Adaptive reclosing hybrid DC circuit breaker for DC transmission and distribution systems

Abstract

The present invention is an adaptive reclosing hybrid DC circuit breaker applicable to DC power transmission and distribution systems, with a two-stage current limiting function, including a first-stage current limiting branch and a second-stage current limiting branch. The adoption of two-stage current limiting can improve the drawbacks of the existing single fixed current limiting mechanism of circuit breakers. When different types and severities of faults occur, the rate of change and the range of change of the fault current are large instantaneously. The two-stage current limiting structure can initially limit the sharp change of the fault current through the first-stage current limiting branch after the fault occurs, and then gradually limit the fault current through the two-stage current limiting structure, achieving the purpose of smoothly limiting the current and reducing the energy impact and electromagnetic interference caused by the sudden large and rapid change of the current to other components and equipment in the circuit. The structure of the fault discrimination branch enables the charging of capacitor C3 without using the power supply, only using the inductive energy of the fault-side line, effectively avoiding the waste of energy.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronic control of a DC power transmission and distribution system, and in particular to an adaptive reclosing hybrid DC circuit breaker suitable for a DC power transmission and distribution system. Background Art

[0002] Flexible DC systems with unique advantages are an effective means of grid connection and consumption of renewable energy. However, the DC grid has the characteristics of "low inertia and low damping", which leads to rapid current development after a fault. If the fault cannot be removed in a short time, it will affect the normal operation of the entire system. Circuit breakers are important components for controlling and protecting DC grids. After a fault occurs, DC circuit breakers can be used to quickly remove the faulty line, which can minimize the impact of the fault on the DC system.

[0003] As the safety guard of building a reliable power system, switchgear can be divided into circuit breakers, disconnectors, fuses, load switches, etc. Among them, circuit breakers are used to disconnect circuits when line faults occur. They are the most important equipment with the most complex technical parameters among switchgear. In recent years, with the increase in voltage levels and the rapid development of distributed power sources, new requirements have been put forward for the performance of switchgear such as breaking current and breaking speed. It has become particularly important to study "modern switchgear" suitable for new scenarios. According to different structures, DC circuit breakers can be divided into three categories, namely mechanical circuit breakers, solid-state circuit breakers and hybrid circuit breakers. Among them, hybrid circuit breakers combine the strong current-carrying capacity of mechanical switches with the fast shutdown capability of power electronic devices. They have the advantages of low on-state loss, fast and controllable disconnection, and high reliability. They have broad application prospects in DC power grids.

[0004] In recent years, with the development of power electronics technology, DC circuit breaker technology has made great progress, and a variety of hybrid DC circuit breakers with current limiting functions have been proposed. For example, the Chinese patent with publication number CN116260118A discloses a hybrid DC circuit breaker with current limiting function. After a fault occurs, the circuit breaker first transfers the current of the main current branch to the thyristor branch to achieve arc-free disconnection of the mechanical switch of the main current branch, and then puts the current limiting branch into use to limit the fault current. However, the circuit breaker cannot bypass the current limiting inductor during the fault current disconnection stage, resulting in a slower rate of decrease of the fault current and a longer time for clearing the fault current. The Chinese patent with publication number CN112865029A discloses a hybrid DC circuit breaker with dual current limiting function. The circuit breaker greatly improves the current limiting capacity and prolongs the current limiting time after the fault through dual current limiting to ensure the safety of the converter station. However, the circuit breaker does not have bidirectional current limiting, bidirectional breaking capacity and adaptive reclosing function, and needs to be equipped with auxiliary circuits to achieve bidirectional limiting and breaking of fault current. The dual current limiting function of the circuit breaker is divided into main current limiting and backup current limiting states. When performing backup current limiting, it is necessary to determine the transfer branch submodule input according to the backup current limiting control scheme. The number of arresters is used to sort the energy absorption of the arresters, determine the triggering order of the parallel submodules of the arresters, and put the corresponding arrester modules into current limiting, which leads to a complex control strategy. The multiple conduction of the arrester will lead to a decrease in device performance and a decrease in service life. The arrester's limiting effect on current is indirectly achieved by limiting the overvoltage. It will only be turned on when the line overvoltage reaches its operating voltage, so that it has a certain action delay, and the current limiting and breaking time is long. In addition, the circuit breaker has poor adaptability and may not be able to limit the rise of the fault current caused by non-overvoltage factors. Compared with the above-mentioned patent using arresters and submodules to achieve backup current limiting, the current limiting principle of the current limiting inductor used in the present invention is more direct and has a faster response speed. At the moment of current mutation, the current limiting inductor will generate an induced electromotive force to hinder the increase of current, which can play a significant inhibitory role on the current at the initial stage of the fault. The current limiting process using the inductor is stable and is not affected by factors such as the fault current waveform and frequency. The system has strong adaptability. Whether it is a short circuit fault, an overload fault or other types of faults, the current limiting structure can limit the fault current.

[0005] At present, the technical problems of hybrid DC circuit breakers are as follows:

[0006] (1) According to the principle of electromagnetic induction, when the circuit breaker interrupts the fault current, if the current limiting inductor is still connected in series in the loop, the current limiting inductor will generate an induced electromotive force that hinders the attenuation of the fault current, prolonging the fault isolation time of the circuit breaker, resulting in reduced operating efficiency of the circuit breaker. In addition, the current limiting inductor will store part of the energy originally in the current in the form of magnetic field energy. Since the energy stored in the current limiting inductor also needs to be consumed by the lightning arrester, the energy consumption requirements of the lightning arrester become higher.

[0007] (2) The working environment of the circuit breaker is complex. When faults of different types and severity occur, the instantaneous current change rate and range of the fault are large. Circuit breakers using a single-stage current limiting method have many limitations. They mainly rely on a single fixed current limiting mechanism. At the moment of the fault, there is a lack of a pre-stage current limiting stage to initially limit the rapid change of the fault current. The current peak cannot be gradually reduced through a multi-stage coordinated current limiting structure. In addition, circuit breakers using a single-stage current limiting method have poor adaptability to complex fault scenarios such as different fault types and different system parameters. It is difficult to flexibly adjust the current limiting strategy according to the specific situation of the fault, which greatly reduces the current limiting effect.

[0008] (3) After the circuit breaker has completed the fault current interruption, it is necessary to perform a reclosing operation to restore the normal current flow state of the line. However, most of the current hybrid circuit breaker topologies are not equipped with an effective fault identification branch. They cannot determine whether the line fault has disappeared through fault characteristics such as line voltage and current. The lack of fault identification capability causes the circuit breaker to be unable to determine the timing of reclosing and the line power supply restoration strategy by itself. It is difficult to independently complete the complete power supply restoration process from fault identification to adaptive reclosing. It still relies heavily on external equipment to assist in fault nature identification and line power supply restoration.

[0009] Therefore, in view of the problems existing in the current hybrid DC circuit breakers, it is necessary to provide an adaptive reclosing hybrid DC circuit breaker suitable for DC transmission and distribution systems, thereby promoting the development of DC transmission and distribution systems. Summary of the invention

[0010] In view of the deficiencies in the prior art, the technical problem that the present invention intends to solve is to provide an adaptive reclosing hybrid DC circuit breaker suitable for a DC transmission and distribution system, which has a two-stage current limiting function to enhance the current limiting and breaking capacity after a DC line fault, and solve the technical problems of the limitations of the single-stage current limiting structure of the DC circuit breaker in the prior art, the lack of fault nature judgment and adaptive reclosing capability, and high energy consumption requirements of the lightning arrester, thereby improving the system reliability and economy and providing new ideas for the development of high-voltage DC circuit breakers.

