bus 18. It should be understood that, although not shown in the figure, other hardware and / or software modules may be used in conjunction with the computer device 12, including but not limited to: microcode, device drivers, redundant processing units, external disk drive arrays, RAID systems, tape drives, and data backup storage systems.

[0081] The processing unit 16 executes various functional applications and data processing by running programs stored in the system memory 28, such as implementing the methods mentioned in the above embodiments.

[0082] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present disclosure. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0083] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of the features. In the description of the present disclosure, "plurality" means at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0084] Any process or method description in a flowchart or otherwise described herein may be understood to represent a module, segment or portion of code that includes one or more executable instructions for implementing the steps of a custom logical function or process, and the scope of the preferred embodiments of the present disclosure includes additional implementations in which functions may not be performed in the order shown or discussed, including performing functions in a substantially simultaneous manner or in reverse order depending on the functions involved, which should be understood by technicians in the technical field to which the embodiments of the present disclosure belong.

[0085] The logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as an ordered list of executable instructions for implementing logical functions, and can be embodied in any computer-readable medium for use by an instruction execution system, device or apparatus (such as a computer-based system, a system including a processor, or other system that can fetch instructions from an instruction execution system, device or apparatus and execute the instructions), or in combination with these instruction execution systems, devices or apparatuses. For the purpose of this specification, "computer-readable medium" can be any device that can contain, store, communicate, propagate or transmit a program for use by an instruction execution system, device or apparatus, or in combination with these instruction execution systems, devices or apparatuses. More specific examples of computer-readable media (a non-exhaustive list) include the following: an electrical connection with one or more wires (electronic device), a portable computer disk box (magnetic device), a random access memory (RAM), a read-only memory (ROM), an erasable and programmable read-only memory (EPROM or flash memory), a fiber optic device, and a portable compact disk read-only memory (CDROM). In addition, the computer-readable medium may even be paper or other suitable medium on which the program is printed, since the program may be obtained electronically, for example, by optically scanning the paper or other medium and then editing, interpreting or processing in other suitable ways if necessary, and then stored in a computer memory.

[0086] It should be understood that the various parts of the present disclosure can be implemented in hardware, software, firmware or a combination thereof. In the above-mentioned embodiments, multiple steps or methods can be implemented in software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented in hardware, as in another embodiment, any one of the following technologies known in the art or a combination thereof can be used to implement: a discrete logic circuit having a logic gate circuit for implementing a logic function for a data signal, a dedicated integrated circuit having a suitable combination of logic gate circuits, a programmable gate array (PGA), a field programmable gate array (FPGA), etc.

[0087] A person skilled in the art may understand that all or part of the steps in the method for implementing the above-mentioned embodiment may be completed by instructing related hardware through a program, and the program may be stored in a computer-readable storage medium, which, when executed, includes one or a combination of the steps of the method embodiment.

[0088] In addition, each functional unit in each embodiment of the present disclosure may be integrated into a processing module, or each unit may exist physically separately, or two or more units may be integrated into one module. The above-mentioned integrated module may be implemented in the form of hardware or in the form of a software functional module. If the integrated module is implemented in the form of a software functional module and sold or used as an independent product, it may also be stored in a computer-readable storage medium.

[0089] The storage medium mentioned above may be a read-only memory, a disk or an optical disk, etc. Although the embodiments of the present disclosure have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limitations of the present disclosure. A person of ordinary skill in the art may change, modify, replace and modify the above embodiments within the scope of the present disclosure.

Claims

1. A method for controlling an offshore boost converter, characterized in that: include: Determine the positive sequence current and fault depth currently output by the MMC; Determining a mode feature corresponding to the MMC according to the positive sequence current and the fault depth; When the mode characteristic is a full modulation mode, reducing the positive sequence voltage of the MMC; Determining the amplitude limit value of the MMC positive sequence voltage according to the negative sequence modulation voltage; Based on the amplitude limiting value, the positive sequence voltage is controlled.

2. The method according to claim 1, characterized in that The determining of the positive sequence current currently output by the MMC and the fault depth comprises: Testing the amplitude of MMC transient overcurrent and overvoltage, and determining the fault depth based on the amplitude; In the case where the fault depth is a shallow fault, determining that the positive sequence current is less than a current limit value; When the fault depth is a deep fault, the positive sequence current is limited to the current limit value.

3. The method according to claim 2, characterized in that The determining, according to the positive sequence current and the fault depth, a mode feature corresponding to the MMC comprises: When the fault depth is a shallow fault and the positive sequence current is less than the current limit value, determining that the mode characteristic is a full modulation mode; When the fault depth is a deep fault and the positive sequence current is limited to the current amplitude limit value, the mode characteristic is determined to be a current limiting mode.

4. The method according to claim 1, characterized in that: Also includes: Regulate the positive sequence current of the grid-side converter to control the overvoltage and overcurrent of the DC transmission system.

5. The method according to claim 2, characterized in that: Before determining that the positive sequence current is less than the current limit value, the method further includes: The current limiting value of the converter in the grid-side converter side of the wind turbine is calculated according to the negative sequence current flowing into the grid-side converter.

6. An offshore boost converter control device, characterized in that: include: The first determination module is used to determine the positive sequence current currently output by the MMC and the fault depth; A second determination module is used to determine a mode feature corresponding to the MMC according to the positive sequence current and the fault depth; A first regulating module, configured to reduce the positive sequence voltage of the MMC when the mode characteristic is a full modulation mode; A third determination module, used to determine the amplitude limit value of the MMC positive sequence voltage according to the negative sequence modulation voltage; A control module is used to control the positive sequence voltage based on the limit value.

7. The device according to claim 6, characterized in that The first determining module includes: A test unit, used to test the amplitude of the MMC transient overcurrent and overvoltage, and determine the fault depth according to the amplitude; A first determining unit, configured to determine, when the fault depth is a shallow fault, that the positive sequence current is less than a current limit value; The limiting unit is used to limit the positive sequence current to the current limit value when the fault depth is a deep fault.

8. The device according to claim 7, characterized in that The second determining module is specifically used to: When the fault depth is a shallow fault and the positive sequence current is less than the current limit value, determining that the mode characteristic is a full modulation mode; When the fault depth is a deep fault and the positive sequence current is limited to the current amplitude limit value, the mode characteristic is determined to be a current limiting mode.

9. The device according to claim 6, characterized in that Also includes: The second regulating module is used to regulate the positive sequence current of the grid-side converter to control the overvoltage and overcurrent of the DC transmission system.

10. The method according to claim 7, characterized in that The first determining unit is further configured to: The current limiting value of the converter in the grid-side converter side of the wind turbine is calculated according to the negative sequence current flowing into the grid-side converter.

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