A pre-current limiting hybrid DC circuit breaker and control method thereof

Abstract

The present invention relates to a pre-current limiting hybrid DC circuit breaker, which includes a current-passing branch and a fault processing branch arranged in parallel; the current-passing branch includes an ultra-fast mechanical switch UFD and an auxiliary current-passing switch LCS arranged in series; the fault processing branch includes a current transfer part, a current limiting part and a disconnecting part. The present invention puts the current limiting circuit into operation in advance when an overcurrent occurs in the power grid, and decides to cut off the fault line or restore normal operation according to the fault detection result, thereby increasing the reliability of the system. The auxiliary capacitor in the current limiting part does not need to be reversely charged, which increases its service life. The present invention uses auxiliary capacitors and semi-controlled device thyristors to achieve rapid switching of current-limiting inductors, limits the growth rate and amplitude of fault current, reduces the requirements of the DC circuit breaker for the current breaking capacity, and increases the reliability and economy of the system.

Description

Technical Field

[0001] The present invention belongs to the field of high-voltage flexible direct current transmission networks, and in particular relates to a pre-current limiting hybrid direct current circuit breaker and a control method thereof. Background Art

[0002] With the continuous development of new energy and power electronics technology, multi-terminal flexible direct current transmission technology based on modular multilevel converter (MMC) has attracted widespread attention at home and abroad. However, due to the low damping and weak inertia of the DC grid, if a fault occurs in the system, the fault current will reach the current withstand limit of the power electronic device in a short time, and the DC fault current itself has no natural zero crossing point, which greatly increases the difficulty of fault removal. Therefore, how to deal with DC faults has become one of the main problems in this field.

[0003] The protection scheme based on high-voltage DC circuit breakers has attracted the attention of researchers at home and abroad due to its selective characteristics. It can cut off the fault line while ensuring the normal operation of the non-fault line in the power grid during the fault period, thereby improving the overall reliability of the system. At present, the commonly used DC circuit breakers can be mainly divided into mechanical, solid-state and hybrid types. Because the hybrid DC circuit breaker has the economy of mechanical DC circuit breakers and the response speed of solid-state DC circuit breakers, it has the advantages of low on-state loss, fast and controllable disconnection, and high reliability, and has broad application prospects in DC power grids. At present, the technology of hybrid DC circuit breakers has been relatively mature and has been applied in engineering, but the hybrid DC circuit breaker with integrated current limiting function is still in the theoretical research stage. In the future, DC systems will inevitably integrate DC circuit breakers and current limiters to improve the economy and reliability of equipment. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a pre-current limiting hybrid DC circuit breaker and a control method thereof, so as to improve the operating reliability of a multi-terminal DC power grid under a DC fault and reduce the requirement on the breaking current capacity of the DC circuit breaker.

[0005] The technical solution adopted by the present invention is:

[0006] A pre-current limiting hybrid DC circuit breaker, comprising a current-carrying branch and a fault processing branch arranged in parallel;

[0007] The through-current branch includes an ultra-fast mechanical switch UFD and an auxiliary through-current switch LCS arranged in series;

[0008] The fault processing branch includes a current transfer part, a current limiting part and a disconnecting part.

[0009] Furthermore, the auxiliary current-passing switch LCS includes an IGBT group T1 with an anti-parallel diode connected in series in reverse order.

[0010] Furthermore, the current transfer part includes branch 1, branch 2, branch 3 and branch 4, the anode of branch 1 is connected in series with the cathode of branch 2, and the connection point between the two is connected to one end of the flow branch; the anode of branch 3 is connected in series with the cathode of branch 4, and the connection point between the two is connected to the other end of the flow branch;

[0011] A branch consisting of branch 1 and branch 2 connected in series is connected in parallel with a branch consisting of branch 3 and branch 4 connected in series.

[0012] Further, the branch 1 includes a thyristor group T2 and a diode group D2 connected in series, the branch 2 includes a thyristor group T3 and a diode group D3 connected in series, the branch 3 includes a thyristor group T4 and a diode group D4 connected in series, and the branch 4 includes a thyristor group T5 and a diode group D5 connected in series.

[0013] Furthermore, the current limiting part includes an auxiliary capacitor C, a current limiting inductor L and a thyristor; wherein,

[0014] The cathode of the thyristor group T7 formed by a certain number of thyristors connected in series is connected to the negative electrode of the capacitor C; the positive electrode of the capacitor C is connected to the cathode of another specific number of thyristor groups T8 connected in series; the anode of T8 is connected to the anode of T7 and the current limiting inductor L respectively; the other end of the current limiting inductor L is connected to the cathode of the branch 1; the anode of the thyristor group T6 formed by a certain number of thyristors connected in series is connected to the cathode of the branch 1, and the cathode of T6 is connected to the anode of the auxiliary capacitor C.

