Reactive power feedback control-based control method for commutation failure in hybrid cascaded high-voltage direct-current power transmission system, storage medium and electronic apparatus

Abstract

The present application provides a reactive power feedback control-based control method for a commutation failure in a hybrid cascaded high-voltage direct-current power transmission system, a storage medium and an electronic apparatus, and particularly relates to a reactive power feedback control-based control method for a commutation failure in a hybrid cascade high-voltage direct-current power transmission system. The method mainly comprises the following steps: acquiring power data of a hybrid cascaded high-voltage direct-current power transmission system; calculating the reactive power supply of an inverter-side MMC-end alternating-current system, the reactive power supply of an inverter-side alternating-current filter, and the reactive power supply of an inverter-side LCC-end alternating-current system; solving a reactive power control instruction of an inverter-side MMC converter; and, on the basis of a critical voltage, determining whether to implement the reactive power feedback control-based control method for a commutation failure in the hybrid cascaded power transmission system. The method can effectively reduce the probability of commutation failures in hybrid cascaded power transmission systems, thus guaranteeing safe and stable operation of large-scale power grids.

Description

Control method, storage medium and electronic device for commutation failure of hybrid cascade HVDC transmission system based on reactive feedback control Technical Field

[0001] The present application relates to the field of high-voltage direct current (HVDC) transmission technology, and in particular to a control method, storage medium, and electronic device for commutation failure in a hybrid cascaded HVDC transmission system based on reactive power feedback control. Background Art

[0002] HVDC technology offers advantages such as large transmission capacity, long transmission distances, and robust control and regulation. It is widely used for long-distance power transmission and regional grid interconnection. At the sending end of the system, a rectifier converts three-phase AC power into DC power. This power is then transmitted via transmission lines. At the receiving end of the system, the DC power is then inverted into three-phase AC power and fed into the receiving AC grid.

[0003] Current HVDC transmission technologies are primarily divided into two categories: conventional DC transmission based on line commutated converters (LCCs); and flexible DC transmission based on modular multilevel converters (MMCs). To combine the technical advantages of LCCs and MMCs, the Baihetan-Jiangsu Hybrid Cascade HVDC Transmission Project in China employs both technologies. The project uses LCCs on the sending end and an LCC in series with three parallel MMCs on the receiving end. The advantages of this structure are that the receiving end utilizes MMC converters, which are immune to commutation failures, significantly reducing the probability of commutation failures. Following a DC fault, the MMC discharge path is blocked by the LCC, enhancing the system's DC fault ride-through capability. The LCC and three MMCs on the receiving end of the system's inverter side are distributed and connected to different AC systems, enabling multi-point power reception and dynamic reactive power support capabilities, resulting in more flexible operation.

[0004] Commutation failure is a common fault in HVDC transmission systems using grid-commutated converters. Repeated commutation failures can lead to a surge in DC current, shorten the life of converter valves, and even cause the DC system to lock up, resulting in significant DC power loss and a serious threat to the safety and stability of the receiving grid. Hybrid cascaded HVDC transmission systems use MMC converters on the low-voltage side, which are not susceptible to commutation failure. However, their high-voltage side still uses LCC converters, so commutation failure is a significant issue.

[0005] Current measures to mitigate commutation failures, such as prematurely triggering the converter, reducing DC current, and modifying converter topology, are mostly designed for conventional LCC (Low-Channel Coordinated Converter) DC transmission systems. Few specifically consider the control and operational characteristics of hybrid cascaded HVDC transmission systems. Given the unique structure of hybrid cascaded HVDC transmission and the superior reactive power regulation capabilities of MMC converters, further research is needed to control the reactive power output of MMC converters and utilize them to mitigate commutation failures.

[0006] Summary of the Invention

[0007] Each exemplary embodiment of the present application provides a control method, storage medium, and electronic device for commutation failure in a hybrid cascaded high-voltage direct current transmission system based on reactive power feedback control, so as to at least achieve the technical effect of utilizing the reactive power output of the MMC to support the inverter-side AC bus voltage and reduce the probability of commutation failure.

