A reclosing DC circuit breaker with high breaking capacity

Abstract

The present invention relates to a reclosing DC circuit breaker with high breaking capacity and a control method, the circuit breaker comprises a main branch, a backup protection branch, a transfer branch, a buffer energy absorption branch and a commutation circuit, the main branch is connected in series with the backup protection branch, the series-connected main branch and the backup protection branch are connected in parallel with the buffer energy absorption branch, the main branch, the transfer branch and the commutation circuit are connected in parallel; the present invention inherits the advantages of low current loss and fast active LC commutation response of the traditional DC circuit breaker mechanical switch, improves the arc-extinguishing breaking capacity of the mechanical switch MS through the voltage clamping effect of the anti-parallel diode D2, and restores the voltage polarity and amplitude of the energy storage capacitor C1 to the pre-charged state after the fault is cleared in combination with the characteristics of the bridge commutation circuit. No external pre-charging circuit is required, which effectively solves the control and volume constraints brought by the cumbersome charging circuit and greatly shortens the reclosing action time.

Description

Technical Field

[0001] The present invention relates to the technical field of high-voltage direct current circuit breakers, and in particular to a reclosing direct current circuit breaker with high breaking capacity. Background Art

[0002] As the energy revolution advances, the flexible direct current transmission technology based on voltage source converter (VSC-HVDC) has been a research hotspot at home and abroad in recent years. China is also steadily promoting the construction of flexible direct current transmission demonstration projects with multiple ports, large capacity and high voltage levels, which has attracted more attention to the research on its protection strategy. DC circuit breakers can flexibly and reliably cut off specific fault lines and are the best solution for DC side fault protection of flexible direct current transmission systems. They have broad development potential and application prospects in future engineering practices.

[0003] The two main technical routes for high-voltage DC circuit breakers are a mechanical solution based on artificial zero crossing and a hybrid solution based on power electronic devices. The current research hotspot is to propose topological solutions with better performance and lower cost around these two routes, but in addition to these, there are still many research directions to be explored.

[0004] In recent years, DC transmission has become a research hotspot due to its advantages such as low power and energy loss, low interference to communications, and low cost of DC lines for transmitting the same power. With the rise of DC transmission technology, DC circuit breakers have attracted much attention as important system protection equipment. When a short circuit fault occurs in a DC system, the short circuit current increases much faster than that of an AC system, and will exceed the breaking capacity of a conventional AC circuit breaker in a very short time, which in turn places high demands on DC circuit breakers. The lagging development of DC current limiters and DC circuit breakers is an important factor currently restricting the development of flexible DC transmission systems. When a short circuit fault occurs in a DC system, the fault current will rise rapidly. If the fault cannot be removed in a short time, it will affect the normal operation of the entire system, which in turn places high demands on DC circuit breakers.

[0005] With the rapid development of flexible DC transmission, a reliable DC breaking solution is urgently needed to ensure the safe operation of DC transmission systems. In AC transmission systems, AC current passes through zero points twice in each cycle, and the circuit breaker can use these two current zero crossings to achieve breaking. However, in DC transmission systems, the current does not have a zero crossing point, and there is a problem that the fault current is difficult to cut off. Therefore, DC circuit breakers need to create artificial zero crossings, and the most common method is to use an active LC oscillation commutation circuit.

[0006] The DC breaking method based on artificial zero crossing is an important method in the high-voltage DC breaking technology solution. Artificial zero crossing breaking technology has been studied and applied in the low-voltage field, and corresponding research has also been carried out in the medium-voltage and high-voltage fields. Whether the artificial zero crossing can be reliably achieved directly affects whether the DC current can be cut off quickly and reliably, which plays a vital role in the safe and reliable operation of the system. However, in the field of high-voltage technology, the breaking reliability of DC circuit breakers is low. The energy storage capacitor of the active LC circuit needs to provide a pre-charging circuit before each breaking of the circuit breaker, which limits the control timing and volume of the DC circuit breaker device. In the existing topological structure of DC circuit breakers, the breaking reliability of DC circuit breakers has always been questioned. The breaking process of DC circuit breakers includes the whole breaking process of milliseconds and the commutation process of microseconds. Existing research rarely goes into the breaking details of circuit breakers, and the research on transient electrical characteristics under these two time dimensions is still insufficient. Moreover, the reclosing problem is a cold spot in the current research of DC circuit breakers. In the existing topological structure of DC circuit breakers, the breaking reliability of DC circuit breakers has always been questioned.

