DC circuit breaker and control method thereof

Abstract

The invention provides a direct-current circuit breaker and a control method thereof, and belongs to the technical field of direct-current middle-high voltage power system fault protection. The short circuit turn-off branch comprises a first capacitor and a first thyristor; the coupling commutation branch comprises a first inductor, a second inductor, a second thyristor and a third capacitor; the rated turn-off branch comprises a first resistor and a second capacitor; the first resistor, the second capacitor, the first capacitor and the second inductor are sequentially connected in series and then are connected with the main switch branch in parallel; the first inductor, the second thyristor and the third capacitor are sequentially connected in series, and the first inductor and the second inductor form mutual inductance. By controlling the on-off of the first thyristor, the first capacitor and the second capacitor are connected in series, the capacitance value is reduced, large-capacitance-value operation of a single group of capacitors is realized, and the problem that the on-off time of rated and lower low-current breaking is relatively long can be solved.

Description

Technical Field

[0001] This invention relates to the field of fault protection technology for DC medium and high voltage power systems, specifically to a DC circuit breaker and its control method. Background Technology

[0002] DC power systems lack zero-crossing points, and circuit breakers have always been a bottleneck restricting their development to higher voltage levels. The manual zero-crossing breaking scheme refers to a technical solution that creates a current zero point by injecting reverse current into a fast-moving mechanical switch to achieve breaking. Under rated operating conditions, this scheme uses a mechanical switch to handle the rated current, resulting in low on-state losses. During breaking, a pre-charged capacitor enables rapid current transfer, leading to a large breaking capacity. Furthermore, compared to using high-power fully controlled devices, this scheme is less expensive and has therefore gained widespread application in engineering projects.

[0003] However, under short-circuit conditions, a large pulse current needs to be injected back into the fast mechanical switch, resulting in a large capacitance value for the capacitor connected in series in the current transfer branch. During high-current interruption, the capacitor can be charged quickly to reach the varistor's turn-on voltage, thus achieving rapid turn-off. However, during low-current interruption at or below the rated rating, due to the small loop current and the large capacitance value, the capacitor requires a long time to establish the interruption voltage, resulting in a long total interruption time, which can reach hundreds of milliseconds or more, making it difficult to meet the system's interruption requirements.

[0004] For a long time, the problem of breaking small currents at or below the rated level has been a challenge for manual zero-crossing breaking technology, and it has been difficult to solve effectively. Summary of the Invention

[0005] In view of this, it is necessary to provide a DC circuit breaker and its control method to solve the technical problem of long breaking time for small currents at and below rated levels.

[0006] To address the aforementioned problems, in a first aspect, the present invention provides a DC circuit breaker, comprising: Main switch branch circuit, including: mechanical switch; The short-circuit turn-off branch includes: a first capacitor and a first thyristor; The coupled commutation branch includes: a first inductor, a second inductor, a second thyristor, and a third capacitor; The rated shutdown branch includes: a first resistor and a second capacitor; The first resistor, the second capacitor, the first capacitor and the second inductor are connected in series in sequence and then connected in parallel with the main switch branch; The first inductor, the second thyristor, and the third capacitor are connected in series, and the first inductor and the second inductor form a mutual inductance.

[0007] In one possible implementation, the DC circuit breaker further includes: A voltage-limiting and energy-dissipating branch is provided, one end of which is connected to one end of the main switch branch, and the other end of which is connected between the first capacitor and the second inductor.

[0008] In one possible implementation, the voltage-limiting energy-dissipating branch includes a varistor.

[0009] In one possible implementation, the varistor is a zinc oxide varistor.

[0010] In one possible implementation, both ends of the main switch branch are connected to the power system.

[0011] In one possible implementation, the DC circuit breaker further includes: The controller is used to control the mechanical switch to close under rated operating conditions, control the mechanical switch to open during the DC circuit breaker disconnection process, control the second thyristor to turn on when the moving and stationary contacts of the mechanical switch move to a preset distance, and generate a reverse pulse current by controlling the on and off of the first thyristor.

[0012] In one possible implementation, a reverse pulse current is generated by controlling the on / off state of the first thyristor, including: When the breaking current is at or below the rated level, the first thyristor is controlled to disconnect.

[0013] In one possible implementation, a reverse pulse current is generated by controlling the on / off state of the first thyristor, including: When the breaking current is the short-circuit current, the first thyristor is controlled to turn on.

[0014] In one possible implementation, the capacitance of the second capacitor is smaller than that of the first capacitor.

