Capacitor assisted turn-off bridge leg circuit, converter and method and apparatus, system

Abstract

The application provides a capacitor-assisted turn-off bridge arm circuit, a converter and a method and device, and a system. The capacitor-assisted turn-off bridge arm circuit comprises a main branch and an auxiliary turn-off branch. The main branch comprises a first half-controlled valve. The auxiliary turn-off branch is connected in parallel with the main branch. The auxiliary turn-off branch comprises a power electronic switch and a first capacitor connected in series. The power electronic switch is bidirectional current flow, bidirectional controllable turn-on, and unidirectional controllable turn-off.

Description

Technical Field

[0001] This application relates to the field of high voltage direct current transmission technology, specifically to bridge arm circuits, converters, methods, devices, and systems with capacitor-assisted turn-off. Background Technology

[0002] High-voltage and ultra-high-voltage direct current (HVDC) transmission system converters typically use a twelve-pulse circuit as the basic unit. Each twelve-pulse circuit consists of two three-phase six-arm circuits connected in series, with each arm using thyristors connected in series. Because the thyristors cannot be controlled to turn off, existing converter structures suffer from commutation failure issues. Flexible HVDC and hybrid HVDC transmission voltage source converters generally employ modular multilevel converters. Each arm consists of half-bridge or full-bridge sub-modules connected in series. These sub-modules use fully controlled devices and capacitors. While this eliminates commutation failure issues, it results in high cost, significant losses, and the risk of oscillation.

[0003] With the increasing number of high-voltage and ultra-high-voltage direct current (HVDC) transmission systems connected to the grid, multi-infeed HVDC transmission systems have formed in many regional power grids. When multiple HVDC lines experience simultaneous commutation failures, it can threaten the safe operation of the AC power grid in those regions. As the proportion of renewable energy generation increases, the AC voltage support capacity decreases, placing higher demands on the stable operation of HVDC transmission systems and their ability to suppress commutation failures and oscillations. Existing HVDC, flexible HVDC, and hybrid HVDC transmission technologies struggle to meet the stringent cost and performance requirements of HVDC transmission systems. Summary of the Invention

[0004] This application provides a bridge arm circuit with capacitor-assisted shutdown, including a main branch and an auxiliary shutdown branch connected in parallel. The main branch includes a first semi-controlled valve, which includes a semi-controlled switch. The auxiliary shutdown branch includes a power electronic switch and a first capacitor connected in series. The power electronic switch allows bidirectional current flow, bidirectional controllable turn-on, and unidirectional controllable turn-off.

[0005] According to some embodiments, the main branch further includes a first fully controlled valve, which is connected in series with the first partially controlled valve; surge arresters are connected in parallel at both ends of the first partially controlled valve and the first fully controlled valve, and a second partially controlled valve is connected in parallel at both ends of the first fully controlled valve, the second partially controlled valve including a partially controlled switch, and the first fully controlled valve including a fully controlled switch.

[0006] According to some embodiments, the auxiliary shutdown branch further includes a resistor and / or a reactance, the resistor and / or the reactance being connected in series with the power electronic switch and the first capacitor; surge arresters are connected in parallel across the power electronic switch and the first capacitor, and the first capacitor includes at least one capacitor element connected in series.

[0007] According to some embodiments, the power electronic switch includes at least one switch group connected in series, the switch group including a fully controlled switch and a partially controlled switch connected in anti-parallel.

[0008] According to some embodiments, the power electronic switch includes at least one switch group connected in series, the switch group including a fully controlled switch, an uncontrolled switch and a semi-controlled switch, the uncontrolled switch being connected in series with the fully controlled switch; the semi-controlled switch being connected in anti-parallel with the series circuit of the fully controlled switch and the uncontrolled switch.

[0009] According to some embodiments, the power electronic switch includes at least one series-connected switch group, the switch group including fully controlled switches connected in anti-parallel.

[0010] According to some embodiments, the power electronic switch includes a first semi-controlled switch group and a fully controlled switch group connected in series. The first semi-controlled switch group includes at least one switch group connected in series, and the switch group includes a semi-controlled switch connected in anti-parallel. The fully controlled switch group includes at least one switch group connected in series, and the switch group includes a fully controlled switch and an uncontrolled switch connected in anti-parallel, and is connected in series with the first semi-controlled switch group. A first capacitor is connected in series between the first semi-controlled switch group and the fully controlled switch group, or in series between the main branch and the first semi-controlled switch group or the fully controlled switch group. According to some embodiments, the power electronic switch includes a second semi-controlled switch group and a fully controlled switch group connected in series. The second semi-controlled switch group includes at least one switch group connected in series, and the switch group includes a semi-controlled switch and an uncontrolled switch connected in anti-parallel. The fully controlled switch group includes at least one switch group connected in series, and the switch group includes a fully controlled switch and an uncontrolled switch connected in anti-parallel, and is connected in series with the second semi-controlled switch group. The first capacitor is connected in series between the second semi-controlled switch group and the fully controlled switch group, or in series between the main branch and the second semi-controlled switch group or the fully controlled switch group.

[0011] According to some embodiments, the power electronic switch includes at least one switch group connected in series, the switch group including a fully controlled switch, an uncontrolled switch, a first semi-controlled switch and a second semi-controlled switch, the first semi-controlled switch being connected in series with the fully controlled switch and the uncontrolled switch; the second semi-controlled switch being connected in anti-parallel with the series circuit of the fully controlled switch, the uncontrolled switch and the first semi-controlled switch.

[0012] According to some embodiments, the power electronic switch includes at least one switch group connected in series, the switch group including: a fully controlled switch, a first semi-controlled switch and a second semi-controlled switch, the first semi-controlled switch being connected in series with the fully controlled switch; the second semi-controlled switch being connected in anti-parallel with the series circuit of the fully controlled switch and the first semi-controlled switch.

[0013] According to some embodiments, the fully controlled switch includes at least one fully controlled device connected in series, the fully controlled device including at least one of IGCT, IGBT, GTO, and MOSFET; the semi-controlled switch includes at least one semi-controlled device connected in series, the semi-controlled device including a thyristor; the uncontrolled switch includes at least one uncontrolled device connected in series, the uncontrolled device including a diode.

[0014] According to some embodiments, the auxiliary shutdown branch further includes a fast disconnect switch, which is connected in series with the power electronic switch.

[0015] This application embodiment also provides a capacitor-assisted turn-off converter, the converter including a three-phase six-arm bridge, at least one arm being a capacitor-assisted turn-off bridge arm circuit as described above.

[0016] According to some embodiments, the auxiliary shutdown branches of the three upper arms of the converter share a first capacitor, and the auxiliary shutdown branches of the three lower arms of the converter share another first capacitor.

[0017] This application also provides a high-voltage direct current transmission system, which includes a capacitor-assisted shutdown converter as described above.

[0018] This application embodiment also provides a control method for a converter with capacitor-assisted turn-off as described above, comprising: controlling the main branch of the bridge arm circuit of the converter to operate in an inverter state; when the commutation of the bridge arm circuit to another bridge arm ends, controlling the power electronic switch of the auxiliary turn-off branch of the bridge arm circuit to conduct in reverse, and the first capacitor of the auxiliary turn-off branch to be charged in reverse, so that the first capacitor presents a negative voltage; when a fault may cause the commutation failure of the bridge arm circuit, controlling the power electronic switch of the auxiliary turn-off branch of the bridge arm circuit to conduct in forward, so that the current of the main branch of the bridge arm circuit is transferred to the auxiliary turn-off branch; after the main branch of the bridge arm circuit is turned off, controlling the power electronic switch of the auxiliary turn-off branch of the bridge arm circuit to turn off in forward, thereby realizing the transfer of current from the phase where the bridge arm circuit is located to another phase.

