Capacitor-assisted shutdown dual converter circuit and control method, device, and system

Abstract

The present application provides a dual converter circuit with capacitor-assisted shutdown and a control method, device, and system. The dual converter circuit with capacitor-assisted shutdown includes a first converter, a second converter, and a connection circuit. The first converter is a three-phase six-bridge arm circuit, and each bridge arm includes a first half-controlled valve; the second converter is a three-phase six-bridge arm circuit, and each bridge arm includes a second half-controlled valve; the connection circuit includes a first capacitor, a second capacitor, a third valve, a fourth valve, a fifth valve, and a sixth valve. The first capacitor and the third valve are connected in series and connected in parallel with the first upper bridge arm of the first converter. The second capacitor and the fourth valve are connected in series and connected in parallel with the first lower bridge arm of the first converter. The fifth valve connects the common end of the first capacitor and the third valve to the positive pole of the DC bus of the second converter, and the sixth valve connects the common end of the second capacitor and the fourth valve to the negative pole of the DC bus of the second converter.

Description

Technical Field

[0001] The present application relates to the field of high-voltage direct current (HVDC) transmission technology, and in particular to a capacitor-assisted shutdown dual-converter circuit, a control method and device, and a HVDC transmission system. Background Art

[0002] High-voltage and ultra-high-voltage direct current (UHVDC) transmission systems have large capacity. Existing technologies use a twelve-pulse circuit. Each twelve-pulse circuit consists of two three-phase, six-arm circuits connected in series. Each arm uses a single large-capacity thyristor in series. Because thyristors cannot control shutdown, the commutation process depends on the AC voltage. This can lead to commutation failure in the event of an AC system fault. Furthermore, large-capacity thyristors are more expensive than parallel solutions with smaller-capacity thyristors.

[0003] With the increasing number of high-voltage and ultra-high-voltage direct current (UHVDC) transmission systems connected, multi-infeed DC transmission systems have emerged in many regional power grids. Simultaneous commutation failures on multiple DC lines can threaten the safe operation of the AC grid in the region. As the proportion of renewable energy generation increases, AC voltage support capacity decreases, placing higher demands on the stable operation of DC transmission systems and their ability to suppress commutation failures. Existing converter structures for high-voltage and ultra-high-voltage direct current transmission systems struggle to meet the stringent cost and performance requirements of DC transmission systems. Summary of the Invention

[0004] An embodiment of the present application provides a dual-converter circuit with capacitor-assisted shutdown, comprising a first converter, a second converter and a connecting circuit, wherein the first converter is a three-phase six-bridge arm circuit, comprising a first upper bridge arm, a second upper bridge arm, a third upper bridge arm, a first lower bridge arm, a second lower bridge arm and a third lower bridge arm, and each bridge arm comprises a first half-controlled valve; the second converter is a three-phase six-bridge arm circuit, comprising a fourth upper bridge arm, a fifth upper bridge arm, a sixth upper bridge arm, a fourth lower bridge arm, a fifth lower bridge arm and a sixth lower bridge arm, and each bridge arm comprises a second half-controlled valve or an uncontrolled valve; the connecting circuit comprises a first capacitor, a second capacitor, a third valve, a fourth valve, a fifth valve and a sixth valve, and the first capacitor and the third valve are connected in series with the first half-controlled valve of the first converter. The upper bridge arms are connected in parallel, the second capacitor and the fourth valve are connected in series and then connected in parallel with the first lower bridge arm of the first converter, the fifth valve connects the common end of the first capacitor and the third valve to the positive pole of the DC bus of the second converter, the sixth valve connects the common end of the second capacitor and the fourth valve to the negative pole of the DC bus of the second converter, the first half-controlled valve and the second half-controlled valve include a half-controlled switch, the uncontrolled valve includes an uncontrolled switch, the third valve and the fourth valve include at least one of a half-controlled switch, a one-way fully-controlled switch, a two-way fully-controlled switch, and an MMC single valve, and the fifth valve and the sixth valve include at least one of a half-controlled switch, a one-way fully-controlled switch, a two-way fully-controlled switch, and an MMC single valve.

[0005] According to some embodiments, the connection circuit further includes a resistor and / or an inductor, and the resistor and / or the inductor is connected in series with the first capacitor or the second capacitor.

[0006] According to some embodiments, the connection circuit also includes a seventh valve and an eighth valve, the seventh valve connecting the positive pole of the DC bus of the first converter and the positive pole of the DC bus of the second converter; the eighth valve connecting the negative pole of the DC bus of the first converter and the negative pole of the DC bus of the second converter; the seventh valve and the eighth valve include at least one of a unidirectional fully-controlled switch, a bidirectional fully-controlled switch, an MMC single valve, a series circuit of a unidirectional or bidirectional fully-controlled switch and a fast isolating switch, the two ends of the seventh valve and the eighth valve are respectively connected to a lightning arrester in parallel, and the two ends of the fifth valve, the sixth valve, the seventh valve or the eighth valve are connected in parallel to a third half-controlled valve.

[0007] According to some embodiments, the connection circuit further includes a ninth valve, a tenth valve, or / and an eleventh valve and a twelfth valve; the first capacitor and the ninth valve are connected in series and connected in parallel with the second upper bridge arm of the first converter; the second capacitor and the tenth valve are connected in series and connected in parallel with the second lower bridge arm of the first converter; the first capacitor and the eleventh valve are connected in series and connected in parallel with the third upper bridge arm of the first converter; the second capacitor and the twelfth valve are connected in series and connected in parallel with the third lower bridge arm of the first converter; the ninth valve, the tenth valve, the eleventh valve, and the twelfth valve include at least one of a half-controlled switch, a one-way fully-controlled switch, a two-way fully-controlled switch, and an MMC single valve; lightning arresters are connected in parallel at both ends of the first half-controlled valve, the second half-controlled valve, the first capacitor, the second capacitor, the third valve, the fourth valve, the fifth valve, the sixth valve, the ninth valve, the tenth valve, the eleventh valve, and the twelfth valve.

