Multi-port direct-current circuit breaker, power flow control method and direct-current fault processing method

Abstract

According to the multi-port direct-current circuit breaker, the power flow control method and the direct-current fault processing method, the circuit breaker comprises an upper direct-current bus, a lower direct-current bus and a plurality of parallel branches connected between the upper direct-current bus and the lower direct-current bus in parallel, and the parallel branches comprise a main circuit breaker branch, an energy absorption branch, a mode switching branch and a plurality of line branches of the same structure. The circuit branch is formed by sequentially connecting an upper side bridge arm, an isolating switch, an electric reactor and a lower side bridge arm in series. According to the application, a multi-port power flow control function and a direct current circuit breaking function are integrated together by utilizing topological structure similarity; wherein the main circuit breaker branch is used as a core component with a direct-current circuit breaking function and can realize a basic function of direct-current circuit breaking, and the plurality of circuit branches undertake an important task of power flow control and can adjust power flow distribution of each circuit; and the energy absorption branch and the mode switching branch provide support for stable operation and function switching of the whole circuit breaker, so that the flexibility and the stability of a direct-current power grid are greatly improved.

Description

Technical Field

[0001] This application relates to the field of power system technology, and in particular to a multi-port DC circuit breaker and power flow control and DC fault handling method. Background Technology

[0002] As DC grid technology continues to evolve, multi-port DC grids, with their efficient power transmission and flexible distribution characteristics, have gradually become a research focus and application trend in the power sector. Currently, the construction of multi-port DC grids mostly adopts a scheme based on modular multilevel converters (MMCs) with half-bridge submodules, combined with DC circuit breakers. This scheme can be applied to DC grids with any number of terminals.

[0003] However, DC circuit breakers primarily focus on DC interruption. While they can quickly disconnect faulty lines during DC line faults, they cannot effectively regulate the flow direction and magnitude of power in the DC grid. Especially in complex DC grid scenarios where the number of transmission lines exceeds the number of converter stations, relying solely on converter stations is insufficient to effectively regulate line power flow, and the lack of power flow control functionality in DC circuit breakers severely limits the flexibility and stability of the DC grid. Summary of the Invention

[0004] The purpose of this application is to at least address one of the aforementioned technical deficiencies, particularly the technical deficiency in the prior art where DC circuit breakers lack power flow control functionality, which greatly limits the flexibility and stability of DC power grids.

[0005] This application provides a multi-port DC circuit breaker, the circuit breaker including an upper DC bus, a lower DC bus, and multiple parallel branches connected between the upper DC bus and the lower DC bus;

[0006] The multiple parallel branches include one main circuit breaker branch, one energy absorption branch, one mode switching branch, and multiple line branches with the same structure.

[0007] The main circuit breaker branch is composed of the main circuit breaker;

[0008] The energy absorption branch is composed of a surge arrester;

[0009] The mode switching branch is composed of a mode switching switch and a capacitor connected in series;

[0010] The line branch is formed by connecting the upper bridge arm, disconnecting switch, reactor and lower bridge arm in series; each bridge arm is formed by connecting a current transfer switch and an ultra-fast mechanical switch in series.

[0011] Optionally, the mode switching switch includes a first mode switch and a second mode switch;

[0012] The first mode switch is used in economic scenarios and consists of a mode switching mechanical switch;

[0013] The second mode switch is used in reliability scenarios and consists of a mode switching current transfer switch and a mode switching mechanical switch connected in series.

[0014] Optionally, one end of the upper bridge arm is connected to the upper DC bus; and one end of the lower bridge arm is connected to the lower DC bus.

[0015] This application also provides a power flow control method applied to the multi-port DC circuit breaker described in any of the above embodiments, the method comprising:

[0016] Switch the mode switching switch and each ultra-fast mechanical switch to the closed state so that the multi-port DC circuit breaker is in power flow control mode.

[0017] The capacitor voltage and line current of each line branch are collected by an external voltage sampling circuit, and the MMC line and relaxation line are determined based on the external connection equipment of each line branch.

[0018] The current transfer switches in the MMC circuit and the relaxation circuit are state-controlled according to the capacitor voltage and the preset voltage reference value.

[0019] The current transfer switches in each of the other line branches are state-controlled based on the line current of the other line branches besides the MMC line and the relaxation line and the preset current reference value.

[0020] Optionally, the step of controlling the state of the current transfer switch in the MMC circuit and the relaxation circuit based on the capacitor voltage and a preset voltage reference value includes:

[0021] A voltage error signal is generated based on the difference between the capacitor voltage and the preset voltage reference value, and an equivalent current control quantity of the voltage error signal is generated through a voltage regulator.

[0022] A complementary PWM signal is generated based on the equivalent current control quantity, and the state control of the current transfer switch in the MMC circuit and the relaxation circuit is performed based on the complementary PWM signal.

[0023] Optionally, the complementary PWM signal includes a first PWM signal and a second PWM signal;

[0024] The step of controlling the state of the current transfer switches in the MMC circuit and the relaxation circuit according to the complementary PWM signal includes:

[0025] The state of the current transfer switch in the upper arm of the MMC line is controlled by the first PWM signal, and the state of the current transfer switch in the lower arm of the MMC line is controlled by the second PWM signal.

