Topological structure of multi-port direct current circuit breaker, control method and parameter determination method of multi-port direct current circuit breaker

Abstract

The invention relates to the technical field of power system protection, in particular to a multi-port direct-current circuit breaker topological structure, a control method and a parameter determination method thereof, and the method comprises the steps that when a multi-port direct-current power grid system operates normally, a through-current branch provides a low-impedance current conduction path for load current; when the multi-port direct-current power grid system has a fault, the fault current is forced to be quickly transferred from the through-current branch to the cut-off branch; the cut-off branch circuit instantaneously conducts the transfer branch circuit and receives transferred fault current in the initial stage of a fault of the multi-port direct-current power grid system, automatically conducts the energy consumption branch circuit when the voltage difference between the two ends of the energy consumption branch circuit reaches a preset overvoltage threshold value, and utilizes the energy consumption branch circuit to absorb line overvoltage energy to quickly cut off the fault current. And non-voltage and non-arc breaking is completed by turning off a rapid mechanical switch of the through-current branch, and complete isolation of fault current is completed. According to the invention, through cooperation of the through-current branch, the cut-off branch and the grounding branch, the fault handling capability of the DC power grid system is effectively improved.

Description

Technical Field

[0001] The present invention relates to the technical field of power system protection, and particularly relates to a multi-port DC circuit breaker topology, a control method thereof, and a parameter determination method thereof. Background Art

[0002] As a key device for DC grid fault isolation, DC circuit breakers play an irreplaceable role in the protection and operation of DC grids. However, existing DC circuit breaker technologies still face many problems in practical applications. Currently, DC circuit breaker technologies are mainly divided into three types according to different breaking principles: mechanical DC circuit breakers, solid-state DC circuit breakers, and hybrid DC circuit breakers. Each type has its own limitations. Among them, mechanical DC circuit breakers use traditional AC mechanical switches as breaking devices, generate an oscillating current through an oscillating circuit to superimpose with the fault current to generate a zero crossing point, and then achieve current interruption. It has advantages such as low on-state loss, high insulation tolerance, and low cost. However, due to its dependence on the action of traditional AC mechanical switches, the breaking time is relatively long, making it difficult to meet the response requirements of flexible DC transmission systems for rapid fault isolation. Solid-state DC circuit breakers use all-power devices to achieve rapid breaking. Although the action speed is extremely fast and no breaking arc is generated, the rated voltage and rated current of the power devices used in solid-state DC circuit breakers are relatively low, and a large number of power devices need to be connected in series and parallel. This not only increases the complexity and cost of the equipment, but also causes a series of problems such as synchronous control of drive pulse signals, voltage and current equalization of switching devices, and increased losses. In addition, hybrid DC circuit breakers combine the current-carrying capacity of mechanical switches and the rapid breaking ability of solid-state switches, balancing the contradiction between breaking speed and on-state loss to a certain extent. However, the existing hybrid circuit breaker has a complex structure and needs to simultaneously meet the coordinated actions of mechanical switches and solid-state switches, increasing the manufacturing cost and maintenance difficulty of the equipment.

[0003] With the continuous expansion of the scale of the DC power grid, to achieve full selectivity of protection, the number of DC circuit breakers that need to be configured in the system increases geometrically. Especially in a multi-terminal DC system, according to the traditional two-port DC circuit breaker scheme, an independent circuit breaker needs to be configured for each outgoing line, which will lead to a significant increase in the number of devices and a remarkable rise in the system investment cost. To address this issue, some researchers have proposed a solution for multi-port DC circuit breakers. By sharing the main breaking switch unit among all the incoming and outgoing lines on the same DC bus, the fault current breaking function for multiple circuits is achieved, thus reducing the number of circuit breaker configurations. However, the current engineering application of multi-port DC circuit breakers faces the problem of cooperative control among modules under a complex structure. It is necessary to solve the electrical parameter matching and action timing coordination among multiple ports. At the same time, the complex topological structure poses extremely high requirements for the real-time performance and accuracy of the control system, and the long-term operation stability under high voltage and large current conditions cannot be guaranteed. In addition, reasonably arranging each functional module within a limited space and balancing performance indicators such as electrical insulation, heat dissipation, and electromagnetic compatibility are also difficult problems that must be solved in practical engineering applications.

[0004] In summary, there are many problems in the existing multi-port DC circuit breaker technology when dealing with DC bus faults. Therefore, constructing a multi-port DC circuit breaker technology that can effectively handle DC bus faults has become a core technical problem in the development of DC power grids. Summary of the Invention

[0005] To solve the above technical problems, the present invention provides a multi-port DC circuit breaker topological structure, a control method, and a method for determining its parameters.

[0006] In the first aspect, the present invention provides a multi-port DC circuit breaker topological structure, based on a hybrid DC circuit breaker architecture, including: a current-carrying branch, a current-breaking branch, and a grounding branch. Among them, the current-carrying branch is connected between the DC bus and each DC bus outgoing line port, and the current-breaking branch is arranged in parallel with the current-carrying branch; The current-carrying branch includes a fast mechanical switch and a load commutation switch with variable impedance connected in series; the current-carrying branch is used to provide a low-impedance current conduction path for the load current during the normal operation of the multi-port DC power grid system, and when a fault occurs in the multi-port DC power grid system, by turning off the load commutation switch, a commutation voltage is generated to force the fault current to quickly transfer from the current-carrying branch to the current-breaking branch; The current interruption branch includes a parallel transfer branch and a power consumption branch; the current interruption branch is used to instantaneously conduct the transfer branch at the initial stage of a fault in the multi-port DC grid system, receive the fault current transferred by the current conduction branch through the transfer branch, and automatically conduct the power consumption branch when the voltage difference across the power consumption branch reaches a preset overvoltage threshold, absorb the line overvoltage energy by the power consumption branch to quickly cut off the fault current, and complete the non-voltage and non-arc interruption by turning off the fast mechanical switch of the current conduction branch, so as to completely isolate the fault current.

[0007] In a further embodiment, the grounding branch is used to conduct the grounding branch and the transfer branch when a grounding fault occurs on the DC bus, form a fault current discharge channel to lead the fault current into the ground through the current interruption branch and the grounding branch to isolate the faulty DC bus, and at the same time cooperate with the energy consumption device configured on the power supply side of the multi-port DC grid system to absorb the residual energy and suppress the voltage fluctuation in the non-fault area.

