Method and system for switching between networked control mode and islanded control mode for a flexible direct current station

Abstract

This application provides a method and system for switching between grid-connected control mode and islanded control mode for a flexible DC converter station, relating to the field of power system control and protection technology. The switching from islanded control mode to grid-connected control mode includes: detecting the phase of the AC voltage of the first power grid; modifying the AC voltage frequency reference value of the flexible DC converter station to synchronize the AC voltage phase of the flexible DC converter station with the AC voltage phase of the first power grid; when the AC voltage phase of the flexible DC converter station is synchronized with the AC voltage phase of the first power grid, modifying the AC voltage phase of the flexible DC converter station to match the AC voltage phase of the first power grid; and closing a control switch to adjust the control mode of the flexible DC converter station from islanded control mode to grid-connected control mode. The switching method of this application can reduce the impact caused by phase difference during the transition from islanded control to grid-connected control and improve the smoothness of the transition.

Description

Technical Field

[0001] This application relates to the field of power system control and protection technology, and more specifically, to a method and system for switching between grid control mode and islanded control mode for flexible DC converter stations. Background Technology

[0002] Flexible direct current (DC) transmission systems play a crucial role in modern power systems, capable of operating in both grid-connected and islanded modes. In grid-connected mode, the DC converter station is connected to the power grid, enabling bidirectional power flow; in islanded mode, it provides stable power support to passive systems. In practical applications, the DC converter station needs to switch between these two modes depending on the power system's requirements and operating conditions.

[0003] However, existing flexible DC converter stations often encounter problems when switching between grid-connected and islanded control modes. Particularly during the transition from islanded to grid-connected control, the difference in voltage phase between the grid and the converter station can cause significant inrush, leading to flexible DC protection activation and converter lockout. Similarly, the abrupt change in the inner loop current reference value during the transition from grid-connected to islanded control can also cause current issues. Summary of the Invention

[0004] To address at least one of the aforementioned problems, this application proposes a method and system for switching between network control mode and islanded control mode in flexible DC converter stations.

[0005] According to a first aspect of this application, at least one embodiment of this application provides a method for switching between a networked control mode and an islanded control mode for a flexible DC converter station. The flexible DC converter station includes a passive network, a first power grid, a switch, and a flexible DC system. The passive network is connected to the flexible DC system, and the first power grid is connected to the flexible DC system through the switch. The switching method includes: controlling the control mode of the flexible DC converter station to switch from the islanded control mode to the networked control mode, including: detecting the phase of the AC voltage of the first power grid; modifying the AC voltage frequency reference value of the flexible DC converter station to synchronize the AC voltage phase of the flexible DC converter station with the AC voltage phase of the first power grid; when the AC voltage phase of the flexible DC converter station is synchronized with the AC voltage phase of the first power grid, modifying the AC voltage phase of the flexible DC converter station to the AC voltage phase of the first power grid; controlling the switch to close, thereby adjusting the control mode of the flexible DC converter station to switch from the islanded control mode to the networked control mode.

[0006] For example, in some embodiments of this application, the method further includes: controlling the control mode of the flexible DC converter station to switch from the network control mode to the islanded control mode, including: controlling the switch to open, adjusting the control mode of the flexible DC converter station to switch from the network control mode to the islanded control mode; at a first moment, controlling the inner loop current reference value of the flexible DC system to be adjusted to the actual inner loop current of the flexible DC system; setting a rate of change limit, and at a second moment, controlling the inner loop current reference value of the flexible DC system to be adjusted to the inner loop current of the flexible DC system when it is in the islanded control mode, and the rate of change of the inner loop current of the flexible DC system when it is in the islanded control mode does not exceed the rate of change limit.

[0007] For example, in some embodiments of this application, detecting the AC voltage phase of the first power grid includes: controlling the flexible DC converter station in the islanded control mode to detect the AC voltage of the first power grid to obtain the AC voltage phase of the first power grid; and / or receiving the AC voltage phase of the first power grid transmitted by other flexible DC converter stations in the network control mode.

[0008] For example, in some embodiments of this application, modifying the AC voltage frequency reference value of the flexible DC converter station to synchronize the AC voltage phase of the flexible DC converter station with the AC voltage phase of the first power grid includes: superimposing the original AC voltage frequency reference value of the flexible DC converter station with a first preset frequency value to obtain a new AC voltage frequency reference value of the flexible DC converter station.