[0008] Each exemplary embodiment of the present application provides a method for controlling commutation failure in a hybrid cascaded high-voltage direct current (HVDC) power transmission system based on reactive power feedback control, comprising the following steps:

[0009] Obtaining power data for hybrid cascaded HVDC systems,

[0010] Calculate the critical voltage, and perform control intervention calculation when the effective value of the AC bus voltage at the LCC end is less than the critical voltage during operation of the system.

[0011] The control intervention calculation includes calculating the reactive power provided by the AC system at the inverter-side modular multilevel converter MMC end, the reactive power provided by the inverter-side AC filter, and the reactive power provided by the AC system at the inverter-side grid-commutated converter LCC end, and solving the reactive power control instruction of the target inverter-side MMC converter, and

[0012] The reactive power control instruction of the inverter-side MMC converter is adjusted to the target reactive power control instruction of the inverter-side MMC converter obtained by the control intervention calculation, so as to control the reactive output of the MMC converter.

[0013] In another aspect of the present application, a computer-readable storage medium is provided, wherein the storage medium stores a computer program, wherein the computer program is configured to execute the steps of any of the above method embodiments when run.

[0014] In another aspect of the present application, an electronic device is proposed, comprising a memory and a processor, wherein a computer program is stored in the memory, and the processor is configured to run the computer program to execute the steps in any one of the above method embodiments.

[0015] The present application has the following beneficial effects: under normal operation, the reactive power consumed by the converter is provided by the AC filter; when the AC system suffers a large disturbance, the reactive local balance of the DC system in steady state is broken; utilizing the MMC reactive power output can reduce the reactive power absorbed by the DC system to the inverter-side AC system, reduce the degree of bus voltage drop, and reduce the risk of subsequent commutation failure of the hybrid cascade system.

[0016] This application introduces the feedback of the measured reactive power measurement value of the AC system on the inverter side LCC end, realizes the closed-loop control of the reactive power on the inverter side, and proposes a hybrid cascade HVDC transmission commutation failure suppression method based on MMC reactive power support, which effectively reduces the probability of hybrid cascade HVDC transmission commutation failure.

[0017] The commutation failure suppression method based on reactive power feedback control proposed in this application takes into account the reactive power provided by the AC system on the inverter side and the MMC side. Under transient conditions, it can reduce the reactive power provided by the AC system on the MMC side, avoid the voltage drop of the AC system on the MMC side, eliminate the obstruction of MMC power transmission, and suppress the occurrence of MMC overvoltage.

[0018] This application features simple calculations and clear physical meaning. It requires no changes to the structure and hardware of the hybrid cascade HVDC transmission system. Simple arithmetic operations based on the existing electrical and control parameters of the DC system are sufficient to implement this application. This application requires minimal hardware and software requirements, offers fast calculation speed, and is suitable for field engineering applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0020] Figure 1 is a schematic diagram of the overall process of this application;

[0021] FIG2 is a simulation diagram of the commutation failure suppression effect of the original control method of the system under three-phase fault in one embodiment of the present application;

[0022] FIG3 is a simulation diagram of the commutation failure suppression effect of the commutation failure suppression method based on MMC reactive PI control under three-phase fault in one embodiment of the present application;

[0023] FIG4 is a simulation diagram of the commutation failure suppression effect of the control method of the present application under a three-phase fault in one embodiment of the present application;

[0024] FIG5 is a schematic diagram of an optional electronic device structure according to an embodiment of the present application. DETAILED DESCRIPTION

[0025] The following will be combined with the drawings in the preferred embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of this application.

[0026] As shown in FIG1 and FIG2 , a method for controlling commutation failure in a hybrid cascade HVDC transmission system based on reactive power feedback control includes the following steps:

[0027] S1, obtains power data of the hybrid cascaded HVDC transmission system.

[0028] S2, calculating a critical voltage, and performing control intervention calculation when the effective value of the AC bus voltage at the LCC end is less than the critical voltage during operation of the system.

