CN114006544A - Active phase change unit and hybrid converter topological structure - Google Patents

Active phase change unit and hybrid converter topological structure Download PDF

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Publication number
CN114006544A
CN114006544A CN202111485868.1A CN202111485868A CN114006544A CN 114006544 A CN114006544 A CN 114006544A CN 202111485868 A CN202111485868 A CN 202111485868A CN 114006544 A CN114006544 A CN 114006544A
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Prior art keywords
branch
branch circuit
power
parallel
diode
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CN202111485868.1A
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Chinese (zh)
Inventor
杨俊�
李婷婷
王蒲瑞
欧阳文敏
贺冬珊
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Global Energy Interconnection Research Institute
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Global Energy Interconnection Research Institute
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Priority to CN202111485868.1A priority Critical patent/CN114006544A/en
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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
    • 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
    • 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
    • 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 an active commutation unit and a hybrid converter topological structure, wherein the active commutation unit comprises: a main branch on which a thyristor valve is arranged; the auxiliary branch circuit is connected with the main branch circuit in parallel, and is provided with a first control valve which has the functions of forward current controllable turn-off and forward and reverse voltage blocking; a second control valve connected with the thyristor valve or the first control valve, comprising at least one power unit comprising: the first branch circuit is sequentially provided with a first diode and a first power device in series; the second branch circuit is connected with the first branch circuit in parallel, and a second power device and a second diode are sequentially connected onto the second branch circuit in series; the first branch circuit and the second branch circuit form a full-bridge form, and the first power device and the second power device are power electronic devices with a turn-off function. By implementing the method, the active phase change of each bridge arm is realized, the phase change failure is avoided, and the stable and safe operation of the power grid is ensured.

Description

Active phase change unit and hybrid converter topological structure
Technical Field
The invention relates to the technical field of current conversion in power electronics, in particular to an active phase conversion unit and a hybrid converter topological structure.
Background
The traditional power grid phase-change 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 in the world. The converter is used as core equipment of direct current transmission, is a core function 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 capacitor commutation converter or a turn-off device is generally connected in series with a thyristor to form a hybrid converter to realize alternating current and direct current electric energy conversion. The capacitor phase-change converter increases the valve phase-change voltage time area through the capacitor voltage to ensure the reliable turn-off of the converter, but realizes the controllable capacitor input and the controllable voltage direction through a controllable capacitor module formed by combining a power electronic switch and a capacitor, and needs a single-stage capacitor with a larger value to ensure the reliable phase change, thereby increasing the voltage and current stress of a core component thyristor, and the topological structure engineering has higher difficulty in realizing; the turn-off device and the thyristor are connected in series to form the hybrid converter, so that each bridge arm of the converter has turn-off capability, and the occurrence of phase commutation failure is avoided. Because the traditional converter mostly adopts a thyristor of a semi-controlled device as a core component to form a six-pulse bridge conversion topology, each bridge arm is formed by serially connecting a multi-stage thyristor and a buffer component thereof, and the thyristor does not have self-turn-off capability, phase change failure is easy to occur under the conditions of AC system failure and the like, so that the direct current is increased rapidly, a large amount of direct current transmission power is lost rapidly, and the stable and safe operation of a power grid is influenced.
Disclosure of Invention
In view of this, embodiments of the present invention provide an active commutation unit and a hybrid converter topology structure to solve the problem that stable operation of a power grid is affected due to a failed commutation.
According to a first aspect, an embodiment of the present invention provides an active commutation unit, which is disposed in a bridge arm circuit of a converter, and has one end connected to an output end of a converter transformer and the other end connected to a dc bus, where the active commutation unit includes: the main branch is provided with a thyristor valve; the auxiliary branch circuit is connected with the main branch circuit in parallel, a first control valve is arranged on the auxiliary branch circuit, and the first control valve has a forward current controllable turn-off function and a forward and reverse voltage blocking function; a second control valve connected with the thyristor valve of the main branch or connected with the first control valve of the auxiliary branch, the second control valve including at least one power unit, the power unit including: the power supply comprises a first branch circuit, a second branch circuit and a third branch circuit, wherein a first diode and a first power device are sequentially arranged on the first branch circuit in series; the second branch circuit is connected with the first branch circuit in parallel, and a second power device and a second diode are sequentially connected to the second branch circuit in series; the first branch circuit and the second branch circuit form a full-bridge form, and the first power device and the second power device are power electronic devices with a turn-off function.
