Direct-current circuit breaker based on thyristor and mutual inductor and control method

Abstract

The invention discloses a direct current circuit breaker based on thyristors and a mutual inductor. A primary side winding of the mutual inductor, a thyristor Tm1, a thyristor Tm2 and a secondary side winding N2 of the mutual inductor are sequentially connected in series between a first endpoint and a second endpoint of a main branch, the thyristor Tm1 and the thyristor Tm2 are reversely connected in parallel, and the N1 and the N2 are dotted terminals; the first capacitor branch comprises a capacitor C1, one end is connected with the first endpoint of the main branch, and the other end is connected with the first charging branch; the first charging branch comprises a charging loop formed by connecting a diode Dc1 and a resistor R1 in series and is used for charging a capacitor C1; the first trigger branch comprises a thyristor Ta1, the anode of the first trigger branch is connected with the non-point end of the primary side winding N1 of the mutual inductor, and the cathode of the first trigger branch is connected with the anode of a diode Dc1; the first buffer branch comprises a diode Ds1 which is connected in series with the lightning arrester M1, the cathode is connected with the first end point of the main branch, and the anode is connected to the anode of the diode Dc1 through the lightning arrester M1. The thyristor type direct current circuit breaker can solve the problems that a traditional thyristor type direct current circuit breaker cannot actively cut off current, the false triggering risk is high, the conduction loss is large, and a reclosing function is lacked.

Description

Technical Field

[0001] This application relates to the technical field of power system protection, and more specifically, to a DC circuit breaker and a control method based on thyristors and current transformers. Background Art

[0002] DC protection is particularly important in power systems, especially widely applied in low-voltage DC scenarios such as data centers, renewable energy systems, and electric vehicle charging. The fault characteristics of DC systems are different from those of AC systems. The short-circuit current rises faster and has a higher amplitude, posing a severe challenge to the safety of equipment and systems. The DC circuit breaker is a key device that can quickly and accurately detect and isolate faults, prevent fault spread and equipment damage, and ensure the stability and reliability of the system. It is an important research direction in the field of power engineering.

[0003] Solid-state DC circuit breakers have been widely studied in recent years because they can quickly interrupt the current and thus effectively protect the DC system. In terms of the selection of power electronic devices, thyristors are considered to be one of the suitable devices for designing DC circuit breakers due to their advantages such as low conduction loss, low cost, and large inrush current capacity. However, the existing thyristor-based solid-state DC circuit breakers still have the following problems:

[0004] Unable to actively interrupt the operating current: The thyristor-based solid-state DC circuit breaker adopts a passive triggering condition that depends on the fault current and cannot actively cut off the current during normal operation; Risk of mis-triggering: When the line current fluctuates, the passive solution may be mis-triggered, thus bringing additional systematic risks; High conduction loss: There are multiple power electronic devices connected in series in the main branch of the circuit breaker, resulting in high conduction energy loss; Lack of reclosing ability: It cannot automatically restore power supply after the fault is cleared, and its practicality is not high.

[0005] Although the thyristor-based circuit breaker in the prior art has the advantage of low conduction loss, the above defects limit its application. Therefore, there is an urgent need for a DC circuit breaker solution with active control, low loss, and high reliability. Summary of the Invention

[0006] In view of at least one defect or improvement requirement of the prior art, the present invention provides a DC circuit breaker and a control method based on thyristors and current transformers, which can solve technical problems such as the inability of traditional thyristor-based DC circuit breakers to interrupt the operating current, high risk of mis-triggering, large conduction loss, and lack of reclosing function, and significantly improve the safety and reliability of the DC system.

