DC circuit breaker and control method thereof

Abstract

The invention provides a direct-current circuit breaker and a control method thereof, and relates to the technical field of high-voltage flexible direct-current transmission and distribution power grids. The direct-current circuit breaker comprises a main branch which is used for being switched on after responding to a normal working signal of a direct-current system and bearing direct current provided by the direct-current system; a high-speed switch in the commutation branch is used for being closed after responding to a normal working signal, and a closing switch of the charging branch is used for being disconnected after the high-speed switch is closed, so that direct current passes through the main branch and the charging branch to charge the capacitor; the high-speed switch is further used for being disconnected after the voltage of the capacitor reaches the preset charging voltage, and the closing switch is used for being connected after responding to a fault signal of the direct current system so as to transfer the direct current to the current conversion branch. According to the invention, rapid, safe and efficient charging of the capacitor is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high-voltage flexible direct current transmission and distribution network, and particularly relates to a direct current circuit breaker and a control method thereof. BACKGROUND

[0002] Flexible interconnection of power grids is the key to realizing grid-connected power generation of new energy. In this process, the direct current circuit breaker plays a crucial role. However, there is still a technical bottleneck in the direct current circuit breaker of the flexible direct current transmission system, which brings complexity to fault isolation and grid networking operation. The mechanical direct current circuit breaker is becoming a research hotspot of direct current networking circuit breakers due to its simple structure, low loss, controllable cost and other advantages.

[0003] At present, the mechanical direct current circuit breaker usually relies on an external large-capacitance device to charge the capacitance when coping with the high-frequency oscillation current demand in fault breaking. However, this external large-capacitance charging method will cause high peak charging current and long charging time. SUMMARY

[0004] The present application provides a direct current circuit breaker and a control method thereof, which realizes fast, safe and efficient charging of the capacitance, provides sufficient energy reserve for subsequent fault breaking, and thus better meets the high-frequency oscillation current demand in fault breaking.

[0005] In a first aspect, the present application provides a direct current circuit breaker, comprising: a main branch, a commutation branch and a charging branch; wherein,

[0006] The main branch comprises a mechanical switch connected in series between a direct current system and a load side, and is used to conduct in response to a normal working signal of the direct current system and carry a direct current provided by the direct current system;

[0007] The commutation branch comprises a closing switch and a capacitance connected in series, a first end of the closing switch is connected with a valve hall side of the direct current system, and a second end of the closing switch is connected with the charging branch and the capacitance respectively;

[0008] The charging branch comprises a series circuit of a high-speed switch and a charging resistor, a first end of the high-speed switch is connected with the second end of the closing switch, and a second end of the high-speed switch is connected to ground through the charging resistor;

[0009] The high-speed switch is used to close in response to the normal working signal, and the closing switch is used to open after the high-speed switch is closed, so that the direct current charges the capacitance through the main branch and the charging branch;

[0010] The high-speed switch is also used to open when the voltage of the capacitance reaches a preset charging voltage, and the closing switch is used to conduct in response to a fault signal of the direct current system, so as to transfer the direct current to the commutation branch.

[0011] In a possible implementation, the commutation branch further comprises: an inductor connected in series with the capacitor, one end of the inductor being connected with the capacitor, and the other end of the inductor being connected with the load side;

[0012] The inductor and the capacitor are used to generate resonance after the closing switch is turned on, to form an oscillating current opposite to the direction of the direct current, so as to make the current of the main branch zero and be disconnected.

[0013] In a possible implementation, the inductor is a variable inductor, and the variable inductor is used to dynamically adjust the inductance value through a mechanical adjustment mechanism or an electronic switch array, so as to dynamically adjust the frequency of resonance.

[0014] In a possible implementation, the circuit further comprises: an energy dissipation branch connected in parallel with the commutation branch, the energy dissipation branch comprising a lightning arrester, used to absorb residual energy after the polarity of the capacitor is reversed.

[0015] In a possible implementation, the circuit further comprises: a smoothing reactor connected in series between the main branch and the load side, used to form a freewheeling loop with the commutation branch and the load side when the main branch is disconnected, so as to smooth the current change in the commutation branch.

[0016] In a possible implementation, the high-speed switch is at least one of a gate-cutoff thyristor, a power transistor, and an insulated gate bipolar transistor.

[0017] In a possible implementation, the circuit further comprises:

[0018] a voltage detection unit, used to detect a voltage value of the capacitor;

[0019] a control unit, connected with the voltage detection unit, the mechanical switch, the closing switch, and the high-speed switch, and used to: control the high-speed switch to be disconnected when it is detected that the voltage of the capacitor reaches a preset charging voltage; and control the mechanical switch to be opened and the closing switch to be turned on when a fault signal is detected.

[0020] In a possible implementation, the control unit is further used to:

[0021] determine whether the fault type is a transient fault or a permanent fault after the main branch is disconnected;

[0022] if the fault type is the permanent fault, control the mechanical switch to be closed and the high-speed switch to be turned on, so that the capacitor is reversely charged to a polarity opposite to that when the fault is disconnected;

[0023] if the fault type is the transient fault, control the mechanical switch to be closed and the high-speed switch to be turned on, so that the capacitor is forwardly charged.

[0024] In a possible implementation, the control unit is further used to:

[0025] After the capacitor is charged, if it is a permanent fault, the high-speed switch is turned off, the mechanical switch is opened, and the closing switch is turned on, so as to realize re-breaking;

[0026] If it is a transient fault, after the capacitor is charged to the system voltage of the DC system, the high-speed switch is turned off, and normal operation is restored.

[0027] In a second aspect, the application provides a control method of a DC circuit breaker, applied to the first aspect and / or various possible implementation manners of the first aspect, the control method comprising:

[0028] In response to a normal working signal of the DC system, the mechanical switch of the main branch in the DC circuit breaker is turned on to carry the DC current provided by the DC system;

[0029] After the normal working signal is responded to, the high-speed switch of the charging branch in the DC circuit breaker is closed;

[0030] After the high-speed switch is closed, the closing switch of the commutation branch in the DC circuit breaker is opened, so that the DC current charges the capacitor through the main branch and the charging branch;

[0031] After the voltage of the capacitor reaches a preset charging voltage, the closing switch is turned on in response to a fault signal of the DC system, so as to transfer the DC current to the commutation branch.

