DC Circuit Breaker and Its Control Method

Abstract

The present invention relates to the field of power electronics technology, and specifically to a DC circuit breaker and a control method thereof, wherein the DC circuit breaker includes at least one current-carrying branch, one end of which is connected to a DC busbar; a disconnecting unit, including a first disconnecting branch and second disconnecting branches corresponding to each current-carrying branch, the first disconnecting branch and the second disconnecting branch having the same structure, one end of the first disconnecting branch being connected to the DC busbar, the other end of the first disconnecting branch being connected to one end of each second disconnecting branch, and the other end of the second disconnecting branch being connected to the other end of the corresponding current-carrying branch; wherein the first disconnecting branch is used to carry and disconnect short-circuit current, and the second disconnecting branch is used to carry and disconnect short-circuit current and to isolate the lines after disconnection. Within a short period of time after the current is disconnected, full voltage isolation between the faulty line and the normal line is achieved through the disconnecting branches belonging to one-half of the faulty line and the disconnecting branches belonging to the other half of the normal lines.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronics, and in particular to a DC circuit breaker and a control method thereof. Background Art

[0002] Today, DC transmission and distribution technology has become an effective means of large-scale transmission and consumption of renewable energy such as wind and solar power, and high-voltage DC circuit breakers are key equipment for the development of DC transmission and distribution towards a more economical and flexible network.

[0003] The development of high-voltage, high-capacity DC power grids, coupled with an increasing number of circuit breakers and demand for higher interrupting capacity, has placed higher demands on the technical and economic performance of high-voltage DC circuit breakers. Mechanical DC circuit breakers offer high interrupting capacity and are economical, but their difficulty interrupting low currents and the significant increase in energy storage device costs associated with the requirement for multiple reclosing operations restrict increases in interrupting capacity. The interrupting capacity of hybrid circuit breakers is limited by the inherent current-interrupting capability of fully controlled devices. Furthermore, the large number of fully controlled devices used contributes to the high cost of circuit breakers. Summary of the Invention

[0004] In view of this, an embodiment of the present invention provides a DC circuit breaker and a control method thereof to solve the problem of low breaking capacity of the DC circuit breaker due to economic limitations.

[0005] According to a first aspect, an embodiment of the present invention provides a DC circuit breaker, comprising:

[0006] at least one through-current branch, one end of which is connected to the DC bus;

[0007] a disconnecting unit comprising a first disconnecting branch and a second disconnecting branch corresponding to each of the through-current branches, wherein the first disconnecting branch and the second disconnecting branch have the same structure, one end of the first disconnecting branch is connected to the DC bus, the other end of the first disconnecting branch is connected to one end of each of the second disconnecting branches, and the other end of the second disconnecting branch is connected to the other end of the corresponding through-current branch;

[0008] The first breaking branch is used for carrying and breaking the short-circuit current, and the second breaking branch is used for carrying and breaking the short-circuit current and isolating the lines after breaking.

[0009] The DC circuit breaker provided in the embodiment of the present invention adopts a half current blocking unit, that is, the first breaking branch and the second breaking branch with the same structure, which are used for current blocking and voltage isolation respectively. The concept of half is relative to the breaking branch of the full voltage level. Specifically, by adopting a half full voltage breaking branch in the breaking branch of the common part and the part where the common part is connected to each current branch, the common part and the independent half breaking branches belonging to the fault line can be used to form a full voltage breaking unit during the fault breaking process to complete the full voltage current breaking. In a short time after the current is broken, the half breaking branch belonging to the fault line and the half breaking branch belonging to each normal line are used to achieve full voltage isolation between the fault line and the normal line. Based on this, the breaking branch in the DC circuit breaker is only 1 / 2 of the main circuit breaker of a single hybrid circuit breaker. In the application scenario of multiple DC outgoing lines, the economic advantage is significantly better than that of a single hybrid circuit breaker.

