CN112838578B - Rapid recovery system for DC fault of half-bridge flexible DC converter and control method - Google Patents
Rapid recovery system for DC fault of half-bridge flexible DC converter and control method Download PDFInfo
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- CN112838578B CN112838578B CN201911162095.6A CN201911162095A CN112838578B CN 112838578 B CN112838578 B CN 112838578B CN 201911162095 A CN201911162095 A CN 201911162095A CN 112838578 B CN112838578 B CN 112838578B
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J1/00—Circuit arrangements for dc mains or dc distribution networks
- H02J1/10—Parallel operation of dc sources
- H02J1/102—Parallel operation of dc sources being switching converters
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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
Abstract
The invention discloses a quick recovery system and a control method for a direct current fault of a half-bridge soft direct current converter, which comprise the half-bridge soft direct current converter, a direct current breaker, a direct current transformer and a protection device. After the direct current fault is removed, the half-bridge flexible direct current converter is unlocked by turning off a thyristor of an internal module of the converter, and a direct current breaker is put into use, so that the fault is quickly recovered. From the occurrence of the fault to the recovery of the fault, the time of the whole process can be controlled within 100ms, the power-off time of the system can be greatly shortened, and the reliability of the system is improved.
Description
Technical Field
The invention belongs to the field of power electronic application, and particularly relates to a quick recovery system for a direct current fault of a half-bridge flexible direct current converter and a control method.
Background
As one of the voltage source type converter topologies for realizing flexible dc transmission engineering, a Modular Multilevel Converter (MMC) has been gradually paid attention from academic and engineering circles in recent years, and compared with the traditional high-voltage dc transmission, the advantage that the modular multilevel converter dc transmission system has no commutation failure, can independently control power, and the like, gradually becomes the mainstream trend of the development of a high-capacity high-voltage flexible dc power grid. At present, a half-bridge modular multilevel converter structure is mostly adopted in an operated flexible direct-current transmission project, the topological structure is simple, the economical efficiency is good, and the self-clearing capability of direct-current short-circuit faults is not provided. A dc bipolar short circuit fault is one of the most severe fault types of a flexible dc power transmission system. When the system has a direct current short circuit fault, the voltage of the direct current bus is rapidly reduced to zero, and the capacitor of the half-bridge submodule discharges, so that the current of the direct current bus and the current of a bridge arm are rapidly increased, and the safety of a current converter and a power grid is threatened. In the prior art, after a control protection system detects a direct-current short-circuit fault, a current converter is locked immediately, fault current begins to attenuate gradually, and after a period of time, an alternating-current breaker acts, so that the fault current is attenuated to zero continuously, and equipment damage is avoided. Therefore, under the prior art conditions, when a dc fault occurs, the prior art system needs to be forced to stop running or needs a longer time to restart. With the development of flexible direct current technology, how to isolate and quickly recover a fault is a problem to be solved urgently. Particularly, the application of a low-voltage direct-current distribution network is gradually enhanced, a flexible direct-current converter is adopted to construct a direct-current medium-voltage power grid, the application scene of supplying power to a direct-current load through a direct-current transformer is more and more in demand, the direct-current load is a terminal user in production or life, and the requirement on power supply reliability is higher. Under the background, how to realize the rapid fault recovery of the whole set of system under the condition of direct current fault and reduce the time of power supply interruption due to fault becomes a more urgent requirement.
Disclosure of Invention
The invention aims to solve the defects of the prior art scheme and provides a direct current fault recovery system of a half-bridge flexible direct current converter, which can coordinate and control different primary and secondary devices of the half-bridge flexible direct current converter, so that the whole system can reliably and quickly recover power supply when a direct current double-pole short circuit occurs, and the power supply interruption time can be effectively shortened compared with the recovery process of tripping an alternating current breaker to stop the converter device after a fault and restarting after the fault is cleared in the prior art.
In order to achieve the above object, the present invention provides a fast recovery system for dc fault of half-bridge soft dc converter, including a half-bridge soft dc converter, a dc breaker, M dc transformers, N load switches; the direct current outlet of the half-bridge flexible direct current converter is connected to a direct current bus through a direct current breaker; one end of the load switch is connected to the direct current bus, the other end of the load switch is directly connected to the direct current load, or the load switch is connected to the high-voltage side of the direct current transformer, and the low-voltage side of the direct current transformer is connected with the low-voltage level direct current load or the low-voltage direct current power supply;
the system also comprises a set of direct current bus protection units, N line protection units and a set of fault recovery coordination controller;
the direct current bus protection unit, the direct current line protection unit, the fault recovery coordination controller, the half-bridge flexible direct current converter, the direct current breaker and the direct current transformer exchange information between primary equipment and secondary equipment through a GOOSE network;
the fault recovery coordination controller is used for realizing fault ride-through coordination control of the direct current breaker, the half-bridge soft direct current converter and the direct current transformer when a bipolar short circuit fault occurs on the direct current side.
