A multi-port DC circuit breaker and its application method

Abstract

The present invention discloses a multi-port DC circuit breaker and an application method thereof. The multi-port DC circuit breaker is connected between a first converter station and a second converter station. The first converter station and the second converter station both include at least two DC outgoing lines. The circuit breaker includes: an electromagnetic coupling converter unit, a current limiting unit, a breaking unit, an energy absorbing unit, a plurality of current passing units, a plurality of first rectifier units, and a plurality of second rectifier units. When the converter station and the connecting line are normal, the energy flow between the converter stations is realized through the current passing unit. When at least one of the converter station and the connecting line fails, the faulty line or all the lines are cut off, the electromagnetic coupling converter unit generates an injection current, and the rectifier unit transfers the faulty current to the current limiting unit and the energy absorbing unit, thereby quickly isolating the faulty line, the faulty converter station, etc., and ensuring the safe, reliable and economical operation of the DC power transmission system.

Description

Technical Field

[0001] The present invention relates to the field of power systems and power electronics technology, and in particular to a multi-port DC circuit breaker and an application method thereof. Background Art

[0002] High-voltage DC circuit breakers are one of the core equipment for the construction of multi-terminal and DC power grids. Their technical and economic performance directly affects the flexibility and extensiveness of DC power grid applications. At present, there are two main mainstream technical routes for high-voltage DC circuit breakers: one is a hybrid DC circuit breaker, in which the mechanical switch conducts current during normal operation, and in case of a fault, the auxiliary commutation branch is used to transfer the current to the parallel-connected power electronic device branch, and then the power electronic device disconnects the current. This type of circuit breaker has low on-state loss and fast disconnection speed, but requires a large number of fully controlled devices in series and parallel, which is costly. The other is a mechanical DC circuit breaker, which achieves arc extinguishing of the mechanical switch by reverse injection of current through the pre-charged capacitor, and finally completes the DC disconnection. The required capacitor capacity is large and the voltage is high, and it faces the problems of economic and reliability design of high-voltage trigger switches. The existing technical solutions are difficult to simultaneously meet the dual requirements of technical and economic performance of DC circuit breakers for large-scale DC power grid construction, which limits the large-scale application of high-voltage DC circuit breakers in multi-terminal and DC power grids. Summary of the invention

[0003] Therefore, the technical problem to be solved by the present invention is to overcome the defects of a large number of high-voltage DC circuit breakers in a high-voltage and large-capacity flexible DC power grid in the prior art and high overall cost, thereby providing a multi-port DC circuit breaker and an application method thereof.

[0004] In order to achieve the above object, the present invention provides the following technical solutions:

[0005] In a first aspect, an embodiment of the present invention provides a multi-port DC circuit breaker, which is connected between a first converter station and a second converter station, wherein the first converter station and the second converter station each include at least two DC outgoing lines, and the circuit breaker includes: an electromagnetic coupling converter unit, a current limiting unit, a breaking unit, an energy absorbing unit, a plurality of current passing units, and a rectifying unit, wherein the rectifying unit includes a plurality of first rectifying units and a plurality of second rectifying units, wherein the first converter station is connected to a second converter station via a current passing unit, and the current passing unit includes: at least one group of fast mechanical switches; the first converter station is also connected to a first end of the breaking unit and a first end of the energy absorbing unit respectively via the first rectifying unit, the electromagnetic coupling converter unit, and the current limiting unit, and after the second end of the breaking unit and the second end of the energy absorbing unit are connected, the first converter station is correspondingly connected to the plurality of second converter stations via the plurality of first rectifying units; The flow station is also connected to the second end of the breaking unit and the second end of the energy absorption unit respectively through the second rectifier unit, and each second converter station is connected to the connection point between the first rectifier unit and the electromagnetic coupling converter unit through a second rectifier unit; when the line where each flow unit is located and the first converter station are operating normally, the flow unit is used to realize the load current transmission between the first converter station and the second converter station; when at least one of the line where the flow unit is located and the first converter station fails, the first rectifier unit and the second rectifier unit are used to transfer the fault current, isolate the fault line, and protect the normal operation of the healthy line; the electromagnetic coupling converter unit is used to generate oscillation and convert the load current from the flow unit to the current limiting unit and the breaking unit; the current limiting unit is used to limit the system fault current; the breaking unit is used to break the system fault current; the energy absorption unit is used to suppress the breaking overvoltage and absorb the energy stored in the system inductive elements.

[0006] In one embodiment, the first rectifying unit and the second rectifying unit are both composed of a first diode connected in series, or a first thyristor connected in series, or a first diode and a mechanical switch connected in series, or a first thyristor and a mechanical switch connected in series.

[0007] In one embodiment, the electromagnetic coupling commutation unit includes: a coupling inductor, a first capacitor and a first switching circuit, wherein the first end of the primary side of the coupling inductor is connected to the first converter station through the first rectifier unit, and the second end of the primary side is connected to the current limiting unit; the first capacitor, the first switching circuit and the secondary side of the coupling inductor are connected in series in sequence to form an electromagnetic coupling loop.