With reference to the first aspect, in a first implementation manner of the first aspect, the power unit further includes: a first capacitive element having one end connected between the first diode and the first power device and the other end connected between the second power device and the second diode.
With reference to the first implementation manner of the first aspect, in a second implementation manner of the first aspect, the power unit further includes: and the protection element is connected with the second branch circuit and the first branch circuit in parallel and is used for transient overvoltage protection.
With reference to the second embodiment of the first aspect, in a third embodiment of the first aspect, the protective element is a lightning arrester.
With reference to the first aspect, in a fourth implementation manner of the first aspect, the power unit further includes: at least one buffer member disposed in parallel in the power device; the buffer member includes: a first buffer branch composed of a second capacitance element; or, the second buffer branch circuit is formed by connecting the first resistor and the third capacitor element in series; or, a third buffer branch of the first resistor and the third capacitor element in parallel; or the first resistor is connected with the third diode in parallel and then connected with the fourth capacitor element in series to form a fourth buffer branch circuit; or the second resistor is connected with the fifth capacitor element in parallel and then connected with the fourth diode in series to form a fifth buffer branch circuit; or, a sixth buffering branch composed of the lightning arrester; or, a plurality of the first buffering branch, the second buffering branch, the third buffering branch, the fourth buffering branch, the fifth buffering branch and the sixth buffering branch are connected in parallel to form a seventh buffering branch.
With reference to the fourth embodiment of the first aspect, in a fifth embodiment of the first aspect, the buffer members are disposed in parallel at both ends of the first diode and both ends of the second diode.
With reference to the fourth embodiment of the first aspect, in a sixth embodiment of the first aspect, the buffering components are disposed in parallel at two ends of the first power device and two ends of the second power device.
With reference to the fourth implementation manner of the first aspect, in a seventh implementation manner of the first aspect, the buffering components are disposed in parallel at two ends of the first diode, two ends of the second diode, two ends of the first power device, and two ends of the second power device.
With reference to the fourth embodiment of the first aspect, in an eighth embodiment of the first aspect, the buffer members are disposed in parallel at both ends of the first branch and both ends of the second branch.
According to a second aspect, an embodiment of the present invention provides a hybrid converter topology, where the topology is connected to an ac power grid through a converter transformer, the topology includes a three-phase six-leg circuit, each phase leg includes an upper leg and a lower leg, and at least one of the upper leg and the lower leg is provided with an active phase change unit according to the first aspect or any one of the first aspect embodiments.
The technical scheme of the invention has the following advantages:
1. the active commutation unit provided by the embodiment of the invention 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 on the main branch or connected with the first control valve on the auxiliary branch, the active commutation unit comprises at least one power unit, the power unit comprises a first branch and a second branch which are connected in parallel, and the first branch and the second branch form a full-bridge form. The first branch is sequentially provided with a first diode and a first power device in series, the second branch is sequentially provided with a second power device and a second diode in series, the first power device and the second power device are power electronic devices with a turn-off function, and therefore the power devices have controllable turn-off of forward current and blocking of forward and reverse voltage, the second control valve has the capability of unidirectional voltage output or unidirectional controllable turn-off, the second control valve is guaranteed to have larger through-current capacity and bear normal running current, and current is transferred to the auxiliary branch from the main branch through the second control valve. The active phase change 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 reliable turn-off of the main branch thyristor valve is ensured, the active phase change of each bridge arm is realized, the phase change failure is avoided, and the stable and safe operation of a power grid is ensured.
