Multi-port DC circuit breaker topology, control method and parameter determination method

Abstract

The present invention relates to the field of power system protection technology, and in particular to a multi-port DC circuit breaker topology structure, control method, and parameter determination method thereof, including a flow branch that provides a low-impedance current conduction path for the load current when the multi-port DC power grid system is operating normally, and forces the fault current to be quickly transferred from the flow branch to the disconnect branch when a fault occurs in the multi-port DC power grid system; the disconnect branch instantaneously conducts the transfer branch and receives the transferred fault current in the initial stage of a fault in the multi-port DC power grid system, automatically conducts the energy-consuming branch when the voltage difference across the energy-consuming branch reaches a preset overvoltage threshold, utilizes the energy-consuming branch to absorb the line overvoltage energy and quickly cuts off the fault current, and completes the voltage-free and arc-free disconnection by shutting off the fast mechanical switch of the flow branch, thereby completing the complete isolation of the fault current. The present invention effectively improves the DC power grid system's ability to cope with faults through the coordinated cooperation of the flow branch, the disconnect branch, and the grounding branch.

Description

Technical Field

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

[0002] As a key device for isolating faults in DC power grids, DC circuit breakers play an irreplaceable role in the protection and operation of DC power grids. However, existing DC circuit breaker technology still faces many problems in practical applications. At present, DC circuit breaker technology is mainly divided into three types according to the 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, and generate an oscillating current through an oscillation circuit to superimpose the oscillating current with the fault current to produce a zero crossing point, thereby realizing current cutting off. It has the advantages of low conduction loss, high insulation tolerance and low cost. However, since it relies on the action of traditional AC mechanical switches, the breaking time is long, which makes it difficult to meet the requirements of flexible DC transmission. The system's response needs for rapid fault isolation; solid-state DC circuit breakers use full-power devices to achieve rapid disconnection. Although the operation speed is extremely fast and no breaking arc is generated, the power devices used in solid-state DC circuit breakers have low rated voltage and rated current, and a large number of power devices need to be combined in series and parallel, which 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 with the fast breaking capability of solid-state switches, balancing the contradiction between breaking speed and on-state loss to a certain extent, but the structure of existing hybrid circuit breakers is complex and requires the coordinated action of mechanical switches and solid-state switches at the same time, which increases the manufacturing cost and maintenance difficulty of the equipment.

[0003] With the continuous expansion of DC power grids, the number of DC circuit breakers required to achieve full selectivity in protection is growing exponentially. This is especially true in multi-terminal DC systems. According to the traditional two-port DC circuit breaker solution, each outgoing line needs to be equipped with an independent circuit breaker, which will lead to a significant increase in the number of equipment and a significant increase in system investment costs. To address this problem, some researchers have proposed a multi-port DC circuit breaker solution. By sharing the main disconnect switch unit for all incoming and outgoing lines on the same DC bus, the fault current interruption function of multiple lines can be realized, thereby reducing the number of circuit breakers configured. However, the current engineering application of multi-port DC circuit breakers faces the problem of inter-module coordinated control under complex structures. It is necessary to solve the electrical parameter matching and action timing coordination between multiple ports. At the same time, the complex topology structure places extremely high demands on the real-time and accuracy of the control system, and the long-term operation stability under high voltage and high current conditions cannot be guaranteed. In addition, the reasonable arrangement of various functional modules in a limited space and the balance of performance indicators such as electrical insulation, heat dissipation and electromagnetic compatibility are also difficult problems that must be solved in actual engineering applications.

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

[0005] In order to solve the above technical problems, the present invention provides a multi-port DC circuit breaker topology structure, a control method and a parameter determination method thereof.

[0006] In a first aspect, the present invention provides a multi-port DC circuit breaker topology structure based on a hybrid DC circuit breaker architecture, comprising: a flow branch, a current-blocking branch, and a grounding branch, wherein the flow branch is connected between a DC bus and each DC bus outlet port, and the current-blocking branch is arranged in parallel with the flow branch;

[0007] The pass-through branch includes a fast mechanical switch and a load-reversing switch with variable impedance connected in series. The pass-through 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. When a fault occurs in the multi-port DC power grid system, the load-reversing switch is turned off to generate a commutation voltage, forcing the fault current to be quickly transferred from the pass-through branch to the disconnecting branch.

[0008] The interrupting branch includes a transfer branch and an energy-consuming branch connected in parallel. The interrupting branch is used to instantaneously conduct the transfer branch in the initial stage of a fault in the multi-port DC power grid system, receive the fault current transferred by the flow 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. The energy-consuming branch absorbs the line overvoltage energy to quickly cut off the fault current. The fast mechanical switch that shuts off the flow branch is used to achieve voltage-free and arc-free disconnection, thereby completely isolating the fault current.

[0009] In a further implementation scheme, the grounding branch is used to connect the grounding branch and the transfer branch when a ground fault occurs in the DC bus, forming a fault current discharge channel to conduct the fault current into the earth through the interrupting 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 power grid system to absorb residual energy and suppress voltage fluctuations in non-fault areas.

[0010] 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 reversing switch when the multi-port DC grid system is operating normally;

[0011] Furthermore, when a fault occurs in the multi-port DC grid system, the fault current in the through-current branch is quickly transferred, and after the fault current transfer is completed, a no-voltage and no-arc breaking action is performed to isolate the through-current branch from the fault point.