[0007] With the development of DC circuit breakers. DC circuit breakers can be mainly divided into three categories: solid-state DC circuit breakers, mechanical DC circuit breakers and hybrid DC circuit breakers. Solid-state DC circuit breakers directly use fully controlled semiconductor devices to shut off the current, and the action speed is very fast, but the large number of semiconductor devices in the load current path will make the conduction loss of solid-state DC circuit breakers too large. Hybrid DC circuit breakers and mechanical DC circuit breakers are the current mainstream research directions. Among them, the representative ones are: the 320kV hybrid DC circuit breaker engineering prototype developed by ABB, the 200kV hybrid DC circuit breaker developed by the State Grid for the Zhoushan Flexible DC Project, and the 160kV mechanical DC circuit breaker developed by the Southern Power Grid for the Nan'ao Flexible DC Project. Compared with hybrid DC circuit breakers, mechanical DC circuit breakers have the advantages of negligible conduction loss, low cost and small footprint. Early mechanical DC circuit breakers used self-excited oscillation to form an artificial current zero point, thereby extinguishing the arc in the mechanical switch, with a long delay. Active oscillation type mechanical DC circuit breakers use pre-charged capacitors in series with inductors and mechanical switches to form an oscillation circuit. When the capacitor discharge current is equal to the current flowing through the mechanical switch in amplitude and opposite in direction, an artificial current zero point is formed. One solution mentioned that the pre-charged capacitor of the mechanical DC circuit breaker discharges to the mechanical switch through the inductor to form an oscillating current; in another DC circuit breaker solution, the pre-charged capacitor on the low-voltage side generates an oscillating current on the high-voltage side through a coupled inductor. Both of the above solutions require the capacitor to be pre-charged through an additional AC power supply, which increases the complexity of the system design and limits the application of DC circuit breakers on the passive grid side.

[0008] Therefore, in order to improve the breaking reliability of DC circuit breakers, it is necessary to design a new DC circuit breaker topology structure that can solve the above problems faced by DC circuit breakers based on artificial zero crossing technology. Providing a reclosing DC circuit breaker with high breaking capacity and a control method that can solve the above technical problems is an issue that technical personnel in this field need to solve urgently. Summary of the invention

[0009] The technical problem to be solved by the present invention is to provide a reclosing DC circuit breaker with high breaking capacity, so as to solve the technical problems of low reliability of the current DC circuit breaker and control and volume constraints caused by the complicated charging circuit.

[0010] The technical solution adopted by the present invention is: a reclosing DC circuit breaker with high breaking capacity, which includes a main branch, a backup protection branch, a transfer branch, a buffer energy absorption branch and a commutation circuit, the main branch and the backup protection branch are connected in series, the series-connected main branch and the backup protection branch are connected in parallel with the buffer energy absorption branch, and the main branch, the transfer branch and the commutation circuit are connected in parallel.

[0011] Furthermore, the main branch includes a mechanical switch MS and a diode valve group D1 connected in series.

[0012] Furthermore, the backup protection branch envelops the explosion switch PB.

[0013] Furthermore, the transfer branch includes a diode valve group D2.

[0014] Furthermore, the buffer energy absorption branch includes a buffer resistor R1, a buffer capacitor C2 and an energy absorption resistor MOV. The buffer resistor R1 is connected in series with the buffer capacitor C2, and the energy absorption resistor MOV is connected in parallel with the series branch of the buffer resistor R1 and the buffer capacitor C2.

[0015] Furthermore, the commutation circuit includes a thyristor SCR1, a thyristor SCR2, an IGBT valve group S1 and an IGBT valve group S2; the thyristor SCR1 is connected in series with the IGBT valve group S1, the thyristor SCR2 is connected in series with the IGBT valve group S2, and the two series branches are connected in parallel.

[0016] Furthermore, the commutation circuit also includes an energy storage capacitor C1 and a modulation inductor L1, one end of the energy storage capacitor C1 is connected to the common connection point of the thyristor SCR1 and the IGBT valve group S1, and the other end is connected to one end of the modulation inductor L1, and the other end of the modulation inductor L1 is connected to the common connection point of the IGBT valve group S2 and the thyristor SCR2.

