CN114709800A - Compact direct-current circuit breaker sharing branch circuit and control method thereof - Google Patents

Abstract

The invention provides a compact direct current breaker sharing a branch circuit and a control method thereof, when the breaker is in normal through-current, the current is conducted through a main mechanical switch of a through-current loop, and the loss of the direct current breaker is extremely low; the direct current circuit breaker of the invention adopts the quick operating mechanism to drive the mechanical switch, can cut off the fault current in a short time, realizes the reclosing function, isolates the fault and protects the flexible direct current system. The control method can generate oscillation current with gradually increased amplitude by sharing the current conversion branch and the energy absorption branch, the oscillation current is superposed on the current of the main loop to generate a current zero crossing point, and finally the current is switched off by the mechanical switch. The circuit breaker is used for breaking and isolating fault current of all external lines on one bus. And each direct-current bus is only provided with one direct-current breaker, so that the cost and the volume of the direct-current breaker in a direct-current power grid are greatly reduced, and the technical support is provided for the construction of the direct-current power grid.

Description

A compact DC circuit breaker with shared branch and its control method

technical field

The invention belongs to the technical field of electric power equipment, in particular to a compact DC circuit breaker with a shared branch and a control method thereof.

Background technique

At present, DC circuit breakers mainly include mechanical DC circuit breakers and hybrid DC circuit breakers. Among them, mechanical circuit breakers have become the preferred technical solution for DC circuit breakers due to their small on-state loss. With the significant increase in demand for distributed DC power supply systems of new energy sources, especially in offshore wind power flexible multi-terminal DC systems, the grid erection space resources are limited, the offshore platform carrying capacity is limited, the fault current is large and the rise rate is fast, so the high voltage DC The volume space, weight, breaking capacity, breaking speed and cost of circuit breakers are extremely demanding. As shown in Figure 1, the traditional DC circuit breaker can only interrupt the fault current of one incoming line and one outgoing line. If the traditional mechanical DC circuit breaker is used in the DC grid, the number of DC circuit breakers installed on each DC bus will be The number of external lines is the same as that of the DC bus. The number of DC circuit breakers that need to be configured in the DC grid is huge, and the DC circuit breaker is expensive and has a large space, which in turn causes a significant increase in the construction cost of the DC grid, and cannot be used in flexible multi-terminal DC systems.

SUMMARY OF THE INVENTION

In order to solve the problems existing in the prior art, the present invention provides a compact DC circuit breaker with a shared branch and a control method thereof, which ensures that each DC bus only needs to be equipped with a DC circuit breaker, which greatly reduces the direct current in the DC grid. The cost and volume of circuit breakers provide technical support for the construction of DC power grids.

To achieve the above object, the present invention provides the following technical solutions:

A compact DC circuit breaker sharing a branch, including a terminal, a current branch, an isolation branch, a breaking unit, a DC bus, an online monitoring system and a control system;

The number of the terminals, the flow branches and the isolation branches are all multiple, and they are connected in one-to-one correspondence;

One end of the through-current branch is connected to the terminal through a mechanical switch, and the other end of the through-current branch is connected to the DC bus;

One end of the flow branch is connected to one end of the isolation branch, the other ends of the isolation branches are all connected to one end of the disconnecting unit, and the other end of the disconnecting unit is connected to the bus bar of the outlet end. connect;

The through-current branch comprises a main mechanical switch; the main mechanical switch comprises one or more vacuum switches connected in series; the isolation branch comprises an auxiliary isolating switch and a thyristor module; the auxiliary isolating switch and the thyristor module are connected in series;

The online monitoring system is used to measure the magnitude and direction of the current flowing through the commutator switch module, the current and direction flowing through the arrester, the voltage and temperature at both ends of the arrester, the magnitude and current of the current flowing through the main mechanical switch of the current branch. direction, the voltage at both ends and the switching stroke, the voltage at both ends of the energy storage capacitor;

The control system is connected to the online monitoring system, and the control system is used to control the main mechanical switch of the current branch, the thyristor and the auxiliary isolating switch of the isolation branch, the converter switch module and the fast mechanical switch.

Preferably, the breaking unit includes a commutation switch module, an oscillating capacitor, an oscillating inductance and a lightning arrester; the commutating switch module is connected in series with the oscillating capacitor and the oscillating inductance to form a commutation branch, and the arrester is connected in parallel with the commutating branch .

