High voltage direct current transmission valve group, series circuit, system, control method, and control device

Abstract

The present application discloses a high voltage direct current transmission valve group, a series circuit, a system, a control method, and a control device. By configuring different connection modes of a voltage source converter or a bridge uncontrolled rectifier circuit, a direct current circuit breaker, a first valve, an energy consumption circuit and a bypass switch, online input, online exit and fault exit of the voltage source converter without full-range voltage regulation capability are realized. In addition, during a fault, the freewheeling current of the first valve is used for reducing the stress when the direct current circuit breaker is disconnected, so that the high voltage direct current transmission valve group formed by the direct current circuit breaker having a low voltage level is connected in series in an ultra high voltage direct current transmission system, and compared to using a modular multi-level converter structure having half-bridge sub-modules and full-bridge sub-modules, the loss is reduced, the fault isolation performance is better. The present application is more suitable for a multi-terminal ultra high voltage flexible or hybrid direct current transmission system and a direct current grid for long-distance transmission.

Description

DC transmission valve group, series circuit, system, control method and control device Technical Field

[0001] The present invention belongs to the technical field of flexible direct current transmission and hybrid direct current transmission, and in particular relates to a direct current transmission valve group, a series circuit, a system, a control method and a control device. Background Art

[0002] Compared with traditional DC transmission technology, flexible DC transmission technology has the following advantages: there is no reactive power compensation and commutation failure problems, it can power passive systems, it can independently adjust active power and reactive power at the same time, it has low harmonic levels, is suitable for forming multi-terminal DC systems, and occupies a small area.

[0003] Compared with traditional DC transmission, flexible DC transmission also has shortcomings, mainly manifested in the following aspects: large losses, high equipment costs, relatively small capacity, and is not very suitable for long-distance overhead line transmission.

[0004] Currently, flexible DC transmission uses two-level or three-level VSCs (Voltage Source Converters) or multi-level MMCs (Modular Multilevel Converters) based on half-bridge submodules. When a short circuit occurs on the DC side, even if all fully controlled devices are turned off, the converter will still feed current to the fault point through the diodes connected in anti-parallel with the fully controlled devices. Existing solutions use DC circuit breakers to clear faults, but the shutdown stress is very high when the line is long. At the same time, due to the limited voltage regulation range, it is impossible to realize online switching on and off of the converter. Flexible DC transmission uses an MMC structure that combines half-bridge and full-bridge submodules. Although it has DC fault ride-through capability and can realize online switching on and off of the converter, it has greater losses than the MMC and DC circuit breaker solutions based on half-bridge submodules and is not suitable for application in DC power grids.

[0005] Summary of the Invention

[0006] Purpose of the invention: The technical problem to be solved by this application is to overcome the defects of the above-mentioned prior art and provide a DC transmission valve group, series circuit, system, control method and control device, which are more suitable for multi-terminal ultra-high voltage flexible or hybrid DC transmission systems and DC power grids for long-distance transmission.

[0007] Technical solution: The present application provides a DC transmission valve group, including a voltage source converter or a bridge uncontrolled rectifier circuit, a DC circuit breaker, a first valve and an energy consumption circuit.

[0008] The voltage source converter or the bridge uncontrolled rectifier circuit is connected in series with the main branch of the DC circuit breaker and then connected in anti-parallel with the series circuit of the first valve and the energy consumption circuit, or the voltage source converter is connected in series with the series circuit of the first valve and the energy consumption circuit and then connected in parallel with the DC circuit breaker.

[0009] In some embodiments, the voltage source converter or the bridge uncontrolled rectifier circuit respectively includes at least three phases and six bridge arms; the DC circuit breaker includes a first two-port DC circuit breaker or a multi-port DC circuit breaker; the first valve includes a first diode valve, a first thyristor valve or a first fully-controlled valve, the first diode valve includes at least one diode connected in series, the first thyristor valve includes at least one thyristor connected in series, the first fully-controlled valve includes at least one fully-controlled device connected in series and the fully-controlled device includes an anti-parallel diode; the energy consumption circuit includes a lightning arrester or a resistor.

[0010] In some embodiments, the voltage source converter comprises at least one of a two-level converter, a three-level converter, a modular multilevel converter, a diode-clamped multilevel converter, a cascaded two-level converter, or a stacked two-level converter.

[0011] In some embodiments, the bridge uncontrolled rectifier circuit includes a six-pulse bridge circuit or a twelve-pulse bridge circuit, and is composed of uncontrolled power semiconductors.

[0012] In some embodiments, the DC circuit breaker is at least one of a hybrid DC circuit breaker, a solid-state DC circuit breaker, or a mechanical DC circuit breaker, wherein the DC circuit breaker includes: a main branch, the first two-port DC circuit breaker includes the main branch, the multi-port DC circuit breaker includes one or more main branches, and all main branches have a common end, the main branch includes a fast disconnect switch and / or a first power switch connected in series; and / or a transfer branch, the transfer branch includes a second power switch connected in series and / or an LC resonant circuit and / or a coupled negative voltage circuit; an energy consumption branch, the energy consumption branch is connected in parallel with the transfer branch, and the energy consumption branch includes a lightning arrester.

[0013] In some embodiments, it also includes a conversion switch group, through which the voltage source converter is connected in series with the main branch of the DC circuit breaker and then connected in anti-parallel with the first valve, for rectification operation or inversion operation of the voltage source converter; or through the conversion switch group, the voltage source converter is connected in series with the first valve and then connected in parallel with the transfer branch of the DC circuit breaker, for inversion operation or online inversion operation of the voltage source converter; or through the conversion switch group, the voltage source converter is connected in parallel with the transfer branch of the DC circuit breaker, for online inversion operation of the voltage source converter.

[0014] In some embodiments, the conversion switch group includes: a first conversion switch, a second conversion switch and a third conversion switch; wherein the first conversion switch connects the positive pole of the voltage source converter and the first end of the DC circuit breaker, the second conversion switch connects the negative pole of the voltage source converter and the first end of the DC circuit breaker, and the third conversion switch connects the positive pole of the voltage source converter and the second end of the DC circuit breaker; or, the first conversion switch connects the negative pole of the voltage source converter and the second end of the DC circuit breaker, the second conversion switch connects the positive pole of the voltage source converter and the second end of the DC circuit breaker, and the third conversion switch connects the negative pole of the voltage source converter and the first end of the DC circuit breaker.

[0015] In some embodiments, the transfer switch group includes: a fourth transfer switch, a fifth transfer switch, and a sixth transfer switch; wherein the fourth transfer switch is connected to the positive terminal of the DC transmission valve group and the second terminal of the DC circuit breaker, the fifth transfer switch is connected to the positive terminal of the DC transmission valve group and the first terminal of the DC circuit breaker, and the sixth transfer switch is connected to the negative terminal of the DC transmission valve group and the second terminal of the DC circuit breaker; or, the fourth transfer switch is connected to the negative terminal of the DC transmission valve group and the first terminal of the DC circuit breaker, the fifth transfer switch is connected to the negative terminal of the DC transmission valve group and the second terminal of the DC circuit breaker, and the sixth transfer switch is connected to the positive terminal of the DC transmission valve group and the first terminal of the DC circuit breaker.

[0016] In some embodiments, the transfer switch group includes: a first transfer switch, a seventh transfer switch, an eighth transfer switch, a ninth transfer switch, and a tenth transfer switch; wherein the first transfer switch is connected to the positive terminal of the voltage source converter and the first terminal of the DC circuit breaker, the seventh transfer switch is connected to the positive terminal of the DC transmission valve group and the cathode of the first valve, the eighth transfer switch is connected to the negative terminal of the DC transmission valve group and the anode of the first valve, the ninth transfer switch is connected to the positive terminal of the voltage source converter and the cathode of the first valve, and the tenth transfer switch is connected to the positive terminal of the DC transmission valve group and the anode of the first valve; or, the first transfer switch is connected to the negative terminal of the voltage source converter and the second terminal of the DC circuit breaker, the seventh transfer switch is connected to the negative terminal of the DC transmission valve group and the anode of the first valve, the eighth transfer switch is connected to the positive terminal of the DC transmission valve group and the cathode of the first valve, the ninth transfer switch is connected to the negative terminal of the DC transmission valve group and the cathode of the first valve.

[0017] In some embodiments, the transfer switch group includes: a first transfer switch, a second transfer switch, a seventh transfer switch, an eighth transfer switch, a ninth transfer switch, and a tenth transfer switch; wherein the first transfer switch is connected to the positive electrode of the voltage source converter and the first end of the DC circuit breaker, the second transfer switch is connected to the negative electrode of the voltage source converter and the first end of the DC circuit breaker, the seventh transfer switch is connected to the positive end of the DC transmission valve group and the cathode of the first valve, the eighth transfer switch is connected to the negative end of the DC transmission valve group and the anode of the first valve, and the ninth transfer switch is connected to the positive electrode of the voltage source converter and the cathode of the first valve. The tenth conversion switch connects the positive terminal of the DC transmission valve group and the anode of the first valve; or, the first conversion switch connects the negative terminal of the voltage source converter and the second terminal of the DC circuit breaker, the second conversion switch connects the positive terminal of the voltage source converter and the second terminal of the DC circuit breaker, the seventh conversion switch connects the negative terminal of the DC transmission valve group and the anode of the first valve, the eighth conversion switch connects the positive terminal of the DC transmission valve group and the cathode of the first valve, the ninth conversion switch connects the negative terminal of the voltage source converter and the anode of the first valve, and the tenth conversion switch connects the negative terminal of the DC transmission valve group and the cathode of the first valve.

[0018] In some embodiments, the voltage source converter is connected in series with the first valve, including: the positive electrode of the voltage source converter is connected to the cathode of the anti-parallel diode of the diode, thyristor or fully-controlled device of the first valve; or the negative electrode of the voltage source converter is connected to the anode of the anti-parallel diode of the diode, thyristor or fully-controlled device of the first valve.

[0019] In some embodiments, the DC transmission valve group further includes at least one residual current isolating switch. When the voltage source converter or the bridge uncontrolled rectifier circuit is connected in series with the DC circuit breaker and then connected in anti-parallel with the first valve, the residual current isolating switch is connected in series between the voltage source converter and the DC circuit breaker, and / or, in series between the DC circuit breaker and the first valve; when the voltage source converter is connected in series with the first valve and then connected in parallel with the DC circuit breaker, the residual current isolating switch is first connected in series with the DC circuit breaker and then connected in parallel with the circuit after the voltage source converter and the first valve are connected in series.

[0020] In some embodiments, the DC transmission valve group further includes a bypass switch, which connects the positive terminal and the negative terminal of the DC transmission valve group; the bypass switch includes at least one of a mechanical switch, a mechanical knife switch, and a third power switch connected in series.

[0021] In some embodiments, the DC transmission valve group further includes: a positive isolation switch, which is connected to the positive end and the first positive input end of the DC transmission valve group; a negative isolation switch, which is connected to the negative end and the first negative input end of the DC transmission valve group; and a bypass switch, which is connected to the first positive input end and the first negative input end of the DC transmission valve group.

[0022] In some embodiments, the DC circuit breaker is a multi-port DC circuit breaker, and the DC transmission valve group further includes: a second valve, the second valve including a second diode valve or a second thyristor valve, the second diode valve including at least one diode connected in series, the second thyristor valve including at least one thyristor connected in series, the cathode of the second valve being the second positive input terminal of the DC transmission valve group, and the anode of the second valve being the second negative input terminal of the DC transmission valve group; one DC transmission valve group constitutes a DC pole, and the voltage source converter is connected in series with the main branch of the multi-port DC circuit breaker and then connected in anti-parallel with the second valve.

[0023] In some embodiments, the DC circuit breaker is a first two-port DC circuit breaker, and the DC transmission valve group further includes: a second two-port DC circuit breaker; a second valve, the second valve including a second diode valve or a second thyristor valve, the second diode valve including at least one diode connected in series, the second thyristor valve including at least one thyristor connected in series, the cathode of the second valve being the second positive input terminal of the DC transmission valve group, and the anode of the second valve being the second negative input terminal of the DC transmission valve group; one DC transmission valve group constitutes a DC pole, and the voltage source converter is connected in series with the second two-port DC circuit breaker and / or the first two-port DC circuit breaker, and then connected in anti-parallel with the second valve.

[0024] In some embodiments, the DC transmission valve group further includes a bypass switch, which is connected in parallel with the energy consumption circuit; the bypass switch includes a mechanical switch and / or a mechanical knife switch.

[0025] An embodiment of the present application further provides a DC transmission valve group series circuit, comprising at least two DC transmission valve groups as described in any of the preceding embodiments; the DC transmission valve group series circuit comprises at least a first DC transmission valve group and a second DC transmission valve group, wherein a first negative input terminal of the first DC transmission valve group is connected to a first positive input terminal of the second DC transmission valve group.

[0026] In some embodiments, both the first DC transmission valve group and the second DC transmission valve group include a multi-port DC circuit breaker and a second valve, or both the first DC transmission valve group and the second DC transmission valve group include a second two-port DC circuit breaker and a second valve, wherein the second negative input terminal of the first DC transmission valve group is connected to the second positive input terminal of the second DC transmission valve group, and the first negative input terminal of the first DC transmission valve group is connected to the first positive input terminal of the second DC transmission valve group.

[0027] In some embodiments, the first DC transmission valve group includes a second two-port DC circuit breaker and a second valve, the first negative input terminal of the first DC transmission valve group is connected to the first positive input terminal of the second DC transmission valve group, the second negative input terminal of the first DC transmission valve group is connected to the first negative input terminal of the second DC transmission valve group or is connected through a disconnect switch, or the second positive input terminal of the first DC transmission valve group is connected to the first positive input terminal of the second DC transmission valve group or is connected through a disconnect switch.

[0028] An embodiment of the present application further provides a DC power transmission system, comprising the DC power transmission valve group as described in any of the preceding embodiments, or the DC power transmission valve group series circuit as described in any of the preceding embodiments; a pole-neutral bus switch is connected in series between the DC power transmission valve group or the DC power transmission valve group series circuit and the ground; the pole-neutral bus switch comprises at least one of a mechanical switch, a mechanical knife switch, and a fourth power switch connected in series.

[0029] A control method for a DC transmission valve group is applied to the DC transmission valve group as described in any of the above embodiments; the control method comprises:

[0030] If the voltage source converter is connected in series with the main branch of the DC circuit breaker and then connected in anti-parallel with the series circuit of the first valve and the energy consumption circuit, during normal operation, the DC circuit breaker is controlled to be turned on, the first valve is controlled to be turned off, and the voltage source converter is controlled to perform rectification or inversion operation;

[0031] If the voltage source converter is connected in series with the first valve and the parallel circuit of the energy consumption circuit and the bypass switch and then connected in parallel with the DC circuit breaker, during normal operation, the DC circuit breaker is controlled to be turned off, the first valve is controlled to be turned on, the bypass switch is controlled to be closed, and the voltage source converter is controlled to operate in inversion.

[0032] In some embodiments, if the voltage source converter is connected in series with the main branch of the DC circuit breaker and then connected in anti-parallel with the series circuit of the first valve and the energy consumption circuit, the control method further includes:

[0033] When the voltage source converter is put into online rectification operation, controlling the voltage source converter to charge, controlling the voltage source converter to unlock, and controlling the DC circuit breaker to turn on;

[0034] When the voltage source converter is in rectification operation and is offline, the bypass switch is controlled to be closed, the DC circuit breaker is controlled to be turned off, and the first valve is controlled to be turned on;

[0035] When the voltage source converter is in rectification operation and the fault is exited, the DC circuit breaker is controlled to be turned off and the first valve is controlled to be turned on; when the fault is exited, the voltage source converter is also controlled to be locked;

[0036] When the voltage source converter is in rectification or inversion operation and a DC fault is being crossed, the DC circuit breaker is controlled to be turned off and the first valve is controlled to be turned on. After the fault is recovered or after a de-ionization time has passed, the DC circuit breaker is controlled to be turned on. The DC fault includes a DC line fault.

[0037] In some embodiments, if the voltage source converter is connected in series with a parallel circuit of the first valve, the energy consumption circuit, and the bypass switch and then connected in parallel with the DC circuit breaker, the control method further includes:

[0038] When the voltage source converter is put into inverter operation online, controlling the voltage source converter to charge, controlling the voltage source converter to unlock, controlling the DC circuit breaker to turn off, and controlling the first valve to turn on;

[0039] When the voltage source converter is in inverter operation and is offline or fault-exited, the DC circuit breaker is controlled to be turned on, or if the DC transmission valve group further includes a bypass switch, the bypass switch is controlled to be turned on and / or the DC circuit breaker is controlled to be turned on;

[0040] When the voltage source converter is in inverter operation and a DC fault is being crossed, the first valve is controlled to be turned on after the fault is recovered or after a de-isolation time has elapsed; the DC fault includes a DC line fault.

[0041] In some embodiments, if the DC transmission valve group further includes a bypass switch,

[0042] When the voltage source converter is in rectification operation and is offline or faulty, after controlling the first valve to be turned on, the bypass switch is also controlled to be turned on;

[0043] When the voltage source converter is in inverter operation and exits online or fails, the bypass switch is controlled to be turned on and the DC circuit breaker is controlled to be turned off; when the fault exit occurs, the voltage source converter is also controlled to be locked.

[0044] In some embodiments, if the DC transmission valve group further includes a disconnect switch, or the DC transmission system in which the DC transmission valve group is located further includes a pole-neutral bus switch, when the voltage source converter is in rectification or inversion operation and a DC fault is being ridden, after the first valve is controlled to be turned on, the disconnect switch or the pole-neutral bus switch is disconnected, and after the fault is recovered or after the de-isolation time has passed, the disconnect switch or the pole-neutral bus switch is reclosed.

