An active current-limiting hybrid DC circuit breaker topology and a control method thereof

Abstract

The application discloses a kind of active current-limiting hybrid DC circuit breaker topologies and control method thereof.The current-carrying branch of the topological structure is formed by the series connection of current-carrying switch CCS and ultrafast mechanical switch UFD;The bridge branch includes four groups of branch circuits, and each branch circuit is formed by diode;The current-limiting branch is a four thyristor bridge structure, including the branch circuit of the capacitor transversely connected inside the bridge structure, the branch circuit of the left lower bridge arm thyristor in anti-parallel connection with the thyristor, and the branch circuit of the right lower bridge arm thyristor in parallel connection with diode, inductor and resistance;The branch circuit is formed by the series connection of diode, capacitor and two thyristors, and the lightning arrester is transversely connected inside the series connection structure;The pre-charging grounding branch is formed by the series connection of thyristor and resistance and grounded;The grounding branch is formed by the series connection of thyristor and resistance and grounded.Through the active current-limiting of RL series branch, the peak value of fault current is reduced, the fault clearing speed is accelerated, the number of IGBT devices used is reduced, and the cost is reduced.

Description

Technical Field

[0001] This invention relates to the field of electrical equipment technology, specifically to an active current-limiting hybrid DC circuit breaker topology and its control method. Background Technology

[0002] As DC transmission technology develops towards inter-regional, large-capacity power transmission, high-voltage DC transmission has become the core carrier for realizing long-distance coordinated allocation of power resources. Flexible DC grids have low equivalent impedance and low system inertia; once a short-circuit fault occurs, the fault current will rise sharply, and the peak current can easily damage various power electronic devices within the system. As the core protection device of flexible DC grids, DC circuit breakers can quickly disconnect and isolate faulty branches within milliseconds, preventing the spread of fault current that could cause grid instability and device damage. They are the core and critical equipment for ensuring the safe and stable operation of flexible DC transmission systems.

[0003] DC circuit breakers are mainly classified into three topologies: mechanical, solid-state, and hybrid. Among them, hybrid DC circuit breakers combine the advantages of low steady-state current loss of mechanical circuit breakers and fast fault response speed of solid-state circuit breakers, and have now become the mainstream research direction in the field of rapid fault clearance for flexible DC transmission projects. However, existing traditional topologies contain a large number of IGBTs, resulting in high costs, and also have many shortcomings such as poor current limiting effect leading to excessively high fault current peaks and slow fault clearance speed. Summary of the Invention

[0004] The purpose of this invention is to provide an active current-limiting hybrid DC circuit breaker topology and its control method. This circuit breaker actively engages current limiting and bypass energy consumption through inductor branches, thereby reducing the peak fault current and shortening the fault clearing time. It also uses thyristor devices to replace traditional IGBT power modules, thus reducing the cost of the circuit breaker.

[0005] To achieve the above-mentioned objectives of this invention, the following technical solutions are used:

[0006] An active current-limiting hybrid DC circuit breaker topology and its control method are disclosed. The circuit breaker topology includes a current-carrying branch, a bridge-type transfer branch, a current-limiting branch, a disconnecting branch, a pre-charge grounding branch, and a grounding branch.

[0007] The current-carrying branch is composed of a current-carrying switch CCS and an ultra-fast mechanical switch UFD connected in series, with the two ends connected to the matching interfaces of the DC line respectively.

[0008] The bridge-type transfer branch includes four sets of branch lines, each of which is composed of diodes;

[0009] The current-limiting branch is a four-thyristor bridge structure, which includes a branch with a capacitor horizontally connected inside the bridge structure, a branch with a thyristor connected in antiparallel to the thyristor of the lower left bridge arm, and a branch with an inductor connected in series with a resistor and simultaneously connected in parallel with a diode and the thyristor of the lower right bridge arm.

[0010] The disconnecting branch consists of a diode, a capacitor, and two thyristors connected in series, with a surge arrester laterally connected inside the series structure.

[0011] The pre-charge grounding branch is formed by a thyristor and a resistor connected in series for grounding;

[0012] The grounding branch is formed by a thyristor and a resistor connected in series for grounding.