Preferably, the breaking unit includes a commutation switch module, an oscillating capacitor, an oscillating inductance and a surge arrester; the commutation switch module is connected in series with the oscillating capacitor, the surge arrester is connected in parallel with the branch formed in series by the two, and the branch formed in parallel is connected in parallel One end of the oscillating inductance, and the other end of the oscillating inductance is connected to the outgoing busbar.

Preferably, the commutation switch module of the breaking unit includes an energy storage capacitor, a charging branch and a power electronic power device;

The power electronic power device includes a fully-controlled power electronic power device ES1, a fully-controlled power electronic power device ES2, a fully-controlled power electronic power device ES3, and a fully-controlled power electronic power device ES4;

The negative electrode of the fully controlled power electronic power device ES1 and the positive electrode of the fully controlled power electronic power device ES3 are connected to N1, and N1 is connected to the isolation branch; the negative electrode of the fully controlled power electronic power device ES2 is connected to the fully controlled power electronic power device ES2. The positive pole of the type power electronic power device ES4 is connected to N2, and N2 is connected to one end of the oscillation capacitor C;

The positive electrode of the fully controlled power electronic power device ES1 and the positive electrode of the fully controlled power electronic power device ES2 are connected to N3, and the negative electrode of the fully controlled power electronic power device ES3 and the fully controlled power electronic power device ES4. The negative phase is connected to N4;

N3 is connected to one end of the energy storage capacitor, and N4 is connected to the other end of the energy storage capacitor; the charging direction of the energy storage capacitor is the same or opposite to the current direction of the main circuit; the charging branch and the energy storage capacitor are connected in parallel.

Further, the power electronic power device is a series-parallel combination of the following single or multiple devices, including GTO, thyristor, MOSFECT, IGBT, and IGCT.

Preferably, the mechanical switch is a mechanical switch based on explosion driving, a mechanical switch based on electromagnetic repulsion, a mechanical switch based on permanent magnet repulsion, a mechanical switch based on a spring operating mechanism or a mechanical switch based on motor driving.

Preferably, the online monitoring system includes a voltage measurement module, a current measurement module, a temperature measurement module, a sound measurement module, an X-ray measurement module, and a magnetic field measurement module, and each measurement module of the online monitoring system is used to monitor the state of the DC circuit breaker, and The time when the control system sends the command signal is determined according to the monitored state of the DC circuit breaker.

A method for controlling a compact DC circuit breaker with a shared branch, characterized in that, based on the compact DC circuit breaker with a shared branch described in any one of the above, the following processes are included:

In the normal current-on state of the system, the main mechanical switches and mechanical switches of the plurality of current-current branches are in the closed state; the thyristors in the plurality of the isolation branches are in the off state; the breaking unit is in the off state The line current is gathered to the DC bus by the current branch where some terminals are located, and then flows out from the DC bus through the current branch where the rest of the terminals are located;

In the fault state, when a terminal fault is detected, the DC circuit breaker sends an opening command to the main mechanical switch of the current branch where the faulty terminal is located and the auxiliary isolating switches of the isolation branch where the other terminals are located. When the main mechanical switch and the auxiliary isolating switch reach the preset distance, a conduction command is sent to the thyristor and the full-bridge converter in the isolation branch where the fault terminal is located, and the two bridge arms of the full-bridge converter Turn on alternately, the pre-charged energy storage capacitor is discharged through the oscillating capacitor and the oscillating inductance, and an oscillating current with a gradually increasing amplitude is generated until the current zero-crossing point is superimposed on the fault current, and the fault current makes the voltage across the oscillating capacitor rise until it reaches the arrester. When the fault current drops to 0, the arc is extinguished, and the fast mechanical switch at the fault terminal opens to cut off the residual current to realize the breaking of the fault current.

Preferably, for a permanent fault, wait for a preset time after the fault current is interrupted, turn on the main mechanical switch of the current-passing branch and the fast mechanical switch connected to it, detect the fault current again, and the DC circuit breaker is repeatedly opened. In the process, after the fault current drops to zero, open the fast mechanical switch connected to the fault terminal and the auxiliary isolating switch in the isolation branch, and close the auxiliary isolating switch in the isolating branch where the other normal terminals are located, thereby isolating the fault line. , and reset the DC circuit breaker to wait for the next operation;

For temporary faults, no fault current is detected after the breaking unit is turned on, and all fast mechanical switches and auxiliary isolating switches are closed to reset the DC circuit breaker and wait for the next operation.

