H-bridge type multi-port direct-current circuit breaker with bus fault clearing capability

Abstract

The invention discloses an H-bridge type multi-port direct-current circuit breaker with bus fault clearing capability. The H-bridge type multi-port direct-current circuit breaker comprises an upper side current transfer switch, a lower side current transfer switch and a common cutoff switch, when the circuit breaker is connected with the positive line, under the normal operation condition, the upper side current transfer switches of all the direct current transmission lines are switched off, the lower side current transfer switches of all the direct current transmission lines are switched on, and the common cut-off switch is switched off; when a bus fault occurs, the common cutoff switch is switched on, and after the common cutoff switch is completely switched on, the upper side current transfer switches of all the direct current transmission lines are switched on, and the lower side current transfer switches of all the direct current transmission lines are switched off; and when the upper side current transfer switches of all the direct current transmission lines are completely switched on and the lower side current transfer switches are completely switched off, the common cutoff switch is switched off, so that the bus fault current is reduced to zero. According to the invention, the direct-current power transmission bus fault can be quickly cleared.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronic systems, and particularly to an H-bridge multi-port DC circuit breaker with the ability to clear bus faults. Background Art

[0002] There are two basic network-formation methods for DC power grids: The first network-formation method uses a modular multilevel converter (MMC) based on half-bridge sub-modules plus a DC circuit breaker, and this network-formation method is applicable to DC power grids with any number of ports; the second network-formation method uses an MMC with the ability to self-clear DC faults, such as an MMC based on full-bridge sub-modules, but without a DC circuit breaker, and this network-formation method is applicable to small-scale DC power grids with less than 10 ports.

[0003] When using the method of an MMC with half-bridge sub-modules plus a DC circuit breaker to form a DC power grid, the DC circuit breaker becomes a key component of the DC power grid. Currently, the H-bridge multi-port DC circuit breaker is based on a hybrid concept, and two low-loss branches composed of a current transfer switch and an ultra-fast mechanical switch in series are installed on each line, forming an H-bridge structure. When faults occur on different DC lines, by turning on or off different switches, the line fault current is transferred to the only main circuit breaker, greatly improving the economy of using DC circuit breakers to build a DC power grid.

[0004] However, in the existing control strategies for H-bridge multi-port DC circuit breakers, all current transfer switches and ultra-fast mechanical switches are in the on state during normal operation, and the current flows through the upper and lower DC buses simultaneously. Therefore, when a DC bus fault occurs on any DC bus under this control strategy, it will have a serious impact on the system, and the existing control strategy cannot clear the DC bus fault, and the reliability is not high. Some existing other two-port or multi-port DC circuit breakers can clear the DC bus fault by tripping all switches when facing a DC bus fault. Although the DC bus fault is isolated in time, it leads to the outage of the entire network, still having a serious impact on the system, and the reliability still needs to be further improved. Summary of the Invention

[0005] The present invention provides an H-bridge multi-port DC circuit breaker with the ability to clear bus faults to solve the technical problem that the existing control strategy cannot clear DC bus faults and has low reliability.

[0006] To solve the above technical problem, an embodiment of the present invention provides an H-bridge multi-port DC circuit breaker with the ability to clear bus faults, including: a plurality of DC transmission lines and a breaking line;

[0007] The DC transmission line includes: an upper-side current transfer switch and a lower-side current transfer switch;

[0008] The first end of the upper current transfer switch is connected to the upper bus, the second end of the upper current transfer switch is connected to the first end of the lower current transfer switch, and the second end of the lower current transfer switch is connected to the lower bus;

[0009] The open - circuit line includes: a common disconnection switch;

[0010] The first end of the common disconnection switch is connected to the upper bus, and the second end of the common disconnection switch is connected to the lower bus;

[0011] When the circuit breaker is connected to the positive - pole line, under normal operating conditions, the upper current transfer switches of all DC transmission lines are open, the lower current transfer switches of all DC transmission lines are closed, and the common disconnection switch is open;

[0012] When a bus fault occurs, the common disconnection switch is closed. After the common disconnection switch is fully closed, the upper current transfer switches of all DC transmission lines are closed and the lower current transfer switches are open; after the upper current transfer switches of all DC transmission lines are fully closed and the lower current transfer switches are fully open, the common disconnection switch is open to reduce the bus fault current to zero.

[0013] As a preferred solution, the DC transmission line further includes: an upper ultra - fast mechanical switch and a lower ultra - fast mechanical switch;

[0014] The first end of the upper ultra - fast mechanical switch is connected to the second end of the upper current transfer switch, and the second end of the upper current transfer switch is connected to the first end of the lower current transfer switch; the first end of the lower ultra - fast mechanical switch is connected to the second end of the lower current transfer switch, and the second end of the lower ultra - fast mechanical switch is connected to the lower bus;

[0015] When the circuit breaker is connected to the positive - pole line, under normal operating conditions, the upper ultra - fast mechanical switches and the lower ultra - fast mechanical switches of all DC transmission lines are closed.

[0016] As a preferred solution, the open - circuit line further includes: a lightning arrester;

[0017] The first end of the lightning arrester is connected to the first end of the common disconnection switch, and the second end of the lightning arrester is connected to the second end of the common disconnection switch.

