Dual converter parallel circuit, control method and device thereof, and DC power transmission system

Abstract

The present application provides a dual-converter parallel circuit, a control method and device thereof, and a direct current transmission system. The dual-converter parallel circuit includes a first converter, a second converter, and a connecting circuit. The first converter includes three first upper bridge arms and three first lower bridge arms, each of which includes a first half-controlled valve and a first full-controlled valve connected in series. The second converter includes three second upper bridge arms and three second lower bridge arms, each of which includes a second valve. The connecting circuit includes a third valve and a fourth valve.

Description

Technical Field

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

[0002] High-voltage and ultra-high-voltage direct current transmission have large capacity. The existing technology uses a grid-commutated converter with a twelve-pulse circuit structure. Each twelve-pulse circuit has two three-phase six-arm circuits connected in series. Each bridge arm uses a single large-capacity thyristor in series. Since the thyristor cannot control the shutdown, the existing converter structure has the problem of commutation failure. At the same time, the cost of large-capacity thyristors is higher than that of small-capacity thyristors in parallel. The voltage source converter of flexible direct current transmission and hybrid direct current transmission uses a modular multi-level converter with a half-bridge structure or a full-bridge structure. Although there is no commutation failure problem, the IGBT (Insulated Gate Bipolar Transistor) device has a small capacity, high cost, and large loss. In addition, the voltage source converter has the risk of oscillation.

[0003] With the increasing number of connected HV and UHV DC transmission systems, 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 that 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. Therefore, existing HVDC, Flexible DC, and Hybrid DC technologies 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 parallel circuit, including a first converter, a second converter, and a connecting circuit, wherein the first converter is a three-phase six-bridge-arm circuit, including three first upper bridge arms and three first lower bridge arms, each of the first upper bridge arm and the first lower bridge arm includes a first half-controlled valve and a first fully-controlled valve connected in series, the first half-controlled valve includes a half-controlled switch, and the first fully-controlled valve includes at least one of a one-way fully-controlled switch, a two-way fully-controlled switch, and an MMC single valve; the second converter is a three-phase six-bridge-arm circuit, including three second upper bridge arms and three second lower bridge arms, each of the second upper bridge arm and the second lower bridge arm includes a second valve; the connecting circuit includes a third valve and a fourth valve, and the second valve, the third valve, and the fourth valve include an uncontrolled switch, a half-controlled switch, and a bidirectional fully-controlled switch. At least one of a switch, a one-way fully-controlled switch, a two-way fully-controlled switch, and an MMC single valve, wherein the third valve is connected to the positive pole of the DC bus of the first converter or the first segmentation point of the first half-controlled valve of the first upper bridge arm and the positive pole of the DC bus of the second converter, and the fourth valve is connected to the negative pole of the DC bus of the first converter or the second segmentation point of the first half-controlled valve of the first lower bridge arm and the negative pole of the DC bus of the second converter; or the third valve is connected to the positive pole of the DC bus of the first converter or the first segmentation point of the first half-controlled valve of the first upper bridge arm and the negative pole of the DC bus of the second converter, and the fourth valve is connected to the negative pole of the DC bus of the first converter or the second segmentation point of the first half-controlled valve of the first lower bridge arm and the positive pole of the DC bus of the second converter.

[0005] According to some embodiments, the first segmentation point divides the first half-controlled valve of the first upper bridge arm into two sections according to the pressure resistance level, and the second segmentation point divides the first half-controlled valve of the first lower bridge arm into two sections according to the pressure resistance level, and the pressure resistance ratio of the two sections ranges from 0.2 to 5.

[0006] According to some embodiments, when the third valve is connected to the first segmentation point, the first segmentation point of the first half-controlled valve of each first upper bridge arm is respectively connected to one of the third valves; when the fourth valve is connected to the second segmentation point, the second segmentation point of the first half-controlled valve of each first lower bridge arm is respectively connected to one of the fourth valves.

[0007] According to some embodiments, lightning arresters or / and second half-controlled valves are connected in parallel at both ends of the first half-controlled valve, the first fully-controlled valve, the second valve, the third valve, and the fourth valve, respectively, and the second half-controlled valve includes a half-controlled switch.

[0008] According to some embodiments, the connection circuit further includes a fifth valve, or a parallel circuit of a first capacitor and a first resistor, or a circuit of the parallel circuit and the fifth valve in series, connecting the positive pole of the DC bus and the negative pole of the DC bus of the second converter, and the first capacitor includes at least one capacitive element connected in series.

[0009] According to some embodiments, the connection circuit also includes a sixth valve and a seventh valve, the sixth 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, and the seventh 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 fifth valve, the sixth valve, and the seventh valve include at least one of an uncontrolled switch, a half-controlled switch, a one-way fully-controlled switch, a two-way fully-controlled switch, an MMC single valve, a fully-controlled switch connected in series, and a fast isolating switch, and a lightning arrester or / and a second half-controlled valve are connected in parallel at both ends of the fifth valve, the sixth valve, the seventh valve, and the first capacitor, respectively.

[0010] According to some embodiments, the connection circuit further includes a lightning arrester, or a parallel circuit of a second capacitor and a second resistor, wherein the lightning arrester is connected in series with the third valve and / or the fourth valve; and a parallel circuit of a second capacitor and a second resistor is connected in series with the third valve and / or the fourth valve.

[0011] 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 through an isolating switch and / or a knife switch, and are connected to the same converter transformer, and the DC bus input ends of the first converter and the second converter are connected in parallel in positive and negative poles through an isolating switch and / or a knife switch.

[0012] An embodiment of the present application further provides a high-voltage direct current (HVDC) power transmission system, comprising the dual-converter parallel circuit as described above.

[0013] An embodiment of the present application also provides a control method for the dual-converter parallel circuit, comprising: controlling the first converter to operate in an inverter state; controlling the second converter to operate in an inverter state or a locked state; controlling the third valve and the fourth valve to operate in a locked state or an uncontrolled state; when a fault occurs that may cause the commutation failure of the commutation bridge arm of the first converter, comprising: controlling the corresponding bridge arm of the second converter corresponding to the commutation bridge arm and the third valve or the fourth valve to be turned on; controlling the first fully-controlled valve of the commutation bridge arm to be turned off, so that the current of the commutation bridge arm is transferred to the corresponding bridge arm of the second converter and the third valve or the fourth valve; after the first half-controlled valve of the commutation bridge arm is turned off, controlling the corresponding bridge arm of the second converter and the third valve or the fourth valve to be turned off, thereby realizing the current transfer from the phase where the commutation bridge arm is located to another phase, and the corresponding bridge arm of the second converter is a bridge arm connected to the same polarity DC bus and the same phase as the commutation bridge arm of the first converter.

[0014] According to some embodiments, when the dual-converter parallel circuit also includes a fifth valve, the control method further includes: controlling the fifth valve to be turned on while controlling the corresponding bridge arm of the second converter corresponding to the phase-changing bridge arm and the third valve or the fourth valve to be turned on; after the first half-controlled valve of the phase-changing bridge arm is turned off, controlling the fifth valve to be turned off to control the corresponding bridge arm of the second converter, the third valve or the fourth valve to be turned off.

[0015] According to some embodiments, when the dual-converter parallel circuit further includes a sixth valve and a seventh valve, the control method further includes: when controlling the first full-control valve of the commutation bridge arm to be closed, locking the second converter, and controlling the sixth valve or the seventh valve to be closed; after the working condition that may cause the commutation failure of the commutation bridge arm of the first converter disappears, controlling the sixth valve and / or the seventh valve to be turned on.

[0016] According to some embodiments, when the dual-converter parallel circuit also includes a fifth valve, the control method also includes: controlling the second converter to operate in a rectification state or a no-load pressurization state to power the drive circuit of the fifth valve; when a second half-controlled valve is connected in parallel at both ends of the fifth valve, and the fifth valve is over-voltage, over-current or faulty, controlling the second half-controlled valve to be turned on; when the fifth valve is controlled to be turned off, and the fifth valve is over-voltage, over-current or faulty, controlling the first half-controlled valve and the first full-controlled valve of the switching bridge arm to be turned on.