Preferably, the commutation includes stage 1 and stage 2;

Stage 1 is: ES1 and ES4 in the commutation switch module are turned on, ES2 and ES3 are turned off, and after ES1 and ES4 are turned on, the energy storage capacitor discharges through the oscillating capacitor and oscillating inductance, generating a sinusoidal oscillating current. When the sine oscillating current completes a sine When the half-wave oscillation and the oscillating current reaches the zero-crossing point, the control system sends a control signal, and the execution stage 2: ES1 and ES4 are turned off, ES2 and ES3 are turned on, the polarity of the energy storage capacitor at this time is consistent with the direction of the discharge current, and the energy storage capacitor Continue to discharge through the oscillating capacitor and oscillating inductance, and the amplitude of the generated sinusoidal oscillating current is higher than that of the first sine half-wave. When the second sine half-wave current reaches the zero-crossing point, the control system sends a control signal, and executes stage 1 and subsequent stages 2 alternates with phase 1.

Compared with the prior art, the present invention has the following beneficial technical effects:

The present invention provides a compact DC circuit breaker with a shared branch. During normal current flow, the current is conducted through the main mechanical switch of the current circuit, and the loss of the DC circuit breaker is extremely low; the DC circuit breaker of the present invention adopts a fast The mechanical switch driven by the operating mechanism can break the fault current in a short time, and realize the reclosing function, isolate the fault, and protect the flexible DC system.

The control method of a compact DC circuit breaker sharing a branch of the present invention can generate an oscillating current with a gradually increasing amplitude from the commutating branch by sharing the commutating branch and the energy-absorbing branch, which is superimposed on the main circuit The current zero-crossing point is generated on the current, and finally the current is interrupted by the mechanical switch. A circuit breaker can break and isolate the fault current of all external lines on a bus, with a small footprint and low construction cost, which is beneficial to the construction of a multi-terminal flexible DC system.

Description of drawings

Figure 1 shows the configuration diagram of a traditional DC circuit breaker in a four-terminal project;

FIG. 2 shows a schematic structural diagram of a specific embodiment of the compact circuit breaker of the present invention;

Fig. 3 shows the schematic diagram of the installation position of the sensor of the compact circuit breaker of the present invention;

FIG. 4 shows a schematic structural diagram of a specific embodiment of the breaking unit in the compact circuit breaker of the present invention;

FIG. 5 shows a schematic structural diagram of another specific embodiment of the breaking unit in the compact circuit breaker of the present invention.

Detailed ways

The present invention will be further described in detail below in conjunction with specific embodiments, which are to explain rather than limit the present invention.

Example

As shown in FIG. 2, the present invention discloses a compact DC circuit breaker with shared branches, including n terminals, n current branches, n isolation branches, a breaking unit, a DC bus, A set of online monitoring system and a set of control system.

One end of each current branch and one end of each isolation branch are respectively connected correspondingly, and connected to the terminal through the fast mechanical switch RCB, the other end of the current branch is connected to the DC bus, and the other end of each isolation branch is connected to the terminal. One end of the breaking unit is connected to N1, and the other end of the breaking unit is connected to the bus bar of the outlet end. The flow branch includes the main mechanical switch CB, and the main mechanical switch CB is composed of a vacuum switch or a series of vacuum switches. The isolation branch includes auxiliary isolation switch S and thyristor module T.

As shown in FIG. 4 , the breaking unit includes a commutation switch module, an oscillating capacitor C _P , an oscillating inductance _LP , and a lightning arrester SA. The commutation switch module is connected in series with the oscillating capacitor C _p , and the _{arrester SA} is connected in parallel with the branch formed by the two series connected in parallel. Or, as shown in FIG. 5 , the commutation switch module is connected in series with the oscillating capacitor C _P and the oscillating inductance _LP to form a commutation branch, and the arrester is connected in parallel with the commutating branch.

The commutation switch module includes an energy storage capacitor C _DC , a charging branch circuit, and a power electronic power device; the charging branch circuit includes a DC power source V _DC , a charging resistor R _CH , and a charging switch S _CH ; the power electronic power device includes a fully controlled power electronic power device Device ES1, fully controlled power electronic power ES2, fully controlled power electronic power device ES3 and fully controlled power electronic power device ES4.