[0032] In a third aspect, the application provides an electronic device, comprising a memory and a processor.

[0033] The memory stores computer execution instructions;

[0034] The processor executes the computer execution instructions stored in the memory, so that the processor executes the first aspect and / or various possible implementation manners of the first aspect.

[0035] In a fourth aspect, the application provides a computer readable storage medium, which stores computer execution instructions, and the computer execution instructions are used to implement the first aspect and / or various possible implementation manners of the first aspect when executed.

[0036] In a fifth aspect, the application provides a computer program product, comprising a computer program, which is used to implement the first aspect and / or various possible implementation manners of the first aspect when executed.

[0037] The direct current circuit breaker and the control method thereof provided by the application relate to the technical field of high-voltage flexible direct current transmission and distribution networks. The direct current circuit breaker comprises a main branch, a commutation branch and a charging branch. The main branch comprises a mechanical switch connected in series between a direct current system and a load side, and is used for conducting in response to a normal working signal of the direct current system and carrying a direct current provided by the direct current system. The commutation branch comprises a closing switch and a capacitor connected in series, a first end of the closing switch is connected to a valve hall side of the direct current system, and a second end of the closing switch is connected to the charging branch and the capacitor respectively. The charging branch comprises a series circuit of a high-speed switch and a charging resistor, a first end of the high-speed switch is connected to the second end of the closing switch, and the high-speed switch is grounded through the charging resistor. The high-speed switch is used for closing in response to the normal working signal, and the closing switch is used for opening after the high-speed switch is closed, so that the direct current charges the capacitor through the main branch and the charging branch. The high-speed switch is also used for opening after the voltage of the capacitor reaches a preset charging voltage, and the closing switch is used for conducting in response to a fault signal of the direct current system, so as to transfer the direct current to the commutation branch. After receiving the normal working signal of the direct current system, the application first conducts the main branch connected in series between the direct current system and the load side, so as to carry the direct current and prepare for subsequent fault breaking and energy storage. Then, the high-speed switch is closed in response to the normal working signal, and the charging branch is conducted. The charging branch comprises a series circuit of the high-speed switch and the charging resistor. The charging resistor connected in series skillfully limits the charging current peak value of the capacitor, avoids excessive charging current caused by directly connecting an external large capacitor, thereby reducing the impact on the capacitor and related devices, and prolonging the service life of the equipment. Through accurate control of the high-speed switch, the charging process is managed, the charging time is shortened, and the response speed is improved. After the voltage of the capacitor reaches the preset charging voltage, the high-speed switch is opened, and the closing switch is conducted. After detecting the fault signal of the direct current system, the closing switch is conducted, and the direct current is transferred to the commutation branch. Through the cooperative action of the closing switch and the charging branch and the accurate timing control, the capacitor is quickly, safely and efficiently charged, and sufficient energy reserve is provided for the high-frequency oscillation current demand in the fault breaking. In summary, the direct current circuit breaker provided by the application can realize quick, safe and efficient charging of the capacitor without an additional external large capacitor, can provide reliable energy support for meeting the high-frequency oscillation current demand, and significantly improves the overall performance and reliability of the direct current circuit breaker. BRIEF DESCRIPTION OF DRAWINGS

[0038] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the application and serve to explain the principles of the application.

[0039] Figure 1 Structure diagram of the direct current circuit breaker provided by the embodiment of the application Figure 1 ;

[0040] Figure 2 Structure diagram of a DC circuit breaker provided for an embodiment of the present application Figure 2

[0041] Figure 3 Working process diagram of a DC circuit breaker provided for an embodiment of the present application

[0042] Figure 4 Timing diagram of a fault breaking stage provided for an embodiment of the present application

[0043] Figure 5 Timing diagram of a reclosing preparation stage provided for an embodiment of the present application

[0044] Figure 6 Timing diagram of a reclosing stage reclosing on a permanent fault working provided for an embodiment of the present application

[0045] Figure 7 Simulation circuit diagram of a DC circuit breaker provided for an embodiment of the present application

[0046] Figure 8 500kV system simulation fault breaking stage current and voltage waveform diagram of a DC circuit breaker provided for an embodiment of the present application

[0047] Figure 9 500kV system simulation reclosing on a permanent fault current and voltage waveform diagram of a DC circuit breaker provided for an embodiment of the present application

[0048] Figure 10 500kV system simulation reclosing on a transient fault current and voltage waveform diagram of a DC circuit breaker provided for an embodiment of the present application

[0049] Figure 11 Structure diagram of an electronic device provided for an embodiment of the present application.

[0050] The specific embodiments of the present application have been shown by the above-described drawings, and will be described in more detail hereinafter. These drawings and written descriptions are not intended to limit the scope of the concept of the present application by any means, but to illustrate the concept of the present application to those skilled in the art by referring to specific embodiments. DETAILED DESCRIPTION

[0051] The exemplary embodiments will be described in detail herein with reference to the attached drawings. The same or similar components are denoted by the same or similar reference numerals throughout the drawings and the following description. The embodiments described in the following exemplary embodiments are not representative of all embodiments consistent with the present application. Rather, they are merely examples of devices and methods consistent with some aspects of the present application as detailed in the appended claims.

[0052] ​Currently, the mechanical HVDC circuit breaker is equipped with a large-capacitance device to provide rapid charging for the capacitor, and this scheme has been reliably applied in the DC engineering grid operation. However, the transfer and distribution of electric field energy among capacitors in this scheme are affected by capacitance, coulomb efficiency and other factors, resulting in low efficiency of charging the capacitor by the large-capacitance device. In order to meet the demand of rapid energy storage for reclosing, multiple sets of large-capacitance devices are usually required, which not only increases the volume of the capacitor device, but also significantly increases the overall cost.

[0053] To solve the above problems, the present application provides a DC circuit breaker comprising a main branch, a commutation branch and a charging branch; wherein the main branch comprises a mechanical switch connected in series between the DC system and the load side, and is used to conduct in response to the normal working signal of the DC system, and carries the DC current provided by the DC system; the commutation branch comprises a closing switch and a capacitor connected in series, the first end of the closing switch is connected with the valve hall side of the DC system, and the second end is connected with the charging branch and the capacitor respectively; the charging branch comprises a series circuit of a high-speed switch and a charging resistor, the first end of the high-speed switch is connected with the second end of the closing switch, and the second end of the high-speed switch is connected to the ground through the charging resistor; the high-speed switch is used to close in response to the normal working signal, and the closing switch is used to open after the high-speed switch is closed, so that the DC current charges the capacitor through the main branch and the charging branch; the high-speed switch is also used to open when the voltage of the capacitor reaches the preset charging voltage, and the closing switch is used to conduct in response to the fault signal of the DC system, so as to transfer the DC current to the commutation branch.