Further, the half-bridge flexible direct current converter adopts a symmetrical monopole connection mode or a true dipole connection mode.
Furthermore, the alternating current port of the submodule of the half-bridge soft direct current converter is connected with a thyristor in parallel, and when a bipolar short circuit occurs, the thyristor is triggered to be turned on, so that fault current flows through the thyristor, and the safety of the half-bridge soft direct current converter submodule IGBT is guaranteed.
Furthermore, the direct current transformer is basically composed of N power units with the same structure, and each power unit is composed of a high-voltage side module, a low-voltage side module, a phase-shifting inductor and a high-frequency isolation transformer.
Further, the dc circuit breaker employs a mechanical or hybrid topology.
The invention also provides a quick recovery control method for the direct current fault of the half-bridge flexible direct current converter, which comprises the following steps:
step 1: the direct current circuit is in a bipolar short circuit, the half-bridge flexible direct current converter is locked due to the overcurrent of a bridge arm caused by fault current, the thyristor inside the submodule is triggered to be conducted at the same time when the half-bridge flexible direct current converter is locked, the IGBT device is protected, and an alternating current side switch of the half-bridge flexible direct current converter is not disconnected when the half-bridge flexible direct current converter is locked; the direct-current transformer correspondingly senses the fault blocking; turning to the step 2;
step 2: breaking the direct current breaker, and cutting off fault current by the breaker; turning to the step 3;
and step 3: protecting and breaking a load switch corresponding to the fault line by the direct current line, and isolating a fault area; turning to step 4;
and 4, step 4: after the direct current breaker cuts off the fault current, the current flowing through the converter is gradually attenuated to 0, and a thyristor in the converter is turned off; turning to step 5;
and 5: the fault recovery coordination controller issues a half-bridge converter starting command, and the half-bridge converter is unlocked again; turning to step 6;
step 6: the fault recovery coordination controller issues a direct-current breaker reclosing command, and the direct-current breaker is switched on; turning to step 7;
and 7: and the fault recovery coordination controller issues an unlocking command of the direct current transformer, the direct current load is recovered to be supplied with power, and the process is ended.
Further, in step 1 of the above method, if a bipolar short-circuit fault occurs on the dc bus side, the half-bridge converter is locked by the bus protection device, and the ac/dc side breaker of the half-bridge converter is tripped, and the process is ended and no fault recovery is performed.
Further, in the step 6 of the above method, if the dc fault is not successfully isolated, and when the dc breaker is closed, the dc breaker is in fault, or the dc bipolar short-circuit fault occurs again in a short time, the method goes to the step 8:
and step 8: the half-bridge flexible-direct current converter triggers a bridge arm to be subjected to overcurrent locking again due to fault current, simultaneously triggers a thyristor in the submodule to be conducted for the second time, protects an IGBT device, and disconnects an alternating-current side switch when the bridge arm is locked; turning to step 9;
and step 9: breaking the direct current breaker, and cutting off fault current by the breaker; turning to step 10;
step 10: issuing a switching-off command of each direct-current transformer by the fault recovery coordination controller, and separating corresponding switch disconnecting links by the direct-current transformers; the flow ends.
The invention has the beneficial effects that:
(1) in the step 1, after the bipolar short circuit of the direct current side occurs, the half-bridge converter is firstly locked and then is separated from the circuit breaker of the direct current side, the IGBT current of the half-bridge converter adopting the mode is smaller, and the smoothing reactor configuration of the direct current side is smaller, so that the system cost can be effectively reduced, the system floor area is reduced, and the economical efficiency and the practicability of the system are improved.
(2) This direct current fault fast recovery control system, through fault recovery coordination device and each one secondary equipment cooperation, through above-mentioned step, divide direct current side circuit breaker and keep exchanging the circuit breaker and closing the position, through the online input and the withdraw from of half-bridge thyristor, can effectively realize direct current fault's fast recovery, realize fault recovery at 100ms, shorten the system time of losing power greatly, improve system reliability.
