Direct current circuit breaker with fault current adaptive regulation of current limiting inductance and current limiting method thereof

Abstract

This invention relates to a DC circuit breaker that adaptively adjusts the current-limiting inductor based on fault current. It includes at least two parallel branches, each branch consisting of a first current limiter, a variable inductor, and a second current limiter connected in series. A switch control circuit is connected in parallel to the first and second current limiters. One end of multiple first current limiters and one end of multiple second current limiters are connected in parallel. The anode of a thyristor is connected between the variable inductor and the second current limiter in the previous branch of the two adjacent branches, and the cathode of the thyristor is connected between the first current limiter and the variable inductor in the next branch of the two adjacent branches. This invention also discloses a current-limiting method for the DC circuit breaker that adaptively adjusts the current-limiting inductor based on fault current. This invention adaptively suppresses the current rise rate, current magnitude, and fault clearance based on the magnitude and rise rate of the fault current in the distribution line, effectively improving fault handling efficiency and the operational safety of the distribution line.

Description

Technical Field

[0001] This invention relates to the field of power system automation technology, and in particular to a DC circuit breaker and its current limiting method that adaptively adjusts the current limiting inductor based on fault current. Background Technology

[0002] Hybrid AC / DC power distribution systems based on energy storage and distributed renewable energy sources represent a crucial future direction for building electrification. In particular, the "photovoltaic-storage-DC-flexible" power distribution system (PV-Storage-DC-Flexible) possesses inherent advantages in improving building energy system efficiency, enhancing user safety, and enhancing ease of use. This system forms an interactive intermediary layer between the power grid, users, and distributed energy sources. It must ensure both the power quality and reliability requirements for users when connected to the grid, and also guarantee the system's independent operation when off-grid. Therefore, it exhibits high complexity in its functions and corresponding equipment. To improve building power quality, when a fault occurs in a PV-Storage-DC-Flexible power distribution system line, it is not possible to simply disconnect the entire line using a switch to avoid a complete power outage. Therefore, a circuit breaker operation is necessary to isolate the faulty line and prevent it from affecting the safe operation of the entire grid.

[0003] Because the fault current rise rate is high when a fault occurs in the "photovoltaic-storage-DC-flexible" power distribution system, it can easily damage the system or the circuit breaker before it takes effect. Existing DC circuit breakers generally do not consider the problem of excessively rapid current rise, meaning they are rarely equipped with current limiting functions. Thus, they only serve to interrupt the circuit, which is far from meeting the line safety requirements of the "photovoltaic-storage-DC-flexible" power distribution system. If a circuit breaker with current limiting simply uses a large inductor of a fixed size in series as the current limiting component, it will affect the response of the "photovoltaic-storage-DC-flexible" power distribution system to normal load changes. If the circuit breaker uses a microcontroller to identify the fault current and select branches with different inductors in series for current limiting, it will increase manufacturing costs and debugging difficulty. Moreover, the response speed to faults depends on the microcontroller's operating speed, which is not fast enough when a fault occurs in the "photovoltaic-storage-DC-flexible" power distribution system. Summary of the Invention

[0004] To achieve safe and rapid disconnection of faulty lines, the primary objective of this invention is to provide a DC circuit breaker that can limit the rate of current rise, quickly disconnect the fault current, and dissipate the energy stored in the system inductor by adaptively adjusting the current-limiting inductor based on the fault current.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: a DC circuit breaker that adaptively adjusts the current-limiting inductor by fault current, comprising at least two parallel branches, each branch consisting of a first current limiter, a variable inductor, and a second current limiter connected in series. A switch control circuit is connected in parallel to both the first and second current limiters. The first and second current limiters have identical structures. One end of multiple first current limiters is connected in parallel, and this parallel connection serves as the input terminal of the DC circuit breaker. One end of multiple second current limiters is connected in parallel, and this parallel connection serves as the output terminal of the DC circuit breaker. The anode of a thyristor is connected between the variable inductor and the second current limiter in the upper branch of the two adjacent branches, and the cathode of the thyristor is connected between the first current limiter and the variable inductor in the lower branch of the two adjacent branches. A limit switch SQ is provided within the switch control circuit.

