Multi-port direct-current fault current limiter and system for flexible direct-current power transmission system

Abstract

The invention relates to the technical field of flexible direct-current power transmission, and discloses a multi-port direct-current fault current limiter and system for a flexible direct-current power transmission system, and the current limiter comprises a first current limiting inductor which is arranged on a direct-current bus, one end of the direct-current bus is suitable for being connected to a current converter, and the other end of the direct-current bus is suitable for being connected with a plurality of direct-current lines; the first energy consumption unit is connected with the first current-limiting inductor in parallel; a plurality of second current-limiting inductors, each of which is connected in series with the corresponding DC line and is connected between the first current-limiting inductor and the corresponding output port; and each second energy consumption unit is connected with the corresponding second current-limiting inductor in parallel so as to consume the follow current of the corresponding second current-limiting inductor under the condition that the flexible direct-current power transmission system breaks down. The method has the beneficial effects that the energy consumption capacity of the MOV in the direct current circuit breaker is reduced, and the fault current clearing efficiency is improved.

Description

Technical Field

[0001] The present application relates to the technical field of flexible direct current transmission, and in particular to a multi-port direct current fault current limiter and system for a flexible direct current transmission system. Background Art

[0002] Flexible DC transmission offers significant advantages in receiving and transmitting clean energy. The high-voltage flexible DC transmission technology it has developed holds broad application prospects in clean energy grid integration and distribution. However, because flexible DC systems contain numerous power electronic devices, a fault on the DC side can cause energy release from submodule capacitors, leading to a rapid increase in short-circuit current. This can significantly impact the DC system and power electronic components in the converters, necessitating the deployment of current limiting devices to ensure safe system operation.

[0003] In the related technologies of fault current limiting in flexible DC transmission systems, current-limiting reactors are usually installed at both ends of the line. Although this current limiting method is simple and reliable, it has the disadvantage of a long tail current of the fault current, which leads to a significant increase in the energy consumption of the Metal Oxide Varistor (MOV) in the DC circuit breaker and reduces the efficiency of dissipating the fault current. Summary of the Invention

[0004] The present application provides a multi-port DC fault current limiter and system for a flexible DC transmission system, which solves the technical problems of high energy consumption of the MOV of the DC circuit breaker and long fault current tail time caused by traditional current limiting methods. It achieves the technical effect of significantly reducing the fault current while reducing the energy consumption capacity of the MOV in the DC circuit breaker, shortening the fault current tail, and improving the fault current clearing efficiency.

[0005] In order to achieve the above objectives, the main technical solutions adopted in this application include: In a first aspect, an embodiment of the present application provides a multi-port DC fault current limiter for a flexible DC transmission system, wherein the flexible DC transmission system uses multiple DC lines for power transmission, each of the DC lines is provided with an output port, and the multi-port DC fault current limiter includes: a first current-limiting inductor provided on a DC bus, wherein one end of the DC bus is adapted to be connected to a converter, and the other end of the DC bus is adapted to be respectively connected to the plurality of DC lines; a first energy consumption unit, connected in parallel with the first current-limiting inductor, and configured to consume a freewheeling current of the first current-limiting inductor when a fault occurs in the flexible HVDC power transmission system; a plurality of second current-limiting inductors, each of which is connected in series to a corresponding DC line and connected between the first current-limiting inductor and a corresponding output port; A plurality of second energy consuming units, each of which is connected in parallel with a corresponding second current-limiting inductor, so as to consume the freewheeling current of the corresponding second current-limiting inductor when a fault occurs in the flexible direct current transmission system.

[0006] The multi-port DC fault current limiter proposed in the embodiments of the present application is designed for a flexible DC power transmission system with multiple output ports, consisting of a busbar connected to multiple DC lines. A first energy-consuming unit and a second energy-consuming unit are connected in parallel with corresponding current-limiting inductors to form a loop, thereby causing the freewheeling current in the current-limiting inductor to form a circulating current in the loop. Compared with existing current-limiting reactor configuration methods, the multi-port DC fault current limiter proposed in the embodiments of the present application is intended to improve the fault current limiting capability of a large-capacity converter transmitting multiple lines through a busbar. While significantly reducing the peak value of the fault current, it also reduces the energy consumption capacity of the MOV in the DC circuit breaker, thereby shortening the fault current clearing time and improving the fault current clearing efficiency.

[0007] Optionally, the first energy dissipation unit includes a diode and a first energy dissipation resistor connected in series.

[0008] Optionally, when the maximum fault current generated on the output port side of the flexible direct current transmission system is less than the maximum fault current generated on the converter side of the flexible direct current transmission system, the anode of the diode is connected to one end of the DC bus, the cathode of the diode is connected to one end of the first energy dissipation resistor, and the other end of the first energy dissipation resistor is connected to the other end of the DC bus.

[0009] The embodiment of the present application takes into account two situations in which the maximum fault currents generated by the fault occurring on the output port side and the converter side are different. The direction of the diode in the first energy consumption unit is set in a targeted manner so that the anode of the diode points to the side where the maximum fault current is larger, that is, to the converter side to ensure that the fault current can flow in the expected direction. In this way, when a large fault current is generated on the converter side, the first energy dissipation resistor can be directly used to partially dissipate the fault current due to the conduction of the diode, so as to maximize the first energy dissipation resistor's ability to consume the fault current and the first current limiting inductor's follow-up current, thereby improving the fault current consumption efficiency.

