Control methods and devices for flexible DC transmission systems

Abstract

This application relates to a control method and apparatus for a flexible DC transmission system. According to the scheme provided in this application, when the AC side connection of the flexible DC transmission system changes, during the transition from grid-connected operation mode to islanded operation mode of the converter during unlocked operation, the DQ-axis component of the reference voltage in islanded operation mode tracks the DQ-axis component of the measured voltage in grid-connected operation mode. This achieves the effect of amplitude and phase synchronization control during the transition from grid-connected operation mode to islanded operation mode. The converter smoothly switches from grid-connected operation mode to islanded operation mode, avoiding system overcurrent and improving the reliability and stability of the flexible DC transmission system's operation mode transition.

Description

Technical Field

[0001] This application relates to the field of flexible DC transmission technology, and in particular to a control method and apparatus for a flexible DC transmission system. Background Technology

[0002] Flexible DC transmission systems are characterized by flexible control, rapid dynamic response, and low harmonic content. They can quickly and independently adjust active and reactive power, and have broad application prospects. In particular, flexible DC transmission systems can operate as passive systems, independently supplying power to the grid, making them especially suitable for island power grids with weak grids.

[0003] When the island power grid has AC power, the flexible DC transmission system can operate in grid-connected mode. However, if AC power is lost due to a fault, the flexible DC transmission system needs to switch from grid-connected mode to islanded mode. To reduce the impact of high-frequency components during islanded operation, direct voltage control is often used. However, if the system immediately switches to direct voltage control after switching from grid-connected to islanded mode, the asynchrony between the reference wave and the actual voltage amplitude and phase can easily cause system overcurrent. Summary of the Invention

[0004] In response to the problems existing in the prior art, the inventors realized that in order to avoid the problems caused by immediately switching to direct voltage control when switching from grid connection to islanding, the flexible DC transmission system needs to consider the synchronization of the reference wave during the grid connection to islanding transition.

[0005] Based on this, according to the first aspect of this application, a control method for a flexible DC transmission system is provided, characterized in that it includes:

[0006] Detecting the frequency at which the flexible DC transmission system is in grid-connected operation mode;

[0007] If the frequency deviation is greater than or equal to the frequency setting value, it is determined that the flexible DC transmission system will be switched from the grid-connected operation mode to the islanded operation mode.

[0008] The AC voltage amplitude is calculated based on the AC voltage detected in the cycle preceding the determination of switching the flexible DC transmission system to the islanded operation mode.

[0009] The reference amplitude value output by the flexible DC transmission system during the transition to the islanded operation mode is determined based on the AC voltage amplitude.

[0010] Based on the reference amplitude value and the D-axis and Q-axis components of the AC voltage detected after switching the flexible DC transmission system to the islanded operation mode, the D-axis and Q-axis components of the reference voltage in the islanded operation mode are determined; and

[0011] In response to the D-axis and Q-axis components of the reference voltage satisfying preset conditions, the D-axis component of the reference voltage is set to the reference amplitude value, and the Q-axis component of the reference voltage is set to 0.

[0012] According to a second aspect of this application, a control device for a flexible DC transmission system is provided, characterized in that it comprises:

[0013] The detection module is used to detect the frequency at which the flexible DC transmission system is in network operation mode;

[0014] The first determining module is used to determine, when the frequency deviation is greater than or equal to the frequency setting value, to switch the flexible DC transmission system from the grid operation mode to the island operation mode.

[0015] The calculation module is used to calculate the AC voltage amplitude based on the AC voltage detected in the previous cycle before determining whether to switch the flexible DC transmission system to the islanded operation mode.

[0016] The second determining module is used to determine the reference wave amplitude value output by the flexible DC transmission system during the transition to the islanded operation mode based on the AC voltage amplitude.

[0017] The third determining module is used to determine the D-axis and Q-axis components of the reference voltage in the islanded operation mode based on the reference amplitude value and the D-axis and Q-axis components of the AC voltage detected after the flexible DC transmission system is switched to the islanded operation mode; and

[0018] The setting module is configured to, in response to the D-axis component and Q-axis component of the reference voltage satisfying preset conditions, set the D-axis component of the reference voltage to the reference amplitude value and set the Q-axis component of the reference voltage to 0.