[0006] The DC circuit breaker includes three parallel branches: the first branch, the second branch, and the third branch. Each branch consists of a first current limiter, a variable inductor, and a second current limiter connected in series. A switch control circuit is connected in parallel to both the first and second current limiters. The first and second current limiters have identical structures. One end of each of the three first current limiters is connected in parallel, serving as the input terminal of the DC circuit breaker. One end of each of the three second current limiters is connected in parallel, serving as the output terminal of the DC circuit breaker. The thyristors include a first thyristor D1 and a second thyristor D2. The anode of the first thyristor D1 is connected between the variable inductor and the second current limiter in the first branch. The cathode of the first thyristor D1 is connected between the first current limiter and the variable inductor in the second branch. The anode of the second thyristor D2 is connected between the variable inductor and the second current limiter in the second branch. The cathode of the second thyristor D2 is connected between the first current limiter and the variable inductor in the third branch.

[0007] The current limiter includes a high-speed mechanical main switch K1, a current-carrying branch, a current-breaking branch, and a voltage-limiting and current-relief branch. The current-carrying branch, current-breaking branch, and voltage-limiting and current-relief branch are connected in parallel, with one end A being the input terminal and the other end B being the output terminal. One end of the high-speed mechanical main switch K1 serves as the input terminal of the DC circuit breaker, and the other end of K1 is connected to end A. The current-carrying branch includes a high-speed mechanical switch K2 and an IGBT transistor Q0. One end of the high-speed mechanical switch K2 is connected to end A, and the other end is connected to the collector of the IGBT transistor Q0. The emitter of the IGBT transistor Q0 is connected to end B. The current-breaking branch includes n IGBT transistors Q1, Q2, ..., Q1 connected in series. n Each IGBT transistor has a buffer capacitor connected in parallel, namely C1, C2, ..., C1. n The pressure limiting and current venting branch adopts a metal oxide surge arrester (MOA).

[0008] The variable inductor includes a toroidal silicon steel core, a strip silicon steel core, an armature, a spring, and a power transmission line. The toroidal silicon steel core includes a left semicircular toroidal silicon steel core and a right semicircular toroidal silicon steel core arranged opposite each other and having the same structure. One end of the two is connected by a coupling, and the other end of the two has a gap. The strip silicon steel core is located inside the toroidal silicon steel core. The armature is welded to the middle of the right semicircular toroidal silicon steel core. The power transmission line is wound around the strip silicon steel core, the left semicircular toroidal silicon steel core, and the right semicircular toroidal silicon steel core in sequence. The limit switch SQ is located between the strip silicon steel core and the armature. The lower opening of the toroidal silicon steel core is welded downward to a mounting part for mounting the spring. The mounting part is composed of two iron plates arranged opposite each other, and the spring is welded to the inner side of the two iron plates. The power transmission line wound on the strip silicon steel core forms an electromagnet, and the power transmission line wound on the toroidal silicon steel core forms a toroidal coil.

[0009] The switch control circuit includes a limit switch SQ, an isolation operational amplifier U1, a first delay chip, and a second delay chip. One end of the limit switch SQ is connected to the input power supply, and the other end is connected to the non-inverting input terminal of the isolation operational amplifier U1. The inverting input terminal of the isolation operational amplifier U1 is grounded. The output terminal of the isolation operational amplifier U1 is connected to the input terminal of the first delay chip. The output terminal of the first delay chip is connected to the input terminal of the second delay chip. The output terminal of the second delay chip is connected to the input terminal of the current limiter. The switch control circuit outputs a control signal to the current limiter.

[0010] Another object of the present invention is to provide a current limiting method for a DC circuit breaker that adaptively adjusts the current limiting inductor based on fault current, the method comprising:

[0011] In normal operating mode: the current of the power distribution line is at a normal value, the current in the first current limiter and the second current limiter mainly flows through the current-carrying branch, the electromagnet and spring in the variable inductor are in the initial state, the air gap is large, and the inductance value of the variable inductor is a small initial value.