[0012] In a further embodiment, the transfer branch adopts a bidirectional conduction topology structure to control the bidirectional conduction of the fault current in the multi-port DC power grid, and the bidirectional conduction topology structure is composed of fully controlled devices, half controlled devices or diode devices in a symmetrical parallel manner.

[0013] 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;

[0014] The controllable switch device is used to be controlled to be turned on when a ground fault occurs in the DC bus, forming a low-impedance discharge path for the fault current to the ground.

[0015] In a second aspect, the present invention provides a control method for a multi-port DC circuit breaker topology structure. Applying the multi-port DC circuit breaker topology structure as described above, the control method comprises the following steps:

[0016] Real-time monitoring of the voltage and current signals of the DC bus and each DC bus output port in the multi-port DC grid system, and identification of the fault type and fault port of the multi-port DC grid system based on the voltage and current signals;

[0017] When the fault type is a DC short circuit fault at the port outlet, the flow branch corresponding to the fault port is controlled to be in an on state, and the interruption branch and the grounding branch are controlled to be in an off state, so that the fault current flows through the flow branch of the fault port;

[0018] In response to the tripping instruction, the transfer branch of the disconnecting branch is turned on, and the load reversing switch in the flow branch of the fault port is turned off, and the commutation voltage generated by the load reversing switch being turned off is used to forcibly transfer the fault current in the flow branch to the transfer branch;

[0019] After the fault current is completely transferred to the transfer branch, the voltage-free and arc-free disconnection is completed by shutting off the fast mechanical switch of the current-carrying branch;

[0020] After the fast mechanical switch is opened to its full position, an instantaneous overvoltage is triggered by shutting off the transfer branch. When the voltage difference across the energy-consuming branch reaches the preset overvoltage threshold, the energy-consuming branch is automatically turned on. The energy-consuming branch absorbs the overvoltage energy of the line, forcing the fault current to return to zero, completing the fault current interruption process and restoring power supply to the non-fault area.

[0021] In a further implementation scheme, 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 connecting the transfer branch of the grounding branch and the interrupting branch, and the current of the conducting branch is controlled to gradually drop to zero.

[0022] In a third aspect, the present invention provides a method for determining parameters of a multi-port DC circuit breaker topology structure. Applying the multi-port DC circuit breaker topology structure described above, the parameter determination method comprises the following steps:

[0023] Based on the actual topology of the multi-port DC grid system, different DC bus fault scenarios are simulated and analyzed to determine the maximum fault current value of each DC bus output port under different fault scenarios;

[0024] Determining a breaking capacity requirement of the interrupting branch based on the maximum fault current value, and determining an initial operating current value of each current-carrying branch according to the breaking capacity requirement of the interrupting branch;

[0025] Selecting a target flow branch from all flow branches in sequence, traversing other non-target flow branch fault scenarios, and obtaining fault current distribution data flowing through the target flow branch under each non-target flow branch fault scenario;

[0026] Iteratively optimizing the initial operating current value of the target flow-through branch according to the fault current distribution data, and screening out the minimum operating current value of each flow-through branch after multiple iterations;

[0027] According to the minimum operating current value of all the current-carrying branches and the breaking capacity requirements of the current-breaking branches, the operating current parameter set of the multi-port DC circuit breaker topology is output.

[0028] In a further embodiment, the step of iteratively optimizing the initial operating current value of the target flow branch according to the fault current distribution data and screening out the minimum operating current value of each flow branch after multiple iterations includes:

[0029] In each iterative optimization, if the operating current value of the current iteration is greater than the DC current flowing through the target flow branch under the current non-target flow branch fault scenario, the operating current value of the current iteration is updated to the DC current flowing through the target flow branch under the current non-target flow branch fault scenario, and the iterative optimization of the next non-target flow branch fault scenario is started. The above process is repeated until all non-target flow branch fault scenarios are traversed and the minimum operating current value of the target flow branch is screened out;

[0030] The initial operating current values ​​of all the flow branches are iteratively optimized in turn, and the minimum operating current value of each flow branch is screened out after multiple iterations.

[0031] In a further embodiment, the parameter determination method further comprises:

[0032] The minimum operating current value of each flow-through branch is compared with the maximum load current of the multi-port DC power grid system during normal operation. If the minimum operating current value is lower than the maximum load current, the current-limiting inductance value of the multi-port DC power grid system is gradually reduced, the difference between the fault current and the maximum load current is increased, and the minimum operating current value is iteratively optimized again until the minimum operating current values ​​of all flow-through branches are higher than the maximum load current of the multi-port DC power grid system during normal operation, thereby obtaining the optimized minimum operating current value of each flow-through branch.

[0033] The present invention provides a multi-port DC circuit breaker topology structure, a control method, and a parameter determination method thereof. The multi-port DC circuit breaker topology structure includes a flow branch, a disconnect branch, and a grounding branch. The flow branch includes a fast mechanical switch and a load reversing switch with variable impedance connected in series. The flow 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. When a fault occurs in the multi-port DC power grid system, the load reversing switch is turned off to generate a commutation voltage, forcing the fault current to be rapidly transferred from the flow branch to the disconnect branch. The disconnect branch includes a transfer branch and an energy dissipation branch connected in parallel. The disconnect branch is used to instantaneously turn on the transfer branch in the initial stage of a fault in the multi-port DC power grid system, receive the fault current transferred by the flow branch through the transfer branch, and automatically turn on the energy dissipation branch when the voltage difference across the energy dissipation branch reaches a preset overvoltage threshold. The energy dissipation branch absorbs line overvoltage energy to rapidly cut off the fault current. The fast mechanical switch that disconnects the flow branch is used to achieve voltage-free and arc-free disconnection, thereby completely isolating the fault current. Compared with existing technologies, this multi-port DC circuit breaker topology achieves rapid transfer and reliable isolation of fault currents through the coordinated cooperation of current-carrying branches, current-blocking branches and grounding branches, effectively improving the DC power grid system's ability to cope with faults and ensuring the safe and stable operation of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 1 is a schematic diagram of a topological structure of a multi-port DC circuit breaker provided in an embodiment of the present invention;

