A DC circuit breaker and control method based on modular series voltage balancing

Abstract

The present invention discloses a DC circuit breaker and control method based on modular series voltage balancing, comprising: a plurality of circuit breaker submodules and an online monitoring system; the circuit breaker submodules comprise: a main branch, a commutation branch, an energy absorption branch, a control module, a first output terminal and a second output terminal; wherein each of the circuit breaker submodules is sequentially connected in series, and a loop formed after the series connection is connected in series with a first lightning arrester; the first end of the main branch is respectively connected to the first output terminal and the first end of the commutation branch, and the second end of the main branch is respectively connected to the second output terminal and the second end of the commutation branch; the first end of the energy absorption branch is connected to the third end of the commutation branch, and the second end of the energy absorption branch is connected to the second end of the main branch; the control module is respectively connected to a mechanical switch in the main branch, a commutation switch unit in the commutation branch and the online monitoring system.

Description

Technical Field

[0001] The present invention relates to the field of circuit breakers, and in particular to a DC circuit breaker based on modular series voltage balancing and a control method. Background Art

[0002] In order to achieve fault isolation of the DC system, the DC circuit breaker should be able to generate a current zero-crossing point in the faulty DC line, so that the arc can be extinguished between the circuit breaker's breaks, thereby disconnecting the current in the line. During the DC current disconnection process, it should absorb the energy stored in the inductive components of the DC system and the energy injected by the AC system, while suppressing transient disconnection overvoltage and reducing the insulation tolerance level of the system equipment.

[0003] With the substantial increase in demand for distributed DC power supply systems for renewable energy, especially in flexible multi-terminal DC systems connected to renewable energy grids, most loads have the dual attributes of power generation and power consumption, which causes uncertainty in the direction of energy flow in flexible multi-terminal DC grids. Moreover, flexible multi-terminal DC systems connected to renewable energy grids often contain a large number of power electronic devices. Once a fault occurs, it is necessary to cut off the fault current in a very short time to prevent damage to the power electronic devices. However, traditional DC circuit breakers take a long time to absorb the residual system energy and gradually reduce the short-circuit current, and cannot be efficiently disconnected, so they cannot be used in flexible multi-terminal DC systems.

[0004] Therefore, there is an urgent need for a circuit breaker to solve the problem of low breaking efficiency of DC circuit breakers. Summary of the invention

[0005] The embodiment of the present invention provides a DC circuit breaker and a control method based on modular series voltage balancing to improve the breaking efficiency of the DC circuit breaker.

[0006] In order to solve the above problems, an embodiment of the present invention provides a DC circuit breaker based on modular series voltage balancing, comprising: a plurality of circuit breaker submodules, a first lightning arrester and an online monitoring system; the circuit breaker submodule comprises: a main branch, a commutation branch, an energy absorption branch, a control module, a first outlet terminal and a second outlet terminal; wherein each of the circuit breaker submodules is sequentially connected in series, and the loop formed by the series connection is connected in parallel with the first lightning arrester;

[0007] The first end of the main branch is connected to the first outgoing terminal and the first end of the commutation branch respectively, and the second end of the main branch is connected to the second outgoing terminal and the second end of the commutation branch respectively; the first end of the energy absorption branch is connected to the third end of the commutation branch, and the second end of the energy absorption branch is connected to the second end of the main branch;

[0008] The control module is respectively connected to the mechanical switch in the main branch, the commutation switch unit in the commutation branch and the online monitoring system; wherein the commutation switch unit includes: a plurality of power electronic power device modules and a single pre-charged energy storage capacitor; the control module is used to receive data transmitted by the online monitoring system and control the opening and closing of the mechanical switch and the commutation switch unit; the online monitoring system is used to collect data of each circuit breaker sub-module.

[0009] As an improvement of the above solution, the main branch includes: one or more mechanical switches; wherein, if there are several mechanical switches, each of the mechanical switches is connected in series.

[0010] As an improvement of the above solution, the commutation branch includes: a commutation switch unit, an oscillating inductor and an oscillating capacitor;

[0011] The first end of the commutation switch unit is connected to the first end of the oscillation capacitor, and the second end of the commutation switch unit is connected to the second end of the main branch;

[0012] The first end of the oscillating inductor is connected to the first end of the main branch, and the second end of the oscillating inductor is connected to the second end of the oscillating capacitor and the first end of the energy absorbing branch respectively;

[0013] The first end of the commutation branch is the first end of the oscillating inductor, the second end of the commutation branch is the second end of the commutation switch unit, and the first end of the commutation branch is the second end of the oscillating inductor.