[0010] Optionally, the first disconnecting branch includes:

[0011] At least one power electronic switch unit, each of the power electronic switch units being cascaded;

[0012] An energy consumption branch is connected in parallel with the at least one power electronic switch unit, and the energy consumption branch is used for overvoltage protection and energy absorption.

[0013] Optionally, the breaking unit further includes a current limiting module connected in series with the first breaking branch, and the current limiting module is used to limit the rising rate of the short-circuit current.

[0014] Optionally, the current limiting module includes:

[0015] Current limiting element;

[0016] A short-circuit switch is connected in parallel with the current-limiting element, wherein the current-limiting element includes at least one of a resistor, a capacitor, or an inductor, and the short-circuit switch includes a first mechanical switch or a power electronic switch.

[0017] Optionally, the DC circuit breaker further includes:

[0018] A power flow controller is used to determine the direction of the line short-circuit current corresponding to each current-carrying branch to adjust the output voltage, and to assist the short-circuit current in transferring to the first disconnecting branch.

[0019] Optionally, the power flow controllers are arranged in a one-to-one correspondence with the flow branches.

[0020] Optionally, the power flow controller is a DC power flow controller, the input source of the DC power flow controller is a modular multi-level sub-module of a converter station, and the DC power flow controller includes multiple full-bridge sub-modules connected in series, and the full-bridge sub-modules connected in series are connected in parallel with the modular multi-level sub-module of the converter station.

[0021] The DC circuit breaker provided in the embodiment of the present invention adopts a power flow controller with a high-voltage MMC submodule of a converter station as an input source. The main circuit can adopt a DC series connection mode of full-bridge submodules, which reduces the number of submodules while eliminating the AC input part and the ground isolation part, and has better economy.

[0022] Optionally, each of the flow branches further includes a second mechanical switch connected in series with the power flow controller.

[0023] According to a second aspect, an embodiment of the present invention further provides a control method for a DC circuit breaker, which is used in the DC circuit breaker described in any of the above embodiments. The control method includes:

[0024] Obtaining the operating status of the DC circuit breaker;

[0025] Based on the working state, the disconnection state of the disconnection unit and the corresponding through-current branch are adjusted.

[0026] The control method for a DC circuit breaker provided in an embodiment of the present invention monitors the operating status of the DC circuit breaker and controls the disconnection status of the disconnecting unit and the current-carrying branch accordingly based on the monitoring results. This method can achieve rapid transfer, current limiting, and disconnection of short-circuit current, and the disconnection current can reach tens of kA.

[0027] Optionally, adjusting the disconnection state of the disconnecting unit and the corresponding flow branch based on the working state includes:

[0028] Before the DC circuit breaker is put into operation, turning on the breaking unit to allow current to flow through the breaking unit;

[0029] When the closing determination condition is met, the at least one flow branch is turned on, so that current flows through the at least one flow branch;

[0030] The disconnect unit is locked.

[0031] Optionally, when a fault occurs in a line where a preset flow branch is located, adjusting the disconnection state of the disconnecting unit and the corresponding flow branch based on the working state includes:

[0032] Conducting the first disconnecting branch and the second disconnecting branch corresponding to the preset flow branch;

[0033] The power flow controller corresponding to the preset flow branch determines the direction of the short-circuit current and controls the power flow controller to output a voltage in a corresponding direction to force the current to transfer to the breaking unit;

[0034] When the current of the preset flow branch passes through zero, disconnecting the second mechanical switch corresponding to the preset flow branch;

[0035] blocking the first disconnecting branch and the second disconnecting branch corresponding to the preset flow branch, so that the current is transferred to the energy-consuming branch in the first disconnecting branch and the second disconnecting branch corresponding to the preset flow branch;

[0036] When the voltage of the first disconnecting branch and the energy-consuming branch in the second disconnecting branch corresponding to the preset current-passing branch is higher than the system DC voltage, the disconnecting unit completes current interruption.