[0013] Preferably, the current-carrying switch CCS of the current-carrying branch consists of four diodes and one IGBT. The anode of the upper left diode is connected to the cathode of the lower left diode, the cathode of the upper left diode is connected to the cathode of the upper right diode, the anode of the lower left diode is connected to the anode of the lower right diode, the anode of the upper right diode is connected to the cathode of the lower right diode, the collector of the IGBT is connected to the cathode of the upper left diode, the emitter of the IGBT is connected to the anode of the lower left diode, the anode of the upper left diode is connected to one end of the ultra-fast mechanical switch UFD, and the anode of the upper right diode is connected to the external DC line interface.

[0014] Preferably, the bridge-type transfer branch includes four sets of branch circuits. The first branch circuit is composed of diode D1, the second branch circuit is composed of diode D2, the third branch circuit is composed of diode D3, and the fourth branch circuit is composed of diode D4. The anode of diode D1 is connected to the cathode of diode D3 and one end of the DC line connected to the ultra-fast mechanical switch UFD of the current-carrying branch. The anode of diode D2 is connected to the cathode of diode D4 and the other end of the DC line connected to the current-carrying branch. The cathode of diode D1 is connected to the cathode of diode D2, and the anode of diode D3 is connected to the anode of diode D4.

[0015] Preferredly, the current-limiting branch is a four-thyristor bridge structure. The cathode of the upper left thyristor T1 is connected to the anode of the lower left thyristor T3. The anode of the upper left thyristor T1 is connected to the anode of the upper right thyristor T2 and the cathode of diode D1, respectively. The cathode of the lower left thyristor T3 is connected to the cathode of the lower right thyristor T4. The cathode of the upper right thyristor T2 is connected to the anode of the lower right thyristor T4. The capacitor C1 is horizontally connected across the inside of the bridge structure and is connected to the cathodes of thyristor T1 and T2, respectively. Thyristor T5 is antiparallel to the lower left bridge arm thyristor T3. Inductor L is connected in series with resistor R and then in parallel with diode D5 and the lower right bridge arm thyristor T4. The anode of diode D5 is connected to the cathode of thyristor T4.

[0016] Preferably, the disconnecting branch is connected to one end of capacitor C2 via the cathode of diode D6, the other end of capacitor C2 via the cathode of thyristor T6, the anode of thyristor T6 via the anode of thyristor T7 and the anode of diode D5, the cathode of thyristor T7 via the anode of diode D6, one end of surge arrester MOA via the cathode of thyristor T7, and the other end of surge arrester MOA via the cathode of thyristor T6.

[0017] Preferably, the pre-charge grounding branch is grounded by connecting the cathode of thyristor T8 and resistor Rc in series, and the anode of thyristor T8 and the cathode of diode D6 are connected.

[0018] Preferably, the grounding branch is the anode of thyristor T9 and resistor R. j After being connected in series and grounded, the cathode of thyristor T9 is connected to the cathode of thyristor T6 and the anode of diode D3, respectively.

[0019] The circuit breaker current limiting and tripping control method based on the present invention is as follows:

[0020] Normal operating procedure: If the circuit breaker is placed on the left side of the high voltage DC line, when the power is supplied in the forward direction, the current flows out from the circuit breaker and is delivered to the line to the right. First, the capacitors C1 and C2 are pre-charged. When the power grid system is operating normally, the current-carrying part is normally connected, that is, the ultra-fast mechanical switch UFD of the current-carrying branch is closed, and the upper left diode, IGBT and lower right diode of the current-carrying switch CCS are all turned on, and the thyristors T1, T4, T6 and T8 are turned on. After the charging is completed, the thyristors T1, T4, T6 and T8 are naturally turned off.