[0008] In one embodiment, the current limiting unit includes a capacitive current limiting circuit or an inductive current limiting circuit, wherein the capacitive current limiting circuit is composed of a first resistor and a nonlinear capacitor connected in parallel; the inductive current limiting circuit includes: a second capacitor, a second thyristor, an inductor and a second switching circuit, wherein the second capacitor, the second thyristor and the inductor are connected in series and then connected in parallel with the second switching circuit.

[0009] In one embodiment, the disconnecting unit is composed of a plurality of third switch circuits connected in series, and the third switch circuit includes: a controllable switch tube, a second diode, a third capacitor, a second resistor and a third resistor, wherein the second diode and the third capacitor are connected in series and then connected in parallel with the controllable switch tube, the second diode and the second resistor are connected in parallel, and the third capacitor and the third resistor are connected in parallel.

[0010] In a second aspect, an embodiment of the present invention provides an application method of a multi-port DC circuit breaker. Based on the multi-port DC circuit breaker of the first aspect, the application method includes: initializing the multi-port circuit breaker to put it in an initialization state, wherein the initialization state includes: each first rectifier unit, second rectifier unit, and current-passing unit are unlocked, and the electromagnetic coupling converter unit, current limiting unit, and breaking unit are locked; during the operation of the multi-port DC circuit breaker, real-time monitoring of the operating state of the first converter station and the line where each current-passing unit is located, and judging whether the first converter station and the line where each current-passing unit is located are operating normally; when the outlet of the first converter station fails, based on the first preset A control method, by controlling the operating status of each current-carrying unit, electromagnetic coupling conversion unit, current limiting unit, and disconnecting unit, the second rectifier unit transfers the system fault current to the energy absorption unit until the system fault current is absorbed by the energy absorption unit and passes through zero; when the first converter station outlet operates normally and a ground fault occurs in the line where at least one current-carrying unit is located, based on a second preset control method, by controlling the operating status of the current-carrying unit, electromagnetic coupling conversion unit, current limiting unit, and disconnecting unit of the ground fault line, the first rectifier unit transfers the system fault current to the energy absorption unit until the system fault current is absorbed by the energy absorption unit and passes through zero.

[0011] In one embodiment, the first preset control method includes: unlocking all third switch circuits and current limiting units of the disconnecting unit, locking all current-passing units, and unlocking the first switch circuit of the electromagnetic coupling unit when the contacts of the mechanical switches of all the current-passing units are separated; judging whether the mechanical switches of all the current-passing units are open enough to withstand the transient disconnecting voltage, and locking the disconnecting unit when they are open enough to withstand the transient disconnecting voltage.

[0012] In one embodiment, the second preset control method includes: unlocking all third switch circuits and the current limiting unit of the disconnecting unit, locking the current passing unit of the grounding fault line, and unlocking the first switch circuit of the electromagnetic coupling unit when the contacts of the mechanical switch of the current passing unit of the grounding fault line are separated; judging whether the mechanical switch of the current passing unit of the grounding fault line is sufficiently opened to withstand the transient disconnecting voltage, and locking the disconnecting unit when it is sufficiently opened to withstand the transient disconnecting voltage.

[0013] In one embodiment, a third preset control method is used to reclose the current-carrying unit of the ground fault line, and the third preset control method includes: unlocking all the third switch circuits of the breaking unit to determine whether the ground fault still exists; if the ground fault still exists, locking all the third switch circuits of the breaking unit; when the ground fault has been cleared, unlocking the current-carrying unit of the ground fault line, and locking all the third switch circuits of the breaking unit after the current of the breaking unit passes through zero.

[0014] The technical solution of the present invention has the following advantages:

[0015] 1. The multi-port DC circuit breaker and application method provided by the present invention are as follows: two converter stations are connected through the multi-port DC circuit breaker; when the converter station and the connecting line are normal, the current passing unit realizes the energy flow between the converter stations; when at least one of the converter station and the connecting line fails, the faulty line or all lines are cut off; the electromagnetic coupling converter unit generates injection current; the rectifier unit transfers the faulty current to the current limiting unit and the energy absorption unit, thereby quickly isolating the faulty line, the DC busbar connected to the faulty converter station, the faulty converter station, multiple faulty DC line sides, etc., to ensure the safe, reliable and economical operation of the DC transmission system.

[0016] 2. The multi-port DC circuit breaker and its application method provided by the present invention, the DC circuit breaker current-carrying unit utilizes a fast mechanical switch to achieve zero energy loss between converter stations, and has the characteristics of fast, bidirectional, strong current breaking, strong scalability, etc., can achieve fast reclosing, has good technical performance, and can meet the different operating requirements of the DC power grid.

[0017] 3. The multi-port DC circuit breaker and its application method provided by the present invention, the first converter station and multiple second converter stations share the electromagnetic coupling conversion unit, current limiting unit, breaking unit and energy absorption unit of the DC circuit breaker, thereby realizing flexible, simple and low-cost expansion as the DC lines increase.