[0015] Secondly, the present invention also provides a control method for a DC circuit breaker, the method being applied to the DC circuit breaker described in any of the above claims, the control method comprising: Under rated operating conditions, control the main switch branch to close; During the DC circuit breaker tripping process, the main switch branch is controlled to trip, and the second thyristor is controlled to conduct. A reverse pulse current is generated by controlling the on and off of the first thyristor.

[0016] The beneficial effects of the above implementation method are as follows: The DC circuit breaker and its control method provided by the present invention consist of a first resistor, a second capacitor, a first capacitor, and a second inductor connected in series and then connected in parallel with the main switch branch; the first inductor, the second thyristor, and the third capacitor are connected in series, with the first inductor and the second inductor forming a mutual inductance. The third capacitor discharges through the first inductor and the second thyristor, and induces an electromotive force of "left negative and right positive" in the second inductor through coil coupling, thereby generating a pulse current. This current is opposite to the current in the mechanical switch and controls the switching of the first thyristor. By connecting the first capacitor and the second capacitor in series and reducing the capacitance value, a mode of single-group capacitor operation with a large capacitance value and two groups of capacitors connected in series with a small capacitance value is achieved. The pulse reverse current generated in the circuit is slightly higher than the rated current of the mechanical switch, realizing manual zero-crossing interruption of the mechanical switch for currents at or below the rated level. This solves the technical problem of long interruption time for small currents at or below the rated level. In other words, it effectively solves the problem of small current interruption in traditional manual zero-crossing schemes and has the advantages of fast interruption speed and low cost. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 A structural diagram of an embodiment of the DC circuit breaker provided by the present invention; Figure 2 Waveform diagrams of current and current parameters of each branch in a low current breaking system of rated level and below provided for the present invention. Figure 3 The topology diagram for low current interruption of rated class and below rated class and reverse charging provided by the present invention; Figure 4 The waveform diagram of the current and current parameters of each branch of the short-circuit current breaking system provided by the present invention. Figure 5 The short-circuit current interruption artificial zero crossing and reverse charging topology diagram provided by the present invention; Figure 6 A waveform comparison diagram of the present invention's solution and the traditional manual zero-crossing solution under low-current interruption conditions. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0020] In the description of the embodiments of this application, unless otherwise stated, "a plurality of" means two or more.

[0021] In this embodiment of the invention, the terms "comprising" and "having" and any variations thereof are intended to cover non-exclusive inclusion, for example, a process, method, apparatus, product or device that includes a series of steps or modules is not necessarily limited to those steps or modules that are explicitly listed, but may include other steps or modules that are not explicitly listed or that are inherent to such process, method, product or device.

[0022] The naming or numbering of steps in the embodiments of the present invention does not mean that the steps in the method flow must be executed in the time / logical order indicated by the naming or numbering. The execution order of the named or numbered process steps can be changed according to the technical purpose to be achieved, as long as the same or similar technical effect can be achieved.

[0023] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0024] This invention provides a DC circuit breaker and its control method, which are described below.

[0025] like Figure 1 As shown, the present invention provides a DC circuit breaker, comprising: The main switch branch includes: a mechanical switch S1; both ends of the main switch branch are connected to the power system; The short-circuit turn-off branch includes: the first capacitor C1 and the first thyristor T1; The coupling commutation branch includes: a first inductor L1, a second inductor L2, a second thyristor T2, and a third capacitor C3; The rated shutdown branch includes: a first resistor R1 and a second capacitor C2; the capacitance of the second capacitor C2 is less than the capacitance of the first capacitor C1. The first resistor R1, the second capacitor C2, the first capacitor C1 and the second inductor L2 are connected in series and then connected in parallel with the main switch branch; The first inductor L1, the second thyristor T2, and the third capacitor C3 are connected in series, and the first inductor L1 and the second inductor L2 form a mutual inductance.

[0026] It is understood that the present invention provides an artificial zero-crossing DC circuit breaker, comprising: a main switch branch, a rated shutdown branch, a short-circuit shutdown branch, a coupling converter branch, and a voltage-limiting energy-dissipating branch. The DC circuit breaker is connected to a power system, with the two connected nodes denoted as N1 and N2. One end of the main switch branch is connected via N1 to one end of each of the rated shutdown branch, the short-circuit shutdown branch, and the voltage-limiting energy-dissipating branch. The other end of the main switch branch is connected via N2 to one end of the second inductor L2 of the coupling converter branch. The main switch branch consists of a fast mechanical switch S1.

[0027] The rated shutdown branch is composed of a first resistor R1 and a second capacitor C2 connected in series. One end of the first resistor R1 is connected to N1, and the external connection point of the second capacitor C2 is denoted as N2.

