CN111463763B

CN111463763B - Multi-port hybrid direct-current circuit breaker with power flow control function and control method

Info

Publication number: CN111463763B
Application number: CN202010387694.4A
Authority: CN
Inventors: 邹贵彬; 张烁; 魏秀燕; 张成泉
Original assignee: Shandong University
Current assignee: Shandong University
Priority date: 2020-05-09
Filing date: 2020-05-09
Publication date: 2021-04-30
Anticipated expiration: 2040-05-09
Also published as: CN111463763A

Abstract

The utility model discloses a multiport hybrid direct current breaker and control method with damp flow control function, includes: a main switch and a tide flow control module; each line is connected to the direct current bus through a diode branch and a shared main disconnecting switch, and the main disconnecting switch is used for breaking current between the direct current bus and each line; one of the lines is connected to the direct current bus through the quick mechanical switch and the load transfer switch, and the other lines are connected to the direct current bus through the quick mechanical switch and the power flow control module respectively. The power flow control function of the present disclosure can avoid overload of the direct current line or influence on the operation of the whole flexible direct current power grid due to the power transmission bottleneck of the direct current line. According to the method and the device, the short-circuit fault current of any port can be quickly cleared and the fault line can be isolated by changing the working mode of the device. In addition, the intelligent control system has a reclosing function, can reduce the power failure time of transient faults, and improves the operation reliability of the flexible direct-current power grid.

Description

Multi-port hybrid direct-current circuit breaker with power flow control function and control method

Technical Field

The disclosure belongs to the technical field of flexible direct-current power grid current control and flexible direct-current power grid direct-current side fault clearing and isolation, and particularly relates to a multi-port hybrid direct-current circuit breaker with a current control function and a control method.

Background

The statements in this section merely provide background information related to the present disclosure and may not necessarily constitute prior art.

The multi-end flexible direct-current power grid has the advantages of independent active power control and reactive power control, capability of supplying power to a passive network, high flexibility, redundancy and the like, and becomes an ideal choice for long-distance power transmission and new energy grid connection. A number of multi-terminal flexible dc grid projects have been proposed or are being constructed worldwide.

Although the flexible direct-current power grid has the advantages that the traditional alternating-current power grid and a direct-current power transmission system based on power grid commutation do not have, a plurality of challenges still exist in the actual operation process, for example, the problems that the direct-current line power flow cannot be actively controlled, the isolation difficulty of the direct-current side short-circuit fault is high, and the like. In a grid-shaped flexible direct-current power grid, the power flow of direct-current lines cannot be independently controlled, and the power flow of each direct-current line is determined by the resistance between nodes. This uncontrollable flow can lead to overloading of the dc link or to an impact on the operation of the entire flexible dc grid due to dc link power transmission bottlenecks. In addition, after a short-circuit fault occurs on the direct-current side in the flexible direct-current power grid, the fault current rises very fast and zero-crossing points do not exist, so that the breaking problem of the direct-current fault current cannot be ignored.

In order to solve the problem of power flow control of direct current lines in a grid-shaped direct current power grid, various power flow controllers have been proposed at present, which are mainly classified into three types, namely, power flow controllers based on a variable resistor, an AC/DC converter and a DC/DC converter. Among them, the DC/DC converter-based power flow controller requires a small number of semiconductor switches and has low operating loss, and thus is the most promising power flow controller. A typical DC/DC converter based power flow controller is a double H-bridgewire power flow controller. In addition, in order to solve the problem of direct current fault current breaking, a direct current breaker needs to be configured on the flexible direct current power grid. Among the dc circuit breakers proposed so far, the hybrid dc circuit breaker is an ideal choice for isolating dc-side faults in a flexible dc power grid due to its low loss and high operating speed. However, since the hybrid dc circuit breaker requires a large number of semiconductor switches to be connected in series to the main breaker to withstand the transient breaking voltage, and a large-capacity arrester to absorb the energy of the fault current, the construction cost per time is high, and it is difficult to apply the hybrid dc circuit breaker on a large scale.