[0014] As an improvement of the above solution, the commutation switch unit includes: a first power electronic power device module, a second power electronic power device module, a third power electronic power device module, a fourth power electronic power device module and a pre-charged energy storage capacitor;

[0015] The positive electrode of the first power electronic power device module is respectively connected to the positive electrode of the second power electronic power device module and the first end of the pre-charged energy storage capacitor; the negative electrode of the first power electronic power device module is respectively connected to the positive electrode of the third power electronic power device module and the first end of the oscillation capacitor; the negative electrode of the second power electronic power device module is respectively connected to the positive electrode of the fourth power electronic power device module and the second end of the main branch; the negative electrode of the third power electronic power device module is respectively connected to the negative electrode of the fourth power electronic power device module and the second end of the pre-charged energy storage capacitor;

[0016] The first end of the commutation switch unit is the negative electrode of the first power electronic power device module, and the second end of the commutation switch unit is the negative electrode of the second power electronic power device module.

[0017] As an improvement of the above solution, the energy absorption branch includes: one or more second lightning arresters; wherein, if there are several second lightning arresters, each of the second lightning arresters is connected in series.

[0018] As an improvement of the above solution, the online monitoring system includes: a first current sensor, a second current sensor, a third current sensor, a fourth current sensor, a fifth current sensor, a first voltage sensor, a second voltage sensor, a third voltage sensor, a fourth voltage sensor, a position sensor, a first temperature sensor and a second temperature sensor;

[0019] The control module is respectively connected to the first current sensor, the second current sensor, the third current sensor, the fourth current sensor, the fifth current sensor, the first voltage sensor, the second voltage sensor, the third voltage sensor, the fourth voltage sensor, the position sensor, the first temperature sensor and the second temperature sensor.

[0020] As an improvement of the above scheme, it also includes:

[0021] The first current sensor is used to measure the current of the lead wire corresponding to the first lead terminal in each of the circuit breaker submodules;

[0022] The second current sensor is used to measure the current of the main branch in each of the circuit breaker submodules;

[0023] The third current sensor is used to measure the current of the commutation branch in each of the circuit breaker submodules;

[0024] The fourth current sensor is used to measure the current of the energy absorption branch in each of the circuit breaker submodules;

[0025] The fifth current sensor is used to measure the current of the energy absorption branch externally connected to each of the circuit breaker submodules;

[0026] The first voltage sensor is used to measure the voltage across the mechanical switch in each of the circuit breaker submodules;

[0027] The second voltage sensor is used to measure the voltage across the second lightning arrester in each of the circuit breaker submodules;

[0028] The third voltage sensor is used to measure the voltage across the pre-charged energy storage capacitor;

[0029] The fourth voltage sensor is used to measure the voltage across the first lightning arrester externally connected to each of the circuit breaker submodules;

[0030] The position sensor is used to detect the contact state of the mechanical switch;

[0031] The first temperature sensor is used to measure the temperature of the second lightning arrester in each of the circuit breaker submodules;

[0032] The second temperature sensor is used to measure the temperature of the first lightning arrester externally connected to each of the circuit breaker sub-modules.

[0033] As an improvement of the above solution, the online monitoring system further includes: a sound measuring device, an X-ray measuring device and a magnetic field measuring device.

[0034] Correspondingly, an embodiment of the present invention further provides a control method of a DC circuit breaker based on modular series voltage balancing, which is applied to a control module of each circuit breaker submodule in the DC circuit breaker according to the present invention. The control method includes:

[0035] Obtaining a tripping instruction; wherein, before obtaining the tripping instruction, current flows into the first outlet terminal, passes through the mechanical switch, and flows out from the second outlet terminal;

[0036] According to the opening instruction, controlling the mechanical switch contacts to separate;

[0037] receiving a switch voltage across the mechanical switch transmitted by an online monitoring system;

[0038] When the switch voltage is greater than the first preset voltage, the commutation switch module is turned on to receive the oscillating current of the commutation branch transmitted by the online monitoring system, and the commutation operation is repeatedly performed according to the oscillating current until the fault arc current value of the mechanical switch reaches the current zero point, then the commutation operation is stopped, and energy absorption inside the circuit breaker submodule is performed by controlling the oscillation capacitor and the lightning arrester.

[0039] As an improvement of the above solution, the commutation operation includes:

[0040] After the current oscillating current reaches the current zero-crossing point, the total number of times the oscillating current of the commutation branch reaches the current zero-crossing point is obtained, and the total number is judged;

[0041] If it is an odd number, the commutation branch is switched to the first commutation state, and the first commutation state is maintained to re-execute the commutation operation; wherein the first commutation state includes: turning on the first power electronic power device module and the fourth power electronic power device module, and turning off the second power electronic power device module and the third power electronic power device module;

[0042] If it is an even number, the commutation branch switches to the second commutation state and maintains the second commutation state to re-execute the commutation operation; wherein the second commutation state includes: turning off the first power electronic power device module and the fourth power electronic power device module, and turning on the second power electronic power device module and the third power electronic power device module.