[0018] 4. The multi-port DC circuit breaker and application method provided by the present invention significantly reduce the equipment cost of the DC circuit breaker used in the high-voltage and large-capacity DC power grid for a multi-DC outgoing converter station, compared with the independent hybrid DC circuit breaker arranged on each DC line, and have high technical and economic efficiency. It also reduces the total volume of the DC circuit breaker in the multi-DC outgoing converter station, which is beneficial to the overall layout and design of the converter station. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0020] Figure 1 A composition diagram of a specific example of a multi-port DC circuit breaker provided in an embodiment of the present invention;

[0021] Figure 2(a) to Figure 2(d) A composition diagram of a specific example of a first rectifying unit and a second rectifying unit provided in an embodiment of the present invention;

[0022] Figure 3(a) to Figure 3(b) A composition diagram of a specific example of an electromagnetic coupling rectifier unit provided in an embodiment of the present invention;

[0023] Figure 4(a) to Figure 4(b) All of them are composition diagrams of specific examples of the current limiting unit provided in the embodiments of the present invention;

[0024] Figure 5 A composition diagram of a specific example of a breaking unit provided in an embodiment of the present invention;

[0025] Figure 6 A flowchart of a specific example of an application method of a multi-port DC circuit breaker provided by an embodiment of the present invention;

[0026] Figure 7 A circuit structure diagram of a specific example of a multi-port DC circuit breaker provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0027] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and "third" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance.

[0029] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, it can also be the internal connection of two components, it can be a wireless connection, or it can be a wired connection. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0030] In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0031] Example 1

[0032] The embodiment of the present invention provides a multi-port DC circuit breaker, which is applied to energy transmission between multiple converter stations, such as Figure 1 As shown, the multi-port DC circuit breaker is connected between the first converter station 11 and the second converter station 12. The first converter station 11 and the second converter station 12 each include at least two DC outgoing lines. The circuit breaker includes: an electromagnetic coupling converter unit 2, a current limiting unit 3, a breaking unit 4, an energy absorption unit 5, a plurality of current passing units 6, and a rectifier unit. The rectifier unit includes a plurality of first rectifier units 71 and a plurality of second rectifier units 72.

[0033] The first converter station 11 of the embodiment of the present invention is connected to a second converter station 12 through a current flow unit 6, and the current flow unit 6 includes: at least one group of fast mechanical switches, wherein the fast mechanical switches need to withstand system load current and short-term overcurrent, and also need to withstand transient overvoltages generated by the disconnection of the DC circuit breaker. According to the above-mentioned electrical stress, it can adopt a multi-break series connection, a multi-branch parallel connection, and a multi-break series-parallel connection mode, so as to achieve zero energy loss between converter stations, and has the characteristics of fast, bidirectional, strong current disconnection, strong scalability, etc., can achieve fast reclosing, has good technical performance, and can meet the different operation requirements of the DC power grid.

[0034] like Figure 1As shown, the first converter station 11 of the embodiment of the present invention is also connected to the first end of the breaking unit 4 and the first end of the energy absorption unit 5 respectively through the first rectifier unit 71, the electromagnetic coupling converter unit 2, and the current limiting unit 3 in sequence. After the second end of the breaking unit 4 and the second end of the energy absorption unit 5 are connected, they are correspondingly connected to multiple second converter stations 12 through multiple first rectifier units 71; the first converter station 11 is also connected to the second end of the breaking unit 4 and the second end of the energy absorption unit 5 respectively through the second rectifier unit 72, and each second converter station 12 is connected to the connection point between a second rectifier unit and the first rectifier unit 71 and the electromagnetic coupling converter unit 2.

[0035] It should be noted that, in the power system, the second converter station 12 also Figure 1 The multi-port DC circuit breaker shown is connected to other converter stations to achieve energy flow between other converter stations, which will not be described in detail here.

[0036] In the embodiment of the present invention, when the line where each current passing unit 6 is located and the first converter station 11 are operating normally, the current passing unit 6 is used to realize the load current transmission between the first converter station 11 and the second converter station 12; when at least one of the line where the current passing unit 6 is located and the first converter station 11 fails, the first rectifier unit 71 and the second rectifier unit 72 are used to transfer the fault current, isolate the faulty line, and protect the normal operation of the healthy line; the electromagnetic coupling commutation unit 2 is used to generate oscillations and convert the load current from the current passing unit 6 to the current limiting unit 3 and the breaking unit 4; the current limiting unit 3 is used to limit the system fault current; the breaking unit 4 is used to break the system fault current; the energy absorption unit 5 is used to suppress the breaking overvoltage and absorb the energy stored in the system inductive elements.

[0037] In the embodiment of the present invention, when Figure 1After the multi-port DC circuit breaker shown is put into the power system, the operating status of each current-passing unit 6 and the first converter station 11 is monitored in real time, and different load current paths are set based on the operating status of the two. For example, when each current-passing unit 6 and the first converter station 11 are operating normally, the DC line #1 to the DC line #N realize the energy flow between the first converter station 11 and the second converter station 12; when a ground fault occurs in a DC line, taking the ground fault of the DC line #1 as an example, at this time, by controlling the on-off status of the current-passing unit 6, the electromagnetic coupling converter unit 2, and the current limiting unit 3 connected to it, the first rectifier unit 71, the electromagnetic coupling converter unit 2, the current limiting unit 3, the breaking unit 4 and the energy absorption unit 5 connected to the first converter station 11, and the second converter station 12 are connected to the DC line. 2, realizes the energy flow between the first converter station 11 and the second converter station 12 connected to the DC line #1, and other normal DC lines #2 to DC lines #N realize the energy flow between the first converter station 11 and the second converter stations 12 connected to the DC lines #2 to DC lines #N; when the outlet of the first converter station 11 fails, the energy flow between the first converter station 11 and all the second converter stations 12 is realized through the second rectifier unit 72 connected to the second converter station 12, the electromagnetic coupling converter unit 2, the current limiting unit 3, the breaking unit 4 and the energy absorption unit 5, and the second rectifier unit 72 connected to the first converter station 11. It should be noted that when the second converter station 12 is connected to the converter station through a multi-port DC circuit breaker.

