RC-IGCT-based superconducting hybrid DC circuit breaker design and working method

Abstract

The invention discloses an RC-IGCT-based superconducting hybrid DC circuit breaker, and relates to the topological structure and working principle analysis of DC circuit breakers. The circuit topology comprises two parts: (1) a resistance-type superconducting fault current limiter R-SFCL and a UDS isolation switch adopting a TP KEMA arc model are connected in series, and (2) a current commutation component composed of diodes VD1-VD4, a current injection branch and a current commutation branch. VD1-VD4 are used for conducting bidirectional current; the current injection branch comprises a pre-charging capacitor C, an inductor L and a thyristor T which are connected in series; the current commutation branch circuit is formed by connecting a power electronic switch, an RCD buffer branch circuit and an energy absorption branch circuit in parallel, and the energy absorption branch circuit is composed of a metal oxide lightning arrester; the invention further discloses a current breaking method of the superconducting hybrid direct-current circuit breaker. According to the invention, quick switching-off can be realized after fault current occurs, the rise rate of the fault current is limited, and the loss and the cost are low under the normal through-current condition.

Description

Technical Field

[0001] The present invention relates to a resistance-type superconducting hybrid DC circuit breaker and a current breaking method thereof, which can be used in DC power supply systems, such as subway DC power supply systems, ship power supply systems, etc. Background Art

[0002] DC systems are increasingly being used in medium and low voltage power distribution, new energy access, ships, and rail transit. However, DC systems have high short-circuit current peaks and rapid short-circuit current rise rates. Traditional mechanical circuit breakers, due to their inherent structural characteristics and the lack of a zero-crossing current in DC systems, take a long time to shut off fault currents or even fail to do so. Therefore, breakthroughs in DC system fault isolation and protection technologies are urgently needed to ensure safe and reliable operation. Hybrid DC circuit breakers, as the most ideal fault isolation method for DC systems, have become a research hotspot in the medium and high voltage electrical equipment field.

[0003] Hybrid DC circuit breakers combine the low-loss current-carrying and rapid insulation recovery capabilities of mechanical DC circuit breakers with the fast-breaking speed of solid-state DC circuit breakers, making them a key development direction for DC circuit breakers. However, traditional hybrid circuit breakers also suffer from arc extinguishing difficulties associated with mechanical switches and limited overload capacity of power electronic components, limiting their rapid shutdown capabilities.

[0004] Combining a resistive superconducting fault current limiter (R-SFCL) with a hybrid circuit breaker can rapidly limit fault current and divert it to the current-commutating branch. This significantly reduces the fault current after being limited by the R-SFCL, and enables rapid commutation after a short-circuit fault. By suppressing the magnitude and rise rate of the fault current, the R-SFCL can effectively reduce the interrupting capacity requirements of the circuit breaker for DC grid faults. Umer Amir Khan proposed connecting a superconducting fault current limiter in series with a conventional hybrid circuit breaker to limit the main circuit current for application in DC transmission. When fault current levels exceed 15kA in a 10kV MVDC grid, multiple insulated-gate bipolar transistors (IGBTs) must be connected in parallel to achieve reliable interruption. This significantly increases the cost of the hybrid circuit breaker. Summary of the Invention

[0005] To address the challenges of the prior art, the present invention provides a superconducting hybrid DC circuit breaker based on RC-IGCT and its operating principle. This hybrid circuit breaker combines a resistive superconducting fault current limiter with an RC-IGCT. Leveraging the current-limiting properties of the resistive fault current limiter and the low loss, high reliability, and cost advantages of the RC-IGCT, it significantly reduces costs while maintaining excellent interrupting capability. Application of this superconducting hybrid DC circuit breaker in medium-voltage DC networks enables integrated current limiting and interruption, further reducing costs.

