A method and related device for suppressing inrush current of DC transformer in flexible DC distribution network

Abstract

The present application discloses a method and related device for suppressing inrush current of a DC transformer in a flexible DC distribution network, wherein the method comprises: when an overcurrent fault occurs on the high-voltage side of the DC transformer, controlling the H-bridge structure of the DC transformer to be locked, and controlling the DAB structure of the DC transformer to maintain an operating state; S2, judging whether the power grid system fails again within a preset time range, if so, executing step S4, otherwise executing step S3; S3, controlling the H-bridge structure of the DC transformer to change from a locked state to a normal operating state, and controlling the power grid system to change from a normal operating mode to a low-voltage side voltage operating mode; S4, shutting down the DC transformer. The technical problem that the inrush current phenomenon of the DC transformer easily leads to the protection shutdown of the DC transformer is solved.

Description

Technical Field

[0001] The present application relates to the field of transformer technology, and in particular to a method and related device for suppressing inrush current of a DC transformer in a flexible DC distribution network. Background Art

[0002] Multi-terminal flexible DC distribution network is an important carrier for building a new power system with new energy as the main body. Although DC distribution network has many advantages, it is still in the stage of exploration and rapid development, and there are still many key technical problems that have not been well solved. Among them, overcurrent conditions in DC transformers, DC-AC converters, and AC-DC microgrid access are important factors affecting the stable operation of flexible DC distribution network.

[0003] At present, in terms of topology, reference [1] proposes a typical high-voltage series and low-voltage parallel DC transformer based on DAB topology. Then, when the AC and DC sides fail, the DC capacitor will discharge rapidly, resulting in a large overcurrent. Based on reference [1], reference [2] proposes a half-bridge structure connected in series at the front end of the high-voltage side of the DAB structure to prevent the DC capacitor from discharging and rushing into the high-voltage side when a fault occurs. However, this structure only considers the flow direction of single-phase fault current. When the multi-port power flow fluctuates, it is easy to cause the system to surge into the DC transformer. Reference [3] proposes a topology structure of a switched capacitor in parallel with the DAB module, but it can still flow into the DC transformer through the anti-parallel diode to cause overcurrent. In terms of control strategy, the DC transformer operates normally in the grid-connected mode [4], and generally adopts a current inner loop and voltage outer loop dual closed-loop control strategy [5]. References [6-7] adopt a constant ratio control strategy to achieve a constant voltage ratio on both sides, with a fast dynamic response speed. Reference [8] proposes a multi-terminal flexible DC grid active power balance coordinated control strategy to achieve active power balance of the system in the dynamic process. Reference [9] proposed an optimal configuration strategy for current limiting reactors in a multi-terminal DC system based on a four-terminal DC system taking into account the converter station lockout, and reduced the fault current amplitude through the optimal current limiting reactor. Reference

[10] analyzed the mutual influence of faults between the DC transformer and the system based on the AC / DC hybrid distribution network system of the DC transformer of the DAB module.

[0004] The inrush current phenomenon can easily lead to the shutdown of the DC transformer protection. However, the above-mentioned literature has not studied the inrush current mechanism and suppression strategy of the DC transformer caused by single-end disturbance in the multi-terminal interconnected flexible DC distribution network system, and there is no report on engineering application.

[0005] The titles and sources of documents 1-10 are as follows:

[0006] Literature[1]: CARRIZOSA MJ, BENCHAIB A, ALOU P, et al.DC transformer for DC / DC connection in HVDC network[C] / / 2013 15th European Conference on PowerElectronics and Applications(EPE).Lille, France: IEEE, 2013: 1-10.

[0007] Literature [2]: ZHAO Biao, SONG Qiang, LI Jianguo, et al. High-frequency-link DCtransformer based on switched capacitor for medium-voltage DC powerdistribution application[J]. IEEE Transactions on Power Electronics, 2016, 31(7): 4766-4777.

[0008] Literature [3]: Song Q, Zhao B, Li J, et al. An Improved DC Solid StateTransformer Based on Switched Capacitor and Multiple-Phase-Shift Shoot-Through Modulation for Integration of LVDC Energy Storage System and MVDCDistribution Grid[J]. IEEE Transactions on Industrial Electronics, 2018, 65(8): 6719-6729.