[0037] The control method for a DC circuit breaker provided in an embodiment of the present invention can independently interrupt the short-circuit current of each line by using the second interrupting branch corresponding to each current-carrying branch, and has the ability to simultaneously interrupt multiple outgoing line short-circuit faults and clear DC bus faults.

[0038] Optionally, when a fault occurs in the DC bus, adjusting the disconnection state of the disconnecting unit and the corresponding current branch based on the working state includes:

[0039] Conducting the first disconnecting branch and the second disconnecting branch;

[0040] The power flow controller corresponding to each of the current-carrying branches determines the direction of the short-circuit current and locks the full-bridge submodule in the power flow controller to force the current to transfer to the breaking unit;

[0041] When the current of the through-current branch passes through zero, disconnecting the through-current branch;

[0042] Locking the first disconnecting branch and each of the second disconnecting branches so that the current is transferred to the first disconnecting branch and the energy-consuming branch in the second disconnecting branch corresponding to each of the current-passing branches;

[0043] When the voltage of the energy-consuming branch in the first disconnecting branch and the second disconnecting branch corresponding to each of the current-passing branches is higher than the system DC voltage, the disconnecting unit completes current interruption. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0045] Figure 1 is a structural schematic diagram of a DC circuit breaker according to an embodiment of the present invention;

[0046] Figure 2a-2d is a structural schematic diagram of a power electronic switch unit according to an embodiment of the present invention;

[0047] Figure 3 is a structural diagram of a first disconnecting branch according to an embodiment of the present invention;

[0048] Figure 4a-4c is a structural diagram of a current limiting module according to an embodiment of the present invention;

[0049] Figure 5 is a structural schematic diagram of a DC circuit breaker according to an embodiment of the present invention;

[0050] Figure 6a-6b is a schematic structural diagram of a power flow controller according to an embodiment of the present invention;

[0051] Figure 6c is a schematic structural diagram of a submodule of a power flow controller according to an embodiment of the present invention;

[0052] Figure 7 is a structural schematic diagram of a DC circuit breaker according to an embodiment of the present invention;

[0053] Figure 8 is a flow chart of a control method of a DC circuit breaker according to an embodiment of the present invention;

[0054] Figure 9a-9b This is a schematic diagram of a process of putting a DC circuit breaker into operation according to an embodiment of the present invention;

[0055] Figure 10a-Figure 10e is a schematic diagram of a switching process of a DC circuit breaker when a line fault occurs according to an embodiment of the present invention;

[0056] Figure 11a-Figure 11e 1 is a schematic diagram of a switching process of a DC circuit breaker when a DC bus fault occurs according to an embodiment of the present invention. DETAILED DESCRIPTION

[0057] To make the purpose, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative efforts shall fall within the scope of protection of the present invention.

[0058] The embodiment of the present invention provides a DC circuit breaker, such as Figure 1 As shown, the DC circuit breaker includes at least one through-current branch and a breaking unit. The through-current branch is used to conduct the load current when the DC system is operating normally. The number of through-current branches can be set accordingly according to actual conditions, and can be 2, 3, or 4, etc. There is no restriction on the specific number. Figure 1 N current-carrying branches are shown in the figure, where current-carrying branch 1 is connected to DC line 1, current-carrying branch 2 is connected to DC line 2, ..., and current-carrying branch N is connected to DC line N.

[0059] like Figure 1 As shown, the disconnect unit comprises two identical disconnect branches: a first disconnect branch and a second disconnect branch. The first disconnect branch is provided on a common disconnect branch for each DC line. Specifically, one end of the first disconnect branch is connected to the DC busbar, and the other end is connected to one end of each second disconnect branch. The other end of the second disconnect branch is connected to the other end of the corresponding current-carrying branch. The first disconnect branch is used to carry and interrupt short-circuit current, while the second disconnect branch is used to carry and interrupt short-circuit current and isolate the lines after interruption.