[0043] As can be seen from the above, the present invention has the following beneficial effects:

[0044] The present invention provides a DC circuit breaker based on modular series voltage balancing, comprising: a plurality of circuit breaker submodules and an online monitoring system; the circuit breaker submodules comprise: a main branch, a commutation branch, an energy absorption branch, a control module, a first outlet terminal and a second outlet terminal; wherein each of the circuit breaker submodules are sequentially connected in series, and a loop formed after the series connection is connected in series with a first lightning arrester; the first end of the main branch is respectively connected to the first outlet terminal and the first end of the commutation branch, and the second end of the main branch is respectively connected to the second outlet terminal and the second end of the commutation branch; the energy absorption branch The first end of the commutation branch is connected to the third end of the commutation branch, and the second end of the energy absorption branch is connected to the second end of the main branch; the control module is respectively connected to the mechanical switch in the main branch, the commutation switch unit in the commutation branch and the online monitoring system; wherein the commutation switch unit includes: a plurality of power electronic power device modules and a single pre-charged energy storage capacitor; the control module is used to receive the data transmitted by the online monitoring system, and control the opening and closing of the mechanical switch and the commutation switch unit; the online monitoring system is used to collect data of each circuit breaker submodule. The present invention realizes fast switching in the commutation operation performed by the power electronic power device through the series connection between each circuit breaker submodule and the coordination between the internal and external lightning arresters of the submodule, combined with the commutation switch unit composed of a plurality of power electronic power device modules and a single pre-charged energy storage capacitor, and improves the overall withstand voltage level of the circuit breaker, and can limit the overvoltage on each module and realize the redundancy of the circuit breaker protection, thereby ensuring that the DC circuit breaker can quickly and reliably cut off the fault, improve the breaking efficiency of the DC circuit breaker, and thus improve the reliability and stability of the power system. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 It is a structural schematic diagram of a DC circuit breaker based on modular series voltage balancing provided by an embodiment of the present invention;

[0046] Figure 2 It is a flow chart of a control method of a DC circuit breaker based on modular series voltage balancing provided by an embodiment of the present invention;

[0047] Figure 3 is a schematic diagram of the installation position of the sensor in the circuit breaker submodule provided by an embodiment of the present invention;

[0048] Figure 4 It is a schematic diagram of the installation position of the sensor outside the circuit breaker submodule provided by an embodiment of the present invention;

[0049] Figure 5 It is a schematic diagram of the installation position of a modular series voltage-sharing DC circuit breaker formed by different series connection methods and a current sensor for measuring the current state of an external energy absorption branch of a sub-module provided by another embodiment of the present invention. DETAILED DESCRIPTION

[0050] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0051] Embodiment 1

[0052] See also Figure 1 , Figure 1 1 is a schematic diagram of a DC circuit breaker based on modular series voltage balancing provided by an embodiment of the present invention, comprising: a plurality of circuit breaker submodules 101, a first lightning arrester 102 and an online monitoring system 103; the circuit breaker submodule comprises: a main branch 1011, a commutation branch 1012, an energy absorption branch 1013, a control module 1014, a first outlet terminal L 2k-1 and the second outlet terminal L 2k ; Each of the circuit breaker submodules is connected in series in sequence, and the loop formed by the series connection is connected in parallel with the first lightning arrester;

[0053] The first end of the main branch is connected to the first outgoing terminal and the first end of the commutation branch respectively, and the second end of the main branch is connected to the second outgoing terminal and the second end of the commutation branch respectively; the first end of the energy absorption branch is connected to the third end of the commutation branch, and the second end of the energy absorption branch is connected to the second end of the main branch;

[0054] The control module is respectively connected to the mechanical switch in the main branch, the commutation switch unit in the commutation branch and the online monitoring system; wherein the commutation switch unit includes: a plurality of power electronic power device modules and a single pre-charged energy storage capacitor; the control module is used to receive data transmitted by the online monitoring system and control the opening and closing of the mechanical switch and the commutation switch unit; the online monitoring system is used to collect data of each circuit breaker sub-module.

[0055] In a specific embodiment, the control module is connected to the mechanical switch in the main branch, the commutation switch unit in the commutation branch and the online monitoring system by wireless connection.

[0056] In a specific embodiment, the online monitoring system is connected to the plurality of circuit breaker submodules and the first lightning arrester in a wireless manner.

[0057] In a specific embodiment, the online monitoring system is used to measure the current and current direction flowing through the commutation switch module, the current and current direction flowing through the commutation branch, the current and current direction flowing through the energy absorption branch, the voltage and switch stroke at both ends of the main branch mechanical switch, the voltage and temperature of the energy absorption branch lightning arrester, and the voltage at both ends of the energy storage capacitor.

[0058] As an improvement of the above solution, the main branch includes: one or more mechanical switches CB; wherein, if there are several mechanical switches, each of the mechanical switches is connected in series.

[0059] In a specific embodiment, the mechanical switch may be an explosion-driven mechanical switch, an electromagnetic repulsion-driven mechanical switch, a permanent magnet repulsion-driven mechanical switch, a spring-operated mechanism-driven mechanical switch, or a motor-driven mechanical switch.