[0012] In the first fault current limiting mode: When the DC circuit breaker detects an increase in the distribution line current, the electromagnet's magnetic force increases due to the increase in the distribution line current. This attracts the left and right semi-circular annular silicon steel cores, causing the gap between them to decrease and tend to close. This also compresses the spring, driving the air gap of the annular coil to decrease, resulting in an increase in the inductance value of the variable inductor and suppressing the rate of current rise. If the distribution line current continues to rise, the air gap of the annular coil will continue to decrease until the air gap of the annular coil is at its minimum. At this time, the inductance value of the variable inductor reaches its maximum.

[0013] In the second fault current limiting mode: When the DC circuit breaker detects that the current in the distribution line continues to rise to a set threshold, at which point the air gap reaches its minimum or has already reached its minimum, the variable inductors in the n branches are switched from parallel to series connection through the control of the switching control circuit. At this time, the current in the distribution line becomes 1 / n of its original value, while the total inductance of the DC circuit breaker becomes n of its original value. 2 ;

[0014] In circuit breaking or recovery mode: If the fault detection system determines that fault clearance is required, it shuts off all first and second current limiters of the DC circuit breaker to break the circuit and cut off the system current; if it determines that the fault is a misjudgment or that the fault has been cleared, it restores the system to normal operation through the control of the switch control circuit.

[0015] As can be seen from the above technical solution, the beneficial effects of the present invention are as follows: First, the electromagnet driving force of the variable inductor in the present invention is directly provided by the fault current of the power distribution line, without the need for an additional power supply, and can react to changes in line current more quickly and directly; Second, the present invention cleverly utilizes the inductor's ability to suppress sudden changes in current. When a fault occurs in the power distribution line, this characteristic of the inductor can suppress rapidly changing current; Third, compared with a fixed-size inductor, the inductance value of the variable inductor will not be very large when the circuit is working normally, which can avoid the suppression of changes in circuit current caused by normal load changes, thereby ensuring the system's speed during normal operation. When an abnormal fault occurs, the inductance value of the variable inductor can increase rapidly, suppressing the increase of fault current and playing a good current limiting role. Attached Figure Description

[0016] Figure 1 This is a circuit structure block diagram of the present invention;

[0017] Figure 2 for Figure 1 Topology diagram of the current limiter;

[0018] Figure 3 for Figure 1 Schematic diagram of the structure of a variable inductor;

[0019] Figure 4 for Figure 1 Circuit diagram of the switch control circuit;

[0020] Figure 5 for Figure 3 A schematic diagram of the installation section. Detailed Implementation

[0021] like Figure 1As shown, a DC circuit breaker that adaptively adjusts the current-limiting inductor based on fault current includes at least two parallel branches. Each branch consists of a first current limiter, a variable inductor, and a second current limiter connected in series. A switch control circuit is connected in parallel to both the first and second current limiters. The first and second current limiters have the same structure. One end of multiple first current limiters is connected in parallel, and the parallel end serves as the input terminal of the DC circuit breaker. One end of multiple second current limiters is connected in parallel, and the parallel end serves as the output terminal of the DC circuit breaker. The anode of a thyristor is connected between the variable inductor and the second current limiter in the upper branch of the two adjacent branches. The cathode of the thyristor is connected between the first current limiter and the variable inductor in the lower branch of the two adjacent branches. A limit switch SQ is provided in the switch control circuit.

[0022] The DC circuit breaker includes three parallel branches: the first branch, the second branch, and the third branch. Each branch consists of a first current limiter, a variable inductor, and a second current limiter connected in series. A switch control circuit is connected in parallel to both the first and second current limiters. The first and second current limiters have identical structures. One end of each of the three first current limiters is connected in parallel, serving as the input terminal of the DC circuit breaker. One end of each of the three second current limiters is connected in parallel, serving as the output terminal of the DC circuit breaker. The thyristors include a first thyristor D1 and a second thyristor D2. The anode of the first thyristor D1 is connected between the variable inductor and the second current limiter in the first branch. The cathode of the first thyristor D1 is connected between the first current limiter and the variable inductor in the second branch. The anode of the second thyristor D2 is connected between the variable inductor and the second current limiter in the second branch. The cathode of the second thyristor D2 is connected between the first current limiter and the variable inductor in the third branch.