[0060] For ease of description below, the first disconnecting branch located on the common disconnecting branch is referred to as disconnecting branch 0, and the second disconnecting branches corresponding to the respective flow-through branches are referred to as disconnecting branches 1 through N, respectively. Because disconnecting branch 0 is located on the common disconnecting branch, it can also be referred to as the main circuit breaker. Accordingly, disconnecting branch 0 is represented as MB0, and disconnecting branches 1 through N are represented as MB1 through MBN.

[0061] Specifically, in addition to the main circuit breaker, the full voltage level breaking branch also includes upper auxiliary breaking branches and lower auxiliary breaking branches corresponding to each current-carrying branch. The main circuit breaker uses M power electronic switch units in cascade.

[0062] However, in this embodiment, the main circuit breaker of the full-voltage level breaking branch is split into a first breaking branch and a second breaking branch, so that half the power electronic switch unit of the full-voltage breaking branch can be used to ensure the same breaking capacity.

[0063] The DC circuit breaker provided in this embodiment adopts a half current blocking unit, that is, the first breaking branch and the second breaking branch with the same structure, which are used for current blocking and voltage isolation respectively. The concept of half is relative to the breaking branch of the full voltage level. Specifically, by adopting a half full voltage breaking branch in the breaking branch of the common part and the part where the common part is connected to each current branch, the full voltage breaking unit can be formed by the common part and the independent half breaking branches belonging to the fault line during the fault breaking process to complete the full voltage current breaking. In a short time after the current is broken, the full voltage isolation between the fault line and the normal line is achieved through the half breaking branch belonging to the fault line and the half breaking branch belonging to each normal line. Based on this, the breaking branch in the DC circuit breaker is only 1 / 2 of the main circuit breaker of a single hybrid circuit breaker. In the application scenario of multiple DC outgoing lines, the economic advantage is significantly better than that of a single hybrid circuit breaker.

[0064] The structure of the first disconnecting branch is the same as that of the second disconnecting branch. In the following description, the structure of the first disconnecting branch is described in detail by taking the first disconnecting branch as an example. In some optional implementations of this embodiment, the first disconnecting branch includes at least one power electronic switch unit and an energy consumption branch. At least one power electronic switch unit is cascaded, and the energy consumption branch is connected in parallel to at least one cascaded power electronic switch unit, and the energy consumption branch is used for overvoltage protection and energy absorption. Optionally, the power electronic switch unit can be composed of fully controlled devices such as IGBT, IGCT, BIGT, and IEGT.

[0065] Figure 2a-2d Four types of power electronic switch units are shown. In the actual application of DC circuit breakers, one of them can be selected and cascaded according to actual needs to form a power electronic switch unit. Optionally, the energy consumption branch can be formed using a nonlinear resistance unit. Figure 3 An optional structure of the first disconnect branch is shown, wherein the power electronic switch unit adopts Figure 2d In the structure, the energy dissipation branch is composed of nonlinear resistor MOV.

[0066] In some optional implementations of this embodiment, the breaking unit further includes a current limiting module connected in series with the first breaking branch, and the current limiting module is used to limit the rising rate of the short-circuit current. Figure 5 As shown, one end of the current limiting module CL is connected to the DC bus, and the other end is connected to the disconnect branch 0.

[0067] The current limiting module can be formed by using a current limiting element, or by using a current limiting element and a short-circuit switch. The current limiting element can be a resistor, a capacitor or an inductor, and the short-circuit switch can be a power electronic switch or a first mechanical switch. Specifically, the current limiting module can be formed by connecting a current limiting element and a short-circuit switch in parallel. For example, Figure 4a-4c Schematic diagrams of three structures of current limiting modules are shown, such as Figure 4a As shown, the current limiting module is composed of a power electronic switch T and an inductor L in parallel; Figure 4b As shown, the current limiting module is composed of a nonlinear capacitor C; Figure 4c As shown, the current limiting module is composed of a power electronic switch T and a resistor R in parallel. It should be noted that Figure 4a-4c These are merely some optional implementations, but the protection scope of the present invention is not limited thereto.