[0009] For example, in some embodiments of this application, the newly obtained AC voltage frequency reference value of the flexible DC converter station is within the safe operating range of the flexible DC converter, wind farm, bridge arm reactor, transformer and switch in the flexible DC converter station.

[0010] For example, in some embodiments of this application, the method further includes: during the process of switching the control mode of the flexible DC converter station from the network control mode to the island control mode, using a proportional limiting algorithm and / or a linear limiting algorithm to limit the reference voltage of the flexible DC converter station, so as to limit the AC voltage of the flexible DC converter station.

[0011] According to a second aspect of this application, at least one embodiment of this application provides a system for switching between network control mode and islanded control mode for a flexible DC converter station, used to execute the switching method as described in any one of the first aspects. The switching system includes: a control mode switching module for controlling the closing or opening of the switch and controlling the switching of the control mode of the flexible DC converter station between the network control mode and the islanded control mode; a phase tracking module for detecting the phase of the grid AC voltage of the first power grid; a frequency adjustment module for modifying the AC voltage frequency reference value of the flexible DC converter station to synchronize the phase of the AC voltage of the flexible DC converter station with the phase of the grid AC voltage of the first power grid; and a phase adjustment module for modifying the phase of the AC voltage of the flexible DC converter station to the phase of the grid AC voltage of the first power grid when the phase of the AC voltage of the flexible DC converter station is synchronized with the phase of the grid AC voltage of the first power grid.

[0012] For example, in some embodiments of this application, when the control mode conversion module controls the switch to close, the control mode conversion module also controls the control mode of the flexible DC converter station to switch from the islanded control mode to the networked control mode; when the control mode conversion module controls the switch to open, the control mode conversion module also controls the control mode of the flexible DC converter station to switch from the networked control mode to the islanded control mode.

[0013] For example, in some embodiments of this application, it further includes: an inner loop current control module, used to control the inner loop current reference value of the flexible DC system to be adjusted to the actual inner loop current of the flexible DC system within a first moment when the control mode of the flexible DC converter station is changed from the network control mode to the islanded control mode; and a rate of change limiting module, used to set a rate of change limit, and within a second moment to control the inner loop current reference value of the flexible DC system to be adjusted to the inner loop current of the flexible DC system when it is in the islanded control mode, and the inner loop current reference value of the flexible DC system is adjusted to such that the rate of change of the inner loop current of the flexible DC system when it is in the islanded control mode does not exceed the rate of change limit.

[0014] For example, in some embodiments of this application, a reference voltage limiting module is further included, which is used to limit the reference voltage of the flexible DC converter station according to a proportional limiting algorithm and / or a linear limiting algorithm during the process of controlling the control mode of the flexible DC converter station to switch from the network control mode to the island control mode, so as to limit the AC voltage of the flexible DC converter station.

[0015] According to a third aspect of this application, at least one embodiment of this application provides an electronic device, comprising: one or more processors; a memory for storing one or more programs; and, when the one or more programs are executed by the one or more processors, causing the one or more processors to perform the method as described in any one aspect of the first application.

[0016] According to a fourth aspect of this application, at least one embodiment of this application provides a computer-readable storage medium having a computer program stored thereon, the program being executed by a processor to implement the method as described in any one of the first aspects.

[0017] Through the above example embodiments, this application provides a method and system for switching between grid control mode and islanded control mode for a flexible DC converter station. By tracking the grid voltage phase before switching from islanded control mode to grid control mode, the flexible DC converter adopts grid voltage phase control, reducing the impact caused by phase difference during the switch from islanded control to grid control. By controlling the inner loop current to track the actual inner loop current for a short time during the switch from grid to islanded control mode, the impact caused by sudden changes in the inner loop current reference value during the switch from grid to island is reduced, thus improving the smoothness of the switch.

[0018] It should be understood that the above general description and the following detailed description are merely exemplary and do not limit this application. Attached Figure Description

[0019] The above and other objects, features, and advantages of this application will become more apparent from the detailed description of exemplary embodiments with reference to the accompanying drawings. The drawings described below are merely some embodiments of this application and are not intended to limit the scope of this application.

[0020] Figure 1 A schematic diagram of the flexible DC converter station of this application is shown;

[0021] Figure 2 A flowchart illustrating an exemplary embodiment of a method for switching between networked control mode and islanded control mode for a flexible DC converter station is provided.