The negative pole of the fully controlled power electronic power device ES1 and the positive pole of the fully controlled power electronic power device ES3 are connected to N1, and N1 is connected to the isolation branch; the negative pole of the fully controlled power electronic power device ES2 is connected to the fully controlled power electronic power The anode of the device ES4 is connected to N2, and N2 is connected to one end of the oscillation capacitor C _p ;

The positive pole of the fully controlled power electronic power device ES1 and the positive pole of the fully controlled power electronic power device ES2 are connected to N3, and the negative pole of the fully controlled power electronic power device ES3 and the negative pole of the fully controlled power electronic power device ES4 are connected to N4;

N3 is connected to one end of the energy storage capacitor C _DC , and N4 is connected to the other end of the energy storage capacitor C _DC ; the charging direction of the energy storage capacitor C _DC is the same or opposite to the current direction of the main circuit; the charging branch is connected in parallel with the energy storage capacitor C _DC .

The line current is gathered to the DC bus by the current branch connected by one or some terminals, and then flows out from the DC bus through the current branches connected by the other terminals.

As shown in Fig. 3, the online detection system includes current sensor groups D11-D1n for measuring the current state of the lead wires of the terminals, current sensor groups D21-D2n for measuring the current state of the current branch, and current sensor groups D21-D2n for measuring the current state of the commutator switch The current sensor D3 of the module, the current sensor D4 used to measure the current state of the arrester, the voltage sensor group V11~V1n used to measure the voltage state of the two ends of the main mechanical switch CB of the current branch, the voltage sensor group V11 to V1n used to measure the voltage state of the two ends of the arrester. Voltage sensor V2, voltage sensor V3 for measuring the voltage state of both ends of the energy storage capacitor C and _DC , displacement sensor group W11-W1n for measuring the motion state of the main mechanical switch CB of the flow path, for measuring the temperature of the arrester SA The temperature sensor M1 of the state, as well as the necessary signal processing circuit, A/D conversion module and communication module.

The control system is connected to the on-line detection system, and the on-line detection system measures the current amplitude, current zero-crossing point, current rate of change of the current branch and the current amplitude, current zero-crossing point, and current rate of change of the commutator switch module. The mechanical switch CB, the fast mechanical switch RCB, the commutation switch module, the auxiliary isolating switch S and the thyristor T can realize fast and reliable shutdown of fault currents of different amplitudes.

In the normal flow-through state of the system, the main mechanical switch CB of the n flow-through branches and the fast mechanical switch RCB connected to it are in the closed state; the thyristors T in the n isolation branches are in the off-state; the breaking unit It is in the off state; at this time, the line current is gathered from the current branch connected by one or some terminals to the DC bus, and then flows out from the DC bus through the current branch where the other terminals are located, and there is no current flow in the breaking unit. Pass.

In the fault state, when the online detection system detects the fault of a certain terminal, the control system will give the auxiliary isolation of the main mechanical switch CB ₁ of the current branch connected to the fault terminal and the isolation branch connected to the other terminals. The switch S issues an opening command. After a certain delay, the electrode contacts of the mechanical switch CB ₁ begin to separate, and arcing occurs between the electrode contacts. When the main mechanical switch CB ₁ and the auxiliary isolating switch S ₁ reach a certain distance, wire the fault. The thyristor T1 in the isolated branch connected to the terminal and the full _- bridge converter send a turn-on command, and the two bridge arms of the full-bridge converter are turned on alternately. The turn-on sequence includes: stage 1, ES1 and ES4 is turned on, ES2 and ES3 are turned off, and after ES1 and ES4 are turned on, the energy storage capacitor C _DC discharges through the oscillating capacitor C _p and the oscillating inductor L _p to generate a sinusoidal oscillating current. When the current reaches the zero-crossing point, the control system sends a control signal to execute stage 2, ES1 and ES4 are turned off, and ES2 and ES3 are turned on. At this time, the polarity of the energy storage capacitor C _DC is consistent with the direction of the discharge current, and the energy storage capacitor C _DC continues to pass through. The oscillating capacitor C _p and the oscillating inductor L _p are discharged, and the amplitude of the generated sinusoidal oscillating current is higher than that of the first sine half-wave. When the second sine half-wave current reaches the zero-crossing point, the control system sends a control signal to execute stage 1, Then phase 2 and phase 1 are alternately executed. The precharged energy storage capacitor C _DC is discharged through the capacitor C and the inductor L, generating an oscillating current with a gradually increasing amplitude until the current zero-crossing point is superimposed on the fault current, the arc is extinguished, and the fault current is transferred to the branch where the commutator switch is located. The voltage across the capacitor C rises until it reaches the operating voltage of the arrester SA. Due to the nonlinear resistance characteristics of the arrester SA, the arrester SA is converted from a high-resistance state to a low-resistance state, and the fault current is transferred to the branch where the arrester SA is located. The electromagnetic energy of the system It is converted into the thermal energy of the arrester SA, and the fault current gradually decreases. When the fault current drops to close to 0, the fast mechanical switch RCB at the fault terminal opens to cut off the residual current, so as to realize the fast and reliable breaking of the fault current.