[0006] To achieve the above technical objectives, the present invention adopts the following technical solutions:

[0007] A superconducting hybrid DC circuit breaker based on RC-IGCT, the circuit topology includes two parts: ① a resistive superconducting fault current limiter R-SFCL and a series-connected UDS disconnector, ② a current commutation component composed of diodes VD1-VD4, a current injection branch, and a current commutation branch. VD1-VD4 are used to conduct bidirectional current; the current injection branch consists of a series-connected pre-charging capacitor C1, an inductor L1, and a thyristor T. After the thyristor conducts, the pre-charging capacitor starts to discharge, thereby realizing the commutation of the fault current and providing a reverse turn-off voltage for the RC-IGCT to ensure that the RC-IGCT can be reliably turned off at a low current level; to achieve the dynamic voltage sharing of the RC-IGCT, an RCD buffer circuit and a MOV group are connected in parallel at both ends of the RC-IGCT.

[0008] Preferably, the active current injection branch includes a pre-charging capacitor C1, an inductor L1, and a thyristor T connected in series in sequence.

[0009] Preferably, the rated current commutation branch includes a parallel-connected RC-IGCT and a metal oxide varistor MOV. The anode of the IGBT module is connected between the cathodes of diodes VD1 and VD2, and the cathode of the RC-IGCT is connected between the anodes of diodes VD3 and VD4.

[0010] Preferably, the RC-IGCT has the advantages of high voltage and large current handling capabilities, low on-state voltage drop, fast switching speed, bidirectional conduction ability, modularity, and reliability.

[0011] Preferably, the disconnector is an ultra-fast disconnector UDS with a TP KEMA arc.

[0012] Preferably, the R-SFCL includes a parallel-connected superconductor Rsc and a bypass resistor Rc. Generally speaking, to achieve a protection effect, the resistance value of the parallel-connected shunt resistor Rc should be less than the resistance value of the current-limiting resistor Rsc after quenching. When the R-SFCL is in the superconducting state, the resistance value of the current-limiting resistor Rsc is 0, and the shunt resistor is short-circuited, and the system current will all flow through the current-limiting resistor Rsc; when a fault occurs in the system, the resistance of the current-limiting resistor of the R-SFCL increases rapidly. At this time, Rc < Rsc. According to the principle of parallel current sharing, most of the short-circuit current is borne by the shunt resistor on the parallel branch, and it also shares the heat generated by the current-limiting resistor Rsc, protecting the current-limiting resistor from being damaged due to overheating.

[0013] The present invention also provides a working principle of a superconducting hybrid DC circuit breaker based on RC-IGCT, including the following steps:

[0014] S1: When the system is in normal working mode, the current flows through the main branch. At this time, the system steady-state current i a for:

[0015]

[0016] Among them, U dc is the DC side voltage, R load is the load, Z1 and Z2 are the line impedances;

[0017] S2: System failure occurs, and the expected steady-state short-circuit current i b for:

[0018]

[0019] When the system detects that the short-circuit current reaches the preset threshold value Iset, the resistive superconducting fault current limiter (R-SFCL) will switch to the quench state, effectively suppressing the growth rate of the fault current through the rapid change of the resistance characteristics. After this protection mechanism is triggered, the system will start the opening operation sequence of the superconducting hybrid DC circuit breaker (SDCCB) in an orderly manner according to the preset time delay strategy. The opening process includes two coordinated actions: on the one hand, the UDS switching device of the main path is disconnected, and on the other hand, the conduction state of the RC-IGCT is activated, thereby driving the main circuit current to the parallel bridge commutation branch. In this commutation stage, the current path will form a closed loop along the VD1 diode ~ the RC-IGCT in the conduction state ~ the VD4 diode. This process is the first current commutation;

[0020] S3: When the main circuit current decays to zero, the system fault current is completely transferred to the bridge commutation topology. After the UDS switch completes full disconnection and isolation, the thyristor T of the active current injection unit is triggered to turn on, and the trigger current path is transferred from the RC-IGCT main channel to the auxiliary energy injection branch. In this stage, the current in the bridge commutation network is along VD 1～ RC-IGCT~VD4 forms a closed loop, and the energy stored in the pre-charge capacitor C1 is transferred through L 1～ The T~RC-IGCT~C1 loop generates a forced commutation impact current. This process is the second current commutation. The system fault current i c for:

[0021]

[0022] Among them, L is the system equivalent inductance, U diode is the voltage across the freewheeling diode, U RC-IGCT is the voltage across the RC-IGCT, i T is the current in thyristor T, i RC-IGCT is the current in the RC-IGCT;

