A thyristor-based dc circuit breaker and a breaking method of a dc circuit breaker

Abstract

The application relates to a thyristor-based direct-current circuit breaker and a breaking method of the direct-current circuit breaker, and belongs to the technical field of fault protection of a direct-current medium-high voltage power system. The direct-current circuit breaker comprises a main switch branch, a current transfer branch, a voltage limiting and energy consumption branch and a pulse commutation loop. The direct-current circuit breaker is connected in series with the power system, two nodes in series are marked as Q1 and Q2, the main switch branch and the voltage limiting and energy consumption branch are connected in parallel through Q1 and Q2, one end of the two high-frequency transformers in the pulse commutation loop is connected to Q1 and Q2 respectively, and the other end is connected to two ends of the current transfer branch respectively. The application effectively solves the problem that a large number of pulse charging and discharging loops are configured to meet the requirement of breaking a large fault current, thereby increasing the volume and cost.

Description

Technical Field

[0001] The present invention relates to the technical field of fault protection for DC medium and high voltage power systems, and in particular to a thyristor-based DC circuit breaker and a breaking method for the DC circuit breaker. Background Art

[0002] Thyristors, with their current-carrying capacity and voltage rating, are ideal semiconductor devices for hybrid circuit breakers in medium / high voltage DC power systems. Transferring fault current from the main switching branch to the current transfer branch is the core of hybrid circuit breaker design. In medium / high voltage DC power systems, the voltage rating of a single device is limited, often requiring multiple devices connected in series to meet the required requirements. This results in the on-state voltage drop in the current transfer branch often exceeding the arc voltage of the fast mechanical switching in the main switching branch, leading to current transfer failure.

[0003] The existing technology proposes to connect a fully controlled semiconductor device IGBT in series with the main switch branch, and use the voltage generated by the IGBT shutdown to achieve fault current transfer. However, this solution suffers from severe losses under rated current-carrying conditions, especially in high current situations. Later, some scholars proposed to connect a coupled inductor in series with the current transfer branch, and use the principle of "coupled negative voltage" to achieve fault current transfer. Since thyristors are semi-controlled devices, they require an external auxiliary pulse circuit to achieve shutdown. If a "coupled negative voltage" pulse circuit is added, two bridge pulse capacitor discharge systems will be required, and corresponding charging and discharging circuits will need to be configured, which will undoubtedly increase the size and cost of the circuit breaker. Summary of the Invention

[0004] In view of this, it is necessary to provide a thyristor-based DC circuit breaker and a DC circuit breaker breaking method to solve the problem in the prior art of configuring a large number of pulse charging and discharging circuits to meet the needs of large fault current interruption, thereby increasing the volume and cost.

[0005] To solve the above problems, the present invention provides a thyristor-based DC circuit breaker, comprising: a main switch branch, a current transfer branch, a voltage-limiting energy-consuming branch, and a pulse commutation circuit. The DC circuit breaker is connected in series with the power system, with the two series nodes being denoted as Q1 and Q2. The main switch branch and the voltage-limiting energy-consuming branch are connected in parallel via Q1 and Q2. In the pulse commutation circuit, one end of the secondary side of two high-frequency transformers is connected to Q1 and Q2, respectively, and the other end is connected to both ends of the current transfer branch.

[0006] The main switch branch is composed of a fast mechanical switch (S);

[0007] The current transfer branch is composed of two groups of thyristors (T1) and (T2) connected in anti-parallel, and the external connection points are marked as N5 and N6;

[0008] The pulse commutation circuit is composed of a pre-charge capacitor (C0), an energy storage inductor (L0), a thyristor (T0), (T 3) , (T4), (T5), (T6), (T7), (T8) and high frequency transformers (M1), (M2);

[0009] The positive electrode of the pre-charge capacitor (C0) and one electrode of the energy storage inductor (L0) are connected in series, and the negative electrode of the capacitor C0 and the other electrode of the energy storage inductor (L0) are respectively recorded as external connection points N4 and N2;

[0010] Thyristor (T3) and thyristor (T4) are connected in anti-parallel, one end is marked as N1 and the other end is connected to N2;

[0011] Thyristor (T5) and thyristor (T6) are connected in anti-parallel, one end is marked as N3 and the other end is connected to N2;

[0012] The cathodes of thyristor (T7) and thyristor (T8) are connected to N4, and the anodes are connected to N1 and N3 respectively;

