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CN112803815B - Topological structure of hybrid converter and control method thereof - Google Patents

Topological structure of hybrid converter and control method thereof Download PDF

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Publication number
CN112803815B
CN112803815B CN202110139638.3A CN202110139638A CN112803815B CN 112803815 B CN112803815 B CN 112803815B CN 202110139638 A CN202110139638 A CN 202110139638A CN 112803815 B CN112803815 B CN 112803815B
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China
Prior art keywords
branch
bridge arm
auxiliary
leg
main
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CN202110139638.3A
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Chinese (zh)
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CN112803815A (en
Inventor
高冲
贺之渊
汤广福
杨俊�
盛财旺
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Global Energy Interconnection Research Institute
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Global Energy Interconnection Research Institute
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Priority to CN202110139638.3A priority Critical patent/CN112803815B/en
Publication of CN112803815A publication Critical patent/CN112803815A/en
Priority to PCT/CN2021/124770 priority patent/WO2022160791A1/en
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Classifications

    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of AC power input into DC power output; Conversion of DC power input into AC power output
    • H02M7/42—Conversion of DC power input into AC power output without possibility of reversal
    • H02M7/44—Conversion of DC power input into AC power output without possibility of reversal by static converters
    • H02M7/48—Conversion of DC power input into AC power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/505—Conversion of DC power input into AC power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a thyratron or thyristor type requiring extinguishing means
    • H02M7/515—Conversion of DC power input into AC power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a thyratron or thyristor type requiring extinguishing means using semiconductor devices only
    • H02M7/521—Conversion of DC power input into AC power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a thyratron or thyristor type requiring extinguishing means using semiconductor devices only in a bridge configuration
    • 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
    • H02J3/00—Circuit arrangements for AC mains or AC distribution networks
    • H02J3/36—Arrangements for transfer of electric power between AC networks via a high-tension DC link
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/32—Means for protecting converters other than automatic disconnection
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/60—Arrangements for transfer of electric power between AC networks or generators via a high voltage DC link [HVCD]

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Rectifiers (AREA)

Abstract

The invention discloses a topological structure of a hybrid current converter and a control method thereof, wherein the topological structure comprises the following components: at least one phase of main branch, wherein each phase of main branch comprises an upper bridge arm main branch and a lower bridge arm main branch, a first thyristor valve is arranged on the upper bridge arm main branch, and a second thyristor valve is arranged on the lower bridge arm main branch; each phase of auxiliary branch comprises an upper bridge arm auxiliary branch and a lower bridge arm auxiliary branch, a first auxiliary reversing valve is arranged on the upper bridge arm auxiliary branch, and a second auxiliary reversing valve is arranged on the lower bridge arm auxiliary branch; the auxiliary branch is connected with the main branch in parallel and is used for carrying out forced commutation when the commutation of the main branch fails; the shutoff valve is arranged on the main branch or the auxiliary branch and is used for transferring the current of the main branch to the auxiliary branch when the phase is forcedly changed. By implementing the invention, the reliable turn-off of the main branch and the active commutation of each phase of bridge arm are realized, the occurrence of commutation failure is avoided, and the stable and safe operation of the power grid is ensured.

Description

Topological structure of hybrid converter and control method thereof
Technical Field
The invention relates to the technical field of current conversion in power electronics, in particular to a topological structure of a hybrid current converter and a control method thereof.
Background
The traditional power grid commutation high-voltage direct current (line commutated converter high voltage direct current, LCC-HVDC) power transmission system has the advantages of long-distance large-capacity power transmission, controllable active power and the like, and is widely applied worldwide. The converter is used as core equipment for direct current transmission, is a core functional unit for realizing alternating current and direct current electric energy conversion, and the operation reliability of the converter determines the operation reliability of an extra-high voltage direct current power grid to a great extent.
Because the traditional converter mostly adopts semi-controlled device thyristors as core components to form a six-pulse bridge converter topology, each bridge arm is formed by connecting multistage thyristors and buffer components thereof in series, and the thyristors do not have self-turn-off capability, the phase conversion failure easily occurs under the conditions of AC system faults and the like, so that the direct current is increased rapidly and the direct current transmission power is lost rapidly and greatly, and the stable and safe operation of a power grid is influenced.
Disclosure of Invention
In view of the above, the embodiment of the invention provides a hybrid converter topology structure and a control method thereof, so as to solve the problem that commutation failure affects stable and safe operation of a power grid.
According to a first aspect, an embodiment of the present invention provides a hybrid converter topology, the topology being connected to an ac grid through a converter transformer, the topology comprising: each phase of main branch comprises an upper bridge arm main branch and a lower bridge arm main branch, a first thyristor valve is arranged on the upper bridge arm main branch, and a second thyristor valve is arranged on the lower bridge arm main branch; one end of the main branch is connected with a direct current bus, and the other end of the main branch is connected with the output end of the converter transformer; each phase of auxiliary branch comprises an upper bridge arm auxiliary branch and a lower bridge arm auxiliary branch, a first auxiliary reversing valve is arranged on the upper bridge arm auxiliary branch, and a second auxiliary reversing valve is arranged on the lower bridge arm auxiliary branch; the auxiliary branch is connected with the main branch in parallel and is used for assisting the main branch in forced commutation when the main branch fails in commutation; and the shutoff valve is arranged on the main branch or the auxiliary branch and is used for transferring the current of the main branch to the auxiliary branch when the phase is forcedly changed.
With reference to the first aspect, in a first implementation manner of the first aspect, the upper bridge arm auxiliary leg is connected in parallel with the upper bridge arm main leg, and the lower bridge arm auxiliary leg is connected in parallel with the lower bridge arm main leg; the shutoff valves are arranged on the main branch of the upper bridge arm of each phase and the main branch of the lower bridge arm of each phase; one end of the shutoff valve arranged on the main leg of the upper bridge arm is connected with the first thyristor valve, and the other end of the shutoff valve is connected with the output end of the converter transformer; one end of the shutoff valve arranged on the main leg of the lower bridge arm is connected with the second thyristor valve, and the other end of the shutoff valve is connected with the negative electrode of the direct current bus.
With reference to the first aspect, in a second implementation manner of the first aspect, the upper bridge arm auxiliary leg is connected in parallel with the upper bridge arm main leg, and the lower bridge arm auxiliary leg is connected in parallel with the lower bridge arm main leg; the shutoff valve is respectively arranged on the upper bridge arm auxiliary branch and the lower bridge arm auxiliary branch; one end of the shutoff valve arranged on the upper bridge arm auxiliary branch is connected with the first auxiliary reversing valve, and the other end of the shutoff valve is connected with the output end of the converter transformer; one end of the shutoff valve arranged on the lower bridge arm auxiliary branch is connected with the second auxiliary reversing valve, and the other end of the shutoff valve is connected with the negative electrode of the direct current bus.
With reference to the first aspect, in a third implementation manner of the first aspect, the upper bridge arm main leg and the lower bridge arm main leg are connected in series; the upper bridge arm auxiliary branch is connected in series with the lower bridge arm auxiliary branch; one end of the shutoff valve is connected with the connecting ends of the upper bridge arm main branch and the lower bridge arm main branch, and the other end of the shutoff valve is connected with the output end of the converter transformer; and the connecting ends of the upper bridge arm auxiliary branch and the lower bridge arm auxiliary branch are connected with the output end of the converter transformer.
With reference to the first aspect, in a fourth implementation manner of the first aspect, the upper bridge arm main leg and the lower bridge arm main leg are connected in series; the upper bridge arm auxiliary branch is connected in series with the lower bridge arm auxiliary branch; one end of the shutoff valve is connected with the connecting ends of the upper bridge arm auxiliary branch and the lower bridge arm auxiliary branch, and the other end of the shutoff valve is connected with the output end of the converter transformer; and the connecting ends of the upper bridge arm main branch and the lower bridge arm main branch are connected with the output end of the converter transformer.
With reference to the first aspect, in a fifth implementation manner of the first aspect, the topology includes two shutoff valves, and the upper bridge arm main branch and the lower bridge arm main branch are connected in series; the upper bridge arm auxiliary branch is connected in series with the lower bridge arm auxiliary branch; one end of the first shutoff valve is connected with the main branch of each phase of upper bridge arm, and the other end of the first shutoff valve is connected with the auxiliary branch of each phase of upper bridge arm; one end of the second shutoff valve is connected with the main branch of the lower bridge arm of each phase, and the other end of the second shutoff valve is connected with the auxiliary branch of the lower bridge arm of each phase.