[0011] The technical solution adopted by the present invention to solve the technical problem is as follows:

[0012] An adaptive reclosing hybrid DC circuit breaker suitable for a DC power transmission and distribution system comprises a current-passing branch, a bridge-type commutation branch, a current transfer branch, a current limiting branch, a disconnecting branch and a pre-charging branch. The hybrid DC circuit breaker further comprises a fault discrimination branch, wherein:

[0013] The bridge commutation branch is composed of a bridge circuit consisting of a thyristor T1, a thyristor T2, a thyristor T3, and a thyristor T4, wherein the positive electrode of the thyristor T1 is connected to the negative electrode of the thyristor T2 and is connected to the input end of the current-passing branch, the positive electrode of the thyristor T3 is connected to the negative electrode of the thyristor T4 and is connected to the output end of the current-passing branch, and the negative electrode of the thyristor T1 is connected to the negative electrode of the thyristor T3, and the positive electrode of the thyristor T2 is connected to the positive electrode of the thyristor T4;

[0014] The current transfer branch is composed of a thyristor T5 and a thyristor T6 connected in series, the negative electrode of the thyristor T5 is connected to the positive electrode of the thyristor T6, the positive electrode of the thyristor T5 is connected to the bridge commutation branch, and the negative electrode of the thyristor T6 is connected to the connection point of the disconnection branch and the current limiting branch;

[0015] The current limiting branch consists of a primary current limiting branch and a secondary current limiting branch. The primary current limiting branch includes a current limiting resistor R1, a current limiting inductor L1, a capacitor C1, a thyristor T8 and a thyristor T 10 The primary current limiting branch is connected in parallel with the thyristor T5 of the current transfer branch; the secondary current limiting branch includes a current limiting resistor R2, a current limiting inductor L2, a capacitor C2, and a thyristor T 12 and thyristor T 14 , the secondary current limiting branch is connected in parallel with the thyristor T6 of the current transfer branch, and the output end of the primary current limiting branch is connected to the input end of the secondary current limiting branch;

[0016] Among them, one end of the current limiting resistor R1 is connected to the negative electrode of the thyristor T5, and the other end is connected to one end of the current limiting inductor L1 and the thyristor T 10 The other end of the current limiting inductor L1 is connected to the negative electrode of the thyristor T8; the thyristor T 10 The positive electrode of is connected to one end of the capacitor C1, and the other end of the capacitor C1 and the positive electrode of the thyristor T8 are both connected to the positive electrode of the thyristor T5;

[0017] Among them, one end of the current limiting resistor R2 is connected to the negative electrode of the thyristor T5, and the other end is connected to the thyristor T 14 The positive electrode and thyristor T 12 The positive electrode of the thyristor T 14 The negative electrode and thyristor T 12 The negative electrode of is connected to one end of the current limiting inductor L2 and the capacitor C2 respectively, and the other ends of the current limiting inductor L2 and the capacitor C2 are connected to the negative electrode of the thyristor T6;

[0018] In the current limiting inductor L1, the current limiting inductor L2, the thyristor T 10 and thyristor T 12 The two ends of the thyristor are connected in parallel with thyristor T9 and thyristor T 15 , Thyristor T 11 and thyristor T 13 ;

[0019] Connect the positive electrode of thyristor T 17 to the negative electrode of thyristor T3 in the bridge commutation branch, and connect the negative electrode of the thyristor T 17 to the pre-charge current-limiting resistor R3; connect the negative electrode of thyristor T6 in the current transfer branch and the positive electrode of thyristor T2 in the bridge commutation branch to the negative electrode and the positive electrode of thyristor T7 respectively; the breaking branch is connected in parallel across both ends of thyristor T7;

[0020] Connect the positive electrode of thyristor T7 to the fault discrimination branch at the same time. The fault discrimination branch includes a reverse-parallel thyristor group, a capacitor C3, and a current-limiting resistor R4; the other end of the current-limiting resistor R4 is grounded; the reverse-parallel thyristor group includes thyristor T 18 and thyristor T 19 ;

[0021] Connect a reverse-parallel thyristor T 16 across both ends of thyristor T4 in the bridge commutation branch;

[0022] The above-mentioned thyristor T7, thyristor T 11 , thyristor T 13 , thyristor T 16 , thyristor T 17 and the pre-charge current-limiting resistor R3 form a pre-charge branch.

[0023] Furthermore, connect an energy-dissipating circuit composed of a mechanical switch and a resistor in parallel across both ends of capacitor C1, capacitor C2, and capacitor C3; the current-carrying branch is composed of a ultra-fast mechanical switch UFD and a load transfer switch LCS connected in series;

[0024] The breaking branch is composed of a breaking switch S and a lightning arrester MOA connected in parallel. The breaking switch S is formed by cascading multiple IGBT valve groups, and each valve group contains several parallel-connected IGBTs and diodes.

[0025] Furthermore, when the system is operating normally, the current flows from the left side to the right side of the DC circuit breaker. Assuming a fault occurs on the right side of the DC circuit breaker, the left side of the DC circuit breaker is the source side and the right side is the fault side. When an overcurrent occurs in the line, the DC circuit breaker has four working modes, namely, low-impedance fault mode, high-impedance fault mode, current-limiting recovery mode, and small-current breaking mode.

[0026] Furthermore, the working process of the low-impedance fault mode is as follows:

[0027] Stage 1 of t < t0: During normal operation, the ultra-fast mechanical switch UFD and the load transfer switch LCS are conducting. At -t0, trigger thyristor T7, thyristor T 11 , thyristor T 13 , thyristor T 16 and thyristor T 17, pre-charge capacitors C1 and C2. As the voltage of capacitors C1 and C2 rises, the charging current gradually decays to 0. Thyristor T7 and Thyristor T 11 , Thyristor T 13 , Thyristor T 16 and thyristor T 17 Natural shutdown, pre-charging ends;

[0028] t0-t2 stage 2: a fault occurs in the DC system at t0, and the DC circuit breaker and the fault detection system start at the same time at t1, triggering thyristors T1, T4, T5, T6 and disconnecting switch S, disconnecting the load transfer switch LCS, and transferring the fault current from the current-carrying branch to the current transfer branch. The ultra-fast mechanical switch UFD starts to disconnect under the zero current state, and at t2 the ultra-fast mechanical switch UFD reaches the rated opening distance;

[0029] t2-t3 Phase 3: t 2' Trigger thyristor T at all times 10 , capacitor C1 discharges, thyristor T5 is turned off by reverse voltage, t 2” At time t3, capacitor C1 is discharged and starts to reverse charge, triggering thyristor T8 at the same time, and current limiting inductor L1 starts to be put into use. As the voltage of capacitor C1 increases, the current of capacitor C1 branch gradually transfers to the current limiting inductor L1 branch. At time t3, capacitor C1 is charged and the current in the branch decays to 0. Thyristor T8 is turned on. 10 Natural shutdown, all current is transferred to the branch where the current limiting inductor L1 is located, and the current limiting inductor L1 is fully engaged in current limiting;

[0030] t3-t4 phase 4: At t3, the fault detection is completed, a low impedance fault occurs in the DC system, and the secondary current limiting is activated. 3' Trigger thyristor T at all times 12 , capacitor C2 discharges, thyristor T6 is turned off by reverse voltage, t 3” At this moment, capacitor C2 is discharged and starts to charge reversely, triggering thyristor T 14 , the current limiting inductor L2 starts to be put into use. As the voltage of capacitor C2 increases, the current of capacitor C2 branch transfers to the current limiting inductor L2 branch. At t4, the charging of capacitor C2 is completed and the thyristor T 12 Natural shutdown, the current limiting inductor L2 is fully engaged in current limiting;

[0031] t5-t6 Phase 5: At t5, the DC circuit breaker receives the disconnection command, turns off the disconnect switch S, and the arrester MOA is put into isolation fault. The fault current begins to decay, and the voltage across the current limiting inductor L1 and the current limiting inductor L2 suddenly changes, triggering the thyristor T9 and thyristor T 15 The current in the current limiting inductor L1 and the current limiting inductor L2 flows through the thyristor T9 and the thyristor T 15A circulating current is formed and remains stable, the current limiting inductor L1 and the current limiting inductor L2 are bypassed, and the fault current decays to 0 at time t6;

[0032] t7-t8 stage 6: t7 triggers thyristor T8 and thyristor T 11 , Thyristor T 13 , Thyristor T 14 , Thyristor T 16 and thyristor T 18 , thyristor T9 is turned off by the reverse voltage of capacitor C1, and the energy stored in the current limiting inductor L1 is transferred to thyristor T8 and thyristor T 11 Transfer to capacitor C1; thyristor T 15 The capacitor C2 is turned off due to the reverse voltage, and the energy stored in the current limiting inductor L2 is discharged through the thyristor T 13 , Thyristor T 14 The inductor energy on the fault side is transferred to capacitor C2 through thyristor T 16 , Thyristor T 18 The energy is transferred to capacitor C3. Capacitors C1, C2 and C3 are connected in parallel with an energy dissipation circuit. At t8, the energy transfer is completed. Thyristor T8 and thyristor T 11 , Thyristor T 13 , Thyristor T 14 , Thyristor T 16 and thyristor T 18 Natural shutdown, at this time, the mechanical switch of the energy dissipation circuit on capacitors C1 and C2 is closed, the energy in capacitors C1 and C2 is consumed through the resistance of the energy dissipation circuit, and the fault line is disconnected;