[0054] The present application is applicable to high-voltage flexible DC transmission systems, especially the rapid breaking and reclosing requirements of DC circuit breakers in new energy grid-connected scenarios.

[0055] The technical solutions of the present application and how the technical solutions of the present application solve the above technical problems will be described in detail below with specific examples. The following specific examples can be combined with each other, and the same or similar concepts or processes may not be described again in some examples. The embodiments of the present application will be described below with reference to the drawings.

[0056] Figure 1 Structure diagram of the DC circuit breaker provided by the embodiments of the present application Figure 1 As shown in Figure 1 , the DC circuit breaker comprises a main branch 101, a commutation branch 102 and a charging branch 103; wherein the main branch 101 comprises a mechanical switch connected in series between the DC system and the load side, and is used to conduct in response to the normal working signal of the DC system, and carries the DC current provided by the DC system;

[0057] The converter branch 102 includes a closing switch and a capacitor connected in series. The first end of the closing switch is connected to the valve hall side of the DC system, and the second end is connected to the charging branch and the capacitor respectively.

[0058] The charging branch 103 includes a series circuit of a high-speed switch and a charging resistor. The first terminal of the high-speed switch is connected to the second terminal of the closing switch, and the second terminal of the high-speed switch is grounded through the charging resistor.

[0059] The high-speed switch is used to close after responding to a normal operating signal, and the closing switch is used to open after the high-speed switch is closed, so that the DC current can charge the capacitor through the main branch and the charging branch.

[0060] The high-speed switch is also used to disconnect the capacitor after the voltage reaches the preset charging voltage, and the closing switch is used to turn on in response to a fault signal of the DC system to transfer the DC current to the commutator branch.

[0061] The DC circuit breaker described in this embodiment is used to provide safe and efficient current interruption in a DC system. This DC circuit breaker includes three key branches: a main branch, a commutation branch, and a charging branch. The main branch is the primary path for carrying current during normal operation of the DC system. The charging branch is connected in parallel with the main branch, and its main function is to provide a temporary commutation path for the current when the main branch current is interrupted, thereby achieving rapid extinction of the DC current. The charging branch's function is to perform current-limited charging of the capacitor during the capacitor charging phase in the commutation branch.

[0062] The operating procedure of the aforementioned DC circuit breaker is as follows: Before receiving a normal operating signal, the mechanical switch of the main branch is open to ensure the safety of the DC system. The high-speed switch in the charging branch is also open. Upon receiving the normal operating signal, both the mechanical switch and the high-speed switch close simultaneously, meaning the charging branch is turned on. If the charging branch is on, the closing switch is open, allowing current in the DC system to flow from the main branch to the converter branch and finally to the charging branch, thus charging the capacitor. The charging resistor acts as a current limiter during this stage, protecting the capacitor from excessive charging current. Current flows through the charging resistor to charge the capacitor in the converter branch.

[0063] Understandably, when the DC system is operating normally, the mechanical switch is in the closed state, the closing switch is in the open state, and the DC current flows through the main branch from left to right. When the high-speed switch is closed, the DC current flows through the main branch, the capacitor, and the charging branch, and the capacitor begins to charge. When the capacitor is charged to the preset charging voltage (such as the system voltage of the DC system), the capacitor voltage direction is negative near the valve hall side and positive near the load side. At this time, the high-speed switch needs to be turned off to disconnect the charging branch.

[0064] When a short-circuit ground fault occurs on the load side, the mechanical switch of the main branch bears the growing DC current from left to right, at this time, the DC system can be considered to have failed, and a closing instruction is sent to the closing switch, and the closing switch is turned on, so that the DC current is transferred to the commutation branch.

[0065] The above-mentioned switch operations collectively ensure the safety, reliability, efficiency and service life of the DC system under normal operation and fault conditions. The high-speed switch operation focuses on smooth mode switching or disconnection under stress-free conditions, while the closing switch operation focuses on fast and effective protection of the DC system under extreme fault conditions.

[0066] After receiving the normal working signal of the DC system, the embodiment of the application first turns on the main branch in series between the DC system and the load side to bear the DC current, and prepares for subsequent fault breaking and energy storage. Then, in response to the normal working signal, the high-speed switch is closed and the charging branch is turned on. The charging branch includes a series circuit of a high-speed switch and a charging resistor. The charging resistor in series skillfully limits the peak value of the charging current of the capacitor, avoiding excessive charging current caused by directly connecting an external large capacitor, thereby reducing the impact on the capacitor and related devices and prolonging the service life of the equipment. Through precise control of the high-speed switch, the charging process is managed, the charging time is shortened, and the response speed is improved. After the capacitor voltage reaches the preset charging voltage, the high-speed switch is turned off, and the closing switch is turned on. After detecting the fault signal of the DC system, the closing switch is turned on to transfer the DC current to the commutation branch. Through the coordinated action of the closing switch and the charging branch and precise timing control, the capacitor is quickly, safely and efficiently charged, providing sufficient energy reserve for the high-frequency oscillation current demand during fault breaking. In summary, the DC circuit breaker provided by the application can realize fast, safe and efficient charging of the capacitor without additional external large capacitors, providing reliable energy support to meet the high-frequency oscillation current demand, and significantly improving the overall performance and reliability of the DC circuit breaker.

[0067] On the basis of the above-mentioned embodiment, the commutation branch further includes: an inductor connected in series with the capacitor, one end of the inductor being connected with the capacitor, and the other end of the inductor being connected with the load side; the inductor and the capacitor are used to generate resonance after the closing switch is turned on, forming an oscillation current opposite in direction to the DC current, so as to make the current of the main branch zero and disconnect.