[0035] Figure 2 This is a flow chart of a control method for a multi-port DC circuit breaker topology structure provided by an embodiment of the present invention;

[0036] Figure 3 1 is a flow chart of a method for determining parameters of a multi-port DC circuit breaker topology structure provided by an embodiment of the present invention;

[0037] Figure 4 1 is an example diagram of a process for determining topology parameters of a multi-port DC circuit breaker provided by an embodiment of the present invention;

[0038] Figure 5 Schematic diagram of the DC fault protection strategy optimization process for two current-carrying branches provided by an embodiment of the present invention;

[0039] Figure 6 3 is a schematic diagram of the DC fault protection strategy optimization process for the other two flow-through branches provided by an embodiment of the present invention.

[0040] Explanation of the accompanying symbols: 1. current-passing branch; 2. current-blocking branch; 3. grounding branch; 11. fast mechanical switch; 12. load reversing switch; 21. transfer branch; 22. energy-consuming branch. DETAILED DESCRIPTION

[0041] The following describes the embodiments of the present invention in detail with reference to the accompanying drawings. The embodiments are provided for illustrative purposes only and are not to be construed as limiting the present invention. The accompanying drawings are provided for reference and illustration only and do not constitute a limitation on the scope of protection of the present invention. Many changes may be made to the present invention without departing from the spirit and scope of the present invention.

[0042] refer to Figure 1 , an embodiment of the present invention provides a multi-port DC circuit breaker topology structure, the multi-port DC circuit breaker topology structure is based on a hybrid DC circuit breaker, such as Figure 1 As shown, the multi-port DC circuit breaker topology structure includes a flow branch 1, a current-breaking branch 2 and a grounding branch 3. The flow branch 1 is connected between the DC bus and each DC bus outlet port, and the current-breaking branch 2 is arranged in parallel with the flow branch 1.

[0043] In some embodiments, the pass-through branch 1 includes a fast mechanical switch 11 and a variable impedance load reversing switch 12 connected in series. In this embodiment, the pass-through 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, the load reversing switch is turned off to generate a commutation voltage, forcing the fault current to be quickly transferred from the pass-through branch to the disconnecting branch.

[0044] Specifically, the through-current branches in this embodiment may include through-current branch A, through-current branch B, through-current branch C, and through-current branch D. During normal system operation, the through-current branches, through the coordinated action of fast mechanical switches and variable impedance load reversing switches, provide a low-impedance conduction path for the load current, ensuring efficient transmission of electrical energy. Furthermore, when a fault occurs in the multi-port DC power grid system, the fast mechanical switches can rapidly transfer the fault current in the through-current branches to the disconnecting branches and, after the fault current is completely transferred, perform a voltage-free, arc-free breaking operation, thereby reliably isolating the through-current branches from the fault point. Specifically, during normal operation of the multi-port DC power grid system, the through-current branches, through the coordinated action of fast mechanical switches and load reversing switches, provide a low-impedance conduction path for the load current. When a fault occurs in the multi-port DC power grid system, the fast mechanical switches rapidly respond, diverting the fault current in the through-current branches to other paths to ensure system safety. After the fault current transfer is complete, the fast mechanical switches perform a voltage-free, arc-free breaking operation, effectively isolating the through-current branches from the fault point, preventing further expansion of the fault, and thereby ensuring stable operation of the entire power grid.

[0045] In some embodiments, the interrupting branch includes a transfer branch 21 and an energy-consuming branch 22 connected in parallel; the interrupting branch is used to instantaneously turn on the transfer branch in the initial stage of a fault in the multi-port DC power grid system, receive the fault current transferred by the flow branch through the transfer branch, and automatically turn on the energy-consuming branch when the voltage difference across the energy-consuming branch reaches a preset overvoltage threshold. The energy-consuming branch absorbs the overvoltage energy of the line to quickly cut off the fault current, and completes voltage-free and arc-free disconnection by shutting off the fast mechanical switch of the flow branch, thereby completely isolating the fault current.

[0046] Specifically, in this embodiment, the interrupting branch includes an interrupting branch E and an interrupting branch F. Each interrupting branch is composed of a transfer branch and an energy-consuming branch, and is used to achieve rapid and reliable interruption of the fault current. When a fault occurs in the multi-port DC power grid system, the fault current will be quickly transferred to the transfer branch. At this time, a gradually increasing voltage difference will be generated at both ends of the energy-consuming branch. When the voltage difference reaches a preset overvoltage threshold, the energy-consuming branch will automatically turn on, and the fault current will be quickly cut off through the energy dissipation mechanism, effectively completing the fault isolation process. In a specific implementation, the interrupting branch is a relatively high-cost part of the multi-port DC circuit breaker. Its transfer branch can adopt a bidirectional conductive topology structure formed by a symmetrical parallel connection. The bidirectional conductive topology includes but is not limited to a bidirectional conductive topology based on fully controlled devices, a bidirectional conductive topology based on semi-controlled devices, or a bidirectional conductive topology based on diode devices to meet the flexibility requirements in different application scenarios; while the energy-consuming branch is mainly composed of a lightning arrester, which dissipates energy by absorbing overvoltage to ensure rapid interruption of the fault current.

