CN112952776B - Current transfer circuit and method suitable for medium-voltage direct-current circuit breaker - Google Patents
Current transfer circuit and method suitable for medium-voltage direct-current circuit breaker Download PDFInfo
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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
- H02H3/08—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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- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
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Abstract
The invention relates to a current transfer circuit and a method suitable for a medium-voltage direct-current circuit breaker. The circuit includes: a main through-current branch, a fault current transfer branch and an energy consumption branch; the main through-current branch, the fault current transfer branch and the energy consumption branch are connected in parallel; the fault current transfer branch comprises a solid-state switch and an auxiliary commutation unit; the auxiliary current conversion unit comprises an energy storage capacitor, a first full-control power electronic device and a second full-control power electronic device; the positive electrode of the first full-control power electronic device is connected with the negative electrode of the second full-control power electronic device to form a first series string; the cathode of the first full-control type power electronic device is connected with the anode of the second full-control type power electronic device to form a second series string; the first series string is connected with the second series string in parallel, and the energy storage capacitor is connected between the first series string and the second series string in parallel, so that an H-bridge type circuit through-current topology is formed. The invention can realize the transfer of fault current and meet the requirement of quickly removing faults in the medium-voltage direct-current power distribution network.
Description
Technical Field
The invention relates to the field of medium-voltage direct-current power distribution networks, in particular to a current transfer circuit and a method suitable for a medium-voltage direct-current circuit breaker.
Background
In recent years, medium-voltage direct-current power distribution networks have good development prospects, and the direct-current power distribution networks have the advantages of good economy, low energy consumption, high power supply reliability, convenience in accessing distributed power supplies and energy storage devices, less occupied land resources, environmental friendliness and the like, and the application range of direct-current power distribution is increasingly wide. Even though the existing electric energy transmission mode mostly takes alternating current as a main part, along with the rapid development of power electronic technology, the power consumption requirements of main occasions such as rail transit, space transportation, high-power medical equipment and the like provide huge development space for the application of a direct current distribution network in recent years.
The direct current circuit breaker is the key equipment of protection low damping direct current system, and hybrid direct current circuit breaker is the more ripe technical scheme of current application, and the rapid development of power electronics technique also provides important technical support for it. The working principle of the hybrid direct current circuit breaker is mainly that the reliable matching of the main through-current branch, the transfer branch and the energy consumption branch is utilized to realize the rapid breaking of fault current. The research on the transfer branch of the hybrid direct current breaker has different solutions proposed in various published documents and works at home and abroad, and the auxiliary commutation measure can be configured in the main through-current branch and the transfer branch. The power semiconductor device is usually used to form a high-power semiconductor switch component, which is used as a core component of the fault transfer branch to realize an auxiliary commutation function.
The existing mature current transfer mode of the direct current circuit breaker can be divided into an impedance type and a power supply type. The impedance type commutation mode mainly means that a high impedance state is created when a fault current is generated, and the power supply type commutation mode mainly forces the fault current to transfer by introducing an independent voltage source or current source. At present, aiming at a power supply type current transfer technical scheme, an energy storage capacitor and the like are mainly used to form an active commutation condition so as to force the main branch current to be transferred. In published patent CN108390362A, a primary inductor and a certain number of fast-conducting switches are used, and a main branch of the fast-conducting switches is still provided with an auxiliary power electronic switch module, and for a direct-current circuit breaker applied in a medium-voltage environment, a water cooling device needs to be additionally arranged, so that the economy is improved to a certain extent, but the operation reliability is relatively poor; although patent CN110401174A mentions that an auxiliary inductor La and an auxiliary capacitor Ca are introduced to form a resonant circuit together, the main point of the patent is to assist in completing the current transfer, the inductor has no practical application condition in the subsequent turn-off process, and the circuit also has a certain influence on the current turn-off process of the circuit breaker due to the introduction of the auxiliary inductor; patent CN105024369B mainly uses capacitor to store energy in advance to assist current transfer, and because of using inductive coupling coil, the current will oscillate at the turn-off link, but its implementation difficulty is simple and cost is low. Patent CN109861183B has also proposed the use of a capacitor to store electrical energy in advance to assist in current transfer, but the device operation reliability is relatively weak due to the use of semi-controlled devices; on the other hand, the structure of the internal auxiliary commutation involves more devices, and compared with a medium-voltage occasion, the structure is not suitable for application mainly due to the fact that the number of devices is large, the control and the structure are complex, and the occupied space is large.