[0007] To achieve the above-mentioned object, according to the first aspect of the present invention, a DC circuit breaker based on a thyristor and a transformer is provided, comprising: a main branch, a first capacitor branch, a second capacitor branch, a first charging branch, a second charging branch, a first trigger branch, a second trigger branch, a first buffer branch and a second buffer branch; a primary winding N of the transformer is connected in series between the first end point and the second end point of the main branch in sequence. 1 Point end, reverse parallel thyristor Tm 1 and thyristor Tm 2 , and the transformer secondary winding N 2 Point end, where N 1 With N 2 The first capacitor branch includes a capacitor C 1 , one end of which is connected to the first end point of the main branch, and the other end is connected to the first charging branch; the first charging branch includes a diode Dc 1 and resistor R 1 The charging circuit formed in series is used to charge the capacitor C 1 Charging; the first trigger branch includes a thyristor Ta 1 , its anode is connected to the primary winding N of the transformer 1 Non-point end, cathode connected to diode Dc 1 anode; the first buffer branch includes a diode Ds 1 With arrester M 1 The cathode is connected to the first terminal of the main branch, and the anode is connected to the arrester M 1 Connect to diode Dc 1 anode; the second capacitor branch, the second charging branch, the second trigger branch and the second buffer branch are symmetrically arranged on the second end side of the main branch with the first capacitor branch, the first charging branch, the first trigger branch and the first buffer branch.

[0008] In one embodiment of the present invention, the primary winding N of the transformer in the main branch 1 Non-point terminal and thyristor Tm 1 Anode and thyristor Tm 2 Cathode connection, thyristor Tm 1 and thyristor Tm 2 The other end is connected to the secondary winding N of the transformer 2 Point end.

[0009] In one embodiment of the present invention, the resistors R in the first charging branch and the second charging branch are 1 and resistor R 2 The resistance value depends on the DC system voltage and capacitance C 1 , capacitor C 2The capacity matching setting is used to ensure that the capacitor is charged to the system voltage.

[0010] In one embodiment of the present invention, the lightning arrester M 1 and the lightning arrester M 2 are zinc oxide lightning arresters, which are used to absorb the overvoltage generated in the energy dissipation process of the first capacitor branch and the second capacitor branch.

[0011] In one embodiment of the present invention, the thyristors Ta 1 in the first trigger branch and the second trigger branch and the thyristor Ta 2 are unidirectional conduction devices, and their trigger signals are output by an external controller according to the current direction judgment logic.

[0012] In one embodiment of the present invention, the transformation ratio range of the transformer in the main branch is 1:1 to 1:5; the rated current of the thyristors Tm 1 and the thyristors Tm 2 is 1.2 - 1.5 times the maximum short-circuit current of the DC system; the diodes Ds 1 and Ds 2 in the first buffer branch and the second buffer branch are fast recovery diodes, and their reverse recovery time is less than 100 ns.

[0013] According to the second aspect of the present invention, there is also provided a control method for a DC circuit breaker based on thyristors and transformers according to any one of the above embodiments, including the steps: S1. Charge the capacitors C 1 , capacitor C 2 in the first capacitor branch and the second capacitor branch to the DC system voltage; S2. Detect whether the system starts or the current in the main branch passes through zero. If the condition is met, enter S3; S3. Conduct the main branch thyristors Tm 1 and the thyristors Tm 2 ; S4. After receiving the opening signal, judge whether the current direction in the main branch is from the first end point to the second end point; S5. If the current direction is from the first end point to the second end point, conduct the first trigger branch, use the electromagnetic effect of the transformer to force the current in the main branch to drop to zero, turn off the thyristor Tm 1 , and discharge the energy of the capacitor C 1 through the first buffer branch; S6. If the current direction is from the second end point to the first end point, conduct the second trigger branch, turn off the thyristor Tm 2 , and discharge the energy of the capacitor C 2 through the second buffer branch; S7. Re-execute S1 to S6 according to the reclosing requirement.

[0014] In one embodiment of the present invention, in step S5, through electromagnetic coupling, on the secondary side winding N 2Induce a voltage in phase with the primary winding N of the current transformer, causing the current in the main branch to rapidly drop to zero. 1

[0015] In one embodiment of the present invention, in steps S5 and S6, the capacitors C 1 and the capacitor C 2 reverse their polarities after discharging energy and absorb the remaining energy through the arresters M 1 and the arrester M 2 in the buffer branch.

[0016] In one embodiment of the present invention, the reclosing judgment logic includes delaying the detection of whether the main branch fault is cleared, and if it is cleared, then reclosing the thyristors Tm 1 and the thyristor Tm 2 in the main branch.