[0028] The short-circuit shutdown branch is composed of a first thyristor T1 and a first capacitor C1 connected in series. The anode of the first thyristor T1 is connected to N1, and the cathode is connected to one pole of the first capacitor C1 and connected to N3. The other pole of the first capacitor C1 is connected to the external connection point, which is denoted as N4. The capacitance of the first capacitor C1 is greater than the capacitance of the second capacitor C2.

[0029] The coupling commutation branch consists of a pre-charge capacitor, namely the third capacitor C3, the second thyristor T2, and mutual coils (L1 / L2). The third capacitor C3, the second thyristor T2, and the first inductor L1 are connected in series to form a pulse discharge circuit. One end of the second inductor L2 is connected to N4, and the other end is connected to N2.

[0030] The beneficial effects of this invention are: by controlling the on and off of the first thyristor T1, this invention realizes the operation mode of a single set of capacitors with a large capacitance value and the operation mode of two sets of capacitors in series with a small capacitance value, realizing rapid disconnection under both fault current and small current conditions, effectively solving the problem of small current disconnection in the traditional "manual zero crossing" scheme, and has the advantages of fast disconnection speed and low cost.

[0031] In some embodiments, the DC circuit breaker further includes: A voltage limiting and energy dissipation branch is provided, one end of which is connected to one end of the main switch branch, and the other end of which is connected between the first capacitor C1 and the second inductor L2.

[0032] The voltage-limiting and energy-dissipating branch includes a varistor. The varistor is a zinc oxide varistor.

[0033] Understandably, after the mechanical switch S1 is disconnected, the system current charges the second capacitor C2 and the first capacitor C1 in series through the first resistor R1. Since the capacitance value is small after being connected in series, it can quickly be charged to the turn-on voltage of the metal oxide varistor MOV, realizing the rapid transfer of fault current to the metal oxide varistor MOV and completing the disconnection.

[0034] In some embodiments, the DC circuit breaker further includes: The controller is used to control the mechanical switch S1 to close under rated operating conditions, control the mechanical switch S1 to open during the DC circuit breaker disconnection process, control the second thyristor T2 to turn on when the moving and stationary contacts of the mechanical switch S1 move to a preset distance, and generate a reverse pulse current by controlling the on and off of the first thyristor T1.

[0035] Under normal operating conditions, the main branch switch's fast mechanical switch S1 closes to carry the system current.

[0036] During the disconnection process, a tripping command is first sent to the fast mechanical switch S1, which then trips quickly and generates an electric arc. After a delay, when the moving and stationary contacts of the fast mechanical switch S1 move to a sufficient opening distance, the second thyristor T2 is turned on. The third capacitor C3 discharges through the first inductor L1 and the second thyristor T2, and induces an electromotive force of "left negative and right positive" in the second inductor L2 through coil coupling, thereby generating a pulse current that is opposite to the current in the fast mechanical switch S1. During the disconnection process, by controlling whether the first thyristor T1 is turned off or not, a corresponding reverse pulse current is generated, which causes the current in the fast mechanical switch S1 to drop to zero quickly, thus achieving manual zero-crossing turn-off. After the fast mechanical switch S1 is turned off, the system voltage rises and quickly reaches the turn-on voltage of the zinc oxide varistor MOV. The fault current is transferred to the zinc oxide varistor MOV, and the fault is interrupted.

[0037] In some embodiments, generating a reverse pulse current by controlling the on / off state of the first thyristor T1 includes: When the breaking current is at or below the rated level, the first thyristor T1 is controlled to disconnect.

[0038] It is understandable that if the breaking current is at or below the rated level: When the moving and stationary contacts of the fast mechanical switch S1 open to a sufficient gap, the second thyristor T2 is turned on while the first thyristor T1 is not turned on. L2-S1-R1-C2-C1 form a circuit. The first capacitor C1 and the second capacitor C2 are connected in series and have a small capacitance. The pulse reverse current generated by the circuit is slightly higher than the rated current of the fast mechanical switch S1, which can realize the artificial zero-crossing interruption of the current of the fast mechanical switch S1 at or below the rated level. At the same time, the series connection of the first resistor R1 avoids the underdamped oscillation of the circuit.

[0039] After the mechanical switch S1 is disconnected, the system current charges the second capacitor C2 and the first capacitor C1 in series through the first resistor R1. Since the capacitance value is small after being connected in series, it can quickly be charged to the turn-on voltage of the metal oxide varistor MOV, realizing the rapid transfer of fault current to the metal oxide varistor MOV and completing the disconnection.

[0040] In some embodiments, generating a reverse pulse current by controlling the on / off state of the first thyristor T1 includes: When the breaking current is the short-circuit current, the first thyristor T1 is controlled to turn on.