Compared with high-voltage direct-current transmission, the existing commercial high-capacity direct-current breaking technology is mostly directed at low-voltage systems, so that the requirement of quick fault removal cannot be met, and the problems of size, cost and the like need to be considered in practical application.
Disclosure of Invention
The invention aims to provide a current transfer circuit and a current transfer method suitable for a medium-voltage direct-current circuit breaker, and aims to solve the problem that the existing high-capacity direct-current breaking technology aims at a low-voltage system and cannot meet the requirement of quickly cutting off faults in a medium-voltage direct-current power distribution network.
In order to achieve the purpose, the invention provides the following scheme:
a current diverting circuit suitable for a medium voltage direct current circuit breaker, comprising: the fault current transfer circuit comprises a main through-current branch, a fault current transfer branch and an energy consumption branch;
the main through-current branch, the fault current transfer branch and the energy consumption branch are connected in parallel;
the fault current transfer branch comprises a solid-state switch and an auxiliary commutation unit; the auxiliary commutation unit comprises an energy storage capacitor, a first fully-controlled power electronic device and a second fully-controlled power electronic device;
the positive electrode of the first fully-controlled power electronic device is connected with the negative electrode of the second fully-controlled power electronic device to form a first series string; the cathode of the first full-control power electronic device is connected with the anode of the second full-control power electronic device to form a second series string; the first series string and the second series string are connected in parallel, and the energy storage capacitor is connected between the first series string and the second series string in parallel to form an H-bridge type circuit through-flow topology;
a fault current transfer stage: the two first fully-controlled power electronic devices are both turned off, the two second fully-controlled power electronic devices are both turned on, and the energy storage capacitor discharges to form negative pressure, so that the main through-current branch transfers fault current;
fault current turn-off phase: after the energy storage capacitor finishes discharging, the two first fully-controlled power electronic devices are still in a turn-off state, and the first series string and the second series string are connected in parallel for through-flow; after a preset duration, the two second fully-controlled power electronic devices are triggered to be turned off, the terminal voltage of the auxiliary current conversion unit is gradually increased to the action voltage of the energy consumption branch, and the residual fault current is exhausted through the energy consumption branch.
Optionally, the first fully-controlled power electronic device and the second fully-controlled power electronic device have the same model;
when the current mode of the auxiliary current conversion unit is a unidirectional current mode, the first fully-controlled power electronic device is a diode; the second full-control power electronic device is an insulated gate bipolar transistor;
and when the current mode of the auxiliary current conversion unit is a bidirectional current mode, the first full-control type power electronic device and the second full-control type power electronic device are both insulated gate bipolar transistors.
Optionally, only a fast mechanical switch is configured in the main through-current branch; the fast mechanical switch is used to achieve millisecond segment requirements for medium voltage dc circuit breakers.
Optionally, the energy consumption branch comprises one or more lightning arresters; and the action voltage of the lightning arrester is set based on the transient voltage generated by the auxiliary commutation unit during the fault current turn-off stage.
Optionally, the energy storage capacitor is a film capacitor.
Optionally, the solid state switches include a direct string solid state switch, a diode bridge solid state switch, and a full bridge solid state switch with a capacitor.
Optionally, after the fault current shutdown phase, if the storage capacitor still stores the residual voltage, the residual voltage is used in a reclosing phase of a next period.
A current diverting method suitable for a medium voltage direct current circuit breaker, comprising:
a fault current generation stage: fault current is generated and flows only through the main current branch;
a fault current transfer stage: two first full-control type power electronic devices in the fault current transfer branch circuit are turned off, two second full-control type power electronic devices are turned on, and the energy storage capacitor discharges to form negative pressure, so that the main through-flow branch circuit transfers fault current; the first series string is formed by connecting the positive electrode of a first fully-controlled power electronic device with the negative electrode of a second fully-controlled power electronic device, and the second series string is formed by connecting the negative electrode of the first fully-controlled power electronic device with the positive electrode of the second fully-controlled power electronic device;
fault current turn-off phase: after the energy storage capacitor is discharged, the two first fully-controlled power electronic devices are still in a turn-off state, and the first series string and the second series string are connected in parallel for through-flow; after a preset time, the two second fully-controlled power electronic devices are triggered to be turned off, the terminal voltage of the auxiliary current conversion unit in the fault current transfer branch is gradually increased to the action voltage of the energy consumption branch, and the residual fault current is exhausted through the energy consumption branch.