[0017] Generally speaking, compared with the prior art, the above technical solution conceived by the present invention can at least achieve the following beneficial effects:

[0018] Adopt a structure of a single pair of reverse-parallel thyristors in series with a current transformer to optimize the main branch topology, reduce the number of devices to reduce conduction losses; combine capacitor energy storage with the electromagnetic effect of the current transformer to implement an active breaking control strategy for operating current and fault current; achieve two-way current handling ability through symmetrically designed capacitor branches and trigger branches to support rapid turn-off of current in any direction; utilize capacitor polarity reset and energy discharge in the buffer branch to ensure the reclosing mechanism for the circuit breaker to be repeatedly closed. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings required in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0020] Figure 1 FIG. is a schematic circuit diagram of a DC circuit breaker based on thyristors and current transformers provided by an embodiment of the present application;

[0021] Figure 2 FIG. is a flowchart of a control method for a DC circuit breaker based on thyristors and current transformers provided by an embodiment of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0022] ​To make the objectives, technical solutions and advantages of the present invention more clear and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0023] The terms "first", "second", "third", etc. in the specification and claims of this application and the above-mentioned drawings are used to distinguish different objects, rather than to describe a specific order. In addition, the terms "comprising" and "having" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device that includes a series of steps or units is not limited to the listed steps or units, but optionally further includes steps or units not listed, or optionally further includes other steps or units inherent to these processes, methods, products or devices.

[0024] As Figure 1 shown, the DC circuit breaker based on thyristors and current transformers proposed in the first embodiment of this application includes: a main branch, a capacitor branch 1, a capacitor branch 2, a charging branch 1, a charging branch 2, a trigger branch 1, a trigger branch 2, a buffer branch 1, and a buffer branch 2.

[0025] Specifically, the first end point of the main branch is point A, and the second end point is point B. From point A to point B, it successively passes through the primary side winding N 1 of the current transformer, a pair of antiparallel thyristors T m1 and T m2 , and the secondary side winding N 2 of the current transformer winding, where the N 1 and N 2 end points are the same-name ends. Further, the non-point end of the primary side winding N 1 of the current transformer is connected to the anode of thyristor T m1 and the cathode of thyristor T m2 , while the other ends of thyristors T m1 and T m2 are connected to the N 2 end point of the secondary side winding of the current transformer.

[0026] The capacitor branch 1 is composed of a capacitor C 1 , one end is connected to point A of the main branch, and the other end is connected to the charging branch 1. The charging branch 1 provides a charging circuit for the capacitor C 1 , and is composed of a diode D c1 and a resistor R 1 . The anode of the diode D c1 is connected to the capacitor C 1 , and the cathode is connected to the resistor R 1, and the resistor R 1 The other end is grounded. The trigger branch 1 consists of a thyristor T a1 The thyristor T a1 The anode is connected to the non-point end of the primary winding N of the mutual inductor 1 while the cathode is connected to the anode of the diode D c1 The buffer branch 1 consists of the diode D s1 and the lightning arrester M 1 The diode D s1 The cathode is connected to point A of the main branch, while the anode is connected to one end of the lightning arrester M 1 The other end of the lightning arrester M 1 is connected to the anode of the diode D c1 .

[0027] The capacitor branch 2 consists of a capacitor C 2 One end is connected to point B of the main branch, and the other end is connected to the charging branch 2. The charging branch 2 provides a charging circuit for the capacitor C 2 and consists of the diode D c2 and the resistor R 2 The diode D c2 The anode is connected to the capacitor C 2 while the cathode is connected to the resistor R 2 , and the other end of the resistor R 2 is grounded. The trigger branch 2 consists of a thyristor T a2 The thyristor T a2 The anode is connected to the point end of the primary winding N of the mutual inductor 2 while the cathode is connected to the anode of the diode D c2 The buffer branch 2 consists of the diode D s2 and the lightning arrester M 2 The diode D s2 The cathode is connected to point B of the main branch, while the anode is connected to one end of the lightning arrester M 2 The other end of the lightning arrester M 2 is connected to the anode of the diode D c2 .

[0028] The above-mentioned DC circuit breaker based on thyristors and mutual inductors proposed in the first embodiment of the present application realizes the optimization of the main branch topology by adopting a structure of a single pair of antiparallel thyristors in series with the mutual inductor, reduces the number of devices to reduce the conduction loss; combines the capacitor energy storage and the electromagnetic effect of the mutual inductor to realize the active breaking control strategy for the operating current and the fault current; realizes the two-way current handling ability through the symmetrically designed capacitor branch and trigger branch, and supports the rapid turn-off of the current in any direction; and uses the capacitor polarity reset and the energy dissipation of the buffer branch to ensure the reclosing mechanism that the circuit breaker can be repeatedly closed.