[0013] The primary and secondary sides of the high-frequency transformer are both composed of high-voltage wires wound around ferrite rings, with the same end wound, and the number of turns on the secondary side is greater than that on the primary side;

[0014] The primary side of the high-frequency transformer (M1) is connected in parallel with the thyristor (T7) through N1 and N4, and the secondary side is connected to the main switch branch and the current transfer branch through nodes Q1 and N5; the primary side of the high-frequency transformer (M2) is connected in parallel with the thyristor (T8) through nodes N3 and N4, and the secondary side is connected to the main switch branch and the current transfer branch through nodes Q2 and N6;

[0015] The voltage-limiting energy-consuming branch is composed of a varistor (MOV);

[0016] The present invention further provides a method for disconnecting a DC circuit breaker, which is applied to the thyristor-based DC circuit breaker described in the above-mentioned device item, and comprises the following steps:

[0017] Under rated operating conditions, close the fast mechanical switch (S) to carry the system current;

[0018] During the short-circuit breaking process, a tripping command is first sent to the fast mechanical switch (S). When the moving and static contacts of the fast mechanical switch (S) are opened to a sufficient distance, the thyristors in the pulse commutation circuit and the thyristors in the current transfer branch are selectively turned on according to the direction of the system current of the power system flowing through the DC circuit breaker.

[0019] In the positive half cycle of the pre-charge capacitor (C0) discharge, the fault current is transferred from the main switch branch to the current transfer branch through the induced electromotive force of the high-frequency transformer (M1) or (M2);

[0020] In the negative half cycle of the pre-charge capacitor (C0) discharging, the induction electromotive force of the high-frequency transformer (M1) or (M2) opens the pressure-sensitive resistor (MOV), so as to realize the fault current transfer from the current transfer branch to the voltage-limiting energy consumption branch, and complete the fault breaking.

[0021] In a possible implementation, the short-circuit breaking process further includes the following steps:

[0022] If the system current flows from Q1 to Q2, when the moving and static contacts of the fast mechanical switch (S) are opened to a preset opening distance, the pulse commutation loop and the current transfer branch are put into operation;

[0023] First, the thyristors (T1) and (T6) are turned on, so that the secondary side of (M2) induces an upper positive and lower negative electromotive force, so as to realize the transfer of the fault current from the fast mechanical switch (S) of the main switch branch to the thyristor (T1) of the current transfer branch;

[0024] After the current transfer is completed, the thyristor (T8) is turned on, so that (M2) exits operation;

[0025] The pre-charge capacitor (C0) is continuously discharged, and after the voltage of the pre-charge capacitor (C0) is reduced to zero, the pre-charge capacitor (C0) is reversely charged, and the thyristor T1 of the current transfer branch carries the system current and the fast mechanical switch S performs dielectric recovery;

[0026] When the voltage in the pre-charge capacitor (C0) reaches a reverse peak value, the thyristors (T5) and (T0) are turned on, so that the pre-charge capacitor (C0) is discharged through the high-frequency transformer (M2), and an upper negative and lower positive electromotive force is induced at the secondary side, so as to open the pressure-sensitive resistor (MOV), and under the action of the reverse voltage, the thyristor (T1) is turned off, so as to realize the transfer of the fault current from the current transfer branch to the voltage-limiting energy consumption branch, and complete the breaking.

[0027] In a possible implementation, the short-circuit breaking process further includes the following steps:

[0028] If the system current flows from Q2 to Q1, when the moving and static contacts of the fast mechanical switch (S) are opened to a preset opening distance, the pulse commutation loop and the current transfer branch are put into operation;

[0029] First, the thyristors (T2) and (T3) are turned on, so that the secondary side of (M1) induces an upper positive and lower negative electromotive force, so as to realize the transfer of the fault current from the fast mechanical switch (S) of the main switch branch to the thyristor (T2) of the current transfer branch;

[0030] After the current transfer is completed, the thyristor (T7) is turned on, so that (M1) exits operation;

[0031] The precharge capacitor (C0) is continuously discharged, and after the voltage drops to zero, it is reversely charged. The current transfer branch thyristor T2 carries the system current, and the fast mechanical switch S performs dielectric recovery.

[0032] When the voltage in the pre-charge capacitor (C0) reaches the reverse peak, the thyristors (T4) and (T0) are turned on, causing the pre-charge capacitor (C0) to discharge through the high-frequency transformer (M1), inducing an electromotive force with a negative top and a positive bottom on the secondary side, thereby turning on the varistor (MOV) and causing the thyristor (T2) to turn off, realizing the transfer of the fault current from the current transfer branch to the voltage-limiting energy-consuming branch, and completing the disconnection.