Optionally, after the fault current shutdown phase, if the storage capacitor still stores the residual voltage, the residual voltage is used in a reclosing phase of a next period.
Optionally, the reclosing stage specifically includes opening at a second time after reclosing once at a first time; the second time is the next time of the first time.
According to the specific embodiment provided by the invention, the invention discloses the following technical effects: the invention provides a current transfer circuit and a method suitable for a medium-voltage direct-current circuit breaker, wherein an auxiliary current conversion unit is configured to pre-charge an energy storage capacitor with a proper amount of voltage, so that the transfer of fault current is realized, and the requirement of a medium-voltage direct-current power distribution network on quick fault removal is met; the invention provides a current transfer circuit and a current transfer method for a medium-voltage hybrid direct-current circuit breaker, which integrate the functions of fault current transfer and turn-off, can meet the requirements of a medium-voltage direct-current distribution network on the size, cost, working reliability and the like of circuit breaker equipment, and have important engineering significance for expanding the application range of the direct-current circuit breaker.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without creative efforts.
Fig. 1 is a schematic diagram of a current transfer circuit suitable for a medium voltage dc circuit breaker according to the present invention;
fig. 2 is a structure diagram of a unidirectional through-current of an auxiliary commutation unit provided by the present invention;
fig. 3 is a bidirectional through-current structure diagram of the auxiliary commutation unit provided by the present invention;
FIG. 4 is a schematic diagram of a collocated string-type solid-state switch unit according to the present invention;
FIG. 5 is a schematic diagram of a bridge-type solid-state switching unit with diodes according to the present invention;
FIG. 6 is a schematic diagram of a capacitor-containing full-bridge solid-state switching unit according to the present invention;
FIG. 7 is a flowchart illustrating the overall operation of the fault current diversion and shutdown process provided by the present invention;
FIG. 8 is a timing diagram illustrating the main control of the fault current diversion and shutdown process provided by the present invention;
FIG. 9 is a waveform diagram illustrating a fault current transfer process and a first reclosing condition provided by the present invention;
fig. 10 is a waveform diagram illustrating a fault current transfer process and a second reclosing condition according to the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The invention aims to provide a current transfer circuit and a current transfer method suitable for a medium-voltage direct-current circuit breaker, which can transfer fault current and meet the requirement of quickly removing faults in a medium-voltage direct-current distribution network.
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in further detail below.
Fig. 1 is a schematic diagram of a current transfer circuit suitable for a medium voltage dc circuit breaker according to the present invention, and as shown in fig. 1, a current transfer circuit suitable for a medium voltage dc circuit breaker includes: a main through-current branch 1, a fault current transfer branch 2 and an energy consumption branch 3; the main through-current branch 1, the fault current transfer branch 2 and the energy consumption branch 3 are connected in parallel; the fault current transfer branch 2 comprises a solid-state switch 4 and an auxiliary commutation unit 5; the auxiliary commutation unit 5 comprises an energy storage capacitor, a first fully-controlled power electronic device and a second fully-controlled power electronic device; the positive electrode of the first fully-controlled power electronic device is connected with the negative electrode of the second fully-controlled power electronic device to form a first series string; the cathode of the first full-control type power electronic device is connected with the anode of the second full-control type power electronic device to form a second series string; the first series string and the second series string are connected in parallel, and the energy storage capacitor is connected between the first series string and the second series string in parallel to form an H-bridge type circuit through-flow topology; a fault current transfer stage: the two first full-control type power electronic devices are both turned off, the two second full-control type power electronic devices are both turned on, and the energy storage capacitor discharges to form negative pressure, so that the main through-flow branch 1 transfers fault current; fault current turn-off phase: after the energy storage capacitor is discharged, the two first fully-controlled power electronic devices are still in a turn-off state, and the first series string and the second series string are connected in parallel for through-current; after a preset time, the two second fully-controlled power electronic devices are triggered and turned off, the terminal voltage of the auxiliary current conversion unit 5 is gradually increased to the action voltage of the energy consumption branch 3, and the residual fault current is exhausted through the energy consumption branch 3.