[0017] A control method for a reclosing DC circuit breaker with high breaking capacity comprises the following steps:

[0018] When the DC line operates normally, the DC current passes through the mechanical switch MS, the diode valve group D1 and the explosion switch PB, and its conduction loss is small;

[0019] When a short circuit fault occurs in the system, the contacts of the mechanical switch MS separate and start arcing, realizing reliable disconnection of large DC current; the commutation circuit IGBT valve group S1 and IGBT valve group S2 are triggered to conduct, and the energy storage capacitor C1 and the modulation inductor L1 form an oscillating discharge until the fault current is equal to that of the fault current, and the mechanical switch MS extinguishes the arc and turns off; at the same time, the transfer branch diode D2 is turned on under the forward voltage condition, and the fault current and oscillating discharge begin to transfer to the diode D2. At the same time, due to the conduction of the diode D2, both ends of MS are clamped in a low voltage state, and at this time, the IGBT valve group S1 and IGBT valve group S2 are disconnected. BT valve group S2 triggers the conduction thyristor SCR1 and thyristor SCR2 at the same time to form a discharge path with the system circuit. The fault current and the energy stored in the modulation inductor L1 continue to positively charge the energy storage capacitor C1 through the thyristor SCR1 and thyristor SCR2. When the voltage across the energy storage capacitor C1 increases to the opening voltage of the buffer energy absorption branch, the buffer energy absorption branch energy absorption resistor MOV is turned on to absorb the energy of the system and the commutation circuit; the commutation circuit current passes through zero, the thyristors SCR1 and SCR2 are turned off, the buffer energy absorption branch completes the energy absorption, and the fault current is completely cleared.

[0020] Furthermore, if the main branch and the current commutation circuit fail, the explosion switch PB is disconnected, the circuit is cut off, and the current is introduced into the energy transfer resistor to avoid the expansion of the fault.

[0021] A computer program is stored thereon, and when the computer program is executed by a processor, the above method is implemented.

[0022] The positive effects of the present invention are:

[0023] The present invention provides a circuit topology and control method of a reclosing DC circuit breaker with high breaking capacity, which inherits the advantages of low current loss of the mechanical switch of the traditional DC circuit breaker and fast active LC commutation response, improves the arc-extinguishing breaking capacity of the mechanical switch MS through the voltage clamping effect of the anti-parallel diode D2, and combines the characteristics of the bridge commutation circuit to restore the voltage polarity and amplitude of the energy storage capacitor C1 to the pre-charged state after the fault is cleared. There is no need to provide an external pre-charging circuit, which effectively solves the control and volume constraints brought by the cumbersome charging circuit, and greatly shortens the reclosing action time. In addition, the explosion switch PB and the diode D1 realize reliable interruption of large DC currents. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0025] Figure 1 It is the work flow chart of the present invention;

[0026] Figure 2 This is the basic structure diagram of the present invention.

[0027] In the accompanying drawings,

[0028] 1- Main branch;

[0029] 2-Backup protection branch;

[0030] 3- Transfer branch;

[0031] 4- Buffer energy absorption branch;

[0032] 5-Commutation circuit. DETAILED DESCRIPTION

[0033] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present application and its application or use. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0034] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0035] Unless otherwise specifically stated, the relative arrangement, numerical expressions and numerical values ​​of the parts and steps set forth in these embodiments do not limit the scope of the present application. At the same time, it should be understood that, for ease of description, the sizes of the various parts shown in the accompanying drawings are not drawn according to the actual proportional relationship. The technology, method and equipment known to those of ordinary skill in the relevant field may not be discussed in detail, but in appropriate cases, the technology, method and equipment should be considered as a part of the authorization specification. In all examples shown and discussed here, any specific value should be interpreted as being merely exemplary, rather than as a limitation. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters represent similar items in the following drawings, so that once a certain item is defined in an accompanying drawing, it does not need to be further discussed in subsequent drawings.

[0036] As attached Figure 1-2 As shown, the present invention discloses a reclosing DC circuit breaker with high breaking capacity, comprising: a main branch 1, a backup protection branch 2, a transfer branch 3, a buffer energy absorption branch 4 and a commutation circuit 5; the main branch 1 is connected in series with the backup protection branch 2, the series-connected main branch 1 and the backup protection branch 2 are connected in parallel with the buffer energy absorption branch 4, and the main branch 1 is connected in parallel with the transfer branch 3 and the commutation circuit 5. The main current flows from node I to node O.

[0037] The main branch includes: a mechanical switch MS and a diode valve group D1 , wherein the mechanical switch MS is connected in series with the diode valve group D1 .

[0038] The backup protection branch of the present invention includes an explosion switch PB.

[0039] The transfer branch of the present invention includes: a diode valve group D2.

[0040] The buffer energy absorption branch of the present invention comprises: a buffer resistor R1, a buffer capacitor C2 and an energy absorption resistor MOV; the buffer resistor R1 and the buffer capacitor C2 are connected in series, and the energy absorption resistor MOV is connected in parallel with the series branch of the buffer resistor R1 and the buffer capacitor C2.