[0033] The beneficial effects of the present invention are as follows: the DC circuit breaker provided by the present invention only uses one set of bridge pulse discharge circuits to achieve the rapid transfer of fault current of hybrid circuit breakers in the medium and high voltage fields and the reliable shutdown of thyristor devices, and the loss is extremely low under rated current-carrying conditions. Compared with the existing technology, the volume and cost of the circuit breaker are greatly reduced. On the other hand, in the same set of bridge pulse discharge circuits, all thyristors that need to be controlled can be integrated into a design, which is conducive to the modular design of the control system and increases the reliability of hybrid disconnection, thereby effectively solving the problem in the existing technology of configuring a large number of pulse charging and discharging circuits to meet the needs of large fault current interruption, thereby increasing the volume and cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 A schematic structural diagram of an embodiment of a thyristor-based DC circuit breaker provided by the present invention;

[0035] Figure 2 A method flow chart of an embodiment of a fault current transfer method provided by the present invention;

[0036] Figure 3 for Figure 2 When the system current flows from Q1 to Q2, step S202 is a method flow chart of an embodiment;

[0037] Figure 4 for Figure 2 When the system current flows from Q2 to Q1, step S202 is a method flow chart of an embodiment;

[0038] Figure 5 Waveform diagram of system current and circuit parameters of each branch during short circuit protection of the circuit breaker provided by the present invention

[0039] Figure 6 The inductive commutation topology diagram provided by the present invention when the current flows from Q1 to Q2;

[0040] Figure 7 The reverse charging topology diagram provided by the present invention when the current flows from Q1 to Q2;

[0041] Figure 8 The high-voltage turn-off topology diagram when the current is Q1 to Q2 in the application provided;

[0042] Figure 9 The inductive commutation topology diagram when the current is Q2 to Q1 in the application provided;

[0043] Figure 10 The reverse charging topology diagram when the current is Q2 to Q1 in the application provided;

[0044] Figure 11 The high-voltage turn-off topology diagram when the current is Q2 to Q1 in the application provided. DETAILED DESCRIPTION

[0045] The preferred embodiments of the present application will be described in detail below with reference to the drawings, which form a part of this application. The drawings and the associated descriptions are provided to illustrate the embodiments of the present application and to provide a comprehensible understanding of the present application, but are not intended to limit the scope of the present application.

[0046] Before the embodiments are described, the following terms are explained:

[0047] In the description of the embodiments of the present application, unless otherwise specified, the meaning of "a plurality of" is two or more. The association relationship of the associated objects is described as "and / or", which means that there can be three relationships, for example: A and / or B, which can represent the three cases of A alone, A and B together, and B alone.

[0048] The "first", "second", and the like described in the embodiments of the present application are only for the purpose of description, and cannot be understood as indicating or implying the relative importance of the technical features indicated or the number of technical features indicated. Therefore, the technical features limited by "first" and "second" can explicitly or implicitly include at least one of the features.

[0049] In this document, the reference to "embodiments" means that the specific features, structures, or characteristics described in connection with the embodiments can be included in at least one embodiment of the present application. The phrase appears in various places in the specification does not necessarily all refer to the same embodiment, nor is it necessarily independent or alternative embodiments to other embodiments. The skilled person in the art explicitly and implicitly understands that the embodiments described herein can be combined with other embodiments.

[0050] In order to solve the above problems, as Figure 1As shown, the present invention provides a thyristor-based DC circuit breaker 10, comprising: a main switch branch, a current transfer branch, a voltage-limiting energy-consuming branch, and a pulse commutation circuit, wherein the DC circuit breaker is connected in series with the power system, the two nodes of the series connection are respectively denoted as Q1 and Q2, the main switch branch and the voltage-limiting energy-consuming branch are connected in parallel via Q1 and Q2, and one end of the secondary side of the two high-frequency transformers in the pulse commutation circuit is connected to Q1 and Q2, respectively, and the other end is connected to both ends of the current transfer branch;

[0051] The main switch branch is composed of a fast mechanical switch S;

[0052] The current transfer branch is composed of two groups of thyristors T1 and T2 connected in anti-parallel, and the external connection points are marked as N5 and N6;

