CN114050556B - High-voltage direct-current circuit breaker based on capacitance commutation and inductance current limiting - Google Patents
High-voltage direct-current circuit breaker based on capacitance commutation and inductance current limiting Download PDFInfo
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- CN114050556B CN114050556B CN202111290601.7A CN202111290601A CN114050556B CN 114050556 B CN114050556 B CN 114050556B CN 202111290601 A CN202111290601 A CN 202111290601A CN 114050556 B CN114050556 B CN 114050556B
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
- H02H7/26—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
- H02H7/268—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured for dc systems
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H3/00—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection
- H02H3/02—Details
- H02H3/021—Details concerning the disconnection itself, e.g. at a particular instant, particularly at zero value of current, disconnection in a predetermined order
- H02H3/023—Details concerning the disconnection itself, e.g. at a particular instant, particularly at zero value of current, disconnection in a predetermined order by short-circuiting
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H3/00—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection
- H02H3/08—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to excess current
- H02H3/087—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to excess current for dc applications
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Abstract
The application discloses a novel high-voltage direct current breaker based on capacitive current conversion and inductive current limiting, which comprises a main current branch 1, a main current branch 2, a capacitive current conversion unit 1, a capacitive current conversion unit 2, a current limiting inductor 1, a current limiting inductor 2, an auxiliary current conversion branch, a mechanical switch K1, a mechanical switch K2 and a lightning arrester unit. The direct current breaker circulates through the power electronic device under normal conditions, the inductor does not influence the normal operation of the direct current breaker, and the on-state loss is small. Under the fault condition, the rising rate of the fault current is restrained through the inductor, the amplitude is reduced, and the turn-off current of the direct current breaker can be greatly improved. The capacitor current converting unit is used for replacing a solid-state direct current breaker in the original hybrid direct current breaker, so that the cost is greatly reduced, the dynamic voltage equalizing problem required by series connection of power electronic devices is solved, and the high-voltage-equalizing capacitor has good economical efficiency.
Description
Technical Field
The application relates to a high-voltage direct-current circuit breaker based on capacitive commutation and inductive current limiting, and belongs to the technical field of circuit breakers.
Background
The circuit breaker electric system is used, and is an important guarantee for the stable and reliable electric energy transmission of overload and short-circuit protection elements.
The circuit breaker can divide into shunt release, thermomagnetic release, electron release and intelligent release according to the tripping operation mode difference, because shunt release and thermomagnetic release action discreteness is big, the error is also big, gradually by electron release and intelligent release replace traditional electron release and intelligent release in some high-end application occasion, mainly detect operating current and realize getting can provide control system with the help of the current transformer and do auxiliary power supply, in order to guarantee all can provide accurate ground current detection function in full current protection scope, need design great current transformer just can satisfy the system needs, this has brought the obstacle for the miniaturized design of circuit breaker.
The publication number is CN106253243A, the name is a closing control method of a high-voltage direct current breaker, the method comprises the steps of firstly closing the breaking valve groups of the breaking branches group by group, then closing the on-state branches, and finally breaking all the breaking valve groups of the breaking branches. In the process of closing the breaking valve groups of the breaking branches group by group, detecting whether a circuit fails after the current breaking valve group is closed. If the line is not in fault, continuously closing the next group of breaking valve groups until all the breaking valve groups are closed, and then continuously operating the next step; if the line fails, all the closed breaking valve groups are broken, and the closing operation and the fault information uploading are finished. The method can realize the controlled charging of the circuit in the switching-on process of the high-voltage direct-current circuit breaker, and reduce the overvoltage generated by switching-on operation.
The high-voltage direct current breaker with the coupling reactor comprises a mechanical switch, a charging current-converting module, a current-converting capacitor and an energy-absorbing voltage-limiting module. The charging and converting module consists of a coupling reactor, a trigger switch and a pre-charging module, wherein the trigger switch and the pre-charging module are connected in series with the secondary side, the pre-charging module is a pre-charging capacitor and a follow current circuit which are connected in parallel, and the follow current circuit consists of a resistor and a diode which are connected in series. The capacitor charging module and the converter capacitor together provide a converter buffer branch for fault current. The forced zero-crossing type high-voltage direct-current breaker with the coupling reactor provided by the application can realize the bidirectional breaking of fault current, and is simple in structure and convenient to control; the speed is high, and the reliability is high.
