A method and device for optimizing low-penetration parameters of a conventional unit through a flexible island sending-out system

Abstract

The application provides a flexible low penetration parameter optimization method and device for a conventional unit through a flexible island sending-out system, comprising setting an initial active current maximum value of the island sending-out system during low voltage penetration according to a conventional method; performing AC line three permanent N-1 fault scanning on the system and performing stability discrimination; recording a positive sequence voltage minimum value of a converter bus during single-phase transient fault; judging a converter bus voltage drop degree according to a voltage level and the positive sequence voltage minimum value of the converter bus during fault and recovery; re-designing the active current maximum value according to the positive sequence voltage drop degree of the converter bus; re-performing fault scanning on the island sending-out system, and if the system is stable, taking the adjusted active current maximum value as an active current limiting value of the island sending-out system during low voltage penetration. The application can automatically adjust the active current limiting value during flexible low voltage penetration according to the converter bus voltage drop degree, thereby enhancing the stability of the system.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of power grid planning and operation of power systems, and particularly relates to a flexible low penetration parameter optimization method and device for a conventional unit through a flexible island sending-out system. BACKGROUND

[0002] In order to meet the demand of power development, it is necessary to transmit clean energy from resource-rich areas to areas with high demand. Specifically, this means that clean energy is transported from western provinces with abundant wind energy, solar energy and hydropower resources to eastern provinces with high demand for electricity. Due to the limited clean energy resources in eastern provinces, the introduction of these clean energy from the west through high-voltage direct-current transmission technology becomes an important means. In addition, considering the small scale of the sending-end power grid, in order to reduce the impact on the sending-end power grid, the direct-current transmission system and related energy facilities are usually set to island operation mode.

[0003] Due to the distribution conditions of new energy and conventional unit resources, the sending end may adopt a multi-terminal direct current form to collect different types of power sources for sending out, and the conventional unit through the flexible island sending-out system may occur. Due to the influence of the time sequence of the conventional unit, the direct current capacity may be greater than the capacity of the matching power source. At this stage, the direct current will be operated at a low power level. The flexible low penetration strategy of the conventional unit will result in a low voltage penetration during a short-circuit fault, and the active current of the flexible direct current will be greater than the normal value. After the fault is cleared, the system static voltage may be unstable, and the safety and stability of the "small unit, large direct current" island sending-out system cannot be met. SUMMARY

[0004] Therefore, the present application provides a flexible low penetration parameter optimization method and device for a conventional unit through a flexible island sending-out system, which aims to optimize the maximum active current limiting during the flexible low penetration, so that the flexible active current limiting during the low penetration is automatically adjusted according to the voltage drop of the converter bus, thereby improving the stability characteristics of the "small unit, large direct current" island sending-out system after a three-phase short-circuit fault.

[0005] In order to achieve the above-mentioned purpose, the technical scheme provided by the present application is as follows:

[0006] In a first aspect, the present application provides a flexible low penetration parameter optimization method for a conventional unit through a flexible island sending-out system, comprising the following steps:

[0007] Setting the initial maximum active current of the island sending-out system during low voltage penetration;

[0008] Performing AC line three permanent N-1 fault scanning on the island sending-out system and performing stability discrimination;

[0009] Recording the minimum positive sequence voltage of the converter bus during single-phase transient fault;

[0010] determining the voltage drop degree of the converter bus according to the voltage level and the minimum positive sequence voltage of the converter bus during the fault and recovery period;

[0011] re-setting the maximum active current of the islanded sending system during the low voltage ride through according to the voltage drop degree of the converter bus;

[0012] re-scanning the AC line three permanent N-1 fault of the islanded sending system based on the adjusted maximum active current, and if the system is stable, taking the adjusted maximum active current as the maximum active current limit of the islanded sending system during the low voltage ride through.