[0017] According to some embodiments, when the dual-converter parallel circuit further includes a sixth valve and a seventh valve, the control method further includes: controlling the sixth valve and the seventh valve to be turned on, so that the first converter and the second converter share a DC bus, so that the second converter operates in an inverter state; when a second half-controlled valve is connected in parallel at both ends of the first fully-controlled valve, the second valve, the third valve, the fourth valve, the sixth valve or the seventh valve, when the first fully-controlled valve, the second valve, the third valve, the fourth valve, the sixth valve or the seventh valve is over-voltage, over-current or faulty, controlling the second half-controlled valve to be turned on; when the corresponding bridge arm, the third valve or the fourth valve, the sixth valve or the seventh valve of the second converter is controlled to be turned off, and the corresponding bridge arm, the third valve or the fourth valve, the sixth valve or the seventh valve of the second converter is over-voltage, over-current or faulty, controlling the first half-controlled valve and the first fully-controlled valve of the commutation bridge arm to be turned on.

[0018] The embodiment of the present application also provides a control device for the dual-converter parallel circuit as described above, comprising a detection unit and a control unit, wherein the detection unit is used to detect the operating parameters and faults of the dual-converter parallel circuit; the control unit controls the first converter to operate in an inverter state based on the operating parameters of the dual-converter parallel circuit; controls the second converter to operate in an inverter state or a locked state; controls the third valve and the fourth valve to operate in a locked state or an uncontrolled state; and when a fault occurs that may cause the commutation arm of the first converter to fail to commutate, the control unit also controls the phase change of the commutation arm of the first converter to be controlled. The corresponding bridge arm of the second converter corresponding to the commutation bridge arm and the third valve or the fourth valve are turned on, and the first full-control valve of the commutation bridge arm is controlled to be turned off, so that the current of the commutation bridge arm is transferred to the corresponding bridge arm of the second converter and the third valve or the fourth valve. After the first half-control valve of the commutation bridge arm is turned off, the corresponding bridge arm, the third valve or the fourth valve of the second converter are controlled to be turned off, so that the current is transferred from the phase where the commutation bridge arm is located to another phase. The corresponding bridge arm of the second converter is the bridge arm connected to the DC bus with the same polarity and the same phase as the commutation bridge arm of the first converter.

[0019] The technical solution provided by the embodiment of the present application is that the bridge arm circuit and the connecting circuit of the second converter form a parallel circuit with the bridge arm circuit of the first converter, and the first full-control valve of the commutation of the first converter is turned off to realize the current transfer to the corresponding bridge arm and connecting circuit of the second converter. By turning off the full-control switch of the corresponding bridge arm or connecting circuit of the second converter, the controllable commutation of the first converter based on the semi-controlled device is realized, which effectively suppresses the occurrence of commutation failure. At the same time, the dual converter composed of the first converter and the second converter can operate in parallel, thereby improving the capacity of the dual converter and increasing the redundancy of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] 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.

[0021] Figure 1 This is one of the schematic diagrams of a dual-converter parallel circuit provided in an embodiment of the present application.

[0022] Figure 2 This is the second schematic diagram of a dual-converter parallel circuit provided in an embodiment of the present application.

[0023] Figure 3 This is the third schematic diagram of a dual-converter parallel circuit provided in an embodiment of the present application.

[0024] Figure 4 This is the fourth schematic diagram of a dual-converter parallel circuit provided in an embodiment of the present application.

[0025] Figure 5 This is the fifth schematic diagram of a dual-converter parallel circuit provided in an embodiment of the present application.

[0026] Figure 6 This is the sixth schematic diagram of a dual-converter parallel circuit provided in an embodiment of the present application.

[0027] Figures 7a-7k This is a schematic diagram of the valve structure provided in an embodiment of the present application.

[0028] Figure 8 This is the seventh schematic diagram of a dual-converter parallel circuit provided in an embodiment of the present application.

[0029] Figure 9 This is the eighth schematic diagram of a dual-converter parallel circuit provided in an embodiment of the present application.

[0030] Figure 10 This is the ninth schematic diagram of a dual-converter parallel circuit provided in an embodiment of the present application.

[0031] Figure 11 This is the tenth schematic diagram of a dual-converter parallel circuit provided in an embodiment of the present application.

[0032] Figure 12 This is the eleventh schematic diagram of a dual-converter parallel circuit provided in an embodiment of the present application.

[0033] Figure 13 This is the twelfth schematic diagram of a dual-converter parallel circuit provided in an embodiment of the present application.

[0034] Figure 14 This is a flow chart of a control method for a dual-converter parallel circuit according to an embodiment of the present application.

[0035] Figure 15 This is a schematic diagram of a control device for a dual-converter parallel circuit provided in an embodiment of the present application. DETAILED DESCRIPTION

[0036] 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.

[0037] It should be understood that the terms "first," "second," "third," "fourth," "fifth," "sixth," "seventh," etc. in the claims, specification, and drawings of this application are used to distinguish different objects, rather than to describe a specific order. The terms "comprise" and "comprising" used in the specification and claims of this application indicate the presence of the described features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or combinations thereof.

[0038] Figure 1 This is one of the schematic diagrams of a dual converter parallel circuit provided in the embodiment of the present application. Figure 1 As shown, the dual-converter parallel circuit includes a first converter 1, a second converter 2 and a connecting circuit.

[0039] The first converter 1 includes three phases and six bridge arms, namely three first upper bridge arms and three first lower bridge arms. Each first upper bridge arm and first lower bridge arm includes a first half-controlled valve and a first full-controlled valve connected in series. The first upper bridge arm of phase A includes a first half-controlled valve V41 and a first full-controlled valve V42 connected in series. The first upper bridge arm of phase B includes a first half-controlled valve V61 and a first full-controlled valve V62 connected in series. The first upper bridge arm of phase C includes a first half-controlled valve V21 and a first full-controlled valve V22 connected in series. The first lower bridge arm of phase A includes a first half-controlled valve V11 and a first full-controlled valve V12 connected in series. The first lower bridge arm of phase B includes a first half-controlled valve V31 and a first full-controlled valve V32 connected in series. The first lower bridge arm of phase C includes a first half-controlled valve V51 and a first full-controlled valve V52 connected in series.

[0040] Second converter 2 includes three phases and six bridge arms, consisting of three second upper bridge arms and three second lower bridge arms. Each second upper bridge arm and each second lower bridge arm includes a second valve. The second upper bridge arm of phase A includes a second valve V43, the second upper bridge arm of phase B includes a second valve V63, the second upper bridge arm of phase C includes a second valve V23, the second lower bridge arm of phase A includes a second valve V13, the second lower bridge arm of phase B includes a second valve V33, and the second lower arm of phase C includes a second valve V53.

[0041] The connection circuit includes a third valve V71 and a fourth valve V72. The third valve V71 connects the DC bus positive electrode P1 of the first converter 1 and the DC bus positive electrode P2 of the second converter 2, and the fourth valve V72 connects the DC bus negative electrode N1 of the first converter 1 and the DC bus negative electrode N2 of the second converter 2. Figure 1 shown.

[0042] According to some embodiments, the third valve V71 is connected to the DC bus positive electrode P1 of the first converter 1 and the DC bus negative electrode N2 of the second converter 2, and the fourth valve V72 is connected to the DC bus negative electrode N1 of the first converter 1 and the DC bus positive electrode P2 of the second converter 2, as shown in FIG. Figure 2 shown.

[0043] Figure 3 This is the third schematic diagram of a dual converter parallel circuit provided by the embodiment of the present application. Figure 3 As shown, the dual-converter parallel circuit includes a first converter 1, a second converter 2 and a connecting circuit.

[0044] The first converter 1 includes three phases and six bridge arms, namely three first upper bridge arms and three first lower bridge arms. Each first upper bridge arm and first lower bridge arm includes a first half-controlled valve and a first full-controlled valve connected in series. The first upper bridge arm of phase A includes a first half-controlled valve V41 and a first full-controlled valve V42 connected in series. The first upper bridge arm of phase B includes a first half-controlled valve V61 and a first full-controlled valve V62 connected in series. The first upper bridge arm of phase C includes a first half-controlled valve V21 and a first full-controlled valve V22 connected in series. The first lower bridge arm of phase A includes a first half-controlled valve V11 and a first full-controlled valve V12 connected in series. The first lower bridge arm of phase B includes a first half-controlled valve V31 and a first full-controlled valve V32 connected in series. The first lower bridge arm of phase C includes a first half-controlled valve V51 and a first full-controlled valve V52 connected in series.