[0029] S3, the control intervention calculation includes calculating the reactive power provided by the AC system at the inverter-side modular multilevel converter MMC end, the reactive power provided by the inverter-side AC filter, and the reactive power provided by the AC system at the inverter-side grid-commutated converter LCC end, so as to obtain a target inverter-side MMC converter reactive power control instruction.

[0030] S4, adjusting the reactive power control instruction of the inverter-side MMC converter to the target reactive power control instruction of the inverter-side MMC converter obtained by the control intervention calculation, so as to control the reactive power output of the MMC converter.

[0031] In an optional embodiment, as shown in FIG1 , the step of obtaining power data of the hybrid cascaded HVDC power transmission system in step S1 includes:

[0032] The sampling frequency f HZ of the control and protection device of the hybrid cascade HVDC transmission system is used to collect the instantaneous value u of the three-phase voltage of the AC busbar at the inverter side LCC end of the system in real time. a 、u b 、u c , the instantaneous value of three-phase current i a 、i b 、i c , the effective value of the AC bus voltage U LL , after AC fault, the AC bus voltage drop value ΔU at the LCC end l , the inverter's turn-off angle γ, the DC current I d , DC power P d .

[0033] In an optional embodiment, in step S2, the step of calculating the critical voltage and performing control intervention calculation when the effective value of the AC bus voltage at the LCC end is less than the critical voltage during operation of the system includes:

[0034] Calculate critical voltage U th , the calculation formula is as follows:

[0035] Among them, U N is the rated value of the AC bus voltage on the inverter side when the system is in steady state operation; γ min is the inverter critical turn-off angle, γ N is the LCC inverter turn-off angle rating, β N is the leading firing angle rating.

[0036] When the system is running, the effective value of the AC bus voltage at the LCC end is U LL Is it less than the critical voltage U th If so, output the control input signal 1 and enter step S3; if not, output the control input signal 0 and return to step S2.

[0037] In an optional embodiment, in step S3, the control intervention calculation includes calculating the reactive power provided by the AC system at the inverter-side modular multilevel converter MMC end, the reactive power provided by the inverter-side AC filter, and the reactive power provided by the AC system at the inverter-side grid-commutated converter LCC end, so as to obtain the target inverter-side MMC converter reactive power control instruction, including:

[0038] S3.1, calculate the inverter side MMC j The reactive power provided by the AC system at the end, where j = 1, 2, 3, represents different MMC converters. The control and protection device first calculates the MMC on the inverter side. j AC bus voltage drop value ΔU j , the calculation formula is as follows:

[0039] Among them, Z lj ,Z j Represents the inverter side MMC j The connection impedance of the AC busbar connected to the LCC and the MMC j The equivalent impedance of the AC system at the end, ΔU l It is the AC bus voltage drop value at the LCC end after an AC fault;

[0040] S3.2, calculate the inverter side MMC j The reactive power ΔQ provided by the AC system acj , the calculation formula is as follows:

[0041] Among them, U Nj MMC is in normal operation j Rating of connected AC bus, S acj It is MMC j Short-circuit capacity of the AC system;

[0042] S3.3, calculate the reactive power provided by the AC filter on the inverter side, according to the effective value of the AC bus voltage U at the LCC end LL Calculate the reactive power Q provided by the inverter side AC filter f , the calculation formula is as follows:

[0043] Among them, B f is the equivalent susceptance of the AC filter;

[0044] S3.4. Calculate the reactive power provided by the AC system at the inverter-side LCC end. First, solve the physical quantities corresponding to the instantaneous values ​​of the three-phase voltage and current of the AC busbar at the inverter-side LCC end in the dq coordinate system. The calculation formula for the dq transformation of the three-phase voltage and current is as follows:

[0045] S3.5, calculate the reactive power Q provided by the AC system at the inverter side LCC end acm , the calculation formula is as follows: Q acm =u q i d -u d i q ,

[0046] S3.6, calculate the inverter side MMC j Converter reactive power control instruction Q MMCrefj , the calculation formula is as follows

[0047] Among them, Q d is the reactive power consumed by the converter, Q acref is the reactive power control command reference value, Q d The calculation formula is as follows:

[0048] Where N is the number of 6-pulse converters on the inverter side, U LL is the effective value of the AC bus voltage, k is the ratio of the converter transformer, Xr is the leakage reactance of the converter transformer, γ is the inverter turn-off angle, I d is the DC current, P d is the DC power.

