Fault detection method for asymmetric flexible interconnection AC / DC hybrid power distribution network

Abstract

The method is used for solving the problem that in the prior art, faults of an asymmetric flexible interconnection alternating current and direct current hybrid power distribution network system cannot be rapidly recognized, responded and processed. Therefore, the invention provides a fault detection method for the asymmetric flexible interconnection AC / DC hybrid power distribution network, and the method comprises the steps: building a fault model according to a topological structure of the asymmetric flexible interconnection AC / DC hybrid power distribution network; and monitoring operation information of the asymmetric flexible interconnection AC / DC hybrid power distribution network in real time, analyzing a fault type based on the topological structure, and adopting a corresponding fault control strategy. After the technical scheme recorded by the invention is adopted, various faults of the asymmetric flexible interconnection alternating current and direct current hybrid power distribution network can be found in time and can be quickly blocked through corresponding protection logic and fault control strategies; therefore, faults possibly occurring in the asymmetric flexible interconnection AC / DC hybrid power distribution network can be quickly identified, responded and processed, and the stability of system operation is ensured.

Description

Technical Field

[0001] The present invention belongs to the technical field of flexible interconnection of medium-voltage distribution networks, and in particular relates to a fault detection method for an asymmetric flexible interconnected AC / DC hybrid distribution network. Background Art

[0002] With the rapid development and widespread application of power electronics technology, the trend of distributed power access, power supply and load DC is becoming increasingly significant. The problems faced by traditional AC distribution networks are becoming more and more prominent, and it is difficult to meet the development needs of the current power system. Especially in medium and low voltage DC distribution networks, the system structure is complex, the fault coupling mechanism of each voltage level after the fault is complex and changeable, and it is deeply affected by the converter topology and system configuration, which makes it difficult to achieve the selectivity of protection. In addition, the fault current is restricted by many factors such as converter topology, control strategy and system configuration, and the characteristics are complex and difficult to identify quickly and accurately. In addition, the fault current of the DC distribution network rises quickly, and it is difficult for the protection system to respond and isolate the fault in time before the converter is locked, which further aggravates the impact of the fault on the power grid. In this regard, in the existing technology, lightweight medium-voltage flexible interconnection devices have been designed to address existing problems. For example, the lightweight medium-voltage flexible interconnection device built in Ningbo in 2024 is installed on the 10 kV standard double-loop network of Ningbo Beilun 110 kV Yongfeng Substation and 110 kV Xuyang Substation. It adopts power electronics + phase-shifting transformer technology and has the ability to adjust the voltage amplitude and phase angle required for 10kV line interconnection, solving the pain points of the "closed-loop design, open-loop operation" network architecture of my country's distribution network for a long time. After the device is put into operation, the power supply capacity will be increased by about 7,500 kilowatts, and the power flow transfer between the two 110 kV substations and lines can be completed within 20 milliseconds, providing solutions for the power grid to cope with the intermittent and variable output of distributed power sources and short-term load fluctuations. This lightweight medium-voltage flexible interconnection device reduces floor space by 80%, reduces construction costs by 70%, and has an efficiency of 99%. It takes into account economy, reliability, miniaturization, and low losses, and meets the requirements for regional distribution network construction in modern cities, industrial parks, etc., ensuring power supply while saving resources.

[0003] However, the medium-voltage flexible interconnection mode in current engineering applications is 10 / 10kV interconnection, with equal operating voltages on both sides, the same control strategy and protection logic, while in some special application scenarios, there is a 6 / 10kV flexible interconnection mode, with unequal operating voltages on both sides, and significant differences in control strategy and protection logic from the 10 / 10kV interconnection scheme, which cannot be directly used. At the same time, the fault recovery strategy of the 6 / 10kV flexible interconnected distribution network also has its particularity, which requires full consideration of the difference in transmission capacity of the lines on both sides, and gradually restores the locked commutation device according to the required transmission power. However, due to the uncertainty of power flow changes, this process is difficult to implement. Summary of the invention

[0004] The purpose of the present invention is to solve the problem that the fault of an asymmetric flexible interconnected AC / DC hybrid distribution network system cannot be quickly identified, responded to, and processed in the prior art. To this end, the present invention provides a method for detecting faults in an asymmetric flexible interconnected AC / DC hybrid distribution network, comprising the steps of:

[0005] According to the topological structure of asymmetric flexible interconnected AC / DC hybrid distribution network, a fault model is established;

[0006] Analyze fault characteristics under different topologies and fault types;

[0007] Collecting operation data of asymmetric flexible interconnected AC / DC hybrid distribution network;

[0008] The operation information of the asymmetric flexible interconnected AC / DC hybrid distribution network is monitored in real time. After a fault occurs, the fault type is analyzed based on the topological structure and a corresponding fault control strategy is adopted.