[0021] Current limiting and disconnection process: When the protection device detects a line fault, it immediately blocks the IGBT in the CCS and triggers the flow of D1, T2, T4, T6 and D4 branches, thus transferring the fault current until no current flows in the current-carrying branches. A trip command signal is then sent to the UFD. When the UFD is fully tripped, thyristor T3 is triggered, and capacitor C1 discharges. Simultaneously, thyristor T4 is turned off due to the reverse voltage provided by capacitor C1, and the RL series branch begins active current limiting. After C1 completes discharge and begins reverse charging, thyristor T3... When the operating current of circuit 3 is less than the holding current, the device cannot maintain its conducting state and is subsequently turned off. The RL series branch completely limits the fault current. At this time, thyristor T7 is turned on. Due to the reverse voltage from C2, T6 is forced to turn off, discharging C2 and then recharging it to the system voltage after the discharge is complete. The fault current in the circuit gradually decreases. Since the inductor current cannot change abruptly, an induced electromotive force appears on both sides of L, with the upper side negative and the lower side positive. D5 is positively charged and turns on the active bypass L. At this time, the energy of L is dissipated by resistor R, triggering T9 to bypass the DC line inductor of the mains. The energy of the DC line inductor of the mains is absorbed by R. jDissipation; C2 reaches the MOA operating voltage after reverse charging, forcing the fault current to commutate to the MOA branch, the MOA surge arrester engages to absorb energy, and all power electronic components naturally turn off, achieving fault isolation; the voltage polarities of C1 and C2 are both negative on the left and positive on the right, triggering thyristors T5, T8, and T9, and C1 and C2 begin to dissipate energy. The energy of C1 is dissipated by R, and the energy of C2 is dissipated by Rc and R j dissipation.

[0022] Compared with the prior art, the beneficial effects of the present invention are:

[0023] 1. The RL series inductor branch of the active current-limiting hybrid DC circuit breaker topology of the present invention can actively engage current limiting during the fault current rising phase and actively bypass during the fault current falling phase, thereby improving the current limiting effect of the circuit breaker, effectively suppressing the fault current rise rate and fault current peak value, and accelerating the fault clearing speed of the circuit breaker.

[0024] 2. In the active current-limiting hybrid DC circuit breaker topology of the present invention, the grounding branch triggers the T9 bypass grid DC line inductor, causing the grid DC line inductor energy to be transferred to R. j Dissipation reduces the energy absorption pressure of the surge arrester MOA, which is beneficial for the selection of surge arrester MOA;

[0025] 3. In this invention, the grounding branch and the pre-charge grounding branch of the active current-limiting hybrid DC circuit breaker topology are combined, reducing the number of branches. By triggering thyristors T8 and T9, the energy of capacitor C2 is converted by Rc and R... j Simultaneously, energy dissipation accelerates the energy leakage rate of capacitor C2;

[0026] 4. In the active current-limiting hybrid DC circuit breaker topology of the present invention, the current-limiting branch, breaking branch, pre-charging grounding branch and grounding branch adopt thyristor groups instead of traditional IGBT groups. The current-carrying switch CCS of the current-carrying branch is composed of 4 diodes and 1 IGBT. While taking into account voltage withstand and current carrying performance, the use of a large number of IGBTs is reduced, thus reducing costs. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the topology of an active current-limiting hybrid DC circuit breaker according to the present invention;

[0028] Figure 2 This is a schematic diagram of the current loop during normal operation of an active current-limiting hybrid DC circuit breaker according to the present invention;

[0029] Figure 3 This is a schematic diagram of the capacitor pre-charging current loop of an active current-limiting hybrid DC circuit breaker according to the present invention.

[0030] Figure 4This is a schematic diagram of the current loops for each operating sequence under the current limiting and breaking operation of an active current limiting hybrid DC circuit breaker according to the present invention.

[0031] Figure 5 This is a schematic diagram of the installation location of an active current-limiting hybrid DC circuit breaker according to the present invention in a four-terminal flexible DC grid with a DC voltage of 400kV.

[0032] Figure 6 This is a comparison diagram of the fault current waveforms of the active current-limiting hybrid DC circuit breaker of the present invention and the traditional classic hybrid circuit breaker during fault clearing. Detailed Implementation Plan

[0033] This invention proposes an active current-limiting hybrid DC circuit breaker topology and its control method. To make the embodiments of this invention clearer, the invention will be described in detail below with reference to the accompanying drawings.

[0034] like Figure 1 As shown, the active current-limiting hybrid DC circuit breaker topology of the present invention includes a current-carrying branch, a bridge transfer branch, a current-limiting branch, a disconnecting branch, a pre-charge grounding branch, and a grounding branch;

[0035] The current-carrying branch is composed of a current-carrying switch CCS and an ultra-fast mechanical switch UFD connected in series, with the two ends connected to the matching interfaces of the DC line respectively.

