Thyristor-based direct-current circuit breaker and on-off method of direct-current circuit breaker

Abstract

The invention relates to a direct-current circuit breaker based on a thyristor and an on-off method of the direct-current circuit breaker, and belongs to the technical field of direct-current middle-high voltage power system fault protection. The direct-current circuit breaker comprises a main switch branch, a current transfer branch, a voltage-limiting energy consumption branch and a pulse commutation loop, the direct-current circuit breaker is connected with a power system in series, and the main switch branch is connected with the current transfer branch. Two nodes connected in series are respectively marked as Q1 and Q2, the main switch branch and the voltage-limiting energy consumption branch are connected in parallel through the Q1 and Q2, one ends of secondary sides of two high-frequency transformers in the pulse commutation loop are respectively connected to the Q1 and Q2, and the other ends of the secondary sides of the two high-frequency transformers in the pulse commutation loop are respectively connected to two ends of the current transfer branch. The problem that in the prior art, a large number of pulse charging and discharging loops are configured for meeting the fault large-current breaking requirement, and consequently the size and cost are increased is effectively solved.

Description

Technical Field

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

[0002] Thyristors are ideal semiconductor devices for hybrid circuit breakers in medium / high voltage DC power systems due to their current carrying capacity and withstand voltage rating. The transfer of fault current from the main switch branch to the current transfer branch is the core link of hybrid disconnection. In medium / high voltage DC power systems, due to the voltage rating of a single device, multiple devices are often required to be used in series to meet the requirements. This results in the on-state voltage drop in the current transfer branch often being greater than the arc voltage of the fast mechanical switch of the main switch branch, resulting in current transfer failure.

[0003] The prior art proposes to connect a fully controlled semiconductor device IGBT in series with the main switch branch, and use the IGBT to generate voltage when it is turned off to achieve the transfer of fault current. However, this solution has serious losses under rated current 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 the thyristor is a semi-controlled device, an external auxiliary pulse circuit is required to achieve shutdown. If a "coupled negative voltage" pulse circuit is added, two sets of bridge pulse capacitor discharge systems are required, and corresponding charging and discharging circuits 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 that a large number of pulse charging and discharging circuits are configured to meet the needs of large fault current breaking, thereby increasing the volume and cost.

[0005] In order 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, 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 through Q1 and Q2, one end of the secondary side of two high-frequency transformers in the pulse commutation circuit is respectively connected to Q1 and Q2, and the other end is respectively connected to the two 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), a thyristor (T0), (T3) , (T4), (T5), (T6), (T7), (T8) and high frequency transformers (M1), (M2); 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; 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-name ends 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 the node Q1 and the node N5; the primary side of the high-frequency transformer (M2) is connected in parallel with the thyristor (T8) through the nodes N3 and N4, and the secondary side is connected to the main switch branch and the current transfer branch through the node Q2 and the node N6; The voltage-limiting energy-consuming branch is composed of a varistor (MOV); The present invention also provides a disconnection method of a DC circuit breaker, which is applied to the DC circuit breaker based on a thyristor described in the above device item, and comprises the following steps: Under rated operating conditions, close the fast mechanical switch (S) to carry the system current; During the short-circuit breaking process, a switch-off 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 opening distance, the thyristors in the pulse commutation circuit and the thyristors in the current transfer branch are selectively turned on according to the direction in which the system current of the power system flows through the DC circuit breaker. In the positive half cycle of the pre-charge capacitor (C0) discharging, 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); In 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-limiting energy consumption branch and complete the fault interruption.

[0006] In a possible implementation, the short circuit breaking process further includes 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) to induce an electromotive force with positive top and negative bottom on the secondary side of (M2), so as to transfer the fault current 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 then reversely charged after the voltage of the pre-charge capacitor (C0) drops to zero, and the current transfer branch thyristor T1 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 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 electromotive force with a negative upper side and a positive lower side is induced on the secondary side to turn on the varistor (MOV), and the thyristor (T1) is turned off under the action of the reverse voltage, so that the fault current is transferred from the current transfer branch to the voltage-limiting energy consumption branch, and the disconnection is completed.

[0007] In a possible implementation, the short circuit breaking process further includes 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) to induce an electromotive force with positive top and negative bottom on the secondary side of (M1), so as to transfer the fault current 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 pre-charge capacitor (C0) is continuously discharged, and then reversely charged after the voltage drops to zero. The current transfer branch thyristor T2 carries the system current and the fast mechanical switch S performs dielectric recovery.

