Hybrid bridge arm and hybrid converter and control method and device, power transmission system

Abstract

The application provides a hybrid bridge arm, a hybrid converter, a control method and device, and a power transmission system. The hybrid bridge arm comprises a main circuit and an auxiliary branch. The main branch comprises a first half-controlled valve. The auxiliary branch is connected in parallel with the main branch. The auxiliary branch comprises a second valve, and the second valve comprises at least one full-bridge sub-module connected in series. In the embodiments of the application, the auxiliary branch of the hybrid bridge arm operates in a reactive compensation state to reduce the reactive power consumed by the first half-controlled valve of the main branch of the hybrid converter, and the auxiliary branch of the hybrid bridge arm operates in a reverse voltage to assist in turning off the first half-controlled valve of the main branch, so that the commutation failure is avoided.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high-voltage direct current transmission, in particular to a hybrid bridge arm and a hybrid converter, a control method and device, and a direct current transmission system. BACKGROUND

[0002] High-voltage and extra-high-voltage direct current transmission has large capacity, and a grid commutated converter with a twelve-pulse circuit structure is adopted in the prior art, each twelve-pulse circuit has two three-phase six-bridge arm circuits connected in series, and each bridge arm adopts a single large-capacity thyristor connected in series. The grid commutated converter has small loss and large capacity, and is suitable for long-distance power transmission. However, since the thyristor cannot be controlled to be turned off, the grid commutated converter has a commutation failure problem, and a large number of reactive power compensation devices need to be configured.

[0003] With the gradual increase in the number of high-voltage and extra-high-voltage direct current transmission systems connected, a multi-infeed direct current transmission system has been formed in multiple regional power grids. When multiple direct currents simultaneously fail to commutate, the safety operation of the regional alternating current power grid may be threatened. With the increasing proportion of new energy power generation, the alternating current voltage support capability decreases, and higher requirements are put forward for the stable operation and commutation failure suppression capability of the direct current transmission system.

[0004] Flexible direct current transmission and hybrid direct current transmission adopt voltage source converters to solve the commutation failure and alternating current voltage support problems, and can flexibly control reactive power. However, the voltage source converter adopts an IGBT (Insulated Gate Bipolar Transistor) device, which has large loss, small capacity, and oscillation risk. Therefore, the existing high-voltage direct current transmission, flexible direct current transmission, and hybrid direct current transmission technologies are difficult to meet the stringent requirements of the direct current transmission system on cost and performance. SUMMARY

[0005] The embodiment of the present application provides a hybrid bridge arm, which comprises a main branch and an auxiliary branch connected in parallel, the main branch comprises a first semi-controlled valve, and the auxiliary branch comprises a second valve, the second valve comprises at least one full-bridge sub-module connected in series.

[0006] According to some embodiments, the auxiliary branch further comprises a third valve and / or a fourth valve, the third valve is connected in series with the second valve, the third valve comprises a half-bridge sub-module connected in series, the fourth valve is connected in series with the second valve, and the fourth valve comprises a circuit in which a controlled device and an uncontrolled device are first connected in anti-parallel connection and then connected in series, or a circuit in which a controlled device and a semi-controlled device are first connected in anti-parallel connection and then connected in series.

[0007] According to some embodiments, the auxiliary branch further comprises a fifth valve connected in series with the second valve, the fifth valve comprising semi-controlled devices or / and uncontrolled devices, the semi-controlled devices or / and uncontrolled devices being connected in anti-parallel first to form a first sub-module, the first sub-module being connected in series second to form the fifth valve; or the semi-controlled devices or / and uncontrolled devices being connected in series first to form a second sub-module, the second sub-module being connected in anti-parallel second to form the fifth valve.

[0008] According to some embodiments, the auxiliary branch further comprises a resistance or / and an inductance connected in series with the second valve.

[0009] According to some embodiments, the hybrid bridge arm further comprises a switch, one end of the switch being connected to the main branch, the other end of the switch being connected to the auxiliary branch, the switch comprising at least one of a mechanical switch, a knife switch, and a power electronic switch.

[0010] According to some embodiments, the full-bridge sub-module comprises a full-bridge circuit composed of four fully-controlled modules and a capacitor, the half-bridge sub-module comprises a half-bridge circuit composed of two fully-controlled modules and a capacitor, the fully-controlled module comprises at least one fully-controlled device connected in series and a semi-controlled device connected in anti-parallel thereto, or at least one fully-controlled device connected in series and an uncontrolled device connected in anti-parallel thereto, the fully-controlled device comprising at least one of an IGCT, an IGBT, a GTO, and a MOSFET, the semi-controlled device comprising a thyristor, the uncontrolled device comprising a diode, and an arrester connected in parallel to both ends of the first semi-controlled valve, the second valve, the third valve, and the fourth valve.

[0011] The embodiments of the present application further provide a hybrid converter, comprising three-phase six bridge arms, at least one of the six bridge arms being the hybrid bridge arm as described above.

[0012] The embodiments of the present application further provide a high-voltage direct-current transmission system, comprising the hybrid converter as described above.

[0013] The embodiments of the present application further provide a control method of the hybrid converter as described above, comprising: controlling the main branch of the hybrid bridge arm of the converter to operate in an inverting state or a rectifying state; controlling the auxiliary branch of the hybrid bridge arm of the converter to operate in a reactive power compensation state, or / and an AC voltage or AC current control state; when the main branch of the hybrid bridge arm of the converter operates in the inverting state, a fault possibly causing a commutation failure of the hybrid bridge arm of the converter, controlling the auxiliary branch of the hybrid bridge arm to be negative, and the current of the main branch of the hybrid bridge arm being transferred to the auxiliary branch of the hybrid bridge arm; after the main branch of the hybrid bridge arm is turned off, controlling the auxiliary branch of the hybrid bridge arm to be turned off.

[0014] According to some embodiments, the control of the auxiliary branch of the hybrid bridge arm of the converter to operate in the reactive power compensation state comprises: controlling the auxiliary branch of the hybrid bridge arm to be turned on before the main branch of the hybrid bridge arm is turned on.

[0015] According to some embodiments, the control of the auxiliary branch of the hybrid bridge arm of the converter to operate in the reactive power compensation state comprises: the auxiliary branches of the three upper bridge arms of the hybrid converter constitute a static reactive power generator, and the auxiliary branches of the three upper bridge arms are controlled to operate in the reactive power compensation state; or / and the auxiliary branches of the three lower bridge arms of the hybrid converter constitute a static reactive power generator, and the auxiliary branches of the three lower bridge arms are controlled to operate in the reactive power compensation state.

[0016] According to some embodiments, when the auxiliary branch of the hybrid bridge arm of the converter is controlled to operate in the AC voltage or AC current control state, the auxiliary branch of the hybrid bridge arm which is not turned on controls the AC voltage or AC current of the phase.

[0017] According to some embodiments, the control of the auxiliary branch of the hybrid bridge arm to be negative voltage comprises: controlling the full-bridge sub-module of the second valve of the auxiliary branch of the hybrid bridge arm to be negative voltage.

[0018] According to some embodiments, the turning off of the main branch of the hybrid bridge arm comprises: the forward current of the first half-controlled valve of the main branch of the hybrid bridge arm is less than the holding current and the forward blocking capability is restored.

[0019] According to some embodiments, the control of the auxiliary branch of the hybrid bridge arm to be turned off comprises: controlling the second valve, the third valve or / and the fourth valve of the auxiliary branch of the hybrid bridge arm to be turned off.