[0041] The commutation circuit of the present invention comprises: thyristors SCR1, SCR2, IGBT valve groups S1, S2, energy storage capacitor C1, and wave modulation inductor L1. The thyristor SCR1 is connected in series with the IGBT valve group S1, and is connected in parallel with the series branch of the IGBT valve group S2 and the thyristor SCR2; one end of the energy storage capacitor C1 is connected to the common connection point of the thyristor SCR1 and the IGBT valve group S1, the other end of the energy storage capacitor C1 is connected to one end of the wave modulation inductor L1, and the other end of the wave modulation inductor L1 is connected to the common connection point of the IGBT valve group S2 and the thyristor SCR2; the thyristors SCR1, SCR2, and the IGBT valve groups S1, S2 are connected according to a bridge rectifier circuit.

[0042] In a specific embodiment, a reclosing DC circuit breaker with high breaking capacity works as follows:

[0043] When the DC line operates normally, the DC current passes through the mechanical switch MS, the diode valve group D1 and the explosion switch PB, and its conduction loss is small.

[0044] When a short circuit occurs in the system, the contacts of the mechanical switch MS separate and start arcing. This ensures reliable disconnection of large DC currents. The IGBT valve groups S1 and S2 in the commutation circuit are triggered and turned on, and the pre-charge capacitor C1 and the wave modulation inductor L1 begin to form an oscillating discharge until the current is equal to the fault current, and then the MS extinguishes the arc and shuts down. The reverse blocking effect of the diode D1 in series with the mechanical switch MS can provide a "zero rest" time for the large current vacuum arc, ensuring that the mechanical switch MS extinguishes the arc and shuts down reliably. At the same time, the transfer branch diode D2 is turned on under the forward voltage condition, and the fault current and oscillation discharge begin to transfer to the diode D2. At the same time, due to the conduction of the diode D2, the two ends of the MS are clamped in a low voltage state; at this time, the IGBT valve group S1 and S2 are disconnected, and the thyristors SCR1 and SCR2 are triggered to form a discharge path with the system circuit. The fault current and the energy stored in the modulation inductor L1 continue to charge the energy storage capacitor C1 forward through SCR1 and SCR2. When the voltage across the energy storage capacitor C1 increases to the buffer energy absorption branch opening voltage, the buffer energy absorption branch energy absorption resistor MOV is turned on to absorb the energy of the system and the commutation circuit; the commutation circuit current passes through zero, the thyristors SCR1 and SCR2 are turned off, and the buffer energy absorption branch completes the energy absorption, and the fault current is completely cleared. The series connection of the buffer resistor R1 and the buffer capacitor C2 can prevent the power electronic devices from being damaged by overvoltage.

[0045] If the main branch and current commutation circuit fail, disconnect the explosion switch PB, quickly cut off the circuit, and introduce the current into the energy transfer resistor to avoid the expansion of the fault.

[0046] The DC circuit breaker circuit topology provided by the embodiment of the present application inherits the advantages of low current loss and fast active LC commutation response of the traditional DC circuit breaker mechanical switch, improves the arc extinguishing breaking capacity of the mechanical switch MS through the voltage clamping effect of the anti-parallel diode D2, and combines the characteristics of the bridge commutation circuit to restore the voltage polarity and amplitude of the energy storage capacitor C1 to the pre-charged state after the fault is cleared. There is no need to provide an external pre-charging circuit, which effectively solves the control and volume constraints brought by the cumbersome charging circuit, and greatly shortens the reclosing action time. In addition, the explosion switch PB and the diode D1 realize reliable interruption of large DC currents.

[0047] In another embodiment of the present invention, a computer-readable storage medium is provided, wherein the computer-readable storage medium stores a computer program, wherein the computer program includes program instructions, and when the program instructions are executed by the processor, all or part of the processes in the above-mentioned embodiment method are implemented, or the computer program can be used to instruct the relevant hardware to complete the process, and the computer program can be stored in a computer-readable storage medium, and when the computer program is executed by the processor, the steps of each of the above-mentioned method embodiments can be implemented. Among them, the computer program includes computer program code, and the computer program code can be in source code form, object code form, executable file or some intermediate form, etc. The computer-readable medium may include: any entity or device capable of carrying computer program code, recording medium, U disk, mobile hard disk, magnetic disk, optical disk, computer memory, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), electric carrier signal, telecommunication signal and software distribution medium, etc. It should be noted that the content contained in the computer-readable medium can be appropriately increased or decreased according to the requirements of legislation and patent practice in the jurisdiction. For example, in some jurisdictions, according to legislation and patent practice, the computer-readable medium does not include electric carrier signal and telecommunication signal.