Disclosure of Invention

In order to overcome the defects of the prior art, the multi-port hybrid direct-current circuit breaker with the power flow control function is provided, and the main breaking switch and the power flow control module are shared by all lines, so that the overall structure is greatly simplified, and the manufacturing cost is reduced. Based on a plurality of control modes, flexible control of the power flow of the flexible direct-current power grid and rapid clearing and isolation of direct-current side faults can be realized.

In order to achieve the above object, one or more embodiments of the present disclosure provide the following technical solutions:

on the one hand, the utility model discloses a multiport hybrid direct current circuit breaker who possesses trend control function includes:

a main switch and a tide flow control module;

each line is connected to a common main disconnecting switch through a corresponding diode branch, the main disconnecting switch is connected to the direct current bus, and the main disconnecting switch is used for current breaking between the direct current bus and each line and isolation of a fault line;

meanwhile, one of the lines is connected to the direct current bus through the fast mechanical switch and the load transfer switch which are connected in series, the other lines are connected to the tide control module through the fast mechanical switches corresponding to the other lines respectively, and the tide control module is connected to the direct current bus.

On the other hand, a control method of a multi-port hybrid direct current breaker with a power flow control function is disclosed, which comprises the following steps:

the CFC bypass mode, the CFC input mode, the current breaking mode and the reclosing mode are adopted, and the CFC is a power flow control module;

the CFC bypass mode: the power flow control module is in a bypass state, and the current of the adjacent direct current lines is passively distributed according to the line resistance between the nodes;

the CFC on mode: the energy storage capacitor is connected in series into the direct current circuit by controlling the switching state of the semiconductor switch in the CFC, and the energy storage capacitor is switched among different direct current circuits by periodically controlling the change of the switching state, so that the power flow control of each adjacent direct current circuit is realized;

the current breaking mode is as follows: when short-circuit fault occurs, the multi-port hybrid direct current circuit breaker is in a CFC bypass mode or a CFC input mode, if the multi-port hybrid direct current circuit breaker is in the CFC input mode, an energy storage capacitor in the bypass CFC is switched off in the fault current breaking process;

the reclosing mode comprises the following steps: when the fault current is attenuated to zero, waiting for the free time of the line, and closing the main break switch again; at the moment, if the current flowing through the main breaking switch rapidly rises and exceeds a preset action threshold, the fault is regarded as a permanent fault, then the main breaking switch is controlled to be opened again, and after the fault current breaking process is finished, a residual current switch is opened to completely isolate a fault point; otherwise, the fault is considered to be disappeared, and the reclosing operation is continued.

The above one or more technical solutions have the following beneficial effects:

the multi-port hybrid direct-current circuit breaker with the power flow control function controls the power flow of a plurality of adjacent direct-current lines under the normal operation condition, and avoids the overload of the direct-current lines or the influence on the operation of the whole flexible direct-current power grid caused by the power transmission bottleneck of the direct-current lines. When any port has short-circuit fault, the working mode of the direct current circuit breaker is controlled, and the multi-port hybrid direct current circuit breaker acts rapidly to clear and isolate the fault. In addition, the multi-port hybrid direct-current circuit breaker has a reclosing function, so that the power failure time of transient faults can be reduced, and the operation reliability of a flexible direct-current power grid is improved.

Drawings

The accompanying drawings, which are included to provide a further understanding of the disclosure, illustrate embodiments of the disclosure and together with the description serve to explain the disclosure and are not to limit the disclosure.