[0036] The bridge-type transfer branch includes four sets of branch lines, each of which is composed of diodes;

[0037] The current-limiting branch is a four-thyristor bridge structure, which includes a branch with a capacitor horizontally connected inside the bridge structure, a branch with a thyristor connected in antiparallel to the thyristor of the lower left bridge arm, and a branch with an inductor connected in series with a resistor and simultaneously connected in parallel with a diode and the thyristor of the lower right bridge arm.

[0038] The disconnecting branch consists of a diode, a capacitor, and two thyristors connected in series, with a surge arrester laterally connected inside the series structure.

[0039] The pre-charge grounding branch is formed by a thyristor and a resistor connected in series for grounding;

[0040] The grounding branch is formed by a thyristor and a resistor connected in series for grounding.

[0041] The current-carrying switch CCS of the current-carrying branch consists of four diodes and one IGBT. The anode of the upper left diode is connected to the cathode of the lower left diode, the cathode of the upper left diode is connected to the cathode of the upper right diode, the anode of the lower left diode is connected to the anode of the lower right diode, and the anode of the upper right diode is connected to the cathode of the lower right diode. The collector of the IGBT is connected to the cathode of the upper left diode, and the emitter of the IGBT is connected to the anode of the lower left diode. The anode of the upper left diode is connected to one end of the ultra-fast mechanical switch UFD, and the anode of the upper right diode is connected to the external DC line interface.

[0042] The bridge-type transfer branch includes four sets of branch circuits. The first branch circuit is composed of diode D1, the second branch circuit is composed of diode D2, the third branch circuit is composed of diode D3, and the fourth branch circuit is composed of diode D4. The anode of diode D1 is connected to the cathode of diode D3 and one end of the DC line connected to the ultra-fast mechanical switch UFD of the current-carrying branch. The anode of diode D2 is connected to the cathode of diode D4 and the other end of the DC line connected to the current-carrying branch. The cathode of diode D1 is connected to the cathode of diode D2, and the anode of diode D3 is connected to the anode of diode D4.

[0043] The current-limiting branch is a four-thyristor bridge structure. The cathode of the upper left thyristor T1 is connected to the anode of the lower left thyristor T3. The anode of the upper left thyristor T1 is connected to the anode of the upper right thyristor T2 and the cathode of diode D1, respectively. The cathode of the lower left thyristor T3 is connected to the cathode of the lower right thyristor T4. The cathode of the upper right thyristor T2 is connected to the anode of the lower right thyristor T4. The capacitor C1 is horizontally connected across the inside of the bridge structure and is connected to the cathodes of thyristor T1 and T2, respectively. Thyristor T5 is antiparallel to the lower left bridge arm thyristor T3. The inductor L is connected in series with the resistor R and then connected in parallel with the diode D5 and the lower right bridge arm thyristor T4. The anode of diode D5 is connected to the cathode of thyristor T4.

[0044] The disconnecting branch is connected to one end of capacitor C2 via the cathode of diode D6, and the other end of capacitor C2 is connected to the cathode of thyristor T6. The anode of thyristor T6 is connected to the anode of thyristor T7 and the anode of diode D5, respectively. The cathode of thyristor T7 is connected to the anode of diode D6. One end of surge arrester MOA is connected to the cathode of thyristor T7, and the other end of surge arrester MOA is connected to the cathode of thyristor T6.

[0045] The pre-charge grounding branch is grounded by connecting the cathode of thyristor T8 and resistor Rc in series, and the anode of thyristor T8 and the cathode of diode D6 are connected.

[0046] The grounding branch is the anode of thyristor T9 and resistor R. jAfter being connected in series and grounded, the cathode of thyristor T9 is connected to the cathode of thyristor T6 and the anode of diode D3, respectively.