[0045] Second converter 2 includes three phases and six bridge arms, consisting of three second upper bridge arms and three second lower bridge arms. Each second upper bridge arm and each second lower bridge arm includes a second valve. The second upper bridge arm of phase A includes a second valve V43, the second upper bridge arm of phase B includes a second valve V63, the second upper bridge arm of phase C includes a second valve V23, the second lower bridge arm of phase A includes a second valve V13, the second lower bridge arm of phase B includes a second valve V33, and the second lower arm of phase C includes a second valve V53.

[0046] The connection circuit includes third valves V71, V81, and V91, and fourth valves V72, V82, and V92. The third valve V71 connects the first split point of the first half-controlled valve V41 and the positive DC bus P2 of the second converter 2. The third valve V81 connects the first split point of the first half-controlled valve V61 and the positive DC bus P2 of the second converter 2. The third valve V91 connects the first split point of the first half-controlled valve V21 and the positive DC bus P2 of the second converter 2. The fourth valve V72 connects the second split point of the first half-controlled valve V11 and the negative DC bus N2 of the second converter 2. The fourth valve V82 connects the second split point of the first half-controlled valve V31 and the negative DC bus N2 of the second converter 2. The fourth valve V92 connects the second split point of the first half-controlled valve V51 and the negative DC bus N2 of the second converter 2.

[0047] According to some embodiments, the third valve V71 is connected to the first segmentation point of the first half-controlled valve V41 and the negative pole N2 of the DC bus of the second converter 2, the third valve V81 is connected to the first segmentation point of the first half-controlled valve V61 and the negative pole N2 of the DC bus of the second converter 2, the third valve V91 is connected to the first segmentation point of the first half-controlled valve V21 and the negative pole N2 of the DC bus of the second converter 2, the fourth valve V72 is connected to the second segmentation point of the first half-controlled valve V11 and the positive pole P2 of the DC bus of the second converter 2, the fourth valve V82 is connected to the second segmentation point of the first half-controlled valve V31 and the positive pole P2 of the DC bus of the second converter 2, and the fourth valve V92 is connected to the second segmentation point of the first half-controlled valve V51 and the positive pole P2 of the DC bus of the second converter 2, as shown in FIG. Figure 4 shown.

[0048] The second valve, the third valve, and the fourth valve include at least one of an uncontrolled switch, a half-controlled switch, a unidirectional fully-controlled switch, a bidirectional fully-controlled switch, and an MMC (Modular Multilevel Converter) single valve, but are not limited thereto.

[0049] Figure 5 This is the fifth schematic diagram of a dual converter parallel circuit provided by the embodiment of the present application. Figure 5 As shown, the dual-converter parallel circuit includes a first converter 1, a second converter 2 and a connecting circuit.

[0050] The first converter 1 includes three phases and six bridge arms, namely three first upper bridge arms and three first lower bridge arms. Each first upper bridge arm and first lower bridge arm includes a first half-controlled valve and a first full-controlled valve connected in series. The first upper bridge arm of phase A includes a first half-controlled valve V41 and a first full-controlled valve V42 connected in series. The first upper bridge arm of phase B includes a first half-controlled valve V61 and a first full-controlled valve V62 connected in series. The first upper bridge arm of phase C includes a first half-controlled valve V21 and a first full-controlled valve V22 connected in series. The first lower bridge arm of phase A includes a first half-controlled valve V11 and a first full-controlled valve V12 connected in series. The first lower bridge arm of phase B includes a first half-controlled valve V31 and a first full-controlled valve V32 connected in series. The first lower bridge arm of phase C includes a first half-controlled valve V51 and a first full-controlled valve V52 connected in series.

[0051] Second converter 2 includes three phases and six bridge arms, consisting of three second upper bridge arms and three second lower bridge arms. Each second upper bridge arm and each second lower bridge arm includes a second valve. The second upper bridge arm of phase A includes a second valve V43, the second upper bridge arm of phase B includes a second valve V63, the second upper bridge arm of phase C includes a second valve V23, the second lower bridge arm of phase A includes a second valve V13, the second lower bridge arm of phase B includes a second valve V33, and the second lower arm of phase C includes a second valve V53.

[0052] The connection circuit includes a third valve V71, a fourth valve V72, and a fifth valve V73. The third valve V71 connects the DC bus positive electrode P1 of the first converter 1 and the DC bus negative electrode N2 of the second converter 2. The fourth valve V72 connects the DC bus negative electrode N1 of the first converter 1 and the DC bus positive electrode P2 of the second converter 2. The fifth valve V73 connects the DC bus positive electrode P2 and the DC bus negative electrode N2 of the second converter 2. Figure 5 shown.

[0053] According to some embodiments, the connection circuit further includes a sixth valve V74 and a seventh valve V75. The sixth valve V74 connects the DC bus positive electrode P1 of the first converter 1 and the DC bus positive electrode P2 of the second converter 2, and the seventh valve V75 connects the DC bus negative electrode N1 of the first converter 1 and the DC bus negative electrode N2 of the second converter 2. Figure 6 shown.

[0054] According to some embodiments, the fifth valve V73 can be replaced by a parallel circuit of a first capacitor and a first resistor, or a series circuit of a parallel circuit of the first capacitor and the first resistor and the fifth valve V73. The first capacitor includes, but is not limited to, at least one capacitive element connected in series. Optionally, to control the charge and discharge time of the first capacitor, a resistor or inductor element can also be connected in series.

[0055] The second valve, the third valve, the fourth valve, the fifth valve, the sixth valve, and the seventh valve include at least one of an uncontrolled switch, a half-controlled switch, a one-way fully-controlled switch, a two-way fully-controlled switch, and an MMC single valve, but are not limited thereto.

[0056] According to some embodiments, the fully-controlled switch includes at least one fully-controlled device connected in series, and the fully-controlled device includes at least one of IGCT (Integrated Gate Commutated Thyristors), IGBT, GTO (Gate Turn-Off Thyristor), and MOSFET (Metal Oxide Semiconductor Field Effect Transistor); the half-controlled switch includes at least one half-controlled device connected in series, and the half-controlled device includes a thyristor; the uncontrolled switch includes at least one uncontrolled device connected in series, and the uncontrolled device includes a diode.

[0057] According to some embodiments, an uncontrolled switch comprises a diode 3 connected in series, such as Figure 7a As shown, it cannot be controlled to open and close, and has unidirectional current-passing capability and unidirectional blocking voltage capability.

[0058] According to some embodiments, a half-controlled switch comprises thyristors 4 connected in series, such as Figure 7b As shown, it only controls the on-state and cannot control the off-state, and has a unidirectional current-carrying capability and a bidirectional blocking voltage capability. Optionally, the half-controlled switch is composed of a thyristor 4 and a diode 3 connected in series or in parallel.

[0059] According to some embodiments, a unidirectional fully controlled switch includes an IGBT module connected in series, the IGBT module including an IGBT 5 and a diode 3 connected in anti-parallel therewith, such as Figure 7c As shown, it only controls opening and closing in one direction, and has the ability of bidirectional current flow and unidirectional blocking voltage.

[0060] According to some embodiments, a unidirectional fully controlled switch includes IGCTs 6 connected in series, such as Figure 7d As shown, it only controls opening and closing in one direction, and has the capability of unidirectional current flow and bidirectional blocking voltage.

[0061] According to some embodiments, a unidirectional fully controlled switch includes an IGBT module and a diode 3 connected in series, such as Figure 7e As shown, it only controls opening and closing in one direction, and has the capability of unidirectional current flow and bidirectional blocking voltage.

[0062] According to some embodiments, a unidirectional fully controlled switch includes an IGCT 6 and a thyristor 4 connected in anti-parallel and then in series. Figure 7f As shown, bidirectional control is turned on and unidirectional control is turned off, with bidirectional current flow and bidirectional blocking voltage capabilities.