[0019] According to some embodiments, the main branch of the bridge arm circuit is shut off when the forward current of the first semi-controlled valve in the main branch of the bridge arm circuit is less than the holding current and the forward blocking capability is restored.

[0020] This application embodiment also provides a control device for a capacitor-assisted turn-off converter as described above, including a detection unit and a control unit. The detection unit is used to detect the operating parameters and faults of the capacitor-assisted turn-off converter. Based on the operating parameters of the capacitor-assisted turn-off converter, the control unit controls the main branch of the bridge arm circuit of the converter to operate in inverter mode. When the commutation of the bridge arm circuit to another bridge arm ends, the power electronic switch of the auxiliary turn-off branch of the bridge arm circuit is controlled to conduct in reverse, and the first capacitor of the auxiliary turn-off branch is reverse-charged, so that the first capacitor presents a negative voltage. When a fault occurs that may cause the commutation failure of the bridge arm circuit, the power electronic switch of the auxiliary turn-off branch of the bridge arm circuit is controlled to conduct in forward, so that the current of the main branch of the bridge arm circuit is transferred to the auxiliary turn-off branch. After the main branch of the bridge arm circuit is turned off, the power electronic switch of the auxiliary turn-off branch of the bridge arm circuit is controlled to turn off in forward, realizing the transfer of current from the phase where the bridge arm circuit is located to another phase.

[0021] The technical solution provided in this application embodiment utilizes the negative voltage generated during bridge arm commutation to reverse charge the capacitor of the auxiliary branch of the bridge arm circuit. In case of a fault, the negative voltage of the capacitor is used to turn off the main branch of the bridge arm circuit, and then the power electronic switch of the auxiliary shutdown branch is used to turn off, forcing the current to transfer from the phase where the bridge arm circuit is located to another phase. This realizes controllable commutation of the grid commutation converter based on semi-controlled devices, effectively suppressing commutation failure and ensuring reliable operation of the converter. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is one of the schematic diagrams of a bridge arm circuit for capacitor-assisted turn-off provided in the embodiments of this application.

[0024] Figure 2 This is a second schematic diagram of a bridge arm circuit with capacitor-assisted turn-off provided in an embodiment of this application.

[0025] Figure 3 This is the third schematic diagram of a bridge arm circuit with capacitor-assisted turn-off provided in the embodiments of this application.

[0026] Figures 4a-4h This is a schematic diagram of a power electronic switch provided in an embodiment of this application.

[0027] Figure 5This is one of the schematic diagrams of a converter with capacitor-assisted shutdown provided in the embodiments of this application.

[0028] Figure 6 This is a second schematic diagram of a converter with capacitor-assisted shutdown provided in an embodiment of this application.

[0029] Figure 7 This is the third schematic diagram of a converter with capacitor-assisted shutdown provided in the embodiments of this application.

[0030] Figure 8 This is the fourth schematic diagram of a capacitor-assisted shutdown converter provided in the embodiments of this application.

[0031] Figure 9 This is the fifth schematic diagram of a capacitor-assisted shutdown converter provided in the embodiments of this application.

[0032] Figure 10 This is the sixth schematic diagram of a capacitor-assisted shutdown converter provided in the embodiments of this application.

[0033] Figure 11 This is the seventh schematic diagram of a capacitor-assisted shutdown converter provided in the embodiments of this application.

[0034] Figure 12 This is the eighth schematic diagram of a capacitor-assisted shutdown converter provided in the embodiments of this application.

[0035] Figure 13 This is the ninth schematic diagram of a capacitor-assisted shutdown converter provided in the embodiments of this application.

[0036] Figure 14 This is a schematic flowchart of a control method for a capacitor-assisted turn-off converter provided in an embodiment of this application.

[0037] Figure 15 This is a schematic diagram of a control device for a capacitor-assisted shutdown converter provided in an embodiment of this application. Detailed Implementation

[0038] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0039] It should be understood that the terms "first," "second," "third," etc., in the claims, specification, and drawings of this application are used to distinguish different objects, rather than to describe a specific order. The terms "comprising" and "including" used in the specification and claims of this application indicate the presence of the described features, integrals, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components, and / or a collection thereof.

[0040] Figure 1 This is one of the schematic diagrams of a bridge arm circuit for capacitor-assisted turn-off provided in the embodiments of this application.

[0041] The bridge arm circuit with capacitor-assisted shutdown includes a main branch 1 and an auxiliary shutdown branch 2 connected in parallel.

[0042] like Figure 1 As shown, the main branch 1 includes a first semi-controlled valve V41. The auxiliary shut-off branch 2 includes a power electronic switch 3 and a first capacitor C42 connected in series. The power electronic switch 3 allows bidirectional current flow, bidirectional controllable opening, and unidirectional controllable shut-off.

[0043] According to some embodiments, the main branch 1 further includes a first fully controlled valve V411, which is connected in series with a first partially controlled valve V41. Figure 2 As shown.

[0044] According to some embodiments, surge arresters are connected in parallel across the first semi-controlled valve V41, the first fully controlled valve V411, the power electronic switch 3, and the first capacitor C42, respectively. A second semi-controlled valve V412 is connected in parallel across the first fully controlled valve V411. The first semi-controlled valve V41 and the second semi-controlled valve V412 each include a semi-controlled switch, and the first fully controlled valve V411 includes a fully controlled switch.

[0045] According to some embodiments, the auxiliary shutdown branch 2 further includes a resistor R42 and / or a reactance L42, wherein the resistor R42 and / or the reactance L42 are connected in series with the power electronic switch 3 and the first capacitor C42, such as Figure 3 As shown, in the auxiliary shutdown branch 2, resistor R42, reactance L42, power electronic switch 3, and first capacitor C42 are connected in series.

[0046] According to some embodiments, the first capacitor C42 includes at least one capacitive element connected in series, and at least one capacitive element of the first capacitor C42 is connected in parallel with an equalizing resistor.

[0047] According to some embodiments, the power electronic switch 3 includes at least one switch group connected in series, the switch group including a fully controlled switch and a partially controlled switch connected in anti-parallel, such as Figure 4a As shown, the fully controlled switch includes IGCT6, and the semi-controlled switch includes thyristor 4, but is not limited to these.

[0048] According to some embodiments, the power electronic switch 3 includes at least one switch group connected in series. The switch group includes a fully controlled switch, an uncontrolled switch, and a partially controlled switch. The fully controlled switch and the uncontrolled switch are connected in series and then connected in anti-parallel with the partially controlled switch. Figure 4b As shown, a fully controlled switch includes IGBT 5 and diode 7 connected in antiparallel to it; an uncontrolled switch includes diode 7; and a semi-controlled switch includes thyristor 4, but is not limited thereto. It should be noted that diode 7 is not necessary in a fully controlled switch.

[0049] According to some embodiments, the power electronic switch 3 includes at least one series-connected switch group, the switch group including fully controlled switches connected in anti-parallel, such as... Figure 4c As shown, the fully controlled switch includes IGCT6, but is not limited to this.

[0050] According to some embodiments, the power electronic switch 3 includes a first semi-controlled switch group 9 and a fully controlled switch group 8. The first semi-controlled switch group 9 and the fully controlled switch group 8 are connected in series. The first semi-controlled switch group 9 includes at least one switch group connected in series, and the switch group includes two semi-controlled switches connected in anti-parallel. The fully controlled switch group 8 includes at least one switch group connected in series, and the switch group includes a fully controlled switch and an uncontrolled switch connected in anti-parallel. Figure 4d As shown, one switch group of the first semi-controlled switch group 9 includes two thyristors 4, and one switch group of the fully controlled switch group 8 includes an IGBT 5 and a diode 7 connected in anti-parallel to it, but is not limited thereto.