[0008] In a further embodiment, the fast mechanical switch is used to provide a low-impedance conduction path for the load current together with the load commutation switch when the multi-port DC grid system is operating normally; and, quickly transfer the fault current in the current conduction branch when a fault occurs in the multi-port DC grid system, and perform a non-voltage and non-arc interruption action to isolate the current conduction branch and the fault point after the transfer of the fault current is completed.

[0009] In a further embodiment, the transfer branch adopts a bidirectional conduction topology to control the bidirectional conduction of the fault current in the multi-port DC grid, and the bidirectional conduction topology is composed of fully controlled devices, semi-controlled devices or diode devices through a symmetric parallel connection method.

[0010] In a further embodiment, the grounding branch includes a controllable switch device, one end of the controllable switch device is connected to the DC bus, and the other end of the controllable switch device is grounded; The controllable switch device is used to be controlled to conduct when a grounding fault occurs on the DC bus, and form a low-impedance discharge path for the fault current to the ground.

[0011] In a second aspect, the present invention provides a control method for a multi-port DC circuit breaker topology, which is applied to the multi-port DC circuit breaker topology as described above. The control method includes the following steps: Real-time monitor the voltage and current signals of the DC bus and each DC bus outlet port in the multi-port DC grid system, and identify the fault type and fault port of the multi-port DC grid system according to the voltage and current signals; When the fault type is a DC short - circuit fault at the port outlet, control the current - conducting branch corresponding to the faulty port to be in the conducting state, and control both the current - interrupting branch and the grounding branch to be in the off state, so that the fault current flows through the current - conducting branch of the faulty port; In response to the opening command, turn on the transfer branch of the current - interrupting branch, and turn off the load commutation switch in the current - conducting branch of the faulty port. Use the commutation voltage generated by the turn - off of the load commutation switch to forcibly transfer the fault current in the current - conducting branch to the transfer branch; After the fault current is completely transferred to the transfer branch, complete the current - free and arcless interruption by turning off the fast mechanical switch in the current - conducting branch; After the fast mechanical switch is opened in place, trigger an instantaneous over - voltage by turning off the transfer branch. When the voltage difference across the energy - dissipating branch reaches the preset over - voltage threshold, automatically turn on the energy - dissipating branch. Use the energy - dissipating branch to absorb the line over - voltage energy to force the fault current to zero, complete the fault - current truncation process, and restore power supply to the non - faulty area.

[0012] In a further embodiment, when the fault type is a DC bus grounding fault, form a low - impedance discharge path for the fault current to the ground by turning on the grounding branch and the transfer branch of the current - interrupting branch, and control the current in the current - conducting branch to gradually drop to zero.

[0013] In a third aspect, the present invention provides a method for determining the parameters of a multi - port DC circuit breaker topology. Applying the multi - port DC circuit breaker topology as described above, the parameter - determination method includes the following steps: Perform simulation analysis on different DC bus fault scenarios according to the actual topology of the multi - port DC power grid system to determine the maximum fault - current values at the outlet ports of each DC bus under different fault scenarios; Based on the maximum fault - current values, determine the requirements for the breaking capacity of the current - interrupting branch, and determine the initial operating current values of each current - conducting branch according to the requirements for the breaking capacity of the current - interrupting branch; Sequentially select a target current - conducting branch from all current - conducting branches, traverse the fault scenarios of other non - target current - conducting branches, and obtain the fault - current distribution data flowing through the target current - conducting branch under each non - target current - conducting - branch fault scenario; Iteratively optimize the initial operating current value of the target current - conducting branch according to the fault - current distribution data. After multiple iterations, screen out the minimum operating current values of each current - conducting branch; According to the minimum operating current values of all current - conducting branches and the requirements for the breaking capacity of the current - interrupting branch, output the action - current parameter set of the multi - port DC circuit breaker topology.

[0014] In a further embodiment, the step of iteratively optimizing the initial operating current value of the target current-carrying branch according to the fault current distribution data and screening out the minimum operating current value of each current-carrying branch after multiple iterations includes: In each iterative optimization, if the operating current value of the current iteration is greater than the DC current flowing through the target current-carrying branch in the current non-target current-carrying branch fault scenario, update the operating current value of the current iteration to the DC current flowing through the target current-carrying branch in the current non-target current-carrying branch fault scenario, and enter the iterative optimization of the next non-target current-carrying branch fault scenario. Repeat the above process until all non-target current-carrying branch fault scenarios are traversed, and screen out the minimum operating current value of the target current-carrying branch; Iteratively optimize the initial operating current values of all current-carrying branches in sequence, and screen out the minimum operating current value of each current-carrying branch after multiple iterations.

[0015] In a further embodiment, the parameter determination method further includes: Compare the minimum operating current value of each current-carrying branch with the maximum load current when the multi-port DC grid system is operating normally. If the minimum operating current value is lower than the maximum load current, gradually reduce the value of the current-limiting inductor of the multi-port DC grid system, increase the difference between the fault current and the maximum load current, and re-iteratively optimize the minimum operating current value until the minimum operating current values of all current-carrying branches are higher than the maximum load current when the multi-port DC grid system is operating normally, so as to obtain the optimized minimum operating current value of each current-carrying branch.

[0016] The present invention provides a multi-port DC circuit breaker topology, a control method thereof, and a parameter determination method thereof. The multi-port DC circuit breaker topology includes a current-carrying branch, a current-interrupting branch, and a grounding branch. The current-carrying branch includes a fast mechanical switch and a load-commutated switch with variable impedance connected in series. The current-carrying branch is used to provide a low-impedance current conduction path for the load current during the normal operation of the multi-port DC power grid system, and to generate a commutation voltage by turning off the load-commutated switch when a fault occurs in the multi-port DC power grid system, forcing the fault current to quickly transfer from the current-carrying branch to the current-interrupting branch. The current-interrupting branch includes a transfer branch and a dissipative branch connected in parallel. The current-interrupting branch is used to instantaneously conduct the transfer branch at the initial stage of a fault in the multi-port DC power grid system, receive the fault current transferred from the current-carrying branch through the transfer branch, and automatically conduct the dissipative branch when the voltage difference across the dissipative branch reaches a preset overvoltage threshold, absorb the line overvoltage energy by the dissipative branch to quickly cut off the fault current, and complete the current interruption without voltage and arc by turning off the fast mechanical switch of the current-carrying branch, thereby completely isolating the fault current. Compared with the prior art, this multi-port DC circuit breaker topology realizes the rapid transfer and reliable isolation of the fault current through the coordinated cooperation of the current-carrying branch, the current-interrupting branch, and the grounding branch, effectively improving the ability of the DC power grid system to cope with faults and ensuring the safe and stable operation of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a schematic diagram of the multi-port DC circuit breaker topology provided by an embodiment of the present invention; Figure 2 is a schematic flow chart of the control method of the multi-port DC circuit breaker topology provided by an embodiment of the present invention; Figure 3 is a schematic flow chart of the parameter determination method of the multi-port DC circuit breaker topology provided by an embodiment of the present invention; Figure 4 is an example diagram of the parameter determination process of the multi-port DC circuit breaker topology provided by an embodiment of the present invention; Figure 5 is a schematic diagram of the optimization process of the DC fault protection strategy for two of the current-carrying branches provided by an embodiment of the present invention; Figure 6 is a schematic diagram of the optimization process of the DC fault protection strategy for another two current-carrying branches provided by an embodiment of the present invention.