2. The hybrid converter topological structure provided by the embodiment of the invention comprises a three-phase six-bridge arm circuit, each phase of bridge arm comprises an upper bridge arm and a lower bridge arm respectively, and at least one upper bridge arm or one lower bridge arm is provided with an active phase change unit. The second control valve in the active phase change unit can turn off the main branch current in advance and provide reverse voltage at the same time, so that the phase change voltage-time area of the main branch thyristor valve is increased, the reliable turn-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 used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and other drawings can be obtained by those skilled in the art without creative efforts.
FIG. 1 is a block diagram of an active commutation cell according to an embodiment of the present invention;
FIG. 2 is a block diagram of a second control valve of the embodiment of the invention;
FIG. 3 is another block diagram of the second control valve according to the embodiment of the present invention;
FIG. 4 is another block diagram of the second control valve according to the embodiment of the present invention;
FIG. 5 is another block diagram of the second control valve according to the embodiment of the present invention;
FIG. 6 is a block diagram of the structure of a buffer member of an embodiment of the present invention;
fig. 7 is another structural block diagram of a second control valve of the embodiment of the invention;
fig. 8 is another structural block diagram of a second control valve of the embodiment of the invention;
fig. 9 is another structural block diagram of the second control valve of the embodiment of the invention;
fig. 10 is another structural block diagram of the second control valve of the embodiment of the invention;
FIG. 11 is a block diagram of a thyristor valve according to an embodiment of the invention;
fig. 12 is a block diagram showing the structure of a first control valve according to the embodiment of the invention;
fig. 13 is a hybrid converter topology of an embodiment of the present invention;
fig. 14 is another topology of a hybrid converter according to an embodiment of the present invention;
fig. 15 is another topology of a hybrid converter according to an embodiment of the present invention;
FIG. 16 is a current flow path for a normal operating condition of an embodiment of the present invention;
FIG. 17 is a trigger control sequence for a normal run state of an embodiment of the present invention;
FIG. 18 is a schematic diagram of the current path through the primary leg commutating to the auxiliary leg of an embodiment of the present invention;
FIG. 19 is a trigger control sequence for a commutation failure or short circuit fault according to an embodiment of the present invention;
FIG. 20 is a control trigger sequence for pre-detecting commutation failure or short circuit fault in accordance with an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The converter is used as core equipment of direct current transmission, is a core function 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, in the conventional converter, a thyristor which is a half-controlled device is mostly adopted as a core component to form a six-pulse bridge conversion topology, each bridge arm is formed by serially connecting a multi-stage thyristor and a buffer component thereof, and the thyristor does not have self-turn-off capability, so that phase change failure is easy to occur under the conditions of AC system faults and the like, so that the direct current is increased rapidly, a large amount of direct current transmission power is lost rapidly, and the stable and safe operation of a power grid is influenced.
Based on the technical scheme, the invention utilizes the advantages that the thyristor and the first control valve can be turned off and the second control valve can be turned off, adopts two branches which are connected in parallel, and realizes the reliable turn-off of the main branch and the active phase change of the whole bridge arm by connecting the auxiliary branch which can provide reverse voltage and has self-turn-off capability in parallel on the basis of the main branch, thereby realizing the auxiliary phase change function in a short time, avoiding the occurrence of phase change failure and ensuring the stable and safe operation of a power grid.
According to an embodiment of the invention, an embodiment of an active commutation cell is provided, the active commutation cell being arranged in a leg circuit of a converter. One end of the active commutation unit is connected to the output end of the converter transformer, and the other end is connected to the dc bus, as shown in fig. 1, the active commutation unit includes: a main branch and an auxiliary branch. Wherein, a thyristor valve V11 is arranged on the main branch, as shown in fig. 11, the thyristor valve V11 comprises at least one thyristor J1 and a buffer component 12 connected in parallel or in series with the thyristor J1, wherein at least one thyristor J1 is arranged in series, and the buffer component 12 is used for protecting the thyristor device from being damaged by high voltage and large current.