[0047] In some embodiments, the grounding branch 3 is used to connect the grounding branch and the transfer branch when a ground fault occurs in the DC bus, forming a fault current discharge channel to conduct the fault current into the ground through the interrupting 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 power grid system to absorb residual energy and suppress voltage fluctuations in non-fault areas. 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 used to be controlled to be turned on when a ground fault occurs in the DC bus, forming a low-impedance discharge path for the fault current to the ground; the energy consumption branch is composed of a lightning arrester.

[0048] Specifically, in the multi-port DC system architecture, the grounding branch can effectively respond to fault conditions that occur in the DC bus. When a DC bus grounding fault occurs in the system, the fault current ultimately flows into the ground via the interrupting branch and the grounding branch, thereby isolating the faulty DC bus and preventing the fault from further spreading and affecting other normally operating equipment. However, since no direct electrical connection is established between the ports in the multi-port DC system, in this architecture, the power transmission channel will be cut off after the fault isolation operation is completed, resulting in power transmission interruption. To address this problem and ensure stable operation of the system after fault isolation, this embodiment requires configuring and activating an energy dissipation device at the sending end. The device is put into operation after fault isolation. The main function of the energy dissipation device is to absorb the residual energy in the system after fault isolation, preventing energy accumulation in the system from causing instability such as overvoltage, thereby maintaining system voltage stability. Through this measure, it is possible to ensure that the non-fault area can still operate continuously and reliably during the fault isolation period, minimizing the impact of the fault on the entire system.

[0049] An embodiment of the present invention provides a multi-port DC circuit breaker topology structure, which includes a flow branch, a disconnect branch, and a grounding branch. The flow branch includes a fast mechanical switch and a variable impedance load reversing switch connected in series. The flow 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. When a fault occurs in the multi-port DC power grid system, the load reversing switch is turned off to generate a commutation voltage, forcing the fault current to be rapidly transferred from the flow branch to the disconnect branch. The disconnect branch includes a transfer branch and an energy consumption branch connected in parallel. The disconnect branch is used to instantaneously turn on the transfer branch in the initial stage of a fault in the multi-port DC power grid system, receive the fault current transferred from the flow branch through the transfer branch, and automatically turn on the energy consumption branch when the voltage difference across the energy consumption branch reaches a preset overvoltage threshold. The energy consumption branch absorbs line overvoltage energy and rapidly cuts off the fault current. The fast mechanical switch that turns off the flow branch is used to achieve voltage-free and arc-free disconnection, thereby completely isolating the fault current. Compared with existing technologies, this multi-port DC circuit breaker topology achieves rapid transfer and reliable isolation of fault currents through the coordinated cooperation of current-carrying branches, current-blocking branches, and grounding branches, effectively improving the DC power grid system's ability to cope with faults, ensuring the system's safe and stable operation, while reducing equipment costs.

[0050] In one embodiment, Figure 2 As shown, an embodiment of the present invention provides a control method for a multi-port DC circuit breaker topology structure. Applying the multi-port DC circuit breaker topology structure as described above, the control method includes the following steps:

[0051] S11. Monitor the voltage and current signals of the DC bus and each DC bus output port in the multi-port DC grid system in real time, and identify the fault type and fault port of the multi-port DC grid system based on the voltage and current signals.

[0052] S12. When the fault type is a DC short circuit fault at the port outlet, the flow branch corresponding to the fault port is controlled to be in the on state, and the interruption branch and the grounding branch are controlled to be in the off state, so that the fault current flows through the flow branch of the fault port.

[0053] S13. In response to the tripping instruction, the transfer branch of the disconnecting branch is turned on, and the load reversing switch in the flow branch of the fault port is turned off, and the commutation voltage generated by the load reversing switch being turned off is used to forcibly transfer the fault current in the flow branch to the transfer branch.

[0054] S14. After the fault current is completely transferred to the transfer branch, the voltage-free and arc-free disconnection is completed by shutting off the fast mechanical switch of the current-carrying branch.

[0055] S15. After the fast mechanical switch is fully opened, a transient overvoltage is triggered by shutting off the transfer branch. When the voltage difference across the energy-consuming branch reaches the preset overvoltage threshold, the energy-consuming branch is automatically turned on. The energy-consuming branch absorbs the overvoltage energy of the line, forcing the fault current to return to zero, completing the fault current interruption process and restoring power supply to the non-fault area.

[0056] In a specific embodiment, this embodiment takes a DC short circuit fault occurring 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 points during the operation of the DC circuit breaker, its working process can be divided into the following four stages:

[0057] Fault occurrence phase (T0-T1 phase): At time T0, a DC short circuit fault occurs at the outlet of port ①, causing the line current to rise sharply. At this time, all the current flows through the flow branch. During this phase, the flow branch A of port ① is in the on state, and the interrupting branch and the grounding branch are both in the off state.

[0058] Current transfer stage (T1-T2 stage): When the DC circuit breaker receives the tripping command, it first turns on the transfer branch 21 in the disconnecting branch, and then turns off the load reversing switch 12 in the flow branch A. At the same time, after the load reversing switch 12 is turned off, a commutation voltage is generated. This commutation voltage forces the current in the flow branch to be transferred to the turned-on transfer branch 21. At this time, the fault current path becomes a multi-port parallel structure. The fault current path is "port ②-disconnecting branch F-disconnecting branch E-fault point", "port ③-disconnecting branch F-disconnecting branch E-fault point" and "port ④-disconnecting branch F-disconnecting branch E-fault point".