[0018] Description of the reference numerals: 1, current-carrying branch; 2, current-interrupting branch; 3, grounding branch; 11, fast mechanical switch; 12, load-commutated switch; 21, transfer branch; 22, dissipative branch. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0019] The embodiments of the present invention will be specifically described below in conjunction with the accompanying drawings. The provided embodiments are for illustrative purposes only and should not be construed as limiting the present invention. The included drawings are for reference and explanation only and do not constitute a limitation on the scope of patent protection of the present invention, because many changes can be made to the present invention without departing from its spirit and scope.

[0020] Reference Figure 1 , an embodiment of the present invention provides a multi-port DC circuit breaker topology. The multi-port DC circuit breaker topology is based on a hybrid DC circuit breaker. As Figure 1 shown, the multi-port DC circuit breaker topology includes a current-carrying branch 1, a current-interrupting branch 2, and a grounding branch 3. The current-carrying branch 1 is connected between the DC bus and each DC bus outgoing port, and the current-interrupting branch 2 is arranged in parallel with the current-carrying branch 1.

[0021] In some embodiments, the current-carrying branch 1 includes a fast mechanical switch 11 and a load-commutated switch 12 with variable impedance connected in series. In this embodiment, the current-carrying branch is used to provide a low-impedance current conduction path for the load current when the multi-port DC power grid system is operating normally, and when a fault occurs in the multi-port DC power grid system, a commutation voltage is generated by turning off the load-commutated switch, forcing the fault current to quickly transfer from the current-carrying branch to the current-interrupting branch.

[0022] Specifically, the current-carrying branch in this embodiment may include a current-carrying branch A, a current-carrying branch B, a current-carrying branch C, and a current-carrying branch D. The current-carrying branch, when the system is operating normally, through the coordinated action of the fast mechanical switch and the load-commutated switch with variable impedance, provides a low-impedance conduction path for the load current to ensure efficient power transmission. In addition, when a fault occurs in the multi-port DC power grid system, the fast mechanical switch can quickly transfer the fault current in the current-carrying branch to the current-interrupting branch and perform a no-voltage and no-arc breaking operation after the fault current is completely transferred, realizing reliable isolation between the current-carrying branch and the fault point. Specifically, when the multi-port DC power grid system is operating normally, the current-carrying branch provides a low-impedance conduction path for the load current through the coordinated action of the fast mechanical switch and the load-commutated switch. When a fault occurs in the multi-port DC power grid system, the fast mechanical switch responds quickly, transferring the fault current in the current-carrying branch to other paths to ensure the safety of the system. After the transfer of the fault current is completed, the fast mechanical switch performs a no-voltage and no-arc breaking operation, effectively isolating the current-carrying branch from the fault point and preventing the further expansion of the fault, thus ensuring the stable operation of the entire power grid.

[0023] In some embodiments, the current interruption branch includes a transfer branch 21 and a power consumption branch 22 connected in parallel; the current interruption branch is configured to instantaneously conduct the transfer branch at the initial stage of a fault in the multi-port DC grid system, receive the fault current transferred by the current conducting branch through the transfer branch, and automatically conduct the power consumption branch when the voltage difference across the power consumption branch reaches a preset overvoltage threshold, absorb the line overvoltage energy by the power consumption branch to quickly cut off the fault current, and complete the non-voltage and non-arc breaking by turning off the fast mechanical switch of the current conducting branch, thereby completely isolating the fault current.

[0024] Specifically, in this embodiment, the current interruption branch includes a current interruption branch E and a current interruption branch F. Each current interruption branch is composed of a transfer branch and a power consumption branch, which is used to achieve fast and reliable opening of the fault current. When a fault occurs in the multi-port DC grid system, the fault current will be quickly transferred to the transfer branch. At this time, a gradually increasing voltage difference will be generated across the power consumption branch. When the voltage difference reaches the preset overvoltage threshold, the power consumption branch will automatically conduct, and the fault current will be quickly cut off through the energy dissipation mechanism, effectively completing the fault isolation process. In specific implementation, as a relatively costly part of the multi-port DC circuit breaker, the transfer branch of the current interruption branch can adopt a bidirectional conduction topology structure formed by symmetric parallel connection. The bidirectional conduction topology structure includes, but is not limited to, a bidirectional conduction topology based on fully controlled devices, a bidirectional conduction topology based on semi-controlled devices, or a bidirectional conduction topology based on diode devices, to meet the flexibility requirements in different application scenarios; while the power consumption branch is mainly composed of lightning arresters, and the energy dissipation is achieved by absorbing the overvoltage to ensure the quick cut-off of the fault current.

[0025] In some embodiments, the grounding branch 3 is configured to conduct the grounding branch and the transfer branch when a grounding fault occurs on the DC bus, form a fault current discharge channel to conduct the fault current into the ground through the current interruption branch and the grounding branch, so as to isolate the faulty DC bus, and at the same time cooperate with the energy consumption device configured on the power supply side of the multi-port DC grid system to absorb the residual energy and suppress the voltage fluctuation in the non-fault area. In this embodiment, the grounding branch includes a controllable switching device, one end of the controllable switching device is connected to the DC bus, and the other end of the controllable switching device is grounded; the controllable switching device is configured to be controlled to conduct when a grounding fault occurs on the DC bus, forming a low-impedance discharge path for the fault current to the ground; the power consumption branch is composed of lightning arresters.