Fig. 1 is a schematic diagram of a conventional hybrid dc circuit breaker topology;

FIG. 2 is a schematic view of a topology of an inter-double H-bridge line power flow controller and an inter-multi H-bridge line power flow controller;

fig. 3 is a schematic diagram of a multi-port hybrid dc circuit breaker topology according to an embodiment of the present disclosure;

FIG. 4 is a schematic diagram of a discharge module topology of an embodiment of the present disclosure;

fig. 5 is an equivalent schematic diagram of a multi-port hybrid dc circuit breaker according to an embodiment of the disclosure operating in a CFC bypass mode;

fig. 6 is an equivalent schematic diagram of a multi-port hybrid dc circuit breaker according to an embodiment of the present disclosure operating in a CFC commissioning mode;

FIG. 7 is a schematic diagram of a CFC controller design under certain operating conditions of an embodiment of the present disclosure;

FIG. 8 is a schematic diagram of a four-terminal flexible DC power grid according to an embodiment of the present disclosure;

FIGS. 9(a) to 9(d) respectively show t as an example of the present disclosure₀<t<t₂；t₂<t<t₄；t₄<t<t₅；t>t₅The equivalent schematic diagram of the corresponding multi-port hybrid direct-current circuit breaker operating in a current breaking mode;

fig. 10(a) -10 (b) simulation results of current breaking function of the multi-port hybrid dc circuit breaker according to the embodiment of the present disclosure: the current waveforms of the direct current lines Line 1 to Line3 and the waveforms of the CFC capacitor voltages.

Detailed Description

It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the disclosure. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs.

It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments according to the present disclosure. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise.

The embodiments and features of the embodiments in the present disclosure may be combined with each other without conflict.

The multi-port hybrid direct-current circuit breaker with the power flow control function comprises a main breaking switch and a power flow control module; each line is connected to the direct current bus through a diode branch and a shared main disconnecting switch, and the main disconnecting switch is used for breaking current between the direct current bus and each line; one of the lines is connected to the direct current bus through the quick mechanical switch and the load transfer switch, and the other lines are connected to the direct current bus through the quick mechanical switch and the power flow control module respectively. The power flow control function of the present disclosure can avoid overload of the direct current line or influence on the operation of the whole flexible direct current power grid due to the power transmission bottleneck of the direct current line. According to the method and the device, the short-circuit fault current of any port can be quickly cleared and the fault line can be isolated by changing the working mode of the device. In addition, the intelligent control system has a reclosing function, can reduce the power failure time of transient faults, and improves the operation reliability of the flexible direct-current power grid.

Example one

The embodiment discloses a multiport hybrid direct current breaker with a power flow control function, the forced commutation characteristic of a branch of a traditional hybrid direct current breaker is fully utilized, main breaking switches are shared by all lines, a traditional double-H bridge inter-line power flow controller is expanded into a multi-H bridge inter-line power flow controller and is integrated into the multiport hybrid direct current breaker in a module mode, power flows of a plurality of adjacent direct current lines are controlled under the normal operation condition, and the direct current line overload is avoided or the influence of the power transmission bottleneck of the direct current lines on the operation of the whole flexible direct current power grid is avoided. When any port has short-circuit fault, the working mode of the direct current circuit breaker is controlled, and the multi-port hybrid direct current circuit breaker acts rapidly to clear and isolate the fault.

In an embodiment, a conventional hybrid dc circuit breaker is shown in fig. 1. Referring to fig. 2, the multi-port hybrid dc circuit breaker with a power flow control function makes full use of the forced commutation characteristic of the branch of the conventional hybrid dc circuit breaker, and greatly reduces the manufacturing cost of the equipment by sharing the main disconnecting switch for each line. In addition, by extending the double H-bridgewire inter-tidal current controller into a multi-H-bridgewire inter-tidal current controller and integrating it into a multi-port hybrid dc circuit breaker in the form of a module, further reductions in equipment manufacturing costs and operating losses are achieved. And through the improvement of above-mentioned scheme on the premise of realizing multiport hybrid direct current circuit breaker rapid action with trouble clearance and isolation's function, simplified the structure of whole equipment, the control mode has also taken place corresponding change simultaneously, compares traditional hybrid direct current circuit breaker, and the control device reduces to possess the trend control function of adjacent direct current circuit.