[0008] According to some embodiments, the AC output ends of the first converter and the second converter are connected in parallel in phase or in parallel in phase via an isolating switch and / or a knife switch, and are connected to the same converter transformer.

[0009] An embodiment of the present application further provides a high-voltage direct current transmission system, comprising the dual-converter circuit with capacitor-assisted shutdown as described above.

[0010] An embodiment of the present application also provides a control method for a dual-converter circuit with capacitor-assisted shutdown as described above, comprising: controlling the first converter to operate in an inverter state; controlling the second converter to operate in an inverter state, a locked state, or an uncontrolled state; controlling the third valve or the fourth valve to conduct to reversely charge the first capacitor or the second capacitor, so that the first capacitor and the second capacitor present a negative pressure; when a fault occurs that may cause the commutation bridge arm of the first converter to fail, controlling the corresponding bridge arm of the second converter and the fifth valve or the sixth valve to conduct so that the current of the first half-controlled valve of the commutation bridge arm is transferred to the corresponding bridge arm of the second converter and the fifth valve or the sixth valve, and the corresponding bridge arm of the second converter is a bridge arm connected to the same phase and the same DC bus as the commutation bridge arm of the first converter.

[0011] According to some embodiments, controlling the third valve and the fourth valve to reversely charge the first capacitor and the second capacitor includes: controlling the third valve to conduct to reversely charge the first capacitor during a period when the first upper bridge arm of the first converter is subjected to reverse voltage, and controlling the fourth valve to conduct to reversely charge the second capacitor during a period when the first lower bridge arm of the first converter is subjected to reverse voltage.

[0012] According to some embodiments, after the commutation bridge arm of the first converter is turned off, if the fifth valve and the sixth valve include at least one of a one-way full-control switch, a two-way full-control switch, and an MMC single valve, the control method further includes: controlling the fifth valve or the sixth valve corresponding to the commutation bridge arm of the first converter to be turned off, and the commutation bridge arm of the first converter is turned off so that the forward current of the first half-controlled valve corresponding to the commutation bridge arm is less than the holding current and the forward blocking capability is restored.

[0013] According to some embodiments, if the connection circuit further includes a seventh valve and an eighth valve, the control method further includes: controlling the seventh valve and the eighth valve to be turned on to control the second converter to operate in an inverter state; when a fault occurs that may cause the commutation bridge arm of the first converter to fail to commutate, controlling the second converter to be locked, and controlling the seventh valve and / or the eighth valve to be turned off.

[0014] According to some embodiments, if the dual converter circuit further includes a ninth valve, a tenth valve, an eleventh valve, and a twelfth valve, the control method further includes: controlling the third valve, the fourth valve, the ninth valve, the tenth valve, the eleventh valve, and the twelfth valve to operate in a rectification state or a no-load pressurization state to reversely charge the first capacitor and the second capacitor.

[0015] An embodiment of the present application also provides a control device for a dual-converter parallel circuit with capacitor-assisted commutation as described above, comprising a detection unit and a control unit, wherein the detection unit is used to detect operating parameters and faults of the dual-converter circuit with capacitor-assisted shutdown; the control unit controls the first converter to operate in an inverter state based on the operating parameters of the dual-converter circuit with capacitor-assisted shutdown; controls the second converter to operate in an inverter state, a locked state, or an uncontrolled state; controls the third valve or the fourth valve to conduct to reversely charge the first capacitor or the second capacitor, so that the first capacitor and the second capacitor present a negative pressure; when a fault occurs that may cause the commutation failure of the commutation bridge arm of the first converter, controls the corresponding bridge arm of the second converter and the fifth valve or the sixth valve to conduct, so that the current of the first half-controlled valve of the commutation bridge arm is transferred to the corresponding bridge arm of the second converter and the fifth valve or the sixth valve, and the corresponding bridge arm of the second converter is a bridge arm connected to the same phase and the same DC bus as the commutation bridge arm of the first converter.

[0016] The technical solution provided in the embodiment of the present application reversely charges the first capacitor and the second capacitor through the third valve and the fourth valve. When a fault occurs, the fifth valve and the sixth valve are controlled to be turned on, and the reverse pressure of the first capacitor and the second capacitor is used to assist in shutting down the commutation bridge arm of the first converter, thereby realizing controllable commutation of the first converter based on a semi-controlled device, and having the function of parallel operation of the first converter and the second converter, effectively suppressing the occurrence of commutation failure and ensuring reliable operation of the converter. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0018] Figure 1 This is one of the schematic diagrams of a dual converter circuit with capacitor-assisted shutdown provided in an embodiment of the present application.

[0019] Figure 2a A circuit is shown in which a first capacitor and a first resistor are connected in series.

[0020] Figure 2b A circuit is shown in which a first capacitor and a first inductor are connected in series.

[0021] Figure 2c A circuit is shown in which a first capacitor, a first resistor, and a first inductor are connected in series.

[0022] Figure 3a-3kThis is the valve structure provided in the embodiment of the present application.

[0023] Figure 4 This is the second schematic diagram of a dual converter circuit with capacitor-assisted shutdown provided in an embodiment of the present application.

[0024] Figure 5 This is the third schematic diagram of a dual converter circuit with capacitor-assisted shutdown provided in an embodiment of the present application.