[0026] Specifically, in the multi-port DC system architecture described above, the grounding branch can effectively handle the fault conditions that occur in the DC bus. When a DC bus grounding fault occurs in the system, the fault current flows through the current-breaking branch and the grounding branch and finally into the ground, thereby isolating the faulty DC bus and preventing the fault from further spreading and affecting other normally operating devices. However, since there is no direct electrical connection established between the ports in the multi-port DC system, in this architecture, when the fault isolation operation is completed, the power transmission channel will be cut off, resulting in the interruption of power transmission. To solve this problem and ensure the stable operation of the system after fault isolation, in this embodiment, an energy-consuming device needs to be configured and put into operation at the sending end. This device is put into operation after fault isolation. The main function of the energy-consuming device is to absorb the residual energy in the system after fault isolation and prevent the accumulation of energy in the system from causing unstable phenomena such as overvoltage, thereby maintaining the stability of the system voltage. Through this measure, it can be ensured that the non-faulty area can still operate continuously and reliably during fault isolation, minimizing the impact of the fault on the entire system.

[0027] The embodiment of the present invention provides a multi-port DC circuit breaker topology. The multi-port DC circuit breaker topology includes a current-carrying branch, a current-breaking branch, and a grounding branch. The current-carrying branch includes a fast mechanical switch and a load-commutated switch with variable impedance connected in series. The current-carrying branch is used to provide a low-impedance current conduction path for the load current when the multi-port DC power grid system is operating normally, and when a fault occurs in the multi-port DC power grid system, by turning off the load-commutated switch, a commutation voltage is generated to force the fault current to quickly transfer from the current-carrying branch to the current-breaking branch. The current-breaking branch includes a transfer branch and an energy-consuming branch connected in parallel. The current-breaking branch is used to instantaneously conduct the transfer branch at the initial stage of a fault occurring in the multi-port DC power grid system, receive the fault current transferred from the current-carrying branch through the transfer branch, and automatically conduct the energy-consuming branch when the voltage difference across the energy-consuming branch reaches a preset overvoltage threshold, and use the energy-consuming branch to absorb the line overvoltage energy to quickly cut off the fault current, and complete the no-voltage and no-arc breaking by turning off the fast mechanical switch of the current-carrying branch, thus completely isolating the fault current. Compared with the prior art, this multi-port DC circuit breaker topology realizes the rapid transfer and reliable isolation of the fault current through the coordinated cooperation of the current-carrying branch, the current-breaking branch, and the grounding branch, effectively improving the ability of the DC power grid system to handle faults, ensuring the safe and stable operation of the system, and at the same time reducing the equipment cost.

[0028] In one embodiment, as Figure 2 shown, the embodiment of the present invention provides a control method for a multi-port DC circuit breaker topology, which applies the multi-port DC circuit breaker topology as described above. The control method includes the following steps: S11. Monitor the voltage and current signals of the DC bus and each DC bus outgoing port in the multi-port DC power grid system in real time, and identify the fault type and fault port of the multi-port DC power grid system according to the voltage and current signals.

[0029] S12. When the fault type is a DC short circuit fault at the port outlet, control the current-carrying branch corresponding to the fault port to be in the conducting state, and control both the current-breaking branch and the grounding branch to be in the off state, so that the fault current flows through the current-carrying branch of the fault port.

[0030] S13. In response to the opening command, conduct the transfer branch of the current-breaking branch, and turn off the load commutation switch in the current-carrying branch of the fault port. Use the commutation voltage generated by the turn-off of the load commutation switch to forcibly transfer the fault current in the current-carrying branch to the transfer branch.

[0031] S14. After the fault current is completely transferred to the transfer branch, complete the current interruption without voltage and arc by turning off the fast mechanical switch of the current-carrying branch.

[0032] S15. After the fast mechanical switch is opened in place, trigger an instantaneous overvoltage by turning off the transfer branch. When the voltage difference across the energy-consuming branch reaches the preset overvoltage threshold, automatically conduct the energy-consuming branch, and use the energy-consuming branch to absorb the line overvoltage energy to force the fault current to zero, complete the fault current interruption process, and restore power supply to the non-fault area.

[0033] In a specific embodiment, this embodiment takes the occurrence of a DC short circuit fault at the outlet of Port ① as an example to illustrate the basic working principle of the multi-port DC circuit breaker. At different time nodes during the operation of the DC circuit breaker, its working process can be divided into the following four stages: Fault occurrence stage (T0 - T1 stage): At time T0, a DC short circuit fault occurs at the outlet of Port ①, resulting in a sharp rise in the line current. At this time, all the current flows through the current-carrying branch. In this stage, the current-carrying branch A of Port ① is in the conducting state, and both the current-breaking branch and the grounding branch are in the off state.

[0034] Current transfer stage (T1 - T2 stage): When the DC circuit breaker receives the opening command, first conduct the transfer branch 21 in the current-breaking branch, then turn off the load commutation switch 12 in the current-carrying branch A. At the same time, a commutation voltage will be generated after the load commutation switch 12 is turned off. This commutation voltage will force the current in the current-carrying branch to transfer to the already-conducted transfer branch 21. At this time, the fault current path becomes a multi-port parallel structure, and the fault current paths are "Port ② - current-breaking branch F - current-breaking branch E - fault point", "Port ③ - current-breaking branch F - current-breaking branch E - fault point", and "Port ④ - current-breaking branch F - current-breaking branch E - fault point".

[0035] Mechanical switch breaking stage (T2 - T3 stage): When all the fault current is transferred to the transfer branch 21, turn off the fast mechanical switch 11, thereby achieving breaking without voltage and without arc (the voltage across the switch approaches 0).

[0036] Energy dissipation stage (T3 - T4 stage): When the fast mechanical switch 11 is opened in place and sufficient insulation ability is established, turn off the transfer branch 21. At this time, an instantaneous overvoltage will be generated across its two ends. If this overvoltage exceeds the reference voltage value of the arrester in the energy dissipation branch 22, the current will be transferred to the arrester for energy dissipation. When the line current drops to 0, the entire breaking process is completed.

[0037] During the above - mentioned entire breaking process, the grounding branch 3 is always in the off state. Among them, T0 represents the initial moment when the fault occurs, T1 represents the moment when the opening command is triggered, T2 represents the moment when the current is completely transferred to the transfer branch, T3 represents the moment when the fast mechanical switch is completely disconnected, and T4 represents the moment when the fault current is completely cleared.