[0033] t=t9 phase 7: After the line is fully deionized, the adaptive reclosing operation starts at t9, triggering the conduction thyristor T4 and thyristor T 19 , if capacitor C3 and thyristor T4 and thyristor T 19 , the fault side inductor, and the current limiting resistor R4 form a discharge circuit for discharge, then it is judged that a permanent fault has occurred, the fault has not disappeared, and the reclosing operation is not performed, waiting for maintenance; if the capacitor C3 and the thyristor T4 and thyristor T 19 , the fault-side inductance and current-limiting resistor R4 cannot form an effective discharge circuit, it is determined that a transient fault has occurred and the fault has disappeared. The DC circuit breaker can be reclosed and the mechanical switch of the energy dissipation circuit on capacitor C3 is closed at the same time. Capacitor C3 discharges energy, all working stages are completed, and wait for the next action command.

[0034] Furthermore, the working process of the high impedance fault mode includes: at time t3, a high impedance fault occurs in the line, and the DC circuit breaker is put into operation to disconnect the branch; at time t4, the disconnecting switch S is turned off, the lightning arrester MOA is put into operation, and the thyristor T9 is triggered at the same time, and the current on the current limiting inductor L1 forms a loop current through the thyristor T9, and the current limiting inductor L1 is bypassed; at time t5, the fault current decays to 0, and the fault isolation is completed; at time t6, the thyristor T8 and the thyristor T9 are triggered. 11 , the energy stored in the current limiting inductor L1 is transferred to the capacitor C1; at t7, the energy transfer is completed, and the capacitor C1 starts to discharge energy. After the energy discharge is completed, all working stages of the DC circuit breaker end and wait for the next action command.

[0035] Furthermore, the working process of the current limiting recovery mode includes: at time t3, the current limiting inductor L1 is fully put into use, and the line has not failed, then the DC circuit breaker needs to exit the current limiting and resume normal operation; at time t4, the thyristor T3 is turned on and the ultra-fast mechanical switch UFD is closed, at which time the thyristor T3, thyristor T4, thyristor T6, thyristor T8 and the disconnecting switch S temporarily bypass the current limiting inductor L1; at time t5, after the ultra-fast mechanical switch UFD is fully closed, the load transfer switch LCS is turned on, the disconnecting switch S is turned off, and the thyristor T 11 , and remove the conduction signal of thyristor T1, thyristor T3, thyristor T4 and thyristor T6, transfer the line current back to the current branch, and the energy stored in the current limiting inductor L1 at time t6 is transferred through thyristor T8 and thyristor T 11 The energy is transferred to the capacitor C1. After the energy transfer of the current-limiting inductor L1 is completed at time t7, the mechanical switch of the energy dissipation circuit on the capacitor C1 is closed to discharge the energy.

[0036] Furthermore, the working process of the small current disconnecting mode includes: when a small current needs to be disconnected, the load transfer switch LCS is turned off, the thyristor T1, the thyristor T4, the thyristor T5, the thyristor T6 and the disconnecting switch S are triggered, and the ultra-fast mechanical switch UFD starts to disconnect under the zero current state, and the current is transferred from the current-carrying branch to the current transfer branch; after the ultra-fast mechanical switch UFD reaches the rated opening distance, the disconnecting switch S is turned off and the lightning arrester MOA is put into operation; when the line current passes through zero, the small current disconnection is completed.

[0037] Compared with the prior art, the present invention is beneficial in that:

[0038] 1. The DC circuit breaker of the present invention has a double-stage current limiting function, including a primary current limiting branch and a secondary current limiting branch. The double-stage current limiting can improve the disadvantages of the single fixed current limiting mechanism of the existing circuit breaker. When faults of different types and severity occur, the fault instantaneous current change rate and change range are large. The double-stage current limiting structure can initially limit the sharp change of the fault current through the primary current limiting branch after the fault occurs, and then gradually limit the fault current through the double-stage current limiting structure, so as to achieve the purpose of smoothly limiting the current and reduce the energy impact and electromagnetic interference caused by the sudden large and rapid change of the current to other components and equipment in the circuit. In addition, DC circuit breakers with double-stage current limiting are more adaptable to complex fault scenarios such as different fault types and different system parameters than ordinary circuit breakers. They can adopt different working modes (mainly including low-impedance fault mode, high-impedance fault mode, current limiting recovery mode and small current disconnection mode) according to the specific fault conditions fed back by the fault line protection scheme. By coordinating with the fault line protection scheme, the current limiting strategy can be flexibly adjusted to achieve all-round protection of the fault line, and the defects of single-stage current limiting of existing circuit breakers are compensated, greatly improving the current limiting effect.

[0039] 2. The present invention can bypass the current limiting inductor L1 and the current limiting inductor L2 when breaking the fault current, and connect the thyristor T9 and the thyristor T2 in parallel at both ends of the current limiting inductor L1 and the current limiting inductor L2 respectively. 15 , so that the circuit breaker has the ability to bypass the current limiting inductor. When the circuit breaker breaks the fault current, the thyristor T9 and the thyristor T 15 The current in the current limiting inductor L1 and the current limiting inductor L2 respectively passes through the thyristor T9 and the thyristor T 15 A circulating current is formed and remains unchanged, so the current limiting inductor L1 and the current limiting inductor L2 are bypassed. The bypass design of the current limiting inductor L1 and the current limiting inductor L2 can shorten the fault isolation time of the circuit breaker and improve the circuit breaker breaking efficiency. After the fault current is broken, the energy stored in the current limiting inductor L1 and the current limiting inductor L2 in the form of magnetic field energy can be respectively transmitted through the thyristor T8 and the thyristor T 11 , Thyristor T 13 and thyristor T 14 The residual inductive energy is transferred to capacitors C1 and C2 respectively, and then consumed through the energy dissipation circuit, thereby reducing the energy consumption requirement of the arrester MOA, and also preventing insulation damage to electrical equipment caused by residual inductive energy.

[0040] 3. The pre-charging branch of the present invention comprises a pre-charging current limiting resistor R3, a thyristor T7, a thyristor T 11 , Thyristor T 13 , Thyristor T 16 , Thyristor T 17The circuit breaker is composed of a plurality of circuit breakers, and is connected to the capacitors C1 and C2. The current of the flow branch in the normal state of the circuit breaker can be used to pre-charge the capacitors C1 and C2, eliminating the need for an additional auxiliary power supply and a complex pre-charging circuit, reducing the system hardware cost and improving the system economy.

[0041] 4. The fault identification branch of the present invention enables the circuit breaker to identify whether the line fault type is a permanent fault or a transient fault according to its own topological structure, thereby achieving the purpose of completing adaptive reclosing by relying on the circuit breaker itself. The fault identification process of the circuit breaker is to use the low impedance fault mode working process stage 6 (t7-t8) time period, the fault side line inductance through the thyristor T 16 and thyristor T 18 The energy transferred to the capacitor C3 in the fault judgment branch is realized. If it is a permanent fault, the capacitor C3 will be connected with the thyristor T4 and the thyristor T 19 and the current-limiting resistor R4 form a discharge circuit, and generate a fault identification current in the discharge circuit; on the contrary, if it is a transient fault, no discharge path can be formed, and no fault identification current will be generated. An identification criterion is constructed based on this difference to achieve effective identification of the nature of the fault, so that the circuit breaker has an adaptive reclosing function, and the structure of the fault identification branch makes it unnecessary to use a power supply to charge the capacitor C3, and only the inductance energy of the fault side line can be used, which effectively avoids energy waste.