[0068] In some alternative implementations of this embodiment, the DC circuit breaker further includes a power flow controller (PFC). The power flow controller determines the direction of the short-circuit current in each of the conducting branches to adjust the output voltage and assist in diverting the short-circuit current to the first disconnecting branch. The power flow controllers are provided in a one-to-one correspondence with the conducting branches.

[0069] Optionally, the power flow controller can be a DC power flow controller, whose input source is derived from the converter station's high-voltage modular level submodules, namely, the converter station high-voltage MMC. Furthermore, the main circuit of the DC power flow control utilizes multiple full-bridge submodules connected in series, which are connected in parallel with the converter station high-voltage MMC. Power flow controllers using high-voltage MMC submodules as input sources can utilize a DC series connection of full-bridge submodules in their main circuit. This reduces the number of submodules while eliminating the AC input and ground isolation components, resulting in improved economic efficiency. Optionally, the power flow controller can also include a mechanical switch K to isolate the main circuit of the power flow controller from the input source.

[0070] For example, Figure 6a An optional implementation of the power flow controller is shown. Figure 6a The lower middle part shows the overall structure of the power flow controller, and the upper part shows the further detailed structure. Figure 6a As shown, the input source of the power flow converter comes from the high-voltage MMC submodule of the converter station. The high-voltage MMC can be formed by connecting multiple MMC submodules in series. The two ends of the power flow controller are respectively connected to each flow branch.

[0071] The main circuit of the power flow controller is composed of multiple full-bridge sub-modules SM connected in series, such as Figure 6a As shown in the figure, N full-bridge submodules are connected in series to form the main part of the power flow controller, namely SM1-SM N . Further, Figure 6c An optional implementation of the full-bridge submodule is shown.

[0072] In some other optional implementations of this embodiment, the power flow controller can also be used as follows Figure 6b The structure shown. This power flow controller is placed on a high-potential platform, isolated from ground potential. One end of the power flow controller is connected to the AC system via a transformer, while the other end consists of a modular multilevel converter (MMC). Its DC output terminals are connected to the DC line. The basic unit block of the MMC is a full-bridge submodule. During stable operation of the DC circuit breaker, the power flow controller can control the voltage output by the MMC in the line, thereby regulating the power flow of the line. During the DC circuit breaker interruption process, the power flow controller can adjust the output voltage by determining the direction of the short-circuit current, thereby diverting the auxiliary current to the interrupted branch.

[0073] As an optional implementation of this embodiment, each flow branch further includes a second mechanical switch UFD connected in series with the power flow controller. That is, the power flow branch includes the power flow controller and the second mechanical switch UFD connected in series.

[0074] Figure 7 An optional embodiment of a DC circuit breaker is shown, which includes two flow branches, each flow branch includes a flow controller and a second mechanical switch connected in series, and the second breaking branch and the first breaking branch corresponding to each flow branch are both Figure 3 The structure only uses one power electronic switch unit, wherein the first disconnecting branch is further connected in series with a current limiting module, which is implemented using a nonlinear capacitor.

[0075] The multi-port DC circuit breaker with flow control and current limiting proposed in the embodiment of the present invention can realize bidirectional DC flow control, bidirectional and rapid transfer, current limiting and interruption of DC current, and the interruption current can reach tens of kA, meeting the application requirements of DC transmission and distribution network system. Furthermore, it has a multi-port interruption function, which can independently interrupt the short-circuit current of each line, and at the same time has the ability to simultaneously interrupt multiple outgoing line short-circuit faults and clear DC bus faults. The interruption branch in the DC circuit breaker is only 1 / 2 of the main circuit breaker of a single hybrid circuit breaker, which has high economy. The proposed shared main circuit breaker method saves more than 20% of the number of fully controlled devices used in the single hybrid circuit breaker solution; the current limiting function reduces the expected interruption current peak by up to 15%, and the overall cost is at least 30% lower than the solution of using an independent single hybrid DC circuit breaker.