[0019] According to a third aspect of this application, an electronic device is provided, comprising:

[0020] Processor; and

[0021] A memory storing computer instructions that, when executed by the processor, cause the processor to perform the method described in the first aspect.

[0022] According to a fourth aspect of this application, a non-transitory computer storage medium is provided, which stores a computer program that, when executed by a plurality of processors, causes the processors to perform the method described in the first aspect.

[0023] According to the control method and apparatus for the flexible DC transmission system provided in this application, when the AC side connection of the flexible DC transmission system changes, during the transition from grid-connected operation mode to islanded operation mode of the converter during unlocked operation, the DQ-axis component of the reference voltage in islanded operation mode tracks the DQ-axis component of the measured voltage in grid-connected operation mode, achieving the effect of amplitude and phase synchronization control during the transition from grid-connected operation mode to islanded operation mode. The converter smoothly switches from grid-connected operation mode to islanded operation mode, avoiding system overcurrent and improving the reliability and stability of the flexible DC transmission system's operation mode transition. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings, without exceeding the scope of protection claimed by this application.

[0025] Figure 1 This is a flowchart of a control method for a flexible DC transmission system according to the first embodiment of this application.

[0026] Figure 2 This is a flowchart of a control method for a flexible DC transmission system according to a second embodiment of this application.

[0027] Figure 3 This is a flowchart of a control method for a flexible DC transmission system according to a third embodiment of this application.

[0028] Figure 4 This is a waveform diagram showing the transition from network operation mode to island operation mode before synchronization.

[0029] Figure 5 This is a waveform diagram of the switch from network operation mode to island operation mode according to the control method of this application.

[0030] Figure 6 This is a schematic diagram of the control device for a flexible DC transmission system according to the first embodiment of this application.

[0031] Figure 7 This is a schematic diagram of the control device for a flexible DC transmission system according to a second embodiment of this application.

[0032] Figure 8 This is a schematic diagram of the control device for a flexible DC transmission system according to a third embodiment of this application.

[0033] Figure 9 This is a structural diagram of an electronic device provided in this application. Detailed Implementation

[0034] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0035] Figure 1 This is a flowchart of a control method for a flexible DC transmission system according to the first embodiment of this application. Figure 1 As shown, the method includes the following steps.

[0036] Step S101: Detect the frequency at which the flexible DC transmission system is in grid-connected operation mode;

[0037] Step S102: If the frequency deviation is greater than or equal to the frequency setting value, determine to switch the flexible DC transmission system from the grid operation mode to the island operation mode.

[0038] Various relevant data of the flexible DC transmission system in grid-connected operation mode, including AC voltage and frequency. The frequency deviation Δf of the flexible DC transmission system is greater than or equal to the frequency setpoint f. set In the case that |Δf|≥f set The decision was made to switch the flexible DC transmission system from grid-connected operation mode to islanded operation mode. According to one embodiment, the frequency setpoint f... set The range is 0.01 to 5 Hz.

[0039] According to one embodiment, in order to prevent misjudgment caused by temporary frequency jumps, the frequency deviation Δf in the flexible DC transmission system is greater than or equal to the frequency setpoint f. set At this time, it is also necessary to wait for a preset delay time and observe whether the frequency deviation Δf is greater than or equal to the frequency setting value f during this preset delay time. set If the rate deviation Δf is greater than or equal to the frequency setting value f within the preset delay time... set Then, it is determined that the flexible DC transmission system will be switched from grid-connected operation mode to islanded operation mode, and the islanded operation mode ISOCTR=1 will be set.

[0040] It should be noted that although it is determined that the flexible DC transmission system will be switched from grid-connected operation mode to islanded operation mode, it does not mean that the system has completed the conversion to islanded operation mode. This application focuses on how the flexible DC transmission system should operate to make the conversion process smoother, avoid system overcurrent, and improve the stability and reliability of system operation during the process from determining to switch to islanded operation mode to actually completing the conversion and switching to islanded DC voltage control.

[0041] According to some embodiments, the frequency setpoint f set The preset delay time can be set to an appropriate value according to actual needs, and this application does not impose any restrictions on it.

[0042] Step S103: Calculate the AC voltage amplitude based on the AC voltage detected in the previous cycle before the flexible DC transmission system is switched to the islanded operation mode.