[0042] 5. The current branch mechanical switch of the present invention can achieve arc-free disconnection, reduce the disconnection pressure of the ultra-fast mechanical switch UFD, improve the disconnection reliability, and extend the service life of the mechanical switch. The commutation capacitor will not discharge until the ultra-fast mechanical switch UFD reaches the rated opening distance. Therefore, the withstand voltage of the load transfer switch LCS is very small, and there is no need for a large number of semiconductor devices to be connected in series, which reduces the voltage equalization difficulty of the load transfer switch LCS and the normal operation loss of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0044] Figure 1 It is a topological schematic diagram of an adaptive reclosing hybrid DC circuit breaker applicable to a DC power transmission and distribution system according to an embodiment of the present invention;

[0045] Figure 2 It is a structural schematic diagram of the energy dissipation circuit in the present invention;

[0046] Figure 3 It is the flowchart of the four working modes of the DC circuit breaker;

[0047] Figure 4 It is the timing diagram of the four working modes of the DC circuit breaker;

[0048] Figure 5 It is the schematic diagram of the current loop during the pre-charging stage of the DC circuit breaker in the low-impedance fault mode when t < t0;

[0049] Figure 6 It is the schematic diagram of the current loop during the t0 - t2 stage of the DC circuit breaker in the low-impedance fault mode;

[0050] Figure 7 It is the schematic diagram of the current loop of the DC circuit breaker in the low-impedance fault mode when t 2' <t<t 2” ;

[0051] Figure 8 It is the schematic diagram of the current loop of the DC circuit breaker in the low-impedance fault mode when t 2” <t<t3;

[0052] Fig. 9 It is the schematic diagram of the current loop of the DC circuit breaker at the t3 moment in the low-impedance fault mode;

[0053] Fig.10 It is the schematic diagram of the current loop of the DC circuit breaker in the low-impedance fault mode when t 3' <t<t 3” ;

[0054] Fig.11 It is the schematic diagram of the current loop of the DC circuit breaker in the low-impedance fault mode when t 3” <t<t4;

[0055] Fig.12 It is the schematic diagram of the current loop of the DC circuit breaker at the t4 moment in the low-impedance fault mode;

[0056] Fig.13 It is the schematic diagram of the current loop of the DC circuit breaker in the low-impedance fault mode when t5 < t < t6;

[0057] Fig.14 It is the schematic diagram of the current loop of the DC circuit breaker in the low-impedance fault mode when t7 < t < t8;

[0058] Fig.15 It is the schematic diagram of the current loop of the DC circuit breaker at the t = t9 moment in the low-impedance fault mode;

[0059] Fig.16 It is the schematic diagram of the current loop of the DC circuit breaker in the high-impedance fault mode when t4 < t < t5;

[0060] Fig.17 is a current loop schematic diagram of a DC circuit breaker in a high impedance fault mode t5<t<t6;

[0061] Fig.18 It is a current loop schematic diagram of the DC circuit breaker in the current limiting recovery mode t3<t<t4;

[0062] Fig.19 It is a current loop schematic diagram of the DC circuit breaker in the current limiting recovery mode t4<t<t5;

[0063] Fig. 20 It is a current loop schematic diagram of the DC circuit breaker in the current limiting recovery mode t5<t<t6;

[0064] Fig.21 It is a current loop schematic diagram of the DC circuit breaker in the small current breaking mode t<t0;

[0065] Fig. 22 It is a current loop schematic diagram of the DC circuit breaker in the small current breaking mode t1<t<t2;

[0066] Fig.23 It is a current loop schematic diagram of the DC circuit breaker in the small current breaking mode t2<t<t3. DETAILED DESCRIPTION

[0067] The technical solutions in the embodiments of this specification will be clearly and completely described below in conjunction with the drawings in the embodiments of this specification, but this is not intended to limit the scope of protection of this application. Obviously, the described embodiments are only part of the embodiments of this specification, not all of the embodiments. Based on the embodiments in this specification, all other embodiments obtained by ordinary technicians in this field without making creative work should fall within the scope of protection of this specification.

[0068] Figure 1 The invention proposes an adaptive reclosing hybrid DC circuit breaker suitable for DC power transmission and distribution systems. The structure mainly includes a flow branch, a bridge commutation branch, a current transfer branch, a current limiting branch, a disconnecting branch, a capacitor pre-charging branch and a fault discrimination branch. The two ends of the capacitor C1, the capacitor C2 and the capacitor C3 are connected in parallel. Figure 2 The energy dissipation circuit shown. Figure 1In the figure, UFD is an ultra-fast mechanical switch, LCS is a load transfer switch, capacitor C1 and capacitor C2 are commutation capacitors of the primary current limiting branch and the secondary current limiting branch respectively, capacitor C3 is a fault discrimination branch capacitor, current limiting inductor L1 and current limiting inductor L2 are current limiting inductors of the primary current limiting branch and the secondary current limiting branch respectively, resistor R1 and resistor R2 are current limiting resistors of the primary current limiting branch and the secondary current limiting branch respectively, resistor R3 is a pre-charge current limiting resistor, MOA is a lightning arrester, and S is a disconnect switch of the IGBT valve group. Specifically,

[0069] The flow branch is composed of an ultra-fast mechanical switch UFD and a load transfer switch LCS in series;

[0070] The bridge commutation branch is composed of a bridge circuit composed of thyristor T1, thyristor T2, thyristor T3 and thyristor T4, wherein the positive electrode of thyristor T1 is connected to the negative electrode of thyristor T2 and is connected to the input end of the current-passing branch, the positive electrode of thyristor T3 is connected to the negative electrode of thyristor T4 and is connected to the output end of the current-passing branch, and the negative electrode of thyristor T1 is connected to the negative electrode of thyristor T3, and the positive electrode of thyristor T2 is connected to the positive electrode of thyristor T4;

[0071] The current transfer branch is composed of a thyristor T5 and a thyristor T6 connected in series, wherein the negative electrode of the thyristor T5 is connected to the positive electrode of the thyristor T6, the positive electrode of the thyristor T5 is connected to the negative electrode of the thyristor T1 of the bridge commutation branch, and the negative electrode of the thyristor T6 is connected to the connection point of the disconnecting branch and the current limiting branch;

[0072] The current limiting branch consists of a primary current limiting branch and a secondary current limiting branch. The primary current limiting branch includes a current limiting resistor R1, a current limiting inductor L1, a capacitor C1, a thyristor T8, and a thyristor T 10 The primary current limiting branch is connected in parallel with the thyristor T5 of the current transfer branch; the secondary current limiting branch includes the current limiting resistor R2, the current limiting inductor L2, the capacitor C2 and the thyristor T 12 , Thyristor T 14 , the secondary current limiting branch is connected in parallel with the thyristor T6 of the current transfer branch, and the output end of the primary current limiting branch is connected to the input end of the secondary current limiting branch.

[0073] Regarding the distinction between the input and output ends of the primary current limiting branch and the secondary current limiting branch, Figure 1The topology is mainly determined by the direction of the fault current. For the primary current limiting branch, after the fault current is transferred, the primary current limiting begins. First, the current flows through the capacitor C1. After the capacitor C1 is reversed, the current limiting inductor L1 is put into operation. In this process, the fault current flows in from the current limiting inductor L1 and the upper part of the capacitor C1, so it is defined as the input end of the primary current limiting branch; the fault current flows out of the primary current limiting branch after passing through the resistor R1, so this port is defined as the output end of the primary current limiting branch. For the secondary current limiting branch, after the fault current flows out of the primary current limiting branch, it flows into the secondary current limiting branch through the resistor R2, so the side where the resistor R2 is located is defined as the input end of the secondary current limiting branch. After that, the capacitor C2 is discharged first and then reversed. After the capacitor C2 is reversed, the current limiting inductor L2 is put into operation. In this process, the fault current flows out from the current limiting inductor L2 and the lower part of the capacitor C2, so it is defined as the output end of the secondary current limiting branch.

[0074] The disconnect branch is composed of a disconnect switch S and a lightning arrester MOA in parallel. The disconnect switch is cascaded by multiple IGBT valve groups. Each valve group contains several parallel IGBTs and diodes. The disconnect branch is connected in parallel at both ends of the thyristor T7 of the pre-charging branch and is connected to the output end of the secondary current limiting branch.

[0075] The pre-charging branch is composed of thyristor T7, thyristor T 11 , Thyristor T 13 , Thyristor T 16 , Thyristor T 17 And pre-charge current limiting resistor R3.

