Hybrid hvdc valve set, hvdc system, control method and control device

Abstract

The application provides a hybrid HVDC valve group, a HVDC system, a control method and a control device, and belongs to the technical field of high voltage direct current transmission. The application comprises an uncontrolled valve group, a semi-controlled valve group or a fully-controlled valve group. When the semi-controlled valve group is connected in series with the uncontrolled valve group, the anode of the semi-controlled valve group is connected with the cathode of the uncontrolled valve group, or the cathode of the semi-controlled valve group is connected with the anode of the uncontrolled valve group. When the fully-controlled valve group is connected in series with the uncontrolled valve group, the negative electrode of the fully-controlled valve group is connected with the cathode of the uncontrolled valve group, or the positive electrode of the fully-controlled valve group is connected with the anode of the uncontrolled valve group. The semi-controlled valve group comprises a grid commutated converter, the fully-controlled valve group comprises a voltage source converter, and the uncontrolled valve group comprises a bridge-type uncontrolled rectifier circuit. The application utilizes the direct current voltage or direct current current control performance of the semi-controlled valve group or the fully-controlled valve group to control the series circuit of the uncontrolled valve group, thereby solving the poor controllability problem of the uncontrolled valve group.

Description

Technical Field

[0001] This application relates to the field of high voltage direct current transmission technology, specifically to hybrid direct current transmission valve groups, direct current transmission systems, control methods, and control devices. Background Technology

[0002] High-voltage and ultra-high-voltage direct current (HVDC) transmissions have large capacities. One existing technology uses a grid-commutated converter with a twelve-pulse circuit structure. Each twelve-pulse circuit has two three-phase six-arm circuits connected in series, and each arm uses a single high-capacity thyristor connected in series. Because the thyristors cannot be controlled to turn off, the existing converter structure requires a large number of reactive power compensation devices. Another existing technology uses a voltage source converter based on a modular multilevel converter. Each arm uses a half-bridge submodule or a full-bridge submodule composed of IGBTs or IGCTs connected in series. This allows for flexible control of active and reactive power, but it is expensive and has high losses.

[0003] With the development of new energy sources in high-altitude areas, deserts, and offshore areas, the requirements for cost and land use of high-voltage direct current transmission systems are becoming increasingly stringent. The bridge uncontrolled rectifier circuit has certain advantages in terms of cost and reactive power loss. However, due to the uncontrolled rectifier, it cannot control the power on its own and cannot suppress DC-side faults, making it difficult to meet the performance requirements of DC transmission systems. Summary of the Invention

[0004] The purpose of this application is to provide a hybrid DC transmission valve group, a DC transmission system, a control method, and a control device that can solve the above-mentioned technical problems.

[0005] In a first aspect, embodiments of this application provide a hybrid DC transmission valve assembly, comprising:

[0006] An uncontrolled valve assembly, the uncontrolled valve assembly including a bridge-type uncontrolled rectifier circuit;

[0007] and a semi-controlled valve group or a fully controlled valve group, wherein the semi-controlled valve group includes a grid phase-switching converter; and the fully controlled valve group includes a voltage source converter.

[0008] Wherein, when the semi-controlled valve group is connected in series with the uncontrolled valve group, the anode of the semi-controlled valve group is connected to the cathode of the uncontrolled valve group, or the cathode of the semi-controlled valve group is connected to the anode of the uncontrolled valve group;

[0009] The fully controlled valve group is connected in series with the uncontrolled valve group. The negative terminal of the fully controlled valve group is connected to the cathode of the uncontrolled valve group, or the positive terminal of the fully controlled valve group is connected to the anode of the uncontrolled valve group.

[0010] In some embodiments, the fully controlled valve group or the uncontrolled valve group further includes a bypass diode valve and / or a DC circuit breaker.

[0011] In some embodiments, when the fully controlled valve group is connected in series with the uncontrolled valve group, if the fully controlled valve group cannot adjust the DC voltage to a negative voltage, both the fully controlled valve group and the uncontrolled valve group include a DC circuit breaker and a bypass diode valve.

[0012] When the fully controlled valve group is connected in series with the uncontrolled valve group, if the fully controlled valve group can adjust the DC voltage to a negative voltage but cannot adjust the rated DC voltage of the uncontrolled valve group to a negative DC voltage, the uncontrolled valve group includes a DC circuit breaker and a bypass diode valve.

[0013] In some embodiments, in the fully controlled valve group: the DC circuit breaker is connected in series with the positive terminal of the voltage source converter to form a series circuit of the voltage source converter and the DC circuit breaker; the bypass diode valve is connected in parallel with the voltage source converter and the DC circuit breaker, that is, the anode of the bypass diode valve is connected to the negative terminal of the voltage source converter, and the cathode of the bypass diode valve is connected to the other end of the series circuit of the voltage source converter and the DC circuit breaker;

[0014] Alternatively, the DC circuit breaker is connected in series with the negative terminal of the voltage source converter to form a series circuit of the voltage source converter and the DC circuit breaker; the bypass diode valve is connected in parallel with the series circuit of the voltage source converter and the DC circuit breaker, that is, the cathode of the bypass diode valve is connected to the positive terminal of the voltage source converter, and the anode of the bypass diode valve is connected to the other end of the series circuit of the voltage source converter and the DC circuit breaker.

[0015] In some embodiments, in the uncontrolled valve group: the DC circuit breaker is connected in series with the positive terminal of the bridge uncontrolled rectifier circuit to form a bridge uncontrolled rectifier circuit and a DC circuit breaker series circuit; the bypass diode valve is connected in parallel with the bridge uncontrolled rectifier circuit and the DC circuit breaker series circuit, that is, the anode of the bypass diode valve is connected to the negative terminal of the bridge uncontrolled rectifier circuit, and the cathode of the bypass diode valve is connected to the other end of the bridge uncontrolled rectifier circuit and the DC circuit breaker series circuit;

[0016] Alternatively, the DC circuit breaker is connected in series with the negative terminal of the bridge uncontrolled rectifier circuit to form a series circuit of the bridge uncontrolled rectifier circuit and the DC circuit breaker; the bypass diode valve is connected in parallel with the bridge uncontrolled rectifier circuit and the DC circuit breaker series circuit, that is, the cathode of the bypass diode valve is connected to the positive terminal of the bridge uncontrolled rectifier circuit, and the anode of the bypass diode valve is connected to the other end of the series circuit of the bridge uncontrolled rectifier circuit and the DC circuit breaker.

[0017] In some embodiments, both the fully controlled valve group and the uncontrolled valve group further include a resistor or surge arrester, and a bypass switch connected in parallel across the resistor or surge arrester.

