CN112865039A - Direct current circuit breaker and control method thereof - Google Patents

Abstract

The invention relates to the technical field of power electronics, in particular to a direct current breaker and a control method thereof, wherein the direct current breaker comprises at least one through-current branch, and one end of the through-current branch is connected with a direct current bus; the breaking unit comprises a first breaking branch and second breaking branches corresponding to the through-flow branches, the first breaking branch and the second breaking branches have the same structure, one end of the first breaking branch is connected with the direct-current bus, the other end of the first breaking branch is connected with one end of each second breaking branch, and the other end of each second breaking branch is connected with the other end of the corresponding through-flow branch; the first cut-off branch circuit is used for bearing and cutting off short-circuit current, and the second cut-off branch circuit is used for bearing and cutting off the short-circuit current and isolating the cut-off lines. And in a short time after the current is cut off, full voltage isolation between the fault line and the normal line is realized through the half cut-off branch to which the fault line belongs and the half cut-off branch to which each normal line belongs.

Description

Direct current circuit breaker and control method thereof

Technical Field

The invention relates to the technical field of power electronics, in particular to a direct current breaker and a control method thereof.

Background

Nowadays, a direct current power transmission and distribution technology becomes an effective means for large-scale delivery and consumption of renewable energy sources such as wind, light and the like, and a high-voltage direct current breaker is a key device for developing the direct current power transmission and distribution to more economical and flexible networking.

With the development of high-voltage large-capacity direct-current power grids, the use number of the circuit breakers is increased, and the requirement for the breaking capacity of the circuit breakers is increased, so that the power grids have higher requirements for the technology and the economy of the high-voltage direct-current circuit breakers. The mechanical direct current circuit breaker is strong in breaking capacity and high in economical efficiency, but the small current breaking difficulty and the cost of the energy storage device caused by multiple reclosing requirements are greatly increased, and the improvement of the breaking capacity is restricted. The breaking capacity of the hybrid circuit breaker is limited by the inherent current-cutting capacity of the full-control device, and the adoption of a large number of full-control devices causes the circuit breaker to be high in cost.

Disclosure of Invention

In view of this, embodiments of the present invention provide a dc circuit breaker and a control method thereof, so as to solve the problem of low breaking capability of the dc circuit breaker due to economic limitation.

According to a first aspect, an embodiment of the present invention provides a dc circuit breaker, including:

one end of the through-flow branch is connected with the direct-current bus;

the breaking unit comprises a first breaking branch and second breaking branches corresponding to the through-flow branches, the first breaking branch and the second breaking branches have the same structure, one end of the first breaking branch is connected with the direct-current bus, the other end of the first breaking branch is connected with one end of each second breaking branch, and the other end of each second breaking branch is connected with the other end of the corresponding through-flow branch;

the first cut-off branch circuit is used for bearing and cutting off short-circuit current, and the second cut-off branch circuit is used for bearing and cutting off the short-circuit current and isolating the cut-off lines.

The direct current circuit breaker provided by the embodiment of the invention adopts a half current blocking unit, namely the first breaking branch and the second breaking branch which have the same structure are respectively used for current blocking and voltage isolation, the half concept is relative to the breaking branch of a full voltage grade, specifically, the breaking branch of a shared part and the part of the shared part connected with each current branch adopt half full voltage breaking branches, and the full voltage breaking unit can be jointly formed by the shared part and each half breaking branch which is independent to a fault line in the fault breaking process, so that the full voltage current breaking is completed. And in a short time after the current is cut off, full voltage isolation between the fault line and the normal line is realized through the half cut-off branch to which the fault line belongs and the half cut-off branch to which each normal line belongs. Based on this, the breaking branch in the direct current breaker is only 1/2 of a single hybrid breaker main breaker, and in an application scene of multiple direct current outgoing lines, the economic advantage of the direct current breaker is more remarkable than that of the single hybrid breaker.

Optionally, the first breaking branch comprises:

at least one power electronic switching unit, each of the power electronic switching units being cascaded;

and the energy consumption branch circuit is connected with the at least one power electronic switching unit in parallel and is used for overvoltage protection and energy absorption.

Optionally, the switching unit further includes a current limiting module connected in series with the first switching branch, and the current limiting module is configured to limit a rising rate of the short-circuit current.