The online monitoring system includes a voltage measurement module, a current measurement module, a temperature measurement module, a sound measurement module, an X-ray measurement module, and a magnetic field measurement module.

The mechanical switch is a mechanical switch based on explosion driving, a mechanical switch based on electromagnetic repulsion, a mechanical switch based on permanent magnet repulsion, a mechanical switch based on a spring operating mechanism, and a mechanical switch based on motor driving.

A single device or a combination of multiple devices in series and parallel in the following period of fully controlled power electronic devices, GTO, thyristor, MOSFECT, IGBT, IGCT.

The arrester SA includes the following single device or a series-parallel combination of multiple devices, metal oxide arrester, gas-insulated metal oxide arrester, porcelain-shell insulated metal oxide arrester, and gapless metal oxide arrester.

In order to achieve the above object, an embodiment of an aspect of the present invention discloses a method for breaking a compact DC circuit breaker with a shared branch, including the above-mentioned compact DC circuit breaker based on a shared branch, and further comprising the following steps :

In the first step, the system current flows from the terminal 1 through the mechanical switches RCB ₁ and CB ₁ into the DC bus, and then flows out from the DC bus through the cables where the remaining terminals are located;

In the second step, when the online monitoring system detects that the system is faulty, it sends a trigger signal to the control system, and the control system immediately issues an opening command after receiving the signal, and the main mechanical switch of the current branch connected to the faulty terminal The auxiliary isolating switch S of the isolating branch connected to CB ₁ and other terminals receives the opening command and starts to open and arc after a certain delay;

In the third step, the opening time of the mechanical switch CB1 reaches _a certain time or the opening distance of the electrode contact reaches _a certain distance, and the thyristor T1 and the commutator switch module in the isolation branch connected to the fault terminal are triggered and turned on, The pre-charged energy storage capacitor C _DC generates an oscillating current through the discharge of the oscillating capacitor C _p and the oscillating inductor L _p ,

The online monitoring system detects the zero-crossing point of the oscillating current, and the control system controls the commutator switch module to alternately execute phase 1 and phase 2 at each zero-crossing point of the oscillating current. The current arc superposition in the main mechanical switch CB ₁ produces a zero-crossing point, and the arc in the main mechanical switch CB ₁ is extinguished.

_In the fourth step, the arc in the main mechanical switch CB1 is extinguished and stops conducting, the system current is transferred to the branch where the commutation switch module is located, and the oscillation capacitor _Cp is charged, and the voltage across the oscillation capacitor _Cp rises rapidly until When the voltage of the oscillating capacitor C _p reaches the operating voltage of the arrester in parallel with it, the arrester SA operates and starts to conduct current, and the system current is transferred to the energy-absorbing branch where the arrester SA is located. The arrester SA absorbs the residual energy in the system. As the energy is gradually absorbed, the current of the arrester SA gradually decreases until it drops to 0, completing the current interruption and isolating the fault line.