[0009] Preferably, the commutation device is a controllable switch type converter on the 6kV side and a controllable power supply type converter on the 10kV side.

[0010] Among them, the controllable switch type converter is a diode clamped three-level converter, which uses third harmonic injection sinusoidal pulse width modulation to increase the modulation ratio width and prevent the injected third harmonic from reaching the DC side. Its topology and operation control are relatively simple and it is often used for low-voltage AC-DC conversion.

[0011] Among them, the fault response characteristics of the controllable switch type converter include inter-pole short-circuit fault characteristics, bipolar short-circuit fault characteristics after IGBT lockout, and unipolar short-circuit fault characteristics.

[0012] Preferably, the controllable power converter is a modular multi-level (MMC) converter. It distributes the concentrated voltage stabilizing capacitors in the two / three-level converter in each submodule to achieve multi-level modulation, which can be used for higher voltage levels and is commonly used in AC / DC conversion of medium voltage DC distribution networks in distribution networks. According to the type of submodule used, it can be divided into half-bridge type, full-bridge type and double-clamp type.

[0013] Among them, the fault response characteristics of the controllable power supply converter include bipolar short circuit fault characteristics, bipolar short circuit fault characteristics after IGBT lockout, and unipolar short circuit fault characteristics.

[0014] Preferably, after a fault occurs, the fault control strategy includes locking the power electronic device and completing the DC side fault ride-through by using control means.

[0015] The present invention also includes an electronic device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the steps of a method for detecting faults in an asymmetric flexible interconnected AC / DC hybrid distribution network when executing the computer program.

[0016] The present invention also includes a computer-readable storage medium, which stores a computer program. When the computer program is executed by a processor, the steps of the asymmetric flexible interconnected AC / DC hybrid distribution network fault detection method are implemented.

[0017] The beneficial effects achieved by the present invention are as follows: after adopting the technical solution recorded in the present invention, various types of faults in the asymmetric flexible interconnected AC / DC hybrid distribution network can be discovered in a timely manner, and quickly blocked through corresponding protection logic and fault control strategy, thereby quickly identifying, responding to and processing possible faults in the asymmetric flexible interconnected AC / DC hybrid distribution network, thereby ensuring the stability of system operation.

[0018] The above invention content is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention, it can be implemented according to the contents of the specification. In order to make the above and other purposes, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Other features, objects and advantages of the present invention will become more apparent by reading the detailed description of non-limiting embodiments made with reference to the following drawings. The drawings are only for the purpose of illustrating preferred embodiments and are not to be considered as limiting the present invention. Also, the same reference symbols are used throughout the drawings to represent the same parts.

[0020] Figure 1 It is a schematic diagram of a diode clamped three-level converter topology structure of an asymmetric flexible interconnected AC / DC hybrid distribution network fault detection method provided in an embodiment of the present invention.

[0021] Figure 2 It is a schematic diagram of a VSC DC side inter-pole short-circuit fault circuit of an asymmetric flexible interconnected AC / DC hybrid distribution network fault detection method provided in an embodiment of the present invention.

[0022] Figure 3 It is a schematic diagram of a single-pole grounding fault circuit when the AC side of the asymmetric flexible interconnected AC / DC hybrid distribution network fault detection method provided by an embodiment of the present invention is grounded through a neutral point.

[0023] Figure 4 It is a schematic diagram of a modular multi-level sub-module topology structure of an asymmetric flexible interconnected AC / DC hybrid distribution network fault detection method provided by an embodiment of the present invention.

[0024] Figure 5 It is a schematic diagram of a modular multi-level converter port inter-pole short-circuit fault circuit of an asymmetric flexible interconnected AC / DC hybrid distribution network fault detection method provided in an embodiment of the present invention.