[0038] In this embodiment, when the fault type is a DC bus grounding fault, a low - impedance discharge path for the fault current to the ground is formed by conducting the transfer branches of the grounding branch and the current - interrupting branch, and the current in the current - conducting branch is controlled to gradually drop to zero. Specifically, when a DC bus grounding fault occurs, its working process can also be divided into four stages: Fault occurrence stage (T0 - T1 stage): At moment T0, a DC short - circuit fault occurs in the DC bus, resulting in an increase in the line current. At this time, all the current flows through the current - conducting branch. In this stage, all the current - conducting branches are in the conducting state, the current - interrupting branch 2 is in the off state, and the grounding branch 3 is also in the off state.

[0039] Current transfer stage (T1 - T2 stage): When the DC circuit breaker receives the opening command, first conduct the transfer branch 21 in the current - interrupting branch and the grounding branch 3, and then turn off the load commutation switch 12 in each current - conducting branch. After the load commutation switch 12 is turned off, a commutation voltage will be generated, and this commutation voltage will force the current in the current - conducting branch to be transferred to the already - conducted transfer branch 21. At this time, the path of the fault current is "port ① - current - interrupting branch - grounding branch - ground", "port ② - current - interrupting branch - grounding branch - ground", "port ③ - current - interrupting branch - grounding branch - ground", and "port ④ - current - interrupting branch - grounding branch - ground".

[0040] Mechanical switch breaking stage (T2 - T3 stage): When all the fault current is transferred to the transfer branch 21, turn off the fast mechanical switch 11, thereby achieving breaking without voltage and without arc.

[0041] Energy dissipation stage (stage T3 - T4): When the fast mechanical switch 11 is opened in place and sufficient insulation ability is established, the current - breaking transfer branch 21 is turned off. At this time, an instantaneous over - voltage will be generated across its two ends. If this over - voltage exceeds the reference voltage value of the arrester in the energy - dissipating branch 22, the current will be transferred to the arrester for energy dissipation. When the line current drops to 0, the entire breaking process is completed.

[0042] It should be noted that the magnitudes of the sequence numbers of the above - mentioned processes do not mean the order of execution. The order of execution of each process should be determined by its function and internal logic, and should not constitute any limitation to the implementation process of the embodiments of this application.

[0043] For the specific limitations on a control method for a multi - port DC circuit breaker topology, reference can be made to the above - mentioned limitations on a multi - port DC circuit breaker topology, which will not be elaborated here. Those of ordinary skill in the art can realize that, combining the various modules and steps described in the embodiments disclosed in this application, they can be implemented in hardware, software, or a combination of both. Whether these functions are executed in hardware or software depends on the specific application and design constraints of the technical solution. Professional technicians can use different methods to implement the described functions for each specific application, but such implementation should not be considered to exceed the scope of this application.

[0044] The embodiment of the present invention provides a control method for a multi - port DC circuit breaker topology. The control method includes: real - time monitoring the voltage and current signals of the DC bus and each DC bus outgoing port in the multi - port DC power grid system, and identifying the fault type and fault port of the multi - port DC power grid system according to the voltage and current signals; when the fault type is a DC short - circuit fault at the port outlet, controlling the current - conducting branch corresponding to the fault port to be in a conducting state, and controlling both the current - breaking branch and the grounding branch to be in a turned - off state, so that the fault current flows through the current - conducting branch of the fault port; in response to a tripping instruction, turning on the transfer branch of the current - breaking branch and turning off the load commutation switch in the current - conducting branch of the fault port, and using the commutation voltage generated by the turn - off of the load commutation switch to forcibly transfer the fault current in the current - conducting branch to the transfer branch; after the fault current is completely transferred to the transfer branch, completing the no - voltage and no - arc breaking by turning off the fast mechanical switch of the current - conducting branch; after the fast mechanical switch is opened in place, triggering an instantaneous over - voltage by turning off the transfer branch, and automatically turning on the energy - dissipating branch when the voltage difference across the energy - dissipating branch reaches a preset over - voltage threshold, using the energy - dissipating branch to absorb the line over - voltage energy to force the fault current to zero, completing the fault - current truncation process, and restoring power supply to the non - fault area. Compared with the prior art, this method realizes a control method for reliably isolating the fault current and quickly restoring power supply to the non - fault area by coordinating the control of the current - conducting branch, the current - breaking branch, and the grounding branch, improves the reliability and selective protection performance of the DC power grid, and at the same time reduces the equipment cost and operation and maintenance complexity.

[0045] In one embodiment, as Figure 3 shown, an embodiment of the present invention provides a method for determining parameters of a multi-port DC circuit breaker topology. Applying the multi-port DC circuit breaker topology as described above, the parameter determination method includes the following steps: S21. Perform simulation analysis on different DC bus fault scenarios according to the actual topology of the multi-port DC power grid system to determine the maximum fault current values of each DC bus outgoing port under different fault scenarios.

[0046] S22. Determine the breaking capacity requirement of the interrupting branch based on the maximum fault current value, and determine the initial operating current values of each current-carrying branch according to the breaking capacity requirement of the interrupting branch.

[0047] S23. Sequentially select a target current-carrying branch from all current-carrying branches, traverse the fault scenarios of other non-target current-carrying branches, and obtain the fault current distribution data flowing through the target current-carrying branch under each non-target current-carrying branch fault scenario.

[0048] S24. Iteratively optimize the initial operating current value of the target current-carrying branch according to the fault current distribution data. After multiple iterations, screen out the minimum operating current values of each current-carrying branch, specifically including: In each iterative optimization, if the operating current value of the current iteration is greater than the DC current flowing through the target current-carrying branch under the current non-target current-carrying branch fault scenario, update the operating current value of the current iteration to the DC current flowing through the target current-carrying branch under the current non-target current-carrying branch fault scenario, and enter the iterative optimization of the next non-target current-carrying branch fault scenario. Repeat the above process until all non-target current-carrying branch fault scenarios are traversed, and screen out the minimum operating current value of the target current-carrying branch; sequentially perform iterative optimization on the initial operating current values of all current-carrying branches, and screen out the minimum operating current values of each current-carrying branch after multiple iterations; Compare the minimum operating current value of each current-carrying branch with the maximum load current when the multi-port DC power grid system is operating normally. If the minimum operating current value is lower than the maximum load current, gradually reduce the value of the current-limiting inductor of the multi-port DC power grid system, increase the difference between the fault current and the maximum load current, and re-iteratively optimize the minimum operating current value until the minimum operating current values of all current-carrying branches are higher than the maximum load current when the multi-port DC power grid system is operating normally, and obtain the optimized minimum operating current values of each current-carrying branch.