[0063] According to some embodiments, a bidirectional fully controlled switch includes a forward IGBT module and a reverse IGBT module connected in series, such as Figure 7g As shown, it can be bidirectionally controlled to open and close, and has bidirectional current-carrying capability and bidirectional blocking voltage capability.

[0064] According to some embodiments, a bidirectional fully controlled switch includes a series circuit of a forward IGCT 6 and a reverse IGCT 6 connected in parallel, such as Figure 7h As shown, it can be bidirectionally controlled to open and close, and has bidirectional current-carrying capability and bidirectional blocking voltage capability.

[0065] According to some embodiments, an MMC single valve includes submodules connected in series, the submodules including two IGBT modules and a capacitor 7, such as Figure 7i As shown, the connection point of the two IGBT modules serves as the positive electrode of the sub-module, and the other end of one of the IGBT modules serves as the negative electrode of the sub-module. The sub-modules are connected in series and are only controlled to be turned on and off in one direction, with bidirectional current flow capability and unidirectional blocking voltage capability.

[0066] According to some embodiments, an MMC single valve includes submodules connected in series, the submodules including four IGBT modules and a capacitor 7, such as Figure 7j As shown, 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 poles of the sub-modules respectively. The sub-modules are connected in series and can be bidirectionally controlled to be turned on and off, and have bidirectional current flow capability and bidirectional blocking voltage capability.

[0067] According to some embodiments, the fifth valve, the sixth valve, and the seventh valve include a full-control switch and a fast isolation switch connected in series, such as Figure 7k As shown, the full-control switch and the fast isolating switch 8 are connected in series. The fast isolating switch 8 provides sufficient pressure resistance, reducing the conduction loss of the fifth valve, the sixth valve, and the seventh valve and the pressure resistance of the full-control switch. It should be noted that Figure 7c 、 Figure 7e 、 Figure 7g 、 Figure 7i 、 Figure 7j and Figure 7k The IGBT in the circuit can be IGCT, GTO, or MOSFET.

[0068] According to some embodiments, the thyristor 4 is configured with a corresponding trigger circuit; the IGBT 5 is configured with a corresponding drive circuit and a snubber circuit; and the IGCT 6 is configured with a corresponding drive circuit and a snubber circuit. The snubber circuit is composed of at least a capacitor, or a resistor and a capacitor in series.

[0069] According to some embodiments, a lightning arrester or / and the second half-controlled valve may be connected in parallel at both ends of the first half-controlled valve, the first fully-controlled valve, the second valve, the third valve, the fourth valve, the fifth valve, the sixth valve, the seventh valve, and the first capacitor. If the first half-controlled valve is segmented, a lightning arrester may be connected in parallel at both ends of each segment.

[0070] According to some embodiments, the third valve V71 is further connected in series with a lightning arrester and then connected to the DC bus positive electrode P1 of the first converter 1, the DC bus positive electrode P2 of the second converter 2, or the DC bus negative electrode N2 of the second converter 2. The fourth valve V72 is further connected in series with a lightning arrester and then connected to the DC bus negative electrode N1 of the first converter 1, the DC bus negative electrode N2 of the second converter 2, or the DC bus positive electrode P2 of the second converter 2. 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 first lightning arresters F11, F21, F31, F41, F51, and F61, respectively. The first full-controlled valves V12, V22, V32, V42, V52, and V62 of the first converter 1 are connected in parallel with the second lightning arresters F12, F22, F32, F42, F52, and F62, respectively. The second valves V13, V23, V33, V43, V53, and V63 of the second converter 2 are connected in parallel with the third lightning arresters F13, F23, F33, F43, F53, and F63, respectively. The third valve V71 is connected in parallel with the fourth lightning arrester F71, the fourth valve V72 is connected in parallel with the fifth lightning arrester F72, the third valve V71 is connected in series with the sixth lightning arrester F76, and the fourth valve V72 is connected in series with the seventh lightning arrester F77. The second lightning arresters F12, F22, F32, F42, F52, and F62 have a higher withstand voltage than the sixth and seventh lightning arresters F76 and F77. It should be noted that the sixth and seventh lightning arresters F76 and F77 do not necessarily have to be connected in series. If the first half-controlled valve is divided into two sections, the first lightning arrester must also be divided into two sections and connected in parallel with the two sections of the first half-controlled valve.

[0071] According to some embodiments, the third valve V71 is also connected in series to the parallel circuit of the second capacitor and the second resistor and then connected to the DC bus positive pole P1 of the first converter 1, the DC bus positive pole P2 of the second converter 2 or the DC bus negative pole N2 of the second converter 2. The fourth valve V72 is also connected in series to the parallel circuit of the second capacitor and the second resistor and then connected to the DC bus negative pole N1 of the first converter 1, the DC bus negative pole N2 of the second converter 2 or the DC bus positive pole P2 of the second converter 2.

[0072] According to some embodiments, the AC output terminals of the first converter 1 and the second converter 2 may be connected in parallel by phase, i.e., 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 9 This is the eighth schematic diagram of a dual converter parallel circuit provided by the embodiment of the present application. Figure 9 As shown, the dual-converter parallel circuit includes a first converter 1, a second converter 2 and a connecting circuit.

[0074] exist Figure 1 Based on the embodiments, according to some embodiments, the AC output terminals of the first converter 1 and the second converter 2 are connected in parallel in phase, that is, A1 and A2 are connected, B1 and B2 are connected, and C1 and C2 are connected, and are connected to the three phases of the same converter transformer, such as Figure 9 shown.

[0075] According to some embodiments, the first half-controlled valve is composed of thyristors 4 connected in series, the first fully-controlled valves V11, V21, V31, V41, V51 and V61 respectively include a one-way fully-controlled switch, which is composed of IGBT modules connected in series, the second valves V13, V23, V33, V43, V53 and V63 respectively include a half-controlled switch, which is composed of thyristors 4 connected in series, the third valve V71 includes a one-way fully-controlled switch, which is composed of IGBT modules connected in series, and the fourth valve V72 includes a one-way fully-controlled switch, which is composed of IGBT modules connected in series.

[0076] According to some embodiments, the first half-controlled valves V11, V21, V31, V41, V51, and V61 of the first converter 1 are respectively connected in parallel with the first lightning arresters F11, F21, F31, F41, F51, and F61, and the first full-controlled valves V12, V22, V32, V42, V52, and V62 of the first converter 1 are respectively connected in parallel with the second lightning arresters F12, F22, F32, F42, F52, and F62. The second valves V13, V23, V33, V43, V53, and V63 of the second converter 2 are respectively connected in parallel with the third lightning arresters F13, F23, F33, F43, F53, and F63. The third valve V71 is connected in parallel with the fourth lightning arrester F71, and the fourth valve V72 is connected in parallel with the fifth lightning arrester F72, as shown in FIG. Figure 9 shown.

[0077] Figure 10 This is the ninth schematic diagram of a dual-converter parallel circuit provided in an embodiment of the present application.

[0078] like Figure 10 As shown, Figure 5 The same as in the embodiment is that the third valve V71 connects the DC bus positive electrode P1 of the first converter 1 and the DC bus negative electrode N2 of the second converter 2, the fourth valve V72 connects the DC bus negative electrode N1 of the first converter 1 and the DC bus positive electrode P2 of the second converter 2. The fifth valve V73 connects the DC bus positive electrode P2 and the DC bus negative electrode N2 of the second converter 2.

[0079] exist Figure 5Based on the embodiment, the first half-controlled valves V11, V21, V31, V41, V51, and V61 of the first converter 1 are connected in parallel with the first lightning arresters F11, F21, F31, F41, F51, and F61, respectively. The first full-controlled valves V12, V22, V32, V42, V52, and V62 of the first converter 1 are connected in parallel with the second lightning arresters F12, F22, F32, F42, F52, and F62, respectively. The second valves V13, V23, V33, V43, V53, and V63 of the second converter 2 are connected in parallel with the third lightning arresters F13, F23, F33, F43, F53, and F63, respectively. The third valve V71 is connected in parallel with the fourth lightning arrester F71, the fourth valve V72 is connected in parallel with the fifth lightning arrester F72, and the fifth valve V73 is connected in parallel with the eighth lightning arrester F73.