[0041] It is understandable that if the breaking current is the short-circuit current: When the moving and stationary contacts of the fast mechanical switch S1 open to a sufficient gap, the first thyristor T1 is turned on at the same time as the second thyristor T2 is turned on. L2-S1-T1-C1 forms a circuit. The capacitance of the first capacitor C1 is relatively large, and the circuit generates a high pulse reverse current, realizing the manual zero-crossing disconnection of the fast mechanical switch S1 under short-circuit conditions.

[0042] After the mechanical switch S1 is disconnected, the system current charges the first capacitor C1. Although the capacitance of the first capacitor C1 is relatively high, the short-circuit current is also larger. It can quickly be charged to the turn-on voltage of the zinc oxide varistor MOV, realizing the rapid transfer of fault current to the zinc oxide varistor MOV and completing the short-circuit interruption.

[0043] In some embodiments, such as Figure 1 As shown, an artificial zero-crossing DC circuit breaker includes: a main switch branch, a rated shutdown branch, a short-circuit shutdown branch, a coupling converter branch, and a voltage-limiting and energy-dissipating branch. The DC circuit breaker is connected to a power system, with two connected nodes denoted as N1 and N2. One end of the main switch branch is connected via N1 to one end of each of the rated shutdown branch, short-circuit shutdown branch, and voltage-limiting and energy-dissipating branch. The other end of the main switch branch is connected via N2 to one end of the inductor L2 of the coupling converter branch. The main switch branch consists of a fast mechanical switch S1; The rated shutdown branch is composed of a first resistor R1 and a second capacitor C2 connected in series. One end of the first resistor R1 is connected to N1, and the external connection point of the second capacitor C2 is denoted as N2. The short-circuit turn-off branch is composed of a first thyristor T1 and a first capacitor C1 connected in series. The anode of the first thyristor T1 is connected to N1, and the cathode is connected to one pole of the first capacitor C1 and connected to N3. The other pole of the first capacitor C1 is connected to the external connection point, which is denoted as N4. The capacitance value of the first capacitor C1 is greater than the capacitance value of the second capacitor C2. The coupling commutation branch consists of a third capacitor C3, a second thyristor T2, and mutual coils (L1 / L2). The third capacitor C3, the second thyristor T2, and the first inductor L1 are connected in series to form a pulse discharge circuit. One end of the second inductor L2 is connected to N4, and the other end is connected to N2. The energy-consuming branch consists of a metal oxide zinc varistor (MOV).

[0044] The present invention also provides a control method for a DC circuit breaker, the method being applied to the DC circuit breaker described in any of the above claims, the control method comprising: Under rated operating conditions, control the main switch branch to close; During the DC circuit breaker tripping process, the main switch branch is controlled to trip, and the second thyristor T2 is controlled to conduct. A reverse pulse current is generated by controlling the switching on and off of the first thyristor T1.

[0045] In some embodiments, a method for breaking a DC circuit breaker with artificial zero-crossing capability includes the following steps: If the breaking current is at or below the rated level, refer to Figure 2 As shown.

[0046] t 0~ t Phase 1: The system operates under rated current-carrying conditions, with the fast mechanical switch S1 closed, carrying the system current. i 0.

[0047] t At moment 1, a command to open the fast mechanical switch S1 is issued, followed by a mechanical delay of several hundred μs. t At time 2, the fast mechanical switch S1 begins actual tripping; t At time 3, the moving and stationary contacts of the fast mechanical switch S1 move to a sufficient opening distance, only conducting the second thyristor T2. The pulse circuit formed by C3-L1-T2 discharges, and simultaneously, an electromotive force (EMF) with "negative on the left and positive on the right" is induced in the second inductor L2. This EMF forms a circuit through L2-S1-R1-C2-C1. At this time, the first capacitor C1 and the second capacitor C2 are connected in series, and their capacitance is relatively small. The circuit generates a reverse pulse current slightly higher than the rated current of the fast mechanical switch S1.i L2 The S1 rapid mechanical switch quickly disconnects when manually zero-crossing, refer to... Figure 3 As shown.

[0048] t At time 4, the current in the fast mechanical switch S1 turns off at zero, and the system current is transferred to the first capacitor C1 and the second capacitor C2 connected in series, causing the voltage of the first capacitor C1 and the second capacitor C2 to rise.

[0049] t At time 5, the voltage across the series connection of capacitors C1 and C2 rises to the turn-on voltage of the zinc oxide varistor (MOV), causing the MOV to turn on. The fault current rapidly transfers into the MOV and... t The break is achieved at time 6.

[0050] If the breaking current is the short-circuit current, refer to Figure 4 As shown.