[0060] For better explanation, the mechanical switch can realize fast disconnection and closing actions upon receiving the control signal. When multiple mechanical switches are connected in series, dynamic and static voltage equalizing devices are installed as needed. The time error of synchronous action of multiple mechanical switches should be less than 50 microseconds. After receiving the disconnection signal, it can provide sufficient withstand voltage level within the specified time.

[0061] As an improvement of the above solution, the commutation branch includes: a commutation switch unit, an oscillating inductor L and an oscillating capacitor C;

[0062] The first end of the commutation switch unit is connected to the first end of the oscillation capacitor, and the second end of the commutation switch unit is connected to the second end of the main branch;

[0063] The first end of the oscillating inductor is connected to the first end of the main branch, and the second end of the oscillating inductor is connected to the second end of the oscillating capacitor and the first end of the energy absorbing branch respectively;

[0064] The first end of the commutation branch is the first end of the oscillating inductor, the second end of the commutation branch is the second end of the commutation switch unit, and the first end of the commutation branch is the second end of the oscillating inductor.

[0065] As an improvement of the above solution, the commutation switch unit includes: a first power electronic power device module ES1, a second power electronic power device module ES2, a third power electronic power device module ES3, a fourth power electronic power device module ES4 and a pre-charged energy storage capacitor C DC ;

[0066] The positive electrode of the first power electronic power device module is respectively connected to the positive electrode of the second power electronic power device module and the first end of the pre-charged energy storage capacitor; the negative electrode of the first power electronic power device module is respectively connected to the positive electrode of the third power electronic power device module and the first end of the oscillation capacitor; the negative electrode of the second power electronic power device module is respectively connected to the positive electrode of the fourth power electronic power device module and the second end of the main branch; the negative electrode of the third power electronic power device module is respectively connected to the negative electrode of the fourth power electronic power device module and the second end of the pre-charged energy storage capacitor;

[0067] The first end of the commutation switch unit is the negative electrode of the first power electronic power device module, and the second end of the commutation switch unit is the negative electrode of the second power electronic power device module.

[0068] In a specific embodiment, each power electronic device module includes m fully-controlled power electronic devices, m≥1; the fully-controlled power electronic devices are the following single devices or a series-parallel combination of multiple devices, including GTO, thyristor, MOSFET, IGBT, IGCT.

[0069] In this embodiment, the positive electrode of the first power electronic power device module ES1 and the positive electrode of the second power electronic power device module ES2 are connected to form an output terminal L3, and the negative electrode of the third power electronic power device module ES3 and the negative electrode of the fourth power electronic power device module ES4 are connected to form an output terminal L4; the negative electrode of the second power electronic power device module ES2 and the positive electrode of the fourth power electronic power device module ES4 are connected to form the output terminal L6 of the converter switch, and the output terminal L6 of the converter switch is connected to the output terminal L2k; the negative electrode of the first power electronic power device module ES1 and the positive electrode of the third power electronic power device module ES3 are connected to form the output terminal L5 of the converter switch, and the output terminal L5 of the converter switch is connected to one end of the oscillation capacitor C; the output terminal L3 is connected to one end of the pre-charged energy storage capacitor, and the output terminal L4 is connected to the other end of the pre-charged energy storage capacitor; the charging direction of the pre-charged energy storage capacitor is the same as or opposite to the direction of the main branch current.

[0070] As an improvement of the above solution, the energy absorption branch includes: one or more second lightning arresters MOV; wherein, if there are more than one second lightning arresters, each of the second lightning arresters is connected in series.

[0071] In a specific embodiment, the sum of the operating voltages of the second lightning arresters in each circuit breaker submodule is higher than the operating voltage of the first lightning arrester connected in series with the circuit breaker submodule, so that most of the energy generated by the current interruption is absorbed by the first lightning arrester, and the design of the circuit breaker submodule is not affected by the energy level required by the second lightning arrester. And by selecting the energy level of the second lightning arrester of the energy absorption branch, the n-1 submodule can successfully operate as a complete circuit breaker, which can limit the overvoltage on each module when the system interrupts the current, protect each submodule, absorb the current energy in the system, and realize the inherent redundancy in the design.

[0072] In a specific embodiment, the lightning arrester is specifically formed by the following single devices or multiple devices connected in series and parallel, including metal oxide lightning arresters, gas insulated metal oxide lightning arresters, porcelain shell insulated metal oxide lightning arresters, and gapless metal oxide lightning arresters; the action voltage of the lightning arrester of the external energy absorption branch is 1.5 to 1.6 times the rated voltage of the system, and the action voltage of the lightning arrester of the internal energy absorption branch is higher than the action voltage of the internal lightning arrester, so that most of the energy generated by the current interruption is absorbed by the external lightning arrester, and the design of the module is not affected by the energy level required by the internal lightning arrester.