[0013] Further, if the voltage value of the converter bus during the fault and recovery period is less than the minimum positive sequence voltage;

[0014] adjusting the maximum active current according to the voltage drop degree of the converter bus, comprising:

[0015] if the voltage value of the converter bus during the fault and recovery period is less than the minimum positive sequence voltage and greater than a first set value, reducing the maximum active current according to the voltage drop degree of the converter bus based on the initial maximum active current;

[0016] if the voltage value of the converter bus during the fault and recovery period is not greater than the first set value, reducing the maximum active current to 0.

[0017] Further, the first set value is , the minimum positive sequence voltage, the allowed maximum voltage drop value.

[0018] Further, when the maximum active current is reduced according to the voltage drop degree of the converter bus, the maximum active current is calculated according to the following formula:

[0019]

[0020] In the formula, is the maximum active current, is the maximum current, is the maximum reactive current, is the voltage value of the converter bus during the fault and recovery period.

[0021] Further, if the voltage value of the converter bus during the fault and recovery period is not less than the minimum positive sequence voltage and less than a second set value, it is determined that the voltage drop degree of the converter bus is not deep, at this time the maximum active current remains the initial set value, and the initial set value is determined according to the following formula:

[0022]

[0023] In the formula, This is the maximum value of the active current. This is the maximum current value. This represents the maximum reactive current.

[0024] Secondly, the present invention provides a device for optimizing the low-profile transmission parameters of a conventional unit via a flexible DC islanding system, comprising the following steps:

[0025] The initial setup module is used to set the initial maximum active current of the islanded transmission system during low voltage ride-through.

[0026] The fault scanning module is used to perform AC line three-terminal N-1 fault scanning on the islanded transmission system and to determine its stability. It is also used to re-scan the AC line three-terminal N-1 fault on the islanded transmission system based on the adjusted maximum active current. If the system is stable, the adjusted maximum active current will be used as the active current limit of the islanded transmission system during low voltage ride-through.

[0027] The voltage recording module is used to record the minimum positive sequence voltage of the converter bus during a single-phase transient fault.

[0028] The voltage drop detection module is used to determine the degree of voltage drop of the converter bus based on the voltage level of the converter bus and the minimum positive sequence voltage during the fault and recovery periods.

[0029] The active current limiting adjustment module is used to reset the maximum active current of the islanded transmission system during low voltage ride-through based on the voltage drop of the converter bus.

[0030] Furthermore, if the voltage value of the converter bus is less than the minimum positive sequence voltage during the fault and recovery period;

[0031] Adjust the maximum active current value according to the degree of voltage drop at the converter bus, including:

[0032] If the voltage value of the converter bus is less than the minimum positive sequence voltage and greater than the first set value during the fault and recovery period, the maximum active current will be reduced according to the degree of voltage drop of the converter bus, based on the initial maximum active current value.

[0033] If the voltage value of the converter bus does not exceed the first set value during the fault and recovery period, the maximum active current will be reduced to 0.

[0034] Furthermore, the first setting value is , This is the minimum positive sequence voltage. This represents the maximum allowable voltage drop.

[0035] Furthermore, when reducing the maximum active current according to the voltage drop across the converter bus, the maximum active current is calculated using the following formula:

[0036]

[0037] In the formula, This is the maximum value of the active current. This is the maximum current value. This is the maximum value of the reactive current. This represents the voltage value of the converter bus during the fault and recovery period.

[0038] Furthermore, if the voltage value of the converter bus during the fault and recovery period is not less than the minimum positive sequence voltage and is less than the second set value, then it is determined that the voltage drop of the converter bus is not deep. At this time, the maximum active current remains at the initial set value, which is determined according to the following formula:

[0039]

[0040] In the formula, This is the maximum value of the active current. This is the maximum current value. This represents the maximum reactive current.