[0068] In this embodiment, it can be understood that when the DC system fails, that is, in response to detecting a fault signal, the capacitance and inductance of the commutation branch begin to respond, and they form a series resonant circuit. The resonant process generates an oscillating current, and the direction of the oscillating current is opposite to the direction of the DC current generated after the fault. Due to the reverse oscillating current generated by the resonance, it is superimposed on the DC current generated when the original DC system fails, that is, superimposed on the fault current. When the amplitude of the reverse current is large enough and matches the duration of the fault current, the superposition effect of them causes the total current flowing through the main branch to be zero instantaneously. The arc extinction of the mechanical switch is turned off after the total current is zero, so that the main branch is disconnected.

[0069] When the main branch is disconnected and the closing switch is closed, the DC current is completed from the main branch to the commutation branch. At this time, the direction of the DC current is still from left to right, and the DC system continues to charge the capacitor, and the voltage direction of the capacitor gradually changes from left negative to right positive to left positive and right negative.

[0070] The above-mentioned resonance of the inductance and the capacitance in the commutation branch forces the main branch current to be zero and disconnected by generating a reverse oscillating current, which is an important technical means for the DC system to achieve fast protection, suppress overvoltage, and protect equipment in the event of a fault.

[0071] On the basis of the above-mentioned embodiment, the inductance described in the above-mentioned embodiment is a variable inductance, and the variable inductance dynamically adjusts the inductance value through a mechanical adjustment mechanism or an electronic switch array, for dynamically adjusting the frequency of resonance. The variable inductance is used to dynamically adjust the frequency of resonance. In order to achieve this dynamic adjustment, two technical paths are mainly adopted: one is to continuously change the magnetic circuit or the effective number of turns of the coil to adjust the inductance value through a mechanical adjustment mechanism (such as moving the magnetic core or sliding the contact), which has high precision but slow response; the other is to use an electronic switch array (such as switching different inductance combinations through semiconductor switches), which can realize fast and digital inductance switching and adapt to the needs of an automatic system. By changing the inductance value through any of the above-mentioned ways, the frequency of the entire resonant circuit can be changed in real time and accurately.

[0072] The embodiment of the present application dynamically adjusts the inductance value of the adjustable inductance, so that the oscillation frequency of the commutation branch matches the DC current characteristics after the DC system fails, thereby speeding up the DC current transfer speed, shortening the breaking time of the mechanical switch, and reducing the risk of arc.

[0073] Further, on the basis of the above-mentioned embodiment, the DC circuit breaker further comprises: an energy consumption branch connected in parallel with the commutation branch, and the energy consumption branch comprises a lightning arrester for absorbing residual energy after the polarity of the capacitor is reversed.

[0074] As the capacitor continues to charge to the operating voltage of the surge arrester, the capacitor's polarity reverses; for example, the voltage direction changes from negative on the left and positive on the right to positive on the left and negative on the right. At this time, the DC current shifts from the commutation branch to the energy-dissipating branch. The surge arrester operates to absorb the residual energy of the DC system after the DC current shifts to the commutation branch, and the fault current begins to gradually decrease.

[0075] Furthermore, when the voltage across the surge arrester drops to the arrester's operating voltage, the surge arrester stops absorbing energy, and the DC system begins charging the capacitor through the closing switch.

[0076] This embodiment of the application uses a parallel connection between the converter branch and the surge arrester to absorb the residual energy after the DC current transfer, preventing damage to the equipment due to excessive voltage. This design improves the reliability of the DC circuit breaker and ensures rapid restoration of normal operation after fault handling, further reducing equipment maintenance costs.

[0077] Based on the above embodiments, the system further includes a smoothing reactor connected in series between the main branch and the load side. This smoothing reactor forms a freewheeling loop with the converter branch and the load side when the main branch is disconnected, thus smoothing the current in the converter branch. The smoothing reactor, connected in series between the main branch and the load side, primarily functions to form a freewheeling loop with the converter branch and the load side when the main branch is disconnected. In this freewheeling loop, the smoothing reactor utilizes its stored energy and its ability to prevent current changes to ensure that the current flows continuously and smoothly through the converter branch and reaches the load side, thereby effectively smoothing the current in the converter branch, reducing current fluctuations and surges, and ensuring stable circuit operation.

[0078] Based on the above embodiments, the high-speed switch is one of a turn-off thyristor, a power transistor, or an insulated gate bipolar transistor.

[0079] Based on the above embodiments, the DC circuit breaker provided in this application further includes: a voltage detection unit for detecting the voltage value of the capacitor; a control unit electrically connected to the voltage detection unit, the mechanical switch, the closing switch and the high-speed switch, for controlling the high-speed switch to open when the voltage of the capacitor reaches a preset charging voltage; and controlling the mechanical switch to open and the closing switch to open when a fault signal is detected.

[0080] In this embodiment, it can be understood that when the control unit detects that the capacitor voltage has reached the preset charging voltage, for example, when it detects that the capacitor voltage has reached the system voltage of the DC system, it will control the high-speed switch to open to disconnect the charging branch. Furthermore, when the control unit detects a fault signal in the DC system, it will also control the mechanical switch to open and control the closing switch to close.

[0081] The application embodiment can perform response operation according to the detected signal, realizes fast, safe and efficient charging of the capacitor, and provides sufficient energy reserve for the demand of high-frequency oscillation current in fault breaking.

[0082] Further, on the basis of the above embodiment, the control unit is further configured to: after the main branch is disconnected, determine whether the fault type is a transient fault or a permanent fault; if the fault type is the permanent fault, control the mechanical switch to close and the high-speed switch to conduct, so that the capacitor is reversely charged to the opposite polarity to that in the fault breaking; if the fault type is the transient fault, control the mechanical switch to close and the high-speed switch to conduct, so that the capacitor is forwardly charged.

[0083] In the embodiment, it can be understood that, after the residual energy is absorbed, the control unit controls the main branch to conduct and the high-speed switch to close in response to the signal, that is, the reclosing stage is performed. After the main branch conducts and the high-speed switch closes, the control unit further determines whether the fault of the DC system disappears, that is, determines whether the fault type of the DC system is a transient fault or a permanent fault.

[0084] Specifically, the DC system recharges the capacitor through the mechanical switch, obtains the capacitor polarity of the capacitor at this time, and determines the fault type according to the capacitor polarity. For example, if the capacitor polarity is left positive and right negative, it can be determined that the fault type is a permanent fault; if the capacitor polarity is left negative and right positive, it can be determined that the fault type is a transient fault.