[0043] Regardless of whether the flexible DC transmission system is in grid-connected or islanded operation mode, it will collect relevant data, such as AC voltage, within a set cycle, once per cycle, and continuously in this manner. When it is determined that the flexible DC transmission system will be switched to islanded operation mode, the acquired AC voltage U... sm It determines the AC voltage detected in the cycle preceding the switch of the flexible DC transmission system to islanded operation mode, and calculates the AC voltage amplitude U based on this AC voltage. sm This calculation process can employ existing calculation methods, and this application makes no restrictions on it.

[0044] Step S104: Determine the reference amplitude value output by the flexible DC transmission system during the transition to the islanded operation mode based on the AC voltage amplitude.

[0045] When it is determined that the flexible DC transmission system will be switched to islanded operation mode, that is, after the ISOCTR of islanded operation mode changes from 0 to 1, the reference amplitude value U in islanded operation mode is determined. refm .

[0046] According to some embodiments, the voltage amplitude U can be used as a basis. sm The numerical range determines the reference amplitude value U. refm The value and changes of the high voltage setpoint U. H and low voltage setting U L , when U sm ≥U H At that time, U refm From U sm According to the first set rate K H Reduce to the voltage rating U refN ; when U sm ≤U L At that time, U refm From U sm According to the second set rate K L Increase to the voltage rating U refN ; when U L <U sm <U H At that time, U refm Set to voltage rating U refN .

[0047] According to some embodiments, the high voltage setpoint U H Low voltage setting U L First set rate K H Second set rate K L and voltage rating U refN It can be configured according to actual requirements, for example, U L =0.9pu, U H =1.3 pu, etc., this application does not impose any restrictions on this.

[0048] Thus, step S104 can specifically include the following steps:

[0049] In response to the AC voltage amplitude being greater than or equal to a high voltage setting value, the reference wave amplitude is reduced from the AC voltage amplitude to the voltage rating set in the islanding operation mode at a first set rate.

[0050] In response to the AC voltage amplitude being less than or equal to a low voltage setting value, the reference waveform amplitude is increased from the AC voltage amplitude to the voltage rating value at a second set rate; and

[0051] In response to the AC voltage amplitude being between the high voltage setting value and the low voltage setting value, the reference amplitude value is set to the voltage rating value.

[0052] Step S105: Based on the reference amplitude value and the D-axis and Q-axis components of the AC voltage detected after the flexible DC transmission system is switched to the islanded operation mode, determine the D-axis and Q-axis components of the reference voltage in the islanded operation mode.

[0053] Step S106: In response to the D-axis component and Q-axis component of the reference voltage satisfying a preset condition, the D-axis component of the reference voltage is set to the reference amplitude value, and the Q-axis component of the reference voltage is set to 0.

[0054] According to some embodiments, during a period of time after the start of islanded operation mode, the D-axis and Q-axis components of the AC voltage output by the converter are continuously detected, and the D-axis and Q-axis components of the reference voltage of the islanded control loop are kept tracking the D-axis and Q-axis components of the current AC voltage output by the converter. When the D-axis and Q-axis components of the reference voltage are detected to meet preset conditions, the D-axis component of the reference voltage is set as the reference amplitude value, and the Q-axis component of the reference voltage is set to 0.

[0055] Determining the D-axis and Q-axis components of the reference voltage in the islanded operation mode includes: keeping the D-axis and Q-axis components of the reference voltage tracking the D-axis and Q-axis components of the AC voltage, including making the D-axis and Q-axis components of the reference voltage equal to the D-axis and Q-axis components of the AC voltage, respectively.

[0056] According to some embodiments, when the ISOCTR in islanded operation mode changes from 0 to 1, the AC voltage of the flexible DC transmission system is detected, and the D-axis component U of the AC voltage of the system operation is obtained. sd and Q-axis component U sq Then, based on the D-axis component U of the AC voltage sd and Q-axis component U sd and the aforementioned reference amplitude value U refm The D-axis component U of the reference voltage in islanded operation mode is obtained. dref and Q-axis component U qref .

[0057] According to some embodiments, the D-axis component U of the reference voltage can be calculated based on equations (1) and (2). dref and Q-axis component U qref :

[0058]

[0059]

[0060] It should be noted that the D-axis component U of the reference voltage calculated above based on equations (1) and (2) dref and Q-axis component U qref This is merely an example; other calculation methods that can be conceived by those skilled in the art based on this are all within the scope of this application.