[0045] In some embodiments, if the first fully-controlled valve of the DC transmission valve group uses a fully-controlled device, when the voltage source converter or the bridge uncontrolled rectifier circuit cannot normally transmit energy and generates an AC or DC overvoltage, the fully-controlled device of the first valve is controlled to be turned on to dissipate energy in the energy consumption circuit. When the voltage source converter or the bridge uncontrolled rectifier circuit can transmit energy normally, the fully-controlled device of the first valve is controlled to be turned off.

[0046] If the first diode valve of the DC transmission valve group adopts an anti-parallel circuit of at least one diode and a thyristor, when the voltage source converter or the bridge uncontrolled rectifier circuit cannot transmit energy normally and generates AC or DC overvoltage, the thyristor of the first valve is controlled to be turned on to dissipate the energy in the energy consumption circuit.

[0047] A control device for a DC transmission valve group, applied to the DC transmission valve group as described in any of the preceding embodiments, and configured to execute the control method for the DC transmission valve group as described in any of the preceding embodiments; the control device comprising: a detection unit, configured to detect operating parameters and faults of the DC transmission valve group; and a control unit, configured to, based on the operating parameters of the DC transmission valve group, control the DC circuit breaker to conduct, the first valve to close, and the voltage source converter to rectifier or inverter operation, if the voltage source converter is connected in series with the main branch of the DC circuit breaker and then connected in anti-parallel with the series circuit of the first valve and the energy consumption circuit during normal operation; and control the DC circuit breaker to close, the first valve to conduct, the bypass switch to close, and the voltage source converter to inverter operation, if the voltage source converter is connected in series with the parallel circuit of the first valve, the energy consumption circuit, and a bypass switch and then connected in parallel with the DC circuit breaker during normal operation.

[0048] Beneficial effects: The embodiments of the present application provide a DC transmission valve group, a series circuit, a system, a control method, and a control device, wherein the DC transmission valve group includes a voltage source converter or a bridge uncontrolled rectifier circuit, a DC circuit breaker, a first valve, and an energy consumption circuit; wherein the voltage source converter or the bridge uncontrolled rectifier circuit is connected in series with the main branch of the DC circuit breaker and then connected in anti-parallel to the series circuit of the first valve and the energy consumption circuit, or the voltage source converter is connected in series with the series circuit of the first valve and the energy consumption circuit and then connected in parallel to the DC circuit breaker. The present application realizes online input, online output and fault output of a voltage source converter that does not have full-range voltage regulation capability by configuring a DC circuit breaker, a first valve, an energy consumption circuit and a bypass switch. At the same time, the stress of the DC circuit breaker when it is interrupted is reduced by utilizing the freewheeling of the first valve during a fault, thereby realizing the series application of a DC transmission valve group composed of low-voltage DC circuit breakers in an ultra-high voltage DC transmission system. Compared with the MMC structure using a mixture of half-bridge submodules and full-bridge submodules, the loss is reduced and the fault isolation performance is better, and it is more suitable for multi-terminal ultra-high voltage flexible or hybrid DC transmission systems and DC power grids for long-distance transmission. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] 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 those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0050] FIG1 is a schematic diagram of a first DC transmission valve group according to an embodiment of the present application;

[0051] FIG2 is a schematic diagram of a second DC transmission valve group according to an embodiment of the present application;

[0052] FIG3 is a schematic diagram of a third DC transmission valve group according to an embodiment of the present application;

[0053] FIG4 is a schematic diagram of a fourth DC transmission valve group according to an embodiment of the present application;

[0054] FIG5 is a schematic diagram of a fifth DC transmission valve group according to an embodiment of the present application;

[0055] FIG6 is a schematic diagram of a sixth DC transmission valve group according to an embodiment of the present application;

[0056] FIG7 is a schematic diagram of a first type of DC transmission valve group suitable for inverter operation according to an embodiment of the present application;

[0057] FIG8 is a schematic diagram of a second DC transmission valve group suitable for inverter operation according to an embodiment of the present application;

[0058] FIG9 is a schematic diagram of a third DC transmission valve group suitable for inverter operation according to an embodiment of the present application;

[0059] FIG10 is a schematic diagram of a fourth DC transmission valve group suitable for inverter operation according to an embodiment of the present application;

[0060] FIG11 is a schematic diagram of a fifth DC transmission valve group suitable for inverter operation according to an embodiment of the present application;

[0061] FIG12 is a schematic diagram of a DC transmission valve group in which the first valve of the present application adopts a fully controlled device;

[0062] FIG13 is a schematic diagram of a DC transmission valve group configured as a first transfer switch group according to an embodiment of the present application;

[0063] FIG14 is a schematic diagram of a DC transmission valve group with a second configuration of a switch group according to an embodiment of the present application;

[0064] FIG15 is a schematic diagram of a DC transmission valve group with a third configuration of a switch group according to an embodiment of the present application;

[0065] FIG16 is a schematic diagram of a DC transmission valve group with a fourth configuration of a transfer switch group according to an embodiment of the present application;

[0066] FIG17 is a schematic diagram of a DC transmission valve group with a fifth configuration of a transfer switch group according to an embodiment of the present application;

[0067] FIG18 is a schematic diagram of a DC transmission valve group with a sixth configuration of a switch group according to an embodiment of the present application;

[0068] FIG19 is a schematic diagram of a DC transmission valve group with a seventh configuration of a transfer switch group according to an embodiment of the present application;

[0069] FIG20 is a schematic diagram of a DC transmission valve group configured with an eighth embodiment of the present application;

[0070] FIG21 is a schematic diagram of a DC transmission valve group configured with a transfer switch group and a bypass switch according to an embodiment of the present application;

[0071] FIG22 is a schematic diagram of a DC transmission valve group configured with a transfer switch group, a bypass switch, and a knife switch according to an embodiment of the present application;

[0072] FIG23 is a schematic diagram of a DC transmission valve group configured with a multi-port DC circuit breaker according to an embodiment of the present application;

[0073] FIG24 is a schematic diagram of another DC transmission valve group configured with a multi-port DC circuit breaker according to an embodiment of the present application;

[0074] FIG25 is a schematic diagram of a DC transmission valve group configured with a second two-port DC circuit breaker according to an embodiment of the present application;

[0075] FIG26 is a schematic diagram of another DC transmission valve group configured with a second two-port DC circuit breaker according to an embodiment of the present application;

[0076] FIG27 is a schematic diagram of a first series circuit of a DC transmission valve group according to an embodiment of the present application;

[0077] FIG28 is a schematic diagram of a second series circuit of a DC transmission valve group according to an embodiment of the present application;

[0078] FIG29 is a schematic diagram of a third series circuit of a DC transmission valve group according to an embodiment of the present application;

[0079] FIG30 is a schematic diagram of a fourth series circuit of a DC transmission valve group according to an embodiment of the present application;

[0080] FIG31 is a schematic diagram of a first two-port DC circuit breaker according to an embodiment of the present application;

[0081] FIG32 is a schematic diagram of a second two-port DC circuit breaker according to an embodiment of the present application;

[0082] FIG33 is a schematic diagram of a third two-port DC circuit breaker according to an embodiment of the present application;

[0083] FIG34 is a schematic diagram of a multi-port DC circuit breaker according to an embodiment of the present application;

[0084] FIG35 is a schematic diagram of a first bypass switch or bypass switch according to an embodiment of the present application;

[0085] FIG36 is a schematic diagram of a second bypass switch or bypass switch according to an embodiment of the present application;

[0086] FIG37 is a schematic diagram of a third bypass switch or bypass switch according to an embodiment of the present application;

[0087] FIG38 is a schematic diagram of a voltage source converter according to an embodiment of the present application;

[0088] FIG39 is a schematic diagram of a bridge uncontrolled rectifier circuit according to an embodiment of the present application;

[0089] FIG40 is a flow chart of a control method for a DC transmission valve group according to an embodiment of the present application;

[0090] FIG41 is a flow chart of another method for controlling a DC transmission valve group according to an embodiment of the present application;

[0091] FIG42 is a schematic diagram of a first DC power transmission system according to an embodiment of the present application;

[0092] FIG43 is a schematic diagram of a second DC power transmission system according to an embodiment of the present application;

[0093] FIG44 is a schematic diagram of a third DC power transmission system according to an embodiment of the present application;

[0094] FIG45 is a schematic diagram of a fourth DC power transmission system according to an embodiment of the present application;

[0095] FIG46 is a schematic diagram of a fifth DC power transmission system according to an embodiment of the present application;

[0096] Figure 47 is a schematic diagram of a control device of a DC transmission valve group according to an embodiment of the present application. DETAILED DESCRIPTION

[0097] It should be noted that the order of description of the following embodiments is not intended to limit the preferred order of the embodiments.

[0098] Please refer to FIG. 1 to FIG. 6 , which are schematic diagrams of various DC transmission valve groups according to embodiments of the present application.

[0099] As shown in FIG1 , a DC transmission valve group according to an embodiment of the present application includes a voltage source converter or a bridge uncontrolled rectifier circuit, a DC circuit breaker 2 , a first valve 3 , and an energy consumption circuit 10 , wherein the positive electrode P1 of the voltage source converter or the bridge uncontrolled rectifier circuit is the high voltage end.

[0100] In this embodiment, the voltage source converter includes at least three phases and six bridge arms and cannot adjust the DC voltage to zero or negative voltage. The voltage source converter includes, but is not limited to, at least one of a two-level converter, a three-level converter, a modular multilevel converter, a diode-clamped multilevel converter, a cascaded two-level converter, or a stacked two-level converter. The modular multilevel converter utilizes a half-bridge submodule. The DC circuit breaker 2 has at least unidirectional DC current interruption capability and includes, but is not limited to, at least one of a hybrid DC circuit breaker, a solid-state DC circuit breaker, or a mechanical DC circuit breaker. The DC circuit breaker 2 is a first two-port DC circuit breaker or a multi-port DC circuit breaker. The first valve 3 includes, but is not limited to, a first diode valve, a first thyristor valve, or a first fully-controlled valve. The first diode valve includes at least one diode connected in series or an anti-parallel circuit of at least one diode and a thyristor. The first thyristor valve includes at least one thyristor connected in series. The first fully-controlled valve includes at least one fully-controlled device connected in series, and the fully-controlled device includes an anti-parallel diode. The energy consumption circuit 10 includes a lightning arrester or a resistor.

[0101] The bridge uncontrolled rectifier circuit also includes at least three phases and six bridge arms, including a six-pulse bridge circuit or a twelve-pulse bridge circuit, which is composed of uncontrolled power semiconductors, such as diodes.

[0102] Specifically, the voltage source converter or bridge uncontrolled rectifier circuit is connected in series with the main branch of the DC circuit breaker 2 and then connected in anti-parallel with the series circuit of the first valve 3 and the energy consumption circuit 10. As shown in FIG1 , the anti-parallel connection comprises the following: the positive electrode P1 of the voltage source converter or bridge uncontrolled rectifier circuit is connected to the cathode K of the first valve 3 through the DC circuit breaker 2, and the negative electrode N1 of the voltage source converter or bridge uncontrolled rectifier circuit is connected to one end of the energy consumption circuit 10. Specifically, the positive electrode P1 of the voltage source converter or bridge uncontrolled rectifier circuit is connected to the first end C of the DC circuit breaker 2, the second end D of the DC circuit breaker 2 is connected to the cathode K of the anti-parallel diode of the diode, thyristor, or fully-controlled device of the first valve 3, and the negative electrode N1 of the voltage source converter or bridge uncontrolled rectifier circuit is connected to one end of the first energy consumption circuit 10.

[0103] In this embodiment, when the DC circuit breaker 2 is turned off, the first valve 3 transfers the current flowing through the voltage source converter or the bridge uncontrolled rectifier circuit by freewheeling, thereby reducing the stress of the DC circuit breaker 2. The energy dissipation circuit 10 is used to quickly attenuate the fault current during a fault.

[0104] As shown in FIG2 , in some embodiments, the DC transmission valve group includes a bypass switch 20 . The bypass switch 20 is connected in parallel to the energy consumption circuit 10 and is used to bypass the energy consumption circuit 10 when the DC transmission valve group is switched on or off.

[0105] In some embodiments, the DC transmission valve group further includes at least one residual current isolating switch, which is connected in series between the voltage source converter or the bridge uncontrolled rectifier circuit and the DC circuit breaker 2 and / or between the DC circuit breaker 2 and the first valve 3. Specifically, as shown in FIG3 , the DC transmission valve group further includes a first residual current isolating switch 60 and / or a second residual current isolating switch 70, wherein the first residual current isolating switch 60 is connected in series between the voltage source converter or the bridge uncontrolled rectifier circuit and the DC circuit breaker 2 and / or the second residual current isolating switch 70 is connected in series between the DC circuit breaker 2 and the first valve 3.

[0106] Furthermore, as shown in FIG4 , the aforementioned anti-parallel connection is such that the positive electrode P1 of the voltage source converter or bridge uncontrolled rectifier circuit is connected to the cathode K of the first valve 3, and the negative electrode N1 of the voltage source converter or bridge uncontrolled rectifier circuit is connected to one end of the energy consumption circuit 10 via the DC circuit breaker 2. The negative electrode N1 of the voltage source converter or bridge uncontrolled rectifier circuit is preferably a high-voltage terminal. Specifically, the negative electrode N1 of the voltage source converter or bridge uncontrolled rectifier circuit is connected to the second end D of the DC circuit breaker 2, the first end C of the DC circuit breaker 2 is connected to one end of the energy consumption circuit 10, and the positive electrode P1 of the voltage source converter is connected to the cathode K of the first valve 3.

[0107] In some embodiments, the DC transmission valve group further includes a bypass switch 12, which connects the positive terminal P2 and the negative terminal N2 of the DC transmission valve group, as shown in FIG5 . The bypass switch 12 includes at least one of a mechanical switch, a mechanical knife switch, and a third power switch connected in series. The third power switch includes a power device, which includes at least one of an IGCT (Integrated Gate Commutated Thyristors), an IGBT (Insulated Gate Bipolar Transistor), a GTO (Gate Turn-Off Thyristor), a MOSFET (Metal Oxide Semiconductor Field Effect Transistor), and a thyristor, but is not limited thereto. Furthermore, the third power switch includes a power device and an uncontrolled device connected in anti-parallel thereto.

[0108] In some embodiments, the DC transmission valve assembly further includes a positive isolation switch 13, a negative isolation switch 14, and a bypass switch 11, as shown in FIG6 . The positive isolation switch 13 connects the positive terminal P2 of the DC transmission valve assembly and the first positive input terminal P. The negative isolation switch 14 connects the negative terminal N2 of the DC transmission valve assembly and the first negative input terminal N. The bypass switch 11 connects the first positive input terminal P and the first negative input terminal N of the DC transmission valve assembly.

[0109] An embodiment of the present application further provides a DC transmission valve group suitable for inverter operation of a voltage source converter, as specifically shown in FIG7 . The DC transmission valve group includes a voltage source converter 1, a DC circuit breaker 2, a first valve 3, and an energy consumption circuit 10, wherein the positive electrode P1 of the voltage source converter 1 is a high-voltage end.

[0110] In this embodiment, the voltage source converter 1 includes at least three phases and six bridge arms, and cannot adjust the DC voltage to zero or negative voltage. The voltage source converter 1 includes, but is not limited to, at least one of a two-level converter, a three-level converter, a modular multilevel converter, a diode-clamped multilevel converter, a cascaded two-level converter, or a stacked two-level converter. The modular multilevel converter utilizes a half-bridge submodule. The DC circuit breaker 2 has at least unidirectional DC current interruption capability, and includes, but is not limited to, a first two-port DC circuit breaker or a multi-port DC circuit breaker. The first valve 3 includes, but is not limited to, a first diode valve, a first thyristor valve, or a first fully-controlled valve. The first diode valve includes at least one diode connected in series, the first thyristor valve includes at least one thyristor connected in series, and the first fully-controlled valve includes at least one fully-controlled device connected in series, and the fully-controlled device includes an anti-parallel diode.

[0111] In some embodiments, the voltage source converter is suitable for a DC transmission valve group for inverter operation and further includes a bypass switch 20. The voltage source converter 1 is connected in series with the first valve 3 and the parallel circuit of the energy consumption circuit 10 and the bypass switch 20, and then connected in parallel with the DC circuit breaker 2, as shown in Figure 7. The above series connection is to connect the positive electrode P1 of the voltage source converter 1 to one end of the parallel circuit of the energy consumption circuit 10 and the bypass switch 20. Specifically, the negative electrode N1 of the voltage source converter 1 is connected to the second end D of the DC circuit breaker 2, the first end C of the DC circuit breaker 2 is connected to the anode A of the first valve 3, and the positive electrode P1 of the voltage source converter 1 is connected to one end of the parallel circuit of the energy consumption circuit 10 and the bypass switch 20.

[0112] In this embodiment, during normal operation, the bypass switch 20 is in the closed position; in the event of a DC fault, the unidirectional conduction characteristic of the first valve 3 is used to block the reverse DC current flowing from the voltage source converter 1 to the fault point.

[0113] Furthermore, the negative electrode N1 of the voltage source converter 1 is connected to one end of the parallel circuit of the energy consumption circuit 10 and the bypass switch 20, the other end of the parallel circuit of the energy consumption circuit 10 and the bypass switch 20 is connected to the anode A of the first valve 3, the positive electrode P1 of the voltage source converter 1 is connected to the first end C of the DC circuit breaker 2, and the second end D of the DC circuit breaker 2 is connected to the cathode K of the first valve 3, as shown in Figure 8, and the negative electrode N1 of the voltage source converter 1 is the high voltage end.

