Method and device for optimizing flexible direct-current low-pass parameters of flexible direct-current island sending-out system of conventional unit

Abstract

The invention provides a flexible DC low-voltage ride-through parameter optimization method and device for a flexible DC island sending-out system of a conventional unit. The method comprises the following steps: setting an initial active current maximum value of the island sending-out system during a low-voltage ride-through period according to a conventional method; aC line three-permanent N-1 fault scanning is carried out on the system, and stability discrimination is carried out; recording the minimum value of the positive sequence voltage of the converter bus during the single-phase transient fault period; judging the voltage drop degree of the converter bus according to the voltage level and the positive sequence voltage minimum value of the converter bus in the fault and recovery period; redesigning the maximum value of the active current according to the positive sequence voltage drop degree of the converter bus; and carrying out fault scanning on the island sending-out system again, and if the system is stable, taking the adjusted maximum value of the active current as the active current amplitude limit of the island sending-out system during the low voltage ride-through period. According to the invention, the active current amplitude limit during the flexible DC low voltage ride-through period can be automatically adjusted according to the voltage drop degree of the commutation bus, so that the stability of the system is enhanced.

Description

Technical Field

[0001] The present invention belongs to the technical field of power grid planning and operation of electric power systems, and specifically relates to a method and device for optimizing flexible direct current low penetration parameters of a conventional unit through a flexible direct current island transmission system. Background Art

[0002] In order to meet the needs of power development, clean energy needs to be transmitted from resource-rich areas to areas with high demand. Specifically, this means transmitting clean electricity from western provinces with abundant wind, solar and hydropower resources to eastern provinces with high electricity demand. Since the eastern provinces have limited clean energy resources themselves, introducing these clean electricity from the west through high-voltage direct current transmission technology has become 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 DC transmission system and its related energy facilities are usually set to island operation mode.

[0003] Limited by the resource distribution conditions of new energy and conventional units, the sending end may use multi-terminal DC to collect different types of power sources and then send them out, which means that conventional units are sent out through flexible direct current islands. Affected by the timing of the commissioning of conventional units, the DC capacity may be greater than the supporting power capacity, and the DC will operate at a low power level during this stage. The conventional low-through strategy of flexible direct current will cause the active current of the flexible direct current to be greater than the normal value during the low voltage ride-through period after a short circuit fault. After the fault is cleared, the static voltage of the system may become unstable, which cannot meet the safe and stable operation requirements of the "small unit, large direct current" island transmission system. Summary of the invention

[0004] In view of this, the present invention provides a method and device for optimizing the flexible DC low-through parameters of a conventional unit through a flexible DC island transmission system, aiming to optimize the maximum active current limit during the flexible DC low-through period so that the active current limit during the low-through period can be automatically adjusted according to the degree of voltage drop of the commutation bus, thereby improving the stability characteristics of the "small unit, large DC" island transmission system after a three-phase short circuit fault.

[0005] In order to achieve the above object, the technical solution provided by the present invention is as follows:

[0006] In a first aspect, the present invention provides a method for optimizing the flexible direct current low penetration parameters of a conventional unit through a flexible direct current island transmission system, comprising the following steps:

[0007] Set the initial maximum active current of the island transmission system during low voltage ride-through;

[0008] Perform AC line Sanyong N-1 fault scan on the island transmission system and make stability judgment;

[0009] Record the minimum positive sequence voltage of the commutation bus during a single-phase instantaneous fault;

[0010] Determine the voltage drop of the commutation bus according to the voltage level of the commutation bus and the minimum value of the positive sequence voltage during the fault and recovery period;

[0011] Reset the maximum active current of the island transmission system during the low voltage ride-through period according to the voltage drop of the commutation bus;

[0012] On the basis of the adjusted maximum active current value, the island transmission system is re-scanned for the AC line three-period N-1 fault. If the system is stable, the adjusted maximum active current value is used as the active current limit of the island transmission system during the low voltage ride-through period.

[0013] Furthermore, if the voltage value of the commutation bus during the fault and restoration period is less than the minimum positive sequence voltage;

[0014] The maximum active current is adjusted accordingly according to the degree of bus voltage drop, including:

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

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

[0017] Furthermore, the first setting value is , is the minimum positive sequence voltage, is the maximum allowable voltage drop value.

[0018] Furthermore, when the maximum active current is reduced according to the degree of voltage drop of the commutation 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 commutation bus during fault and recovery.