[0051] According to some embodiments, the power electronic switch 3 includes a second semi-controlled switch group 10 and a fully controlled switch group 8. The second semi-controlled switch group 10 and the fully controlled switch group 8 are connected in series. The second semi-controlled switch group 10 includes at least one switch group connected in series, which includes a semi-controlled switch and an uncontrolled switch connected in anti-parallel. The fully controlled switch group 8 includes at least one switch group connected in series, which includes a fully controlled switch and an uncontrolled switch connected in anti-parallel. Figure 4e As shown, one switch group of the second semi-controlled switch group 10 includes a thyristor 4 and a diode 7 connected in antiparallel to it, and one switch group of the fully controlled switch group 8 includes an IGBT 5 and a diode 7 connected in antiparallel to it. The power electronic switch 3 in this embodiment can also be as follows... Figure 4f As shown, the semi-controlled switch and the uncontrolled switch are connected in anti-parallel before being connected in series with the fully controlled switch, but this is not the only possibility.

[0052] According to some embodiments, the power electronic switch 3 includes at least one switch group connected in series. The switch group includes a fully controlled switch 11, an uncontrolled switch 13, a first half-controlled switch 12, and a second half-controlled switch 14. The fully controlled switch 11, the uncontrolled switch 13, and the first half-controlled switch 12 are connected in series, and the second half-controlled switch 14 is connected in anti-parallel to the series circuit of the aforementioned fully controlled switch 11, the uncontrolled switch 13, and the first half-controlled switch 12. Figure 4g As shown, the fully controlled switch 11 includes an IGBT 5 connected in series and a diode 7 connected in antiparallel with it, the uncontrolled switch 13 includes a diode 7 connected in series, the first semi-controlled switch 12 includes a thyristor 4 connected in series, the second semi-controlled switch 14 includes a thyristor 4 connected in series, and so on.

[0053] According to some embodiments, the power electronic switch 3 includes at least one switch group connected in series. The switch group includes a fully controlled switch 11, a first half-controlled switch 12, and a second half-controlled switch 14. The fully controlled switch 11 and the first half-controlled switch 12 are connected in series, and the second half-controlled switch 14 is connected in anti-parallel to the series circuit of the fully controlled switch 11 and the first half-controlled switch 12. Figure 4h As shown, the fully controlled switch 11 includes an IGBT 5 connected in series and a diode 7 connected in antiparallel with it, the first semi-controlled switch 12 includes a thyristor 4 connected in series, and the second semi-controlled switch 14 includes a thyristor 4 connected in series, but is not limited thereto.

[0054] A fully controlled switch includes at least one fully controlled device connected in series, which includes at least one of the following: IGCT (Integrated Gate Commutated Thyristors), IGBT (Insulated Gate Bipolar Transistor), GTO (Gate Turn-Off Thyristor), and MOSFET (Metal Oxide Semiconductor Field Effect Transistor). A semi-controlled switch includes at least one semi-controlled device connected in series, which includes a thyristor. An uncontrolled switch includes at least one uncontrolled device connected in series, which includes, but is not limited to, a diode. Optionally, a fully controlled switch includes at least one fully controlled device connected in series and an uncontrolled device connected in antiparallel to it.

[0055] Thyristor 4 is equipped with a corresponding trigger circuit and a buffer circuit. IGBT5 is equipped with a corresponding drive circuit and a buffer circuit. IGBT6 is equipped with a corresponding drive circuit and a buffer circuit. The buffer circuit consists of at least a capacitor, or a resistor and a capacitor in series.

[0056] According to some embodiments, the auxiliary shutdown circuit 2 also includes a fast disconnect switch, which is a mechanical switch connected in series with the power electronic switch 3.

[0057] Figure 5 This is a schematic diagram of a capacitor-assisted turn-off converter provided in an embodiment of this application.

[0058] One type is the capacitor-assisted shutdown converter, which has three phases and six arms, with each arm consisting of... Figure 1

[0059] The bridge arm circuit shown is configured as follows.

[0060] Each bridge arm circuit includes a main branch and an auxiliary shutdown branch connected in parallel. The main branch includes a first semi-controlled valve. The auxiliary shutdown branch includes a power electronic switch and a first capacitor connected in series. The power electronic switch allows bidirectional current flow, bidirectional controllable turn-on, and unidirectional controllable turn-off.

[0061] The main branch of the upper arm of phase A consists of the first semi-controlled valve V41, and the auxiliary shut-off branch consists of the power electronic switch 3 and the first capacitor C42 connected in series.

[0062] The main branch of the upper arm of phase B consists of the first semi-controlled valve V61, and the auxiliary shut-off branch consists of the power electronic switch 3 and the first capacitor C62 connected in series.

[0063] The main branch of the upper arm of phase C consists of the first semi-controlled valve V21, and the auxiliary shut-off branch consists of the power electronic switch 3 and the first capacitor C22 connected in series.

[0064] The main branch of the lower arm of phase A consists of the first semi-controlled valve V11, and the auxiliary shut-off branch consists of the power electronic switch 3 and the first capacitor C12 connected in series.

[0065] The main branch of the B-phase lower arm consists of the first semi-controlled valve V31, and the auxiliary shut-off branch consists of the power electronic switch 3 and the first capacitor C32 connected in series.

[0066] The main branch of the lower arm of phase C consists of the first semi-controlled valve V51, and the auxiliary shut-off branch consists of the power electronic switch 3 and the first capacitor C52 connected in series.

[0067] Figure 6 This is a second schematic diagram of a converter with capacitor-assisted shutdown provided in an embodiment of this application.

[0068] exist Figure 5 Based on the embodiments, the power electronic switch adopts, for example Figure 4a The structure includes multiple series-connected switch groups, each consisting of anti-parallel connected fully controlled switches and semi-controlled switches. The fully controlled switch includes an IGCT6, and the semi-controlled switch includes a thyristor 4. A first semi-controlled valve, a power electronic switch, and a first capacitor are connected in parallel with surge arresters for protection.

[0069] like Figure 6 As shown, the following surge arresters are connected in parallel: First semi-controlled valve V41 with surge arrester F41, power electronic switch V42 with surge arrester F42, and first capacitor C42 with surge arrester F74. First semi-controlled valve V61 with surge arrester F61, power electronic switch V62 with surge arrester F62, and first capacitor C62 with surge arrester F76. First semi-controlled valve V21 with surge arrester F21, power electronic switch V22 with surge arrester F22, and first capacitor C22 with surge arrester F72. First semi-controlled valve V11 with surge arrester F11, power electronic switch V12 with surge arrester F12, and first capacitor C12 with surge arrester F71. First semi-controlled valve V31 with surge arrester F31, power electronic switch V32 with surge arrester F32, and first capacitor C32 with surge arrester F73. The first semi-controlled valve V51 is connected to the surge arrester F51 in parallel, the power electronic switch V52 is connected to the surge arrester F52 in parallel, and the first capacitor C52 is connected to the surge arrester F75 in parallel.

[0070] According to some embodiments, the power electronic switch adopts, for example... Figure 4a The structure consists of only one series-connected switch group, which includes anti-parallel connected fully controlled switches and semi-controlled switches, such as... Figure 7 As shown, the fully controlled switch includes an IGCT6 connected in series, and the semi-controlled switch includes a thyristor 4 connected in series.