[0049] S25. Output the operating current parameter set of the multi-port DC circuit breaker topology according to the minimum operating current values of all current-carrying branches and the breaking capacity requirement of the interrupting branch.

[0050] In a specific embodiment, after determining the basic topology of the multi-port DC circuit breaker, its basic parameters are designed according to the basic topology of the multi-port DC circuit breaker to ensure the reliable operation of the device under various DC fault conditions. Since the design of the current-breaking branch needs to meet the reliable breaking requirements of the system under various DC fault conditions, therefore, in this embodiment, systematic analysis and comparison of different types of DC fault currents are required. Specifically, in this embodiment, simulation technology is used to simulate the DC short-circuit current levels at different fault positions in the system, and the DC short-circuit current levels at each position are recorded. The maximum fault current value is used as the basis for determining the breaking capacity of the current-breaking branch. For the sake of easy understanding, as Figure 4 shown, this embodiment provides a flowchart for determining the breaking capacity of the current-breaking branch in a typical four-terminal DC system. In terms of the selection of fault types, since DC bipolar faults have more severe fault characteristics compared to single-pole faults, in actual engineering, this embodiment mainly focuses on DC bipolar fault conditions. For a four-terminal DC system, this embodiment takes the analysis of DC fault currents in five typical fault scenarios as an example. The five typical fault scenarios include DC bus faults and faults at the exits of each port. As the number of system ports increases, the number of fault scenarios to be considered will also increase accordingly. Through this systematic method of analyzing fault currents, this embodiment can ensure that the current-breaking branch has sufficient fault-breaking capacity, while avoiding unnecessary over-design, thereby reducing the equipment cost.

[0051] In Figure 4 , this embodiment inputs DC bipolar fault currents at different positions. The DC bipolar fault currents at different positions include , , and . Among them, represents the maximum fault current when a DC bipolar short-circuit fault occurs at the exit of Port ①; represents the maximum fault current when a DC bipolar short-circuit fault occurs at the exit of Port ②; represents the maximum fault current when a DC bipolar short-circuit fault occurs at the exit of Port ③; represents the maximum fault current when a DC bipolar short-circuit fault occurs at the exit of Port ④; represents the total fault current when a DC bipolar short-circuit fault occurs on the DC bus, and its value is the arithmetic sum of the fault currents of Ports ① to ④; represents the fault current of the i-th port; the subscript i represents the port index; I represents the required breaking capacity value of the current-breaking branch; n represents the index of the fault scenario. The maximum value of n in this embodiment is 5. Those skilled in the art can set the maximum value of n according to the specific implementation situation, not limited to this embodiment; denotes the maximum fault current in the nth fault scenario. In this embodiment, the maximum fault current values at the outlets of each port in five types of fault scenarios and the total fault current when a DC bipolar short-circuit fault occurs on the DC bus are obtained through electromagnetic transient simulation, and the breaking capacity of the current-breaking branch is determined based on this. In Figure 4 this embodiment, the requirement value of the breaking capacity of the current-breaking branch is initialized , n = 2, and then it is judged whether holds. If it holds, continue to process; otherwise, the process ends. Then, compare the requirement value I of the breaking capacity of the current-breaking branch with the maximum fault current in the current fault scenario. If , update the requirement value of the breaking capacity of the current-breaking branch, and increase the value of n by 1, i.e., n = n + 1. Repeat the above steps until all fault scenarios are traversed to determine the requirement value I of the breaking capacity of the current-breaking branch.

[0052] On the basis of determining the breaking capacity of the current-breaking branch, this embodiment also needs to further optimize the protection setting value strategy of each current-carrying branch. A reasonable operating current threshold is crucial for ensuring the selective protection of the system. In this embodiment, the operating current threshold of each current-carrying branch is set to be higher than the maximum load current with a certain margin to prevent the equipment from malfunctioning during normal operation. At the same time, this embodiment needs to consider the distribution characteristics of the fault current to ensure that the branches on the non-fault side will not malfunction under the action of the through-fault current, while the branches on the fault side can reliably act to isolate the fault.

[0053] The lower the protection setting value, the faster the fault can be detected and removed in time. To quickly detect the fault and remove it in time and reduce the impact on the system, this embodiment needs to determine the minimum operating current. On this basis, this embodiment proposes a protection setting value strategy for the multi-port DC circuit breaker. In this embodiment, , , and denote the operating current values of current-carrying branch A, current-carrying branch B, current-carrying branch C, and current-carrying branch D respectively; , , and denote the maximum fault currents at each port under different fault positions. For example, denotes the maximum fault current flowing through port ① when a DC bipolar short-circuit fault occurs at the outlet of port ②; denotes the maximum fault current flowing through port ② when a fault occurs at the outlet of port ①; denotes the maximum fault current flowing through port ③ when a fault occurs at the outlet of port ①; Indicates the maximum fault current flowing through port ④ when a fault occurs at the outlet of port ①. By analogy, more parameters can be defined in this embodiment to describe the fault current distribution characteristics of each port under different fault positions; Indicates the maximum fault current flowing through port ① under the nth fault scenario; Indicates the maximum load current of port ① when the system is operating normally; Indicates the maximum fault current flowing through port ② under the nth fault scenario; Indicates the maximum load current of port ② when the system is operating normally; Indicates the maximum fault current flowing through port ③ under the nth fault scenario; Indicates the maximum load current of port ③ when the system is operating normally; Indicates the maximum fault current flowing through port ④ under the nth fault scenario; Indicates the maximum load current of port ④ when the system is operating normally; Indicates excluding the faults of the current branch itself (e.g., excluding the fault scenarios of port 2 when optimizing branch 2).

[0054] Such as Figure 5 、 Figure 6 As shown, this embodiment takes a system with a current-limiting inductor of 100 mH as an example to illustrate the optimization process of the DC fault protection strategy. First, this embodiment inputs the initial operating current values 、 、 and of each current-carrying branch, and inputs the current-limiting inductor value of 100 mH. At the same time, for each current-carrying branch, the initial operating current value is set to the maximum fault current under a specific fault scenario. For example, this embodiment sets the initial value of the operating current of the current-carrying branch to . Then, this embodiment traverses other fault scenarios and analyzes the fault scenarios of n = 1 to 5 in sequence (n = 1 to 4 are port faults, and n = 5 is a bus fault). By analyzing the DC current distribution characteristics at different fault positions (excluding the faults occurring in this branch), this embodiment compares the current operating current value with the maximum fault current under this fault scenario. If the current operating current value is greater than the DC current flowing through port ① of the current-carrying branch under fault scenario n, then the operating current is updated to the value at this time. Repeat the above steps until all fault scenarios are traversed. Through multiple iterations of optimization, this embodiment can screen out the minimum operating current value of the current-carrying branch. This optimization process can not only effectively prevent the misoperation of the current-carrying branch when DC faults occur at other positions, but also ensure that when a DC fault occurs at this port, the current-carrying branch can reliably isolate the fault.