The main through-current branch 1 in the invention only comprises a quick mechanical switch and does not comprise a solid-state power electronic switch, so that the problems of loss and heating caused by long-term conduction of the solid-state switch 4 are solved.
The fully-controlled power electronic device used in the auxiliary commutation unit 5 should be the same type of IGBT. If the device types are not consistent, in the transition process of two commutation stages, the through-current of the two parallel IGBT branches of the auxiliary commutation unit 5 is not uniform, a single branch device can bear transient electrical stress, and the power electronic device has failure risk.
The auxiliary current conversion unit 5 mainly undertakes the fault current transfer and turn-off processes of the circuit breaker, is integrated with the solid-state switch 4 assembly, and is placed in the fault current transfer branch 2.
Fig. 2 is a structure diagram of a unidirectional through-current of an auxiliary commutation unit provided by the present invention; fig. 3 is a bidirectional through-current structure diagram of an auxiliary current conversion unit provided by the present invention; in fig. 2, 503 and 504 are two first full-control power electronic devices of the same type, where the first full-control power electronic devices are diodes, 501 and 502 are second full-control power electronic devices of the same type, and the second full-control power electronic devices are Insulated Gate Bipolar Transistors (IGBTs); 505 is a pre-charged energy storage capacitor before operation, and a thin film capacitor can be selected generally; in fig. 3, 506 and 507 are first full-control power electronic devices, and both the first full-control power electronic device and the second full-control power electronic device are IGBTs.
FIG. 4 is a schematic diagram of a collocated straight-string solid-state switch unit according to the present invention; FIG. 5 is a schematic diagram of a bridge-type solid-state switching unit with diodes according to the present invention; FIG. 6 is a schematic diagram of a capacitor-containing full-bridge solid-state switching unit according to the present invention; the direct-series solid-state switch 401 adopts a direct series connection mode of IGBT devices; the diode bridge solid-state switch 402 is formed by a diode, a middle IGBT device and a buffer capacitor; the full-bridge solid-state switch 403 with capacitance mainly uses IGBT devices to form a full-bridge manner, where the capacitor is used as a buffer capacitance in the turn-off phase. The solid-state switch units corresponding to each collocation scheme can be connected in series to expand the voltage application level.
The energy consumption branch 3 comprises one or more lightning arresters; the action voltage of the lightning arrester is set based on the transient voltage generated by the auxiliary commutation unit 5 during the turn-off of the fault current in the turn-off stage; the lightning arrester is a metal oxide lightning arrester.
A current diverting method suitable for a medium voltage direct current circuit breaker, comprising:
a fault current generation stage: a fault current is generated and flows only through the main current branch 1.
A fault current transfer stage: two first fully-controlled power electronic devices in the fault current transfer branch 2 are both turned off, two second fully-controlled power electronic devices are both turned on, and the energy storage capacitor discharges to form negative pressure, so that the main through-current branch 1 transfers fault current; the first series string is formed by connecting the positive electrode of a first fully-controlled power electronic device with the negative electrode of a second fully-controlled power electronic device, and the second series string is formed by connecting the negative electrode of the first fully-controlled power electronic device with the positive electrode of the second fully-controlled power electronic device.
A fault current cut-off stage: after the energy storage capacitor finishes discharging, the two first full-control type power electronic devices are still in a turn-off state, and the first series string and the second series string are connected in parallel for through-flow; after a preset time, the two second fully-controlled power electronic devices are triggered to be turned off, the terminal voltage of the auxiliary current conversion unit 5 in the fault current transfer branch 2 is gradually increased to the action voltage of the energy consumption branch 3, and the residual fault current is exhausted through the energy consumption branch 3.