[0010] Optionally, when the maximum fault current generated on the output port side of the flexible direct current transmission system is greater than the maximum fault current generated on the converter side of the flexible direct current transmission system, the cathode of the diode is connected to one end of the DC bus, the anode of the diode is connected to one end of the first energy dissipation resistor, and the other end of the first energy dissipation resistor is connected to the other end of the DC bus.

[0011] The embodiment of the present application takes into account two situations in which the maximum fault currents generated by the fault occurring on the output port side and the converter side are different. The direction of the diode in the first energy consumption unit is set in a targeted manner so that the anode of the diode points to the side where the maximum fault current is larger, that is, points to the output port side to ensure that the fault current can flow in the expected direction. In this way, when a large fault current is generated on the output port side, the first energy dissipation resistor can be directly used to partially dissipate the fault current due to the conduction of the diode, so as to maximize the first energy dissipation resistor's ability to consume the fault current and the first current limiting inductor's follow-up current, thereby improving the fault current consumption efficiency.

[0012] Optionally, the first energy consumption unit is further configured to be put into operation when an oscillating current appears on the converter side of the flexible direct current transmission system, so as to suppress the oscillating current.

[0013] When the voltage and current at the converter output oscillate, the first energy-consuming unit can adaptively operate, avoiding the adverse effects on system stability caused by the current-limiting inductor being connected, preventing system instability after the system is disturbed, and improving system stability. Compared with traditional current-limiting reactors that have a single function and do not function in non-fault conditions, the multi-port DC fault current limiter proposed in the embodiment of the present application places the first energy-consuming unit on the converter side. This allows for both fault current limiting and adaptive suppression of power flow fluctuations in the flexible DC transmission system, thereby improving the utilization rate of power devices.

[0014] Optionally, a plurality of the second energy consumption units share a second energy consumption resistor.

[0015] For each second current-limiting inductor connected in series on the DC line, sharing the second energy-dissipating resistor can save the number of power electronic devices and energy-dissipating resistors without reducing the overall current-limiting capability, thereby achieving the effect of consuming the follow-on current of the current-limiting inductor and effectively reducing the cost of the current limiter.

[0016] Optionally, each of the second energy consumption units includes: A bidirectional controllable switch, one end of which is connected to one end of a corresponding second current-limiting inductor via the second energy-dissipating resistor, and the other end of which is connected to the other end of the corresponding second current-limiting inductor.

[0017] A bidirectional controllable switch is provided in the second energy consumption unit, so no matter which direction the freewheeling current of the second current limiting inductor is, the second energy consumption unit can be turned on to dissipate the freewheeling current, thereby improving the utilization rate of the second energy consumption unit.

[0018] Optionally, in the event of a fault on the output port side of the flexible direct current transmission system, each of the second energy consumption units and the corresponding second current limiting inductor form an energy dissipation loop; in the event of a fault on the converter side of the flexible direct current transmission system, the first energy consumption unit and the first current limiting inductor form an energy dissipation loop, and each of the second energy consumption units and the corresponding second current limiting inductor form an energy dissipation loop.

[0019] When the anode of the diode of the first energy consuming unit faces the converter side, by designing the circuit connection structure between the first energy consuming unit, the second energy consuming unit and the corresponding current limiting inductor, the corresponding energy dissipation circuit is turned on due to the specified orientation of the diode for different fault locations of the flexible DC transmission system, thereby achieving the energy dissipation function of the current limiting inductor within the multi-port DC fault current limiter.

[0020] Optionally, in the event of a fault on the output port side of the flexible direct current transmission system, the first energy consumption unit and the first current limiting inductor form an energy dissipation loop, and each second energy consumption unit and the corresponding second current limiting inductor form an energy dissipation loop; in the event of a fault on the converter side of the flexible direct current transmission system, each second energy consumption unit and the corresponding second current limiting inductor form an energy dissipation loop.

[0021] When the anode of the diode of the first energy consuming unit is oriented toward the output port, by designing the circuit connection structure between the first energy consuming unit, the second energy consuming unit, and the corresponding current-limiting inductor, the corresponding energy dissipation circuit is turned on due to the specified orientation of the diode for different fault locations of the flexible direct current transmission system, thereby achieving the energy dissipation function of the current-limiting inductor within the multi-port DC fault current limiter.

[0022] In a second aspect, an embodiment of the present application provides a flexible direct current transmission system, comprising the multi-port direct current fault current limiter described in the above embodiment.