[0049] It should be noted that the principle of the control intervention calculation in step S3 is:

[0050] Under normal operation, the reactive power consumed by the converter is provided by the AC filter; when the AC system is subjected to a large disturbance, the reactive power balance of the DC system in steady state is broken. Using the MMC reactive power output can reduce the reactive power absorbed by the DC system to the inverter side AC system, reduce the degree of bus voltage drop, and reduce the risk of subsequent commutation failure of the hybrid cascade system. Therefore, the above Q d The design principle of the calculation formula is as follows.

[0051] Specifically, the reactive power consumption of the converter under transient conditions can be calculated using the following formula:

[0052] Where N is the number of 6-pulse converters on the inverter side, U LL is the effective value of the AC bus voltage, k is the ratio of the converter transformer, Xr is the leakage reactance of the converter transformer, γ is the inverter turn-off angle, I d is the DC current, P d is the DC power, U d is the DC voltage, U d0 is the ideal no-load DC voltage, is the power factor of the converter.

[0053] Then calculate the inverter side MMC j After calculating the reactive power provided by the AC system on the inverter side (j=1, 2, 3, representing different MMC converters), the reactive power provided by the AC filter on the inverter side, and the reactive power provided by the AC system on the LCC side on the inverter side, the reactive power balance relationship on the inverter side is constructed as follows:

[0054] in, It represents the difference between the expected value and the measured value of reactive power exchanged between the DC system and the inverter-side AC system.

[0055] Furthermore, the inverter side MMC can be obtained j Converter reactive power control instructions:

[0056] Furthermore, the inverter side MMC is judged and controlled based on the AC bus real-time voltage and critical voltage to determine whether it is necessary to put the inverter side MMC into operation. j Converter reactive power control instruction, and when the conditions of step S4 are met, the inverter side MMC j The reactive power control command of the converter is adjusted to the obtained MMC j Converter reactive power command regulation Q MMCrefj , the reactive output of the MMC converter is controlled to suppress commutation failure.

[0057] In an optional implementation manner, the sampling frequency f is set to 10k-100k, and 10k is used as an example in this embodiment.

[0058] In an optional embodiment, the critical turn-off angle γ min The value of is 7 or 10. It should be noted that this critical turn-off angle is a fixed value with a clear physical meaning; the value is determined based on engineering experience.

[0059] In an optional implementation manner, the reactive power control instruction reference value Q used in this embodiment is acref The value of refers to the value of the stable operation of the DC system. Based on artificial setting, the value of this embodiment is 0.

[0060] The following is an example of a specific embodiment of the present application.

[0061] Step A: Obtaining power data of the hybrid cascaded HVDC transmission system

[0062] The control and protection device of the hybrid cascade HVDC transmission system collects the instantaneous value u of the three-phase AC bus voltage at the inverter side LCC end of the system at a sampling frequency of f HZ in real time. a 、u b 、u c , the instantaneous value of three-phase current i a 、i b 、i c , AC bus voltage effective value U LL , after AC fault, the AC bus voltage drop value ΔU at the LCC end l , the inverter's turn-off angle γ, the DC current I d , DC power P d ;

[0063] Step B1: Calculate critical voltage U th , the calculation formula is as follows

[0064] Among them, U N is the rated value of the AC bus voltage on the inverter side when the system is in steady state operation; γ min is the inverter critical turn-off angle, γ N is the LCC inverter turn-off angle rating, β N is the leading firing angle rating;

[0065] Step B2: When the system is running, the effective value of the AC bus voltage at the LCC end is U LL Is it less than the critical voltage U th If yes, output the control input signal 1 and go to step C; if no, output the control input signal 0 and return to step B2;

[0066] Step C: Inverter side MMC j (j=1, 2, 3, representing different MMC converters) end AC system reactive power supply calculation

[0067] The control protection device first calculates the inverter side MMC j AC bus voltage drop value ΔU j , the calculation formula is as follows:

