Superconducting hybrid direct-current circuit breaker based on IGBT full-bridge module and working method of superconducting hybrid direct-current circuit breaker

Abstract

The invention discloses a superconducting hybrid direct-current circuit breaker based on an IGBT (Insulated Gate Bipolar Translator) full-bridge module, and relates to topological structures and working principle analysis of direct-current circuit breakers. The circuit topology comprises two parts: (1) a current commutation component consisting of a resistance-type superconducting fault current limiter R-SFCL and a series UDS isolation switch, and (2) diodes VD1-VD4, a current injection branch and a current commutation branch. 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 comprises an IGBT full-bridge module, a buffer circuit and an MOV group, wherein the buffer circuit and the MOV group are connected in parallel at two ends of the IGBT full-bridge module in order to realize dynamic voltage sharing of the IGBT full-bridge module. The fault current interruption capability of the hybrid circuit breaker is greatly improved by utilizing the current limiting characteristic of the resistance-type superconducting fault current limiter, the good interruption capability of the circuit breaker can be guaranteed, the operation loss is greatly reduced, and the cost is further reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of superconducting switches, and particularly to a superconducting hybrid DC circuit breaker based on an IGBT full-bridge module and its working principle. Background Art

[0002] Due to the advantages of flexible power allocation, high system efficiency, large power supply capacity, low line loss, and high power quality, DC systems are increasingly widely used in high-voltage power transmission, medium- and low-voltage power distribution and utilization, new energy access, ship and rail transit fields. However, the main wiring structure of the DC system is complex and the operation mode is diverse, which leads to multiple fault modes, fast fault development, and wide influence range. Therefore, it is urgent to break through the fault isolation and protection technology of the DC system to ensure the safe and reliable operation of the DC system. As the most ideal fault isolation method for the DC system, the DC circuit breaker has become a research hotspot in the field of medium- and high-voltage electrical appliances.

[0003] The hybrid DC circuit breaker has the low-loss current-carrying and insulation fast recovery capabilities of the mechanical DC circuit breaker and the fast breaking ability of the solid-state DC circuit breaker, and has become one of the main development directions of the DC circuit breaker. However, the traditional hybrid circuit breaker also has problems such as difficult arc extinguishing of mechanical switches and limited overload capacity of power electronic devices, and the achievable fast breaking ability is limited.

[0004] Combining a resistive superconducting fault current limiter (R-SFCL) with a hybrid circuit breaker, the R-SFCL can quickly limit the fault current and transfer the current to the current commutation branch. The fault current limited by the R-SFCL is greatly reduced and fast commutation is achieved after a short-circuit fault. By using the R-SFCL to suppress the magnitude and rising speed of the fault current, the requirement for the breaking capacity of the circuit breaker in the DC power grid fault can be effectively reduced. Umer Amir Khan proposed to connect a superconducting fault current limiter in series with a traditional hybrid circuit breaker to limit the main circuit current for application in the DC power transmission field. When the fault current level in a 10 kV MVDC power grid is greater than 15 kA, multiple insulated gate bipolar transistors (IGBTs) need to be connected in parallel to achieve reliable interruption. This greatly increases the cost of the hybrid circuit breaker. Summary of the Invention

[0005] To solve the problems of the prior art, the present invention provides a superconducting hybrid DC circuit breaker based on an IGBT full-bridge module and its working principle. By combining a resistive superconducting fault current limiter with a hybrid circuit breaker based on an IGBT full-bridge module, and utilizing the current-limiting characteristics of the resistive fault current limiter and the strong current-carrying capacity, high voltage level, and cost advantages of the IGBT full-bridge module, the cost can be greatly reduced while ensuring good interruption ability of the circuit breaker. The application of this superconducting hybrid DC circuit breaker in a medium-voltage DC network can achieve integration of current limiting and interruption, and further reduce 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 an IGBT full-bridge module, 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 pre-charging capacitor C1, an inductor L1, and a thyristor T connected in series. After the thyristor conducts, the pre-charging capacitor starts to discharge, thereby realizing fault current commutation and providing a reverse turn-off voltage for the IGBT full-bridge module to ensure that the IGBT full-bridge module can be reliably turned off at a low current level; to achieve dynamic voltage equalization of the IGBT module, an RCD buffer circuit and a MOV group are connected in parallel at both ends of the IGBT module.