[0023] The flexible direct current transmission system proposed in the embodiment of the present application consists of a busbar connected to multiple direct current lines to form multiple output ports. The first energy-consuming unit and the second energy-consuming unit in the multi-port direct current limiter are respectively connected in parallel with the corresponding current-limiting inductor to form a loop, so that the follow-on current in the current-limiting inductor forms a circulating current in the loop. Compared with the existing current-limiting reactor configuration method, the multi-port direct current fault limiter proposed in the embodiment of the present application is intended to improve the fault current limiting capability of the system of large-capacity converters transmitting multiple lines through the busbar, while significantly reducing the fault current peak value and shortening the fault current clearing time, thereby reducing the energy consumption capacity of the MOV in the direct current circuit breaker and improving the fault current clearing efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the specific implementation methods of the present application or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the specific implementation methods or the description of the prior art. Obviously, the drawings described below are some implementation methods of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0025] Figure 1 A schematic structural diagram of a multi-port DC fault current limiter for a flexible DC transmission system proposed in an embodiment of the present application in one scenario; Figure 2 A schematic structural diagram of a multi-port DC fault current limiter for a flexible DC transmission system proposed in an embodiment of the present application in another case; Figure 3 A schematic diagram of the working principle of the multi-port DC fault current limiter proposed in an embodiment of the present application in the current limiting stage of a fault on the output port side; Figure 4 A schematic diagram of the working principle of the multi-port DC fault current limiter proposed in an embodiment of the present application during the stage of clearing a fault on the output port side; Figure 5 A schematic diagram of the working principle of the multi-port DC fault current limiter proposed in an embodiment of the present application in the recovery phase of a fault on the output port side Figure 6 A schematic diagram of the working principle of the multi-port DC fault current limiter proposed in an embodiment of the present application during the current limiting stage of a converter-side fault; Figure 7 A schematic diagram of the working principle of the multi-port DC fault current limiter proposed in an embodiment of the present application during the converter-side fault clearing stage; Figure 8 A schematic diagram of the working principle of the multi-port DC fault current limiter proposed in an embodiment of the present application during the recovery phase of a converter-side fault; Figure 9 A schematic diagram of another working principle of the multi-port DC fault current limiter proposed in an embodiment of the present application during the current limiting stage of a fault on the output port side; Figure 10 A schematic diagram of another working principle of the multi-port DC fault current limiter proposed in an embodiment of the present application during the stage of clearing a fault on the output port side; Figure 11 Schematic diagram of another working principle of the multi-port DC fault current limiter proposed in an embodiment of the present application during the recovery phase of a fault on the output port side Figure 12 A schematic diagram of another working principle of the multi-port DC fault current limiter proposed in an embodiment of the present application during the current limiting stage of a converter-side fault; Figure 13 A schematic diagram of another working principle of the multi-port DC fault current limiter proposed in an embodiment of the present application during the converter-side fault clearing stage; Figure 14 A schematic diagram of another working principle of the multi-port DC fault current limiter proposed in an embodiment of the present application during the recovery phase of a converter-side fault; Figure 15 This is a schematic structural diagram of a flexible direct current transmission system proposed in an embodiment of the present application. DETAILED DESCRIPTION

[0026] To make the purpose, technical solutions, and advantages of the embodiments of the present application more clear, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without making creative efforts shall fall within the scope of protection of this application.

[0027] Flexible DC transmission technology has been widely used due to its advantages in long-distance power transmission, improving grid stability, and reducing transmission losses. However, flexible DC transmission systems still face many technical challenges during operation. In particular, how to effectively limit fault current and quickly clear the fault when a system fault occurs has become a key issue that needs to be addressed.

[0028] The typical fault current limiting method in existing flexible DC transmission systems involves installing current-limiting reactors at both ends of the line. This current-limiting approach results in high energy consumption in the DC circuit breaker's MOVs and a long tail time for the fault current. Fault tail time refers to the time it takes for the fault current in a power system to gradually decay to zero after a fault occurs. The length of this time depends on system parameters such as inductance and capacitance. Typically, after the circuit breaker executes protective action, the MOV energy dissipation device in the circuit breaker not only absorbs the fault current supplied by the system but also dissipates the energy stored in the current-limiting reactor, thereby increasing the capacity burden of the DC circuit breaker's MOV.

[0029] The multi-port DC fault current limiter provided in this specification can be applied to a flexible DC transmission system with a port structure consisting of a DC busbar connected to multiple DC lines, and is suitable for DC systems with different maximum fault currents when the current limiter fails in the forward and reverse directions. Figure 1 and Figure 2 As shown in Figure 1, a DC bus extends from the converter output and connects multiple DC lines to form multiple output ports. A forward fault occurs on the output port side, also known as a line-side fault. A reverse fault occurs on the converter side, also known as a back-side fault.

[0030] Figure 1 and Figure 2 FIG is a structural diagram of a multi-port DC fault current limiter for a flexible DC transmission system proposed in an embodiment of the present application. Figure 1 and Figure 2 As shown, the flexible DC power transmission system uses multiple DC lines for power transmission, each of which is provided with an output port. The multi-port DC fault current limiter 100 includes: a first current-limiting inductor 10 provided on a DC bus, wherein one end of the DC bus is adapted to be connected to a converter, and the other end of the DC bus is adapted to be respectively connected to the plurality of DC lines; a first energy consumption unit 20, connected in parallel with the first current-limiting inductor 10, and configured to consume the freewheeling current of the first current-limiting inductor 10 in the event of a fault in the flexible DC transmission system; a plurality of second current-limiting inductors 30, each of the second current-limiting inductors 30 being connected in series to a corresponding DC line and connected between the first current-limiting inductor 10 and a corresponding output port; A plurality of second energy consuming units 40 are provided, and each second energy consuming unit 40 is connected in parallel with a corresponding second current limiting inductor 30 to consume the freewheeling current of the corresponding second current limiting inductor 30 when a fault occurs in the flexible direct current transmission system.