[0047] The circuit breaker current limiting and tripping control method based on the present invention is as follows:

[0048] Normal operating procedure: If the circuit breaker is placed on the left side of the high voltage DC line, when the power is supplied in the forward direction, the current flows out from the circuit breaker and is delivered to the line to the right. First, the capacitors C1 and C2 are pre-charged. When the power grid system is operating normally, the current-carrying part is normally connected, that is, the ultra-fast mechanical switch UFD of the current-carrying branch is closed, and the upper left diode, IGBT and lower right diode of the current-carrying switch CCS are all turned on, and the thyristors T1, T4, T6 and T8 are turned on. After the charging is completed, the thyristors T1, T4, T6 and T8 are naturally turned off.

[0049] Current limiting and disconnection process: When the protection device detects a line fault, it immediately blocks the IGBT in the CCS and triggers the flow of D1, T2, T4, T6 and D4 branches, thus transferring the fault current until no current flows in the current-carrying branches. A trip command signal is then sent to the UFD. When the UFD is fully tripped, thyristor T3 is triggered, and capacitor C1 discharges. Simultaneously, thyristor T4 is turned off due to the reverse voltage provided by capacitor C1, and the RL series branch begins active current limiting. After C1 completes discharge and begins reverse charging, thyristor T3... When the operating current of circuit 3 is less than the holding current, the device cannot maintain its conducting state and is subsequently turned off. The RL series branch completely limits the fault current. At this time, thyristor T7 is turned on. Due to the reverse voltage from C2, T6 is forced to turn off, discharging C2 and then recharging it to the system voltage after the discharge is complete. The fault current in the circuit gradually decreases. Since the inductor current cannot change abruptly, an induced electromotive force appears on both sides of L, with the upper side negative and the lower side positive. D5 is positively charged and turns on the active bypass L. At this time, the energy of L is dissipated by resistor R, triggering T9 to bypass the DC line inductor of the mains. The energy of the DC line inductor of the mains is absorbed by R. j Dissipation; C2 reaches the MOA operating voltage after reverse charging, forcing the fault current to commutate to the MOA branch, the MOA surge arrester engages to absorb energy, and all power electronic components naturally turn off, achieving fault isolation; the voltage polarities of C1 and C2 are both negative on the left and positive on the right, triggering thyristors T5, T8, and T9, and C1 and C2 begin to dissipate energy. The energy of C1 is dissipated by R, and the energy of C2 is dissipated by Rc and R j dissipation.

[0050] See attached document Figure 2 As shown, in one embodiment, the circuit breaker is placed at the left end of the DC transmission line. During normal operation, the current-carrying branch carries current normally, and the current path flows from the left end of the circuit breaker through the current-carrying branch to the right end of the circuit breaker. At this time, both the current-carrying switch CCS and the ultra-fast mechanical switch UFD are in the closed state.

[0051] See attached document Figure 3 As shown, before any operating state, the circuit breaker's internal capacitors are pre-charged. Diode D1, thyristor T1, capacitor C1, thyristor T4, thyristor T6, capacitor C2, thyristor T8, charging resistor Rc, and ground constitute a charging circuit. During normal operation of the DC transmission line, thyristors T1, T4, T6, and T8 are turned on to pre-charge capacitors C1 and C2. After the charging phase is completed, both capacitors have a voltage polarity of positive potential on the left and negative potential on the right, the charging current decreases to 0, and thyristors T1, T4, T6, and T8 are naturally turned off. During the actual charging operation phase, the charging current of the capacitor branch can be flexibly adjusted by changing the parameter of the charging resistor Rc.

[0052] See attached document Figure 4 As shown, the circuit breaker of this invention operates in current-limiting breaking mode. The colored path represents the current loop under the corresponding timing sequence, and the arrow indicates the current corresponding to the loop:

[0053] in Figure 4 (a) When the protection device detects a fault, it transmits a control command to the DC circuit breaker to clear the fault. The protection device sends a turn-off signal to the IGBT in the current-carrying switch CCS, turning on thyristors T2, T4, and T6. Diode D1, thyristor T2, thyristor T4, thyristor T6, and diode D4 form a transfer branch, and the fault current i dc The circuit is completely transferred from the current-carrying branch to the transfer branch, giving the UFD (Ultra-Fast Mechanical Switch) tripping command.