[0026] The current transfer switch in the upper arm of the relaxation line is controlled by the second PWM signal, and the current transfer switch in the lower arm of the relaxation line is controlled by the first PWM signal.

[0027] Optionally, the step of controlling the state of the current transfer switch in each of the other line branches based on the line current of the other line branches besides the MMC line and the relaxed line and a preset current reference value includes:

[0028] For each line branch other than the MMC line and the relaxed line, determine the line current and preset current reference value for that line branch;

[0029] A current error signal is generated based on the difference between the line current and the preset current reference value, and a line current control quantity of the current error signal is generated through a current regulator.

[0030] A complementary PWM signal is generated based on the line current control quantity, and the state of the current transfer switch in the line branch is controlled based on the complementary PWM signal.

[0031] Optionally, the method further includes:

[0032] After all line branch power flow control is completed, the mode switching switch and each ultra-fast mechanical switch are switched to the disconnect state so that the multi-port DC circuit breaker is in a stable operating mode.

[0033] This application also provides a DC fault handling method, applied to the multi-port DC circuit breaker described in any of the above embodiments, the method comprising:

[0034] The line branch with a line fault is marked as a faulty line, and the other line branches besides the faulty lines are marked as normal lines.

[0035] Control the main circuit breaker to be turned on, and control the current transfer switch in the upper bridge arm of the normal line to be turned on and the current transfer switch in the lower bridge arm to be turned off, and control the current transfer switch in the upper bridge arm of the faulty line to be turned off and the current transfer switch in the lower bridge arm to be turned on.

[0036] Disconnect the ultra-fast mechanical switch in the lower arm of the normal line, the ultra-fast mechanical switch in the upper arm of the faulty line, and the mode switching switch in the mode switching branch.

[0037] The main circuit breaker is controlled to open, so that the fault current is transferred to the surge arrester, and the energy consumption is quickly reduced by the surge arrester.

[0038] Once the energy consumption of the fault current is detected to have decreased to 0, the isolating switch in the faulty circuit is controlled to open.

[0039] Optionally, the method further includes:

[0040] If the mode switching switch is a first mode switch consisting of a mode switching current transfer switch and a mode switching mechanical switch connected in series, then after the main circuit breaker is turned on, the mode switching current transfer switch in the first mode switch is turned off.

[0041] As can be seen from the above technical solutions, the embodiments of this application have the following advantages:

[0042] The multi-port DC circuit breaker and power flow control and DC fault handling method provided in this application include an upper DC bus, a lower DC bus, and multiple parallel branches connected between the upper and lower DC buses. The parallel branches include a main circuit breaker branch consisting of a main circuit breaker, an energy absorption branch consisting of a surge arrester, a mode switching branch consisting of a mode switching switch and a capacitor connected in series, and multiple line branches with the same structure. The line branches are formed by connecting the upper bridge arm, the disconnecting switch, the reactor, and the lower bridge arm in series. Each bridge arm is formed by connecting a current transfer switch and an ultra-fast mechanical switch in series. This application utilizes topological similarity to integrate multi-port power flow control with DC circuit breaking function. The main circuit breaker branch, as the core component of the DC circuit breaking function, can realize the basic function of DC circuit breaking, while multiple line branches undertake the important task of power flow control and can adjust the power flow distribution of each line. The energy absorption branch and mode switching branch provide support for the stable operation and function switching of the entire circuit breaker, thereby greatly improving the flexibility and stability of the DC power grid. Attached Figure Description

[0043] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0044] Figure 1 A schematic diagram of the structure of a multi-port DC circuit breaker provided in this application embodiment;

[0045] Figure 2A flowchart illustrating a power flow control method provided in an embodiment of this application;

[0046] Figure 3 A schematic diagram of waveform simulation results based on power flow control provided for an embodiment of this application;

[0047] Figure 4 A flowchart illustrating a DC fault handling method provided in an embodiment of this application;

[0048] Figure 5 This is a schematic diagram of the waveform simulation results based on DC fault processing provided in an embodiment of this application. Detailed Implementation

[0049] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0050] In one embodiment, such as Figure 1 The above, Figure 1 This is a schematic diagram of the structure of a multi-port DC circuit breaker provided in an embodiment of this application. This application provides a multi-port DC circuit breaker, including an upper DC bus, a lower DC bus, and multiple parallel branches connected between the upper DC bus and the lower DC bus.

[0051] The multiple parallel branches include one main circuit breaker branch, one energy absorption branch, one mode switching branch, and multiple line branches with the same structure.

[0052] The main circuit breaker branch circuit consists of the main circuit breaker.

[0053] The energy absorption branch consists of surge arresters.

[0054] The mode switching branch consists of a mode switching switch and a capacitor connected in series.

[0055] The line branch is formed by connecting the upper bridge arm, disconnecting switch, reactor and lower bridge arm in series; each bridge arm is formed by connecting a current transfer switch and an ultra-fast mechanical switch in series.