[0009] Reference [4]: ​​Zhao Biao, An Feng, Song Qiang, et al. Development and application of dual-active bridge DC transformer [J]. Proceedings of the CSEE, 2021, 41(01): 288-298.

[0010] Reference [5]: Li Jianguo, Zhao Biao, Song Qiang, et al. Research on voltage balance control strategy of high frequency link DC transformer in DC distribution network [J]. Proceedings of the CSEE, 2016, 36(2): 327-334.

[0011] Literature [6]: SHI Haixu, SUN Kai, LI Yunwei, et al.Virtual transformer control for DC-DC interlinking converters in DC microgrids[C] / / 2019IEEE EnergyConversion Congress and Exposition(ECCE).Baltimore, MD, USA: IEEE, 2019: 4268-4273.

[0012] Literature [7]: AN Feng, ZHAO Biao, WANG Jing, et al. An adaptive control method of DC transformers imitating AC transformers for flexible DC distribution application [C] / / 2020IEEE Applied Power Electronics Conference and Exposition (APEC). New Orleans, LA, USA: IEEE, 2020: 332-337.

[0013] Reference [8]: Li Zhou, Li Yazhou, Lu Yuping, et al. Active power balance coordination control strategy for multi-terminal flexible DC power grid [J]. Automation of Electric Power Systems, 2019, 43(17): 117-124.

[0014] Reference [9]: Li Jialin, Liao Kai, Yang Jianwei, et al. Optimal configuration strategy of current-limiting reactors in multi-terminal DC systems considering converter station blocking [J]. Automation of Electric Power Systems, 2021, 45(11): 102-110.

[0015] Reference

[10] : Qi Xiaomin, Pei Wei, Li Luyang, et al. Fault characteristics analysis of multi-voltage AC / DC hybrid distribution network based on DAB DC transformer [J]. Proceedings of the CSEE, 2019, 39(06): 1582-1591. Summary of the invention

[0016] The present application provides a method and related device for suppressing inrush current of a DC transformer in a flexible DC distribution network, which are used to solve the technical problem that inrush current in a DC transformer easily leads to protection shutdown of the DC transformer.

[0017] In view of this, the first aspect of the present application provides a method for suppressing inrush current of a DC transformer in a flexible DC distribution network, the method comprising:

[0018] S1. When an overcurrent fault occurs on the high-voltage side of the DC transformer, the H-bridge structure of the DC transformer is controlled to be locked, and the DAB structure of the DC transformer is controlled to maintain an operating state;

[0019] S2, determine whether the power grid system fails again within the preset time range, if so, execute step S4, otherwise execute step S3;

[0020] S3, controlling the H-bridge structure of the DC transformer to change from a locked state to a normal operating state, and controlling the power grid system to change from a normal operating mode to a low voltage side voltage operating mode;

[0021] S4. Shut down the DC transformer.

[0022] Optionally, when an overcurrent fault occurs on the high-voltage side of the DC transformer, the H-bridge structure of the DC transformer is controlled to be locked, and the DAB structure of the DC transformer is controlled to maintain a running state, specifically including:

[0023] Continuously monitoring the current on the high voltage side of the DC transformer;

[0024] When a ±10kV overcurrent fault occurs on the high-voltage side of the DC transformer, the controller of the DC transformer sends a control command to the module control board, so that the H-bridge structure of the DC transformer changes from a normal operating state to a locked state, and the DAB structure of the DC transformer remains in an operating state.

[0025] Optionally, the determining whether the power grid system fails again within a preset time range is specifically: determining whether a ±10kV overcurrent fault occurs again in the power grid system within 2ms.

[0026] Optionally, the determining whether the power grid system fails again within a preset time range specifically includes: determining whether an undervoltage or overvoltage fault occurs in the power grid system within a preset time range.