[0018] As a preferred solution, after the upper current transfer switches of all DC transmission lines are fully closed and the lower current transfer switches are fully open, the common disconnection switch is open to reduce the bus fault current to zero, including:

[0019] After the upper current transfer switches of all DC transmission lines are fully conducting and the lower current transfer switches are fully open, the lower ultra-fast mechanical switches of all DC transmission lines open, and after the lower ultra-fast mechanical switches of all DC transmission lines are fully open, the common current interruption switch opens, so that the bus fault current is transferred to the arrester and reduced to zero.

[0020] As a preferred solution, when the circuit breaker is connected to the positive line, if a DC transmission line fault occurs, the common current interruption switch conducts, and after the common current interruption switch is fully conducting, the upper current transfer switches of all normal DC transmission lines conduct, the lower current transfer switches of all normal DC transmission lines open, the upper current transfer switch of the faulty DC transmission line opens, and the lower current transfer switch of the faulty DC transmission line conducts;

[0021] After the upper current transfer switches of all normal DC transmission lines are fully conducting, the lower current transfer switches of all normal DC transmission lines are fully open, the upper current transfer switch of the faulty DC transmission line is fully open, and the lower current transfer switch of the faulty DC transmission line is fully conducting, the lower ultra-fast mechanical switches of the normal DC transmission lines open and the upper ultra-fast mechanical switches of the faulty DC transmission lines open;

[0022] After the lower ultra-fast mechanical switches of the normal DC transmission lines are fully open and the upper ultra-fast mechanical switches of the faulty DC transmission lines are fully open, the common current interruption switch opens, so that the line fault current of the faulty DC transmission line is transferred to the arrester and reduced to zero.

[0023] As a preferred solution, when the circuit breaker is connected to the negative line, under normal operating conditions, the upper current transfer switches of all DC transmission lines conduct, the lower current transfer switches of all DC transmission lines open, the upper ultra-fast mechanical switches of all DC transmission lines conduct, the lower ultra-fast mechanical switches of all DC transmission lines conduct, and the common current interruption switch opens;

[0024] When a bus fault occurs, the common current interruption switch conducts, and after the common current interruption switch is fully conducting, the upper current transfer switches of all DC transmission lines open and the lower current transfer switches conduct;

[0025] After the upper current transfer switches of all DC transmission lines are fully open and the lower current transfer switches are fully conducting, the upper ultra-fast mechanical switches of all DC transmission lines open, and after the upper ultra-fast mechanical switches of all DC transmission lines are fully open, the common current interruption switch opens, so that the bus fault current is transferred to the arrester and reduced to zero.

[0026] As a preferred solution, when the circuit breaker is connected to the negative line, if a DC transmission line fault occurs, the common disconnector switch conducts. After the common disconnector switch is fully conducted, the upper current transfer switches of all normal DC transmission lines disconnect, the lower current transfer switches of all normal DC transmission lines conduct, the upper current transfer switch of the faulty DC transmission line conducts, and the lower current transfer switch of the faulty DC transmission line disconnects;

[0027] After the upper current transfer switches of all normal DC transmission lines are fully disconnected, the lower current transfer switches of all normal DC transmission lines are fully conducted, the upper current transfer switch of the faulty DC transmission line is fully conducted, and the lower current transfer switch of the faulty DC transmission line is fully disconnected, the upper ultra-fast mechanical switch of the normal DC transmission line disconnects and the lower ultra-fast mechanical switch of the faulty DC transmission line disconnects;

[0028] After the upper ultra-fast mechanical switch of the normal DC transmission line is fully disconnected and the lower ultra-fast mechanical switch of the faulty DC transmission line is fully disconnected, the common disconnector switch disconnects, so that the line fault current of the faulty DC transmission line is transferred to the arrester and reduced to zero.

[0029] As a preferred solution, the DC transmission line further includes: a series reactor;

[0030] The first end of the series reactor is connected to the second end of the upper ultra-fast mechanical switch, and the second end of the series reactor is connected to the DC system MMC or the DC system line.

[0031] As a preferred solution, the DC transmission line further includes: a disconnector;

[0032] The first end of the disconnector is connected to the second end of the series reactor, and the second end of the disconnector is connected to the DC system MMC or the DC system line;

[0033] Under normal operating conditions, the disconnector conducts.

[0034] As a preferred solution, when a DC transmission line fault occurs, after the common disconnector switch disconnects to transfer the line fault current of the faulty DC transmission line to the arrester and reduce it to zero, it further includes:

[0035] The disconnector disconnects to clear the line fault of the faulty DC transmission line.