[0038] The multi-port DC circuit breaker provided in the embodiment of the present invention is used to connect two converter stations through the multi-port DC circuit breaker. When the converter station and the connecting line are normal, the current passing unit realizes the energy flow between the converter stations. When at least one of the converter station and the connecting line fails, the faulty line or all lines are cut off, the electromagnetic coupling converter unit generates injection current, and the rectifier unit transfers the faulty current to the current limiting unit and the energy absorption unit, thereby quickly isolating the faulty line, the faulty converter station, etc., and ensuring the safe, reliable and economical operation of the DC transmission system.

[0039] In a specific embodiment, the first rectifier unit 71 and the second rectifier unit 72 are both composed of switch components, but the current flow directions controlled by the two are different. The switch components include a combination of a first diode D1, a first thyristor S1 and a mechanical switch K1, etc. For example: as shown in FIG2(a), the first rectifier unit 71 and the second rectifier unit 72 are both composed of a diode rectifier valve section composed of a first diode D1 connected in series, or as shown in FIG2(b), the first rectifier unit 71 and the second rectifier unit 72 are both composed of a thyristor rectifier valve section composed of a first thyristor S1 connected in series, or as shown in FIG2(c), the first rectifier unit 71 and the second rectifier unit 72 are both composed of a diode and mechanical switch K1 series rectifier valve section composed of a first diode D1 and a mechanical switch K1 connected in series, or as shown in FIG2(d), the first rectifier unit 71 and the second rectifier unit 72 are both composed of a thyristor and mechanical switch K1 series rectifier valve section composed of a first thyristor S1 and a mechanical switch K1 connected in series.

[0040] In a specific embodiment, as shown in Figures 3(a) and 3(b), the electromagnetic coupling commutation unit 2 includes: a coupling inductor L1, a first capacitor C1 and a first switch circuit 21, wherein the first end of the primary side of the coupling inductor L1 is connected to the first converter station 11 through the first rectifier unit 71, and the second end of the primary side is connected to the current limiting unit 3; the first capacitor C1, the first switch circuit 21 and the secondary side of the coupling inductor L1 are connected in series in sequence to form an electromagnetic coupling loop, the first switch circuit 21 in Figure 3(a) is composed of anti-parallel thyristors and diodes, and the first switch circuit 21 in Figure 3(b) is composed of anti-parallel IGBTs and diodes.

[0041] In a specific embodiment, the current limiting unit 3 includes a capacitive current limiting circuit 31 or an inductive current limiting circuit 32, wherein, as shown in FIG4(a), the capacitive current limiting circuit 31 is composed of a first resistor R1 and a nonlinear capacitor C2 connected in parallel; as shown in FIG4(b), the inductive current limiting circuit 32 includes: a second capacitor C3, a second thyristor S2, an inductor L2 and a second switch circuit 321, wherein the second switch circuit 321 can be composed of anti-parallel thyristors, and the second capacitor C3, the second thyristor S2, and the inductor L2 are connected in series and then connected in parallel with the second switch circuit 321.

[0042] In a specific embodiment, if Figure 5 As shown, the disconnecting unit 4 is composed of a plurality of third switch circuits 41 connected in series, and the third switch circuit 41 includes: a controllable switch tube S3, a second diode D2, a third capacitor C4, a second resistor R2 and a third resistor R3, wherein the second diode D2 is connected in series with the third capacitor C4 and then connected in parallel with the controllable switch tube S3, the second diode D2 is connected in parallel with the second resistor R2, and the third capacitor C4 is connected in parallel with the third resistor R3.

[0043] It should be noted that in the entire power system, each converter station can be connected to other converter stations through a multi-port DC circuit breaker. The converter station that emits energy is regarded as the above-mentioned first converter station 11, and the converter station that receives energy is regarded as the above-mentioned second converter station 12. Since the first rectifier unit 71 and the second rectifier unit 72 are used to isolate and realize energy flow, the connection direction of the first rectifier unit 71 and the second rectifier unit 72 is set according to actual conditions, so the multi-port DC circuit breaker can also be applied according to the above method.

[0044] In the multi-port DC circuit breaker provided by the embodiment of the present invention, the electromagnetic coupling conversion unit, the current limiting unit, the breaking unit and the energy absorption unit of the DC circuit breaker are shared between the first converter station and the multiple second converter stations, thereby realizing flexible, simple and low-cost expansion as the DC lines increase; for a converter station with multiple DC outgoing lines, compared with an independent hybrid DC circuit breaker arranged on each DC line, the equipment cost of the DC circuit breaker used in a high-voltage and large-capacity DC power grid is significantly reduced, and it has high technical and economic efficiency, and the total volume of the DC circuit breaker in the converter station with multiple DC outgoing lines is reduced, which is beneficial to the overall layout and design of the converter station.