[0018] The circuit consisting of the resistor or surge arrester and the bypass switch connected in parallel is connected in series with a bypass diode valve.

[0019] In some embodiments, the semi-controlled valve group, the fully controlled valve group, and the uncontrolled valve group all include a bypass isolation circuit, and the grid phase-commutation converter, the voltage source converter, and the bridge uncontrolled rectifier circuit are all connected in parallel to the bypass isolation circuit.

[0020] In some embodiments, the bypass isolation circuit includes a bypass circuit and an isolation circuit.

[0021] In some embodiments, the bypass circuit includes a bypass switch and a bypass knife switch, which are connected in parallel.

[0022] In some embodiments, the isolation circuit includes two isolation switches, and an isolation switch is provided at each of the two connection nodes of the bypass switch and the bypass switch.

[0023] In some embodiments, in the semi-controlled valve group: the two isolating switches are connected in series with the cathode and anode of the grid phase-commutation converter, respectively, and the two ends of the bypass switch are connected to the ends of the two isolating switches away from the grid phase-commutation converter, respectively;

[0024] In the fully controlled valve group: the two isolating switches are connected in series with the positive and negative terminals of the voltage source converter, or the voltage source converter and the DC circuit breaker, respectively; the two ends of the bypass switch are connected to the ends of the two isolating switches that are away from the voltage source converter.

[0025] In the uncontrolled valve group: the two isolating switches are connected in series with the positive and negative terminals of the bridge uncontrolled rectifier circuit, or the bridge uncontrolled rectifier circuit and the DC circuit breaker series circuit, respectively; the two ends of the bypass switch are respectively connected to the ends of the two isolating switches away from the bridge uncontrolled rectifier circuit.

[0026] In some embodiments, the grid phase-commutation converter includes a six-pulse bridge circuit or a twelve-pulse bridge circuit;

[0027] The six-pulse bridge circuit or the twelve-pulse bridge circuit includes non-turn-off semi-controlled power semiconductors.

[0028] In some embodiments, the voltage source converter includes 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.

[0029] The modular multilevel converter is composed of half-bridge sub-modules, full-bridge sub-modules, or a combination of hybrid sub-modules.

[0030] The hybrid submodule includes the half-bridge submodule and the full-bridge submodule.

[0031] In some embodiments, the bridge uncontrolled rectifier circuit includes a six-pulse bridge circuit or a twelve-pulse bridge circuit;

[0032] The six-pulse bridge circuit or the twelve-pulse bridge circuit includes uncontrolled power semiconductors.

[0033] Secondly, embodiments of this application provide a DC transmission system including a hybrid DC transmission valve group as described in any of the first aspects.

[0034] In some embodiments, the grid phase-commutation converter of the semi-controlled valve group, the voltage source converter of the fully controlled valve group, and the bridge uncontrolled rectifier circuit of the uncontrolled valve group are all connected to a converter transformer and connected to the AC system.

[0035] The converter transformer includes a tap changer for adjusting the grid-side voltage and valve-side voltage ratio.

[0036] Thirdly, embodiments of this application provide a control method for a hybrid DC transmission valve group in a DC transmission system as described in the second aspect, comprising the following steps:

[0037] The semi-controlled valve group or the fully controlled valve group operates in rectification mode, and the uncontrolled valve group operates in uncontrolled rectification mode;

[0038] If the DC voltage of the uncontrolled valve group changes, the DC voltage of the semi-controlled valve group or the fully controlled valve group is adjusted to maintain the stability of the DC voltage or current in the hybrid DC transmission valve group. The adjustment direction of the DC voltage of the semi-controlled valve group or the fully controlled valve group is opposite to the change direction of the DC voltage of the uncontrolled valve group. If a fault occurs in the DC line and an inrush current flows into the fault point, the firing angle of the grid commutation converter of the semi-controlled valve group is controlled, the DC voltage of the voltage source converter of the fully controlled valve group is reduced, and / or the DC circuit breaker of the fully controlled valve group or the uncontrolled valve group is turned off to suppress the inrush current flowing into the fault point.

[0039] In some embodiments, the control method further includes:

[0040] If the semi-controlled valve group fails, the bypass circuit of the semi-controlled valve group is turned on, the grid-side AC switch of the semi-controlled valve group is turned off, the grid phase-commutation converter is locked, and the grid phase-commutation converter is isolated through the isolation circuit of the semi-controlled valve group.

[0041] In some embodiments, the control method further includes:

[0042] If the fully controlled valve group fails, disconnect the AC switch of the fully controlled valve group, control the bypass circuit of the fully controlled valve group to conduct, lock the voltage source converter, and isolate the voltage source converter through the isolation circuit of the fully controlled valve group.

[0043] In some embodiments, the control method further includes:

[0044] If the uncontrolled valve group fails, disconnect the AC switch of the uncontrolled valve group, control the bypass circuit of the uncontrolled valve group to conduct, and isolate the bridge uncontrolled rectifier circuit through the isolation circuit of the uncontrolled valve group.

[0045] In some embodiments, the control method further includes:

[0046] If the fully controlled valve group or the semi-controlled valve group fails, the DC circuit breaker in the fully controlled valve group or the semi-controlled valve group is disconnected, and the DC current of the fully controlled valve group or the semi-controlled valve group continues through the bypass diode valve of the fully controlled valve group or the semi-controlled valve group.

[0047] In some embodiments, the control method further includes:

[0048] If the hybrid DC transmission valve group is connected to a high-proportion new energy power system, the voltage source converter of the fully controlled valve group operates based on a grid-type control strategy.

[0049] In some embodiments, the control method further includes:

[0050] In the uncontrolled valve group: the tap of the uncontrolled valve group controls the valve-side voltage of the uncontrolled valve group.

[0051] When the grid voltage increases, adjust the tap position to reduce the increase in valve-side voltage; when the grid voltage decreases, adjust the tap position to reduce the decrease in valve-side voltage, thereby controlling the DC voltage of the uncontrolled valve group within the specified range.

[0052] In some embodiments, the control method further includes:

[0053] The semi-controlled valve group reduces grid-side voltage fluctuations by adjusting the firing angle or switching AC filters; or the fully controlled valve group reduces grid-side voltage fluctuations by adjusting reactive power.

