CN114257104B - Active commutation unit and forced commutation hybrid converter topology - Google Patents
Active commutation unit and forced commutation hybrid converter topology Download PDFInfo
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- CN114257104B CN114257104B CN202111651615.7A CN202111651615A CN114257104B CN 114257104 B CN114257104 B CN 114257104B CN 202111651615 A CN202111651615 A CN 202111651615A CN 114257104 B CN114257104 B CN 114257104B
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- 238000006243 chemical reaction Methods 0.000 description 4
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Classifications
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- 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
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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
- 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
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- 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
- H02M7/66—Conversion of AC power input into DC power output; Conversion of DC power input into AC power output with possibility of reversal
- H02M7/68—Conversion of AC power input into DC power output; Conversion of DC power input into AC power output with possibility of reversal by static converters
- H02M7/72—Conversion of AC power input into DC power output; Conversion of DC power input into AC power output with possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/75—Conversion of AC power input into DC power output; Conversion of DC power input into AC power output with 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
- H02M7/757—Conversion of AC power input into DC power output; Conversion of DC power input into AC power output with 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
- H02M7/7575—Conversion of AC power input into DC power output; Conversion of DC power input into AC power output with 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 for high voltage direct transmission link
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- 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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Abstract
本发明公开了一种主动换相单元以及强迫换相的混合式换流器拓扑结构，其中，主动换相单元设置在换流器的桥臂电路中，其一端连接换流变压器的输出端，另一端连接直流母线，该主动换相单元包括：主支路，该主支路上设置有晶闸管阀；辅助支路，与主支路并联设置，该辅助支路上设置有第一控制阀，且第一控制阀具备正向电流可控关断和正反向电压阻断功能；第二控制阀，与晶闸管阀连接或与第一控制阀连接，该第二控制阀用于将电流从主支路转移至辅助支路，第二控制阀包括至少一个功率单元，且该功率单元用于正向电流的可控关断以及正反向电压的可控阻断。通过实施本发明，实现各个桥臂的主动换相，避免换相失败，保障了电网的稳定安全运行。
The present invention discloses a hybrid converter topology structure of an active commutation unit and forced commutation, wherein the active commutation unit is arranged in the bridge arm circuit of the converter, one end of which is connected to the output end of the converter transformer, and the other end is connected to the DC bus, and the active commutation unit comprises: a main branch, on which a thyristor valve is arranged; an auxiliary branch, which is arranged in parallel with the main branch, on which a first control valve is arranged, and the first control valve has the functions of controllable shutdown of forward current and blocking of forward and reverse voltages; a second control valve, which is connected to the thyristor valve or the first control valve, and the second control valve is used to transfer current from the main branch to the auxiliary branch, and the second control valve comprises at least one power unit, and the power unit is used for controllable shutdown of forward current and controllable blocking of forward and reverse voltages. By implementing the present invention, active commutation of each bridge arm is realized, commutation failure is avoided, and stable and safe operation of the power grid is guaranteed.
Description
Technical Field
The invention relates to the technical field of commutation in power electronics, in particular to an active commutation unit and a forced commutation hybrid converter topological structure.
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.
At present, a capacitive commutation converter or a hybrid converter formed by connecting a turn-off device and a thyristor in series is generally adopted to realize the conversion of alternating current and direct current electric energy. The capacitor phase-change converter is characterized in that the valve phase-change voltage time area is increased through capacitor voltage to ensure reliable turn-off, but a controllable capacitor module is formed by combining a power electronic switch and a capacitor to realize controllable capacitor input and voltage direction, a single-stage capacitor is required to take a larger value to ensure reliable phase change, so that the voltage and current stress of a thyristor which is a core component is increased, the realization difficulty of the topological structure engineering is higher, and a hybrid converter is formed by connecting a turn-off device and the thyristor in series, so that each bridge arm of the converter has turn-off capability, the occurrence of phase-change failure is avoided, and because of the large transmission capacity of conventional direct current transmission, each bridge arm of the converter bears high voltage and high current, and the realization cost and difficulty are higher. 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 an active commutation unit and a hybrid converter topology structure for forced commutation, so as to solve the problem that the stable operation of a power grid is affected due to commutation failure.