[0085] If it is determined that the fault type of the DC system is a permanent fault, the control unit controls the mechanical switch to close and the high-speed switch to conduct, so that the capacitor is reversely charged to the opposite polarity to that in the fault breaking; if it is determined that the fault type of the DC system is a transient fault, the control unit controls the mechanical switch to close and the high-speed switch to conduct, so that the capacitor is forwardly charged.

[0086] The application embodiment can ensure that the energy stored in the capacitor is most effectively used to offset the fault current, reduce energy waste, and improve the overall efficiency of the DC circuit breaker by adjusting the charging direction of the capacitor according to the fault type of the DC system.

[0087] Further, the control unit is further configured to: after the capacitor is charged, if the fault type is a permanent fault, control the high-speed switch to turn off, the mechanical switch to open, and the reclosing switch to conduct, so as to break again; if the fault type is a transient fault, control the high-speed switch to turn off after the capacitor is charged to the system voltage of the DC system, and restore normal operation.

[0088] In this embodiment, it is understood that when the fault type of the DC system is determined to be a permanent fault, the control unit will instruct the high-speed switch to turn off, terminating further operation on the charging branch. Immediately afterwards, the mechanical switch in the main branch will trip, achieving physical isolation of the faulty section. Simultaneously, the closing switch will be turned on, safely guiding the DC current to the converter branch, where capacitors effectively absorb or extinguish any potential arcing. This series of coordinated actions ensures that the permanent fault is completely and safely interrupted, thereby maximizing the stability and safety of the DC system.

[0089] When the fault type of the DC system is determined to be transient, the control unit will instruct the high-speed switch to close to facilitate further operation of the charging branch. Immediately afterwards, the mechanical switch in the main branch will close, allowing the DC current supplied by the DC system to flow through the main branch, the converter branch, and finally to the charging branch, thus forward charging the capacitor. This series of coordinated actions ensures that the DC circuit breaker can quickly restore the main branch conduction after the transient fault disappears and has the capability to attempt automatic reclosing, minimizing unplanned power outages.

[0090] The aforementioned dual protection enables DC circuit breakers to provide more comprehensive and reliable protection under various operating conditions, greatly improving the overall operating efficiency and safety of DC systems.

[0091] Based on the above embodiments, this application also provides a control method for a DC circuit breaker, which is applied to the DC circuit breaker as described in the above embodiments. The control method includes: activating the mechanical switch of the main branch of the DC circuit breaker in response to a normal operating signal of the DC system to carry the DC current provided by the DC system; closing the high-speed switch of the charging branch of the DC circuit breaker in response to the normal operating signal; opening the closing switch of the converter branch of the DC circuit breaker after the high-speed switch is closed, so that the DC current charges the capacitor through the main branch and the charging branch; disconnecting the capacitor after the voltage reaches a preset charging voltage; and activating the closing switch in response to a fault signal of the DC system to transfer the DC current to the converter branch. It should be noted that the detailed principles have been described in detail in the previous embodiments, therefore, this application will not repeat them here.

[0092] Next, examples will be given to illustrate how to utilize the DC circuit breaker provided in the embodiments of this application. Figure 2 A schematic diagram of the structure of the DC circuit breaker provided in the embodiments of this application. Figure 2 .like Figure 2 As shown, the DC circuit breaker includes a power dissipation branch, a main branch, a converter branch, and a charging branch. One end of the DC circuit breaker is connected to the valve hall side, and the other end is connected to the smoothing reactor L. dcThe series connection is connected to the load side, the energy consumption branch, the main branch and the commutation branch are connected in parallel, the energy consumption branch includes a lightning arrester MOV, the main branch includes a mechanical switch MS, the commutation branch includes a closing switch K, a capacitor C and an inductor L connected in series, one end of the closing switch K is connected to the valve hall side, the other end is connected to the charging branch and the capacitor C respectively, the capacitor C and one end of the inductor L are connected in series, the charging branch includes a high-speed switch T and a charging resistor R connected in series, one end of the charging branch is connected to the end of the capacitor C close to the valve hall side, and the other end is grounded; the other end of the inductor L is connected to a smoothing reactor L dc .

[0093] Figure 3 The working process diagram of the DC circuit breaker provided by the embodiment of the application is shown in the figure. Figure 3 As shown, the working process mainly includes three stages, namely, a fault breaking stage, a reclosing preparation stage and a reclosing stage. The action principles of the stages will be described in detail.

[0094] Figure 4 The timing diagram of the fault breaking stage provided by the embodiment of the application is shown in the figure. Figure 4 The working process of the fault breaking stage is as follows.

[0095] The DC system is in normal operation, the mechanical switch is in the closed state, the closing switch is in the open state, the system current flows through the main branch, and the current direction is from left to right according to the connection mode, the high-speed switch is closed, the DC system current flows through the main branch, the capacitor and the charging branch, and the capacitor starts to charge. Figure 2

[0096] At t0, the DC system charges the capacitor to the system voltage of the DC system, the capacitor voltage direction is negative close to the valve hall side and positive close to the load side, for the sake of simplicity, the capacitor voltage direction is expressed as left negative and right positive according to the connection mode, and the high-speed switch is turned off. Figure 2

[0097] At t1, a short-circuit-to-ground fault occurs at the load side, and the mechanical switch of the main branch bears the growing fault current from left to right.

[0098] At t2, the control system determines that a short-circuit fault occurs in the DC system, sends a closing instruction to the mechanical switch, and sends a closing instruction to the closing switch, and the mechanical switch contacts start to separate.

[0099] At t3, the mechanical switch contacts separate to the rated opening distance, can withstand the rated voltage of the mechanical switch without arcing, the closing switch is closed, and the capacitor and the inductor start to generate high-frequency oscillation current which is superimposed on the mechanical switch in the opposite direction, and the fault current starts to transfer from the main branch to the commutation branch.

[0100] ​​At time t4, the main branch current crosses zero, the mechanical switch is turned off and the fault current is completely transferred to the converter branch. The direction of the fault current is still from left to right. The DC system charges the capacitor, and the direction of the capacitor voltage gradually changes from left negative to right positive.