[0015] Furthermore, the disconnecting part includes an IGBT group T9 with an anti-parallel diode and a lightning arrester MOA arranged in parallel, one end of the disconnecting part is connected to the positive electrode of the auxiliary capacitor C, and the other end is connected to the anode of the branch 2.

[0016] Furthermore, the number of thyristors in branch 1, branch 2, branch 3 and branch 4 is the same.

[0017] Furthermore, the number of diodes in branch 1, branch 2, branch 3 and branch 4 is the same.

[0018] Furthermore, the number of thyristors in the thyristor group is determined according to the DC bus voltage that needs to be interrupted and the pre-charge voltage of the auxiliary capacitor C.

[0019] Furthermore, the inductance value of the current limiting inductor L is determined according to a desired current limiting effect.

[0020] A control method for a pre-current limiting hybrid DC circuit breaker includes the following process:

[0021] Assuming that the system operates normally, the current flows from the left side to the right side of the DC circuit breaker, and the short circuit fault occurs at the right end of the DC circuit breaker. The left side of the DC circuit breaker is called the non-fault side, and the right side is called the fault side.

[0022] Phase 1 (t 0- ): When the system is working normally, the current flows through the current branch;

[0023] Phase 2 (t0-t1): When the grid current abnormality is detected at time t0, a conduction trigger signal is sent to T2, T5, T6 and T9, and T1 in the flow branch is turned off and a trip command is sent to UFD. At this time, the system current is naturally transferred from the flow branch to the fault handling branch;

[0024] Phase 3 (t1-t2): At t1, UFD completes disconnection, and sends a conduction trigger signal to T7 and T8, and removes the conduction trigger signal of T6. After T6 is completely turned off, the current limiting inductor L and the auxiliary capacitor C are connected in series to the line;

[0025] Phase 4 (t2-t3): At t2, the auxiliary capacitor C is discharged, and T8 is turned on due to the forward voltage drop, while T7 is turned off due to the reverse voltage. At this time, all the current is transferred to the branch where T8 is located, the auxiliary capacitor C is bypassed, and the current limiting inductor L is fully put into use, thereby realizing the pre-current limiting function;

[0026] Phase 5 (t3-t4): At t3, the fault detection is completed. If a fault is confirmed, a shutdown signal is sent to T9 in the disconnecting part; if no fault is confirmed, a conduction trigger signal is sent to T4 in branch 3, and UFD is closed at the same time.

[0027] Phase 6 (t4-t5): At t4, the UFD is fully closed, turning on T1 of the flow branch and turning off T9 of the disconnecting part, and removing the conduction trigger signal of T2, T4, T5, T7 and T8, so that the current of the fault handling branch can be transferred to the flow branch; when the current flowing through T2, T4, T5, T7 and T8 is less than its holding current, natural shutdown is achieved.

[0028] The positive effects of the present invention are:

[0029] By adopting the technical solution of the present invention, the current limiting circuit is put into operation in advance when an overcurrent occurs in the power grid, and the fault line is cut off or normal operation is restored according to the fault detection result, thereby increasing the reliability of the system. The auxiliary capacitor in the current limiting part does not need to be reversely charged, which increases its service life. The present invention uses auxiliary capacitors and semi-controlled device thyristors to achieve rapid switching of current limiting inductors, limits the growth rate and amplitude of fault current, reduces the requirements of the DC circuit breaker for the breaking current capacity, and increases the reliability and economy of the system. The present invention has good use value and economic benefits in the field of multi-port flexible DC transmission and other occasions. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] 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.

[0031] Figure 1 It is a topological schematic diagram of the present invention;

[0032] Figure 2 This is a schematic diagram of the fault processing branch topology of the present invention;

[0033] Figure 3 This is a topological schematic diagram of the current limiting part of the present invention;

[0034] Figure 4 This is a schematic diagram of the topology of the disconnected part of the present invention. DETAILED DESCRIPTION

[0035] 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.

[0036] 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.

[0037] As attached Figure 1 As shown, in order to improve the operational reliability of a multi-terminal DC power grid under a DC fault and reduce the requirements for the current breaking capacity of a DC circuit breaker, the present invention proposes a pre-current limiting hybrid DC circuit breaker and a control method thereof, so as to effectively limit the rising rate and amplitude of the fault current after a system fault, and realize reliable fault ride-through suitable for a multi-terminal DC power grid.

[0038] Specifically, the present invention includes a flow branch and a fault processing branch; wherein:

[0039] The through-current branch is composed of an ultra-fast mechanical switch UFD and an auxiliary through-current switch LCS in series; the fault handling branch is composed of a current transfer part, a current limiting part and a disconnecting part.