[0061] Based on the above reference amplitude value U refm And the D-axis component U of the AC voltage sd and Q-axis component U sq Determine the D-axis component U of the reference voltage dref and Q-axis component U qref During the process, the D-axis component U of the AC voltage sd and Q-axis component U sq It changes constantly, while the reference amplitude value U refm Voltage rating U refN Previously, the reference amplitude value U refm It is also constantly changing, for example, according to the first set rate K. H Reduce or follow the second set rate K L If the value increases, then the D-axis component U of the reference voltage... dref and Q-axis component Uqref It is also constantly changing. Real-time monitoring of the D-axis component U of the reference voltage. dref and Q-axis component U qref The value and range of the value, when the preset conditions are met, will be the D-axis component U of the reference voltage. dref Set as reference amplitude value U refm and the Q-axis component U of the reference voltage qref Set to 0. Wherein, the reference amplitude value U refm To satisfy the preset conditions, the corresponding reference amplitude value, if the reference amplitude value U refm The D-axis component U of the constantly changing reference voltage dref It changes accordingly.

[0062] According to some embodiments, when and when, the islanded operation reference wave switching flag U is set. swi =1, set U dref ≥U dset ,|U qref |≤U qset , among which, U dset U is the reference voltage D-axis component synchronization setting value for islanded operation. qset This is the synchronization setting value for the Q-axis component of the reference voltage during islanded operation. It can be set according to actual needs, for example, U... dset ≥0.5pu, U qset ≥0.2 pu, this application does not impose any restrictions on this.

[0063] Therefore, according to one specific embodiment, the preset conditions include that the D-axis component of the reference voltage is greater than or equal to the synchronous setting value of the D-axis component of the reference voltage, and the Q-axis component of the reference voltage is less than or equal to the synchronous setting value of the Q-axis component of the reference voltage. According to some embodiments, the synchronous setting value Dset of the D-axis component of the reference voltage satisfies a certain range, for example, 0 ≤ Dset ≤ 1.0, and the synchronous setting value Qset of the Q-axis component of the reference voltage satisfies a certain range, for example, 0 ≤ Qset ≤ 1.0.

[0064] Figure 2 This is a flowchart of a control method for a flexible DC transmission system according to a second embodiment of this application. Figure 1 compared to, Figure 2 Steps S201 to S206 and Figure 1 Steps S101 to S106 are the same. The difference lies in that... Figure 2 The method further includes step S202' after step S202.

[0065] In step S202', the frequency of the flexible DC transmission system is switched from the actual grid frequency to the first self-generated frequency.

[0066] The flexible DC transmission system collects relevant data, such as frequency, within a set period, once per period, and continues to collect data in this way. Among these data, the actual grid frequency f... s It is the grid frequency obtained in the cycle preceding the transition of the flexible DC transmission system to islanded operation mode, the first self-generated frequency f1 and the actual grid frequency f s The difference is greater than or equal to the frequency offset setting value α, i.e., |f1-f s |≥α. The frequency difference setting value α can be set as needed, for example, the frequency difference setting value range is 0≤fset1≤5Hz, etc., and this application does not impose any restrictions on it.

[0067] Figure 3 This is a flowchart of a control method for a flexible DC transmission system according to a third embodiment of this application. Figure 1 compared to, Figure 3 Steps S301 to S306 and Figure 1 Steps S101 to S106 are the same. The difference lies in that... Figure 3 The method further includes step S306' after step S306.

[0068] In step S306', the frequency of the flexible DC transmission system is switched to the second self-generated frequency, wherein the second self-generated frequency is the rated frequency corresponding to the operation in the islanded operation mode.

[0069] According to some implementations, when the islanded operation mode ISOCTR=1 and U swi When f = 1, the frequency of the flexible DC transmission system is switched to the second self-generated frequency f2, wherein the second self-generated frequency f2 is the rated frequency f corresponding to the islanded operation mode. N That is, f2 = f N .

[0070] Thus, when the actual transition to islanded operation mode and switch to islanded DC voltage control is completed, the D-axis component U of the reference voltage... dref Reference amplitude value U refm The Q-axis component U of the reference voltage qref When the frequency is 0, the flexible DC transmission system switches to its self-generated frequency, which is the rated frequency f. N .