[0048] The computer-readable storage medium may be an internal storage unit of the terminal of any of the foregoing embodiments, such as a hard disk or memory of the terminal. The computer-readable storage medium may also be an external storage device of the terminal, such as a plug-in hard disk, a smart memory card (Smart Media Card, SMC), a secure digital (Secure Digital, SD) card, a flash card (Flash Card), etc. equipped on the terminal. Further, the computer-readable storage medium may also include both an internal storage unit of the terminal and an external storage device. The computer-readable storage medium is used to store computer programs and other programs and data required by the terminal. The computer-readable storage medium may also be used to temporarily store data that has been output or is to be output.

[0049] Those of ordinary skill in the art will appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of the two. In order to clearly illustrate the interchangeability of hardware and software, the composition and steps of each example have been generally described in terms of function in the above description. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of the present invention.

[0050] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features thereof may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A reclosing DC circuit breaker with high breaking capacity, characterized in that It comprises a main branch (1), a backup protection branch (2), a transfer branch (3), a buffer energy absorption branch (4) and a commutation circuit (5), wherein the main branch (1) and the backup protection branch (2) are connected in series, the series-connected main branch (1) and the backup protection branch (2) are connected in parallel with the buffer energy absorption branch (4), and the main branch (1), the transfer branch (3) and the commutation circuit (5) are connected in parallel. The main branch (1) comprises a mechanical switch MS and a diode valve group D1 connected in series; The transfer branch (3) comprises a diode valve group D2; The buffer energy absorption branch (4) comprises a buffer resistor R1, a buffer capacitor C2 and an energy absorption resistor MOV, the buffer resistor R1 is connected in series with the buffer capacitor C2, and the energy absorption resistor MOV is connected in parallel with the series branch of the buffer resistor R1 and the buffer capacitor C2; The commutation circuit (5) comprises a thyristor SCR1, a thyristor SCR2, an IGBT valve group S1 and an IGBT valve group S2; the thyristor SCR1 is connected in series with the IGBT valve group S1, the thyristor SCR2 is connected in series with the IGBT valve group S2, and the two series branches are connected in parallel; it also comprises an energy storage capacitor C1 and a wave modulation inductor L1, one end of the energy storage capacitor C1 is connected to the common connection point of the thyristor SCR1 and the IGBT valve group S1, and the other end is connected to one end of the wave modulation inductor L1, and the other end of the wave modulation inductor L1 is connected to the common connection point of the IGBT valve group S2 and the thyristor SCR2; When the DC line operates normally, the DC current passes through the mechanical switch MS, the diode valve group D1 and the explosion switch PB, and its conduction loss is small; When a short circuit fault occurs in the system, the contacts of the mechanical switch MS separate and start arcing, realizing reliable disconnection of large DC current; the commutation circuit IGBT valve group S1 and IGBT valve group S2 are triggered to conduct, and the energy storage capacitor C1 and the modulation inductor L1 form an oscillating discharge until the fault current is equal to that of the fault current, and the mechanical switch MS extinguishes the arc and turns off; at the same time, the transfer branch diode D2 is turned on under the forward voltage condition, and the fault current and oscillating discharge begin to transfer to the diode D2. At the same time, due to the conduction of the diode D2, both ends of MS are clamped in a low voltage state, and at this time, the IGBT valve group S1 and IGBT valve group S2 are disconnected. BT valve group S2 triggers the conduction thyristor SCR1 and thyristor SCR2 at the same time to form a discharge path with the system circuit. The fault current and the energy stored in the modulation inductor L1 continue to positively charge the energy storage capacitor C1 through the thyristor SCR1 and thyristor SCR2. When the voltage across the energy storage capacitor C1 increases to the opening voltage of the buffer energy absorption branch, the buffer energy absorption branch energy absorption resistor MOV is turned on to absorb the energy of the system and the commutation circuit; the commutation circuit current passes through zero, the thyristors SCR1 and SCR2 are turned off, the buffer energy absorption branch completes the energy absorption, and the fault current is completely cleared.

2. A reclosing DC circuit breaker with high breaking capacity according to claim 1, characterized in that The backup protection branch (2) comprises an explosion switch PB.

3. A reclosing DC circuit breaker with high breaking capacity according to claim 1, characterized in that If the main branch and the current commutation circuit fail, disconnect the explosion switch PB, cut off the circuit, and introduce the current into the energy transfer resistor to avoid the expansion of the fault.

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