Optionally, the current limiting module comprises:

a current limiting element;

a short circuit switch in parallel with the current limiting element, wherein the current limiting element comprises at least one of a resistor, a capacitor, or an inductor, and the short circuit switch comprises a first mechanical switch or a power electronic switch.

Optionally, the dc circuit breaker further comprises:

and the power flow controller is used for judging the short-circuit current direction of the line corresponding to each through-current branch so as to adjust the output voltage and assist the short-circuit current to transfer to the first cut-off branch.

Optionally, the power flow controllers are arranged in one-to-one correspondence with the through-flow branches.

Optionally, the power flow controller is a direct current power flow controller, an input source of the direct current power flow controller is a converter station modular multilevel submodule, the direct current power flow controller includes a plurality of series-connected full-bridge submodules, and the series-connected full-bridge submodules are connected in parallel with the converter station modular multilevel submodule.

According to the direct-current circuit breaker provided by the embodiment of the invention, the current controller with the converter station high-voltage MMC sub-module as an input source is adopted, and the main circuit can adopt a full-bridge sub-module direct-current series connection mode, so that the number of sub-modules is reduced, an alternating-current input part and a ground isolation part are omitted, and the direct-current circuit breaker has better economy.

Optionally, each of the current branches further comprises a second mechanical switch connected in series with the power flow controller.

According to a second aspect, an embodiment of the present invention further provides a method for controlling a dc circuit breaker, which is used in the dc circuit breaker described in any of the foregoing embodiments, and the method includes:

acquiring the working state of the direct current breaker;

and adjusting the on-off state of the on-off unit and the corresponding through-flow branch circuit based on the working state.

According to the control method of the direct current breaker provided by the embodiment of the invention, the working state of the direct current breaker is monitored, and the on-off state of the on-off unit and the on-off state of the through-current branch circuit are correspondingly controlled according to the monitoring result, so that the short-circuit current can be rapidly transferred, limited and switched on and off, and the on-off current can reach dozens of kA.

Optionally, the adjusting the on-off state of the on-off unit and the corresponding through-flow branch based on the operating state includes:

before the direct current breaker is put into operation, the switching-on and switching-off unit is conducted so that current flows through the switching-on and switching-off unit;

when a switching-on judgment condition is met, the at least one through-current branch is conducted, so that current flows through the at least one through-current branch;

and locking the breaking unit.

Optionally, when a line where a preset current branch is located fails, adjusting the disconnection unit and the corresponding disconnection state of the current branch based on the working state includes:

conducting the first cut-off branch and a second cut-off branch corresponding to the preset through-current branch;

the power flow controller corresponding to the preset through-current branch circuit judges the direction of the short-circuit current and controls the power flow controller to output voltage in the corresponding direction so as to force the current to be transferred to the switching-off unit;

when the current of the preset through-current branch passes zero, disconnecting a second mechanical switch corresponding to the preset through-current branch;

locking the first cut-off branch and a second cut-off branch corresponding to the preset through-current branch, so that the current is transferred to an energy consumption branch in the first cut-off branch and the second cut-off branch corresponding to the preset through-current branch;

and when the voltage of the energy consumption branch in the first cut-off branch and the second cut-off branch corresponding to the preset through current branch is higher than the direct current voltage of the system, the cut-off unit finishes current cut-off.

According to the control method of the direct current breaker provided by the embodiment of the invention, the second cut-off branch corresponding to each through-current branch can be used for independently cutting off the short-circuit current of each line, and the control method of the direct current breaker has the capabilities of simultaneously cutting off the short-circuit fault of multiple outgoing lines and clearing the fault of the direct current bus.

Optionally, when the dc bus fails, the adjusting the open state of the opening unit and the corresponding through-current branch circuit based on the operating state includes:

conducting the first cut-off branch and the second cut-off branch;

the power flow controller corresponding to each through-current branch circuit judges the direction of short-circuit current and locks a full-bridge submodule in the power flow controller so as to force the current to be transferred to the switching-on/off unit;

when the current of the through-current branch passes zero, the through-current branch is disconnected;

locking the first cut-off branch and each second cut-off branch so that current is transferred to energy-consuming branches in the first cut-off branch and the second cut-off branch corresponding to each through-current branch;

when the voltage of the energy consumption branch in the first cut-off branch and the second cut-off branch corresponding to each through-current branch is higher than the direct-current voltage of the system, the cut-off unit finishes current cut-off.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and other drawings can be obtained by those skilled in the art without creative efforts.