The multi-port hybrid dc circuit breaker topology with power flow control function proposed by the present disclosure is shown in fig. 3, in which UFD₀-UFD_nIs a quick mechanical switch; LCS₀Is a load transfer switch; d₀-D_nIs a diode series branch circuit; RCB₀-RCB_nIs a residual current switch; the CFC is a tide control module integrated in the multi-port hybrid direct current breaker; DM is a discharging module (the structure is shown in fig. 4), which is used to release the energy stored in the energy storage capacitor of CFC; MB is a main disconnecting switch and comprises a large number of sub-modules and a lightning arrester; compared with the traditional hybrid direct current circuit breaker, the multi-port hybrid direct current circuit breaker main disconnecting switch provided by the disclosure can realize the current breaking function only by half of the semiconductor switches because the direction of the flowing current is fixed.

In another embodiment, the multi-port hybrid dc circuit breaker with power flow control function has the following four operation modes: CFC bypass mode, CFC throw-in mode, current breaking mode, and reclosing mode.

Note that, regarding the CFC bypass mode: when the power flow control is not needed by each direct current line, the CFC bypass mode is operated.

CFC input mode: when the direct current line has no fault and the direct current line power flow control is needed, the CFC switching mode is operated.

Current breaking mode: when the multi-port hybrid direct-current circuit breaker operates in a CFC bypass mode or a CFC switching-in mode, after any adjacent direct-current circuit has a short-circuit fault, the multi-port hybrid direct-current circuit breaker enters a current breaking mode to clear and isolate the direct-current circuit fault.

Reclosing mode: after the fault line is isolated, the multi-port hybrid direct current circuit breaker enters a reclosing mode after a certain time so as to try to recover the power supply of the isolated fault direct current line.

The operation principle and the control method of each operation mode will be described in detail below. For the sake of analysis, it is assumed that the dc bus connects four dc lines in common, i.e. n is 3 in fig. 3. It should be clear that the following analysis can be generalized to the case where n is any value.

CFC bypass mode

In this mode, the power flow control module CFC integrated in the multi-port hybrid dc circuit breaker is in a bypass state, so that the current of adjacent dc lines cannot be actively controlled, but is passively distributed according to the resistance between the nodes. The equivalent circuit of the multi-port hybrid dc circuit breaker in CFC bypass mode is shown in fig. 5. In this mode, the main switch MB and the discharging module DM are switched off, while LCS₀，UFD₀-UFD₃，RCB₀-RCB₃Is in a conducting state. In order to reduce the operation loss of the multi-port hybrid direct current circuit breaker, all semiconductor switches in the integrated multi-port current control module CFC are in a conducting state, and at the moment, an energy storage capacitor in the CFC is bypassed.

CFC injection mode

In this mode, the current I of Port 1-Port 3, which is the adjacent line current, can be actively controlled by the CFC integrated with the multi-Port hybrid DC breaker₁～I₃. The power flow control principle is as follows: the energy storage capacitor can be connected in series into the direct current circuit by controlling the switching state of the semiconductor switch in the CFC, the process can be equivalent to the process that a voltage-adjustable voltage source is connected in series into the direct current circuit, and the energy storage capacitor is switched among different direct current circuits by periodically controlling the change of the switching state, so that the power flow control of each adjacent direct current circuit is realized. The direction of the equivalent series-wound dc voltage source is related to the flow direction of the power flow and the switching state of the CFC, and the specific relationship is shown in table 1. The table shows the current I in FIG. 6₀～I₃The relationship between the switch state and the equivalent voltage source direction when both positive and negative. U in watch_cFor storing capacitor voltage, U_OA～U_OCIs the voltage source voltage equivalent to the series connection of the DC line. Each H in the tidal control Module CFCThe control signals of the two semiconductor switches in the legs of the bridge being complementary (e.g. S)_a1In the on state 1, then S_b1In off state 0; s_a1In the OFF state 0, then S_b1In the on state 1), table 1 lists the switching states of only one switch in each H-bridge leg.