According to a first aspect, an embodiment of the invention provides an active commutation unit, which is arranged in a bridge arm circuit of a converter, one end of the active commutation unit is connected with an output end of the converter transformer, the other end of the active commutation unit is connected with a direct current bus, the active commutation unit comprises a main branch, an auxiliary branch, a first control valve and a second control valve, the main branch is provided with a thyristor valve of the main branch, the auxiliary branch is provided with a forward current controllable turn-off function and a forward and reverse voltage blocking function, the second control valve is connected with the thyristor valve of the main branch or the first control valve of the auxiliary branch, the second control valve is used for transferring current from the main branch to the auxiliary branch, and the second control valve comprises at least one power unit, and the power unit is used for controllable turn-off of forward current and controllable blocking of forward and reverse voltage.
With reference to the first aspect, in a first implementation manner of the first aspect, the power unit includes a third branch, a first power device and a first diode are arranged on the first branch, the first power device is connected in series with the first diode, a second branch, the second branch is connected in parallel with the first branch, the second branch includes at least one first capacitor, the at least one first capacitor is connected in series, a third branch is connected in parallel with the first branch and the second branch respectively, a second power device and a first resistor are arranged on the third branch, the second power device is connected in series with the first resistor, and the first power device and the second power device are all power electronic devices with a turn-off function.
With reference to the first aspect, in a second implementation manner of the first aspect, the power unit includes a fourth branch, a fifth branch and a fifth branch, wherein a first inductance element or a transformer is arranged on the fourth branch, the fifth branch is arranged in parallel with the fourth branch, the fifth branch includes a discharge switch, a second capacitor and a first charging circuit, the discharge switch is arranged in series with the second capacitor, and the charging circuit is arranged in parallel with the second capacitor.
With reference to the first aspect, in a third implementation manner of the first aspect, the power unit includes a sixth branch including at least one third power device, where the at least one third power device is disposed in series, a seventh branch having a structure identical to that of the sixth branch, and disposed in parallel with the sixth branch, and the third power device is a power electronic device with a shutdown function.
With reference to the first aspect, in a fourth implementation manner of the first aspect, the power unit includes an eighth branch including at least one first sub-branch, where the at least one first sub-branch is arranged in series, the first sub-branch includes a fourth power device arranged in parallel and a third capacitor or a second resistor, and the fourth power device is a power electronic device with a shutdown function.
With reference to the first aspect, in a fifth implementation manner of the first aspect, the power unit includes a ninth branch including at least one branch including a second sub-branch, a third sub-branch and a fourth capacitor or a third resistor, at least one of the branches is disposed in series, wherein the second sub-branch includes a fifth power device and a sixth power device disposed in series, a first end of the fifth power device is connected to a first end of the sixth power device, the third sub-branch includes a seventh power device and an eighth power device disposed in series, a second end of the seventh power device is connected to a second end of the eighth power device, one end of the fourth capacitor or the third resistor is connected between the fifth power device and the sixth power device, and one end of the fourth capacitor or the third resistor is connected between the seventh power device and the eighth power device, and the fifth power device, the sixth power device, the seventh power device and the eighth power device are power electronic devices with a turn-off function.
With reference to the first aspect, in a sixth implementation manner of the first aspect, the power unit includes a tenth branch, a ninth power device is disposed on the tenth branch, an eleventh branch is disposed in parallel with the tenth branch, the eleventh branch includes a tenth power device, a second inductor, a fifth capacitor and a second charging circuit, the tenth power device, the second inductor and the fifth capacitor are disposed in series, the second charging circuit is disposed in parallel with the fifth capacitor, and the ninth power device and the tenth power device are power electronic devices with a turn-off function.
With reference to the first aspect or any one of the first to sixth embodiments of the first aspect, in a seventh embodiment of the first aspect, the second control valve further includes at least one buffer component, where the buffer component is disposed in parallel in the power device, and the buffer component includes a first buffer branch composed of a sixth capacitor, or a second buffer branch composed of a fourth resistor and a seventh capacitor in series, or a third buffer branch composed of the fourth resistor and the seventh capacitor in parallel, or a fourth buffer branch composed of a fifth resistor and a third diode in parallel and then in series with an eighth capacitor, or a fifth buffer branch composed of a sixth resistor and a ninth capacitor in parallel and then in series with a fourth diode, or a sixth buffer branch composed of a lightning arrester, or a seventh buffer branch composed of 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 a second aspect, an embodiment of the present invention provides a hybrid converter topology with forced commutation, where the topology is connected to an ac power grid through a converter transformer, and the topology includes three-phase six-leg circuits, where each phase leg includes an upper leg and a lower leg, and at least one upper leg or lower leg is provided with an active commutation unit according to the first aspect or any embodiment of the first aspect.
