Economical direct-current circuit breaker with zero-region rapid recovery capability and control method

Abstract

The invention relates to an economical direct-current circuit breaker with zero-region rapid recovery capability and a control method. The circuit breaker solid state topology comprises a main through-flow branch, a resonance commutation loop, a damping energy consumption loop, a capacitor reset loop, a weak current breaking loop, a pre-charging branch and an MOV energy release module. When it is judged that the system has a short-circuit fault, fault current is introduced into a resonance commutation loop and a damping energy consumption loop, the short-circuit fault is rapidly removed, and safe opening time is provided for a vacuum switch of a main through-flow branch; if special conditions such as manual system maintenance are judged, a weak current on-off loop is put into use; a capacitor of a resonant circuit does not need to be externally provided with a charging circuit, a main through-flow branch adopts a vacuum switch to replace a power electronic device, a fault processing module adopts a half-control device, and the economic performance of the whole machine is excellent; the capacitor reset loop recovers the preset voltage of the capacitor, and the secondary breaking capacity of the circuit breaker is ensured under the medium-high voltage working condition. The device has good use value and economic benefit in the field of direct current power transmission and distribution and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of flexible DC power transmission and distribution systems, and particularly to an economical DC circuit breaker with zero-region fast recovery capability and a control method therefor. Background Art

[0002] At present, intermittent renewable energy sources such as solar energy are gradually replacing traditional fossil energy and becoming an important source of energy storage and supply in new power systems. At the same time, the voltage level of the power system is gradually increasing, the transmission capacity and the system load pressure are increasing, especially the flexible DC power transmission and distribution system is gradually showing new characteristics such as low damping and weak inertia, which puts forward higher requirements for the reliability and stability of the power transmission and distribution network and DC control and protection equipment. The short-circuit fault handling technology of traditional AC power transmission and distribution systems is mature, but the removal of short-circuit faults in the DC environment is still a difficult problem in the protection and control of DC power transmission systems, bringing many troubles to the long-distance transmission and asynchronous networking technologies of future smart grids. As the main switching device in the field of DC control and protection, the key technical parameters such as the control form, breaking speed, and breaking capacity of the DC circuit breaker and its topological structure need to be improved and perfected urgently.

[0003] At present, according to the development of DC circuit breakers, they can be divided into three categories: mechanical DC circuit breakers, all-solid-state DC circuit breakers, and hybrid DC circuit breakers. Mechanical circuit breakers have a long development history and mature technology. By simulating the AC fault interruption method, an LC oscillation commutation circuit is built to construct an artificial zero-crossing point, and the main current-carrying branch fault current is cut off by a high-frequency and high-amplitude recoil current to achieve fast isolation of short-circuit faults. The patent "An Economical Mechanical High-Voltage DC Circuit Breaker" (Patent No. 202110948435) proposes a DC circuit breaker structure with a semi-controlled type as the main control unit, which consists of a main circuit breaker unit, a commutation unit, and a power-consuming unit, and has excellent economic performance. However, after the fault interruption, the main branch switch has not reached the safe opening distance, and it will directly withstand a relatively high level of system transient recovery voltage, which is prone to re-breakdown and cause the failure of the circuit breaker to interrupt short-circuit faults. Therefore, it is very difficult for mechanical circuit breakers to shape zero-region fast recovery for the main current-carrying branch switch. At the same time, traditional mechanical circuit breakers overly rely on the arc-blowing performance of the arc chamber and lack coordination with power electronic devices with high-efficiency commutation capabilities. Therefore, using power electronic switch devices with low conduction voltage drop to construct an additional commutation circuit is an ideal solution to improve the reliable and fast arc extinguishing of the switch.

[0004] The fully solid-state DC circuit breaker adopts a fully power electronic topology commutation structure, which can usually achieve fault location and rapid isolation within dozens or hundreds of microseconds, and has the characteristics of arc-free opening of the main current-carrying branch. Patent 201710399243.0, "A Control Method for a DC Solid-State Circuit Breaker with Adaptive Current Limiting Ability", mentions a solid-state topology that effectively combines fault current limiting, protection, and breaking to ensure reliable fault ride-through of the remaining network. In this circuit breaker topology, the main current-carrying branch consists of multiple IGBT modules connected in cascade to form an LCS impedance commutation module, which realizes ultra-fast switch arc-free breaking during the fault commutation process. However, this impedance commutation module will generate power losses of dozens of kilowatts during the normal operation and commutation operation of the system, and additional heat dissipation equipment needs to be equipped, reducing the economic efficiency and transmission efficiency of the entire circuit breaker. Therefore, using a vacuum switch with strong magnetic blow arc extinguishing ability to replace the LCS to build a hybrid circuit breaker is a reasonable way to reduce costs and increase efficiency for DC breaking equipment.