[0025] Figure 6 This is the fourth schematic diagram of a dual-converter parallel circuit with capacitor-assisted shutdown provided in an embodiment of the present application.

[0026] Figure 7 This is the fifth schematic diagram of a dual-converter parallel circuit with capacitor-assisted shutdown provided in an embodiment of the present application.

[0027] Figure 8 This is the sixth schematic diagram of a dual-converter parallel circuit with capacitor-assisted shutdown provided in an embodiment of the present application.

[0028] Figure 9 This is a flow chart of a control method for a dual-converter parallel circuit with capacitor-assisted shutdown provided in an embodiment of the present application.

[0029] Figure 10 Schematic diagram of a control device for a dual-converter parallel circuit with capacitor-assisted shutdown provided in an embodiment of the present application. DETAILED DESCRIPTION

[0030] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without making creative efforts are within the scope of protection of this application.

[0031] It should be understood that the terms "include" and "comprising" used in the description and claims of this application indicate the presence of described features, wholes, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components and / or collections thereof.

[0032] Figure 1 This is one of the schematic diagrams of a dual converter circuit with capacitor-assisted shutdown provided in an embodiment of the present application.

[0033] The dual-converter circuit with capacitor-assisted shutdown includes a first converter 1 , a second converter 2 and a connecting circuit 3 .

[0034] The first converter 1 is a three-phase six-bridge arm circuit, including a first upper bridge arm, a second upper bridge arm, a third upper bridge arm, a first lower bridge arm, a second lower bridge arm and a third lower bridge arm, and each bridge arm includes a first half-controlled valve.

[0035] like Figure 1 As shown, the first converter 1 includes three phases and six bridge arms, the first upper bridge arm is composed of the first half-controlled valve V41, the second upper bridge arm is composed of the first half-controlled valve V61, the third upper bridge arm is composed of the first half-controlled valve V21, the first lower bridge arm is composed of the first half-controlled valve V11, the second lower bridge arm is composed of the first half-controlled valve V31, and the third lower bridge arm is composed of the first half-controlled valve V51.

[0036] The second converter 2 is a three-phase six-bridge arm circuit, including a fourth upper bridge arm, a fifth upper bridge arm, a sixth upper bridge arm, a fourth lower bridge arm, a fifth lower bridge arm and a sixth lower bridge arm, each bridge arm including a second half-controlled valve or an uncontrolled valve.

[0037] like Figure 1 As shown, the fourth upper bridge arm is composed of the second half-controlled valve V42, the fifth upper bridge arm is composed of the second half-controlled valve V62, the sixth upper bridge arm is composed of the second half-controlled valve V22, the fourth lower bridge arm is composed of the second half-controlled valve V12, the fifth lower bridge arm is composed of the second half-controlled valve V32, and the sixth lower bridge arm is composed of the second half-controlled valve V52.

[0038] like Figure 1 As shown, the connection circuit 3 includes a first capacitor C81, a second capacitor C82, a third valve V43, a fourth valve V13, a fifth valve V71, and a sixth valve V72. The first capacitor C81 and the third valve V43 are connected in series and then connected in parallel with the first upper bridge arm of the first converter. The second capacitor C82 and the fourth valve V13 are connected in series and then connected in parallel with the first lower bridge arm of the first converter. The fifth valve V71 connects the common terminal P3 of the first capacitor C81 and the third valve V43 to the positive terminal P2 of the DC bus of the second converter. The sixth valve V72 connects the common terminal N3 of the second capacitor C82 and the fourth valve V13 to the negative terminal N2 of the DC bus of the second converter.

[0039] According to some embodiments, the connection circuit 3 further includes a resistor and / or an inductor connected in series with the first capacitor C81 or the second capacitor C82, such as Figure 2a-2c As shown, but not limited to this. Figure 2a A circuit is shown in which a first capacitor C81 and a first resistor R81 are connected in series. Figure 2b A circuit is shown in which a first capacitor C81 and a first inductor L81 are connected in series. Figure 2c A circuit is shown in which a first capacitor C81, a first resistor R81, and a first inductor L81 are connected in series.

[0040] According to some embodiments, the AC output terminals of the first converter and the second converter are connected in parallel in phase or in parallel in phase via an isolating switch and / or a knife switch, and are connected to the same converter transformer.

[0041] Arrester devices are connected in parallel at both ends of the first half-controlled valve, the second half-controlled valve, the first capacitor, the second capacitor, the third valve, the fourth valve, the fifth valve and the sixth valve respectively. The first capacitor and the second capacitor respectively include capacitance elements connected in series, and the above-mentioned capacitance elements are respectively connected in parallel with equalizing resistors, but this is not limited to this.

[0042] The first half-controlled valve and the second half-controlled valve include but are not limited to half-controlled switches, the uncontrolled valve includes but is not limited to uncontrolled switches, the third valve V43 and the fourth valve V13 include but are not limited to at least one of a half-controlled switch, a one-way fully-controlled switch, a two-way fully-controlled switch, and an MMC (Modular Multilevel Converter) single valve, and the fifth valve V71 and the sixth valve V72 include but are not limited to at least one of a half-controlled switch, a one-way fully-controlled switch, a two-way fully-controlled switch, and an MMC single valve.

[0043] The uncontrolled switch includes at least one uncontrolled device connected in series, and the uncontrolled device includes but is not limited to a diode.

[0044] According to some embodiments, the uncontrolled switch comprises a diode 7 connected in series, such as Figure 3a As shown, it cannot be controlled to open and close, and has unidirectional current-passing capability and unidirectional blocking voltage capability.