The technical scheme of the invention has the following advantages:
1. The active phase-change unit comprises a main branch and an auxiliary branch which are connected in parallel, and a second control valve arranged on the main branch or the auxiliary branch, wherein the main branch is provided with a thyristor valve, the auxiliary branch is provided with a first control valve with forward and reverse voltage blocking capability, the second control valve is connected with the thyristor valve or the first control valve, and the active phase-change unit comprises at least one power unit which is used for controllable turn-off of forward current and blocking of forward and reverse voltage, so that the second control valve has unidirectional voltage output or unidirectional controllable turn-off capability, the second control valve is guaranteed to have larger current passing capability and bear normal running current, and the current is transferred from the main branch to the auxiliary branch through the second control valve. The active commutation unit controls the forward turn-off voltage through the second control valve to prolong the reverse recovery time of the main branch thyristor valve, so that the main branch thyristor valve is ensured to be reliably turned off, the active commutation of each bridge arm is further realized, the commutation failure is avoided, and the stable and safe operation of the power grid is ensured.
2. The embodiment of the invention provides a forced commutation hybrid converter topological structure, which comprises a three-phase six-leg circuit, wherein each phase leg comprises an upper leg and a lower leg, and at least one upper leg or lower leg is provided with an active commutation unit. The second control valve in the active phase-change unit can switch off the main branch current in advance and provide reverse voltage, so that the phase-change voltage-time area of the main branch thyristor valve is increased, the reliable switch-off of the main branch thyristor valve is ensured, the problem of phase-change failure is avoided, and the stable and safe operation of a power grid is ensured.
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. 1 is a block diagram of an active commutation cell according to an embodiment of the present invention;
FIG. 2 is another block diagram of the second control valve of an embodiment of the present invention;
FIG. 3 is another block diagram of the second control valve of an embodiment of the present invention;
FIG. 4 is another block diagram of the second control valve of an embodiment of the present invention;
FIG. 5 is another block diagram of the second control valve of an embodiment of the present invention;
FIG. 6 is another block diagram of the second control valve of an embodiment of the present invention;
FIG. 7 is another block diagram of the second control valve of an embodiment of the present invention;
FIG. 8 is another block diagram of a second control valve according to an embodiment of the present invention;
FIG. 9 is another block diagram of the second control valve of the embodiment of the present invention;
FIG. 10 is another block diagram of the second control valve of the embodiment of the present invention;
FIG. 11 is a block diagram of the structure of a cushioning component of an embodiment of the present invention;
fig. 12 is a block diagram of a thyristor valve according to an embodiment of the invention;
FIG. 13 is a block diagram of a first control valve according to an embodiment of the present invention;
Fig. 14 is a topology of a forced commutation hybrid inverter according to an embodiment of the invention;
Fig. 15 is another topology of a forced commutation hybrid converter in accordance with an embodiment of the present invention;
Fig. 16 is another topology of a forced commutation hybrid converter in accordance with an embodiment of the invention;
fig. 17 is a current flow path in a normal operation state of the embodiment of the present invention;
FIG. 18 is a trigger control sequence for a normal operating condition of an embodiment of the present invention;
FIG. 19 is a schematic diagram of the current path of the main leg commutating to the auxiliary leg according to an embodiment of the present invention;
FIG. 20 is a trigger control sequence for a commutation failure or short circuit fault in accordance with an embodiment of the present invention;
Fig. 21 is a control trigger timing of detecting commutation failure or short-circuit failure in advance according to an embodiment of the present invention.
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 utilizes the advantages that the thyristor, the first control valve and the second control valve can be turned off, adopts two branches to be connected in parallel, can provide reverse voltage and an auxiliary branch with self-turn-off capability on the basis of the main branch to realize reliable turn-off of the main branch and active phase change of the whole bridge arm, thereby realizing the auxiliary phase change function in a short time, avoiding phase change failure and ensuring stable and safe operation of the power grid.
According to an embodiment of the present invention, an embodiment of an active commutation cell is provided, which is arranged in a bridge arm circuit of a converter. One end of the active phase-change unit is connected with the output end of the converter transformer, and the other end of the active phase-change unit is connected with the direct current bus, as shown in figure 1, and the active phase-change unit comprises a main branch and an auxiliary branch. Wherein the main branch is provided with a thyristor valve V11, as shown in fig. 12, the thyristor valve V11 comprises at least one thyristor and a buffer member connected in parallel or in series with the thyristor, respectively, wherein the at least one thyristor is arranged in series, and the buffer member is used for the thyristor device to be protected from being damaged by high voltage and high current.