[0054] Figure 4 (b) When the ultra-fast mechanical switch UFD reaches the rated opening distance, the circuit breaker is opened; a trigger signal is given to thyristor T3, and capacitor C1 discharges with a discharge current of i. c1 At this time, the RL series branch starts to actively limit the current. Because the thyristor T4 is turned off due to the reverse voltage from capacitor C1, the fault current flows through the C1-T3 branch and the RL series branch.

[0055] Figure 4 (c) After capacitor C1 has finished discharging and started to reverse charge, as the voltage of capacitor C1 reverse charging increases, the charging current gradually decreases, and the fault current flowing through the RL series branch gradually increases.

[0056] Figure 4 (d) When the reverse charging of capacitor C1 is completed, the fault current flows through the RL series branch completely. Thyristor T3 turns off naturally because the current flowing through it is less than its holding current. The RL series branch is fully engaged in current limiting and suppression of the fault current.

[0057] Figure 4(e) When the protection system determines that a fault has occurred, it turns on thyristor T7 and diode D6. Due to the reverse voltage from capacitor C2, thyristor T6 is forced to turn off, and capacitor C2 begins to discharge with a discharge current of i. c2 ;

[0058] Figure 4 (f) After capacitor C2 discharges, it is reverse-charged to the system voltage. At this time, the fault current begins to decrease. Since the inductor current cannot change abruptly, an induced electromotive force (EMF) with negative voltage on top and positive voltage on the bottom will be induced across L. Diode D5 is subjected to a positive voltage from the induced EMF and conducts the active bypass RL series branch. In the bypass circuit, the energy of L is dissipated by R. The bypass circuit current is i. L =i p Due to the decrease in fault current, an induced electromotive force (EMF) is also generated across the DC line inductor (negative on the left, positive on the right), causing thyristor T9 to experience a positive voltage. This triggers T9 to bypass the DC line inductor. In this bypass circuit, the energy of the DC line inductor is transferred from R... j Dissipation occurs, with current i j ;

[0059] Figure 4 (g) When the reverse charging voltage of capacitor C2 reaches the MOA operating voltage, the surge arrester MOA is triggered, and the surge arrester MOA begins to dissipate energy with a current of i. MOA Once the fault current drops to 0, all power electronic components will automatically turn off, thus clearing the fault.

[0060] Figure 4 (h) At this time, the voltage polarity of capacitors C1 and C2 is negative on the left and positive on the right. Thyristors T5, T8, and T9 are all subjected to positive voltage, triggering thyristors T5, T8, and T9 to conduct. Energy is discharged from capacitor C1 through the circuit C1-RL-T5-C1, and energy is discharged through the circuit C2-T8-Rc-R j -T9-C2 discharges energy from capacitor C2.

[0061] Simulation analysis: Refer to the appendix Figure 5 The 400kV four-terminal flexible DC power grid structure shown is simulated using the PSCAD simulation platform. Table 1 shows the simulation parameters of the four-terminal flexible DC power grid.

[0062] Table 1 Simulation parameters of a four-terminal flexible DC grid Converter station (MMC) MMC capacity / MW Smoothing reactance / mH Bridge arm inductance / mH Submodule capacitance value / mF 1 500 150 50 7.5 2 1000 150 50 7.5 3 1500 150 100 15 4 1000 150 100 15

[0063] To verify the superior performance of the active current-limiting hybrid DC circuit breaker topology and its control method proposed in this invention, the fault clearing method of this invention is compared and analyzed with the fault clearing method of traditional classic hybrid circuit breakers. Let Scheme A be the fault clearing method of traditional classic hybrid circuit breakers, and Scheme B be the fault clearing method of this invention. In the active current-limiting hybrid DC circuit breaker topology proposed in this invention, the built-in capacitor C1 is 10μF, C2 is 6μF, the current-limiting inductor L is 200mH, the current-limiting resistor R is 20Ω, and the energy-dissipating resistor R... j Choose a 10Ω resistor and a 200Ω resistor Rc.