[0005] The hybrid circuit breaker combines the dynamic and static characteristics of mechanical circuit breakers and fully solid-state circuit breakers well, and is the mainstream direction of the current research on flexible DC control and protection equipment. Patent 201811579301.9, "A Bidirectional Breaking DC Circuit Breaker", proposes a hybrid topology composed of a solid-state switch branch and an oscillation transfer branch, which can achieve bidirectional fault removal. However, the capacitor of the oscillation transfer branch has a high energy storage level after the fault current is removed, and the capacitor cannot be restored to the initial voltage level. If a permanent fault occurs in the system, the circuit breaker cannot achieve secondary breaking, and the reliability is low. In addition, for some topologies, after the first fault breaking, the line state is detected first, and then personnel are dispatched for maintenance to reset the capacitor voltage of the oscillation branch. However, this process is time-consuming and labor-intensive, and is not sufficient to meet the requirements of the rapidity and reliability of DC circuit breaker fault breaking in modern new power systems.

[0006] Therefore, aiming at the defects and deficiencies of current various types of DC circuit breakers, a new type of hybrid circuit breaker topology needs to be provided to solve the above problems. Summary of the Invention

[0007] To improve the operation stability of the flexible DC power transmission and distribution network, and at the same time reduce the cost of the DC circuit breaker and the voltage and current stresses on the equipment side, the present invention proposes an economical DC circuit breaker with zero-region rapid recovery ability and a control method to improve the dielectric insulation strength recovery ability of the vacuum switch after the fault current passes through zero, and at the same time improve the secondary breaking performance of medium and high voltage DC circuit breakers and the pre-charging path of active components, and improve the economic efficiency of the entire machine and the reliability of the DC system. In addition, the circuit breaker has a weak current breaking mode to cope with special situations such as system manual maintenance.

[0008] The technical solution of the present invention is as follows:

[0009] An economical DC circuit breaker with zero - zone fast recovery ability, the circuit breaker includes a main current - conducting branch, a fault - handling module, and a pre - charging branch;

[0010] The main current - conducting branch includes a mechanical vacuum circuit breaker MVCB. The left end of the main current - conducting branch is connected to the cathodes of thyristor groups T2 and T4 and the anodes of thyristor groups T1 and T6, and the right end is connected to the cathodes of thyristor groups T3 and T5 and the anode of T7; After thyristor groups T2 and T1 are reversely paralleled, they are connected to the anode of thyristor group T3. The anode of thyristor group T4 is connected to the anode of thyristor group T5. The cathode of thyristor group T6 is connected to the cathode of thyristor group T7. An oscillation branch 1 is paralleled between the anode of thyristor group T5 and the anode of thyristor group T3. An oscillation branch 2 and a diode group D1 are paralleled between the anode of thyristor group T5 and the cathode of thyristor group T7. A branch 7 composed of a series connection of thyristor group T8 and resistor R1 is paralleled between the anode of thyristor group T3 and the cathode of thyristor group T7;

[0011] A discharging energy module is paralleled at both ends of the main current - conducting branch;

[0012] The oscillation branch 1 is composed of a series connection of an inductor L1 and a capacitor C1. One end of the capacitor C1 is connected to the anode of thyristor group T3. One end of the inductor L1 is connected to the anode of thyristor group T5 and the cathode of the diode group D1. The anode of the diode group D1 is connected to the cathode of thyristor group T7 and the anode of thyristor group T9 in the pre - charging branch. The cathode of thyristor group T9 is connected to one end of a resistor R0, and the other end of the resistor R0 is grounded;

[0013] The oscillation branch 2 is composed of a parallel connection of a diode group D2 and a current - limiting resistor R2, which are then connected in series with an inductor L2 and a capacitor C2. One end of the capacitor C2 is connected to the anode of thyristor group T5.

[0014] A branch 1 is composed of a reverse parallel connection of thyristor groups T1 and T2. A branch 2 is composed of thyristor group T3. A branch 3 is composed of thyristor group T4. A branch 4 is composed of thyristor group T5. A branch 5 is composed of thyristor group T6. A branch 6 is composed of thyristor group T7. A branch 8 is composed of the diode group D1;

[0015] Branch 4, branch 6, and the oscillation branch 2 form a resonant commutation loop. One end of the oscillation branch 2 is connected to the intersection point of branch 3 and branch 4, and the other end is connected to the intersection point of branch 5 and branch 6;

[0016] Branch 8 and the oscillation branch 2 form a damping energy - consuming loop,

[0017] Branch 4, Branch 6, Branch 7, Branch 8, Oscillation Branch 1 and Oscillation Branch 2 form a capacitor reset loop; Branch 7 consists of a thyristor bank T8 and R1 in series. One end of Oscillation Branch 1 is connected to the junction of Branch 1 and Branch 2, and the other end is connected to the junction of Branch 3 and Branch 4;

[0018] Branch 2, Branch 5, Branch 6, the damping energy dissipation loop and Oscillation Branch 1 form a weak current interruption loop,

[0019] The fault handling module consists of a resonant commutation loop, a damping energy dissipation loop, a capacitor reset loop, a weak current interruption loop and an energy discharging module.

[0020] The voltage values of capacitor C1 and capacitor C2 after performing the reset operation are jointly determined by the resonant frequencies of Oscillation Branch 1 and Oscillation Branch 2, the voltage values of capacitor C1 and capacitor C2 after the first interruption, and the resistance values of resistor R2 and R1.