The two prior art techniques described above do not provide a miniaturized design of the circuit breaker.
Disclosure of Invention
The application aims to solve the technical problem of providing a high-voltage direct current breaker based on capacitive commutation and inductive current limiting, which can effectively inhibit the amplitude of short-circuit current through a current limiting inductor and avoid the problems of synchronous driving and voltage equalizing of large-order IGBT series connection by means of capacitive buffering.
In order to solve the problems, the application adopts the following technical scheme:
a high-voltage direct current breaker based on capacitance commutation and inductance current limiting comprises a main circulation branch 1, a main circulation branch 2, a capacitance commutation unit 1, a capacitance commutation unit 2, a current limiting inductance 1, a current limiting inductance 2, an auxiliary conduction branch, a mechanical switch K1, a mechanical switch K2 and a lightning arrester unit;
the capacitor current conversion unit 1, the current limiting inductor 1, the main current through branch 2 and the mechanical switch K2 are sequentially connected in series from the side A of line current to the side B of line current and then connected with the lightning arrester unit in parallel;
the mechanical switch K1, the main current branch 1, the current limiting inductor 2 and the capacitor converter unit 2 are sequentially connected in series and then connected to the lightning arrester unit in parallel;
one end of the auxiliary conduction branch is electrically connected to the branch between the main conduction branch 1 and the current-limiting inductor 2, and the other end of the auxiliary conduction branch is electrically connected to the branch between the current-limiting inductor 1 and the main conduction branch 2.
As a further development of the application, the mechanical switches K1, K2 run through a rated current in normal operating conditions,
in the event of a fault, the motor is operated rapidly in the zero-current state, with an on-off time of 2ms;
the main flow branch 1 and the main flow branch 2 have the same structure and are composed of IGBT valve groups, and are connected in anti-series to realize bidirectional conduction, and the functions of the main flow branch 1 and the main flow branch 2 are that the IGBT on the main flow branch is triggered under the fault condition by means of the rapid controllability of the IGBT, the main flow branch IGBT is turned off, the current flow path under the fault condition of the line is changed, and the isolation of the fault line is realized;
the capacitor current conversion units 1 and 2 have the same structure, compared with a full-bridge submodule, 2 IGBT modules are omitted, when the voltage of the submodule capacitor reaches the action voltage of the lightning arrester unit, the current is transferred to a branch of the lightning arrester unit, the lightning arrester unit absorbs residual energy, and the fault current gradually drops to 0 through the buffer function of the capacitor in the submodule; the submodule capacitor is connected with an energy discharging resistor in parallel, and after the lightning arrester unit acts, the capacitor discharges;
the auxiliary conduction branch is formed by connecting thyristor valve groups in series and parallel.
Under the normal operation condition, assuming that line current flows from side A to side B, mechanical switches K1 and K2 of the direct current breaker are closed, all IGBTs in the capacitive converter unit are blocked, and the current flows through a main current-carrying branch and an auxiliary current-carrying branch, at the moment, a current-limiting inductor is not connected, and the breaker presents low impedance characteristics to the outside.
As a further improvement of the application, in the event of a fault, the high-voltage direct-current circuit breaker operates as follows:
step S1, in a first stage, after a direct current circuit is grounded or has an interelectrode short circuit fault at a time t0, a circuit ultra-high speed protection device sends a tripping command to a direct current circuit breaker after detecting a system fault at a time t 1;
step S2, in the second stage, after the IGBT on the main flow path is locked, an on-off signal is applied to the ultra-fast mechanical switch, and the on-off time is 2ms;
step S3, in the third stage, all IGBTs in the capacitive commutation unit are locked at t3, and the fault current starts to charge the capacitor in the capacitive commutation unit module;
step S4, a fourth stage, in which the voltage at two sides of the current breaking unit rises rapidly, and when the voltage reaches the action threshold of the lightning arrester at the time t4, the short-circuit current is completely transferred to the lightning arrester until the complete consumption of the inductance energy of the direct current network is achieved;
and S5, in a fifth stage, after the direct-current line fault current is 0, the circuit breaker enters a reclosing state.