[0071] like Figure 7 As shown, the first semi-controlled valve V41 is connected to surge arrester F41 in parallel. The power electronic switch includes a fully controlled switch V43 and a semi-controlled switch V44 connected in anti-parallel, and the power electronic switch is connected to surge arrester F43 in parallel. The first capacitor C42 is connected to surge arrester F74 in parallel. The first semi-controlled valve V61 is connected to surge arrester F61 in parallel. The power electronic switch includes a fully controlled switch V63 and a semi-controlled switch V64 connected in anti-parallel, and surge arrester F63 in parallel. The first capacitor C62 is connected to surge arrester F76 in parallel. The first semi-controlled valve V21 is connected to surge arrester F21 in parallel. The power electronic switch includes a fully controlled switch V23 and a semi-controlled switch V24 connected in anti-parallel, and surge arrester F23 in parallel. The first capacitor C22 is connected to surge arrester F72 in parallel. The first semi-controlled valve V11 is connected to surge arrester F11 in parallel. The power electronic switch includes a fully controlled switch V13 and a semi-controlled switch V14 connected in anti-parallel, and surge arrester F13 is connected in parallel. The first capacitor C12 is connected to surge arrester F71 in parallel. The first semi-controlled valve V31 is connected to surge arrester F31 in parallel. The power electronic switch includes a fully controlled switch V33 and a semi-controlled switch V34 connected in anti-parallel, and surge arrester F33 is connected in parallel. The first capacitor C32 is connected to surge arrester F73 in parallel. The first semi-controlled valve V51 is connected to surge arrester F51 in parallel. The power electronic switch includes a fully controlled switch V53 and a semi-controlled switch V54 connected in anti-parallel, and surge arrester F53 is connected in parallel. The first capacitor C52 is connected to surge arrester F75 in parallel.

[0072] Figure 8 This is the fourth schematic diagram of a capacitor-assisted shutdown converter provided in the embodiments of this application.

[0073] exist Figure 5 Based on the embodiments, the power electronic switch adopts, for example Figure 4d The structure shown includes a first semi-controlled switch group and a fully controlled switch group connected in series. The first semi-controlled switch group includes at least one switch group connected in series, and the switch group includes anti-parallel connected semi-controlled switches, each semi-controlled switch including a thyristor. The fully controlled switch group includes at least one switch group connected in series, and the switch group includes a fully controlled switch and an uncontrolled switch connected in series. The fully controlled switch includes an IGBT, and the uncontrolled switch includes a diode. A surge arrester is connected in parallel with the first semi-controlled valve, the first semi-controlled switch group, the fully controlled switch group, and the first capacitor, respectively, serving as a protection device. The first capacitor is connected in series between the main branch and the fully controlled switch group.

[0074] In the upper arm of phase A, the first semi-controlled valve V41 is connected in parallel with surge arrester F41, the first semi-controlled switch group V45 includes at least one switch group connected in series, the switch group includes a semi-controlled switch connected in anti-parallel, the first semi-controlled switch group V45 is connected in parallel with surge arrester F44, the fully controlled switch group V46 includes at least one switch group connected in series, the switch group includes a fully controlled switch and an uncontrolled switch connected in anti-parallel, the fully controlled switch group V46 is connected in parallel with surge arrester F45, and the first capacitor C42 is connected in parallel with surge arrester F74.

[0075] In the upper arm of phase B, the first semi-controlled valve V61 is connected in parallel with surge arrester F61, the first semi-controlled switch group V65 includes at least one switch group connected in series, the switch group includes a semi-controlled switch connected in anti-parallel, the first semi-controlled switch group V65 is connected in parallel with surge arrester F64, the fully controlled switch group V66 includes at least one switch group connected in series, the switch group includes a fully controlled switch and an uncontrolled switch connected in anti-parallel, the fully controlled switch group V66 is connected in parallel with surge arrester F65, and the first capacitor C62 is connected in parallel with surge arrester F76.

[0076] In the upper arm of phase C, the first semi-controlled valve V21 is connected in parallel with surge arrester F21, the first semi-controlled switch group V25 includes at least one switch group connected in series, the switch group includes a semi-controlled switch connected in anti-parallel, the first semi-controlled switch group V25 is connected in parallel with surge arrester F24, the fully controlled switch group V26 includes at least one switch group connected in series, the switch group includes a fully controlled switch and an uncontrolled switch connected in anti-parallel, the fully controlled switch group V26 is connected in parallel with surge arrester F25, and the first capacitor C22 is connected in parallel with surge arrester F72.

[0077] In the lower arm of phase A, the first semi-controlled valve V11 is connected in parallel with surge arrester F11, the first semi-controlled switch group V15 includes at least one switch group connected in series, the switch group includes a semi-controlled switch connected in anti-parallel, the first semi-controlled switch group V15 is connected in parallel with surge arrester F14, the fully controlled switch group V16 includes at least one switch group connected in series, the switch group includes a fully controlled switch and an uncontrolled switch connected in anti-parallel, the fully controlled switch group V16 is connected in parallel with surge arrester F15, and the first capacitor C12 is connected in parallel with surge arrester F71.

[0078] In the lower arm of phase B, the first semi-controlled valve V31 is connected in parallel with surge arrester F31, the first semi-controlled switch group V35 includes at least one switch group connected in series, the switch group includes a semi-controlled switch connected in anti-parallel, the first semi-controlled switch group V35 is connected in parallel with surge arrester F34, the fully controlled switch group V36 includes at least one switch group connected in series, the switch group includes a fully controlled switch and an uncontrolled switch connected in anti-parallel, the fully controlled switch group V36 is connected in parallel with surge arrester F35, and the first capacitor C32 is connected in parallel with surge arrester F73.

[0079] In the lower arm of phase C, the first semi-controlled valve V51 is connected in parallel with surge arrester F51, the first semi-controlled switch group V55 includes at least one switch group connected in series, the switch group includes a semi-controlled switch connected in anti-parallel, the first semi-controlled switch group V55 is connected in parallel with surge arrester F54, the fully controlled switch group V56 includes at least one switch group connected in series, the switch group includes a fully controlled switch and an uncontrolled switch connected in anti-parallel, the fully controlled switch group V56 is connected in parallel with surge arrester F55, and the first capacitor C52 is connected in parallel with surge arrester F75.

[0080] Figure 9 This is the fifth schematic diagram of a capacitor-assisted shutdown converter provided in the embodiments of this application.

[0081] exist Figure 5 Based on the embodiments, the power electronic switch adopts, for example Figure 4e The structure shown includes a second semi-controlled switch group and a fully controlled switch group connected in series. The second semi-controlled switch group includes at least one switch group connected in series, which includes a semi-controlled switch and an uncontrolled switch connected in anti-parallel. The semi-controlled switch includes a thyristor, and the uncontrolled switch includes a diode. The fully controlled switch group includes at least one switch group connected in series, which includes a fully controlled switch and an uncontrolled switch connected in series. The fully controlled switch includes an IGBT, and the uncontrolled switch includes a diode. A first semi-controlled valve, the second semi-controlled switch group, the fully controlled switch group, and a first capacitor are connected in parallel with surge arresters as protective devices. The first capacitor is connected in series between the main branch and the fully controlled switch group.

[0082] In the upper arm of phase A, the first semi-controlled valve V41 is connected in parallel with surge arrester F41, the second semi-controlled switch group V47 includes at least one switch group connected in series, the switch group includes an uncontrolled switch and a semi-controlled switch connected in anti-parallel, the second semi-controlled switch group V47 is connected in parallel with surge arrester F44, the fully controlled switch group V46 includes at least one switch group connected in series, the switch group includes a fully controlled switch and an uncontrolled switch connected in anti-parallel, the fully controlled switch group V46 is connected in parallel with surge arrester F46, and the first capacitor C42 is connected in parallel with surge arrester F74.