[0080] 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 connected to the three phases of the same converter transformer.

[0081] The first half-controlled valves V11, V21, V31, V41, V51 and V61 respectively include half-controlled switches, which are composed of thyristors 4 in series. The first fully-controlled valves V12, V22, V32, V42, V52 and V62 respectively include unidirectional fully-controlled switches, which are composed of IGBT modules in series. The second valves V13, V23, V33, V43, V53 and V63 respectively include half-controlled switches, which are composed of thyristors 4 in series. The third valve V71 includes an uncontrolled switch, which is composed of diodes 3 in series. The fourth valve V72 includes an uncontrolled switch, which is composed of diodes 3 in series. The fifth valve V73 includes a unidirectional fully-controlled switch, which is composed of IGBT modules in series.

[0082] Figure 11 This is the tenth schematic diagram of a dual-converter parallel circuit provided in an embodiment of the present application.

[0083] like Figure 11 As shown, Figure 10 The same as in the embodiment is that the third valve V71 connects the DC bus positive electrode P1 of the first converter 1 and the DC bus negative electrode N2 of the second converter 2, the fourth valve V72 connects the DC bus negative electrode N1 of the first converter 1 and the DC bus positive electrode P2 of the second converter 2. The fifth valve V73 connects the DC bus positive electrode P2 and the DC bus negative electrode N2 of the second converter 2.

[0084] exist Figure 10Based on the embodiment, second half-controlled valves V14 , V24 , V34 , V44 , V54 and V64 are respectively connected in parallel at both ends of the first fully-controlled valves V12 , V22 , V32 , V42 , V52 and V62 . The first half-controlled valves V11, V21, V31, V41, V51 and V61 respectively include half-controlled switches, which are composed of 4 thyristors in series. The first fully-controlled valves V12, V22, V32, V42, V52 and V62 respectively include one-way fully-controlled switches, which are composed of 4 IGBT modules in series. The second valves V13, V23, V33, V43, V53 and V63 respectively include half-controlled switches, which are composed of 4 thyristors in series. The third valve V71 includes a half-controlled switch, which is composed of 4 thyristors in series. The fourth valve V72 includes a half-controlled switch, which is composed of 4 thyristors in series. The fifth valve V73 includes a one-way fully-controlled switch, which is composed of 4 IGBT modules in series. The second half-controlled valves V14, V24, V34, V44, V54 and V64 respectively include half-controlled switches, which are composed of 4 thyristors in series.

[0085] According to some embodiments, the second valve may further include an uncontrolled switch composed of diodes 3 connected in series.

[0086] Figure 12 This is the eleventh schematic diagram of a dual-converter parallel circuit provided in an embodiment of the present application.

[0087] like Figure 12 As shown, Figure 6 The embodiments are similar in that the third valve V71 connects the DC bus positive electrode P1 of the first converter 1 and the DC bus negative electrode N2 of the second converter 2, the fourth valve V72 connects the DC bus negative electrode N1 of the first converter 1 and the DC bus positive electrode P2 of the second converter 2. The fifth valve V73 connects the DC bus positive electrode P2 and the DC bus negative electrode N2 of the second converter 2. The sixth valve V74 connects the DC bus positive electrode P1 of the first converter 1 and the DC bus positive electrode P2 of the second converter 2, and the seventh valve V75 connects the DC bus negative electrode N1 of the first converter 1 and the DC bus negative electrode N2 of the second converter 2.

[0088] exist Figure 6Based on the embodiment, the fifth valve V73 is connected in parallel with the eighth lightning arrester F73, the sixth valve V74 is connected in parallel with the ninth lightning arrester F74, and the seventh valve V75 is connected in parallel with the tenth lightning arrester F75. The AC output terminals of the first converter 1 and the second converter 2 are connected in parallel in phases via disconnectors or / and switches S13, S14, S15, S23, S24, and S25, and are connected to the three phases of the same converter transformer. The DC bus input terminal of the first converter 1 is connected in parallel in positive and negative polarity via disconnectors or / and switches S10 and S20, and the DC bus input terminal of the second converter 2 is connected in parallel in positive and negative polarity via disconnectors or / and switches S12 and S21. The first half-controlled valves V11, V21, V31, V41, V51 and V61 respectively include half-controlled switches, which are composed of thyristors 4 in series. The first fully-controlled valves V12, V22, V32, V42, V52 and V62 respectively include unidirectional fully-controlled switches, which are composed of IGBT modules in series. The second valves V13, V23, V33, V43, V53 and V63 respectively include half-controlled switches, which are composed of thyristors 4 in series. The third valve V71 includes a half-controlled switch, which is composed of thyristors 4 in series. The fourth valve V72 includes a half-controlled switch, which is composed of thyristors 4 in series. The fifth valve V73 includes a unidirectional fully-controlled switch, which is composed of IGBT modules in series. The sixth valve V74 includes a unidirectional fully-controlled switch, which is composed of IGBT modules in series. The seventh valve V75 includes a unidirectional fully-controlled switch, which is composed of IGBT modules in series.

[0089] When the first converter 1 needs maintenance, the isolating switch or / and the knife switches S13, S14, S15, S10 and S20 are controlled to separate to isolate the first converter 1; when the second converter 2 needs maintenance, the isolating switch or / and the knife switches S23, S24, S25, S12 and S21 are controlled to separate to isolate the second converter 2.

[0090] Figure 13 This is the twelfth schematic diagram of a dual-converter parallel circuit provided in an embodiment of the present application.

[0091] like Figure 13 As shown, Figure 5 The same as the embodiment is that the third valve V71 connects the DC bus positive pole P1 of the first converter 1 and the DC bus negative pole N2 of the second converter 2, and the fourth valve V72 connects the DC bus negative pole N1 of the first converter 1 and the DC bus positive pole P2 of the second converter 2.

[0092] like Figure 13 As shown, in Figure 5 According to the embodiment, the fifth valve is replaced by a parallel circuit of a first capacitor C11 and a first resistor R11.

[0093] The parallel circuit of the first capacitor C11 and the first resistor R11 is connected in series between the positive DC bus P2 and the negative DC bus N2 of the second converter 2. The first capacitor C11 is connected in parallel with an eleventh lightning arrester F78. The AC output terminals of the first converter 1 and the second converter 2 are connected in parallel, phase by phase—i.e., A1 and A2, B1 and B2, and C1 and C2—and are connected to the three phases of the same converter transformer. The first half-controlled valves V11, V21, V31, V41, V51 and V61 respectively include half-controlled switches, which are composed of thyristor 4 connected in series. The first fully-controlled valves V12, V22, V32, V42, V52 and V62 respectively include unidirectional fully-controlled switches, which are composed of IGBT modules connected in series. The second valves V13, V23, V33, V43, V53 and V63 respectively include half-controlled switches, which are composed of thyristor 4 connected in series. The third valve V71 includes a unidirectional fully-controlled switch, which is composed of IGCT6 and thyristor 4 connected in parallel and then in series. The fourth valve V72 includes a unidirectional fully-controlled switch, which is composed of IGCT6 and thyristor 4 connected in parallel and then in series. The first capacitor C11 is composed of capacitance elements connected in series.

[0094] An embodiment of the present application further provides a high-voltage direct current (HVDC) power transmission system, which includes the dual-converter parallel circuit described above.

[0095] Figure 14 This is a flow chart of a control method for a dual-converter parallel circuit provided in an embodiment of the present application, which includes the following process.

[0096] In S110 , the first converter is controlled to operate in an inverter state.

[0097] In the inverter state, the first fully controlled valve of the first converter is closed after the first half controlled valve is closed. Figure 9 、 Figure 10 、 Figure 11 、 Figure 12 and Figure 13 As shown, taking the first upper bridge arm of phase A as an example, the first fully-controlled valve V42 of the first converter 1 is closed after the first half-controlled valve V41 is closed.