[0041] In summary, this invention provides a method and apparatus for optimizing the low-voltage ride-through parameters of a conventional unit's power transmission system via a flexible DC islanding system. The method includes setting the initial maximum active current value of the islanded power transmission system during low-voltage ride-through; performing a three-phase N-1 fault scan of the AC lines in the islanded power transmission system and determining its stability; recording the minimum positive-sequence voltage of the converter bus during a single-phase transient fault; determining the voltage drop of the converter bus based on the voltage level and minimum positive-sequence voltage during the fault and recovery periods; resetting the maximum active current value based on the voltage drop of the converter bus; and, based on the adjusted maximum active current value, re-performing a three-phase N-1 fault scan of the AC lines in the islanded power transmission system. If the system is stable, the adjusted maximum active current value is used as the active current limit for the islanded power transmission system during low-voltage ride-through. This invention can automatically adjust the active current limit according to the voltage drop level of the converter bus, thereby enhancing the stability of the system during flexible DC low-voltage ride-through. By performing fault scanning and active current limiting adjustment, the optimal active current limiting value is finally determined to ensure the stable operation of the system during low voltage ride-through. Attached Figure Description

[0042] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0043] Figure 1 A flowchart of a method for optimizing the low-profile transmission parameters of a conventional unit via a flexible direct current islanding system, provided as an embodiment of the present invention;

[0044] Figure 2 This is a schematic diagram of the conventional unit's power transmission system via flexible direct current islanding provided by the present invention;

[0045] Figure 3 The active current curve of the converter bus-hydro generator group 1 after a three-permanent N-1 fault is provided under the initial parameters of the flexible DC-DC converter according to the embodiment of the present invention.

[0046] Figure 4 The active power diagram of the converter bus-hydro generator group 1 after a three-permanent N-1 fault is provided for the initial parameters of the flexible DC power generation in the embodiments of the present invention.

[0047] Figure 5 The voltage curve of the flexible DC bus after a three-terminal N-1 fault occurs in the converter bus-hydro generator group 1 under the initial flexible DC parameters provided in the embodiment of the present invention;

[0048] Figure 6 The active current curve of the converter bus-hydro generator group 1 after a three-permanent N-1 fault is shown in the figure provided by the flexible DC optimized parameters in the embodiment of the present invention.

[0049] Figure 7 The active power diagram of the converter bus-hydro generator group 1 after a three-permanent N-1 fault occurs under the flexible DC optimized parameters provided in the embodiments of the present invention;

[0050] Figure 8 The voltage curve of the flexible DC bus after a three-terminal N-1 fault occurs in the converter bus-hydro generator group 1 under the flexible DC optimized parameters provided in the embodiments of the present invention;

[0051] Figure 9 This is a block diagram of a flexible direct current (DC) low-profile parameter optimization device for a conventional unit's DC-DC isolated island power transmission system, provided as an embodiment of the present invention. Detailed Implementation

[0052] To make the objectives, features, and advantages of this invention more apparent and understandable, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described below are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0053] Please see Figure 1 and Figure 2 , Figure 1 The flowchart of a method for optimizing the low-profile transmission parameters of a conventional unit via a flexible direct current islanding system according to the present invention is shown. Figure 2 This illustrates a conventional unit's power transmission system via a flexible vertical island.

[0054] The following first combines Figure 2 This paper introduces the potential problems of conventional low-profile transmission strategy when existing conventional units transmit power via flexible vertical transmission islands.

[0055] Figure 2 This demonstrates a typical multi-terminal direct current (MTDC) transmission system structure, which includes multiple hydropower generator groups and converter stations. Specifically, the sending-end converter station is located on the left, connecting three different hydropower generator groups. These hydropower generator groups are connected to the sending-end converter station via different lines. From the sending-end converter station, multiple lines lead to the receiving-end converter station on the right.

[0056] Among them, Hydropower Group 1 has an installed capacity of 1.1 million kilowatts, Hydropower Group 2 has an installed capacity of 0.6 million kilowatts, and Hydropower Group 3 has an installed capacity of 1.6 million kilowatts, for a total installed hydropower capacity of 3.3 million kilowatts and a flexible DC capacity of 5 million kilowatts. The DC capacity is far greater than the supporting power supply capacity, and under normal operating conditions, the DC system may not operate at full load. The traditional low-voltage ride-through (LVRT) strategy of flexible DC may lead to excessive active current after a short-circuit fault, thereby increasing the risk of static voltage instability in the system. This effect is particularly pronounced in islanded systems with "small generating units and large DC capacity," because the DC system has lower inertia and is more susceptible to external disturbances.