[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 IGBT module 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 IGBT module is connected between the anodes of diodes VD3 and VD4.

[0010] Preferably, the IGBT full-bridge module has the advantages of high voltage and large current handling capabilities, low conduction voltage drop, fast switching speed, bidirectional conduction ability, modularity, and reliability.

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

[0012] Preferably, the R-SFCL includes a superconductor Rsc and a bypass resistor Rc connected in parallel. Generally, to achieve a protection effect, the resistance value of the shunt resistor Rc connected in parallel should be less than the resistance value of the current-limiting resistor Rsc after quenching. In the superconducting state of the R-SFCL, the resistance value of the current-limiting resistor Rsc is 0, 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 shunting, 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 an operating principle of a superconducting hybrid DC circuit breaker based on an IGBT full-bridge module, including the following steps:

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

[0015]

[0016] where E is the DC side voltage, Rload is the load, and Z1, Z2 are the line impedances;

[0017] S2: When a fault occurs in the system, the expected steady-state short-circuit current i b is:

[0018]

[0019] When the system detects that the short-circuit current reaches the preset threshold I set , the resistive superconducting fault current limiter (R-SFCL) will activate the quenching conversion mechanism to effectively suppress 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. This opening process includes two coordinated actions: on the one hand, disconnect the UDS switching device in the main path, and on the other hand, activate the conduction state of the IGBT full-bridge module, so as to drive the main circuit current to transfer to the parallel bridge-type commutation branch. During this commutation stage, the current path will form a closed loop along the VD1 diode - the IGBT full-bridge module 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 is fully opened and isolated, the thyristor T of the active current injection unit is triggered to conduct, and the trigger current path is transferred from the main channel of the IGBT full-bridge module to the auxiliary energy injection branch. At this stage, the current forms a closed loop in the bridge commutation network along the VD1 diode - the conducting body of the IGBT module - the VD4 diode. At the same time, the stored energy of the pre-charge capacitor C1 generates a forced commutation impact current through the L1 - T - IGBT - C1 loop. This process is the second current commutation, and the system fault current i c is:

[0021]

[0022] where L is the equivalent inductance of the system, U diode is the voltage across the freewheeling diode, U IGBT is the voltage across the IGBT, iT is the current in the thyristor T, and i IGBT is the current in the IGBT;

[0023] S4: When the current in the IGBT module completely decays to zero, the pre-charge capacitor C1 is deeply discharged so that its stored energy level is lower than the critical threshold. At this time, the freewheeling diode D enters the conducting freewheeling state. In this stage, the current path is reconstructed in the bridge commutation architecture into an energy dissipation channel composed of the VD1 diode - the C1 energy storage unit - the L1 inductor - the T thyristor - the VD4 diode. At the same time, a closed oscillation loop is formed between C1 and L1, T, D, generating an LC oscillation current path jointly affected by the residual energy of the capacitor and the inductance characteristics. This process is the freewheeling of the freewheeling diode D during the second current commutation; the system fault current i d is:

[0024]

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

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

[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 starts to commutate from the active current injection branch to the MOV. The current flows through the diode VD1, MOV, and diode VD4 in sequence in the bridge-type current commutation circuit until the fault current in the MOV drops to 0, and the entire disconnection of the fault current is completed. This process is the third current commutation, and the system fault energy is dissipated through the MOV; the energy dissipated by the MOV is E mov It is expressed as:

[0029]

[0030] where t1 and t2 are the start and end times of the MOV dissipating the fault energy, U MOV , I MOV are the voltage and current of the MOV respectively, I peak is the peak value reached by the fault current, (di MOV / dt) avg is the average decline rate of the fault current;

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

[0032]

[0033] where T d is the turn-off delay time of the IGBT.

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

[0035] Compared with the traditional hybrid DC circuit breaker, the superconducting hybrid DC circuit breaker based on the IGBT full-bridge module combines power electronic switches and superconducting technology, and can achieve functions such as limiting fault current, rapid interruption, and commutation. The IGBT full-bridge module effectively disperses the conduction loss through dynamic current sharing control, and cooperates with the low thermal resistance packaging process to ensure the thermal stability under large-capacity conditions while maintaining an ultra-low on-state voltage drop. Due to the quenching characteristics of the R-SFCL and the low on-resistance of the IGBT, rapid commutation of the fault current can be achieved, which helps the dielectric recovery of the mechanical contact and significantly improves the large-current breaking ability.