With reference to the first aspect, in a sixth implementation manner of the first aspect, the topology further includes: at least one isolation valve is disposed on the ac bus for isolating the voltage between the main branch and the auxiliary branch.
With reference to the sixth implementation manner of the first aspect, in a seventh implementation manner of the first aspect, a first end of the at least one isolation valve is connected to a connection end of each phase of the upper bridge arm main leg and each phase of the lower bridge arm main leg, and a second end of the at least one isolation valve is connected to a connection end of the upper bridge arm auxiliary leg and the lower bridge arm auxiliary leg; the topological structure comprises two shutoff valves, and the main branch of the upper bridge arm and the main branch of the lower bridge arm are connected in series; the upper bridge arm auxiliary branch is connected in series with the lower bridge arm auxiliary branch; one end of the first shutoff valve is connected with the main branch of each phase of upper bridge arm, and the other end of the first shutoff valve is connected with the auxiliary branch of each phase of upper bridge arm; one end of the second shutoff valve is connected with the main branch of the lower bridge arm, and the other end of the second shutoff valve is connected with the auxiliary branch of the lower bridge arm.
With reference to the sixth implementation manner of the first aspect, in an eighth implementation manner of the first aspect, the upper bridge arm main leg and the lower bridge arm main leg are connected in series; the upper bridge arm auxiliary branch is connected in series with the lower bridge arm auxiliary branch; the upper bridge arm main branch and the lower bridge arm main branch are respectively provided with the shutoff valve; the connecting end between the shutoff valve of the main branch of the upper bridge arm of each phase and the shutoff valve of the main branch of the lower bridge arm of each phase is connected with the first end of the isolation valve.
With reference to the sixth implementation manner of the first aspect, in a ninth implementation manner of the first aspect, the upper bridge arm main leg and the lower bridge arm main leg are connected in series; the upper bridge arm auxiliary branch is connected in series with the lower bridge arm auxiliary branch; the upper bridge arm auxiliary branch and the lower bridge arm auxiliary branch are respectively provided with the shutoff valves, and the connection end between the shutoff valves of the upper bridge arm auxiliary branch and the lower bridge arm auxiliary branch is connected with the second end of the at least one isolation valve.
With reference to the sixth implementation manner of the first aspect, in a tenth implementation manner of the first aspect, the upper bridge arm main leg and the lower bridge arm main leg are connected in series; the upper bridge arm auxiliary branch is connected in series with the lower bridge arm auxiliary branch; one end of the shutoff valve is connected with the first end of the at least one isolation valve, and the other end of the shutoff valve is connected with the connecting ends of the upper bridge arm auxiliary branch and the lower bridge arm auxiliary branch.
With reference to the sixth implementation of the first aspect, in an eleventh implementation of the first aspect, the first thyristor valve and the second thyristor valve each include: at least one controllable device for reverse voltage blocking, the at least one controllable device being arranged in series; at least one first auxiliary component arranged in parallel with the at least one controllable device; the controllable device comprises one or more of a thyristor, a GTO and a reverse resistance IGCT.
With reference to the first aspect, in a twelfth implementation manner of the first aspect, the shutoff valve includes: at least one first power unit for on-control and off-control of the auxiliary branch; and the second auxiliary component is arranged in parallel with the first power unit.
With reference to the twelfth implementation manner of the first aspect, in a thirteenth implementation manner of the first aspect, the first power unit includes: the first branch circuit is provided with a first power device; or, a second leg and a third leg; at least one first power device is arranged on the second branch, and the at least one first power device is arranged in series; the third branch is identical to the second branch in structure, and the third branch is arranged in parallel with the second branch; or, a fourth branch and a fifth branch; the fourth branch is provided with at least one first diode, and the at least one first diode is arranged in series; the fifth branch is identical to the fourth branch in structure, and the fourth branch is arranged in parallel with the fifth branch; or, a sixth branch and a seventh branch; the sixth branch is provided with the first power device; the seventh branch is provided with the first power device and the second auxiliary component, and the first power device and the second auxiliary component are connected in parallel; the sixth branch is arranged in parallel with the seventh branch.
With reference to the first aspect, in a fourteenth implementation manner of the first aspect, the first auxiliary reversing valve and the second auxiliary reversing valve include: at least one second power cell, the at least one second power cell being in series; at least one third auxiliary component is connected in parallel with the at least one second power unit.
With reference to the fourteenth implementation manner of the first aspect, in a fifteenth implementation manner of the first aspect, the second power unit includes: the first connecting branch is provided with a second power device; or, a second connection leg; at least one second power device is arranged on the second connecting branch, and the at least one second power device is connected in reverse series; or, at least one third connection leg and at least one fourth connection leg; the third connecting branch is identical to the first connecting branch in structure, and the fourth connecting branch is provided with a second diode or a first thyristor; the at least one third connecting branch and the at least one fourth connecting branch are arranged in staggered series; or, a fifth connection leg and a sixth connection leg; at least one second power device is arranged on the fifth connecting branch, and the at least one second power device is arranged in series; the sixth connecting branch is identical to the fifth connecting branch in structure, and the fifth connecting branch is arranged in parallel with the sixth connecting branch; the fifth connecting branch, the sixth connecting branch and the third auxiliary component form a full-bridge structure; or, a seventh connection leg, an eighth connection leg, and a ninth connection leg; wherein, the seventh connecting branch is provided with at least one third diode, and the at least one third diode is arranged in series; at least one second power device is arranged on the eighth connecting branch, and the at least one second power device is arranged in series; the ninth connecting branch is identical to the seventh connecting branch in structure, and the ninth connecting branch is connected in parallel with the eighth connecting branch and the seventh connecting branch; the seventh connecting branch, the eighth connecting branch, the ninth connecting branch and the third auxiliary component form an H-bridge structure.
With reference to the eleventh or twelfth or fourteenth implementation of the first aspect, in a sixteenth implementation of the first aspect, the first, second and third auxiliary components comprise: a first buffer branch composed of capacitors; or, a resistor and the capacitor are connected in series with the second buffer branch; or, the capacitor and the resistor are connected in parallel with the third buffer branch; or, the resistor is connected in parallel with the fifth diode and then connected in series with the capacitor to form a fourth buffer branch; or, the resistor and the capacitor are connected in parallel and then connected in series with the fifth diode to form a fifth buffer branch; or a sixth buffer branch consisting of lightning arresters; or, a seventh buffer branch formed by a plurality of parallel connection among the first buffer branch, the second buffer branch, the third buffer branch, the fourth buffer branch, the fifth buffer branch and the sixth buffer branch.
According to a second aspect, an embodiment of the present invention provides a method for controlling a hybrid converter topology, which is used in the hybrid converter topology according to the first aspect or any implementation manner of the first aspect, and includes the following steps: switching off auxiliary branches and/or a switchable valve of the hybrid converter topology; switching on a main branch and/or a shutoff valve of a hybrid converter topology; an auxiliary branch and/or a shutoff valve of the hybrid converter topology are/is conducted; switching off auxiliary branches and/or a switchable valve of the hybrid converter topology; after a control period, the thyristor valve of the main branch of the topological structure of the hybrid converter is conducted, wherein,。
With reference to the second aspect, in a first implementation manner of the second aspect, the method further includes: the main branch and the auxiliary branch of the topological structure of the hybrid converter run periodically and alternately.
The technical scheme of the invention has the following advantages:
1. The topological structure of the hybrid current converter provided by the embodiment of the invention comprises at least one phase of main branch, at least one phase of auxiliary branch and a shutoff valve, wherein the main branch and the auxiliary branch are arranged in parallel, and the shutoff valve is arranged on the main branch or the auxiliary branch. During normal operation, the auxiliary branch can be kept in an off state, and only voltage stress is needed to be born, and normal operation current is borne by the main branch; when the main branch fails to commutate or the AC short circuit fails, the auxiliary branch is conducted, and the current of the main branch is transferred to the auxiliary branch by combining the turn-off or the conduction of the turn-off valve. The auxiliary branch which can provide reverse voltage and has self-turn-off capability is connected in parallel on the basis of the main branch, so that the reliable turn-off of the main branch and the active phase change of each phase of bridge arm are realized, the auxiliary phase change function is realized in a short time, the occurrence of phase change failure is avoided, and the stable and safe operation of a power grid is ensured.
2. According to the topological structure of the hybrid current converter, the auxiliary branch can switch off the current of the main branch in advance, and meanwhile, reverse voltage is provided for the main branch, so that the main branch is reliably switched off, and the problem of commutation failure is avoided.