[0031] The multi-port DC fault current limiter 100 provided in this embodiment is designed for a flexible DC power transmission system with multiple output ports, consisting of a busbar connected to multiple DC lines. By connecting a first energy-consuming unit 20 and a second energy-consuming unit 40 in parallel with corresponding current-limiting inductors to form a loop, the freewheeling current in the current-limiting inductor forms a circulating current within the loop. Compared to existing current-limiting reactor configuration methods, the multi-port DC fault current limiter proposed in this embodiment of the application is designed to improve the fault current-limiting capability of a large-capacity converter system transmitting power via multiple busbar lines. While significantly reducing the peak fault current, it also reduces the energy consumption capacity of the MOV in the DC circuit breaker, thereby shortening the fault current clearing time and improving the fault current clearing efficiency.

[0032] Depend on Figure 1 and Figure 2 It can be seen that the flexible DC transmission system consists of a DC busbar connected to n DC lines to form n output ports, and DC circuit breakers are set at the outlet of the converter and at the output ports. L0 is the first current limiting inductor connected in series to the DC busbar, L1, L2...L n is the second current-limiting inductor connected in series with the corresponding DC line.

[0033] In the embodiment of the present application, the first energy consumption unit 20 includes a diode D and a first energy consumption resistor R1 connected in series.

[0034] Specifically, if Figure 1 As shown, when the maximum fault current generated on the output port side of the flexible DC transmission system is less than the maximum fault current generated on the converter side of the flexible DC transmission system, the anode of the diode D is connected to one end of the DC bus, the cathode of the diode D is connected to one end of the first energy dissipation resistor R1, and the other end of the first energy dissipation resistor R1 is connected to the other end of the DC bus.

[0035] like Figure 2 As shown, when the maximum fault current generated on the output port side of the flexible DC transmission system is greater than the maximum fault current generated on the converter side of the flexible DC transmission system, the cathode of the diode D is connected to one end of the DC bus, the anode of the diode D is connected to one end of the first energy dissipation resistor R1, and the other end of the first energy dissipation resistor R1 is connected to the other end of the DC bus.

[0036] The embodiment of the present application takes into account two situations in which the maximum fault currents generated by the fault occurring on the output port side and the converter side are different. The direction of the diode in the first energy consumption unit is set in a targeted manner so that the anode of the diode points to the side where the maximum fault current is larger, so as to ensure that the fault current can flow in the expected direction. In this way, when a larger fault current is generated on the converter side, the first energy dissipation resistor can be directly used to partially dissipate the fault current due to the conduction of the diode, so as to maximize the first energy dissipation resistor's ability to consume the fault current and the first current limiting inductor's follow-up current, thereby improving the fault current consumption efficiency.

[0037] In the implementation of this application, in order to determine the maximum fault current on the converter side and the output port side, it is usually necessary to consider the system parameters and fault types on both sides. The system parameters include voltage level, internal impedance and load conditions, etc. The fault types mainly include short circuit faults and ground faults. The embodiment of this application adopts the power system simulation software commonly used in this field to simulate different fault types based on certain system parameters, so as to determine the maximum fault current according to the simulation results.

[0038] Because fault current tends to flow from the end with a larger supply to the end with a smaller supply, setting the anode of the diode toward the end with the larger maximum fault current can guide the larger fault current to the first energy-dissipating resistor R1 when a fault occurs, thereby quickly dissipating the fault current. If the fault occurs at the end with the smaller fault current, the fault current at this time will place less energy burden on the multi-port DC fault current limiter and other components in the system than on the end with the larger maximum fault current. Therefore, setting the anode of the diode toward the end with the larger maximum fault current not only helps improve the efficiency of eliminating larger fault currents, but also reduces the energy burden on the multi-port DC fault current limiter and other components in the system.

[0039] In addition, in the embodiment of the present application, the first energy consumption unit 20 is further configured to be put into operation when an oscillating current appears on the converter side of the flexible DC transmission system, so as to suppress the oscillating current.

[0040] The converter is an important node in the flexible HVDC transmission system, used to convert AC power into DC power or vice versa. In some cases, such as when the system is disturbed by a fault or a sudden voltage change, the output voltage and current of the converter may oscillate. If this oscillation is not controlled, it will affect the stability of the entire HVDC transmission system. Figure 1 and Figure 2 The current structure shown utilizes the single-phase conduction characteristic of the diode. If the diode's forward threshold is exceeded by the oscillating voltage and current, the diode automatically conducts, requiring no additional control signals and thus exhibiting a certain degree of adaptive input characteristics. When the diode conducts, it allows the oscillating voltage and current to pass through the first energy-dissipating resistor R1, dissipating excess energy. This dissipation helps to reduce oscillations, thereby preventing system instability after a disturbance and improving system stability.