[0057] Based on this, the present invention provides a method and apparatus for optimizing the low-profile transmission parameters of conventional units via flexible direct current islanding systems to solve the above-mentioned problems.

[0058] Please see Figure 1 The following describes an embodiment of the method for optimizing the low-profile transmission parameters of a conventional unit via a flexible direct current islanding system according to the present invention.

[0059] This embodiment provides a method for optimizing the low-profile transmission parameters of a conventional unit via a flexible DC islanding system, including the following steps:

[0060] Step 1: Set the initial maximum active current for the islanded transmission system during low voltage ride-through.

[0061] It should be noted that Low Voltage Ride Through (LVRT) refers to the ability of generating equipment to continue operating for a period of time without disconnecting from the grid when the grid voltage suddenly drops. Maximum active current, on the other hand, refers to the maximum allowable active current during a system fault.

[0062] In this step, a reasonable initial maximum active current value can be set using conventional methods to ensure that the system does not immediately enter an unstable state when a voltage drop occurs.

[0063] Step 2: Perform a fault scan of the three-terminal N-1 line of the isolated transmission system and determine its stability.

[0064] It should be noted that the three-phase N-1 fault of an AC line refers to a permanent three-phase short-circuit fault on an AC line, and the primary equipment (such as a circuit breaker) has already disconnected the faulty component (i.e., the N-1 principle), but the system is still in a fault state.

[0065] In this step, the system stability is tested by simulating a three-phase permanent fault in the AC line. Starting with the mildest fault, the severity is gradually increased, and the system stability is continuously observed.

[0066] Step 3: Record the minimum positive sequence voltage of the converter bus during a single-phase transient fault.

[0067] It should be noted that the converter bus is the bus used to connect the converter and other equipment in a DC transmission system. Positive sequence voltage represents the average three-phase voltage under symmetrical fault conditions.

[0068] When performing a three-phase N-1 fault scan and a single-phase transient fault occurs on the converter bus, record the minimum positive-sequence voltage on the converter bus during the fault period. This value can be used to assess the degree of voltage drop and provide a basis for further adjustment of the active current.

[0069] Step 4: Determine the degree of voltage drop of the converter bus based on the voltage level and minimum positive sequence voltage of the converter bus during the fault and recovery periods.

[0070] It should be noted that the data recorded in step three is used to compare the voltage level of the converter bus during the fault and recovery periods with the minimum positive-sequence voltage to determine the extent of the voltage drop. This step is to quantify the degree of voltage drop in order to adjust the maximum active current in the next step.

[0071] Step 5: Reset the maximum active current of the islanded power transmission system during low voltage ride-through based on the voltage drop of the converter bus.

[0072] It should be noted that the maximum active current should be redesigned based on the degree of voltage drop. For example, if the voltage drop is minor, the active current can be maintained; conversely, if the voltage drop is severe, the active current needs to be reduced to ensure system stability.

[0073] Step 6: Based on the adjusted maximum active current, perform a new AC line three-terminal N-1 fault scan on the islanded transmission system. If the system is stable, the adjusted maximum active current will be used as the active current limit for the islanded transmission system during low voltage ride-through.

[0074] It should be noted that after adjusting the maximum active current value, a fault scan is performed again to verify whether the adjusted value can keep the system stable during a fault. If the system is stable, the adjusted value is used as the new active current limit. If the system is still unstable, grid reinforcement measures are required to improve system stability.