[0021] Furthermore, if the voltage value of the commutation bus during the fault and recovery period is not less than the minimum positive sequence voltage and less than the second set value, it is judged that the voltage drop of the commutation bus is not deep, and the maximum active current is maintained at the initial setting value. The initial setting value is determined according to the following formula:

[0022]

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

[0024] In a second aspect, the present invention provides a device for optimizing the low penetration parameters of a conventional unit through a flexible direct current island transmission system, comprising the following steps:

[0025] The initial setting module is used to set the initial maximum active current of the island transmission system during the low voltage ride-through period;

[0026] The fault scanning module is used to scan the AC line three-phase N-1 faults of the isolated island transmission system and make stability judgments; it is also used to re-scan the AC line three-phase N-1 faults of the isolated island transmission system 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 isolated island transmission system during the low voltage ride-through period;

[0027] A voltage recording module is used to record the minimum positive sequence voltage of the commutation bus during a single-phase instantaneous fault;

[0028] A voltage drop judgment module is used to judge the voltage drop degree of the commutation bus according to the voltage level of the commutation bus and the minimum value of the positive sequence voltage during the fault and recovery period;

[0029] The active current limit adjustment module is used to reset the maximum active current of the island transmission system during low voltage ride-through according to the degree of commutation bus voltage drop.

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

[0031] The maximum active current is adjusted accordingly according to the degree of bus voltage drop, including:

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

[0033] If the voltage value of the commutation bus during the fault and recovery period is not greater than the first set value, the maximum active current is reduced to 0.

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

[0035] Furthermore, when the maximum active current is reduced according to the degree of voltage drop of the commutation bus, the maximum active current is calculated according to the following formula:

[0036]

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

[0038] Furthermore, if the voltage value of the commutation bus during the fault and recovery period is not less than the minimum positive sequence voltage and less than the second set value, it is judged that the voltage drop of the commutation bus is not deep, and the maximum active current is maintained at the initial setting value. The initial setting value is determined according to the following formula:

[0039]

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

[0041] In summary, the present invention provides a method and device for optimizing the parameters of flexible direct current low voltage ride-through of a conventional unit through a flexible direct current island transmission system, including setting the initial maximum active current of the island transmission system during low voltage ride-through; performing a three-phase N-1 fault scan of the AC line of the island transmission system and performing stability judgment; recording the minimum positive sequence voltage of the commutation bus during a single-phase instantaneous fault; judging the voltage drop of the commutation bus according to the voltage level and the minimum positive sequence voltage of the commutation bus during the fault and recovery period; resetting the maximum active current according to the voltage drop of the commutation bus; based on the adjusted maximum active current, re-scanning the AC line three-phase N-1 fault of the island transmission system, if the system is stable, the adjusted maximum active current is used as the active current limit of the island transmission system during low voltage ride-through. The present invention can automatically adjust the active current limit according to the voltage drop level of the commutation bus, thereby enhancing the stability of the system during the flexible direct current low voltage ride-through. Through fault scanning and active current limit adjustment, the optimal active current limit value is finally determined to ensure stable operation of the system during low voltage ride-through. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0043] Figure 1 A flow chart of a method for optimizing the flexible direct current low penetration parameters of a conventional unit through a flexible direct current island transmission system provided by an embodiment of the present invention;

[0044] Figure 2 Schematic diagram of the conventional unit transmission system through flexible direct current island provided by the present invention;

[0045] Figure 3 The flexible direct current active current curve diagram after the three-permanent N-1 fault occurs in the commutation bus-hydrogenerator group 1 under the flexible direct current initial parameters provided in the embodiment of the present invention;

[0046] Figure 4 The flexible direct current active power diagram after the three permanent N-1 faults occur in the commutation bus-hydrogenerator group 1 under the flexible direct current initial parameters provided in the embodiment of the present invention;

[0047] Figure 5 The voltage curve of the flexible direct current bus after the three-phase N-1 fault occurs in the commutation bus-hydrogenerator group 1 under the flexible direct current initial parameters provided in the embodiment of the present invention;

[0048] Figure 6 The flexible direct current active current curve diagram after the three-permanent N-1 fault occurs in the commutation bus-hydrogenerator group 1 under the flexible direct current optimization parameters provided in the embodiment of the present invention;

[0049] Figure 7 The flexible direct current active power diagram after the three permanent N-1 faults occur in the commutation bus-hydrogenerator group 1 under the flexible direct current optimization parameters provided in the embodiment of the present invention;