[0114] In some embodiments, the DC transmission valve assembly further includes at least one residual current isolating switch, which is first connected in series with the DC circuit breaker and then connected in parallel with the circuit formed by the series connection of the voltage source converter and the first valve. Specifically, as shown in FIG9 , the DC transmission valve assembly further includes a third residual current isolating switch 80 and / or a fourth residual current isolating switch 90 . The third residual current isolating switch 80 and / or the fourth residual current isolating switch 90 are first connected in series with the DC circuit breaker 2 and then connected in parallel with the circuit formed by the series connection of the voltage source converter 1 and the first valve 3 , the energy consumption circuit 10 , and the bypass switch 20 .

[0115] In some embodiments, the DC transmission valve group further includes a second bypass switch 52 , which is connected to the positive terminal P2 and the negative terminal N2 of the DC transmission valve group, as shown in FIG10 .

[0116] In some embodiments, the DC transmission valve assembly further includes a third isolation switch 53, a fourth isolation switch 54, and a second bypass switch 51, as shown in Figure 11. The third isolation switch 53 is connected to the positive terminal P2 and the positive input terminal P of the DC transmission valve assembly. The fourth isolation switch 54 is connected to the negative terminal N2 and the negative input terminal N of the DC transmission valve assembly. The second bypass switch 51 is connected to the positive input terminal P and the negative input terminal N of the DC transmission valve assembly.

[0117] An embodiment of the present application further provides a DC transmission valve group in which the first valve adopts a fully controlled device. Specifically, as shown in FIG12 , the DC transmission valve group includes a voltage source converter or a bridge uncontrolled rectifier circuit, a DC circuit breaker 2, a first valve 3, and an energy consumption circuit 10. The positive electrode P1 of the voltage source converter or the bridge uncontrolled rectifier circuit is the high voltage end.

[0118] In this embodiment, the voltage source converter includes at least three phases and six bridge arms and cannot adjust the DC voltage to zero or negative voltage. The voltage source converter includes, but is not limited to, at least one of a two-level converter, a three-level converter, a modular multilevel converter, a diode-clamped multilevel converter, a cascaded two-level converter, or a stacked two-level converter. The modular multilevel converter uses a half-bridge submodule. The DC circuit breaker 2 has at least a unidirectional DC current interruption capability. The DC circuit breaker 2 includes, but is not limited to, at least one of a hybrid DC circuit breaker, a solid-state DC circuit breaker, or a mechanical DC circuit breaker. The DC circuit breaker 2 is a first two-port DC circuit breaker or a multi-port DC circuit breaker. The first valve 3 includes a first fully-controlled valve, which includes at least one fully-controlled device connected in series, and the fully-controlled device includes an anti-parallel diode.

[0119] The bridge uncontrolled rectifier circuit includes at least three phases and six bridge arms, including a six-pulse bridge circuit or a twelve-pulse bridge circuit, which is composed of uncontrolled power semiconductors, such as diodes.

[0120] The voltage source converter or bridge uncontrolled rectifier circuit is connected in series with the main branch of the DC circuit breaker 2 and then connected in anti-parallel with the series circuit of the first valve 3 and the energy consumption circuit 10. As shown in Figure 12, this anti-parallel connection involves the positive electrode P1 of the voltage source converter or bridge uncontrolled rectifier circuit being connected to the cathode K of the first valve 3 through the DC circuit breaker 2, and the negative electrode N1 of the voltage source converter or bridge uncontrolled rectifier circuit being connected to one end of the energy consumption circuit 10. Specifically, the positive electrode P1 of the voltage source converter or bridge uncontrolled rectifier circuit is connected to the first end C of the DC circuit breaker 2, the second end D of the DC circuit breaker 2 is connected to the cathode K of the anti-parallel diode of the first valve 3, and the negative electrode N1 of the voltage source converter 1 is connected to one end of the energy consumption circuit 10.

[0121] In this embodiment, when the DC circuit breaker 2 is off, the first valve 3 transfers the current flowing through the voltage source converter or the bridge uncontrolled rectifier circuit by freewheeling, thereby reducing the stress of the DC circuit breaker 2. The energy dissipation circuit 10 is used to quickly attenuate the fault current during a fault.

[0122] When the voltage source converter or the bridge uncontrolled rectifier circuit cannot deliver energy normally, such as a three-phase short circuit fault occurs on the inverter side, the fully controlled device of the first valve 3 is controlled to be turned on, and the energy is dissipated in the energy consumption circuit 10. When the energy of the voltage source converter or the bridge uncontrolled rectifier circuit can be delivered normally, the fully controlled device of the first valve 3 is controlled to be turned off.

[0123] In some embodiments, the first valve comprises a first diode valve, which includes an anti-parallel circuit of at least one diode and a thyristor. When the voltage source converter or bridge uncontrolled rectifier circuit fails to deliver energy normally, such as when a three-phase short circuit occurs on the inverter side, the thyristor of the first valve 3 is controlled to conduct, dissipating energy in the energy consumption circuit 10.

[0124] In some embodiments, there is also a DC transmission valve group configured with a transfer switch group, as shown in FIG13 . The DC transmission valve group includes a voltage source converter 1, a DC circuit breaker 2, a first valve 3, an energy consumption circuit 10, a bypass switch 20, a first transfer switch 4, a second transfer switch 5, and a third transfer switch 6, and is suitable for a case where the positive electrode P1 of the voltage source converter 1 is the high voltage end.

[0125] Specifically, this embodiment is based on the embodiment of Figure 2, and adds three conversion switches: a first conversion switch 4, a second conversion switch 5 and a third conversion switch 6, which are used to convert the connection relationship of the DC circuit breaker 2, so that the voltage source converter 1 can operate in rectification or inversion or be put into online inversion operation.

[0126] The first transfer switch 4 connects the positive electrode P1 of the voltage source converter 1 and the first terminal C of the DC circuit breaker 2. The second transfer switch 5 connects the negative electrode N1 of the voltage source converter 1 and the first terminal C of the DC circuit breaker 2. The third transfer switch 6 connects the positive electrode P1 of the voltage source converter 1 and the second terminal D of the DC circuit breaker 2.

[0127] Furthermore, there may be an embodiment of the following connection method: the first transfer switch 4 connects the negative electrode N1 of the voltage source converter 1 and the second terminal D of the DC circuit breaker 2. The second transfer switch 5 connects the positive electrode P1 of the voltage source converter 1 and the second terminal D of the DC circuit breaker 2. The third transfer switch 6 connects the negative electrode N1 of the voltage source converter 1 and the first terminal C of the DC circuit breaker 2, as specifically shown in FIG14 , where the negative electrode N1 of the voltage source converter 1 is the high voltage terminal.

[0128] As shown in FIG13 and FIG14 , when the voltage source converter is in rectification operation, the bypass switch 20 is opened, the first transfer switch 4 is closed, and the second transfer switch 5 and the third transfer switch 6 are opened.

[0129] When the voltage source converter is in inversion operation, the bypass switch 20 is closed, the first transfer switch 4 is closed, and the second transfer switch 5 and the third transfer switch 6 are opened.

[0130] When the voltage source converter is put into online inverter operation, the bypass switch 20 is closed, the first transfer switch 4 is opened, and the second transfer switch 5 and the third transfer switch 6 are closed.

[0131] In some embodiments, there is another DC transmission valve group configured with a conversion switch group, as shown in Figure 15. The DC transmission valve group includes a voltage source converter 1, a DC circuit breaker 2, a first valve 3, an energy consumption circuit 10, a bypass switch 20, a fourth conversion switch 7, a fifth conversion switch 8, and a sixth conversion switch 9, and is suitable for the positive pole P1 of the voltage source converter 1 as the high voltage end.

[0132] This embodiment is also based on the embodiment of Figure 2, and adds three conversion switches: a fourth conversion switch 7, a fifth conversion switch 8 and a sixth conversion switch 9, which are used to convert the connection relationship of the DC circuit breaker 2, so that the voltage source converter 1 can operate in rectification or inversion or be put into online inversion operation.

[0133] In one embodiment, as shown in FIG15 , a fourth transfer switch 7 connects the second terminal D of the DC circuit breaker 2 and the positive terminal P2 of the DC transmission valve group. A fifth transfer switch 8 connects the positive terminal P2 of the DC transmission valve group and the first terminal C of the DC circuit breaker 2. A sixth transfer switch 9 connects the second terminal D of the DC circuit breaker 2 and the negative terminal N2 of the DC transmission valve group.

[0134] In another embodiment, a fourth transfer switch 7 connects the first terminal C of the DC circuit breaker 2 and the negative terminal N2 of the DC transmission valve group. A fifth transfer switch 8 connects the negative terminal N2 of the DC transmission valve group and the second terminal D of the DC circuit breaker 2. A sixth transfer switch 9 connects the first terminal C of the DC circuit breaker 2 and the positive terminal P2 of the DC transmission valve group, as shown in FIG16 , where the negative terminal N1 of the voltage source converter 1 is the high voltage terminal.

[0135] As shown in FIG15 and FIG16 , when the voltage source converter is in rectification operation, the bypass switch 20 is opened, the fourth transfer switch 7 is closed, and the fifth transfer switch 8 and the sixth transfer switch 9 are opened.

[0136] When the voltage source converter is in inverter operation, the bypass switch 20 is closed, the fourth transfer switch 7 is closed, and the fifth transfer switch 8 and the sixth transfer switch 9 are opened.

[0137] When the voltage source converter is put into inverter operation online, the bypass switch 20 is closed, the fourth transfer switch 7 is opened, and the fifth transfer switch 8 and the sixth transfer switch 9 are closed.

[0138] In some embodiments, there is also a DC transmission valve group configured with a conversion switch group, as shown in Figure 17. The DC transmission valve group includes a voltage source converter 1, a DC circuit breaker 2, a first valve 3, an energy consumption circuit 10, a bypass switch 20, a first conversion switch 4, a second conversion switch 5, a seventh conversion switch 15, an eighth conversion switch 16, a ninth conversion switch 17, and a tenth conversion switch 18, and is suitable for the positive pole P1 of the voltage source converter 1 as the high voltage end.

[0139] This embodiment adds six transfer switches on the basis of the embodiment of FIG2 : a first transfer switch 4 , a second transfer switch 5 , a seventh transfer switch 15 , an eighth transfer switch 16 , a ninth transfer switch 17 , and a tenth transfer switch 18 , which are used to convert the connection relationship between the voltage source converter 1 , the DC circuit breaker 2 , and the first valve 3 , so that the voltage source converter 1 can operate in rectification or inversion or be put into online inversion operation.

[0140] In one embodiment, a first conversion switch 4 connects the positive electrode P1 of the voltage source converter 1 and the first terminal C of the DC circuit breaker 2. A second conversion switch 5 connects the negative electrode N1 of the voltage source converter 1 and the first terminal C of the DC circuit breaker 2. A seventh conversion switch 15 connects the cathode K of the first valve 3 and the positive terminal P2 of the DC transmission valve group. An eighth conversion switch 16 connects one end of the parallel circuit of the energy consumption circuit 10 and the bypass switch 20 and the negative terminal N2 of the DC transmission valve group. A ninth conversion switch 17 connects the cathode K of the first valve 3 and the positive electrode P1 of the voltage source converter. A tenth conversion switch 18 connects the positive terminal P2 of the DC transmission valve group and one end of the parallel circuit of the energy consumption circuit 10 and the bypass switch 20.

[0141] In another embodiment, a first conversion switch 4 connects the negative electrode N1 of the voltage source converter 1 and the second terminal D of the DC circuit breaker 2. A second conversion switch 5 connects the positive electrode P1 of the voltage source converter 1 and the second terminal D of the DC circuit breaker 2. A seventh conversion switch 15 connects one end of the parallel circuit of the energy consumption circuit 10 and the bypass switch 20 and the negative terminal N2 of the DC transmission valve group. An eighth conversion switch 16 connects the cathode K of the first valve 3 and the positive terminal P2 of the DC transmission valve group. A ninth conversion switch 17 connects one end of the parallel circuit of the energy consumption circuit 10 and the bypass switch 20 and the negative electrode N1 of the voltage source converter. A tenth conversion switch 18 connects the negative terminal N2 of the DC transmission valve group and the cathode K of the first valve 3, as shown in FIG18 , where the negative electrode N1 of the voltage source converter 1 is the high voltage end.

[0142] As shown in Figures 17 and 18, when the voltage source converter is in rectification operation, the bypass switch 20 is opened, the first transfer switch 4, the seventh transfer switch 15 and the eighth transfer switch 16 are closed, and the second transfer switch 5, the ninth transfer switch 17 and the tenth transfer switch 18 are opened.

[0143] During the inverter operation of the voltage source converter, the bypass switch 20 is closed, the first transfer switch 4, the seventh transfer switch 15 and the eighth transfer switch 16 are closed, and the second transfer switch 5, the ninth transfer switch 17 and the tenth transfer switch 18 are opened.

[0144] Optionally, when the voltage source converter is in inversion operation, the bypass switch 20 is closed, the first transfer switch 4, the seventh transfer switch 15 and the eighth transfer switch 16 are separated, and the second transfer switch 5, the ninth transfer switch 17 and the tenth transfer switch 18 are closed.

[0145] When the voltage source converter is put into online inverter operation, the bypass switch 20 is closed, the first transfer switch 4, the seventh transfer switch 15 and the eighth transfer switch 16 are opened, and the second transfer switch 5, the ninth transfer switch 17 and the tenth transfer switch 18 are closed.

[0146] In some embodiments, a DC transmission valve group configured with a conversion switch group is further provided, which includes a voltage source converter 1, a DC circuit breaker 2, a first valve 3, a first conversion switch 4, a fourth conversion switch 7, a fifth conversion switch 8, a sixth conversion switch 9, a seventh conversion switch 15, an eighth conversion switch 16, a ninth conversion switch 17 and a tenth conversion switch 18, and is suitable for the positive pole P1 of the voltage source converter 1 as the high voltage end.

[0147] This embodiment adds five conversion switches on the basis of the embodiment of Figure 15: a first conversion switch 4, a fourth conversion switch 7, a fifth conversion switch 8, a sixth conversion switch 9, a seventh conversion switch 15, an eighth conversion switch 16, a ninth conversion switch 17, and a tenth conversion switch 18, which are used to convert the connection relationship between the voltage source converter 1, the DC circuit breaker 2 and the first valve 3, so that the voltage source converter 1 can operate in rectification or inversion or be put into online inversion operation function.

[0148] One embodiment of the connection method is as follows: the first transfer switch 4 connects the positive terminal P1 of the voltage source converter 1 and the first terminal C of the DC circuit breaker 2. The fourth transfer switch 7 connects the second terminal D of the DC circuit breaker 2 and the positive terminal P2 of the DC transmission valve group. The fifth transfer switch 8 connects the positive terminal P2 of the DC transmission valve group and the first terminal C of the DC circuit breaker 2. The sixth transfer switch 9 connects the second terminal D of the DC circuit breaker 2 and the negative terminal N2 of the DC transmission valve group. The seventh transfer switch 15 connects the cathode K of the first valve 3 and the positive terminal P2 of the DC transmission valve group. The eighth transfer switch 16 connects one end of the parallel circuit of the energy consumption circuit 10 and the bypass switch 20 and the negative terminal N2 of the DC transmission valve group. The ninth transfer switch 17 connects the cathode K of the first valve 3 and the positive terminal P1 of the voltage source converter. The tenth transfer switch 18 connects the positive terminal P2 of the DC transmission valve group and one end of the parallel circuit of the energy consumption circuit 10 and the bypass switch 20.

[0149] Another embodiment of the connection method is as follows: the first transfer switch 4 connects the negative terminal N1 of the voltage source converter 1 and the second terminal D of the DC circuit breaker 2. The fourth transfer switch 7 connects the first terminal C of the DC circuit breaker 2 and the negative terminal N2 of the DC transmission valve group. The fifth transfer switch 8 connects the negative terminal N2 of the DC transmission valve group and the second terminal D of the DC circuit breaker 2. The sixth transfer switch 9 connects the first terminal C of the DC circuit breaker 2 and the positive terminal P2 of the DC transmission valve group. The seventh transfer switch 15 connects one end of the parallel circuit of the energy consumption circuit 10 and the bypass switch 20 to the negative terminal N2 of the DC transmission valve group. The eighth transfer switch 16 connects the cathode K of the first valve 3 to the positive terminal P2 of the DC transmission valve group. The ninth transfer switch 17 connects one end of the parallel circuit of the energy consumption circuit 10 and the bypass switch 20 to the negative terminal N1 of the voltage source converter. The tenth transfer switch 18 connects the negative terminal N2 of the DC transmission valve group and the cathode K of the first valve 3. Specifically, as shown in FIG20 , the negative electrode N1 of the voltage source converter 1 is the high voltage end.

[0150] As shown in Figures 19 and 20, when the voltage source converter is in rectification operation, the bypass switch 20 is opened, the first transfer switch 4, the fourth transfer switch 7, the seventh transfer switch 15 and the eighth transfer switch 16 are closed, and the fifth transfer switch 8, the sixth transfer switch 9, the ninth transfer switch 17 and the tenth transfer switch 18 are opened.

[0151] When the voltage source converter is in inverter operation, the bypass switch 20 is closed, the first transfer switch 4, the fourth transfer switch 7, the seventh transfer switch 15 and the eighth transfer switch 16 are closed, and the fifth transfer switch 8, the sixth transfer switch 9, the ninth transfer switch 17 and the tenth transfer switch 18 are opened.

[0152] Optionally, when the voltage source converter is in inverter operation, the bypass switch 20 is closed, the first transfer switch 4, the fourth transfer switch 7, the seventh transfer switch 15 and the eighth transfer switch 16 are separated, and the fifth transfer switch 8, the sixth transfer switch 9, the ninth transfer switch 17 and the tenth transfer switch 18 are closed.

[0153] When the voltage source converter is put into inverter operation online, the bypass switch 20 is closed, the first transfer switch 4, the fourth transfer switch 7, the seventh transfer switch 15 and the eighth transfer switch 16 are separated, and the fifth transfer switch 8, the sixth transfer switch 9, the ninth transfer switch 17 and the tenth transfer switch 18 are closed.