[0045] The half-controlled switch includes at least one half-controlled device connected in series, including but not limited to a thyristor. The half-controlled device is configured with a corresponding trigger circuit. Optionally, the half-controlled switch comprises a thyristor and a diode connected in series or in parallel.

[0046] According to some embodiments, the half-controlled switch comprises thyristors 4 connected in series, such as Figure 3b As shown, it can only be controlled to be turned on but not turned off, and has unidirectional current-carrying capability and bidirectional voltage-blocking capability.

[0047] A fully-controlled switch includes at least one fully-controlled device connected in series. The fully-controlled device includes, but is not limited to, at least one of an IGCT (integrated gate commutated thyristor), an IGBT (insulated gate bipolar transistor), a GTO (gate turn-off thyristor), and a MOSFET (metal oxide semiconductor field effect transistor). The fully-controlled device is equipped with a corresponding drive circuit and / or buffer circuit.

[0048] According to some embodiments, the unidirectional fully controlled switch includes an IGBT module connected in series, the IGBT module including an IGBT 5 and a diode 7 connected in anti-parallel thereto, such as Figure 3c As shown, it only controls opening and closing in one direction, and has the ability of bidirectional current flow and unidirectional blocking voltage.

[0049] According to some embodiments, the unidirectional fully controlled switch includes IGCT6 connected in series, such as Figure 3d As shown, it only controls opening and closing in one direction, and has the capability of unidirectional current flow and bidirectional blocking voltage.

[0050] According to some embodiments, the unidirectional fully controlled switch includes an IGBT module and a diode 7 connected in series, such as Figure 3e As shown, it only controls opening and closing in one direction, and has the capability of unidirectional current flow and bidirectional blocking voltage.

[0051] According to some embodiments, the unidirectional fully controlled switch includes a switch group connected in series, and the switch group includes an IGCT 6 and a thyristor 4 connected in parallel, such as Figure 3f As shown, it only controls opening and closing in one direction, and has bidirectional current flow and bidirectional blocking voltage capabilities.

[0052] According to some embodiments, the bidirectional fully controlled switch includes a forward IGBT module and a reverse IGBT module connected in series, such as Figure 3g As shown, it can be bidirectionally controlled to open and close, and has bidirectional current flow and bidirectional blocking voltage capabilities.

[0053] According to some embodiments, the bidirectional fully controlled switch includes a switch group connected in series, and the switch group includes a forward IGCT 6 and a reverse IGCT 6 connected in parallel, such as Figure 3h As shown, it can be bidirectionally controlled to open and close, and has bidirectional current flow and bidirectional blocking voltage capabilities.

[0054] According to some embodiments, the MMC single valve includes submodules connected in series, each submodule including two IGBT modules and a capacitor 8, wherein the connection point of the two IGBT modules serves as the positive electrode of the submodule, and the other end of one of the IGBT modules serves as the negative electrode of the submodule. The submodules are connected in series, such as Figure 3i As shown, it only controls opening and closing in one direction, and has bidirectional current-carrying capability and unidirectional blocking voltage capability.

[0055] According to some embodiments, the MMC single valve includes submodules connected in series, each of which includes four IGBT modules and a capacitor 8. The IGBT modules are connected in series in pairs and then in parallel, and are also connected in parallel with the capacitor 7. The connection points of the IGBT modules connected in series in pairs serve as the positive and negative electrodes of the submodules, respectively. Figure 3j As shown, it can be bidirectionally controlled to open and close, and has bidirectional current-carrying capability and bidirectional blocking voltage capability.

[0056] According to some embodiments, the seventh valve V73 and the eighth valve V74 are composed of a full-control switch and a fast isolation switch in series, such as Figure 3k The fast isolating switch 9 is used to provide a sufficient pressure resistance level, reduce the conduction loss of the seventh valve V73 and the eighth valve V74 and the pressure resistance level of the full-control switch. It should be noted that Figure 3c 、 Figure 3e 、 Figure 3g 、 Figure 3i 、 Figure 3j and Figure 3k The IGBT in the circuit can be IGCT, GTO, or MOSFET.

[0057] The thyristor 4 is equipped with a corresponding trigger circuit, the IGBT 5 is equipped with a corresponding drive circuit and a buffer circuit, and the IGCT 6 is equipped with a corresponding drive circuit and a buffer circuit. The buffer circuit is composed of at least a capacitor or a resistor and a capacitor in series.

[0058] Figure 4 This is the second schematic diagram of a dual converter circuit with capacitor-assisted shutdown provided in an embodiment of the present application.

[0059] exist Figure 1 Based on the embodiment, the connection circuit 3 also includes a seventh valve V73 and an eighth valve V74. The seventh valve V73 connects the DC bus positive pole P1 of the first converter 1 and the DC bus positive pole P2 of the second converter 2. The eighth valve V74 connects the DC bus negative pole N1 of the first converter 1 and the DC bus negative pole N2 of the second converter 2.

[0060] The seventh valve V73 and the eighth valve V74 include but are not limited to at least one of a one-way full-control switch, a two-way full-control switch or an MMC single valve.

[0061] Figure 5This is the third schematic diagram of a dual converter circuit with capacitor-assisted shutdown provided in an embodiment of the present application.

[0062] exist Figure 1 Based on the embodiment, the capacitor-assisted shutdown dual converter circuit further includes a ninth valve V63, a tenth valve V33, an eleventh valve V23 and a twelfth valve V53.