[0040] The auxiliary current-passing switch LCS is composed of an IGBT group T1 with an anti-parallel diode connected in series in reverse order;

[0041] The current transfer part includes branch 1, branch 2, branch 3 and branch 4; each branch is composed of a certain number of thyristors and diodes in series, wherein the anode of branch 1 composed of thyristor T2 and diode D2 in series is connected in series with the cathode of branch 2 composed of thyristor T3 and diode D3 in series, and their connection point is connected to one end of the current branch; the anode of branch 3 composed of thyristor T4 and diode D4 is connected in series with the cathode of branch 4 composed of thyristor T5 and diode D5, and their connection point is connected to the other end of the current branch. The branch composed of branch 1 and branch 2 in series is connected in parallel with the branch composed of branch 3 and branch 4 in series;

[0042] The current limiting part is composed of an auxiliary capacitor C, a current limiting inductor L and a thyristor; wherein a certain number of thyristors are connected in series to form a thyristor group T7, whose cathode is connected to the negative electrode of the auxiliary capacitor C; the positive electrode of the auxiliary capacitor C is connected to the cathode of another specific number of thyristor groups T8 connected in series; the anode of T8 is connected to the anode of T7 and the current limiting inductor L respectively; the other end of the current limiting inductor L is connected to the cathode of branch 1; the anode of the thyristor group T6, which is formed by a certain number of thyristors connected in series, is connected to the cathode of branch 1, and the cathode of T6 is connected to the anode of the auxiliary capacitor C;

[0043] The disconnecting part is composed of an IGBT group T9 with an anti-parallel diode connected in series and in parallel with a lightning arrester MOA, wherein one end of the disconnecting part is connected to the positive electrode of the auxiliary capacitor C, and the other end is connected to the anode of the branch 2.

[0044] The number of thyristors and diodes in branch 1, branch 2, branch 3 and branch 4 is the same. The number of thyristors in the thyristor group is determined by the DC bus voltage to be switched and the pre-charge voltage of the auxiliary capacitor C. The inductance value of the current limiting inductor L is determined by the desired current limiting effect.

[0045] The control method of the pre-current limiting hybrid DC circuit breaker includes the following process:

[0046] Assuming that the system operates normally, the current flows from the left side to the right side of the DC circuit breaker, and the short circuit fault occurs at the right end of the circuit breaker. The left side of the circuit breaker is called the non-fault side, and the right side is called the fault side.

[0047] Phase 1 (t0-): When the system is working normally, the current flows through the current branch;

[0048] Phase 2 (t0-t1): When the grid current abnormality is detected at time t0, a trigger signal is sent to T2, T5, T6 and T9, and T1 in the flow branch is turned off and a trip command is issued to UFD. At this time, the grid current can be naturally transferred from the flow branch to the fault handling branch;

[0049] Phase 3 (t1-t2): At t1, UFD is disconnected, and a trigger signal is sent to T7 and T8, and the trigger signal of T6 is removed. Since the auxiliary capacitor C has been pre-charged, T6 will withstand a period of reverse voltage, thereby restoring its forward blocking capability. After T6 is completely turned off, the current limiting inductor L and the auxiliary capacitor C are connected in series to the circuit, where the current limiting inductor L plays a current limiting role.

[0050] Phase 4 (t2-t3): At t2, the auxiliary capacitor C is discharged, and T8 is turned on due to the forward voltage drop, while T7 is turned off due to the reverse voltage. At this time, all the current is transferred to the branch where T8 is located, the auxiliary capacitor C is bypassed, and the current limiting inductor L is fully put into use, thereby realizing the pre-current limiting function;

[0051] Phase 5 (t3-t4): At t3, the fault detection is completed. If a fault is confirmed, a shutdown signal is sent to T9 in the disconnecting part. At this time, the current is transferred to MOA. Because the volt-ampere characteristic of MOA itself will present a large reverse voltage in the fault line, the fault current is cut off. If no fault is confirmed, a conduction signal is sent to T4 in branch 3 to form a discharge circuit of the current-limiting inductor and close UFD at the same time.

[0052] Phase 6 (t4-t5): At t4, the UFD is fully closed, turning on T1 of the flow branch and turning off T9 of the disconnecting part, and removing the conduction signal of T2, T4, T5, T7 and T8, so that the current of the fault handling branch can be transferred to the flow branch; when the current flowing through T2, T4, T5, T7 and T8 is less than its holding current, natural shutdown is achieved.

[0053] The present invention uses auxiliary capacitors and semi-controlled device thyristors to achieve rapid switching of current-limiting inductors, limits the growth rate and amplitude of fault current, reduces the requirements of DC circuit breakers on breaking current capacity, and increases the reliability and economy of the system.

[0054] The present invention has good use value and economic benefits in the field of multi-port flexible direct current power transmission and other occasions.