The auxiliary branch circuit is connected with the main branch circuit in parallel, a first control valve V13 is arranged on the auxiliary branch circuit 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. 12, the first control valve V13 includes a power device W and a thyristor J2, which are arranged in series, wherein the thyristor J2 has a reverse blocking function, the power device W has a controllable turn-off of a forward current and a blocking function of a forward and reverse voltage, and the power device W is a power electronic device having a turn-off function, and the power electronic device is one or more of turn-off devices such as an IGBT, an IGCT, an IEGT, a GTO, or a MOSFET.
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 form of a plurality of power devices and thyristors as long as the topology form can realize the functions of forward current controllable shutoff and forward and reverse voltage blocking capability, and the topology form of the first control valve V13 is not limited in the present application.
The second control valve V12 may be connected to the thyristor valve V11 of the main branch, or may be connected to the first control valve V13 of the auxiliary branch, and the first control valve V12 is a low-voltage shutoff valve having a one-way voltage-controllable output capability or a one-way controllable shutoff function, as shown in fig. 2, and the second control valve V12 includes: at least one power cell 11, the power cell 11 comprising: a first branch and a second branch.
A first diode D1 and a first power device W1 are sequentially arranged on the first branch in series; the second branch circuit is connected with the first branch circuit in parallel, a second power device W2 and a second diode D2 are sequentially connected to the second branch circuit in series, and the first branch circuit and the second branch circuit form a full-bridge form. Specifically, the power unit 11 includes a first connection terminal O1 and a second connection terminal O2, an anode of the first diode D1 is connected to the first connection terminal O1, a cathode of the first diode D1 is connected to one end of the first power device W1, another end of the first power device W1 is connected to the second connection terminal O2, one end of the second power device W2 is connected to the first connection terminal O1, another end of the second power device W2 is connected to an anode of the second diode D2, a cathode of the second diode D2 is connected to the second connection terminal O2, and the first diode D1, the first power device W1, the second power device W2, and the second diode D2 form a full bridge. The first power device W1 and the second power device W2 are power electronic devices with turn-off function, and the power electronic devices are one or more of turn-off devices such as IGBTs, IGCTs, IEGTs, GTOs, or MOSFETs. The power unit 11 can realize the controllable turn-off of the forward current and the blocking of the forward voltage and the reverse voltage, so that the first control valve V12 has the controllable turn-off function of unidirectional voltage output, and the current of the main branch circuit is turned off and the reverse voltage is provided for the main branch circuit, thereby ensuring that the thyristor valve of the main branch circuit has enough turn-off time to perform reliable turn-off.
The active phase-changing unit provided by this embodiment includes a main branch and an auxiliary branch connected in parallel, and a second control valve disposed on the main branch or the auxiliary branch, where the main branch is provided with a thyristor valve, the auxiliary branch is provided with a first control valve having forward and reverse voltage blocking capabilities, the second control valve is connected with the thyristor valve of the main branch or connected with the first control valve of the auxiliary branch, the active phase-changing unit includes at least one power unit, the power unit includes a first branch and a second branch connected in parallel, and the first branch and the second branch form a full-bridge form. The first branch is sequentially provided with a first diode and a first power device in series, the second branch is sequentially provided with a second power device and a second diode in series, the first power device and the second power device are power electronic devices with a turn-off function, and therefore the power devices have controllable turn-off of forward current and blocking of forward and reverse voltage, the second control valve has the capability of unidirectional voltage output or unidirectional controllable turn-off, the second control valve is guaranteed to have larger through-current capacity and bear normal running current, and current is transferred to the auxiliary branch from the main branch through the second control valve. The active phase change 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 reliable turn-off of the main branch thyristor valve is ensured, the active phase change of each bridge arm is realized, the phase change failure is avoided, and the stable and safe operation of a power grid is ensured.
Optionally, as shown in fig. 3, the power unit 11 may further include: the first capacitive element C1. One end of the first capacitive element C1 is connected between the first diode D1 and the first power device W1, and the other end of the first capacitive element C1 is connected between the second power device W2 and the second diode D2.
Optionally, as shown in fig. 4, the power unit 11 may further include: and a protective element B. The protection element B is a protection element for overvoltage transient protection. In particular, the protective element B is arranged in parallel with the second branch and the first branch.