[0025] Figure 6 It is an equivalent circuit diagram of a DC two-stage short-circuit fault after IGBT locking of the asymmetric flexible interconnected AC / DC hybrid distribution network fault detection method provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0026] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific implementation method described herein is only an optimal embodiment of the present invention, which is only used to explain the present invention and does not limit the scope of protection of the present invention. All other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0027] Before discussing the exemplary embodiments in more detail, it should be mentioned that some exemplary embodiments are described as processes or methods depicted as flow charts. Although the flow charts describe the operations (or steps) as sequential processes, many of the operations (or steps) therein can be implemented in parallel, concurrently or simultaneously. In addition, the order of the operations can be rearranged. The process can be terminated when its operation is completed, but it can also have additional steps not included in the drawings; the process can correspond to a method, function, procedure, subroutine, subprogram, etc. The terms "first", "second", "third", "fourth", etc. (if any) in the specification of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchangeable where appropriate, so that the embodiments of the present invention described here can be implemented in an order other than those illustrated or described here. It should also be understood that in various embodiments of the present invention, the size of the sequence number of each process does not mean the order of execution, and the execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0028] It should be understood that in the present invention, "plurality" means two or more. "and /

[0029] "Or" is just a variable relationship that describes the associated objects, indicating that there may be three relationships. It should be understood that in the present invention, "B corresponding to A", "B corresponding to A", "A corresponds to B" or "B corresponds to A" means that B is associated with A, and B can be determined based on A. Determining B based on A does not mean determining B based only on A, but B can also be determined based on A and / or other information. The match between A and B means that the similarity between A and B is greater than or equal to a preset threshold.

[0030] Scholars from various countries have conducted a lot of research on distribution network fault handling and power supply reliability analysis. In terms of fault impact analysis and fault recovery, the traditional distribution network is a single-power radial distribution network with unidirectional power flow, and its power supply recovery problem has been studied a lot. The solution strategies adopted include artificial intelligence algorithms, mathematical programming methods, and heuristic optimization algorithms. However, with the high penetration rate of distributed power sources (DG) connected to the grid, the traditional single-power distribution network has gradually transformed into an active distribution network. Its topology and system operation mode are significantly different from those of the traditional distribution network, making it difficult to apply the traditional distribution network fault recovery method. Therefore, the study proposed an improved genetic algorithm to solve the established active distribution network fault recovery model, obtain the optimal switch operation combination of the network, and apply the fault recovery method to actual engineering, achieving good results. The prior art also gives a calculation formula for the reliability index of the transmission network, and then performs sensitivity derivative calculations on parameters such as component failure rate and repair time. At the same time, based on the minimum cut set, the fault tree and reliability index analytical expressions of the DC transmission system are given, and the probability sensitivity of different DC component fault parameters is calculated. In addition, according to the structural characteristics of the transmission system, the importance of the components in the loop is calculated by taking the power grid loop as the basic unit and combining the Birnbaum constant method. However, compared with the AC distribution network, the AC / DC flexible interconnected distribution network has less damping and responds faster to power disturbances. When a short circuit fault occurs, the fault current rises quickly and has a wide range of impact. Due to the existence of a large number of distributed power sources and the widespread use of various types of converters, there are a large number of power electronic devices in the AC / DC flexible interconnected distribution network. If the system fault is not cleared in time, the fault current will rise rapidly, causing damage to a large number of power electronic equipment in the distribution network and endangering the safe operation of the system. Therefore, the AC / DC flexible interconnected distribution network needs to quickly and accurately identify and isolate faults.

[0031] In summary, distribution network fault handling and power supply reliability analysis is a complex and important research field, involving multiple aspects such as fault recovery, reliability modeling and analysis, and weak link identification. With the development of high-penetration grid connection of distributed power sources and flexible DC distribution networks, research in this field is also deepening, but the field of fault detection in the asymmetric flexible interconnected AC / DC hybrid distribution network described in the present invention is still blank.

[0032] This is because the fault mechanism, fault type and fault handling method of the asymmetric flexible interconnected AC / DC hybrid distribution network are completely different from those of the traditional AC distribution network. The traditional AC distribution network consists of primary equipment such as cables, transformers, switches and supporting secondary equipment, and does not involve power electronic devices or equipment. Its faults are generally caused by harsh environment, external force damage, and equipment aging, including three major categories: phase-to-phase short circuit, single-phase grounding, and line break. The fault section isolation and non-fault section restoration are completed through relay protection and distribution automation. The asymmetric flexible interconnected AC / DC hybrid distribution network consists of AC distribution lines and related equipment, and asymmetric flexible interconnection devices. Its core is the power electronic converter device. In addition to the above-mentioned fault types of the traditional AC distribution network, its fault types also include inter-pole short circuit faults, bipolar short circuit faults, and unipolar short circuit faults that are unique to the power electronic system. Therefore, its fault handling is mainly achieved by locking power electronic devices and adopting specific fault control strategies to achieve fault crossing.