[0068] where Z lj ,Z j Represents the inverter side MMC j The connection impedance of the AC busbar connected to the LCC and the MMC j The equivalent impedance of the AC system at the end, ΔU l It is the AC bus voltage drop value at the LCC end after an AC fault;

[0069] Next, calculate the reactive power ΔQ provided by the AC system at the MMC end of the inverter side acj , the calculation formula is as follows

[0070] Among them U Nj MMC is in normal operation j Rating of connected AC bus, S acj It is MMC j Short-circuit capacity of the AC system;

[0071] Step D: Calculate the reactive power provided by the AC filter on the inverter side

[0072] According to the effective value of the AC bus voltage at the LCC end U LL Calculate the reactive power Q provided by the inverter side AC filter f , the calculation formula is as follows:

[0073] Among them, B f is the equivalent susceptance of the AC filter;

[0074] Step E: Calculate the reactive power provided by the AC system at the inverter side LCC end

[0075] First, solve the physical quantities corresponding to the instantaneous values ​​of the three-phase voltage and current of the AC busbar at the LCC end of the inverter side in the dq coordinate system. The calculation formula for the dq transformation of the three-phase voltage and current is as follows:

[0076] Then calculate the reactive power Q provided by the AC system at the inverter side LCC end acm , the calculation formula is as follows Q acm =u q i d -u d i q ,

[0077] Step F: Inverter-side MMCj Converter reactive power control instruction calculation

[0078] Combined with the inverter side MMC calculated in steps C, D, and E j The reactive power provided by the AC system at the end, the reactive power provided by the AC filter at the inverter side, the reactive power provided by the AC system at the LCC end at the inverter side, and the MMC at the inverter side are solved. j Converter reactive power control instruction Q MMCrefj , the calculation formula is as follows

[0079] Among them, Q d is the reactive power consumed by the converter, Q acref is the reactive power control command reference value, Q d The calculation formula is as follows:

[0080] Where N is the number of 6-pulse converters on the inverter side, U LL is the effective value of the AC bus voltage, k is the ratio of the converter transformer, Xr is the leakage reactance of the converter transformer, γ is the inverter turn-off angle, I d is the DC current, P d is the DC power.

[0081] Step G: Inverter side MMC j The reactive power control command of the converter is adjusted to the MMC calculated in step F. j Converter reactive power command regulation Q MMCrefj , to control the reactive output of the MMC converter.

[0082] In this embodiment, the sampling frequency f in step A is exemplarily selected to be 10k. The critical turn-off angle γ in step B1 min The value of is 7°. The reactive control instruction reference value Q in step F acref The value of is 0.

[0083] Simulation experiment:

[0084] To verify the effectiveness of the proposed control method in reducing commutation failures in a hybrid cascaded HVDC system, an electromagnetic transient simulation model of a hybrid cascaded HVDC transmission system based on the Baihetan-Jiangsu HVDC transmission project was constructed using the PSCAD / EMTDC software platform. An inductive ground fault was set at the inverter-side AC busbar. A smaller ground inductance indicates a more severe fault. The effectiveness of the following three control methods in suppressing commutation failures was compared and analyzed: 1) the original system control method; 2) a commutation failure suppression method based on MMC reactive power PI control; and 3) the method described in this invention.

[0085] The three-phase ground fault, which is the most serious fault, was selected to verify the commutation failure suppression effect of the three methods. As shown in Figures 2 to 4, a comparison of the effects of the three methods under a three-phase ground fault is given. The electrical quantities from top to bottom are the reactive power provided by the AC system on the LCC side, the reactive power provided by the AC system on the MMC side, the reactive power output by the MMC, the effective value of the commutation bus voltage on the LCC side, the DC current of the DC system, the LCC shutdown angle, and the MMC DC voltage. It can be seen that the original method caused the bus voltage to continue to drop due to the increase in reactive power consumption of the LCC converter after the fault, resulting in subsequent commutation failure and causing MMC overvoltage; the commutation failure suppression method based on MMC reactive power PI control can provide some reactive power to support the bus voltage, but the reactive power provided cannot match the system reactive power demand, resulting in subsequent commutation failure in the system; the method of the present invention adopts the idea of ​​reactive power feedback control to suppress commutation failure, achieves reactive power supply balance on the inverter side under transient conditions, reduces the degree of AC bus voltage drop, and thus suppresses the occurrence of subsequent commutation failure.