After the fault current turn-off stage, if the storage capacitor still stores residual voltage, the residual voltage is used for a reclosing stage of the next time period; the reclosing stage specifically comprises switching off at a second moment after reclosing once at a first moment; the second time is the next time of the first time.
In practical application, the current transfer method suitable for the medium-voltage direct-current circuit breaker provided by the invention comprises the following specific processes:
as shown in fig. 7, the method includes a fault current generation stage, a stage in which the second fully-controlled power electronic device 501 and the second fully-controlled power electronic device 502 are turned on and the energy storage capacitor 505 is discharged, a stage in which two parallel branches of the second fully-controlled power electronic device 501 and the second fully-controlled power electronic device 502 are connected in a current-flowing manner, a stage in which the second fully-controlled power electronic device 501 and the second fully-controlled power electronic device 502 are triggered to turn off, and a stage in which the lightning arrester consumes energy. Specifically, fig. 8 shows the timing of the control of the precharge of the storage capacitor 505, the fast mechanical switching and the devices 501 and 502 of the present invention.
It should be clear that the auxiliary commutation unit 5 in the present invention has a bidirectional current flowing function, so that the following five stages are specifically described in chronological order by taking the case that the current flows from left to right when the system is in normal operation as an example:
a) Fault current generation phase (t) 1 Before time): a fault current is generated and flows only through the main current branch 1.
B) Fault current transfer phase (t) 1 ～t 2 Time period): IGBT devices 501 and 502 are controlled to turn on, while devices 506 and 507 are controlled to turn off strictly. At this point, the storage capacitor 505 begins to discharge and the devices 501, 502 flow in series with the capacitor 505.
C) Fault current transfer branch 2 through-flow phase (t) 2 ～t 3 Time period): the storage capacitor 505 is at t 2 When the discharge is finished, the devices 506 and 507 are still strictly controlled to be turned off, at the moment, the device 501 is connected with the freewheeling diode of the device 507 in series, the device 502 is connected with the freewheeling diode of the device 506 in series, and the two series branches are connected in parallel for through-flow.
D) Fault current off phase (t) 3 ～t 4 Time period): the devices 501 and 502 are triggered to be turned off, the capacitor 505 is connected with the freewheeling diodes of the devices 506 and 507 in series, the residual current forms a path, the terminal voltage of the auxiliary commutation unit 5 is gradually established and gradually increased to the energy consumption branch3 operating voltage of the lightning arrester. After the arrester reaches the action voltage, the residual fault current is exhausted only through the energy consumption branch 3. At this time, the capacitor 505 of the auxiliary commutation unit 5 still has a residual voltage for the next stage of reclosing.
E) Reclosing stage (t) 4 ～t 4 Time period): the specific steps are as follows 4 After reclosing once at moment, at t 5 The brake is opened at the moment, and the situation is divided into two ways.
The first is that the branch is first reclosed, as shown in fig. 9, that is, the auxiliary commutation unit 5 is controlled to be through-current, if a fault occurs, the fault current is immediately cut off, that is, the above-mentioned stages B) to D) are repeated, if the fault current is exhausted, the fault current does not need to be cut off again, and the energy storage capacitor 505 can still maintain a part of voltage.
The other is to directly control the fast mechanical switch of the main current-circulating branch 1 to be switched on, as shown in fig. 10, considering that the energy storage capacitor 505 in the auxiliary current-converting unit 5 still has residual voltage, the condition of secondary auxiliary current conversion is provided. When the whole machine completes the opening again, the action process of the circuit breaker can still be realized by repeating the steps A) to D), and after the opening of the whole machine is completed, the capacitor energy storage 505 in the auxiliary commutation unit 5 still stores partial voltage.
After the pre-charging energy storage capacitor finishes discharging in the fault current transfer process, the pre-charging energy storage capacitor can also be used as a buffer capacitor in the fault current turn-off process, namely, the auxiliary current conversion unit 5 establishes voltage in the turn-off stage so as to be matched with action voltage required by the working of the arrester of the energy consumption branch 3; meanwhile, the residual voltage of the capacitor can be conveniently used for the fault current transfer process of the circuit breaker in the next fault breaking process, so that the secondary charging cost of the capacitor is saved; in addition, the residual voltage of the capacitor can be flexibly controlled when the circuit breaker works next time, and secondary charging is completed.