[0023] like Figure 2 As shown, the current limiter includes a high-speed mechanical main switch K1, a current-carrying branch, a current-breaking branch 9, and a voltage-limiting and current-relief branch. The current-carrying branch, the current-breaking branch 9, and the voltage-limiting and current-relief branch are connected in parallel, with one end A of the parallel connection serving as the input terminal and the other end B serving as the output terminal. One end of the high-speed mechanical main switch K1 serves as the input terminal of the DC circuit breaker, and the other end of the high-speed mechanical main switch K1 is connected to end A. The current-carrying branch includes a high-speed mechanical switch K2 and an IGBT transistor Q0. One end of the high-speed mechanical switch K2 is connected to end A, and the other end is connected to the collector of the IGBT transistor Q0. The emitter of the IGBT transistor Q0 is connected to end B. The current-breaking branch 9 includes n IGBT transistors Q1, Q2, ..., Q1 connected in series. n Each IGBT transistor has a buffer capacitor connected in parallel, namely C1, C2, ..., C1. n The pressure limiting and current venting branch adopts a metal oxide surge arrester (MOA).

[0024] like Figure 3 , 5As shown, the variable inductor includes a toroidal silicon steel core, a strip silicon steel core 4, an armature 3, a spring 2, and a transmission line 5. The toroidal silicon steel core includes a left semicircular toroidal silicon steel core 6 and a right semicircular toroidal silicon steel core 7 arranged opposite each other and having the same structure. One end of the two is connected by a connecting shaft 1, and this end has a through hole. They are connected by a shaft, allowing them to move around the shaft. The other end of the two has a gap. The strip silicon steel core 4 is located inside the toroidal silicon steel core, and the armature 3 is welded to the right semicircular toroidal silicon steel core 7. In the middle, the transmission line 5 is wound in sequence with a strip silicon steel magnetic core 4, a left semi-circular annular silicon steel magnetic core 6, and a right semi-circular annular silicon steel magnetic core 7. The limit switch SQ is located between the strip silicon steel magnetic core 4 and the armature 3. The lower opening of the annular silicon steel magnetic core is welded downward to the mounting part 8 for installing the spring. The mounting part 8 is composed of two iron plates arranged opposite each other. The spring 2 is welded to the inner side of the two iron plates. The transmission line 5 is wound on the strip silicon steel magnetic core 4 to form an electromagnet, and the transmission line 5 is wound on the annular silicon steel magnetic core to form an annular coil.

[0025] like Figure 4 As shown, the switch control circuit includes a limit switch SQ, an isolation operational amplifier U1, a first delay chip, and a second delay chip. One end of the limit switch SQ is connected to the input power supply, and the other end is connected to the non-inverting input terminal of the isolation operational amplifier U1. The inverting input terminal of the isolation operational amplifier U1 is grounded. The output terminal of the isolation operational amplifier U1 is connected to the input terminal of the first delay chip. The output terminal of the first delay chip is connected to the input terminal of the second delay chip. The output terminal of the second delay chip is connected to the input terminal of a current limiter. The switch control circuit outputs a control signal to the current limiter. Specifically, the isolation operational amplifier U1 outputs a control signal G1 to the high-speed mechanical switch K2, and the first delay chip outputs a control signal G2 to the IGBT transistors Q1, Q2, ..., Q6. n The second delay chip outputs control signal G3 to the high-speed mechanical master switch K1.

[0026] This rate limiting method includes:

[0027] In normal operating mode: the current of the power distribution line is at the normal value, the current in the first current limiter and the second current limiter mainly flows through the current-carrying branch, the electromagnet and spring 2 in the variable inductor are in the initial state, the air gap is large, and the inductance value of the variable inductor is a small initial value.

[0028] In the variable inductor, spring 2 is in a compressed state, and the electromagnet has an attractive force on armature 3. Under the combined action of the elastic force of spring 2 and the magnetic force of electromagnet, the relative positions of the left semi-circular annular silicon steel core 6 and the right semi-circular annular silicon steel core 7 are in the initial state, and the air gap is large. Therefore, the inductance value of the variable inductor is very small.

[0029] Furthermore, since the three branches of the DC circuit breaker are in parallel, the inductance can be further reduced, that is, the total inductance is 1 / 3 of that of a single variable inductor.