[0076] The fault judgment branch consists of capacitor C3, reverse parallel thyristor group (thyristor T 18 With thyristor T 19 ) and a current limiting resistor R4. One end of the reverse parallel thyristor group is connected to the positive electrode of the thyristor T7, and the other end is connected to the ground through the capacitor C3 and the resistor R4.

[0077] The two ends of the current limiting inductor L1 and the current limiting inductor L2 are connected in parallel with a thyristor T9 and a thyristor T 15 .

[0078] A mechanical switch and a resistor are respectively connected in parallel at both ends of the capacitor C1, the capacitor C2 and the capacitor C3, and the mechanical switch and the resistor are connected in series to form an energy dissipation circuit of the capacitor C1, the capacitor C2 and the capacitor C3.

[0079] In the present invention, the DC system fault protection can be divided into fault line protection and fault current limiting and disconnecting equipment protection. The fault line protection scheme mainly extracts the fault line characteristic signal, establishes the fault protection judgment criterion, realizes fault detection, fault location, and fault type identification. The fault identification in the fault line protection scheme is used to judge the fault types such as single-pole grounding fault, bipolar short circuit fault, low impedance fault and high impedance fault. Its function is to provide fault information to the subsequent fault protection equipment so that the DC circuit breaker can adjust the current limiting strategy and adopt different working modes. The fault line protection content is implemented according to the existing technology. The fault current limiting and disconnecting equipment protection mainly realizes the current limiting and rapid disconnection of the fault line by providing a circuit breaker with current limiting and disconnecting capabilities. This application belongs to the fault current limiting and disconnecting equipment protection. The DC circuit breaker uses the fault identification branch to identify the fault type (only to identify whether it is a transient fault or a permanent fault). It is used to determine whether the circuit breaker can be reclosed to restore the power supply of the line after the circuit breaker completes the fault current disconnection. If it is a transient fault, it can be closed and restored. If it is a permanent fault, the power supply cannot be restored and it is necessary to wait for maintenance. Through the coordination of the above two protections, all-round protection of the fault line is achieved.

[0080] When an overcurrent occurs in the line, the control method of the adaptive reclosing hybrid DC circuit breaker (DC circuit breaker or circuit breaker for short) applicable to the DC power transmission and distribution system includes the following process:

[0081] When the system is operating normally, the current flows from the left side to the right side of the DC circuit breaker. Assuming that a fault occurs on the right end of the circuit breaker, the left side of the circuit breaker is the source side and the right side is the fault side. The present invention has four working modes, namely low impedance fault mode, high impedance fault mode, current limiting recovery mode and small current breaking mode (see Figure 3 and Figure 4 );

[0082] During the operation of the DC circuit breaker, capacitors C1 and C2 are first precharged when the line is operating normally. When a fault signal is detected, the ultra-fast mechanical switch UFD starts to disconnect. After the ultra-fast mechanical switch UFD is disconnected, if a low-impedance fault occurs, the current limiting inductor L1 needs to be put into operation first. After the primary current limiting is fully put into operation, the current limiting inductor L2 is put into operation. After the secondary current limiting is fully put into operation, fault isolation and energy dissipation are started. The turn-on timing of the main components corresponding to this mode is as follows: Figure 4 As shown in the low impedance fault mode in;

[0083] If a high impedance fault occurs, the current limiting inductor L1 needs to be switched on first. After the primary current limiting is fully switched on, the fault isolation and energy dissipation can be directly performed. The turn-on timing of the main components corresponding to this mode is as follows: Figure 4 As shown in the high impedance fault mode in;

[0084] If current limiting recovery is required, the current limiting inductor L1 needs to be energized first. After the first-stage current limiting is fully energized, the ultra-fast mechanical switch UFD needs to be closed first. After the ultra-fast mechanical switch UFD is closed, the load transfer switch LCS is then turned on to complete the line recovery. The conduction timing of the main devices corresponding to this mode is as shown in Figure 4 the current limiting recovery mode in;

[0085] If small current interruption is required, current limiting is not needed. After the ultra-fast mechanical switch UFD is interrupted, fault isolation can be directly performed. The conduction timing of the main devices corresponding to this mode is as shown in Figure 4 the small current interruption mode in.

[0086] Embodiment 1: Low impedance mode

[0087] This embodiment is premised on a low impedance fault and requires first-stage current limiting, second-stage current limiting, and interruption of the faulty line. When a large overcurrent occurs in the system, the DC circuit breaker performs first-stage current limiting. After fault detection (this is prior art), a low impedance fault occurs in the line, and at this time, second-stage current limiting is required. In this embodiment, "large" overcurrent means that the current in the faulty line exceeds 20% of the line rated current at this time, that is, the fault current exceeds 1.2 times the line rated current. At this time, it is considered that a fault occurs in the DC line. The current loops in each operation stage in the low impedance fault mode are as shown in Figure 5-15 shown, where U dc is the equivalent DC voltage source, R s is the equivalent resistance of the converter station, L dc is the smoothing reactor, R line is the equivalent resistance of the DC line, and L line is the equivalent reactance of the DC line. The specific process is as follows:

[0088] Stage 1 (t < t0) Pre-charging stage: During normal operation, the ultra-fast mechanical switch UFD and the load transfer switch LCS are turned on. At -t0, thyristors T7, thyristor T 11 , thyristor T 13 , thyristor T 16 , and thyristor T 17 are triggered to pre-charge capacitors C1 and C2. As the capacitor voltage rises, the charging current gradually decays to 0, and thyristors T7, thyristor T 11 , thyristor T 13 , thyristor T 16 , and thyristor T 17 naturally turn off, and the pre-charging ends. The current path in this stage is as shown in Figure 5 shown;

[0089] When capacitors C1 and C2 are pre-charged, the current path is:

[0090] Power supply side-UFD-LCS-T 16 -T7-C2-T 13 -R2-R1-T 11 -C1-T 17 -R3.

[0091] Phase 2 (t0-t2): A fault occurs in the DC system at time t0. At time t1, the DC circuit breaker and the fault detection system start simultaneously, triggering thyristors T1, T4, T5, T6 and disconnecting switch S, turning off the load transfer switch LCS, and transferring the fault current from the current-carrying branch to the current transfer branch. The ultra-fast mechanical switch UFD starts to disconnect under the zero current state. At time t2, the ultra-fast mechanical switch UFD reaches the rated opening distance. The current path in this phase is as follows: Figure 6 As shown;

[0092] After the load transfer switch LCS is turned off, the current flows into the current transfer branch. At this time, the current path is:

[0093] Power supply side - T1 - T5 - T6 - S - T4 - fault side.

[0094] Stage 3 (t2-t3) primary current limiting input: t 2' Trigger thyristor T at all times 10 , capacitor C1 discharges, thyristor T5 is turned off by reverse voltage, and the current path in this stage is shown in 7. 2” At this moment, the capacitor C1 is discharged and starts to reverse charge, and at the same time, the thyristor T8 is triggered, and the current limiting inductor L1 starts to be put into use. As the voltage of the capacitor C1 increases, the current of the capacitor C1 branch transfers to the current limiting inductor L1 branch. The current path at this stage is as follows Figure 8 At t3, the capacitor C1 is fully charged, the current in the branch is decayed to 0, and the thyristor T 10 Natural shutdown, all current flows through the branch where the current limiting inductor L1 is located, and the current limiting inductor L1 is fully put into current limiting, that is, the first-level current limiting is fully put into use. The current path at this stage is as follows Fig. 9 shown.

[0095] The current is completely transferred to the branch where the current limiting inductor L1 is located, which means that the capacitor C1 is fully charged and the thyristor T 10 When the circuit is turned off, all the current flows through the branch where the current limiting inductor L1 is located.