Realize fast reclosing, specifically including: for permanent fault, wait for a certain time after the fault current is interrupted, turn on the main mechanical switch CB ₁ of the current branch and the fast mechanical switch RCB ₁ connected to it, and detect the fault current again , the DC circuit breaker repeats the breaking process, waits for the fault current to drop to zero, opens the fast mechanical switch RCB ₁ of the fault terminal and the auxiliary isolating switch S ₁ in the isolation branch, and closes the isolation branch where the rest of the normal terminals are located. Auxiliary isolating switch S in , thereby isolating the faulty line and resetting the DC circuit breaker for the next operation; for temporary faults, no fault current is detected after switching on the starter unit, closing all fast mechanical switches RCB and auxiliary isolating switches S to reset the DC circuit breaker and wait for the next operation.

The present invention provides a compact DC circuit breaker with a shared branch. During normal current flow, the current is conducted through the mechanical switch of the current branch, and the loss of the DC circuit breaker is extremely low; the DC circuit breaker of the present invention adopts a fast The mechanical switch driven by the operating mechanism can break the fault current in a short time, and realize the function of reclosing, isolate the fault, and protect the flexible DC system; the invention can realize the opening of one circuit breaker by sharing the commutation branch and the energy absorption branch. It can cut off and isolate the fault current of all external lines on a bus, which has a small footprint and low construction cost, which is conducive to the construction of a multi-terminal flexible DC system.

Claims (10)