[0033] In addition, there are also significant differences in the topological structure and control strategy between the asymmetric flexible interconnected AC / DC hybrid distribution network and the symmetrical medium-voltage flexible interconnected distribution network. The topological structure of the symmetrical medium-voltage flexible interconnected distribution network is symmetrical on both sides, and the control strategy is strictly consistent; the asymmetric flexible interconnected AC / DC hybrid distribution network adopts an asymmetric topological structure, and the control strategies on both sides are different.

[0034] In this regard, the present invention provides a method for detecting faults in an asymmetric flexible interconnected AC / DC hybrid distribution network, comprising the steps of:

[0035] According to the topological structure of asymmetric flexible interconnected AC / DC hybrid distribution network, a fault model is established;

[0036] Analyze fault characteristics under different topologies and fault types;

[0037] Collecting operation data of asymmetric flexible interconnected AC / DC hybrid distribution network;

[0038] The operation information of the asymmetric flexible interconnected AC / DC hybrid distribution network is monitored in real time. After a fault occurs, the fault type is analyzed based on the topological structure and a corresponding fault control strategy is adopted.

[0039] It should be noted that the voltages on both sides of the asymmetric flexible interconnected AC / DC hybrid distribution network described in the present invention are not equal. At present, the medium-voltage flexible interconnection modes in engineering applications are all interconnected at the same voltage level, while in some special application scenarios, there are overhead radial lines of different voltage levels that are interconnected through medium-voltage flexible interconnection devices, thereby improving power supply reliability and effectively avoiding electromagnetic ring network problems that may occur when the lines are closed and transferred.

[0040] In the embodiment of the present invention, we take a medium voltage flexible interconnected AC / DC hybrid distribution network with voltages of 6 kV and 10 kV on both sides as an example.

[0041] The fault characteristics of the 6 / 10kV medium voltage flexible interconnected AC / DC hybrid distribution network depend on the fault response characteristics of each converter in the power grid, and the fault response characteristics of the converter are closely related to the topology and fault control strategy of the converter. The topology of the converter is the boundary of the fault control strategy. Therefore, it is necessary to focus on analyzing the mechanism of the topology on the fault characteristics of the converter, as well as the impact of the fault control strategy on the fault characteristics before and after the action of the fault control strategy.

[0042] When the commutation device on the 6kV side is a three-level converter,

[0043] The diode clamped three-level converter topology is as follows: Figure 1 As shown. Compared with the three-level converter, the voltage stress of the switching device is reduced; when the waveform quality is the same, the required switching frequency is lower. The modulation strategy of the diode clamped three-level converter is similar to that of the two-level converter, but necessary measures must be taken to overcome the neutral point voltage offset problem.

[0044] The fault response characteristics that may be obtained at this time include inter-pole short-circuit fault characteristics: From the three-level converter topology, it can be seen that the DC side voltage stabilizing capacitor is one of the cores of the entire topology. When an inter-pole short-circuit fault occurs on the DC side, the capacitor will first discharge to the fault point through the fault loop. The discharge loop can be equivalent to a second-order discharge loop of the capacitor to the impedance, such as Figure 2 As shown in the fault circuit 1. Before the converter takes self-protection blocking, the AC power grid will discharge to the fault point through power electronic devices. The discharge circuit can be equivalent to a DC source with internal resistance discharging to the fault point on the DC side, and can be equivalent to an AC power supply discharging to the phase-to-phase fault point on the AC side, as shown in Figure 2 After the converter adopts self-protection blocking, the AC grid will discharge to the fault point through the diode. The discharge circuit is equivalent to the DC side short-circuit fault circuit of the uncontrolled rectifier circuit. The fault circuit is still as shown in Figure 2 As shown in the fault circuit 2. When the capacitor discharges, the DC side inductor will have a freewheeling effect on the short-circuit current, forming a freewheeling circuit through the three-phase bridge arm, as shown in Figure 2 As shown in the fault circuit 3.

[0045] Figure 2 The parameters of the equivalent second-order circuit of a DC bipolar short-circuit fault are shown in equation (1).