[0096] Stage 4 (t3-t4) Secondary current limiting is activated: At t3, fault detection is completed and a low impedance fault is found in the DC system. Secondary current limiting is required. 3' Trigger thyristor T at all times 12 , capacitor C2 discharges, thyristor T6 is turned off by reverse voltage, and the current path is as follows Fig.10 As shown, t 3”At this moment, capacitor C2 is discharged and starts to charge reversely, triggering thyristor T 14 , the current limiting inductor L2 starts to be put into use. As the voltage of capacitor C2 increases, the current of capacitor C2 branch transfers to the current limiting inductor L2 branch. The current path is as follows: Fig.11 As shown, at time t4, the capacitor C2 is charged and the thyristor T 12 Natural shutdown, the current limiting inductor L2 is fully engaged in current limiting, and the current path is as follows Fig.12 As shown;

[0097] The time period t2-t3 is the primary current limiting time. The process consists of three parts: the capacitor C1 discharges at time t2, 2” At time t3, the capacitor C1 starts to reverse charge, the current limiting inductor L1 starts to be put into use, and at time t3, the current limiting inductor L1 is fully put into use. Similarly, the time period t3-t4 is the secondary current limiting time. This process also has three parts, namely, t 3' At the moment capacitor C2 discharges, t 3” At time t4, the capacitor C2 starts to reverse charge and the current limiting inductor L2 starts to be put into operation. At time t4, the current limiting inductor L2 is fully put into operation.

[0098] Phase 5 (t5-t6): At t5, the DC circuit breaker receives the disconnection command, turns off the disconnect switch S, and the arrester MOA is put into isolation fault. The current limiting inductor L1 and the current limiting inductor L2 are still connected in series in the loop, which will hinder the current decay, prolong the fault isolation time, and increase the energy consumption requirement of the arrester MOA. Therefore, the inductor is bypassed in this phase. The specific method is as follows: at t5, the fault current begins to decay, the voltage across the inductor suddenly changes, and the thyristor T9 and thyristor T 15 The current in the current limiting inductor L1 and the current limiting inductor L2 respectively passes through the thyristor T9 and the thyristor T 15 A circulating current is formed and remains stable. The current limiting inductor L1 and the current limiting inductor L2 are bypassed. At t6, the fault current decays to 0. The current path at this stage is as follows: Fig.13 shown.

[0099] Phase 6 (t7-t8): Thyristor T8 is triggered at time t7. 11 , Thyristor T 13 , Thyristor T 14 , Thyristor T 16 and thyristor T 18 , thyristor T9 is turned off by the reverse voltage of capacitor C1, and the energy stored in the current limiting inductor L1 is transferred to thyristor T8 and thyristor T 11 Transfer to capacitor C1; thyristor T 15 The capacitor C2 is turned off due to the reverse voltage, and the energy stored in the current limiting inductor L2 is discharged through the thyristor T 13 , Thyristor T 14 The inductor energy on the fault side is transferred to capacitor C2 through thyristor T16 , Thyristor T 18 Transfer to capacitor C3, capacitors C1, C2, and C3 are connected in parallel with an energy dissipation circuit. The current path at this stage is as follows: Fig.14 As shown, the energy transfer is completed at time t8, and the thyristor T8 and thyristor T 11 , Thyristor T 13 , Thyristor T 14 , Thyristor T 16 and thyristor T 18 It is naturally turned off. At this time, the mechanical switch of the energy dissipation circuit of capacitors C1 and C2 is closed. The energy in capacitors C1 and C2 is consumed through the resistance of the energy dissipation circuit, and the fault line is disconnected.

[0100] Phase 7 (t = t9): After the line is fully deionized, the adaptive reclosing operation begins at t9. First, the fault type must be determined and the thyristor T4 and thyristor T 19 , when a permanent fault occurs, capacitor C3 will connect with thyristor T4 and thyristor T 19 , the fault side inductor and current limiting resistor R4 form a discharge circuit for discharge. The system determines that the fault has not disappeared and does not perform the reclosing operation, waiting for maintenance. If a transient fault occurs, an effective discharge circuit cannot be formed. The system determines that the fault has disappeared, and the DC circuit breaker will reclose and close the mechanical switch of the energy dissipation circuit on the capacitor C3 at the same time. The capacitor C3 is discharged, and all working stages are completed, waiting for the next action command. The current path in this stage is as follows: Fig.15 shown.

[0101] Embodiment 2: When an overcurrent occurs in the system, after the primary current limiting of the DC circuit breaker is put into operation, a high impedance fault occurs in the line after fault detection (the fault detection at this time is the fault detection result obtained through the fault line protection scheme, and the specific types of fault detection results are low impedance fault, high impedance fault, single-pole grounding or bipolar short circuit and other fault types. This application only considers the two fault conditions of low impedance fault and high impedance fault). Therefore, there is no need to put the secondary current limiting branch into operation, and it can be directly disconnected. The specific process of the high impedance fault working mode is as follows:

[0102] Phase 1 (t0-t3): The operation process is the same as the low impedance fault mode during the period t0-t3. The current path in this phase is as follows: Figure 5-Figure 9 As shown, no further description is given here;

[0103] Phase 2 (t3-t4): At t3, the protection system of the fault line protection scheme determines that a high impedance fault has occurred in the line, and the DC circuit breaker needs to be put into operation to disconnect the branch;

[0104] Phase 3 (t4-t5): At time t4, the disconnect switch S is turned off, the arrester MOA is switched on, and the thyristor T9 is triggered at the same time. The current on the current-limiting inductor L1 forms a loop current through the thyristor T9, and the current-limiting inductor L1 is thus bypassed. The current path in this phase is as follows: Fig.16 As shown;

[0105] Phase 4 (t5-t6): At t5, the fault current decays to 0, the fault is isolated, and thyristor T8 and thyristor T6 are triggered. 11 , the energy stored in the current limiting inductor L1 is transferred to the capacitor C1, and the current path is as follows Fig.17 As shown, at time t7, the energy transfer is completed, and the capacitor C1 starts to discharge energy. After the energy discharge is completed, the working stage of the DC circuit breaker ends and waits for the next action command.

[0106] Embodiment 3: When an overcurrent occurs in the system, after the primary current limiting of the circuit breaker is activated, the line fault disappears after fault detection. At this time, the line needs to be restored to a normal current-carrying state. The specific working process is as follows:

[0107] Phase 1 (t0-t3): The current limiting recovery mode has the same operation process as the low impedance fault mode during the t0-t3 period. The current path in this phase is as follows: Figure 5-Figure 8 As shown, no further description is given here;

[0108] Phase 2 (t3-t4): At t3, the current limiting inductor L1 is fully switched on. The current path in this phase is as follows: Fig.18 As shown, if the protection system determines that there is no fault in the line, the DC circuit breaker needs to exit current limiting and resume normal operation;

[0109] Phase 3 (t4-t5): At time t4, thyristor T3 is turned on and the ultra-fast mechanical switch UFD is closed. At this time, thyristor T3, thyristor T4, thyristor T6, thyristor T8 and disconnecting switch S temporarily bypass the current limiting inductor L1. The current path in this phase is as follows: Fig.19 As shown;

[0110] The principle and purpose of bypassing the current limiting inductor L1 in this stage are different from the principle and purpose of bypassing the current limiting inductor L1 and the current limiting inductor L2 in the fault current breaking stage in the low impedance fault mode. In the low impedance fault mode, the current limiting inductor L1 and the current limiting inductor L2 are bypassed in the fault current breaking stage to make the current in the current limiting inductor L1 and the current limiting inductor L2 pass through the thyristor T9 and the thyristor T 15A circulating current is formed and remains unchanged, so as to avoid the induced electromotive force generated by the current limiting inductor during the fault current breaking process from hindering the attenuation of the fault current, shorten the fault isolation time of the circuit breaker, and improve the breaking efficiency of the circuit breaker. In the current limiting recovery mode, the current limiting inductor L1 is bypassed to form a circulating current with the resistor R1, the disconnecting switch S, and the thyristors T3, T4, T6, and T8, so as to avoid the influence of the energy storage of the current limiting inductor L1. During the current limiting process, the current limiting inductor L1 will store energy in the form of magnetic field energy. If the current limiting inductor L1 is not bypassed when the ultra-fast mechanical switch UFD is closed and the normal current flow state of the line is restored, the energy stored in the inductor L1 will be released in the circuit, which may cause transient processes such as overvoltage and overcurrent, causing impact and damage to the electrical equipment in the system and affecting the stable operation of the system. In the current limiting recovery mode, the current path when bypassing is L1-R1-T6-S-T4-T3-T8-L1. The reason why the thyristor T9 is not directly turned on to bypass the current limiting inductor L1 in this process is that through the above-mentioned bypass method, multiple components including the current limiting resistor R1 and the disconnect switch S can be bypassed together, thereby reducing the equivalent impedance during the process of the ultra-fast mechanical switch UFD closing and restoring normal current flow, accelerating the current limiting recovery process, and improving the dynamic response speed of the system.