As shown in fig. 5, the protection component B may also be connected to the first connection O1 of the first power unit 11 at one end and connected to the second connection O2 of the last power unit 11 at the other end.
Optionally, the protection element B may be an arrester, but may also be other elements capable of achieving overvoltage protection, and is not limited herein.
Optionally, the power unit 11 may further include: and the at least one buffer component 12 is arranged in the power unit 11 in parallel, so that the second control valve is prevented from being damaged by high-voltage large current, and the second control valve V12 is ensured to work stably. As shown in fig. 6, the buffer member 12 is formed of one or more of a capacitor, a rc circuit, a diode, an inductor, and a surge arrester.
Specifically, the buffer member 12 may be a first buffer branch composed of a second capacitive element; a second buffer branch which is formed by connecting a first resistor and a third capacitor element in series; a third buffer branch connected in parallel by a first resistor and a third capacitor element; a fourth buffering branch RCD1 formed by a first resistor, a third diode and a fourth capacitor element in parallel connection; a fifth buffer branch RCD2 formed by a second resistor connected in parallel with a fifth capacitive element and connected in series with a fourth diode; the sixth buffering branch circuit can also be composed of lightning arresters; the buffer circuit can also be 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.
Alternatively, as shown in fig. 7, the buffer unit 12 may be disposed in parallel at both ends of the first diode D1 and both ends of the second diode D2, respectively.
Alternatively, as shown in fig. 8, the buffer member 12 may be disposed in parallel at both ends of the first power device W1 and both ends of the second power device W2, respectively.
Alternatively, as shown in fig. 9, the buffer unit 12 may be disposed in parallel at both ends of the first diode D1, both ends of the second diode D2, both ends of the first power device W1, and both ends of the second power device W2, respectively.
Alternatively, as shown in fig. 10, the buffer member 12 may be disposed in parallel at both ends of the first branch and both ends of the second branch.
The second control valve V12 is a low-voltage shutoff valve, 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 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 topological form of the second control valve V12 is not limited in the present application, and may be any topological form that has a one-way voltage-controllable output or a one-way controllable shut-off function. The topological form of the power unit may also be the cooperation of a power electronic device without a reverse blocking function and a diode, a multistage series structure form may be formed by the cooperation of a single-stage power electronic device without a reverse blocking function, a single-stage diode and a buffer component, a multistage combination of a power electronic device without a reverse blocking function and a buffer component may be connected in series with a multistage combination of a diode and a buffer component, a multistage combination of a power electronic device without a reverse blocking function and a multistage diode may also be connected in series alternately, and of course, other topological forms may also be possible, which are not specifically limited herein, and those skilled in the art may determine the topological form according to actual needs.
According to an embodiment of the invention, a topology of a hybrid converter is provided, which is connected to an ac power grid through a converter transformer. The hybrid converter topological structure comprises a three-phase six-bridge arm circuit, each phase of bridge arm comprises an upper bridge arm and a lower bridge arm respectively, and at least one upper bridge arm or one lower bridge arm is provided with the active phase change unit.
Specifically, the hybrid converter topology as depicted in fig. 13 includes 3 upper legs and 3 lower legs. Each active commutation cell acts as a converter valve, and the hybrid converter topology for forced commutation described with respect to fig. 13, i.e. comprises converter valves V1, V2, V3, V4, V5 and 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 arms respectively comprise thyristor valves V21, V41, V61 and second control valves V22, V42 and V62, and the auxiliary branches of the 3 lower arms respectively comprise first control valves V23, V43 and V63. The on-off and the on-off of the thyristor valve, the first control valve and the second control valve are controlled by a control trigger control system.
Specifically, the hybrid converter topology as described in fig. 14 includes 3 upper legs and 3 lower legs. Each active commutation cell acts as a converter valve, and the hybrid converter topology for forced commutation described with respect to fig. 14, i.e. comprises converter valves V1, V2, V3, V4, V5 and 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 arms respectively comprise thyristor valves V21, V41 and V61, and the auxiliary branches of the 3 lower arms respectively comprise first control valves V23, V43 and V63 and second control valves V22, V42 and V62. The on-off and the on-off of the thyristor valve, the first control valve and the second control valve are controlled by a control trigger control system.