(3) Through the direct-current fault rapid recovery control method, a direct-current breaker reclosing command is issued by the fault recovery coordination device, when fault recovery is realized, if the fault occurs or a bipolar short circuit occurs again, the bridge arm overcurrent lock can be triggered again, meanwhile, a thyristor in the module is triggered to conduct for the second time, and the safety of equipment is protected.
(4) The fault recovery system is applicable to both the symmetric unipolar mode and the true bipolar mode.
Drawings
FIG. 1 is a schematic diagram of a fault recovery system of the present invention;
FIG. 2 is a schematic diagram of networking communication among devices in the present invention;
FIG. 3 is a schematic diagram of a half-bridge soft DC converter topology according to the present invention;
FIG. 4 is a schematic diagram of a symmetrical single-pole connection mode of the half-bridge soft DC converter according to the present invention;
FIG. 5 is a schematic diagram of a true bipolar connection of the half-bridge soft DC converter of the present invention;
FIG. 6 is a schematic diagram of a DC transformer topology according to the present invention;
fig. 7 is a timing diagram of the normal failure recovery steps of the present invention.
Detailed Description
The technical scheme of the invention is explained in detail in the following with the accompanying drawings.
Fig. 1 shows an embodiment of a fast dc fault recovery control system for a half-bridge soft dc converter according to the present invention, which includes a half-bridge soft dc converter, a dc breaker, M dc transformers, and N load switches; the direct current outlet of the half-bridge flexible direct current converter is connected to a direct current bus through a direct current breaker; one end of the load switch is connected to the direct current bus, the other end of the load switch is directly connected to the direct current load, or the load switch is connected to the high-voltage side of the direct current transformer, and the low-voltage side of the direct current transformer is connected with the low-voltage level direct current load or the low-voltage direct current power supply;
the system also comprises a set of direct current bus protection units, N line protection units and a set of fault recovery coordination controller;
the direct current bus protection unit, the direct current line protection unit, the fault recovery coordination controller, the half-bridge flexible direct current converter, the direct current breaker and the direct current transformer exchange information between primary equipment and secondary equipment through a GOOSE network; the devices are networked as shown in fig. 2, and may also communicate with the telecontrol equipment and the monitoring system via an MMS network.
The fault recovery coordination controller is used for realizing fault ride-through coordination control of the direct current breaker, the half-bridge soft direct current converter and the direct current transformer when a bipolar short circuit fault occurs on the direct current side.
As shown in fig. 3, a topological schematic diagram of a half-bridge flexible-direct current converter is shown, and an MMC topological structure is adopted, each phase includes two symmetrical upper and lower single valves, and three phases total six bridge arms, and each bridge arm includes the same number of modular sub-units (hereinafter referred to as sub-modules) composed of semiconductor switches and capacitors. The alternating current port of the submodule is connected with a thyristor in parallel, and when a bipolar short circuit occurs, the thyristor is triggered to be switched on, so that fault current flows through the thyristor, and the safety of the half-bridge soft-direct current converter submodule IGBT is guaranteed.
For example, the half-bridge soft-direct current converter in fig. 4 can adopt a symmetrical monopole connection mode.
For example, the half-bridge soft direct current converter in fig. 5 can adopt a true monopole connection mode.
As shown in fig. 6, the dc transformer topology is a dc transformer topology, which can realize dc voltage conversion, and is basically configured as N power units having the same structure, where each power unit is composed of a high-voltage side module, a low-voltage side module, a phase-shift inductor, and a high-frequency isolation transformer.
The direct current breaker can adopt a mechanical type or a mixed type topology, can separate fault current and can realize fault current cutoff within 5 ms.