[0086] According to another aspect of the embodiments of the present application, an electronic device for implementing the aforementioned method for controlling commutation failure in a hybrid cascaded HVDC transmission system based on reactive power feedback control is also provided. The electronic device can be, but is not limited to, used in a server. As shown in FIG5 , the electronic device includes a memory 502 and a processor 504. The memory 502 stores a computer program, and the processor 504 is configured to execute the steps of any of the aforementioned method embodiments using the computer program.

[0087] Optionally, in this embodiment, the electronic device may be located in at least one network device among a plurality of network devices of a computer network.

[0088] Optionally, in this embodiment, the processor may be configured to execute the following steps through a computer program:

[0089] S1, obtains power data of the hybrid cascaded HVDC transmission system.

[0090] S2, calculating a critical voltage, and performing control intervention calculation when the effective value of the AC bus voltage at the LCC end is less than the critical voltage during operation of the system.

[0091] S3, the control intervention calculation includes calculating the reactive power provided by the AC system at the inverter-side modular multilevel converter MMC end, the reactive power provided by the inverter-side AC filter, and the reactive power provided by the AC system at the inverter-side grid-commutated converter LCC end, and solving the target inverter-side MMC converter reactive power control instruction.

[0092] S4, adjusting the reactive power control instruction of the inverter-side MMC converter to the target reactive power control instruction of the inverter-side MMC converter obtained by the control intervention calculation, so as to control the reactive power output of the MMC converter.

[0093] Alternatively, those skilled in the art will appreciate that the structure shown in FIG5 is merely illustrative, and the electronic device may also be a terminal device such as a mobile internet device (MID) or a PAD. FIG5 does not limit the structure of the electronic device. For example, the electronic device may include more or fewer components (such as a network interface) than shown in FIG5 , or may have a configuration different from that shown in FIG5 .

[0094] The memory 502 may include a high-speed random access memory (RAM) and may also include a non-volatile memory, such as one or more magnetic storage devices, flash memory, or other non-volatile solid-state memory. In some instances, the memory 502 may further include a memory remotely located relative to the processor 504, and these remote memories may be connected to the terminal via a network. Examples of the aforementioned network include, but are not limited to, the Internet, an intranet, a local area network, a mobile communication network, and combinations thereof. As an example, as shown in FIG5 , the aforementioned memory 502 may include, but is not limited to, a storage module and an alarm module, etc., which will not be described in detail in this example.

[0095] Optionally, the transmission device 506 is configured to receive or send data via a network. Specific examples of the aforementioned network may include wired networks and wireless networks. In one embodiment, the transmission device 506 includes a network interface controller (NIC), which can be connected to other network devices and a router via a network cable to communicate with the Internet or a local area network. In one embodiment, the transmission device 506 is a radio frequency (RF) module, which is configured to communicate with the Internet wirelessly.

[0096] In addition, the electronic device further includes: a display 508 for displaying current simulation results; and a connection bus 510 for connecting various module components in the electronic device.

[0097] An embodiment of the present application further provides a computer-readable storage medium, in which a computer program is stored, wherein the computer program is configured to execute the steps of any of the above method embodiments when run.

[0098] Optionally, in this embodiment, the storage medium may be configured to store a computer program for performing the following steps:

[0099] S1, obtains power data of the hybrid cascaded HVDC transmission system.

[0100] S2, calculating a critical voltage, and performing control intervention calculation when the effective value of the AC bus voltage at the LCC end is less than the critical voltage during operation of the system.

[0101] S3, the control intervention calculation includes calculating the reactive power provided by the AC system at the inverter-side modular multilevel converter MMC end, the reactive power provided by the inverter-side AC filter, and the reactive power provided by the AC system at the inverter-side grid-commutated converter LCC end, and solving the target inverter-side MMC converter reactive power control instruction.