Specifically, the hybrid converter topology as shown in fig. 15 includes 3 upper legs and 3 lower legs. Each active commutation cell acts as a converter valve, and the hybrid converter topology for forced commutation described with respect to fig. 15, i.e. comprises converter valves V1, V2, V3, V4, V5 and 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 end of each of the phase change control valves Va2, Vb2 and Vc2 is connected between the upper bridge arm and the lower bridge arm, the other end of each of the phase change control valves Va2, Vb2 and Vc2 is connected to the output end of the converter transformer, and the phase change 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. The thyristor valve, the first control valve and the second control valve are controlled to be switched off and on by controlling the trigger control system, so that the reliable switching off of the main branch and the active phase change of the whole bridge arm are realized.
The hybrid converter topological structure can provide reverse voltage and an auxiliary branch with self-turn-off capability by being connected in parallel on the basis of the thyristor valve, so that reliable turn-off of a main branch and active phase change of the whole bridge arm are realized, namely, a turn-off control valve is introduced for each bridge arm.
The hybrid converter topology structure provided by the embodiment comprises a three-phase six-bridge arm circuit, each phase of bridge arm comprises an upper bridge arm and a lower bridge arm, and at least one upper bridge arm or one lower bridge arm is provided with an active phase change unit. The second control valve in the active phase change unit can turn off the main branch current in advance and provide reverse voltage at the same time, so that the phase change voltage-time area of the main branch thyristor valve is increased, the reliable turn-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 phase-change control method is provided, which can be used in the hybrid converter topology described above, taking the example that the second control valve V12 is disposed in the auxiliary branch, and the phase-change control method includes the following steps:
(1) and the thyristor valve of the main branch of the ith bridge arm of the hybrid converter topological structure is conducted.
(2) And the first control valve and the second control valve are used for conducting the auxiliary branch of the ith bridge arm of the hybrid converter topological structure.
(3) And switching off the first control valve and the second control valve of the auxiliary branch of the ith bridge arm of the hybrid converter topology.
(4) And after a control period, switching on a thyristor valve of a main branch of the ith bridge arm of the hybrid converter topological structure, wherein i belongs to [1,6 ].
Specifically, as shown in fig. 16, the valve current flow path of the hybrid converter topology under normal operating conditions is shown, the main branch is subjected to voltage and current stress periodically, the auxiliary branch is always in an off state, and the auxiliary branch is subjected to voltage stress only 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 a turn-off state, and the thyristor valve of the main branch of the ith bridge arm of the hybrid converter topological structure is switched on, so that the hybrid converter topological structure can work in a normal phase change operation mode, namely in a temporary phase change operation mode, the auxiliary branch is in a turn-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 a phase change failure or an alternating current short circuit fault occurs, a first control valve and a second control valve of an auxiliary branch of the ith bridge arm of the hybrid converter topological structure are conducted; and forcibly transferring the current of the main branch to the auxiliary branch, and turning 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 when the current transfer is finished, so as to realize the forced phase change of the hybrid converter. After a control period, returning to the step of conducting the thyristor valve of the main branch of the ith bridge arm of the hybrid converter topological structure, and continuing to independently and normally operate by the main branch, thereby ensuring that the auxiliary branch bears the turn-off voltage stress only when in fault, reducing the loss of the device and further prolonging the service life of the device.
FIG. 17 shows the trigger control sequence in the normal operation mode, t0Indicating the initial trigger time.