In step S1, a blocking signal is applied to the IGBT of the main current branch, and the fault current is transferred to the capacitive converter circuit, and the current limiting inductor is connected in series to the fault circuit to suppress the amplitude and the rising rate of the fault current.
In step S2, the current flow path of the second stage process is the same as the current flow path of the first stage in that the ultra-fast mechanical switch is turned on and off at time t 2.
As a further improvement of the application, the differential equation is written into the equivalent circuit column of the second stage, and the solution is carried out after the Laplace transformation is carried out on the equivalent circuit column;
wherein Led represents the equivalent value of the current limiting inductor and the line inductance; red represents the on-state resistance and the fault point transition resistance values of the circuit and the power electronic device; udc represents the voltage; idc represents the current; t represents the start time; s represents the cross-sectional area of the line;
since the current branch immediately shifts after the main current branch trips at time t1, the fault current at this stage is initially idc (0) =idc (t 1).
As a further improvement of the application, the differential equation is written into the equivalent circuit column in the third stage, and the solution is carried out after the Laplace transformation is carried out on the equivalent circuit column;
wherein Ced is the equivalent capacitance value of all the capacitors in the converter unit, and the initial values of the capacitor voltage and the fault current at this stage are
U c (0_)＝0 (7)
i dc (0_)＝i dc (t 3 ) (8)
In the formula, idc (t 3) is the line current passing through the blocking capacitor converter unit IGBT at time t 3.
As a further improvement of the application, in the fifth stage, the capacitor is connected in series with an energy discharging resistor to consume energy and reduce voltage amplitude; for the series RC circuit, the time constant is tau=RC, and 5 tau is the charge and discharge.
As a further improvement of the present application, the dump resistance value is calculated as r=trs/5C, where TRS is the time after occurrence of the fault until the reclosing operation is started.
The beneficial effects of adopting above-mentioned technical scheme to produce lie in:
the application provides a high-voltage direct current breaker topological structure based on inductance current limiting and capacitance current converting based on the existing hybrid direct current breaker, the direct current breaker circulates through a power electronic device under normal conditions, the inductance does not influence the normal operation of the direct current breaker, and the on-state loss is small. Under the fault condition, the rising rate of the fault current is restrained through the inductor, the amplitude is reduced, and the turn-off current of the direct current breaker can be greatly improved. The capacitor current converting unit is used for replacing a solid-state direct current breaker in the original hybrid direct current breaker, so that the cost is greatly reduced, the dynamic voltage equalizing problem required by series connection of power electronic devices is solved, and the high-voltage-equalizing capacitor has good economical efficiency.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings that are needed in the embodiments or the description of the prior art will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present application, and that other drawings can be obtained according to these drawings without inventive effort for a person skilled in the art.
Fig. 1 is a topology of a high voltage dc circuit breaker;
FIG. 2 is a second stage equivalent circuit diagram;
FIG. 3 is a third stage equivalent circuit diagram;
fig. 4 is a schematic diagram of a four-terminal MMC-HVDC system.
Detailed Description
The following description of the embodiments of the present application will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present application, but not all embodiments. The following description of at least one exemplary embodiment is merely exemplary in nature and is in no way intended to limit the application, its application, or uses. All other embodiments, which can be made by those skilled in the art based on the embodiments of the application without making any inventive effort, are intended to be within the scope of the application.
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 exemplary embodiments according to the present application. As used herein, the singular is also intended to include the plural unless the context clearly indicates otherwise, and furthermore, it is to be understood that the terms "comprises" and/or "comprising" when used in this specification are taken to specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof.
The relative arrangement of the components and steps, numerical expressions and numerical values set forth in these embodiments do not limit the scope of the present application unless it is specifically stated otherwise. Techniques, methods, and apparatus known to one of ordinary skill in the relevant art may not be discussed in detail, but should be considered part of the specification where appropriate. In all examples shown and discussed herein, any specific values should be construed as merely illustrative, and not a limitation.