[0075] This embodiment provides a method for optimizing the low-voltage ride-through parameters of a conventional generator unit's islanded DC transmission system. By iteratively adjusting the maximum active current and continuously testing the system's stability, an optimal active current limit is found that ensures stable system operation during faults while maintaining the system's active power output to a certain extent. Optimizing the active current limit effectively prevents static voltage instability caused by excessive active current during low-voltage ride-through. The method provided in this embodiment, through fine-tuning of system parameters, enables the "small generator unit, large DC" islanded transmission system to operate more robustly during faults, improving the overall reliability and safety of the system.

[0076] In one embodiment, if the voltage value of the converter bus is less than the minimum positive sequence voltage during the fault and recovery period, the maximum active current is adjusted according to the degree of voltage drop of the converter bus, including:

[0077] If the voltage value of the converter bus is less than the minimum positive sequence voltage and greater than the first set value during the fault and recovery period, the maximum active current will be reduced according to the degree of voltage drop of the converter bus, based on the initial maximum active current value.

[0078] If the voltage value of the converter bus does not exceed the first set value during the fault and recovery period, the maximum active current will be reduced to 0.

[0079] In this embodiment, when the current voltage value of the converter bus is less than the minimum positive-sequence voltage but greater than a first set value, the voltage drop is considered relatively mild, but the active current still needs to be reduced to ensure system stability. In this case, the maximum active current needs to be reduced according to the degree of voltage drop. The specific adjustment amount can be calculated based on a pre-set formula or curve to reflect the impact of voltage drop on system stability.

[0080] When the current voltage value of the converter bus is not greater than the first set value, the voltage drop is considered to be very severe. In order to prevent system instability, the maximum active current must be reduced to 0. Reducing the active current to 0 can prevent the flexible DC system from experiencing static voltage instability due to excessive active current under extreme voltage drop conditions.

[0081] This embodiment achieves the goal of maintaining the system's active power output as much as possible while ensuring system stability by accurately judging the degree of voltage drop on the converter bus and adjusting the maximum value of the active current accordingly. This improves the overall operating efficiency and reliability of the "small unit, large DC" islanded power transmission system.

[0082] In a further embodiment, the set value is... , This is the minimum positive sequence voltage. This represents the maximum allowable voltage drop.

[0083] In a further embodiment, when reducing the maximum active current according to the degree of voltage drop at the converter bus, the maximum active current is calculated according to the following formula:

[0084]

[0085] In the formula, This is the maximum value of the active current. This is the maximum current value. This is the maximum value of the reactive current. This represents the voltage value of the converter bus during the fault and recovery period.

[0086] In one embodiment, if the current voltage value of the converter bus is not less than the minimum positive sequence voltage and is less than the second set value, it is determined that the voltage drop of the converter bus is not deep. At this time, the maximum active current remains at the initial set value, which is determined according to the following formula:

[0087]

[0088] In the formula, This is the maximum value of the active current. This is the maximum current value. This represents the maximum reactive current.

[0089] In this embodiment, two threshold values ​​(minimum positive-sequence voltage and a second set value) are set to determine whether there is a significant voltage drop at the converter bus. When the voltage is between the two values, it is considered that there is no significant voltage drop, so there is no need to adjust the maximum active current value, and it remains at the initial set value. The initial maximum active current value is calculated based on the maximum reactive current value and the maximum total current value, and is not affected by the real-time voltage level of the system.

[0090] The following example illustrates the optimization method for the low-profile transmission parameters of a conventional unit via a flexible direct current islanding system according to the present invention.

[0091] This example is based on Figure 2 The conventional unit shown is transmitted via a flexible direct current islanding system, which includes the following steps:

[0092] 1. The maximum reactive current during the low-voltage ride-through period is specified as I using conventional methods. qmax =0.35pu, I max =1.05pu, maximum active current is I dmax = .

[0093] 2. In this example, after a three-terminal N-1 fault occurs at the converter bus-hydro generator group 1, the active current, active power, and converter bus voltage curves are as follows: Figures 3-5 As shown. By Figures 3-5 It can be seen that after the fault occurred, the active current, active power and bus voltage all dropped rapidly and fluctuated violently. After a period of time, they gradually stabilized, but still showed certain oscillation characteristics throughout the observation period.