[0063] The first capacitor C81 and the ninth valve V63 are connected in series and then connected in parallel with the second upper bridge arm of the first converter 1. The second capacitor C82 and the tenth valve V33 are connected in series and then connected in parallel with the second lower bridge arm of the first converter 1. The first capacitor C81 and the eleventh valve V23 are connected in series and then connected in parallel with the third upper bridge arm of the first converter 1. The second capacitor C82 and the twelfth valve V53 are connected in series and then connected in parallel with the third lower bridge arm of the first converter 1.

[0064] The ninth valve V63, the tenth valve V33, the eleventh valve V23, and the twelfth valve V53 include but are not limited to at least one of a half-controlled switch, a one-way fully-controlled switch, a two-way fully-controlled switch, or an MMC single valve.

[0065] Figure 6 This is the fourth schematic diagram of a dual-converter parallel circuit with capacitor-assisted shutdown provided in an embodiment of the present application.

[0066] exist Figure 1 On the basis of the embodiment, the first half-controlled valves V11, V21, V31, V41, V51 and V61, and the second half-controlled valves V12, V22, V32, V42, V52 and V62 adopt half-controlled switches, which are composed of thyristors connected in series; the third valve V43 and the fourth valve V13 adopt half-controlled switches, which are composed of thyristors connected in series; the fifth valve V71 and the sixth valve V72 adopt unidirectional fully-controlled switches, which are composed of an IGBT and a diode connected in anti-parallel in series.

[0067] like Figure 6 As shown, the first half-controlled valves V11, V21, V31, V41, V51 and V61 of the first converter 1 are connected in parallel with lightning arresters F11, F21, F31, F41, F51 and F61 respectively; the second half-controlled valves V12, V22, V32, V42, V52 and V62 of the second converter 2 are connected in parallel with lightning arresters F12, F22, F32, F42, F52 and F62 respectively; the third valve V43 is connected in parallel with lightning arrester F43; the fourth valve V13 is connected in parallel with lightning arrester F13; the fifth valve V71 is connected in parallel with lightning arrester F71; and the sixth valve V72 is connected in parallel with lightning arrester F72.

[0068] The AC output terminals of the first converter 1 and the second converter 2 are connected in parallel according to phases, that is, A1 and A2 are connected, B1 and B2 are connected, and C1 and C2 are connected, and are respectively connected to the three phases of the same converter transformer.

[0069] Figure 7 This is the fifth schematic diagram of a dual-converter parallel circuit with capacitor-assisted shutdown provided in an embodiment of the present application.

[0070] exist Figure 4 On the basis of the embodiment, the first half-controlled valves V11, V21, V31, V41, V51 and V61, and the second half-controlled valves V12, V22, V32, V42, V52 and V62 adopt half-controlled switches, which are composed of thyristors connected in series; the third valve V43 and the fourth valve V13 adopt half-controlled switches, which are composed of thyristors connected in series; the fifth valve V71, the sixth valve V72, the seventh valve V73 and the eighth valve V74 adopt unidirectional fully-controlled switches, which are composed of an IGBT and a diode connected in anti-parallel in series.

[0071] like Figure 7 As shown, the first half-controlled valves V11, V21, V31, V41, V51 and V61 of the first converter 1 are connected in parallel with lightning arresters F11, F21, F31, F41, F51 and F61 respectively; the second half-controlled valves V12, V22, V32, V42, V52 and V62 of the second converter 2 are connected in parallel with lightning arresters F12, F22, F32, F42, F52 and F62 respectively; the third valve V43 is connected in parallel with lightning arrester F43; the fourth valve V13 is connected in parallel with lightning arrester F13; the fifth valve V71 is connected in parallel with lightning arrester F71; the sixth valve V72 is connected in parallel with lightning arrester F72; the seventh valve V73 is connected in parallel with lightning arrester F73; and the eighth valve V74 is connected in parallel with lightning arrester F74.

[0072] The AC output terminals of the first converter 1 and the second converter 2 are connected in parallel according to phases, that is, A1 and A2 are connected, B1 and B2 are connected, and C1 and C2 are connected, and are respectively connected to the three phases of the same converter transformer.

[0073] Figure 8 This is the sixth schematic diagram of a dual-converter parallel circuit with capacitor-assisted shutdown provided in an embodiment of the present application.

[0074] exist Figure 5 On the basis of the embodiment, the first half-controlled valves V11, V21, V31, V41, V51 and V61, and the second half-controlled valves V12, V22, V32, V42, V52 and V62 adopt half-controlled switches, which are composed of thyristors connected in series; the third valve V43, the fourth valve V13, the ninth valve V63, the tenth valve V33, the eleventh valve V23 and the twelfth valve V53 adopt half-controlled switches, which are composed of thyristors connected in series; the fifth valve V71, the sixth valve V72, the seventh valve V73 and the eighth valve V74 adopt unidirectional fully-controlled switches, which are composed of an IGBT and a diode connected in anti-parallel in series.

[0075] like Figure 8As shown, the first half-controlled valves V11, V21, V31, V41, V51 and V61 of the first converter 1 are connected in parallel with the lightning arresters F11, F21, F31, F41, F51 and F61 respectively; the second half-controlled valves V12, V22, V32, V42, V52 and V62 of the second converter 2 are connected in parallel with the lightning arresters F12, F22, F32, F42, F52 and F62 respectively; the third valve V43 is connected in parallel with the lightning arresters F11, F21, F31, F41, F51 and F61 respectively. Lightning arrester F43, the fourth valve V13 is connected in parallel with the lightning arrester F13, the ninth valve V63 is connected in parallel with the lightning arrester F63, the tenth valve V33 is connected in parallel with the lightning arrester F33, the eleventh valve V23 is connected in parallel with the lightning arrester F23, the twelfth valve V53 is connected in parallel with the lightning arrester F53, the fifth valve V71 is connected in parallel with the lightning arrester F71, the sixth valve V72 is connected in parallel with the lightning arrester F72, the seventh valve V73 is connected in parallel with the lightning arrester F73, and the eighth valve V74 is connected in parallel with the lightning arrester F74.