[0023] S4: When the current of the RC-IGCT completely decays to zero, the pre-charged capacitor C1 has a deep discharge, so that its energy storage level is lower than the critical threshold. At this time, the freewheeling diode D enters the on-state. At this stage, the current path is reconstructed in the bridge commutation structure into an energy dissipation channel consisting of VD1 ~ capacitor C1 ~ inductor L1 ~ thyristor T ~ VD4. At the same time, a closed oscillation loop is formed between C1 and L1, T, and D, generating an LC oscillation current path caused by the combined action of the residual energy of the capacitor and the inductance characteristics. This process is the freewheeling of the freewheeling diode D in the second current commutation; the system fault current i d for:

[0024]

[0025] Among them, U C1 is the voltage of the pre-charge capacitor C1, U T is the voltage of thyristor T, i D is the current in the freewheeling diode D;

[0026] S5: The pre-charge capacitor C1 is reversely charged by the fault current, the voltage across the superconducting hybrid DC circuit breaker begins to rise, the current commutates from the RC-IGCT to the active current injection branch, the second current commutation ends, and the current flows through the diode VD1, pre-charge capacitor C1, inductor L1, thyristor T, and diode VD4 in the bridge current commutation circuit in sequence. The system fault current i e for:

[0027]

[0028] S6: When the voltage across the superconducting hybrid DC circuit breaker reaches the rated voltage of the metal oxide varistor MOV, the current begins to commutate from the active current injection branch to the MOV. The current flows through the diode VD1, MOV, and diode VD4 in the bridge current commutation circuit in sequence until the fault current in the MOV drops to 0. The entire fault current is disconnected. This process is the third current commutation, and the system fault energy is dissipated through the MOV; the MOV dissipates energy E MOV Expressed as:

[0029]

[0030] Among them, t1 and t2 are the time when MOV starts and ends dissipating fault energy, U MOV , I MOV are the voltage and current of MOV, I peak is the peak value of the fault current, (di MOV / dt) avgis the average rate of decrease of fault current;

[0031] The fault clearing time Δt of the DC system is:

[0032]

[0033] Among them, T d is the turn-off delay time of RC-IGCT.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] Compared to traditional hybrid DC circuit breakers, superconducting hybrid DC circuit breakers based on IGBT full-bridge modules combine power electronic switches and superconducting technology to achieve fault current limiting, rapid interruption, and commutation. The IGBT full-bridge module effectively distributes conduction losses through dynamic current sharing. Combined with a low-thermal-resistance packaging process, it maintains an ultra-low on-state voltage drop while ensuring thermal stability under high-capacity conditions. The quenching properties of the R-SFCL and the low on-resistance of the IGBT enable rapid commutation of fault currents, facilitating dielectric recovery of the mechanical contacts and significantly improving high-current interrupting capability.

[0036] The current-limiting characteristics of the R-SFCL significantly suppress the DC fault current, accelerate the interruption process, and significantly reduce the current interruption stress of the SDCCB components. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 is the topological structure diagram of the DC transmission system;

[0038] Figure 2 This is the topology diagram of SDCCB;

[0039] Figure 3 This is the physical model diagram of R-SFCL;

[0040] Figure 4 is the current commutation process of SDCCB during interruption of different fault currents; DETAILED DESCRIPTION

[0041] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0042] The topology of the DC transmission system is as follows: Figure 1As shown, the AC grid is connected to the AC side of a voltage source converter (VSCC) via a transformer for AC / DC conversion. The DC side of the VSC is connected to the load resistor via two DC transmission lines with impedances Z1 and Z2. SDCCBs are installed near the DC side of the VSC.

[0043] The topology of SDCCB is as follows Figure 2 As shown, the circuit topology consists of two components: ① a resistive superconducting fault current limiter (R-SFCL) and a series-connected UDS disconnector; and ② a current commutation component consisting of diodes VD1-VD4, a current injection branch, and a current commutation branch. The bridge current commutation circuit includes a first leg, a second leg, a rated current commutation branch, and an active current injection branch. The first leg includes two cathode-connected diodes VD1 and VD2, while the second leg includes two anode-connected diodes VD3 and VD4. The rated current commutation branch and the active current injection branch are connected between the cathodes of diodes VD1 and VD2 and between the anodes of diodes VD3 and VD4. The current injection branch includes resistor C1, inductor L1, and thyristor T. The current commutation branch includes an RC-IGCT, an RCD snubber circuit connected in parallel with the RC-IGCT, and an MOV energy absorption device.