The auxiliary branch is connected with the main branch in parallel, a first control valve V13 is arranged on the auxiliary branch along the direction from the output end of the converter transformer to the direct current bus, and the first control valve V13 has a forward current controllable turn-off function and a forward and reverse voltage blocking function. As shown in fig. 13, the first control valve V13 includes a power device and a thyristor that are arranged in series, where the thyristor has a reverse blocking function, the power device has a controllable turn-off function of forward current and a blocking function of forward and reverse voltage, and the power device is a power electronic device having a turn-off function, and the power electronic device is one or more of a IGBT, IGCT, IEGT, GTO or MOSFET or other turn-off devices.
The first control valve V13 is a high-voltage shutoff valve, and of course, the first control valve V13 may also be a series connection of a plurality of power devices and thyristors, so long as the topology form of the function of controllably shutting off forward current and blocking forward and reverse voltage can be realized, and the topology form of the first control valve V13 is not limited in the present application.
The second control valve V12 can be connected with the thyristor valve V11 of the main branch, and can also be connected with the first control valve V13 on the auxiliary branch, and the second control valve V12 comprises at least one power unit 11, wherein the power unit 11 is used for controllably switching off forward current and blocking forward and reverse voltage, so that the first control valve V12 has a unidirectional voltage output controllable switching-off function. The second control valve V12 may be a low-voltage shutoff valve with unidirectional voltage controllable output capability or unidirectional controllable shutoff function, and is configured to shut off the main branch current and provide a reverse voltage for the main branch current, so as to ensure that the thyristor valve of the main branch has enough shutoff time to perform reliable shutoff.
The active phase-change unit provided by the embodiment comprises a main branch and an auxiliary branch which are connected in parallel, and a second control valve arranged on the main branch or the auxiliary branch, wherein the main branch is provided with a thyristor valve, the auxiliary branch is provided with a first control valve with forward and reverse voltage blocking capability, the second control valve is connected with the thyristor valve of the main branch or the first control valve of the auxiliary branch, the active phase-change unit comprises at least one power unit, and the power unit is used for controllable turn-off of forward current and blocking of forward and reverse voltage, so that the second control valve has unidirectional voltage output or unidirectional controllable turn-off capability, the second control valve is guaranteed to have larger current passing capability and bear normal running current, and the current is transferred from the main branch to the auxiliary branch through the second control valve. The active commutation unit controls the forward turn-off voltage through the second control valve to prolong the reverse recovery time of the main branch thyristor valve, so that the main branch thyristor valve is ensured to be reliably turned off, the active commutation of each bridge arm is further realized, the commutation failure is avoided, and the stable and safe operation of the power grid is ensured.
Alternatively, as shown in fig. 2, the power unit 11 may be a power electronic unit composed of a first branch, a second branch, and a third branch.
The first branch is provided with a first power device W1 and a first diode D1, and the first power device W1 and the first diode D1 are arranged in series. The first power device W1 is a power electronic device with a turn-off function, and the power electronic device is one or more of IGBT, IGCT, IEGT, GTO or MOSFET or other turn-off devices. The second branch is connected with the third branch in parallel, and at least one first capacitor C1 is arranged on the second branch, wherein the at least one first capacitor C1 is arranged in series. And the third branch is respectively connected with the first branch and the second branch in parallel, and is provided with a second power device W2 and a first resistor R1, and the second power device W2 and the first resistor R1 are connected in series. The second power device W2 is a power electronic device with a turn-off function, and the power electronic device is one or more of IGBT, IGCT, IEGT, GTO or MOSFET and other turn-off devices.
Alternatively, as shown in fig. 3, the power unit 11 may be a power electronic unit composed of a fourth branch and a fifth branch.
The fourth branch is provided with a first inductance element L1, the fifth branch is connected with the fourth branch in parallel, the fifth branch is provided with a discharge switch K1, a second capacitor C2 and a first charging circuit P1, the discharge switch K1 is connected with the second capacitor C2 in series, and the charging circuit P1 is connected with the second capacitor C2 in parallel. As shown in fig. 3, the discharge switch K1 is composed of a thyristor and a diode, one end of the first inductance element L1 is connected to the anode of the thyristor and the cathode of the diode, the other end of the first inductance element L1 is connected to one end of the second capacitance C2, and the other end of the second capacitance C2 is connected to the cathode of the thyristor and the anode of the diode.
Alternatively, as shown in fig. 4, the power unit 11 may be a power electronic unit composed of a fourth branch and a fifth branch.