[0064] A single-pole ground fault occurred on Line 1-2 at 1.0s. The protection system detected the abnormal current at 1.001s and confirmed the fault occurrence at 1.0057s. (See attached diagram.) Figure 6 As shown, the fault current waveforms of the two schemes are compared. The peak fault currents of Scheme A and Scheme B are approximately 8.89kA and 6.16kA, respectively. Scheme B reduces the current by approximately 32.3% compared to Scheme A, demonstrating better fault current limiting performance. The time required for the fault current to decrease to zero is reduced by approximately 0.75ms in Scheme B compared to Scheme A, indicating faster fault clearing speed in Scheme B. In both schemes, the current-limiting branch, breaking branch, pre-charging grounding branch, and grounding branch of this invention use thyristor groups instead of the corresponding IGBT groups in the traditional classic hybrid circuit breaker topology, reducing the extensive use of IGBTs and lowering costs. Scheme B proposed in this invention has significant advantages in breaking performance and economy, and possesses better engineering application prospects.

[0065] For those skilled in the art, the embodiments listed above are merely illustrative and exemplary, and are not intended to limit the scope of protection of this invention. Without departing from the core technical solution of this invention, those skilled in the art can make various optimized implementations of the technical solution of this invention. All such modifications, alterations, and derivative solutions based on the technical essence of this invention are included within the protection scope of this invention and fall within the technical spirit and protection scope claimed by this invention.

Claims

1. This invention provides an active current-limiting hybrid DC circuit breaker topology and its control method, characterized in that, The circuit breaker topology includes current-carrying branches, bridge transfer branches, current-limiting branches, disconnecting branches, pre-charge grounding branches, and grounding branches; The current-carrying branch is composed of a current-carrying switch CCS and an ultra-fast mechanical switch UFD connected in series, with the two ends connected to the matching interfaces of the DC line respectively. The bridge-type transfer branch includes four sets of branch lines, each of which is composed of diodes; The current-limiting branch is a four-thyristor bridge structure, which includes a branch with a capacitor horizontally connected inside the bridge structure, a branch with a thyristor connected in antiparallel to the thyristor of the lower left bridge arm, and a branch with an inductor connected in series with a resistor and simultaneously connected in parallel with a diode and the thyristor of the lower right bridge arm. The disconnecting branch consists of a diode, a capacitor, and two thyristors connected in series, with a surge arrester laterally connected inside the series structure. The pre-charge grounding branch is formed by a thyristor and a resistor connected in series for grounding; The grounding branch is formed by a thyristor and a resistor connected in series for grounding.

2. The active current-limiting hybrid DC circuit breaker topology and its control method as described in claim 1, characterized in that, The current-carrying switch CCS of the current-carrying branch consists of four diodes and one IGBT. The anode of the upper left diode is connected to the cathode of the lower left diode, the cathode of the upper left diode is connected to the cathode of the upper right diode, the anode of the lower left diode is connected to the anode of the lower right diode, and the anode of the upper right diode is connected to the cathode of the lower right diode. The collector of the IGBT is connected to the cathode of the upper left diode, and the emitter of the IGBT is connected to the anode of the lower left diode. The anode of the upper left diode is connected to one end of the ultra-fast mechanical switch UFD, and the anode of the upper right diode is connected to the external DC line interface.

3. The active current-limiting hybrid DC circuit breaker topology and its control method as described in claim 1, characterized in that, The bridge-type transfer branch includes four sets of branch circuits. The first branch circuit is composed of diode D1, the second branch circuit is composed of diode D2, the third branch circuit is composed of diode D3, and the fourth branch circuit is composed of diode D4. The anode of diode D1 is connected to the cathode of diode D3 and one end of the DC line connected to the ultra-fast mechanical switch UFD of the current-carrying branch. The anode of diode D2 is connected to the cathode of diode D4 and the other end of the DC line connected to the current-carrying branch. The cathode of diode D1 is connected to the cathode of diode D2, and the anode of diode D3 is connected to the anode of diode D4.