[0021] When the resonant commutation loop and the damping energy dissipation loop are working, the vacuum switch on the main current-carrying branch withstands an extremely low level of transient recovery voltage, that is, the conduction voltage drop of the power electronic switch tube, providing a zero-zone fast recovery time for the vacuum switch.

[0022] If the fault current source is a line-to-ground short circuit fault, the control method of the above-mentioned economical DC circuit breaker with zero-zone fast recovery ability includes the following process:

[0023] When the DC system is operating normally, the mechanical vacuum switch MVCB is closed, and the current flows from the DC power supply side along the main current-carrying branch from left to right to the load side to supply energy to the load; a short circuit fault occurs on the load side of the DC system; the left side of the DC circuit breaker is called the non-fault side or source side, and the right side is called the fault side;

[0024] Stage 0 (t 0- ): The mechanical vacuum switch remains closed, the system operates stably, trigger signals are applied to thyristor bank T1 and thyristor bank T9, the source side charges capacitor C1 and capacitor C2, and when the sum of the voltages of capacitor C1 and capacitor C2 is equal to the source side voltage, the pre-charging branch current is 0, and thyristor bank T1 and thyristor bank T9 automatically turn off, and capacitor C1 and capacitor C2 reach the initial voltage level;

[0025] Stage 1 (t0): Capacitor C1 and capacitor C2 maintain the pre-charging voltage, and the system remains in a stable operating state;

[0026] Stage 2 (t0 - t1): At time t1, the system detects an abnormal current on the fault side, and the relay protection device starts to operate;

[0027] Stage 3 (t1 - t2): After a short relay delay, at time t2, the mechanical vacuum switch receives the operation instruction sent by the relay protection device and starts to arc and open. At the same time, trigger signals are applied to thyristor group T5, thyristor group T6, and thyristor group T7. The oscillation branch 2 and the main current-carrying branch conduct current simultaneously. The inductance L2 and the capacitor C2 generate an oscillating current that is reversely injected into the main current-carrying branch. When the fault current in the main current-carrying branch is cut off, the arc in the mechanical vacuum switch extinguishes;

[0028] Stage 4 (t2 - t3): After the fault current in the main current-carrying branch is cut off, thyristor group T7 conducts, and the resonant commutation circuit is put into operation. At this time, the mechanical vacuum switch only withstands the conduction voltage drops of thyristor group T5 and thyristor group T6, and the dielectric insulation strength inside the mechanical vacuum switch recovers rapidly;

[0029] Stage 5 (t3 - t4): At time t3, the current in oscillation branch 2 is equal to the system current. Diode group D2 and thyristor group T7 automatically turn off, and diode group D1 automatically conducts. The damping energy-consuming circuit is put into operation. The mechanical vacuum switch only withstands the conduction voltage drops of thyristor group T5, thyristor group T6, and diode group D1;

[0030] Stage 6 (t4 - t5): At time t4, a trigger signal is applied to thyristor group T3, and oscillation branch 1 is put into operation. When the sum of the conduction voltage drops of thyristor group T3, thyristor group T6, and diode group D1 and the terminal voltage of inductance L1 and capacitor C1 reaches the rated operating voltage of the MOV, the current is transferred from oscillation branch 1 to the energy-dissipating module, and the energy-dissipating module is put into operation to complete the current cut-off; At time t5, the whole breaker opening is completed;

[0031] Stage 7 (t5 - t6): At time t6, a trigger signal is applied to thyristor group T8, and the capacitor reset circuit is put into operation. The current path of one oscillation of the capacitor reset circuit is C1 - L1 - C2 - L2 - R2 - R1 - T8. After the oscillation process ends, thyristor group T8 automatically turns off. In the secondary oscillation, the current path of capacitor C1 is C1 - L1 - T4 - T1, and the current path of capacitor C2 is the damping energy-consuming circuit and the resonant commutation circuit; After the reset, the voltages of capacitor C2 and capacitor C1 return to the initial level;

[0032] Stage 8 (t6 - t7): At time t7, if the fault is a temporary fault, the DC breaker does not operate again. If the fault is a permanent fault, repeat from stage 2 to stage 7 for fault breaking and voltage reset operations;

[0033] Thus, one cycle of control is completed.

[0034] t 0-The previous moment close to t0; t0 is the moment when the pre-charge branch finishes working; t1 is the moment when the short-circuit fault occurs; t2 is the moment when the vacuum switch opens and the fault handling module is put into operation; t3 is the moment when the damping energy dissipation loop is put into operation; t4 is the moment when the MOV energy dissipation branch is put into operation; t5 is the moment when the whole machine interruption is completed after the fault occurs; t6 is the moment when the capacitor reset loop works; t7 is the moment to judge whether to put into the secondary interruption process after the fault is detected.