The transformer B1 is arranged on the fourth branch, the fifth branch and the fourth branch are arranged in parallel, the discharge switch K1, the second capacitor C2 and the first charging circuit P1 are arranged on the fifth branch, the discharge switch K1 and the second capacitor C2 are arranged in series, and the charging circuit P1 and the second capacitor C2 are arranged in parallel. As shown in fig. 4, the discharge switch K1 is composed of a thyristor and a diode, one end of the transformer B1 is connected to the anode of the thyristor and the cathode of the diode, the other end of the transformer B1 is connected to one end of the second capacitor C2, and the other end of the second capacitor C2 is connected to the cathode of the thyristor and the anode of the diode.
Alternatively, as shown in fig. 5, the power unit 11 may be a power electronic unit composed of a sixth branch and a seventh branch.
At least one third power device W3 is disposed on the sixth branch, and at least one third power device W3 is disposed in series, where the third power device W3 is a power electronic device with a turn-off function, and the power electronic device is one or more of IGBT, IGCT, IEGT, GTO or MOSFET devices that can be turned off. The seventh branch is identical to the sixth branch in structure, and the seventh branch is arranged in parallel with the sixth branch.
Alternatively, as shown in fig. 6, the power unit 11 may be a power electronic unit composed of an eighth branch. The eighth branch circuit is composed of at least one first sub-branch circuit, the at least one first sub-branch circuit is arranged in series, the first sub-branch circuit is composed of a fourth power device W4 and a third capacitor C3 which are arranged in parallel, wherein the fourth power device W4 is a power electronic device with a turn-off function, and the power electronic device is one or more of IGBT, IGCT, IEGT, GTO or MOSFET and other turn-off devices.
Alternatively, as shown in fig. 8, the power unit 11 may be a power electronic unit composed of an eighth branch. The eighth branch circuit is composed of at least one first sub-branch circuit, the at least one first sub-branch circuit is arranged in series, the first sub-branch circuit is composed of a fourth power device W4 and a second resistor R2 which are arranged in parallel, wherein the second resistor R2 is a nonlinear resistor, the fourth power device W4 is a power electronic device with a turn-off function, and the power electronic device is one or more of IGBT, IGCT, IEGT, GTO or MOSFET and other turn-off devices.
Alternatively, as shown in fig. 7, the power unit 11 may be a power electronic unit formed by a ninth branch, where the ninth branch includes at least one branch formed by a second sub-branch, a third sub-branch, and a fourth capacitor C4, and at least one branch is disposed in series.
The second sub-branch comprises a fifth power device W5 and a sixth power device W6 which are arranged in series, the fifth power device W5 and the sixth power device W6 are respectively provided with a first end and a second end, the first end of the fifth power device W5 is connected with the first end of the sixth power device W6, the third sub-branch comprises a seventh power device W7 and an eighth power device W8 which are arranged in series, the seventh power device W7 and the eighth power device W8 are respectively provided with a first end and a second end, the second end of the seventh power device W7 is connected with the second end of the eighth power device W8, one end of a fourth capacitor C4 is connected between the fifth power device W5 and the sixth power device W6, and the other end of the fourth capacitor C4 is connected between the seventh power device W7 and the eighth power device W8. The fifth power device W5, the sixth power device W6, the seventh power device W7 and the eighth power device W8 are all power electronic devices with a turn-off function, and the power electronic devices are one or more of IGBT, IGCT, IEGT, GTO, MOSFET and other turn-off devices.
Alternatively, as shown in fig. 9, the power unit 11 may be a power electronic unit composed of a ninth branch. The ninth branch comprises at least one branch consisting of a second sub-branch, a third sub-branch and a third resistor R3, and at least one branch is arranged in series.
The second sub-branch comprises a fifth power device W5 and a sixth power device W6 which are arranged in series, the fifth power device W5 and the sixth power device W6 are respectively provided with a first end and a second end, the first end of the fifth power device W5 is connected with the first end of the sixth power device W6, the third sub-branch comprises a seventh power device W7 and an eighth power device W8 which are arranged in series, the seventh power device W7 and the eighth power device W8 are respectively provided with a first end and a second end, the second end of the seventh power device W7 is connected with the second end of the eighth power device W8, one end of a third resistor R3 is connected between the fifth power device W5 and the sixth power device W6, and the other end of the third resistor R3 is connected between the seventh power device W7 and the eighth power device W8. The fifth power device W5, the sixth power device W6, the seventh power device W7 and the eighth power device W8 are all power electronic devices with a turn-off function, and the power electronic devices are one or more of IGBT, IGCT, IEGT, GTO, MOSFET and other turn-off devices.