[0094] 3. A single-phase transient fault occurs on the converter bus. Record the minimum positive sequence voltage of the converter bus during the fault period as U1 = 0.65pu.

[0095] 4. Redetermine the maximum reactive current during the low-voltage ride-through period as I. qmax =0.35pu, I dmax The calculation is based on the monitored voltage drop level, where I max =1.05pu, U1=0.65pu.

[0096] 5. A fault scan of the AC line three-phase N-1 fault was performed on the isolated transmission system. In this example, the system operated stably after the occurrence of the AC line three-phase N-1 fault. After the occurrence of the three-phase N-1 fault at the converter bus-hydro generator group 1, the active current, active power, and converter bus voltage curves of the flexible DC power supply are as follows: Figures 6-8 As shown. Figures 6-8 It can be seen that after the fault occurred, the active current, active power and bus voltage all fluctuated briefly, and gradually stabilized after a period of time.

[0097] As can be seen from this example, the stability of the system is improved after the active current limiting optimization is performed using the parameter optimization method of the present invention.

[0098] Based on the same inventive concept, this application also provides a device for optimizing the low-voltage transmission parameters of conventional units via flexible DC islanding systems, used to implement the aforementioned method for optimizing the low-voltage transmission parameters of conventional units via flexible DC islanding systems. The solution provided by this device is similar to the solution described in the above method. Therefore, the specific limitations in the embodiments of the device for optimizing the low-voltage transmission parameters of conventional units via flexible DC islanding systems provided below can be found in the limitations of the optimization method for flexible DC islanding systems of conventional units described above, and will not be repeated here.

[0099] Please see Figure 9 This invention also provides a device for optimizing the low-profile transmission parameters of conventional units via a flexible DC islanding system, comprising the following steps:

[0100] The initial setup module is used to set the initial maximum active current of the islanded transmission system during low voltage ride-through.

[0101] The fault scanning module is used to perform AC line three-permanent N-1 fault scanning on the islanded transmission system and to determine its stability; it is also used to perform AC line three-permanent N-1 fault scanning on the islanded transmission system again based on the adjusted maximum active current value. If the system is stable, the adjusted maximum active current value is used as the active current limit of the islanded transmission system during low voltage ride-through.

[0102] The voltage recording module is used to record the minimum positive sequence voltage of the converter bus during a single-phase transient fault.

[0103] The voltage drop judgment module is used to judge the degree of voltage drop of the converter bus based on the voltage level of the converter bus during the fault and recovery period and the minimum value of the positive sequence voltage.

[0104] The active current limiting adjustment module is used to reset the maximum active current of the islanded transmission system during low voltage ride-through based on the voltage drop of the converter bus.

[0105] In one embodiment, if the voltage value of the converter bus is less than the minimum positive sequence voltage during the fault and recovery period;

[0106] Adjust the maximum active current value according to the degree of voltage drop at the converter bus, including:

[0107] If the voltage value of the converter bus is less than the minimum positive sequence voltage and greater than the first set value during the fault and recovery period, the maximum active current will be reduced according to the degree of voltage drop of the converter bus, based on the initial maximum active current value.

[0108] If the voltage value of the converter bus does not exceed the first set value during the fault and recovery period, the maximum active current will be reduced to 0.

[0109] In a further embodiment, the first set value is , This is the minimum positive sequence voltage. This represents the maximum allowable voltage drop.

[0110] In a further embodiment, when reducing the maximum active current according to the degree of voltage drop at the converter bus, the maximum active current is calculated according to the following formula:

[0111]

[0112] In the formula, This is the maximum value of the active current. This is the maximum current value. This is the maximum value of the reactive current. This represents the voltage value of the converter bus during the fault and recovery period.