[0059] Mechanical switch disconnection stage (T2-T3 stage): After the fault current is completely transferred to the transfer branch 21, the fast mechanical switch 11 is turned off, thereby achieving voltage-free and arc-free disconnection (the voltage across the switch approaches 0).

[0060] Energy dissipation stage (T3-T4 stage): When the fast mechanical switch 11 is opened to its full position and sufficient insulation capacity is established, the transfer branch 21 is shut off. At this time, a transient overvoltage will be generated at both ends of it. If the overvoltage exceeds the reference voltage value of the lightning arrester in the energy dissipation branch 22, the current will be transferred to the lightning arrester and energy will be dissipated. When the line current drops to 0, the entire breaking process is completed.

[0061] During the entire breaking process mentioned above, the grounding branch 3 is always in the off state, where T0 represents the initial moment of the fault occurrence, 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.

[0062] 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 connecting the transfer branch of the grounding branch and the interrupting branch, and the current of the 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:

[0063] Fault occurrence phase (T0-T1 phase): At time T0, a DC short circuit fault occurs in the DC bus, causing the line current to increase. At this time, all the current flows through the current-carrying branches. In this phase, all the current-carrying branches are in the on state, the current-blocking branch 2 is in the off state, and the grounding branch 3 is also in the off state.

[0064] Current transfer stage (T1-T2 stage): When the DC circuit breaker receives the tripping command, it first turns on the transfer branch 21 and the grounding branch 3 in the disconnecting branch, and then turns off the load reversing switch 12 in each current-carrying branch. After the load reversing switch 12 is turned off, a commutation voltage is generated, which forces the current in the current-carrying branch to transfer to the turned-on transfer branch 21. At this time, the fault current paths are "port ①-disconnecting branch-grounding branch-earth", "port ②-disconnecting branch-grounding branch-earth", "port ③-disconnecting branch-grounding branch-earth" and "port ④-disconnecting branch-grounding branch-earth".

[0065] Mechanical switch disconnection stage (T2-T3 stage): After the fault current is completely transferred to the transfer branch 21, the fast mechanical switch 11 is turned off, thereby achieving voltage-free and arc-free disconnection.

[0066] Energy dissipation stage (T3-T4 stage): When the fast mechanical switch 11 is opened to its full position and sufficient insulation capacity is established, the transfer branch 21 is shut off. At this time, a transient overvoltage will be generated at both ends of it. If the overvoltage exceeds the reference voltage value of the lightning arrester in the energy dissipation branch 22, the current will be transferred to the lightning arrester and energy will be dissipated. When the line current drops to 0, the entire breaking process is completed.

[0067] It should be noted that the size of the serial numbers of the above-mentioned processes does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiment of this application.

[0068] For the specific definition of the control method of a multi-port DC circuit breaker topology structure, please refer to the above-mentioned definition of a multi-port DC circuit breaker topology structure, which will not be repeated here. A person of ordinary skill in the art will appreciate that the various modules and steps described in conjunction with the embodiments disclosed in this application can be implemented in hardware, software, or a combination of both. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of this application.

[0069] An embodiment of the present invention provides a control method for a multi-port DC circuit breaker topology structure. The control method includes real-time monitoring of voltage and current signals of a DC bus and each DC bus outlet port in a multi-port DC power grid system, and identifying a fault type and a faulty port of the multi-port DC power grid system based on the voltage and current signals; when the fault type is a DC short circuit fault at a port outlet, controlling a flow branch corresponding to the faulty port to be in an on state, and controlling both a flow-blocking branch and a grounding branch to be in an off state, so that the fault current flows through the flow branch of the faulty port; and in response to a tripping instruction, connecting a transfer branch of the flow-blocking branch. The load reversing switch in the fault port's flow branch is turned off, and the commutation voltage generated by the load reversing switch is used to force the fault current in the flow branch to be transferred to the transfer branch. After the fault current is completely transferred to the transfer branch, the fast mechanical switch in the flow branch is turned off to complete the voltage-free and arc-free disconnection. After the fast mechanical switch is fully opened, the transfer branch is turned off to trigger a transient overvoltage. When the voltage difference between the two ends of the energy-consuming branch reaches a preset overvoltage threshold, the energy-consuming branch is automatically turned on. The energy-consuming branch absorbs the line overvoltage energy, forcing the fault current to zero, completing the fault current interruption process and restoring power supply to the non-fault area. Compared with the existing technology, this method realizes a control method for reliably isolating the fault current and quickly restoring power supply to the non-fault area by collaboratively controlling the flow branch, the disconnecting branch, and the grounding branch, thereby improving the reliability and selective protection performance of the DC power grid while reducing equipment cost and operation and maintenance complexity.

[0070] In one embodiment, Figure 3 As shown, an embodiment of the present invention provides a method for determining parameters of a multi-port DC circuit breaker topology structure. Applying the multi-port DC circuit breaker topology structure as described above, the parameter determination method includes the following steps:

[0071] S21. Perform simulation analysis on different DC bus fault scenarios based on the actual topology of the multi-port DC grid system to determine the maximum fault current value of each DC bus output port under different fault scenarios.