[0008] When the voltage in the pre-charge capacitor (C0) reaches the reverse peak value, the thyristors (T4) and (T0) are turned on, so that the pre-charge capacitor (C0) is discharged through the high-frequency transformer (M1), and an electromotive force with a negative upper side and a positive lower side is induced on the secondary side to turn on the varistor (MOV) and cause the thyristor (T2) to turn off, thereby realizing the transfer of the fault current from the current transfer branch to the voltage-limiting energy consumption branch, and completing the disconnection.

[0009] The beneficial effects of the present invention are as follows: a DC circuit breaker provided by the present invention only uses one set of bridge pulse discharge circuits to achieve rapid transfer of fault current of hybrid circuit breakers in the medium and high voltage fields and 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 in design, which is conducive to the modular design of the control system and increases the reliability of hybrid breaking, 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 breaking, which leads to increased volume and cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 A schematic structural diagram of an embodiment of a thyristor-based DC circuit breaker provided by the present invention; Figure 2 A method flow chart of an embodiment of a fault current transfer method provided by the present invention; Figure 3 for Figure 2 When the system current flows from Q1 to Q2, step S202 is a method flow chart of an embodiment; Figure 4 for Figure 2 When the system current flows from Q2 to Q1, step S202 is a method flow chart of an embodiment; 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 Figure 6 The inductive commutation topology diagram provided by the present invention when the current flows from Q1 to Q2; Figure 7 A reverse charging topology diagram when the current provided by the present invention flows from Q1 to Q2; Figure 8 A high voltage shutdown topology diagram when the current provided by the present invention flows from Q1 to Q2; Fig. 9 The inductive commutation topology diagram provided by the present invention when the current flows from Q2 to Q1; Fig.10 A reverse charging topology diagram when the current provided by the present invention flows from Q2 to Q1; Fig.11 The present invention provides a high voltage shutdown topology diagram when the current flows from Q2 to Q1. DETAILED DESCRIPTION

[0011] The preferred embodiments of the present invention are described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not used to limit the scope of the present invention.

[0012] Before showing the embodiments, the following terms are explained: In the description of the embodiments of the present invention, unless otherwise specified, "multiple" means two or more than two. "And / or" describes the association relationship of associated objects, indicating that three relationships may exist. For example, "A and / or B" may mean: A exists alone, A and B exist at the same time, and B exists alone.

[0013] The descriptions of "first", "second", etc. involved in the embodiments of the present invention are only for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the technical features defined as "first" and "second" may explicitly or implicitly include at least one of the features.

[0014] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present invention. The appearance of the phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0015] In order to solve the above problems, Figure 1 As 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 in 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 through Q1 and Q2, one end of the secondary side of two high-frequency transformers in the pulse commutation circuit is respectively connected to Q1 and Q2, and the other end is respectively connected to the two ends of the current transfer branch; The main switch branch consists 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 pre-charge capacitor C0, energy storage inductor L0, thyristors T0, T3, T4, T5, T6, T7, T8 and high-frequency transformers M1 and M2; 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; 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 thyristors T7 and T8 are commonly 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-name ends wound, and the number of turns on the secondary side is not less 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 the node Q1 and the node N5; the primary side of the high-frequency transformer M2 is connected in parallel with the thyristor T8 through the nodes N3 and N4, and the secondary side is connected to the main switch branch and the current transfer branch through the node Q2 and the node N6; The voltage-limiting energy-consuming branch is composed of a varistor MOV.

[0016] Compared with the prior art, 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 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, which is conducive to the modular design of the control system and increases the reliability of hybrid breaking, thereby effectively solving the problem in the prior art that a large number of pulse charging and discharging circuits are configured to meet the needs of large fault current breaking, resulting in increased volume and cost.

[0017] like Figure 2 The present invention also provides a disconnection method of a DC circuit breaker, which is applied to the DC circuit breaker based on a thyristor described in the above-mentioned device item, and comprises the following steps: S201, under rated operating conditions, close the fast mechanical switch S to carry the system current; S202. During the short-circuit breaking process, a breaking 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 opening distance, the thyristors in the pulse commutation circuit and the thyristors in the current transfer branch are selectively turned on according to the direction in which the system current of the power system flows through the DC circuit breaker; in 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; in 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 to realize the transfer of the fault current from the current transfer branch to the voltage-limiting energy consumption branch, and complete the fault breaking.