[0036] The current limiting characteristic of the R-SFCL significantly suppresses the DC fault current, speeds up the interruption process, and significantly reduces the current interruption stress of the SDCCB components. Brief Description of the Drawings

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

[0038] Figure 2It is the topological structure diagram of SDCCB;

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

[0040] Figure 4 It is the topological structure diagram of the IGBT full-bridge sub-module;

[0041] Figure 5 It is the current path when the IGBT full-bridge sub-module is in the conducting state;

[0042] Figure 6 It is the current path when the IGBT full-bridge sub-module is in the blocked state; Specific implementation manners

[0043] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0044] The topological structure of the DC power transmission system is as Figure 1 shown. The AC power grid is connected to the AC side of the voltage source converter through a transformer for AC-DC conversion. The DC side of the voltage source converter is connected to both ends of the load resistor through two DC power transmission lines, and the impedances of the two DC power transmission lines are Z1 and Z2. SDCCBs are respectively arranged near the DC side of the voltage source converter on the two DC power transmission lines.

[0045] The topological structure of SDCCB is as Figure 2 shown. The circuit topology includes two parts: ① a resistive superconducting fault current limiter R-SFCL and a series-connected UDS disconnect switch, ② a current commutation component composed of diodes VD1-VD4, a current injection branch, and a current commutation branch. The bridge-type 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 with cathodes connected, and the second bridge arm includes two diodes VD3 and VD4 with anodes connected. One end of the rated current commutation branch and the active current injection branch is connected between the cathodes of the diodes VD1 and VD2, and the other end is connected between the anodes of the diodes VD3 and VD4. The current injection branch includes a resistor C1, an inductor L1, and a thyristor T; the current commutation branch includes: an IGBT full-bridge module, an RCD buffer circuit in parallel with the IGBT full-bridge module, and a MOV energy absorption device.

[0046] As Figure 3As shown, the R-SFCL includes a superconductor Rsc and a bypass resistor Rc connected in parallel. The resistance of the superconductor Rsc is 0 in the superconducting state and becomes a high-resistance state resistance after quenching. The bypass resistor Rc is used to prevent the superconductor from being burned out due to overcurrent. Ia1 and Ia2 respectively represent the currents flowing through Rsc and Rc, and I represents the total current. The quenching phenomenon of the R-SFCL is shown as follows:

[0047]

[0048] Among them, Rm is the maximum quenching resistance, Tsc is the time constant for transitioning to the quenching state, and t0 represents the start time of quenching, that is, the fault occurrence time;

[0049] As Figure 4 shown, the IGBT full-bridge sub-module consists of 4 IGBTs with anti-parallel diodes, a sub-module capacitor C, and a discharge resistor R. The size of the sub-module capacitor C is 100 μF, and the size of the resistor R is 50 kΩ. The resistor R is used to discharge the energy stored in the sub-module capacitor after the circuit breaker is tripped. Its discharge time constant is 5 s. Therefore, during the millisecond-level tripping process of the circuit breaker, its effect can be ignored.

[0050] Different from conventional applications, the 4 IGBTs included in the full-bridge sub-module always maintain the same switching state, that is, they are turned on or blocked simultaneously. Therefore, there are only 2 working states for the full-bridge sub-module in the circuit breaker: the on state and the blocked state.

[0051] As Figure 4 shown, the present invention also provides a working method for the IGBT full-bridge module, including the following steps:

[0052] S1: All 4 IGBTs in the full-bridge sub-module are in the on state, and the full-bridge sub-module can conduct bidirectional current.

[0053] As Figure 5 (a) shown, when the full-bridge sub-module conducts forward current, the current flows through the branches composed of V1 and IGBT4 and the branches composed of IGBT2 and V3 respectively.

[0054] S2: As Figure 5 (b) shown, when the full-bridge sub-module conducts reverse current, the current flows through the branches composed of IGBT1 and V4 and the branches composed of V2 and IGBT3 respectively.

[0055] It can be seen that the full-bridge sub-module realizes bidirectional current conduction through two symmetric branches composed of IGBTs and freewheeling diodes.