3. The topological structure of the hybrid converter provided by the embodiment of the invention can conduct the auxiliary branch at any time, effectively reduces the loss of the main branch, and can realize low-voltage and low-turn-off angle operation at the same time, thereby reducing reactive power of the inversion side.
4. According to the control method for the hybrid current converter topological structure, the auxiliary branch of the ith bridge arm of the hybrid current converter topological structure is kept in the off state, and the main branch and/or the shutoff valve of the ith bridge arm of the hybrid current converter topological structure are/is conducted, so that the hybrid current converter topological structure with forced commutation can work in a normal commutation operation mode, namely in a temporary commutation operation mode, the auxiliary branch is in the off state when the hybrid current converter normally operates, only bears voltage stress, and the increase of current converter loss in long-term operation is reduced. When commutation failure or alternating current short circuit failure occurs, an auxiliary branch and/or a shutoff valve of an ith bridge arm of the hybrid converter topology structure are/is conducted, current of the main branch is forcedly transferred to the auxiliary branch, and when current transfer is completed, the auxiliary branch and/or the shutoff valve of the ith bridge arm of the hybrid converter topology structure are/is turned off, so that forceful commutation of the hybrid converter is realized. After a control period, the step of turning on the main branch and/or the shutoff valve of the ith bridge arm of the topological structure of the hybrid converter is returned, and the main branch continues to independently and normally operate, so that the auxiliary branch is ensured to bear the shutoff voltage stress only when in failure, the loss of the device is reduced, and the service life of the device is prolonged.
5. According to the forced commutation control method provided by the embodiment of the invention, through the periodical alternate operation of the main branch and the auxiliary branch, not only can commutation failure be resisted, but also the commutation failure is not required to be predicted. Meanwhile, the operation mode that the hybrid current converter works at a small off angle is ensured, and reactive power consumption of the hybrid current converter is reduced.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are needed in the description of the embodiments or the prior art will be briefly described, and it is obvious that the drawings in the description below are some embodiments of the present invention, and other drawings can be obtained according to the drawings without inventive effort for a person skilled in the art.
Fig. 1a is a schematic block diagram of a hybrid converter topology according to an embodiment of the invention;
fig. 1b is another schematic block diagram of a hybrid converter topology according to an embodiment of the invention;
Fig. 2 is a block diagram of an alternative hybrid converter topology in accordance with an embodiment of the invention;
Fig. 3 is another block diagram of an alternative hybrid converter topology in accordance with an embodiment of the invention;
fig. 4 is another block diagram of an alternative hybrid converter topology in accordance with an embodiment of the invention;
fig. 5 is another block diagram of an alternative hybrid converter topology in accordance with an embodiment of the invention;
Fig. 6 is another block diagram of an alternative hybrid converter topology in accordance with an embodiment of the invention;
Fig. 7 is another functional block diagram of a hybrid converter topology according to an embodiment of the invention;
Fig. 8 is another block diagram of an alternative hybrid converter topology in accordance with an embodiment of the invention;
Fig. 9 is another block diagram of an alternative hybrid converter topology in accordance with an embodiment of the invention;
fig. 10 is another block diagram of an alternative hybrid converter topology in accordance with an embodiment of the invention;
fig. 11 is another block diagram of an alternative hybrid converter topology in accordance with an embodiment of the invention;
FIG. 12 is a block diagram of the structure of a main branch according to an embodiment of the present invention;
FIG. 13 is a block diagram of a shut-off valve according to an embodiment of the present invention;
FIG. 14 is a block diagram of an auxiliary phase change valve according to an embodiment of the present invention;
FIG. 15 is a block diagram of a buffer component according to an embodiment of the present invention;
fig. 16 is a flow chart of a method of controlling a hybrid converter topology according to an embodiment of the invention;
fig. 17 is a bridge arm current flow path in a normal operating state according to an embodiment of the present invention;
FIG. 18 is a current flow process of a primary leg commutating to a secondary leg according to an embodiment of the present invention;
FIG. 19 is a timing of the periodic trigger control of the primary and secondary legs according to an embodiment of the present invention;
FIG. 20 is a normal trigger control timing of a main leg according to an embodiment of the present invention;
Fig. 21 is a bridge arm current flow path in a normal operating state according to an embodiment of the present invention;
FIG. 22 is a trigger control sequence for a main leg commutation failure or short circuit fault according to an embodiment of the present invention;
FIG. 23 is a current flow process of a primary leg commutating to a secondary leg according to an embodiment of the present invention;
FIG. 24 is a primary and secondary leg periodic trigger control timing according to an embodiment of the present invention;
fig. 25 is a bridge arm current flow path in a normal operating state according to an embodiment of the present invention;
FIG. 26 is a timing sequence of valve triggering control according to an embodiment of the present invention;
FIG. 27 is a current flow process of a primary leg commutating to a secondary leg according to an embodiment of the present invention;
FIG. 28 is a primary and secondary leg periodic trigger control timing according to an embodiment of the present invention;
FIG. 29 is a timing sequence of valve triggering control according to an embodiment of the present invention;
FIG. 30 is a current flow process of a primary leg commutating to a secondary leg according to an embodiment of the present invention;
FIG. 31 is a primary and secondary leg periodic trigger control timing according to an embodiment of the present invention;
FIG. 32 is a timing sequence of valve triggering control according to an embodiment of the present invention;
FIG. 33 is a current flow process of a primary leg commutating to a secondary leg according to an embodiment of the present invention;
FIG. 34 is a primary and secondary leg periodic trigger control timing according to an embodiment of the present invention;
FIG. 35 is a timing sequence for the triggering control of valves according to an embodiment of the present invention;
FIG. 36 is a current flow process of a primary leg commutating to a secondary leg according to an embodiment of the present invention;
Fig. 37 is a timing of the trigger control of the primary and secondary legs periodically according to an embodiment of the present invention.
The figure shows that the valve comprises a 1-main branch, a 2-auxiliary branch, a 3-shutoff valve, a 4-isolation valve, a 11-first thyristor valve, a 12-second thyristor valve, a 21-first auxiliary phase-changing valve and a 22-second auxiliary phase-changing valve.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments of the present invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
The converter is used as core equipment for direct current transmission, is a core functional unit for realizing alternating current and direct current electric energy conversion, and the operation reliability of the converter determines the operation reliability of an extra-high voltage direct current power grid to a great extent. However, as the traditional converter mostly adopts semi-controlled device thyristors as core components to form a six-pulse bridge converter topology, each bridge arm is formed by connecting multistage thyristors and buffer components thereof in series, and the thyristors do not have self-turn-off capability, the converter failure easily occurs under the conditions of AC system faults and the like, so that the DC current is increased rapidly and the DC transmission power is lost rapidly and greatly, and the stable and safe operation of a power grid is influenced.
Based on the above, the technical scheme of the invention sets the auxiliary branch on the basis of the main branch, and utilizes the shutoff capability of the shutoff valve to realize the reliable shutoff of the main branch, avoid the occurrence of commutation failure and ensure the stability and the safety of the operation of the power grid.
According to an embodiment of the invention, an embodiment of a hybrid converter topology is provided, which is connected to an ac grid through a converter transformer. Specifically, as shown in fig. 1a and 1b, the hybrid converter topology includes: at least one phase main branch, at least one phase auxiliary branch and a shutoff valve. One end of the main branch is connected to the direct current bus, the other end of the main branch is connected to the output end of the converter transformer, each phase of main branch comprises an upper bridge arm main branch and a lower bridge arm main branch, a first thyristor valve is arranged on the upper bridge arm main branch, a second thyristor valve is arranged on the lower bridge arm main branch, and the first thyristor valve and the second thyristor valve are mainly used for through flow; the auxiliary branch is connected with the main branch in parallel and is used for carrying out forced commutation when the commutation of the main branch fails, each phase of auxiliary branch comprises an upper bridge arm auxiliary branch and a lower bridge arm auxiliary branch, a first auxiliary reversing valve is arranged on the upper bridge arm auxiliary branch, a second auxiliary reversing valve is arranged on the lower bridge arm auxiliary branch, and the first auxiliary reversing valve and the second auxiliary reversing valve have the functions of controllable forward current shutoff and forward and reverse voltage blocking; the shut-off valve may be provided on the main branch, as shown in fig. 1 a; the shut-off valve may also be arranged on the auxiliary branch, as shown in fig. 1 b. The broken line boxes in the drawings represent a plurality of identical units.
When the hybrid current converter is in normal operation, the auxiliary branch can be kept in an off state, and only voltage stress is needed to be born, and normal operation current is borne by the main branch; when the main branch fails to commutate or the AC short circuit fails, the auxiliary branch is conducted, and the current of the main branch is transferred to the auxiliary branch by combining the turn-off or the conduction of the turn-off valve.