[0111] Phase 4 (t5-t6): After the ultra-fast mechanical switch UFD is fully closed at time t5, the load transfer switch LCS is turned on, the disconnect switch S is turned off, and the thyristor T is triggered at the same time. 11 , and remove the conduction signal of thyristor T1, thyristor T3, thyristor T4 and thyristor T6, the line current can be transferred back to the current branch. At time t6, the energy stored in the current limiting inductor L1 is transferred through thyristor T8 and thyristor T 11 Transfer to capacitor C1, the current path at this stage is as follows Fig. 20 As shown, at time t7, after the energy transfer of the current-limiting inductor L1 is completed, the mechanical switch of the energy dissipation loop on the capacitor C1 is closed to discharge the energy.

[0112] Example 4: In some cases, it is necessary to disconnect a small current, such as line maintenance, etc., and there is no need to limit the current, and the current can be disconnected directly. The working process of the small current disconnection mode is as follows:

[0113] Phase 1 (t<t0): When t<t0, the current flows through the current branch. The current path in this phase is as follows: Fig.21 As shown;

[0114] Phase 2 (t1-t2): At t1, when a small current needs to be disconnected, the load transfer switch LCS is turned off, and the thyristor T1, thyristor T4, thyristor T5, thyristor T6 and the disconnecting switch S are triggered. The ultra-fast mechanical switch UFD starts to disconnect under the zero current state, and the current is transferred from the current-carrying branch to the current transfer branch. The current path in this phase is as follows: Fig. 22 As shown;

[0115] Phase 3 (t2-t3): At t2, after the ultra-fast mechanical switch UFD reaches the rated opening distance, the disconnector S is turned off and the arrester MOA is switched on. At t3, the line current passes through zero and the small current is disconnected. The current limiting inductor in this mode is not switched on, so the inductor has no energy storage and no bypass or energy transfer is required. The current path in this phase is as follows: Fig.23 shown.

[0116] The various embodiments of the present invention are described in a progressive manner, and the same or similar parts between the various embodiments can be referenced to each other, and each embodiment focuses on the differences from other embodiments.

[0117] The adaptive reclosing hybrid DC circuit breaker suitable for DC transmission and distribution systems proposed in the present invention mainly adopts semi-controlled power electronic devices. The single device has a high withstand voltage level and mature series-parallel technology, which can realize bidirectional, fast and arc-free fault current interruption; it is powered by the DC system during pre-charging, and there is no need to be equipped with a high-voltage isolation auxiliary power supply, which simplifies the equipment structure; the two-stage current limiting topology can improve the current limiting degree and extend the current limiting time; and the DC circuit breaker can realize self-identification of the fault type through the fault discrimination branch, so that it has adaptive reclosing capability. For the adaptive reclosing function, it can automatically adjust the reclosing strategy according to the nature of the fault (transient or permanent fault). For example, in the event of a transient fault, adaptive reclosing can be quickly realized to restore power supply; for permanent faults, unnecessary reclosing operations are avoided to reduce the impact and damage to power system equipment.

[0118] In summary, the performance of the DC circuit breaker of the present invention is improved in many aspects.

[0119] The above is only a specific implementation method of the present invention, and its purpose is to enable people familiar with this technology to understand the content of the present invention and implement it, but the protection scope of the present invention is not limited to this. Any changes or substitutions that can be easily thought of by any technician familiar with this field within the technical scope disclosed in this application should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

[0120] Any matters not described in the present invention are applicable to the prior art.

Claims

1. An adaptive reclosing hybrid DC circuit breaker suitable for a DC power transmission and distribution system, comprising a current-passing branch, a bridge-type commutation branch, a current transfer branch, a current-limiting branch, a disconnecting branch and a pre-charging branch, characterized in that: The hybrid DC circuit breaker further includes a fault determination branch, wherein: The bridge commutation branch is composed of a bridge circuit consisting of a thyristor T1, a thyristor T2, a thyristor T3, and a thyristor T4, wherein the positive electrode of the thyristor T1 is connected to the negative electrode of the thyristor T2 and is connected to the input end of the current-passing branch, the positive electrode of the thyristor T3 is connected to the negative electrode of the thyristor T4 and is connected to the output end of the current-passing branch, and the negative electrode of the thyristor T1 is connected to the negative electrode of the thyristor T3, and the positive electrode of the thyristor T2 is connected to the positive electrode of the thyristor T4; The current transfer branch is composed of a thyristor T5 and a thyristor T6 connected in series, the negative electrode of the thyristor T5 is connected to the positive electrode of the thyristor T6, the positive electrode of the thyristor T5 is connected to the bridge commutation branch, and the negative electrode of the thyristor T6 is connected to the connection point of the disconnection branch and the current limiting branch; The current limiting branch consists of a primary current limiting branch and a secondary current limiting branch. The primary current limiting branch includes a current limiting resistor R1, a current limiting inductor L1, a capacitor C1, a thyristor T8 and a thyristor T 10 The primary current limiting branch is connected in parallel with the thyristor T5 of the current transfer branch; the secondary current limiting branch includes a current limiting resistor R2, a current limiting inductor L2, a capacitor C2, and a thyristor T 12 and thyristor T 14 , the secondary current limiting branch is connected in parallel with the thyristor T6 of the current transfer branch, and the output end of the primary current limiting branch is connected to the input end of the secondary current limiting branch; Among them, one end of the current limiting resistor R1 is connected to the negative electrode of the thyristor T5, and the other end is connected to one end of the current limiting inductor L1 and the thyristor T 10 The other end of the current limiting inductor L1 is connected to the negative electrode of the thyristor T8; the thyristor T 10 The positive electrode of is connected to one end of the capacitor C1, and the other end of the capacitor C1 and the positive electrode of the thyristor T8 are both connected to the positive electrode of the thyristor T5; Among them, one end of the current limiting resistor R2 is connected to the negative electrode of the thyristor T5, and the other end is connected to the thyristor T 14 The positive electrode and thyristor T 12 The positive electrode of the thyristor T 14 The negative electrode and thyristor T 12 The negative electrode of is connected to one end of the current limiting inductor L2 and the capacitor C2 respectively, and the other ends of the current limiting inductor L2 and the capacitor C2 are connected to the negative electrode of the thyristor T6; In the current limiting inductor L1, the current limiting inductor L2, the thyristor T 10 and thyristor T 12 The two ends of the thyristor are connected in parallel with thyristor T9 and thyristor T 15 , Thyristor T 11 and thyristor T 13 ; Connect thyristor T to the negative electrode of thyristor T3 in the bridge commutation branch. 17 The positive electrode of the thyristor T 17 The negative electrode of the thyristor T6 in the current transfer branch and the positive electrode of the thyristor T2 in the bridge commutation branch are respectively connected to the negative electrode and positive electrode of the thyristor T7; the disconnecting branch is connected in parallel at both ends of the thyristor T7; The positive electrode of the thyristor T7 is connected to a fault determination branch, which includes a reverse parallel thyristor group, a capacitor C3 and a current limiting resistor R4; the other end of the current limiting resistor R4 is grounded; the reverse parallel thyristor group includes thyristors T 18 and thyristor T 19 ; At both ends of the thyristor T4 of the bridge commutation branch, there is a thyristor T connected in reverse parallel. 16 ; The above-mentioned thyristor T7, thyristor T 11 , Thyristor T 13 , Thyristor T 16 , Thyristor T 17 And the pre-charge current limiting resistor R3 form a pre-charge branch.

2. The adaptive reclosing hybrid DC circuit breaker suitable for a DC power transmission and distribution system according to claim 1, characterized in that: Energy dissipation circuits consisting of a mechanical switch and a resistor in series are connected in parallel at both ends of capacitors C1, C2 and C3; the flow branch is composed of an ultra-fast mechanical switch UFD and a load transfer switch LCS in series; The disconnecting branch is composed of a disconnecting switch S and a lightning arrester MOA in parallel. The disconnecting switch S is cascaded by a plurality of IGBT valve groups, and each valve group includes a plurality of parallel-connected IGBTs and diodes.