[0076] The embodiment of the present invention further provides a control method for a DC circuit breaker, wherein the specific structure of the DC circuit breaker is described above and will not be described again here. Figure 8As shown, the control method includes:

[0077] S11, obtaining the working status of the DC circuit breaker.

[0078] The operating status of a DC circuit breaker includes whether the breaker is in operation, interrupted by a line-side short-circuit fault, and interrupted by a DC bus-side short-circuit fault. The operating status of the DC circuit breaker can be determined by monitoring it. The specific monitoring method is not limited here; it only needs to ensure that the DC circuit breaker can detect its current operating status.

[0079] S12, adjusting the disconnection state of the disconnection unit and the corresponding flow branch based on the working state.

[0080] After determining its operating state, the DC circuit breaker adjusts the interruption state of the disconnecting unit and the corresponding current-carrying branch circuit based on the different operating states. For example, when the DC circuit breaker is put into operation, the main disconnecting unit can be turned on first, and then the current-carrying branch circuit can be put into use when the closing time is reached. When the line side is short-circuited, the disconnecting unit is activated to disconnect the short-circuited line side from the DC system. When the DC bus side is short-circuited, the disconnecting unit is activated to disconnect the short-circuited bus line side from the DC system.

[0081] The control method for a DC circuit breaker provided in this embodiment monitors the operating status of the DC circuit breaker and controls the interruption status of the interrupting unit and the current-carrying branch accordingly based on the monitoring results. This method can achieve rapid transfer, current limiting, and interruption of short-circuit current, and the interruption current can reach tens of kA.

[0082] When the DC circuit breaker is put into operation, the above S12 may include the following steps:

[0083] (1) Before the DC circuit breaker is put into operation, the breaking unit is turned on to allow current to flow through the breaking unit.

[0084] (2) When the closing determination condition is met, at least one of the current branches is turned on so that current flows through the at least one current branch.

[0085] (3) Locking and disconnecting unit.

[0086] by Figure 7 Taking the structure of the DC circuit breaker shown in the figure as an example, before the DC circuit breaker is put into operation, the main circuit breakers MB0, MB1 and MB2 are turned on, and the current flows through the broken branches, as shown in FIG. Figure 9a As shown in the figure, after the closing judgment condition is met, the mechanical switches UFD1 and UFD2 of the flow branch are closed, and the power flow controller PFC maintains zero voltage output. After UFD1 and UFD2 are turned on, the load current flows through the flow branch, as shown in the figure. Figure 9b As shown, MB remains locked and the circuit breaker is put into operation.

[0087] When a fault occurs in the line where the preset flow branch is located, the above S12 may include the following steps:

[0088] (1) The first disconnecting branch and the second disconnecting branch corresponding to the preset flow branch are turned on.

[0089] (2) The current flow controller corresponding to the preset flow branch determines the direction of the short-circuit current and controls the current flow controller to output the corresponding direction voltage to force the current to transfer to the breaking unit.

[0090] (3) When the current of the preset flow branch passes through zero, the second mechanical switch corresponding to the preset flow branch is disconnected.

[0091] (4) Locking the first disconnecting branch and the second disconnecting branch corresponding to the preset flow branch, so that the current is transferred to the energy-consuming branch in the first disconnecting branch and the second disconnecting branch corresponding to the preset flow branch.

[0092] (5) When the voltage of the first disconnecting branch and the energy-consuming branch in the second disconnecting branch corresponding to the preset current-passing branch is higher than the system DC voltage, the disconnecting unit completes the current interruption.