[0020] According to some embodiments, after the auxiliary branch of the hybrid bridge arm is controlled to be turned off, if overvoltage occurs in the second valve, the third valve or / and the fourth valve, the method further comprises: controlling the main branch of the hybrid bridge arm to be turned on.

[0021] According to some embodiments, the control method further comprises: when the main branch of the hybrid bridge arm of the converter operates in the blocking state, or if the main branch of the hybrid bridge arm and the auxiliary branch of the hybrid bridge arm are connected through switches and when the switches of the main branch of the hybrid bridge arm are separated and the switches of the auxiliary branch of the hybrid bridge arm are closed, controlling the auxiliary branch of the hybrid bridge arm of the converter to operate in the inverter state or the rectifier state.

[0022] The application further provides a control device of the hybrid converter, comprising a detection unit and a control unit, the detection unit is used for detecting the operation parameters and faults of the hybrid converter; the control unit controls the main branch of the hybrid bridge arm of the converter to operate in an inverter state or a rectifier state based on the operation parameters of the hybrid converter; controls the auxiliary branch of the hybrid bridge arm of the converter to operate in a reactive power compensation state, or / and an AC voltage or AC current control state; when a fault occurs and may cause the hybrid bridge arm of the converter to fail to commutate, controls the auxiliary branch of the hybrid bridge arm to be negative pressure, and the current of the main branch of the hybrid bridge arm is transferred to the auxiliary branch of the hybrid bridge arm; after the main branch of the hybrid bridge arm is turned off, the control unit controls the auxiliary branch of the hybrid bridge arm to be turned off.

[0023] The technical scheme provided by the application forms the main branch and the auxiliary branch of the hybrid bridge arm by connecting at least a full-bridge sub-module in parallel to the bridge arm based on the half-controlled device, and the auxiliary branch is turned on to perform reactive power compensation before the main branch is turned on, thereby reducing the reactive power consumed by the converter and improving the efficiency of the converter compared with the traditional grid commutated converter; the full-bridge sub-module of the auxiliary branch is controlled to be negative pressure, so that the first half-controlled valve of the main branch can be reliably turned off, and then the auxiliary branch is turned off, thereby realizing the controllable commutation of the converter based on the half-controlled device, effectively inhibiting the occurrence of commutation failure, and ensuring the reliable operation of the converter; meanwhile, the current flowing through the auxiliary branch is small, the capacity of the selected device is small, and the cost is low. BRIEF DESCRIPTION OF DRAWINGS

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the application, the following will briefly introduce the drawings needed to be used in the embodiment description. Obviously, the drawings in the following description are only some embodiments of the application, and other drawings can be obtained by those skilled in the art without any creative effort based on these drawings.

[0025] Figure 1 is one of the schematic diagrams of the hybrid bridge arm provided by the embodiments of the application.

[0026] Figure 2 is the second schematic diagram of the hybrid bridge arm provided by the embodiments of the application.

[0027] Figure 3 is the third schematic diagram of the hybrid bridge arm provided by the embodiments of the application.

[0028] Figure 4 is the fourth schematic diagram of the hybrid bridge arm provided by the embodiments of the application.

[0029] Figure 5a is the schematic diagram of the full-bridge sub-module provided by the embodiments of the application.

[0030] Figure 5b is a half-bridge submodule schematic diagram provided by an embodiment of the present application.

[0031] Figure 6a is a second valve schematic diagram provided by an embodiment of the present application.

[0032] Figure 6b is a third valve schematic diagram provided by an embodiment of the present application.

[0033] Figure 6c is a fourth valve schematic diagram provided by an embodiment of the present application.

[0034] Figure 6d is another fourth valve schematic diagram provided by an embodiment of the present application.

[0035] Figure 7a is a fifth valve schematic diagram provided by an embodiment of the present application.

[0036] Figure 7b is another fifth valve schematic diagram provided by an embodiment of the present application.

[0037] Figure 7c is still another fifth valve schematic diagram provided by an embodiment of the present application.

[0038] Figure 7d is yet another fifth valve schematic diagram provided by an embodiment of the present application.

[0039] Figure 8 is one of mixed converter schematic diagrams provided by an embodiment of the present application.

[0040] Figure 9 is another mixed converter schematic diagram provided by an embodiment of the present application.

[0041] Figure 10 is still another mixed converter schematic diagram provided by an embodiment of the present application.

[0042] Figure 11 is yet another mixed converter schematic diagram provided by an embodiment of the present application.

[0043] Figure 12 is one of mixed converter schematic diagrams provided by an embodiment of the present application.

[0044] Figure 13 is a control method flowchart of a mixed converter provided by an embodiment of the present application.

[0045] Figure 14 is a control device schematic diagram of a mixed converter provided by an embodiment of the present application. DETAILED DESCRIPTION

[0046] 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, not all, of the embodiments of this application. 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.

[0047] It should be understood that 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 collections thereof.

[0048] Figure 1 This is one of the schematic diagrams of a hybrid bridge arm provided in the embodiments of this application. The hybrid bridge arm includes a main branch and an auxiliary branch connected in parallel.

[0049] like Figure 1 As shown, main branch 1 includes a first semi-controlled valve V41. The first semi-controlled valve V41 includes, but is not limited to, semi-controlled devices connected in series. Auxiliary branch 2 includes a second valve V42, which includes a full-bridge submodule connected in series.

[0050] According to some embodiments, the auxiliary branch also includes a third valve and / or a fourth valve. For example... Figure 2 As shown, the third valve V43 is connected in series with the second valve V42, and the third valve V43 includes a series-connected half-bridge submodule. Figure 3 As shown, the fourth valve V44 is connected in series with the second valve V42. The fourth valve V44 includes a fully controlled device connected in series and an uncontrolled device connected in antiparallel with it.

[0051] According to some embodiments, the auxiliary branch 2 also includes a fifth valve V45 connected in series with the second valve V42, such as... Figure 4 As shown. The fifth valve V45 includes semi-controlled devices and / or uncontrolled devices. The semi-controlled devices and / or uncontrolled devices are first connected in anti-parallel to form a first submodule, and the first submodule is then connected in series to form the fifth valve. Alternatively, the semi-controlled devices and / or uncontrolled devices are first connected in series to form a second submodule, and the second submodule is then connected in anti-parallel to form the fifth valve.

[0052] According to some embodiments, the auxiliary branch also includes a resistor and / or an inductor connected in series with the second valve.

[0053] According to some embodiments, the full-bridge submodule includes a full-bridge circuit consisting of four fully controlled modules and capacitor 4, such as... Figure 5a As shown. The half-bridge submodule consists of two fully controlled modules and a half-bridge circuit composed of capacitor 4, as shown. Figure 5bAs shown. The aforementioned fully controlled module includes at least one fully controlled device connected in series and an uncontrolled device connected in antiparallel to it. Figure 5a and Figure 5b The full control module uses an IGBT module, which includes an IGBT3 and a diode 7 connected in anti-parallel. The second valve V42 includes a series-connected full-bridge submodule, such as... Figure 6a As shown, the full-bridge submodule consists of IGBT modules connected in series in pairs and then in parallel, and is also connected in parallel with capacitor 4. The connection points of the IGBT modules connected in series in pairs serve as the positive and negative terminals of the full-bridge submodule, respectively. The third valve V43 includes a half-bridge submodule connected in series, such as... Figure 6b As shown, two IGBT modules are connected in series and then in parallel with capacitor 4. The connection point of the two IGBT modules in series serves as the positive terminal of the sub-module, and the other end of one IGBT module serves as the negative terminal of the sub-module. The fourth valve V44 includes a fully controlled device connected in series and an uncontrolled device connected in antiparallel. The fully controlled device is an IGBT, and the uncontrolled device is a diode. IGBT3 and diode 7 are first connected in antiparallel and then in series, as shown. Figure 6c As shown. The fourth valve V44 includes a fully controlled device and a semi-controlled device. The fully controlled device uses an IGCT, and the semi-controlled device uses a thyristor. IGCT5 and thyristor 6 are first connected in anti-parallel and then in series, as shown. Figure 6d As shown.