4. The active current-limiting hybrid DC circuit breaker topology and its control method as described in claim 1, characterized in that, The current-limiting branch is a four-thyristor bridge structure. The cathode of the upper left thyristor T1 is connected to the anode of the lower left thyristor T3. The anode of the upper left thyristor T1 is connected to the anode of the upper right thyristor T2 and the cathode of diode D1, respectively. The cathode of the lower left thyristor T3 is connected to the cathode of the lower right thyristor T4. The cathode of the upper right thyristor T2 is connected to the anode of the lower right thyristor T4. The capacitor C1 is horizontally connected across the inside of the bridge structure and is connected to the cathodes of thyristor T1 and T2, respectively. Thyristor T5 is antiparallel to the lower left bridge arm thyristor T3. The inductor L is connected in series with the resistor R and then connected in parallel with the diode D5 and the lower right bridge arm thyristor T4. The anode of diode D5 is connected to the cathode of thyristor T4.

5. The active current-limiting hybrid DC circuit breaker topology and its control method as described in claim 1, characterized in that, The disconnecting branch is connected to one end of capacitor C2 via the cathode of diode D6, and the other end of capacitor C2 is connected to the cathode of thyristor T6. The anode of thyristor T6 is connected to the anode of thyristor T7 and the anode of diode D5, respectively. The cathode of thyristor T7 is connected to the anode of diode D6. One end of surge arrester MOA is connected to the cathode of thyristor T7, and the other end of surge arrester MOA is connected to the cathode of thyristor T6.

6. The active current-limiting hybrid DC circuit breaker topology and its control method as described in claim 1, characterized in that, The pre-charge grounding branch is grounded by connecting the cathode of thyristor T8 and resistor Rc in series, and the anode of thyristor T8 and the cathode of diode D6 are connected.

7. The active current-limiting hybrid DC circuit breaker topology and its control method as described in claim 1, characterized in that, The grounding branch is the anode of thyristor T9 and resistor R. j After being connected in series and grounded, the cathode of thyristor T9 is connected to the cathode of thyristor T6 and the anode of diode D3, respectively.

8. The active current-limiting hybrid DC circuit breaker topology and its control method as described in claim 1, characterized in that, The circuit breaker current limiting and tripping control method is as follows: Normal operating procedure: If the circuit breaker is placed on the left side of the high voltage DC line, when the power is supplied in the forward direction, the current flows out from the circuit breaker and is delivered to the line to the right. First, the capacitors C1 and C2 are pre-charged. When the power grid system is operating normally, the current-carrying part is normally connected, that is, the ultra-fast mechanical switch UFD of the current-carrying branch is closed, and the upper left diode, IGBT and lower right diode of the current-carrying switch CCS are all turned on, and the thyristors T1, T4, T6 and T8 are turned on. After the charging is completed, the thyristors T1, T4, T6 and T8 are naturally turned off. Current limiting and disconnection process: When the protection device detects a line fault, it immediately blocks the IGBT in the CCS and triggers the flow of D1, T2, T4, T6 and D4 branches, thus transferring the fault current until no current flows in the current-carrying branches. A trip command signal is then sent to the UFD. When the UFD is fully tripped, thyristor T3 is triggered, and capacitor C1 discharges. Simultaneously, thyristor T4 is turned off due to the reverse voltage provided by capacitor C1, and the RL series branch begins active current limiting. After C1 completes discharge and begins reverse charging, thyristor T3... When the operating current of circuit 3 is less than the holding current, the device cannot maintain its conducting state and is subsequently turned off. The RL series branch completely limits the fault current. At this time, thyristor T7 is turned on. Due to the reverse voltage from C2, T6 is forced to turn off, discharging C2 and then recharging it to the system voltage after the discharge is complete. The fault current in the circuit gradually decreases. Since the inductor current cannot change abruptly, an induced electromotive force appears on both sides of L, with the upper side negative and the lower side positive. D5 is positively charged and turns on the active bypass L. At this time, the energy of L is dissipated by resistor R, triggering T9 to bypass the DC line inductor of the mains. The energy of the DC line inductor of the mains is absorbed by R. j Dissipation; C2 reaches the MOA operating voltage after reverse charging, forcing the fault current to commutate to the MOA branch, the MOA surge arrester engages to absorb energy, and all power electronic components naturally turn off, achieving fault isolation; the voltage polarities of C1 and C2 are both negative on the left and positive on the right, triggering thyristors T5, T8, and T9, and C1 and C2 begin to dissipate energy. The energy of C1 is dissipated by R, and the energy of C2 is dissipated by Rc and R j dissipation.

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