1. A compact DC circuit breaker with a shared branch, characterized in that it comprises a terminal, a current branch, an isolation branch, a breaking unit, a DC bus, an online monitoring system and a control system; The number of the terminals, the flow branches and the isolation branches are all multiple, and they are connected in one-to-one correspondence; One end of the through-current branch is connected to the terminal through a mechanical switch, and the other end of the through-current branch is connected to the DC bus; One end of the flow branch is connected to one end of the isolation branch, the other ends of the isolation branches are all connected to one end of the disconnecting unit, and the other end of the disconnecting unit is connected to the bus bar of the outlet end. connect; The through-current branch comprises a main mechanical switch; the main mechanical switch comprises one or more vacuum switches connected in series; the isolation branch comprises an auxiliary isolating switch and a thyristor module; the auxiliary isolating switch and the thyristor module are connected in series; The online monitoring system is used to measure the magnitude and direction of the current flowing through the commutator switch module, the current and direction flowing through the arrester, the voltage and temperature at both ends of the arrester, the magnitude and current of the current flowing through the main mechanical switch of the current branch. direction, the voltage at both ends and the switching stroke, the voltage at both ends of the energy storage capacitor; The control system is connected to the online monitoring system, and the control system is used to control the main mechanical switch of the current branch, the thyristor and the auxiliary isolating switch of the isolation branch, the converter switch module and the fast mechanical switch. 2 . The compact DC circuit breaker sharing a branch according to claim 1 , wherein the breaking unit comprises a commutation switch module, an oscillating capacitor, an oscillating inductance and a lightning arrester; The switch module is connected in series with the oscillating capacitor and the oscillating inductance to form a commutation branch, and the arrester is connected in parallel with the commutation branch. 3 . The compact DC circuit breaker sharing a branch according to claim 1 , wherein the breaking unit comprises a commutation switch module, an oscillating capacitor, an oscillating inductance and a lightning arrester; The oscillating capacitors are connected in series, and the arrester is connected in parallel with the branch formed by the two series connected in parallel. 4 . The compact DC circuit breaker sharing a branch according to claim 1 , wherein the commutation switch module of the breaking unit comprises an energy storage capacitor, a charging branch and a power electronic power device; 5 . The power electronic power device includes a fully-controlled power electronic power device ES1, a fully-controlled power electronic power device ES2, a fully-controlled power electronic power device ES3, and a fully-controlled power electronic power device ES4; The negative electrode of the fully controlled power electronic power device ES1 and the positive electrode of the fully controlled power electronic power device ES3 are connected to N1, and N1 is connected to the isolation branch; the negative electrode of the fully controlled power electronic power device ES2 is connected to the fully controlled power electronic power device ES2. The positive pole of the type power electronic power device ES4 is connected to N2, and N2 is connected to one end of the oscillation capacitor C; The positive electrode of the fully controlled power electronic power device ES1 and the positive electrode of the fully controlled power electronic power device ES2 are connected to N3, and the negative electrode of the fully controlled power electronic power device ES3 and the fully controlled power electronic power device ES4. The negative phase is connected to N4; N3 is connected to one end of the energy storage capacitor, and N4 is connected to the other end of the energy storage capacitor; the charging direction of the energy storage capacitor is the same or opposite to the current direction of the main circuit; the charging branch and the energy storage capacitor are connected in parallel. 5. The compact DC circuit breaker sharing a branch according to claim 4, wherein the power electronic power device is a series-parallel combination of the following single or multiple devices, including GTO, thyristor, MOSFECT, IGBT, IGCT. 6 . The compact DC circuit breaker sharing a branch according to claim 1 , wherein the mechanical switch is a mechanical switch based on explosion driving, a mechanical switch based on electromagnetic repulsion, and a mechanical switch based on permanent magnet repulsion. 7 . Switches, spring-operated mechanical switches or motor-driven mechanical switches. 7 . The compact DC circuit breaker of claim 1 , wherein the online monitoring system comprises a voltage measurement module, a current measurement module, a temperature measurement module, a sound measurement module, and an X-ray measurement module. 8 . The module, the magnetic field measurement module, and each measurement module of the online monitoring system are used to monitor the state of the DC circuit breaker, and determine the time when the control system sends the command signal according to the monitored state of the DC circuit breaker. 8. A method for controlling a compact DC circuit breaker sharing a branch, wherein the compact DC circuit breaker sharing a branch based on any one of claims 1 to 7 comprises the following process: In the normal current-on state of the system, the main mechanical switches and mechanical switches of the plurality of current-current branches are in the closed state; the thyristors in the plurality of the isolation branches are in the off state; the breaking unit is in the off state The line current is gathered to the DC bus by the current branch where some terminals are located, and then flows out from the DC bus through the current branch where the rest of the terminals are located; In the fault state, when a terminal fault is detected, the DC circuit breaker sends an opening command to the main mechanical switch of the current branch where the faulty terminal is located and the auxiliary isolating switches of the isolation branch where the other terminals are located. When the main mechanical switch and the auxiliary isolating switch reach the preset distance, a conduction command is sent to the thyristor and the full-bridge converter in the isolation branch where the fault terminal is located, and the two bridge arms of the full-bridge converter Turn on alternately, the pre-charged energy storage capacitor is discharged through the oscillating capacitor and the oscillating inductance, and an oscillating current with a gradually increasing amplitude is generated until the current zero-crossing point is superimposed on the fault current, and the fault current makes the voltage across the oscillating capacitor rise until it reaches the arrester. When the fault current drops to 0, the arc is extinguished, and the fast mechanical switch at the fault terminal opens to cut off the residual current to realize the breaking of the fault current. 9 . The method for controlling a compact DC circuit breaker with a shared branch according to claim 8 , wherein, for a permanent fault, after the fault current is interrupted, wait for a preset time, and turn on the current-passing branch. 10 . The main mechanical switch and the fast mechanical switch connected to it detect the fault current again, and the DC circuit breaker repeats the process of opening and closing. After the fault current drops to zero, the fast mechanical switch connected to the fault terminal and the isolation branch are opened. The auxiliary isolating switch is closed, and the auxiliary isolating switch in the isolating branch where the rest of the normal terminals are located, so as to isolate the fault line and reset the DC circuit breaker to wait for the next operation; For temporary faults, no fault current is detected after the breaking unit is turned on, and all fast mechanical switches and auxiliary isolating switches are closed to reset the DC circuit breaker and wait for the next operation. 10 . The method for controlling a compact DC circuit breaker sharing a branch according to claim 8 , wherein the commutation comprises stage 1 and stage 2; 10 . Stage 1 is: ES1 and ES4 in the commutation switch module are turned on, ES2 and ES3 are turned off, and after ES1 and ES4 are turned on, the energy storage capacitor discharges through the oscillating capacitor and oscillating inductance, generating a sinusoidal oscillating current. When the sine oscillating current completes a sine When the half-wave oscillation and the oscillating current reaches the zero-crossing point, the control system sends a control signal, and the execution stage 2: ES1 and ES4 are turned off, ES2 and ES3 are turned on, the polarity of the energy storage capacitor at this time is consistent with the direction of the discharge current, and the energy storage capacitor Continue to discharge through the oscillating capacitor and oscillating inductance, and the amplitude of the generated sinusoidal oscillating current is higher than that of the first sine half-wave. When the second sine half-wave current reaches the zero-crossing point, the control system sends a control signal, and executes stage 1 and subsequent stages 2 alternates with phase 1.

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