[0027] A second aspect of the present application provides a DC transformer inrush current suppression system for a flexible DC distribution network, the system comprising:

[0028] A first control unit is used to control the H-bridge structure of the DC transformer to be locked and control the DAB structure of the DC transformer to maintain an operating state when an overcurrent fault occurs on the high-voltage side of the DC transformer;

[0029] A judgment unit, used to judge whether the power grid system fails again within a preset time range, and if so, trigger the third control unit, otherwise trigger the second control unit;

[0030] A second control unit is used to control the H-bridge structure of the DC transformer to change from a locked state to a normal operating state, and to control the power grid system to change from a normal operating mode to a low-voltage side voltage operating mode;

[0031] The third control unit is used to shut down the DC transformer.

[0032] Optionally, the first control unit is specifically configured to:

[0033] The current on the high-voltage side of the DC transformer is continuously monitored; when a ±10kV overcurrent fault occurs on the high-voltage side of the DC transformer, the controller of the DC transformer sends a control command to the module control board, so that the H-bridge structure of the DC transformer is changed from a normal operating state to a locked state, and the DAB structure of the DC transformer remains in an operating state.

[0034] Optionally, the judging unit is specifically configured to:

[0035] Determine whether the power grid system has a ±10kV overcurrent fault again within 2ms. If so, trigger the third control unit, otherwise trigger the second control unit.

[0036] Optionally, the judging unit is specifically configured to:

[0037] Determine whether an undervoltage or overvoltage fault occurs in the power grid system within a preset time range. If so, trigger the third control unit, otherwise trigger the second control unit.

[0038] A third aspect of the present application provides a DC transformer inrush current suppression device for a flexible DC distribution network, the device comprising a processor and a memory:

[0039] The memory is used to store program code and transmit the program code to the processor;

[0040] The processor is used to execute the steps of the method for suppressing inrush current of a DC transformer in a flexible DC distribution network as described in the first aspect according to the instructions in the program code.

[0041] A fourth aspect of the present application provides a computer-readable storage medium, wherein the computer-readable storage medium is used to store program code, and the program code is used to execute the method for suppressing inrush current of a DC transformer in a flexible DC distribution network as described in the first aspect.

[0042] It can be seen from the above technical solutions that this application has the following advantages:

[0043] The present application provides a method for suppressing inrush current of a DC transformer in a flexible DC distribution network, comprising: S1, when an overcurrent fault occurs on the high-voltage side of the DC transformer, controlling the H-bridge structure of the DC transformer to be locked, and controlling the DAB structure of the DC transformer to maintain an operating state; S2, judging whether the power grid system fails again within a preset time range, if so, executing step S4, otherwise executing step S3; S3, controlling the H-bridge structure of the DC transformer to change from a locked state to a normal operating state, and controlling the power grid system to change from a normal operating mode to a low-voltage side voltage operating mode; S4, shutting down the DC transformer.

[0044] The flexible DC distribution network DC transformer inrush current suppression method of the present application can increase a certain degree of overcurrent suppression capability when the power step fluctuates through the H-bridge structure temporary blocking + DAB non-blocking suppression strategy, while retaining the current suppression capability and protection threshold setting during the DC side short-circuit fault. The method proposed in the present application has been successfully applied in the actual multi-terminal interconnected flexible DC distribution network system engineering, and has engineering practical value, thereby solving the technical problem that the inrush current phenomenon of the DC transformer easily leads to the protection shutdown of the DC transformer. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 A schematic flow chart of a method for suppressing inrush current of a DC transformer in a flexible DC distribution network provided in an embodiment of the present application;

[0046] Figure 2 A schematic diagram of a method for suppressing inrush current of a DC transformer in a flexible DC distribution network provided in an embodiment of the present application;

[0047] Figure 3 This is a schematic diagram of the entire process of a DC transformer inrush current fault;

[0048] Figure 4 This is a schematic diagram of the potential flow path of the DC transformer inrush current;

[0049] Figure 5 It is a schematic diagram of transient equivalent circuit after the single converter station is locked;

[0050] Figure 6 This is the equivalent circuit diagram of a proposed method for suppressing inrush current of DC transformers in flexible DC distribution networks;

[0051] Figure 7 The equivalent circuit diagram of the traditional suppression method is provided. DETAILED DESCRIPTION

[0052] In order to enable those skilled in the art to better understand the solution of the present application, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0053] The following is the mechanism process of the DC transformer obtained by the applicant through analysis of the inrush current phenomenon of the DC transformer in actual engineering operation:

[0054] See also Figure 3 , 3 is a schematic diagram of the entire process of surge current fault.