[0101] At time t5, the capacitor is charged to the arrester's operating voltage. The capacitor voltage direction is positive on the left and negative on the right. The arrester operates, and the fault current is transferred from the converter branch to the energy dissipation branch. The arrester absorbs the residual energy of the line, and the fault current gradually decreases.

[0102] At time t6, when the voltage across the surge arrester drops to the arrester's operating voltage, the surge arrester stops absorbing energy, and the DC system begins charging the capacitor through the closing switch.

[0103] At time t7, the capacitor voltage is charged to the system voltage of the DC system. The direction of the capacitor voltage is positive on the left and negative on the right. The current in the commutator branch is 0, and the closing switch is opened.

[0104] Figure 5 The timing diagram for the reclosing preparation stage provided in the embodiments of this application is as follows: Figure 5 As shown, the workflow for the reclosing preparation phase is as follows:

[0105] At time t8, the fault deionization is completed, the mechanical switch S closes, the high-speed switch closes, the control system determines whether the fault has disappeared, and the DC system recharges the capacitor through the mechanical switch, with the capacitor voltage direction gradually changing from positive on the left and negative on the right to negative on the left and positive on the right.

[0106] At time t9, the control system completes the fault type determination, and the capacitor voltage direction changes to negative on the left and positive on the right.

[0107] Reclosing stage:

[0108] Figure 6 The timing diagram for reclosing during a permanent fault provided in the embodiments of this application is as follows: Figure 6 As shown, at time t9, if the control system determines that the fault type is a permanent fault, the capacitor voltage reaches the set value, and the direction of the capacitor voltage is positive on the left and negative on the right, which is consistent with the initial direction of the capacitor voltage when the fault is interrupted. The control system then turns off the high-speed switch, the mechanical switch contacts begin to separate, and the closing switch begins to close.

[0109] During the process and fault interruption phase Similarly, I will not elaborate further.

[0110] At time t9, if the control system determines that the fault type is transient, the DC current flows through the mechanical switch, the DC system returns to normal operation, and the capacitor voltage is charged by the DC system to the system voltage of the DC system before being turned off. The direction of the capacitor voltage is negative on the left and positive on the right.

[0111] Further, a simulation model is built in simulation software to verify that the circuit breaker provided in the embodiments has the ability of self-charging and reclosing. Figure 7 The simulation circuit diagram of the DC circuit breaker is provided in the embodiments. In the simulation test, the system voltage U of the DC system is 500 kV, the rated current of the DC system is 3 kA, the smoothing reactor L of the DC system is 100 mH, the fault determination time t is 3 ms, the time from the start of separation of the mechanical switch contact to the rated opening distance is 2 ms, the designed DC circuit breaker has the ability of breaking 22 kA current, the oscillation current frequency of the commutation branch is 6000 Hz, the capacitance of the commutation branch is 1.33 uF, and the inductance of the commutation branch is 0.53 mH. dc The system voltage U of the DC system is 500 kV, the rated current of the DC system is 3 kA, the smoothing reactor L of the DC system is 100 mH, the fault determination time t is 3 ms, the time from the start of separation of the mechanical switch contact to the rated opening distance is 2 ms, the designed DC circuit breaker has the ability of breaking 22 kA current, the oscillation current frequency of the commutation branch is 6000 Hz, the capacitance of the commutation branch is 1.33 uF, and the inductance of the commutation branch is 0.53 mH. The system voltage U of the DC system is 500 kV, the rated current of the DC system is 3 kA, the smoothing reactor L of the DC system is 100 mH, the fault determination time t is 3 ms, the time from the start of separation of the mechanical switch contact to the rated opening distance is 2 ms, the designed DC circuit breaker has the ability of breaking 22 kA current, the oscillation current frequency of the commutation branch is 6000 Hz, the capacitance of the commutation branch is 1.33 uF, and the inductance of the commutation branch is 0.53 mH.

[0112] Figure 8 The simulation circuit diagram of the DC circuit breaker is provided in the embodiments. In the simulation test, the system voltage U of the DC system is 500 kV, the rated current of the DC system is 3 kA, the smoothing reactor L of the DC system is 100 mH, the fault determination time t is 3 ms, the time from the start of separation of the mechanical switch contact to the rated opening distance is 2 ms, the designed DC circuit breaker has the ability of breaking 22 kA current, the oscillation current frequency of the commutation branch is 6000 Hz, the capacitance of the commutation branch is 1.33 uF, and the inductance of the commutation branch is 0.53 mH. Figure 8 is to simulate the closing of the high-speed switch at t=0.18 s, Figure 8 The i in the formula (1) is the current flowing through the closing switch; k The i in the formula (1) is the current flowing through the closing switch; The i in the formula (1) is the current flowing through the closing switch; The i in the formula (1) is the current flowing through the closing switch; The i in the formula (1) is the current flowing through the closing switch; The V in the formula (1) is the voltage of the mechanical switch; and The V in the formula (1) is the voltage of the mechanical switch; and Figure 8 It can be known from the formula (1) that at t=0.184 s, the capacitor has been charged to -500 kV, the peak charging current in the capacitor charging stage 1 is about 600 A, at t=0.2 s, the short-circuit fault of the DC system occurs, at t=0.205 s, the mechanical switch is separated to the rated opening distance, the closing switch is closed, the main branch current is zero, the mechanical switch is turned off, and the peak fault current is about 20 kA, at t=0.229 s, the energy absorption of the arrester is completed, at t=0.238 s, the capacitor voltage is stabilized at 500 kV.

[0113] Figure 9 The simulation circuit diagram of the DC circuit breaker is provided in the embodiments. In the simulation test, the system voltage U of the DC system is 500 kV, the rated current of the DC system is 3 kA, the smoothing reactor L of the DC system is 100 mH, the fault determination time t is 3 ms, the time from the start of separation of the mechanical switch contact to the rated opening distance is 2 ms, the designed DC circuit breaker has the ability of breaking 22 kA current, the oscillation current frequency of the commutation branch is 6000 Hz, the capacitance of the commutation branch is 1.33 uF, and the inductance of the commutation branch is 0.53 mH. Figure 9 As shown in the formula (2), at t=0.3 s, the mechanical switch is closed, the high-speed switch is closed, the capacitor voltage is charged to -490 kV after 5 ms, at this time, the charging branch current is about 15 A, so the high-speed switch in this design has the ability of breaking tens of amperes of DC current, then the main branch current is zero, the mechanical switch is opened, and the reclosing breaking is realized.