[0113] In one embodiment, if the voltage value of the converter bus during the fault and recovery period is not less than the minimum positive sequence voltage and is less than the second set value, it is determined that the voltage drop of the converter bus is not deep. At this time, the maximum active current remains at the initial set value, which is determined according to the following formula:

[0114]

[0115] In the formula, This is the maximum value of the active current. This is the maximum current value. This represents the maximum reactive current.

[0116] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the above-described division of functional units and modules is merely an example. In practical applications, the above functions can be assigned to different functional units and modules as needed, that is, the internal structure of the system can be divided into different functional units or modules to complete all or part of the functions described above. The functional units and modules in the embodiments can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit. Furthermore, the specific names of the functional units and modules are only for easy differentiation and are not intended to limit the scope of protection of this application. The specific working process of the units and modules in the above system can be referred to the corresponding process in the foregoing method embodiments, and will not be repeated here.

[0117] This invention also provides a computer device, including: a memory and a processor, and a computer program stored in the memory. When the computer program is executed on the processor, it implements the method for optimizing the low-profile transmission parameters of a conventional unit via a flexible DC islanding system as described in any of the above methods.

[0118] The computer device may be a desktop computer, laptop, handheld computer, or cloud server, etc. This computer device may include, but is not limited to, a processor and memory.

[0119] The processor referred to can be a Central Processing Unit (CPU), but it can also be other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. A general-purpose processor can be a microprocessor or any conventional processor.

[0120] In some embodiments, the memory may be an internal storage unit of the computer device, such as a hard drive or RAM. In other embodiments, the memory may be an external storage device of the computer device, such as a plug-in hard drive, Smart Media Card (SMC), Secure Digital (SD) card, or Flash Card. Furthermore, the memory may include both internal and external storage units of the computer device. The memory is used to store the operating system, applications, bootloader, data, and other programs, such as the program code of the computer program. The memory can also be used to temporarily store data that has been output or will be output.

[0121] This invention also provides a computer-readable storage medium storing a computer program thereon. When the computer program is run by a processor, it implements the method for optimizing the low-profile transmission parameters of a conventional unit via a flexible DC islanding system as described in any of the above methods.

[0122] In this embodiment, if the integrated unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, all or part of the processes in the methods of the above embodiments can be implemented by a computer program instructing related hardware. The computer program can be stored in a computer-readable storage medium, and when executed by a processor, it can implement the steps of the various method embodiments described above. The computer program includes computer program code, which can be in the form of source code, object code, executable files, or certain intermediate forms. The computer-readable medium can include at least: any entity or device capable of carrying computer program code to a photographing device / terminal device, a recording medium, a computer memory, a read-only memory (ROM), a random access memory (RAM), an electrical carrier signal, a telecommunication signal, and a software distribution medium. Examples include USB flash drives, portable hard drives, magnetic disks, or optical disks. In some jurisdictions, according to legislation and patent practice, computer-readable media cannot be electrical carrier signals or telecommunication signals.

[0123] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail or recorded in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0124] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0125] In the embodiments disclosed in this application, it should be understood that the disclosed devices / terminal equipment and methods can be implemented in other ways. For example, the device / terminal equipment embodiments described above are merely illustrative. For instance, the division of modules or 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 displayed or discussed mutual coupling or direct coupling or communication connection may be through some interfaces; the indirect coupling or communication connection between devices or units may be electrical, mechanical, or other forms.