[0071] Figure 4 This is a waveform diagram showing the transition from network operation mode to island operation mode before synchronization. Figure 5 This is a waveform diagram showing the transition from networked operation mode to islanded operation mode according to the control method of this application. Synchronous control according to the scheme provided in this application yields the following results. Figure 5As shown, during the instant of switching from grid connection to islanding (ISOCTRL changes from 0 to 1), the phases of the reference voltages UREF_L1, UREF_L2, and UREF_L3 do not change, achieving the effect of amplitude and phase synchronization control during the grid-to-islanding transition. There is no overcurrent in the valve-side currents IV_C_LA, IV_C_LB, and IV_C_LC, and the system continues to operate (DEBLOCKED = 1), improving the stability and reliability of the flexible DC system. Without the synchronization control method of this application, the waveform during the instant of switching from grid connection to islanding (ISOCTRL changes from 0 to 1) is as follows: Figure 4 As shown, reference voltages UREF_L1, UREF_L2, and UREF_L3 experienced jumps, leading to overcurrent tripping of valve-side currents IV_C_LA, IV_C_LB, and IV_C_LC (DEBLOCKED changed from 1 to 0). Figure 4 and Figure 5 In this context, DEBLOCKED indicates a signal indicating that the system is running or shut down. "DEBLOCKED=1" indicates that the system is running, and "DEBLOCKED=0" indicates that the system is shut down.

[0072] Based on the aforementioned control method for flexible DC transmission systems, according to another aspect of this application, a control device for a flexible DC transmission system is provided, such as... Figure 6 As shown, the device includes: a detection module 601 for detecting the frequency of the flexible DC transmission system in grid-connected operation mode; a first determination module 602 for determining, when the frequency deviation is greater than or equal to a frequency set value, to switch the flexible DC transmission system from grid-connected operation mode to islanded operation mode; a calculation module 603 for calculating the AC voltage amplitude based on the AC voltage detected in the cycle preceding the determination to switch the flexible DC transmission system to islanded operation mode; and a second determination module 604 for determining the flexible DC transmission system's frequency based on the AC voltage amplitude. The system outputs a reference amplitude value during the transition to the islanded operation mode; a third determining module 605 is used to determine the D-axis and Q-axis components of the reference voltage in the islanded operation mode based on the reference amplitude value and the D-axis and Q-axis components of the AC voltage detected after the flexible DC transmission system is transitioned to the islanded operation mode; and a setting module 606 is used to set the D-axis component of the reference voltage to the reference amplitude value and set the Q-axis component of the reference voltage to 0 in response to the D-axis and Q-axis components of the reference voltage satisfying a preset condition.

[0073] According to some embodiments, the second determining module 604 can be specifically used for:

[0074] In response to the AC voltage amplitude being greater than or equal to a high voltage setting value, the reference wave amplitude is reduced from the AC voltage amplitude to the voltage rating set in the islanding operation mode at a first set rate.

[0075] In response to the AC voltage amplitude being less than or equal to a low voltage setting value, the reference waveform amplitude is increased from the AC voltage amplitude to the voltage rating value at a second set rate; and

[0076] In response to the AC voltage amplitude being between the high voltage setting value and the low voltage setting value, the reference amplitude value is set to the voltage rating value.

[0077] According to some embodiments, the preset conditions include: the D-axis component of the reference voltage is greater than or equal to the synchronous setting value of the D-axis component of the reference voltage, and the Q-axis component of the reference voltage is less than or equal to the synchronous setting value of the Q-axis component of the reference voltage.

[0078] Figure 7 This is a schematic diagram of a control device for a flexible DC transmission system according to a second embodiment of this application. Figure 6 compared to, Figure 7 Modules 701 to 706 and Figure 6 Modules 601 to 606 are the same. The difference lies in... Figure 7 The device also includes a first frequency switching module 702', used to switch the frequency of the flexible DC transmission system from the actual grid frequency to a first self-generated frequency, wherein the actual grid frequency is the grid frequency obtained in the previous cycle before the flexible DC transmission system is switched to the islanded operation mode, and the difference between the first self-generated frequency and the actual grid frequency is greater than or equal to the frequency difference setting value.