[0054] According to some embodiments, the semi-controlled device uses thyristors. Thyristors 6 are first connected in anti-parallel to form a first sub-module, and the first sub-module is then connected in series to form a fifth valve, such as... Figure 7a As shown. The semi-controlled devices use thyristors, and the uncontrolled devices use diodes. Thyristor 6 and diode 7 are first connected in anti-parallel to form the first sub-module. The first sub-module is then connected in series to form the fifth valve, as shown. Figure 7b As shown. The semi-controlled device uses thyristors. Thyristors 6 are first connected in series to form the second sub-module. Two second sub-modules are then connected in anti-parallel to form the fifth valve, as shown. Figure 7c As shown. The semi-controlled devices use thyristors, and the uncontrolled devices use diodes. Thyristor 6 and diode 7 are first connected in series to form two second sub-modules, and the two second sub-modules are then connected in anti-parallel to form the fifth valve, as shown. Figure 7d As shown.

[0055] Fully controlled devices include, but are not limited to, IGCT (Integrated Gate Commutated Thyristors), IGBT, GTO (Gate Turn-Off Thyristor), and MOSFET (Metal-Oxide Semiconductor Field Effect Transistor). Semi-controlled devices include, but are not limited to, thyristors. Uncontrolled devices include, but are not limited to, diodes. Fully controlled devices are configured with corresponding drive circuits and / or buffer circuits, while semi-controlled devices are configured with corresponding trigger circuits.

[0056] According to some embodiments, surge arresters are connected in parallel at both ends of the first semi-controlled valve V41, the second valve V42, the third valve V43, or the fourth valve V44.

[0057] According to some embodiments, a second semi-control valve is connected in parallel across the two ends of the second valve V42, the third valve V43, or the fourth valve V44 to protect the fully controllable components of the second valve V42, the third valve V43, or the fourth valve V44.

[0058] According to some embodiments, surge arresters are connected in parallel across the fifth valve V45.

[0059] Figure 8 This is one of the schematic diagrams of a hybrid converter provided in the embodiments of this application. The hybrid converter includes a three-phase six-arm bridge, and each arm adopts the hybrid arm as described above.

[0060] like Figure 8 As shown, the main branch of the upper arm of phase A consists of the first semi-controlled valve V41, and the auxiliary branch consists of the second valve V42. The second valve V42 includes a full-bridge submodule.

[0061] The main branch of the upper arm of phase B consists of the first semi-controlled valve V61, and the auxiliary branch consists of the second valve V62. The second valve V62 includes a full-bridge submodule.

[0062] The main branch of the upper arm of phase C consists of the first semi-controlled valve V21, and the auxiliary branch consists of the second valve V22. The second valve V22 includes a full-bridge submodule.

[0063] The main branch of the lower arm of phase A consists of the first semi-controlled valve V11, and the auxiliary branch consists of the second valve V12. The second valve V12 includes a full-bridge submodule.

[0064] The main branch of the B-phase lower arm consists of the first semi-controlled valve V31, and the auxiliary branch consists of the second valve V32. The second valve V32 includes a full-bridge submodule.

[0065] The main branch of the lower arm of phase C consists of the first semi-controlled valve V51, and the auxiliary branch consists of the second valve V52. The second valve V52 includes a full-bridge submodule.

[0066] According to some embodiments, the four fully controlled modules of the full-bridge submodule employ multiple fully controlled devices connected in series, and are applied in high-voltage converters.

[0067] Figure 9 This is a second schematic diagram of a hybrid converter provided in the embodiments of this application.

[0068] exist Figure 8 Based on the previous embodiment, the second valve of the auxiliary branch of each bridge arm includes three full-bridge sub-modules connected in series. The first semi-controlled valve of the main branch of each bridge arm is connected in parallel with a surge arrester.

[0069] The first semi-controlled valve V41 of the main circuit of the upper arm of phase A is connected in parallel with surge arrester F41. The first semi-controlled valve V61 of the main circuit of the upper arm of phase B is connected in parallel with surge arrester F61. The first semi-controlled valve V21 of the main branch of the upper arm of phase C is connected in parallel with surge arrester F21. The first semi-controlled valve V11 of the main branch of the lower arm of phase A is connected in parallel with surge arrester F11. The first semi-controlled valve V31 of the main branch of the lower arm of phase B is connected in parallel with surge arrester F31. The first semi-controlled valve V51 of the main branch of the lower arm of phase C is connected in parallel with surge arrester F51.

[0070] According to some embodiments, the above three full-bridge submodules can be expanded into multiple full-bridge submodules connected in series according to the voltage level.

[0071] Figure 10 This is the third schematic diagram of a hybrid converter provided in the embodiments of this application.

[0072] exist Figure 8 Based on the previous embodiment, the auxiliary branch of each bridge arm includes a second valve and a third valve connected in series. The second valve includes two full-bridge submodules connected in series, and the third valve includes a half-bridge submodule. The first half-controlled valve of the main circuit of each bridge arm is connected in parallel to the surge arrester.

[0073] like Figure 10 As shown, the main branch of the upper arm of phase A consists of the first semi-controlled valve V41, and the auxiliary branch consists of the second valve V42 and the third valve V43 connected in series. The second valve V42 includes two full-bridge sub-modules connected in series, and the third valve V43 includes one half-bridge module. The first semi-controlled valve V41 is connected in parallel with the surge arrester F41.

[0074] The main branch of the upper arm of phase B consists of the first semi-controlled valve V61, and the auxiliary branch consists of the second valve V62 and the third valve V63 connected in series. The second valve V62 includes two full-bridge sub-modules connected in series, and the third valve V63 includes one half-bridge module. The first semi-controlled valve V61 is connected in parallel with the surge arrester F61.

[0075] The main branch of the upper arm of phase C consists of the first semi-controlled valve V21, and the auxiliary branch consists of the second valve V22 and the third valve V23 connected in series. The second valve V22 includes two full-bridge sub-modules connected in series, and the third valve V23 includes one half-bridge module. The first semi-controlled valve V21 is connected in parallel with the surge arrester F21.

[0076] The main branch of the lower arm of phase A consists of the first semi-controlled valve V11, and the auxiliary branch consists of the second valve V12 and the third valve V13 connected in series. The second valve V12 includes two full-bridge sub-modules connected in series, and the third valve V13 includes one half-bridge module. The first semi-controlled valve V11 is connected in parallel with the surge arrester F11.

[0077] The main branch of the B-phase lower arm consists of the first semi-controlled valve V31, and the auxiliary branch consists of the second valve V32 and the third valve V33 connected in series. The second valve V32 includes two full-bridge sub-modules connected in series, and the third valve V33 includes one half-bridge module. The first semi-controlled valve V31 is connected in parallel with the surge arrester F31.