[0054] Fourthly, embodiments of this application provide a control device for executing the control method for a hybrid DC transmission valve group in a DC transmission system as described in any of the third aspects, the control device comprising:

[0055] The detection unit is used to detect the operating parameters and fault data of the hybrid DC transmission valve group;

[0056] The control unit is used to control the semi-controlled valve group or fully controlled valve group to operate in rectification mode based on the operating parameters and fault data detected by the detection unit; to control the uncontrolled valve group to operate in uncontrolled rectification mode; when an AC system fault may cause the DC voltage of the uncontrolled valve group to drop or rise, to maintain the stability of the DC voltage or current in the hybrid DC transmission valve group by increasing or decreasing the DC voltage of the semi-controlled valve group or fully controlled valve group; when a DC line fault occurs, to suppress the current flowing into the fault point by controlling the firing angle of the grid commutation converter of the semi-controlled valve group, or by decreasing the DC voltage of the fully controlled valve group, or by controlling the DC circuit breaker of the fully controlled valve group or semi-controlled valve group to turn off.

[0057] The beneficial effects of this application are as follows: Compared with the prior art, this application provides a hybrid DC transmission valve group, DC transmission system, control method and control device, which uses the DC voltage or DC current of a semi-controlled valve group or a fully controlled valve group to control the performance, solves the problem of poor controllability of uncontrolled valve groups, and achieves controllable transmission power by controlling the firing angle of the grid commutation converter of the semi-controlled valve group or the DC voltage of the voltage source converter of the fully controlled valve group. At the same time, it uses the semi-controlled valve group, the fully controlled valve group or the DC circuit breaker to suppress the fault current of the bridge uncontrolled rectifier circuit when a DC side fault occurs, effectively overcomes the defects of the bridge uncontrolled rectifier circuit, and realizes a low-cost high voltage DC transmission scheme. Attached Figure Description

[0058] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0059] Figures 1(a), 1(b), 1(c) and 1(d) are schematic diagrams of a hybrid DC transmission valve group provided in an embodiment of this application;

[0060] Figure 2 This is a schematic diagram of a semi-controlled valve assembly provided in an embodiment of this application;

[0061] Figure 3 This application provides a power grid phase-commutation converter using a twelve-pulse bridge circuit.

[0062] Figures 4(a), 4(b), and 4(c) are schematic diagrams of a fully controllable valve assembly provided in an embodiment of this application;

[0063] Figure 5 This application provides a voltage source converter employing a modular multilevel converter.

[0064] Figure 6This is a schematic diagram of the structure of a full-bridge submodule adopted in the embodiments of this application;

[0065] Figure 7 This is a schematic diagram of the structure of a half-bridge submodule adopted in the embodiments of this application;

[0066] Figure 8 This is a schematic diagram of the structure of a DC circuit breaker provided in an embodiment of this application;

[0067] Figure 9 This is a schematic diagram of the structure of a bypass diode valve provided in an embodiment of this application;

[0068] Figures 10(a), 10(b), and 10(c) are schematic diagrams of an uncontrolled valve assembly provided in an embodiment of this application;

[0069] Figure 11 This application provides a bridge uncontrolled rectifier circuit using a twelve-pulse bridge circuit.

[0070] Figure 12 This is a schematic diagram of a DC power transmission system according to an embodiment of this application;

[0071] Figure 13 This is a schematic diagram of another DC power transmission system according to an embodiment of this application;

[0072] Figure 14 This is a schematic flowchart of a control method for a hybrid DC transmission valve group provided in an embodiment of this application;

[0073] Figure 15 This is a schematic diagram of a control device for a hybrid DC transmission valve group provided in an embodiment of this application. Detailed Implementation

[0074] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0075] In the description of this application, it should be understood that the terms "center", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0076] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, unless otherwise stated, "a plurality of" means two or more.

[0077] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection, a direct connection, or an indirect connection through an intermediate medium; or they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0078] Example 1:

[0079] This application provides a hybrid DC transmission valve group, including an uncontrolled valve group, a semi-controlled valve group, or a fully controlled valve group. The hybrid DC transmission valve group in this application combines the above three types of valve groups, with four series connection topologies: Semi-controlled valve groups connected in series with uncontrolled valve groups: the anode of the semi-controlled valve group is connected to the cathode of the uncontrolled valve group, or the cathode of the semi-controlled valve group is connected to the anode of the uncontrolled valve group; or fully controlled valve groups connected in series with uncontrolled valve groups: the negative terminal of the fully controlled valve group is connected to the cathode of the uncontrolled valve group, or the positive terminal of the fully controlled valve group is connected to the anode of the uncontrolled valve group. In specific designs, the semi-controlled valve group includes a grid-commutated converter with a bypass isolation circuit connected in parallel; the fully controlled valve group includes a voltage source converter with a bypass isolation circuit connected in parallel; and the uncontrolled valve group includes a bridge uncontrolled rectifier circuit with a bypass isolation circuit connected in parallel. This application utilizes the control performance of DC voltage or DC current of semi-controlled valve groups or fully controlled valve groups to control uncontrolled valve groups, solving the problem of poor controllability of uncontrolled valve groups; by controlling the firing angle of the grid commutation converter of the semi-controlled valve group or the DC voltage of the voltage source converter of the fully controlled valve group, the transmission power can be controlled; by using semi-controlled valve groups, fully controlled valve groups or DC circuit breakers to suppress the fault current of the bridge uncontrolled rectifier circuit when a DC side fault occurs, the defects of the bridge uncontrolled rectifier circuit can be effectively overcome, realizing a low-cost high-voltage DC transmission scheme.

[0080] In specific designs, Figures 1(a) and 1(b) show a semi-controlled valve group connected in series with an uncontrolled valve group: Figure 1(a) shows the anode X4 of the semi-controlled valve group connected to the cathode X1 of the uncontrolled valve group, and Figure 1(b) shows the cathode X3 of the semi-controlled valve group connected to the anode X2 of the uncontrolled valve group; Figures 1(c) and 1(d) show a fully controlled valve group connected in series with an uncontrolled valve group: Figure 1(c) shows the negative terminal X6 of the fully controlled valve group connected to the cathode X1 of the uncontrolled valve group, and Figure 1(d) shows the positive terminal X5 of the fully controlled valve group connected to the anode X2 of the uncontrolled valve group.

[0081] In the specific design, such as Figure 2 As shown, Figure 2 This is a schematic diagram of a semi-controlled valve assembly. The semi-controlled valve assembly of this application includes a grid-connected phase converter 1, a first isolating switch 5, a second isolating switch 6, a bypass switch 3, and a bypass switch 4. The bypass switch 3 and the bypass switch 4 form a bypass circuit, and are connected in parallel. The first isolating switch 5 and the second isolating switch 6 form an isolation circuit. The first isolating switch 5 and the second isolating switch 6 are respectively located at the connection node where the bypass switch 3 and the bypass switch 4 are connected in parallel, and the two ends of the bypass switches are respectively connected to the ends of the first and second isolating switches 5 and 6 furthest from the grid-connected phase converter. In this application, the grid-connected phase converter 1 includes a six-pulse bridge circuit or a twelve-pulse bridge circuit, which is composed of non-turn-off semi-controlled power semiconductors such as thyristors. Figure 3 As shown, this is a grid-commutated converter using a twelve-pulse bridge circuit.