[0036] Compared with the prior art, the embodiments of the present invention have the following beneficial effects:

[0037] The present invention provides an H-bridge multi-port DC circuit breaker with the ability to clear bus faults, including: several DC transmission lines and a breaking line; the DC transmission lines include: an upper-side current transfer switch and a lower-side current transfer switch; the first end of the upper-side current transfer switch is connected to the upper-side bus, the second end of the upper-side current transfer switch is connected to the first end of the lower-side current transfer switch, and the second end of the lower-side current transfer switch is connected to the lower-side bus; the breaking line includes: a common current interruption switch; the first end of the common current interruption switch is connected to the upper-side bus, and the second end of the common current interruption switch is connected to the lower-side bus; when the circuit breaker is connected to the positive line, under normal operating conditions, the upper-side current transfer switches of all DC transmission lines are disconnected, the lower-side current transfer switches of all DC transmission lines are conducting, and the common current interruption switch is disconnected; when a bus fault occurs, the common current interruption switch conducts, and after the common current interruption switch is fully conducting, the upper-side current transfer switches of all DC transmission lines conduct and the lower-side current transfer switches disconnect; after the upper-side current transfer switches of all DC transmission lines are fully conducting and the lower-side current transfer switches are fully disconnected, the common current interruption switch disconnects to reduce the bus fault current to zero.

[0038] The H-bridge multi-port DC circuit breaker of the present invention includes several DC transmission lines and a circuit breaker. The DC transmission lines include an upper-side current transfer switch and a lower-side current transfer switch, and the circuit breaker includes a common current interruption switch. When a bus fault occurs, the rapid clearing of the DC transmission bus fault can be achieved by controlling the conduction and interruption of the upper-side current transfer switch, the lower-side current transfer switch, and the common current interruption switch, improving the reliability of the circuit breaker. Brief Description of the Drawings

[0039] Figure 1 It is a schematic structural diagram of an H-bridge multi-port DC circuit breaker with the ability to clear bus faults provided by an embodiment of the present invention;

[0040] Figure 2 It is a schematic diagram of a simulation waveform in the case of a DC line fault when the circuit breaker is installed on the positive line;

[0041] Figure 3 It is a schematic diagram of a simulation waveform in the case of a DC line fault when the circuit breaker is installed on the negative line. Detailed Embodiments

[0042] To make the objectives, technical solutions, and advantages of this application clearer, the following will clearly and completely describe the technical solutions in this application with reference to the accompanying drawings in the embodiments of this application. Obviously, the described embodiments are some, but not all, of the embodiments of this application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in this application without making creative efforts fall within the scope of protection of this application.

[0043] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification and claims of this application and the above description of the drawings are intended to cover non-exclusive inclusion.

[0044] In the description of the embodiments of this application, technical terms such as "first" and "second" are only used to distinguish different objects and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity, specific order, or primary-secondary relationship of the indicated technical features. In the description of the embodiments of this application, the meaning of "a plurality of" is two or more unless otherwise specifically defined.

[0045] Referring to "embodiments" herein means that specific features, structures, or characteristics described in connection with the embodiments can be included in at least one embodiment of this application. The phrase appears in various places in the specification and does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art will explicitly and implicitly understand that the embodiments described herein can be combined with other embodiments.

[0046] In the description of the embodiments of this application, the term "and / or" is merely a description of the association relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this text generally represents an "or" relationship between the associated objects before and after.

[0047] In the description of the embodiments of this application, the term "a plurality of" refers to two or more (including two). Similarly, "a plurality of groups" refers to two or more groups (including two groups), and "a plurality of pieces" refers to two or more pieces (including two pieces).

[0048] In the description of the embodiments of the present application, unless otherwise clearly specified and limited, technical terms such as "installation", "connection", "connection", "fixation", etc. should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or integrated; it can also be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two components or the interaction relationship between two components. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present application can be understood according to specific circumstances.

[0049] Embodiment 1

[0050] Please refer to Figure 1 , which is a schematic structural diagram of an H-bridge multi-port DC circuit breaker with the ability to clear bus faults provided by an embodiment of the present invention, including: several DC transmission lines and a breaking line;

[0051] The DC transmission line includes: an upper current transfer switch and a lower current transfer switch;

[0052] The first end of the upper current transfer switch is connected to the upper bus, the second end of the upper current transfer switch is connected to the first end of the lower current transfer switch, and the second end of the lower current transfer switch is connected to the lower bus;

[0053] The breaking line includes: a common current interruption switch;

[0054] The first end of the common current interruption switch is connected to the upper bus, and the second end of the common current interruption switch is connected to the lower bus;

[0055] When the circuit breaker is connected to the positive line, under normal operating conditions, the upper current transfer switches of all DC transmission lines are disconnected, the lower current transfer switches of all DC transmission lines are conducting, and the common current interruption switch is disconnected;

[0056] When a bus fault occurs, the common current interruption switch conducts. After the common current interruption switch is fully conducting, the upper current transfer switches of all DC transmission lines conduct and the lower current transfer switches disconnect; after the upper current transfer switches of all DC transmission lines are fully conducting and the lower current transfer switches are fully disconnected, the common current interruption switch disconnects to reduce the bus fault current to zero.

[0057] Preferably, the DC transmission line further includes: an upper ultra-fast mechanical switch and a lower ultra-fast mechanical switch; a first end of the upper ultra-fast mechanical switch is connected to a second end of the upper current transfer switch, and the second end of the upper current transfer switch is connected to a first end of the lower current transfer switch; a first end of the lower ultra-fast mechanical switch is connected to a second end of the lower current transfer switch, and a second end of the lower ultra-fast mechanical switch is connected to the lower bus; when the circuit breaker is connected to the positive line, in normal operating conditions, the upper ultra-fast mechanical switches and the lower ultra-fast mechanical switches of all DC transmission lines are turned on.