[0055] 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 pre-current limiting hybrid DC circuit breaker, characterized in that It includes a flow branch and a fault processing branch arranged in parallel; The through-current branch includes an ultra-fast mechanical switch UFD and an auxiliary through-current switch LCS arranged in series; The fault handling branch includes a current transfer part, a current limiting part and a disconnecting part; The current transfer part includes branch 1, branch 2, branch 3 and branch 4, the anode of branch 1 is connected in series with the cathode of branch 2, and the connection point between the two is connected to one end of the flow branch; the anode of branch 3 is connected in series with the cathode of branch 4, and the connection point between the two is connected to the other end of the flow branch; A branch consisting of branch 1 and branch 2 connected in series is connected in parallel with a branch consisting of branch 3 and branch 4 connected in series; The current limiting part includes an auxiliary capacitor C, a current limiting inductor L and a thyristor; wherein, The cathode of the thyristor group T7 formed by a certain number of thyristors connected in series is connected to the negative electrode of the capacitor C; the positive electrode of the capacitor C is connected to the cathode of another specific number of thyristor groups T8 connected in series; the anode of T8 is connected to the anode of T7 and the current limiting inductor L respectively; the other end of the current limiting inductor L is connected to the cathode of the branch 1; the anode of the thyristor group T6 formed by a certain number of thyristors connected in series is connected to the cathode of the branch 1, and the cathode of T6 is connected to the anode of the auxiliary capacitor C.

2. A pre-current limiting hybrid DC circuit breaker according to claim 1, characterized in that The auxiliary current pass switch LCS includes an IGBT group T1 with an anti-parallel diode connected in series.

3. A pre-current limiting hybrid DC circuit breaker according to claim 1, characterized in that The branch 1 includes a thyristor group T2 and a diode group D2 connected in series, the branch 2 includes a thyristor group T3 and a diode group D3 connected in series, the branch 3 includes a thyristor group T4 and a diode group D4 connected in series, and the branch 4 includes a thyristor group T5 and a diode group D5 connected in series.

4. A pre-current limiting hybrid DC circuit breaker according to claim 1, characterized in that The disconnecting part includes an IGBT group T9 with anti-parallel diodes and a lightning arrester MOA arranged in parallel. One end of the disconnecting part is connected to the positive electrode of the auxiliary capacitor C, and the other end is connected to the anode of the branch 2.

5. A pre-current limiting hybrid DC circuit breaker according to claim 1, characterized in that The number of thyristors and the number of diodes in branch 1, branch 2, branch 3 and branch 4 are the same.

6. A pre-current limiting hybrid DC circuit breaker according to claim 4, characterized in that The number of thyristors in the thyristor group is determined according to the DC bus voltage that needs to be interrupted and the pre-charge voltage of the auxiliary capacitor C.

7. A pre-current limiting hybrid DC circuit breaker according to claim 1, characterized in that The inductance value of the current limiting inductor L is determined according to the desired current limiting effect.

8. A control method for a pre-current limiting hybrid DC circuit breaker, characterized in that It includes the following processes: Assuming that the system operates normally, the current flows from the left side to the right side of the DC circuit breaker, and the short circuit fault occurs at the right end of the DC circuit breaker. The left side of the DC circuit breaker is called the non-fault side, and the right side is called the fault side. Phase 1 (t0): When the system is working normally, the current flows through the current branch; Phase 2 (t0-t1): When the grid current abnormality is detected at time t0, a conduction trigger signal is sent to T2, T5, T6 and T9, and T1 in the flow branch is turned off and a trip command is sent to UFD. At this time, the system current is naturally transferred from the flow branch to the fault handling branch; Phase 3 (t1-t2): At t1, UFD completes disconnection, and sends a conduction trigger signal to T7 and T8, and removes the conduction trigger signal of T6. After T6 is completely turned off, the current limiting inductor L and the auxiliary capacitor C are connected in series to the line; Phase 4 (t2-t3): At t2, the auxiliary capacitor C is discharged, and T8 is turned on due to the forward voltage drop, while T7 is turned off due to the reverse voltage. At this time, all the current is transferred to the branch where T8 is located, the auxiliary capacitor C is bypassed, and the current limiting inductor L is fully put into use, thereby realizing the pre-current limiting function; Phase 5 (t3-t4): At time t3, fault detection is completed. If a fault is confirmed, a shutdown signal is sent to T9 in the disconnecting part; If it is confirmed that no fault has occurred, a conduction trigger signal is sent to T4 in branch 3, and UFD is closed at the same time; Phase 6 (t4-t5): At t4, the UFD is fully closed, turning on T1 of the flow branch and turning off T9 of the disconnecting part, and removing the conduction trigger signal of T2, T4, T5, T7 and T8, so that the current of the fault handling branch can be transferred to the flow branch; when the current flowing through T2, T4, T5, T7 and T8 is less than its holding current, natural shutdown is achieved.

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