The hybrid converter topological structure provided by the embodiment can be connected in parallel with the auxiliary branch circuit with reverse voltage and self-turn-off capability on the basis of the main branch circuit, so that the reliable turn-off of the main branch circuit and the active phase change of each phase of bridge arm are realized, the auxiliary phase change function is realized in a short time, the occurrence of phase change failure is avoided, and the stable and safe operation of a power grid is ensured.
Specifically, as shown in fig. 2, the topology structure is a three-phase six-leg circuit, the upper leg auxiliary leg corresponding to each phase leg is connected in parallel with the upper leg main leg, the lower leg auxiliary leg is connected in parallel with the lower leg main leg, and the shutoff valve is arranged on each phase upper leg main leg and each phase lower leg main leg. One end of the shutoff valve arranged on the main leg of the upper bridge arm is connected with the first thyristor valve, and the other end of the shutoff valve is connected with the output end of the converter transformer; one end of a shutoff valve arranged on the main leg of the lower bridge arm is connected with the second thyristor valve, and the other end of the shutoff valve is connected with the negative electrode of the direct current bus.
When the hybrid current converter is in normal operation, the auxiliary branch can be kept in an off state, and the thyristor valve and the turn-off valve of the main branch of the ith bridge arm are conducted, so that the auxiliary branch only needs to bear voltage stress, and normal operation current is borne by the main branch; when the main branch fails to commutate or the AC short circuit is failed, the shutoff valve is turned off, the auxiliary branch is turned on, the current of the main branch is transferred to the auxiliary branch, and when the current of the main branch is completely transferred to the auxiliary branch, the auxiliary branch is turned off, so that the forced commutation of the main branch is realized.
Specifically, as shown in fig. 3, the topology structure is a three-phase six-leg circuit, an upper leg auxiliary leg is connected in parallel with an upper leg main leg, a lower leg auxiliary leg is connected in parallel with a lower leg main leg, and shutoff valves are respectively arranged on the upper leg auxiliary leg and the lower leg auxiliary leg. One end of the shutoff valve arranged on the upper bridge arm auxiliary branch is connected with the first auxiliary reversing valve, the other end of the shutoff valve is connected with the output end of the converter transformer, one end of the shutoff valve arranged on the lower bridge arm auxiliary branch is connected with the second auxiliary reversing valve, and the other end of the shutoff valve is connected with the negative electrode of the direct current bus.
When the hybrid current converter is in normal operation, the auxiliary branch can be kept in an off state, and the thyristor valve of the main branch of the ith bridge arm is conducted, so that the auxiliary branch only needs to bear voltage stress, and the main branch bears normal operation current; when the main branch fails to commutate or the alternating current short circuit is failed, the shutoff valve of the auxiliary branch and the auxiliary commutation valve of the upper bridge arm are conducted, the current of the main branch is transferred to the auxiliary branch, and when the current of the main branch is completely transferred to the auxiliary branch, the auxiliary commutation valve of the upper bridge arm and the shutoff valve are turned off, so that forced commutation of the main branch is realized.
Specifically, as shown in fig. 4, the topology structure includes a three-phase six-leg circuit, an upper leg main leg and a lower leg main leg are connected in series, an upper leg auxiliary leg and a lower leg auxiliary leg are connected in series, one end of a shutoff valve is connected with a connection end between the upper leg main leg and the lower leg main leg, the other end of the shutoff valve is connected with an output end of the converter transformer, and the connection ends of the upper leg auxiliary leg and the lower leg auxiliary leg are connected with the output end of the converter transformer. Similar to the concept of fig. 2, the arrangement of the shutoff valve on the main branch is equivalent to that of the upper bridge arm main branch and the lower bridge arm main branch, and one end of the shutoff valve is connected with the connecting end between the upper bridge arm main branch and the lower bridge arm main branch, and the other end is connected with the output end of the converter transformer, so that the upper bridge arm main branch and the lower bridge arm main branch can share one shutoff valve, and the series number of the shutoff valves is reduced.
When the hybrid current converter is in normal operation, the auxiliary branch can be kept in an off state, and the thyristor valve and the turn-off valve of the main branch of the ith bridge arm are conducted, so that the auxiliary branch only needs to bear voltage stress, and normal operation current is borne by the main branch; when the main branch fails to commutate or the AC short circuit is failed, the shutoff valve is turned off, the auxiliary branch is turned on, the current of the main branch is transferred to the auxiliary branch, and when the current of the main branch is completely transferred to the auxiliary branch, the auxiliary branch is turned off, so that the forced commutation of the main branch is realized.
Specifically, as shown in fig. 5, the topology structure includes a three-phase six-leg circuit, an upper leg main leg and a lower leg main leg are connected in series, an upper leg auxiliary leg and a lower leg auxiliary leg are connected in series, one end of a shutoff valve is connected with the connection ends of the upper leg auxiliary leg and the lower leg auxiliary leg, the other end is connected with the output end of the converter transformer, and the connection ends of the upper leg main leg and the lower leg main leg are connected with the output end of the converter transformer. Similar to the concept of fig. 3, the arrangement of the shutoff valve on the auxiliary branch circuit is equivalent to that of the upper bridge arm auxiliary branch circuit and the lower bridge arm auxiliary branch circuit, and one end of the shutoff valve is connected with the connection ends of the upper bridge arm auxiliary branch circuit and the lower bridge arm auxiliary branch circuit, and the other end is connected with the output end of the converter transformer, so that the upper bridge arm auxiliary branch circuit and the lower bridge arm auxiliary branch circuit can share one shutoff valve, and the series number of the shutoff valves is reduced.
When the hybrid current converter is in normal operation, the auxiliary branch can be kept in an off state, and the thyristor valve of the main branch of the ith bridge arm is conducted, so that the auxiliary branch only needs to bear voltage stress, and the main branch bears normal operation current; when the main branch fails to commutate or the alternating current short circuit is failed, the shutoff valve of the auxiliary branch and the auxiliary commutation valve of the upper bridge arm are conducted, the current of the main branch is transferred to the auxiliary branch, and when the current of the main branch is completely transferred to the auxiliary branch, the auxiliary commutation valve of the upper bridge arm and the shutoff valve are turned off, so that forced commutation of the main branch is realized.
Specifically, as shown in fig. 6, the topology structure includes a three-phase main branch and a three-phase auxiliary branch, and the three-phase main branch and the three-phase auxiliary branch are all three-phase six-bridge-arm structures, and at this time, two shutoff valves may be set in the topology structure. One end of the first shutoff valve is connected with the main branch of each phase of upper bridge arm, and the other end of the first shutoff valve is connected with the auxiliary branch of each phase of upper bridge arm; one end of the second shutoff valve is connected with the main branch of the lower bridge arm of each phase, and the other end of the second shutoff valve is connected with the auxiliary branch of the lower bridge arm of each phase.
When the hybrid current converter is in normal operation, the auxiliary branch can be kept in an off state, and the thyristor valve and the turn-off valve of the main branch of the ith bridge arm are conducted, so that the auxiliary branch only needs to bear voltage stress, and normal operation current is borne by the main branch; when the main branch fails to commutate or the AC short circuit is failed, the shutoff valve is turned off, the upper bridge arm auxiliary commutation valve of the auxiliary branch is turned on, the current of the main branch is transferred to the auxiliary branch, and when the current on the main branch is completely transferred to the auxiliary branch, the upper bridge arm auxiliary commutation valve of the auxiliary branch is turned off, so that forced commutation of the main branch is realized.
By arranging the two shutoff valves on the direct current bus connected with the main branch and the auxiliary branch respectively, the three-phase upper bridge arm main branch can share one shutoff valve and the three-phase lower bridge arm main branch can share one shutoff valve, and the series number of the shutoff valves is reduced.
In particular, as shown in fig. 7, the topology may also include at least one isolation valve. The isolation valve is arranged on an alternating current bus which is connected with the output end of the converter transformer. Wherein the isolation valve is used for isolating high voltage generated between the main branch and the auxiliary branch.
Specifically, as shown in fig. 8, the topology structure includes a three-phase main branch and a one-phase auxiliary branch, and the three-phase main branch is of a three-phase six-leg structure, the upper leg main branch and the lower leg main branch are connected in series, and the upper leg auxiliary branch and the lower leg auxiliary branch are connected in series, so that two shutoff valves can be set in the topology structure. One end of the first shutoff valve is connected with the main branch of each phase of upper bridge arm, and the other end of the first shutoff valve is connected with the auxiliary branch of the upper bridge arm; one end of the second shutoff valve is connected with the main branch of the lower bridge arm of each phase, and the other end of the second shutoff valve is connected with the auxiliary branch of the lower bridge arm. The first ends of the three isolation valves are respectively connected with the connecting ends of the upper bridge arm main branch and the lower bridge arm main branch of each phase, and the second ends of the three isolation valves are connected with the connecting ends between the upper bridge arm auxiliary branch and the lower bridge arm auxiliary branch.