3. The adaptive reclosing hybrid DC circuit breaker suitable for a DC power transmission and distribution system according to claim 2, characterized in that: When the system operates normally, the current flows from the left side to the right side of the DC circuit breaker. Assuming that a fault occurs at the right end of the DC circuit breaker, the left side of the DC circuit breaker is the source side and the right side is the fault side. When an overcurrent occurs in the line, the DC circuit breaker has four working modes, namely, low impedance fault mode, high impedance fault mode, current limiting recovery mode and small current disconnection mode.

4. The adaptive reclosing hybrid DC circuit breaker suitable for a DC power transmission and distribution system according to claim 3, characterized in that: The working process of the low impedance fault mode is: Stage 1 when t < t0: During normal operation, the ultra-fast mechanical switch UFD and the load transfer switch LCS are turned on. At -t0, thyristors T7, T 11 , T 13 , T 16 and T 17 are triggered to pre-charge capacitors C1 and C2. As the voltages of C1 and C2 rise, the charging current gradually decays to 0, and thyristors T7, T 11 , T 13 , T 16 and T 17 turn off naturally, and the pre-charging is completed; t0-t2 stage 2: a fault occurs in the DC system at t0, and the DC circuit breaker and the fault detection system start at the same time at t1, triggering thyristors T1, T4, T5, T6 and disconnecting switch S, disconnecting the load transfer switch LCS, and transferring the fault current from the current-carrying branch to the current transfer branch. The ultra-fast mechanical switch UFD starts to disconnect under the zero current state, and at t2 the ultra-fast mechanical switch UFD reaches the rated opening distance; t2-t3 Phase 3: t 2' Trigger thyristor T at all times 10 , capacitor C1 discharges, thyristor T5 is turned off by reverse voltage, t 2” At time t3, capacitor C1 is discharged and starts to reverse charge, triggering thyristor T8 at the same time, and current limiting inductor L1 starts to be put into use. As the voltage of capacitor C1 increases, the current of capacitor C1 branch gradually transfers to the current limiting inductor L1 branch. At time t3, capacitor C1 is charged and the current in the branch decays to 0. Thyristor T8 is turned on. 10 Natural shutdown, all current is transferred to the branch where the current limiting inductor L1 is located, and the current limiting inductor L1 is fully engaged in current limiting; t3-t4 phase 4: At t3, the fault detection is completed, a low impedance fault occurs in the DC system, and the secondary current limiting is activated. 3' Trigger thyristor T at all times 12 , capacitor C2 discharges, thyristor T6 is turned off by reverse voltage, t 3” At this moment, capacitor C2 is discharged and starts to charge reversely, triggering thyristor T 14 , the current limiting inductor L2 starts to be put into use. As the voltage of capacitor C2 increases, the current of capacitor C2 branch transfers to the current limiting inductor L2 branch. At t4, the charging of capacitor C2 is completed and the thyristor T 12 Natural shutdown, the current limiting inductor L2 is fully engaged in current limiting; t5-t6 Phase 5: At t5, the DC circuit breaker receives the disconnection command, turns off the disconnect switch S, and the arrester MOA is put into isolation fault. The fault current begins to decay, and the voltage across the current limiting inductor L1 and the current limiting inductor L2 suddenly changes, triggering the thyristor T9 and thyristor T 15 The current in the current limiting inductor L1 and the current limiting inductor L2 flows through the thyristor T9 and the thyristor T 15 A circulating current is formed and remains stable, the current limiting inductor L1 and the current limiting inductor L2 are bypassed, and the fault current decays to 0 at time t6; t7-t8 stage 6: t7 triggers thyristor T8 and thyristor T 11 , Thyristor T 13 , Thyristor T 14 , Thyristor T 16 and thyristor T 18 , thyristor T9 is turned off by the reverse voltage of capacitor C1, and the energy stored in the current limiting inductor L1 is transferred to thyristor T8 and thyristor T 11 Transfer to capacitor C1; thyristor T 15 The capacitor C2 is turned off due to the reverse voltage, and the energy stored in the current limiting inductor L2 is discharged through the thyristor T 13 , Thyristor T 14 The inductor energy on the fault side is transferred to capacitor C2 through thyristor T 16 , Thyristor T 18 The energy is transferred to capacitor C3. Capacitors C1, C2 and C3 are connected in parallel with an energy dissipation circuit. At t8, the energy transfer is completed. Thyristor T8 and thyristor T 11 , Thyristor T 13 , Thyristor T 14 , Thyristor T 16 and thyristor T 18 Natural shutdown, at this time, the mechanical switch of the energy dissipation circuit on capacitors C1 and C2 is closed, the energy in capacitors C1 and C2 is consumed through the resistance of the energy dissipation circuit, and the fault line is disconnected; t=t9 phase 7: After the line is fully deionized, the adaptive reclosing operation starts at t9, triggering the conduction thyristor T4 and thyristor T 19 , if capacitor C3 and thyristor T4 and thyristor T 19 , the fault side inductor, and the current limiting resistor R4 form a discharge circuit for discharge, then it is judged that a permanent fault has occurred, the fault has not disappeared, and the reclosing operation is not performed, waiting for maintenance; if the capacitor C3 and the thyristor T4 and thyristor T 19 , the fault-side inductance and current-limiting resistor R4 cannot form an effective discharge circuit, it is determined that a transient fault has occurred and the fault has disappeared. The DC circuit breaker can be reclosed and the mechanical switch of the energy dissipation circuit on capacitor C3 is closed at the same time. Capacitor C3 discharges energy, all working stages are completed, and wait for the next action command.

5. The adaptive reclosing hybrid DC circuit breaker suitable for a DC power transmission and distribution system according to claim 3, characterized in that: The working process of the high impedance fault mode includes: at time t3, a high impedance fault occurs in the line, and the DC circuit breaker is put into operation to disconnect the branch; at time t4, the disconnecting switch S is turned off, the lightning arrester MOA is put into operation, and the thyristor T9 is triggered at the same time, and the current on the current limiting inductor L1 forms a loop current through the thyristor T9, and the current limiting inductor L1 is bypassed; at time t5, the fault current decays to 0, and the fault isolation is completed; at time t6, the thyristor T8 and the thyristor T 11 , the energy stored in the current limiting inductor L1 is transferred to the capacitor C1; at t7, the energy transfer is completed, and the capacitor C1 starts to discharge energy. After the energy discharge is completed, all working stages of the DC circuit breaker end and wait for the next action command.

6. The adaptive reclosing hybrid DC circuit breaker suitable for a DC power transmission and distribution system according to claim 3, characterized in that: The working process of the current limiting recovery mode includes: at time t3, the current limiting inductor L1 is fully put into use, and there is no fault in the line, then the DC circuit breaker needs to exit the current limiting and resume normal operation; at time t4, the thyristor T3 is turned on and the ultra-fast mechanical switch UFD is closed, at this time, the thyristor T3, thyristor T4, thyristor T6, thyristor T8 and the disconnecting switch S temporarily bypass the current limiting inductor L1; at time t5, after the ultra-fast mechanical switch UFD is fully closed, the load transfer switch LCS is turned on, and the disconnecting switch S is turned off, and the thyristor T 11 , and remove the conduction signal of thyristor T1, thyristor T3, thyristor T4 and thyristor T6, transfer the line current back to the current branch, and the energy stored in the current limiting inductor L1 at time t6 is transferred through thyristor T8 and thyristor T 11 The energy is transferred to the capacitor C1. After the energy transfer of the current-limiting inductor L1 is completed at time t7, the mechanical switch of the energy dissipation circuit on the capacitor C1 is closed to discharge the energy.

7. The adaptive reclosing hybrid DC circuit breaker suitable for a DC power transmission and distribution system according to claim 3, characterized in that: The working process of the small current disconnecting mode includes: when a small current needs to be disconnected, the load transfer switch LCS is turned off, the thyristor T1, the thyristor T4, the thyristor T5, the thyristor T6 and the disconnecting switch S are triggered, and the ultra-fast mechanical switch UFD starts to disconnect under the zero current state, and the current is transferred from the current-carrying branch to the current transfer branch; after the ultra-fast mechanical switch UFD reaches the rated opening distance, the disconnecting switch S is turned off and the lightning arrester MOA is put into operation; when the line current passes through zero, the small current disconnection is completed.

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