When the system normally operates, the half-bridge converter and the direct current transformer are in an unlocked state, the direct current breaker is in a closed position, and the direct current system normally supplies power to a direct current load. When a double-click short-circuit fault occurs in a system, the embodiment of the quick recovery control method for the direct-current fault of the half-bridge flexible direct-current converter comprises the following steps:
step 1: the direct current circuit is in a bipolar short circuit, the half-bridge flexible direct current converter is locked due to the overcurrent of a bridge arm caused by fault current, the thyristor inside the submodule is triggered to be conducted at the same time when the half-bridge flexible direct current converter is locked, the IGBT device is protected, and an alternating current side switch of the half-bridge flexible direct current converter is not disconnected when the half-bridge flexible direct current converter is locked; the direct-current transformer correspondingly senses the fault blocking; turning to the step 2;
and 2, step: breaking the direct current breaker, and cutting off fault current by the breaker; turning to the step 3;
and step 3: protecting and breaking a load switch corresponding to the fault line by using the direct current line, and isolating a fault area; turning to step 4;
and 4, step 4: after the direct current breaker cuts off the fault current, the current flowing through the converter is gradually attenuated to 0, and the thyristor in the converter is turned off; turning to step 5;
and 5: the fault recovery coordination controller issues a half-bridge converter starting command, and the half-bridge converter is unlocked again; turning to step 6;
and 6: the fault recovery coordination controller issues a direct-current breaker reclosing command, and the direct-current breaker is switched on; turning to step 7;
and 7: and the fault recovery coordination controller issues a direct-current transformer unlocking command, the direct-current load is recovered to be supplied with power, and the process is finished.
As shown in fig. 7, a timing diagram of the normal fault recovery steps of the present invention is described.
Wherein:
t0<5 ms: the circuit breaker acts and cuts off the time;
t1<10 ms: after the circuit breaker is cut off, judging that the fault current is less than the on-off capacity time of the load switch, wherein the time is less than 10 ms;
t2<10 ms: after the protection action of the direct current line protection unit, successfully isolating a fault area;
t3<5 ms: starting the communication delay of the fault recovery device after the protection action of the direct-current line protection unit;
t4<70 ms: the fault recovery device system recovers the longest time, including recovering the unlocking of the half-bridge converter to establish direct-current voltage and closing a direct-current side circuit breaker;
maximum time for fault recovery: t-t 0+ t1+ t2+ t3+ t4<100 ms. The whole-process fault recovery time is less than 100ms, and the normal fault can be quickly recovered.
Since step 1 occurs before step 2, the rated current of the IGBT corresponding to the half-bridge converter is small and the smoothing reactor on the dc side is small, so that the half-bridge converter is locked preferentially because the fault current exceeds the tolerance current of the bridge arm before the dc circuit breaker is disconnected. The IGBT current of the half-bridge converter is small, the smoothing reactance of the direct current side is small, the system cost can be effectively reduced, the system floor area is reduced, and the economy and the practicability of the system are improved.
In another embodiment, in step 1 of the above method, if a double-pole short-circuit fault occurs on the dc bus side, the half-bridge converter is locked by the bus protection device, and the ac/dc side breaker of the half-bridge converter is tripped, and the process is ended and no fault recovery is performed.
In another embodiment, in the step 6 of the method, if the dc fault is not successfully isolated, and when the dc breaker is switched on, the dc breaker is switched on to have a fault, or a dc bipolar short-circuit fault occurs again in a short time, the method goes to the step 8:
and 8: the half-bridge flexible direct current converter triggers the bridge arm to be subjected to overcurrent locking again due to fault current, simultaneously triggers a thyristor in the submodule to be conducted for the second time, protects an IGBT device, and disconnects an AC side switch during locking; turning to step 9;
and step 9: breaking the direct current breaker, and cutting off fault current by the breaker; turning to step 10;
step 10: issuing a switching-off command of each direct-current transformer by the fault recovery coordination controller, and separating corresponding switch knife switches by the direct-current transformers; the flow ends.
The above embodiments are only for illustrating the technical solution of the present invention and not for limiting the same, and various modifications or changes made with reference to the above embodiments are within the scope of the present invention.
Claims (8)
1. A quick recovery control method for a direct current fault of a half-bridge flexible direct current converter is characterized by comprising the following steps:
step 1: the direct current circuit is in a bipolar short circuit, the half-bridge flexible direct current converter is locked due to the overcurrent of a bridge arm caused by fault current, the thyristor inside the submodule is triggered to be conducted at the same time when the half-bridge flexible direct current converter is locked, the IGBT device is protected, and an alternating current side switch of the half-bridge flexible direct current converter is not disconnected when the half-bridge flexible direct current converter is locked; the direct-current transformer correspondingly senses fault blocking; turning to the step 2;
step 2: breaking the direct current breaker, and cutting off fault current by the breaker; turning to the step 3;
and step 3: protecting and breaking a load switch corresponding to the fault line by the direct current line, and isolating a fault area; turning to the step 4;
and 4, step 4: after the direct current breaker cuts off the fault current, the current flowing through the converter is gradually attenuated to 0, and the thyristor in the converter is turned off; turning to step 5;
and 5: the fault recovery coordination controller issues a half-bridge converter starting command, and the half-bridge converter is unlocked again; turning to step 6;
and 6: the fault recovery coordination controller issues a direct-current breaker reclosing command, and the direct-current breaker is switched on; turning to step 7;
and 7: and the fault recovery coordination controller issues a direct-current transformer unlocking command, the direct-current load is recovered to be supplied with power, and the process is finished.