[0056] In this embodiment, as Figure 1As shown, the multi-port DC circuit breaker mainly consists of multiple branches, including one main circuit breaker branch, one energy absorption branch, one mode switching branch, and m line branches with identical structures. The main circuit breaker branch includes the main circuit breaker 19; the energy absorption branch includes the surge arrester 20; the mode switching branch includes the mode switching switch and capacitor 21; the first line branch includes the current transfer switch 1 and ultra-fast mechanical switch 2, disconnecting switch 3, and reactor 4 on the upper bridge arm, and the current transfer switch 5 and ultra-fast mechanical switch 6 on the lower bridge arm; similarly, the second line branch includes the current transfer switch 7 and ultra-fast mechanical switch 8, disconnecting switch 9, and reactor 10 on the upper bridge arm, and the current transfer switch 11 and ultra-fast mechanical switch 12 on the lower bridge arm; the m-th line branch includes the current transfer switch 13 and ultra-fast mechanical switch 14 on the upper bridge arm, disconnecting switch 15, reactor 16, and the current transfer switch 17 and ultra-fast mechanical switch 18 on the lower bridge arm.

[0057] Specifically, in a multi-port DC circuit breaker, each branch has a clearly defined function and works in concert. The main circuit breaker branch can quickly interrupt the main current when a fault occurs, preventing the fault from escalating; the energy absorption branch can use surge arresters to absorb the energy generated by the fault in a timely manner, protecting equipment from excessive voltage surges; the mode switching branch can flexibly switch between different operating modes through the series connection of mode switching switches and capacitors to adapt to different grid operating conditions; and the line branch not only participates in power flow control but also isolates faulty lines during local faults. Through the multi-branch coordinated operation of the circuit breaker in this application, the efficiency and reliability of fault handling can be greatly improved, ensuring the safe and stable operation of the DC grid under various operating conditions.

[0058] Furthermore, since the line branch is composed of an upper bridge arm, a disconnecting switch, a reactor, and a lower bridge arm connected in series, and each bridge arm is formed by a current transfer switch and an ultra-fast mechanical switch connected in series, in terms of power flow control, each line branch can quickly and accurately control the on / off state and magnitude of the current using the series combination of the current transfer switch and the ultra-fast mechanical switch. Combined with the adjustment of the line electrical parameters by the reactor, the power flow control becomes more precise. Moreover, the high response speed of the ultra-fast mechanical switch can quickly respond to changes in the power flow of the power grid and adjust the power flow distribution of the line in a timely manner, meeting the real-time requirements of the DC power grid for power flow control.

[0059] Understandably, this application leverages the high degree of overlap between power flow control and fault handling functions in the topology, integrating a multi-port DC circuit breaker originally used for DC fault interruption with a power flow controller used for multi-terminal power distribution through deep topology fusion to construct a multi-port DC circuit breaker with power flow control functionality. Therefore, this application eliminates the need for separate power flow controller modules and separate power flow adjustment units for multiple lines. This allows m DC lines to share the same bridge arm devices, mode switching switches, and energy handling branches in both power flow control and fault clearing scenarios, significantly reducing the overall number of components used. While ensuring system operational flexibility and safety, this greatly improves the overall economic efficiency of the device.

[0060] In the above embodiments, the circuit breaker includes an upper DC bus, a lower DC bus, and multiple parallel branches connected between the upper and lower DC buses. These parallel branches include a main circuit breaker branch consisting of a main circuit breaker, an energy absorption branch consisting of surge arresters, a mode switching branch consisting of a mode switching switch and a capacitor connected in series, and multiple line branches with identical structures. These line branches are formed by connecting the upper bridge arm, disconnecting switch, reactor, and lower bridge arm in series. Each bridge arm is formed by connecting a current transfer switch and an ultra-fast mechanical switch in series. This application integrates multi-port power flow control with DC circuit breaking functionality using topological similarity. The main circuit breaker branch, as the core component of the DC circuit breaking function, can realize the basic function of DC circuit breaking. The multiple line branches undertake the important task of power flow control, adjusting the power flow distribution of each line. The energy absorption branch and the mode switching branch provide support for the stable operation and function switching of the entire circuit breaker, thereby greatly improving the flexibility and stability of the DC power grid.

[0061] In one embodiment, the mode switching switch may include a first mode switch and a second mode switch.

[0062] The first-mode switch is used in economical scenarios and consists of a mode-switching mechanical switch.

[0063] The second-mode switch is used in reliability scenarios and consists of a mode-switching current transfer switch and a mode-switching mechanical switch connected in series.

[0064] In this embodiment, the mode switching switch in the mode switching branch can be configured as a first mode switch or a second mode switch according to different application requirements, so as to achieve a flexible trade-off between economy and reliability, thereby enhancing the adaptability and engineering availability of the entire multi-port DC circuit breaker.

[0065] Specifically, such as Figure 1As shown, the mode switching switch may include a first mode switch and a second mode switch; wherein, the first mode switch can be applied to economic scenarios, and it is mainly composed of a mode switching mechanical switch 22; while the second mode switch can be applied to reliability scenarios, and it is mainly composed of a mode switching current transfer switch 23 and a mode switching mechanical switch 22 connected in series.