[0082] In the specific design, such as Figure 3 As shown, Figure 3 This is a structural diagram of a grid-commutated converter using a twelve-pulse bridge circuit, where each bridge arm consists of thyristors 23 connected in series. The three-phase inputs 21 and 22 of the grid-commutated converter 1 are connected to the valve side of the YY-type converter transformer and the valve side of the YD-type converter transformer, respectively.

[0083] In the specific design, the fully controlled valve group includes a voltage source converter 2, an isolation circuit, and a bypass circuit. The isolation circuit includes a first isolation switch 5 and a second isolation switch 6, and the bypass circuit includes a bypass switch 3 and a bypass switch 4. As shown in Figure 4(a), the voltage source converter 2 is preferably a modular multilevel converter composed of full-bridge submodules. As shown in Figure 4(b), the fully controlled valve group also includes a DC circuit breaker 7 and / or a bypass diode valve 8. The positive terminal of the DC circuit breaker 7 and the voltage source converter 2 are connected in series, and the bypass diode valve 8 and the series circuit of the DC circuit breaker 7 and the voltage source converter 2 of the fully controlled valve group are connected in parallel. The anode of the bypass diode valve 8 and the negative terminal of the voltage source converter 2 are at the same potential. The voltage source converter 2 is preferably a modular multilevel converter composed of half-bridge submodules. As shown in Figure 4(c), the fully controlled valve group also includes a surge arrester 9 and a bypass switch 10. The surge arrester 9 is connected in series with the bypass diode valve 8, and the bypass switch 10 is connected in parallel with the surge arrester 9. The voltage source converter 2 is preferably a modular multilevel converter composed of half-bridge sub-modules.

[0084] In the specific design, such as Figure 5 As shown, Figure 5 The voltage source converter 2 provided in this embodiment employs a modular multilevel converter, wherein each arm of the converter consists of a submodule 27 and a current-limiting reactor 28 connected in series. The three-phase input 24 of the voltage source converter 2 is connected to the valve side of the converter transformer. The voltage source converter 2 also includes an isolating switch 25 and a charging resistor 26. The isolating switch 25 is three-phase, and the charging resistor 26 is connected in parallel across the isolating switch 25.

[0085] In the specific design, such as Figure 6 As shown, Figure 6 This is a schematic diagram of submodule 27 using a full-bridge submodule structure, including four IGBT devices 29 and one capacitor 30, forming a full-bridge structure. If... Figure 5 If all or more than 50% of the submodules of the voltage source converter shown are composed of a full-bridge submodule structure, then the fully controlled valve group can regulate the DC voltage to a negative voltage.

[0086] In the specific design, such as Figure 7 As shown, Figure 7 This is a schematic diagram of submodule 27 using a half-bridge submodule structure, including two IGBT devices 31 and one capacitor 32, forming a half-bridge structure. If... Figure 5 If all submodules of the voltage source converter shown are composed of a half-bridge submodule structure, then the fully controlled valve group cannot adjust the DC voltage to a negative voltage.

[0087] In the specific design, such as Figure 8 As shown, Figure 8This is a schematic diagram of the DC circuit breaker 7, including a main branch 33, a transfer branch 36, and an energy dissipation branch 39. The main branch 33 includes a fast disconnect switch 34 and a first power switch connected in series, used to conduct steady-state current and reduce losses. The first power switch uses power devices 35 in a forward and reverse series structure, capable of bidirectionally interrupting DC current. Power devices 35 include, but are not limited to, forward and reverse IGBTs connected in series, with diodes connected in anti-parallel to the forward and reverse IGBTs respectively. The transfer branch 36 includes a second power switch and a diode 37, used to interrupt DC current under high-voltage operating conditions. It should be noted that the diode 37 allows current from either direction of the DC circuit breaker to flow unidirectionally into the second power switch; when the second power switch is open, it can interrupt current from either direction of the DC circuit breaker. The second power switch in the transfer branch 36 uses power devices 38 in a forward series structure, capable of unidirectionally interrupting DC current. Power devices 38 include, but are not limited to, IGBTs and anti-parallel diodes. The energy dissipation branch 39 includes a surge arrester 40, used to suppress overvoltage and absorb energy.

[0088] In the specific design, such as Figure 9 As shown, Figure 9 This is a schematic diagram of the bypass diode valve 8, which consists of diodes 41 connected in series.

[0089] In the specific design, such as Figure 10(a) , 10(b) Figures 10(a), 10(b), and 10(c) are schematic diagrams of an uncontrolled valve group. The uncontrolled valve group includes a bridge uncontrolled rectifier circuit 11, an isolation circuit, and a bypass circuit. The isolation circuit includes a first isolation switch 5 and a second isolation switch 6. The bypass circuit includes a bypass switch 3 and a bypass switch 4, as shown in Figure 10(a). As shown in Figure 10(b), the uncontrolled valve group also includes a DC circuit breaker 7 and / or a bypass diode valve 8. The DC circuit breaker 7 is connected in series with the positive terminal of the bridge uncontrolled rectifier circuit 11. The bypass diode valve 8 and the DC circuit breaker 7 of the fully controlled valve group are connected in parallel with the series circuit of the bridge uncontrolled rectifier circuit 11. The anode of the bypass diode valve 8 and the negative terminal of the bridge uncontrolled rectifier circuit 11 are at the same potential. As shown in Figure 10(c), the fully controlled valve group also includes a surge arrester 9 and a bypass switch 10. The surge arrester 9 is connected in series with the bypass diode valve 8, and the bypass switch 10 is connected in parallel with the surge arrester 9. The bridge uncontrolled rectifier circuit 11 includes a six-pulse bridge circuit or a twelve-pulse bridge circuit, which is composed of uncontrolled power semiconductors (such as diodes).

[0090] In the specific design, such as Figure 11 As shown, this is a bridge uncontrolled rectifier circuit using a twelve-pulse bridge circuit, where each bridge arm consists of diodes 44 connected in series. The three-phase inputs 42 and 43 of the bridge uncontrolled rectifier circuit are connected to the valve side of the YY-type converter transformer and the valve side of the YD-type converter transformer, respectively.