Alternatively, as shown in fig. 10, the power unit 11 may be a power electronic unit composed of a tenth branch and an eleventh branch.
The tenth branch is provided with a ninth power device W9, the eleventh branch is parallel to the tenth branch, the eleventh branch includes a tenth power device W10, a second inductor L2, a fifth capacitor C5, and a second charging circuit P2, and the tenth power device W10, the second inductor L2, and the fifth capacitor C5 are serially connected, and the second charging circuit P2 is parallel to the fifth capacitor C5. The ninth power device W9 and the tenth power device W10 are power electronic devices having a turn-off function, and the power electronic devices are one or more of IGBT, IGCT, IEGT, GTO or MOSFET or other turn-off devices.
The second control valve V12 is a low-voltage shutoff valve, and has a unidirectional voltage controllable output capability or a unidirectional controllable shutoff function, and is mainly used for shutting off the main branch current and providing reverse voltage for the main branch current, so that the thyristor valve of the main branch is ensured to have enough shutoff time for reliable shutoff. The topology of the second control valve V12 is not limited in the present application, and any topology may be used as long as it has a unidirectional voltage controllable output or unidirectional controllable shut-off function. The topology of the power unit may be the matching of the power electronic device without reverse blocking function and the diode, the power electronic device without reverse blocking function, the single-stage diode and the buffer component may be matched to form a multistage serial structure, the multistage power electronic device without reverse blocking function and the buffer component combination thereof may be serial to the multistage diode and the buffer component combination thereof, or the multistage power electronic device without reverse blocking function and the multistage diode may be alternatively serial to each other, or of course, other topology may be used, which is not limited herein specifically, and the skilled person may determine according to the actual needs.
Optionally, the second control valve V12 may further comprise at least one damping member arranged in parallel in the power unit 11. The parallel connection of the buffer element to the power unit 11 is known to those skilled in the art, and is not particularly limited herein. Optionally, as shown in fig. 11, the buffer component is formed by one or more of capacitance, a resistive-capacitive loop, a diode, an inductor, or a lightning arrester, and at least one power unit 11 may form a full bridge circuit with at least one buffer component, so as to make the second control valve V12 work stably.
Specifically, as shown in fig. 11, the buffer component may be a first buffer branch composed of a sixth capacitor, a second buffer branch composed of a fourth resistor and a seventh capacitor, a third buffer branch composed of a fourth resistor and a seventh capacitor in parallel, a fourth buffer branch RCD1 composed of a fifth resistor and a third diode in parallel and then in series with an eighth capacitor, a fifth buffer branch RCD2 composed of a sixth resistor and a ninth capacitor in parallel and then in series with a fourth diode, a sixth buffer branch composed of a lightning arrester, and a seventh buffer branch composed of 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 the embodiment of the invention, a hybrid converter topology structure of forced commutation is provided, and the topology structure is connected into an alternating current power grid through a converter transformer. The topology structure of the forced phase-change hybrid converter comprises a three-phase six-bridge-arm circuit, wherein each phase bridge arm comprises an upper bridge arm and a lower bridge arm, and at least one upper bridge arm or lower bridge arm of the topology structure is provided with the active phase-change unit.
Specifically, the forced commutation hybrid converter topology as depicted in fig. 14 includes 3 upper legs and 3 lower legs. Each active commutation unit is used as a converter valve, and the topology structure of the forced commutation hybrid converter shown in fig. 14 includes a converter valve V1, a converter valve V2, a converter valve V3, a converter valve V4, a converter valve V5 and a converter valve V6. The main branches of the 3 upper bridge arms respectively comprise thyristor valves V11, V31, V51 and second control valves V12, V32 and V52, and the auxiliary branches of the 3 upper bridge arms respectively comprise first control valves V13, V33 and V53. The main branches of the 3 lower bridge arms respectively comprise thyristor valves V21, V41, V61 and second control valves V22, V42 and V62, and the auxiliary branches of the 3 lower bridge arms respectively comprise first control valves V23, V43 and V63. The thyristor valve, the first control valve and the second control valve are controlled to be turned off and turned on by controlling the trigger control system.