[0078] The main branch of the C-phase lower arm consists of the first semi-controlled valve V51, and the auxiliary branch consists of the second valve V52 and the third valve V53 connected in series. The second valve V52 includes two full-bridge sub-modules connected in series, and the third valve V53 includes one half-bridge module. The first semi-controlled valve V51 is connected in parallel with the surge arrester F51.

[0079] According to some embodiments, the two full-bridge submodules can be expanded into multiple full-bridge submodules connected in series according to the voltage level, and the one half-bridge submodule can be expanded into multiple half-bridge submodules connected in series according to the voltage level.

[0080] Optionally, surge arresters are connected in parallel across the second or third valve.

[0081] Figure 11 This is the fourth schematic diagram of a hybrid converter provided in the embodiments of this application.

[0082] exist Figure 8 Based on the embodiment, the auxiliary branch of each bridge arm includes a second valve, a fourth valve, and a fifth valve connected in series. The second valve includes two full-bridge sub-modules connected in series, the fourth valve includes a fully controlled device and an uncontrolled device connected in antiparallel, and the fifth valve includes two semi-controlled devices connected in antiparallel. The first semi-controlled valve of the main branch of each bridge arm is connected in parallel with a surge arrester.

[0083] like Figure 11As shown, the main branch of the upper arm of phase A consists of the first semi-controlled valve V41, and the auxiliary branch consists of the second valve V42, the fourth valve V44 and the fifth valve V45 connected in series. The second valve V42 includes two full-bridge sub-modules connected in series. The fourth valve V44 includes a fully controlled device and an uncontrolled device connected in antiparallel to it. The fifth valve V45 includes two semi-controlled devices connected in antiparallel. The first semi-controlled valve V41 is connected in parallel with the surge arrester F41.

[0084] The main branch of the upper arm of phase B consists of the first semi-controlled valve V61, and the auxiliary branch consists of the second valve V62, the fourth valve V64 and the fifth valve V65 connected in series. The second valve V62 includes two full-bridge sub-modules connected in series. The fourth valve V64 includes a fully controlled device and an uncontrolled device connected in antiparallel to it. The fifth valve V65 includes two semi-controlled devices connected in antiparallel. The first semi-controlled valve V61 is connected in parallel with the surge arrester F61.

[0085] The main branch of the upper arm of phase C consists of the first semi-controlled valve V21, and the auxiliary branch consists of the second valve V22, the fourth valve V24 and the fifth valve V25 connected in series. The second valve V22 includes two full-bridge sub-modules connected in series. The fourth valve V24 includes a fully controlled device and an uncontrolled device connected in antiparallel to it. The fifth valve V25 includes two semi-controlled devices connected in antiparallel. The first semi-controlled valve V21 is connected in parallel with the surge arrester F21.

[0086] The main branch of the lower arm of phase A consists of the first semi-controlled valve V11, and the auxiliary branch consists of the second valve V12, the fourth valve V14 and the fifth valve V15 connected in series. The second valve V12 includes two full-bridge sub-modules connected in series. The fourth valve V14 includes a fully controlled device and an uncontrolled device connected in antiparallel to it. The fifth valve V15 includes two semi-controlled devices connected in antiparallel. The first semi-controlled valve V11 is connected in parallel with the surge arrester F11.

[0087] The main branch of the B-phase lower arm consists of the first semi-controlled valve V31, and the auxiliary branch consists of the second valve V32, the fourth valve V34 and the fifth valve V35 connected in series. The second valve V32 includes two full-bridge sub-modules connected in series. The fourth valve V34 includes a fully controlled device and an uncontrolled device connected in antiparallel. The fifth valve V35 includes two semi-controlled devices connected in antiparallel. The first semi-controlled valve V31 is connected in parallel with the surge arrester F31.

[0088] The main branch of the lower arm of phase C consists of the first semi-controlled valve V51, and the auxiliary branch consists of the second valve V52, the fourth valve V54 and the fifth valve V55 connected in series. The second valve V52 includes two full-bridge sub-modules connected in series. The fourth valve V54 includes a fully controlled device and an uncontrolled device connected in antiparallel to it. The fifth valve V55 includes two semi-controlled devices connected in antiparallel. The first semi-controlled valve V51 is connected in parallel with the surge arrester F51.

[0089] According to some embodiments, the two full-bridge submodules mentioned above can be expanded into multiple full-bridge submodules connected in series according to the voltage level; the one fully controlled device and the uncontrolled device connected in antiparallel to it can be expanded into multiple fully controlled devices and uncontrolled devices connected in antiparallel to it connected in series according to the voltage level; and the group of two antiparallel semi-controlled devices can be expanded into multiple groups connected in series according to the voltage level.

[0090] Optionally, surge arresters are connected in parallel across the second, fourth, or fifth valve.

[0091] Figure 12 This is the fifth schematic diagram of a hybrid converter provided in the embodiments of this application.

[0092] exist Figure 9 Based on the previous embodiment, the main branch and the auxiliary branch are connected by a switch.

[0093] like Figure 12 As shown, the main branch of the upper arm of phase A consists of the first semi-controlled valve V41, and the auxiliary branch consists of the second valve V42. The second valve V42 includes three full-bridge sub-modules connected in series. The upper arm of phase A is connected in parallel with the surge arrester F41. The main branch and the auxiliary branch are connected through switches S71, S73, S41 and S42.

[0094] The main branch of the upper arm of phase B consists of the first semi-controlled valve V61, and the auxiliary branch consists of the second valve V62. The second valve V62 includes three full-bridge sub-modules connected in series. The upper arm of phase B is connected in parallel with the surge arrester F61. The main branch and the auxiliary branch are connected through switches S71, S73, S61 and S62.

[0095] The main branch of the upper arm of phase C consists of the first semi-controlled valve V21, and the auxiliary branch consists of the second valve V22. The second valve V22 includes three full-bridge sub-modules connected in series. The upper arm of phase C is connected in parallel with the surge arrester F21. The main branch and the auxiliary branch are connected through switches S71, S73, S21 and S22.

[0096] The main branch of the lower arm of phase A consists of the first semi-controlled valve V11, and the auxiliary branch consists of the second valve V12. The second valve V12 includes three full-bridge sub-modules connected in series. The lower arm of phase A is connected in parallel with the surge arrester F11. The main branch and the auxiliary branch are connected through switches S72, S74, S11 and S12.

[0097] The main branch of the B-phase lower arm consists of the first semi-controlled valve V31, and the auxiliary branch consists of the second valve V32. The second valve V32 includes three full-bridge sub-modules connected in series. The B-phase lower arm is connected in parallel with a surge arrester F31. The main branch and the auxiliary branch are connected through switches S72, S74, S31 and S32.

[0098] The main branch of the lower arm of phase C consists of the first semi-controlled valve V51, and the auxiliary branch consists of the second valve V52. The second valve V52 includes three full-bridge sub-modules connected in series. The lower arm of phase C is connected in parallel with the surge arrester F51. The main branch and the auxiliary branch are connected through switches S72, S74, S51 and S52.

[0099] According to some embodiments, the above three full-bridge submodules can be expanded into multiple full-bridge submodules connected in series according to the voltage level.

[0100] This application also provides a high-voltage direct current transmission system, including the hybrid converter described above.

[0101] Figure 13 This is a schematic flowchart of a control method for a hybrid converter provided in an embodiment of this application.

[0102] In S110, the main branch of the hybrid arm of the control converter operates in either inverter or rectifier mode.