Fig. 1 is a schematic structural diagram of a dc circuit breaker according to an embodiment of the present invention;

fig. 2 a-2 d are schematic structural views of a power electronic switching unit according to an embodiment of the invention;

FIG. 3 is a schematic diagram of a first open branch according to an embodiment of the present invention;

FIGS. 4 a-4 c are schematic diagrams of a current limiting module according to an embodiment of the present invention;

fig. 5 is a schematic structural diagram of a dc circuit breaker according to an embodiment of the present invention;

fig. 6 a-6 b are schematic structural diagrams of a power flow controller according to an embodiment of the invention;

FIG. 6c is a schematic structural diagram of a submodule of a power flow controller according to an embodiment of the invention;

fig. 7 is a schematic structural diagram of a dc circuit breaker according to an embodiment of the present invention;

fig. 8 is a flowchart of a control method of a direct current circuit breaker according to an embodiment of the present invention;

fig. 9 a-9 b are schematic diagrams of a dc circuit breaker commissioning process according to an embodiment of the present invention;

fig. 10 a-10 e are schematic diagrams of a dc breaker switching process at line fault according to an embodiment of the invention;

fig. 11 a-11 e are schematic diagrams of the switching process of the direct current breaker when the direct current bus fails according to the embodiment of the invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

An embodiment of the present invention provides a dc circuit breaker, as shown in fig. 1, including at least one current branch and a breaking unit. The number of the current branches may be set according to actual conditions, and may be 2, 3, or 4, and the specific number of the current branches is not limited at all. Fig. 1 shows N current branches, current branch 1 leading into dc line 1, current branch 2 leading into dc lines 2, … …, and current branch N leading into dc line N.

As shown in fig. 1, the breaking unit includes two breaking branches with the same structure, namely a first breaking branch and a second breaking branch. The first cut-off branch is arranged on a common cut-off branch of each direct current line, specifically, one end of the first cut-off branch is connected with the direct current bus, the other end of the first cut-off branch is connected with one end of each second cut-off branch, and the other end of each second cut-off branch is connected with the other end of the corresponding through current branch. The first on-off branch is used for bearing and switching off short-circuit current, and the second on-off branch is used for bearing and switching off the short-circuit current and isolating the switched lines.

For convenience of description, a first open branch disposed in the common open branch is referred to as open branch 0, and second open branches corresponding to the respective through-flow branches are referred to as open branch 1-open branch N, respectively. Since the open branch 0 is provided on the common open branch, the open branch 0 may also be referred to as a main breaker. Accordingly, open branch 0 is denoted MB0 and open branches 1-N are denoted MB 1-MBN.

Specifically, the full-voltage class breaking branch is provided with an upper auxiliary breaking branch and a lower auxiliary breaking branch corresponding to each current branch, in addition to the main circuit breaker. The main circuit breaker adopts M power electronic switch units in cascade connection.

However, in this embodiment, the main circuit breaker of the full-voltage class breaking branch is split into the first breaking branch and the second breaking branch, so that the same breaking capability can be ensured by using one-half power electronic switch unit of the full-voltage class breaking branch.

The dc circuit breaker provided by this embodiment adopts a half current blocking unit, that is, the first breaking branch and the second breaking branch with the same structure are used for current blocking and voltage isolation, respectively, and the half concept is relative to the breaking branch of full voltage class. Specifically, the full-voltage cut-off unit can be jointly formed by the common part and the independent half cut-off branches belonging to the fault line in the fault cut-off process by adopting the half full-voltage cut-off branches in the common part and the parts of the common part connected with the through-current branches, so that the full-voltage current cut-off is completed. And in a short time after the current is cut off, full voltage isolation between the fault line and the normal line is realized through the half cut-off branch to which the fault line belongs and the half cut-off branch to which each normal line belongs. Based on this, the breaking branch in the direct current breaker is only 1/2 of a single hybrid breaker main breaker, and in an application scene of multiple direct current outgoing lines, the economic advantage of the direct current breaker is more remarkable than that of the single hybrid breaker.