Specifically, the forced commutation hybrid converter topology as depicted in fig. 15 includes 3 upper legs and 3 lower legs. Each active commutation unit is used as a converter valve, and the topology structure of the forced commutation hybrid converter shown in fig. 15 includes a converter valve V1, a converter valve V2, a converter valve V3, a converter valve V4, a converter valve V5 and a converter valve V6. The main branches of the 3 upper bridge arms respectively comprise thyristor valves V11, V31 and V51, and the auxiliary branches of the 3 upper bridge arms respectively comprise first control valves V13, V33 and V53 and second control valves V12, V32 and V52. The main branches of the 3 lower bridge arms respectively comprise thyristor valves V21, V41 and V61, and the auxiliary branches of the 3 lower bridge arms respectively comprise first control valves V23, V43 and V63 and second control valves V22, V42 and V62. The thyristor valve, the first control valve and the second control valve are controlled to be turned off and turned on by controlling the trigger control system.
Specifically, the hybrid converter topology shown in fig. 16 includes 3 upper legs and 3 lower legs. Each active commutation unit is used as a converter valve, and the hybrid converter topology structure of forced commutation described in fig. 16 includes a converter valve V1, a converter valve V2, a converter valve V3, a converter valve V4, a converter valve V5 and a converter valve V6. The main branches of the 3 upper bridge arms respectively comprise thyristor valves V11, V31 and V51, and the auxiliary branches of the 3 upper bridge arms respectively comprise first control valves V13, V33 and V53. The main branches of the 3 lower bridge arms respectively comprise thyristor valves V21, V41 and V61, and the auxiliary branches of the 3 lower bridge arms respectively comprise first control valves V23, V43 and V63. One ends of the commutation control valves Va2, vb2 and Vc2 are respectively connected between the upper bridge arm and the lower bridge arm, the other ends are respectively connected to the output ends of the converter transformer, the commutation control valves Va2, vb2 and Vc2 can have a forward and reverse current turn-off function and a forward and reverse voltage output function at the same time, and the commutation control valves can be formed by forward and reverse series connection of the second control valves V12 in the above embodiment so as to be shared by the upper bridge arm and the lower bridge arm of each phase, so that the number of the second control valves is reduced, and the topological structure of the hybrid converter is simplified. The thyristor valve, the first control valve and the second control valve are controlled to be turned off and turned on by the control trigger control system, so that the reliable turn-off of the main branch and the active phase change of the whole bridge arm are realized.
The hybrid converter topology structure with forced commutation can provide reverse voltage and an auxiliary branch with self-turn-off capability by connecting the auxiliary branch in parallel on the basis of a thyristor valve, so that reliable turn-off of a main branch and active commutation of the whole bridge arm are realized. The auxiliary branch is formed by connecting second control valves with bidirectional bearing capacity in series, namely, a shutoff valve is introduced for each bridge arm.
The topology structure of the forced commutation hybrid converter provided by the embodiment comprises three-phase six-bridge-arm circuits, wherein each phase bridge arm respectively comprises an upper bridge arm and a lower bridge arm, and at least one upper bridge arm or lower bridge arm is provided with an active commutation unit. The second control valve in the active phase-change unit can switch off the main branch current in advance, and simultaneously provides reverse voltage, so that the phase-change voltage-time area of the main branch thyristor valve is increased, the reliable switch-off of the main branch thyristor valve is ensured, the problem of phase-change failure is avoided, and the stable and safe operation of a power grid is ensured.
In this embodiment, a control method for forced commutation is provided, which can be used in the topology structure of the hybrid converter for forced commutation, taking the case that the second control valve V12 is disposed in the auxiliary branch, and the control method for forced commutation includes the following steps:
(1) And switching on a thyristor valve of a main branch of an ith bridge arm of the topological structure of the hybrid converter.
(2) And the first control valve and the second control valve of the auxiliary branch of the ith bridge arm of the topological structure of the hybrid converter are conducted.
(3) And switching off the first control valve and the second control valve of the auxiliary branch of the ith bridge arm of the topological structure of the hybrid converter.
(4) After a control period, the thyristor valve of the main branch of the ith bridge arm of the topological structure of the hybrid converter is conducted, wherein i is E [1,6].
Specifically, as shown in fig. 17, the valve current flow path of the hybrid converter topology under normal operation conditions is shown, the main branch is periodically subjected to voltage and current stress, the auxiliary branch is always in the off state, and the auxiliary branch is only subjected to voltage stress when the thyristor valve of the main branch is turned off. The first control valve and the second control valve of the auxiliary branch of the ith bridge arm of the hybrid converter topological structure are kept in an off state, and the thyristor valve of the main branch of the ith bridge arm of the hybrid converter topological structure is conducted, so that the hybrid converter topological structure with forced commutation can work in a normal commutation operation mode, namely, in the temporary commutation operation mode, the auxiliary branch is in an off state when the hybrid converter normally operates, only bears voltage stress, and the increase of converter loss in long-term operation is reduced.