[0076] The AC output terminals of the first converter 1 and the second converter 2 are connected in parallel according to phases, that is, A1 and A2 are connected, B1 and B2 are connected, and C1 and C2 are connected, and are respectively connected to the three phases of the same converter transformer.

[0077] An embodiment of the present application further provides a high-voltage direct current transmission system, comprising the dual-converter circuit with capacitor-assisted shutdown as described above.

[0078] Figure 9 This is a flow chart of a control method for a dual-converter parallel circuit with capacitor-assisted shutdown provided in an embodiment of the present application.

[0079] In S110 , the first converter is controlled to operate in an inverter state.

[0080] In S120, the second converter is controlled to operate in an inverter state, a blocking state, or an uncontrolled state.

[0081] When the DC side of the second converter 2 is powered, its AC output is connected to the AC system via a converter transformer, and each bridge arm includes a second half-controlled valve, the second converter operates in the inverter state. When the DC side of the second converter 2 is powered, its AC output is connected to the AC system via a converter transformer, and each bridge arm includes an uncontrolled valve, the second converter operates in the uncontrolled state. Otherwise, the second converter 2 operates in the locked state.

[0082] like Figure 6 As shown, if there is no power supply between the DC bus positive electrode P2 of the second converter 2 and the DC bus negative electrode N2 of the second converter 2, the second converter 2 operates in a locked state.

[0083] If the connection circuit further includes a seventh valve and an eighth valve, the control process S120 further includes S121.

[0084] S121, controlling the seventh valve and the eighth valve to be turned on, so as to control the second converter to operate in the inverter state.

[0085] like Figure 7 and Figure 8 As shown, power is supplied between the positive DC bus P1 and the negative DC bus N1 of first converter 1. When the seventh valve V73 and the eighth valve V74 are conductive, power is supplied to the DC side of second converter 2. The AC output terminals of first converter 1 and second converter 2 are connected in parallel, with phases A1 and A2 connected, B1 and B2 connected, and C1 and C2 connected. These terminals are connected to the three phases of the same converter transformer. Second converter 2 operates in an inverter mode, in parallel with first converter 1.

[0086] In S130 , the third valve or the fourth valve is controlled to be turned on to reversely charge the first capacitor or the second capacitor, so that the first capacitor or the second capacitor presents a negative pressure.

[0087] like Figure 6 and Figure 7 As shown, during the period when the first upper bridge arm of the first converter 1 is subjected to reverse voltage, the third valve V43 is controlled to conduct, reversely charging the first capacitor C81, causing the first capacitor C81 to present a negative voltage. During the period when the first lower bridge arm of the first converter 1 is subjected to reverse voltage, the fourth valve V13 is controlled to conduct, reversely charging the second capacitor C82, causing the second capacitor C82 to present a negative voltage. It should be noted that the positive direction of the voltage of the first capacitor C81 is directed from the positive terminal P1 of the DC bus of the first converter 1 to the common terminal P3 of the first capacitor C81 and the third valve V43, and the positive direction of the voltage of the second capacitor C82 is directed from the common terminal N3 of the second capacitor C82 and the fourth valve V13 to the negative terminal N1 of the DC bus of the first converter 1. Optionally, when the negative voltage of the first capacitor C81 or the second capacitor C82 reaches a first voltage setting value, the third valve V43 and the fourth valve V44 are no longer controlled to conduct. The first voltage setting value ranges from 0.01 to 1.0 times the maximum voltage of the bridge arm.

[0088] If the connection circuit further includes a ninth valve V63, a tenth valve V33, an eleventh valve V23 and a twelfth valve V53, the control process S130 further includes S131.

[0089] S131 , controlling the third valve, the fourth valve, the ninth valve, the tenth valve, the eleventh valve, and the twelfth valve to operate in a rectification state or a no-load pressurization state to reversely charge the first capacitor and the second capacitor.

[0090] like Figure 8 As shown, the third valve V43, the fourth valve V13, the ninth valve V63, the tenth valve V33, the eleventh valve V23 and the twelfth valve V53 are controlled to operate in a no-load pressurized state to reversely charge the first capacitor C81 and the second capacitor C82.

[0091] In S140, when a fault occurs that may cause the commutation failure of the commutation bridge arm of the first converter, the corresponding bridge arm and the fifth valve or the sixth valve of the second converter are controlled to be turned on, so that the current of the first half-controlled valve of the commutation bridge arm is transferred to the corresponding bridge arm and the fifth valve or the sixth valve of the second converter.

[0092] The corresponding bridge arm of the second converter is a bridge arm connected to the same phase and the same DC bus as the commutation bridge arm of the first converter.

[0093] like Figure 6 、 Figure 7 and Figure 8 As shown, taking the first upper arm as an example, when a fault occurs that may cause commutation failure in the first upper arm of the first converter 1, the second half-controlled valve V42 and the fifth valve V71 of the fourth upper arm of the second converter 2 are controlled to be conductive. Taking the first lower arm as an example, when a fault occurs that may cause commutation failure in the first lower arm of the first converter 1, the second half-controlled valve V12 and the sixth valve V72 of the fourth lower arm of the second converter 2 are controlled to be conductive.