When the hybrid converter normally operates, the isolation valve is turned off, the auxiliary branch is kept in a turned-off state, the thyristor valve and the turn-off valve of the main branch of the ith bridge arm are turned on, and at the moment, the auxiliary branch only needs to bear voltage stress, and the main branch bears normal operation current; when the main branch fails to commutate or the AC short circuit is failed, the shutoff valve is turned off, the isolation valve and the upper bridge arm auxiliary commutation valve of the auxiliary branch are turned on, the current of the main branch is transferred to the auxiliary branch, and when the current on the main branch is completely transferred to the auxiliary branch, the upper bridge arm auxiliary commutation valve of the auxiliary branch is turned off, so that forced commutation of the main branch is realized.
Specifically, as shown in fig. 9, the topology structure includes a three-phase main branch and a one-phase auxiliary branch, and the three-phase main branch is of a three-phase six-leg structure, the upper leg main branch is connected in series with the lower leg main branch, and the upper leg auxiliary branch is connected in series with the lower leg auxiliary branch, where six shutoff valves may be set in the topology structure, that is, the upper leg main branch and the lower leg main branch are both provided with a shutoff valve. The connecting ends between the shutoff valves of the main branches of the upper bridge arm of each phase and the shutoff valves of the main branches of the lower bridge arm of each phase are respectively connected with the first ends of the three isolation valves; the connecting end between the upper bridge arm auxiliary branch and the lower bridge arm auxiliary branch is connected with the second end of each isolation valve.
Similar to the concept of fig. 9, in order to precisely control the operation of each main leg, a shutoff valve is provided in both the upper leg main leg and the lower leg main leg of each phase. When the hybrid converter normally operates, the isolation valve is turned off, the auxiliary branch is kept in a turned-off state, the thyristor valve and the turn-off valve of the main branch of the ith bridge arm are turned on, and at the moment, the auxiliary branch only needs to bear voltage stress, and the main branch bears normal operation current; when the main branch fails to commutate or the AC short circuit is failed, the shutoff valve is turned off, the isolation valve and the upper bridge arm auxiliary commutation valve of the auxiliary branch are turned on, the current of the main branch is transferred to the auxiliary branch, and when the current on the main branch is completely transferred to the auxiliary branch, the upper bridge arm auxiliary commutation valve of the auxiliary branch is turned off, so that forced commutation of the main branch is realized. And before or simultaneously starting the thyristor valve of the main branch of the ith bridge arm to be conducted in the next control period, the isolation valve is turned off, and the main branch is independently operated.
Specifically, as shown in fig. 10, the topology structure includes a three-phase main branch and a one-phase auxiliary branch, where the three-phase main branch is of a three-phase six-leg structure, the upper leg main branch is connected in series with the lower leg main branch, and the upper leg auxiliary branch is connected in series with the lower leg auxiliary branch, where two shutoff valves may be set in the topology structure, that is, a shutoff valve is set on each of the upper leg auxiliary branch and the lower leg auxiliary branch. The connecting ends between the shutoff valves of the main branches of the upper bridge arm of each phase and the shutoff valves of the main branches of the lower bridge arm of each phase are respectively connected with the first ends of the three isolation valves; the second end of each isolation valve is connected with the connecting end between the shutoff valve of the upper bridge arm auxiliary branch and the shutoff valve of the lower bridge arm auxiliary branch.
The topology structure of fig. 10 is equivalent to that a turn-off valve is arranged on an auxiliary branch, when the hybrid converter is in normal operation, the isolation valve is turned off, the auxiliary branch is kept in a turn-off state, and a thyristor valve of a main branch of an ith bridge arm is turned on, at the moment, the auxiliary branch only needs to bear voltage stress, and normal operation current is borne by the main branch; when the main branch fails to commutate or the AC short circuit is failed, the isolation valve, the shutoff valve and the upper bridge arm auxiliary commutation valve of the auxiliary branch are turned on, the current of the main branch is transferred to the auxiliary branch, and when the current on the main branch is completely transferred to the auxiliary branch, the shutoff valve and the upper bridge arm auxiliary commutation valve of the auxiliary branch are turned off, so that forced commutation of the main branch is realized. And before or simultaneously starting the thyristor valve of the main branch of the ith bridge arm to be conducted in the next control period, the isolation valve is turned off, and the main branch is independently operated.
Specifically, as shown in fig. 11, the topology structure includes a three-phase main branch and a one-phase auxiliary branch, where the three-phase main branch is of a three-phase six-leg structure, the upper leg main branch is connected in series with the lower leg main branch, and the upper leg auxiliary branch is connected in series with the lower leg auxiliary branch, where a shutoff valve may be disposed in the topology structure, that is, one end of the shutoff valve is connected with the first ends of the three isolation valves, and the other end is connected with the connection ends of the upper leg auxiliary branch and the lower leg auxiliary branch.
When the hybrid converter is in normal operation, the isolation valve and the shutoff valve are turned off, the auxiliary branch is kept in a turned-off state, the thyristor valve of the main branch of the ith bridge arm is turned on, and at the moment, the auxiliary branch only needs to bear voltage stress, and the main branch bears normal operation current; when the main branch fails to commutate or the AC short circuit is failed, the isolation valve, the shutoff valve and the upper bridge arm auxiliary commutation valve of the auxiliary branch are turned on, the current of the main branch is transferred to the auxiliary branch, and when the current on the main branch is completely transferred to the auxiliary branch, the shutoff valve and the upper bridge arm auxiliary commutation valve of the auxiliary branch are turned off, so that forced commutation of the main branch is realized. And before or simultaneously starting the thyristor valve of the main branch of the ith bridge arm to be conducted in the next control period, the isolation valve is turned off, and the main branch is independently operated.
Optionally, the upper leg main leg in fig. 1 to 11 is provided with a first thyristor valve, and the lower leg main leg is provided with a second thyristor valve. Specifically, as shown in fig. 12, the first thyristor valve and the second thyristor valve may each include: at least one controllable device and at least one first auxiliary component, wherein the at least one controllable device is arranged in series, and the at least one first auxiliary component is arranged in parallel with the at least one controllable device respectively, namely the number of the first auxiliary components is equal to the number of the controllable devices. The controllable device is mainly used for reverse voltage blocking, and may include one or more of a thyristor, a GTO and a reverse-resistance IGCT, which is not particularly limited herein.
Alternatively, the shutoff valve in fig. 1 to 11 may include: the power supply comprises at least one first power unit and a second auxiliary component, wherein the first power unit is used for conducting control and switching control of an auxiliary branch, and the second auxiliary component is arranged in parallel with the first power unit.
Specifically, as shown in fig. 13a, the first power unit may be a power electronic unit formed by a first branch, where a first power device is disposed on the first branch. As shown in fig. 13b, the first power unit may be a power electronic unit composed of a second branch and a third branch. At least one first power device is arranged on the second branch, and the at least one first power device is arranged in series; the third branch is identical to the second branch in structure, and the third branch is arranged in parallel with the second branch. As shown in fig. 13c, the first power unit may be a power electronic unit composed of a fourth branch and a fifth branch. The fourth branch is provided with at least one first diode, and the at least one first diode is arranged in series; the fifth branch is identical to the fourth branch in structure, and the fourth branch is arranged in parallel with the fifth branch. As shown in fig. 13d, the first power unit may also be a power electronic unit composed of a sixth branch and a seventh branch. The sixth branch is provided with a first power device; the seventh branch is connected with the sixth branch in parallel, the seventh branch is provided with a first power device and a second auxiliary component, and the first power device and the second auxiliary component are connected in parallel. The first power device is a fully-controlled power electronic device, and the fully-controlled power electronic device may be one or more of IGBT, IGCT, GTO and a MOSFET, which is not limited herein.
Optionally, the upper leg auxiliary branch in fig. 1 to 11 is provided with a first auxiliary reversing valve, and the lower leg auxiliary branch is provided with a second auxiliary reversing valve. The first auxiliary reversing valve and the second auxiliary reversing valve may each include: at least one second power unit and at least one third auxiliary component, and at least one second power unit is connected in series, at least one third auxiliary component is connected in parallel with at least one second power unit, i.e. the number of third auxiliary components is the same as the number of second power devices.