[0066] Understandably, the first-mode switch is designed for cost-sensitive applications, consisting only of a mode-switching mechanical switch. Its simple structure, fewer components, and smaller footprint significantly reduce the overall cost of the device while meeting basic mode-switching requirements. In applications with higher reliability requirements, a second-mode switch can be used. This switch consists of a mode-switching current transfer switch and a mode-switching mechanical switch connected in series. The two types of switches work together, making current transfer during mode switching more controllable. The mechanical switch can also disconnect under near-zero current conditions, effectively preventing arcing and damage to switch contacts, resulting in higher operational reliability and a longer service life.

[0067] In one embodiment, in a line branch:

[0068] One end of the upper bridge arm is connected to the upper DC bus.

[0069] One end of the lower bridge arm is connected to the lower DC bus.

[0070] In this embodiment, in the structure of the line branch, one end of the upper bridge arm can be connected to the side DC bus, and one end of the lower bridge arm can be connected to the lower DC bus.

[0071] Understandably, by connecting the upper and lower bridge arms to the upper and lower DC buses respectively, the line branches can naturally have an independent current path from the upper bus to the lower bus in terms of physical topology. This not only enables the line branches to participate independently in multi-port power flow regulation during power flow control, but also allows for directional control of the current transfer switches and ultra-fast mechanical switches of the upper and lower bridge arms during fault handling, ensuring that the current is rapidly transferred within the controlled path and ultimately interrupted by the main circuit breaker and surge arrester.

[0072] The power flow control method and DC fault handling method provided in the embodiments of this application are described below. The power flow control method and DC fault handling method described below are applied to the multi-port DC circuit breaker described above.

[0073] In one embodiment, such as Figure 2 As shown, Figure 2 This application provides a flowchart illustrating a power flow control method according to an embodiment of the present application. The application also provides a power flow control method applied to a multi-port DC circuit breaker, specifically including the following:

[0074] S110: Switch the mode switching switch and each ultra-fast mechanical switch to the closed state so that the multi-port DC circuit breaker is in power flow control mode.

[0075] S120: Collects the capacitor voltage and line current of each line branch through an external voltage sampling circuit, and determines the MMC line and relaxation line based on the external connection equipment of each line branch.

[0076] S130: Performs state control on the current transfer switches in the MMC circuit and relaxation circuit based on the capacitor voltage and the preset voltage reference value.

[0077] S140: The current transfer switch in each other line branch is state controlled according to the line current of the other line branches excluding the MMC line and the relaxation line and the preset current reference value.

[0078] In this embodiment, during power flow control, the microcontroller can switch the mode switching switch and each ultra-fast mechanical switch to the closed state to put the multi-port DC circuit breaker in power flow control mode. Then, it collects the capacitor voltage and the line current of each line branch through an external voltage sampling circuit, and determines the MMC line and the relaxation line based on the external connection devices of each line branch. Subsequently, based on the capacitor voltage and the preset voltage reference value, the microcontroller can perform state control on the current transfer switches in the MMC line and the relaxation line. Also, based on the line current of other line branches besides the MMC line and the relaxation line and the preset current reference value, the microcontroller can perform state control on the current transfer switches in each of the other line branches.

[0079] Among them, MMC lines refer to line branches whose external connection equipment is an MMC converter station, and their current is regulated by the MMC converter station. Relaxation circuits, on the other hand, refer to systems whose external connection object is a system with strong and stable voltage, such as the main AC power grid or energy storage systems. They are responsible for the energy balance of the DC system or the voltage support of the DC bus. Therefore, the power flow control methods of these two branches are different from those of other ordinary line branches.

[0080] Specifically, when the mode switching switch is closed, the capacitor in the mode switching branch is connected to the system. At this time, the circuit breaker is in power flow control mode. After all ultra-fast mechanical switches are closed, the bridge arms of all line branches will form a complete circuit, and the current can be adjusted by the microcontroller. In this state, the external voltage sampling circuit can collect the capacitor voltage and the line current of each line branch and transmit the data to the microcontroller so that the microcontroller can perform power flow control by controlling each line branch.

[0081] In power flow control, capacitor voltage characterizes the system's energy state. Maintaining its stability is equivalent to maintaining the energy balance of the entire multi-port system. Therefore, the difference between the capacitor voltage and a preset voltage reference value can be calculated to determine whether the voltage is too high or too low. This difference is then used to adjust the direction and magnitude of the current in the line by controlling the MMC current and the current transfer switch in the relaxation circuit, thereby redistributing energy among multiple ports and stabilizing the bus voltage. For other ordinary line branches, the line current represents the power flow to be regulated. Therefore, the microcontroller can independently control the current transfer switch in each line branch based on the line current and its preset current reference value, ensuring that the power flow among the multi-ports achieves the specified distribution.

[0082] In one embodiment, the process of controlling the state of the current transfer switch in the MMC circuit and the relaxation circuit according to the capacitor voltage and a preset voltage reference value in step S130 may include:

[0083] S131: Generate a voltage error signal based on the difference between the capacitor voltage and the preset voltage reference value, and generate an equivalent current control quantity for the voltage error signal through a voltage regulator.

[0084] S132: Generate a complementary PWM signal based on the equivalent current control quantity, and perform state control on the current transfer switches in the MMC circuit and relaxation circuit based on the complementary PWM signal.