[0045] Example 2

[0046] The embodiment of the present invention provides an application method of a multi-port DC circuit breaker, such as Figure 6 As shown, based on the multi-port DC circuit breaker of embodiment 1, the application method includes:

[0047] Step S11: Initialize the multi-port circuit breaker to put it in an initialization state, the initialization state includes: each of the first rectifier unit, the second rectifier unit, and the current passing unit are unlocked, and the electromagnetic coupling commutation unit, the current limiting unit, and the breaking unit are locked.

[0048] Step S12: During the operation of the multi-port DC circuit breaker, the operating status of the first converter station and the line where each current passing unit is located is monitored in real time, and it is determined whether the first converter station and the line where each current passing unit is located are operating normally.

[0049] Step S13: When the first converter station outlet fails, based on the first preset control method, by controlling the operating status of each current-passing unit, electromagnetic coupling converter unit, current limiting unit, and disconnecting unit, the second rectifier unit transfers the system fault current to the energy absorption unit until the system fault current is absorbed by the energy absorption unit and passes through zero.

[0050] Step S14: When the outlet of the first converter station operates normally and a ground fault occurs in the line where at least one current-carrying unit is located, based on the second preset control method, by controlling the operating states of the current-carrying unit, the electromagnetic coupling converter unit, the current limiting unit, and the breaking unit of the ground fault line, the first rectifier unit transfers the system fault current to the energy absorption unit until the system fault current is absorbed by the energy absorption unit and passes through zero.

[0051] Now as Figure 7 An example of a specific circuit structure of a multi-port DC circuit breaker is shown. Figure 7 In the invention, the first converter station is connected to the two second converter stations through a multi-port DC circuit breaker, the multi-port circuit breaker includes three first rectifier units, three second rectifier units, and two current-passing units, the current-passing unit is composed of a mechanical switch, the first switch circuit of the electromagnetic coupling converter unit is composed of anti-parallel thyristors and diodes, the current limiting unit adopts an inductive current limiting circuit, and the first rectifier unit and the second rectifier unit are composed of a first diode and a mechanical switch connected in series.

[0052] like Figure 7 The multi-port DC circuit breaker shown, when the operating status of the first converter station #1, DC line #11 and DC line #12 are all normal, the first rectifier unit #1, the first rectifier unit #11, the first rectifier unit #12, the second rectifier unit #2, the second rectifier unit #21 and the second rectifier unit #22 are all unlocked.

[0053] like Figure 7 For the multi-port DC circuit breaker shown in FIG. 1 , when energy needs to flow from the first converter station #1 to the second converter station #21 and the second converter station #22, respectively, the application method of the multi-port DC circuit breaker of the embodiment of the present invention is as follows:

[0054] (1) When the first converter station #1, DC line #11 and DC line #12 are operating normally, the electromagnetic coupling converter unit, the current limiting unit and the breaking unit are all locked, and the current passing unit #11 and the current passing unit #12 are unlocked, that is, the energy between the first converter station #1 and the second converter station #21 flows through the DC line #1, and the energy between the first converter station #1 and the second converter station #22 flows through the DC line #2.

[0055] (2) When the outlet of the first converter station #1 fails, based on the first preset control method, the current passing unit #11 and the current passing unit #12 are locked, and the electromagnetic coupling converter unit, the current limiting unit, and the disconnecting unit are all unlocked. At this time, the capacitor on the secondary side of the electromagnetic coupling rectifier unit and the inductor on the secondary side of the coupling reactor oscillate, and the primary side of the coupling reactor induces voltage, so that the energy output by the second converter station #21 flows to the first converter station #1 through the second rectifier unit #21, the electromagnetic coupling unit, the current limiting unit, the energy absorption unit, and the second rectifier unit #2 in sequence, and the energy output by the second converter station #22 flows to the first converter station #1 through the second rectifier unit #22, the electromagnetic coupling unit, the current limiting unit, the energy absorption unit, and the second rectifier unit #2 in sequence, until the fault current is absorbed by the energy absorption unit.

[0056] (3)① When a ground fault occurs in DC line #1 and DC line #2 operates normally, based on the second preset control method, the current unit #11 is locked, and the current unit #12, the electromagnetic coupling converter unit, the current limiting unit, and the disconnecting unit are all unlocked. At this time, the capacitor on the secondary side of the electromagnetic coupling rectifier unit and the inductor on the secondary side of the coupling reactor oscillate, and the primary side of the coupling reactor induces voltage, so that the fault current output by the first converter station #1 passes through the first rectifier unit #1, the electromagnetic coupling converter unit, the current limiting unit, the disconnecting unit (or the energy absorbing unit), and the first rectifier unit #11 in sequence until the fault current is absorbed by the energy absorbing unit, and the energy between the first converter station #1 and the second converter station #22 still flows through the DC line #2.