[0073] As an improvement of the above solution, the online monitoring system includes: a first current sensor D1 k , the second current sensor D2 k , the third current sensor D3 k , the fourth current sensor D4 k 、Fifth current sensor D5 k , first voltage sensor V1 k , the second voltage sensor V2 k , the third voltage sensor V3 k , the fourth voltage sensor V4 k 、Position sensor W1 k , the first temperature sensor T1 k and the second temperature sensor T2 k ;

[0074] The control module is respectively connected to the first current sensor, the second current sensor, the third current sensor, the fourth current sensor, the fifth current sensor, the first voltage sensor, the second voltage sensor, the third voltage sensor, the fourth voltage sensor, the position sensor, the first temperature sensor and the second temperature sensor.

[0075] In a specific embodiment, to better illustrate the configuration of the online monitoring system, see Figure 3 and Figure 4 ;

[0076] Figure 3 The distribution position relationship of the components of the online monitoring system inside the circuit breaker submodule; Figure 4 It is the distribution position relationship of the components of the online monitoring system outside several circuit breaker sub-modules and in the circuit where several circuit breaker sub-modules are connected in series.

[0077] Accordingly, see Figure 5 , Figure 5 A schematic diagram of the installation position of a modular series voltage-equalizing DC circuit breaker formed by another series connection mode of each circuit breaker sub-module and a current sensor for measuring the current state of the external energy absorption branch of the sub-module is provided. The diagram is simplified for the convenience of representation. Multiple first lightning arresters are respectively connected to the two output terminals L2k and L2k-1 of each sub-module. The first lightning arrester is composed of one or more lightning arresters according to actual needs. The total operating voltage of the branch where the first lightning arrester is located is 1.5 to 1.6 times the rated voltage of the system, which can absorb most of the energy during the short circuit process.

[0078] As an improvement of the above scheme, it also includes:

[0079] The first current sensor is used to measure the current of the lead wire corresponding to the first lead terminal in each of the circuit breaker submodules;

[0080] The second current sensor is used to measure the current of the main branch in each of the circuit breaker submodules;

[0081] The third current sensor is used to measure the current of the commutation branch in each of the circuit breaker submodules;

[0082] The fourth current sensor is used to measure the current of the energy absorption branch in each of the circuit breaker submodules;

[0083] The fifth current sensor is used to measure the current of the energy absorption branch externally connected to each of the circuit breaker submodules;

[0084] The first voltage sensor is used to measure the voltage across the mechanical switch in each of the circuit breaker submodules;

[0085] The second voltage sensor is used to measure the voltage across the second lightning arrester in each of the circuit breaker submodules;

[0086] The third voltage sensor is used to measure the voltage across the pre-charged energy storage capacitor;

[0087] The fourth voltage sensor is used to measure the voltage across the first lightning arrester externally connected to each of the circuit breaker submodules;

[0088] The position sensor is used to detect the contact state of the mechanical switch;

[0089] The first temperature sensor is used to measure the temperature of the second lightning arrester in each of the circuit breaker submodules;

[0090] The second temperature sensor is used to measure the temperature of the first lightning arrester externally connected to each of the circuit breaker sub-modules.

[0091] As an improvement of the above solution, the online monitoring system further includes: a sound measuring device, an X-ray measuring device and a magnetic field measuring device.

[0092] See also Figure 2 , Figure 2 FIG. 1 is a flow chart of a control method of a DC circuit breaker based on modular series voltage balancing provided by an embodiment of the present invention. Figure 2 As shown, this embodiment includes steps 201 to 204, and each step is specifically as follows:

[0093] Step 201: Obtain a tripping instruction; wherein, before obtaining the tripping instruction, current flows in from the first outlet terminal, passes through the mechanical switch, and flows out from the second outlet terminal.

[0094] In this embodiment, the opening instruction is generated by receiving a user operation; the opening instruction may also be automatically generated when a circuit short circuit is detected.

[0095] Step 202: Control the mechanical switch contacts to separate according to the opening instruction.

[0096] In this embodiment, after receiving the opening command, the mechanical switch starts opening and arcing after a certain delay.

[0097] Step 203: Receive the switch voltage across the mechanical switch transmitted by the online monitoring system.

[0098] In this embodiment, when the opening time of the mechanical switch reaches a certain time or the opening distance of the electrode contacts reaches a certain distance, the switch voltage at both ends of the mechanical switch is monitored by the online monitoring system.

[0099] Step 204: When the switch voltage is greater than the first preset voltage, the commutation switch module is turned on to receive the oscillating current of the commutation branch transmitted by the online monitoring system, and the commutation operation is repeatedly performed according to the oscillating current until the fault arc current value of the mechanical switch reaches the current zero point, then the commutation operation is stopped, and the energy inside the circuit breaker submodule is absorbed by controlling the oscillation capacitor and the lightning arrester.