[0058] Preferably, the circuit breaker line further includes: a lightning arrester; a first end of the lightning arrester is connected to a first end of the common current breaking switch, and a second end of the lightning arrester is connected to a second end of the common current breaking switch.

[0059] Preferably, after the upper current transfer switches of all DC transmission lines are fully turned on and the lower current transfer switches are fully turned off, the common current breaking switch is turned off to reduce the bus fault current to zero, including: after the upper current transfer switches of all DC transmission lines are fully turned on and the lower current transfer switches are fully turned off, the lower ultra-fast mechanical switches of all DC transmission lines are turned off, and after the lower ultra-fast mechanical switches of all DC transmission lines are fully turned off, the common current breaking switch is turned off to transfer the bus fault current to the lightning arrester and reduce it to zero.

[0060] Preferably, when the circuit breaker is connected to the positive line, if a DC transmission line fault occurs, the common current breaking switch is turned on, and after the common current breaking switch is fully turned on, the upper current transfer switches of all normal DC transmission lines are turned on, the lower current transfer switches of all normal DC transmission lines are turned off, the upper current transfer switches of the faulty DC transmission line are turned off, and the lower current transfer switches of the faulty DC transmission line are turned on; after the upper current transfer switches of all normal DC transmission lines are fully turned on, the lower current transfer switches of all normal DC transmission lines are fully turned off, the upper current transfer switches of the faulty DC transmission line are fully turned off, and the lower current transfer switches of the faulty DC transmission line are fully turned on, the lower ultra-fast mechanical switches of the normal DC transmission lines are turned off and the upper ultra-fast mechanical switches of the faulty DC transmission line are turned off; after the lower ultra-fast mechanical switches of the normal DC transmission lines are fully turned off and the upper ultra-fast mechanical switches of the faulty DC transmission line are fully turned off, the common current breaking switch is turned off to transfer the line fault current of the faulty DC transmission line to the lightning arrester and reduce it to zero.

[0061] Preferably, when the circuit breaker is connected to the negative line, under normal operating conditions, the upper current transfer switches of all DC transmission lines are turned on, the lower current transfer switches of all DC transmission lines are turned off, the upper ultra-fast mechanical switches of all DC transmission lines are turned on, the lower ultra-fast mechanical switches of all DC transmission lines are turned on, and the common disconnector switch is turned off; when a busbar fault occurs, the common disconnector switch is turned on, and after the common disconnector switch is fully turned on, the upper current transfer switches of all DC transmission lines are turned off and the lower current transfer switches are turned on; after the upper current transfer switches of all DC transmission lines are fully turned off and the lower current transfer switches are fully turned on, the upper ultra-fast mechanical switches of all DC transmission lines are turned off, and after the upper ultra-fast mechanical switches of all DC transmission lines are fully turned off, the common disconnector switch is turned off, so that the busbar fault current is transferred to the arrester and reduced to zero.

[0062] Preferably, when the circuit breaker is connected to the negative line, if a DC transmission line fault occurs, the common disconnector switch is turned on, and after the common disconnector switch is fully turned on, the upper current transfer switches of all normal DC transmission lines are turned off, the lower current transfer switches of all normal DC transmission lines are turned on, the upper current transfer switch of the faulty DC transmission line is turned on, and the lower current transfer switch of the faulty DC transmission line is turned off; after the upper current transfer switches of all normal DC transmission lines are fully turned off, the lower current transfer switches of all normal DC transmission lines are fully turned on, the upper current transfer switch of the faulty DC transmission line is fully turned on, and the lower current transfer switch of the faulty DC transmission line is fully turned off, the upper ultra-fast mechanical switches of the normal DC transmission lines are turned off and the lower ultra-fast mechanical switches of the faulty DC transmission line are turned off; after the upper ultra-fast mechanical switches of the normal DC transmission lines are fully turned off and the lower ultra-fast mechanical switches of the faulty DC transmission line are fully turned off, the common disconnector switch is turned off, so that the line fault current of the faulty DC transmission line is transferred to the arrester and reduced to zero.

[0063] Preferably, the DC transmission line further includes: a series reactor; the first end of the series reactor is connected to the second end of the upper ultra-fast mechanical switch, and the second end of the series reactor is connected to the DC system MMC or the DC system line.

[0064] Preferably, the DC transmission line further includes: a disconnector switch; the first end of the disconnector switch is connected to the second end of the series reactor, and the second end of the disconnector switch is connected to the DC system MMC or the DC system line; under normal operating conditions, the disconnector switch is turned on.

[0065] Preferably, when a DC transmission line fault occurs, after the common disconnection switch is disconnected to transfer the line fault current of the faulty DC transmission line to the arrester and reduce it to zero, the method further includes: disconnecting the disconnector to clear the line fault of the faulty DC transmission line.