For the integration of equipment inside the device, the current transfer system provided by the invention can reduce the functional redundancy of the breaker device; meanwhile, the current transfer method provided by the invention mainly uses the diode and the full-control type solid-state switch 4 and avoids using passive devices such as an auxiliary inductor and the like, so that the reliability and the turn-off transient characteristic of the current transfer of the circuit breaker can be improved. In summary, the invention aims to improve the cost and the use space of the device and provide certain guiding significance for the application optimization of the medium-voltage direct-current circuit breaker.
The embodiments in the present description are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other. For the system disclosed by the embodiment, the description is relatively simple because the system corresponds to the method disclosed by the embodiment, and the relevant points can be referred to the method part for description.
The principles and embodiments of the present invention have been described herein using specific examples, which are provided only to help understand the method and the core concept of the present invention; meanwhile, for a person skilled in the art, according to the idea of the present invention, the specific embodiments and the application range may be changed. In view of the foregoing, the description is not to be taken in a limiting sense.
Claims (7)
1. A current transfer circuit adapted for use in a medium voltage direct current circuit breaker, comprising: the fault current transfer circuit comprises a main through-current branch, a fault current transfer branch and an energy consumption branch;
the main through-current branch, the fault current transfer branch and the energy consumption branch are connected in parallel;
the fault current transfer branch comprises a solid-state switch and an auxiliary commutation unit; the auxiliary current conversion unit comprises an energy storage capacitor, a first full-control power electronic device and a second full-control power electronic device;
the anode of the first fully-controlled power electronic device is connected with the cathode of the second fully-controlled power electronic device to form a first series string; the cathode of the first full-control type power electronic device is connected with the anode of the second full-control type power electronic device to form a second series string; the first series string is connected with the second series string in parallel, and the energy storage capacitor is connected between the first series string and the second series string in parallel to form an H-bridge type circuit through-flow topology;
the first fully-controlled power electronic device and the second fully-controlled power electronic device are the same in model;
when the current mode of the auxiliary current conversion unit is a unidirectional current mode, the first fully-controlled power electronic device is a diode; the second full-control type power electronic device is an insulated gate bipolar transistor;
when the current mode of the auxiliary current conversion unit is a bidirectional current mode, the first full-control power electronic device and the second full-control power electronic device are both insulated gate bipolar transistors;
a fault current generation stage: fault current is generated and flows only through the main current branch;
a fault current transfer stage: the two first full-control type power electronic devices are both turned off, the two second full-control type power electronic devices are both turned on, the energy storage capacitor discharges electricity, and the two second full-control type power electronic devices and the energy storage capacitor are connected in series and pass through the current to form negative voltage, so that the main current-passing branch transfers fault current;
and the fault current transfer branch circuit current stage: the energy storage capacitor finishes discharging at the initial moment of the through-flow stage of the fault current transfer branch, the two first full-control type power electronic devices are still strictly controlled to be turned off, at the moment, the second full-control type power electronic device in the first series string is connected with the fly-wheel diode of the first full-control type power electronic device in series, the second full-control type power electronic device in the second series string is connected with the fly-wheel diode of the first full-control type power electronic device in series, and the two series branches are connected in parallel for through-flow;
fault current turn-off phase: after a preset time, triggering and turning off the two second fully-controlled power electronic devices, gradually increasing the terminal voltage of the auxiliary current conversion unit to the action voltage of the energy consumption branch, and exhausting residual fault current through the energy consumption branch;
after the fault current turn-off stage, if the energy storage capacitor still stores residual voltage, the residual voltage is used for a reclosing stage in the next time period;
a reclosing stage: after reclosing once at the initial moment of the reclosing stage, switching off at the end moment of the reclosing stage again, wherein the situation is divided into two modes:
firstly, a transfer branch is reclosed firstly, namely the auxiliary commutation unit is controlled to be in through-current, if a fault occurs, the fault current is immediately cut off, namely the fault current transfer stage is repeated to the fault current cut-off stage, if the fault current is exhausted, the fault current does not need to be cut off again, and the energy storage capacitor can still maintain a part of voltage;
and secondly, the rapid mechanical switch of the main through-current branch is directly controlled to be switched on, and the condition of secondary auxiliary current conversion is provided in consideration of the fact that the energy storage capacitor in the auxiliary current conversion unit still has residual voltage.