Specifically, as shown in fig. 14a, the second power unit may be a power electronic unit formed by a first connection branch, where the first connection branch is provided with a second power device. As shown in fig. 14b, the second power unit may be a power electronic unit formed by a second connection branch, where at least one second power device is disposed on the second connection branch, and at least one second power device is connected in reverse series. As shown in fig. 14c, the second power unit may be a power electronic unit formed by at least one third connection branch and at least one fourth connection branch, where the third connection branch has the same structure as the first connection branch, and the fourth connection branch is provided with a second diode or a first thyristor, and at least one third connection branch and at least one fourth connection branch are staggered and connected in series. As shown in fig. 14d, the second power unit may be a power electronic unit formed by a fifth connection branch and a sixth connection branch, where at least one second power device is disposed on the fifth connection branch, and at least one second power device is disposed in series, the sixth connection branch has the same structure as the fifth connection branch, and the fifth connection branch and the sixth connection branch are disposed in parallel, and the fifth connection branch, the sixth connection branch, and the third auxiliary component form a full bridge structure. As shown in fig. 14e, the second power unit may be a power electronic unit formed by a seventh connection branch, an eighth connection branch and a ninth connection branch, where at least one third diode is disposed on the seventh connection branch, and at least one third diode is disposed in series, at least one second power device is disposed on the eighth connection branch, and at least one second power device is disposed in series, the ninth connection branch and the seventh connection branch have the same structure, the ninth connection branch, the eighth connection branch and the seventh connection branch are connected in parallel, and the seventh connection branch, the eighth connection branch, the ninth connection branch and the third auxiliary component form an H bridge structure. The second power device is a fully-controlled power electronic device, which may be one or more of IGBT, IGCT, GTO and a MOSFET, and is not limited herein.
Specifically, as shown in fig. 15, the first auxiliary component, the second auxiliary component, and the third auxiliary component may be a first buffer branch composed of a capacitor; a second buffer branch connected in series by a resistor and a capacitor; a third buffer branch connected in parallel by a capacitor and a resistor; the fourth buffer branch RCD1 is formed by connecting a resistor and a fifth diode in parallel and then connecting a capacitor in series; a fifth buffer branch RCD2 formed by connecting a resistor and a capacitor in parallel and connecting a fifth diode in series; the sixth buffer branch is also formed by lightning arresters; the buffer circuit may further include a seventh buffer branch formed by connecting a plurality of the first buffer branch, the second buffer branch, the third buffer branch, the fourth buffer branch, the fifth buffer branch, and the sixth buffer branch in parallel.
According to an embodiment of the present invention, there is provided an embodiment of a control method of a hybrid converter topology, it being noted that the steps shown in the flowchart of the figures may be performed in a computer system such as a set of computer executable instructions, and that although a logical order is shown in the flowchart, in some cases the steps shown or described may be performed in an order different from that shown herein.
In this embodiment, a control method of a hybrid converter topology is provided, which may be used in the above hybrid converter topology, and fig. 16 is a flowchart of a control method of a hybrid converter topology according to an embodiment of the present invention, as shown in fig. 16, where the flowchart includes the following steps:
S11, a main branch and/or a shutoff valve of an ith bridge arm of the topological structure of the hybrid converter are/is conducted.
S12, an auxiliary branch and/or a shutoff valve of an ith bridge arm of the topological structure of the hybrid converter are/is conducted;
S13, an auxiliary branch and/or a shutoff valve of an ith bridge arm of the topological structure of the hybrid converter are/is turned off;
s14, after a control period, the main branch and/or the shutoff valve of the ith bridge arm of the topological structure of the hybrid converter are/is conducted, wherein, 。
Specifically, the hybrid converter topology is subject to voltage and current stresses periodically on the primary leg under normal operating conditions, with the auxiliary leg always in an off state, and is subject to voltage stresses only when the primary leg is off. The auxiliary branch of the ith bridge arm of the hybrid current converter topological structure is kept in an off state, and the main branch and/or the shutoff valve of the ith bridge arm of the hybrid current converter topological structure are/is conducted, so that the hybrid current converter topological structure with forced commutation can work in a normal commutation operation mode, namely in a temporary commutation operation mode, the auxiliary branch is in an off state when the hybrid current converter normally operates, only bears voltage stress, and the increase of the current converter loss in long-term operation is reduced. When commutation failure or alternating current short circuit failure occurs, an auxiliary branch and/or a shutoff valve of an ith bridge arm of the hybrid converter topology structure are/is conducted, current of the main branch is forcedly transferred to the auxiliary branch, and when current transfer is completed, the auxiliary branch and/or the shutoff valve of the ith bridge arm of the hybrid converter topology structure are/is turned off, so that forceful commutation of the hybrid converter is realized. And after a control period, returning to the step of conducting the main branch and/or the shutoff valve of the ith bridge arm of the topological structure of the hybrid converter, and continuously and independently operating normally by the main branch.
The control method of the topological structure of the hybrid converter provided by the embodiment of the invention realizes that the auxiliary branch is only subjected to turn-off voltage stress when in fault, reduces the loss of the device and further prolongs the service life of the device.
For the topology shown in fig. 2, the control method mainly includes the following steps:
s21, a thyristor valve and a shutoff valve of a main branch of an ith bridge arm of the topological structure of the hybrid converter are conducted.
S22, an auxiliary branch of an ith bridge arm of the topological structure of the hybrid converter is conducted.
S23, switching off a shutoff valve of a main branch of an ith bridge arm of the hybrid converter topology.
S24, the auxiliary branch of the ith bridge arm of the topological structure of the hybrid converter is turned off.
S25, after a control period, switching on a thyristor valve and a shutoff valve of a main branch of an ith bridge arm of the topological structure of the hybrid converter, wherein,。
As shown in fig. 17, which shows the valve current flow path of the hybrid converter topology under normal operating conditions, the primary leg is periodically subjected to voltage and current stresses, and the auxiliary leg is always in an off state, and is only subjected to voltage stresses when the thyristor valve of the primary leg is turned off.
Fig. 18a, 18b and 18c show the main branch being switched off and the auxiliary branch beginning to receive voltage stress during the main branch to auxiliary branch commutation, the process being divided into three phases, fig. 18a shows the main branch to auxiliary branch commutation phase, the auxiliary branch receiving a trigger signal to be switched on, the auxiliary branch receiving a switch-on signal, the main branch's shutoff valve receiving a switch-off signal, the main branch's current being diverted to the auxiliary branch, and the main branch being applied with a reverse voltage; FIG. 18b is a secondary leg current flow stage in which the primary leg has been fully turned off and the primary leg current has been fully diverted to the secondary leg; fig. 18c shows a secondary branch off phase, which turns off the secondary branch when receiving the off signal, and the primary branch is in an off state and is subject to voltage. The turn-off valve is turned on before or simultaneously with the turn-on of the thyristor valve of the main branch of the next control cycle. The operation process can be put into operation when the commutation failure or the predicted commutation failure occurs.
Fig. 19 is a timing diagram of trigger control of a hybrid converter topology in the event of commutation failure or ac short circuit failure. In fig. 19, after the commutation failure of the main branch is monitored at time t f, the valve of the auxiliary branch V13 is turned on when the first preset time period Δt 1 passes, the valve of the main branch is turned off when the second preset time period Δt 2 passes, the process of commutating the main branch to the auxiliary branch is performed, and Δt 2≥Δt1 is equal to or greater than 0. The main branch current I11 gradually decreases to zero, the auxiliary branch current I12 gradually increases, the auxiliary branch is turned off after a third preset time period Deltat 3, the time from zero crossing of the main branch current I11 to the turning-off of the auxiliary branch is the turn-off time t off of the thyristor valve, and t off is larger than the minimum turn-off time of the thyristor valve to ensure that the thyristor valve of the main branch has enough time to turn off. After the auxiliary branch is turned off, the current of the auxiliary branch commutates to the adjacent main branch until the current I12 reaches, so as to finish the commutation of the main branch, successfully resist commutation failure faults, and then conduct the turn-off valve of the main branch before or simultaneously with the turn-on of the thyristor valve of the next control period. When the commutation failure is predicted to occur or the commutation failure is detected to occur, the operation mode is started, the commutation failure can be successfully avoided, the operation mode is stopped when the commutation process of the converter is recovered to be normal, the auxiliary branch is kept in a cut-off state, and the main branch independently and normally operates.