[0030] In the first fault current limiting mode: When the DC circuit breaker detects an increase in the distribution line current, the electromagnet's magnetic force increases due to the increase in the distribution line current, attracting the left semi-circular annular silicon steel core 6 and the right semi-circular annular silicon steel core 7, causing the gap between them to decrease and tend to close, and compressing the spring 2, which drives the air gap of the annular coil to decrease, resulting in an increase in the line inductance value and suppressing the current rise rate; if the distribution line current continues to rise, the air gap of the annular coil will continue to decrease until the annular coil air gap is at its minimum, at which point the inductance value of the variable inductor reaches its maximum;

[0031] If the current threshold is set to 200A, the magnetic circuit length of the toroidal silicon steel core is 600mm, the relative permeability of the toroidal silicon steel core is 10000, and the cross-sectional areas S1 and S2 are taken as 0.005... 2 πm 2 N1 is 10, N2 is 60, and δ0 is 1e. -3m Based on the above derivation, the stiffness of spring 2 that meets the threshold setting is 1343 N / m. Under normal operating conditions, such as a current of 50 A, δ1 is 0.99e. -3m The inductance value of the variable inductor can be calculated to be 3.9217e. -5H When the current exceeds the threshold of 200A, the electromagnet's attractive force is always greater than the spring force of spring 2, the air gap of the toroidal coil decreases to 0, that is, δ1 is 0, and the inductance value of the variable inductor reaches its maximum value. At this time, the calculated inductance is 5.9e. -3H It is 151 times the inductance value when the current is 50A.

[0032] In the second fault current limiting mode: When the DC circuit breaker detects that the current in the distribution line continues to rise to a set threshold, at which point the air gap reaches its minimum or has already reached its minimum, the variable inductors in the n branches are switched from parallel to series connection through the control of the switching control circuit. At this time, the current in the distribution line becomes 1 / n of its original value, while the total inductance of the DC circuit breaker becomes n times its original value. 2 ;

[0033] When executing the second fault current limiting mode operation, the three variable inductors can be switched from parallel to series connection through the second current limiter of the first branch, the first current limiter of the second branch, the second current limiter of the second branch, and the first current limiter of the third branch. The specific operating steps for the above four current limiters are consistent: as follows... Figure 2As shown, firstly, the IGBT transistor Q0 in the current-carrying branch is turned off. After the current is transferred to the current-breaking branch 9, the high-speed mechanical switch K2 is disconnected. After the contacts of the high-speed mechanical switch K2 are completely separated, the n IGBT transistors (Q1, Q2, ..., Qn) in the current-breaking branch 9 are turned off. Among them, the buffer capacitors C1, C2, ..., Cn, and the metal oxide surge arrester group MOA will protect the IGBT transistors. At the same time, since multiple IGBT transistors are connected in series, they can withstand higher blocking voltages. After both the current-carrying branch and the current-breaking branch 9 are turned off, the metal oxide surge arrester group MOA will also play the role of storing energy in the discharge inductor. Finally, the high-speed mechanical main switch K1 is turned off to prevent subsequent line operations from impacting the current limiter.

[0034] When the current in the distribution line increases to the point where the air gap of the magnetic core is completely closed, the armature 3 moves and collides with the contacts of the normally open limit switch SQ, causing the limit switch SQ to close, thereby turning on the switch control circuit. According to the execution sequence of the second fault current limiting mode, the control signal G1, amplified by the isolation operational amplifier U1, controls the high-speed mechanical switch K2 to open; after passing through several delay chips, control signal G1 can obtain control signals G2 and G3. Control signal G2 controls the n IGBT transistors (Q1, Q2, ..., Qn) in the current-breaking branch 9 to turn off, and control signal G3 controls the high-speed mechanical main switch to open. After passing through several delay chips, different switches can be turned off in a time-sharing manner. Furthermore, delay chips can be added and the switching sequence adjusted according to actual control needs.

[0035] After the three variable inductors are switched from parallel to series through the above operations, since the current in the inductor cannot change abruptly, the total current of the distribution line will be reduced to 1 / 3 of the original, while the total inductance will increase to 9 times the original. Therefore, the ability to suppress the current rise rate can be further improved while reducing the fault current.