[0022] Figure 3 A schematic diagram of an exemplary embodiment of a system for switching between networked control mode and islanded control mode for a flexible DC converter station is shown.

[0023] Figure 4 This diagram illustrates the structure of an electronic device provided in this application. Detailed Implementation

[0024] Exemplary embodiments will now be described more fully with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many forms and should not be construed as limited to the embodiments set forth herein; rather, they are provided so that this application will be thorough and complete, and will fully convey the concept of the exemplary embodiments to those skilled in the art. The same reference numerals in the drawings denote the same or similar parts, and therefore repeated descriptions of them will be omitted.

[0025] The described features, structures, or characteristics can be combined in any suitable manner in one or more embodiments. Numerous specific details are provided in the following description to give a full understanding of embodiments of this disclosure. However, those skilled in the art will recognize that the technical solutions of this disclosure can be practiced without one or more of these specific details, or other methods, components, materials, devices, etc. In these cases, well-known structures, methods, devices, implementations, materials, or operations will not be shown or described in detail.

[0026] The flowcharts shown in the accompanying drawings are merely illustrative and do not necessarily include all content and operations / steps, nor do they necessarily have to be performed in the described order. For example, some operations / steps can be broken down, while others can be combined or partially combined; therefore, the actual execution order may change depending on the specific circumstances.

[0027] The terms "first," "second," etc., in the specification, claims, and accompanying drawings of this application are used to distinguish different objects, not to describe a specific order. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to these processes, methods, products, or apparatuses.

[0028] Those skilled in the art will understand that the accompanying drawings are merely schematic diagrams of exemplary embodiments, and the modules or processes in the drawings are not necessarily essential for implementing this application, and therefore cannot be used to limit the scope of protection of this application.

[0029] Figure 1 A schematic diagram of the flexible DC converter station of this application is shown.

[0030] like Figure 1 As shown, the flexible DC converter station includes: a passive system 101, a flexible DC system 201, a first power grid 501, a switch 401, and a second power grid 301.

[0031] The passive system 101 is connected to the second power grid 301 via the flexible DC system 201. Simultaneously, the first power grid 501 is connected to both the passive system 101 and the flexible DC system 201 via switch 401. The flexible DC converter station 2011 can be connected to the first power grid 501 by closing switch 401, operating in network control mode; or it can operate in islanded control mode by opening switch 401. The second power grid 301 and the first power grid 501 can be electrically connected or electrically isolated.

[0032] Figure 2 A flowchart illustrating an exemplary embodiment of a method for switching between networked control mode and islanded control mode for a flexible DC converter station is provided.

[0033] like Figure 2 As shown, the steps for switching the control mode of the flexible DC converter station from islanded control mode to networked control mode include:

[0034] Detecting the phase θ of the AC voltage of the first power grid Grid Modify the AC voltage frequency reference value of the flexible DC converter station to ensure that the AC voltage phase θ of the flexible DC converter station is adjusted. VSC Phase θ of the AC voltage of the first power grid Grid Synchronization; AC voltage phase θ at the flexible DC converter station VSC Phase θ of the AC voltage of the first power grid Grid In the case of synchronization, modify the AC voltage phase of the flexible DC converter station to the AC voltage phase θ of the first power grid. Grid When control switch 401 is closed, the control mode of the flexible DC converter station is switched from islanded control mode to networked control mode.

[0035] According to some embodiments, the phase θ of the AC voltage of the first power grid is... Grid The phase of the AC voltage of the first power grid can be obtained by detecting the AC voltage of the first power grid through a flexible DC converter station in islanded control mode; and / or the flexible DC converter station can receive the phase of the AC voltage of the first power grid transmitted by other flexible DC converter stations in network control mode.

[0036] According to some embodiments, modifying the AC voltage frequency reference value of the flexible DC converter station means: changing the original AC voltage frequency reference value F of the flexible DC converter station. ref-before The value is superimposed on the first preset frequency value ΔF to obtain a new AC voltage frequency reference value F for the flexible DC converter station. ref-after .

[0037] Among them, the newly obtained AC voltage frequency reference value F of the flexible DC converter station ref-after It must be within the allowable safe operation range of the flexible DC converter, wind farm, bridge arm reactor, transformer and switch in the flexible DC converter station.