[0035] If the fault current source is system manual maintenance, execute the weak current interruption mode, including the following processes:

[0036] When the DC system operates stably, the mechanical vacuum circuit breaker MVCB is closed, and the current flows from the DC power supply side along the main current-carrying branch from left to right to the load side to supply energy to the load; the short-circuit fault of the DC system occurs on the load side; the left side of the DC circuit breaker is called the non-fault side or source side, and the right side is called the fault side;

[0037] Stage 0 (t 0- ): The mechanical vacuum switch remains closed, the system operates stably, trigger signals are applied to the thyristor group T1 and the thyristor group T9, the source side charges the capacitors C1 and C2, when the sum of the voltages of the capacitors C1 and C2 is equal to the source side voltage, the current of the pre-charge branch is 0, the thyristor group T1 and the thyristor group T9 automatically turn off, and the capacitors C1 and C2 reach the initial voltage level;

[0038] Stage 1 (t0): The capacitors C1 and C2 maintain the pre-charge voltage, and the system remains in a stable operating state;

[0039] Stage 2 (t0 - t1): At the moment t1, the system detects abnormal current on the fault side, and the relay protection device starts to operate;

[0040] Stage 3 (t1 - t2): After a short delay, at the moment t2, the mechanical vacuum switch receives the action instruction sent by the relay protection device and starts to arc and open, and at the same time, trigger signals are applied to the thyristor group T3, the thyristor group T6 and the thyristor group T7, the oscillation branch 1 and the oscillation branch 2 are in parallel with the main current-carrying branch to conduct current at the same time, and the generated oscillation current is injected into the main current-carrying branch in the reverse direction. When the fault current in the main current-carrying branch is cut off, the arc in the mechanical vacuum switch goes out;

[0041] Stage 4 (t2 - t3): After the fault current in the main current-carrying branch is cut off, the mechanical vacuum switch only withstands the conduction voltage drop of the thyristor group T6 and the thyristor group T7, and the dielectric insulation strength inside the mechanical vacuum switch recovers rapidly; at the moment t3, the damping energy dissipation loop is put into operation, and the thyristor group T7 automatically turns off;

[0042] Stage 5 (t3 - t4): At the moment t4, the damping energy dissipation loop completes the current cut-off, and the whole machine interruption of the circuit breaker is completed;

[0043] Thus, the control of one cycle is completed.

[0044] t 0- is the previous moment close to t0; t0 is the moment when the pre-charging branch finishes working; t1 is the moment when the short-circuit fault occurs; t2 is the moment when the vacuum switch opens and the fault handling module is put into operation; t3 is the moment when the damping energy-consuming loop is put into operation; t4 is the moment when the whole machine opening is completed after the fault occurs.

[0045] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0046] The present invention is an economical DC circuit breaker with the ability of zero-region fast recovery. It uses a mechanical vacuum switch to replace the LCS load commutation module in the traditional solid-state DC circuit breaker and the hybrid circuit breaker, and cooperates with a fault handling module based on the LC oscillation principle to realize the transfer and interruption of the fault current. At the same time, diodes and semi-controlled devices are used as control means to reduce the number of power semiconductor devices such as IGBT modules and the manufacturing, operation and maintenance costs of the whole machine, and at the same time reduce the on-state loss and turn-off loss.

[0047] In addition, based on the bridge topology structure, the present invention proposes a capacitor reset circuit for the DC circuit breaker to improve the secondary interruption ability of the DC circuit breaker in the medium and high voltage environment. The damping energy-consuming loop reduces the current stress of the power electronic devices in the fault handling module and increases the stability and reliability of the whole machine operation of the circuit breaker. This DC circuit breaker also has the function of interrupting weak current to cope with special situations of system manual maintenance.

[0048] In the fault handling module of the DC circuit breaker of the present invention, the damping energy-consuming loop and the resonant commutation loop provide a zero-region fast recovery time with a low transient recovery voltage for the mechanical vacuum switch of the main current-carrying branch, which is more conducive to the arc extinction of the mechanical vacuum switch and improves the dielectric breakdown resistance after the arc in the vacuum gap. Brief Description of the Drawings

[0049] Figure 1 is a topological schematic diagram of the economical DC circuit breaker with the ability of zero-region fast recovery of the present invention. Detailed Embodiments

[0050] The following describes the present invention in detail with reference to the drawings, but this is not used as a limitation to the protection scope of the present application.

[0051] Figure 1 is the topology of the economical DC circuit breaker with the ability of zero-region fast recovery proposed by the present invention, including a main current-carrying branch, a fault handling module and a pre-charging branch; among them,

[0052] The main current-carrying branch includes a mechanical vacuum circuit breaker MVCB. The left end of the main current-carrying branch is connected to the cathodes of thyristor groups T2 and T4 and the anodes of thyristor groups T1 and T6, and the right end is connected to the cathodes of thyristor groups T3 and T5 and the anode of T7. Thyristor groups T2 and T1 are reversely connected in parallel and then connected to the anode of thyristor group T3. The anode of thyristor group T4 is connected to the anode of thyristor group T5. The cathode of thyristor group T6 is connected to the cathode of thyristor group T7. Oscillation branch 1 is connected in parallel between the anode of thyristor group T5 and the anode of thyristor group T3. Oscillation branch 2 and diode group D1 are connected in parallel between the anode of thyristor group T5 and the cathode of thyristor group T7. A branch composed of thyristor group T8 and resistor R1 in series is connected in parallel between the anode of thyristor group T3 and the cathode of thyristor group T7.