[0154] It should be noted that if the connection relationship of the residual current isolating switch is the same as that of the above-mentioned transfer switch, the residual current isolating switch and the transfer switch share the same switch.

[0155] Based on the embodiment shown in FIG19 , the DC transmission valve group further includes a bypass switch 12 , which is connected to the positive terminal P2 and the negative terminal N2 of the DC transmission valve group, as shown in FIG21 .

[0156] Furthermore, based on the embodiment shown in FIG21 , the DC transmission valve assembly further includes a positive isolation switch 13, a negative isolation switch 14, and a bypass switch 11, as shown in FIG22 . The positive isolation switch 13 connects the positive terminal P2 of the DC transmission valve assembly and the first positive input terminal P. The negative isolation switch 14 connects the negative terminal N2 of the DC transmission valve assembly and the first negative input terminal N. The bypass switch 11 connects the first positive input terminal P and the first negative input terminal N of the DC transmission valve assembly.

[0157] In some embodiments, the DC circuit breaker of the DC transmission valve group is a multi-port DC circuit breaker. In this case, the DC transmission valve group includes a voltage source converter or a bridge uncontrolled rectifier circuit, a multi-port DC circuit breaker 19, a first valve 3, an energy consumption circuit 10, a bypass switch 20, a second valve 28, a second energy consumption circuit 30, and a second bypass switch 96, where the positive electrode P1 of the voltage source converter or the bridge uncontrolled rectifier circuit is the high voltage end.

[0158] This embodiment is a further improvement on the embodiment of FIG. 2 . The DC circuit breaker 19 is a multi-port DC circuit breaker capable of at least unidirectionally shutting off DC current. The first valve 3 comprises a first diode valve, a first thyristor valve, or a first fully controlled valve. The first diode valve comprises at least one diode connected in series, or an anti-parallel circuit comprising at least one diode and a thyristor, and the first thyristor valve comprises at least one thyristor connected in series. The second valve 28 comprises a second diode valve or a second thyristor valve. The second diode valve comprises at least one diode connected in series, or an anti-parallel circuit comprising at least one diode and a thyristor, and the second thyristor valve comprises at least one thyristor connected in series.

[0159] In this embodiment, a voltage source converter or bridge-type uncontrolled rectifier circuit is connected in series with the main branch of the multi-port DC circuit breaker 19, then connected in series with the parallel circuit of the first valve 3, the energy consumption circuit 10, and the bypass switch 20, before being connected in anti-parallel. The voltage source converter or bridge-type uncontrolled rectifier circuit is connected in series with the main branch of the multi-port DC circuit breaker 19, then connected in series with the parallel circuit of the second valve 28, the second energy consumption circuit 30, and the second bypass switch 96, before being connected in anti-parallel. This anti-parallel connection involves connecting the positive electrode P1 of the voltage source converter or bridge-type uncontrolled rectifier circuit to the cathode K of the first valve 3 or the second valve 28 via the multi-port DC circuit breaker 19, and the negative electrode N1 of the voltage source converter or bridge-type uncontrolled rectifier circuit to one end of the parallel circuit of the energy consumption circuit 10 and the bypass switch 20, or one end of the parallel circuit of the second energy consumption circuit 30 and the second bypass switch 96.

[0160] Specifically, as shown in Figure 23, the positive electrode P1 of the voltage source converter or bridge uncontrolled rectifier circuit is connected to the first terminal C of the multi-port DC circuit breaker 19, the second terminal D of the multi-port DC circuit breaker 19 is connected to the cathode K of the first valve 3, and the negative electrode N1 of the voltage source converter or bridge uncontrolled rectifier circuit is connected to one end of the parallel circuit of the energy consumption circuit 10 and the bypass switch 20. The third terminal E of the multi-port DC circuit breaker 19 is connected to the cathode K of the second valve 28, and the negative electrode N1 of the voltage source converter or bridge uncontrolled rectifier circuit is connected to one end of the parallel circuit of the second energy consumption circuit 30 and the second bypass switch 96.

[0161] Optionally, the negative electrode N1 of the voltage source converter or bridge uncontrolled rectifier circuit is connected to the second terminal D of the multi-port DC circuit breaker 19, the first terminal C of the multi-port DC circuit breaker 19 is connected to one end of the parallel circuit of the energy consumption circuit 10 and the bypass switch 20, and the positive electrode P1 of the voltage source converter or bridge uncontrolled rectifier circuit is connected to the cathode K of the first valve 3. The third terminal E of the multi-port DC circuit breaker 19 is connected to one end of the parallel circuit of the second energy consumption circuit 30 and the second bypass switch 96, and the positive electrode P1 of the voltage source converter or bridge uncontrolled rectifier circuit is connected to the cathode K of the second valve 28. Specifically, as shown in FIG. 24 , the negative electrode N1 of the voltage source converter or bridge uncontrolled rectifier circuit is preferably the high voltage terminal.

[0162] FIG25 is a schematic diagram of a DC transmission valve group configured with a second two-port DC circuit breaker according to an embodiment of the present application, which is applicable to a voltage source converter or a bridge uncontrolled rectifier circuit where the positive electrode P1 is the high voltage end.

[0163] Based on Figure 2, the DC transmission valve group further includes a second two-port DC circuit breaker 27, a second valve 28, a second energy consumption circuit 30, and a second bypass switch 96. The voltage source converter or bridge uncontrolled rectifier circuit is connected in series with the second two-port DC circuit breaker 27 and the first two-port DC circuit breaker 2, then connected in series with the parallel circuit of the second valve 28, the second energy consumption circuit 30, and the second bypass switch 96, and then connected in anti-parallel.

[0164] Specifically, as shown in FIG25 , the first positive input terminal P of the DC transmission valve group is connected to the first terminal C of the second two-port DC circuit breaker 27, the second terminal D of the second two-port DC circuit breaker 27 is connected to the cathode K of the second valve 28, and the first negative input terminal N of the DC transmission valve group is connected to one end of the parallel circuit of the second energy consumption circuit 30 and the bypass switch 96.

[0165] Optionally, based on FIG3 , the first negative input terminal N of the DC transmission valve group is connected to the second terminal D of the second two-port DC circuit breaker 27, the first terminal C of the second two-port DC circuit breaker 27 is connected to one end of the parallel circuit of the second energy consumption circuit 30 and the second bypass switch 96, and the first positive input terminal P of the DC transmission valve group is connected to the cathode K of the second valve 28. Specifically, as shown in FIG26 , the negative electrode N1 of the voltage source converter or the bridge uncontrolled rectifier circuit is the high voltage terminal.

[0166] FIG27 is a schematic diagram of a series circuit of a DC transmission valve group according to an embodiment of the present application, comprising two DC transmission valve groups shown in FIG2 connected in series. Specifically, the first negative input terminal N of the first DC transmission valve group 29 is connected to the first positive input terminal P of the second DC transmission valve group 37.

[0167] Figure 28 is a schematic diagram of another series circuit of a DC transmission valve group according to an embodiment of the present application, comprising two DC transmission valve groups shown in Figure 23 connected in series. Specifically, the first negative input terminal N of the third DC transmission valve group 38 is connected to the first positive input terminal P of the fourth DC transmission valve group 39, the second negative input terminal N3 of the third DC transmission valve group 38 is connected to the second positive input terminal P3 of the fourth DC transmission valve group 39, and the first negative input terminal N and the second negative input terminal N3 of the third DC transmission valve group 38 are separated.

[0168] Figure 29 is a schematic diagram of another series circuit of a DC transmission valve group according to an embodiment of the present application, comprising two DC transmission valve groups shown in Figure 25 connected in series. Specifically, the first negative input terminal N of the fifth DC transmission valve group 47 is connected to the first positive input terminal P of the sixth DC transmission valve group 48, and the second negative input terminal N3 of the fifth DC transmission valve group 47 is connected to the second positive input terminal P3 of the sixth DC transmission valve group 48. The first negative input terminal N and the second negative input terminal N3 of the fifth DC transmission valve group 47 are separate.

[0169] Figure 30 is a schematic diagram of another series circuit of a DC transmission valve group according to an embodiment of the present application, comprising the DC transmission valve group shown in Figure 23 and the DC transmission valve group shown in Figure 2 connected in series. Specifically, the first negative input terminal N of the seventh DC transmission valve group 40 is connected to the first positive input terminal P of the eighth DC transmission valve group 50, and the second negative input terminal N3 of the seventh DC transmission valve group 40 is connected to the first negative input terminal N of the eighth DC transmission valve group 50.

[0170] The DC circuit breakers in the embodiments of the present application include, but are not limited to, hybrid DC circuit breakers, solid-state DC circuit breakers, or mechanical DC circuit breakers. Figure 31 is a schematic diagram of a two-port DC circuit breaker in an embodiment of the present application. The DC circuit breaker is a hybrid DC circuit breaker, comprising a main branch 49, a transfer branch 57, and an energy consumption branch 58 connected in parallel.

[0171] The main branch 49 includes but is not limited to a series-connected fast disconnect switch and / or a first power switch. As shown in Figure 31, the main branch 49 comprises a series-connected fast disconnect switch 59 and a first power switch, which conduct steady-state current and reduce losses. The first power switch utilizes a first power device 67 in a forward-reverse series configuration, capable of bidirectionally shutting off DC current. The first power device 67 comprises but is not limited to a series-connected forward IGBT and a reverse IGBT, each with an anti-parallel diode connected to the forward and reverse IGBTs. The transfer branch 57 includes but is not limited to a series-connected second power switch and / or an LC resonant circuit and / or a coupled negative voltage circuit. As shown in Figure 31, the transfer branch 57 comprises a second power switch and a diode 69, which are used to shut off DC current under high-voltage operating conditions. It should be noted that diode 69 diverts current in either direction of the DC circuit breaker to the second power switch. When the second power switch is disconnected, the DC circuit breaker can shut off current in either direction. The second power switch in the transfer branch 57 utilizes a second power device 68 in a forward-reverse series configuration, capable of unidirectionally shutting off DC current. The second power device 68 comprises but is not limited to an IGBT and an anti-parallel diode. The energy dissipation branch 58 includes but is not limited to a lightning arrester 77, which is used to suppress overvoltage and absorb energy.

[0172] The first power switch includes at least one first power device 67 connected in series. The first power device 67 includes at least one of an IGCT, an IGBT, a GTO, and a MOSFET, but is not limited thereto.

[0173] The second power switch includes at least one second power device 68 connected in series. The second power device 68 includes at least one of an IGCT, an IGBT, a GTO, a MOSFET, and a thyristor, but is not limited thereto.

[0174] Optionally, the first power switch and the second power switch include at least one power device connected in series and an uncontrolled device connected in anti-parallel thereto.

[0175] FIG32 is a schematic diagram of another two-port DC circuit breaker according to an embodiment of the present application. The DC circuit breaker is a hybrid DC circuit breaker, which includes a main branch 49 , a transfer branch 57 , and an energy consumption branch 58 connected in parallel.

[0176] Main branch 49 includes, but is not limited to, a series-connected fast disconnect switch and / or a first power switch. As shown in FIG32 , main branch 49 comprises a series-connected fast disconnect switch 59 and a first power switch, configured to conduct steady-state current and reduce losses. The first power switch of main branch 49 utilizes a third power device 78 in a forward series configuration, capable of unidirectionally shutting off DC current. This third power device 78 includes, but is not limited to, an IGBT and an anti-parallel diode circuit. The transfer branch includes, but is not limited to, a series-connected second power switch and / or an LC resonant circuit and / or a coupled negative voltage circuit. As shown in FIG32 , transfer branch 57 includes a second power switch for shutting off DC current under high-voltage operating conditions. The second power switch utilizes a second power device 68 in a forward series configuration, capable of unidirectionally shutting off DC current. This second power device 68 includes, but is not limited to, an IGBT and an anti-parallel diode. The energy dissipation branch 58 includes, but is not limited to, a lightning arrester 77, configured to suppress overvoltage and absorb energy.

[0177] FIG33 is a schematic diagram of another two-port DC circuit breaker according to an embodiment of the present application. The DC circuit breaker is a solid-state DC circuit breaker, comprising a transfer branch 57 and an energy-consuming branch 58 connected in parallel. The transfer branch 57 includes but is not limited to a second power switch connected in series and / or an LC resonant circuit and / or a coupled negative voltage circuit. As shown in FIG33 , the transfer branch 57 includes but is not limited to a second power switch connected in series, which is used to shut off the DC current under high-voltage operating conditions. The second power switch of the transfer branch 57 adopts a second power device 68 with a forward series structure and has the ability to shut off the DC current in one direction. The second power device 68 includes but is not limited to an IGBT and an anti-parallel diode. The energy-consuming branch 58 includes but is not limited to a lightning arrester 77, which is used to suppress the overvoltage of the interruption and absorb energy.

[0178] Multi-port DC circuit breakers include multi-port hybrid DC circuit breakers or multi-port mechanical DC circuit breakers. Figure 34 is a schematic diagram of a multi-port DC circuit breaker according to an embodiment of the present application. The multi-port DC circuit breaker is a multi-port hybrid DC circuit breaker and includes a main branch 49, a second main branch 79, a third main branch 87, a first selector switch 88, a second selector switch 89, a third selector switch 91, a transfer branch 57, and an energy consumption branch 58. The main branch 49, the second main branch 79, and the third main branch 87 include, but are not limited to, series-connected fast disconnect switches and / or first power switches. As shown in Figure 31, the main branch 49, the second main branch 79, and the third main branch 87 each include a series-connected fast disconnect switch 59 and a first power switch for conducting steady-state current and reducing losses. The first power switches of the main branch 49, the second main branch 79, and the third main branch 87 each utilize a first power device 67 in a forward and reverse series configuration, capable of bidirectionally shutting off DC current. The first power switch includes, but is not limited to, a forward IGBT and a reverse IGBT connected in series, each with an anti-parallel diode connected to the forward IGBT and the reverse IGBT. The first selector switch 88, the second selector switch 89, and the third selector switch 91 include, but are not limited to, at least one of a mechanical switch, a mechanical knife switch, and a third power switch connected in series. The transfer branch 57 includes, but is not limited to, a second power switch connected in series and / or an LC resonant circuit and / or a coupled negative voltage circuit. As shown in FIG33 , the transfer branch 57 includes a second power switch and a diode 69, which are used to shut off DC current under high-voltage operating conditions. It should be noted that the diode 69 directs current in either direction of the DC circuit breaker to flow unidirectionally into the second power switch. Once the second power switch is disconnected, the current in either direction of the DC circuit breaker can be shut off. The second power switch of the transfer branch 57 utilizes a second power device 68 of a forward series switch structure, capable of unidirectionally shutting off DC current. The second power device 68 includes, but is not limited to, an anti-parallel circuit of an IGBT and a diode.

[0179] The energy dissipation branch 58 includes but is not limited to a lightning arrester 77, which is used to suppress overvoltage and absorb energy.

[0180] Figures 35 to 37 are schematic diagrams of various bypass switches or bypass switches according to embodiments of the present application. The bypass switch or bypass switch includes but is not limited to at least one of a mechanical switch, a mechanical knife switch, or at least one third power switch connected in series.

[0181] As shown in FIG35 , the bypass switch or bypass switch includes a first mechanical switch 92. As shown in FIG36 , the bypass switch or bypass switch includes a third power switch and the first mechanical switch 92 connected in series. As shown in FIG37 , the bypass switch or bypass switch includes the third power switch and the first mechanical switch 92 connected in series, and also includes a second mechanical switch 94 connected in parallel with the series circuit. The third power switch includes a fourth power device 93 connected in series, which includes, but is not limited to, a thyristor. The third power switch includes at least one fourth power device 93 connected in series, which includes, but is not limited to, an IGCT, an IGBT, a GTO, a MOSFET, or a thyristor.

[0182] Figure 38 is a schematic diagram of a voltage source converter according to an embodiment of the present application. The voltage source converter utilizes a modular multilevel converter, with each submodule utilizing a half-bridge structure. Figure 39 is a schematic diagram of an uncontrolled bridge rectifier circuit according to an embodiment of the present application. This uncontrolled bridge rectifier circuit utilizes a twelve-pulse bridge circuit, with each bridge arm consisting of a series connection of diodes.

[0183] Accordingly, an embodiment of the present application provides a control method for a DC transmission valve group, which is applied to the DC transmission valve group of the aforementioned embodiment. The control method includes:

[0184] If the voltage source converter is connected in series with the main branch of the DC circuit breaker and then connected in anti-parallel with the series circuit of the first valve and the energy consumption circuit, during normal operation, the DC circuit breaker is controlled to be turned on, the first valve is controlled to be turned off, and the voltage source converter is controlled to operate in rectification or inversion;

[0185] If the voltage source converter is connected in series with the first valve and the parallel circuit of the energy consumption circuit and the bypass switch and then connected in parallel with the DC circuit breaker, during normal operation, the DC circuit breaker is controlled to be turned off, the first valve is controlled to be turned on, the bypass switch is controlled to be closed, and the voltage source converter is controlled to operate in inversion.

[0186] In some embodiments, if the voltage source converter is connected in series with the main branch of the DC circuit breaker and then connected in anti-parallel with the series circuit of the first valve and the energy consumption circuit, the control method further includes:

[0187] When the voltage source converter is put into rectification operation online, the voltage source converter is controlled to charge, the voltage source converter is controlled to unlock, and the DC circuit breaker is controlled to conduct;

[0188] When the voltage source converter is in rectification operation and is offline, the bypass switch is controlled to be closed, the DC circuit breaker is controlled to be turned off, and the first valve is controlled to be turned on;

[0189] When the voltage source converter is in rectification operation and the fault is exited, the DC circuit breaker is controlled to be turned off and the first valve is controlled to be turned on; when the fault is exited, the voltage source converter is also controlled to be locked;

[0190] When the voltage source converter is in rectification or inversion operation and a DC fault is passing through, the DC circuit breaker is controlled to be turned off and the first valve is controlled to be turned on. After the fault is recovered or the de-ionization time has passed, the DC circuit breaker is controlled to be turned on. The DC fault includes a DC line fault.