[0103] like Figure 9 , Figure 10 , Figure 11 and Figure 12 As shown, the first semi-controlled valves V41, V61, V21, V11, V31, and V51 operate in either inverter or rectifier mode. Their working principle is the same as that of a grid-commutated converter.

[0104] In S120, the auxiliary branch of the hybrid arm of the control converter operates in reactive power compensation state and / or AC voltage or AC current control state.

[0105] By controlling the conduction of auxiliary branches before the main branches of the hybrid bridge arm are conducted, the auxiliary branches of the hybrid bridge arm can be made to operate in a reactive power compensation state.

[0106] like Figure 9As shown, taking the upper arm of phase A as an example, before the first half-control valve V41 is turned on, the number of full-bridge submodules connected by the second valve V42 is controlled according to the phase of the phase A voltage, thus controlling the phase A current. After the first half-control valve V41 is turned on, the second valve V42 is locked, that is, the pulses of the IGBTs of the full-bridge submodules of the second valve V42 are stopped. When the IGBTs of full-control modules T41 and T44 are turned on, the corresponding full-bridge submodules are connected, and the voltage is the voltage across capacitor C41. When the IGBT of full-control module T41 is turned on and the IGBT of full-control module T44 is turned off, the corresponding full-bridge submodule is deactivated. When the IGBTs of full-control modules T45 and T48 are turned on, the corresponding full-bridge submodules are connected, and the voltage is the voltage across capacitor C42. When the IGBT of full-control module T45 is turned on and the IGBT of full-control module T48 is turned off, the corresponding full-bridge submodule is deactivated. When the IGBTs of the full control modules T49 and T72 are turned on, the full-bridge submodules are engaged, and the voltage is the voltage across capacitor C43. When the IGBTs of the full control modules T49 and T72 are turned off, the full-bridge submodules are disengaged.

[0107] like Figure 10 As shown, taking the upper bridge arm of phase A as an example, before the first half-control valve V41 is turned on, the number of full-bridge sub-modules connected by the second valve V42 and the number of half-bridge sub-modules connected by the second valve V43 are controlled according to the phase of the phase A voltage, thereby controlling the phase A current. After the first half-control valve V41 is turned on, the second valve V42 and the third valve V43 are blocked, that is, the pulses of the IGBTs of the full-bridge sub-module of the second valve V42 and the half-bridge sub-module of the third valve V43 are stopped. When the IGBTs of fully controlled modules T41 and T44 are turned on, the corresponding full-bridge submodule is engaged, and the voltage is the voltage across capacitor C41. When the IGBT of fully controlled module T41 is turned on and the IGBT of fully controlled module T44 is turned off, the corresponding full-bridge submodule is disengaged. When the IGBTs of fully controlled modules T45 and T48 are turned on, the corresponding full-bridge submodule is engaged, and the voltage is the voltage across capacitor C42. When the IGBT of fully controlled module T45 is turned on and the IGBT of fully controlled module T48 is turned off, the corresponding full-bridge submodule is disengaged. When the IGBT of fully controlled module T83 is turned on and the IGBT of fully controlled module T84 is turned off, the corresponding half-bridge submodule is engaged, and the voltage is the voltage across capacitor C44. When the IGBT of fully controlled module T83 is turned off and the IGBT of fully controlled module T84 is turned on, the corresponding half-bridge submodule is disengaged, and the voltage is zero.

[0108] like Figure 11As shown, taking the upper arm of phase A as an example, before the first half-control valve V41 is turned on, the fourth valve V44 and the fifth valve V45 are turned on according to the phase of the phase A voltage, the number of full-bridge sub-modules connected by the second valve V42 is controlled, and the phase A current is controlled. After the first half-control valve V41 is turned on, the second valve V42, the fourth valve V44 and the fifth valve V45 are blocked, that is, the pulses of the IGBT of the full-bridge sub-module of the second valve V42 are stopped, the pulses of the IGBT of the full-control module T95 of the fourth valve V44 are stopped, and the pulses of the thyristor of the half-control module T96 of the fifth valve V45 are stopped. When the IGBTs of fully controlled modules T41 and T44 are turned on, the corresponding full-bridge submodule is activated, and the voltage is the voltage across capacitor C41. When the IGBT of fully controlled module T41 is turned on and the IGBT of fully controlled module T44 is turned off, the corresponding full-bridge submodule is deactivated. When the IGBTs of fully controlled modules T45 and T48 are turned on, the corresponding full-bridge submodule is activated, and the voltage is the voltage across capacitor C42. When the IGBT of fully controlled module T45 is turned on and the IGBT of fully controlled module T48 is turned off, the corresponding full-bridge submodule is deactivated.

[0109] like Figure 12 As shown, taking the upper bridge arm of phase A as an example, before the first half-control valve V41 is turned on, the number of full-bridge sub-modules put into the second valve V42 is controlled according to the phase of the phase A voltage, and the phase A current is controlled. After the first half-control valve V41 is turned on, the second valve V42 is locked, that is, the pulse of the IGBT of the full-bridge sub-module of the second valve V42 is stopped. When the IGBTs of fully controlled modules T41 and T44 are turned on, the corresponding full-bridge submodule is activated, and the voltage is the voltage across capacitor C41. When the IGBT of fully controlled module T41 is turned on and the IGBT of fully controlled module T44 is turned off, the corresponding full-bridge submodule is deactivated. When the IGBTs of fully controlled modules T45 and T48 are turned on, the corresponding full-bridge submodule is activated, and the voltage is the voltage across capacitor C42. When the IGBT of fully controlled module T45 is turned on and the IGBT of fully controlled module T48 is turned off, the corresponding full-bridge submodule is deactivated. When the IGBTs of fully controlled modules T49 and T72 are turned on, the corresponding full-bridge submodule is activated, and the voltage is the voltage across capacitor C43. When the IGBT of fully controlled module T49 is turned on and the IGBT of fully controlled module T72 is turned off, the corresponding full-bridge submodule is deactivated.

[0110] Optionally, the auxiliary branches of the three upper arms of the hybrid converter form a static var generator (SVG), which controls the auxiliary branches of the three upper arms of the hybrid converter to operate in a reactive power compensation state; or / and the auxiliary branches of the three lower arms of the hybrid converter form a static var generator, which controls the auxiliary branches of the three lower arms of the hybrid converter to operate in a reactive power compensation state, thereby enabling the auxiliary branches of the hybrid arms to operate in a reactive power compensation state.

[0111] like Figure 9 As shown, the second valve V42 of the upper bridge arm of phase A, the second valve V62 of the upper bridge arm of phase B, and the second valve V22 of the upper bridge arm of phase C are operated in reactive power compensation state, with the same working principle as the static var generator; or / and the second valve V12 of the lower bridge arm of phase A, the second valve V32 of the lower bridge arm of phase B, and the second valve V52 of the lower bridge arm of phase C are operated in reactive power compensation state, with the same working principle as the static var generator.

[0112] like Figure 10 As shown, the second valve V42 and the third valve V43 of the upper bridge arm of phase A, the second valve V62 and the third valve V63 of the upper bridge arm of phase B, and the second valve V22 and the third valve V23 of the upper bridge arm of phase C are operated in reactive power compensation state, with the same working principle as the static var generator; or / and the second valve V12 and the third valve V13 of the lower bridge arm of phase A, the second valve V32 and the third valve V33 of the lower bridge arm of phase B, and the second valve V52 and the third valve V53 of the lower bridge arm of phase C are operated in reactive power compensation state, with the same working principle as the static var generator.