[0041] It can be seen that compared with traditional current-limiting reactors with a single function and no function in non-fault conditions, the multi-port DC fault current limiter proposed in the embodiment of the present application sets the first energy consumption unit on the converter side, so that while playing the role of fault current limiting, it can also realize the function of adaptive suppression when power flow fluctuations occur in the flexible DC transmission system, thereby improving the utilization rate of power devices.

[0042] like Figure 1 and Figure 2 In the embodiment shown, a plurality of the second energy consuming units 40 share the second energy consuming resistor R2. n The shared second energy-dissipating resistor R2 can save the number of power electronic devices and energy-dissipating resistors without reducing the overall current limiting capability, thereby achieving the effect of consuming the continuous current of the current-limiting inductor and effectively reducing the cost of the current limiter.

[0043] Specifically, each of the second energy consumption units 40 includes: A bidirectional controllable switch, one end of which is connected to one end of a corresponding second current-limiting inductor via the second energy-dissipating resistor, and the other end of which is connected to the other end of the corresponding second current-limiting inductor.

[0044] Depend on Figure 1 and Figure 2 It can be seen that the second energy dissipation resistor R2 and each of the bidirectional controllable switches constitute multiple second energy dissipation units 40, wherein the controllable switch is composed of two anti-parallel thyristors, namely thyristor J 11 and thyristor J 12 The bidirectional controllable switch and the second energy dissipation resistor R2 form a second energy dissipation unit 40 connected in parallel with the current limiting inductor L1. The thyristor J 21 and thyristor J 22 The bidirectional controllable switch and the second energy dissipation resistor R2 form a second energy dissipation unit 40 connected in parallel with the current limiting inductor L2. Similarly, the thyristor J n1 and thyristor J n2 The bidirectional controllable switch and the second energy dissipation resistor R2 form a current limiting inductor L n A second energy consumption unit 40 connected in parallel.

[0045] A bidirectional controllable switch is provided in the second energy consumption unit, so no matter which direction the freewheeling current of the second current limiting inductor is, the second energy consumption unit can be turned on to dissipate the freewheeling current, thereby improving the utilization rate of the second energy consumption unit.

[0046] The embodiment of the present application is to target different situations in which fault current is generated. Figure 1 and Figure 2 The circuit structure shown forms a corresponding energy dissipation loop. Figure 1 and Figure 2 The circuit structures of the two diodes in different directions are shown, and the circuit principles are explained for the two situations where the fault occurs on the converter side and the output port side respectively.

[0047] Figures 3 to 5 It shows that when the maximum fault current generated on the output port side of the flexible DC transmission system is less than the maximum fault current generated on the converter side of the flexible DC transmission system, the corresponding Figure 1 Based on the circuit structure, this is a schematic diagram of the circuit's working principle when a fault occurs on the output port side.

[0048] In the event that a fault occurs on the output port side of the flexible HVDC power transmission system, each of the second energy consumption units 40 forms an energy dissipation loop with the corresponding second current-limiting inductor 30 .

[0049] Specifically, Figure 3 Shown Figure 1 The circuit structure shown in the figure is a schematic diagram of the working principle of the fault current limiting stage. At this time, the fault occurs at the position marked f on the output port side. The red arrow in the figure shows the flow direction of the fault current. In the early stage after the DC system fault occurs, the current limiting inductors L1, L2...L n To achieve the desired non-delayed fault current limiting function, the bidirectional controllable switch in the second energy dissipation unit 40 remains in the off state, and no current flows through the second energy dissipation resistor R2. It should be noted that a very small portion of the fault current will flow through the current-limiting inductor L0, which can be ignored in the embodiment of the present application. The majority of the fault current will flow through the first energy dissipation branch 20, that is, through the diode D and the first energy dissipation resistor R1. At this time, the fault current will be partially dissipated due to the consumption effect of the first energy dissipation resistor R1 before flowing through the current-limiting inductor L1.

[0050] Figure 4 Shown Figure 1 The circuit structure shown in the figure is a schematic diagram of the working principle of the fault clearing stage. The red arrow in the figure still indicates the flow direction of the fault current. At this time, after the multi-port DC fault current limiter receives the trip signal, it turns on the bidirectional controllable switch in each second energy consumption unit 40, so that each second energy consumption unit 40 and the corresponding current limiting inductor L1, L2...L n Form an energy dissipation loop, current limiting inductors L1, L2...L n The freewheeling current generated during the current limiting operation will form a loop current through the second energy dissipation resistor R2. The blue arrow in the figure shows the direction of the loop current. It can be seen that during the fault clearing phase, the MOV of the circuit breaker only needs to dissipate the fault energy of the system without dissipating the current limiting inductors L1, L2...L n Therefore, the energy consumption capacity requirement of the MOV of the DC circuit breaker is greatly reduced, which in turn greatly improves the speed of clearing the fault current.

[0051] Figure 5 Shown Figure 1 The circuit structure shown in the figure works in the recovery stage of the fault. After the fault current is cleared, the current limiting inductors L1, L2...L n The remaining freewheeling current is dissipated through the second energy dissipation resistor R2, thereby enabling the current limiter to recover. The blue arrows in the figure indicate the circulation direction of the remaining freewheeling current in the energy dissipation loop.