According to the control method for forced commutation, when commutation fails or a short circuit fails, the topological structure of the hybrid current converter is controlled to start the operation mode of forced commutation, the occurrence of commutation failure is avoided, the operation mode of forced commutation is exited when the commutation process of the hybrid current converter is recovered to be normal, the auxiliary branch is kept in the off state, and the main branch is independently and normally operated, so that the auxiliary branch is guaranteed to bear the off voltage stress only when the fault occurs, the loss of a device is reduced, and the service life of the device is prolonged.
Fig. 20 shows a control trigger timing when a hybrid converter topology detects a commutation failure or a short-circuit failure in advance, where a main leg and an auxiliary leg periodically operate alternately. The specific operation is shown in fig. 18a, 18b and 18 c. And at the starting moment of the commutation of the main branch, namely the time delay of the thyristor valve trigger pulse Sg1 of the main branch is 120 degrees, or the auxiliary branch is triggered nearby the starting moment, and the shutoff valve of the main branch is turned off in a short time (such as 1s, 5s and the like), so that the commutation from the main branch to the auxiliary branch is realized. After the current of the main branch crosses zero, the main branch is turned off and bears reverse voltage, the time from the zero crossing of the current of the main branch to the turn-off of the auxiliary branch is the turn-off time t off of the thyristor valve, and the time t off is larger than the minimum turn-off time of the thyristor valve to ensure the reliable turn-off, so far, the current of the V1 valve is completely transferred to the auxiliary branch, the auxiliary branch valve starts to be turned off after the current of the delta t, the main branch starts to bear forward voltage, and then the turn-off valve of the main branch is turned on before the thyristor valve of the main branch is turned on in the next working cycle. In the operation mode, the main branch and the auxiliary branch in the bridge arm of the topological structure of the hybrid current converter periodically run alternately, so that the prediction of commutation failure is not needed on the basis of the capability of resisting the commutation failure, and meanwhile, the hybrid current converter can be in a small-turn-off angle operation mode, and reactive power consumption of the hybrid current converter is reduced.
For the topology shown in fig. 3, the control method mainly includes the following steps:
s31, the main branch of the ith bridge arm of the topological structure of the hybrid converter is conducted.
S32, an auxiliary branch and a shutoff valve of an ith bridge arm of the topological structure of the hybrid converter are conducted.
S33, an auxiliary branch and a shutoff valve of an ith bridge arm of the hybrid converter topological structure are turned off.
S34, after a control period, the main branch of the ith bridge arm of the topological structure of the hybrid converter is conducted, wherein,。
Specifically, as shown in fig. 21, which shows the current flow path of the hybrid converter topology under normal operation conditions, the main branch is periodically subjected to voltage and current stress, and the auxiliary branch is always in an off state, and is only subjected to voltage stress when the thyristor valve of the main branch is turned off.
Fig. 22 is a trigger control timing of the hybrid converter topology, where t0 represents an initial trigger time.
23A, 23b and 23c are the main branch to auxiliary branch commutation, the auxiliary branch starts to bear voltage stress, the process is divided into three stages, FIG. 23a is the main branch to auxiliary branch commutation stage, the auxiliary branch receives the trigger signal to conduct, the turn-off valve arranged on the auxiliary branch receives the turn-on signal, reverse voltage is applied to the main branch, and the current of the main branch is transferred to the auxiliary branch; FIG. 23b shows a secondary leg current flow stage in which the primary leg has been fully turned off and the primary leg current is fully diverted to the secondary leg; fig. 23c shows an auxiliary branch off phase, in which, when receiving the off signal, the upper bridge arm auxiliary phase-change valve of the auxiliary branch is turned off first, and the main branch is in an off state for bearing the forward voltage, and then the turn-off valve is turned off before the thyristor valve of the main branch is turned on in the next control period. The operation process can be put into operation when the commutation failure or the predicted commutation failure occurs.
Fig. 24 shows control trigger sequences when a forced commutation hybrid converter topology detects commutation failure or short-circuit failure in advance, and each valve control trigger sequence when the main branch and the auxiliary branch periodically operate alternately, and the specific operation process is shown in fig. 23a, 23b and 23 c. In the operation mode, the main branch and the auxiliary branch in the bridge arm of the topological structure of the hybrid converter with forced commutation periodically run alternately, so that the hybrid converter can be in a small turn-off angle operation mode without predicting commutation failure on the basis of having the capability of resisting commutation failure, and reactive power consumption of the hybrid converter is reduced.
Based on the control method described above, for the topology shown in fig. 5, its normal operation mode is shown in fig. 25. Fig. 26 is a trigger control timing of the hybrid converter topology, where t0 represents an initial trigger time. Fig. 27a, 27b and 27c illustrate the main branch to auxiliary branch commutation process. Fig. 28 shows the control trigger timing of each valve when the main branch and the auxiliary branch are periodically operated alternately, and the specific operation process is shown in fig. 27a, 27b and 27c.
The control method of the topology structure shown in fig. 4 is similar to that of the topology structure shown in fig. 5, and will not be repeated here.
Based on the control method described above, fig. 29 shows a trigger control sequence of the hybrid converter topology for the topology shown in fig. 6, where t0 represents an initial trigger time. Fig. 30a, 30b and 30c illustrate the main branch to auxiliary branch commutation process. Fig. 31 shows the valve control trigger sequences of the main branch and the auxiliary branch in periodic alternate operation, and the specific operation process is shown in fig. 30a, 30b and 30c.
Based on the above control method, for the topology shown in fig. 8, fig. 32 is a trigger control timing sequence of the hybrid converter topology, where t0 represents an initial trigger time. Fig. 33a, 33b and 33c are the main branch to auxiliary branch commutation process. Fig. 34 shows the control trigger timing of each valve when the main branch and the auxiliary branch are periodically operated alternately, and the specific operation process is shown in fig. 33a, 33b and 33c.
The control method of the topology structure shown in fig. 9 and 10 is similar to that of the topology structure shown in fig. 8, and will not be described again.
Based on the above control method, for the topology shown in fig. 11, fig. 35 is a trigger control timing sequence of the hybrid converter topology, where t0 represents an initial trigger time. Fig. 36a, 36b and 36c illustrate the main leg to auxiliary leg commutation process. Fig. 37 shows the control trigger timing of each valve when the main branch and the auxiliary branch are periodically operated alternately, and the specific operation process is shown in fig. 36a, 36b and 36c.
The control method of the hybrid topology structure has the same conception, and the auxiliary branch is kept in the off state in the normal running state, and the main branch is used for independent work. And when the main branch fails to commutate or the AC short circuit fails, the auxiliary branch is started to assist the main branch to commutate, so that commutation failure is avoided.
Although embodiments of the present invention have been described in connection with the accompanying drawings, various modifications and variations may be made by those skilled in the art without departing from the spirit and scope of the invention, and such modifications and variations fall within the scope of the invention as defined by the appended claims.

Claims (14)

1. A hybrid converter topology for accessing an ac power grid through a converter transformer, the topology comprising:
Each phase of main branch comprises an upper bridge arm main branch and a lower bridge arm main branch, a first thyristor valve is arranged on the upper bridge arm main branch, and a second thyristor valve is arranged on the lower bridge arm main branch; one end of the main branch is connected with a direct current bus, and the other end of the main branch is connected with the output end of the converter transformer;
Each phase of auxiliary branch comprises an upper bridge arm auxiliary branch and a lower bridge arm auxiliary branch, a first auxiliary reversing valve is arranged on the upper bridge arm auxiliary branch, and a second auxiliary reversing valve is arranged on the lower bridge arm auxiliary branch; the auxiliary branch is connected with the main branch in parallel and is used for assisting the main branch in forced commutation when the main branch fails in commutation;
the shutoff valve is arranged on the main branch or the auxiliary branch and is used for transferring the current of the main branch to the auxiliary branch when the phase is forcedly changed;
At least one isolation valve disposed on the ac bus for isolating a voltage between the main branch and the auxiliary branch;
the first thyristor valve and the second thyristor valve each include: at least one controllable device for reverse voltage blocking, the at least one controllable device being arranged in series; at least one first auxiliary component arranged in parallel with the at least one controllable device; the controllable device comprises one or more of a thyristor, a GTO and a reverse resistance IGCT;
the shutoff valve includes: at least one first power unit for on-control and off-control of the auxiliary branch; a second auxiliary component arranged in parallel with the first power unit;
the first auxiliary reversing valve and the second auxiliary reversing valve include: at least one second power cell, the at least one second power cell being in series; at least one third auxiliary component is connected in parallel with the at least one second power unit.