[0050] Figure 8 The flexible direct current bus voltage curve diagram after the three-phase N-1 fault occurs in the commutation bus-hydrogenerator group 1 under the flexible direct current optimization parameters provided in the embodiment of the present invention;

[0051] Fig. 9 A block diagram of the composition of a device for optimizing flexible direct current low penetration parameters of a conventional unit through a flexible direct current island transmission system provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0052] In order to make the purpose, features and advantages of the present invention more obvious and easy to understand, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described below are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0053] See also Figure 1 and Figure 2 , Figure 1 The present invention shows a process of optimizing the flexible direct current low penetration parameters of a conventional unit through a flexible direct current island transmission system; Figure 2 A conventional unit is shown via a flexible direct current island transmission system.

[0054] The following first combines Figure 2 This paper introduces the possible problems of the flexible direct current conventional low-penetration strategy when the existing conventional units are transmitted through flexible direct current islands.

[0055] Figure 2 A typical multi-terminal DC transmission system (MTDC) structure is shown, which contains multiple hydropower groups and converter stations. Specifically: The sending-end converter station is located on the left, connecting three different hydropower groups. These hydropower groups are connected to the sending-end converter station through different lines. From the sending-end converter station, there are multiple lines leading to the receiving-end converter station on the right.

[0056] Among them, the installed capacity of hydropower group 1 is 1.1 million kilowatts, the installed capacity of hydropower group 2 is 600,000 kilowatts, and the installed capacity of hydropower group 3 is 1.6 million kilowatts. The total installed capacity of hydropower is 3.3 million kilowatts, and the flexible direct current capacity is 5 million kilowatts. The DC capacity is much larger than the supporting power capacity. Under normal operating conditions, the DC system may not operate at full load. The low voltage ride-through (LVRT) strategy of traditional flexible direct current may cause excessive active current after a short-circuit fault, thereby increasing the risk of static voltage instability in the system. This effect is particularly obvious in the "small unit, large direct current" island system, because the inertia of the DC system is small and more susceptible to external disturbances.

[0057] Based on this, the present invention provides a method and device for optimizing the flexible direct current low penetration parameters of a conventional unit through a flexible direct current island transmission system to solve the above problems.

[0058] See also Figure 1 The following is an introduction to an embodiment of a method for optimizing the flexible direct current low penetration parameters of a conventional unit through a flexible direct current island transmission system of the present invention.

[0059] This embodiment provides a method for optimizing the flexible direct current low penetration parameters of a conventional unit through a flexible direct current island transmission system, comprising the following steps:

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

[0061] It should be noted that Low Voltage Ride Through (LVRT) refers to the ability of power generation equipment to continue to operate for a period of time without being disconnected from the grid when the grid voltage suddenly drops. The maximum active current refers to the maximum active current allowed during a system fault.

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

[0063] Step 2: Scan the AC line three-phase N-1 fault of the island transmission system and make stability judgment.

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

[0065] In this step, the stability of the system is tested by simulating a three-phase permanent fault on the AC line. Starting from the mildest fault, gradually increase the fault severity and continue to observe whether the system is stable.

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

[0067] It should be noted that the commutation bus is a bus used to connect the converter and other equipment in the DC transmission system. The positive sequence voltage represents the average value of the three-phase voltage under symmetrical faults.

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

[0069] Step 4: Determine the voltage drop of the commutation bus according to the voltage level of the commutation bus during the fault and recovery period and the minimum positive sequence voltage.

[0070] It should be noted that the voltage level of the commutation busbar during the fault and recovery period is compared with the minimum positive sequence voltage using the data recorded in step 3 to determine the extent of the voltage drop. This step is to quantify the extent of the voltage drop so as to adjust the maximum active current in the next step.

[0071] Step 5: Reset the maximum active current of the island transmission system during the low voltage ride-through period according to the degree of commutation bus voltage drop.

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

[0073] Step 6: Based on the adjusted maximum active current value, re-scan the AC line three-period N-1 fault of the island transmission system. If the system is stable, the adjusted maximum active current value is used as the active current limit of the island transmission system during the low voltage ride-through period.

[0074] It should be noted that after adjusting the maximum active current, perform fault scanning again to verify whether the adjusted value can keep the system stable during the 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 flexible direct current low-voltage ride-through parameters of a conventional unit through a flexible direct current island transmission system. By iteratively adjusting the maximum value of the active current and continuously testing the stability of the system, an optimal active current limit is found that can not only ensure the stable operation of the system during a fault, but also maintain the active power output of the system to a certain extent. By optimizing the active current limit, the static voltage instability caused by excessive active current during low voltage ride-through can be effectively prevented. The method provided in this embodiment enables the "small unit, large direct current" island transmission system to operate more robustly in the event of a fault, thereby improving the overall reliability and safety of the system through fine-tuning of system parameters.