[0094] The aforementioned faults include AC system faults or DC system faults in the parallel circuit connection of the dual converters. AC system faults can be determined based on, but not limited to, an increase in the AC voltage zero-sequence component, a sudden change in the AC voltage, a drop in the AC voltage amplitude, an increase in the AC voltage harmonics, or an increase in the DC current. DC system faults can be determined based on, but not limited to, a drop in the DC voltage or an increase in the DC current. The aforementioned potential commutation failure of the first half-controlled valve in the commutation bridge arm of the first converter is determined based on the shutoff time of the commutation bridge arm and the AC voltage. If the first half-controlled valve in the commutation bridge arm has not shut off at the shutoff time under normal AC voltage, it is determined that a commutation failure of the commutation bridge arm of the first converter is likely to occur, but not limited to, this.

[0095] If the connection circuit 3 further includes a seventh valve V73 and an eighth valve V74 , the control process S140 further includes S141 .

[0096] S141, when a fault occurs that may cause commutation failure of the commutation bridge arm of the first converter, control the second converter to be locked, and control the seventh valve and / or the eighth valve to be closed.

[0097] like Figure 7 and Figure 8 As shown, taking the first upper bridge arm as an example, when a fault occurs that may cause the commutation failure of the first upper bridge arm of the first converter 1, the second converter 2 is controlled to be locked, and the seventh valve V73 and the eighth valve V74 are controlled to be turned off; taking the first lower bridge arm as an example, when a fault occurs that may cause the commutation failure of the first lower bridge arm of the first converter 1, the second converter 2 is controlled to be locked, and the seventh valve V73 and the eighth valve V74 are controlled to be turned off.

[0098] According to some embodiments, if the fifth valve and the sixth valve include at least one of a one-way full-control switch, a two-way full-control switch, and an MMC single valve, the control method further includes S150.

[0099] S150: After the commutation bridge arm of the first converter 1 is turned off, the fifth valve V71 or the sixth valve V72 is controlled to be turned off.

[0100] If the commutation arm is the upper arm, the fifth valve V71 is controlled to be closed. If the commutation arm is the lower arm, the sixth valve V72 is controlled to be closed. The commutation arm of the first converter 1 is closed when the forward current of the first half-controlled valve of the commutation 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 the shutdown time has been extended. The shutdown time is less than 700 μs, but this is not limited to this.

[0101] Figure 10 3 is a schematic diagram of a control device for a dual-converter parallel circuit with capacitor-assisted shutdown provided in an embodiment of the present application. The control device 300 includes a detection unit 310 and a control unit 320.

[0102] The detection unit 310 is used to detect the operating parameters and faults of the capacitor-assisted shutdown dual-converter parallel circuit, including the AC voltage, DC voltage, DC current, the operating status of the first and second converters, and the operating status of the third, fourth, fifth, and sixth valves. Based on the operating parameters of the capacitor-assisted shutdown dual-converter parallel circuit, the control unit 320 controls the first converter to operate in an inverter state; controls the second converter to operate in an inverter state, a locked state, or an uncontrolled state; and controls the third and fourth valves to conduct to reversely charge the first or second capacitor, resulting in a negative voltage on the first and second capacitors. When a fault occurs that may cause the commutation failure of the first upper bridge arm of the first converter, the control unit 320 controls the corresponding bridge arm and the fifth valve of the second converter to be turned on. When a fault occurs that may cause the commutation failure of the commutation bridge arm of the first converter, the control unit 320 controls the corresponding bridge arm and the sixth valve of the second converter to be turned on, so that the current of the first half-controlled valve of the commutation bridge arm is transferred to the corresponding bridge arm and the fifth valve, or the sixth valve, of the second converter.

[0103] The above embodiments are only for illustrating the technical ideas of the present application and cannot be used to limit the scope of protection of the present application. Any changes made on the basis of the technical solutions in accordance with the technical ideas proposed in the present application shall fall within the scope of protection of the present application.

Claims

1. A dual-converter circuit with capacitor-assisted shutdown, comprising: The first converter is a three-phase six-bridge arm circuit, including a first upper bridge arm, a second upper bridge arm, a third upper bridge arm, a first lower bridge arm, a second lower bridge arm and a third lower bridge arm, each bridge arm including a first half-controlled valve; The second converter is a three-phase six-bridge arm circuit, including a fourth upper bridge arm, a fifth upper bridge arm, a sixth upper bridge arm, a fourth lower bridge arm, a fifth lower bridge arm and a sixth lower bridge arm, each bridge arm including a second half-controlled valve or an uncontrolled valve; The connection circuit includes a first capacitor, a second capacitor, a third valve, a fourth valve, a fifth valve and a sixth valve. The first capacitor and the third valve are connected in series and then connected in parallel with the first upper bridge arm of the first converter. The second capacitor and the fourth valve are connected in series and then connected in parallel with the first lower bridge arm of the first converter. The fifth valve connects the common end of the first capacitor and the third valve to the positive pole of the DC bus of the second converter. The sixth valve connects the common end of the second capacitor and the fourth valve to the negative pole of the DC bus of the second converter. The first half-controlled valve and the second half-controlled valve include a half-controlled switch, the uncontrolled valve includes an uncontrolled switch, the third valve and the fourth valve include at least one of a half-controlled switch, a one-way fully-controlled switch, a two-way fully-controlled switch, and an MMC single valve. The fifth valve and the sixth valve include at least one of a half-controlled switch, a one-way fully-controlled switch, a two-way fully-controlled switch, and an MMC single valve.

2. The dual converter circuit according to claim 1, wherein: The connecting circuit further comprises: A resistor and / or an inductor is connected in series with the first capacitor or the second capacitor.