[0038] The steps for switching the control mode of the flexible DC converter station from network control mode to islanded control mode include:

[0039] Control switch 401 is opened, and the control mode of the flexible DC converter station is switched from network control mode to islanded control mode; at the first moment, the inner loop current reference value I of the flexible DC system is controlled. d_ref I q_ref Adjusted to the actual inner loop current I of the flexible DC system d I q Set a limit on the rate of change, and at the second moment, control the inner loop current reference value I of the flexible DC system. d_ref I q_ref Adjusting the inner loop current I of the flexible DC system in islanded control mode d_ref_IS I q_ref_IS Furthermore, when the reference value of the inner loop current of the flexible DC system is adjusted to be in islanded control mode, the rate of change of the inner loop current of the flexible DC system shall not exceed the rate of change limit.

[0040] According to some embodiments, the inner loop current reference value I of the flexible DC system is calculated according to the following formula. d_ref I q_ref Adjusted to the actual inner loop current I d_ref_IS I q_ref_IS Rate of change:

[0041]

[0042] Where α1 and α2 are the reference values ​​I of the inner loop current of the flexible DC system. d_ref I q_ref Adjusting the inner loop current I of the flexible DC system in islanded control mode d_ref_IS I q_ref_IS rate of change, I set To set the current reference value. The rate of change limit, the first time step, and the second time step can be set by the user, with the first time step preceding the second time step.

[0043] According to some embodiments, during the step of switching the control mode of the flexible DC converter station from network control mode to island control mode, it is necessary to use a proportional limiting algorithm, a linear limiting algorithm, or other limiting algorithms to limit the reference voltage of the flexible DC converter station in order to limit the increase of the AC voltage of the flexible DC converter station during the conversion process.

[0044] This application also provides a system for switching between network control mode and islanded control mode for a flexible DC converter station, used to execute the switching method for network control mode and islanded control mode for a flexible DC converter station as described above. Figure 3As shown, the conversion system includes: a control mode conversion module 301, a phase tracking module 302, a frequency adjustment module 303, a phase adjustment module 304, an inner loop current control module 305, a rate of change limiting module 306, and a reference voltage limiting module 307.

[0045] The control mode conversion module 301 controls the closing or opening of the switch and switches the control mode of the flexible DC converter station between network control mode and islanded control mode. When the switch is closed, the control mode conversion module 301 also controls the flexible DC converter station to switch from islanded control mode to network control mode. When the switch is open, the control mode conversion module 301 also controls the flexible DC converter station to switch from network control mode to islanded control mode.

[0046] The phase tracking module 302 is used to detect the phase of the AC voltage of the first power grid.

[0047] The frequency adjustment module 303 is used to modify the AC voltage frequency reference value of the flexible DC converter station so that the AC voltage phase of the flexible DC converter station is synchronized with the AC voltage phase of the first power grid.

[0048] The phase adjustment module 304 is used to modify the AC voltage phase of the flexible DC converter station to the AC voltage phase of the first power grid when the AC voltage phase of the flexible DC converter station is synchronized with the AC voltage phase of the first power grid.

[0049] The inner loop current control module 305 is used to adjust the reference value of the inner loop current of the flexible DC system to the actual inner loop current of the flexible DC system in the first instant when the control mode of the flexible DC converter station changes from the network control mode to the island control mode.

[0050] The rate of change limiting module 306 is used to set the rate of change limit, and within the second moment, controls the inner loop current reference value of the flexible DC system to be adjusted to the inner loop current of the flexible DC system when it is in islanded control mode, and the inner loop current reference value of the flexible DC system is adjusted to ensure that the rate of change of the inner loop current of the flexible DC system when it is in islanded control mode does not exceed the rate of change limit.

[0051] The reference voltage limiting module 307 is used to limit the reference voltage of the flexible DC converter station according to a proportional limiting algorithm, a linear limiting algorithm, or other limiting algorithms during the process of switching the control mode of the flexible DC converter station from a network control mode to an island control mode, so as to limit the AC voltage of the flexible DC converter station.