[0191] In some embodiments, if the voltage source converter is connected in series with the parallel circuit of the first valve, the energy consumption circuit, and the bypass switch and then connected in parallel with the DC circuit breaker, the control method further includes:

[0192] When the voltage source converter is put into inverter operation online, the voltage source converter is controlled to charge, the voltage source converter is controlled to unlock, the DC circuit breaker is controlled to be turned off, and the first valve is controlled to be turned on;

[0193] When the voltage source converter is in inverter operation and is offline or fault-exited, the DC circuit breaker is controlled to be turned on, or if the DC transmission valve group further includes a bypass switch, the bypass switch is controlled to be turned on and / or the DC circuit breaker is controlled to be turned on;

[0194] When the voltage source converter is in inverter operation and a DC fault is being crossed, the first valve is controlled to be turned on after the fault is recovered or after a de-ionization time has elapsed; the DC fault includes a DC line fault.

[0195] In some embodiments, if the DC transmission valve group further includes a bypass switch,

[0196] When the voltage source converter is in rectification operation and is offline or faulty, after controlling the first valve to be turned on, the bypass switch is also controlled to be turned on;

[0197] When the voltage source converter is in inverter operation and exits online or exits due to a fault, the bypass switch is controlled to be turned on and the DC circuit breaker is controlled to be turned off; when exiting due to a fault, the voltage source converter is also controlled to be locked.

[0198] In some embodiments, if the DC transmission valve group further includes a disconnect switch, or the DC transmission system in which the DC transmission valve group is located further includes a pole-neutral bus switch, when the voltage source converter is in rectification or inversion operation and a DC fault is crossed, after the first valve is controlled to be turned on, the disconnect switch or the pole-neutral bus switch is disconnected, and after the fault is recovered or the de-ionization time has passed, the disconnect switch or the pole-neutral bus switch is reclosed.

[0199] In some embodiments, if the first fully-controlled valve of the DC transmission valve group uses a fully-controlled device, when the voltage source converter or the bridge uncontrolled rectifier circuit cannot normally transmit energy and generates an AC or DC overvoltage, the fully-controlled device of the first valve is controlled to be turned on to dissipate energy in the energy consumption circuit. When the voltage source converter or the bridge uncontrolled rectifier circuit can transmit energy normally, the fully-controlled device of the first valve is controlled to be turned off.

[0200] If the first diode valve of the DC transmission valve group adopts an anti-parallel circuit of at least one diode and a thyristor, when the voltage source converter or the bridge uncontrolled rectifier circuit cannot transmit energy normally and generates AC or DC overvoltage, the thyristor of the first valve is controlled to be turned on to dissipate the energy in the energy consumption circuit.

[0201] Figure 40 is a flow chart of a control method for a DC transmission valve assembly according to an embodiment of the present application. The DC transmission valve assembly, as shown in Figures 1 to 6, 13 to 20, and 21 to 22, comprises a voltage source converter connected in series with the main branch of the DC circuit breaker, which is then connected in anti-parallel to the series circuit of the first valve and the energy consumption circuit. The control method is as follows.

[0202] In S110, the DC circuit breaker 2 is controlled to be turned on, the first valve 3 is controlled to be turned off, and if the DC transmission valve group includes a bypass switch 20, the bypass switch 20 is controlled to be closed, and the voltage source converter 1 is controlled to operate in rectification; or the DC circuit breaker 2 is controlled to be turned on, the first valve 3 is controlled to be turned off, and if the DC transmission valve group includes a bypass switch 20, the bypass switch 20 is controlled to be opened, and the voltage source converter 1 is controlled to operate in inversion.

[0203] In S120 , when the voltage source converter 1 is in rectification or inversion operation and a DC fault is riding through, the DC circuit breaker 2 is controlled to be off and the first valve 3 is controlled to be on. After the fault is recovered or the de-ionization time has passed, the DC circuit breaker 2 is controlled to be on.

[0204] The above-mentioned DC fault includes a DC line fault.

[0205] In S130, when the voltage source converter 1 is in rectification operation and is offline or faulty, the DC circuit breaker 2 is controlled to be closed, the first valve 3 is controlled to be turned on, and if the DC transmission valve group includes a bypass switch 20, the bypass switch 20 is controlled to be closed; when the voltage source converter 1 is faulty, it also includes controlling the voltage source converter 1 to be locked.

[0206] If the DC transmission valve group further includes a first residual current isolating switch 60 and a second residual current isolating switch 70 , after the DC circuit breaker 2 is controlled to be turned off, the first residual current isolating switch 60 and the second residual current isolating switch 70 are controlled to be separated.

[0207] If the DC transmission valve group also includes a bypass switch 12, when the voltage source converter 1 is in rectifier operation and offline, the DC circuit breaker 2 is controlled to be closed, the first valve 3 is controlled to be conductive, and the bypass switch 12 is controlled to be closed. When the voltage source converter 1 is in rectifier operation and fault-exited, the bypass switch 12 is controlled to be closed, the DC circuit breaker 2 is controlled to be closed, and the voltage source converter 1 is controlled to be locked.

[0208] If the DC transmission valve group also includes a bypass switch 12, when the voltage source converter 1 is in inverter operation and exits online or exits due to a fault, the bypass switch 12 is controlled to close and the DC circuit breaker 2 is controlled to be turned off; when exiting due to a fault, the voltage source converter 1 is also controlled to be locked.

[0209] Optionally, the voltage source converter 1 is not locked when it is offline, but operates in reactive power compensation mode.

[0210] In S140, when the voltage source converter 1 is put into online rectification operation, if the DC transmission valve group includes a bypass switch 20, the bypass switch 20 is controlled to be closed, the voltage source converter 1 is controlled to be charged, the voltage source converter 1 is controlled to be unlocked, and the DC circuit breaker 2 is controlled to be turned on.

[0211] If the first valve 3 only includes a diode connected in series, the first valve 3 does not need to be controlled, and the above-mentioned step of controlling the first valve 3 to be turned on or off can be omitted.

[0212] Figure 41 is a flow chart of another control method for a DC transmission valve assembly according to an embodiment of the present application. The DC transmission valve assembly, as shown in Figures 7-11, comprises a voltage source converter 1 connected in series with a first valve 3, and a parallel circuit comprising an energy consumption circuit 10 and a bypass switch 20, which is then connected in parallel with a DC circuit breaker 2. The control method is as follows.

[0213] In S210 , the DC circuit breaker 2 is controlled to be turned off, the first valve 3 is controlled to be turned on, the bypass switch 20 is controlled to be closed, and the voltage source converter 1 is controlled to be operated in an inverter mode.

[0214] If the DC transmission valve group further includes a third residual current isolating switch 80 and a fourth residual current isolating switch 90 , after the DC circuit breaker 2 is controlled to be turned off, the third residual current isolating switch 80 and the fourth residual current isolating switch 90 are controlled to be opened.

[0215] In S220 , when the voltage source converter 1 is in inverter operation and a DC fault ride-through occurs, the first valve 3 is controlled to be turned on after the fault is recovered or after a de-isolation time has elapsed.

[0216] In S230, when the voltage source converter 1 is in inverter operation and is online-exited or fault-exited, the DC circuit breaker 2 is controlled to be turned on; when fault-exited, the voltage source converter 1 is also controlled to be locked.

[0217] Alternatively, if the DC transmission valve group further includes a bypass switch 12, when the voltage source converter 1 is in inverter operation and is online-exited or fault-exited, the DC circuit breaker 2 is controlled to be turned on and / or the bypass switch 12 is controlled to be turned on; when fault-exited, the voltage source converter 1 is also controlled to be locked.

[0218] Optionally, the voltage source converter 1 is not locked when it is offline, but operates in reactive power compensation mode.

[0219] If the DC transmission valve group further includes a third residual current isolating switch 80 and a fourth residual current isolating switch 90 , before controlling the DC circuit breaker 2 to be turned on, the third residual current isolating switch 80 and the fourth residual current isolating switch 90 are controlled to be closed.

[0220] In S240 , when the voltage source converter 1 is put into inverter operation online, the voltage source converter 1 is controlled to charge, the voltage source converter 1 is controlled to unlock, the DC circuit breaker 2 is controlled to be turned off, and the first valve 3 is controlled to be turned on.

[0221] If the DC transmission valve group further includes a third residual current isolating switch 80 and a fourth residual current isolating switch 90 , after the DC circuit breaker 2 is controlled to be turned off, the third residual current isolating switch 80 and the fourth residual current isolating switch 90 are controlled to be opened.

[0222] If the DC transmission valve group further includes a bypass switch 12 , the bypass switch 12 is controlled to be opened before the DC circuit breaker 2 is controlled to be turned off.

[0223] The DC transmission valve groups shown in Figures 13 to 20, with the addition of a transfer switch group, have the function of online inverter operation. For example, in the DC transmission valve groups shown in Figures 13 and 14, when the voltage source converter 1 is online and in inverter operation, the bypass switch 20 is closed, the second and third transfer switches 5 and 6 are closed, the first transfer switch 4 is opened, the DC circuit breaker 2 is turned on, the current is transferred to the DC circuit breaker 2, the voltage source converter 1 is charged, the voltage source converter 1 is unlocked, the DC circuit breaker 2 is turned off, and the first valve 3 is turned on, transferring the current to the voltage source converter 1.

[0224] As shown in the DC transmission valve group of Figures 15 and 16, when the voltage source converter 1 is put into inverter operation online, the bypass switch 20 is controlled to be closed, the fifth conversion switch 8 and the sixth conversion switch 9 are controlled to be closed, the fourth conversion switch 7 is controlled to be open, the DC circuit breaker 2 is controlled to be turned on, and the current is transferred to the DC circuit breaker 2. The voltage source converter 1 is controlled to charge. After charging, the voltage source converter 1 is controlled to be unlocked, the DC circuit breaker 2 is controlled to be turned off, the first valve 3 is controlled to be turned on, and the current is transferred to the voltage source converter 1.

[0225] As shown in the DC transmission valve group of Figures 17 and 18, when the voltage source converter 1 is put into inverter operation online, the bypass switch 20 is controlled to be closed, the second transfer switch 5, the ninth transfer switch 17 and the tenth transfer switch 18 are controlled to be closed, the first transfer switch 4, the seventh transfer switch 15 and the eighth transfer switch 16 are controlled to be open, the DC circuit breaker 2 is controlled to be turned on, and the current is transferred to the DC circuit breaker 2. The voltage source converter 1 is controlled to charge. After charging, the voltage source converter 1 is controlled to be unlocked, the DC circuit breaker 2 is controlled to be turned off, the first valve 3 is controlled to be turned on, and the current is transferred to the voltage source converter 1.

[0226] As shown in the DC transmission valve group of Figures 19 and 20, when the voltage source converter 1 is put into inverter operation online, the bypass switch 20 is controlled to be closed, the fifth transfer switch 8, the sixth transfer switch 9, the ninth transfer switch 17 and the tenth transfer switch 18 are controlled to be closed, the first transfer switch 4, the fourth transfer switch 7, the seventh transfer switch 15 and the eighth transfer switch 16 are controlled to be open, the DC circuit breaker 2 is controlled to be turned on, the current is transferred to the DC circuit breaker 2, the voltage source converter 1 is controlled to be charged, and after charging, the voltage source converter 1 is controlled to be unlocked, the DC circuit breaker 2 is controlled to be turned off, the first valve 3 is controlled to be turned on, and the current is transferred to the voltage source converter 1.

[0227] If the first valve 3 only includes a diode connected in series, the first valve 3 does not need to be controlled, and the above-mentioned step of controlling the first valve 3 to be turned on or off can be omitted.

[0228] The present application also provides a direct current (DC) transmission system. As shown in FIG42 , the DC transmission system is a UHV flexible DC transmission system. The main circuit of the UHV flexible DC transmission system includes a rectifier station 100 , an inverter station 200 , a first DC line 150 , a second DC line 160 , a rectifier station grounding electrode line 114 , a rectifier station grounding electrode 115 , and an inverter station grounding electrode line 214 , a inverter station grounding electrode 215 .

[0229] The rectifier station 100 includes a first DC pole 110, a second DC pole 120, a first AC system 140 and a converter transformer incoming line switch (as shown by the numbers 131, 132, 133 and 134 in Figure 42), a first metal return line transfer switch 113, a first earth return line transfer switch 190, and a bipolar neutral zone isolation knife switch (as shown by the numbers 174, 175, 184 and 185 in Figure 42).

[0230] The first DC pole 110 includes a first high-end DC transmission valve group 111, a first low-end DC transmission valve group 112, a first high-end converter transformer 116, a first low-end converter transformer 117, a first smoothing reactor 105, a first pole neutral busbar switch 119, a first pole busbar disconnector 172, and a first DC line disconnector 173. The first high-end DC transmission valve group 111 and the first low-end DC transmission valve group 112 are connected in series.

[0231] The first high-end DC transmission valve group 111 and the first low-end DC transmission valve group 112 each include a voltage source converter, a DC circuit breaker, a first valve, an energy consumption circuit, a bypass switch 20 , a bypass knife switch, a bypass switch, a positive isolation knife switch, and a negative isolation knife switch.

[0232] The first high-side DC transmission valve group 111 includes a voltage source converter 1, a DC circuit breaker 2, a first valve 3, an energy consumption circuit 10, a bypass switch 20, a bypass switch 11, a bypass switch 12, a positive isolation switch 13, and a negative isolation switch 14. The bypass switch 12 is connected to the positive and negative terminals of the first high-side DC transmission valve group 111. The positive isolation switch 13 is connected to the positive terminal and the first positive input terminal of the first high-side DC transmission valve group 111. The negative isolation switch 14 is connected to the negative terminal and the first negative input terminal of the first high-side DC transmission valve group 111. The bypass switch 11 is connected to the first positive input terminal and the first negative input terminal of the first high-side DC transmission valve group 111.

[0233] The first low-end DC transmission valve group 112 includes a first low-end voltage source converter 102, a first low-end DC circuit breaker 25, a first low-end valve 26, a first low-end energy consumption circuit 191, a first low-end bypass switch 192, a first low-end bypass switch 21, a first low-end bypass switch 22, a first low-end positive isolation switch 23, and a first low-end negative isolation switch 24. The first low-end bypass switch 22 is connected to the positive and negative terminals of the first low-end DC transmission valve group 112, the first low-end positive isolation switch 23 is connected to the positive terminal and the first positive input terminal of the first low-end DC transmission valve group 112, the first low-end negative isolation switch 24 is connected to the negative terminal and the first negative input terminal of the first low-end DC transmission valve group 112, and the first low-end bypass switch 21 is connected to the first positive input terminal and the first negative input terminal of the first low-end DC transmission valve group 112.

[0234] The voltage source converters, DC circuit breakers and first valves of the first high-end DC transmission valve group 111 and the first low-end DC transmission valve group 112 are connected in the structure shown in FIG2 .

[0235] The voltage source converter includes but is not limited to at least one of a two-level converter, a three-level converter, a modular multilevel converter, a diode-clamped multilevel converter, a cascaded two-level converter or a stacked two-level converter. The above-mentioned modular multilevel converter includes but is not limited to a modular multilevel converter MMC with a half-bridge submodule structure.

[0236] The second DC pole 120 includes a second low-end DC transmission valve group 121, a second high-end DC transmission valve group 122, a second low-end converter transformer 126, a second high-end converter transformer 127, a second smoothing reactor 106, a second pole neutral busbar switch 129, a second pole busbar disconnector 182, and a second DC line disconnector 183. The second low-end DC transmission valve group 121 and the second high-end DC transmission valve group 122 are connected in series.

[0237] The second high-end DC transmission valve group 122 and the second low-end DC transmission valve group 121 each include a voltage source converter, a DC circuit breaker, a first valve, an energy consumption circuit, a bypass switch, a bypass knife switch, a bypass switch, a positive isolation knife switch and a negative isolation knife switch.

[0238] The second high-end DC transmission valve group 122 includes a second high-end voltage source converter 104, a second high-end DC circuit breaker 45, a second high-end valve 46, a second high-end energy consumption circuit 195, a second high-end bypass switch 196, a second high-end bypass switch 41, a second high-end bypass switch 42, a second high-end positive isolation switch 43, and a second high-end negative isolation switch 44. The second high-end bypass switch 42 is connected to the positive and negative terminals of the second high-end DC transmission valve group 122, the second high-end positive isolation switch 43 is connected to the positive terminal and the first positive input terminal of the second high-end DC transmission valve group 122, the second high-end negative isolation switch 44 is connected to the negative terminal and the first negative input terminal of the second high-end DC transmission valve group 122, and the second high-end bypass switch 41 is connected to the first positive input terminal and the first negative input terminal of the second high-end DC transmission valve group 122.

[0239] The second low-end DC transmission valve group 121 includes a second low-end voltage source converter 103, a second low-end DC circuit breaker 35, a second low-end valve 36, a second low-end energy consumption circuit 193, a second low-end bypass switch 194, a second low-end bypass switch 31, a second low-end bypass switch 32, a second low-end positive isolation switch 33, and a second low-end negative isolation switch 34. The second low-end bypass switch 32 is connected to the positive and negative terminals of the second low-end DC transmission valve group 121, the second low-end positive isolation switch 33 is connected to the positive terminal and the first positive input terminal of the second low-end DC transmission valve group 121, the second low-end negative isolation switch 34 is connected to the negative terminal and the first negative input terminal of the second low-end DC transmission valve group 121, and the second low-end bypass switch 31 is connected to the first positive input terminal and the first negative input terminal of the second low-end DC transmission valve group 121.