[0046]

[0047] Where: R C , L Care the equivalent resistance and reactance of the converter under the condition of DC bipolar short circuit fault; L arm , R arm Respectively represent the bridge arm reactance and bridge arm equivalent resistance; C C is the DC side capacitance value; L dc Represents DC reactor; R dc Represents the equivalent resistance of the DC line; N is the number of sub-modules in each bridge arm.

[0048] According to Kirchhoff's voltage law (KVL), the second-order equivalent circuit equation can be obtained:

[0049]

[0050] Assume that the initial value of the capacitor voltage is μ dc , the initial value of the inductor current is i dc0 , it can be obtained from formula (1) that the DC bipolar short-circuit fault current i after ignoring the short-circuit current injected on the AC side is dc (t) is

[0051]

[0052] Where: θ dc =arctan(τ dc ω dc ),

[0053] Formula (3) shows that after a fault, within a few milliseconds before the IGBT is locked, the capacitor discharge current rises rapidly, and the magnitude of the fault current is proportional to R dis Negatively correlated, while R dis The size of is related to the equivalent resistance, reactance, DC side capacitance of the converter and the equivalent resistance and reactance of the line.

[0054] The fault response characteristics that may be obtained at this time may also include the bipolar short-circuit fault characteristics after the IGBT is locked: after the IGBT is locked, the AC power grid injects fault current into the short-circuit point through the anti-parallel diode, and the DC bipolar short-circuit fault current i dc (t) is

[0055]

[0056] Where: U sm is the AC side voltage; L ac , L arm are the equivalent reactance of the AC side and the bridge arm reactance respectively; Z dc is the equivalent impedance of the DC line, and its size is related to the location of the fault point; I dcB is the DC side current when the IGBT is locked; τ dcBis the time constant, whose value is closely related to the inductance of the DC reactor and is generally around 10ms; k is a coefficient related to the conduction overlap angle γ, and the value range of k is 2 / 3≤k≤1.

[0057] Formula (4) shows that after the IGBT is locked, the inter-electrode short-circuit current will gradually stabilize to Generally, after a fault occurs, the IGBT is locked within 1 to 2 ms, and the capacitor continues to discharge until the discharge is completed. The short-circuit current will rise first and then stabilize to process.

[0058] The fault response characteristics that may be obtained at this time also include single-pole short-circuit fault characteristics: The single-pole short-circuit fault characteristics on the DC side of the three-level converter are closely related to the neutral point grounding mode:

[0059] 1) If both sides are not grounded, it is called an ungrounded system. A single-pole grounding fault on the DC side is the same as a single-phase grounding fault on the AC side. It will only raise the voltage of the non-fault pole to the pole-to-pole voltage, and there will be no short-circuit current.

[0060] 2) If the DC side is grounded and the grounding point is the neutral point of the capacitor, when a single-pole grounding fault occurs in the power grid, the fault pole capacitor will discharge to the fault point through the fault loop. After the discharge is completed, the short-circuit current disappears and the system can still operate normally;

[0061] 3) If the DC side is grounded and the grounding point is the positive or negative pole, when a non-grounded pole single-pole grounding fault occurs in the power grid, the fault characteristics are consistent with the bipolar short-circuit characteristics; when a grounded pole single-pole grounding fault occurs in the power grid, there is no short-circuit current;

[0062] 4) If the neutral point of the AC side is grounded, the short-circuit current of a single-pole ground fault is related to the magnitude of the neutral point grounding resistance and the magnitude of the resistance and inductance in the fault loop. The inductance in the fault loop determines the rate of rise of the short-circuit current, and the resistance determines the magnitude of the fault steady-state current. Figure 3 shown.

[0063] When the commutation device on the 10kV side is a modular multilevel converter,

[0064] The Modular Multilevel Converter (MMC) converter is a typical representative of the controllable power converter. It distributes the concentrated voltage stabilizing capacitors in the two / three-level VSC converter in each submodule to achieve multi-level modulation. It can be used for higher voltage levels and is commonly used for AC / DC conversion in medium-voltage DC distribution networks in distribution networks. According to the type of submodule used, it can be divided into half-bridge type, full-bridge type and double-clamp type, such as Figure 4 shown.

[0065] The grid-level control strategy of the modular multilevel converter is consistent with that of the VSC, which also includes active power control and reactive power control. In the internal control, sub-module voltage balancing control and commutation inhibition control are also added to achieve the requirement of reducing operating losses.