Fig. 18 shows that the V1 valve is turned off when the main branch is commutating to the auxiliary branch, and the auxiliary branch starts to bear voltage stress, the process is divided into three stages, fig. 18 (left) shows that the main branch is commutating to the auxiliary branch, the auxiliary branch receives the trigger signal to turn on, and the V12 valve and the V13 valve receive the turn-on signal, so as to transfer the current of the main branch to the auxiliary branch and apply the reverse voltage to the main branch; FIG. 18 (middle) is the auxiliary branch current flow phase, where the main branch has been completely turned off and the main branch current has been fully diverted to the auxiliary branch; fig. 18 (right) shows the auxiliary branch off phase, which, when receiving the off signal, first turns off the auxiliary branch V13 valve, while the V1 valve is in the off state for receiving the forward voltage, and then turns off the V12 valve before or at the same time as the V11 valve of the main branch is opened in the next control period. The above-described operation can be put into operation when a commutation fault is detected or predicted.
Fig. 19 is a timing diagram of the trigger control of the hybrid converter topology in the event of a commutation failure or ac short circuit fault. At t in FIG. 19fWhen the phase change failure of the V1 valve to the V3 valve is monitored at the moment, the first preset time delta t is passed1The auxiliary branch V13 valve is conducted for a second preset time period delta t2The V12 valve of the auxiliary branch is switched on, the commutation process of the main branch to the auxiliary branch is carried out, and delta t2≥Δt1Is more than or equal to 0. The main branch current I11 is gradually reduced to zero, the auxiliary branch current I12 is gradually increased, and the current passes through a third preset time period delta t3The auxiliary branch V13 valve is turned off, andthe time from the zero crossing of the main branch current to the closing of the V13 valve is the closing time t of the thyristor valveoffHere, toffGreater than the minimum turn-off time of the thyristor valve to ensure that the thyristor valve V11 has sufficient time to turn off. After the auxiliary branch V13 valve is turned off, the auxiliary branch current will commutate to the V3 valve until the direct current Id is reached, so that the phase change of the V1 valve to the V3 valve is completed, the failure fault of phase change is successfully resisted, and then the auxiliary branch V12 valve is turned off before the V11 valve of the next control period is turned on. The operation mode is started when the phase commutation failure is predicted to occur or detected to occur, the phase commutation failure can be successfully avoided, the operation mode is exited when the phase commutation process of the converter is recovered to be normal, the auxiliary branch keeps a turn-off state, and the main branch independently and normally operates.
When the phase change fails or short circuit faults occur, the hybrid converter topological structure is controlled to start the operation mode of forced phase change, the occurrence of the phase change failure is avoided, the operation mode of the forced phase change is quitted when the phase change process of the hybrid converter is recovered to be normal, the auxiliary branch circuit continues to be in a turn-off state, and the main branch circuit independently and normally operates, so that the auxiliary branch circuit is guaranteed to bear turn-off voltage stress only when the faults occur, the loss of devices is reduced, and the service life of the devices is prolonged.
Fig. 20 shows a control trigger sequence when the hybrid converter topology detects a phase change failure or a short-circuit fault in advance, and a specific operation process of each valve control trigger sequence when the main branch and the auxiliary branch of the V1 valve periodically and alternately operate is shown in fig. 18. At the beginning of the commutation of the V1 valve and the V3 valve, i.e., the V1 valve trigger pulse Sg1 is delayed by 120 °, or in the vicinity of this moment the auxiliary branch V13 valve is triggered and the auxiliary branch V12 valve is opened over a short period of time (e.g., 1s, 5s, etc.), effecting commutation of the main branch to the auxiliary branch. After the main branch current crosses zero, the main branch V11 valve is closed and bears reverse voltage, and the time from the main branch current crossing zero to the auxiliary branch V13 valve closing is the closing time t of the thyristor valveoffAnd t isoffThe minimum turn-off time of the thyristor valve is longer than that of the thyristor valve, so that the thyristor valve is reliably turned off, the current of the V1 valve is completely transferred to the auxiliary branch, and the auxiliary branch passes through delta tValve V13 begins to close, valve V1 begins to withstand the forward voltage, and then the auxiliary branch V12 valve is closed before or at the same time that valve V11 opens for the next duty cycle. In the operation mode, the main branch and the auxiliary branch in the bridge arm of the hybrid converter topological structure for forced commutation periodically and alternately operate, on the basis of resisting commutation failure, commutation failure does not need to be predicted, and meanwhile the hybrid converter can be in a small turn-off angle operation mode, so that reactive power consumption of the hybrid converter is reduced.