[0091] Example 2:

[0092] Embodiment 2 of this application provides a high-voltage current transmission system, including the hybrid current transmission valve group described in any one of Embodiment 1.

[0093] like Figure 12 As shown, for ease of description, identical components in different locations will be distinguished by prefixes such as "first", "second", "number one", and "number two". The DC transmission system is an ultra-high voltage DC transmission system. The main circuit of the ultra-high voltage DC transmission system includes rectifier station 100, inverter station 200, first DC line 150, second DC line 160, rectifier station grounding electrode line 114, rectifier station grounding electrode 115, inverter station grounding electrode line 214, and inverter station grounding electrode 215.

[0094] The rectifier station 100 includes a first DC pole I110, a second DC pole II120, a first AC system 140, and converter transformer incoming line switches (as shown by numbers 131, 132, 133 and 134 in the figure), a first metallic return line changeover switch 113, a first earth return line changeover switch 190, and a bipolar neutral zone isolating switch (as shown by numbers 174, 175, 184 and 185 in the figure).

[0095] The first DC pole I110 includes a first high-end uncontrolled valve group 111, a first low-end semi-controlled 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 bus switch 119, a first pole bus isolating switch 172, and a first DC line isolating switch 173. The first high-end uncontrolled valve group 111 and the first low-end semi-controlled valve group 112 are connected in series.

[0096] The first high-end uncontrolled valve group 111 includes a bridge uncontrolled rectifier circuit 11, a first DC circuit breaker 17, a first bypass diode valve 18, a first bypass knife switch 14, a first bypass switch 13, a first isolating knife switch 15, and a second isolating knife switch 16. The first bypass switch 13 connects the anode and cathode of the bridge uncontrolled rectifier circuit 11 and is connected to one end of the first isolating knife switch 15 and the second isolating knife switch 16. The first bypass knife switch 14 connects to the other end of the first isolating knife switch 15 and the second isolating knife switch 16. The first low-end semi-controlled valve group 112 includes a grid commutation converter 1, a bypass knife switch 4, a bypass switch 3, a first isolating knife switch 5, and a second isolating knife switch 6. The bypass switch 3 connects the anode and cathode of the grid commutation converter 1 and is connected to one end of the first isolating knife switch 5 and the second isolating knife switch 6. The bypass knife switch 4 connects to the other end of the first isolating knife switch 5 and the second isolating knife switch 6.

[0097] The second DC pole II120 includes a second low-end semi-controlled valve group 121, a second high-end uncontrolled 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 bus switch 129, a second pole bus isolating switch 182, and a second DC line isolating switch 183. The second low-end semi-controlled valve group 121 and the second high-end uncontrolled valve group 122 are connected in series.

[0098] The second high-end uncontrolled valve group 122 includes a second bridge uncontrolled rectifier circuit 104, a second DC circuit breaker 49, a second bypass diode valve 50, a second bypass knife switch 46, a second bypass switch 45, a second first isolating knife switch 47, and a second second isolating knife switch 48. The second bypass switch 45 connects the positive and negative terminals of the second bridge uncontrolled rectifier circuit 104 and is connected to one end of the second first isolating knife switch 47 and the second second isolating knife switch 48. The second bypass knife switch 46 connects to the other end of the second first isolating knife switch 47 and the second second isolating knife switch 48. The second low-end semi-controlled valve group 121 includes a second grid commutation converter 101, a third bypass knife switch 56, a third bypass switch 55, a third first isolating knife switch 57, and a third second isolating knife switch 58. The third bypass switch 55 connects the positive and negative terminals of the second grid phase converter 101 and is connected to one end of the third first isolating switch 57 and the third second isolating switch 58. The second bypass switch 46 connects to the other end of the third first isolating switch 57 and the third second isolating switch 58.

[0099] The structures of the first high-end uncontrolled valve group 111 and the second high-end uncontrolled valve group 122 are the same as those in Figure 10(b), and the structure in Figure 10(c) can also be used; the structures of the first low-end semi-controlled valve group 112 and the second low-end semi-controlled valve group 121 are the same as those in Figure 10(b). Figure 2 same.

[0100] The inverter station 200 includes a third DC pole I210, a fourth DC pole II220, a second AC system 240, and converter transformer incoming line switches (as shown by numbers 231, 232, 233, and 234 in the figure), a second metallic return line switching switch 213, a second earth return line switching switch 290, and a bipolar neutral zone isolating switch (as shown by numbers 274, 275, 284, and 285 in the figure).

[0101] The third DC pole I210 includes a third high-end semi-controlled valve group 211, a third low-end semi-controlled 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 isolating switch 272, and a third DC line isolating switch 273. The third high-end semi-controlled valve group 211 and the third low-end semi-controlled valve group 212 are connected in series.

[0102] The third high-end semi-controlled valve group 211 includes a third grid phase-changing converter 201, a third bypass switch 51, a third bypass switch 52, a fourth first isolating switch 53, and a fourth second isolating switch 54. The third bypass switch 52 connects to the positive and negative terminals of the third grid phase-changing converter 201 and is connected to one end of the fourth first isolating switch 53 and the fourth second isolating switch 54. The third bypass switch 51 connects to the other end of the fourth first isolating switch 53 and the fourth second isolating switch 54. The third low-end semi-controlled valve group 212 includes a fourth grid phase-changing converter 202, a fourth bypass switch 61, a fourth bypass switch 62, a fifth first isolating switch 63, and a fifth second isolating switch 64. The fourth bypass switch 62 connects to the positive and negative terminals of the fourth grid phase-changing converter 202 and is connected to one end of the fifth first isolating switch 63 and the fifth second isolating switch 64. The fourth bypass switch 61 connects to the other end of the fifth first isolating switch 63 and the fifth second isolating switch 64.

[0103] The fourth DC pole II 220 includes a fourth low-end semi-controlled valve group 221, a fourth high-end semi-controlled 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 isolating switch 282, and a fourth DC line isolating switch 283. The fourth low-end semi-controlled valve group 221 and the fourth high-end semi-controlled valve group 222 are connected in series.

[0104] The fourth high-end semi-controlled valve group 222 includes a fifth grid phase-changing converter 204, a fifth bypass switch 81, a fifth bypass switch 82, a sixth first isolating switch 83, and a sixth second isolating switch 84. The fifth bypass switch 82 connects to the positive and negative terminals of the fifth grid phase-changing converter 204 and is connected to one end of the sixth first isolating switch 83 and the sixth second isolating switch 84. The fifth bypass switch 81 connects to the other end of the sixth first isolating switch 83 and the sixth second isolating switch 84. The fourth low-end semi-controlled valve group 221 includes a sixth grid phase-changing converter 203, a sixth bypass switch 71, a sixth bypass switch 72, a seventh first isolating switch 73, and a seventh second isolating switch 74. The sixth bypass switch 72 connects to the positive and negative terminals of the sixth grid phase-changing converter 203 and is connected to one end of the seventh first isolating switch 73 and the seventh second isolating switch 74. The sixth bypass switch 71 connects to the other end of the seventh first isolating switch 73 and the seventh second isolating switch 74.