[0057] ② When a ground fault occurs in DC line #2 and DC line #1 operates normally, based on the second preset control method, the current unit #12 is locked, and the current unit #11, the electromagnetic coupling conversion unit, the current limiting unit, and the breaking unit are all unlocked. At this time, the capacitor on the secondary side of the electromagnetic coupling rectifier unit and the inductance on the secondary side of the coupling reactor oscillate, and the coupling reactor induces voltage on the primary side, so that the fault current output by the first converter station #1 passes through the first rectifier unit #1, the electromagnetic coupling conversion unit, the current limiting unit, the breaking unit (or energy absorption unit), and the first rectifier unit #12 in sequence until the fault current is absorbed by the energy absorption unit, and the energy between the first converter station #1 and the second converter station #22 still flows through the DC line #1.

[0058] ③ When ground faults occur in both DC line #1 and DC line #2, based on the second preset control method, the current passing unit #11 and the current passing unit #12 are locked, and the electromagnetic coupling conversion unit, the current limiting unit, and the breaking unit are all unlocked. At this time, the capacitor on the secondary side of the electromagnetic coupling rectifier unit and the inductance on the secondary side of the coupling reactor oscillate, and the coupling reactor induces voltage on the primary side, so that the fault current output by the first converter station #1 passes through the first rectifier unit #1, the electromagnetic coupling conversion unit, the current limiting unit, the breaking unit (or energy absorption unit), the first rectifier unit #11 and the first rectifier unit #12 in sequence until the fault current is absorbed by the energy absorption unit.

[0059] It should be noted that in the entire power system, each converter station can be connected to other converter stations through a multi-port DC circuit breaker. The converter station that emits energy is regarded as the above-mentioned first converter station, and the converter station that receives energy is regarded as the above-mentioned second converter station. Since the first rectifier unit and the second rectifier unit are used for isolation and energy flow, the connection direction of the first rectifier unit and the second rectifier unit is set according to actual conditions, so the multi-port DC circuit breaker can also be applied according to the above method.

[0060] In a specific embodiment, the first preset control method includes:

[0061] Step S21: unlocking all third switch circuits and current limiting units of the breaking unit, locking all current passing units, and when the contacts of the mechanical switches of all current passing units are separated, unlocking the first switch circuit of the electromagnetic coupling unit.

[0062] Step S22: Determine whether the mechanical switches of all current-carrying units are open enough to withstand the transient breaking voltage. If they are open enough to withstand the transient breaking voltage, lock the breaking units.

[0063] In the embodiment of the present invention, Figure 7 The multi-port DC circuit breaker shown in the figure specifically describes steps S21 to S22:

[0064] When the outlet of the first converter station #1 fails, the specific implementation process of the above-mentioned application method (2) is as follows: first, all the third switch circuits and current limiting units in the breaking unit are unlocked, and the current passing units #11 and #12 are locked. Then, when the contacts of the fast mechanical switches of the current passing units #11 and #12 are separated, the first switch circuit of the electromagnetic coupling converter unit is unlocked, and the capacitor on the secondary side of the electromagnetic coupling rectifier unit and the inductor on the secondary side of the coupling reactor oscillate, and the voltage is induced on the primary side of the coupling reactor, so that the overall conduction voltage of the breaking unit is lower than the arc voltage of the fast mechanical switch, and the current is forced to be transferred from the current passing units #11 and #12. At this time, the energy output by the second converter station #21 passes through the second rectifier unit #21, the electromagnetic coupling unit, the current limiting unit, The breaking unit and the second rectifier unit #2 flow to the first converter station #1, and the energy output by the second converter station #22 flows to the first converter station #1 through the second rectifier unit #22, the electromagnetic coupling unit, the current limiting unit, the breaking unit, and the second rectifier unit #2 in sequence. Then, when the mechanical switches of the through-current unit #11 and the through-current unit #12 are sufficiently opened to withstand the transient breaking voltage, all the third switch circuits of the breaking unit are locked. At this time, the fault current output by the second converter station #21 is transmitted to the energy absorption unit via the second rectifier unit #21, the electromagnetic coupling converter unit, and the current limiting unit. The fault current output by the second converter station #22 is transmitted to the energy absorption unit via the second rectifier unit #22, the electromagnetic coupling converter unit, and the current limiting unit, and the fault current is absorbed by the energy absorption unit.

[0065] In a specific embodiment, the second preset control method includes:

[0066] Step S31: unlocking all third switch circuits and the current limiting unit of the breaking unit, locking the current passing unit of the ground fault line, and unlocking the first switch circuit of the electromagnetic coupling unit when the contacts of the mechanical switch of the current passing unit of the ground fault line are separated.

[0067] Step S32: determine whether the mechanical switch of the current-carrying unit of the ground fault line is sufficiently opened to withstand the transient breaking voltage, and if it is sufficiently opened to withstand the transient breaking voltage, lock the breaking unit.