[0053] Energy-dissipating modules are connected in parallel at both ends of the main current-carrying branch.

[0054] Oscillation branch 1 is composed of an inductor L1 and a capacitor C1 connected in series. One end of capacitor C1 is connected to the anode of thyristor group T3. One end of inductor L1 is connected to the anode of thyristor group T5 and the cathode of diode group D1. The anode of diode group D1 is connected to the cathode of thyristor group T7 and the anode of thyristor group T9 in the pre-charging branch. The cathode of thyristor group T9 is connected to one end of resistor R0, and the other end of resistor R0 is grounded.

[0055] Oscillation branch 2 is composed of diode group D2 and current-limiting resistor R2 connected in parallel and then connected in series with inductor L2 and capacitor C2. One end of capacitor C2 is connected to the anode of thyristor group T5.

[0056] In the above, a branch is composed of thyristor groups T1 and T2 connected in anti-parallel, a branch is composed of thyristor group T3, a branch is composed of thyristor group T4, a branch is composed of thyristor group T5, a branch is composed of thyristor group T6, a branch is composed of thyristor group T7, and a branch is composed of diode group D1.

[0057] Branch 4, branch 6 and oscillation branch 2 form a resonant commutation circuit. One end of oscillation branch 2 is connected to the junction point of branch 3 and branch 4, and the other end is connected to the junction point of branch 5 and branch 6.

[0058] Branch 8 and oscillation branch 2 form a damping energy-consuming circuit.

[0059] Branch 4, branch 6, branch 7, branch 8, oscillation branch 1 and oscillation branch 2 form a capacitor reset circuit. Branch 7 is composed of thyristor group T8 and R1 connected in series. One end of oscillation branch 1 is connected to the junction point of branch 1 and branch 2, and the other end is connected to the junction point of branch 3 and branch 4.

[0060] Branch 2, Branch 5, Branch 6, the damping energy dissipation loop, and Oscillation Branch 1 form a weak current breaking loop.

[0061] The fault handling module consists of a resonant commutation loop, a damping energy dissipation loop, a capacitor reset loop, a weak current breaking loop, and an energy discharging module.

[0062] The resonant commutation loop and the damping energy dissipation loop enable the vacuum switch in the main current-carrying branch to withstand an extremely low-level transient recovery voltage, i.e., the conduction voltage drop of the power electronic switch tube, and provide a fast recovery time in the zero region.

[0063] When the resonant commutation loop and the damping energy dissipation loop are working, the mechanical vacuum switch in the main current-carrying branch withstands an extremely low-level transient recovery voltage, i.e., the conduction voltage drop of the power electronic switch tube, and provides a fast recovery time in the zero region for the vacuum switch.

[0064] There is no additional active charging device in the capacitor charging circuit. Using the energy during the normal operation of the DC system, the capacitors C1 and C2 are charged through the pre-charging branch.

[0065] The main current-carrying branch only contains a mechanical vacuum switch MVCB and no power electronic devices. The fault handling module only contains semi-controlled devices and diodes and no fully-controlled devices, resulting in low overall cost and control complexity of the whole machine.

[0066] The energy discharging module consists of MOV elements and is connected in parallel at both ends of the main current-carrying branch, effectively suppressing the high-voltage spikes and high-frequency noise generated by the oscillation at both ends of the inductor and capacitor.

[0067] The voltage values of capacitors C1 and C2 after the capacitor reset loop finishes working are jointly determined by the resonant frequencies of Oscillation Branch 1 and Oscillation Branch 2, the voltage values of capacitors C1 and C2 after the first breaking, and the resistance values of resistors R2 and R1.

[0068] This DC circuit breaker has no additional active charging device. Using the energy during the normal operation of the DC system, the capacitors C1 and C2 are charged through the pre-charging branch.

[0069] If the fault current source is a line-to-ground short circuit fault, the method includes the following processes:

[0070] When the DC system is operating stably, the mechanical vacuum switch MVCB is closed, and the current flows from the DC power supply side along the main current-carrying branch from left to right to the load side to supply energy to the load. The DC system short circuit fault occurs on the load side. The left side of the DC circuit breaker is called the non-fault side or source side, and the right side is called the fault side.

[0071] Stage 0 (t 0-): The mechanical vacuum switch remains closed, and the system operates stably. Trigger signals are applied to thyristor group T1 and thyristor group T9. The source side charges capacitors C1 and C2. When the sum of the voltages of capacitors C1 and C2 equals the source side voltage, the pre-charge branch current is 0, thyristor group T1 and thyristor group T9 automatically turn off, and capacitors C1 and C2 reach the initial voltage level.

[0072] Phase 1 (t0): Capacitors C1 and C2 maintain the pre-charge voltage, and the system remains in a stable operating state.

[0073] Phase 2 (t0 - t1): At time t1, the system detects abnormal fault side current, and the relay protection device starts to operate.