2. The topology of claim 1, wherein said upper leg auxiliary leg is connected in parallel with said upper leg main leg, and said lower leg auxiliary leg is connected in parallel with said lower leg main leg;
The shutoff valves are arranged on the main branch of the upper bridge arm of each phase and the main branch of the lower bridge arm of each phase; one end of the shutoff valve arranged on the main leg of the upper bridge arm is connected with the first thyristor valve, and the other end of the shutoff valve is connected with the output end of the converter transformer; one end of the shutoff valve arranged on the main leg of the lower bridge arm is connected with the second thyristor valve, and the other end of the shutoff valve is connected with the negative electrode of the direct current bus.
3. The topology of claim 1, wherein said upper leg auxiliary leg is connected in parallel with said upper leg main leg, and said lower leg auxiliary leg is connected in parallel with said lower leg main leg;
the shutoff valve is respectively arranged on the upper bridge arm auxiliary branch and the lower bridge arm auxiliary branch; one end of the shutoff valve arranged on the upper bridge arm auxiliary branch is connected with the first auxiliary reversing valve, and the other end of the shutoff valve is connected with the output end of the converter transformer; one end of the shutoff valve arranged on the lower bridge arm auxiliary branch is connected with the second auxiliary reversing valve, and the other end of the shutoff valve is connected with the negative electrode of the direct current bus.
4. The topology of claim 1, wherein said upper leg main leg and lower leg main leg are connected in series; the upper bridge arm auxiliary branch is connected in series with the lower bridge arm auxiliary branch;
One end of the shutoff valve is connected with the connecting ends of the upper bridge arm main branch and the lower bridge arm main branch, and the other end of the shutoff valve is connected with the output end of the converter transformer; and the connecting ends of the upper bridge arm auxiliary branch and the lower bridge arm auxiliary branch are connected with the output end of the converter transformer.
5. The topology of claim 1, wherein said upper leg main leg and lower leg main leg are connected in series; the upper bridge arm auxiliary branch is connected in series with the lower bridge arm auxiliary branch;
one end of the shutoff valve is connected with the connecting ends of the upper bridge arm auxiliary branch and the lower bridge arm auxiliary branch, and the other end of the shutoff valve is connected with the output end of the converter transformer; and the connecting ends of the upper bridge arm main branch and the lower bridge arm main branch are connected with the output end of the converter transformer.
6. The topology of claim 1, wherein the topology comprises two shutoff valves, the upper leg main leg and lower leg main leg being connected in series; the upper bridge arm auxiliary branch is connected in series with the lower bridge arm auxiliary branch;
one end of the first shutoff valve is connected with the main branch of each phase of upper bridge arm, and the other end of the first shutoff valve is connected with the auxiliary branch of each phase of upper bridge arm;
One end of the second shutoff valve is connected with the main branch of the lower bridge arm of each phase, and the other end of the second shutoff valve is connected with the auxiliary branch of the lower bridge arm of each phase.
7. The topology of claim 1, wherein a first end of said at least one isolation valve is connected to a connection end of each phase upper leg main leg and each phase lower leg main leg, respectively, and a second end is connected to a connection end of said upper leg auxiliary leg and said lower leg auxiliary leg;
The topological structure comprises two shutoff valves, and the main branch of the upper bridge arm and the main branch of the lower bridge arm are connected in series; the upper bridge arm auxiliary branch is connected in series with the lower bridge arm auxiliary branch;
one end of the first shutoff valve is connected with the main branch of each phase of upper bridge arm, and the other end of the first shutoff valve is connected with the auxiliary branch of each phase of upper bridge arm;
One end of the second shutoff valve is connected with the main branch of the lower bridge arm, and the other end of the second shutoff valve is connected with the auxiliary branch of the lower bridge arm.
8. The topology of claim 1, wherein said upper leg main leg and lower leg main leg are connected in series; the upper bridge arm auxiliary branch is connected in series with the lower bridge arm auxiliary branch;
The upper bridge arm main branch and the lower bridge arm main branch are respectively provided with the shutoff valve; the connecting end between the shutoff valve of the main branch of the upper bridge arm of each phase and the shutoff valve of the main branch of the lower bridge arm of each phase is connected with the first end of the isolation valve; and the connecting end between the upper bridge arm auxiliary branch and the lower bridge arm auxiliary branch is connected with the second end of each isolation valve.
9. The topology of claim 1, wherein said upper leg main leg and lower leg main leg are connected in series; the upper bridge arm auxiliary branch is connected in series with the lower bridge arm auxiliary branch;
The upper bridge arm auxiliary branch and the lower bridge arm auxiliary branch are respectively provided with the shutoff valves, and the connection end between the shutoff valves of the upper bridge arm auxiliary branch and the lower bridge arm auxiliary branch is connected with the second end of the at least one isolation valve.
10. The topology of claim 1, wherein said upper leg main leg and lower leg main leg are connected in series; the upper bridge arm auxiliary branch is connected in series with the lower bridge arm auxiliary branch;
One end of the shutoff valve is connected with the first end of the at least one isolation valve, and the other end of the shutoff valve is connected with the connecting ends of the upper bridge arm auxiliary branch and the lower bridge arm auxiliary branch.
11. The topology of claim 1, wherein said first power cell comprises:
The first branch circuit is provided with a first power device;
or, a second leg and a third leg; at least one first power device is arranged on the second branch, and the at least one first power device is arranged in series; the third branch is identical to the second branch in structure, and the third branch is arranged in parallel with the second branch;
or, a fourth branch and a fifth branch; the fourth branch is provided with at least one first diode, and the at least one first diode is arranged in series; the fifth branch is identical to the fourth branch in structure, and the fourth branch is arranged in parallel with the fifth branch;
Or, a sixth branch and a seventh branch; the sixth branch is provided with the first power device; the seventh branch is provided with the first power device and the second auxiliary component, and the first power device and the second auxiliary component are connected in parallel; the sixth branch is arranged in parallel with the seventh branch.
12. The topology of claim 1, wherein said second power cell comprises:
the first connecting branch is provided with a second power device;
or, a second connection leg; at least one second power device is arranged on the second connecting branch, and the at least one second power device is connected in reverse series;
or, at least one third connection leg and at least one fourth connection leg; the third connecting branch is identical to the first connecting branch in structure, and the fourth connecting branch is provided with a second diode or a first thyristor; the at least one third connecting branch and the at least one fourth connecting branch are arranged in staggered series;
Or, a fifth connection leg and a sixth connection leg; at least one second power device is arranged on the fifth connecting branch, and the at least one second power device is arranged in series; the sixth connecting branch is identical to the fifth connecting branch in structure, and the fifth connecting branch is arranged in parallel with the sixth connecting branch; the fifth connecting branch, the sixth connecting branch and the third auxiliary component form a full-bridge structure;
Or, a seventh connection leg, an eighth connection leg, and a ninth connection leg; wherein, the seventh connecting branch is provided with at least one third diode, and the at least one third diode is arranged in series; at least one second power device is arranged on the eighth connecting branch, and the at least one second power device is arranged in series; the ninth connecting branch is identical to the seventh connecting branch in structure, and the ninth connecting branch is connected in parallel with the eighth connecting branch and the seventh connecting branch; the seventh connecting branch, the eighth connecting branch, the ninth connecting branch and the third auxiliary component form an H-bridge structure.
13. The topology of claim 1, wherein the first auxiliary component, the second auxiliary component, and the third auxiliary component comprise:
a first buffer branch composed of capacitors;
or, a second buffer branch with a resistor and a capacitor connected in series;
Or, a third buffer branch with a capacitor and a resistor connected in parallel;
or, the resistor is connected in parallel with the fifth diode and then connected in series with the capacitor to form a fourth buffer branch;
Or, the resistor and the capacitor are connected in parallel and then connected in series with a fifth diode to form a fifth buffer branch;
Or a sixth buffer branch consisting of lightning arresters;
Or, a seventh buffer branch formed by multiple parallel connection of the first buffer branch, the second buffer branch, the third buffer branch, the fourth buffer branch, the fifth buffer branch and the sixth buffer branch.
14. A method of controlling a hybrid converter topology according to any of claims 1-13, comprising the steps of:
the main branch and/or the shutoff valve of the ith bridge arm of the topological structure of the hybrid converter are/is conducted;
An auxiliary branch and/or a turn-off valve of an ith bridge arm of the topological structure of the hybrid converter are/is conducted;
the auxiliary branch and/or the shutoff valve of the ith bridge arm of the topological structure of the hybrid converter are/is shut down;
After a control period, the main branch and/or the shutoff valve of the ith bridge arm of the topological structure of the hybrid converter are/is conducted, wherein, ；
The main branch and the auxiliary branch of the topological structure of the hybrid converter periodically and alternately operate.
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