[0053] The pulse commutation circuit consists of a pre-charge capacitor C0, an energy storage inductor L0, thyristors T0, T3, T4, T5, T6, T7, T8 and high-frequency transformers M1 and M2;

[0054] The positive electrode of the pre-charge capacitor C0 is connected in series with one electrode of the energy storage inductor L0, and the negative electrode of the capacitor C0 and the other electrode of the energy storage inductor L0 are respectively recorded as external connection points N4 and N2;

[0055] Thyristor T3 and thyristor T4 are connected in anti-parallel, one end is marked as N1 and the other end is connected to N2;

[0056] Thyristor T5 and thyristor T6 are connected in anti-parallel, one end is marked as N3, and the other end is connected to N2;

[0057] The cathodes of thyristors T7 and T8 are connected to N4, and the anodes are connected to N1 and N3 respectively.

[0058] The primary and secondary sides of the high-frequency transformer are both composed of high-voltage wires wound around ferrite rings, with the same end wound, and the number of turns on the secondary side is not less than that on the primary side;

[0059] The primary side of the high-frequency transformer M1 is connected in parallel with the thyristor T7 through N1 and N4, and the secondary side is connected to the main switch branch and the current transfer branch through nodes Q1 and N5. The primary side of the high-frequency transformer M2 is connected in parallel with the thyristor T8 through nodes N3 and N4, and the secondary side is connected to the main switch branch and the current transfer branch through nodes Q2 and N6.

[0060] The voltage-limiting energy-consuming branch is composed of a varistor MOV.

[0061] Compared with the prior art, the DC circuit breaker provided by the present invention only uses a set of bridge pulse discharge circuits to achieve the rapid transfer of fault current of hybrid circuit breakers in the medium and high voltage fields and the reliable shutdown of thyristor devices, and the loss is extremely low under rated current-carrying conditions. Compared with the prior art, the volume and cost of the circuit breaker are greatly reduced. On the other hand, in the same set of bridge pulse discharge circuits, all thyristors that need to be controlled can be integrated into a design, which is conducive to the modular design of the control system and increases the reliability of hybrid disconnection, thereby effectively solving the problem in the prior art of configuring a large number of pulse charging and discharging circuits to meet the needs of large fault current disconnection, thereby increasing the volume and cost.

[0062] like Figure 2 The present invention also provides a method for disconnecting a DC circuit breaker, which is applied to the thyristor-based DC circuit breaker described in the above-mentioned device item, and includes the following steps:

[0063] S201. Under rated operating conditions, close the fast mechanical switch S to carry the system current.

[0064] S202. During the short-circuit breaking process, a tripping command is first sent to the fast mechanical switch S. When the moving and static contacts of the fast mechanical switch S are opened to a sufficient distance, the thyristors in the pulse commutation circuit and the thyristors in the current transfer branch are selectively turned on according to the direction of the system current of the power system flowing through the DC circuit breaker. During the positive half-cycle of the discharge of the pre-charge capacitor C0, the fault current is transferred from the main switch branch to the current transfer branch through the induced electromotive force of the high-frequency transformer M1 or M2. During the negative half-cycle of the discharge of the pre-charge capacitor C0, the induced electromotive force of the high-frequency transformer M1 or M2 turns on the varistor MOV, thereby transferring the fault current from the current transfer branch to the voltage-limiting energy-consuming branch and completing the fault breaking.

[0065] like Figure 3 In a possible implementation, step S202 includes the following steps:

[0066] S301. If the system current flows from Q1 to Q2, when the moving and static contacts of the fast mechanical switch S open to the preset opening distance, the pulse commutation circuit and the current transfer branch are put into operation;

[0067] S302, first turn on thyristors T1 and T6, so that the secondary side of M2 induces an electromotive force that is positive at the top and negative at the bottom, so as to transfer the fault current from the fast mechanical switch S in the main switch branch to the thyristor T1 in the current transfer branch;

[0068] S303, after the current transfer is completed, turn on the thyristor T8, so that M2 stops running;

[0069] S304 , the pre-charge capacitor C0 is continuously discharged, and reversely charged after the voltage of the pre-charge capacitor C0 drops to zero, the current transfer branch thyristor T1 carries the system current, and the fast mechanical switch S performs dielectric recovery;

[0070] S305. When the voltage in the pre-charge capacitor C0 reaches the reverse peak, the thyristors T5 and T0 are turned on, causing the pre-charge capacitor C0 to discharge through the high-frequency transformer M2, inducing an electromotive force with a negative upper side and a positive lower side on the secondary side to turn on the varistor MOV, and under the action of the reverse voltage, the thyristor T1 is forced to turn off, realizing the transfer of the fault current from the current transfer branch to the voltage-limiting energy consumption branch, and completing the disconnection.