[0083] In the upper arm of phase B, the first semi-controlled valve V61 is connected in parallel with surge arrester F61, the second semi-controlled switch group V67 includes at least one switch group connected in series, the switch group includes an uncontrolled switch and a semi-controlled switch connected in anti-parallel, the second semi-controlled switch group V67 is connected in parallel with surge arrester F64, the fully controlled switch group V66 includes at least one switch group connected in series, the switch group includes a fully controlled switch and an uncontrolled switch connected in anti-parallel, the fully controlled switch group V66 is connected in parallel with surge arrester F66, and the first capacitor C62 is connected in parallel with surge arrester F76.

[0084] In the upper arm of phase C, the first semi-controlled valve V21 is connected in parallel with surge arrester F21, the second semi-controlled switch group V27 includes at least one switch group connected in series, the switch group includes an uncontrolled switch and a semi-controlled switch connected in anti-parallel, the second semi-controlled switch group V27 is connected in parallel with surge arrester F24, the fully controlled switch group V26 includes at least one switch group connected in series, the switch group includes a fully controlled switch and an uncontrolled switch connected in anti-parallel, the fully controlled switch group V26 is connected in parallel with surge arrester F26, and the first capacitor C22 is connected in parallel with surge arrester F72.

[0085] In the lower arm of phase A, the first semi-controlled valve V11 is connected in parallel with surge arrester F11, the second semi-controlled switch group V17 includes at least one switch group connected in series, the switch group includes an uncontrolled switch and a semi-controlled switch connected in anti-parallel, the second semi-controlled switch group V17 is connected in parallel with surge arrester F14, the fully controlled switch group V16 includes at least one switch group connected in series, the switch group includes a fully controlled switch and an uncontrolled switch connected in anti-parallel, the fully controlled switch group V16 is connected in parallel with surge arrester F16, and the first capacitor C12 is connected in parallel with surge arrester F71.

[0086] In the lower arm of phase B, the first semi-controlled valve V31 is connected in parallel with surge arrester F31, the second semi-controlled switch group V37 includes at least one switch group connected in series, the switch group includes an uncontrolled switch and a semi-controlled switch connected in anti-parallel, the second semi-controlled switch group V37 is connected in parallel with surge arrester F34, the fully controlled switch group V36 includes at least one switch group connected in series, the switch group includes a fully controlled switch and an uncontrolled switch connected in anti-parallel, the fully controlled switch group V36 is connected in parallel with surge arrester F36, and the first capacitor C32 is connected in parallel with surge arrester F73.

[0087] In the lower arm of phase C, the first semi-controlled valve V51 is connected in parallel with surge arrester F51, the second semi-controlled switch group V57 includes at least one switch group connected in series, the switch group includes an uncontrolled switch and a semi-controlled switch connected in anti-parallel, the second semi-controlled switch group V57 is connected in parallel with surge arrester F54, the fully controlled switch group V56 includes at least one switch group connected in series, the switch group includes a fully controlled switch and an uncontrolled switch connected in anti-parallel, the fully controlled switch group V56 is connected in parallel with surge arrester F56, and the first capacitor C52 is connected in parallel with surge arrester F75.

[0088] According to some embodiments, the first capacitor can also be connected in series between the second semi-controlled switch group and the fully controlled switch, such as... Figure 10 As shown.

[0089] Figure 11 This is the seventh schematic diagram of a capacitor-assisted shutdown converter provided in the embodiments of this application.

[0090] exist Figure 5 Based on the embodiment, the auxiliary shutdown branch includes a power electronic switch, a resistor, and a first capacitor connected in series. The power electronic switch adopts the following... Figure 4a The structure shown includes multiple series-connected switch groups, each consisting of anti-parallel connected fully controlled switches and semi-controlled switches. The fully controlled switch includes an IGCT6, and the semi-controlled switch includes a thyristor 4. A first semi-controlled valve, a power electronic switch, and a first capacitor are connected in parallel with a surge arrester. The three upper bridge arms share the first capacitor and resistor, and the three lower bridge arms also share the first capacitor and resistor.

[0091] In the upper arm of phase A, the first semi-controlled valve V41 is connected to surge arrester F41 in parallel, the power electronic switch V42 is connected to surge arrester F42 in parallel, and the first capacitor C42 is connected to surge arrester F74 in parallel.

[0092] In the upper arm of phase B, the first semi-controlled valve V61 is connected to surge arrester F61 in parallel, the power electronic switch V62 is connected to surge arrester F62 in parallel, and the first capacitor C42 is connected to surge arrester F74 in parallel.

[0093] In the upper arm of phase C, the first semi-controlled valve V21 is connected to surge arrester F21 in parallel, the power electronic switch V22 is connected to surge arrester F22 in parallel, and the first capacitor C42 is connected to surge arrester F74 in parallel.

[0094] In the lower arm of phase A, the first semi-controlled valve V11 is connected to surge arrester F11 in parallel, the power electronic switch V12 is connected to surge arrester F12 in parallel, and the first capacitor C12 is connected to surge arrester F71 in parallel.

[0095] In the lower arm of phase B, the first semi-controlled valve V31 is connected to surge arrester F31 in parallel, the power electronic switch V32 is connected to surge arrester F32 in parallel, and the first capacitor C12 is connected to surge arrester F71 in parallel.

[0096] In the lower arm of phase C, the first semi-controlled valve V51 is connected to surge arrester F51 in parallel, the power electronic switch V52 is connected to surge arrester F52 in parallel, and the first capacitor C12 is connected to surge arrester F71 in parallel.

[0097] The three upper bridge arms share the first capacitor V42 and resistor R42, and the power electronic switches of the three upper bridge arms are connected to the same bus P2; the three lower bridge arms share the first capacitor V12 and resistor R12, and the power electronic switches of the three lower bridge arms are connected to the same bus N2.

[0098] Figure 12 This is the eighth schematic diagram of a capacitor-assisted shutdown converter provided in the embodiments of this application.

[0099] exist Figure 5 Based on the embodiments, the power electronic switch adopts, for example Figure 4d The structure shown includes a first semi-controlled switch group and a fully controlled switch group connected in series. The first semi-controlled switch group includes at least one switch group connected in series, and the switch group includes anti-parallel connected semi-controlled switches, each semi-controlled switch including a thyristor. The fully controlled switch group includes at least one switch group connected in series, and the switch group includes a fully controlled switch and an uncontrolled switch connected in series. The fully controlled switch includes an IGBT, and the uncontrolled switch includes a diode. A surge arrester and protective devices are connected in parallel to the first semi-controlled valve, the first semi-controlled switch group, the fully controlled switch group, and the first capacitor. The three upper bridge arms share the first capacitor and the fully controlled switch group, and the three lower bridge arms also share the first capacitor and the fully controlled switch group.

[0100] In the upper arm of phase A, the first semi-controlled valve V41 is connected to surge arrester F41 in parallel, the first semi-controlled switch group V45 is connected to surge arrester F44 in parallel, the fully controlled switch group V46 is connected to surge arrester F45 in parallel, and the first capacitor C42 is connected to surge arrester F74 in parallel.

[0101] In the upper arm of phase B, the first semi-controlled valve V61 is connected to surge arrester F61 in parallel, the first semi-controlled switch group V65 is connected to surge arrester F64 in parallel, the fully controlled switch group V46 is connected to surge arrester F45 in parallel, and the first capacitor C42 is connected to surge arrester F74 in parallel.

[0102] In the upper arm of phase C, the first semi-controlled valve V21 is connected to surge arrester F21 in parallel, the first semi-controlled switch group V25 is connected to surge arrester F24 in parallel, the fully controlled switch group V46 is connected to surge arrester F45 in parallel, and the first capacitor C42 is connected to surge arrester F74 in parallel.