[0029] In one embodiment, the resistor R in the charging branch 1 and the charging branch 21 and resistor R 2 The resistance value is set according to the DC system voltage and capacitor C 1 and capacitor C 2 's capacitance to ensure that the capacitor is charged to the system voltage.

[0030] In one embodiment, the arrester M 1 and arrester M 2 is a zinc oxide arrester, which is used to absorb the overvoltage generated in the energy discharge process of capacitor branch 1 and capacitor branch 2.

[0031] In one embodiment, the thyristors Ta 1 and thyristors Ta 2 in trigger branch 1 and trigger branch 2 are unidirectional conduction devices, and their trigger signals are output by an external controller according to the current direction judgment logic.

[0032] In one embodiment, the transformation ratio range of the transformer in the main branch is from 1:1 to 1:5, which is used to match the current breaking requirements under different DC voltage levels. The rated current of the thyristor Tm 1 and Tm 2 is 1.2 - 1.5 times the maximum short-circuit current of the DC system to ensure reliable turn-off. The diodes Ds 1 and Ds 2 in buffer branch 1 and buffer branch 2 are fast recovery diodes, and their reverse recovery time is less than 100 ns, so as to improve the energy discharge efficiency.

[0033] In addition, the second embodiment of the present invention proposes a control method applied to the DC circuit breaker based on thyristors and transformers described in the first embodiment, including the steps of:

[0034] S1, charge the capacitors C 1 and capacitor C 2 in the first capacitor branch and the second capacitor branch to the DC system voltage; wait until the capacitors C 1 and C 2 are respectively charged to the DC system voltage and then enter S2;

[0035] S2, detect whether the system starts or whether the current in the main branch is zero during operation. If the condition is met, enter S3, otherwise return to S1;

[0036] S3, simultaneously turn on the main branch thyristors Tm 1 and thyristor Tm 2 , and enter S4; further, the turn-on signals of the main branch thyristors Tm 1 and thyristor Tm 2 are generated by a pulse width modulation (PWM) controller to reduce the turn-on loss;

[0037] S4. Determine whether an opening signal is received. After receiving the opening signal, determine whether the current direction of the main branch is from the first end point A to the second end point B. The opening signal is generated by an external protection device according to the fault detection result of the DC system, including at least one of short circuit, overcurrent or insulation fault.

[0038] S5. If the current direction is from the first end point A to the second end point B, turn on the first trigger branch, use the electromagnetic effect of the mutual inductor to force the current of the main branch to drop to zero, and turn off the thyristor Tm. 1 And discharge the energy of the capacitor C through the first buffer branch. 1 Energy.

[0039] S6. If the current direction is from the first end point B to the second end point A, turn on the second trigger branch, turn off the thyristor Tm. 2 And discharge the energy of the capacitor C through the second buffer branch. 2 Energy.

[0040] S7. Re-execute S1 to S6 according to the reclosing requirement.

[0041] In one embodiment, in step S5, through the electromagnetic coupling of the mutual inductors N 1 and N 2 , a voltage in the same phase as the primary side winding N 2 of the mutual inductor is induced in the secondary side winding N 1 of the mutual inductor, so that the current of the main branch quickly drops to zero.

[0042] In one embodiment, in steps S5 and S6, the polarities of the capacitors C 1 and C 2 are reversed after discharging energy, and the remaining energy is absorbed by the lightning arresters M 1 and M 2 in the buffer branch.

[0043] In one embodiment, the reclosing judgment logic includes detecting whether the fault of the main branch is cleared after a delay. If it is cleared, the main branch thyristor Tm 1 and the thyristor Tm 2 are reclosed.

[0044] It is worth mentioning that for the specific structure and the functions implemented by the DC circuit breaker based on thyristors and mutual inductors applicable to the control method proposed in this embodiment, reference can be made to the content described in the first embodiment, which will not be elaborated here in detail. And the beneficial effects of this embodiment are the same as those of the aforementioned first embodiment. For the sake of brevity, they will not be repeated here.