[0105] The structure of the third high-end semi-controlled valve group 211, the third low-end semi-controlled valve group 212, the fourth high-end semi-controlled valve group 222, and the fourth low-end semi-controlled valve group 221 are similar to... Figure 2 Same. The various switches or disconnectors mentioned above include at least one of mechanical switches, disconnectors, DC circuit breakers, and thyristor valves.

[0106] Real-time Example 3:

[0107] Based on the same inventive concept as Embodiment 3, Embodiment 3 of this application also provides a schematic diagram of a DC power transmission system.

[0108] like Figure 13 As shown, for ease of description, identical components in different locations will be distinguished by prefixes such as "first", "second", "number one", and "number two". The DC transmission system is an ultra-high voltage DC transmission system. The main circuit of the ultra-high voltage DC transmission system includes rectifier station 100, inverter station 200, first DC line 150, second DC line 160, rectifier station grounding electrode line 114, rectifier station grounding electrode 115, inverter station grounding electrode line 214, and inverter station grounding electrode 215.

[0109] The rectifier station 100 includes a first DC pole I110, a second DC pole II120, a first AC system 140, and converter transformer incoming line switches (as shown by numbers 131, 132, 133 and 134 in the figure), a first metallic return line changeover switch 113, a first earth return line changeover switch 190, and a bipolar neutral zone isolating switch (as shown by numbers 174, 175, 184 and 185 in the figure).

[0110] The first DC pole I110 includes a first high-end uncontrolled valve group 111, a first low-end fully controlled valve group 141, a first high-end converter transformer 116, a first low-end converter transformer 143, a first smoothing reactor 105, a first pole neutral bus switch 119, a first pole bus isolating switch 172, and a first DC line isolating switch 173. The first high-end uncontrolled valve group 111 and the first low-end fully controlled valve group 141 are connected in series.

[0111] The first high-end uncontrolled valve group 111 includes a bridge uncontrolled rectifier circuit 11, a first DC circuit breaker 17, a first bypass diode valve 18, a first bypass knife switch 14, a first bypass switch 13, a first isolation knife switch 15, and a second isolation knife switch 16. The first bypass switch 13 connects the positive and negative terminals of the bridge uncontrolled rectifier circuit 11 and is connected to one end of the first isolation knife switch 15 and the second isolation knife switch 16. The first bypass knife switch 14 connects to the other end of the first isolation knife switch 15 and the second isolation knife switch 16. The first low-end fully controlled valve group 141 includes a voltage source converter 2, a DC circuit breaker 7, a bypass diode valve 8, a bypass knife switch 4, a bypass switch 3, a first isolation knife switch 5, and a second isolation knife switch 6. The bypass switch 3 connects the positive and negative terminals of the voltage source converter 2 and is connected to one end of the first isolation knife switch 5 and the second isolation knife switch 6. The bypass switch 4 is connected to the other end of the first isolating switch 5 and the second isolating switch 6.

[0112] The second DC pole II120 includes a second low-end fully controlled valve group 142, a second high-end uncontrolled valve group 122, a second low-end converter transformer 144, a second high-end converter transformer 127, a second smoothing reactor 106, a second pole neutral bus switch 129, a second pole bus isolating switch 182, and a second DC line isolating switch 183. The second low-end fully controlled valve group 142 and the second high-end uncontrolled valve group 122 are connected in series.

[0113] The second high-end uncontrolled valve group 122 includes a second bridge uncontrolled rectifier circuit 104, a second DC circuit breaker 49, a second bypass diode valve 50, a second bypass knife switch 46, a second bypass switch 45, a second first isolating knife switch 47, and a second second isolating knife switch 48. The second bypass switch 45 connects the positive and negative terminals of the second bridge uncontrolled rectifier circuit 104 and is connected to one end of the second first isolating knife switch 47 and the second second isolating knife switch 48. The second bypass knife switch 46 connects to the other end of the second first isolating knife switch 47 and the second second isolating knife switch 48. The second low-end fully controlled valve group 142 includes a voltage source converter 102, a DC circuit breaker 59, a bypass diode valve 60, a third bypass knife switch 56, a third bypass switch 55, a third first isolating knife switch 57, and a third second isolating knife switch 58. The third bypass switch 55 connects to the positive and negative terminals of the voltage source converter 102, and is connected to one end of the third first isolating switch 57 and the third second isolating switch 58. The third bypass switch 56 connects to the other end of the third first isolating switch 57 and the third second isolating switch 58.

[0114] The structures of the first high-end uncontrolled valve group 111 and the second high-end uncontrolled valve group 122 are the same as those in Figure 10(b), and the structure in Figure 10(c) can also be used; the structures of the first low-end fully controlled valve group 141 and the second low-end fully controlled valve group 142 are the same as those in Figure 4(b), and the structure in Figure 4(c) can also be used.

[0115] Voltage source converters include, but are not limited to, at least one of two-level converters, three-level converters, modular multilevel converters, diode-clamped multilevel converters, cascaded two-level converters, or stacked two-level converters. The aforementioned modular multilevel converters include, but are not limited to, modular multilevel converters (MMCs) with a half-bridge sub-module structure.

[0116] The inverter station 200 includes a third DC pole I210, a fourth DC pole II220, a second AC system 240, and converter transformer incoming line switches (as shown by numbers 231, 232, 233, and 234 in the figure), a second metallic return line switching switch 213, a second earth return line switching switch 290, and a bipolar neutral zone isolating switch (as shown by numbers 274, 275, 284, and 285 in the figure).

[0117] The third DC pole I210 includes a third high-end semi-controlled valve group 211, a third low-end semi-controlled 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 isolating switch 272, and a third DC line isolating switch 273. The third high-end semi-controlled valve group 211 and the third low-end semi-controlled valve group 212 are connected in series.