[0100] In this embodiment, after the voltage between the contacts reaches a sufficient withstand voltage level (the voltage corresponding to the withstand voltage level is the first preset voltage described in the present invention, which can be adjusted by the user), the control module triggers the commutation switch module, the commutation switch unit is triggered to turn on, and the energy storage capacitor discharges through the oscillation capacitor C and the oscillation inductor L to generate an oscillating current. The online monitoring system detects the zero crossing point of the oscillating current. The control module controls the commutation switch module to alternately perform commutation operations at each zero crossing point of the oscillating current. The amplitude of the oscillating current increases once every half sinusoidal oscillation cycle until it is superimposed with the current arc in the mechanical switch CB of the main branch to generate a zero crossing point, and the arc in the main mechanical switch CB is extinguished;

[0101] The arc in the mechanical switch CB is extinguished and stops conducting. The system current is transferred to the branch where the commutation switch module is located, and the capacitor in the commutation branch is charged. The voltage across the oscillation capacitor C rises rapidly until the capacitor voltage in the branch reaches the action voltage of the external energy absorption branch arrester connected in parallel with it. The arrester acts and starts to conduct current. The system current is transferred to the energy absorption branch where the external arrester is located. At this stage, the internal arrester will also absorb a small amount of energy. As the energy is gradually absorbed, the current in the system gradually decreases until it drops to 0, completing the current interruption.

[0102] As an improvement of the above solution, the commutation operation includes:

[0103] After the current oscillating current reaches the current zero-crossing point, the total number of times the oscillating current of the commutation branch reaches the current zero-crossing point is obtained, and the total number is judged;

[0104] If it is an odd number, the commutation branch is switched to the first commutation state, and the first commutation state is maintained to re-execute the commutation operation; wherein the first commutation state includes: turning on the first power electronic power device module and the fourth power electronic power device module, and turning off the second power electronic power device module and the third power electronic power device module;

[0105] If it is an even number, the commutation branch switches to the second commutation state and maintains the second commutation state to re-execute the commutation operation; wherein the second commutation state includes: turning off the first power electronic power device module and the fourth power electronic power device module, and turning on the second power electronic power device module and the third power electronic power device module.

[0106] In a specific embodiment, the commutation operation includes: commutation step 1 and commutation step 2:

[0107] The commutation step 1 is as follows: the first power electronic power device module ES1 and the fourth power electronic power device module ES4 are turned on, and the second power electronic power device module ES2 and the third power electronic power device module ES3 are turned off; after the first power electronic power device module ES1 and the fourth power electronic power device module ES4 are turned on, the pre-charge capacitor discharges the oscillation capacitor and the oscillation inductor through the turned-on commutation switch unit to generate a sinusoidal oscillation current, and according to the signal of the online monitoring system, when the sinusoidal oscillation current completes a sinusoidal half-wave oscillation and the oscillation current reaches the zero crossing point, the control system sends a control signal to execute the commutation step 2;

[0108] Commutation step 2 is: the first power electronic power device module ES1 and the fourth power electronic power device module ES4 are turned off, and the second power electronic power device module ES2 and the third power electronic power device module ES3 are turned on. At this time, the polarity of the pre-charge capacitor is consistent with the current direction of the oscillating current in the branch, and the pre-charge capacitor continues to discharge the oscillation capacitor and the oscillation inductor. The amplitude of the generated sinusoidal oscillation current is higher than that of the first sinusoidal half-wave. According to the signal of the online monitoring system, when the second sinusoidal half-wave current reaches the zero point, the control system sends a control signal to execute commutation step 1; then, when each sinusoidal half-wave current reaches the zero point, commutation step 2 is executed alternately with commutation step 1.

[0109] In addition, this embodiment can also realize fast reclosing, specifically including: for permanent faults, after the fault current is disconnected, wait for a set time, turn on the disconnecting unit, detect the fault current again, and turn off the disconnecting unit again to isolate the fault line; for temporary faults, no fault current is detected after turning on the disconnecting unit, close the main branch mechanical switch to reset the DC circuit breaker and wait for the next operation.

[0110] This embodiment provides a modular series voltage-equalizing DC circuit breaker. Compared with the traditional current injection type mechanical DC circuit breaker, the current injection branch needs to be equipped with a large capacitor, and the pre-charge voltage of the capacitor is relatively high, which leads to an increase in the cost of the capacitor and the cost of the charging circuit. The self-excited oscillation type mechanical circuit breaker requires the arc to have good negative resistance characteristics, and has high design requirements for mechanical switches. Long-term arcing will also reduce the life and increase maintenance problems. The DC circuit breaker of the present invention accelerates the development of the oscillating current by using power electronic devices to assist the oscillation, and can generate multiple artificial current zero crossings, which can cut off the circuit in a short time, isolate faults, and protect the flexible DC system.