The embodiment provides a topological structure of a hybrid high-voltage circuit breaker. The direct current breaker uses the design concept of the existing hybrid direct current breaker to improve the turn-off capability of the circuit under the condition of short circuit by means of capacitive energy storage and inductive current limiting, and reduces the instantaneous impulse voltage and current amplitude born by the power electronic device. Under the steady-state operation condition, the current limiting reactor is not connected into the current loop, so that the better dynamic characteristic of the direct current power grid is ensured; when a fault occurs, the fault circuit is connected in series into the fault loop, so that the fault circuit has a good fault current inhibition effect, more time is striven for fault identification, a fault line is accurately cut off, and erroneous judgment is prevented. Finally, the applicability and the effectiveness of the direct current breaker in the flexible direct current power grid are verified through PSCAD/EMTDC simulation.
As shown in fig. 1, compared with a flexible direct current transmission system adopting a cable transmission project and an overhead line, the flexible direct current transmission system has the advantages that the probability of fault occurrence is greatly improved due to the fact that the line is exposed outside, and the stability and the reliability of the power system are easy to be impacted. In order to realize that each converter is not locked before and after the fault of the overhead line, the power of each converter station is not interrupted to be transmitted, the defects of the current high-voltage direct-current breaker such as breaking capacity and breaking capacity are overcome, and the cost is reduced, the high-voltage direct-current breaker based on capacitance conversion and inductance current limiting is provided, and the high-voltage direct-current breaker comprises a main circulation branch 1, a main circulation branch 2, a capacitance conversion unit 1, a capacitance conversion unit 2, a current limiting inductance 1, a current limiting inductance 2, an auxiliary conduction branch, a mechanical switch K1, a mechanical switch K2 and a lightning arrester unit; the capacitor current conversion unit 1, the current limiting inductor 1, the main current through branch 2 and the mechanical switch K2 are sequentially connected in series from the side A of line current to the side B of line current and then connected with the lightning arrester unit in parallel;
the mechanical switch K1, the main current branch 1, the current limiting inductor 2 and the capacitor converter unit 2 are sequentially connected in series and then connected to the lightning arrester unit in parallel;
one end of the auxiliary conduction branch is electrically connected to the branch between the main conduction branch 1 and the current-limiting inductor 2, and the other end of the auxiliary conduction branch is electrically connected to the branch between the current-limiting inductor 1 and the main conduction branch 2.
In this embodiment, the mechanical switches K1 and K2 flow through rated current under normal operation, and fast act under zero current state under fault condition, and the on-off time is 2ms;
the main flow branch 1 and the main flow branch 2 have the same structure and are composed of IGBT valve groups, and are connected in anti-series to realize bidirectional conduction, and the functions of the main flow branch 1 and the main flow branch 2 are that the IGBT on the main flow branch is triggered under the fault condition by means of the rapid controllability of the IGBT, the main flow branch IGBT is turned off, the current flow path under the fault condition of the line is changed, and the isolation of the fault line is realized;
the capacitor current conversion units 1 and 2 have the same structure, compared with a full-bridge submodule, 2 IGBT modules are omitted, when the voltage of the submodule capacitor reaches the action voltage of the lightning arrester unit, the current is transferred to a branch of the lightning arrester unit, the lightning arrester unit absorbs residual energy, and the fault current gradually drops to 0 through the buffer function of the capacitor in the submodule; the submodule capacitor is connected with an energy discharging resistor in parallel, and after the lightning arrester unit acts, the capacitor discharges;
the circuit breaker presents a low reactance and low loss path to the outside during normal operation. The current limiting inductor is put into the moment that the fault is detected, a larger reactance value is presented to the outside at the moment, the current limiting operation is performed in a current limiting mode, the rising rate of fault current can be effectively restrained, the breaking capacity of the circuit breaker is improved, the protection effect is achieved for the power electronic device with weak current capacity, meanwhile, time is strived for fault identification and diagnosis, and the protection reliability is improved. In the switching-on and switching-off process, the inductance voltage is limited to rise in a short time, and the fast mechanical switch, the main conduction branch and the power electronic devices on the auxiliary conduction branch bear the current-limiting inductance voltage together. The auxiliary conduction branch is formed by connecting thyristor valve groups in series and parallel, and the advantages of high rated voltage, large current, low price and the like of the thyristor device are fully utilized, so that the volume and cost of the part are effectively reduced.