[0240] The voltage source converters, DC circuit breakers and first valves of the second high-end DC transmission valve group 122 and the second low-end DC transmission valve group 121 are connected in the structure shown in FIG4 .

[0241] The inverter station 200 includes a third DC pole 210, a fourth DC pole 220 and a second AC system 240 and a converter transformer incoming line switch (indicated by numbers 231, 232, 233, and 234 in Figure 42), a second metal return line switching switch 213, a second earth return line switching switch 290, and a bipolar neutral zone isolation switch (indicated by numbers 274, 275, 284, and 285 in Figure 42).

[0242] The third DC pole 210 includes a third high-end DC transmission valve group 211, a third low-end DC transmission valve group 212, a third high-end converter transformer 216, a third low-end converter transformer 217, a third smoothing reactor 205, a third pole neutral bus switch 219, a third pole bus disconnector 272, and a fifth DC line disconnector 273. The third high-end DC transmission valve group 211 and the third low-end DC transmission valve group 212 are connected in series.

[0243] The third high-end DC transmission valve group 211 and the third low-end DC transmission valve group 212 each include a voltage source converter, a DC circuit breaker, a first valve, an energy consumption circuit, a bypass switch 20, a bypass knife switch, a bypass switch, a positive isolation knife switch, and a negative isolation knife switch.

[0244] The third high-end DC transmission valve group 211 includes a third high-end voltage source converter 201, a third high-end DC circuit breaker 55, a third high-end valve 56, a third high-end energy consumption circuit 297, a third high-end bypass switch 298, a second bypass switch 51, a second bypass switch 52, a third isolation switch 53, and a fourth isolation switch 54. The third high-end bypass switch 52 is connected to the positive and negative terminals of the third high-end DC transmission valve group 211. The third isolation switch 53 is connected to the positive terminal and the first positive input terminal of the third high-end DC transmission valve group 211. The fourth isolation switch 54 is connected to the negative terminal and the first negative input terminal of the third high-end DC transmission valve group 211. The second bypass switch 51 is connected to the first positive input terminal and the first negative input terminal of the third high-end DC transmission valve group 211.

[0245] The third low-end DC transmission valve group 212 includes a third low-end voltage source converter 202, a third low-end DC circuit breaker 65, a third low-end valve 66, a third low-end energy consumption circuit 291, a third low-end bypass switch 292, a third low-end bypass switch 61, a third low-end bypass switch 62, a third low-end positive isolation switch 63, and a third low-end negative isolation switch 64. The third low-end bypass switch 62 is connected to the positive and negative terminals of the third low-end DC transmission valve group 212, the third low-end positive isolation switch 63 is connected to the positive terminal and the first positive input terminal of the third low-end DC transmission valve group 212, the third low-end negative isolation switch 64 is connected to the negative terminal and the first negative input terminal of the third low-end DC transmission valve group 212, and the third low-end bypass switch 61 is connected to the first positive input terminal and the first negative input terminal of the third low-end DC transmission valve group 212.

[0246] The voltage source converters, DC circuit breakers and first valves of the third high-end DC transmission valve group 211 and the third low-end DC transmission valve group 212 are connected in the structure shown in FIG2 .

[0247] The fourth DC pole 220 includes a fourth low-end DC transmission valve group 221, a fourth high-end DC transmission valve group 222, a fourth low-end converter transformer 226, a fourth high-end converter transformer 227, a fourth smoothing reactor 206, a fourth pole neutral bus switch 229, a fourth pole bus disconnector 282, and a sixth DC line disconnector 283. The fourth low-end DC transmission valve group 221 and the fourth high-end DC transmission valve group 222 are connected in series.

[0248] The fourth high-end DC transmission valve group 222 and the fourth low-end DC transmission valve group 221 each include a voltage source converter, a DC circuit breaker, a first valve, an energy consumption circuit, a bypass switch 20, a bypass knife switch, a bypass switch, a positive isolation knife switch, and a negative isolation knife switch.

[0249] The fourth high-end DC transmission valve group 222 includes a fourth high-end voltage source converter 204, a fourth high-end DC circuit breaker 85, a fourth high-end valve 86, a fourth high-end energy consumption circuit 295, a fourth high-end bypass switch 296, a fourth high-end bypass switch 81, a fourth high-end bypass switch 82, a fourth high-end positive isolation switch 83, and a fourth high-end negative isolation switch 84. The fourth high-end bypass switch 82 is connected to the positive and negative terminals of the fourth high-end DC transmission valve group 222. The fourth high-end positive isolation switch 83 is connected to the positive terminal and the first positive input terminal of the fourth high-end DC transmission valve group 222. The fourth high-end negative isolation switch 84 is connected to the negative terminal and the first negative input terminal of the fourth high-end DC transmission valve group 222. The fourth high-end bypass switch 81 is connected to the first positive input terminal and the first negative input terminal of the fourth high-end DC transmission valve group 222.

[0250] The fourth low-end DC transmission valve group 221 includes a fourth low-end voltage source converter 203, a fourth low-end DC circuit breaker 75, a fourth low-end valve 76, a fourth low-end energy consumption circuit 293, a fourth low-end bypass switch 294, a fourth low-end bypass switch 71, a fourth low-end bypass switch 72, a fourth low-end positive isolation switch 73, and a fourth low-end negative isolation switch 74. The fourth low-end bypass switch 72 is connected to the positive and negative terminals of the fourth low-end DC transmission valve group 221. The fourth low-end positive isolation switch 73 is connected to the positive terminal and the first positive input terminal of the fourth low-end DC transmission valve group 221. The fourth low-end negative isolation switch 74 is connected to the negative terminal and the first negative input terminal of the fourth low-end DC transmission valve group 221. The fourth low-end bypass switch 71 is connected to the first positive input terminal and the first negative input terminal of the fourth low-end DC transmission valve group 221.

[0251] The voltage source converter, DC circuit breaker, and first valve of the fourth high-end DC transmission valve group 222 and the fourth low-end DC transmission valve group 221 are connected in the structure shown in Figure 4. The various switches mentioned above include at least one of a mechanical switch, a knife switch, a DC circuit breaker, and a thyristor valve.

[0252] It should be noted that the above-mentioned first valve 3, first low-end valve 26, second high-end valve 46, second low-end valve 36, third high-end valve 56, third low-end valve 66, fourth high-end valve 86 and fourth low-end valve 76 are all switching valves. The switching valve can be a first diode valve or a first thyristor valve or a first fully-controlled valve. The first diode valve includes at least one diode connected in series or an anti-parallel circuit of at least one diode and a thyristor. The first thyristor valve includes at least one thyristor connected in series. The first fully-controlled valve includes at least one fully-controlled device connected in series and the fully-controlled device includes an anti-parallel diode.

[0253] As shown in FIG42 , taking pole I of the UHV flexible DC transmission system as an example, in the initial state, the first high-end DC transmission valve group 111 and the first low-end DC transmission valve group 112 of the rectifier station 100 are in operation, and the third high-end DC transmission valve group 211 and the third low-end DC transmission valve group 212 of the inverter station 200 are in operation. The bypass switch 20 of the rectifier station 100 is in position, the bypass switch 11 is in position, the bypass switch 12 is in position, the positive isolating switch 13 is closed, the negative isolating switch 14 is closed, the first low-end bypass switch 192 is in position, the first low-end bypass switch 21 is in position, the first low-end bypass switch 22 is in position, the first low-end positive isolating switch 23 is closed, and the first low-end negative isolating switch 24 is closed; the third high-end bypass switch 298 of the inverter station 200 is in position, the second bypass switch 51 is in position, the second bypass switch 52 is in position, the third isolating switch 53 is closed, the fourth isolating switch 54 is closed, the third low-end bypass switch 292 is in position, the third low-end bypass switch 61 is in position, the third low-end bypass switch 62 is in position, the third low-end positive isolating switch 63 is closed, and the third low-end negative isolating switch 64 is closed.

[0254] The rectifier station 100 controls the DC breaker 2 of the first high-end DC transmission valve group 111 to be turned on and the first valve 3 to be turned off. It also controls the first low-end DC breaker 25 of the first low-end DC transmission valve group 112 to be turned on and the first low-end valve 26 to be turned off, causing the voltage source converter 1 and the first low-end voltage source converter 102 to operate in rectification mode. The inverter station 200 controls the third high-end DC breaker 55 of the third high-end DC transmission valve group 211 to be turned on and the third high-end valve 56 to be turned off. It also controls the third low-end DC breaker 65 of the third low-end DC transmission valve group 212 to be turned on and the third low-end valve 66 to be turned off, causing the third high-end voltage source converter 201 and the third low-end voltage source converter 202 to operate in inversion mode.

[0255] When a DC fault occurs in the voltage source converters of the first high-end DC transmission valve group 111 and the first low-end DC transmission valve group 112 of the rectifier station 100, the DC circuit breaker 2 of the first high-end DC transmission valve group 111 and the first low-end DC circuit breaker 25 of the first low-end DC transmission valve group 112 are controlled to be off, and the first valve 3 of the first high-end DC transmission valve group 111 and the first low-end valve 26 of the first low-end DC transmission valve group 112 are controlled to be on. The energy consumption circuit 10 and the first low-end energy consumption circuit 191 can suppress fault current oscillation. After the fault is restored or the de-isolation time has elapsed, the DC circuit breaker 2 of the first high-end DC transmission valve group 111 and the first low-end DC circuit breaker 25 of the first low-end DC transmission valve group 112 are controlled to be on. When a DC fault occurs in the voltage source converters of the third high-end DC transmission valve group 211 and the third low-end DC transmission valve group 212 of the inverter station 200, the third high-end DC circuit breaker 55 of the third high-end DC transmission valve group 211 and the third low-end DC circuit breaker 65 of the third low-end DC transmission valve group 212 are controlled to be turned off, and the third high-end valve 56 of the third high-end DC transmission valve group 211 and the third low-end valve 66 of the third low-end DC transmission valve group 212 are controlled to be turned on. After the fault is restored or the de-isolation time has elapsed, the third high-end DC circuit breaker 55 of the third high-end DC transmission valve group 211 and the third low-end DC circuit breaker 65 of the third low-end DC transmission valve group 212 are controlled to be turned on.

[0256] When the voltage source converter 1 of the rectifier station 100 is offline, the bypass switch 20 in the rectifier station 100 is controlled to close, the DC circuit breaker 2 in the rectifier station 100 is controlled to close, the first valve 3 in the rectifier station 100 is controlled to open, and the bypass switch 12 in the rectifier station 100 is controlled to close. When the voltage source converter 1 of the rectifier station 100 is offline due to a fault, the bypass switch controls the DC circuit breaker 2 in the rectifier station 100 to close, the first valve 3 in the rectifier station 100 to open, and the voltage source converter 1 in the rectifier station 100 to lock. When the third high-end voltage source converter 201 of the inverter station 200 is offline, the third high-end bypass switch 298 of the inverter station 200 is controlled to close, the second bypass switch 52 of the inverter station 200 is controlled to close, and the third high-end DC circuit breaker 55 of the inverter station 200 is controlled to close. When the third high-end voltage source converter 201 of the inverter station 200 fails and exits, the second bypass switch 52 within the inverter station 200 is controlled to close, the third high-end DC circuit breaker 55 within the inverter station 200 is controlled to close, the third high-end valve 56 within the inverter station 200 is controlled to open, and the third high-end voltage source converter 201 of the inverter station 200 is controlled to lock. The inverter station 200 of the aforementioned UHV flexible DC transmission system requires a transfer switch group to have online operation capability. When the voltage source converter is online, fails, or is online, coordination between the rectifier station 100 and the inverter station 200 is required to achieve this.

[0257] Figure 43 is a schematic diagram of another DC power transmission system according to an embodiment of the present application. Based on the embodiment of Figure 42 , the voltage source converter, DC circuit breaker, and first valve of the third high-end DC transmission valve group 211 and the third low-end DC transmission valve group 212 are connected in the same manner as shown in Figure 7 ; the voltage source converter, DC circuit breaker, and first valve of the fourth high-end DC transmission valve group 222 and the fourth low-end DC transmission valve group 221 are connected in the same manner as shown in Figure 8 .

[0258] As shown in FIG43 , taking pole I of the DC transmission system as an example, in the initial state, the first high-end DC transmission valve group 111 and the first low-end DC transmission valve group 112 of the rectifier station 100 are in operation, and the third high-end DC transmission valve group 211 and the third low-end DC transmission valve group 212 of the inverter station 200 are in operation. The bypass switch 20 of the rectifier station 100 is in position, the bypass switch 11 is in position, the bypass switch 12 is in position, the positive isolating switch 13 is closed, the negative isolating switch 14 is closed, the first low-end bypass switch 192 is in position, the first low-end bypass switch 21 is in position, the first low-end bypass switch 22 is in position, and the first low-end positive isolating switch 23 is closed; the third high-end bypass switch 298 of the inverter station 200 is closed, the second bypass switch 51 is in position, the second bypass switch 52 is in position, the third isolating switch 53 is closed, the fourth isolating switch 54 is closed, the third low-end bypass switch 292 is closed, the third low-end bypass switch 61 is in position, the third low-end bypass switch 62 is in position, the third low-end positive isolating switch 63 is closed, and the third low-end negative isolating switch 64 is closed.

[0259] The rectifier station 100 controls DC breaker 2 of the first high-end DC transmission valve group 111, closing the first valve 3. It also controls the first low-end DC breaker 25 of the first low-end DC transmission valve group 112 to be conductive, closing the first low-side valve 26, and enabling the voltage source converter 1 and the first low-end voltage source converter 102 to operate in rectification mode. The inverter station 200 controls the third high-end DC breaker 55 of the third high-end DC transmission valve group 211 to be closed, closing the third high-end valve 56, and enabling the third low-end DC breaker 65 of the third low-end DC transmission valve group 212 to be closed, closing the third low-side valve 66, and enabling the third high-end voltage source converter 201 and the third low-end voltage source converter 202 to operate in inversion mode.

[0260] When a DC fault occurs in the voltage source converter of rectifier station 100, DC circuit breakers 2 and 25 are controlled to be closed, and first valve 3 and first low-end valve 26 are controlled to be open. Energy consumption circuit 10 and first low-end energy consumption circuit 191 can suppress fault current oscillation. After the fault is restored or the de-isolation time has passed, DC circuit breaker 2 and first low-end DC circuit breaker 25 are controlled to be open. When a DC fault occurs in the voltage source converter of inverter station 200, third high-end valve 56 and third low-end valve 66 reversely block the fault current. After the fault is restored or the de-isolation time has passed, third high-end valve 56 and third low-end valve 66 are controlled to be open.

[0261] When the voltage source converter 1 of the rectifier station 100 exits online, the bypass switch 20 is controlled to close, the DC circuit breaker 2 is controlled to close, and the first valve 3 is controlled to open. Bypass switch 20 controls the bypass switch 12 to close. When the voltage source converter 1 of the rectifier station 100 exits due to a fault, the bypass switch 12 controls the first valve 3 to open, the DC circuit breaker 2 to close, the voltage source converter 1 to lock, and the bypass switch 12 to close. The third high-end voltage source converter 201 of the inverter station 200 exits online or due to a fault, controlling the third high-end DC circuit breaker 55 to open and / or the second bypass switch 52 to close.

[0262] In the initial state, the first low-end DC transmission valve group 112 of the rectifier station 100 is in operation, and the third low-end DC transmission valve group 212 of the inverter station 200 is in operation. When the voltage source converter 1 of the first high-side DC transmission valve group 111 of the rectifier station 100 is put online, the voltage source converter 1 of the first high-side DC transmission valve group 111 is controlled to charge, the bypass switch 20 of the first high-side DC transmission valve group 111 is controlled to close, and the first valve 3 of the first high-side DC transmission valve group 111 is controlled to be turned on. The bypass switch 20 controls the bypass switch 12 of the first high-side DC transmission valve group 111 to open, and the current is transferred from the bypass switch 12 of the first high-side DC transmission valve group 111 to the first valve 3 of the first high-side DC transmission valve group 111. The voltage source converter 1 of the first high-side DC transmission valve group 111 is controlled to be unlocked, and the DC circuit breaker 2 of the first high-side DC transmission valve group 111 is controlled to be turned on, and the current is transferred from the first valve 3 of the first high-side DC transmission valve group 111 to the voltage source converter 1 of the first high-side DC transmission valve group 111. When the voltage source converter of the third high-end DC transmission valve group 211 of the inverter station 200 is put into operation online, the third high-end bypass switch 298 of the third high-end DC transmission valve group 211 is controlled to be closed, the third high-end voltage source converter 201 of the third high-end DC transmission valve group 211 is controlled to be charged, the third high-end voltage source converter 201 of the third high-end DC transmission valve group 211 is controlled to be unlocked, the third high-end DC circuit breaker 55 of the third high-end DC transmission valve group 211 is controlled to be turned on, and the second bypass switch 298 of the third high-end DC transmission valve group 211 is controlled to be closed. The bypass switch 52 is opened, and the current is transferred from the second bypass switch 52 of the third high-end DC transmission valve group 211 to the third high-end DC circuit breaker 55 of the third high-end DC transmission valve group 211. The third high-end valve 56 of the third high-end DC transmission valve group 211 is controlled to be conductive, and the third high-end DC circuit breaker 55 of the third high-end DC transmission valve group 211 is controlled to be closed. The current is transferred from the third high-end DC circuit breaker 55 of the third high-end DC transmission valve group 211 to the third high-end voltage source converter 201 of the third high-end DC transmission valve group 211. When the voltage source converter is online, shut down due to a fault, or put online, coordination and cooperation between the rectifier station 100 and the inverter station 200 are required to achieve this.

[0263] It should be noted that the rectifier station 100 or inverter station 200 in Figures 42 and 43 can also use a valve group for a grid-commutated converter or a valve group for a voltage source converter based on a mix of half-bridge and full-bridge submodules, mixed with the aforementioned DC transmission valve group. The voltage source converter of the DC transmission valve group in the rectifier station 100 can be replaced with a bridge-type uncontrolled rectifier circuit.