[0079] Figure 8 This is a schematic diagram of a control device for a flexible DC transmission system according to a third embodiment of this application. Figure 6 compared to, Figure 8 Modules 801 to 806 and Figure 6 Modules 601 to 606 are the same. The difference lies in... Figure 8 The device also includes a second frequency switching module 806', used to switch the frequency of the flexible DC transmission system to a second self-generated frequency, wherein the second self-generated frequency is the rated frequency corresponding to the operation in the islanded operation mode.

[0080] According to the control method and apparatus for the flexible DC transmission system provided in this application, when the AC side connection of the flexible DC transmission system changes, during the transition from grid-connected operation mode to islanded operation mode of the converter during unlocked operation, the DQ-axis component of the reference voltage in islanded operation mode tracks the DQ-axis component of the measured voltage in grid-connected operation mode, achieving the effect of amplitude and phase synchronization control during the transition from grid-connected operation mode to islanded operation mode. The converter smoothly switches from grid-connected operation mode to islanded operation mode, avoiding system overcurrent and improving the reliability and stability of the flexible DC transmission system's operation mode transition.

[0081] In the above embodiments, the descriptions of each embodiment have different focuses. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions in other embodiments.

[0082] It should be noted that, for the sake of simplicity, the foregoing method embodiments are all described as a series of actions. However, those skilled in the art should understand that this application is not limited to the described order of actions, as some steps may be performed in other orders or simultaneously according to this application. Furthermore, those skilled in the art should also understand that the embodiments described in the specification are all optional embodiments, and the actions and modules involved are not necessarily essential to this application.

[0083] In the several embodiments provided in this application, it should be understood that the disclosed apparatus can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between devices or units may be an electrical connection or other forms.

[0084] See Figure 9 , Figure 9 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: Figures 1 to 3 The method and its detailed scheme are shown.

[0085] It should be understood that the above-described device embodiments are merely illustrative, and the device disclosed in this invention can be implemented in other ways. For example, the division of units / modules described 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, integrated into another system, or some features may be ignored or not executed.

[0086] Furthermore, unless otherwise specified, the functional units / modules in the various embodiments of the present invention 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.

[0087] If the integrated unit / module is 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, the 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.

[0088] 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 invention, 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 electronic device (which may be a personal computer, server, or network electronic device, etc.) to execute all or part of the steps of the methods described in the various embodiments of this disclosure. The aforementioned memory includes various media capable of storing program code, such as USB flash drives, read-only memory (ROM), random access memory (RAM), portable hard drives, magnetic disks, or optical disks.

[0089] This application embodiment 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... Figures 1 to 3 The method and its detailed scheme are shown.

[0090] The embodiments of this application have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the embodiments above are only for the purpose of helping to understand the method and core ideas of this application. Furthermore, any changes or modifications made by those skilled in the art based on the ideas of this application, and on the specific implementation methods and application scope of this application, are all within the scope of protection of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A control method for a flexible DC transmission system, characterized in that, include: Detecting the frequency at which the flexible DC transmission system is in grid-connected operation mode; If the frequency deviation is greater than or equal to the frequency setting value, it is determined that the flexible DC transmission system will be switched from the grid-connected operation mode to the islanded operation mode. The AC voltage amplitude is calculated based on the AC voltage detected in the cycle preceding the determination of switching the flexible DC transmission system to the islanded operation mode. The reference amplitude value output by the flexible DC transmission system during the transition to the islanded operation mode is determined based on the AC voltage amplitude. Based on the reference amplitude value and the D-axis and Q-axis components of the AC voltage detected after the flexible DC transmission system is switched to the islanded operation mode, the D-axis and Q-axis components of the reference voltage in the islanded operation mode are determined. as well as In response to the D-axis component and Q-axis component of the reference voltage satisfying a preset condition, the D-axis component of the reference voltage is set to the reference amplitude value, and the Q-axis component of the reference voltage is set to 0. The step of determining the reference waveform amplitude in the islanding operation mode based on the AC voltage amplitude includes: In response to the AC voltage amplitude being greater than or equal to a high voltage setting value, the reference wave amplitude is reduced from the AC voltage amplitude to the voltage rating set in the islanded operation mode at a first set rate; In response to the AC voltage amplitude being less than or equal to a low voltage setting value, the reference waveform amplitude is increased from the AC voltage amplitude to the voltage rating value at a second set rate. In response to the AC voltage amplitude being between the high voltage setting value and the low voltage setting value, the reference amplitude value is set to the voltage rating value.