[0036] In circuit breaking or recovery mode: If the fault detection system determines that fault clearance is required, it shuts off all first and second current limiters of the DC circuit breaker to break the circuit and cut off the system current; if it determines that the fault is a misjudgment or that the fault has been handled, it restores the normal working state through the control of the switch control circuit, that is, the limit switch is reset, the current-carrying branch in the current limiter is opened, and the power distribution line is restored to the normal working state.

[0037] The following combination Figures 1 to 4 The present invention will be further described below.

[0038] Assume that when no current flows, the initial distance between the electromagnet and armature 3 is δ0. Let spring 2 be relaxed and without force at this point, meaning its original length is δ0. When current I flows, the distance between the electromagnet and armature 3 is δ1. Then, the elastic force F compressing spring 2 at this moment... x yes:

[0039] F x = k*(δ0-δ1)

[0040] k is the spring stiffness;

[0041] At this time, the attraction force of the electromagnet on armature 3 is:

[0042]

[0043] Where N1 is the number of turns of the electromagnet winding, and μ0 is the free permeability, with a value of 4π × 10⁻⁶. -7 Wb / A·m, S1 is the cross-sectional area of ​​the magnetic circuit;

[0044] In the working state, that is, when current I flows through, there is F x =F y Established.

[0045] And when the current is I and the air gap length is approximately δ1, the inductance of the variable inductor is:

[0046]

[0047] When there is no air gap:

[0048]

[0049] Where N2 is the number of turns of the toroidal coil, S2 is the cross-sectional area of ​​the toroidal silicon steel core, and μ r L represents the relative permeability of a toroidal silicon steel core. m For effective magnetic flux linkage.

[0050] When the current in the power distribution line increases, the air gap of the toroidal core can be reduced by the combined action of the electromagnet and spring 2, thereby increasing the inductance value and suppressing the rate of current rise.

[0051] In summary, this invention can adaptively perform operations such as current rise rate suppression, current magnitude suppression, and fault clearing based on the magnitude and rise rate of the fault current in the power distribution line, effectively improving fault handling efficiency and the operational safety of the power distribution line.

Claims

1. A DC circuit breaker that adaptively adjusts the current-limiting inductor based on fault current, characterized in that: It includes at least two parallel branches, each branch consisting of a first current limiter, a variable inductor, and a second current limiter connected in series. A switch control circuit is connected in parallel to both the first and second current limiters. The first and second current limiters have the same structure. One end of multiple first current limiters is connected in parallel and serves as the input terminal of a DC circuit breaker. One end of multiple second current limiters is connected in parallel and serves as the output terminal of a DC circuit breaker. The anode of the thyristor is connected between the variable inductor and the second current limiter in the upper branch of the two adjacent branches. The cathode of the thyristor is connected between the first current limiter and the variable inductor in the lower branch of the two adjacent branches. A limit switch SQ is provided in the switch control circuit. The variable inductor includes a toroidal silicon steel core, a strip silicon steel core, an armature, a spring, and a power transmission line. The toroidal silicon steel core includes a left semicircular toroidal silicon steel core and a right semicircular toroidal silicon steel core arranged opposite each other and having the same structure. One end of the two is connected by a coupling, and the other end of the two has a gap. The strip silicon steel core is located inside the toroidal silicon steel core. The armature is welded to the middle of the right semicircular toroidal silicon steel core. The power transmission line is wound around the strip silicon steel core, the left semicircular toroidal silicon steel core, and the right semicircular toroidal silicon steel core in sequence. The limit switch SQ is located between the strip silicon steel core and the armature. The lower opening of the toroidal silicon steel core is welded downward to a mounting part for mounting the spring. The mounting part is composed of two iron plates arranged opposite each other, and the spring is welded to the inner side of the two iron plates. The power transmission line wound on the strip silicon steel core forms an electromagnet, and the power transmission line wound on the toroidal silicon steel core forms a toroidal coil.