[0113] like Figure 11 As shown, the second valve V42, the fourth valve V44, and the fifth valve V45 of the upper bridge arm of phase A, the second valve V62, the fourth valve V64, and the fifth valve V65 of the upper bridge arm of phase B, and the second valve V22, the fourth valve V24, and the fifth valve V25 of the upper bridge arm of phase C are operated in reactive power compensation mode, with the same working principle as a static var generator; or / and the second valve V12, the fourth valve V14, and the fifth valve V15 of the lower bridge arm of phase A, the second valve V32, the fourth valve V34, and the fifth valve V35 of the lower bridge arm of phase B, and the second valve V52, the fourth valve V54, and the fifth valve V55 of the lower bridge arm of phase C are operated in reactive power compensation mode, with the same working principle as a static var generator.

[0114] like Figure 12 As shown, the second valve V42 of the upper bridge arm of phase A, the second valve V62 of the upper bridge arm of phase B, and the second valve V22 of the upper bridge arm of phase C operate in reactive power compensation mode, with the same working principle as the static var generator. Optionally, the switch S73 of the auxiliary branch can be disconnected; or / and the second valve V12 of the lower bridge arm of phase A, the second valve V32 of the lower bridge arm of phase B, and the second valve V52 of the lower bridge arm of phase C operate in reactive power compensation mode, with the same working principle as the static var generator. Optionally, the switch S74 of the auxiliary branch can be disconnected.

[0115] By controlling the AC voltage or AC current of the phase in the auxiliary branch of the hybrid bridge arm, which is not connected to the main branch, the auxiliary branch of the hybrid bridge arm can be operated in an AC voltage or AC current control state.

[0116] like Figure 9As shown, when the first half-control valve V41 of the upper bridge arm of phase A and the first half-control valve V51 of the lower bridge arm of phase C are open, the second valve V12 of the lower bridge arm of phase A controls the AC voltage or AC current of phase A, the second valve V62 of the upper bridge arm of phase B or the second valve V32 of the lower bridge arm of phase B controls the AC voltage or AC current of phase B, and the second valve V22 of the upper bridge arm of phase C controls the AC voltage or AC current of phase C. When the first half-control valve V41 of the upper bridge arm of phase A, the first half-control valve V61 of the upper bridge arm of phase B and the first half-control valve V51 of the lower bridge arm of phase C are open, the second valve V12 of the lower bridge arm of phase A controls the AC voltage or AC current of phase A, the second valve V32 of the lower bridge arm of phase B controls the AC voltage or AC current of phase B, and the second valve V22 of the upper bridge arm of phase C controls the AC voltage or AC current of phase C.

[0117] like Figure 10 As shown, when the first half-control valve V41 of the upper bridge arm of phase A and the first half-control valve V51 of the lower bridge arm of phase C are turned on, the second valve V12 and the third valve V13 of the lower bridge arm of phase A control the AC voltage or AC current of phase A, the second valve V62 and the third valve V63 of the upper bridge arm of phase B or the second valve V32 and the third valve V33 of the lower bridge arm of phase B control the AC voltage or AC current of phase B, and the second valve V22 and the third valve V23 of the upper bridge arm of phase C control the AC voltage or AC current of phase C. When the first half-control valve V41 of the upper bridge arm of phase A, the first half-control valve V61 of the upper bridge arm of phase B, and the first half-control valve V51 of the lower bridge arm of phase C are turned on, the second valve V12 and the third valve V13 of the lower bridge arm of phase A control the AC voltage or AC current of phase A, the second valve V32 and the third valve V33 of the lower bridge arm of phase B control the AC voltage or AC current of phase B, and the second valve V22 and the third valve V23 of the upper bridge arm of phase C control the AC voltage or AC current of phase C.

[0118] like Figure 11As shown, when the first half-control valve V41 of the upper bridge arm of phase A and the first half-control valve V51 of the lower bridge arm of phase C are turned on, the second valve V12, the fourth valve V14 and the fifth valve V15 of the lower bridge arm of phase A control the AC voltage or AC current of phase A, the second valve V62, the fourth valve V64 and the fifth valve V65 of the upper bridge arm of phase B or the second valve V32, the fourth valve V34 and the fifth valve V35 of the lower bridge arm of phase B control the AC voltage or AC current of phase B, and the second valve V22, the fourth valve V24 and the fifth valve V25 of the upper bridge arm of phase C control the AC voltage or AC current of phase C. When the first half-control valve V41 of the upper arm of phase A, the first half-control valve V61 of the upper arm of phase B, and the first half-control valve V51 of the lower arm of phase C are turned on, the second valve V12, the fourth valve V14, and the fifth valve V15 of the lower arm of phase A control the AC voltage or AC current of phase A; the second valve V32, the fourth valve V34, and the fifth valve V35 of the lower arm of phase B control the AC voltage or AC current of phase B; and the second valve V22, the fourth valve V24, and the fifth valve V25 of the upper arm of phase C control the AC voltage or AC current of phase C.

[0119] like Figure 12 As shown, when the first half-control valve V41 of the upper bridge arm of phase A and the first half-control valve V51 of the lower bridge arm of phase C are open, the second valve V12 of the lower bridge arm of phase A controls the AC voltage or AC current of phase A, the second valve V62 of the upper bridge arm of phase B or the second valve V32 of the lower bridge arm of phase B controls the AC voltage or AC current of phase B, and the second valve V22 of the upper bridge arm of phase C controls the AC voltage or AC current of phase C. When the first half-control valve V41 of the upper bridge arm of phase A, the first half-control valve V61 of the upper bridge arm of phase B and the first half-control valve V51 of the lower bridge arm of phase C are open, the second valve V12 of the lower bridge arm of phase A controls the AC voltage or AC current of phase A, the second valve V32 of the lower bridge arm of phase B controls the AC voltage or AC current of phase B, and the second valve V22 of the upper bridge arm of phase C controls the AC voltage or AC current of phase C.

[0120] When the main branch of the hybrid arm of the converter is in the locked state, or if the main branch and the auxiliary branch are connected by a switch and the switch is open, the auxiliary branch controlling the hybrid arm of the converter is in the inverter state or the rectifier state.

[0121] like Figure 12 As shown, when the switches S71 and S41 of the main branch are open and the switches S73 and S42 of the auxiliary branch are closed, the auxiliary branch of the hybrid bridge arm of the hybrid converter is controlled to operate in either inverter or rectification mode. When the switches S71, S72 and S41, S61, S21, S11, S31, and S51 of the main branch are open and the switches S73, S74 and S42, S62, S22, S12, S32, and S52 of the auxiliary branch are closed, the auxiliary branch of the hybrid converter is controlled to operate in either inverter or rectification mode, with the same operating principle as the voltage source converter.

[0122] In S130, when the main branch of the hybrid arm of the converter is operating in inverter mode and a fault may cause the hybrid arm of the converter to fail to commutate, the auxiliary branch of the hybrid arm is controlled to be under negative voltage, and the current of the main branch of the hybrid arm is transferred to the auxiliary branch.

[0123] According to some embodiments, 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, but are not limited to these. The aforementioned potential causes of commutation failure in the hybrid arm of the converter are determined based on the shut-off time of the first half-controlled valve of the hybrid arm and the AC voltage. If the first half-controlled valve of the hybrid arm has not closed by the shut-off time under normal AC voltage, it is determined to be a potential cause of commutation failure in the hybrid arm of the converter, but is not limited to this. Controlling the auxiliary branch of the aforementioned hybrid arm to negative pressure is achieved by controlling the second valve full-bridge submodule to negative pressure.