In particular, as shown in fig. 2, under the normal operation condition, assuming that the line current flows from the a side to the B side, the mechanical switches K1 and K2 of the dc breaker are closed, all IGBTs in the capacitive converter unit are blocked, the current flows through the main current-carrying branch and the auxiliary current-carrying branch, at this time, the current-limiting inductor is not connected, and the circuit breaker presents a low impedance characteristic to the outside.
In particular, in the case of a fault, the operation steps of the high-voltage direct-current circuit breaker are as follows:
step S1, in a first stage, after a direct current circuit is grounded or has an interelectrode short circuit fault at a time t0, a circuit ultra-high speed protection device sends a tripping command to a direct current circuit breaker after detecting a system fault at a time t 1;
step S2, in the second stage, after the IGBT on the main flow path is locked, an on-off signal is applied to the ultra-fast mechanical switch, and the on-off time is 2ms;
step S3, in the third stage, all IGBTs in the capacitive commutation unit are locked at t3, and the fault current starts to charge the capacitor in the capacitive commutation unit module;
step S4, a fourth stage, in which the voltage at two sides of the current breaking unit rises rapidly, and when the voltage reaches the action threshold of the lightning arrester at the time t4, the short-circuit current is completely transferred to the lightning arrester until the complete consumption of the inductance energy of the direct current network is achieved;
and S5, in a fifth stage, after the direct-current line fault current is 0, the circuit breaker enters a reclosing state.
In step S1, the first-stage current flow path is to apply a blocking signal to the IGBT of the main current flow path, transfer the fault current into the capacitive converter unit loop, and at this time, the current limiting inductor is connected in series with the fault loop to suppress the amplitude and the rising rate of the fault current.
In step S2, the current flow path of the second stage process is the same as that of the first stage in that the ultra-fast mechanical switch is turned on at time t 2.
In this embodiment, as shown in fig. 3, the equivalent circuit of the second stage writes a differential equation to the equivalent circuit of the second stage, and solves the differential equation after laplace transformation is performed on the differential equation;
wherein Led represents the equivalent value of the current limiting inductor and the line inductance; red represents the on-state resistance and the fault point transition resistance values of the circuit and the power electronic device; udc represents the voltage; idc represents the current; t represents the start time; s represents the cross-sectional area of the line;
since the current branch immediately shifts after the main current branch trips at time t1, the fault current at this stage is initially idc (0) =idc (t 1).
At this time, the dc breaker may function as a current limiter. When the reactor is put into operation, the current rise rate is suppressed, and a sufficient time is provided for the system to detect whether or not a line fault has occurred. And when the line fault occurs, entering a third stage to disconnect the direct current breaker. If transient overcurrent such as lightning stroke occurs, the normal operation mode is shifted to. The circuit breaker can effectively avoid fault misjudgment and improve the reliability of the system.
Comprehensively considering fault point positions, information transmission delay and detection algorithm are time-consuming, and fault detection time is usually longer than 2ms. The current-limiting direct current breaker provided by the embodiment can quickly restrain fault current after faults are suspected to occur, ensures that a bridge arm current value is smaller than an IGBT double rated current value, does not need to be locked, and provides sufficient fault detection time for a system. The existing flexible direct current power grid overhead line main protection mostly adopts traveling wave protection and undervoltage differential protection, the backup protection adopts undervoltage overcurrent protection and differential protection, and the main protection can effectively identify faults within 3 ms.