The structure of the first open branch is the same as that of the second open branch, and in the following description, the structure of the first open branch is taken as an example and is described in detail. In some optional embodiments of the present embodiment, the first disconnection branch comprises at least one power electronic switching unit and an energy consumption branch. The energy consumption branch circuit is used for overvoltage protection and energy absorption. Alternatively, the power electronic switch unit may be formed by fully-controlled devices such as an IGBT, an IGCT, a BIGT, and an IEGT.

Fig. 2 a-2 d show 4 forms of power electronic switch units, one of which can be selected to cascade according to actual requirements during practical application of the dc circuit breaker to form a power electronic switch unit. Optionally, the energy consumption branch may be formed by a nonlinear resistance unit. Fig. 3 shows an alternative configuration of the first disconnection branch, in which the power electronic switching unit adopts the configuration of fig. 2d and the dissipation branch is formed by a non-linear resistor MOV.

In some optional embodiments of this embodiment, the switching unit further includes a current limiting module connected in series with the first switching branch, and the current limiting module is configured to limit a rising rate of the short-circuit current. As shown in fig. 5, one end of the current limiting module CL is connected to the dc bus, and the other end is connected to the open branch 0.

The current limiting module may be formed by a current limiting element, or may be formed by a current limiting element and a short-circuit switch. The current limiting element may be a resistor, a capacitor or an inductor, and the short-circuit switch may be a power electronic switch or a first mechanical switch. In particular, the current limiting module may be formed by a current limiting element in parallel with a short circuit switch. For example, fig. 4 a-4 c show 3 schematic structural diagrams of a current limiting module, as shown in fig. 4a, the current limiting module is formed by connecting a power electronic switch T and an inductor L in parallel; as shown in fig. 4b, the current limiting module is composed of a nonlinear capacitor C; as shown in fig. 4c, the current limiting module is formed by connecting a power electronic switch T in parallel with a resistor R. It should be noted that fig. 4 a-4 c are only some alternative embodiments, but the scope of the present invention is not limited thereto.

In other optional embodiments of this embodiment, the dc circuit breaker further includes a power flow controller PFC, and the power flow controller adjusts an output voltage by determining a line short-circuit current direction corresponding to each of the through-current branches, and assists a transfer of the short-circuit current to the first open branch. Wherein, the power flow controller is arranged corresponding to the through-flow branch one by one.

Alternatively, the power flow controller may be a dc power flow controller, and the input source of the dc power flow controller is from a converter station high voltage modular level submodule, i.e. a converter station high voltage MMC. Furthermore, the main circuit for controlling the DC source tide adopts a plurality of series-connected full-bridge submodules, and the series-connected full-bridge submodules are connected in parallel with the converter station high-voltage MMC. The power flow controller with the high-voltage MMC sub-module as an input source has the advantages that the main circuit can adopt a full-bridge sub-module direct-current series connection mode, the number of the sub-modules is reduced, an alternating-current input part and a ground isolation part are omitted, and the power flow controller has better economical efficiency. Optionally, a mechanical switch K may be further included in the power flow controller for isolating the main circuit of the power flow controller from the input source.

For example, fig. 6a shows an alternative embodiment of a power flow controller. The lower part in fig. 6a shows the overall structure of the power flow controller, and the upper part shows a further refined structure. As shown in fig. 6a, the input source of the power flow converter is from a converter station high voltage MMC submodule, and the high voltage MMC may be formed by connecting a plurality of MMC submodules in series. And the two ends of the power flow controller are respectively connected into the through-flow branches.

The main circuit of the power flow controller is formed by connecting a plurality of full-bridge submodules SM in series, as shown in fig. 6a, the main part of the power flow controller is formed by connecting N full-bridge submodules SM in series, and each of the N full-bridge submodules SM is₁-SM_N. Further, fig. 6c shows an alternative embodiment of the full bridge sub-module.

In other alternative embodiments of this embodiment, the power flow controller may also adopt a structure as shown in fig. 6 b. The power flow controller is placed in an independent power flow controller isolated from a high-potential platform and ground potential, wherein one end of the power flow controller is connected with an alternating current system through a transformer, the other end of the power flow controller is composed of a Modular Multilevel Converter (MMC), the direct current output ends of the modular multilevel converter are respectively connected with a direct current circuit, and basic unit blocks of the MMC are full-bridge sub-modules. When the direct current breaker stably operates, the power flow controller can control the voltage value output by the MMC in the circuit, and then the power flow of the circuit where the MMC is located is adjusted. In the process of switching on and switching off the direct current breaker, the power flow controller can adjust output voltage by judging the direction of short-circuit current and assist the current to be transferred to the switching-on branch.