[0055] After determining the minimum operating current of each current-carrying branch of the multi-port DC circuit breaker, this embodiment needs to further verify its compatibility with the normal operating state of the system. Specifically, this embodiment needs to ensure that the selected minimum operating current value is higher than the maximum load current during normal system operation, so as to prevent the protection device from malfunctioning due to current fluctuations during normal system operation, thus affecting the stable operation of the system. During the verification process, if it is detected that the minimum operating current value of a certain current-carrying branch is lower than the system's maximum load current, corresponding optimization measures need to be taken. The specific method is to gradually reduce the value of the current-limiting inductor of the system. By reducing the value of the current-limiting inductor, the difference between the fault current and the maximum load current is increased, thereby improving the action reliability of the protection device when a fault occurs, until the minimum operating current of all current-carrying branches meets the requirement of being greater than the system's maximum load current. This optimization process not only ensures the reliability of the protection system and avoids malfunctions caused by improper setting of the operating current, but also takes into account the stability of system operation and prevents other potential problems caused by too small a value of the current-limiting inductor, providing a strong technical guarantee for the safe and stable operation of the DC system. After completing the optimization of the operating current of one current-carrying branch, the operating current values of other current-carrying branches should be determined in turn according to the same method and steps, ensuring that all current-carrying branches of the entire multi-port DC circuit breaker system can achieve fast and accurate fault detection and isolation under various operating conditions, thereby ensuring the safe, stable and efficient operation of the DC power grid.

[0056] Compared with the traditional solution that uses multiple two-port DC circuit breakers, the multi-port DC circuit breaker architecture adopted in this embodiment significantly reduces the equipment cost and enhances the economy of the system. At the same time, in response to the existing research method of adding sub-modules in the current-breaking branch or designing more complex circuits to ensure that the current flows unidirectionally through the transfer branch, this embodiment introduces a two-way current-breaking branch design. This improvement not only greatly simplifies the control logic of the power electronic switch, but also significantly improves the overall reliability of the system. When a DC bus fault occurs, this embodiment realizes the effective dissipation of fault energy through the coordinated action of the grounding branch and the two two-way current-breaking branches, and quickly isolates the faulty DC bus, further enhancing the reliability performance of the equipment. In terms of the protection setting value strategy, this embodiment comprehensively considers the fault current characteristics under various DC fault scenarios. This strategy can effectively prevent the occurrence of protection malfunctions during normal system operation. At the same time, under the influence of the cross-through fault current, it can ensure the stable operation of the non-faulty side branch and avoid malfunctions, and can ensure that the faulty side branch can respond and act quickly and accurately when a fault occurs. This protection setting value strategy significantly improves the operation reliability and protection accuracy of the multi-port DC circuit breaker, providing a strong guarantee for the safe and stable operation of the DC system.

[0057] It should be noted that the sequence numbers of the above processes do not imply the order of execution. The order of execution of each process should be determined by its function and internal logic, and should not impose any limitation on the implementation process of the embodiments of the present application.

[0058] For the specific limitations on the parameter determination method of a multi-port DC breaker topology structure, reference can be made to the above limitations on a multi-port DC breaker topology structure, which will not be elaborated here. Those of ordinary skill in the art can realize that, in combination with the various modules and steps described in the embodiments disclosed in the present application, they can be implemented in hardware, software, or a combination of both. Whether these functions are executed in hardware or software depends on the specific application and design constraints of the technical solution. Professional technicians can use different methods to implement the described functions for each specific application, but such implementation should not be considered to exceed the scope of the present application.

[0059] The embodiment of the present invention provides a parameter determination method for a multi-port DC breaker topology structure. The parameter determination method includes performing simulation analysis on different DC bus fault scenarios according to the actual topology structure of the multi-port DC power grid system to determine the maximum fault current values of each DC bus outgoing port under different fault scenarios; determining the breaking capacity requirements of the interrupting branches based on the maximum fault current values, and determining the initial operating current values of each current-carrying branch according to the breaking capacity requirements of the interrupting branches; sequentially selecting a target current-carrying branch from all current-carrying branches, traversing the fault scenarios of other non-target current-carrying branches, and obtaining the fault current distribution data flowing through the target current-carrying branch under each non-target current-carrying branch fault scenario; iteratively optimizing the initial operating current value of the target current-carrying branch according to the fault current distribution data, and screening out the minimum operating current values of each current-carrying branch after multiple iterations; and outputting the operating current parameter set of the multi-port DC breaker topology structure according to the minimum operating current values of all current-carrying branches and the breaking capacity requirements of the interrupting branches. Compared with the prior art, through accurate simulation analysis and iterative optimization, this parameter determination method realizes the accurate configuration of the breaker parameters, ensures that the breaker can act quickly and accurately and the system can operate stably under various fault scenarios, and significantly improves the fault response ability and adaptability of the multi-port DC breaker.

[0060] The above embodiments only represent several preferred implementation manners of the present application, and the description thereof is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the technical principle of the present invention, several improvements and substitutions can be made, and these improvements and substitutions should also be regarded as the protection scope of the present application. Therefore, the protection scope of the patent of the present application should be subject to the protection scope of the claims.

Claims

1. A multi-port DC circuit breaker topology, based on a hybrid DC circuit breaker architecture, is characterized in that Comprising: A current-carrying branch, a current-breaking branch, and a grounding branch. Among them, the current-carrying branch is connected between the DC bus and each DC bus outgoing port, and the current-breaking branch is arranged in parallel with the current-carrying branch; The current-carrying branch includes a fast mechanical switch and a load-commutated switch with variable impedance connected in series; the current-carrying branch is used to provide a low-impedance current conduction path for the load current when the multi-port DC grid system is operating normally, and when a fault occurs in the multi-port DC grid system, a commutation voltage is generated by turning off the load-commutated switch, forcing the fault current to quickly transfer from the current-carrying branch to the current-breaking branch; The current-breaking branch includes a transfer branch and a dissipative branch connected in parallel; the current-breaking branch is used to instantaneously conduct the transfer branch at the initial stage of a fault in the multi-port DC grid system, receive the fault current transferred from the current-carrying branch through the transfer branch, and automatically conduct the dissipative branch when the voltage difference across the dissipative branch reaches a preset overvoltage threshold, use the dissipative branch to absorb the line overvoltage energy and quickly cut off the fault current, and complete the non-voltage and non-arc breaking by turning off the fast mechanical switch of the current-carrying branch to completely isolate the fault current.