[0118] The third high-end semi-controlled valve group 211 includes a third grid phase-changing converter 201, a third bypass switch 51, a third bypass switch 52, a fourth first isolating switch 53, and a fourth second isolating switch 54. The third bypass switch 52 connects to the positive and negative terminals of the third grid phase-changing converter 201 and is connected to one end of the fourth first isolating switch 53 and the fourth second isolating switch 54. The third bypass switch 51 connects to the other end of the fourth first isolating switch 53 and the fourth second isolating switch 54. The third low-end semi-controlled valve group 212 includes a fourth grid phase-changing converter 202, a fourth bypass switch 61, a fourth bypass switch 62, a fifth first isolating switch 63, and a fifth second isolating switch 64. The fourth bypass switch 62 connects to the positive and negative terminals of the fourth grid phase-changing converter 202 and is connected to one end of the fifth first isolating switch 63 and the fifth second isolating switch 64. The fourth bypass switch 61 connects to the other end of the fifth first isolating switch 63 and the fifth second isolating switch 64.

[0119] The fourth DC pole II 220 includes a fourth low-end semi-controlled valve group 221, a fourth high-end semi-controlled 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 isolating switch 282, and a fourth DC line isolating switch 283. The fourth low-end semi-controlled valve group 221 and the fourth high-end semi-controlled valve group 222 are connected in series.

[0120] The fourth high-end semi-controlled valve group 222 includes a fifth grid phase-changing converter 204, a fifth bypass switch 81, a fifth bypass switch 82, a sixth first isolating switch 83, and a sixth second isolating switch 84. The fifth bypass switch 82 connects to the positive and negative terminals of the fifth grid phase-changing converter 204 and is connected to one end of the sixth first isolating switch 83 and the sixth second isolating switch 84. The fifth bypass switch 81 connects to the other end of the sixth first isolating switch 83 and the sixth second isolating switch 84. The fourth low-end semi-controlled valve group 221 includes a sixth grid phase-changing converter 203, a sixth bypass switch 71, a sixth bypass switch 72, a seventh first isolating switch 73, and a seventh second isolating switch 74. The sixth bypass switch 72 connects to the positive and negative terminals of the sixth grid phase-changing converter 203 and is connected to one end of the seventh first isolating switch 73 and the seventh second isolating switch 74. The sixth bypass switch 71 connects to the other end of the seventh first isolating switch 73 and the seventh second isolating switch 74.

[0121] The structure of the third high-end semi-controlled valve group 211, the third low-end semi-controlled valve group 212, the fourth high-end semi-controlled valve group 222, and the fourth low-end semi-controlled valve group 221 are similar to... Figure 2 Same. The various switches or disconnectors mentioned above include at least one of mechanical switches, disconnectors, DC circuit breakers, and thyristor valves.

[0122] Example 4:

[0123] Based on the DC transmission system provided in Embodiment 2 or Embodiment 3, Embodiment 4 of this application provides a control method for a hybrid DC transmission valve group, such as... Figure 14 As shown, it includes the following steps:

[0124] S110: Controls the operation of the semi-controlled or fully controlled valve group in rectification mode.

[0125] As shown in Figure 1(a), the semi-controlled valve group is controlled to operate in the rectification state; as shown in Figure 1(b), the semi-controlled valve group is controlled to operate in the rectification state; as shown in Figure 1(c), the fully controlled valve group is controlled to operate in the rectification state; as shown in Figure 1(d), the fully controlled valve group is controlled to operate in the rectification state.

[0126] Specifically, such as Figure 2 and Figure 3 As shown, controlling the semi-controlled valve group to operate in rectification mode is equivalent to controlling the grid commutator converter 1 to operate in rectification mode. (See Figures 4(a), 4(b), 4(c) and...) Figure 5 As shown, controlling the entire control valve group to operate in rectification mode is equivalent to controlling the voltage source converter 2 to operate in rectification mode.

[0127] S120: Controls the uncontrolled valve group to operate in uncontrolled rectification mode.

[0128] As shown in Figure 1(a), the uncontrolled valve group is operated in the rectification state; as shown in Figure 1(b), the uncontrolled valve group is operated in the rectification state; as shown in Figure 1(c), the uncontrolled valve group is operated in the rectification state; as shown in Figure 1(d), the uncontrolled valve group is operated in the rectification state.

[0129] Specifically, as shown in Figures 10(a), 10(b), 10(c), and... Figure 11 As shown, the uncontrolled valve group operates in the rectification state after the three-phase input of the bridge uncontrolled rectifier circuit 11 is energized.

[0130] S130: Controls the DC voltage of a semi-controlled or fully controlled valve group to maintain the DC current or DC voltage of a hybrid DC transmission valve group.

[0131] When an AC system voltage change or fault may cause the DC voltage of the uncontrolled valve group to drop or rise, the DC current or DC voltage of the hybrid DC transmission valve group is maintained by increasing or decreasing the DC voltage of the semi-controlled valve group or the fully controlled valve group.

[0132] When a change or fault in the AC system voltage may cause a drop in the DC voltage of the uncontrolled valve group, as shown in Figure 1(a), the DC voltage of the semi-controlled valve group is increased to maintain the DC current or DC voltage of the hybrid DC transmission valve group; as shown in Figure 1(b), the DC voltage of the semi-controlled valve group is increased to maintain the DC current or DC voltage of the hybrid DC transmission valve group; as shown in Figure 1(c), the DC voltage of the fully controlled valve group is increased to maintain the DC current or DC voltage of the hybrid DC transmission valve group; as shown in Figure 1(d), the DC voltage of the fully controlled valve group is increased to maintain the DC current or DC voltage of the hybrid DC transmission valve group.

[0133] When a change or fault in the AC system voltage may cause an increase in the DC voltage of the uncontrolled valve group, as shown in Figure 1(a), the DC voltage of the semi-controlled valve group is reduced to maintain the DC current or DC voltage of the hybrid DC transmission valve group; as shown in Figure 1(b), the DC voltage of the semi-controlled valve group is reduced to maintain the DC current or DC voltage of the hybrid DC transmission valve group; as shown in Figure 1(c), the DC voltage of the fully controlled valve group is reduced to maintain the DC current or DC voltage of the hybrid DC transmission valve group; as shown in Figure 1(d), the DC voltage of the fully controlled valve group is reduced to maintain the DC current or DC voltage of the hybrid DC transmission valve group.

[0134] S140: Reduce the DC voltage of a semi-controlled or fully controlled valve group or control the DC circuit breaker to shut off.

[0135] When a DC line fault occurs, the current flowing into the fault point is suppressed by controlling the firing angle of the grid phase converter 1 of the semi-controlled valve group, or by reducing the DC voltage of the voltage source converter of the fully controlled valve group, or by controlling the DC circuit breaker 7 of the fully controlled valve group or / and the uncontrolled valve group to turn off.