[0052] This application provides a method and system for switching between grid-connected control mode and islanded control mode in a flexible DC converter station. Before switching from islanded control mode to grid-connected control mode, the grid voltage phase is tracked, and the flexible DC converter adopts grid voltage phase control, reducing the impact caused by phase difference during the switch from islanded control to grid-connected control. When switching from grid-connected control mode to islanded control mode, the control inner loop current is briefly tracked by the actual inner loop current, reducing the impact caused by sudden changes in the inner loop current reference value during the switch from grid-connected to islanded control, and improving the smoothness of the switch.

[0053] Figure 4 This diagram illustrates the structure of an electronic device provided in this application.

[0054] See Figure 4 , Figure 4 An electronic device is provided, including a processor and a memory. The memory stores computer instructions, which, when executed by the processor, cause the processor to perform the computer instructions to achieve the following: Figure 2 The method and its detailed scheme are shown.

[0055] It should be understood that the above-described device embodiments are merely illustrative, and the device disclosed in this application can also be implemented in other ways. For example, the division of units / modules in the above embodiments is only a logical functional division, and there may be other division methods in actual implementation. For example, multiple units, modules, or components may be combined, or integrated into another system, or some features may be ignored or not executed.

[0056] Furthermore, unless otherwise specified, the functional units / modules in the various embodiments of this application can be integrated into one unit / module, or each unit / module can exist physically separately, or two or more units / modules can be integrated together. The integrated units / modules described above can be implemented in hardware or as software program modules.

[0057] When integrated units / modules are implemented in hardware, the hardware can be digital circuits, analog circuits, etc. The physical implementation of the hardware structure includes, but is not limited to, transistors, memristors, etc. Unless otherwise specified, the processor or chip can be any suitable hardware processor, such as a CPU, GPU, FPGA, DSP, and ASIC, etc. Unless otherwise specified, on-chip cache, off-chip memory, and storage can be any suitable magnetic or magneto-optical storage medium, such as Resistive Random Access Memory (RRAM), Dynamic Random Access Memory (DRAM), Static Random Access Memory (SRAM), Enhanced Dynamic Random Access Memory (EDRAM), High-Bandwidth Memory (HBM), Hybrid Memory Cube (HMC), etc.

[0058] If the integrated unit / module is implemented as a software program module and sold or used as an independent product, it can be stored in a computer-readable storage device (CMD). Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a memory and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods of the various embodiments disclosed herein. The aforementioned memory includes various media capable of storing program code, such as a USB flash drive, read-only memory (ROM), random access memory (RAM), portable hard drive, magnetic disk, or optical disk.

[0059] This application also provides a non-transitory computer storage medium storing a computer program, which, when executed by multiple processors, causes the processors to perform actions such as... Figure 2 The method and its detailed scheme are shown.

[0060] It should be clearly understood that this application describes how specific examples are formed and used, but this application is not limited to any details of these examples. Rather, based on the teachings of the disclosure of this application, these principles can be applied to many other embodiments.

[0061] Furthermore, it should be noted that the above figures are merely illustrative representations of the processes included in the method according to exemplary embodiments of this application, and are not intended to be limiting. It is readily understood that the processes shown in the above figures do not indicate or limit the temporal order of these processes. Additionally, it is readily understood that these processes may be executed synchronously or asynchronously, for example, in multiple modules.

[0062] Exemplary embodiments of this application have been specifically shown and described above. It should be understood that this application is not limited to the detailed structures, arrangements, or implementation methods described herein; rather, this application is intended to cover various modifications and equivalent arrangements that fall within the objectives and scope of the appended claims.

Claims

1. A method for switching between network control mode and islanded control mode in a flexible DC converter station, characterized in that, The flexible DC converter station includes a passive network, a first power grid, a switch, and a flexible DC system. The passive network is connected to the flexible DC system, and the first power grid is connected to the flexible DC system through the switch. The conversion method includes: The control mode of the flexible DC converter station is switched from the islanded control mode to the networked control mode, including: Detect the phase of the AC voltage of the first power grid; Modify the AC voltage frequency reference value of the flexible DC converter station to synchronize the AC voltage phase of the flexible DC converter station with the AC voltage phase of the first power grid. When the AC voltage phase of the flexible DC converter station is synchronized with the AC voltage phase of the first power grid, the AC voltage phase of the flexible DC converter station is modified to the AC voltage phase of the first power grid. By controlling the switch to close, the control mode of the flexible DC converter station is adjusted from the islanded control mode to the networked control mode.