[0102] S4, adjusting the reactive power control instruction of the inverter-side MMC converter to the target reactive power control instruction of the inverter-side MMC converter obtained by the control intervention calculation, so as to control the reactive power output of the MMC converter.

[0103] Optionally, the storage medium is further configured to store a computer program for executing the steps included in the method in the above embodiment, which will not be described in detail in this embodiment.

[0104] Optionally, in this embodiment, a person of ordinary skill in the art may understand that all or part of the steps in the various methods of the above embodiments may be completed by instructing the hardware related to the terminal device through a program, and the program may be stored in a computer-readable storage medium, which may include: a flash drive, a read-only memory (ROM), a random access memory (RAM), a magnetic disk or an optical disk, etc.

[0105] The serial numbers of the above embodiments of the present application are for description only and do not represent the advantages or disadvantages of the embodiments.

[0106] If the integrated units in the above embodiments are implemented in the form of software functional units and sold or used as independent products, they can be stored in the above-mentioned computer-readable storage medium. Based on this understanding, the technical solution of the present application, or the part that contributes to the prior art, or all or part of the technical solution can be embodied in the form of a software product, which is stored in a storage medium and includes several instructions for enabling one or more computer devices (which can be personal computers, servers, or network devices, etc.) to execute all or part of the steps of the methods described in each embodiment of the present application.

[0107] In the above embodiments of the present application, the description of each embodiment has its own focus. For parts that are not described in detail in a certain embodiment, please refer to the relevant description of other embodiments.

[0108] In the several embodiments provided in this application, it should be understood that the disclosed client can be implemented in other ways. Among them, the device embodiments described above are merely illustrative. For example, the division of the units is merely a logical function division. In actual implementation, there may be other division methods, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. In addition, the mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, indirect coupling or communication connection of units or modules, and can be electrical or other forms.

[0109] The units described as separate components may or may not be physically separate, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed across multiple network units. Some or all of these units may be selected to achieve the purpose of this embodiment according to actual needs.

[0110] In addition, the functional units in the various embodiments of the present application may be integrated into a single processing unit, or each unit may exist physically separately, or two or more units may be integrated into a single unit. The aforementioned integrated units may be implemented in the form of hardware or software functional units.

[0111] The above is only a preferred embodiment of the present application. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present application. These improvements and modifications should also be regarded as the scope of protection of the present application.

[0112] Although the preferred embodiments of the present application have been described, those skilled in the art may make additional changes and modifications based on these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present application.

[0113] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. 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 application.

Claims

1. A control method for commutation failure of a hybrid cascaded HVDC transmission system based on reactive power feedback control, wherein, It includes the following steps: Obtain the power data of the hybrid cascaded HVDC transmission system, Calculate the critical voltage, and perform control intervention calculation when the effective value of the AC bus voltage at the LCC end is less than the critical voltage during the operation of the system, The control intervention calculation includes calculating the reactive power provided by the AC system at the modular multilevel converter (MMC) end on the inverter side, the reactive power provided by the AC filter on the inverter side, and the reactive power provided by the AC system at the line-commutated converter (LCC) end on the inverter side, solving the reactive power control command for the target MMC converter on the inverter side, and Adjust the reactive power control command of the MMC converter on the inverter side to the target reactive power control command of the MMC converter on the inverter side obtained by the control intervention calculation to control the reactive power output of the MMC converter.

2. The control method for commutation failure of a hybrid cascaded HVDC transmission system based on reactive power feedback control according to claim 1, wherein, The step of obtaining the power data of the hybrid cascaded HVDC transmission system includes: The sampling frequency f HZ of the control and protection device for the hybrid cascaded HVDC transmission system is used to collect the instantaneous values u of the three-phase voltages of the AC bus at the LCC end of the inverter side of the system in real time a 、u b 、u c ,the instantaneous values i of the three-phase currents a 、i b 、i c ,the effective value U of the AC bus voltage LL ,the voltage drop value ΔU of the AC bus at the LCC end after an AC fault l ,the turn-off angle γ of the inverter, the DC current I d ,the DC power P d 。 3. The control method for commutation failure of a hybrid cascaded HVDC transmission system based on reactive power feedback control according to claim 2, wherein, The step of calculating the critical voltage includes: Calculate the critical voltage U th , and the calculation formula is as follows: Among them, U N is the rated value of the AC bus voltage on the inverter side during the steady-state operation of the system; γ min is the critical turn-off angle of the inverter, γ N is the rated value of the turn-off angle of the LCC inverter, β N is the rated value of the leading trigger angle.