[0055] A fault occurred on the B phase of the 10kV line on the AC side of a converter station I, triggering a temporary lockout of the converter station. Within 1ms, the control of the ±10kV DC bus voltage was transferred to the converter station II. At t=3.3ms, a surge fault occurred on the high-voltage side of the DC transformer system, and the DC transformer was urgently locked. At the same time, the level control protection A logic was urgently locked at the converter station II. At t=7.8ms, the DC circuit breaker was opened, and the multi-terminal interconnected flexible DC distribution network system stopped operating.

[0056] When AC disturbance causes the converter station to lock up, causing a step-like large fluctuation in the power flow of the remaining ports and redistributing the power, for the convenience of analysis, the inrush current effect of the single-ended converter station injecting energy into the DC transformer is considered. Figure 4 The potential path of inrush current in the DC transformer in the actual operation of the project shown in the figure. Figure 4 It can be seen that when the converter station I is locked, the power flow of the converter station II must find a flow path instantly, and the H-bridge structure of the DC transformer provides a loop for the transfer of the power flow. The instantaneous power flow forms a loop through the H-bridge anti-parallel diode of the DC transformer, which is the mechanism of the DC transformer inrush current.

[0057] Considering the overall system process, the modeling analysis is carried out. In this project, the switching frequency of the DC transformer is 20kHz, and the controller cycle is set to 100μs. Within two cycles after the Tangjia converter station is locked, the other two converter stations and the DC transformer maintain a certain transient state when they are working normally, and when considering the transient current change, the capacitor can be equivalent to a short circuit. Then the DC side of this four-port system can be simplified as follows: Figure 5 The circuit shown.

[0058] Among them, LPET is approximately the high-voltage side port reactance of the DC transformer, and L1 and L2 are the parallel reactances of the three bridge arms of Jishan I and Jishan II converter stations respectively. According to the slow change and small amplitude of the DC voltage after the fault recording block, the port voltages of the converter transformer and the DC transformer are approximately equal, and are equivalent to unchanged within 200μs, then:

[0059]

[0060] Therefore, for a DC transformer, the current is:

[0061]

[0062] It can be seen that the parallel branch with the smallest reactance must bear a greater change. In summary, when the DC current at a single port of the flexible DC power distribution system fluctuates rapidly and significantly, the key to reducing the overcurrent at the DC transformer port is to increase the reactance value of the DC transformer port.

[0063] The above analysis of the inrush current mechanism can be extended to large-scale multi-terminal interconnected systems. The instantaneous power flow redistribution caused by the lockout of a single station, and the low-impedance equipment provides an impedance loop for the power flow transfer. As long as the topology of the DC transformer (half-bridge, full-bridge, switched capacitor, etc.) has an anti-parallel diode, this potential inrush current loop exists naturally, which makes the DC transformer easily shut down for protection.

[0064] When the applicant was conducting research, he considered that when achieving fault crossing by not locking, the DC inrush current in the unlocking mode of the DC transformer rises too fast. If the overcurrent protection threshold of the DC transformer is released, the equipment will have a greater risk of safe operation. In addition, when a DC fault occurs in the system, it is easy to cause reactance saturation in a very short time. Release of the protection threshold will more easily cause equipment damage. Increasing the reactance value is a feasible solution. However, it will increase the cost and equipment size. Therefore, it is possible to consider suppressing the DC transformer inrush current phenomenon from the control strategy level of the DC transformer.