[0085] In this embodiment, during power flow control, the microprocessor can generate a voltage error signal based on the difference between the capacitor voltage and the preset voltage reference value, and generate an equivalent current control quantity of the voltage error signal through a voltage regulator. Then, a complementary PWM signal can be generated based on the equivalent current control quantity, and the current transfer switch in the MMC circuit and the relaxation circuit can be state controlled based on the complementary PWM signal.

[0086] Specifically, by comparing the actual voltage value of the capacitor branch with a preset voltage reference value, a voltage error signal reflecting the system's energy balance can be obtained. The microcontroller then sends this voltage error signal to the voltage regulator, where it is converted into an equivalent current control quantity after proportional-integral calculation. This quantity indicates the amount of power injected or absorbed into the circuit to restore the capacitor voltage to the target level. Based on this equivalent current control quantity, the microprocessor can modulate and generate a pair of complementary PWM signals: one to control the current transfer switch of the upper bridge arm, and the other to control the current transfer switch of the lower bridge arm, ensuring that the two switches are always interlocked. This creates a controllable current path within the MMC and relaxation circuits.

[0087] Understandably, by continuously adjusting the duty cycle of the PWM signal, the MMC circuit can actively adjust the flow of energy into or out of the DC bus according to system requirements, while the relaxation circuit cooperates with the MMC circuit in the opposite power direction to keep the overall system in power balance and voltage stability.

[0088] In one embodiment, the complementary PWM signal in step S132 may include a first PWM signal and a second PWM signal; wherein, the process of controlling the state of the current transfer switch in the MMC circuit and the relaxation circuit according to the complementary PWM signal may include:

[0089] S1321: The current transfer switch in the upper arm of the MMC line is controlled by the first PWM signal, and the current transfer switch in the lower arm of the MMC line is controlled by the second PWM signal.

[0090] S1322: The current transfer switch in the upper arm of the relaxation line is controlled by the second PWM signal, and the current transfer switch in the lower arm of the relaxation line is controlled by the first PWM signal.

[0091] In this embodiment, the MMC circuit and the relaxation circuit are symmetrically adjusted. For the MMC circuit, the microcontroller can control the state of the current transfer switch in its upper bridge arm using a first PWM signal, and control the state of the current transfer switch in its lower bridge arm using a second PWM signal; for the relaxation current, the microcontroller can control the state of the current transfer switch in its upper bridge arm using a second PWM signal, and control the state of the current transfer switch in its lower bridge arm using a first PWM signal.

[0092] Specifically, for an MMC circuit, the microcontroller can use a first PWM signal to drive the current transfer switch in its upper bridge arm, allowing it to precisely adjust the current flowing through the circuit on the upper DC bus according to the duty cycle. It can also use a second PWM signal to drive the current transfer switch in its lower bridge arm, ensuring that the circuit maintains a complementary conduction state on the lower DC bus. Correspondingly, for a relaxed circuit, the microcontroller controls the current transfer switch in its upper bridge arm via the second PWM signal and the current transfer switch in its lower bridge arm via the first PWM signal. This results in the relaxed circuit exhibiting the opposite effect to the MMC circuit in terms of current direction and energy regulation.

[0093] Understandably, in symmetrical regulation mode, the MMC circuit can actively inject current into or absorb current from the bus according to system requirements, while the relaxation circuit plays the role of balancing the remaining power, maintaining the overall energy of the DC bus through opposite current regulation. The two circuits are coordinated and controlled by the same set of complementary PWM signals, achieving consistency in the switching action of the bridge arm, avoiding control delays, inconsistent actions, or circulating current problems between different circuits, and also reducing the complexity of the control logic.

[0094] In one embodiment, the process of controlling the state of the current transfer switch in each other line branch based on the line current of the other line branches besides the MMC line and the relaxed line and a preset current reference value in step S140 may include:

[0095] S141: For each line branch except for MMC lines and relaxed lines, determine the line current and preset current reference value for that line branch.

[0096] S142: A line current control quantity that generates a current error signal based on the difference between the line current and the preset current reference value, and generates the current error signal through a current regulator.

[0097] S143: Generate a complementary PWM signal based on the line current control quantity, and perform state control on the current transfer switch in the line branch based on the complementary PWM signal.

[0098] In this embodiment, for each line branch other than the MMC line and the relaxation line, the microcontroller can determine the line current and the preset current reference value of the line branch, then generate a current error signal based on the difference between the line current and the preset current reference value, and generate a line current control quantity of the current error signal through the current regulator. Then, a complementary PWM signal can be generated based on the line current control quantity, and the state control of the current transfer switch in the line branch can be performed based on the complementary PWM signal.

[0099] Specifically, by comparing the actual current values ​​of other line branches with preset current reference values, a current error signal reflecting the deviation between the current load state of the line and the target power distribution can be obtained. Subsequently, the microcontroller can send this current error signal to the current regulator, which uses proportional-integral processing to generate the required line current control quantity for the current line, thereby quantifying the current amplitude that the line should increase or decrease to meet the overall power flow planning needs of the system. Based on this line current control quantity, the microcontroller can modulate and generate a pair of complementary PWM signals, which are used to drive the current transfer switches in the upper and lower bridge arms of the line, respectively, so that the bridge arm current can be continuously and controllably adjusted according to the PWM duty cycle.