4. The control method for commutation failure of a hybrid cascaded HVDC transmission system based on reactive power feedback control according to claim 3, wherein, The control intervention calculation includes calculating the reactive power provided by the AC system at the modular multilevel converter (MMC) end on the inverter side, the reactive power provided by the AC filter on the inverter side, and the reactive power provided by the AC system at the line-commutated converter (LCC) end on the inverter side. The step of solving the reactive power control command for the target MMC converter on the inverter side includes: Calculate the MMC on the inverter side j The reactive power provided by the AC system at the terminal. Here, j = 1, 2, 3 represents different MMC converters. The control and protection device first calculates the MMC on the inverter side j The voltage drop value ΔU of the AC bus at the terminal j , and the calculation formula is as follows: Among them, Z lj , Z j respectively represent the connection impedance between the AC bus connected to the MMC on the inverter side and the AC bus connected to the LCC, and the equivalent impedance of the AC system at the MMC j terminal. ΔU j is the voltage drop value of the AC bus at the LCC terminal after the AC fault; l ​ Calculating the MMC on the inverter side j The reactive power ΔQ provided by the AC system at the terminal acj , and the calculation formula is as follows: Among them, U Nj is the rated value of the MMC j connected to the AC bus during normal operation, and S acj is the short-circuit capacity of the AC system at the MMC j terminal; Calculate the reactive power provided by the AC filter on the inverter side. Based on the effective value U of the AC bus voltage at the LCC end LL Calculate the reactive power Q provided by the AC filter on the inverter side f , and the calculation formula is as follows: Among them, B f is the equivalent susceptance of the AC filter; Calculate the reactive power provided by the AC system at the LCC end on the inverter side. First, solve the LCC on the inverter side in the dq coordinate system Physical quantities corresponding to the instantaneous values of the three-phase voltages and currents of the terminal AC bus. The calculation formulas for the dq transformation of the three-phase voltages and currents are as follows: Calculate the reactive power Q provided by the AC system at the LCC terminal on the inverter side acm , and the calculation formula is as follows: Q acm = u q i d - u d i q , Calculate the MMC on the inverter side j Reactive power control command Q of the converter MMCrefj , and the calculation formula is as follows Among them, Q d is the reactive power consumed by the converter, and Q acref is the reference value of the reactive power control command. The calculation formula of Q d is as follows: Among them, N is the number of 6-pulse converters on the inverter side, U LL is the effective value of the AC bus voltage, k is the turns ratio of the converter transformer, Xr is the leakage reactance of the converter transformer, γ is the inverter turn-off angle, I d is the DC current, P d is the DC power.

5. The control method for commutation failure of a hybrid cascaded HVDC transmission system based on reactive power feedback control according to claim 2, wherein, The sampling frequency f ranges from 10k to 100k.

6. The control method for commutation failure of a hybrid cascaded HVDC transmission system based on reactive power feedback control according to claim 3, wherein, Critical turn-off angle γ min takes a value of 7 or 10.

7. The control method for commutation failure of a hybrid cascaded HVDC transmission system based on reactive power feedback control according to claim 4, wherein, Reference value Q of the reactive power control command acref The value is referenced from the value for the stable operation of the DC system and is based on manual setting.

8. A computer-readable storage medium, characterized in that, A computer program is stored in the storage medium, wherein the computer program is configured to execute the method described in any one of claims 1 to 7 when running.

9. An electronic device, comprising a memory and a processor, characterized in that, A computer program is stored in the memory, and the processor is configured to run the computer program to execute the method described in any one of claims 1 to 7.

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