When the commutation failure or the alternating current short circuit failure occurs, the first control valve and the second control valve of the auxiliary branch of the ith bridge arm of the topological structure of the hybrid current converter are conducted, the current of the main branch is forcedly transferred to the auxiliary branch, and when the current transfer is completed, the first control valve and the second control valve of the auxiliary branch of the ith bridge arm of the topological structure of the hybrid current converter are turned off, so that the forceful commutation of the hybrid current converter is realized. After a control period, the step of turning on the thyristor valve of the main branch of the ith bridge arm of the topological structure of the hybrid converter is returned, and the main branch is continued to independently and normally operate, so that the auxiliary branch is ensured to bear the turn-off voltage stress only when in failure, the loss of the device is reduced, and the service life of the device is prolonged.
Fig. 18 shows the trigger control timing in the normal operation mode, where t 0 represents the initial trigger timing.
Fig. 19 shows the main branch to auxiliary branch commutation turning off the V1 valve, the auxiliary branch starts to receive voltage stress, the process is divided into three phases, fig. 19 (left) shows the main branch to auxiliary branch commutation phase, the auxiliary branch receives the trigger signal to turn on, the auxiliary branch V12 valve and the V13 valve receive the on signal to transfer the current of the main branch to the auxiliary branch, the reverse voltage is applied to the main branch, fig. 19 (middle) shows the auxiliary branch current-through phase, the main branch has been completely turned off, the main branch current has been completely transferred to the auxiliary branch, fig. 19 (right) shows the auxiliary branch turn-off phase, the auxiliary branch V13 valve is turned off first when the turn-off signal is received, the V1 valve at this time is in the turn-off state for receiving the forward voltage, and then the V12 valve is turned off before or simultaneously with the V11 valve of the main branch in the next control period. The operation process can be put into operation when the commutation failure or the predicted commutation failure occurs.
Fig. 20 is a timing diagram of the trigger control of the forced commutation hybrid converter topology in the event of commutation failure or ac short circuit failure. In fig. 20, after failure of commutation from the V1 valve to the V3 valve is monitored at time t f, the auxiliary branch V13 valve is turned on when the first preset time period Δt 1 passes, the auxiliary branch V12 valve is turned on when the second preset time period Δt 2 passes, and a process of commutation from 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 V13 valve is turned off after the third preset time period Deltat 3 is passed, the time from zero crossing of the main branch current to the turning-off of the V13 valve is the turning-off time t off of the thyristor valve, and t off is larger than the minimum turning-off time of the thyristor valve to ensure that the thyristor valve V11 has enough time to turn off. After the auxiliary branch V13 valve is closed, the auxiliary branch current commutates to the V3 valve until reaching the direct current Id, so as to finish the commutation from the V1 valve to the V3 valve, successfully resist the commutation failure fault, and then the auxiliary branch V12 valve is closed before the V11 valve of the next control period is opened. 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.
When the commutation fails or the short circuit fails, the topological structure of the hybrid current converter is controlled to start the operation mode of forced commutation, the occurrence of the 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 an off state, and the main branch is independently and normally operated, so that the auxiliary branch is ensured to bear the off voltage stress only when in failure, the loss of a device is reduced, and the service life of the device is prolonged.
Fig. 21 shows control trigger timing when the topology of the hybrid converter with forced commutation detects commutation failure or short-circuit failure in advance, and the specific operation process is shown in fig. 19. And at the commutation starting time of the V1 valve and the V3 valve, namely, the time delay of the V1 valve trigger pulse Sg1 is 120 degrees, or the auxiliary branch V13 valve is triggered nearby the moment, and the auxiliary branch V12 valve is opened in a short time (for example, 1s, 5s and the like), so that the commutation from the main branch to the auxiliary branch is realized. After the main branch current crosses zero, the main branch V11 valve is turned off and bears reverse voltage, the time from the main branch current crossing zero to the auxiliary branch V13 valve being turned off 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 reliable turn-off, so that the V1 valve current is completely transferred to the auxiliary branch, the auxiliary branch V13 valve starts to be turned off after the delta t, the V1 valve starts to bear forward voltage, and then the auxiliary branch V12 valve is turned off before or simultaneously with the turn-on of the V11 valve in the next working period. 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.
According to the forced commutation control method provided by the embodiment, through the periodical alternate operation of the main branch and the auxiliary branch, not only can commutation failure be resisted, but also prediction of the commutation failure is not needed. 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.
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.
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