In this embodiment, the equivalent circuit diagram is shown in fig. 4, and at this time, the capacitor is connected in series to the loop, and a differential equation is written into the equivalent circuit column in the third stage, and is solved after laplace transformation is performed on the equivalent circuit column;
wherein Ced is the equivalent capacitance value of all the capacitors in the converter unit, and the initial values of the capacitor voltage and the fault current at this stage are
U c (0_)＝0 (7)
i dc (0_)＝i dc (t 3 ) (8)
In the formula, idc (t 3) is the line current passing through the blocking capacitor converter unit IGBT at time t 3.
Wherein 4 variables are determined by circuit parameters:
A＝i dc (t 3 )
B＝U dc /L eq
the capacitor voltage value at this stage is
Wherein: VC (vitamin C) eq (t 3+ ) The initial value of the capacitor voltage is IGBT conducting voltage.
From the formulas (9) and (11), it is understood that the larger the capacitance value is, the slower the commutation capacitance voltage value of the circuit breaker reaches the lightning arrester trigger level. At the same time, the increase of the inductance value can inhibit the rising rate of the current and also affect the opening time of the circuit breaker. Considering both, the capacitance value of this embodiment is chosen to be 50 μF.
In general, after a transient fault occurs in an overhead line of a flexible direct current power grid, a system generally requires hundreds of milliseconds to start reclosing operation, and if the internal capacitor voltage of a capacitor converter unit is higher at this time, a capacitor C directly discharges an IGBT connected with the capacitor C, so that the risk of damaging a direct current breaker exists. In order to ensure the safety and reliability of reclosing, a capacitor is generally connected in series with an energy discharging resistor to consume the energy and reduce the voltage amplitude. In the fifth stage, the capacitor is connected in series with an energy discharging resistor to consume energy and reduce voltage amplitude; for the series RC circuit, the time constant is tau=RC, and 5 tau is the charge and discharge.
In this embodiment, the dump resistor value is calculated to be r=trs/5C, where TRS is the time from when the fault occurs to when the reclosing operation is started.
The direct current breaker scheme of the embodiment has the advantages of small implementation difficulty, large breaking capacity and excellent dynamic performance, and is suitable for the field of high-voltage and extra-high-voltage direct current transmission.
Claims (9)
1. A high-voltage direct current breaker based on capacitance commutation and inductance current limiting is characterized in that: the device comprises a main circulation branch 1, a main circulation branch 2, a capacitor converter unit 1, a capacitor converter unit 2, a current limiting inductor 1, a current limiting inductor 2, an auxiliary conduction branch, a mechanical switch K1, a mechanical switch K2 and a lightning arrester unit;
the capacitor current conversion unit 1, the current limiting inductor 1, the main current through branch 2 and the mechanical switch K2 are sequentially connected in series from the side A of line current to the side B of line current and then connected with the lightning arrester unit in parallel;
the mechanical switch K1, the main current branch 1, the current limiting inductor 2 and the capacitor converter unit 2 are sequentially connected in series and then connected to the lightning arrester unit in parallel;
one end of the auxiliary conduction branch is electrically connected to a branch between the main conduction branch 1 and the current-limiting inductor 2, and the other end of the auxiliary conduction branch is electrically connected to a branch between the current-limiting inductor 1 and the main conduction branch 2;
the mechanical switches K1 and K2 flow through rated current under the normal operation condition, and fast act under the zero current state under the fault condition, and the on-off time is 2ms;
the main flow branch 1 and the main flow branch 2 have the same structure and are composed of IGBT valve groups, and are connected in anti-series to realize bidirectional conduction, and the functions of the main flow branch 1 and the main flow branch 2 are that the IGBT on the main flow branch is triggered under the fault condition by means of the rapid controllability of the IGBT, the main flow branch IGBT is turned off, the current flow path under the fault condition of the line is changed, and the isolation of the fault line is realized;
the capacitor current conversion units 1 and 2 have the same structure, compared with a full-bridge submodule, 2 IGBT modules are omitted, when the voltage of the submodule capacitor reaches the action voltage of the lightning arrester unit, the current is transferred to a branch of the lightning arrester unit, the lightning arrester unit absorbs residual energy, and the fault current gradually drops to 0 through the buffer function of the capacitor in the submodule; the submodule capacitor is connected with an energy discharging resistor in parallel, and after the lightning arrester unit acts, the capacitor discharges;
the auxiliary conduction branch is formed by connecting thyristor valve groups in series and parallel.