[0103] In the lower arm of phase A, the first semi-controlled valve V11 is connected to surge arrester F11 in parallel, the first semi-controlled switch group V15 is connected to surge arrester F14 in parallel, the fully controlled switch group V16 is connected to surge arrester F15 in parallel, and the first capacitor C12 is connected to surge arrester F71 in parallel.

[0104] In the lower arm of phase B, the first semi-controlled valve V31 is connected to surge arrester F31 in parallel, the first semi-controlled switch group V35 is connected to surge arrester F34 in parallel, the fully controlled switch group V16 is connected to surge arrester F15 in parallel, and the first capacitor C12 is connected to surge arrester F71 in parallel.

[0105] In the lower arm of phase C, the first semi-controlled valve V51 is connected to surge arrester F51 in parallel, the first semi-controlled switch group V55 is connected to surge arrester F54 in parallel, the fully controlled switch group V16 is connected to surge arrester F15 in parallel, and the first capacitor C12 is connected to surge arrester F71 in parallel.

[0106] The three upper bridge arms share a fully controlled switch V46 and a first capacitor V42, and the first semi-controlled switch groups of the three upper bridge arms are connected to the same busbar P2. The three lower bridge arms share a fully controlled switch V16 and a first capacitor V12, and the first semi-controlled switch groups of the three lower bridge arms are connected to the same busbar N2.

[0107] Figure 13 This is the ninth schematic diagram of a capacitor-assisted shutdown converter provided in the embodiments of this application.

[0108] exist Figure 5 Based on the embodiments, the power electronic switch adopts, for example Figure 4g The structure shown includes a series-connected switch group, comprising a fully controlled switch, an uncontrolled switch, a first semi-controlled switch, and a second semi-controlled switch. The fully controlled switch, the uncontrolled switch, and the first semi-controlled switch are connected in series. The second semi-controlled switch is connected in anti-parallel to the series circuit of the aforementioned fully controlled switch, uncontrolled switch, and first semi-controlled switch. The fully controlled switch includes an IGBT connected in series and a diode connected in anti-parallel to it. The uncontrolled switch includes a diode 7 connected in series. The first semi-controlled switch includes a thyristor 4 connected in series, and the second semi-controlled switch includes a thyristor 4 connected in series. The first semi-controlled valve, the fully controlled switch, the uncontrolled switch, the first semi-controlled switch, the second semi-controlled switch, and the first capacitor are each connected in parallel with surge arresters.

[0109] In the upper arm of phase A, the first semi-controlled valve V41 is connected to surge arrester F41 in parallel, the fully controlled switch V46 is connected to surge arrester F45 in parallel, the uncontrolled switch V48 is connected to surge arrester F47 in parallel, the first semi-controlled switch V49 is connected to surge arrester F48 in parallel, and the first capacitor C42 is connected to surge arrester F74 in parallel.

[0110] In the upper arm of phase B, the first semi-controlled valve V61 is connected in parallel with surge arrester F61, and the uncontrolled switch V68 is connected in parallel with surge arrester F67.

[0111] In the upper arm of phase C, the first semi-controlled valve V21 is connected in parallel with surge arrester F21, and the uncontrolled switch V28 is connected in parallel with surge arrester F27.

[0112] In the lower arm of phase A, the first semi-controlled valve V11 is connected to surge arrester F11 in parallel, the fully controlled switch V16 is connected to surge arrester F15 in parallel, the uncontrolled switch V18 is connected to surge arrester F17 in parallel, the first semi-controlled switch V19 is connected to surge arrester F18 in parallel, and the first capacitor C12 is connected to surge arrester F71 in parallel.

[0113] In the lower arm of phase B, the first semi-controlled valve V31 is connected in parallel with surge arrester F31, and the uncontrolled switch V38 is connected in parallel with surge arrester F37.

[0114] In the lower arm of phase C, the first semi-controlled valve V51 is connected in parallel with surge arrester F51, and the uncontrolled switch V58 is connected in parallel with surge arrester F57.

[0115] The three upper bridge arms share a fully controlled switch V46, a first half-controlled switch V49, and a first capacitor C42. The uncontrolled switches of the three upper bridge arms are connected to the same busbar P2. The three lower bridge arms share a fully controlled switch V16, a first half-controlled switch V19, and a first capacitor C12. The uncontrolled switches of the three lower bridge arms are connected to the same busbar N2.

[0116] In this embodiment, only the upper bridge arm of phase A and the lower bridge arm of phase A adopt the above-mentioned bridge arm circuit with capacitor-assisted turn-off, and are respectively configured with a second half-controlled switch V40 and a second half-controlled switch V10.

[0117] This application also provides a high-voltage direct current transmission system, which includes a capacitor-assisted shutdown converter as described above.

[0118] Figure 14 This is a schematic flowchart of a control method for a capacitor-assisted turn-off converter provided in an embodiment of this application.

[0119] In S110, the main branch of the control converter arm circuit operates in inverter mode.

[0120] Control as above Figures 6-13 The first semi-controlled valves V11, V21, V31, V41, V51 and V61 of the main branch 1 of the converter are operating in inverter mode.

[0121] In S120, when the commutation of the bridge arm circuit to another bridge arm ends, the power electronic switch of the auxiliary shut-off branch controlling the bridge arm circuit is reverse-biased, and the first capacitor of the auxiliary shut-off branch is reverse-charged, so that the first capacitor presents a negative voltage.

[0122] For example Figure 6 and Figure 11 Taking the upper arm of phase A as an example, when the commutation from the upper arm of phase A to the upper arm of phase B of the converter ends, the power electronic switch V42 of the auxiliary shut-off branch 2 controlling the upper arm of phase A is reverse-biased, and the first capacitor C42 of the auxiliary shut-off branch 2 is reverse-charged, so that the first capacitor C42 presents a negative voltage.

[0123] For example Figure 7 Taking the upper arm of phase A as an example, when the commutation from the upper arm of phase A to the upper arm of phase B of the converter ends, the semi-controlled switch V44 of the auxiliary shut-off branch 2 controlling the upper arm of phase A is reverse-biased, and the first capacitor C42 of the auxiliary shut-off branch 2 is reverse-charged, so that the first capacitor C42 presents a negative voltage.

[0124] For example Figure 8 and Figure 12 Taking the upper arm of phase A as an example, when the commutation from the upper arm of phase A to the upper arm of phase B of the converter ends, the first semi-controlled switch group V45 of the auxiliary shut-off branch 2 controlling the upper arm of phase A is reverse-conducted, and the first capacitor C42 of the auxiliary shut-off branch 2 is reverse-charged, so that the first capacitor C42 presents a negative voltage.

[0125] For example Figure 9 and Figure 10 Taking the upper arm of phase A as an example, when the commutation from the upper arm of phase A to the upper arm of phase B of the converter ends, the second semi-controlled switch group V47 of the auxiliary shut-off branch 2 controlling the upper arm of phase A is reverse-conducted, and the first capacitor C42 of the auxiliary shut-off branch 2 is reverse-charged, so that the first capacitor C42 presents a negative voltage.

[0126] For example Figure 13 Taking the upper arm of phase A as an example, when the commutation from the upper arm of phase A to the upper arm of phase B of the converter ends, the second half-controlled switch V40 of the auxiliary shut-off branch 2 controlling the upper arm of phase A is turned on in reverse, and the first capacitor C42 of the auxiliary shut-off branch 2 is charged in reverse, so that the first capacitor C42 presents a negative voltage.

[0127] The positive voltage direction of the upper bridge arm is from the positive terminal of the DC bus of the converter to the AC phase. Figure 6 Taking the upper arm of phase A as an example, the positive direction of the voltage of the first capacitor C42 is from the positive terminal P1 of the DC bus of the converter to the terminal A1 of phase A. Figure 6 Taking the lower bridge arm of phase A as an example, the positive direction of the voltage of the first capacitor C12 is from the A-phase terminal A1 to the negative terminal N1 of the DC bus of the converter.