As an alternative to this embodiment, each current branch further comprises a second mechanical switch UFD in series with the power flow controller. That is, the power flow branch comprises a power flow controller and a second mechanical switch UFD in series.

Fig. 7 shows an alternative embodiment of a dc circuit breaker, which includes 2 current branches, each current branch includes a power flow controller and a second mechanical switch connected in series, and the second and first open branches corresponding to each current branch adopt the structure shown in fig. 3, in which only one power electronic switching unit is adopted. The first cut-off branch is also connected with a current limiting module in series, and the current limiting module is realized by adopting a nonlinear capacitor.

The multi-port direct current breaker with power flow control and current limiting provided by the embodiment of the invention can realize bidirectional direct current power flow control, bidirectional and rapid transfer, current limiting and cut-off of direct current, the cut-off current can reach dozens of kA, and the application requirements of a direct current power transmission and distribution networking system are met. Furthermore, the multi-port switching-off device has a multi-port switching-off function, can independently switch off short-circuit current of each line, and simultaneously has the capability of simultaneously switching off short-circuit faults of multiple outgoing lines and clearing faults of the direct-current bus. The open branch of the direct current breaker is only 1/2 of a single hybrid breaker main breaker, and the direct current breaker has high economical efficiency. Compared with a single hybrid circuit breaker scheme, the provided method for sharing the main circuit breaker saves the using quantity of full-control devices by more than 20 percent; the current limiting function reduces the expected breaking current peak value by 15 percent at most, and the whole cost is saved by more than 30 percent compared with the scheme of adopting an independent single hybrid direct current breaker.

The embodiment of the present invention further provides a method for controlling a dc circuit breaker, wherein the specific structure of the dc circuit breaker is described above, and is not described herein again. As shown in fig. 8, the control method includes:

and S11, acquiring the working state of the direct current breaker.

The working state of the direct current breaker comprises the operation of the direct current breaker, the disconnection of a line side short-circuit fault and the disconnection of a direct current bus side short-circuit fault. The working state of the direct current circuit breaker can be obtained by monitoring the direct current circuit breaker, the specific monitoring mode is not limited at all, and only the direct current circuit breaker is required to be guaranteed to be capable of knowing the current working state.

S12, adjusting the open state of the opening unit and the corresponding current branch based on the operating state.

After the working state of the direct current circuit breaker is determined, the on-off state of the on-off unit and the on-off state of the corresponding through-current branch circuit are adjusted based on different working states. For example, when the dc circuit breaker is put into operation, the main breaking unit may be turned on first, and when the closing timing is reached, the through-current branch is put into use; when the line side is short-circuited, the short-circuited line side is disconnected from the direct current system by using the action of the disconnection unit; when the direct current bus line side is short-circuited, the short-circuited bus line side is disconnected from the direct current system by the operation of the disconnection means.

According to the control method of the direct current breaker, the working state of the direct current breaker is monitored, and the on-off state of the on-off unit and the on-off state of the through-current branch are correspondingly controlled according to the monitoring result, so that the short-circuit current can be rapidly transferred, limited and switched off, and the on-off current can reach dozens of kA.

When the dc breaker is put into operation, the step S12 may include the steps of:

(1) before the direct current breaker is put into operation, the breaking unit is conducted, so that current flows through the breaking unit.

(2) When the closing judgment condition is met, at least one through-current branch is conducted so that current flows through the at least one through-current branch.

(3) A lockout disconnect unit.

Taking the configuration of the dc circuit breaker shown in fig. 7 as an example, before the dc circuit breaker is put into operation, the main circuit breakers MB0, MB1, and MB2 are turned on, and a current flows through the open branch, as shown in fig. 9 a; and after the switching-on judgment condition is met, the mechanical switches UFD1 and UFD2 of the through-current branch are switched on, and the power flow controller PFC keeps zero voltage output. When UFD1 and UFD2 are switched on, the load current flows through the current branch, as shown in fig. 9b, MB remains latched and the circuit breaker is put into operation.