According to the commutation control method provided by the embodiment, through the periodic alternate operation of the main branch and the auxiliary branch, not only the commutation failure can be resisted, but also the commutation failure does not need to be predicted. Meanwhile, the hybrid converter is ensured to work in a small-cut-off-angle operation mode, and the reactive power consumption of the hybrid converter is reduced.
Although the embodiments of the present invention have been described in conjunction with the accompanying drawings, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the invention, and such modifications and variations fall within the scope defined by the appended claims.

Claims (10)

1. An active commutation unit is arranged in a bridge arm circuit of a current converter, one end of the active commutation unit is connected with the output end of a converter transformer, and the other end of the active commutation unit is connected with a direct current bus, and the active commutation unit is characterized by comprising:
the main branch is provided with a thyristor valve;
the auxiliary branch circuit is connected with the main branch circuit in parallel, a first control valve is arranged on the auxiliary branch circuit, and the first control valve has a forward current controllable turn-off function and a forward and reverse voltage blocking function;
a second control valve connected with the thyristor valve of the main branch or connected with the first control valve of the auxiliary branch, the second control valve including at least one power unit, the power unit including:
the power supply comprises a first branch circuit, a second branch circuit and a third branch circuit, wherein a first diode and a first power device are sequentially arranged on the first branch circuit in series;
the second branch circuit is connected with the first branch circuit in parallel, and a second power device and a second diode are sequentially connected to the second branch circuit in series;
the first branch circuit and the second branch circuit form a full-bridge form, and the first power device and the second power device are power electronic devices with a turn-off function.
2. The active commutation cell of claim 1, wherein the power cell further comprises:
a first capacitive element having one end connected between the first diode and the first power device and the other end connected between the second power device and the second diode.
3. The active commutation cell of claim 2, wherein the power cell further comprises:
and the protection element is connected with the second branch circuit and the first branch circuit in parallel and is used for transient overvoltage protection.
4. The active commutation cell of claim 3, wherein the protective element is a lightning arrester.
5. The active commutation cell of claim 1, wherein the power cell further comprises:
at least one buffer member disposed in parallel in the power device;
the buffer member includes:
a first buffer branch composed of a second capacitance element;
or, the second buffer branch circuit is formed by connecting the first resistor and the third capacitor element in series;
or, a third buffer branch of the first resistor and the third capacitor element in parallel;
or the first resistor is connected with the third diode in parallel and then connected with the fourth capacitor element in series to form a fourth buffer branch circuit;
or the second resistor is connected with the fifth capacitor element in parallel and then connected with the fourth diode in series to form a fifth buffer branch circuit;
or, a sixth buffering branch composed of the lightning arrester;
or, a plurality of the first buffering branch, the second buffering branch, the third buffering branch, the fourth buffering branch, the fifth buffering branch and the sixth buffering branch are connected in parallel to form a seventh buffering branch.
6. The active commutation cell of claim 5, wherein the buffer component is disposed in parallel across the first diode and across the second diode.
7. The active commutation cell of claim 5, wherein the buffer component is disposed in parallel across the first power device and across the second power device.
8. The active commutation cell of claim 5, wherein the buffer component is disposed in parallel across the first diode, across the second diode, across the first power device, and across the second power device.
9. The active commutation cell of claim 5, wherein the buffer components are disposed in parallel at both ends of the first branch and at both ends of the second branch.
10. A hybrid converter topological structure which is connected to an alternating current power grid through a converter transformer comprises a three-phase six-leg circuit, each phase of bridge leg comprises an upper bridge leg and a lower bridge leg respectively, and the hybrid converter topological structure is characterized in that at least one upper bridge leg or one lower bridge leg is provided with an active phase change unit according to any one of claims 1 to 9.
CN202111485868.1A 2021-12-07 2021-12-07 Active phase change unit and hybrid converter topological structure Pending CN114006544A (en)

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