[0052] Figures 6 to 8It shows that when the maximum fault current generated on the output port side of the flexible DC transmission system is less than the maximum fault current generated on the converter side of the flexible DC transmission system, the corresponding Figure 1 Based on the circuit structure, a schematic diagram of the circuit working principle when a fault occurs on the converter side is shown.

[0053] In the event of a fault on the converter side of the flexible HVDC system, the first energy consuming unit and the first current limiting inductor form an energy dissipation loop, and each of the second energy consuming units and the corresponding second current limiting inductor form an energy dissipation loop.

[0054] Specifically, Figure 6 Shown Figure 1 The circuit structure shown in the figure is a schematic diagram of the working principle of the fault current limiting stage. At this time, the fault occurs at the position marked f on the converter side. The red arrow in the figure shows the flow direction of the fault current. In the early stage after the DC system fault occurs, the current limiting inductors L0, L1, L2...L n The diode D and the bidirectional controllable switch in the second energy consumption unit 40 are in the off state, and no current flows through the second energy consumption resistor R2 to play the role of current limiting without time delay.

[0055] Figure 7 Shown Figure 1 The circuit structure shown in the figure is a schematic diagram of the working principle of the fault clearing stage. The red arrow in the figure still indicates the flow direction of the fault current. At this time, after the multi-port DC fault current limiter receives the trip signal, it turns on the bidirectional controllable switch in each second energy consumption unit 40. Therefore, the current limiting inductor L0 also forms an energy dissipation loop with the first energy consumption unit 20. At the same time, each second energy consumption unit 40 and the corresponding current limiting inductor L1, L2...L n The freewheeling current generated by the current limiting inductor L0 during the current limiting action will form a loop current through the first energy dissipation resistor R1. n The freewheeling current generated during the current limiting operation will form a loop current through the second energy dissipation resistor R2. The blue arrow in the figure shows the direction of the loop current. It can be seen that during the fault clearing phase, the MOV of the circuit breaker only needs to dissipate the fault energy of the system without dissipating the current limiting inductors L0, L1, L2...L n Therefore, the energy consumption capacity requirement of the MOV of the DC circuit breaker is greatly reduced, which in turn greatly improves the speed of clearing the fault current.

[0056] Figure 8 Shown Figure 1The circuit structure shown in the figure is a schematic diagram of the working principle of the fault recovery stage. After the fault current is cleared, the remaining freewheeling current of the current limiting inductor L0 is dissipated through the first energy dissipation resistor R1, and the current limiting inductors L1, L2...L n The remaining freewheeling current is dissipated through the second energy dissipation resistor R2, thereby enabling the current limiter to recover. The blue arrows in the figure indicate the circulation direction of the remaining freewheeling current in the energy dissipation loop.

[0057] In summary, when the anode of the diode of the first energy consuming unit is oriented toward the converter side, by designing the circuit connection structure between the first energy consuming unit and the second energy consuming unit and the corresponding current-limiting inductor, the corresponding energy dissipation circuit is turned on due to the specified orientation of the diode for different fault locations of the flexible DC transmission system, thereby achieving the energy dissipation function of the current-limiting inductor inside the multi-port DC fault current limiter.

[0058] Figures 9 to 11 It shows that when the maximum fault current generated on the output port side of the flexible DC transmission system is greater than the maximum fault current generated on the converter side of the flexible DC transmission system, the corresponding Figure 2 Based on the circuit structure, this is a schematic diagram of the circuit's working principle when a fault occurs on the output port side.

[0059] When a fault occurs on the output port side of the flexible direct current transmission system, the first energy consumption unit and the first current-limiting inductor form an energy dissipation loop, and each of the second energy consumption units and the corresponding second current-limiting inductor form an energy dissipation loop.

[0060] Specifically, Figure 9 Shown Figure 2 The circuit structure shown in the figure is a schematic diagram of the working principle of the fault current limiting stage. At this time, the fault occurs at the position marked f on the output port side. The red arrow in the figure shows the flow direction of the fault current. In the early stage after the DC system fault occurs, the current limiting inductors L0, L1, L2...L n The diode D and the bidirectional controllable switch in the second energy consumption unit 40 are in the off state, and no current flows through the second energy consumption resistor R2 to play the role of current limiting without time delay.

[0061] Figure 10 Shown Figure 2 The circuit structure shown in the figure is a schematic diagram of the working principle of the fault clearing stage. The red arrow in the figure still indicates the flow direction of the fault current. At this time, after the multi-port DC fault current limiter receives the trip signal, it turns on the bidirectional controllable switch in each second energy consumption unit 40. Therefore, the current limiting inductor L0 also forms an energy dissipation loop with the first energy consumption unit 20. At the same time, each second energy consumption unit 40 and the corresponding current limiting inductor L1, L2...Ln The freewheeling current generated by the current limiting inductor L0 during the current limiting action will form a loop current through the first energy dissipation resistor R1. n The freewheeling current generated during the current limiting operation will form a loop current through the second energy dissipation resistor R2. The blue arrow in the figure shows the direction of the loop current. It can be seen that during the fault clearing phase, the MOV of the circuit breaker only needs to dissipate the fault energy of the system without dissipating the current limiting inductors L0, L1, L2...L n Therefore, the energy consumption capacity requirement of the MOV of the DC circuit breaker is greatly reduced, which in turn greatly improves the speed of clearing the fault current.