[0072] S22. Determine the breaking capacity requirement of the interrupting branch based on the maximum fault current value, and determine the initial operating current value of each current-carrying branch according to the breaking capacity requirement of the interrupting branch.

[0073] S23. Select a target flow branch from all flow branches in sequence, traverse other non-target flow branch fault scenarios, and obtain fault current distribution data flowing through the target flow branch under each non-target flow branch fault scenario.

[0074] S24. Iteratively optimize the initial operating current value of the target flow branch according to the fault current distribution data, and screen out the minimum operating current value of each flow branch after multiple iterations, specifically including:

[0075] In each iterative optimization, if the operating current value of the current iteration is greater than the DC current flowing through the target flow branch under the current non-target flow branch fault scenario, the operating current value of the current iteration is updated to the DC current flowing through the target flow branch under the current non-target flow branch fault scenario, and the iterative optimization of the next non-target flow branch fault scenario is entered. The above process is repeated until all non-target flow branch fault scenarios are traversed and the minimum operating current value of the target flow branch is screened out; the initial operating current values ​​of all flow branches are iteratively optimized in turn, and the minimum operating current value of each flow branch is screened out after multiple iterations;

[0076] The minimum operating current value of each flow-through branch is compared with the maximum load current of the multi-port DC power grid system during normal operation. If the minimum operating current value is lower than the maximum load current, the current-limiting inductance value of the multi-port DC power grid system is gradually reduced, the difference between the fault current and the maximum load current is increased, and the minimum operating current value is iteratively optimized again until the minimum operating current values ​​of all flow-through branches are higher than the maximum load current of the multi-port DC power grid system during normal operation, thereby obtaining the optimized minimum operating current value of each flow-through branch.

[0077] S25. Output an operating current parameter set of the multi-port DC circuit breaker topology structure based on the minimum operating current value of all the current-carrying branches and the breaking capacity requirements of the current-breaking branches.

[0078] In a specific embodiment, after determining the basic topology of the multi-port DC circuit breaker, the basic parameters of the multi-port DC circuit breaker are designed according to the basic topology to ensure reliable operation of the equipment under various DC fault conditions. Since the design of the interrupting branch needs to meet the reliable interruption requirements of the system under various DC fault conditions, the present embodiment needs to systematically analyze and compare different types of DC fault currents. Specifically, the present embodiment simulates the DC short-circuit current level of the system at different fault locations through simulation technology, and records the DC short-circuit current level at each location. The maximum fault current value is used as the basis for determining the interrupting capacity of the interrupting branch. For ease of understanding, as shown in FIG. Figure 4 As shown, this embodiment provides a flowchart for determining the interrupting capacity of a typical four-terminal DC system. In terms of fault type selection, since DC bipolar faults have more severe fault characteristics than unipolar 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 under five typical fault scenarios as an example. The five typical fault scenarios include DC bus faults and faults at the outlets of each port. As the number of system ports increases, the number of fault scenarios that need to be considered will also increase accordingly. Through this systematic fault current analysis method, this embodiment can ensure that the interrupting branch has sufficient fault interrupting capacity while avoiding unnecessary over-design, thereby reducing equipment costs.

[0079] exist Figure 4 In this embodiment, the DC bipolar fault current at different locations is input, and the DC bipolar fault current at different locations includes 、 、 and ,in, Indicates the maximum fault current when a DC bipolar short circuit fault occurs at the outlet of port ①; Indicates the maximum fault current when a DC bipolar short circuit fault occurs at the output of port ②; Indicates the maximum fault current when a DC bipolar short circuit fault occurs at the output of port ③; Indicates the maximum fault current when a DC bipolar short circuit fault occurs at the output of port ④; Indicates the total fault current when a DC bipolar short circuit fault occurs on the DC bus. Its value is the arithmetic sum of the fault currents at 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 interrupting branch; n represents the index of the fault scenario. In this embodiment, the maximum value of n is 5. Those skilled in the art can set the maximum value of n according to specific implementation conditions and is not limited to this embodiment; Indicates the maximum fault current under the nth fault scenario. This embodiment obtains the maximum fault current value of each port outlet under five types of fault scenarios and the total fault current when a DC bipolar short circuit fault occurs on the DC bus through electromagnetic transient simulation, and uses this to determine the breaking capacity of the interrupting branch. Figure 4 In this embodiment, the breaking capacity requirement value of the interruption branch is initialized , n=2, then judge Is it true? If so, continue processing; otherwise, the process ends and then compares the breaking capacity requirement value I of the current interruption branch with the maximum fault current under the current fault scenario The size of , then update the breaking capacity requirement value of the interruption branch , and increase the value of n to make n=n+1. Repeat the above steps until all fault scenarios are traversed and the breaking capacity requirement value I of the interrupting branch is determined.

[0080] On the basis of determining the breaking capacity of the interrupting branch, this embodiment also needs to further optimize the protection constant setting strategy of each flow-through branch. A reasonable operating current threshold is crucial to ensuring the selective protection of the system. This embodiment sets the operating current threshold of each flow-through branch to be higher than the maximum load current and leaves 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 branch on the non-fault side will not malfunction under the action of the through fault current, while the branch on the fault side can reliably operate to isolate the fault.