When the line where the preset current branch is located has a fault, S12 may include the following steps:

(1) and the first cut-off branch and a second cut-off branch corresponding to the preset through-current branch are conducted.

(2) And the power flow controller corresponding to the preset through-current branch circuit judges the direction of the short-circuit current and controls the power flow controller to output voltage in the corresponding direction so as to force the current to be transferred to the switching-off unit.

(3) And when the current of the preset through-current branch passes zero, disconnecting the second mechanical switch corresponding to the preset through-current branch.

(4) And locking the first cut-off branch and the second cut-off branch corresponding to the preset through-current branch, so that the current is transferred to the energy consumption branch in the first cut-off branch and the second cut-off branch corresponding to the preset through-current branch.

(5) When the voltage of the energy consumption branch in the first cut-off branch and the second cut-off branch corresponding to the preset through-current branch is higher than the direct-current voltage of the system, the cut-off unit finishes current cut-off.

Taking the structure of the dc circuit breaker shown in fig. 7, a short-circuit fault of the line 1 corresponding to the current branch is taken as an example. When the dc circuit breaker receives an open/close command or an overcurrent protection action, the open/close branch MB and the auxiliary switch are turned on, the thyristor valve T is kept off, the direction of the through-flow current of the power flow controller PFC1 in the through-flow branch 1 is determined, the submodule is turned on and off, a voltage leading to the short-circuit current is output from the through-flow branch, and the current is forced to be transferred to the open/close branch, as shown in fig. 10 a.

After the current of the current branch 1 crosses zero, the current is maintained to be circulated in the open branch, the UFD1 in the current branch 1 is switched off until the UFD1 reaches the withstand voltage open distance, the voltage of the nonlinear capacitor rises nonlinearly in the process, and the rising rate of the short-circuit current is reduced, as shown in fig. 10 b.

When the UFD1 reaches a withstand voltage, the main breaker MB and the auxiliary switch are closed, and the current charges the capacitor in the full bridge module, as shown in fig. 10c, the voltage rises to act as a parallel MOV, and the current is transferred to the MOV for circulation, as shown in fig. 10 d.

The MOV voltage is higher than the system dc voltage, the short circuit current continuously drops to zero crossing, the circuit breaker completes the current breaking, and the current branch UFD1 and the breaking branch MB isolate the faulty line, as shown in fig. 10 e.

After the breaker is opened, the breaker can be subjected to rapid reclosing operation according to the requirements of a power grid system, and the reclosing operation process is similar to the closing process.

When the dc bus fails, S12 may include the following steps:

(1) and the first cut-off branch and the second cut-off branch are conducted.

(2) And the power flow controller corresponding to each through-current branch judges the direction of the short-circuit current and locks the full-bridge submodule in the power flow controller so as to force the current to be transferred to the switching-off unit.

(3) And when the current of the through-current branch passes zero, the through-current branch is disconnected.

(4) And locking the first cut-off branch and each second cut-off branch so that the current is transferred to the energy consumption branch in the second cut-off branch corresponding to the first cut-off branch and each through-current branch.

(5) When the voltage of the energy consumption branch circuits in the first cut-off branch circuit and the second cut-off branch circuits corresponding to the through-current branch circuits is higher than the direct-current voltage of the system, the cut-off unit finishes current cut-off.

With the structure of the dc circuit breaker shown in fig. 7, the principle of disconnection when the dc circuit breaker fails on the power supply side is the same as the principle of disconnection when the line side fails, and the disconnection process is as shown in fig. 11a to 11 e.

Although the embodiments of the present invention have been described in conjunction with the accompanying drawings, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the invention, and such modifications and variations fall within the scope defined by the appended claims.

Claims (12)

1. A direct current circuit breaker, comprising:

one end of the through-flow branch is connected with the direct-current bus;

the breaking unit comprises a first breaking branch and second breaking branches corresponding to the through-flow branches, the first breaking branch and the second breaking branches have the same structure, one end of the first breaking branch is connected with the direct-current bus, the other end of the first breaking branch is connected with one end of each second breaking branch, and the other end of each second breaking branch is connected with the other end of the corresponding through-flow branch;

the first cut-off branch circuit is used for bearing and cutting off short-circuit current, and the second cut-off branch circuit is used for bearing and cutting off the short-circuit current and isolating the cut-off lines.