[0045] The third embodiment of the present invention further provides an electronic device, for example, including: at least one processing unit and at least one storage unit. Among them, the storage unit stores a computer program. When the computer program is executed by the processing unit, the processing unit is caused to execute the method described in the first embodiment, and the beneficial effects of the electronic device provided in this embodiment are the same as those of the control method applied to the DC circuit breaker based on thyristors and current transformers provided in the second embodiment.

[0046] The fourth embodiment of the present invention further provides a computer-readable storage medium, on which a computer program is stored. When the program is executed by a processor, the steps of the above method are implemented, and the beneficial effects of the computer-readable storage medium provided in this embodiment are the same as those of the control method applied to the DC circuit breaker based on thyristors and current transformers provided in the second embodiment.

[0047] Among them, the computer-readable storage medium may include, but is not limited to, any type of disk, including floppy disks, optical disks, DVDs, CD-ROMs, microdrives, and magneto-optical disks, ROMs, RAMs, EPROMs, EEPROMs, DRAMs, VRAMs, flash memory devices, magnetic cards or optical cards, nanosystems (including molecular memory ICs), or any type of medium or device suitable for storing instructions and / or data.

[0048] It should be noted that, for the foregoing method embodiments, for the sake of simple description, they are all expressed as a series of action combinations. However, those skilled in the art should know that the present application is not limited by the described action sequence, because according to the present application, certain steps can be performed in other sequences or simultaneously. Secondly, those skilled in the art should also know that the embodiments described in the specification are all preferred embodiments, and the actions and modules involved are not necessarily essential to the present application.

[0049] In the above embodiments, the descriptions of each embodiment have their own emphases. For the parts not detailed in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0050] In several embodiments provided by the present application, it should be understood that the disclosed device can be implemented in other ways. For example, the device embodiments described above are merely illustrative. For example, the division of the units is only a logical function division. In actual implementation, there may be other division methods. For example, multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the displayed or discussed coupling or direct coupling or communication connection to each other can be through some service interfaces. The indirect coupling or communication connection of the device or unit can be in an electrical or other form.

[0051] The unit described as a separation component may or may not be physically separated. The component shown as a unit may or may not be a physical unit, that is, it may be located in one place or distributed to multiple network units. Some or all of the units can be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0052] In addition, each functional unit in various embodiments of the present application may be integrated in a processing unit, may exist separately physically for each unit, or two or more units may be integrated in one unit. The above-mentioned integrated unit can be implemented in the form of hardware or in the form of a software functional unit.

[0053] If the integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable memory. Based on such an understanding, the technical solution of the present application, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a memory and includes several instructions to enable a computer device (which can be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the methods described in various embodiments of the present application. The aforementioned memory includes: USB flash drives, read-only memory (ROM), random access memory (RAM), mobile hard disks, magnetic disks, or optical disks, etc., which can store program codes.

[0054] Those of ordinary skill in the art can understand that all or part of the steps in the various methods of the above embodiments can be completed by instructing relevant hardware through a program. This program can be stored in a computer-readable memory, and the memory can include: flash drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks, etc.

[0055] The above are only exemplary embodiments of the present disclosure, and the scope of the present disclosure cannot be limited thereby. That is, any equivalent changes and modifications made according to the teachings of the present disclosure still fall within the scope covered by the present disclosure. After considering the specification and practicing the present disclosure, those skilled in the art will easily think of other implementation manners of the present disclosure. The present application aims to cover any variations, uses, or adaptive changes of the present disclosure, and these variations, uses, or adaptive changes follow the general principles of the present disclosure and include common general knowledge or conventional technical means in the technical field not recorded in the present disclosure. The specification and embodiments are only regarded as exemplary, and the scope and spirit of the present disclosure are defined by the claims.

[0056] The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope recorded in this specification.

[0057] Those skilled in the art can easily understand that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention should be included within the protection scope of the present invention.