[0100] Understandably, since each ordinary line uses the same regulation logic and hardware structure, this independent and consistent closed-loop control method not only enables the multi-port system to finely distribute the current of all lines under complex operating conditions and ensure that the power flow between each port conforms to the preset operating strategy, but also enables the system to quickly restore the bus voltage and power flow balance through the coordinated regulation of each branch when the system is disturbed.

[0101] In one embodiment, the method may further include:

[0102] S150: After all line branch power flow control is completed, switch the mode switching switch and each ultra-fast mechanical switch to the disconnect state so that the multi-port DC circuit breaker is in stable operation mode.

[0103] In this embodiment, after all line branches have completed power flow control and entered a steady state, the microcontroller can switch the mode switching switch and the ultra-fast mechanical switches in each line branch to the disconnect state according to the system operating status, so that the current transfer channels and mechanical branches involved in the power flow control process are removed from the main current path. At this time, the multi-port DC circuit breaker retains only the current path necessary for normal power transmission, and all bridge arm switches used for power flow regulation are restored to the non-conducting state, thereby enabling the device to return to a stable operating mode with low loss and low switching frequency.

[0104] In one specific embodiment, this application uses a single-pole 500kV test system for simulation verification. It has four DC transmission lines connected to the DC bus, one of which is directly connected to the MMC, and the other three are connected to DC cables. The current in the three cables is respectively... , , This refers to the fact that the multi-port DC circuit breaker of this application can then be used for power flow control. For example... Figure 3 As shown, Figure 3 The diagram below shows the waveform simulation results based on power flow control provided in this application embodiment, where (a) is the waveform simulation result of the current of three cables and (b) is the waveform simulation result of the capacitor voltage.

[0105] Figure 3 In the case where 1s < t < 2s, the system is in a steady state and no power flow control is performed, =1.93kA, =1.92kA, =1.48kA. When t=2s, the first set of current reference values ​​is given to the four-port DC circuit breaker with power flow control capability. At this time, the power flow control mode is activated, the capacitor voltage is rapidly charged to the rated value of 40kV, and the current of each cable is controlled to... =1.00kA, =1.50kA, =1.83kA. When t=3s, the second set of current reference values ​​is given to the four-port DC circuit breaker with power flow control capability. At this time, the reference value of cable 1 current is -0.5kA. It can be seen that the proposed topology achieves tracking of the reverse current reference value after a transient process of 0.27s, and the current of each cable is controlled to 1.83kA. =2.50kA, =-0.50kA, =3.33kA. When t=4s, the third set of current reference values ​​is given to the four-port DC circuit breaker with power flow control capability. At this time, the reference value of the current of cable 1 is 0. It can be seen that the proposed topology achieves tracking of the current reference value after a transient process of 0.13s, and the current of each cable is controlled to 3.33kA. =0kA, =3.00kA, =2.33kA. When t=5s, a fault occurs at the outlet of cable 3, and the proposed topology switches to DC disconnect mode. The capacitor is bypassed by the main circuit breaker, and the capacitor voltage drops rapidly to 0. When 5s < t < 6s, no power flow control is performed on the system. After the fault in cable 3 is completely cleared... =2.60kA, =2.72kA. When t=6s, the fourth set of current reference values ​​is given to the four-port DC circuit breaker with power flow control capability. At this time, the proposed topology switches back to power flow control mode, and the capacitor voltage is quickly charged to the rated value of 40kV. It can be seen that after clearing the DC fault, the proposed topology can still effectively control the power flow of the remaining healthy line current, and the current of the remaining two cables is controlled to 2.72kA. =2.00kA, =3.32kA.

[0106] In one embodiment, such as Figure 4 As shown, Figure 4 This application provides a flowchart illustrating a DC fault handling method according to an embodiment of the present application. The present application also provides a DC fault handling method, specifically including the following:

[0107] S210: Mark the line branch with a line fault as a faulty line, and mark other line branches other than the faulty line as normal lines.

[0108] S220: Controls the main circuit breaker to be turned on, and controls the current transfer switch in the upper arm of the normal line to be turned on and the current transfer switch in the lower arm of the normal line to be turned off, and controls the current transfer switch in the upper arm of the faulty line to be turned off and the current transfer switch in the lower arm of the faulty line to be turned on.

[0109] S230: Disconnect the ultra-fast mechanical switch in the lower arm of the normal line, the ultra-fast mechanical switch in the upper arm of the faulty line, and the mode switching switch in the mode switching branch.

[0110] S240: Controls the main circuit breaker to open, so that the fault current is transferred to the surge arrester, and the surge arrester quickly reduces energy consumption.

[0111] S250: After detecting that the energy consumption of the fault current has decreased to 0, the disconnecting switch in the faulty circuit is opened.