2. The method as claimed in claim 1, wherein in step 1, if the double short-circuit fault occurs on the dc bus side, the bus protection device locks the half-bridge converter and trips the ac/dc side breaker of the half-bridge converter, and the process is ended and no fault recovery is performed.
3. The method according to claim 1, wherein in step 6, if the dc fault is not successfully isolated, and when the dc breaker is closed, the dc breaker is switched to the fault, or the dc double short-circuit fault occurs again in a short time, the method goes to step 8:
and step 8: the half-bridge flexible-direct current converter triggers a bridge arm to be subjected to overcurrent locking again due to fault current, simultaneously triggers a thyristor in the submodule to be conducted for the second time, protects an IGBT device, and disconnects an alternating-current side switch when the bridge arm is locked; turning to step 9;
and step 9: breaking the direct current breaker, and cutting off fault current by the breaker; turning to step 10;
step 10: issuing a switching-off command of each direct-current transformer by the fault recovery coordination controller, and separating corresponding switch knife switches by the direct-current transformers; the flow ends.
4. A fast recovery system of DC fault of a half-bridge soft DC converter applying the fast recovery control method of DC fault of the half-bridge soft DC converter according to claim 1 is characterized by comprising a half-bridge soft DC converter, a DC breaker, M DC transformers and N load switches; a direct current outlet of the half-bridge flexible direct current converter is connected to a direct current bus through a direct current breaker; one end of the load switch is connected to the direct current bus, the other end of the load switch is directly connected to the direct current load, or the load switch is connected to the high-voltage side of the direct current transformer, and the low-voltage side of the direct current transformer is connected with the low-voltage level direct current load or the low-voltage direct current power supply;
the system also comprises a set of direct current bus protection units, N line protection units and a set of fault recovery coordination controller;
the direct current bus protection unit, the direct current line protection unit, the fault recovery coordination controller, the half-bridge flexible direct current converter, the direct current breaker and the direct current transformer exchange information between primary equipment and secondary equipment through a GOOSE network;
the fault recovery coordination controller is used for realizing fault ride-through coordination control of the direct current breaker, the half-bridge soft direct current converter and the direct current transformer when a bipolar short circuit fault occurs on the direct current side.
5. The half-bridge soft dc converter dc fault fast recovery system of claim 4, wherein: the half-bridge flexible direct current converter adopts a symmetrical unipolar connection mode or a true bipolar connection mode.
6. The half-bridge soft dc converter dc fault fast recovery system of claim 4, wherein: the alternating current port of the submodule of the half-bridge soft direct current converter is connected with a thyristor in parallel, and the thyristor is triggered to be turned on when a bipolar short circuit occurs, so that fault current flows through the thyristor, and the safety of the IGBT of the submodule of the half-bridge soft direct current converter is guaranteed.
7. The half-bridge soft dc converter dc fault fast recovery system of claim 4, wherein: the direct current transformer is basically composed of N power units with the same structure, and each power unit is composed of a high-voltage side module, a low-voltage side module, a phase-shifting inductor and a high-frequency isolation transformer.
8. The half-bridge soft dc converter dc fault fast recovery system of claim 4, wherein: the dc circuit breaker employs a mechanical or hybrid topology.
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN106602531A (en) * | 2016-10-18 | 2017-04-26 | 华北电力大学 | Bridge arm bypass protection circuit of modularization multi-level converter aiming at direct current short circuit fault |
| CN107069679A (en) * | 2017-03-30 | 2017-08-18 | 华中科技大学 | A kind of symmetrical bipolar MMC DC sides monopolar grounding fault is passed through and restoration methods |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN106602531A (en) * | 2016-10-18 | 2017-04-26 | 华北电力大学 | Bridge arm bypass protection circuit of modularization multi-level converter aiming at direct current short circuit fault |
| CN107069679A (en) * | 2017-03-30 | 2017-08-18 | 华中科技大学 | A kind of symmetrical bipolar MMC DC sides monopolar grounding fault is passed through and restoration methods |
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