[0066] The fault response characteristics that may be obtained at this time include bipolar short-circuit fault characteristics: After a bipolar short-circuit fault occurs on the DC side of a symmetrical unipolar DC system based on a modular multilevel converter, the fault current mainly includes the submodule capacitor discharge current and the three-phase short-circuit current provided by the AC power supply. Among them, the capacitor discharge current is the main component of the fault current, and the current rises very quickly, reaching the order of kiloamperes within 1ms after the fault. In order to protect the IGBT device from damage, its trigger pulse is generally locked within 1 to 2ms. After the trigger pulse is locked, the submodule capacitor no longer provides discharge current. If a half-bridge submodule is used, there is still a fault current from the AC power supply; if a full-bridge or double-clamp submodule is used, there is no fault current from the AC power supply.

[0067] From the perspective of fault mechanism, the fault characteristics of the modular multilevel converter before pulse blocking are consistent with the fault loop 1 of the VSC, and the fault characteristics of the half-bridge modular multilevel converter after pulse blocking are consistent with the fault loop 2 of the VSC.

[0068] The changing pattern of the fault current is completely different before and after the trigger pulse is blocked:

[0069] 1) Characteristics of bipolar short-circuit fault before IGBT lockout. Before IGBT lockout, the submodule capacitor discharges rapidly. The fault equivalent circuit at this stage is as follows: Figure 5 shown.

[0070] Figure 5 The parameters in the equivalent second-order circuit of a DC bipolar short-circuit fault are shown in equation (5).

[0071]

[0072] Where: R m , L m , C m are the equivalent resistance, reactance and capacitance of the MMC converter under the condition of DC bipolar short circuit fault; L arm , R arm They represent the bridge arm reactance and bridge arm equivalent resistance of the MMC converter respectively; C SM is the submodule capacitance; L dc is the reactance of the DC reactor; R dc is the equivalent resistance of the DC line; N is the number of sub-modules in each bridge arm.

[0073] The fault equivalent circuit thereafter is the same as that of the VSC.

[0074] 2) Bipolar short-circuit fault characteristics after IGBT lockout. After the IGBT of the half-bridge module is locked out, the AC grid injects fault current into the short-circuit point through the anti-parallel diode. The fault equivalent circuit is as follows: Figure 6 This is consistent with the fault loop 2 feature of the VSC.

[0075] The fault response characteristics that may be obtained at this time also include single-pole short-circuit fault characteristics: the single-pole short-circuit fault characteristics of the modular multilevel converter are consistent with those of the VSC, and are closely related to the grounding method.

[0076] The embodiment of the present invention collects and monitors the operation data of the asymmetric flexible interconnected AC / DC hybrid distribution network in real time, including the AC / DC side current, the voltage of each pole to ground, etc.; when abnormal operation information is monitored, the fault type is quickly analyzed according to the fault characteristics of the above-mentioned 6kV side three-level converter and the fault characteristics of the 10kV side modular multilevel converter; when the current constant is reached, the corresponding power electronic devices are directly locked, and other fault control strategies are used to achieve fault crossing.

[0077] In summary, the 6 / 10kV asymmetric flexible interconnected AC / DC hybrid distribution network has a unique VSC-MMC hybrid topology and adopts its unique control strategy. Therefore, the currently widely used distribution network fault detection method is not applicable to the scenario involved in the present invention. A new fault detection method is needed to quickly identify, respond to, and process various possible faults to ensure the stability of the flexible interconnection system.

[0078] The embodiment of the present invention further provides a computer device, the computer device comprising: a processor, a memory, and a computer program stored in the memory and executable on the processor. The processor calls the computer program stored in the memory to execute each step of the asymmetric flexible interconnected AC / DC hybrid distribution network fault detection method provided in the embodiment of the present invention, and can achieve the same technical effect, refer to the description in the above embodiment, which will not be repeated here.

[0079] It should be pointed out that those skilled in the art can understand that the electronic device in the embodiment of the present invention is a device that can automatically perform numerical calculations and / or information processing according to pre-set or stored instructions, and its hardware includes but is not limited to microprocessors, application specific integrated circuits (ASIC), field-programmable gate arrays (FPGA), digital signal processors (DSP), embedded devices, etc. The electronic device can be a computing device such as a desktop computer, a notebook, a handheld computer, and a cloud server. The electronic device can perform human-computer interaction through a keyboard, a mouse, a remote control, a touchpad, or a voice-controlled device.