[0098] If the first full-control valve is also connected in parallel with the second half-control valve, when the first full-control valve is over-pressure, over-current or fails, the second half-control valve will be controlled to conduct. Figure 11 As shown, taking the first upper bridge arm of phase A as an example, when the first fully-controlled valve V42 is over-pressured, over-currented or fails, the second half-controlled valve V44 is controlled to be turned on.

[0099] In S120, the second converter is controlled to operate in an inverter state or a blocking state.

[0100] When there is power on the DC side of the second converter and the AC output terminal is connected to the AC system through the converter transformer, the second converter operates in the inverter state; otherwise, the second converter operates in the blocking state.

[0101] In S130 , the third valve and the fourth valve are controlled to operate in a locked state or an uncontrolled state.

[0102] It should be pointed out that only when the dual-converter parallel circuit also includes a fifth valve, and the fifth valve is a one-way fully-controlled switch, a two-way fully-controlled switch or an MMC single valve, the third and fourth valves are selected as uncontrolled switches or half-controlled switches. When the third and fourth valves are uncontrolled switches, the third and fourth valves operate in an uncontrolled state.

[0103] like Figure 10 As shown, the third valve V71 and the fourth valve V72 are selected as uncontrolled switches, and the third valve V71 and the fourth valve V72 are controlled to operate in an uncontrolled state. Figure 11 and Figure 12 As shown, the third valve V71 and the fourth valve V72 use half-controlled switches.

[0104] In this embodiment, the first converter and the second converter can operate independently or in parallel.

[0105] When the dual converter parallel circuit further includes a fifth valve, such as Figure 10 and Figure 11 As shown, the control method further includes the following S131.

[0106] S131, controlling the second converter to operate in a rectification state or a no-load pressurization state to supply power to the drive circuit of the fifth valve.

[0107] like Figure 10 and Figure 11 As shown, the no-load pressurized state of the second converter 2 is that the second converter 2 controls the trigger angle to achieve voltage regulation and power the drive circuit of the fifth valve V73 when the DC side is open, thereby achieving high-potential energy extraction.

[0108] If the fifth valve V73 is also connected in parallel with a second half-controlled valve, when the fifth valve V73 is over-pressured, over-currented or fails, the second half-controlled valve is controlled to be turned on.

[0109] When the fifth valve is controlled to be closed and the fifth valve is over-pressured, over-currented or fails, the first half-controlled valve and the first full-controlled valve of the phase-changing bridge arm are controlled to be turned on.

[0110] When the dual converter parallel circuit further includes the sixth valve and the seventh valve, as shown in FIG. Figure 12 As shown, the control method further includes the following S132.

[0111] S132, controlling the sixth valve and the seventh valve to be turned on, so that the first converter and the second converter share a DC bus, unlocking the second converter, and making the second converter operate in an inverter state.

[0112] like Figure 12 As shown, the sixth valve V74 and the seventh valve V75 are controlled to be turned on, so that the first converter 1 and the second converter 2 share the DC bus P1, and the second converter 2 is unlocked, so that the second converter 2 operates in the inverter state.

[0113] like Figure 14 As shown, when a fault occurs that may cause the commutation arm of the first converter to fail to commutate, the control method further includes the following process.

[0114] In S140, the corresponding bridge arm of the second converter and the third valve or the fourth valve are controlled to be turned on. The corresponding bridge arm of the second converter is a bridge arm connected to the DC bus with the same polarity and the same phase as the commutation bridge arm of the first converter.

[0115] It should be noted that controlling the conduction of the corresponding bridge arm and the third or fourth valve of the second converter involves applying a trigger pulse to the corresponding bridge arm and the third or fourth valve of the second converter. For the corresponding bridge arm and the third or fourth valve of the second converter to conduct current, the corresponding bridge arm and the third or fourth valve of the second converter must also withstand a forward voltage to cause conduction. The aforementioned commutation bridge arm is the bridge arm that commutates to another bridge arm during normal operation.

[0116] When a fault occurs that may cause commutation failure of the first upper bridge arm of the first converter, the corresponding upper bridge arm of the second converter and the third valve are controlled to be turned on. When a fault occurs that may cause commutation failure of the first lower bridge arm of the first converter, the corresponding lower bridge arm of the second converter and the fourth valve are controlled to be turned on.

[0117] like Figure 9 and Figure 13 As shown, taking the first upper arm of phase A as an example, when the first upper arm of phase A commutates to the first upper arm of phase B, if a fault occurs that may cause the commutation failure of the first upper arm of phase A of the first converter, the second upper arm of phase A and the third valve V71 of the second converter are controlled to be conductive. Taking the first lower arm of phase A as an example, when the first lower arm of phase A commutates to the first lower arm of phase B, if a fault occurs that may cause the commutation failure of the first lower arm of phase A of the first converter, the second lower arm of phase A and the fourth valve V72 of the second converter are controlled to be conductive.

[0118] The aforementioned faults include AC system faults or DC system faults in the parallel circuit connection of 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 cause of commutation failure in the commutation arm of the first converter is determined based on the closing time of the first half-controlled valve of the commutation arm and the AC voltage. If the first half-controlled valve of the commutation arm has not closed at the closing time under normal AC voltage, it is determined that commutation failure in the commutation arm of the first converter is likely to occur, but not limited to, this.

[0119] When the dual converter parallel circuit further includes a fifth valve, such as Figure 10 、 Figure 11 and Figure 12 As shown, S140 also includes the following process S141.

[0120] S141 , while controlling the corresponding bridge arm of the second converter and the third valve or the fourth valve to be turned on, control the fifth valve to be turned on.

[0121] like Figure 10 、 Figure 11 and Figure 12 As shown, taking the first upper bridge arm of phase A as an example, when the first upper bridge arm of phase A is commutated to the first upper bridge arm of phase B, at this time, if a fault occurs that may cause the commutation of the first upper bridge arm of phase A of the first converter to fail, the second upper bridge arm of phase A and the third valve V71 and the fifth valve V73 of the second converter are controlled to be turned on; taking the first lower bridge arm of phase A as an example, when the first lower bridge arm of phase A is commutated to the first lower bridge arm of phase B, at this time, if a fault occurs that may cause the commutation of the first lower bridge arm of phase A of the first converter to fail, the second lower bridge arm of phase A and the fourth valve V72 and the fifth valve V73 of the second converter are controlled to be turned on.

[0122] In S150, the first fully-controlled valve of the commutation bridge arm is controlled to be closed, so that the current of the commutation bridge arm is transferred to the corresponding bridge arm of the second converter and the third valve or the fourth valve.

[0123] It should be pointed out that only after the first full-control valve controlling the commutation bridge arm is closed, the corresponding bridge arm of the second converter and the third valve or the fourth valve are subjected to the forward voltage that causes the valve to conduct, and the corresponding bridge arm of the second converter and the third valve or the fourth valve conduct current.

[0124] In the event of a fault, the first fully controlled valve of the first converter is closed before the first half controlled valve is closed. Figure 9 、 Figure 10 、 Figure 11 、 Figure 12 and Figure 13As shown, taking the first upper bridge arm of phase A as an example, the first full-control valve V42 of the first upper bridge arm of phase A of the first converter 1 is controlled to be closed, so that the current of the first upper bridge arm of phase A is transferred to the second upper bridge arm V43 of phase A and the third valve V71 of the second converter 2; taking the first lower bridge arm of phase A as an example, the first full-control valve V12 of the first lower bridge arm of phase A of the first converter 1 is controlled to be closed, so that the current of the first lower bridge arm of phase A is transferred to the second lower bridge arm V13 of phase A and the fourth valve V72 of the second converter 2.

[0125] In S160, after the first half-controlled valve of the commutation bridge arm is turned off, the corresponding bridge arm, the third valve or the fourth valve of the second converter corresponding to the commutation bridge arm is controlled to be turned off, thereby realizing the current transfer from the phase where the commutation bridge arm is located to another phase.