Claims

1. A DC circuit breaker based on thyristor and transformer, characterized in that: include: A main branch, a first capacitor branch, a second capacitor branch, a first charging branch, a second charging branch, a first triggering branch, a second triggering branch, a first buffer branch, and a second buffer branch; The first end point and the second end point of the main branch are connected in series in sequence with the transformer primary winding point N1, the reverse parallel thyristor Tm1 and the thyristor Tm2, ​​and the transformer secondary winding point N2, wherein N1 and N2 are the same-named ends; The first capacitor branch includes a capacitor C1, one end of which is connected to the first end point of the main branch, and the other end of which is connected to the first charging branch; The first charging branch includes a charging loop formed by a diode Dc1 and a resistor R1 connected in series, and is used to charge the capacitor C1; The first trigger branch includes a thyristor Ta1, whose anode is connected to the non-point end of the primary winding N1 of the transformer, and whose cathode is connected to the anode of the diode Dc1; The first buffer branch includes a diode Ds1 connected in series with a lightning arrester M1, a cathode of which is connected to the first end of the main branch, and an anode of which is connected to the anode of the diode Dc1 through the lightning arrester M1; The second capacitor branch, the second charging branch, the second trigger branch and the second buffer branch are symmetrically arranged on the second end side of the main branch with the first capacitor branch, the first charging branch, the first trigger branch and the first buffer branch.

2. The DC circuit breaker according to claim 1, characterized in that: The non-point end of the primary winding N1 of the transformer in the main branch is connected to the anode of the thyristor Tm1 and the cathode of the thyristor Tm2, ​​and the other ends of the thyristor Tm1 and the thyristor Tm2 are commonly connected to the point end of the secondary winding N2 of the transformer.

3. The DC circuit breaker according to claim 1, characterized in that: The resistance values ​​of the resistor R1 and the resistor R2 in the first charging branch and the second charging branch are set according to the DC system voltage and the capacity matching of the capacitor C1 and the capacitor C2 to ensure that the capacitor is charged to the system voltage.

4. The DC circuit breaker according to claim 1, characterized in that: The lightning arrester M1 and the lightning arrester M2 are zinc oxide lightning arresters, which are used to absorb overvoltage generated by the first capacitor branch and the second capacitor branch during energy dissipation.

5. The DC circuit breaker according to claim 1, characterized in that: The thyristor Ta1 and the thyristor Ta2 in the first trigger branch and the second trigger branch are unidirectional conducting devices, and the trigger signals thereof are output by an external controller according to the current direction judgment logic.

6. The DC circuit breaker according to claim 1, characterized in that: The transformation ratio range of the transformer in the main branch is 1:1 to 1:5; the rated current of the thyristor Tm1 and the thyristor Tm2 is 1.2-1.5 times the maximum short-circuit current of the DC system; the diode Ds1 and the diode Ds2 in the first buffer branch and the second buffer branch are fast recovery diodes, and their reverse recovery time is less than 100ns.

7. A control method for a DC circuit breaker according to any one of claims 1 to 6, characterized in that: Includes steps: S1, charging the capacitors C1 and C2 of the first capacitor branch and the second capacitor branch to a DC system voltage; S2, detects whether the system starts or the main branch current passes zero, and if the conditions are met, enters S3; S3, turns on the main branch thyristor Tm1 and thyristor Tm2; S4, after receiving the disconnection signal, determining whether the current direction of the main branch is from the first end point to the second end point; S5, if the current direction is from the first end point to the second end point, the first trigger branch is turned on, the electromagnetic effect of the mutual inductor is used to force the main branch current to drop to zero, the thyristor Tm1 is turned off, and the energy of the capacitor C1 is discharged through the first buffer branch; S6, if the current direction is from the second end point to the first end point, the second trigger branch is turned on, the thyristor Tm2 is turned off, and the energy of the capacitor C2 is discharged through the second buffer branch; S7, re-execute S1 to S6 according to the reclosing requirement.

8. The control method according to claim 6, characterized in that: In the step S5, a voltage having the same phase as that of the primary winding N1 of the transformer is induced in the secondary winding N2 of the transformer through electromagnetic coupling, so that the main branch current drops rapidly to zero.

9. The control method according to claim 6, characterized in that: In the steps S5 and S6, the polarities of the capacitors C1 and C2 are reversed after discharging energy, and the lightning arresters M1 and M2 in the buffer branch absorb the remaining energy.

10. The control method according to claim 6, characterized in that: The reclosing judgment logic includes delaying detection of whether the main branch fault is cleared, and if cleared, reclosing the thyristor Tm1 and the thyristor Tm2 of the main branch.

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