[0056] S3: When all 4 IGBTs in the full-bridge sub-module are in the locked state, the full-bridge sub-module is in the locked state. At this time, the capacitor C of the full-bridge sub-module is connected in series to the circuit, and the current flowing through the full-bridge sub-module charges the sub-module capacitor C through the freewheeling diode.

[0057] As Figure 6 (a) shows, when a forward current flows, the current flows through V1 and V3 to charge the sub-module capacitor C;

[0058] S4: As Figure 6 (b) shows, when a reverse current flows, the current flows through V2 and V4 to charge the sub-module capacitor C.

Claims

1. A superconducting hybrid DC circuit breaker based on an IGBT full-bridge module, the circuit topology includes two parts: ① a resistive superconducting fault current limiter R-SFCL and a UDS disconnector connected in series, ② a current switching component consisting of diodes VD1-VD4, a current injection branch and a current switching branch. The bridge current switching circuit includes a first bridge arm, a second bridge arm, a rated current switching branch, and an active current injection branch. The first bridge arm includes two cathode-connected diodes VD1 and VD2, and the second bridge arm includes two anode-connected diodes VD3 and VD4. One end of the rated current switching branch and the active current injection branch are connected between the cathodes of diodes VD1 and VD2, and the other end is connected between the anodes of diodes VD3 and VD4.

2. The superconducting hybrid DC circuit breaker based on the IGBT full-bridge module according to claim 1 is characterized in that: Using IGBT modules, different from conventional applications, the 4 IGBTs contained in the full-bridge submodule always maintain the same switching state, that is, they are turned on or off at the same time.

3. The superconducting hybrid DC circuit breaker based on IGBT full-bridge module according to claim 1, characterized in that: The rated current commutation branch includes parallel IGBT full-bridge modules, and the full-bridge sub-modules are composed of 4 IGBTs with anti-parallel diodes, sub-module capacitors C and discharge resistors R, where the sub-module capacitor C is 100μF and the resistor R is 50kΩ. The resistor R is used to discharge the energy stored in the sub-module capacitor after the circuit breaker is disconnected, and its discharge time constant is 5s, so its role can be ignored during the millisecond-level disconnection process of the circuit breaker.

4. The superconducting hybrid DC circuit breaker based on the IGBT full-bridge module according to claim 3 is characterized in that: The snubber consists of a series resistor R s , capacitor C s and diode D.

5. The superconducting hybrid DC circuit breaker based on IGBT full-bridge module according to claim 1, characterized in that: The disconnector is an ultra-fast disconnector UDS with Mayr arc.

6. The superconducting hybrid DC circuit breaker based on IGBT full-bridge module according to claim 1, characterized in that: The R-SFCL consists of parallel superconductors R sc and bypass resistor R c .

7. The working method of the superconducting hybrid DC circuit breaker based on the IGBT full-bridge module 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: Where, E is the DC side voltage, R load is the load, Z1 and Z2 are the line impedances; S2: The system fails, 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 activate the quenching conversion mechanism, effectively suppressing the growth rate of the fault current through the rapid transformation 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 IGBT full-bridge module is activated, thereby driving the main circuit current to transfer to the parallel bridge commutation branch. In this commutation stage, the current path will form a closed loop along the VD1 diode-the IGBT full-bridge module 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, triggering the current path to transfer from the main channel of the IGBT full-bridge module to the auxiliary energy injection branch. In this stage, the current forms a closed loop in the bridge commutation network along the VD1 diode-IGBT module conductor-VD4 diode. At the same time, the energy storage of the pre-charged capacitor C1 generates a forced commutation impact current through the L1-T-IGBT-C1 circuit. This process is the second current commutation. The system fault current i c for: Where, L is the system equivalent inductance, U diode is the voltage across the freewheeling diode, U IGBT is the voltage across the IGBT, i T is the current in thyristor T, i IGBT is the current in the IGBT; S4: When the current of the IGBT module completely decays to the zero state, the pre-charge capacitor C1 has a deep discharge and 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 architecture into an energy dissipation channel consisting of VD1 diode-C1 energy storage unit-L1 inductor-T thyristor-VD4 diode. 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 in this process is 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 is commutated from the IGBT module 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. 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; MOV dissipates energy E MOV It is 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 the IGBT module.

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