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

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

[0078] If the voltage value of the commutation bus during the fault and recovery period is not greater than the first set value, the maximum active current is reduced to 0.

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

[0080] When the current voltage value of the commutation bus is not greater than the first set value, the voltage drop is considered to be very serious. In order to prevent the system from becoming unstable, the maximum active current must be reduced to 0. Reducing the active current to 0 can prevent the flexible DC system from causing static voltage instability due to excessive active current in the case of extreme voltage drops.

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

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

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

[0084]

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

[0086] In one embodiment, if the current voltage value of the commutation bus is not less than the minimum positive sequence voltage value and less than the second set value, it is determined that the voltage drop of the commutation bus is not deep, and the maximum active current is maintained at the initial setting value. The initial setting value is determined according to the following formula:

[0087]

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

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

[0090] The following is a calculation example to illustrate the method for optimizing the flexible direct current low penetration parameters of a conventional unit through a flexible direct current island transmission system of the present invention.

[0091] This example is based on Figure 2 The conventional unit shown is implemented through a flexible direct current island transmission system, including the following steps:

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

[0093] 2. In this example, after the commutation busbar-hydropower generator group 1 has a three-way N-1 fault, the flexible direct current active current, active power, and commutation busbar voltage curves are as follows: Figure 3-Figure 5 As shown. Figure 3-5 It can be seen that after the fault occurs, the active current, active power and bus voltage drop rapidly and fluctuate violently. They gradually stabilize after a period of time, but still show certain oscillation characteristics during the entire observation time.

[0094] 3. A single-phase instantaneous fault occurs on the commutation bus, and the minimum positive sequence voltage of the commutation bus during the fault period is recorded as U1=0.65pu.

[0095] 4. Re-determine the maximum value of reactive current during low voltage ride-through as I qmax =0.35pu,I dmax Calculate according to the monitored voltage drop level, where I max =1.05pu, U1=0.65pu.

[0096] 5. Scan the AC line three-way N-1 fault of the isolated island transmission system. In this example, the system can operate stably after the AC line three-way N-1 fault occurs. After the three-way N-1 fault occurs in the commutation bus-hydropower generator group 1, the active current, active power, and commutation bus voltage curves of the flexible direct current are as follows: Figure 6-Figure 8 As shown. Figure 6-8 It can be seen that after the fault occurs, the active current, active power and bus voltage all fluctuate briefly and gradually stabilize after a period of time.

[0097] It can be seen from this calculation example that after the parameter optimization method of the present invention is used to optimize the active current limiting, the stability of the system is improved.

[0098] Based on the same inventive concept, the embodiment of the present application also provides a conventional unit through a flexible direct current island transmission system flexible direct current low penetration parameter optimization device for realizing the above-mentioned conventional unit through a flexible direct current island transmission system flexible direct current low penetration parameter optimization method. The implementation scheme for solving the problem provided by the device is similar to the implementation scheme recorded in the above-mentioned method, so the specific limitations in the embodiment of the conventional unit through a flexible direct current island transmission system flexible direct current low penetration parameter optimization device provided below can refer to the limitations of the conventional unit through a flexible direct current island transmission system flexible direct current low penetration parameter optimization method in the above text, and will not be repeated here.

[0099] See also Fig. 9 The embodiment of the present invention also provides a device for optimizing the low penetration parameters of a conventional unit through a flexible direct current island transmission system, comprising the following steps:

[0100] The initial setting module is used to set the initial maximum active current of the island transmission system during the low voltage ride-through period;

[0101] A fault scanning module is used to perform an AC line three-way N-1 fault scan on the isolated island transmission system and perform stability judgment; it is also used to re-perform an AC line three-way N-1 fault scan on the isolated island transmission system based on the adjusted active current maximum value, and if the system is stable, the adjusted active current maximum value is used as the active current limit of the isolated island transmission system during the low voltage ride-through period;

[0102] A voltage recording module is used to record the minimum positive sequence voltage of the commutation bus during a single-phase instantaneous fault;

[0103] A voltage drop judgment module is used to judge the voltage drop degree of the commutation bus according to the voltage level of the commutation bus during the fault and recovery period and the minimum value of the positive sequence voltage;

[0104] The active current limit adjustment module is used to reset the maximum active current of the island transmission system during the low voltage ride-through period according to the voltage drop degree of the commutation bus.