[0062] Figure 11 Shown Figure 2 The circuit structure shown in the figure is a schematic diagram of the working principle of the fault recovery stage. After the fault current is cleared, the remaining freewheeling current of the current limiting inductor L0 is dissipated through the first energy dissipation resistor R1, and the current limiting inductors L1, L2...L n The remaining freewheeling current is dissipated through the second energy dissipation resistor R2, thereby enabling the current limiter to recover. The blue arrows in the figure indicate the circulation direction of the remaining freewheeling current in the energy dissipation loop.

[0063] Figures 12 to 14 When the maximum fault current generated on the output port side of the flexible DC transmission system is greater than the maximum fault current generated on the converter side of the flexible DC transmission system, Figure 2 Based on the circuit structure, a schematic diagram of the circuit working principle when a fault occurs on the converter side is shown.

[0064] In the event that a fault occurs on the converter side of the flexible direct current transmission system, each of the second energy consumption units and the corresponding second current-limiting inductor form an energy dissipation loop.

[0065] Specifically, Figure 12 Shown Figure 2 The circuit structure shown in the figure is a schematic diagram of the working principle of the current limiting stage of the fault. At this time, the fault occurs at the position marked f on the converter side. The red arrow in the figure shows the flow direction of the fault current. In the early stage after the DC system fault occurs, the current limiting inductors L1, L2...L nTo achieve the desired non-delayed fault current limiting function, the bidirectional controllable switch in the second energy dissipation unit 40 remains in the off state, and no current flows through the second energy dissipation resistor R2. It should be noted that a very small portion of the fault current will flow through the current-limiting inductor L0, which can be ignored in the embodiment of the present application. The majority of the fault current will flow through the first energy dissipation branch 20, that is, through the diode D and the first energy dissipation resistor R1. At this time, the fault current will be partially dissipated due to the consumption effect of the first energy dissipation resistor R1 before flowing through the current-limiting inductor L1.

[0066] Figure 13 Shown Figure 2 The circuit structure shown in the figure is a schematic diagram of the working principle of the fault clearing stage. The red arrow in the figure still indicates the flow direction of the fault current. At this time, after the multi-port DC fault current limiter receives the trip signal, it turns on the bidirectional controllable switch in each second energy consumption unit 40, so that each second energy consumption unit 40 and the corresponding current limiting inductor L1, L2...L n Form an energy dissipation loop, current limiting inductors L1, L2...L n The freewheeling current generated during the current limiting operation will form a loop current through the second energy dissipation resistor R2. The blue arrow in the figure shows the direction of the loop current. It can be seen that during the fault clearing phase, the MOV of the circuit breaker only needs to dissipate the fault energy of the system without dissipating the current limiting inductors L1, L2...L n Therefore, the energy consumption capacity requirement of the MOV of the DC circuit breaker is greatly reduced, which in turn greatly improves the speed of clearing the fault current.

[0067] Figure 14 Shown Figure 2 The circuit structure shown in the figure works in the recovery stage of the fault. After the fault current is cleared, the current limiting inductors L1, L2...L n The remaining freewheeling current is dissipated through the second energy dissipation resistor R2, thereby enabling the current limiter to recover. The blue arrows in the figure indicate the circulation direction of the remaining freewheeling current in the energy dissipation loop.

[0068] In summary, due to Figure 2 and Figure 1 Compared to the diode in the circuit, the direction is opposite, so Figures 9 to 14 The directions of the fault current and freewheeling current shown in the figure are also opposite, thus influencing the formation of the energy dissipation loop in the opposite manner. Similarly, when the anode of the diode of the first energy consuming unit is oriented toward the output port, by designing the circuit connection structure between the first and second energy consuming units and the corresponding current-limiting inductors, the corresponding energy dissipation loop is connected due to the specified orientation of the diodes for different fault locations in the flexible DC transmission system, thereby achieving the freewheeling current dissipation function of the current-limiting inductor within the multi-port DC fault current limiter.

[0069] Accordingly, please refer to Figure 15 An embodiment of the present application provides a flexible direct current transmission system, including the multi-port direct current fault current limiter 100 described in the above embodiment.

[0070] The flexible DC transmission system also includes a converter 200. A DC bus extends from the outlet of the converter 200, connecting multiple DC lines and forming multiple output ports. The multi-port DC fault current limiter 100 is disposed between the outlet of the converter 200 and the multiple output ports. A converter-side DC circuit breaker 300 is provided at the outlet of the converter 200, and an output-port-side DC circuit breaker 400 is provided at the output ports.

[0071] The further functional description of each of the above modules and units is the same as that of the above corresponding embodiments and will not be repeated here.