[0081] The lower the protection setting value is, the faster the fault can be discovered and removed in time. In order to quickly discover the fault and remove it in time to 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 setting strategy for a multi-port DC circuit breaker. In this embodiment, 、 、 and Respectively represent the operating current values ​​of the through-current branch A, through-current branch B, through-current branch C and through-current branch D; 、 、 and Indicates the maximum fault current of each port under different fault locations, for example, Indicates the maximum fault current flowing through port ① when a DC bipolar short circuit fault occurs at the outlet of port ②; Indicates the maximum fault current flowing through port ② when a fault occurs at the outlet of port ①; Indicates 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. Similarly, in this embodiment, more parameters can be defined to describe the fault current distribution characteristics of each port at different fault locations; 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; represents 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 that the fault on the current branch has been eliminated (for example, when optimizing branch 2, the fault on port 2 has been eliminated).

[0082] like Figure 5 、 Figure 6 As shown, this embodiment takes a system with a current limiting inductance of 100mH as an example to illustrate the optimization process of the DC fault protection strategy. First, this embodiment inputs the initial action current value of each current branch 、 、 and , and input the current limiting inductance value of 100mH. At the same time, for each flow branch, the initialization action current value is the maximum fault current under a specific fault scenario. For example, this embodiment sets the action current of the flow branch to The initial value is Then, this embodiment traverses other fault scenarios and analyzes the fault scenarios of n=1~5 in turn (n=1~4 are port faults, n=5 is bus fault). This embodiment analyzes the DC current distribution characteristics under different fault locations (excluding the fault situation occurring in this branch) and compares the current operating current value with the maximum fault current under the fault scenario. If the current operating current value is If the DC current flowing through the flow branch port ① under fault scenario n is greater than the DC current flowing through the flow branch port ① under fault scenario n, the operating current Updated to this time The above steps are repeated until all fault scenarios are traversed. Through multiple iterative optimizations, this embodiment can screen out the minimum operating current value of the flow branch. This optimization process can not only effectively prevent the flow branch from malfunctioning when a DC fault occurs at other locations, but also ensure that when a DC fault occurs at this port, the flow branch can reliably isolate the fault.

[0083] After determining the minimum operating current of each flow 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 screened minimum operating current value is higher than the maximum load current of the system during normal operation, so as to prevent the protection device from malfunctioning due to current fluctuations during normal operation of the system, thereby affecting the stable operation of the system. During the verification process, if it is detected that the minimum operating current value of a flow branch is lower than the maximum load current of the system, corresponding optimization measures need to be taken. The specific method is to gradually reduce the current limiting inductance value of the system. By reducing the current limiting inductance value, the difference between the fault current and the maximum load current is increased, thereby improving the action of the protection device when a fault occurs. The optimization process not only ensures the reliability of the protection system and avoids false operation due to improper setting of the operating current, but also takes into account the stability of the system operation and prevents other potential problems caused by too small current-limiting inductance value, which provides a strong technical guarantee for the safe and stable operation of the DC system. After completing the optimization of the operating current of a current-limiting branch, the operating current values ​​of other current-limiting branches should be determined in turn according to the same method and steps to ensure that all current-limiting 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.

[0084] Compared with the traditional solution of using multiple dual-port DC circuit breakers, the multi-port DC circuit breaker architecture adopted in this embodiment significantly reduces equipment costs and enhances the economy of the system. At the same time, in response to the existing research practice of adding sub-modules to the interruption branch or designing more complex circuits to ensure unidirectional current flow through the transfer branch, this embodiment introduces a bidirectional interruption 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 achieves effective dissipation of fault energy through the synergistic effect of the grounding branch and the two bidirectional interruption branches. , and quickly isolate the faulty DC bus, further enhancing the reliability of the equipment. In terms of the protection setting strategy, this embodiment comprehensively considers the fault current characteristics under various DC fault scenarios. This strategy can effectively prevent the occurrence of protection misoperation during normal system operation. At the same time, under the influence of through-fault current, it can ensure the stable operation of the non-fault side branch and avoid misoperation, and can ensure that the fault side branch can respond and operate quickly and accurately when a fault occurs. This protection setting strategy significantly improves the operating 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.

[0085] It should be noted that the size of the serial numbers of the above-mentioned processes does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiment of this application.

[0086] For the specific definition of the parameter determination method of a multi-port DC circuit breaker topology structure, please refer to the above-mentioned definition of a multi-port DC circuit breaker topology structure, which will not be repeated here. A person of ordinary skill in the art will appreciate that the various modules and steps described in conjunction with the embodiments disclosed in this application can be implemented in hardware, software, or a combination of both. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of this application.

[0087] An embodiment of the present invention provides a parameter determination method for a multi-port DC circuit breaker topology structure. The parameter determination method includes simulating and analyzing different DC bus fault scenarios based on the actual topology structure of the multi-port DC power grid system to determine the maximum fault current value of each DC bus outlet port under different fault scenarios; determining the breaking capacity requirement of the interrupting branch based on the maximum fault current value, and determining the initial operating current value of each flow branch based on the breaking capacity requirement of the interrupting branch; selecting a target flow branch from all flow branches in sequence, traversing other non-target flow branch fault scenarios, and obtaining fault current distribution data flowing through the target flow branch under each non-target flow branch fault scenario; iteratively optimizing the initial operating current value of the target flow branch based on the fault current distribution data, and screening out the minimum operating current value of each flow branch after multiple iterations; and outputting an operating current parameter set for the multi-port DC circuit breaker topology structure based on the minimum operating current value of all flow branches and the breaking capacity requirement of the interrupting branch. Compared with existing technologies, this parameter determination method achieves precise configuration of circuit breaker parameters through precise simulation analysis and iterative optimization, ensuring that the circuit breaker can operate quickly and accurately and the system can operate stably under various fault scenarios, significantly improving the fault response capability and adaptability of multi-port DC circuit breakers.