2. The conversion method as described in claim 1, characterized in that, Also includes: The control mode of the flexible DC converter station is switched from the network control mode to the islanded control mode, including: The switch is turned off, and the control mode of the flexible DC converter station is switched from the network control mode to the island control mode. At the first moment, the reference value of the inner loop current of the flexible DC system is adjusted to the actual inner loop current of the flexible DC system; A change rate limit is set. At the second moment, the reference value of the inner loop current of the flexible DC system is adjusted to the inner loop current of the flexible DC system when it is in the islanded control mode, and the change rate of the inner loop current of the flexible DC system is adjusted to not exceed the change rate limit.

3. The conversion method as described in claim 1, characterized in that, The detection of the AC voltage phase of the first power grid includes: The flexible DC converter station, operating in the islanded control mode, detects the AC voltage of the first power grid to obtain the phase of the AC voltage of the first power grid; and / or Receive the grid AC voltage phase of the first power grid from other flexible DC converter stations in the network control mode.

4. The conversion method as described in claim 1, characterized in that, Modifying the AC voltage frequency reference value of the flexible DC converter station to synchronize the AC voltage phase of the flexible DC converter station with the AC voltage phase of the first power grid includes: The original AC voltage frequency reference value of the flexible DC converter station is superimposed with the first preset frequency value to obtain a new AC voltage frequency reference value of the flexible DC converter station.

5. The conversion method as described in claim 4, characterized in that, The newly obtained AC voltage frequency reference value of the flexible DC converter station is within the safe operating range of the flexible DC converter, wind farm, bridge arm reactor, transformer and switchgear in the flexible DC converter station.

6. The conversion method as described in claim 2, characterized in that, Also includes: During the process of switching the control mode of the flexible DC converter station from the network control mode to the island control mode, a proportional limiting algorithm and / or a linear limiting algorithm are used to limit the reference voltage of the flexible DC converter station in order to limit the AC voltage of the flexible DC converter station.

7. A system for switching between network control mode and islanded control mode in a flexible DC converter station, characterized in that, The conversion system is used to perform the conversion method as described in any one of claims 1-6, the conversion system comprising: The control mode switching module is used to control the closing or opening of the switch, and to control the switching of the control mode of the flexible DC converter station between the network control mode and the island control mode; A phase tracking module is used to detect the phase of the AC voltage of the first power grid; The frequency adjustment module is used to modify the AC voltage frequency reference value of the flexible DC converter station so that the AC voltage phase of the flexible DC converter station is synchronized with the AC voltage phase of the first power grid. The phase adjustment module is used to modify the AC voltage phase of the flexible DC converter station to the AC voltage phase of the first power grid when the AC voltage phase of the flexible DC converter station is synchronized with the AC voltage phase of the first power grid.

8. The conversion system as described in claim 7, characterized in that, When the control mode conversion module controls the switch to close, the control mode conversion module also controls the control mode of the flexible DC converter station to switch from the islanded control mode to the networked control mode; When the control mode conversion module controls the switch to be turned off, the control mode conversion module also controls the control mode of the flexible DC converter station to be switched from the network control mode to the island control mode.

9. The conversion system as described in claim 7, characterized in that, Also includes: The inner loop current control module is used to adjust the reference value of the inner loop current of the flexible DC system to the actual inner loop current of the flexible DC system within the first moment when the control mode of the flexible DC converter station is changed from the network control mode to the island control mode. The rate of change limiting module is used to set a rate of change limit and, within a second time moment, control the inner loop current reference value of the flexible DC system to be adjusted to the inner loop current of the flexible DC system when it is in the islanded control mode, and the rate of change of the inner loop current of the flexible DC system when it is in the islanded control mode does not exceed the rate of change limit.

10. The conversion system as described in claim 8, characterized in that, Also includes: The reference voltage limiting module is used to limit the reference voltage of the flexible DC converter station according to a proportional limiting algorithm and / or a linear limiting algorithm during the process of switching the control mode of the flexible DC converter station from the network control mode to the island control mode, so as to limit the AC voltage of the flexible DC converter station.

11. An electronic device, characterized in that, include: One or more processors; Memory, used to store one or more programs; When the one or more programs are executed by the one or more processors, the one or more processors perform the method as described in any one of claims 1-6.

12. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the program is executed by the processor, it implements the method as described in any one of claims 1-6.

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