[0065] The inrush current phenomenon caused by the instantaneous redistribution of the multi-terminal interconnected system is not a DC system fault condition. Therefore, the present application proposes a DC transformer inrush current temporary lockout suppression strategy. After the DC transformer is locked, the overcurrent will be suppressed and quickly restored to normal value. At this time, the command to disconnect the high and low voltage side circuit breakers will not be executed. Since the overcurrent protection threshold has sufficient margin for short-circuit faults, for temporary overcurrent faults caused by power step conditions, a temporary lockout suppression strategy can be added on the basis of the original protection. The temporary lockout function only locks the high-voltage side H-bridge of the module, and the DAB module is always in operation.

[0066] Therefore, the following method for suppressing inrush current of DC transformer in flexible DC distribution network is proposed:

[0067] See also Figure 1 , a method for suppressing inrush current of a DC transformer in a flexible DC distribution network provided in an embodiment of the present application includes:

[0068] Step 101: When an overcurrent fault occurs on the high voltage side of the DC transformer, the H-bridge structure of the DC transformer is controlled to be locked, and the DAB structure of the DC transformer is controlled to maintain an operating state.

[0069] Step 102 , determining whether the power grid system fails again within a preset time range, if so, executing step 104 , otherwise executing step 103 .

[0070] Step 103: Control the H-bridge structure of the DC transformer to change from a locked state to a normal operating state, and control the power grid system to change from a normal operating mode to a low voltage side voltage operating mode.

[0071] Step 104: Shut down the DC transformer.

[0072] The flexible DC distribution network DC transformer inrush current suppression method of the embodiment of the present application, when an overcurrent fault occurs on the high-voltage side of the DC transformer, the controller sends an H-bridge temporary lockout + DAB operation command to the module control board. At this time, the module control board changes from the normal operating state to the H-bridge lockout + DAB operation state, and DAB continues to control the capacitor voltage on the high-voltage side of the module. Since this overcurrent process is short in time, the controller executes the temporary lockout control logic, and after detecting that there is no new fault in the system within 2ms, it executes the post-lockout restart logic and restart command, and the normal operation of the system is controlled to the low-voltage side voltage mode. During the temporary lockout recovery startup process, if the ±10kV side overcurrent occurs again, the DC transformer is shut down to avoid repeated grid connection of the DC transformer due to factors such as grid connection failure.

[0073] The key to the inrush current suppression method of the DC transformer in the flexible DC distribution network of this application lies in the temporary blocking of the H-bridge structure and the non-blocking control of the DAB structure. Due to the support of energy storage, the voltage of the DC microgrid will not fluctuate greatly within 2ms. Compared with the traditional direct blocking control strategy, the DAB control signal of the solution of this application is not blocked, and the current path of the DAB module is retained.

[0074] See also Figure 6 and Figure 7 , Figure 6 and Figure 7 This is an equivalent circuit diagram comparing the suppression method proposed in this application and the traditional original wave protection logic solution.

[0075] Under the traditional direct blocking control strategy, when the overcurrent reaches a fixed value, all controllable switches of the DC transformer are blocked, and the current can only be charged to the capacitors of each module through the diode, and cannot be discharged. The equivalent circuit is a reactance series diode and a comprehensive equivalent capacitor C H1 :

[0076]

[0077] From the start of the wave protection, the external circuit can be considered as a voltage source, and the equivalent circuit of the DC transformer is an LC series circuit with an initial current. Its second-order dynamic equation is as follows:

[0078]

[0079] The accurate calculation of the DC bus voltage after the wave blocking is relatively complex, and the DC side voltage changes slightly and slowly. It can be assumed that its rate of change is constant before the DC transformer current drops to zero. Substituting the boundary conditions, the DC transformer input current i HV Approximate expression, due to the existence of the diode, i HV It must be greater than 0, and it will not change after decaying to 0. The input current is:

[0080]

[0081]

[0082] The initial state of the current when the DC transformer locks out the pulse is known, and the current peak value can be obtained by equations (3) and (4). Compared with the traditional control, the temporary lockout suppression strategy proposed in this application adds a current path in the equivalent circuit, which is equivalent to increasing the reactance and leakage reactance of the DAB high-frequency transformer, and the suppression effect on current changes is increased, which can ensure that the current peak is lower than the result obtained by the above calculation formula. Therefore, the temporary lockout suppression strategy proposed in this application can achieve the crossing of the short-term overcurrent fault of the DC transformer. After the abnormal state of the power grid is eliminated, the DC transformer resumes normal operation. The system operation mode is not changed during the whole process, thereby improving the system reliability.