[0126] like Figure 9 and Figure 13 As shown, taking the first upper bridge arm of phase A as an example, after the first half-controlled valve V41 is turned off, the third valve V71 is controlled to be turned off, forcing the current to switch from phase A to phase B. Accordingly, the third lightning arrester F71 is activated to absorb the shutdown energy of the third valve V71; taking the first lower bridge arm of phase A as an example, after the first half-controlled valve V11 is turned off, the fourth valve V72 is controlled to be turned off, forcing the current to switch from phase A to phase B. Accordingly, the fourth lightning arrester F72 is activated to absorb the shutdown energy of the fourth valve V72. Figure 13 In this process, the electricity absorbed by the first capacitor C11 is released through the first resistor R11.

[0127] like Figure 9 and Figure 13 As shown, taking the first upper bridge arm of phase A as an example, when the third valve V71 is controlled to be closed, if the third valve V71 is over-voltage, over-current or faulty, the first half-controlled valve V41 and the first full-controlled valve V42 of the first upper bridge arm of the first converter are controlled to be turned on; taking the first lower bridge arm of phase A as an example, when the fourth valve V72 is controlled to be closed, if the fourth valve V72 is over-voltage, over-current or faulty, the first half-controlled valve V11 and the first full-controlled valve V12 of the first upper bridge arm of the first converter are controlled to be turned on.

[0128] In this embodiment, when the first converter may fail to commutate due to a fault, the second converter and the connecting circuit are controlled to be turned on, and the current is transferred to the second converter and the connecting circuit of the series-connected fully-controlled device. By controlling the fully-controlled device to shut down, the controllable commutation of the first converter based on the half-controlled device is achieved, effectively suppressing the occurrence of commutation failure and ensuring the reliable operation of the dual converter.

[0129] The first half-controlled valve of the commutation bridge arm is shut off when the forward current of the first half-controlled valve 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 is extended, and the shutdown time is less than 700 μs, but is not limited thereto.

[0130] When the dual converter parallel circuit further includes a fifth valve, such as Figure 10 、 Figure 11 and Figure 12 As shown, S160 also includes the following process S161.

[0131] S161, after the first half-controlled valve of the commutation bridge arm is turned off, the fifth valve is controlled to be turned off to control the corresponding bridge arm and the third valve or the fourth valve of the second converter to be turned off.

[0132] like Figure 10 、 Figure 11 and Figure 12 As shown, taking the first upper bridge arm of phase A as an example, after the first half-controlled valve V41 is turned off, the fifth valve V73 is controlled to be turned off, forcing the current to switch from phase A to phase B. Accordingly, the eighth lightning arrester F73 is activated to absorb the shutdown energy of the fifth valve V73; taking the first lower bridge arm of phase A as an example, after the first half-controlled valve V11 is turned off, the fifth valve V73 is controlled to be turned off, forcing the current to switch from phase A to phase B. Accordingly, the eighth lightning arrester F73 is activated to absorb the shutdown energy of the fifth valve V73. Taking the first upper bridge arm of phase A as an example, when the fifth valve V73 is controlled to be closed, if the fifth valve V73 is over-voltage, over-current or faulty, the first half-controlled valve V41 and the first full-controlled valve V42 of the first upper bridge arm of phase A of the first converter 1 are controlled to be turned on; taking the first lower bridge arm of phase A as an example, when the fifth valve V73 is controlled to be closed, if the fifth valve V73 is over-voltage, over-current or faulty, the first half-controlled valve V11 and the first full-controlled valve V12 of the first upper bridge arm of phase A of the first converter 1 are controlled to be turned on.

[0133] When the dual converter parallel circuit further includes the sixth valve and the seventh valve, as shown in FIG. Figure 12 As shown, S160 also includes the following processes S162 and S163.

[0134] S162, when the first full-control valve of the commutation bridge arm is closed, the second converter is locked and the sixth valve or the seventh valve is controlled to be closed.

[0135] like Figure 12 As shown, taking the first upper bridge arm of phase A as an example, when the first full-control valve V42 of the first upper bridge arm of phase A is controlled to be closed, the sixth valve V74 is controlled to be closed; taking the first lower bridge arm of phase A as an example, when the first full-control valve V12 of the first lower bridge arm of phase A is controlled to be closed, the seventh valve V75 is controlled to be closed.

[0136] S163: When the working condition that may cause the commutation failure of the commutation bridge arm of the first converter disappears, control the sixth valve and / or the seventh valve to be turned on.

[0137] like Figure 12As shown, when the working conditions that may cause the commutation failure of the commutation bridge arm of the first converter disappear, the sixth valve V74 and the seventh valve V75 are controlled to be turned on, the second converter 2 is unlocked, the second converter 2 operates in the inverter state, and the first converter 1 and the second converter 2 operate in parallel.

[0138] The embodiment of the present application further provides a control device 300 for the dual-converter parallel circuit as described above. Figure 15 As shown, the control device includes a detection unit 310 and a control unit 320 .

[0139] The detection unit 310 is used to detect operating parameters and faults in the dual-converter parallel circuit. Based on the operating parameters of the dual-converter parallel circuit, the control unit 320 controls the first converter to operate in an inverter state, the second converter to operate in an inverter state or a locked state, and the third and fourth valves to operate in a locked state or an uncontrolled state. When a fault occurs that may cause commutation failure in the commutation arm of the first converter, the control unit further controls the corresponding arm of the second converter and the third or fourth valve of the corresponding commutation arm to conduct, controls the first fully-controlled valve of the commutation arm to close, and transfers the current in the commutation arm to the corresponding arm of the second converter and the third or fourth valve. After the first half-controlled valve of the commutation arm is closed, the corresponding arm of the second converter and the third or fourth valve of the corresponding commutation arm are controlled to close, thereby transferring current from the phase of the commutation arm to another phase. The corresponding arm of the second converter is the arm connected to the same polarity DC bus and the same phase as the commutation arm of the first converter.

[0140] 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 parallel circuit, comprising: A first converter is a three-phase six-bridge arm circuit, including three first upper bridge arms and three first lower bridge arms, each of the first upper bridge arm and the first lower bridge arm including a first half-controlled valve and a first full-controlled valve connected in series, the first half-controlled valve including a half-controlled switch, and the first full-controlled valve including at least one of a one-way full-controlled switch, a two-way full-controlled switch, and an MMC single valve, and a DC power supply is input from the DC side of the first converter; The second converter is a three-phase six-bridge-arm circuit, including three second upper bridge arms and three second lower bridge arms, each of the second upper bridge arm and the second lower bridge arm includes a second valve, and the second valve is an uncontrolled switch or / and a half-controlled switch; The connecting circuit includes a third valve and a fourth valve, wherein the third valve and the fourth valve include at least one of an uncontrolled switch, a half-controlled switch, a one-way fully controlled switch, a two-way fully controlled switch, and an MMC single valve, wherein: The third valve is connected to the positive pole of the DC bus of the first converter or the first segmentation point of the first half-controlled valve of the first upper bridge arm and the positive pole of the DC bus of the second converter, and the fourth valve is connected to the negative pole of the DC bus of the first converter or the second segmentation point of the first half-controlled valve of the first lower bridge arm and the negative pole of the DC bus of the second converter; or The third valve connects the positive pole of the DC bus of the first converter or the first segmentation point of the first half-controlled valve of the first upper bridge arm and the negative pole of the DC bus of the second converter, and the fourth valve connects the negative pole of the DC bus of the first converter or the second segmentation point of the first half-controlled valve of the first lower bridge arm and the positive pole of the DC bus of the second converter.

2. The dual-converter parallel circuit according to claim 1, wherein: The first segmentation point divides the first half-controlled valve of the first upper bridge arm into two sections according to the pressure resistance level, and the second segmentation point divides the first half-controlled valve of the first lower bridge arm into two sections according to the pressure resistance level. The pressure resistance ratio of the two sections ranges from 0.2 to 5.

3. The dual-converter parallel circuit according to claim 1, wherein: When the third valve is connected to the first segmentation point, the first segmentation point of the first half-controlled valve of each first upper bridge arm is respectively connected to one of the third valves; when the fourth valve is connected to the second segmentation point, the second segmentation point of the first half-controlled valve of each first lower bridge arm is respectively connected to one of the fourth valves.

4. The dual-converter parallel circuit according to claim 1, wherein: Arrester or / and second half-controlled valve are connected in parallel at both ends of the first half-controlled valve, the first fully-controlled valve, the second valve, the third valve and the fourth valve respectively, and the second half-controlled valve includes a half-controlled switch.