[0068] In the embodiment of the present invention, Figure 7 The multi-port DC circuit breaker shown in the figure specifically describes steps S31 to S32:

[0069] When a ground fault occurs in DC line #1 and DC line #2 operates normally, the specific implementation process of the first method of the above-mentioned application method (3) is as follows: first, all the third switch circuits and current limiting units in the breaking unit are unlocked, the current passing unit #11 is locked, and the current passing unit #12 is kept in the unlocked state. Then, when the contacts of the fast mechanical switch of the current passing unit #11 are separated, the first switch circuit of the electromagnetic coupling conversion unit is unlocked, the capacitor on the secondary side of the electromagnetic coupling rectifier unit and the inductor on the secondary side of the coupling reactor oscillate, and the induced voltage on the primary side of the coupling reactor is generated, so that the overall conduction voltage of the breaking unit is reduced. Due to the arc voltage of the fast mechanical switch, the current is forced to transfer from the current-carrying unit #11, so that the fault current output by the first converter station #1 is completely transferred to the current-limiting unit and the breaking unit. Then, when the mechanical switches of the current-carrying unit #11 are sufficiently opened to withstand the transient breaking voltage, all the third switch circuits of the breaking unit are locked. At this time, the fault current output by the first converter station #1 is transmitted to the second converter station #21 via the first rectifier unit #1, the electromagnetic coupling converter unit, the current limiting unit, the energy absorption unit, and the first rectifier unit #11, and the energy between the first converter station #1 and the second converter station #22 flows through the DC circuit #2. It should be noted that when the first converter station #1 operates normally, a ground fault occurs in the DC line #2, the DC line #1 operates normally, or when a ground fault occurs in both the DC line #1 and the DC line #2, also according to the principle of the above method, the energy between the first converter station #1 and the second converter station #22 flows through the electromagnetic coupling rectifier unit, the current limiting unit, the breaking unit and the energy absorption unit, and the energy between the first converter station #1 and the second converter station #21 flows through the DC line #1.

[0070] In a specific embodiment, a third preset control method is used to reclose the current-carrying unit of the ground fault line. The third preset control method includes:

[0071] Step S41: unlocking all the third switch circuits of the disconnecting unit to determine whether the ground fault still exists.

[0072] Step S42: If the ground fault still exists, lock all the third switch circuits of the breaking unit; when the ground fault has been cleared, unlock the current-carrying unit of the ground fault line, and lock all the third switch circuits of the breaking unit after the current of the breaking unit passes through zero.

[0073] In the embodiment of the present invention, Figure 7 The multi-port DC circuit breaker shown in FIG. 1 specifically describes steps S41 to S42:

[0074] When the first converter station #1 is operating normally, a ground fault occurs in the DC line #1, and the DC line #2 is operating normally, the current unit #12 is always in an unlocked state. The specific implementation process of the process of reclosing the fast mechanical switch in the current unit #11 is: after step S32, first unlock all the third switch circuits of the disconnecting unit to determine whether the ground fault still exists. If the ground fault still exists, lock all the third switch circuits of the disconnecting unit; when the ground fault has been cleared, unlock the current unit #11, and after the current of the disconnecting unit passes through zero, lock all the third switch circuits of the disconnecting unit. At this time, the current output by the first converter station #1 is transmitted to the second converter station #21 and the second converter station #22 through the DC line #1 and the DC line #2 respectively.

[0075] It should be noted that in the entire power system, each converter station can be connected to other converter stations through a multi-port DC circuit breaker. The converter station that emits energy is regarded as the above-mentioned first converter station, and the converter station that receives energy is regarded as the above-mentioned second converter station. Since the first rectifier unit and the second rectifier unit are used for isolation and energy flow, the connection direction of the first rectifier unit and the second rectifier unit is set according to actual conditions, so the multi-port DC circuit breaker can also be applied according to the above method.

[0076] The application method of the multi-port DC circuit breaker provided in the embodiment of the present invention is that two converter stations are connected through the multi-port DC circuit breaker. When the converter station and the connecting line are normal, the current passing unit realizes the energy flow between the converter stations. When at least one of the converter station and the connecting line fails, the faulty line or all lines are cut off, and the electromagnetic coupling converter unit automatically senses the voltage and transfers the faulty current to the current limiting unit and the energy absorbing unit, thereby quickly isolating the faulty line, the faulty converter station, etc., to ensure the safe, reliable and economical operation of the DC transmission system.

[0077] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the scope of protection of the invention.