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

[0106] The maximum active current is adjusted accordingly according to the degree of bus voltage drop, including:

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

[0108] If the voltage value of the commutation bus during the fault and recovery period is not greater than the first set value, the maximum active current is reduced to 0.

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

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

[0111]

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

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

[0114]

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

[0116] Those skilled in the art can clearly understand that, for the convenience and simplicity of description, only the division of the above-mentioned functional units and modules is used as an example for illustration. In practical applications, the above-mentioned function allocation can be completed by 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 embodiment can be integrated in a processing unit, or each unit can exist physically separately, or two or more units can be integrated in one unit. The above-mentioned integrated unit can be implemented in the form of hardware or in the form of software functional units. In addition, the specific names of the functional units and modules are only for the convenience of distinguishing each other, and are not used to limit the scope of protection of this application. The specific working process of the units and modules in the above-mentioned system can refer to the corresponding process in the aforementioned method embodiment, which will not be repeated here.

[0117] An embodiment of the present invention also provides a computer device, comprising: 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 flexible direct current low penetration parameters of a conventional unit through a flexible direct current island transmission system as described in any one of the above methods.

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

[0119] The processor may be a central processing unit (CPU), other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA) or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. A general-purpose processor may be a microprocessor or any conventional processor, etc.

[0120] In some embodiments, the memory may be an internal storage unit of the computer device, such as a hard disk or memory of the computer device. In other embodiments, the memory may also be an external storage device of the computer device, such as a plug-in hard disk, a smart media card (SMC), a secure digital (SD) card, a flash card, etc. equipped on the computer device. Further, the memory may include both an internal storage unit and an external storage device of the computer device. The memory is used to store an operating system, an application program, a boot loader (BootLoader), data, and other programs, such as the program code of the computer program. The memory may also be used to temporarily store data that has been output or is to be output.

[0121] An embodiment of the present invention further provides a computer-readable storage medium having a computer program stored thereon. When the computer program is executed by a processor, the method for optimizing the flexible direct current low penetration parameters of a conventional unit through a flexible direct current island transmission system as described in any one of the above methods is implemented.

[0122] In this embodiment, if the integrated unit is implemented in the form of 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, the present application implements all or part of the processes in the above-mentioned embodiment method, which can be completed by instructing the relevant hardware through a computer program. The computer program can be stored in a computer-readable storage medium. When the computer program is executed by the processor, the steps of the above-mentioned various method embodiments can be implemented. Among them, the computer program includes computer program code, and the computer program code can be in source code form, object code form, executable file or some intermediate form. The computer-readable medium can at least include: any entity or device that can carry the computer program code to the camera / terminal device, recording medium, computer memory, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), electric carrier signal, telecommunication signal and software distribution medium. For example, USB flash drive, mobile hard disk, disk or optical disk. In some jurisdictions, according to legislation and patent practice, computer-readable media cannot be electric carrier signals and telecommunication signals.

[0123] In the above embodiments, the description of each embodiment has its own emphasis. For parts that are not described or recorded in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0124] Those of ordinary skill in the art will appreciate that the units and algorithm steps of each example 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 performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of this application.

[0125] In the embodiments disclosed in the present 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 only schematic. For example, the division of the modules or units is only a logical function division. There may be other division methods in actual implementation, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, indirect coupling or communication connection of devices or units, which can be electrical, mechanical or other forms.

[0126] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for optimizing the low penetration parameters of flexible direct current transmission system of conventional units through flexible direct current island transmission, characterized in that: The steps include: Set the initial maximum active current of the island transmission system during low voltage ride-through; Performing AC line three-way N-1 fault scanning on the island transmission system and making stability judgment; Record the minimum positive sequence voltage of the commutation bus during a single-phase instantaneous fault; Determining the voltage drop degree of the commutation bus according to the voltage level of the commutation bus during the fault and recovery period and the minimum value of the positive sequence voltage; Resetting the maximum active current of the island transmission system during the low voltage ride-through period according to the voltage drop degree of the commutation bus; On the basis of the adjusted maximum active current value, the island transmission system is re-scanned for three-phase N-1 faults in the AC line. If the system is stable, the adjusted maximum active current value is used as the active current limit of the island transmission system during the low voltage ride-through period.