[0112] In this embodiment, during DC fault handling, the line branch with the fault can be marked as the faulty line, and other line branches can be marked as normal lines. Then, the main circuit breaker can be turned on, and the current transfer switch in the upper arm and lower arm of the normal line can be turned on and off. Conversely, the current transfer switch in the upper arm and lower arm of the faulty line can be turned off and on. Then, the ultra-fast mechanical switch in the lower arm of the normal line, the ultra-fast mechanical switch in the upper arm of the faulty line, and the mode-switching mechanical switch in the mode-switching branch can be turned off. Next, the microcontroller can control the main circuit breaker to open, transferring the fault current to the surge arrester, which rapidly reduces energy consumption. When the energy consumption of the fault current is detected to have decreased to zero, the microcontroller can control the disconnecting switch in the faulty line to open.

[0113] Specifically, after a fault occurs, the current in the line branch will rise sharply. To protect the line branch, the microcontroller can turn on the main circuit breaker, allowing it to handle the large current path during the fault and creating zero-voltage or near-zero-current conditions for subsequent switching of the switches in the line branch. Subsequently, the microcontroller can turn on the upper bridge arm current transfer switch of the normal line while keeping the lower bridge arm current transfer switch off, thus lifting the normal line from the main current path and isolating it from the fault current. The faulty line adopts the opposite configuration, with its upper bridge arm current transfer switch off and its lower bridge arm current transfer switch on, guiding the fault current to the lower path and concentrating it into the main circuit breaker branch, providing favorable conditions for final energy absorption and breaking.

[0114] After the current transfer path is established and stabilized, the microprocessor can continue to control the ultra-fast mechanical switch in the lower arm of the normal line, the ultra-fast mechanical switch in the upper arm of the faulty line, and the mode-switching mechanical switch in the mode-switching branch to disconnect sequentially, gradually forming a complete physical isolation break. Subsequently, the microcontroller can control the main circuit breaker to open, allowing the fault current to be rapidly transferred to the surge arrester, where the surge arrester absorbs the fault energy and quickly reduces the current to zero. When it is detected that the fault current has been completely eliminated, the microcontroller finally drives the disconnecting switch in the faulty line to open, completely disconnecting the faulty line from the system and restoring normal power flow operation to the normal line.

[0115] In one embodiment, the method may further include:

[0116] S260: If the mode switching switch is a first mode switch consisting of a mode switching current transfer switch and a mode switching mechanical switch connected in series, then after the main circuit breaker is turned on, the mode switching current transfer switch in the first mode switch is turned off.

[0117] In this embodiment, if the mode switching switch adopts a first mode switch structure consisting of a mode switching current transfer switch and a mode switching mechanical switch connected in series, then during fault handling, after the main circuit breaker is controlled to conduct and assume the main path of the fault current, the microcontroller can immediately order the mode switching current transfer switch in the first mode switch to open, so that the mode switching branch exits the parallel relationship with the main current path in advance before the bridge arm current is redistributed. Since the early conduction of the main circuit breaker ensures that the voltage and current stress borne by the mode switching current transfer switch is significantly reduced when it is opened, the mode switching current transfer switch can safely complete the operation under conditions closer to zero current, and will not be damaged by arcing or transient overshoot.

[0118] In one specific embodiment, this application uses a single-pole 500kV test system for simulation verification. It has four DC transmission lines connected to the DC bus, one of which is directly connected to the MMC, and the other three are connected to DC cables. The current in the three cables is respectively... , , This refers to the fact that the multi-port DC circuit breaker of this application can then be used for fault handling. For example... Figure 5 As shown, Figure 5 The diagram below shows the waveform simulation results of DC fault handling provided in this application embodiment, where (a) is the waveform simulation result of the current of three cables, (b) is the waveform simulation result of the current of the metal oxide arrester, (c) is the waveform simulation result of the current of the main circuit breaker, and (d) is the waveform simulation result of the voltage of the metal oxide arrester.

[0119] Figure 5In the circuit, after a fault occurs in cable 3 at t=5s, the current in each line rises rapidly. After a 1ms fault detection delay, the microcontroller detects the fault and sends a conduction signal to the main circuit breaker. The main circuit breaker conducts 0.25ms later, sending a disconnect command to the faulty line, specifically the current transfer switch on the upper arm of cable 3, and the current transfer switches on the lower arms of other normal lines. If the mode switching switch uses a second mode switch, a disconnect signal is also sent to the mode switching current transfer switch. After 0.25ms, the aforementioned current transfer switches disconnect, and the current flowing through them rapidly decreases to 0. At this point, a disconnect signal is sent to the faulty line, specifically the ultra-fast mechanical switch on the upper arm of cable 3, the ultra-fast mechanical switches on the lower arms of other normal lines, and the mode switching ultra-fast mechanical switch in the mode switching switch. After 2ms, the aforementioned ultra-fast mechanical switch opens, the current transfer switch connected in series with it is no longer under pressure, and the capacitor is completely deactivated. At this time, the microcontroller sends a disconnect signal to the main circuit breaker. After 0.25ms, the main circuit breaker opens, the metal oxide surge arrester is activated, and the fault current drops rapidly to 0. At t=5.0172s, cable 3 is disconnected, and the fault is completely isolated.

[0120] Finally, it should be noted that in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0121] The various embodiments in this specification are described in a progressive manner. Each embodiment focuses on the differences from other embodiments. The various embodiments can be combined as needed, and the same or similar parts can be referred to each other.