[0126] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for optimizing the low-profile transmission parameters of a conventional unit via a flexible DC islanding system, characterized in that, Includes the following steps: Set the initial maximum active current for the islanded transmission system during low-voltage ride-through; Perform a three-terminal N-1 fault scan on the isolated transmission system and determine its stability. Record the minimum positive sequence voltage of the converter bus during a single-phase transient fault; The degree of voltage drop of the converter bus is determined based on the voltage level of the converter bus during the fault and recovery period and the minimum value of the positive sequence voltage. The maximum active current of the islanded power transmission system during low voltage ride-through is reset according to the degree of voltage drop at the converter bus. Based on the adjusted maximum active current, the islanded transmission system is re-scanned for AC line three-terminal N-1 faults. If the system is stable, the adjusted maximum active current is used as the active current limit for the islanded transmission system during low voltage ride-through. If the voltage value of the converter bus is less than the minimum positive sequence voltage during the fault and recovery period; Adjusting the maximum active current value according to the degree of voltage drop at the converter bus includes: If the voltage value of the converter bus is less than the minimum positive sequence voltage and greater than the first set value during the fault and recovery period, the maximum active current value is reduced according to the degree of voltage drop of the converter bus, based on the initial maximum active current value. If the voltage value of the converter bus during the fault and recovery period is not greater than the first set value, then the maximum active current value is reduced to 0. The first setting value is , This is the minimum value of the positive sequence voltage. The maximum allowable voltage drop value; If the voltage value of the converter bus during the fault and recovery period is not less than the minimum positive sequence voltage and is less than the second set value, then it is determined that the voltage drop of the converter bus is not deep. At this time, the maximum active current remains at the initial set value, which is determined according to the following formula: ； In the formula, This refers to the maximum value of the active current. This is the maximum current value. This represents the maximum reactive current.

2. The method for optimizing the low-profile transmission parameters of a conventional unit via a flexible direct current islanding system according to claim 1, characterized in that, When the maximum active current is reduced according to the degree of voltage drop at the converter bus, the maximum active current is calculated according to the following formula: ； In the formula, This refers to the maximum value of the active current. This is the maximum current value. This is the maximum value of the reactive current. This represents the voltage value of the converter bus during the fault and recovery period.

3. A parameter optimization device for low-profile transmission through a conventional unit via a flexible direct current islanding system, characterized in that: include: The initial setup module is used to set the initial maximum active current of the islanded transmission system during low voltage ride-through. The fault scanning module is used to perform AC line three-terminal N-1 fault scanning on the isolated transmission system and to determine its stability. It is also used to re-scan the AC line three-terminal N-1 fault of the islanded transmission system based on the adjusted maximum value of the active current. If the system is stable, the adjusted maximum value of the active current is used as the active current limit of the islanded transmission system during low voltage ride-through. The voltage recording module is used to record the minimum positive sequence voltage of the converter bus during a single-phase transient fault. The voltage drop judgment module is used to judge the degree of voltage drop of the converter bus based on the voltage level of the converter bus during the fault and recovery period and the minimum value of the positive sequence voltage. An active current limiting adjustment module is used to reset the maximum active current of the islanded transmission system during low voltage ride-through based on the voltage drop of the converter bus. If the voltage value of the converter bus is less than the minimum positive sequence voltage during the fault and recovery period; Adjusting the maximum active current value according to the degree of voltage drop at the converter bus includes: If the voltage value of the converter bus is less than the minimum positive sequence voltage and greater than the first set value during the fault and recovery period, the maximum active current value is reduced according to the degree of voltage drop of the converter bus, based on the initial maximum active current value. If the voltage value of the converter bus during the fault and recovery period is not greater than the first set value, then the maximum active current value is reduced to 0. The first setting value is , This is the minimum value of the positive sequence voltage. The maximum allowable voltage drop value; If the voltage value of the converter bus during the fault and recovery period is not less than the minimum positive sequence voltage and is less than the second set value, then it is determined that the voltage drop of the converter bus is not deep. At this time, the maximum active current remains at the initial set value, which is determined according to the following formula: ； In the formula, This refers to the maximum value of the active current. This is the maximum current value. This represents the maximum reactive current.

4. The conventional unit's flexible direct current islanding transmission system flexible direct current low-penetration parameter optimization device according to claim 3, characterized in that, When the maximum active current is reduced according to the degree of voltage drop at the converter bus, the maximum active current is calculated according to the following formula: ； In the formula, This refers to the maximum value of the active current. This is the maximum current value. This is the maximum value of the reactive current. This represents the voltage value of the converter bus during the fault and recovery period.

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