[0083] The above is an embodiment of a method for suppressing inrush current of a DC transformer in a flexible DC distribution network provided by the present application, and the above is an embodiment of a system for suppressing inrush current of a DC transformer in a flexible DC distribution network provided by the present application.

[0084] See also Figure 2 , an embodiment of the present application provides a flexible DC distribution network DC transformer inrush current suppression system, comprising:

[0085] The first control unit 201 is used to control the H-bridge structure of the DC transformer to be locked and control the DAB structure of the DC transformer to maintain an operating state when an overcurrent fault occurs on the high-voltage side of the DC transformer.

[0086] The judgment unit 202 is used to judge whether the power grid system fails again within a preset time range, and if so, trigger the second control unit 203, otherwise trigger the third control unit 204.

[0087] The second control unit 203 is used to control the H-bridge structure of the DC transformer to change from a locked state to a normal operating state, and control the power grid system to change from a normal operating mode to a low-voltage side voltage operating mode.

[0088] The third control unit 204 is used to shut down the DC transformer.

[0089] The flexible DC distribution network DC transformer inrush current suppression system of the present application can increase a certain degree of overcurrent suppression capability when the power step fluctuates through the suppression strategy of temporary blocking of the H-bridge structure + non-blocking of DAB, while retaining the current suppression capability and protection threshold setting during the DC side short-circuit fault. The method proposed in the present application has been successfully applied in the actual multi-terminal interconnected flexible DC distribution network system engineering, and has engineering practical value, thereby solving the technical problem that the inrush current phenomenon of the DC transformer easily leads to the protection shutdown of the DC transformer.

[0090] Furthermore, the present application also provides a flexible DC distribution network DC transformer inrush current suppression device, the device comprising a processor and a memory:

[0091] The memory is used to store program code and transmit the program code to the processor;

[0092] The processor is used to execute the method for suppressing inrush current of a DC transformer in a flexible DC distribution network according to the instructions in the program code described in the above method embodiment.

[0093] Furthermore, the present application also provides a computer-readable storage medium, which is used to store program code, and the program code is used to execute the method for suppressing inrush current of a DC transformer in a flexible DC distribution network as described in the above method embodiment.

[0094] Those skilled in the art can clearly understand that, for the convenience and brevity of description, the specific working processes of the systems and units described above can refer to the corresponding processes in the aforementioned method embodiments and will not be repeated here.

[0095] The terms "first", "second", "third", "fourth", etc. in the specification of the present application 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 application described herein can be implemented in an order other than those illustrated or described herein, for example. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device comprising a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0096] It should be understood that in the present application, "at least one (item)" means one or more, and "plurality" means two or more. "And / or" is used to describe the association relationship of associated objects, indicating that three relationships may exist. For example, "A and / or B" can mean: only A exists, only B exists, and A and B exist at the same time, where A and B can be singular or plural. The character " / " generally indicates that the objects associated before and after are in an "or" relationship. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single or plural items. For example, at least one of a, b or c can mean: a, b, c, "a and b", "a and c", "b and c", or "a and b and c", where a, b, c can be single or multiple.

[0097] In the several embodiments provided in the present application, it should be understood that the disclosed systems, devices and methods can be implemented in other ways. For example, the device embodiments described above are only schematic. For example, the division of the 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 an indirect coupling or communication connection through some interfaces, devices or units, which can be electrical, mechanical or other forms.

[0098] The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed on multiple network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0099] In addition, each functional unit in each embodiment of the present application may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit. The above-mentioned integrated unit may be implemented in the form of hardware or in the form of software functional units.

[0100] 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 technical solution of the present application is essentially 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, and the computer software product is stored in a storage medium, including a number of instructions to enable a computer device (which can be a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the method described in each embodiment of the present application. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (full name in English: Read-Only Memory, English abbreviation: ROM), random access memory (full name in English: Random Access Memory, English abbreviation: RAM), disk or optical disk and other media that can store program codes.