[0066] Specifically, according to Figure 1 the structural schematic diagram of the H-bridge multi-port DC circuit breaker with the ability to clear bus faults shown in the figure, where 1 is the upper DC bus, which is the standby bus when the circuit breaker is installed at the positive pole and the main bus when the circuit breaker is installed at the negative pole; 2 is the lower DC bus, which is the main bus when the circuit breaker is installed at the positive pole and the standby bus when the circuit breaker is installed at the negative pole; 3 is the upper current transfer switch of the m-th line, 4 is the upper ultra-fast mechanical switch of the m-th line, 5 is the m-th reactor, 6 is the disconnector of the m-th line, 7 is the lower current transfer switch of the m-th line, 8 is the lower ultra-fast mechanical switch of the m-th line, 9 is the main breaking line, 10 is the common disconnection switch, 11 is the metal oxide arrester, 12 is the upper current transfer switch of the first line, 13 is the upper ultra-fast mechanical switch of the first line, 14 is the first reactor, 15 is the disconnector of the first line, 16 is the lower current transfer switch of the first line, 17 is the lower ultra-fast mechanical switch of the first line, 18 is the upper current transfer switch of the (m - 1)-th line, 19 is the upper ultra-fast mechanical switch of the (m - 1)-th line, 20 is the (m - 1)-th reactor, 21 is the disconnector of the (m - 1)-th line, 22 is the lower current transfer switch of the (m - 1)-th line, 23 is the lower ultra-fast mechanical switch of the (m - 1)-th line.

[0067] The H-bridge multi-port DC circuit breaker includes 2m current transfer switches, 2m ultra-fast mechanical switches, m disconnectors, m line series reactors, and 1 main breaking line, where the main breaking line consists of 1 common disconnection switch and 1 arrester.

[0068] Specifically, the control strategy with the ability to clear DC line and bus faults applicable to the H-bridge multi-port DC circuit breaker of the present invention will vary depending on whether the circuit breaker is installed on the positive line or the negative line. When the wiring mode of the flexible DC transmission system is bipolar wiring, there will be a positive line and a negative line. Since the "ground" potential is 0, in the positive line, "ground" is the low potential, and in the negative line, "ground" is the high potential. To meet the fault clearing requirements of the two lines, the present invention separately designs the line and bus fault clearing strategies applicable to the positive line and the negative line.

[0069] 1. When the circuit breaker is installed on the positive line, under normal operating conditions, it will control the upper-side current transfer switch to open, the lower-side current transfer switch to conduct, all ultra-fast mechanical switches to conduct, and the common current interruption switch to open, making the upper-side busbar the standby busbar and the lower-side busbar the main busbar.

[0070] When a line fault occurs, the control strategy for clearing the DC line fault includes the following steps:

[0071] S1. After the system detects the occurrence of a line fault, it will control the common current interruption switch to conduct;

[0072] S2. After the common current interruption switch is fully conducted, it will control the upper-side current transfer switch of the normal line to conduct, the lower-side current transfer switch to open, the upper-side current transfer switch of the fault line to open, and the lower-side current transfer switch to conduct, so that the direction of the fault current flowing through the common current interruption switch is rectified from top to bottom;

[0073] S3. After the above current transfer switches are fully conducted or opened, it will control the lower-side ultra-fast mechanical switch of the normal line and the upper-side ultra-fast mechanical switch of the fault line to open;

[0074] Among them, the reason for opening the ultra-fast mechanical switch after the current transfer switch is fully opened is that the current transfer switch is a power electronic switch that can actively reduce the current to 0, but it cannot withstand a high voltage; the ultra-fast mechanical switch is a mechanical switch that can only be opened when the current flowing through it drops to 0, but it can withstand a very high voltage. Therefore, it is necessary to fully open the current transfer switch to reduce the current to 0, and then open the ultra-fast mechanical switch to withstand the subsequent transient overvoltage.

[0075] S4. After the above ultra-fast mechanical switches are fully opened, it will control the common current interruption switch to open, so that the line fault current is transferred to the metal oxide arrester, and the line fault current consumes energy through the metal oxide arrester and quickly drops to 0;

[0076] S5. After the line fault current drops to 0, it will control the isolation switch of the fault line to open, completely clearing the line fault, and the remaining normal lines will resume normal power flow.

[0077] When a busbar fault occurs, the control strategy for clearing the DC busbar fault includes the following steps:

[0078] S1. After the system detects the occurrence of a busbar fault, it will control the common current interruption switch to conduct;

[0079] S2. After the common current interruption switch is fully conducted, it will control the upper-side current transfer switches of all lines to conduct and the lower-side current transfer switches to open, so that the busbar fault current flows through the common current interruption switch from top to bottom;

[0080] S3. After the above current transfer switch is fully turned on or off, control the ultra-fast mechanical switches on the lower sides of all lines to turn off;

[0081] S4. After the above ultra-fast mechanical switches are fully turned off, control the common current breaking switch to turn off, so that the bus fault current is transferred to the metal oxide arrester. The bus fault current dissipates energy through the metal oxide arrester and quickly drops to 0;

[0082] S5. After the bus fault current drops to 0, the power of each line resumes normal flow through the standby bus.