[0114] Figure 10 The simulation circuit diagram of the DC circuit breaker is provided in the embodiments. In the simulation test, the system voltage U of the DC system is 500 kV, the rated current of the DC system is 3 kA, the smoothing reactor L of the DC system is 100 mH, the fault determination time t is 3 ms, the time from the start of separation of the mechanical switch contact to the rated opening distance is 2 ms, the designed DC circuit breaker has the ability of breaking 22 kA current, the oscillation current frequency of the commutation branch is 6000 Hz, the capacitance of the commutation branch is 1.33 uF, and the inductance of the commutation branch is 0.53 mH. Figure 10As shown, t = 0.3s, the mechanical switch is closed, the high-speed switch is closed, after 6ms, the system current through the main branch has recovered to the rated current, the DC system is in normal operation, the capacitor is charged to the system voltage of the DC system, which is -500kV, and the charging branch current is reduced to 0, at this time, the high-speed switch can be turned off.

[0115] Further, the fault deionization time is generally about 300ms, and in the simulation, the deionization time is set to be less than 300ms, the circuit breaker still has self-charging and reclosing capabilities, and it can be verified that the DC circuit breaker can realize no additional capacitor power supply and has reclosing function.

[0116] In summary, the embodiment of the application cooperatively designs the topological structure of the smoothing reactor and the DC circuit breaker, realizes self-charging of the capacitor by using the characteristics of the DC system itself, and adjusts the polarity of the capacitor voltage dynamically to adapt to the breaking requirements of different fault types (transient and permanent), thereby breaking through the "breaking capacity-economy-reliability" triangular contradiction.

[0117] It should be noted that the division of each module of the above device is only a logical functional division, and all or part of them can be integrated into one physical entity, or physically separated. These modules can all be implemented in the form of software called by a processing element; all can be implemented in the form of hardware; or part of the modules can be implemented in the form of software called by a processing element, and part of the modules can be implemented in the form of hardware. For example, the processing module can be a separately established processing element, or can be integrated in a certain integrated circuit of the above device, in addition, it can also be stored in the memory of the above device in the form of program code, and the functions of the above processing module are called and executed by a certain processing element of the above device. The implementation of other modules is similar. In addition, all or part of these modules can be integrated together, or can be independently implemented. The processing element here can be an integrated circuit with signal processing capability. In the implementation process, each step of the above method or each module can be completed by the integrated logic circuit of the hardware in the processor element or the instructions in the form of software.

[0118] For example, the above modules can be one or more integrated circuits configured to implement the above methods, such as one or more Application Specific Integrated Circuits (ASICs), or one or more Digital Signal Processors (DSPs), or one or more Field Programmable Gate Arrays (FPGAs), etc. For another example, when a certain module above is implemented in the form of a processing element disposing program code, the processing element can be a general-purpose processor, such as a Central Processing Unit (CPU) or other processor that can invoke program code. For another example, the modules can be integrated together to implement in the form of a System-On-a-Chip (SOC).

[0119] Figure 11 A structural schematic diagram of an electronic device provided by an embodiment of the present application is shown. As shown in the figure, the electronic device 1100 provided by the embodiment of the present application can include a processor 1101 and a memory 1102 in communication connection with the processor, wherein: Figure 11

[0120] The memory stores computer execution instructions.

[0121] The processor executes the computer execution instructions stored by the memory to implement the method described in the foregoing method embodiment.

[0122] It should be understood that the processor 1101 can be a Central Processing Unit (CPU), and can also be other general-purpose processors, Digital Signal Processors (DSPs), Application Specific Integrated Circuits (ASICs), etc. The general-purpose processor can be a microprocessor or the processor can also be any conventional processor, etc. The steps of the method disclosed in combination with the application can be directly embodied as execution completed by a hardware processor, or executed by a combination of hardware and software modules in the processor. The memory 1102 can include a high-speed Random Access Memory (RAM), and can also include a non-volatile memory NVM (non-volatile memory), such as at least one disk memory, and can also be a U disk, a mobile hard disk, a read-only memory, a magnetic disk or an optical disk, etc.

[0123] ​Optionally, the electronic device 1100 can further include a communication interface 1103. In a specific implementation, if the communication interface 1103, the memory 1102 and the processor 1101 are implemented independently, the communication interface 1103, the memory 1102 and the processor 1101 can be connected with each other through a bus and complete communication between each other. The bus can be an Industry Standard Architecture (ISA) bus, a Peripheral Component (PCI) bus or an Extended Industry Standard Architecture (EISA) bus, etc. The bus can be divided into an address bus, a data bus, a control bus, etc., but it does not mean that there is only one bus or one type of bus.

[0124] Optionally, in a specific implementation, if the communication interface 1103, the memory 1102 and the processor 1101 are integrated on an integrated circuit, the communication interface 1103, the memory 1102 and the processor 1101 can complete communication through an internal interface.

[0125] The embodiment of the present application further provides a computer readable storage medium, the computer readable storage medium stores computer execution instructions, and the computer execution instructions are used for implementing the method described in any of the foregoing embodiments when executed.

[0126] It can be understood that the computer readable storage medium can be implemented by any type of volatile or non-volatile storage device or a combination thereof, such as a Static Random Access Memory (SRAM), an Electrically Erasable Programmable Read Only Memory (EEPROM), an Erasable Programmable Read Only Memory (EPROM), a Programmable Read Only Memory (PROM), a Read Only Memory (ROM), a magnetic memory, a flash memory, a magnetic disk or an optical disk. The readable storage medium can be any available medium that can be accessed by a general or special purpose computer.

[0127] An example computer-readable storage medium is coupled to the processor such that the processor can read information from the computer-readable storage medium and can write information to the computer-readable storage medium. Of course, the computer-readable storage medium can be a part of the processor. The processor and the computer-readable storage medium can be located in an ASIC. Of course, the processor and the computer-readable storage medium can be located in discrete components as well.

[0128] The integrated modules in the form of software function modules described above can be stored in a computer-readable storage medium. The software function modules described above are stored in a computer-readable storage medium, and include a plurality of instructions for causing an electronic device (which can be a personal computer, a server, or a network device, etc.) or a processor to perform some steps of the methods described in various embodiments of the present application.