[0051] t 0~ t Phase 1: The system operates under rated current-carrying conditions, with the fast mechanical switch S1 closed, carrying the system current. i 0.

[0052] t A short circuit fault occurs at moment 1, and the system current rises rapidly.

[0053] t At time 2, a fault was detected and a command to open the fast mechanical switch S1 was issued. After a mechanical delay of several hundred μs, the fast mechanical switch S1 began to actually open. t At time 3, the moving and stationary contacts of the fast mechanical switch S1 move to a sufficient opening distance, simultaneously turning on the first thyristor T1 and the second thyristor T2. The pulse circuit formed by C3-L1-T2 discharges, and at the same time, the second inductor L2 induces an electromotive force with "negative on the left and positive on the right." This electromotive force forms a circuit through L2-S1-T1-C1. The first capacitor C1 has a relatively large capacitance, and the circuit generates a high pulse reverse current, realizing the manual zero-crossing disconnection of the fast mechanical switch S1 under short-circuit conditions. (Refer to...) Figure 5 As shown.

[0054] t At time 4, the current in the fast mechanical switch S1 turns off at zero, and the system current is transferred to the first capacitor C1 connected in series, causing the voltage of the first capacitor C1 to rise.

[0055] tAt time 5, the voltage across the first capacitor C1 rises to the turn-on voltage of the zinc oxide varistor (MOV), causing the MOV to turn on. The fault current rapidly transfers into the MOV and... t The break is achieved at time 6.

[0056] Compared to traditional manual zero-crossing methods, this invention significantly improves the breaking speed of currents at and below the rated level, and substantially reduces the total breaking time, thus effectively meeting the system protection requirements. (Refer to...) Figure 6 As shown. Without increasing size and weight, a simple control method effectively solves the problem of small current interruption using traditional manual zero-crossing methods.

[0057] The DC circuit breaker and its control method provided by the present invention have been described in detail above. Specific examples have been used to illustrate the principle and implementation of the present invention. The description of the above embodiments is only for the purpose of helping to understand the method and core idea of ​​the present invention. At the same time, for those skilled in the art, there will be changes in the specific implementation and application scope based on the idea of ​​the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A DC circuit breaker, characterized in that, include: Main switch branch circuit, including: mechanical switch; The short-circuit turn-off branch includes: a first capacitor and a first thyristor; The coupled commutation branch includes: a first inductor, a second inductor, a second thyristor, and a third capacitor; The rated shutdown branch includes: a first resistor and a second capacitor; The first resistor, the second capacitor, the first capacitor and the second inductor are connected in series in sequence and then connected in parallel with the main switch branch; The first inductor, the second thyristor, and the third capacitor are connected in series, and the first inductor and the second inductor form a mutual inductance.

2. The DC circuit breaker according to claim 1, characterized in that, Also includes: A voltage-limiting and energy-dissipating branch is provided, one end of which is connected to one end of the main switch branch, and the other end of which is connected between the first capacitor and the second inductor.

3. The DC circuit breaker according to claim 2, characterized in that, The voltage-limiting energy-dissipating branch includes: a varistor.

4. The DC circuit breaker according to claim 3, characterized in that, The varistor is a zinc oxide varistor.

5. The DC circuit breaker according to claim 1, characterized in that, Both ends of the main switch branch are connected to the power system.

6. The DC circuit breaker according to claim 1, characterized in that, Also includes: The controller is used to control the mechanical switch to close under rated operating conditions, control the mechanical switch to open during the DC circuit breaker disconnection process, control the second thyristor to turn on when the moving and stationary contacts of the mechanical switch move to a preset distance, and generate a reverse pulse current by controlling the on and off of the first thyristor.

7. The DC circuit breaker according to claim 6, characterized in that, Generating a reverse pulse current by controlling the on / off state of the first thyristor includes: When the breaking current is at or below the rated level, the first thyristor is controlled to disconnect.

8. The DC circuit breaker according to claim 6, characterized in that, Generating a reverse pulse current by controlling the on / off state of the first thyristor includes: When the breaking current is the short-circuit current, the first thyristor is controlled to turn on.

9. The DC circuit breaker according to any one of claims 1-8, characterized in that, The capacitance of the second capacitor is less than that of the first capacitor.

10. A control method for a DC circuit breaker, characterized in that, The method is applied to the DC circuit breaker according to any one of claims 1-9, and the control method includes: Under rated operating conditions, control the main switch branch to close; During the DC circuit breaker tripping process, the main switch branch is controlled to trip, and the second thyristor is controlled to conduct. A reverse pulse current is generated by controlling the on and off of the first thyristor.

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