[0083] Among them, the current transfer switch cannot withstand a very high voltage. Therefore, it is necessary to wait until the ultra-fast mechanical switch has fully tripped and can withstand the voltage before tripping the common current breaking switch to put the metal oxide arrester into operation.

[0084] Under normal operating conditions, the common current breaking switch is turned off to prevent it from being put into the operating line and reduce the on-state loss; after a fault occurs, the common current breaking switch is turned on first to transfer the fault current to it; then the common current breaking switch is tripped to put the metal oxide arrester into operation, reducing the fault current to 0.

[0085] Second, when the circuit breaker is installed on the negative line, under normal operating conditions, it will control the upper current transfer switch to turn on, the lower current transfer switch to turn off, all ultra-fast mechanical switches to turn on, and the common current breaking switch to turn off, making the upper bus the main bus and the lower bus the standby bus.

[0086] When a line fault occurs, the control strategy for clearing the DC line fault includes the following steps:

[0087] S1. After the system detects the occurrence of a line fault, control the common current breaking switch to turn on;

[0088] S2. After the common current breaking switch is fully turned on, control the upper current transfer switch of the normal line to turn off, the lower current transfer switch to turn on, the upper current transfer switch of the fault line to turn on, and the lower current transfer switch to turn off, so that the direction of the fault current flowing through the common current breaking switch is rectified from top to bottom;

[0089] S3. After the above current transfer switch is fully turned on or off, control the upper ultra-fast mechanical switch of the normal line and the lower ultra-fast mechanical switch of the fault line to turn off;

[0090] S4. After the above ultra-fast mechanical switches are fully turned off, control the common current breaking switch to turn off, so that the line fault current is transferred to the metal oxide arrester. The line fault current dissipates energy through the metal oxide arrester and quickly drops to 0;

[0091] S5. After the line fault current drops to 0, control the disconnection of the fault line disconnector to completely clear the line fault, and the remaining normal lines resume normal power flow.

[0092] When a busbar fault occurs, the control strategy for clearing the DC busbar fault includes the following steps:

[0093] S1. After the system detects the occurrence of a busbar fault, control the common disconnector switch to conduct;

[0094] S2. After the common disconnector switch is fully conducted, control the disconnection of the upper-side current transfer switches of all lines and the conduction of the lower-side current transfer switches;

[0095] S3. After the above current transfer switches are fully conducted or disconnected, control the disconnection of the ultra-fast mechanical switches on the upper side of all lines, so that the busbar fault current flows through the common disconnector switch from top to bottom;

[0096] S4. After the above ultra-fast mechanical switches are fully disconnected, control the disconnection of the common disconnector switch, so that the busbar fault current is transferred to the metal oxide arrester, and the busbar fault current consumes energy through the metal oxide arrester and quickly drops to 0;

[0097] S5. After the busbar fault current drops to 0, the power of each line resumes normal flow through the standby busbar.

[0098] The control strategy proposed by the present invention controls the disconnection of different current transfer switches according to whether the circuit breaker is installed on the positive or negative pole under normal operating conditions, so as to form a main busbar put into operation under normal operating conditions and a standby busbar suspended under normal operating conditions. By reducing the number of DC busbars, the possibility of busbar faults is reduced, and the reliability of the power grid is improved. This control strategy can not only quickly clear DC line faults, but also quickly clear DC busbar faults. At the same time, when clearing the main busbar fault, the standby busbar will be put into operation to carry the normal operating current, and there is no need for the entire network to stop operating.

[0099] In another specific embodiment, a single-pole 320 kV test system is used for simulation verification. There are three positive-pole DC transmission lines connected at the same position, and the DC circuit breaker is as Figure 1 shown circuit breaker.

[0100] It is assumed that the test system has entered a steady state before the simulation starts. At t = 1.0 s, a single-pole ground short circuit occurs on DC line 1. After a fault detection time of 1 ms, the DC circuit breaker starts to operate. Please refer to Figure 2 , which is a schematic diagram of the simulation waveform in the case of a DC line fault with the circuit breaker installed on the positive-pole line, Figure 2Among them, (a), (b), (c), (d), (e), and (f) are respectively the curve diagram of the change in DC line current, the curve diagram of the current flowing through the upper-side current transfer switch, the curve diagram of the current flowing through the lower-side current transfer switch, the curve diagram of the current flowing through the common disconnector switch, the curve diagram of the current flowing through the arrester, and the curve diagram of the change in the voltage borne by the arrester. From Figure 2 it can be seen that after the fault occurs, the DC current rises rapidly. After 1 ms, the upper-side current transfer switches of the second and third lines are turned on, and the lower-side current transfer switches are turned off. The upper-side current transfer switch of the first line is turned off, and the lower-side current transfer switch is turned on, causing the current to transfer to the main circuit breaker. After the above current transfer switches complete their operations, the lower-side ultra-fast mechanical switches of the second and third lines are turned off, and the upper-side ultra-fast mechanical switch of the first line is turned off, so that the current transfer switches are no longer under pressure. After the ultra-fast mechanical switches are completely turned off, the common disconnector switch is turned off, and the current further transfers to the arrester branch. At the same time, an overvoltage of approximately 700 kV is generated in the main circuit breaker. The DC circuit breaker can clear the DC line fault within a short time of several milliseconds, and the power of the remaining lines resumes normal flow, indicating that the circuit breaker has good current-breaking characteristics and reliability.