2. The multi-port DC circuit breaker topology according to claim 1, characterized in that: The grounding branch is used to conduct the grounding branch and the transfer branch when a grounding fault occurs on the DC bus, form a fault current discharge channel to lead the fault current into the ground through the current-breaking branch and the grounding branch to isolate the faulty DC bus, and at the same time cooperate with the dissipative device configured on the power supply side of the multi-port DC grid system to absorb the residual energy and suppress the voltage fluctuation in the non-fault area.

3. A multi-port DC circuit breaker topology according to claim 1, characterized in that: The fast mechanical switch is used to provide a low-impedance conduction path for the load current together with the load-commutated switch when the multi-port DC grid system is operating normally; And, quickly transfer the fault current in the current-carrying branch when a fault occurs in the multi-port DC grid system, and perform a non-voltage and non-arc breaking action to isolate the current-carrying branch and the fault point after the transfer of the fault current is completed.

4. The multi-port DC circuit breaker topology according to claim 1, characterized in that: The transfer branch adopts a bidirectional conduction topology to control the bidirectional conduction of the fault current in the multi-port DC grid, and the bidirectional conduction topology is composed of fully controlled devices, semi-controlled devices or diode devices through a symmetric parallel connection method.

5. The multi-port DC circuit breaker topology according to claim 1, wherein: The grounding branch includes a controllable switch device, one end of the controllable switch device is connected to the DC bus, and the other end of the controllable switch device is grounded; The controllable switch device is used to be controlled to conduct when a grounding fault occurs on the DC bus, forming a low-impedance discharge path for the fault current to the ground.

6. A control method for a multi-port DC circuit breaker topology, characterized in that, Applying the multi-port DC circuit breaker topology according to any one of claims 1 to 5, the control method includes the following steps: Real-time monitor the voltage and current signals of the DC bus and each DC bus outgoing port in the multi-port DC grid system, and identify the fault type and fault port of the multi-port DC grid system according to the voltage and current signals; When the fault type is a DC short circuit fault at the port outlet, control the current-carrying branch corresponding to the fault port to be in a conducting state, and control both the current-breaking branch and the grounding branch to be in a cut-off state, so that the fault current flows through the current-carrying branch of the fault port; In response to a circuit breaker opening command, the transfer branch of the current interruption branch is turned on, and the load commutation switch in the current-carrying branch of the faulty port is turned off. The commutation voltage generated by the turn-off of the load commutation switch is used to forcibly transfer the fault current in the current-carrying branch to the transfer branch; After the fault current is completely transferred to the transfer branch, the fast mechanical switch in the current-carrying branch is turned off to complete the current interruption without voltage and without arc; After the fast mechanical switch is opened in place, an instantaneous overvoltage is triggered by turning off the transfer branch. When the voltage difference across the energy dissipation branch reaches the preset overvoltage threshold, the energy dissipation branch is automatically turned on. The energy dissipation branch is used to absorb the line overvoltage energy to force the fault current to zero, complete the fault current interruption process, and restore power supply to the non-faulty area.

7. The control method of a multi-port DC circuit breaker topology according to claim 6, characterized in that: When the fault type is a DC bus grounding fault, a low-impedance discharge path for the fault current to the ground is formed by turning on the grounding branch and the transfer branch of the current interruption branch, and the current in the current-carrying branch is controlled to gradually drop to zero.

8. A method for determining parameters of a multi-port DC circuit breaker topology, characterized in that Applying the multi-port DC circuit breaker topology structure as described in any one of claims 1 to 5, the parameter determination method includes the following steps: Perform simulation analysis on different DC bus fault scenarios according to the actual topology structure of the multi-port DC power grid system to determine the maximum fault current values of each DC bus outgoing line port under different fault scenarios; Based on the maximum fault current value, determine the breaking capacity requirement of the current interruption branch, and determine the initial operating current value of each current-carrying branch according to the breaking capacity requirement of the current interruption branch; Sequentially select a target current-carrying branch from all current-carrying branches, traverse the fault scenarios of other non-target current-carrying branches, and obtain the fault current distribution data flowing through the target current-carrying branch under each non-target current-carrying branch fault scenario; Iteratively optimize the initial operating current value of the target current-carrying branch according to the fault current distribution data. After multiple iterations, the minimum operating current values of each current-carrying branch are screened out; According to the minimum operating current values of all current-carrying branches and the breaking capacity requirement of the current interruption branch, output the operating current parameter set of the multi-port DC circuit breaker topology structure.

9. The parameter determination method for a multi-port DC circuit breaker topology according to claim 8, characterized in that The step of iteratively optimizing the initial operating current value of the target current-carrying branch according to the fault current distribution data and screening out the minimum operating current values of each current-carrying branch after multiple iterations includes: In each iterative optimization, if the operating current value of the current iteration is greater than the DC current flowing through the target current-carrying branch in the current non-target current-carrying branch fault scenario, update the operating current value of the current iteration to the DC current flowing through the target current-carrying branch in the current non-target current-carrying branch fault scenario, and enter the iterative optimization of the next non-target current-carrying branch fault scenario. Repeat the above process until all non-target current-carrying branch fault scenarios are traversed, and the minimum operating current value of the target current-carrying branch is screened out; Iteratively optimize the initial operating current values of all current-carrying branches in sequence. After multiple iterations, the minimum operating current values of each current-carrying branch are screened out.

10. The parameter determination method of a multi-port DC circuit breaker topology according to claim 8, characterized in that, The parameter determination method further includes: Compare the minimum operating current value of each current-carrying branch with the maximum load current when the multi-port DC power grid system is operating normally. If the minimum operating current value is lower than the maximum load current, gradually reduce the value of the current-limiting inductor of the multi-port DC power grid system, increase the difference between the fault current and the maximum load current, and re-iterate to optimize the minimum operating current value until the minimum operating current values of all current-carrying branches are higher than the maximum load current when the multi-port DC power grid system is operating normally, so as to obtain the optimized minimum operating current values of each current-carrying branch.

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