[0111] In addition, this embodiment sets a main branch composed of mechanical switches, and the mechanical switches are driven by a fast operating mechanism. The energy stored in the fast operating mechanism can ensure that the mechanical switch can continuously perform opening-closing-opening-closing operations during the fault current breaking and reclosing process, and the opening time is several milliseconds. During normal operation, the rated current can be conducted by the main branch mechanical switch, and the conduction loss of the DC circuit breaker during operation is extremely low, without obvious heat and power loss. In addition, the series connection between the sub-modules improves the overall withstand voltage of the circuit breaker, and can be better used in high-voltage direct current transmission systems. Through the series connection between the various circuit breaker modules and the cooperation between the internal and external lightning arresters, the overvoltage on each module can be limited and the redundancy of the circuit breaker protection can be achieved. Thereby ensuring that the DC circuit breaker can quickly and reliably cut off the fault, and improving the reliability and stability of the power system.

[0112] The above is a preferred embodiment of the present invention. It should be pointed out that a person skilled in the art can make several improvements and modifications without departing from the principle of the present invention. These improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A DC circuit breaker based on modular series voltage balancing, It is characterized in that include: Several circuit breaker submodules, the first lightning arrester and an online monitoring system; The circuit breaker submodule comprises: a main branch, a commutation branch, an energy absorption branch, a control module, a first outlet terminal and a second outlet terminal; wherein each of the circuit breaker submodules is connected in series in sequence, and the loop formed by the series connection is connected in parallel with the first lightning arrester; The first end of the main branch is connected to the first outgoing terminal and the first end of the commutation branch respectively, and the second end of the main branch is connected to the second outgoing terminal and the second end of the commutation branch respectively; the first end of the energy absorption branch is connected to the third end of the commutation branch, and the second end of the energy absorption branch is connected to the second end of the main branch; The control module is respectively connected to the mechanical switch in the main branch, the commutation switch unit in the commutation branch and the online monitoring system; wherein the commutation switch unit includes: a plurality of power electronic power device modules and a single pre-charged energy storage capacitor; the control module is used to receive data transmitted by the online monitoring system, and control the opening and closing of the mechanical switch and the commutation switch unit; the online monitoring system is used to collect data of each circuit breaker submodule; the control module applies the following control method: Obtaining a tripping instruction; wherein, before obtaining the tripping instruction, current flows into the first outlet terminal, passes through the mechanical switch, and flows out from the second outlet terminal; According to the opening instruction, controlling the mechanical switch contacts to separate; receiving a switch voltage across the mechanical switch transmitted by an online monitoring system; When the switch voltage is greater than the first preset voltage, the commutation switch module is turned on, the oscillating current of the commutation branch transmitted by the online monitoring system is received, and the commutation operation is repeatedly performed according to the oscillating current until the fault arc current value of the mechanical switch reaches the current zero point, the commutation operation is stopped, and the energy inside the circuit breaker submodule is absorbed by controlling the oscillation capacitor and the lightning arrester; wherein the commutation operation includes: after the current oscillation current reaches the current zero point, the total number of times the oscillation current of the commutation branch reaches the current zero point is obtained, and the total number is judged; if it is an odd number, the commutation branch is switched to the commutation branch; The first state of commutation is switched to the first state of commutation, and the commutation operation is re-executed by maintaining the first state of commutation; wherein the first state of commutation includes: turning on the first power electronic power device module and the fourth power electronic power device module, and turning off the second power electronic power device module and the third power electronic power device module; if it is an even number, the commutation branch is switched to the second state of commutation, and the commutation operation is re-executed by maintaining the second state of commutation; wherein the second state of commutation includes: turning off the first power electronic power device module and the fourth power electronic power device module, and turning on the second power electronic power device module and the third power electronic power device module; The sum of the operating voltages of the second lightning arresters in each circuit breaker submodule is higher than the operating voltage of the first lightning arrester connected in series with the circuit breaker submodule.

2. The DC circuit breaker based on modular series voltage balancing according to claim 1, It is characterized in that The main branch includes: one or more mechanical switches; wherein, if there are several mechanical switches, each of the mechanical switches is connected in series.

3. The DC circuit breaker based on modular series voltage balancing according to claim 1, It is characterized in that The commutation branch comprises: a commutation switch unit, an oscillating inductor and an oscillating capacitor; The first end of the commutation switch unit is connected to the first end of the oscillation capacitor, and the second end of the commutation switch unit is connected to the second end of the main branch; The first end of the oscillating inductor is connected to the first end of the main branch, and the second end of the oscillating inductor is connected to the second end of the oscillating capacitor and the first end of the energy absorbing branch respectively; The first end of the commutation branch is the first end of the oscillating inductor, the second end of the commutation branch is the second end of the commutation switch unit, and the third end of the commutation branch is the second end of the oscillating inductor.