[0128] In S130, when a fault occurs that may cause the commutation failure of the bridge arm circuit of the converter to be capacitor-assisted shut off, the power electronic switch of the auxiliary shut-off branch of the bridge arm circuit that controls the commutation is forward-biased, so that the current of the main branch of the commutation bridge arm circuit is transferred to the auxiliary shut-off branch.

[0129] The bridge arm circuit mentioned above is the bridge arm that switches to another bridge arm during normal operation.

[0130] The aforementioned faults include, but are not limited to, AC system faults or DC system faults connected to the converter. AC system faults can be identified based on an increase in the zero-sequence component of AC voltage, a sudden change in AC voltage, a drop in AC voltage amplitude, an increase in AC voltage harmonics, and an increase in DC current. DC system faults can be identified based on a drop in DC voltage and an increase in DC current. The commutation failure of the converter's arm circuit that may cause capacitor-assisted shutdown is determined based on the shut-off time of the first half-controlled valve in the main branch of the arm circuit and the AC voltage. If the first half-controlled valve in the main branch of the arm circuit has not closed by the normal shut-off time under AC voltage, it is considered a possible cause of commutation failure in the converter's arm circuit, but this is not a limitation.

[0131] For example Figure 6 and Figure 11 Taking the upper arm of phase A as an example, when the first upper arm of phase A switches to the first upper arm of phase B, if a fault occurs that may cause the switching of the upper arm of phase A of the converter to fail due to capacitor-assisted shutdown, the power electronic switch V42 of the auxiliary shutdown branch 2 of the upper arm of phase A is forward-biased, and the first capacitor C42 of the auxiliary shutdown branch 2 of the upper arm of phase A applies reverse voltage to the main branch 1, and the current of the main branch 1 is transferred to the auxiliary shutdown branch 2.

[0132] For example Figure 7 Taking the upper arm of phase A as an example, when the first upper arm of phase A switches to the first upper arm of phase B, if a fault occurs that may cause the switching of the upper arm of phase A of the converter to fail due to capacitor-assisted shutdown, the full control switch V43 of the auxiliary shutdown branch 2 of the upper arm of phase A is forward-biased, and the first capacitor C42 of the auxiliary shutdown branch 2 of the upper arm of phase A is reverse-voltaged to the main branch 1, and the current in the main branch 1 is transferred to the auxiliary shutdown branch 2.

[0133] For example Figure 8 and Figure 12 Taking the A-phase upper bridge arm as an example, when the first upper bridge arm of phase A switches to the first upper bridge arm of phase B, if a fault occurs that may cause the A-phase upper bridge arm of the converter to fail to switch due to capacitor-assisted shutdown, the first half-controlled switch group V45 and the full-controlled switch group V46 of the auxiliary shutdown branch 2 of the A-phase upper bridge arm will be forward-biased, and the first capacitor C42 of the auxiliary shutdown branch 2 of the A-phase upper bridge arm will apply reverse voltage to the main branch 1, and the current in the main branch 1 will be transferred to the auxiliary shutdown branch 2.

[0134] For example Figure 9 and Figure 10Taking the A-phase upper bridge arm as an example, when the first upper bridge arm of phase A switches to the first upper bridge arm of phase B, if a fault occurs that may cause the A-phase upper bridge arm of the converter to fail to switch due to capacitor-assisted shutdown, the second half-controlled switch group V47 and the full-controlled switch group V46 of the auxiliary shutdown branch 2 of the A-phase upper bridge arm will be forward-biased. The first capacitor C42 of the auxiliary shutdown branch 2 of the A-phase upper bridge arm will apply a reverse voltage to the main branch 1, and the current in the main branch 1 will be transferred to the auxiliary shutdown branch 2.

[0135] For example Figure 13 Taking the A-phase upper bridge arm as an example, when the first upper bridge arm of phase A commutates to the first upper bridge arm of phase B, if a fault occurs that could cause the commutation of the A-phase upper bridge arm of the converter to fail due to capacitor-assisted shutdown, the fully controlled switch V46 and the first half-controlled switch V49 of the auxiliary shutdown branch 2 shared by the three upper bridge arms will be forward-biased. The first capacitor C42 of the auxiliary shutdown branch 2 shared by the three upper bridge arms will apply reverse voltage to the main branch 1 of the A-phase upper bridge arm, and the current in the main branch 1 of the A-phase upper bridge arm will be transferred to the auxiliary shutdown branch 2. Figure 13 Taking the B-phase upper bridge arm as an example, when the first upper bridge arm of the B-phase switches to the first upper bridge arm of the C-phase, if a fault occurs that may cause the capacitor-assisted shutdown of the converter, the commutation of the B-phase upper bridge arm will fail. In this case, the full control switch V46 and the first half control switch V49 of the auxiliary shutdown branch 2 shared by the three upper bridge arms will be forward-biased. The first capacitor C42 of the auxiliary shutdown branch 2 shared by the three upper bridge arms will apply a reverse voltage to the main branch 1 of the B-phase upper bridge arm, and the current in the main branch 1 of the B-phase upper bridge arm will be transferred to the auxiliary shutdown branch 2.

[0136] In S140, after the main branch of the bridge arm circuit is turned off, the power electronic switch controlling the auxiliary turn-off branch of the bridge arm circuit is turned off in the forward direction, realizing the transfer of current from the phase where the bridge arm circuit is located to another phase.

[0137] For example Figure 6 and Figure 11 Taking the upper arm of phase A as an example, after the first half-control valve V41 of the upper arm of phase A is turned off, the power electronic switch V42 of the auxiliary turn-off branch 2 of the upper arm of phase A is turned off in the forward direction, and the forced current is switched from phase A to phase B.

[0138] For example Figure 7 Taking the upper arm of phase A as an example, after the first half-control valve V41 of the upper arm of phase A is turned off, the full control switch V43 of the auxiliary turn-off branch 2 of the upper arm of phase A is turned off in the forward direction, and the forced current is switched from phase A to phase B.

[0139] For example Figure 8 , Figure 9 , Figure 10 , Figure 12 and Figure 13Taking the upper arm of phase A as an example, after the first half-control valve V41 of the upper arm of phase A is turned off, the full control switch V46 of the auxiliary turn-off branch 2 of the upper arm of phase A is turned off in the forward direction, and the forced current is switched from phase A to phase B.

[0140] The main branch of the bridge arm circuit is turned off when the forward current of the first half-controlled valve in the main branch of the bridge arm circuit is less than the holding current and the forward blocking capability is restored. Specifically, restoring the forward blocking capability means restoring the forward blocking capability after the forward current is less than the holding current and after a delayed turn-off time, with the turn-off time being less than 700µs, but not limited to this.

[0141] Figure 15 This is a schematic diagram of a control device for a capacitor-assisted shutdown converter provided in an embodiment of this application. The control device 300 includes a detection unit 310 and a control unit 320.

[0142] The detection unit 310 is used to detect the operating parameters of the converter with capacitor-assisted shutdown.

[0143] The control unit 320 controls the main branch of the converter's arm circuit to operate in inverter mode based on the operating parameters of the converter with capacitor-assisted turn-off. When the commutation of the arm circuit to another arm ends, the control unit 320 controls the power electronic switch of the auxiliary turn-off branch of the arm circuit to conduct in reverse, and the first capacitor of the auxiliary turn-off branch is charged in reverse, making the first capacitor present a negative voltage. When a fault occurs that may cause the arm circuit to fail to commutate, the control unit 320 controls the power electronic switch of the auxiliary turn-off branch of the arm circuit to conduct in forward, so that the current in the main branch of the arm circuit is transferred to the auxiliary turn-off branch. After the main branch of the arm circuit is turned off, the control unit 320 controls the power electronic switch of the auxiliary turn-off branch of the arm circuit to turn off in forward, realizing the transfer of current from the phase where the arm circuit is located to another phase.