TABLE 1 relationship between CFC switch state and equivalent voltage source for current control module

The power flow control method of the power flow control module CFC integrated with the multi-port hybrid dc circuit breaker is explained below for specific working conditions. It should be clear that, although the following analysis is performed for specific operating conditions, the integrated current control module of the multi-port hybrid dc circuit breaker can achieve the purpose of current control under other operating conditions.

Let I₀～I₃Are both positive and before the CFC is put into operation I₁Is greater than I₂And I₃. It is therefore desirable to pass the current I through the integrated current control module CFC₁Is reduced and correspondingly increased I₂And I₃The amplitude of (c). To achieve this goal, the voltage source of the equivalent series Port 1 needs to be positive, while the voltage sources of the

equivalent series ports

2 and 3 need to be negative. As can be seen from table 1, there are a variety of switch state combinations that can achieve the above control objectives. The control method adopted by the present disclosure is shown in fig. 7, and can realize the control of any line power flow and the voltage of the energy storage capacitor in the power flow control module.

C. Current breaking mode

The fault current breaking process of the multi-port hybrid dc circuit breaker proposed by the present disclosure is analyzed using a grid-shaped flexible dc power grid as shown in fig. 8. As can be seen from the figure, the flexible dc power grid comprises 4 converter stations based on modular multilevel converters MMC, respectively numbered as MMC₀,MMC₁,MMC₂,MMC₃。L_kkIs MMC_kAnd (c) a current-limiting inductor (k ═ 0,1,2,3) at the outlet. To simplify the analysis, let the initial value of the current of Port k before the occurrence of the fault be I_pk.preThe current change rate of Port k is constant after the fault occurs, and the absolute value is CR_pk。

Isolating short circuit fault F₁

When t is reached as shown in FIG. 9(a)₀Moment short-circuit fault F₁Then, Port 3 of the multi-Port hybrid dc breaker needs to act to isolate the fault point. It is noted here that the multi-port hybrid dc circuit breaker may be in either CFC bypass mode or CFC plunge mode when a short circuit fault occurs. If the multi-port hybrid direct current circuit breaker is in a CFC switching-in mode, the energy storage capacitor in the CFC is bypassed in the fault current breaking process, and the energy storage capacitor is prevented from being damaged in the fault process. Suppose a DC breaker is at t₁And a tripping command is received at any time, and the main breaking switch is closed firstly. During this period (t)₀<t<t₁) The current flowing through each port of the multi-port hybrid dc circuit breaker can be calculated by the following formula:

after a short delay at t₂All semiconductor switches S of the H-bridge connected to the faulty port in the time locked tidal flow control Module CFC_a3-S_d3Thereby, the fault current is transferred to the main disconnecting switch, and the circulation path of the fault current is as follows: port 0-Port 2-UFD₀～UFD₂–MB–D₃-a point of failure. Meanwhile, the UFD is rapidly and mechanically switched₃The operation starts from opening. In addition, if the multi-port hybrid direct current circuit breaker is in a CFC (carbon fiber type) switching-in mode when a fault occurs, the energy storage capacitor in a current control module CFC is bypassed, and the specific operation method is to lock a switch pair S on a sound line H bridge_bk,S_dkWhile turning on the other switch pair S_ak,S_ck(k is 0,1, 2). The process can prevent the energy storage capacitor from continuing to charge and discharge after the fault occurs. At t₃Instant, fast mechanical switch UFD₃And (6) completing the brake opening. The opening time of the fast mechanical switch UFD is assumed to be 2 milliseconds. Before the next operation, the equivalent circuit of the multi-port hybrid dc breaker is as shown in fig. 9 (b). On fast mechanical switch UFD₃In the opening process, the current expressions of all parts in the multi-port hybrid direct current breaker are as follows:

i_MB(t)＝i_SM(t)＝CR_p3(t-t₀)-I_p3.pre＝i_d3(t)

i_UFD3(t)＝i_dk(t)＝i_MOV(t)＝0k＝0,1,2

at t₄The main disconnector MB is opened at a moment, and the fault current is commutated into the arrester for dissipation and finally decays to zero. The fault current thus reaches its maximum value at the instant the main breaker MB opens. Meanwhile, the discharging module DM is closed to absorb energy stored by the energy storage capacitor in the integrated power flow control module CFC. The equivalent circuit of the multi-port hybrid dc breaker during the energy consumption of the fault current is shown in fig. 9 (c).