[0101] As described above, 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 method for suppressing inrush current of a DC transformer in a flexible DC distribution network, characterized in that: include: S1. When an overcurrent fault occurs on the high-voltage side of the DC transformer, the H-bridge structure of the DC transformer is controlled to be locked, and the DAB structure of the DC transformer is controlled to maintain an operating state; S2, determine whether the power grid system fails again within the 2ms time range, if so, execute step S4, otherwise execute step S3; S3, controlling the H-bridge structure of the DC transformer to change from a locked state to a normal operating state, and controlling the power grid system to change from a normal operating mode to a low voltage side voltage operating mode; S4. Shut down the DC transformer.

2. The method for suppressing inrush current of a DC transformer in a flexible DC distribution network according to claim 1, characterized in that: When an overcurrent fault occurs on the high-voltage side of the DC transformer, the H-bridge structure of the DC transformer is controlled to be locked, and the DAB structure of the DC transformer is controlled to maintain a running state, specifically including: Continuously monitoring the current on the high voltage side of the DC transformer; When a ±10kV overcurrent fault occurs on the high-voltage side of the DC transformer, the controller of the DC transformer sends a control command to the module control board, so that the H-bridge structure of the DC transformer changes from a normal operating state to a locked state, and the DAB structure of the DC transformer remains in an operating state.

3. The method for suppressing inrush current of a DC transformer in a flexible DC distribution network according to claim 2, characterized in that: The determining whether the power grid system fails again within a preset time range specifically includes: determining whether the power grid system fails again within 2ms.

4. The method for suppressing inrush current of a DC transformer in a flexible DC distribution network according to claim 1, characterized in that: The determining whether the power grid system fails again within a preset time range specifically includes: determining whether an undervoltage or overvoltage fault occurs in the power grid system within a preset time range.

5. A DC transformer inrush current suppression system for a flexible DC distribution network, characterized in that: include: A first control unit is used to control the H-bridge structure of the DC transformer to be locked and control the DAB structure of the DC transformer to maintain an operating state when an overcurrent fault occurs on the high-voltage side of the DC transformer; A judgment unit, used to judge whether the power grid system fails again within a time range of 2ms, and if so, trigger the third control unit, otherwise trigger the second control unit; A second control unit is used to control the H-bridge structure of the DC transformer to change from a locked state to a normal operating state, and to control the power grid system to change from a normal operating mode to a low-voltage side voltage operating mode; The third control unit is used to shut down the DC transformer.

6. The flexible DC distribution network DC transformer inrush current suppression system according to claim 5, characterized in that: The first control unit is specifically used for: The current on the high-voltage side of the DC transformer is continuously monitored; when a ±10kV overcurrent fault occurs on the high-voltage side of the DC transformer, the controller of the DC transformer sends a control command to the module control board, so that the H-bridge structure of the DC transformer is changed from a normal operating state to a locked state, and the DAB structure of the DC transformer remains in an operating state.

7. The flexible DC distribution network DC transformer inrush current suppression system according to claim 6, characterized in that: The judging unit is specifically used for: Determine whether the power grid system has a ±10kV overcurrent fault again within 2ms. If so, trigger the third control unit, otherwise trigger the second control unit.

8. The flexible DC distribution network DC transformer inrush current suppression system according to claim 5, characterized in that: The judging unit is specifically used for: Determine whether an undervoltage or overvoltage fault occurs in the power grid system within a preset time range. If so, trigger the third control unit, otherwise trigger the second control unit.

9. A DC transformer inrush current suppression device for a flexible DC distribution network, characterized in that: The device comprises a processor and a memory: The memory is used to store program code and transmit the program code to the processor; The processor is used to execute the method for suppressing inrush current of a DC transformer in a flexible DC distribution network according to the instructions in the program code.

10. A computer-readable storage medium, characterized in that: The computer-readable storage medium is used to store program codes, and the program codes are used to execute the method for suppressing inrush current of a DC transformer in a flexible DC distribution network according to any one of claims 1 to 4.

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