[0074] Phase 3 (t1 - t2): After a short relay delay, at time t2, the mechanical vacuum switch receives the action command from the relay protection device and starts to arc and open. At the same time, trigger signals are applied to thyristor group T5, thyristor group T6, and thyristor group T7. Oscillation branch 2 and the main current-carrying branch conduct current simultaneously. Inductor L2 and capacitor C2 generate an oscillating current that is injected reversely into the main current-carrying branch. When the fault current in the main current-carrying branch is cut off, the arc in the mechanical vacuum switch extinguishes.

[0075] Phase 4 (t2 - t3): After the fault current in the main current-carrying branch is cut off, thyristor group T7 conducts, and the resonant commutation circuit is put into operation. At this time, the mechanical vacuum switch only withstands the conduction voltage drops of thyristor group T5 and thyristor group T6, and the dielectric insulation strength inside the mechanical vacuum switch quickly recovers.

[0076] Phase 5 (t3 - t4): At time t3, the current in oscillation branch 2 equals the system current, diode group D2 and thyristor group T7 automatically turn off, diode group D1 automatically conducts, and the damping energy dissipation circuit is put into operation. The mechanical vacuum switch only withstands the conduction voltage drops of thyristor group T5, thyristor group T6, and diode group D1.

[0077] Phase 6 (t4 - t5): At time t4, a trigger signal is applied to thyristor group T3, and oscillation branch 1 is put into operation. When the sum of the conduction voltage drops of thyristor group T3, thyristor group T6, and diode group D1 and the voltages at both ends of inductor L1 and capacitor C1 reaches the rated operating voltage of MOV, the current is transferred from oscillation branch 1 to the energy dissipation module, and the arrester MOV is put into operation to complete the current cut-off. At time t5, the whole breaker opening is completed.

[0078] Phase 7 (t5 - t6): At time t6, a trigger signal is applied to the thyristor bank T8, and the capacitor reset circuit is put into operation. The current path of the first oscillation of the capacitor reset circuit is C1 - L1 - C2 - L2 - R2 - R1 - T8. After the oscillation process ends, the thyristor bank T8 automatically turns off. During the second oscillation, the current path of capacitor C1 is C1 - L1 - T4 - T1, and the current path of capacitor C2 is the damping energy dissipation circuit and the resonant commutation circuit. After the reset is completed, the voltages of capacitor C2 and capacitor C1 return to the initial level.

[0079] Phase 8 (t6 - t7): At time t7, if the fault is a temporary fault, the DC circuit breaker is no longer put into operation. If the fault is a permanent fault, repeat phases 2 to 7 for fault interruption and voltage reset operations.

[0080] Thus, one cycle of control is completed.

[0081] If the fault current source is system manual maintenance, the weak current interruption mode is executed, including the following process:

[0082] When the DC system is operating stably, the mechanical vacuum circuit breaker MVCB is closed, and the current flows from the DC power supply side along the main current-carrying branch from left to right to the load side to supply energy to the load. The DC system short-circuit fault occurs on the load side. The left side of the DC circuit breaker is called the non-fault side or source side, and the right side is called the fault side.

[0083] Phase 0 (t 0- ): The mechanical vacuum switch remains closed, the system operates stably, trigger signals are applied to the thyristor bank T1 and the thyristor bank T9, and the source side charges capacitors C1 and C2. When the sum of the voltages of capacitors C1 and C2 is equal to the source side voltage, the current of the pre-charging branch is 0, and the thyristor banks T1 and T9 automatically turn off, and capacitors C1 and C2 reach the initial voltage level.

[0084] Phase 1 (t0): Capacitors C1 and C2 maintain the pre-charging voltage, and the system remains in a stable operating state.

[0085] Phase 2 (t0 - t1): At time t1, the system detects abnormal current on the fault side, and the relay protection device starts to operate.

[0086] Phase 3 (t1 - t2): After a short delay, at time t2, the mechanical vacuum switch receives the action command sent by the relay protection device and starts to arc and open. At the same time, trigger signals are applied to the thyristor bank T3, the thyristor bank T6, and the thyristor bank T7. The oscillation branch 1 and the oscillation branch 2 conduct current simultaneously with the main current-carrying branch, and the generated oscillation current is injected into the main current-carrying branch in the reverse direction. When the fault current in the main current-carrying branch is cut off, the arc in the mechanical vacuum switch goes out.

[0087] Stage 4 (t2 - t3): After the fault current in the main current-carrying branch is cut off, the mechanical vacuum switch only withstands the conduction voltage drops of thyristor groups T6 and T7, and the dielectric insulation strength inside the mechanical vacuum switch quickly recovers; at time t3, the damping energy-consuming circuit is put into operation, and thyristor group T7 automatically turns off.

[0088] Stage 5 (t3 - t4): At time t4, the damping energy-consuming circuit completes the current cut-off, and the whole breaker opening is completed.

[0089] Thus, the control of one cycle is completed.

[0090] What the present invention does not cover is applicable to the prior art.