[0124] like Figure 9 As shown, taking the upper bridge arm of phase A as an example, when the upper bridge arm of phase A switches to the upper bridge arm of phase B, if a fault occurs that may cause the first semi-control valve V41 to fail to switch, the second control valve V42 will be under negative pressure. When the IGBTs of the full control modules T42 and T43 are turned on, the full bridge submodule presents a reverse voltage across capacitor C41, which is a negative voltage. When the IGBTs of the full control modules T46 and T47 are turned on, the full bridge submodule presents a reverse voltage across capacitor C42, which is a negative voltage. When the IGBTs of the full control modules T40 and T71 are turned on, the full bridge submodule presents a reverse voltage across capacitor C43, which is a negative voltage.

[0125] like Figure 10 As shown, taking the upper bridge arm of phase A as an example, when the upper bridge arm of phase A switches to the upper bridge arm of phase B, if a fault occurs that may cause the first half-control valve V41 to fail to switch, the second control valve V42 will be under negative pressure, and the third control valve V43 will be under zero pressure. When the IGBTs of the full control modules T42 and T43 are turned on, the full bridge submodule presents a reverse voltage across capacitor C41, which is a negative voltage. When the IGBTs of the full control modules T46 and T47 are turned on, the full bridge submodule presents a reverse voltage across capacitor C42, which is a negative voltage. When the IGBT of the full control module T83 is turned off and the IGBT of the full control module T84 is turned on, the half bridge submodule is deactivated, and the voltage is zero.

[0126] like Figure 11As shown, taking the upper bridge arm of phase A as an example, when the upper bridge arm of phase A switches to the upper bridge arm of phase B, if a fault occurs that may cause the first semi-controlled valve V41 to fail to switch, the second valve V42 will be controlled to be at a negative pressure, the fourth valve will be controlled to be open, and the fifth valve will be controlled to be open. When the IGBTs of the full control modules T42 and T43 are turned on, the full bridge submodule presents a reverse voltage across capacitor C41, which is a negative voltage. When the IGBTs of the full control modules T46 and T47 are turned on, the full bridge submodule presents a reverse voltage across capacitor C42, which is a negative voltage.

[0127] like Figure 12 As shown, taking the upper bridge arm of phase A as an example, when the upper bridge arm of phase A switches to the upper bridge arm of phase B, if a fault occurs that may cause the first semi-control valve V41 to fail to switch, the second control valve V42 will be under negative pressure. When the IGBTs of the full control modules T42 and T43 are turned on, the full bridge submodule presents a reverse voltage across capacitor C41, which is a negative voltage. When the IGBTs of the full control modules T46 and T47 are turned on, the full bridge submodule presents a reverse voltage across capacitor C42, which is a negative voltage. When the IGBTs of the full control modules T40 and T71 are turned on, the full bridge submodule presents a reverse voltage across capacitor C43, which is a negative voltage.

[0128] When the hybrid arm commutation of the converter does not fail, return to S110.

[0129] In S140, after the main branch of the hybrid bridge arm is turned off, the auxiliary branch of the hybrid bridge arm is turned off, thus realizing the transfer of current from the phase where the hybrid bridge arm is located to another phase.

[0130] The main branch shutdown of the hybrid bridge arm is achieved when the forward current of the first semi-controlled valve of the main branch of the hybrid bridge arm 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 shutdown time, with a shutdown time of less than 700µs, but not limited to this.

[0131] The auxiliary branch of the control hybrid bridge arm is shut off by controlling the second, third and / or fourth valves of the auxiliary branch.

[0132] like Figure 9 As shown, taking the upper bridge arm of phase A as an example, when the forward current of the first semi-controlled valve V41 is less than the holding current and the forward blocking capability is restored, the second valve V42 is turned off, that is, the IGBTs of the full control modules T42 and T43 are turned off, the IGBTs of the full control modules T46 and T47 are turned off, the IGBTs of the full control modules T40 and T71 are turned off, and the forced current is switched from the upper bridge arm of phase A to the upper bridge arm of phase B.

[0133] likeFigure 10 As shown, taking the upper bridge arm of phase A as an example, when the forward current of the first semi-controlled valve V41 is less than the holding current and the forward blocking capability is restored, the second valve V42 and the third valve V43 are turned off, that is, the IGBTs of the full control modules T42 and T43 are turned off, the IGBTs of the full control modules T46 and T47 are turned off, the IGBT of the full control module T84 is turned off, and the forced current is switched from the upper bridge arm of phase A to the upper bridge arm of phase B.

[0134] like Figure 11 As shown, taking the upper bridge arm of phase A as an example, when the forward current of the first semi-controlled valve V41 is less than the holding current and the forward blocking capability is restored, the second valve V42 and the fourth valve V44 are turned off, that is, the IGBTs of the full control modules T42 and T43 are turned off, the IGBTs of the full control modules T46 and T47 are turned off, the IGBT of the full control module T95 is turned off, and the forced current is switched from the upper bridge arm of phase A to the upper bridge arm of phase B.

[0135] like Figure 12 As shown, taking the upper bridge arm of phase A as an example, when the forward current of the first semi-controlled valve V41 is less than the holding current and the forward blocking capability is restored, the second valve V42 is turned off, that is, the IGBTs of the full control modules T42 and T43 are turned off, the IGBTs of the full control modules T46 and T47 are turned off, the IGBTs of the full control modules T40 and T71 are turned off, and the forced current is switched from the upper bridge arm of phase A to the upper bridge arm of phase B.

[0136] After the auxiliary branch of the control hybrid bridge arm is turned off, if the second, third, or fourth valve experiences an overvoltage, the main branch is turned on to protect the devices of the second, third, or fourth valve.

[0137] like Figure 9 As shown, taking the upper arm of phase A as an example, after the auxiliary branch of the hybrid arm is turned off, if the second valve V42 experiences an overvoltage, the first semi-controlled valve V41 of the main branch 1 will be turned on.

[0138] like Figure 10 As shown, taking the upper arm of phase A as an example, after the auxiliary branch of the hybrid arm is turned off, if the second valve V42 or the third valve V43 experiences overvoltage, the first semi-controlled valve V41 of the main branch 1 is turned on.

[0139] like Figure 11 As shown, taking the upper arm of phase A as an example, after the auxiliary branch of the hybrid arm is turned off, if the second valve V42 or the fourth valve V44 experiences overvoltage, the first semi-controlled valve V41 of the main branch 1 is turned on.

[0140] like Figure 12As shown, taking the upper arm of phase A as an example, after the auxiliary branch of the hybrid arm is turned off, if the second valve V42 experiences an overvoltage, the first semi-controlled valve V41 of the main branch 1 will be turned on.

[0141] Back to S110.

[0142] Figure 14 This is a schematic diagram of a control device for a hybrid converter provided in an embodiment of this application. The control device 300 includes a detection unit 310 and a control unit 320.