[0101] In another specific embodiment, a single-pole 320 kV test system is used for simulation verification. There are a total of three positive-pole DC transmission lines connected at the same position, and the DC circuit breaker is as Figure 1 shown in the circuit breaker.

[0102] It is assumed that the test system has entered a steady-state operation before the simulation starts. At t = 1.0 s, a single-pole ground short circuit occurs on the main bus. After a fault detection time of 1 ms, the DC circuit breaker starts to operate. Please refer to Figure 3 , which is a schematic diagram of the simulation waveform when the circuit breaker is installed on the negative line and a DC line fault occurs. Figure 3 Among them, (a), (b), (c), (d), (e), and (f) are respectively the curve diagrams of the DC line current, the current flowing through the upper-side current transfer switch, the current flowing through the lower-side current transfer switch, the current flowing through the common disconnector switch, the current flowing through the arrester, and the change in the voltage borne by the arrester. From Figure 3As can be seen, after the fault occurs, the DC current rises rapidly. After 1 ms, the upper-side current transfer switches of all lines are turned on and the lower-side current transfer switches are turned off, causing the current to transfer to the main circuit breaker. After the above-mentioned current transfer switches complete their operations, the ultra-fast mechanical switches on the lower sides of all lines are turned off, relieving the current transfer switches of the pressure. After the ultra-fast mechanical switches are completely turned off, the common current interruption switch is turned off, and the current further transfers to the arrester branch. At the same time, an overvoltage of approximately 700 kV is generated in the main circuit breaker. The DC circuit breaker can clear the main bus fault in a relatively short time of several milliseconds, and the power of each line resumes normal flow through the standby bus, indicating that the circuit breaker has good current interruption characteristics and reliability.

[0103] Thus, the present invention provides an H-bridge multi-port DC circuit breaker with the ability to clear bus faults. In the normal operation state, according to whether the circuit breaker is installed on the positive or negative pole, different current transfer switches are controlled to be turned off, thereby forming a main bus that is put into operation in the normal operation state and a standby bus that is suspended in the normal operation state. By reducing the number of DC buses, the possibility of bus faults is reduced, and the reliability of the power grid is improved. It can not only quickly clear DC line faults, but also quickly clear DC bus faults. At the same time, when clearing the main bus fault, the standby bus will be put into use to carry the normal operating current, without the need for a full network outage.

[0104] The above are the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements are also regarded as the protection scope of the present invention.

Claims

1. An H-bridge multi-port DC circuit breaker with the ability to clear bus faults, characterized in that Including: A number of DC transmission lines and a breaker line; The DC transmission line includes: an upper-side current transfer switch and a lower-side current transfer switch; The first end of the upper-side current transfer switch is connected to the upper-side bus, the second end of the upper-side current transfer switch is connected to the first end of the lower-side current transfer switch, and the second end of the lower-side current transfer switch is connected to the lower-side bus; The breaker line includes: a common disconnector switch; The first end of the common disconnector switch is connected to the upper-side bus, and the second end of the common disconnector switch is connected to the lower-side bus; When the circuit breaker is connected to the positive line, under normal operating conditions, the upper-side current transfer switches of all DC transmission lines are disconnected, the lower-side current transfer switches of all DC transmission lines are conducting, and the common disconnector switch is disconnected; When a busbar fault occurs, the common disconnector switch conducts. After the common disconnector switch is fully conducting, the upper-side current transfer switches of all DC transmission lines conduct and the lower-side current transfer switches disconnect; after the upper-side current transfer switches of all DC transmission lines are fully conducting and the lower-side current transfer switches are fully disconnected, the common disconnector switch disconnects to reduce the busbar fault current to zero.

2. The H-bridge multi-port DC circuit breaker with busbar fault clearing capability according to claim 1, wherein The DC transmission line further includes: an upper-side ultra-fast mechanical switch and a lower-side ultra-fast mechanical switch; The first end of the upper-side ultra-fast mechanical switch is connected to the second end of the upper-side current transfer switch, and the second end of the upper-side current transfer switch is connected to the first end of the lower-side current transfer switch; the first end of the lower-side ultra-fast mechanical switch is connected to the second end of the lower-side current transfer switch, and the second end of the lower-side ultra-fast mechanical switch is connected to the lower-side bus; When the circuit breaker is connected to the positive line, under normal operating conditions, the upper-side ultra-fast mechanical switches and the lower-side ultra-fast mechanical switches of all DC transmission lines are conducting.

3. The H-bridge multi-port DC circuit breaker with the ability to clear busbar faults according to claim 2, wherein, The breaker line further includes: a lightning arrester; The first end of the lightning arrester is connected to the first end of the common disconnector switch, and the second end of the lightning arrester is connected to the second end of the common disconnector switch.