[0071] like Figure 4 In a possible implementation, step S202 further includes the following steps:

[0072] S401. If the system current flows from Q2 to Q1, when the moving and static contacts of the fast mechanical switch S open to the preset opening distance, the pulse commutation circuit and the current transfer branch are activated;

[0073] S402, first turn on thyristors T2 and T3, so that the secondary side of M1 induces an electromotive force with a positive top and a negative bottom, so as to transfer the fault current from the fast mechanical switch S in the main switch branch to the thyristor T2 in the current transfer branch;

[0074] S403, after the current transfer is completed, turn on the thyristor T7 to stop the operation of M1;

[0075] S404: The pre-charge capacitor C0 is continuously discharged, and after the voltage drops to zero, it is reversely charged. The current transfer branch thyristor T2 carries the system current, and the fast mechanical switch S performs dielectric recovery.

[0076] S405. When the voltage in the pre-charge capacitor C0 reaches the reverse peak, the thyristors T4 and T0 are turned on, causing the pre-charge capacitor C0 to discharge through the high-frequency transformer M1, inducing an electromotive force with a negative upper side and a positive lower side on the secondary side, thereby turning on the varistor MOV and causing the thyristor T2 to turn off, realizing the transfer of the fault current from the current transfer branch to the voltage-limiting energy-consuming branch, and completing the disconnection.

[0077] Figure 5 The diagram shows the circuit parameter waveforms of the system and each branch of the DC circuit breaker provided by the present invention during operation.

[0078] in accordance with Figure 5 The disconnecting method of the DC circuit breaker provided by the present invention is further described:

[0079] t 0~ t Stage 1: The system operates at rated current carrying conditions, the fast mechanical switch S is closed, carrying the system currenti 0. The fast mechanical switch has extremely low on-state loss, achieving low loss under rated current carrying conditions.

[0080] t At time 1, a short circuit occurs, and the current in the system rises rapidly. First, a command is sent to open the fast mechanical switch S. After a period of inherent delay, the moving and static contacts of the fast mechanical switch S open.

[0081] t 2. When the moving and static contacts of the fast mechanical switch S reach the appropriate opening distance, the pulse commutation circuit and the current transfer branch are put into operation (the specific conduction of the thyristor is determined by the current direction). The specific control is as follows:

[0082] When the system short-circuit current flows from Q1 to Q2, the thyristor T1 in the current transfer branch and the thyristor T6 in the pulse commutation circuit are turned on, the C0-L0-T6-M2 circuit is turned on, and the secondary side of the high-frequency transformer M2 induces an induced electromotive force with positive upper side and negative lower side. The current in the main switch branch is quickly transferred to the thyristor T1 in the current transfer branch. Figure 6 shown.

[0083] t At time 3, the current transfer is completed, and the fast mechanical switch S of the main switch branch extinguishes the arc and turns off. Subsequently, the thyristor T8 is turned on, the C0-L0-T6-T8 circuit is connected, and the high-frequency transformer M2 stops operating. On the one hand, it ensures that the two ends of the fast mechanical switch S are not subjected to high voltage, and on the other hand, it ensures that sufficient energy can be recharged into the capacitor C0. Capacitor C0 continues to discharge in the positive half cycle. In this stage, the system current is carried by the thyristor T1, and the fast mechanical switch S achieves dielectric recovery at approximately "zero voltage". Figure 7 shown.

[0084] t At time 4, the voltage across capacitor C0 reaches the reverse peak. Thyristors T5 and T0 are turned on, the C0-M2-T5-T0 loop is turned on, and the pre-charged capacitor C0 is discharged through the high-frequency transformer M2. The energy storage inductor L0 stops running, and the voltage across C0 is fully loaded on the primary side of the transformer M2. A high-voltage electromotive force with a negative top and a positive bottom is induced on the secondary side of the high-frequency transformer M2. The varistor is turned on, and the thyristor T1 is turned off under the action of this voltage. The fault current is transferred to the voltage-limited energy consumption branch and t 6. Realize zero-crossing shutdown at any time, refer to Figure 8 shown.