Claims

1. An economical DC circuit breaker with zero zone fast recovery capability, characterized in that: The circuit breaker comprises a main current-carrying branch and a pre-charging branch; The main current branch includes a mechanical vacuum switch MVCB, the left end of the main current branch is connected to the cathodes of the thyristor group T2 and the thyristor group T4 and the anodes of the thyristor group T1 and the thyristor group T6, and the right end is connected to the cathodes of the thyristor group T3 and the thyristor group T5 and the anode of T7; the thyristor group T2 and the thyristor group T1 are connected in reverse parallel and then connected to the anode of the thyristor group T3, the anode of the thyristor group T4 is connected to the anode of the thyristor group T5, the cathode of the thyristor group T6 is connected to the cathode of the thyristor group T7, an oscillation branch 1 is connected in parallel between the anode of the thyristor group T5 and the anode of the thyristor group T3, an oscillation branch 2 and a diode group D1 are connected in parallel between the anode of the thyristor group T5 and the cathode of the thyristor group T7, and a branch 7 composed of a thyristor group T8 and a resistor R1 connected in series is connected in parallel between the anode of the thyristor group T3 and the cathode of the thyristor group T7; Energy dissipation modules are connected in parallel at both ends of the main flow branch; The oscillation branch 1 is composed of an inductor L1 and a capacitor C1 connected in series, one end of the capacitor C1 is connected to the anode of the thyristor group T3, one end of the inductor L1 is connected to the anode of the thyristor group T5 and the cathode of the diode group D1, the anode of the diode group D1 is connected to the cathode of the thyristor group T7 and the anode of the thyristor group T9 in the pre-charging branch, the cathode of the thyristor group T9 is connected to one end of the resistor R0, and the other end of the resistor R0 is grounded; The oscillation branch 2 is composed of a diode group D2 and a current limiting resistor R2 connected in parallel, and an inductor L2 and a capacitor C2 connected in series. One end of the capacitor C2 is connected to the anode of the thyristor group T5.

2. The economical DC circuit breaker with zero zone fast recovery capability according to claim 1, characterized in that: Thyristor group T1 and thyristor group T2 are connected in anti-parallel to form branch 1, thyristor group T3 forms branch 2, thyristor group T4 forms branch 3, thyristor group T5 forms branch 4, thyristor group T6 forms branch 5, thyristor group T7 forms branch 6, and diode group D1 forms branch 8; Branch 4, branch 6 and oscillation branch 2 form a resonant commutation circuit, one end of oscillation branch 2 is connected to the junction of branch 3 and branch 4, and the other end is connected to the junction of branch 5 and branch 6; Branch 8 and oscillation branch 2 form a damping energy dissipation circuit. Branch 4, branch 6, branch 7, branch 8, oscillation branch 1 and oscillation branch 2 form a capacitor reset circuit; branch 7 is composed of a thyristor group T8 and R1 connected in series, one end of the oscillation branch 1 is connected to the junction of branch 1 and branch 2, and the other end is connected to the junction of branch 3 and branch 4; Branch 2, branch 5, branch 6, damping energy dissipation circuit and oscillation branch 1 form a weak current breaking circuit. The fault processing module is composed of a resonant commutation circuit, a damping energy consumption circuit, a capacitor reset circuit, a weak current breaking circuit and an energy dissipation module.

3. The economical DC circuit breaker with zero zone fast recovery capability according to claim 2, characterized in that: When the resonant commutation circuit and the damping energy dissipation circuit are working, the vacuum switch of the main current branch withstands an extremely low level of transient recovery voltage, that is, the conduction voltage drop of the power electronic switch tube, providing a zero-zone fast recovery time for the vacuum switch.

4. The economical DC circuit breaker with zero zone fast recovery capability according to claim 2, characterized in that: The voltage values ​​of capacitors C1 and C2 after the capacitor reset circuit ends operation are determined by the resonant frequencies of oscillation branch 1 and oscillation branch 2, the voltage values ​​of capacitors C1 and C2 after one disconnection, and the resistance values ​​of resistors R2 and R1.

5. The economical DC circuit breaker with zero zone fast recovery capability according to claim 2, characterized in that: When special situations occur in the system, including manual maintenance, a weak current circuit breaker is used to cut off the short-circuit current.

6. The economical DC circuit breaker with zero zone fast recovery capability according to claim 1, characterized in that: The energy dissipation module is composed of a lightning arrester MOV, which is connected in parallel at both ends of the main current branch.