[0044] like Figure 3 As shown, an R-SFCL consists of a parallel superconductor, Rsc, and a shunt resistor, Rc. Superconductor Rsc has zero resistance in its superconducting state and becomes a high-resistance resistor after a quench. The shunt resistor, Rc, protects the superconductor from burnout due to overcurrent. Ia1 and Ia2 represent the currents flowing through Rsc and Rc, respectively, and I represents the total current. The quench phenomenon in an R-SFCL is represented as follows:

[0045]

[0046] Where Rm is the maximum quench resistance, Tsc is the time constant for transition to the quench state, and t0 represents the quench start time, i.e. the time when the fault occurs.

[0047] like Figure 4 As shown, the present invention also provides a working method of a superconducting hybrid DC circuit breaker based on RC-IGCT, comprising the following steps:

[0048] S1: If Figure 4 As shown in (a), when the system is in normal working mode, the current flows through the main branch. At this time, the system steady-state current i a for:

[0049]

[0050] Among them, U dc is the DC side voltage, Rload is the load, Z1 and Z2 are the line impedances;

[0051] S2: If Figure 4 As shown in (b), a fault occurs in the system. At this time, the expected steady-state short-circuit current i b for:

[0052]

[0053] When the system detects that the short-circuit current reaches the preset threshold value Iset, the resistive superconducting fault current limiter (R-SFCL) will switch to the quench state, effectively suppressing the growth rate of the fault current through the rapid change of the resistance characteristics. After this protection mechanism is triggered, the system will start the opening operation sequence of the superconducting hybrid DC circuit breaker (SDCCB) in an orderly manner according to the preset time delay strategy. The opening process includes two coordinated actions: on the one hand, the UDS switching device of the main path is disconnected, and on the other hand, the conduction state of the RC-IGCT is activated, thereby driving the main circuit current to the parallel bridge commutation branch. In this commutation stage, the current path will form a closed loop along the VD1 diode ~ the RC-IGCT in the conduction state ~ the VD4 diode. This process is the first current commutation;

[0054] S3: If Figure 4 As shown in (c), when the main circuit current decays to zero, the system fault current is completely transferred to the bridge commutation topology. After the UDS switch completes full disconnection and isolation, the thyristor T of the active current injection unit is triggered to turn on, and the trigger current path is transferred from the RC-IGCT main channel to the auxiliary energy injection branch. In this stage, the current in the bridge commutation network is along VD 1～ RC-IGCT~VD4 forms a closed loop, and the energy stored in the pre-charge capacitor C1 is transferred through L 1～ The T~RC-IGCT~C1 loop generates a forced commutation impact current. This process is the second current commutation. The system fault current i c for:

[0055]

[0056] Among them, L is the system equivalent inductance, U diode is the voltage across the freewheeling diode, U RC-IGCT is the voltage across the RC-IGCT, i T is the current in thyristor T, i RC-IGCT is the current in the RC-IGCT;

[0057] S4: As Figure 4As shown in (d), when the current of the RC-IGCT completely decays to zero, the pre-charged capacitor C1 has a deep discharge, so that its energy storage level is lower than the critical threshold. At this time, the freewheeling diode D enters the on-state freewheeling state. At this stage, the current path is reconstructed in the bridge commutation structure into an energy dissipation channel consisting of VD1 ~ capacitor C1 ~ inductor L1 ~ thyristor T ~ VD4. At the same time, a closed oscillation loop is formed between C1 and L1, T, and D, generating an LC oscillation current path caused by the combined action of the residual energy of the capacitor and the inductance characteristics. This process is the freewheeling of the freewheeling diode D in the second current commutation; the system fault current i d for:

[0058]

[0059] Among them, U C1 is the voltage of the pre-charge capacitor C1, U T is the voltage of thyristor T, i D is the current in the freewheeling diode D;