[0072] For the convenience of description, the above devices are described as being divided into various units according to their functions. Of course, when implementing this application, the functions of each unit can be implemented in the same or multiple software and / or hardware.

[0073] It should be noted that the terms "comprises," "includes," or any other variations thereof are intended to encompass non-exclusive inclusion, such that a process, method, commodity, or apparatus that includes a series of elements includes not only those elements but also other elements not explicitly listed, or includes elements inherent to such process, method, commodity, or apparatus. In the absence of further limitations, an element defined by the phrase "comprises a..." does not exclude the presence of other identical elements in the process, method, commodity, or apparatus that includes the element.

[0074] The various embodiments in this specification are described in a progressive manner. Similar parts between the various embodiments can be referred to in conjunction with each other. Each embodiment focuses on the differences between the other embodiments. In particular, the system embodiments are generally similar to the method embodiments, so the description is relatively simple. For relevant parts, refer to the description of the method embodiments.

[0075] The terms "first" and "second" in this specification are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of the technical features indicated. Therefore, a feature specified as "first" or "second" may explicitly or implicitly include at least one of such features. In the description of the present invention, "plurality" means at least two, for example, two, three, etc., unless otherwise specifically defined.

[0076] The foregoing is merely an embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various changes and variations. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application should all be included within the scope of the claims of the present application.

[0077] Although the embodiments of the present application have been described with reference to the accompanying drawings, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the present application, and such modifications and variations shall fall within the scope defined by the appended claims.

Claims

1. A multi-port DC fault current limiter for a flexible DC transmission system, characterized in that: The flexible direct current power transmission system uses a plurality of direct current lines for power transmission, each of the direct current lines is provided with an output port, and the multi-port direct current fault current limiter comprises: a first current-limiting inductor arranged on a DC bus, wherein one end of the DC bus is suitable for being connected to a converter, and the other end of the DC bus is suitable for being respectively connected to the plurality of DC lines; a first energy consumption unit, wherein the first energy consumption unit is connected in parallel with the first current limiting inductor, and the first energy consumption unit is used to consume the follow-up current of the first current limiting inductor when a fault occurs in the flexible direct current transmission system; A plurality of second current-limiting inductors, each of which is connected in series to a corresponding DC line and connected between the first current-limiting inductor and a corresponding output port; A plurality of second energy consuming units, each of which is connected in parallel with a corresponding second current limiting inductor, so as to consume the follow-up current of the corresponding second current limiting inductor when a fault occurs in the flexible direct current transmission system.

2. The multi-port DC fault current limiter according to claim 1, characterized in that: The first energy consumption unit includes a diode and a first energy consumption resistor connected in series.

3. The multi-port DC fault current limiter according to claim 2, characterized in that: When the maximum fault current generated on the output port side of the flexible DC power transmission system is less than the maximum fault current generated on the converter side of the flexible DC power transmission system, the anode of the diode is connected to one end of the DC bus, the cathode of the diode is connected to one end of the first energy dissipation resistor, and the other end of the first energy dissipation resistor is connected to the other end of the DC bus.

4. The multi-port DC fault current limiter according to claim 2, characterized in that: When the maximum fault current generated on the output port side of the flexible DC power transmission system is greater than the maximum fault current generated on the converter side of the flexible DC power transmission system, the cathode of the diode is connected to one end of the DC bus, the anode of the diode is connected to one end of the first energy dissipation resistor, and the other end of the first energy dissipation resistor is connected to the other end of the DC bus.

5. The multi-port DC fault current limiter according to any one of claims 1 to 4, characterized in that: The first energy consumption unit is further used to be put into operation when an oscillating current appears on the converter side of the flexible direct current transmission system, so as to suppress the oscillating current.

6. The multi-port DC fault current limiter according to any one of claims 1 to 4, characterized in that: A plurality of the second energy consumption units share a second energy consumption resistor.

7. The multi-port DC fault current limiter according to claim 6, characterized in that: Each of the second energy consumption units comprises: A bidirectional controllable switch, one end of which is connected to one end of a corresponding second current-limiting inductor through the second energy-consuming resistor, and the other end of which is connected to the other end of the corresponding second current-limiting inductor.

8. The multi-port DC fault current limiter according to claim 3, characterized in that: In the event of a fault on the output port side of the flexible direct current transmission system, each of the second energy consuming units and the corresponding second current limiting inductor form an energy dissipation loop; in the event of a fault on the converter side of the flexible direct current transmission system, the first energy consuming unit and the first current limiting inductor form an energy dissipation loop, and each of the second energy consuming units and the corresponding second current limiting inductor form an energy dissipation loop.

9. The multi-port DC fault current limiter according to claim 4, characterized in that: In the event of a fault on the output port side of the flexible direct current transmission system, the first energy consumption unit and the first current limiting inductor form an energy dissipation loop, and each of the second energy consumption units and the corresponding second current limiting inductor form an energy dissipation loop; in the event of a fault on the converter side of the flexible direct current transmission system, each of the second energy consumption units and the corresponding second current limiting inductor form an energy dissipation loop.

10. A flexible direct current transmission system, characterized in that: It comprises a multi-port DC fault current limiter according to any one of claims 1-9.

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