[0144] The above embodiments are only for illustrating the technical concept of this application and should not be used to limit the scope of protection of this application. Any modifications made to the technical solution based on the technical concept proposed in this application shall fall within the scope of protection of this application.

Claims

1. A capacitor-assisted turn-off converter, the converter comprising a three-phase six-arm bridge, at least one arm being a capacitor-assisted turn-off bridge arm circuit, the bridge arm circuit comprising: The main branch includes a first semi-controlled valve, which includes a semi-controlled switch. An auxiliary shutdown branch is connected in parallel with the main branch. The auxiliary shutdown branch includes a power electronic switch and a first capacitor connected in series. The power electronic switch includes at least one switch group connected in series. The power electronic switch is configured to allow bidirectional current flow, bidirectional controllable turn-on, and unidirectional controllable turn-off. The first capacitor is configured to receive a reverse voltage through the reverse conduction of the power electronic switch at the end of the commutation of the bridge arm circuit to the other bridge arm, so that the first capacitor presents a negative voltage.

2. The converter as claimed in claim 1, wherein, The main branch also includes: A first fully controlled valve is connected in series with the first partially controlled valve; surge arresters are connected in parallel at both ends of the first partially controlled valve and the first fully controlled valve; a second partially controlled valve is connected in parallel at both ends of the first fully controlled valve; the second partially controlled valve includes a partially controlled switch; and the first fully controlled valve includes a fully controlled switch.

3. The converter as claimed in claim 1, wherein, The auxiliary shutdown branch also includes: A resistor and / or reactance are connected in series with the power electronic switch and the first capacitor; surge arresters are connected in parallel across the power electronic switch and the first capacitor, and the first capacitor includes at least one capacitor element connected in series.

4. The converter as claimed in claim 1, wherein, The power electronic switch includes: At least one series-connected switch group, the switch group comprising a fully controlled switch and a partially controlled switch connected in anti-parallel.

5. The converter as claimed in claim 1, wherein, The power electronic switch includes: At least one series-connected switch group, the switch group comprising: Full control switch; An uncontrolled switch is connected in series with the fully controlled switch; A semi-controlled switch is connected in anti-parallel to the series circuit of the fully controlled switch and the uncontrolled switch.

6. The converter as claimed in claim 1, wherein, The power electronic switch includes: At least one series-connected switch group, the switch group comprising fully controlled switches connected in anti-parallel.

7. The converter as claimed in claim 1, wherein, The power electronic switch includes: The first semi-controlled switch group includes at least one switch group connected in series, the switch group including semi-controlled switches connected in anti-parallel; A fully controlled switch group includes at least one switch group connected in series, wherein the switch group includes a fully controlled switch and an uncontrolled switch connected in anti-parallel, and is connected in series with the first semi-controlled switch group; The first capacitor is connected in series between the first semi-controlled switch group and the fully controlled switch group, or in series between the main branch and the first semi-controlled switch group or the fully controlled switch group.

8. The converter as claimed in claim 1, wherein, The power electronic switch includes: The second semi-controlled switch group includes at least one switch group connected in series, the switch group including a semi-controlled switch and an uncontrolled switch connected in anti-parallel; A fully controlled switch group includes at least one switch group connected in series, wherein the switch group includes a fully controlled switch and an uncontrolled switch connected in anti-parallel, and is connected in series with the second semi-controlled switch group; The first capacitor is connected in series between the second semi-controlled switch group and the fully controlled switch group, or in series between the main branch and the second semi-controlled switch group or the fully controlled switch group.

9. The converter as claimed in claim 1, wherein, The power electronic switch includes: At least one series-connected switch group, the switch group comprising: Full control switch; Uncontrolled switch; The first semi-controlled switch is connected in series with the fully controlled switch and the uncontrolled switch; The second semi-controlled switch is connected in anti-parallel to the series circuit of the fully controlled switch, the uncontrolled switch, and the first semi-controlled switch.

10. The converter as claimed in claim 1, wherein, The power electronic switch includes: At least one series-connected switch group, the switch group comprising: Full control switch; The first semi-controlled switch is connected in series with the fully controlled switch; The second semi-controlled switch is connected in anti-parallel to the series circuit of the fully controlled switch and the first semi-controlled switch.

11. The converter as claimed in claim 5, wherein, The fully controlled switch includes at least one fully controlled device connected in series, the fully controlled device including at least one of IGCT, IGBT, GTO, and MOSFET; the semi-controlled switch includes at least one semi-controlled device connected in series, the semi-controlled device including a thyristor; the uncontrolled switch includes at least one uncontrolled device connected in series, the uncontrolled device including a diode.

12. The converter as claimed in claim 1, wherein, The auxiliary shutdown branch also includes: A fast disconnect switch is connected in series with the power electronic switch.

13. The converter as claimed in claim 1, wherein, The auxiliary shutdown branches of the three upper arms of the converter share a first capacitor, and the auxiliary shutdown branches of the three lower arms of the converter share another first capacitor.

14. A high-voltage direct current transmission system, the high-voltage direct current transmission system comprising a converter with capacitor-assisted shutdown as described in any one of claims 1-13.

15. A control method for a converter with capacitor-assisted turn-off as described in any one of claims 1-13, comprising: The main branch of the bridge arm circuit of the converter is controlled to operate in inverter mode; When the commutation of the bridge arm circuit to another bridge arm ends, the power electronic switch controlling the auxiliary shutdown branch of the bridge arm circuit is turned on in reverse, and the first capacitor of the auxiliary shutdown branch is charged in reverse, so that the first capacitor presents a negative voltage. When a fault occurs that may cause the commutation failure of the bridge arm circuit, the power electronic switch controlling the auxiliary shutdown branch of the bridge arm circuit is forward turned on, so that the current of the main branch of the bridge arm circuit is transferred to the auxiliary shutdown branch. After the main branch of the bridge arm circuit is turned off, the power electronic switch controlling the auxiliary turn-off branch of the bridge arm circuit is turned off in the forward direction, realizing the transfer of current from the phase where the bridge arm circuit is located to another phase.

16. The control method as described in claim 15, wherein, The main branch of the bridge arm circuit is shut off when the forward current of the first semi-controlled valve in the main branch of the bridge arm circuit is less than the holding current and the forward blocking capability is restored.

17. A control device for a converter with capacitor-assisted turn-off as described in any one of claims 1-13, comprising: The detection unit is used to detect the operating parameters and faults of the converter with capacitor-assisted shutdown. The control unit controls the main branch of the bridge arm circuit of the converter to operate in inverter mode based on the operating parameters of the converter that is turned off by the capacitor. When the commutation of one bridge arm circuit to another is completed, the power electronic switch of the auxiliary shutdown branch of the bridge arm circuit is reverse-biased, and the first capacitor of the auxiliary shutdown branch is reverse-charged, making the first capacitor present a negative voltage. When a fault may cause the commutation of the bridge arm circuit to fail, the power electronic switch of the auxiliary shutdown branch of the bridge arm circuit is forward-biased, so that the current of the main branch of the bridge arm circuit is transferred to the auxiliary shutdown branch. After the main branch of the bridge arm circuit is turned off, the power electronic switch of the auxiliary shutdown branch of the bridge arm circuit is forward-biased, realizing the transfer of current from the phase where the bridge arm circuit is located to another phase.

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