The energy dissipation time of the fault current typically takes a few milliseconds. At t₅At the moment, the fault current is attenuated to zero and corresponds to a residual current switch RCB₃The current in (1) is reduced to zero, and RCB₀～RCB₂To the normal load current. Afterward residual current switch RCB₃Start opening the gate and at t₆And the switching-off is finished at all times. The equivalent circuit of the multi-port hybrid dc breaker during this time period is shown in fig. 9 (d). The integrated tide control module in the multi-port hybrid dc circuit breaker can then be restarted.

Since the arrester is a non-linear element, in order to simplify the analysis process, only the ideal arrester model is considered below. Suppose the voltage of the arrester is at t at the main disconnector MB₄Reaches the residual voltage U immediately after being opened at any time_resUntil the end of the fault current energy dissipation process (t)₅Time of day). Residual voltage U of lightning arrester_resRated voltage U of flexible direct current power grid_dcIn this regard, it can be expressed as:

U_res＝γU_dc

where γ is a constant with a value in the range of 1 to 2. In the energy dissipation process, the process that the main disconnecting switch MB opens the lightning arrester to be put into operation is equivalent to the process that the residual voltage U of the lightning arrester is connected in series in a fault loop_resOf the voltage source. Due to residual voltage U of lightning arrester_resGreater than the rated voltage U of the flexible direct current power grid_dcTherefore, the fault current starts to decrease, and the rate of change of the fault current in the main disconnection switch MB is approximately constant, assuming that its value is-CR_MB. Thus, the time t of completion of the energy dissipation₅Can be calculated from the following formula:

thus, the energy dissipated by the arrester can be calculated as:

isolating short circuit fault F₂

When Port 0 has short-circuit fault F₂Then, the main switch MB should be closed first, and the load transfer switch LCS should be closed after a short delay₀And controlling a fast mechanical switch UFD₀Starting the brake separating. In addition, if the multi-port hybrid dc circuit breaker is operated in CFC-on mode when a fault occurs, the energy storage capacitor in the integrated power flow control module CFC should be bypassed, which may be achieved by turning on the switch set S_ak,S_ckAnd the locking switch set S_bk,S_dk(k is 0,1, 2). At UFD₀After the opening of the brake is completed, the main disconnecting switch MB is opened so as to convert the fault current into the lightning arrester for energy consumption. At the same time, the discharging module DM should be closed to absorb the energy stored by the energy storage capacitor in the integrated power flow control module CFC. When the energy dissipation of the fault current is completed, the RCB is turned on₃The fault is completely isolated. Thereafter, the power transmission of the adjacent line gradually returns to normal.

D. Reclosing mode

Because the probability of overhead line faults is high, and most faults are transient faults. Therefore, in order to reduce the influence of transient faults and improve the operational reliability of the flexible dc power grid, the dc circuit breaker is required to have reclosing capability. The reclosing method of the multi-port hybrid direct-current circuit breaker comprises the following steps: after the fault current decays to zero, waiting for the line to free (about 300 milliseconds), and reclosing the main switch; at the moment, if the current flowing through the main breaking switch rapidly rises and exceeds a preset action threshold, the fault is regarded as a permanent fault, the main breaking switch is controlled to be opened again, and a residual current switch is opened to completely isolate a fault point after the fault current breaking process is finished; otherwise, the fault is considered to disappear, reclosing operation is continued, and the fast mechanical switch UFD and the load transfer switch LCS of the fault Port are reclosed in sequence (for ports 1 to 3, all semiconductor switches corresponding to the Port H bridge in the integrated power flow control module CFC are conducted), so that the reclosing process can be completed.