5. The dual-converter parallel circuit according to claim 1, wherein: The connecting circuit further comprises: A fifth valve, or a circuit of a first capacitor and a first resistor in parallel and the fifth valve in series, connects the DC bus positive pole and the DC bus negative pole of the second converter, wherein the first capacitor includes at least one capacitive element connected in series.

6. The dual-converter parallel circuit according to claim 1, wherein: The connection circuit further includes: a parallel circuit of a first capacitor and a first resistor, connecting the DC bus positive electrode and the DC bus negative electrode of the second converter, and the first capacitor includes at least one capacitive element connected in series.

7. The dual-converter parallel circuit according to claim 5, wherein: The connecting circuit further comprises: a sixth 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, a seventh 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 fifth valve includes at least one of an uncontrolled switch, a half-controlled switch, a one-way fully-controlled switch, a two-way fully-controlled switch, an MMC single valve, a fully-controlled switch connected in series, and a fast isolating switch. The sixth valve and the seventh valve include at least one of a one-way fully-controlled switch, a two-way fully-controlled switch, an MMC single valve, a fully-controlled switch connected in series, and a fast isolating switch. A lightning arrester or / and the second half-controlled valve are connected in parallel at both ends of the fifth valve, the sixth valve, the seventh valve, and the first capacitor, respectively.

8. The dual-converter parallel circuit according to claim 1, wherein: The connecting circuit further comprises: a lightning arrester connected in series with the third valve and / or the fourth valve; or A parallel circuit of a second capacitor and a second resistor is connected in series with the third valve and / or the fourth valve.

9. The dual-converter parallel 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. The DC bus input ends of the first converter and the second converter are connected in parallel in positive and negative poles through an isolating switch and / or a knife switch.

10. A high voltage direct current transmission system comprising the dual converter parallel circuit according to any one of claims 1 to 9.

11. A control method for a dual-converter parallel circuit according to any one of claims 1 to 9, comprising: controlling the first converter to operate in an inverter state; controlling the second converter to operate in an inverter state or a blocking state; Controlling the third valve and the fourth valve to operate in a locked state or an uncontrolled state; When a fault occurs and is about to cause commutation failure of the commutation bridge arm of the first converter, the method includes: Controlling the corresponding bridge arm of the second converter corresponding to the phase-changing bridge arm and the third valve or the fourth valve to be turned on; Controlling the first full-control valve of the commutation bridge arm to turn off, so that the current of the commutation bridge arm is transferred to the corresponding bridge arm of the second converter and the third valve or the fourth valve; After the first half-controlled valve of the commutation bridge arm is turned off, the corresponding bridge arm of the second converter, the third valve or the fourth valve is controlled to be turned off, thereby realizing the current transfer from the phase where the commutation bridge arm is located to another phase. The corresponding bridge arm of the second converter is a bridge arm connected to the DC bus with the same polarity and the same phase as the commutation bridge arm of the first converter.

12. A control method for a dual-converter parallel circuit according to claim 5 or 7, comprising: controlling the first converter to operate in an inverter state; controlling the second converter to operate in an inverter state or a blocking state; Controlling the third valve and the fourth valve to operate in a locked state or an uncontrolled state; When a fault occurs and is about to cause commutation failure of the commutation bridge arm of the first converter, the method includes: Controlling the corresponding bridge arm of the second converter corresponding to the phase-changing bridge arm and the third valve or the fourth valve to be turned on; While controlling the corresponding bridge arm of the second converter corresponding to the commutation bridge arm and the third valve or the fourth valve to be turned on, controlling the fifth valve to be turned on; Controlling the first full-control valve of the commutation bridge arm to turn off, so that the current of the commutation bridge arm is transferred to the corresponding bridge arm of the second converter and the third valve or the fourth valve; After the first half-controlled valve of the commutation bridge arm is closed, the fifth valve is controlled to be closed to control the corresponding bridge arm of the second converter, and the third valve or the fourth valve is closed to realize the current transfer from the phase where the commutation bridge arm is located to another phase. The corresponding bridge arm of the second converter is a bridge arm connected to the DC bus with the same polarity and the same phase as the commutation bridge arm of the first converter.

13. The control method according to claim 12, further comprising: controlling the second converter to operate in a rectification state or a no-load pressurization state to supply power to a drive circuit of the fifth valve; When a second half-controlled valve is connected in parallel at both ends of the fifth valve, and the fifth valve is over-pressured, over-currented or fails, the second half-controlled valve is controlled to be turned on; When the fifth valve is controlled to be closed and the fifth valve is over-pressured, over-currented or fails, the first half-controlled valve and the first full-controlled valve of the phase-changing bridge arm are controlled to be turned on.

14. A control method for a dual-converter parallel circuit according to claim 7, comprising: controlling the first converter to operate in an inverter state; controlling the second converter to operate in an inverter state or a blocking state; Controlling the third valve and the fourth valve to operate in a locked state or an uncontrolled state; When a fault occurs and is about to cause commutation failure of the commutation bridge arm of the first converter, the method includes: Controlling the corresponding bridge arm of the second converter corresponding to the phase-changing bridge arm and the third valve or the fourth valve to be turned on; controlling the first fully-controlled valve of the commutation bridge arm to be closed, so that the current of the commutation bridge arm is transferred to the corresponding bridge arm of the second converter and the third valve or the fourth valve; when the first fully-controlled valve of the commutation bridge arm is controlled to be closed, locking the second converter and controlling the sixth valve or the seventh valve to be closed; After the first half-controlled valve of the commutation bridge arm is turned off, the corresponding bridge arm of the second converter, the third valve or the fourth valve is controlled to be turned off, so that the current is transferred from the phase where the commutation bridge arm is located to another phase. The corresponding bridge arm of the second converter is a bridge arm connected to the DC bus with the same polarity and the same phase as the commutation bridge arm of the first converter; After the working condition that will cause the commutation failure of the commutation bridge arm of the first converter disappears, the sixth valve and / or the seventh valve are controlled to be turned on.

15. The control method according to claim 14, further comprising: Controlling the sixth valve and the seventh valve to be turned on so that the first converter and the second converter share a DC bus and the second converter operates in an inverter state; When a second half-controlled valve is connected in parallel at both ends of the first fully-controlled valve, the second valve, the third valve, the fourth valve, the sixth valve or the seventh valve, and the first fully-controlled valve, the second valve, the third valve, the fourth valve, the sixth valve or the seventh valve has an overpressure, an overcurrent or a fault, the second half-controlled valve is controlled to be turned on; When the corresponding bridge arm, third valve or fourth valve, sixth valve or seventh valve of the second converter is controlled to be closed, and the corresponding bridge arm, third valve or fourth valve, sixth valve or seventh valve of the second converter is over-voltage, over-current or faulty, the first half-controlled valve and the first full-controlled valve of the phase-changing bridge arm are controlled to be turned on.

16. A control device for a dual-converter parallel circuit according to any one of claims 1 to 9, comprising: a detection unit, configured to detect operating parameters and faults of the dual-converter parallel circuit; A control unit, based on the operating parameters of the dual-converter parallel circuit, controls the first converter to operate in an inverter state; controls the second converter to operate in an inverter state or a locked state; and controls the third valve and the fourth valve to operate in a locked state or an uncontrolled state. When a fault occurs and is about to cause commutation failure of the commutation bridge arm of the first converter, the control unit further controls the corresponding bridge arm of the second converter and the third valve or the fourth valve corresponding to the commutation bridge arm to be turned on, controls the first fully-controlled valve of the commutation bridge arm to be turned off, so that the current of the commutation bridge arm is transferred to the corresponding bridge arm of the second converter and the third valve or the fourth valve. After the first half-controlled valve of the commutation bridge arm is turned off, the corresponding bridge arm of the second converter and the third valve or the fourth valve are controlled to be turned off, thereby realizing the current transfer from the phase where the commutation bridge arm is located to another phase. The corresponding bridge arm of the second converter is the bridge arm connected to the DC bus with the same polarity and the same phase as the commutation bridge arm of the first converter.

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