[0060] S5: If Figure 4 As shown in (e), the pre-charge capacitor C1 is reversely charged by the fault current, the voltage across the superconducting hybrid DC circuit breaker begins to rise, and the current commutates from the RC-IGCT to the active current injection branch. The second current commutation ends, and the current flows through the diode VD1, pre-charge capacitor C1, inductor L1, thyristor T, and diode VD4 in the bridge current commutation circuit in sequence. The system fault current i e for:

[0061]

[0062] S6: As Figure 4 As shown in Figure (f), when the voltage across the superconducting hybrid DC circuit breaker reaches the rated voltage of the metal oxide varistor MOV, the current begins to commutate from the active current injection branch to the MOV. The current flows through the diode VD1, MOV, and diode VD4 in the bridge current commutation circuit in sequence until the fault current in the MOV drops to 0. The entire fault current is disconnected. This process is the third current commutation, and the system fault energy is dissipated through the MOV; the MOV dissipates energy E MOV Expressed as:

[0063]

[0064] Among them, t1 and t2 are the time when MOV starts and ends dissipating fault energy, U MOV , I MOV are the voltage and current of MOV, I peak is the peak value of the fault current, (di MOV / dt)avg is the average rate of decrease of fault current;

[0065] The fault clearing time Δt of the DC system is:

[0066]

[0067] Among them, T d is the turn-off delay time of RC-IGCT.

Claims

1. A superconducting hybrid DC circuit breaker based on RC-IGCT, characterized by: The invention comprises a main branch of a resistive superconducting fault current limiter R-SFCL and a UDS adopting a TP KEMA arc model connected in series; and a current reversing component composed of diodes VD1-VD4, a current injection branch and a current reversing branch.

2. The superconducting hybrid DC circuit breaker based on RC-IGCT according to claim 1, characterized in that: The main branch is composed of a resistive fault current limiter and a UDS in series. The resistive fault current limiter R-SFCL can quickly limit the fault current and transfer the current to the current reversing branch. The fault current limited by the R-SFCL is greatly reduced, which is consistent with the working characteristics of the TP-KEMA low current model.

3. The superconducting hybrid DC circuit breaker based on RC-IGCT according to claim 1, characterized in that: The bridge current commutation circuit includes a first bridge arm, a second bridge arm, a rated current commutation branch, and an active current injection branch. The first bridge arm includes two diodes VD1 and VD2 connected at the cathode, and the second bridge arm includes two diodes VD3 and VD4 connected at the anode. One end of the rated current commutation branch and the active current injection branch are connected between the cathodes of diodes VD1 and VD2, and the other end are connected between the anodes of diodes VD3 and VD4.

4. The superconducting hybrid DC circuit breaker based on RC-IGCT according to claim 1, characterized in that: The R-SFCL consists of parallel superconductors R SC and bypass resistor R C .

5. The superconducting hybrid DC circuit breaker based on RC-IGCT according to claim 1, characterized in that: The R-SFCL quench phenomenon is expressed as follows: Among them, R m is the maximum quench resistance, T SC is the time constant for transition to the quench state, and t0 represents the quench start time, that is, the fault occurrence time.

6. The superconducting hybrid DC circuit breaker based on RC-IGCT according to claim 3, characterized in that: The active current injection branch consists of a pre-charge capacitor C1, an inductor L1, and a thyristor T. After the thyristor is turned on, the pre-charge capacitor begins to discharge, thereby achieving fault current commutation and providing a reverse turn-off voltage for the RC-IGCT, ensuring that the RC-IGCT can be reliably turned off at low current levels.

7. The superconducting hybrid DC circuit breaker based on RC-IGCT according to claim 3, characterized in that: The rated current commutation branch comprises a solid-state power electronic switch (RC-IGCT), an RCD snubber circuit, and an energy absorption branch. The RC-IGCT is a key component of the circuit breaker for current interruption and commutation. Its high interruption capacity and fast commutation speed effectively reduce costs. The diode D primarily functions as a freewheeling current, allowing the pre-charged capacitor to fully discharge. The RC snubber circuit utilizes the characteristic of capacitor voltage that it cannot change suddenly to limit the rate of voltage rise. The energy absorption branch consists of a metal oxide surge arrester (MOSA).