[0018] like Figure 3 In a possible implementation, step S202 includes the following steps: S301, if the system current flows from Q1 to Q2, when the moving and static contacts of the fast mechanical switch S are opened to the preset opening distance, the pulse commutation circuit and the current transfer branch are put into operation; S302, first turn on the thyristors T1 and T6, so that the secondary side of M2 induces an electromotive force with positive top and negative bottom, 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; S303, after the current transfer is completed, turn on the thyristor T8 to make M2 stop running; 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; S305. When the voltage in the pre-charge capacitor C0 reaches the 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 electromotive force with a negative upper side and a positive lower side is induced on the secondary side to turn on the varistor MOV, and the thyristor T1 is turned off under the action of the reverse voltage, 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 disconnection.

[0019] like Figure 4 In a possible implementation, step S202 further includes the following steps: S401, if the system current flows from Q2 to Q1, when the moving and static contacts of the fast mechanical switch S are opened to the preset opening distance, the pulse commutation circuit and the current transfer branch are put into operation; S402, first turn on the thyristors T2 and T3, so that the secondary side of M1 induces an electromotive force with positive top and negative bottom, 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; S403, after the current transfer is completed, turn on the thyristor T7 to make M1 stop running; S404, the pre-charge capacitor C0 is continuously discharged, and after the voltage drops to zero, it is reversely charged, and the current transfer branch thyristor T2 carries the system current and the fast mechanical switch S performs dielectric recovery; S405. When the voltage in the pre-charge capacitor C0 reaches the reverse peak value, the thyristors T4 and T0 are turned on, so that the pre-charge capacitor C0 is discharged through the high-frequency transformer M1, and an electromotive force with a negative upper side and a positive lower side is induced on the secondary side to turn on the varistor MOV and cause the thyristor T2 to turn off, thereby realizing the transfer of the fault current from the current transfer branch to the voltage-limiting energy consumption branch, and completing the disconnection.

[0020] Figure 5The waveform diagram of circuit parameters of the system and each branch of the DC circuit breaker provided by the present invention during operation is shown.

[0021] in accordance with Figure 5 The breaking method of the DC circuit breaker provided by the present invention is further described: t 0~ t Stage 1: The system operates at rated current carrying conditions, the fast mechanical switch S is closed, carrying the system current i 0. Fast mechanical switching with extremely low on-state losses enables low losses at rated current carrying conditions.

[0022] t At time 1, a short circuit occurs and the current in the system rises rapidly. First, the opening command of the fast mechanical switch S is sent. After a period of inherent delay, the moving and static contacts of the fast mechanical switch S open.

[0023] t 2. At the moment when the moving and static contacts of the fast mechanical switch S are separated to a suitable opening distance, the pulse commutation circuit and the current transfer branch are put into operation (the specific conduction thyristor is determined by the current direction). The specific control is as follows: 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 and negative lower sides. The current in the main switch branch is quickly transferred to the thyristor T1 in the current transfer branch. Figure 6 shown.

[0024] 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 loop is turned on, and the high-frequency transformer M2 is shut down. 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 enough energy can be charged into the capacitor C0 again. 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 realizes dielectric recovery at approximately "zero voltage". Refer to Figure 7 shown.

[0025] t At time 4, the voltage across capacitor C0 reaches the reverse peak. Turn on thyristors T5 and T0, 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 transformer M2, inducing a high-voltage electromotive force with negative top and positive bottom on the secondary side of high-frequency transformer M2. The varistor is turned on, and at the same time, the thyristor T1 is turned off under the action of this voltage, and the fault current is transferred to the voltage-limited energy consumption branch and t6. Realize zero-crossing shutdown at any time, refer to Figure 8 shown.

[0026] At the same time, according to Figure 5 It can be seen from the voltage waveform of the current transfer branch that after the current in thyristor T1 passes zero, t 4~ t Phase 5 can withstand sufficient reverse voltage to ensure restoration of forward blocking capability.

[0027] 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 C0-L0-T3-M1 circuit is turned on, and the secondary side of the high-frequency transformer M1 induces an induced electromotive force with positive upper and negative lower sides. The current in the main switch branch is quickly transferred to the thyristor T2 in the current transfer branch. Fig. 9 shown.