[0093] by Figure 7 The structure of the DC circuit breaker shown in the figure takes a short-circuit fault in line 1 corresponding to the flow branch as an example. When the DC circuit breaker receives a trip command or overcurrent protection is activated, it turns on the disconnect branch MB and the auxiliary switch, and the thyristor valve T remains closed. The power flow controller PFC1 in the flow branch 1 determines the direction of the flow current, opens and closes the submodule, and outputs a voltage in the flow branch that matches the direction of the short-circuit current, forcing the current to flow to the disconnect branch, as shown in Figure 1. Figure 10a shown.

[0094] After the current in the through-flow branch 1 passes through zero, the current maintains flowing in the disconnected branch, and the UFD1 in the through-flow branch 1 is opened until the UFD1 reaches the withstand voltage opening distance. During this process, the nonlinear capacitor voltage rises nonlinearly, reducing the rising rate of the short-circuit current, such as Figure 10b shown.

[0095] After UFD1 reaches the withstand voltage opening distance, the main circuit breaker MB and the auxiliary switch are locked, and the current charges the capacitor in the full-bridge module, such as Figure 10c As shown, the voltage rises until the parallel MOV is actuated, and the current is transferred to the MOV and flows as shown in Figure 10d shown.

[0096] The MOV voltage is higher than the system DC voltage, the short-circuit current continues to drop to zero, the circuit breaker completes the current interruption, the current branch UFD1 and the interruption branch MB isolate the fault line, such as Figure 10e shown.

[0097] After the circuit breaker is opened, it can be quickly reclosed according to the needs of the power grid system. The reclosing operation process is similar to the closing process.

[0098] When a fault occurs in the DC bus, the above S12 may include the following steps:

[0099] (1) The first disconnecting branch and the second disconnecting branch are turned on.

[0100] (2) The power flow controller corresponding to each flow branch determines the direction of the short-circuit current and locks the full-bridge submodule in the power flow controller to force the current to transfer to the breaking unit.

[0101] (3) When the current in the flow branch passes through zero, the flow branch is disconnected.

[0102] (4) Locking the first disconnecting branch and each second disconnecting branch so that the current is transferred to the energy-consuming branch in the first disconnecting branch and each second disconnecting branch corresponding to the current-carrying branch.

[0103] (5) When the voltage of the energy-consuming branch in the first disconnecting branch and the second disconnecting branch corresponding to each current-passing branch is higher than the system DC voltage, the disconnecting unit completes current interruption.

[0104] by Figure 7 The structure of the DC circuit breaker is shown in the figure. The breaking principle of the DC circuit breaker when a fault occurs on the power supply side is the same as that of the line side fault. The breaking process is as follows: Figure 11a-Figure 11e shown.

[0105] Although the embodiments of the present invention have been described with reference to the accompanying drawings, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the present invention. Such modifications and variations are all within the scope defined by the appended claims.

Claims

1. A DC circuit breaker, characterized in that: include: at least one through-current branch, one end of which is connected to the DC bus; a disconnecting unit comprising a first disconnecting branch and a second disconnecting branch corresponding to each of the through-current branches, wherein the first disconnecting branch and the second disconnecting branch have the same structure, one end of the first disconnecting branch is connected to the DC bus, the other end of the first disconnecting branch is connected to one end of each of the second disconnecting branches, and the other end of the second disconnecting branch is connected to the other end of the corresponding through-current branch; The first breaking branch is used to carry and break the short-circuit current, and the second breaking branch is used to carry and break the short-circuit current and isolate the lines after breaking; The first disconnecting branch includes: At least one power electronic switch unit, each of the power electronic switch units being cascaded; An energy consumption branch is connected in parallel with the at least one power electronic switch unit. The energy consumption branch is used for overvoltage protection and energy absorption. The energy consumption branch is composed of a nonlinear resistance unit.