[0264] Figure 44 is a schematic diagram of another DC transmission system according to an embodiment of the present application. The DC transmission system is a four-terminal DC power grid, comprising Station 1 310, Station 2 320, Station 3 330, Station 4 340, a third DC line 351, a fourth DC line 352, a fifth DC line 353, a sixth DC line 354, a first metallic return line 411, a second metallic return line 412, a third metallic return line 413, and a fourth metallic return line 414. Station 1 310 includes the DC transmission valve assembly shown in Figure 23, as well as the fifth-pole neutral bus switch 315 and the sixth-pole neutral bus switch 316. The DC transmission valve assembly also includes a first disconnect switch 317. Station 2 320 includes the DC transmission valve assembly shown in Figure 23, as well as the seventh-pole neutral bus switch 325 and the eighth-pole neutral bus switch 326. The DC transmission valve assembly also includes a second disconnect switch 327. Station 3 330 includes the DC transmission valve assembly shown in FIG23 , as well as the ninth-pole neutral bus switch 335 and the tenth-pole neutral bus switch 336. The DC transmission valve assembly also includes a third disconnect switch 337. Station 4 340 includes the DC transmission valve assembly shown in FIG23 , as well as the eleventh-pole neutral bus switch 345 and the twelfth-pole neutral bus switch 346. The DC transmission valve assembly also includes a fourth disconnect switch 347.

[0265] As shown in Figure 44, during normal operation, the multi-port DC circuit breaker 19, the second multi-port DC circuit breaker 322, the third multi-port DC circuit breaker 332, and the fourth multi-port DC circuit breaker 342 are controlled to be turned on, the first valve 3, the eleventh valve 323, the twelfth valve 333, and the thirteenth valve 343 are controlled to be turned off, the second valve 28, the twenty-first valve 324, the twenty-second valve 334, and the twenty-third valve 344 are controlled to be turned off, the voltage source converter 1, the second voltage source converter 321, the third voltage source converter 331, and the fourth voltage source converter 341 are controlled to operate, and the bypass switch 20 and the second bypass switch 96 of station one 310, the third bypass switch 329 and the fourth bypass switch 314 of station two 320, the fifth bypass switch 339 and the sixth bypass switch 319 of station three 330, and the seventh bypass switch 349 and the eighth bypass switch 362 of station four 340 are controlled to be opened.

[0266] It should be noted that the second valve 28 , the twenty-first valve 324 , the twenty-second valve 334 , the twenty-third valve 344 , and the twenty-fourth valve 308 are all on-off valves.

[0267] Taking the instantaneous fault of the third DC line 351 as an example, when the DC fault of the voltage source converter 1 and the second voltage source converter 321 passes through, the first terminal C and the second terminal D, the second terminal D and the third terminal E of the multi-port DC circuit breaker 19 are controlled to be closed, the first valve 3 is controlled to be turned on, the first terminal C and the third terminal E, the second terminal D and the third terminal E of the second multi-port DC circuit breaker 322 are controlled to be closed, the twenty-first valve 324 is controlled to be turned on, and optionally, the fifth-pole neutral bus switch 315 and the first disconnecting switch 3 are disconnected. 17. The eighth-pole neutral bus switch 326 and the second disconnect switch 327 rapidly attenuate the fault current. After the fault is restored or the de-ionization time has elapsed, the fifth-pole neutral bus switch 315, the first disconnect switch 317, the eighth-pole neutral bus switch 326, and the second disconnect switch 327 are reclosed to control the first terminal C and the second terminal D, as well as the second terminal D and the third terminal E, of the multi-port DC circuit breaker 19 to be conductive. The first terminal C and the third terminal E, as well as the second terminal D and the third terminal E of the second multi-port DC circuit breaker 322 to be conductive.

[0268] Taking a permanent fault in the third DC line 351 as an example, when the voltage source converter 1 and the second voltage source converter 321 are locked and isolated, the first end C and the second end D, the second end D and the third end E of the multi-port DC circuit breaker 19 are controlled to be closed, the first valve 3 is controlled to be turned on, the first end C and the third end E, the second end D and the third end E of the second multi-port DC circuit breaker 322 are controlled to be closed, the twenty-first valve 324 is controlled to be turned on, and optionally, the fifth-pole neutral bus switch 315, the first disconnect switch 317, the eighth-pole neutral bus switch 326, and the second disconnect switch 327 are disconnected to isolate the faulty third DC line 351.

[0269] When the voltage source converter 1 fails and is locked, the first terminal C and the second terminal D, the first terminal C and the third terminal E of the multi-port DC circuit breaker 19 are controlled to be turned off, and the voltage source converter 1 is controlled to be locked. Optionally, the first valve 3 is controlled to be turned on.

[0270] Figure 45 is a schematic diagram of another DC transmission system according to an embodiment of the present application. The DC transmission system is a four-terminal ultra-high voltage flexible DC transmission system, comprising station five 360, station six 370, station seven 380, station eight 390, a seventh DC line 355, an eighth DC line 356, and a ninth DC line 357. Station five 360 ​​includes the DC transmission valve group series circuit shown in Figure 27, equipped with a bypass switch 12, a first low-side bypass switch 22, and a first-pole neutral bus switch 119. Station six 370 includes the DC transmission valve group series circuit shown in Figure 27, equipped with a fifth bypass switch 374, a sixth bypass switch 378, and a fourteenth-pole neutral bus switch 379, as well as a first high-speed switch 301, a second high-speed switch 302, and a third high-speed switch 303. Station seven 380 includes the DC transmission valve group series circuit shown in Figure 27, equipped with a third bypass switch 384, a seventh bypass switch 388, and a fifteenth-pole neutral bus switch 389. It also includes a fourth high-speed switch 304, a fifth high-speed switch 305, and a sixth high-speed switch 306. Station eight 390 includes the DC transmission valve group series circuit shown in Figure 27, equipped with a fourth bypass switch 394, an eighth bypass switch 398, and a sixteenth-pole neutral bus switch 399.

[0271] As shown in FIG45 , during normal operation, the first high-speed switch 301, the second high-speed switch 302, the third high-speed switch 303, the fourth high-speed switch 304, the fifth high-speed switch 305, and the sixth high-speed switch 306 are closed, and the DC circuit breaker 2, the first low-end DC circuit breaker 25, the second DC circuit breaker 372, the third DC circuit breaker 376, the fourth DC circuit breaker 382, ​​the fifth DC circuit breaker 386, the sixth DC circuit breaker 392, and the seventh DC circuit breaker 396 are turned on, and the first valve 3, the first low-end valve 26, the fourteenth valve 373, the fifteenth valve 377, the sixteenth valve 383, the seventeenth valve 387, and the tenth valve 398 are turned on. The eighth valve 393 and the nineteenth valve 397 are closed, and the bypass switch 12 and the first low-end bypass switch 22 of the control station five 360, the fifth bypass switch 374 and the sixth bypass switch 378 of the control station six 370, the third bypass switch 384 and the seventh bypass switch 388 of the control station seven 380, and the fourth bypass switch 394 and the eighth bypass switch 398 of the control station eight 390 are separated, and the voltage source converter 1, the first low-end voltage source converter 102, the fifth voltage source converter 371, the sixth voltage source converter 375, the seventh voltage source converter 381, the eighth voltage source converter 385, the ninth voltage source converter 391, and the tenth voltage source converter 395 are controlled to operate.

[0272] It should be noted that, among them, the DC circuit breaker 2, the first low-end DC circuit breaker 25, the second DC circuit breaker 372, the third DC circuit breaker 376, the fourth DC circuit breaker 382, ​​the fifth DC circuit breaker 386, the sixth DC circuit breaker 392 and the seventh DC circuit breaker 396 have the same structure; the first valve 3, the first low-end valve 26, the eleventh valve 323, the twelfth valve 333, the thirteenth valve 343, the fourteenth valve 373, the fifteenth valve 377, the sixteenth valve 383, the seventeenth valve 387, the eighteenth valve 393 and the nineteenth valve 397 are all on-off valves.

[0273] Taking the instantaneous fault of the seventh DC line 355 as an example, when the DC fault of the voltage source converter is crossed, the DC circuit breaker 2, the first low-end DC circuit breaker 25, the second DC circuit breaker 372, the third DC circuit breaker 376, the fourth DC circuit breaker 382, ​​the fifth DC circuit breaker 386, the sixth DC circuit breaker 392, and the seventh DC circuit breaker 396 are controlled to be closed, and the first valve 3, the first low-end valve 26, the fourteenth valve 373, the fifteenth valve 377, the sixteenth valve 383, the seventeenth valve 387, the eighteenth valve 393, and the nineteenth valve 397 are controlled to be turned on, thereby realizing the series connection of the low-voltage DC circuit breaker to shut down the high-voltage DC line, while reducing the stress of the DC circuit breaker. Optionally, the first-pole neutral bus switch 119, the fourteenth-pole neutral bus switch 379, the fifteenth-pole neutral bus switch 389, and the sixteenth-pole neutral bus switch 399 are disconnected to quickly decay the fault current. After the fault is restored or the de-ionization time has passed, the first-pole neutral bus switch 119, the fourteenth-pole neutral bus switch 379, the fifteenth-pole neutral bus switch 389, and the sixteenth-pole neutral bus switch 399 are reclosed to control the DC circuit breaker 2, the first low-end DC circuit breaker 25, the second DC circuit breaker 372, the third DC circuit breaker 376, the fourth DC circuit breaker 382, ​​the fifth DC circuit breaker 386, the sixth DC circuit breaker 392, and the seventh DC circuit breaker 396 to be turned on.

[0274] When the voltage source converter 1 is locked due to a DC fault, if the pole is selected to be locked, the DC circuit breaker 2 and the first low-end DC circuit breaker 25 are controlled to be turned off, the voltage source converter 1 is controlled to be locked, the first high-speed switch 301 is controlled to be opened, and optionally, the first pole neutral bus switch 119 is disconnected.

[0275] Taking station five 360 ​​and station six 370 in rectification operation and station seven 380 and station eight 390 in inverter operation as an example, when the voltage source converter 1 of station five 360 ​​is offline, the bypass switch 20 of station five 360 ​​is controlled to be closed, the bypass switch 364 is controlled to be closed, the third bypass switch 384 and the fourth bypass switch 394 are controlled to be closed, the DC circuit breaker 2, the second DC circuit breaker 372, the fourth DC circuit breaker 382 and the sixth DC circuit breaker 392 are controlled to be turned off, the first valve 3 and the fourteenth valve 373 are controlled to be turned on, the bypass switch 12 and the fifth bypass switch 374 are controlled to be closed, and optionally, the voltage source converter 1, the fifth voltage source converter 371, the seventh voltage source converter 381 and the voltage source converter 391 are controlled to be locked. When the voltage source converter 1 fails and exits, the bypass switch 12 is controlled to be closed, the DC circuit breaker 2 is controlled to be turned off, the third bypass switch 384 and the fourth bypass switch 394 are controlled to be closed, the second DC circuit breaker 372, the fourth DC circuit breaker 382, ​​and the sixth DC circuit breaker 392 are controlled to be turned off, the fourteenth valve 373 is controlled to be turned on, the fifth bypass switch 374 is controlled to be closed, and the voltage source converter 1 is controlled to be locked. Optionally, the fifth voltage source converter 371, the seventh voltage source converter 381, and the voltage source converter 391 are controlled to be locked.

[0276] Station 7 380 and Station 8 390 of the above-mentioned four-terminal ultra-high voltage flexible direct current transmission system need to be equipped with a transfer switch group to have the online input function.

[0277] Figure 46 is a schematic diagram of another direct current transmission system according to an embodiment of the present application. The direct current transmission system is a four-terminal ultra-high voltage flexible direct current transmission system, including station five 360, station six 370, station seven 380, station eight 390, a seventh direct current line 355, an eighth direct current line 356 and a ninth direct current line 357. Station five 360 ​​includes a DC transmission valve group series circuit shown in FIG27 and equipped with a bypass switch 12, a first low-side bypass switch 22 and a first-pole neutral bus switch 119; station six 370 includes a DC transmission valve group series circuit shown in FIG30 and equipped with a fifth bypass switch 374, a sixth bypass switch 378, a fifth disconnect switch 311 and a fourteenth-pole neutral bus switch 379; station seven 380 includes a DC transmission valve group series circuit shown in FIG30 and equipped with a third bypass switch 384, a seventh bypass switch 388, a sixth disconnect switch 312 and a fifteenth-pole neutral bus switch 389; station eight 390 includes a DC transmission valve group series circuit shown in FIG27 and equipped with a fourth bypass switch 394, an eighth bypass switch 398 and a sixteenth-pole neutral bus switch 399.

[0278] As shown in FIG46 , during normal operation, the DC circuit breaker 2, the first low-end DC circuit breaker 25, the second DC circuit breaker 372, the third DC circuit breaker 376, the second two-port DC circuit breaker 27, the fourth DC circuit breaker 382, ​​the fifth DC circuit breaker 386, the third two-port DC circuit breaker 307, the sixth DC circuit breaker 392, and the seventh DC circuit breaker 396 are controlled to be turned on, and the first valve 3, the first low-end valve 26, the fourteenth valve 373, the fifteenth valve 377, the second valve 28, the sixteenth valve 383, the seventeenth valve 387, the twenty-fourth valve 308, the eighteenth valve 393, and the nineteenth valve 397 are controlled to be turned off. The bypass switch 20 and the first low-end bypass switch 192 of the control station five 360, the ninth bypass switch 364 and the tenth bypass switch 366 of the control station six 370, the eleventh bypass switch 368 and the twelfth bypass switch 402 of the control station seven 380, and the thirteenth bypass switch 404 and the fourteenth bypass switch 406 of the control station eight 390 are separated, and the control voltage source converter 1, the first low-end voltage source converter 102, the fifth voltage source converter 371, the sixth voltage source converter 375, the seventh voltage source converter 381, the eighth voltage source converter 385, the ninth voltage source converter 391, and the tenth voltage source converter 395 are operated.

[0279] Taking a transient fault on the seventh DC line 355 as an example, when the voltage source converter DC fault ride-through occurs, DC breaker 2 and the first low-end DC breaker 25 in station 5 360, and the second two-port DC breaker 27 in station 6 370 are controlled to be off, and the first valve 3, the first low-end valve 26, and the second valve 28 are controlled to be on. Optionally, the first-pole neutral busbar switch 119 and the fifth disconnecting switch 311 are disconnected to rapidly attenuate the fault current. After the de-ionization time, the first-pole neutral busbar switch 119 is reclosed, and DC breaker 2 and the first low-end DC breaker 25 are controlled to be on. If the fault disappears, the fifth disconnecting switch 311 is reclosed, and the second two-port DC breaker 27 is controlled to be on. During the DC fault ride-through process, stations 6 370, 7 380, and 8 390 are isolated from the fault point via the second two-port DC breaker 27, without affecting their power transmission.

[0280] When voltage source converter 1 is locked due to a DC fault, if the selected pole is locked, DC breaker 2, first low-end DC breaker 25, and second two-port DC breaker 27 are controlled to be shut down, and voltage source converter 1 and first low-end voltage source converter 102 are controlled to be locked. Optionally, first-pole neutral bus switch 119 and fifth disconnect switch 311 are also opened. During the DC fault lockout process, stations 6 370, 7 380, and 8 390 are isolated from the fault point via the second two-port DC breaker 27, without affecting their power transmission.

[0281] Taking the rectification operation of station five 360 ​​and station six 370, and the inverter operation of station seven 380 and station eight 390 as an example, when the voltage source converter 1 is offline, the third bypass switch 384 and the fourth bypass switch 394 are controlled to be closed, the first valve 3 and the fourteenth valve 373 are controlled to be turned on, the DC circuit breaker 2, the second DC circuit breaker 372, the fourth DC circuit breaker 382, ​​and the sixth DC circuit breaker 392 are controlled to be turned off, and the bypass switch 12 and the fifth bypass switch 374 are controlled to be closed. Optionally, the voltage source converter 1, the fifth voltage source converter 371, the seventh voltage source converter 381, and the ninth voltage source converter 391 are controlled to be locked. When the voltage source converter 1 fails and exits, the bypass switch 12 is controlled to be turned on, the DC circuit breaker 2 is controlled to be turned off, the third bypass switch 384 and the fourth bypass switch 394 are controlled to be closed, the second DC circuit breaker 372, the fourth DC circuit breaker 382, ​​and the sixth DC circuit breaker 392 are controlled to be turned off, the fourteenth valve 373 is controlled to be turned on, the fifth bypass switch 374 is controlled to be closed, and the voltage source converter 1 is controlled to be locked. Optionally, the fifth voltage source converter 371, the seventh voltage source converter 381, and the ninth voltage source converter 391 are controlled to be locked.

[0282] Stations 7 380 and 8 390 of the four-terminal UHV flexible DC transmission system require a transfer switch group to enable online operation. The second two-port DC circuit breaker 27 and the third two-port DC circuit breaker 307 must meet the voltage level of the DC transmission valve group series circuit.

[0283] FIG47 is a structural diagram of a control device 400 of a DC transmission valve group provided in the present application. The control device includes a detection unit 410 and a control unit 420 .

[0284] The detection unit 410 is used to detect the operating parameters and faults of the DC transmission valve group, including the AC voltage, DC voltage, DC current, operating status of the voltage source converter, operating status of the DC circuit breaker, operating status of the first valve, and switch and knife switch positions of the DC transmission valve group.