[0085] At the same time, according to Figure 5 The voltage waveform of the current transfer branch shows that after the current in the thyristor T1 passes through zero, t 4~ t Phase 5 can withstand sufficient reverse voltage to ensure restoration of forward blocking capability.

[0086] When the system short-circuit current flows from Q2 to Q1, the thyristor T2 in the current transfer branch and the thyristor T3 in the pulse commutation circuit are turned on, the CO-LO-T3-M1 circuit is turned on, the upper positive and lower negative induced electromotive force is induced on the secondary side of the high-frequency transformer M1, the current in the main switch branch is rapidly transferred to the thyristor T2 in the current transfer branch, and the current transfer is completed at the 3rd moment, the fast mechanical switch S in the main switch branch is arc extinguishing and turned off. Subsequently, the thyristor T7 is turned on, the CO-LO-T3-T7 circuit is turned on, the high-frequency transformer M1 is turned off, on the one hand, the high voltage is not borne by the fast mechanical switch S, and on the other hand, sufficient energy can be charged into the capacitor CO again. The capacitor CO continues to discharge in the positive half cycle, the fast mechanical switch S is realized under the condition of approximate “zero voltage”, and the dielectric recovery is realized, as shown in Figure 9 .

[0087] t The current transfer is completed at the 3rd moment, the fast mechanical switch S in the main switch branch is arc extinguishing and turned off. Subsequently, the thyristor T7 is turned on, the CO-LO-T3-T7 circuit is turned on, the high-frequency transformer M1 is turned off, on the one hand, the high voltage is not borne by the fast mechanical switch S, and on the other hand, sufficient energy can be charged into the capacitor CO again. The capacitor CO continues to discharge in the positive half cycle, the fast mechanical switch S is realized under the condition of approximate “zero voltage”, and the dielectric recovery is realized, as shown in Figure 10 .

[0088] t The capacitor CO continues to discharge in the positive half cycle, the fast mechanical switch S is realized under the condition of approximate “zero voltage”, and the dielectric recovery is realized, as shown in t The zero-crossing turn-off is realized at the 6th moment, as shown in Figure 11 . Meanwhile, according to the voltage waveform of the current transfer branch in Figure 5 , it can be seen that after the zero-crossing of the current in the thyristor, t 4~ t 5stage can bear sufficient reverse voltage to ensure the recovery of the forward blocking capability.

[0089] The above describes in detail the DC circuit breaker based on the thyristor and the breaking method of the DC circuit breaker, the principle and the implementation mode of the present application are described by using specific examples, the above description of the examples is only used to help understand the method and the core idea of the present application; meanwhile, according to the idea of the present application, the specific implementation mode and the application range can be modified by the person skilled in the art, and the above description should not be understood as the limitation of the present application.

Claims

1. A thyristor-based DC circuit breaker, characterized in that: include: The main switch branch, current transfer branch, voltage-limiting energy-consuming branch, and pulse commutation circuit are shown. The DC circuit breaker is connected in series with the power system. The two series nodes are marked as Q1 and Q2. The main switch branch and the voltage-limiting energy-consuming branch are connected in parallel through Q1 and Q2. One end of the secondary side of the two high-frequency transformers in the pulse commutation circuit is connected to Q1 and Q2, respectively, and the other end is connected to both ends of the current transfer branch. The main switch branch is composed of a fast mechanical switch (S); The current transfer branch is composed of two groups of thyristors (T1) and (T2) connected in anti-parallel, and the external connection points are marked as N5 and N6; The pulse commutation circuit is composed of a pre-charge capacitor (C0), an energy storage inductor (L0), thyristors (T0), (T3), (T4), (T5), (T6), (T7), (T8) and high-frequency transformers (M1), (M2); The positive electrode of the pre-charge capacitor (C0) and one electrode of the energy storage inductor (L0) are connected in series, and the negative electrode of the capacitor C0 and the other electrode of the energy storage inductor (L0) are respectively recorded as external connection points N4 and N2; Thyristor (T3) and thyristor (T4) are connected in anti-parallel, one end is marked as N1 and the other end is connected to N2; Thyristor (T5) and thyristor (T6) are connected in anti-parallel, one end is marked as N3 and the other end is connected to N2; The cathodes of thyristor (T7) and thyristor (T8) are connected to N4, and the anodes are connected to N1 and N3 respectively; The primary and secondary sides of the high-frequency transformer are both composed of high-voltage wires wound around ferrite rings, with the same end wound, and the number of turns on the secondary side is greater than that on the primary side; The primary side of the high-frequency transformer (M1) is connected in parallel with the thyristor (T7) through N1 and N4, and the secondary side is connected to the main switch branch and the current transfer branch through nodes Q1 and N5; the primary side of the high-frequency transformer (M2) is connected in parallel with the thyristor (T8) through nodes N3 and N4, and the secondary side is connected to the main switch branch and the current transfer branch through nodes Q2 and N6; The voltage-limiting energy-consuming branch is composed of a varistor (MOV).