In another embodiment, the control system of the multi-port hybrid dc circuit breaker with power flow control function includes:

and the controllers are respectively connected to the switching devices of the circuit breaker and control the working states of the switching devices, so that the circuit breaker is in different working modes.

For a specific control process, reference is made to the description of the detailed operation mode of the above example, and details are not described here.

Effect verification:

a four-terminal flexible direct-current power grid simulation model based on the modular multilevel converter is constructed by utilizing PSCAD/EMTDC software (as shown in figure 8), and the feasibility of the multi-port hybrid direct-current circuit breaker with the power flow control function provided by the disclosure is subjected to simulation verification:

1) modeling

A direct current line in the simulation model adopts a distributed frequency-dependent model, and the MMC and the lightning arrester both adopt detailed models. The main parameters of the flexible dc grid and the multi-port hybrid dc breaker are shown in table 2. The action time of the dc line protection is 1 millisecond. The control method of the multi-port hybrid direct current circuit breaker in each working mode is as described above.

TABLE 2 Flexible DC network and Multi-Port hybrid DC Circuit breaker Primary parameters

2) Simulation analysis

The multi-port hybrid dc circuit breaker operates in CFC bypass mode for a time period of 0-3 seconds. At 3 seconds, the multi-port hybrid direct current circuit breaker enters the CFC input mode from the CFC bypass mode. In the CFC input mode, the reference current of Line 1 and Line3 is set to be 1.15kA (the average value of the total load current of Line 1 to Line 3), and the voltage of the energy storage capacitor is set to be 4 kV. At 4.5 seconds, a metallic ground fault F is set at the Line3 midpoint₁As shown in fig. 8. The multi-port hybrid dc circuit breaker received a trip signal at 4.501 seconds. The simulation results of the power flow control and fault current breaking functions of the multi-port hybrid direct current circuit breaker are shown in fig. 10(a) -fig. (b).

When the multi-port hybrid direct current circuit breaker enters a CFC input mode from a CFC bypass mode, the current of each direct current line and the voltage of the energy storage capacitor reach preset values after about 0.5 second. When the Line3 has a short-circuit fault, the fault current is increased to 6.8kA at most, and finally the fault current is reduced to zero under the action of the direct-current circuit breaker. After fault isolation, the power flow control module integrated by the multi-port hybrid direct current circuit breaker is put into operation again, the Line 1 current preset value is 1.77kA, and the energy storage capacitor voltage control quantity is also set to be 4 kV. The Line 1 current reaches the preset value in less than 0.1 second after fault isolation.

From the above analysis, it can be seen that the multi-port hybrid dc circuit breaker with the tidal current control function according to the present disclosure performs well in terms of the tidal current control and the fault current breaking, and compared with a scheme in which the tidal current controller and the conventional hybrid dc circuit breaker are separately configured, the manufacturing cost is greatly reduced.

Those skilled in the art will appreciate that the modules or steps of the present disclosure described above can be implemented using general purpose computer means, or alternatively, they can be implemented using program code executable by computing means, whereby the modules or steps may be stored in memory means for execution by the computing means, or separately fabricated into individual integrated circuit modules, or multiple modules or steps thereof may be fabricated into a single integrated circuit module. The present disclosure is not limited to any specific combination of hardware and software.

The above description is only a preferred embodiment of the present disclosure and is not intended to limit the present disclosure, and various modifications and changes may be made to the present disclosure by those skilled in the art. Any modification, equivalent replacement, improvement and the like made within the spirit and principle of the present disclosure should be included in the protection scope of the present disclosure.

Although the present disclosure has been described with reference to specific embodiments, it should be understood that the scope of the present disclosure is not limited thereto, and those skilled in the art will appreciate that various modifications and changes can be made without departing from the spirit and scope of the present disclosure.