2. Current transfer circuit suitable for a medium voltage direct current circuit breaker according to claim 1, characterized in that only a fast mechanical switch is provided within the main through-flow branch; the fast mechanical switch is used to achieve millisecond segment requirements for medium voltage dc circuit breakers.
3. Current transfer circuit suitable for a medium voltage direct current circuit breaker according to claim 1, characterized in that said energy consuming branch comprises one or more arresters; and the action voltage of the lightning arrester is set based on the transient voltage generated by the auxiliary commutation unit when the auxiliary commutation unit is turned off in the fault current turn-off stage.
4. Current transfer circuit suitable for a medium voltage direct current circuit breaker according to claim 1, characterized in that the energy storage capacitor is a film capacitor.
5. The current transfer circuit for a medium voltage direct current circuit breaker according to claim 1 wherein said solid state switches comprise dc-string solid state switches, diode bridge solid state switches and capacitor-containing full bridge solid state switches.
6. A current transfer method for a medium voltage dc circuit breaker, wherein the current transfer method for a medium voltage dc circuit breaker is applied to the current transfer circuit for a medium voltage dc circuit breaker according to any one of claims 1 to 5, and the current transfer method for a medium voltage dc circuit breaker comprises:
a fault current generation stage: fault current is generated and flows only through the main through-current branch;
a fault current transfer stage: the two first full-control type power electronic devices are both turned off, the two second full-control type power electronic devices are both turned on, the energy storage capacitor discharges electricity, and the two second full-control type power electronic devices and the energy storage capacitor are connected in series and pass through the current to form negative voltage, so that the main current-passing branch transfers fault current;
and the fault current transfer branch circuit is in a current passing stage: the energy storage capacitor finishes discharging at the initial moment of the through-flow stage of the fault current transfer branch, the two first full-control type power electronic devices are still strictly controlled to be turned off, at the moment, the second full-control type power electronic device in the first series string is connected with the fly-wheel diode of the first full-control type power electronic device in series, the second full-control type power electronic device in the second series string is connected with the fly-wheel diode of the first full-control type power electronic device in series, and the two series branches are connected in parallel for through-flow;
fault current turn-off phase: after a preset time, triggering and turning off the two second fully-controlled power electronic devices, gradually increasing the terminal voltage of the auxiliary current conversion unit to the action voltage of the energy consumption branch, and exhausting residual fault current through the energy consumption branch;
after the fault current turn-off stage, if the energy storage capacitor still stores residual voltage, the residual voltage is used for a reclosing stage in the next time period;
a reclosing stage: after reclosing once at the initial moment of the reclosing stage, switching off at the end moment of the reclosing stage again, wherein the situation is divided into two modes:
firstly, a transfer branch is reclosed firstly, namely the auxiliary commutation unit is controlled to be in through-current, if a fault occurs, the fault current is immediately cut off, namely the fault current transfer stage is repeated to the fault current cut-off stage, if the fault current is exhausted, the fault current does not need to be cut off again, and the energy storage capacitor can still maintain a part of voltage;
and secondly, the rapid mechanical switch of the main through-current branch is directly controlled to be switched on, and the condition of secondary auxiliary current conversion is provided in consideration of the fact that the energy storage capacitor in the auxiliary current conversion unit still has residual voltage.
7. The current transfer method suitable for medium voltage direct current circuit breakers according to claim 6, characterized in that said reclosing phase comprises in particular the opening at a second moment after one reclosing at a first moment; the second time is the next time of the first time.
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| CN113964788B (en) * | 2021-10-26 | 2023-02-28 | 西安交通大学 | Bidirectional direct current breaker |
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| CN114498546B (en) * | 2021-12-28 | 2023-01-20 | 清华大学 | Hybrid dual-bridge type direct current breaker topological circuit and control method thereof |
| CN116865737B (en) * | 2023-09-04 | 2023-11-24 | 中国科学院电工研究所 | Direct-current solid-state circuit breaker circuit topology based on full-control device and control method |
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