4. The DC circuit breaker based on modular series voltage balancing according to claim 3, It is characterized in that The commutation switch unit comprises: a first power electronic power device module, a second power electronic power device module, a third power electronic power device module, a fourth power electronic power device module and a pre-charged energy storage capacitor; The positive electrode of the first power electronic power device module is respectively connected to the positive electrode of the second power electronic power device module and the first end of the pre-charged energy storage capacitor; the negative electrode of the first power electronic power device module is respectively connected to the positive electrode of the third power electronic power device module and the first end of the oscillation capacitor; the negative electrode of the second power electronic power device module is respectively connected to the positive electrode of the fourth power electronic power device module and the second end of the main branch; the negative electrode of the third power electronic power device module is respectively connected to the negative electrode of the fourth power electronic power device module and the second end of the pre-charged energy storage capacitor; The first end of the commutation switch unit is the negative electrode of the first power electronic power device module, and the second end of the commutation switch unit is the negative electrode of the second power electronic power device module.

5. The DC circuit breaker based on modular series voltage balancing according to claim 1, It is characterized in that The energy absorption branch includes: one or more second lightning arresters; wherein, if there are more than one second lightning arresters, each of the second lightning arresters is connected in series.

6. The DC circuit breaker based on modular series voltage balancing according to claim 1, It is characterized in that The online monitoring system comprises: a first current sensor, a second current sensor, a third current sensor, a fourth current sensor, a fifth current sensor, a first voltage sensor, a second voltage sensor, a third voltage sensor, a fourth voltage sensor, a position sensor, a first temperature sensor and a second temperature sensor; The control module is respectively connected to the first current sensor, the second current sensor, the third current sensor, the fourth current sensor, the fifth current sensor, the first voltage sensor, the second voltage sensor, the third voltage sensor, the fourth voltage sensor, the position sensor, the first temperature sensor and the second temperature sensor.

7. The DC circuit breaker based on modular series voltage balancing according to claim 6, It is characterized in that Also includes: The first current sensor is used to measure the current of the lead wire corresponding to the first lead terminal in each of the circuit breaker submodules; The second current sensor is used to measure the current of the main branch in each of the circuit breaker submodules; The third current sensor is used to measure the current of the commutation branch in each of the circuit breaker submodules; The fourth current sensor is used to measure the current of the energy absorption branch in each of the circuit breaker submodules; The fifth current sensor is used to measure the current of the energy absorption branch externally connected to each of the circuit breaker submodules; The first voltage sensor is used to measure the voltage across the mechanical switch in each of the circuit breaker submodules; The second voltage sensor is used to measure the voltage across the second lightning arrester in each of the circuit breaker submodules; The third voltage sensor is used to measure the voltage across the pre-charged energy storage capacitor; The fourth voltage sensor is used to measure the voltage across the first lightning arrester externally connected to each of the circuit breaker submodules; The position sensor is used to detect the contact state of the mechanical switch; The first temperature sensor is used to measure the temperature of the second lightning arrester in each of the circuit breaker submodules; The second temperature sensor is used to measure the temperature of the first lightning arrester externally connected to each of the circuit breaker sub-modules.

8. The DC circuit breaker based on modular series voltage balancing according to claim 1, It is characterized in that The online monitoring system also includes: a sound measuring device, an X-ray measuring device and a magnetic field measuring device.

9. A control method for a DC circuit breaker based on modular series voltage balancing. It is characterized in that A control module applied to each circuit breaker submodule in a DC circuit breaker according to any one of claims 1 to 8, wherein the control method comprises: Obtaining a tripping instruction; wherein, before obtaining the tripping instruction, current flows into the first outlet terminal, passes through the mechanical switch, and flows out from the second outlet terminal; According to the opening instruction, controlling the mechanical switch contacts to separate; receiving a switch voltage across the mechanical switch transmitted by an online monitoring system; When the switch voltage is greater than the first preset voltage, the commutation switch module is turned on, the oscillating current of the commutation branch transmitted by the online monitoring system is received, and the commutation operation is repeatedly performed according to the oscillating current until the fault arc current value of the mechanical switch reaches the current zero point, the commutation operation is stopped, and the energy inside the circuit breaker submodule is absorbed by controlling the oscillation capacitor and the lightning arrester; wherein the commutation operation includes: after the current oscillation current reaches the current zero point, the total number of times the oscillation current of the commutation branch reaches the current zero point is obtained, and the total number is judged; if it is an odd number, the commutation branch is switched to the commutation branch; The commutation branch switches to the first commutation state, and maintains the first commutation state to re-execute the commutation operation; wherein, the first commutation state includes: turning on the first power electronic power device module and the fourth power electronic power device module, and turning off the second power electronic power device module and the third power electronic power device module; if it is an even number, the commutation branch switches to the second commutation state, and maintains the second commutation state to re-execute the commutation operation; wherein, the second commutation state includes: turning off the first power electronic power device module and the fourth power electronic power device module, and turning on the second power electronic power device module and the third power electronic power device module.

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