[0143] The detection unit 310 is used to detect the operating parameters and faults of the hybrid converter. Based on the operating parameters of the hybrid converter, the control unit 320 controls the main branch of the hybrid arm to operate in inverter or rectification mode; controls the auxiliary branch of the hybrid arm to operate in reactive power compensation mode and / or AC voltage or AC current control mode; when a fault occurs that may cause commutation failure of the hybrid arm, the auxiliary branch of the hybrid arm is controlled to be under negative voltage, and the current in the main branch of the hybrid arm is transferred to the auxiliary branch; after the main branch of the hybrid arm is turned off, the auxiliary branch is also turned off, thus transferring the current from the phase where the hybrid arm 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 hybrid bridge arm, comprising: Main branch circuit, including the first semi-control valve; An auxiliary branch is connected in parallel with the main branch, and the auxiliary branch includes: The second valve includes at least one full-bridge submodule connected in series; A third valve is connected in series with the second valve, the third valve including a half-bridge sub-module connected in series; or / and a fourth valve is connected in series with the second valve, the fourth valve including a circuit in which fully controlled devices and uncontrolled devices are first connected in anti-parallel and then in series, or a circuit in which fully controlled devices and half-controlled devices are first connected in anti-parallel and then in series. The auxiliary branch operates in a reactive power compensation state and / or an AC voltage or AC current control state.

2. The hybrid bridge arm as described in claim 1, wherein, The auxiliary branch also includes: A fifth valve is connected in series with the second valve. The fifth valve includes a semi-controlled device and / or a non-controlled device. The semi-controlled device and / or the non-controlled device are first connected in anti-parallel to form a first sub-module, and the first sub-module is then connected in series to form the fifth valve; or the semi-controlled device and / or the non-controlled device are first connected in series to form a second sub-module, and the second sub-module is then connected in anti-parallel to form the fifth valve.

3. The hybrid bridge arm as described in claim 1, wherein, The auxiliary branch also includes: A resistor and / or an inductor are connected in series with the second valve.

4. The hybrid bridge arm as described in claim 1, further comprising: The switch has one end connected to the main branch or the auxiliary branch and the other end connected to the DC side, or one end connected to the main branch or the auxiliary branch and the other end connected to the AC side. The switch includes at least one of a mechanical switch and a power electronic switch, wherein the mechanical switch includes a knife switch.

5. The hybrid bridge arm as described in claim 1, wherein, The full-bridge submodule includes a full-bridge circuit consisting of four fully controlled modules and capacitors. The half-bridge submodule includes a half-bridge circuit consisting of two fully controlled modules and capacitors. Each fully controlled module includes at least one fully controlled device connected in series and a half-controlled device connected in antiparallel to it, or at least one fully controlled device connected in series and an uncontrolled device connected in antiparallel to it. The fully controlled device includes at least one of IGCT, IGBT, GTO, and MOSFET. The half-controlled device includes a thyristor. The uncontrolled device includes a diode. Lightning arresters are connected in parallel across the first half-controlled valve, the second valve, the third valve, and the fourth valve.

6. A hybrid converter comprising a three-phase six-arm bridge, wherein the six arms include at least one hybrid arm as described in any one of claims 1 to 5.

7. A high-voltage direct current transmission system, comprising a hybrid converter as described in claim 6.

8. A control method for a hybrid converter, the hybrid converter comprising a three-phase six-arm bridge, wherein the six-arm bridge includes at least one hybrid arm, the hybrid arm comprising: The system includes a main branch and an auxiliary branch, the main branch and the auxiliary branch being connected in parallel. The main branch includes a first semi-controlled valve, and the auxiliary branch includes a second valve, the second valve including at least one full-bridge submodule connected in series. The control method includes: The main branch of the hybrid arm of the converter is controlled to operate in either inverter or rectifier mode. The auxiliary branch of the hybrid arm of the converter is controlled to operate in a reactive power compensation state and / or an AC voltage or AC current control state. When the main branch of the hybrid arm of the converter is operating in inverter mode, and a fault may cause the hybrid arm to fail to commutate, the auxiliary branch of the hybrid arm is controlled to be negative, and the current of the main branch of the hybrid arm is transferred to the auxiliary branch of the hybrid arm. After the main branch of the hybrid bridge arm is turned off, the auxiliary branch of the hybrid bridge arm is turned off, thereby transferring the current from the phase where the hybrid bridge arm is located to another phase.

9. The control method as described in claim 8, wherein, The auxiliary branch controlling the hybrid arm of the converter operates in a reactive power compensation state, including: The auxiliary branch of the hybrid bridge arm is controlled to be turned on before the main branch of the hybrid bridge arm is turned on.

10. The control method as described in claim 8, wherein, The auxiliary branch controlling the hybrid arm of the converter operates in a reactive power compensation state, including: The auxiliary branches of the three upper arms of the hybrid converter form a static var generator, which controls the auxiliary branches of the three upper arms to operate in a reactive power compensation state; or / and the auxiliary branches of the three lower arms of the hybrid converter form a static var generator, which controls the auxiliary branches of the three lower arms to operate in a reactive power compensation state.

11. The control method as described in claim 8, wherein, When the auxiliary branch of the hybrid arm controlling the converter is operating in AC voltage or AC current control state, the AC voltage or AC current of the phase controlled by the auxiliary branch of the hybrid arm where the main branch is not conducting is controlled.

12. The control method as described in claim 8, wherein, The auxiliary branch controlling the hybrid bridge arm to be under negative pressure includes: The full-bridge submodule of the second valve controlling the auxiliary branch of the hybrid bridge arm is under negative pressure.

13. The control method as described in claim 8, wherein, The main branch shutdown of the hybrid bridge arm includes: The forward current of the first semi-controlled valve of the main branch of the hybrid bridge arm is less than the holding current and the forward blocking capability is restored.

14. The control method as described in claim 8, wherein, The control of the auxiliary branch shutdown of the hybrid bridge arm includes: The second, third, and / or fourth valves of the auxiliary branch of the hybrid bridge arm are shut off.

15. The control method as described in claim 8, wherein, After the auxiliary branch controlling the hybrid bridge arm is shut off, if an overvoltage occurs in the second valve, third valve, or / and fourth valve, the following further step is taken: Control the main branch of the hybrid bridge arm to conduct.

16. The control method as described in claim 8, wherein, The control method further includes: When the main branch of the hybrid arm of the converter is in a locked state, or if the main branch of the hybrid arm and the auxiliary branch of the hybrid arm are connected by a switch and the switch of the main branch of the hybrid arm is open and the switch of the auxiliary branch of the hybrid arm is closed, the auxiliary branch of the hybrid arm of the converter is controlled to operate in an inverter state or a rectifier state.

17. A control device for a hybrid converter, the hybrid converter comprising a three-phase six-arm bridge, wherein the six arms include at least one hybrid arm, the hybrid arm comprising: The control device comprises: a main branch and an auxiliary branch, wherein the main branch and the auxiliary branch are connected in parallel; the main branch includes a first semi-controlled valve; the auxiliary branch includes a second valve, wherein the second valve includes at least one full-bridge submodule connected in series; and the control device includes: The detection unit is used to detect the operating parameters and faults of the hybrid converter; The control unit, based on the operating parameters of the hybrid converter, controls the main branch of the hybrid bridge arm of the converter to operate in inverter mode or rectification mode; controls the auxiliary branch of the hybrid bridge arm of the converter to operate in reactive power compensation mode and / or AC voltage or AC current control mode; when a fault occurs that may cause the hybrid bridge arm of the converter to fail to commutate, the control unit controls the auxiliary branch of the hybrid bridge arm to be under negative voltage, and the current of the main branch of the hybrid bridge arm is transferred to the auxiliary branch of the hybrid bridge arm; after the main branch of the hybrid bridge arm is turned off, the control unit controls the auxiliary branch of the hybrid bridge arm to be turned off, thereby realizing the transfer of current from the phase where the hybrid bridge arm is located to another phase.

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