7. A control method for an economical DC circuit breaker with zero-zone rapid recovery capability as claimed in claim 2, characterized in that: If the fault current source is a line-to-ground short circuit fault, the control method includes the following process: When the DC system is operating normally, the mechanical vacuum switch MVCB is closed, and the current flows from the DC power supply side along the main current branch from left to right to the load side, supplying energy to the load; The short-circuit fault of the DC system occurs on the load side; the left side of the DC circuit breaker is called the non-fault side or source side, and the right side is called the fault side; Phase 0 (t 0- ): The mechanical vacuum switch remains closed, the system operates stably, a trigger signal is applied to the thyristor group T1 and the thyristor group T9, the source side charges the capacitor C1 and the capacitor C2, when the sum of the voltage of the capacitor C1 and the capacitor C2 is equal to the source side voltage, the pre-charge branch current is 0, the thyristor group T1 and the thyristor group T9 are automatically closed, and the capacitor C1 and the capacitor C2 reach the initial voltage level; Phase 1 (t0): Capacitors C1 and C2 maintain the pre-charge voltage, and the system maintains a stable operating state; Phase 2 (t0-t1): At t1, the system detects abnormal current on the fault side and the relay protection device starts to operate; Phase 3 (t1-t2): After a short relay delay, at t2, the mechanical vacuum switch receives the action command from the relay protection device and starts arcing and opening. At the same time, a trigger signal is applied to the thyristor group T5, the thyristor group T6 and the thyristor group T7. The oscillation branch 2 and the main current branch are simultaneously conducting. The inductor L2 and the capacitor C2 generate an oscillating current that is reversely injected into the main current branch. When the fault current of the main current branch is cut off, the arc in the mechanical vacuum switch is extinguished. Stage 4 (t2-t3): After the fault current of the main current branch is cut off, the thyristor group T7 is turned on, and the resonant commutation circuit is put into operation. At this time, the mechanical vacuum switch can only withstand the conduction voltage drop of the thyristor group T5 and the thyristor group T6, and the dielectric insulation strength inside the mechanical vacuum switch is quickly restored; Phase 5 (t3-t4): At t3, the current of oscillation branch 2 is equal to the system current, diode group D2 and thyristor group T7 are automatically turned off, diode group D1 is automatically turned on, the damping energy consumption circuit is put into use, and the mechanical vacuum switch can only withstand the conduction voltage drop of thyristor group T5, thyristor group T6 and diode group D1; Phase 6 (t4-t5): At t4, a trigger signal is applied to the thyristor group T3, and the oscillation branch 1 is put into operation. When the sum of the conduction voltage drop of the thyristor group T3, the thyristor group T6 and the diode group D1 and the voltage at the terminals of the inductor L1 and the capacitor C1 reaches the rated action voltage of the MOV, the current is transferred from the oscillation branch 1 to the energy dissipation module, and the energy dissipation module is put into operation to complete the current cutoff. At t5, the circuit breaker is disconnected. Stage 7 (t5-t6): At time t6, a trigger signal is applied to the thyristor group T8, and the capacitor reset circuit is put into operation. The current flow path of the capacitor reset circuit in the first oscillation is C1-L1-C2-L2-R2-R1-T8. After the oscillation process is completed, the thyristor group T8 is automatically turned off. In the secondary oscillation, the current path of the capacitor C1 is C1-L1-T4-T1, and the current path of the capacitor C2 is the damping energy consumption circuit and the resonant commutation circuit. After the reset is completed, the voltage of the capacitor C2 and the capacitor C1 returns to the initial level; Stage 8 (t6-t7): At time t7, if the fault is a temporary fault, the DC circuit breaker will no longer be put into operation. If the fault is a permanent fault, repeat stages 2 to 7 to perform fault disconnection and voltage reset operations; This completes one cycle of control.

8. The control method according to claim 7, characterized in that: If the fault current source is manual maintenance of the system, execute the weak current breaking mode, including the following process: When the DC system is running stably, the mechanical vacuum switch MVCB is closed, and the current flows from the DC power supply side along the main current branch from left to right to the load side, supplying energy to the load; The short-circuit fault of the DC system occurs on the load side; the left side of the DC circuit breaker is called the non-fault side or source side, and the right side is called the fault side; Phase 0 (t 0- ): The mechanical vacuum switch remains closed, the system operates stably, a trigger signal is applied to the thyristor group T1 and the thyristor group T9, the source side charges the capacitor C1 and the capacitor C2, when the sum of the voltage of the capacitor C1 and the capacitor C2 is equal to the source side voltage, the pre-charge branch current is 0, the thyristor group T1 and the thyristor group T9 are automatically closed, and the capacitor C1 and the capacitor C2 reach the initial voltage level; Phase 1 (t0): Capacitors C1 and C2 maintain the pre-charge voltage, and the system maintains a stable operating state; Phase 2 (t0-t1): At t1, the system detects abnormal current on the fault side and the relay protection device starts to operate; Phase 3 (t1-t2): After a short delay, at t2, the mechanical vacuum switch receives the action command from the relay protection device and starts arcing and opening. At the same time, a trigger signal is applied to the thyristor group T3, the thyristor group T6 and the thyristor group T7. The oscillation branch 1 and the oscillation branch 2 are simultaneously conducting with the main flow branch. The generated oscillating current is reversely injected into the main flow branch. When the fault current of the main flow branch is cut off, the arc in the mechanical vacuum switch is extinguished. Stage 4 (t2-t3): After the fault current of the main current branch is cut off, the mechanical vacuum switch can only withstand the conduction voltage drop of the thyristor group T6 and the thyristor group T7, and the dielectric insulation strength inside the mechanical vacuum switch recovers quickly; at t3, the damping energy dissipation circuit starts to work, and the thyristor group T7 is automatically turned off; Stage 5 (t3-t4): At t4, the damping energy dissipation circuit completes current cutting and the circuit breaker is disconnected; This completes one cycle of control.

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