Claims

1. Multiport hybrid direct current circuit breaker that possesses trend control function, characterized by includes:

a main switch and a tide flow control module;

meanwhile, one of all the lines is connected to the direct current bus through the fast mechanical switch and the load transfer switch which are connected in series, the other lines are connected to the tide control module through the fast mechanical switches corresponding to the other lines respectively, and the tide control module is connected to the direct current bus; all the circuits are also connected with a residual current switch in series;

the multi-port hybrid direct-current circuit breaker is characterized in that a traditional double-H bridge inter-line tide controller is expanded into a multi-H bridge inter-line tide controller and is integrated into the multi-port hybrid direct-current circuit breaker in a module mode, when any port has a short-circuit fault, the working mode of the direct-current circuit breaker is controlled, and the multi-port hybrid direct-current circuit breaker rapidly acts to clear and isolate the fault;

the power flow control module comprises a discharging module used for releasing energy stored in an energy storage capacitor in the power flow control module.

2. The multi-port hybrid direct current circuit breaker with the tidal current control function according to claim 1, wherein the direct current circuit breaker realizes the tidal current control of a direct current line and the fault clearing and isolation in the fault process when being respectively in the working modes of CFC bypass, CFC input, current breaking or reclosing, and the CFC is a tidal current control module.

3. The method for controlling a multi-port hybrid dc breaker with a power flow control function according to claim 1 or 2, comprising:

the CFC bypass mode: the power flow control module is in a bypass state, and the current of the adjacent direct current lines is passively distributed according to the resistance between the nodes;

the current breaking mode is as follows: when a short-circuit fault occurs, the multi-port hybrid direct current circuit breaker is in a CFC bypass mode or a CFC input mode, and if the multi-port hybrid direct current circuit breaker is in the CFC input mode, an energy storage capacitor in the CFC is bypassed in a fault current breaking process;

the reclosing mode comprises the following steps: and after the fault current is attenuated to zero, waiting for the line to free, and reclosing the main breaking switch.

4. The method of claim 3, wherein in the reclosure mode: if the current flowing through the main disconnecting switch rapidly rises and exceeds a preset action threshold value, the fault is regarded as a permanent fault, then the main disconnecting switch is controlled to be opened again, and after the fault current breaking process is finished, a residual current switch is opened to completely isolate a fault point; otherwise, the fault is considered to be disappeared, and the reclosing operation is continued.

5. The method as claimed in claim 3, wherein in the CFC bypass mode, the main switch and the discharging module are in an off state, the load transfer switch, the fast mechanical switch, and the residual current switch are in an on state, all semiconductor switches in the CFC are in an on state, and the energy storage capacitor in the CFC is bypassed.

6. A method as claimed in claim 3, wherein the energy storage capacitor is connected in series to the dc line by controlling the switching state of the semiconductor switch in the CFC, and the process is equivalent to connecting a voltage source with adjustable voltage in series to the dc line, and the direction of the equivalent series connected dc voltage source is related to the direction of the power flow and the switching state of the CFC.

7. The method as claimed in claim 3, wherein in the current breaking mode, after a short-circuit fault occurs, the corresponding port of the multi-port hybrid dc breaker needs to be activated to isolate the fault line.

8. The method as claimed in claim 3, wherein in the current breaking mode, when a short-circuit fault occurs in a line corresponding to a port of the load transfer switch, the main breaking switch is closed first, the load transfer switch is locked after a delay, the fast mechanical switch is controlled to start the opening, and the main breaking switch is opened after the opening of the fast mechanical switch is completed to isolate the fault line;

if the multi-port hybrid direct current circuit breaker works in a CFC (switching center) switching mode when a fault occurs, an energy storage capacitor in an integrated power flow control module CFC is bypassed.

9. The control system of the multi-port hybrid direct current circuit breaker with the power flow control function as claimed in claim 1 or 2, comprising a controller, wherein the controller is respectively connected to the switching devices of the circuit breaker as claimed in any one of claims 1-2, and controls the working states of the switching devices so that the circuit breaker is in different working modes.