4. The H-bridge multi-port DC circuit breaker with bus fault clearing ability according to claim 3, characterized in that, When the upper-side current transfer switches of all DC transmission lines are fully conducting and the lower-side current transfer switches are fully disconnected, the common disconnector switch disconnects to reduce the busbar fault current to zero, including: When the upper-side current transfer switches of all DC transmission lines are fully conducting and the lower-side current transfer switches are fully disconnected, the lower-side ultra-fast mechanical switches of all DC transmission lines disconnect, and after the lower-side ultra-fast mechanical switches of all DC transmission lines are fully disconnected, the common disconnector switch disconnects to transfer the busbar fault current into the lightning arrester and reduce it to zero.

5. The H-bridge multi-port DC circuit breaker with busbar fault clearing capability according to claim 4, wherein, When the circuit breaker is connected to the positive line, if a DC transmission line fault occurs, the common disconnector switch conducts, and after the common disconnector switch is fully conducting, the upper-side current transfer switches of all normal DC transmission lines conduct, the lower-side current transfer switches of all normal DC transmission lines disconnect, the upper-side current transfer switch of the faulty DC transmission line disconnects, and the lower-side current transfer switch of the faulty DC transmission line conducts; After the upper current transfer switches of all normal HVDC transmission lines are fully conducting, the lower current transfer switches of all normal HVDC transmission lines are fully open, the upper current transfer switch of the faulty HVDC transmission line is fully open, and the lower current transfer switch of the faulty HVDC transmission line is fully conducting, the lower ultra-fast mechanical switch of the normal HVDC transmission line opens and the upper ultra-fast mechanical switch of the faulty HVDC transmission line opens; After the lower ultra-fast mechanical switch of the normal HVDC transmission line is fully open and the upper ultra-fast mechanical switch of the faulty HVDC transmission line is fully open, the common current interruption switch opens to transfer the line fault current of the faulty HVDC transmission line to the arrester and reduce it to zero.

6. The H-bridge multi-port DC circuit breaker with bus fault clearing capability according to claim 5, characterized in that, When the circuit breaker is connected to the negative line, under normal operating conditions, the upper current transfer switches of all HVDC transmission lines are conducting, the lower current transfer switches of all HVDC transmission lines are open, the upper ultra-fast mechanical switches of all HVDC transmission lines are conducting, the lower ultra-fast mechanical switches of all HVDC transmission lines are conducting, and the common current interruption switch is open; When a bus fault occurs, the common current interruption switch conducts. After the common current interruption switch is fully conducting, the upper current transfer switches of all HVDC transmission lines open and the lower current transfer switches conduct; After the upper current transfer switches of all HVDC transmission lines are fully open and the lower current transfer switches are fully conducting, the upper ultra-fast mechanical switches of all HVDC transmission lines open. And after the upper ultra-fast mechanical switches of all HVDC transmission lines are fully open, the common current interruption switch opens to transfer the bus fault current to the arrester and reduce it to zero.

7. The H-bridge multi-port DC circuit breaker with busbar fault clearing ability according to claim 6, wherein, When the circuit breaker is connected to the negative line, if a fault occurs in the HVDC transmission line, the common current interruption switch conducts. After the common current interruption switch is fully conducting, the upper current transfer switches of all normal HVDC transmission lines open, the lower current transfer switches of all normal HVDC transmission lines conduct, the upper current transfer switch of the faulty HVDC transmission line conducts, and the lower current transfer switch of the faulty HVDC transmission line opens; After the upper current transfer switches of all normal HVDC transmission lines are fully open, the lower current transfer switches of all normal HVDC transmission lines are fully conducting, the upper current transfer switch of the faulty HVDC transmission line is fully conducting, and the lower current transfer switch of the faulty HVDC transmission line is fully open, the upper ultra-fast mechanical switch of the normal HVDC transmission line opens and the lower ultra-fast mechanical switch of the faulty HVDC transmission line opens; After the upper ultra-fast mechanical switch of the normal HVDC transmission line is fully open and the lower ultra-fast mechanical switch of the faulty HVDC transmission line is fully open, the common current interruption switch opens to transfer the line fault current of the faulty HVDC transmission line to the arrester and reduce it to zero.

8. The H-bridge multi-port DC circuit breaker with bus fault clearing capability according to claim 7, wherein, The HVDC transmission line further includes: a series reactor; The first end of the series reactor is connected to the second end of the upper ultra-fast mechanical switch, and the second end of the series reactor is connected to the DC system MMC or the DC system line.

9. The H-bridge multi-port DC circuit breaker with busbar fault clearing capability according to claim 8, wherein, The DC transmission line further includes: a disconnector; The first end of the disconnector is connected to the second end of the series reactor, and the second end of the disconnector is connected to the DC system MMC or the DC system line; Under normal operating conditions, the disconnector is conducting.

10. The H-bridge multi-port DC circuit breaker with busbar fault clearing ability according to claim 9, characterized in that, When a fault occurs in the DC transmission line, after the common disconnection switch is opened to transfer the line fault current of the faulty DC transmission line to the arrester and reduce it to zero, it further includes: The disconnector is opened to clear the line fault of the faulty DC transmission line.

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