[0122] The above description of the disclosed embodiments enables those skilled in the art to make or use this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A multi-port DC circuit breaker, characterized by, The circuit breaker comprises an upper DC bus, a lower DC bus, and a plurality of parallel branches connected in parallel between the upper DC bus and the lower DC bus; The plurality of parallel branches comprises a main circuit breaker branch, an energy absorption branch, a mode switching branch, and a plurality of line branches with the same structure; The main circuit breaker branch is composed of a main circuit breaker; The energy absorption branch is composed of a lightning arrester; The mode switching branch is composed of a mode switching switch and a capacitor connected in series; The line branch is obtained by connecting an upper bridge arm, a disconnector, a reactor, and a lower bridge arm in series; each bridge arm is obtained by connecting a current transfer switch and a super-fast mechanical switch in series.

2. The multi-port DC circuit breaker according to claim 1, characterized in that The mode switching switch comprises a first mode switch and a second mode switch; The first mode switch is composed of a mode switching mechanical switch; The second mode switch is composed of a mode switching current transfer switch and a mode switching mechanical switch connected in series.

3. The multi-port DC circuit breaker according to claim 1, characterized in that, One end of the upper bridge arm is connected to the upper DC bus; one end of the lower bridge arm is connected to the lower DC bus.

4. A power flow control method applied to the multi-port DC circuit breaker of any one of claims 1-3, characterized in that, The method comprises: Switching the mode switching switch and each super-fast mechanical switch to a closed state, so that the multi-port DC circuit breaker is in a power flow control mode; Collecting the capacitor voltage of the capacitor and the line current of each line branch through an external voltage sampling circuit, and determining the MMC line and the slack line from the external connection equipment of each line branch; Controlling the state of the current transfer switch in the MMC line and the slack line according to the capacitor voltage and a preset voltage reference value; Controlling the state of the current transfer switch in each of the other line branches except the MMC line and the slack line according to the line current of the other line branches and a preset current reference value.

5. The power flow control method according to claim 4, wherein The state control of the current transfer switch in the MMC line and the slack line according to the capacitor voltage and a preset voltage reference value comprises: Generating a voltage error signal according to the difference between the capacitor voltage and the preset voltage reference value, and generating an equivalent current control amount of the voltage error signal through a voltage regulator; Generating a complementary PWM signal according to the equivalent current control amount, and controlling the state of the current transfer switch in the MMC line and the slack line according to the complementary PWM signal.

6. The power flow control method according to claim 5, wherein The complementary PWM signal comprises a first PWM signal and a second PWM signal; The state control of the current transfer switch in the MMC line and the slack line according to the complementary PWM signal comprises: Controlling the state of the current transfer switch in the upper bridge arm of the MMC line through the first PWM signal, and controlling the state of the current transfer switch in the lower bridge arm of the MMC line through the second PWM signal; Controlling the state of the current transfer switch in the upper bridge arm of the slack line through the second PWM signal, and controlling the state of the current transfer switch in the lower bridge arm of the slack line through the first PWM signal.

7. The power flow control method of claim 4, wherein, The line current and preset current reference value of each other line branch except the MMC line and the slack line are used to control the state of the current transfer switch in each other line branch, including: For each line branch except the MMC line and the slack line, the line current and preset current reference value of the line branch are determined; A current error signal is generated according to the difference between the line current and the preset current reference value, and a line current control amount of the current error signal is generated through a current regulator; A complementary PWM signal is generated according to the line current control amount, and the state of the current transfer switch in the line branch is controlled according to the complementary PWM signal.

8. The power flow control method of claim 4, wherein, The method further includes: When the current flow control of all line branches is completed, the mode switching switch and each ultrafast mechanical switch are switched to the breaking state, so that the multi-port DC circuit breaker is in a stable operation mode.

9. A DC fault handling method applied to the multi-port DC circuit breaker of any one of claims 1-3, characterized in that, The method includes: The line branch where the line fault exists is marked as a fault line, and the other line branches except the fault line are marked as normal lines; The main circuit breaker is controlled to be turned on, and the current transfer switches in the upper bridge arm and the current transfer switches in the lower bridge arm of the normal line are controlled to be turned on and turned off, respectively, and the current transfer switches in the upper bridge arm and the current transfer switches in the lower bridge arm of the fault line are controlled to be turned off and turned on, respectively; The ultrafast mechanical switches in the lower bridge arm of the normal line, the ultrafast mechanical switches in the upper bridge arm of the fault line, and the mode switching switch in the mode switching branch are controlled to be turned off; The main circuit breaker is controlled to be turned off, so that the fault current is transferred to the arrester, and the energy consumption is rapidly reduced through the arrester; After detecting that the energy consumption of the fault current is reduced to 0, the disconnector in the fault line is controlled to be turned off.

10. The DC fault handling method of claim 9, wherein, The method further includes: If the mode switching switch is a first mode switch composed of a mode switching current transfer switch and a mode switching mechanical switch in series, after the main circuit breaker is controlled to be turned on, the mode switching current transfer switch in the first mode switch is controlled to be turned off.

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