[0285] Based on the operating parameters of the DC transmission valve group, the control unit 420 controls the DC circuit breaker to be turned on, the first valve to be turned off, and the voltage source converter to be rectified or inverted during normal operation if the voltage source converter is connected in series with the main branch of the DC circuit breaker and then connected in anti-parallel to the series circuit of the first valve and the energy consumption circuit; and controls the DC circuit breaker to be turned off, the first valve to be turned on, the bypass switch to be closed, and the voltage source converter to be inverted during normal operation if the voltage source converter is connected in series with the parallel circuit of the first valve, the energy consumption circuit, and the bypass switch and then connected in parallel to the DC circuit breaker.

Claims

1. A DC power transmission valve group, characterized in that: It includes a voltage source converter or a bridge type uncontrolled rectifier circuit, a DC circuit breaker, a first valve and an energy consumption circuit; Among them, the voltage source converter or the bridge uncontrolled rectifier circuit is connected in series with the main branch of the DC circuit breaker and then connected in anti-parallel with the series circuit of the first valve and the energy consumption circuit, or the voltage source converter is connected in series with the series circuit of the first valve and the energy consumption circuit and then connected in parallel with the DC circuit breaker.

2. The DC power transmission valve group according to claim 1, characterized in that: The voltage source converter or the bridge type uncontrolled rectifier circuit comprises at least three phases and six bridge arms respectively; The DC circuit breaker comprises a first two-port DC circuit breaker or a multi-port DC circuit breaker; The first valve comprises a first diode valve or a first thyristor valve or a first fully-controlled valve, the first diode valve comprises at least one diode connected in series or an anti-parallel circuit of at least one diode and a thyristor, the first thyristor valve comprises at least one thyristor connected in series, the first fully-controlled valve comprises at least one fully-controlled device connected in series and the fully-controlled device comprises an anti-parallel diode; The energy consumption circuit includes a lightning arrester or a resistor.

3. The DC power transmission valve group according to claim 1, characterized in that: The voltage source converter comprises: at least one of a two-level converter, a three-level converter, a modular multi-level converter, a diode clamped multi-level converter, a cascaded two-level converter or a stacked two-level converter.

4. The DC power transmission valve group according to claim 1, characterized in that: The bridge-type uncontrolled rectifier circuit includes a six-pulse bridge circuit or a twelve-pulse bridge circuit, and is composed of uncontrolled power semiconductors.

5. The DC power transmission valve group according to claim 1, characterized in that: The DC circuit breaker is at least one of a hybrid DC circuit breaker, a solid-state DC circuit breaker or a mechanical DC circuit breaker, wherein the DC circuit breaker comprises: A main branch, the main branch includes a fast disconnect switch and / or a first power switch connected in series, wherein the first two-port DC circuit breaker includes the main branch, the multi-port DC circuit breaker includes one or more main branches, and all the main branches have a common terminal; and / or A transfer branch, the transfer branch comprising a second power switch connected in series, and / or an LC resonant circuit, and / or a coupled negative voltage circuit; An energy consumption branch is connected in parallel with the transfer branch, and the energy consumption branch includes a lightning arrester.

6. The DC power transmission valve group according to claim 1, characterized in that: The DC transmission valve group also includes a conversion switch group, through which the voltage source converter is connected in series with the main branch of the DC circuit breaker and then connected in anti-parallel with the first valve, for rectification operation or inversion operation of the voltage source converter; or the voltage source converter is connected in series with the first valve and then connected in parallel with the transfer branch of the DC circuit breaker, for inversion operation or online inverter operation of the voltage source converter; or the voltage source converter is connected in parallel with the transfer branch of the DC circuit breaker, for online inverter operation of the voltage source converter.

7. The DC power transmission valve group according to claim 6, characterized in that: The transfer switch group includes: a first transfer switch, a second transfer switch and a third transfer switch; in, The first conversion switch connects the positive electrode of the voltage source converter and the first end of the DC circuit breaker, The second conversion switch connects the negative electrode of the voltage source converter and the first end of the DC circuit breaker, The third conversion switch connects the positive electrode of the voltage source converter and the second end of the DC circuit breaker; or, The first conversion switch connects the negative electrode of the voltage source converter and the second end of the DC circuit breaker, The second conversion switch connects the positive electrode of the voltage source converter and the second end of the DC circuit breaker, The third conversion switch connects the negative pole of the voltage source converter and the first end of the DC circuit breaker.

8. The DC power transmission valve group according to claim 6, characterized in that: The transfer switch group includes: a fourth transfer switch, a fifth transfer switch and a sixth transfer switch; in, The fourth conversion switch connects the positive terminal of the DC transmission valve group and the second terminal of the DC circuit breaker. The fifth conversion switch connects the positive terminal of the DC transmission valve group and the first terminal of the DC circuit breaker. The sixth conversion switch is connected to the negative terminal of the DC transmission valve group and the second terminal of the DC circuit breaker; or, The fourth conversion switch is connected to the negative terminal of the DC transmission valve group and the first terminal of the DC circuit breaker. The fifth conversion switch connects the negative terminal of the DC transmission valve group and the second terminal of the DC circuit breaker. The sixth conversion switch connects the positive terminal of the DC transmission valve group and the first terminal of the DC circuit breaker.

9. The DC power transmission valve group according to claim 6, characterized in that: The transfer switch group includes: a first transfer switch, a seventh transfer switch, an eighth transfer switch, a ninth transfer switch and a tenth transfer switch; in, The first conversion switch connects the positive electrode of the voltage source converter and the first end of the DC circuit breaker, The seventh conversion switch connects the positive terminal of the DC transmission valve group and the cathode of the first valve. The eighth conversion switch connects the negative terminal of the DC transmission valve group and the anode of the first valve. The ninth conversion switch connects the positive electrode of the voltage source converter and the cathode of the first valve, The tenth conversion switch connects the positive terminal of the DC transmission valve group and the anode of the first valve; or, The first conversion switch connects the negative electrode of the voltage source converter and the second end of the DC circuit breaker, The seventh conversion switch connects the negative terminal of the DC transmission valve group and the anode of the first valve. The eighth conversion switch connects the positive terminal of the DC transmission valve group and the cathode of the first valve. The ninth conversion switch connects the negative electrode of the voltage source converter and the anode of the first valve, The tenth conversion switch connects the negative terminal of the DC transmission valve group and the cathode of the first valve.

10. The DC power transmission valve group according to claim 6, characterized in that: The transfer switch group includes: a first transfer switch, a second transfer switch, a seventh transfer switch, an eighth transfer switch, a ninth transfer switch, and a tenth transfer switch; in, The first conversion switch connects the positive electrode of the voltage source converter and the first end of the DC circuit breaker, The second conversion switch connects the negative electrode of the voltage source converter and the first end of the DC circuit breaker, The seventh conversion switch connects the positive terminal of the DC transmission valve group and the cathode of the first valve. The eighth conversion switch connects the negative terminal of the DC transmission valve group and the anode of the first valve. The ninth conversion switch connects the positive electrode of the voltage source converter and the cathode of the first valve, The tenth conversion switch connects the positive end of the DC transmission valve group and the anode of the first valve; or, The first conversion switch connects the negative electrode of the voltage source converter and the second end of the DC circuit breaker, The second conversion switch connects the positive electrode of the voltage source converter and the second end of the DC circuit breaker, The seventh conversion switch connects the negative terminal of the DC transmission valve group and the anode of the first valve. The eighth conversion switch connects the positive terminal of the DC transmission valve group and the cathode of the first valve. The ninth conversion switch connects the negative electrode of the voltage source converter and the anode of the first valve, The tenth conversion switch connects the negative terminal of the DC transmission valve group and the cathode of the first valve.

11. The DC power transmission valve group according to claim 1, characterized in that: The voltage source converter is connected in series with the first valve, comprising: The positive pole of the voltage source converter is connected to the cathode of the anti-parallel diode of the diode, thyristor or fully-controlled device of the first valve; or the negative pole of the voltage source converter is connected to the anode of the anti-parallel diode of the diode, thyristor or fully-controlled device of the first valve.

12. The DC power transmission valve assembly according to claim 1, characterized in that: Also includes: At least one residual current isolating switch. When the voltage source converter or the bridge uncontrolled rectifier circuit is connected in series with the DC circuit breaker and then connected in anti-parallel with the first valve, the residual current isolating switch is connected in series between the voltage source converter and the DC circuit breaker, and / or in series between the DC circuit breaker and the first valve. When the voltage source converter is connected in series with the first valve and then connected in parallel with the DC circuit breaker, the residual current isolating switch is first connected in series with the DC circuit breaker and then connected in parallel with the circuit after the voltage source converter and the first valve are connected in series.

13. The DC power transmission valve assembly according to claim 1, characterized in that: Also includes: A bypass switch, the bypass switch connecting the positive terminal and the negative terminal of the DC transmission valve group; Said beside The on switch includes at least one of a mechanical switch, a mechanical knife switch, and a third power switch connected in series.

14. The DC power transmission valve assembly according to claim 1, characterized in that: Also includes: A positive isolation switch, wherein the positive isolation switch is connected to the positive end of the DC transmission valve group and the first positive input end; A negative isolation switch, wherein the negative isolation switch is connected to the negative end of the DC transmission valve group and the first negative input end; A bypass switch is connected to the first positive input terminal and the first negative input terminal of the DC transmission valve group.

15. The DC power transmission valve assembly according to claim 1, characterized in that: The DC circuit breaker is a multi-port DC circuit breaker, and the DC power transmission valve group further includes: a second valve, wherein the second valve comprises a second diode valve or a second thyristor valve, wherein the second diode valve comprises at least one diode connected in series, wherein the second thyristor valve comprises at least one thyristor connected in series, wherein the cathode of the second valve is the second positive input terminal of the DC transmission valve group, and the anode of the second valve is the second negative input terminal of the DC transmission valve group; One of the DC transmission valve groups constitutes a DC pole, and the voltage source converter is connected in series with the main branch of the multi-port DC circuit breaker and then connected in anti-parallel with the second valve.

16. The DC power transmission valve assembly according to claim 1, characterized in that: The DC circuit breaker is a first two-port DC circuit breaker, and the DC power transmission valve group further includes: a second two-port DC circuit breaker; a second valve, wherein the second valve comprises a second diode valve or a second thyristor valve, wherein the second diode valve comprises at least one diode connected in series, wherein the second thyristor valve comprises at least one thyristor connected in series, wherein the cathode of the second valve is the second positive input terminal of the DC transmission valve group, and the anode of the second valve is the second negative input terminal of the DC transmission valve group; One of the DC transmission valve groups constitutes a DC pole, and the voltage source converter is connected in series with the second two-port DC circuit breaker and / or the first two-port DC circuit breaker and then connected to the second Valves are connected in anti-parallel.

17. The DC power transmission valve assembly according to claim 6, characterized in that: It also includes a bypass switch, which is connected in parallel with the energy consumption circuit; the bypass switch includes a mechanical switch and / or a mechanical knife switch.

18. A DC power transmission valve group series circuit, characterized in that: The method comprises at least two DC transmission valve groups according to any one of claims 1 to 17; the DC transmission valve group series circuit comprises at least a first DC transmission valve group and a second DC transmission valve group, and a first negative input terminal of the first DC transmission valve group is connected to a first positive input terminal of the second DC transmission valve group.

19. The DC power transmission valve group series circuit according to claim 18, characterized in that: The first DC transmission valve group and the second DC transmission valve group both include a multi-port DC circuit breaker and a second valve, or the first DC transmission valve group and the second DC transmission valve group both include a second two-port DC circuit breaker and a second valve, wherein the second negative input terminal of the first DC transmission valve group is connected to the second positive input terminal of the second DC transmission valve group, and the first negative input terminal of the first DC transmission valve group is connected to the first positive input terminal of the second DC transmission valve group.

20. The DC power transmission valve group series circuit according to claim 18, characterized in that: The first DC transmission valve group includes a second two-port DC circuit breaker and a second valve, the first negative input terminal of the first DC transmission valve group is connected to the first positive input terminal of the second DC transmission valve group, the second negative input terminal of the first DC transmission valve group is connected to the first negative input terminal of the second DC transmission valve group or is connected through a disconnect switch, or the second positive input terminal of the first DC transmission valve group is connected to the first positive input terminal of the second DC transmission valve group or is connected through a disconnect switch.

21. A direct current transmission system, characterized in that: It comprises a DC transmission valve group as described in any one of claims 1 to 17 or a DC transmission valve group series circuit as described in any one of claims 18 to 20; a pole-neutral bus switch is connected in series between the DC transmission valve group or the series circuit and the ground; the pole-neutral bus switch comprises at least one of a mechanical switch, a mechanical knife switch, and a fourth power switch connected in series.

22. A method for controlling a DC power transmission valve group, characterized in that: Applicable to a DC transmission valve group according to any one of claims 1 to 17; the control method comprises: If the voltage source converter is connected in series with the main branch of the DC circuit breaker and then connected in anti-parallel with the series circuit of the first valve and the energy consumption circuit, during normal operation, the DC circuit breaker is controlled to be turned on, the first valve is controlled to be turned off, and the voltage source converter is controlled to be rectified or inverted; If the voltage source converter is connected in series with the first valve and the parallel circuit of the energy consumption circuit and the bypass switch and then connected in parallel with the DC circuit breaker, during normal operation, the DC circuit breaker is controlled to be turned off, the first valve is controlled to be turned on, the bypass switch is controlled to be closed, and the voltage source converter is controlled to be inverted.

23. The DC transmission valve group control method according to claim 22, characterized in that: If the voltage source converter is connected in series with the main branch of the DC circuit breaker and then connected in anti-parallel with the series circuit of the first valve and the energy consumption circuit, the control method further includes: When the voltage source converter is put into rectification operation online, controlling the voltage source converter to charge, controlling the voltage source converter to unlock, and controlling the DC circuit breaker to conduct; When the voltage source converter is in rectification operation and is offline, the bypass switch is controlled to be closed, the DC circuit breaker is controlled to be turned off, and the first valve is controlled to be turned on; When the voltage source converter is in rectification operation and the fault is exited, the DC circuit breaker is controlled to be turned off and the first valve is controlled to be turned on; when the fault is exited, the voltage source converter is also controlled to be locked; When the voltage source converter is in rectification or inversion operation and a DC fault is traversed, the DC circuit breaker is controlled to be turned off, and the first valve is controlled to be turned on; after the fault is recovered or after a de-ionization time, the DC circuit breaker is controlled to be turned on; the DC fault includes a DC line fault.

24. The DC transmission valve group control method according to claim 22, characterized in that: If the voltage source converter is connected in series with the first valve, the energy consumption circuit and the bypass switch in parallel and then connected in parallel with the DC circuit breaker, the control method further includes: When the voltage source converter is put into inversion operation online, the voltage source converter is controlled to charge, Controlling the voltage source converter to unlock, controlling the DC circuit breaker to turn off, and controlling the first valve to turn on; When the voltage source converter is in inverter operation and is offline or faulty, the DC circuit breaker is controlled to be turned on, or if the DC transmission valve group further includes a bypass switch, the bypass switch is controlled to be turned on and / or the DC circuit breaker is controlled to be turned on; When the voltage source converter is in inverter operation and a DC fault is crossed, the first valve is controlled to be turned on after the fault is recovered or after a de-ionizing time; the DC fault includes a DC line fault.

25. The DC transmission valve group control method according to claim 23, characterized in that: If the DC transmission valve group further includes a bypass switch, When the voltage source converter is in rectification operation and is off-line or off due to a fault, after controlling the first valve to be turned on, the bypass switch is also controlled to be turned on; When the voltage source converter is in inverter operation and exits online or fails, the bypass switch is controlled to be turned on and the DC circuit breaker is controlled to be turned off; when the fault exit occurs, the voltage source converter is also controlled to be locked.

26. The DC transmission valve group control method according to claim 23, characterized in that: If the DC transmission valve group also includes a disconnect switch, or the DC transmission system where the DC transmission valve group is located also includes a pole-neutral bus switch, when the voltage source converter is in rectification or inversion operation and a DC fault is crossed, after the first valve is controlled to be turned on, the disconnect switch or the pole-neutral bus switch is disconnected, and after the fault is restored or the de-ionization time has passed, the disconnect switch or the pole-neutral bus switch is reclosed.

27. The DC transmission valve group control method according to claim 22, characterized in that: If the first fully-controlled valve of the DC transmission valve group adopts a fully-controlled device, when the energy of the voltage source converter or the bridge-type uncontrolled rectifier circuit cannot be normally transmitted to generate AC or DC overvoltage, the fully-controlled device of the first valve is controlled to be turned on to dissipate the energy in the energy consumption circuit, and when the energy of the voltage source converter or the bridge-type uncontrolled rectifier circuit can be normally transmitted, the fully-controlled device of the first valve is controlled to be turned off; If the first diode valve of the DC transmission valve group adopts an anti-parallel circuit of at least one diode and a thyristor, when the energy of the voltage source converter or the bridge uncontrolled rectifier circuit cannot be delivered normally to generate AC or DC overvoltage, the thyristor of the first valve is controlled to be turned on to dissipate the energy in the energy consumption circuit.

28. A DC transmission valve group control device, characterized in that: Applicable to a DC transmission valve group according to any one of claims 1 to 17, and used to execute a DC transmission valve group control method according to any one of claims 22 to 27; the control device comprises: A detection unit, used to detect operating parameters and faults of the DC transmission valve group; A control unit, based on the operating parameters of the DC transmission valve group, controls the DC circuit breaker to be turned on, the first valve to be turned off, and the voltage source converter to be rectified or inverted during normal operation if the voltage source converter is connected in series with the main branch of the DC circuit breaker and then connected in anti-parallel to the series circuit of the first valve and the energy consumption circuit based on the operating parameters of the DC transmission valve group; and controls the DC circuit breaker to be turned off, the first valve to be turned on, the bypass switch to be closed, and the voltage source converter to be inverted during normal operation if the voltage source converter is connected in series with the first valve and the parallel circuit of the energy consumption circuit and the bypass switch and then connected in parallel to the DC circuit breaker based on the operating parameters of the DC transmission valve group.

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