Claims

1. A multi-port DC circuit breaker, characterized in that: The multi-port DC circuit breaker is connected between the first converter station and the second converter station. The first converter station and the second converter station each include at least two DC outgoing lines. The circuit breaker includes: an electromagnetic coupling converter unit, a current limiting unit, a breaking unit, an energy absorption unit, a plurality of current passing units, and a rectifying unit. The rectifying unit includes a plurality of first rectifying units and a plurality of second rectifying units. The first converter station is connected to a second converter station via a flow unit, and the flow unit includes: at least one group of fast mechanical switches; The first converter station is also connected to the first end of the breaking unit and the first end of the energy absorbing unit respectively through the first rectifying unit, the electromagnetic coupling commutating unit, and the current limiting unit in sequence. After the second end of the breaking unit and the second end of the energy absorbing unit are connected, they are correspondingly connected to the plurality of second converter stations through the plurality of first rectifying units; The first converter station is also connected to the second end of the breaking unit and the second end of the energy absorbing unit respectively through the second rectifier unit, and each second converter station is connected to the connection point between the first rectifier unit and the electromagnetic coupling converter unit through a second rectifier unit; When the line where each current-passing unit is located and the first converter station operate normally, the current-passing unit is used to realize load current transmission between the first converter station and the second converter station; When at least one of the line where the current-carrying unit is located and the first converter station fails, the first rectifier unit and the second rectifier unit are used to transfer the fault current, isolate the faulty line, and protect the normal operation of the healthy line; the electromagnetic coupling commutation unit is used to generate oscillations to convert the load current from the current-carrying unit to the current limiting unit and the disconnecting unit; the current limiting unit is used to limit the system fault current; the disconnecting unit is used to disconnect the system fault current; the energy absorption unit is used to suppress the disconnection overvoltage and absorb the energy stored in the system inductive element; the first rectifier unit and the second rectifier unit are both composed of a first diode connected in series, or a first thyristor connected in series, or a first diode and a mechanical switch connected in series, or a first thyristor and a mechanical switch connected in series; The electromagnetic coupling commutation unit comprises: a coupling reactor, a first capacitor and a first switch circuit, wherein: The first end of the primary side of the coupling reactor is connected to the first converter station through the first rectifier unit, and the second end of the primary side is connected to the current limiting unit; The first capacitor, the first switch circuit and the secondary side of the coupling reactor are connected in series in sequence to form an electromagnetic coupling loop.

2. The multi-port DC circuit breaker according to claim 1, characterized in that: The current limiting unit includes a capacitive current limiting circuit or an inductive current limiting circuit, wherein: The capacitive current limiting circuit is composed of a first resistor and a nonlinear capacitor connected in parallel; The inductive current limiting circuit includes: a second capacitor, a second thyristor, an inductor and a second switch circuit, wherein the second capacitor, the second thyristor and the inductor are connected in series and then connected in parallel with the second switch circuit.

3. The multi-port DC circuit breaker according to claim 1, characterized in that: The disconnecting unit is composed of a plurality of third switch circuits connected in series, and the third switch circuit includes: a controllable switch tube, a second diode, a third capacitor, a second resistor and a third resistor, wherein: The second diode and the third capacitor are connected in series and then connected in parallel with the controllable switch tube. The second diode and the second resistor are connected in parallel, and the third capacitor and the third resistor are connected in parallel.

4. An application method of a multi-port DC circuit breaker, characterized in that: Based on the multi-port DC circuit breaker according to any one of claims 1 to 3, the application method comprises: Initializing the multi-port DC circuit breaker to put it in an initialization state, wherein the initialization state includes: each of the first rectifier unit, the second rectifier unit, and the current passing unit are unlocked, and the electromagnetic coupling commutation unit, the current limiting unit, and the breaking unit are locked; During the operation of the multi-port DC circuit breaker, the operating status of the first converter station and the line where each current passing unit is located are monitored in real time, and whether the first converter station and the line where each current passing unit is located are operating normally; When the first converter station outlet fails, based on the first preset control method, by controlling the operating state of each current-passing unit, electromagnetic coupling converter unit, current limiting unit, and disconnecting unit, the second rectifier unit transfers the system fault current to the energy absorption unit until the system fault current is absorbed by the energy absorption unit and passes through zero; When the outlet of the first converter station operates normally and a ground fault occurs in the line where at least one current-carrying unit is located, based on the second preset control method, by controlling the operating states of the current-carrying unit, the electromagnetic coupling converter unit, the current limiting unit, and the breaking unit of the ground fault line, the first rectifier unit transfers the system fault current to the energy absorption unit until the system fault current is absorbed by the energy absorption unit and passes through zero.

5. The application method of the multi-port DC circuit breaker according to claim 4, characterized in that: The first preset control method includes: Unlock all third switch circuits and current limiting units of the breaking unit, lock all current-passing units, and when the contacts of the mechanical switches of all current-passing units are separated, unlock the first switch circuit of the electromagnetic coupling unit; Determine whether the mechanical switches of all current-carrying units are open enough to withstand the transient breaking voltage. When they are open enough to withstand the transient breaking voltage, lock the breaking unit.

6. The application method of the multi-port DC circuit breaker according to claim 4, characterized in that: The second preset control method includes: Unlock all third switch circuits and the current limiting unit of the breaking unit, and lock the current passing unit of the grounding fault line, and when the contacts of the mechanical switch of the current passing unit of the grounding fault line are separated, unlock the first switch circuit of the electromagnetic coupling unit; It is determined whether the mechanical switch of the current-carrying unit of the ground fault line is open enough to withstand the transient breaking voltage. When it is open enough to withstand the transient breaking voltage, the breaking unit is locked.

7. The application method of the multi-port DC circuit breaker according to claim 6, characterized in that: The third preset control method is used to reclose the current-carrying unit of the ground fault line, and the third preset control method includes: Unlock all third switch circuits of the disconnecting unit to determine whether the ground fault still exists; If the ground fault still exists, all the third switch circuits of the breaking unit are locked; when the ground fault has been cleared, the current-carrying unit of the ground fault line is unlocked, and after the current of the breaking unit passes through zero, all the third switch circuits of the breaking unit are locked.

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