3. The dual converter circuit according to claim 1, wherein: The connecting circuit further comprises: a seventh valve, connecting the positive pole of the DC bus of the first converter and the positive pole of the DC bus of the second converter; an eighth valve, connecting the negative pole of the DC bus of the first converter and the negative pole of the DC bus of the second converter; The seventh valve and the eighth valve include at least one of a one-way full-control switch, a two-way full-control switch, an MMC single valve, and a series circuit of a one-way or two-way full-control switch and a fast isolating switch. Lightning arresters are connected in parallel at both ends of the seventh valve and the eighth valve, and a third half-controlled valve is connected in parallel at both ends of the fifth valve, the sixth valve, the seventh valve or the eighth valve.

4. The dual converter circuit according to claim 1, wherein: The connecting circuit also includes a ninth valve and a tenth valve, wherein the first capacitor and the ninth valve are connected in series and then connected in parallel with the second upper bridge arm of the first converter, and the second capacitor and the tenth valve are connected in series and then connected in parallel with the second lower bridge arm of the first converter; or / and an eleventh valve and a twelfth valve, wherein the first capacitor and the eleventh valve are connected in series and then connected in parallel to the third upper bridge arm of the first converter, and the second capacitor and the twelfth valve are connected in series and then connected in parallel to the third lower bridge arm of the first converter; The ninth valve, the tenth valve, the eleventh valve, and the twelfth valve include at least one of a half-controlled switch, a one-way fully-controlled switch, a two-way fully-controlled switch, and an MMC single valve. Lightning arresters are respectively connected in parallel at both ends of the first half-controlled valve, the second half-controlled valve, the first capacitor, the second capacitor, the third valve, the fourth valve, the fifth valve, the sixth valve, the ninth valve, the tenth valve, the eleventh valve, and the twelfth valve.

5. The dual converter circuit according to claim 1, wherein: The AC output ends of the first converter and the second converter are connected in parallel in phase or in parallel in phase through an isolating switch and / or a knife switch, and are connected to the same converter transformer.

6. A high-voltage direct current transmission system, comprising the capacitor-assisted shutdown dual-converter circuit according to any one of claims 1 to 5.

7. A method for controlling a dual-converter circuit with capacitor-assisted shutdown according to any one of claims 1 to 5, comprising: controlling the first converter to operate in an inverter state; controlling the second converter to operate in an inverter state, a blocking state, or an uncontrolled state; controlling the third valve or the fourth valve to conduct to reversely charge the first capacitor or the second capacitor, so that the first capacitor and the second capacitor present a negative pressure; When a fault occurs that may cause the commutation bridge arm of the first converter to fail, the corresponding bridge arm of the second converter and the fifth valve or the sixth valve are controlled to be turned on, so that the current of the first half-controlled valve of the commutation bridge arm is transferred to the corresponding bridge arm of the second converter and the fifth valve or the sixth valve. The corresponding bridge arm of the second converter is the bridge arm connected to the same phase and the same DC bus as the commutation bridge arm of the first converter.

8. The control method according to claim 7, wherein: Controlling the third valve and the fourth valve to reversely charge the first capacitor and the second capacitor includes: During the period when the first upper bridge arm of the first converter is subjected to reverse voltage, the third valve is controlled to be turned on to reverse charge the first capacitor. During the period when the first lower bridge arm of the first converter is subjected to reverse voltage, the fourth valve is controlled to be turned on to reverse charge the second capacitor.

9. The control method according to claim 7, wherein after the commutation bridge arm of the first converter is turned off, if the fifth valve and the sixth valve include at least one of a one-way fully controlled switch, a two-way fully controlled switch, and an MMC single valve, the control method further comprises: The fifth valve or the sixth valve corresponding to the commutation bridge arm of the first converter is controlled to be turned off. The commutation bridge arm of the first converter is turned off when the forward current of the first half-controlled valve of the commutation bridge arm is less than the holding current and the forward blocking capability is restored.

10. The control method according to claim 7, wherein: If the connection circuit further includes a seventh valve and an eighth valve, the control method further includes: controlling the seventh valve and the eighth valve to be turned on to control the second converter to operate in an inverter state; When a fault occurs that may cause the commutation arm of the first converter to fail, the second converter is controlled to be locked, and the seventh valve and / or the eighth valve are controlled to be closed.

11. The control method according to claim 7, wherein: If the dual converter circuit further includes a ninth valve, a tenth valve, an eleventh valve, and a twelfth valve, the control method further includes: The third valve, the fourth valve, the ninth valve, the tenth valve, the eleventh valve, and the twelfth valve are controlled to operate in a rectification state or a no-load pressurization state to reversely charge the first capacitor and the second capacitor.

12. A control device for a capacitor-assisted commutation dual-converter parallel circuit according to any one of claims 1 to 5, comprising: a detection unit, configured to detect operating parameters and faults of the capacitor-assisted shutdown dual converter circuit; A control unit, based on the operating parameters of the dual converter circuit with capacitor-assisted shutdown, controls the first converter to operate in an inverter state; controls the second converter to operate in an inverter state, a locked state or an uncontrolled state; controls the third valve or the fourth valve to conduct to reversely charge the first capacitor or the second capacitor, so that the first capacitor and the second capacitor present a negative pressure; when a fault occurs that may cause the commutation failure of the commutation bridge arm of the first converter, controls the corresponding bridge arm of the second converter and the fifth valve or the sixth valve to conduct, so that the current of the first half-controlled valve of the commutation bridge arm is transferred to the corresponding bridge arm of the second converter and the fifth valve or the sixth valve, and the corresponding bridge arm of the second converter is the bridge arm connected to the same phase and the same DC bus as the commutation bridge arm of the first converter.

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