2. The direct current circuit breaker according to claim 1, characterized in that said first breaking branch comprises:

at least one power electronic switching unit, each of the power electronic switching units being cascaded;

and the energy consumption branch circuit is connected with the at least one power electronic switching unit in parallel and is used for overvoltage protection and energy absorption.

3. The dc circuit breaker according to claim 2, characterized in that said breaking unit further comprises a current limiting module in series with said first breaking branch, said current limiting module being adapted to limit the rate of rise of the short circuit current.

4. The direct current circuit breaker according to claim 3, characterized in that said current limiting module comprises:

a current limiting element;

a short circuit switch in parallel with the current limiting element, wherein the current limiting element comprises at least one of a resistor, a capacitor, or an inductor, and the short circuit switch comprises a first mechanical switch or a power electronic switch.

5. The dc circuit breaker according to claim 1, characterized in that the dc circuit breaker further comprises:

and the power flow controller is used for judging the short-circuit current direction of the line corresponding to each through-current branch so as to adjust the output voltage and assist the short-circuit current to transfer to the first cut-off branch.

6. The direct current circuit breaker according to claim 5, characterized in that the power flow controllers are arranged in one-to-one correspondence with the current branches.

7. The direct current circuit breaker according to claim 6, wherein the power flow controller is a direct current power flow controller, an input source of the direct current power flow controller is a converter station modular multilevel sub-module, the direct current power flow controller comprises a plurality of series-connected full-bridge sub-modules, and the series-connected full-bridge sub-modules are connected with the converter station modular multilevel sub-module in parallel.

8. The dc circuit breaker of claim 6, wherein each of said current branches further comprises a second mechanical switch in series with said power flow controller.

9. A control method for a dc circuit breaker, for use in the dc circuit breaker of any one of claims 1-8, the control method comprising:

acquiring the working state of the direct current breaker;

and adjusting the on-off state of the on-off unit and the corresponding through-flow branch circuit based on the working state.

10. The method of claim 9, wherein adjusting the open state of the opening unit and the corresponding flow branch based on the operating condition comprises:

before the direct current breaker is put into operation, the switching-on and switching-off unit is conducted so that current flows through the switching-on and switching-off unit;

when a switching-on judgment condition is met, the at least one through-current branch is conducted, so that current flows through the at least one through-current branch;

and locking the breaking unit.

11. The method according to claim 9, wherein when a fault occurs in a line in which a predetermined current branch is located, said adjusting the open state of the open unit and the corresponding current branch based on the operating state comprises:

conducting the first cut-off branch and a second cut-off branch corresponding to the preset through-current branch;

the power flow controller corresponding to the preset through-current branch circuit judges the direction of the short-circuit current and controls the power flow controller to output voltage in the corresponding direction so as to force the current to be transferred to the switching-off unit;

when the current of the preset through-current branch passes zero, disconnecting a second mechanical switch corresponding to the preset through-current branch;

locking the first cut-off branch and a second cut-off branch corresponding to the preset through-current branch, so that the current is transferred to an energy consumption branch in the first cut-off branch and the second cut-off branch corresponding to the preset through-current branch;

and when the voltage of the energy consumption branch in the first cut-off branch and the second cut-off branch corresponding to the preset through current branch is higher than the direct current voltage of the system, the cut-off unit finishes current cut-off.

12. The control method according to claim 9, wherein when the dc bus fails, the adjusting the open state of the opening unit and the corresponding through-flow branch based on the operating state comprises:

conducting the first cut-off branch and the second cut-off branch;

the power flow controller corresponding to each through-current branch circuit judges the direction of short-circuit current and locks a full-bridge submodule in the power flow controller so as to force the current to be transferred to the switching-on/off unit;

when the current of the through-current branch passes zero, the through-current branch is disconnected;

locking the first cut-off branch and each second cut-off branch so that current is transferred to energy-consuming branches in the first cut-off branch and the second cut-off branch corresponding to each through-current branch;

when the voltage of the energy consumption branch in the first cut-off branch and the second cut-off branch corresponding to each through-current branch is higher than the direct-current voltage of the system, the cut-off unit finishes current cut-off.

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