[0129] The embodiments of the present application also provide a computer program product, which comprises a computer program, and the computer program is executed to implement the method described in any of the foregoing embodiments.

[0130] It should be noted that, for the foregoing method embodiments, in order to simply describe, they are all described as a series of action combinations, but those skilled in the art should know that the present application is not limited to the order of the actions described, because according to the present application, some steps can be performed in other order or simultaneously. Secondly, those skilled in the art should know that the embodiments described in the specification all belong to optional embodiments, and the actions and modules involved are not necessarily required by the present application.

[0131] It should be further noted that, although each step in the flowchart is displayed in sequence according to the arrow, these steps are not necessarily executed in sequence according to the arrow. Unless otherwise stated in this article, the execution of these steps has no strict order limit, and these steps can be executed in other order. Moreover, at least part of the steps in the flowchart can include multiple sub-steps or multiple stages, which are not necessarily executed at the same time, but can be executed at different times, and the execution order of these sub-steps or stages is not necessarily sequential, but can be alternately executed with other steps or sub-steps or stages of other steps.

[0132] In the above embodiments, the description of each embodiment has its own focus, and the parts not described in detail in a certain embodiment can be referred to the related description of other embodiments. The technical features of the above embodiments can be combined arbitrarily, and in order to make the description concise, the possible combinations of the technical features in the above embodiments are not described, however, as long as the combinations of these technical features do not exist contradictions, they should be considered as the scope of the present application.

[0133] Other embodiments of the application will be apparent to those skilled in the art from consideration of the specification and practice of the application disclosed herein. It is intended that the specification and examples be considered as exemplary only, with the true scope and spirit of the application being indicated by the following claims.

[0134] It is to be understood that the application is not limited to the precise construction herein described and as shown in the attached drawings, and that various modifications and changes can be made by those skilled in the art without departing from the scope of the application. The scope of the application is to be indicated by the appended claims, rather than the description and examples.

Claims

1. A DC circuit breaker, characterized in that, include: Main branch, converter branch and charging branch; among which, The main branch includes a mechanical switch connected in series between the DC system and the load side, used to turn on in response to the normal operation signal of the DC system and to carry the DC current provided by the DC system; The converter branch includes a closing switch and a capacitor connected in series. The first end of the closing switch is connected to the valve hall side of the DC system, and the second end is connected to the charging branch and the capacitor, respectively. The charging branch includes a series circuit of a high-speed switch and a charging resistor. The first terminal of the high-speed switch is connected to the second terminal of the closing switch, and the second terminal of the high-speed switch is grounded through the charging resistor. The high-speed switch is used to close after responding to the normal operation signal, and the closing switch is used to open after the high-speed switch is closed, so that the DC current can charge the capacitor through the main branch and the charging branch; The high-speed switch is also used to disconnect after the voltage of the capacitor reaches the preset charging voltage, and the closing switch is used to turn on after responding to the fault signal of the DC system, so as to transfer the DC current to the commutator branch.

2. The DC circuit breaker according to claim 1, characterized in that, The commutation branch further includes: an inductor connected in series with the capacitor, one end of the inductor being connected to the capacitor, and the other end of the inductor being connected to the load side; The inductor and the capacitor are used to generate resonance after the closing switch is turned on, forming an oscillating current in the opposite direction to the DC current, so that the current in the main branch crosses zero and is disconnected.

3. The DC circuit breaker according to claim 2, characterized in that, The inductor is a variable inductor, which is used to dynamically adjust the inductance value through a mechanical adjustment mechanism or an electronic switch array to dynamically adjust the resonant frequency.

4. The DC circuit breaker according to claim 2, characterized in that, Also includes: A power dissipation branch connected in parallel with the converter branch, the power dissipation branch including a surge arrester, is used to absorb residual energy after the capacitor polarity is reversed.

5. The DC circuit breaker according to any one of claims 1 to 4, characterized in that, Also includes: A smoothing reactor connected in series between the main branch and the load side is used to form a freewheeling loop with the converter branch and the load side when the main branch is disconnected, so as to smooth the current change in the converter branch.

6. The DC circuit breaker according to any one of claims 1 to 4, characterized in that, The high-speed switch is at least one of a turn-off thyristor, a power transistor, and an insulated gate bipolar transistor.

7. The DC circuit breaker according to any one of claims 1 to 4, characterized in that, Also includes: A voltage detection unit is used to detect the voltage value of the capacitor; The control unit is electrically connected to the voltage detection unit, the mechanical switch, the closing switch, and the high-speed switch, and is used to control the high-speed switch to open when the voltage of the capacitor reaches the preset charging voltage; and to control the mechanical switch to open and the closing switch to open when the fault signal is detected.

8. The DC circuit breaker according to claim 7, characterized in that, The control unit is also used for: After the main branch is disconnected, determine whether the fault type is a transient fault or a permanent fault; If the fault is permanent, the mechanical switch is closed and the high-speed switch is turned on, causing the capacitor to be charged in reverse to the opposite polarity to that when the fault was interrupted. In the event of a transient fault, the mechanical switch is closed and the high-speed switch is turned on, causing the capacitor to charge in the forward direction.

9. The DC circuit breaker according to claim 8, characterized in that, The control unit is also used for: After the capacitor has finished charging, if the fault is permanent, the high-speed switch is turned off, the mechanical switch is opened, and the closing switch is turned on to achieve a restart. In the case of a transient fault, the high-speed switch is controlled to turn off after the capacitor is charged to the system voltage of the DC system, thus restoring normal operation.

10. A control method for a DC circuit breaker, characterized in that, The control method, applied to a DC circuit breaker as described in any one of claims 1 to 9, comprises: Upon responding to the normal operation signal of the DC system, the mechanical switch of the main branch in the DC circuit breaker is turned on to carry the DC current provided by the DC system; The high-speed switch of the charging branch in the DC circuit breaker is closed after responding to the normal operation signal; After the high-speed switch is closed, the closing switch of the converter branch in the DC circuit breaker is disconnected so that the DC current can charge the capacitor through the main branch and the charging branch. After the voltage of the capacitor reaches the preset charging voltage, it is disconnected. In response to the fault signal of the DC system, the closing switch is turned on to transfer the DC current to the converter branch.

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