[0088] The above-described embodiments merely represent several preferred implementations of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art could make several improvements and substitutions without departing from the technical principles of the present invention, and these improvements and substitutions should also be considered within the scope of protection of the present application. Therefore, the scope of protection of the present patent application shall be based on the scope of protection of the claims.

Claims

1. A method for determining parameters of a multi-port DC circuit breaker topology structure, characterized in that: The invention is applied to a multi-port DC circuit breaker topology structure. The multi-port DC circuit breaker topology structure is based on a hybrid DC circuit breaker architecture and includes: a flow branch, a current-blocking branch, and a grounding branch. The flow branch is connected between the DC bus and each DC bus outlet port, and the current-blocking branch is arranged in parallel with the flow branch. The flow branch includes a fast mechanical switch and a load reversing switch with variable impedance connected in series. The flow 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 to shut down the load current when a fault occurs in the multi-port DC grid system. The commutating switch generates a commutation voltage, forcing the fault current to quickly transfer from the flow branch to the disconnecting branch; the disconnecting branch includes a transfer branch and an energy-consuming branch connected in parallel; the disconnecting branch is configured to instantaneously turn on the transfer branch in the initial stage of a fault in the multi-port DC power grid system, receive the fault current transferred from the flow branch through the transfer branch, and automatically turn on the energy-consuming branch when the voltage difference across the energy-consuming branch reaches a preset overvoltage threshold. The energy-consuming branch absorbs line overvoltage energy to quickly cut off the fault current, and achieves voltage-free and arc-free disconnection by shutting off the fast mechanical switch of the flow branch, thereby completely isolating the fault current. The parameter determination method comprises the following steps: Based on the actual topology of the multi-port DC grid system, different DC bus fault scenarios are simulated and analyzed to determine the maximum fault current value of each DC bus output port under different fault scenarios; Determining a breaking capacity requirement of the interrupting branch based on the maximum fault current value, and determining an initial operating current value of each current-carrying branch according to the breaking capacity requirement of the interrupting branch; Selecting a target flow branch from all flow branches in sequence, traversing other non-target flow branch fault scenarios, and obtaining fault current distribution data flowing through the target flow branch under each non-target flow branch fault scenario; Iteratively optimizing the initial operating current value of the target flow-through branch according to the fault current distribution data, and screening out the minimum operating current value of each flow-through branch after multiple iterations; According to the minimum operating current value of all the current-carrying branches and the breaking capacity requirements of the current-breaking branches, the operating current parameter set of the multi-port DC circuit breaker topology is output.

2. The method for determining parameters of a multi-port DC circuit breaker topology structure according to claim 1, wherein: The step of iteratively optimizing the initial operating current value of the target flow branch according to the fault current distribution data and screening out the minimum operating current value of each flow 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 flow branch under the current non-target flow branch fault scenario, the operating current value of the current iteration is updated to the DC current flowing through the target flow branch under the current non-target flow branch fault scenario, and the iterative optimization of the next non-target flow branch fault scenario is started. The above process is repeated until all non-target flow branch fault scenarios are traversed and the minimum operating current value of the target flow branch is screened out; The initial operating current values ​​of all the flow branches are iteratively optimized in turn, and the minimum operating current value of each flow branch is screened out after multiple iterations.

3. The method for determining parameters of a multi-port DC circuit breaker topology structure according to claim 1, wherein: The parameter determination method further includes: The minimum operating current value of each flow-through branch is compared with the maximum load current of the multi-port DC power grid system during normal operation. If the minimum operating current value is lower than the maximum load current, the current-limiting inductance value of the multi-port DC power grid system is gradually reduced, the difference between the fault current and the maximum load current is increased, and the minimum operating current value is iteratively optimized again until the minimum operating current values ​​of all flow-through branches are higher than the maximum load current of the multi-port DC power grid system during normal operation, thereby obtaining the optimized minimum operating current value of each flow-through branch.

4. The method for determining parameters of a multi-port DC circuit breaker topology structure according to claim 1, wherein: The grounding branch is used to connect the grounding branch and the transfer branch when a ground fault occurs in the DC bus, forming a fault current discharge channel to conduct the fault current into the earth through the interrupting branch and the grounding branch, thereby isolating the faulty DC bus. At the same time, it cooperates with the energy consumption device configured on the power supply side of the multi-port DC power grid system to absorb residual energy and suppress voltage fluctuations in non-fault areas.

5. The method for determining parameters of a multi-port DC circuit breaker topology structure according to claim 1, wherein: The fast mechanical switch is used to provide a low-impedance conduction path for the load current together with the load reversing switch when the multi-port DC power grid system is operating normally; Furthermore, when a fault occurs in the multi-port DC grid system, the fault current in the through-current branch is quickly transferred, and after the fault current transfer is completed, a no-voltage and no-arc breaking action is performed to isolate the through-current branch from the fault point.

6. The method for determining parameters of a multi-port DC circuit breaker topology structure according to claim 1, wherein: The transfer branch adopts a bidirectional conduction topology structure to control the bidirectional conduction of the fault current in the multi-port DC power grid. The bidirectional conduction topology structure is composed of fully controlled devices, half controlled devices or diode devices in a symmetrical parallel manner.

7. The method for determining parameters of a multi-port DC circuit breaker topology structure 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 be turned on when a ground fault occurs in the DC bus, forming a low-impedance discharge path for the fault current to the ground.

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