2. A method for disconnecting a DC circuit breaker, applied to the thyristor-based DC circuit breaker according to claim 1, characterized in that: The following steps are involved: Under rated operating conditions, close the fast mechanical switch (S) to carry the system current; During the short-circuit breaking process, a tripping command is first sent to the fast mechanical switch (S). When the moving and static contacts of the fast mechanical switch (S) are opened to a sufficient distance, the thyristors in the pulse commutation circuit and the thyristors in the current transfer branch are selectively turned on according to the direction of the system current of the power system flowing through the DC circuit breaker. In the positive half cycle of the pre-charge capacitor (C0) discharge, the fault current is transferred from the main switch branch to the current transfer branch through the induced electromotive force of the high-frequency transformer (M1) or (M2); During the negative half cycle of the pre-charge capacitor (C0) discharge, the varistor (MOV) is turned on by the induced electromotive force of the high-frequency transformer (M1) or (M2), so as to transfer the fault current from the current transfer branch to the voltage-limited energy-consuming branch and complete the fault interruption.

3. The method for disconnecting a DC circuit breaker according to claim 2, wherein: The short-circuit breaking process comprises the following steps: If the system current flows from Q1 to Q2, when the moving and static contacts of the fast mechanical switch (S) open to the preset opening distance, the pulse commutation circuit and the current transfer branch are put into operation; First, turn on the thyristors (T1) and (T6), so that the secondary side of (M2) induces a positive electromotive force at the top and a negative electromotive force at the bottom, so that the fault current is transferred from the fast mechanical switch (S) of the main switch branch to the thyristor (T1) of the current transfer branch; After the current transfer is completed, the thyristor (T8) is turned on, causing (M2) to stop operating; The pre-charge capacitor (C0) is continuously discharged and reversely charged after the voltage of the pre-charge capacitor (C0) drops to zero. The thyristor (T1) of the current transfer branch carries the system current and the fast mechanical switch (S) performs dielectric recovery. When the voltage in the pre-charge capacitor (C0) reaches the reverse peak, the thyristors (T5) and (T0) are turned on, causing the pre-charge capacitor (C0) to discharge through the high-frequency transformer (M2), inducing an electromotive force with a negative upper side and a positive lower side on the secondary side to turn on the varistor (MOV), and under the action of the reverse voltage, the thyristor (T1) is forced to turn off, realizing the transfer of the fault current from the current transfer branch to the voltage-limiting energy consumption branch, and completing the disconnection.

4. The method for disconnecting a DC circuit breaker according to claim 2, wherein: The short-circuit breaking process further comprises the following steps: If the system current flows from Q2 to Q1, when the moving and static contacts of the fast mechanical switch (S) open to the preset opening distance, the pulse commutation circuit and the current transfer branch are put into operation; First, turn on the thyristors (T2) and (T3), so that the secondary side of (M1) induces a positive electromotive force at the top and a negative electromotive force at the bottom, so that the fault current is transferred from the fast mechanical switch (S) of the main switch branch to the thyristor (T2) of the current transfer branch; After the current transfer is completed, the thyristor (T7) is turned on, causing (M1) to stop operating; The precharge capacitor (C0) continuously discharges, and after the voltage drops to zero, it is reversely charged. The current transfer branch thyristor T2 carries the system current, and the fast mechanical switch S performs dielectric recovery. When the voltage in the pre-charge capacitor (C0) reaches the reverse peak, the thyristors (T4) and (T0) are turned on, causing the pre-charge capacitor (C0) to discharge through the high-frequency transformer (M1), inducing an electromotive force with a negative top and a positive bottom on the secondary side, thereby turning on the varistor (MOV) and causing the thyristor (T2) to turn off, realizing the transfer of the fault current from the current transfer branch to the voltage-limiting energy-consuming branch, and completing the disconnection.

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