2. The DC circuit breaker with adaptive adjustment of current-limiting inductor based on fault current as described in claim 1, characterized in that: The DC circuit breaker includes three parallel branches: the first branch, the second branch, and the third branch. Each branch consists of a first current limiter, a variable inductor, and a second current limiter connected in series. A switch control circuit is connected in parallel to both the first and second current limiters. The first and second current limiters have identical structures. One end of each of the three first current limiters is connected in parallel, serving as the input terminal of the DC circuit breaker. One end of each of the three second current limiters is connected in parallel, serving as the output terminal of the DC circuit breaker. The thyristors include a first thyristor D1 and a second thyristor D2. The anode of the first thyristor D1 is connected between the variable inductor and the second current limiter in the first branch. The cathode of the first thyristor D1 is connected between the first current limiter and the variable inductor in the second branch. The anode of the second thyristor D2 is connected between the variable inductor and the second current limiter in the second branch. The cathode of the second thyristor D2 is connected between the first current limiter and the variable inductor in the third branch.

3. The DC circuit breaker with adaptive adjustment of current-limiting inductor based on fault current as described in claim 1, characterized in that: The current limiter includes a high-speed mechanical main switch K1, a current-carrying branch, a current-breaking branch, and a voltage-limiting and current-relief branch. The current-carrying branch, current-breaking branch, and voltage-limiting and current-relief branch are connected in parallel, with one end A being the input terminal and the other end B being the output terminal. One end of the high-speed mechanical main switch K1 serves as the input terminal of the DC circuit breaker, and the other end of K1 is connected to end A. The current-carrying branch includes a high-speed mechanical switch K2 and an IGBT transistor Q0. One end of the high-speed mechanical switch K2 is connected to end A, and the other end is connected to the collector of the IGBT transistor Q0. The emitter of the IGBT transistor Q0 is connected to end B. The current-breaking branch includes n IGBT transistors Q1, Q2, ..., Q1 connected in series. n Each IGBT transistor has a buffer capacitor connected in parallel, namely C1, C2, ..., C1. n The pressure limiting and current venting branch adopts a metal oxide surge arrester (MOA).

4. The DC circuit breaker with adaptive adjustment of current-limiting inductance based on fault current as described in claim 1, characterized in that: The switch control circuit includes a limit switch SQ, an isolation operational amplifier U1, a first delay chip, and a second delay chip. One end of the limit switch SQ is connected to the input power supply, and the other end is connected to the non-inverting input terminal of the isolation operational amplifier U1. The inverting input terminal of the isolation operational amplifier U1 is grounded. The output terminal of the isolation operational amplifier U1 is connected to the input terminal of the first delay chip. The output terminal of the first delay chip is connected to the input terminal of the second delay chip. The output terminal of the second delay chip is connected to the input terminal of the current limiter. The switch control circuit outputs a control signal to the current limiter.

5. The current limiting method of a DC circuit breaker that adaptively adjusts the current limiting inductor based on fault current according to any one of claims 1 to 4, characterized in that: The method includes: In normal operating mode: the current of the power distribution line is at a normal value, the current in the first current limiter and the second current limiter mainly flows through the current-carrying branch, the electromagnet and spring in the variable inductor are in the initial state, the air gap is large, and the inductance value of the variable inductor is a small initial value. In the first fault current limiting mode: When the DC circuit breaker detects an increase in the distribution line current, the electromagnet's magnetic force increases due to the increase in the distribution line current. This attracts the left and right semi-circular annular silicon steel cores, causing the gap between them to decrease and tend to close. This also compresses the spring, driving the air gap of the annular coil to decrease, resulting in an increase in the inductance value of the variable inductor and suppressing the rate of current rise. If the distribution line current continues to rise, the air gap of the annular coil will continue to decrease until the air gap of the annular coil is at its minimum. At this time, the inductance value of the variable inductor reaches its maximum. In the second fault current limiting mode: When the DC circuit breaker detects that the current in the distribution line continues to rise to a set threshold, at which point the air gap reaches its minimum or has already reached its minimum, the variable inductors in the n branches are switched from parallel to series connection through the control of the switching control circuit. At this time, the current in the distribution line becomes 1 / n of its original value, while the total inductance of the DC circuit breaker becomes n of its original value. 2 ; In circuit breaking or recovery mode: If the fault detection system determines that fault clearance is required, it shuts off all first and second current limiters of the DC circuit breaker to break the circuit and cut off the system current; if it determines that the fault is a misjudgment or that the fault has been cleared, it restores the system to normal operation through the control of the switch control circuit.

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