[0028] 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 T7 is turned on, the C0-L0-T3-T7 loop is turned on, and the high-frequency transformer M1 is shut down. On the one hand, it ensures that the two ends of the fast mechanical switch S are not subjected to high voltage; on the other hand, it ensures that enough energy can be charged into the capacitor C0 again. Capacitor C0 continues to discharge in the positive half cycle. In this stage, the system current is carried by the thyristor T2, and the fast mechanical switch S realizes dielectric recovery at approximately "zero voltage". Refer to Fig.10 shown.

[0029] t At time 4, the voltage across capacitor C0 reaches the reverse peak. Turn on thyristors T4 and T0, the C0-M1-T4-T0 loop is turned on, and the pre-charged capacitor C0 is discharged through the high-frequency transformer M1. The energy storage inductor L0 exits operation, and the voltage across C0 is fully loaded on the primary side of transformer M1, inducing a high-voltage electromotive force with negative top and positive bottom on the secondary side of high-frequency transformer M1. The varistor turns on, and at the same time, the thyristor T2 is turned off under the action of this voltage, and the fault current is transferred to the voltage-limited energy consumption branch and t 6. Realize zero-crossing shutdown at any time, refer to Fig.11 At the same time, according to Figure 5 It can be seen from the voltage waveform of the current transfer branch that after the current in the thyristor passes zero, t 4~ t Phase 5 can withstand sufficient reverse voltage to ensure restoration of forward blocking capability.

[0030] The above is a detailed introduction to a thyristor-based DC circuit breaker and a DC circuit breaker breaking method provided by the present invention. Specific examples are used in this article to illustrate the principle and implementation method of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea; at the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be modifications in the specific implementation method and application scope. In summary, the content of this specification should not be understood as a limitation on the present invention.

Claims

1. A thyristor-based DC circuit breaker, characterized in that: include: Main switch branch, current transfer branch, voltage limiting energy consumption branch and pulse commutation circuit, wherein the DC circuit breaker is connected in series with the power system, the two nodes in series are respectively marked as Q1 and Q2, the main switch branch and the voltage limiting energy consumption 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 the two ends of the current transfer branch respectively: 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) 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; 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-name ends 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 the node Q1 and the node N5; the primary side of the high-frequency transformer (M2) is connected in parallel with the thyristor (T8) through the nodes N3 and N4, and the secondary side is connected to the main switch branch and the current transfer branch through the node Q2 and the node N6; The voltage-limiting energy-consuming branch is composed of a varistor (MOV).

2. A method for breaking 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 switch-off command is firstly sent to the fast mechanical switch (S). When the moving and static contacts of the fast mechanical switch (S) are opened to a sufficient opening distance, the thyristors in the pulse commutation circuit and the thyristors in the current transfer branch are selectively turned on according to the direction in which the system current of the power system flows through the DC circuit breaker. In the positive half cycle of the pre-charge capacitor (C0) discharging, 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); In 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-limiting energy consumption branch and complete the fault interruption.

3. The method for disconnecting a DC circuit breaker according to claim 2, characterized in that: 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) to induce an electromotive force with positive top and negative bottom on the secondary side of (M2), so as to transfer the fault current 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 then reversely charged after the voltage of the pre-charge capacitor (C0) drops to zero, and the current transfer branch thyristor (T1) 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 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 electromotive force with a negative upper side and a positive lower side is induced on the secondary side to turn on the varistor (MOV), and the thyristor (T1) is turned off under the action of the reverse voltage, so that the fault current is transferred from the current transfer branch to the voltage-limiting energy consumption branch, and the disconnection is completed.

4. The method for disconnecting a DC circuit breaker according to claim 2, characterized in that: 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) to induce an electromotive force with positive top and negative bottom on the secondary side of (M1), so as to transfer the fault current 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 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; When the voltage in the pre-charge capacitor (C0) reaches the reverse peak value, the thyristors (T4) and (T0) are turned on, so that the pre-charge capacitor (C0) is discharged through the high-frequency transformer (M1), and an electromotive force with a negative upper side and a positive lower side is induced on the secondary side to turn on the varistor (MOV) and cause the thyristor (T2) to turn off, thereby realizing the transfer of the fault current from the current transfer branch to the voltage-limiting energy consumption branch, and completing the disconnection.

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