2. The control method for a flexible DC transmission system as described in claim 1, wherein determining the D-axis and Q-axis components of the reference voltage in the islanded operation mode includes: Maintaining the D-axis and Q-axis components of the reference voltage to track the D-axis and Q-axis components of the AC voltage includes ensuring that the D-axis and Q-axis components of the reference voltage are equal to the D-axis and Q-axis components of the AC voltage, respectively.

3. The method as described in claim 1, characterized in that, After determining to switch the flexible DC transmission system from the grid-connected operation mode to the islanded operation mode, the method further includes: The frequency of the flexible DC transmission system is switched from the actual grid frequency to a first self-generated frequency, wherein the actual grid frequency is the grid frequency obtained in the previous cycle before the flexible DC transmission system is switched to the islanded operation mode, and the difference between the first self-generated frequency and the actual grid frequency is greater than or equal to the frequency difference setting value.

4. The method as described in claim 1 or 2, characterized in that, After setting the Q-axis component of the reference voltage to 0, the method further includes: The frequency of the flexible DC transmission system is switched to a second self-generated frequency, wherein the second self-generated frequency is the rated frequency corresponding to the operation in the islanded operation mode.

5. The method as described in claim 1 or 2, characterized in that, The preset conditions include: the D-axis component of the reference voltage is greater than or equal to the synchronous setting value of the D-axis component of the reference voltage, and the Q-axis component of the reference voltage is less than or equal to the synchronous setting value of the Q-axis component of the reference voltage.

6. A control device for a flexible DC transmission system, characterized in that, include: The detection module is used to detect the frequency at which the flexible DC transmission system is in network operation mode; The first determining module is used to determine, when the frequency deviation is greater than or equal to the frequency setting value, to switch the flexible DC transmission system from the grid operation mode to the island operation mode. The calculation module is used to calculate the AC voltage amplitude based on the AC voltage detected in the previous cycle before determining whether to switch the flexible DC transmission system to the islanded operation mode. The second determining module is used to determine the reference wave amplitude value output by the flexible DC transmission system during the transition to the islanded operation mode based on the AC voltage amplitude. The third determining module is used to determine the D-axis component and Q-axis component of the reference voltage in the islanding operation mode based on the reference amplitude value and the D-axis component and Q-axis component of the AC voltage detected after the flexible DC transmission system is switched to the islanding operation mode. as well as The setting module is configured to, in response to the D-axis component and Q-axis component of the reference voltage satisfying preset conditions, set the D-axis component of the reference voltage to the reference amplitude value and set the Q-axis component of the reference voltage to 0. The second determining module is used for: In response to the AC voltage amplitude being greater than or equal to a high voltage setting value, the reference wave amplitude is reduced from the AC voltage amplitude to the voltage rating set in the islanded operation mode at a first set rate; In response to the AC voltage amplitude being less than or equal to a low voltage setting value, the reference waveform amplitude is increased from the AC voltage amplitude to the voltage rating value at a second set rate. In response to the AC voltage amplitude being between the high voltage setting value and the low voltage setting value, the reference amplitude value is set to the voltage rating value.

7. The apparatus as claimed in claim 6, characterized in that, Also includes: The first frequency switching module is used to switch the frequency of the flexible DC transmission system from the actual grid frequency to the first self-generated frequency. The actual grid frequency is the grid frequency obtained in the previous cycle before the flexible DC transmission system is switched to the islanded operation mode. The difference between the first self-generated frequency and the actual grid frequency is greater than or equal to the frequency difference setting value.

8. The apparatus as claimed in claim 6 or 7, characterized in that, Also includes: The second frequency switching module is used to switch the frequency of the flexible DC transmission system to a second self-generated frequency, wherein the second self-generated frequency is the rated frequency corresponding to the operation in the islanded operation mode.

9. An electronic device, characterized in that, The device includes a memory and a processor, wherein the memory stores a computer program, and the processor, when executing the computer program in the memory, implements the method of any one of claims 1 to 5.

10. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores a computer program that, when executed by a processor, implements the method of any one of claims 1 to 5.

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