2. The method for optimizing the flexible direct current low penetration parameters of a conventional unit through a flexible direct current island transmission system according to claim 1 is characterized in that: If the voltage value of the commutation bus during the fault and recovery period is less than the minimum positive sequence voltage; The maximum active current value is correspondingly adjusted according to the voltage drop degree of the commutation bus, including: If the voltage value of the commutation bus during the fault and recovery period is less than the minimum positive sequence voltage value and greater than the first set value, then based on the initial maximum active current value, the maximum active current value is reduced according to the degree of voltage drop of the commutation bus; If the voltage value of the commutation bus during the fault and recovery period is not greater than the first set value, the maximum active current value is reduced to 0.

3. The method for optimizing the flexible direct current low penetration parameters of a conventional unit through a flexible direct current island transmission system according to claim 2 is characterized in that: The first setting value is , is the minimum positive sequence voltage, is the maximum allowable voltage drop value.

4. The method for optimizing the flexible direct current low penetration parameters of a conventional unit through a flexible direct current island transmission system according to claim 3 is characterized in that: When the maximum active current value is reduced according to the commutation bus voltage drop degree, the maximum active current value is calculated according to the following formula: In the formula, is the maximum value of the active current, is the maximum current, is the maximum reactive current, is the voltage value of the commutation bus during fault and recovery.

5. The method for optimizing the flexible direct current low penetration parameters of a conventional unit through a flexible direct current island transmission system according to claim 1 is characterized in that: If the voltage value of the commutation bus during the fault and recovery period is not less than the minimum positive sequence voltage and less than the second set value, it is judged that the voltage drop of the commutation bus is not deep, and the maximum active current is maintained at the initial setting value. The initial setting value is determined according to the following formula: In the formula, is the maximum value of the active current, is the maximum current, is the maximum value of reactive current.

6. A device for optimizing the low penetration parameters of a conventional unit through a flexible direct current island transmission system, characterized in that: The steps include: The initial setting module is used to set the initial maximum active current of the island transmission system during the low voltage ride-through period; A fault scanning module is used to scan the AC line three-way N-1 fault of the island transmission system and make stability judgment; It is also used to re-scan the AC line three-permanent N-1 fault of the island transmission system 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 island transmission system during the low voltage ride-through period; A voltage recording module is used to record the minimum positive sequence voltage of the commutation bus during a single-phase instantaneous fault; A voltage drop judgment module is used to judge the voltage drop degree of the commutation bus according to the voltage level of the commutation bus during the fault and recovery period and the minimum value of the positive sequence voltage; The active current limit adjustment module is used to reset the maximum active current of the island transmission system during the low voltage ride-through period according to the voltage drop degree of the commutation bus.

7. The device for optimizing the flexible direct current low penetration parameters of the conventional unit through the flexible direct current island transmission system according to claim 6 is characterized in that: If the voltage value of the commutation bus during the fault and recovery period is less than the minimum positive sequence voltage; The maximum active current value is correspondingly adjusted according to the voltage drop degree of the commutation bus, including: If the voltage value of the commutation bus during the fault and recovery period is less than the minimum positive sequence voltage value and greater than the first set value, then based on the initial maximum active current value, the maximum active current value is reduced according to the degree of voltage drop of the commutation bus; If the voltage value of the commutation bus during the fault and recovery period is not greater than the first set value, the maximum active current value is reduced to 0.

8. The device for optimizing the flexible direct current low penetration parameters of the conventional unit through the flexible direct current island transmission system according to claim 7 is characterized in that: The first setting value is , is the minimum positive sequence voltage, is the maximum allowable voltage drop value.

9. The device for optimizing the flexible direct current low penetration parameters of the conventional unit through the flexible direct current island transmission system according to claim 8 is characterized in that: When the maximum active current value is reduced according to the commutation bus voltage drop degree, the maximum active current value is calculated according to the following formula: In the formula, is the maximum value of the active current, is the maximum current, is the maximum reactive current, is the voltage value of the commutation bus during fault and recovery.

10. The device for optimizing the flexible direct current low penetration parameters of the conventional unit through the flexible direct current island transmission system according to claim 6, characterized in that: If the voltage value of the commutation bus during the fault and recovery period is not less than the minimum positive sequence voltage and less than the second set value, it is judged that the voltage drop of the commutation bus is not deep, and the maximum active current is maintained at the initial setting value. The initial setting value is determined according to the following formula: In the formula, is the maximum value of the active current, is the maximum current, is the maximum value of reactive current.

Images