[0080] An embodiment of the present invention also provides a computer-readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, the various processes and steps in the asymmetric flexible interconnected AC / DC hybrid distribution network fault detection method provided by the embodiment of the present invention are implemented, and the same technical effect can be achieved. To avoid repetition, it will not be repeated here.

[0081] It should be noted that the readable storage medium includes flash memory, hard disk, multimedia card, card-type memory (for example, SD or DX memory, etc.), random access memory (RAM), static random access memory (SRAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), programmable read-only memory (PROM), magnetic memory, disk, optical disk, etc. In some embodiments, the memory may be an internal storage unit of an electronic device, such as a hard disk or memory of the electronic device. In other embodiments, the memory may also be an external storage device of an electronic device, such as a plug-in hard disk, a smart memory card (Smart Media Card, SMC), a secure digital (Secure Digital, SD) card, a flash card (Flash Card), etc. equipped on the electronic device. Of course, the memory may also include both the internal storage unit of the electronic device and its external storage device. In this embodiment, the memory is generally used to store operating devices and various application software installed in the electronic device, such as program codes of a method for detecting faults in an asymmetric flexible interconnected AC / DC hybrid distribution network, etc. In addition, the memory may also be used to temporarily store various types of data that have been output or are to be output.

[0082] Those skilled in the art can understand that all or part of the processes in the above-mentioned embodiment method can be completed by instructing the relevant hardware through a computer program, and the program can be stored in a computer-readable storage medium. When the program is executed, it can include the processes of various embodiments of the above-mentioned asymmetric flexible interconnected AC / DC hybrid distribution network fault detection method. Among them, the storage medium can be a disk, an optical disk, a read-only memory (ROM) or a random access memory (RAM).

[0083] The above specific implementation is a preferred implementation of an asymmetric flexible interconnected AC / DC hybrid distribution network fault detection method of the present invention, and is not intended to limit the specific implementation scope of the present invention. The scope of the present invention includes but is not limited to this specific implementation. All equivalent changes made in accordance with the shape and structure of the present invention are within the protection scope of the present invention.

Claims

1. A method for detecting faults in an asymmetric flexible interconnected AC / DC hybrid distribution network, characterized in that: The steps include: According to the topological structure of asymmetric flexible interconnected AC / DC hybrid distribution network, a fault model is established; Analyze fault characteristics under different topologies and fault types; Collecting operation data of asymmetric flexible interconnected AC / DC hybrid distribution network; The operation information of the asymmetric flexible interconnected AC / DC hybrid distribution network is monitored in real time. After a fault occurs, the fault type is analyzed based on the topological structure and a corresponding fault control strategy is adopted.

2. The asymmetric flexible interconnected AC / DC hybrid distribution network fault detection method according to claim 1 is characterized in that: The asymmetric flexible interconnection device is a controllable switch type converter or a controllable power supply type converter.

3. The asymmetric flexible interconnected AC / DC hybrid distribution network fault detection method according to claim 2 is characterized in that: The controllable switch type converter is a diode clamped three-level converter, which adopts third harmonic injection sinusoidal pulse width modulation to increase the modulation ratio width and prevent the injected third harmonic from reaching the DC side.

4. The asymmetric flexible interconnected AC / DC hybrid distribution network fault detection method according to claim 3 is characterized in that: The fault response characteristics of the controllable switch type converter include inter-pole short circuit fault characteristics, bipolar short circuit fault characteristics after IGBT lockout, and unipolar short circuit fault characteristics.

5. The asymmetric flexible interconnected AC / DC hybrid distribution network fault detection method according to claim 2 is characterized in that: The controllable power supply type converter is a modular multi-level converter.

6. The method for detecting faults in an asymmetric flexible interconnected AC / DC hybrid distribution network according to claim 5, characterized in that: The fault response characteristics of the controllable power source converter include bipolar short circuit fault characteristics and unipolar short circuit fault characteristics.

7. The method for detecting faults in an asymmetric flexible interconnected AC / DC hybrid distribution network according to claim 1, 4 or 6, characterized in that: After a fault occurs, the corresponding fault control strategy is adopted, including locking of power electronic devices and using control means to complete DC side fault riding.

8. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the computer program, the steps of the asymmetric flexible interconnected AC / DC hybrid distribution network fault detection method according to any one of claims 1 to 7 are implemented.

9. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the steps of the asymmetric flexible interconnected AC / DC hybrid distribution network fault detection method according to any one of claims 1 to 7 are implemented.

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