2. The DC circuit breaker according to claim 1, characterized in that: The breaking unit further includes a current limiting module connected in series with the first breaking branch, and the current limiting module is used to limit the rising rate of the short-circuit current.

3. The DC circuit breaker according to claim 2, characterized in that: The current limiting module includes: Current limiting element; A short-circuit switch is connected in parallel with the current-limiting element, wherein the current-limiting element includes at least one of a resistor, a capacitor, or an inductor, and the short-circuit switch includes a first mechanical switch or a power electronic switch.

4. The DC circuit breaker according to claim 1, characterized in that: The DC circuit breaker further includes: A power flow controller is used to determine the direction of the line short-circuit current corresponding to each current-carrying branch to adjust the output voltage, and to assist the short-circuit current in transferring to the first disconnecting branch.

5. The DC circuit breaker according to claim 4, characterized in that: The flow controllers are arranged in a one-to-one correspondence with the flow branches.

6. The DC circuit breaker according to claim 5, characterized in that: The power flow controller is a DC power flow controller, the input source of which is a modular multi-level sub-module of a converter station. The DC power flow controller includes a plurality of full-bridge sub-modules connected in series, and the full-bridge sub-modules connected in series are connected in parallel with the modular multi-level sub-module of the converter station.

7. The DC circuit breaker according to claim 5, characterized in that: Each of the flow branches further includes a second mechanical switch connected in series with the power flow controller.

8. A control method for a DC circuit breaker, characterized in that: In the DC circuit breaker according to any one of claims 1 to 7, the control method comprises: Obtaining the operating status of the DC circuit breaker; Based on the working state, the disconnection state of the disconnection unit and the corresponding through-current branch are adjusted.

9. The control method according to claim 8, characterized in that: The adjusting the disconnection state of the disconnecting unit and the corresponding flow branch based on the working state includes: Before the DC circuit breaker is put into operation, turning on the breaking unit to allow current to flow through the breaking unit; When the closing determination condition is met, the at least one flow branch is turned on, so that current flows through the at least one flow branch; The disconnect unit is locked.

10. The control method according to claim 8, characterized in that: When a fault occurs in a line where a preset flow branch is located, adjusting the disconnection state of the disconnecting unit and the corresponding flow branch based on the working state includes: Conducting the first disconnecting branch and the second disconnecting branch corresponding to the preset flow branch; The power flow controller corresponding to the preset flow branch determines the direction of the short-circuit current and controls the power flow controller to output a voltage in a corresponding direction to force the current to transfer to the breaking unit; When the current of the preset flow branch passes through zero, disconnecting the second mechanical switch corresponding to the preset flow branch; blocking the first disconnecting branch and the second disconnecting branch corresponding to the preset flow branch, so that the current is transferred to the energy-consuming branch in the first disconnecting branch and the second disconnecting branch corresponding to the preset flow branch; When the voltage of the first disconnecting branch and the energy-consuming branch in the second disconnecting branch corresponding to the preset current-passing branch is higher than the system DC voltage, the disconnecting unit completes current interruption.

11. The control method according to claim 8, characterized in that: When a fault occurs in the DC bus, adjusting the disconnection state of the disconnecting unit and the corresponding current branch based on the working state includes: Conducting the first disconnecting branch and the second disconnecting branch; The power flow controller corresponding to each of the current-carrying branches determines the direction of the short-circuit current and locks the full-bridge submodule in the power flow controller to force the current to transfer to the breaking unit; When the current of the through-current branch passes through zero, disconnecting the through-current branch; Locking the first disconnecting branch and each of the second disconnecting branches so that the current is transferred to the first disconnecting branch and the energy-consuming branch in the second disconnecting branch corresponding to each of the current-passing branches; When the voltage of the energy-consuming branch in the first disconnecting branch and the second disconnecting branch corresponding to each of the current-passing branches is higher than the system DC voltage, the disconnecting unit completes current interruption.

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