8. The operating method of the superconducting hybrid DC circuit breaker based on RC-IGCT according to any one of claims 1 to 7, characterized in that: The steps include: S1: When the system is in normal working mode, the current flows through the main branch. At this time, the system steady-state current i a for: Among them, U dc is the DC side voltage, R load is the load, Z1 and Z2 are the line impedances; S2: System failure occurs, and the expected steady-state short-circuit current i b for: When the system detects that the short-circuit current reaches the preset threshold value Iset, the resistive superconducting fault current limiter (R-SFCL) will switch to the quench state, effectively suppressing the growth rate of the fault current through the rapid change of the resistance characteristics. After this protection mechanism is triggered, the system will start the opening operation sequence of the superconducting hybrid DC circuit breaker (SDCCB) in an orderly manner according to the preset time delay strategy. The opening process includes two coordinated actions: on the one hand, the UDS switching device of the main path is disconnected, and on the other hand, the conduction state of the RC-IGCT is activated, thereby driving the main circuit current to the parallel bridge commutation branch. In this commutation stage, the current path will form a closed loop along the VD1 diode ~ the RC-IGCT in the conduction state ~ the VD4 diode. This process is the first current commutation; S3: When the main circuit current decays to zero, the system fault current is completely transferred to the bridge commutation topology. After the UDS switch completes full disconnection and isolation, the thyristor T of the active current injection unit is triggered to turn on, and the trigger current path is transferred from the RC-IGCT main channel to the auxiliary energy injection branch. In this stage, the current in the bridge commutation network is along VD 1～ RC-IGCT~VD4 forms a closed loop, and the energy stored in the pre-charge capacitor C1 is transferred through L 1～ The T~RC-IGCT~C1 loop generates a forced commutation impact current. This process is the second current commutation. The system fault current i c for: Among them, L is the system equivalent inductance, U diode is the voltage across the freewheeling diode, U RC-IGCT is the voltage across the RC-IGCT, i T is the current in thyristor T, i RC-IGCT is the current in the RC-IGCT; S4: When the current of the RC-IGCT completely decays to zero, the pre-charged capacitor C1 has a deep discharge, so that its energy storage level is lower than the critical threshold. At this time, the freewheeling diode D enters the on-state. At this stage, the current path is reconstructed in the bridge commutation structure into an energy dissipation channel consisting of VD1 ~ capacitor C1 ~ inductor L1 ~ thyristor T ~ VD4. At the same time, a closed oscillation loop is formed between C1 and L1, T, and D, generating an LC oscillation current path caused by the combined action of the residual energy of the capacitor and the inductance characteristics. This process is the freewheeling of the freewheeling diode D in the second current commutation; the system fault current i d for: Among them, U C1 is the voltage of the pre-charge capacitor C1, U T is the voltage of thyristor T, i D is the current in the freewheeling diode D; S5: The pre-charge capacitor C1 is reversely charged by the fault current, the voltage across the superconducting hybrid DC circuit breaker begins to rise, the current commutates from the RC-IGCT to the active current injection branch, the second current commutation ends, and the current flows through the diode VD1, pre-charge capacitor C1, inductor L1, thyristor T, and diode VD4 in the bridge current commutation circuit in sequence. The system fault current i e for: S6: When the voltage across the superconducting hybrid DC circuit breaker reaches the rated voltage of the metal oxide varistor MOV, the current begins to commutate from the active current injection branch to the MOV. The current flows through the diode VD1, MOV, and diode VD4 in the bridge current commutation circuit in sequence until the fault current in the MOV drops to 0. The entire fault current is disconnected. This process is the third current commutation, and the system fault energy is dissipated through the MOV; the MOV dissipates energy E MOV Expressed as: Among them, t1 and t2 are the time when MOV starts and ends dissipating fault energy, U MOV , I MOV are the voltage and current of MOV, I peak is the peak value of the fault current, (di MOV / dt)avg is the average rate of decrease of fault current; The fault clearing time Δt of the DC system is: Among them, T d is the turn-off delay time of RC-IGCT.

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