2. A high voltage dc breaker based on capacitive commutation and inductive current limiting as claimed in claim 1, wherein: under the normal operation condition, assuming that line current flows from the side A to the side B, the mechanical switches K1 and K2 of the direct current circuit breaker are closed, all IGBTs in the capacitive inversion unit are blocked, the current flows through the main current through branch and the auxiliary current through branch, at the moment, the current limiting inductor is not connected, and the circuit breaker presents low impedance characteristics to the outside.
3. A high voltage direct current breaker based on capacitive commutation and inductive current limiting according to claim 2, characterized in that in case of a fault, the high voltage direct current breaker operates as follows:
step S1, in a first stage, after a direct current circuit is grounded or has an interelectrode short circuit fault at a time t0, a circuit ultra-high speed protection device sends a tripping command to a direct current circuit breaker after detecting a system fault at a time t 1;
step S2, in the second stage, after the IGBT on the main flow path is locked, an on-off signal is applied to the ultra-fast mechanical switch, and the on-off time is 2ms;
step S3, in the third stage, all IGBTs in the capacitive commutation unit are locked at t3, and the fault current starts to charge the capacitor in the capacitive commutation unit module;
step S4, a fourth stage, in which the voltage at two sides of the current breaking unit rises rapidly, and when the voltage reaches the action threshold of the lightning arrester at the time t4, the short-circuit current is completely transferred to the lightning arrester until the complete consumption of the inductance energy of the direct current network is achieved;
and S5, in a fifth stage, after the direct-current line fault current is 0, the circuit breaker enters a reclosing state.
4. A high voltage dc breaker based on capacitive commutation and inductive current limiting as claimed in claim 3, wherein: in step S1, the first-stage current flow path is to apply a blocking signal to the IGBT of the main current flow branch, and transfer the fault current into the capacitive commutation unit loop, and at this time, the current limiting inductor is connected in series to the fault loop, so as to inhibit the amplitude and the rising rate of the fault current.
5. A high voltage dc breaker based on capacitive commutation and inductive current limiting as claimed in claim 4, wherein: in step S2, the current flow path in the second stage is the same as that in the first stage in that the ultrafast mechanical switch is turned on and off at time t 2.
6. A high voltage dc breaker based on capacitive commutation and inductive current limiting as claimed in claim 3, wherein: writing differential equations into the equivalent circuit column in the second stage, and solving after Laplacian transformation;
wherein Led represents the equivalent value of the current limiting inductor and the line inductance; red represents the on-state resistance and the fault point transition resistance values of the circuit and the power electronic device; udc represents the voltage; idc represents the current; t represents the start time; s represents the cross-sectional area of the line;
since the current branch immediately shifts after the main current branch trips at time t1, the fault current at this stage is initially idc (0) =idc (t 1).
7. A high voltage dc breaker based on capacitive commutation and inductive current limiting as claimed in claim 3, wherein: writing differential equations into the equivalent circuit column in the third stage, and solving after Laplacian transformation;
wherein Ced is the equivalent capacitance value of all the capacitors in the converter unit, and the initial values of the capacitor voltage and the fault current at this stage are
U c (0_)＝0 (7)
i dc (0_)＝i dc (t 3 ) (8)
In the formula, idc (t 3) is the line current passing through the blocking capacitor converter unit IGBT at time t 3.
8. A high voltage dc breaker based on capacitive commutation and inductive current limiting as claimed in claim 3, wherein: in the fifth stage, the capacitor is connected with an energy discharging resistor in series to consume energy and reduce voltage amplitude; for the series RC circuit, the time constant is tau=RC, and 5 tau is the charge and discharge.
9. A high voltage dc breaker based on capacitive commutation and inductive current limiting as claimed in claim 8, wherein: calculating the energy discharging resistance value to obtain R=T RS 5C, wherein T RS To start reclosing operation after 5 a fault occursIs a time of (a) to be used.
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