[0136] like Figure 3 As shown, when a DC line fault occurs, the current flowing into the fault point is suppressed by controlling the firing angle of the grid commutator 1 of the semi-controlled valve group, such as by increasing the firing angle or shifting the phase by controlling the current to zero. As shown in Figure 4(a), the structure of its voltage source converter 2 is as follows: Figure 5 As shown, if Figure 5 The submodule 27 shown adopts Figure 6 The illustrated full-bridge submodule structure, when a DC line fault occurs, suppresses the current flowing into the fault point by reducing the DC voltage of the voltage source converter 2 of the fully controlled valve group, such as by controlling the current to zero. Figure 4(b) and 4(c) As shown, the structure of its voltage source converter 2 is as follows: Figure 5 As shown, if Figure 5 The submodule 27 shown adopts Figure 7 The half-bridge sub-module structure shown suppresses the current flowing into the fault point by controlling the DC circuit breaker 7 of the fully controlled valve group or / and the DC circuit breaker 7 of the uncontrolled valve group to turn off when a DC line fault occurs.

[0137] After the deionization time, the hybrid DC transmission valve group is restarted by controlling the firing angle of the grid commutator 1 of the semi-controlled valve group, or by increasing the DC voltage of the voltage source converter 2 of the fully controlled valve group, or by controlling the DC circuit breaker 7 of the fully controlled valve group and / or the uncontrolled valve group to conduct.

[0138] When the semi-controlled valve assembly fails, the bypass circuit controlling the semi-controlled valve assembly is activated, i.e., the control... Figure 2 When the bypass switch 3 shown is turned on, the AC switch of the converter transformer of the semi-controlled valve group is tripped, blocking the grid commutator 1, i.e., stopping the trigger pulse, and isolating the grid commutator 1 through the isolation circuit, thus controlling... Figure 2 After the bypass switch 4 shown is turned on, it separates. Figure 2 The first isolating switch 5 and the second isolating switch 6 are shown.

[0139] When the fully controlled valve group fails, the bypass circuit of the fully controlled valve group is activated, that is, the bypass switch 3 shown in Figures 4(a), 4(b), and 4(c) is activated, tripping the AC switch of the converter transformer of the fully controlled valve group, blocking the voltage source converter 2, that is, stopping the trigger pulse, and isolating the voltage source converter 2 through the isolation circuit, thus controlling... Figure 2 After the bypass switch 4 shown is turned on, it separates. Figure 2 The first isolating switch 5 and the second isolating switch 6 are shown.

[0140] When the uncontrolled valve group fails, the bypass circuit controlling the uncontrolled valve group is activated, that is, the bypass switch 3 shown in Figures 4(a), 4(b), and 4(c) is activated, tripping the AC switch of the converter transformer of the uncontrolled valve group, and isolating the bridge uncontrolled rectifier circuit 11 through the isolation circuit, that is, controlling... Figure 2 After the bypass switch 4 shown is turned on, it separates. Figure 2 The first isolating switch 5 and the second isolating switch 6 are shown.

[0141] When the fully controlled valve group or the semi-controlled valve group of the hybrid DC transmission valve group includes a DC circuit breaker, the above control method further includes: when the fully controlled valve group fails, the DC circuit breaker 7 is disconnected, and the DC current of the fully controlled valve group continues through the bypass circuit, that is, through the bypass diode valve 8 in Figures 4(b) and 4(c); when the uncontrolled valve group fails, the DC circuit breaker 7 is disconnected, and the DC current of the uncontrolled valve group continues through the bypass circuit, that is, through the bypass diode valve 8 in Figures 4(b) and 4(c).

[0142] When the aforementioned hybrid DC transmission valve group is connected to a high-proportion new energy power system, the voltage source converter of the fully controlled valve group adopts a grid-following strategy or a grid-connected control strategy.

[0143] If the converter transformer connected to the uncontrolled valve group has a tap that adjusts the voltage ratio of the grid side and the valve side, the tap is used to control the valve side voltage of the uncontrolled valve group. That is, when the grid side voltage increases, the tap position is adjusted to reduce the increase of the valve side voltage; when the grid side voltage decreases, the tap position is adjusted to reduce the decrease of the valve side voltage.

[0144] Semi-controlled valve groups reduce grid-side voltage fluctuations by adjusting the firing angle or switching AC filters; or fully controlled valve groups reduce grid-side voltage fluctuations by regulating reactive power.

[0145] Figure 12 This is a schematic diagram of a DC transmission system according to an embodiment of this application, to... Figure 12 Taking pole I of a DC transmission system as an example, the initial state is that the first high-end uncontrolled valve group 111 and the first low-end semi-controlled valve group 112 of the rectifier station 100 are in operation, and the third high-end semi-controlled valve group 211 and the third low-end semi-controlled valve group 212 of the inverter station 200 are in operation. The first bypass disconnect switch 14 of the rectifier station 100 is open, the first bypass switch 13 is open, the first isolating disconnect switch 15 is closed, the first isolating disconnect switch 16 is closed, the bypass disconnect switch 4 is open, the bypass switch 3 is open, the first isolating disconnect switch 5 is closed, and the second isolating disconnect switch 6 is closed. The third bypass disconnect switch 51 of the inverter station 200 is open, the third bypass switch 52 is open, the fourth isolating disconnect switch 53 is closed, the fourth isolating disconnect switch 54 is closed, the fourth bypass disconnect switch 61 is open, the fourth bypass switch 62 is open, the fifth isolating disconnect switch 63 is closed, and the fifth isolating disconnect switch 64 is closed.

[0146] Rectifier station 100 controls the rectifier operation of grid phase-commutator 1. Inverter station 200 controls the inverter operation of the third grid phase-commutator 201 and the fourth grid phase-commutator 202.

[0147] When the grid-side voltage of the converter transformer 116 connected to the uncontrolled valve group increases, the firing angle of the grid-commutated converter 1 is controlled to reduce the DC voltage; at the same time, the tap position of the converter transformer 116 is adjusted to reduce the increase in the valve-side voltage, thereby suppressing the increase in DC voltage. When the grid-side voltage decreases, the firing angle of the grid-commutated converter 1 is controlled to increase the DC voltage; at the same time, the tap position of the converter transformer 116 is adjusted to reduce the decrease in the valve-side voltage, thereby suppressing the decrease in DC voltage.

[0148] When a DC fault occurs in the bridge uncontrolled rectifier circuit 11 or the grid-commutated converter 1 of the rectifier station 100, the firing angle of the grid-commutated converter 1 is controlled to suppress the fault current. After the fault is recovered or after the deionization time, the DC voltage of the grid-commutated converter 1 is increased. When a DC fault occurs in the third grid-commutated converter 201 or the fourth grid-commutated converter 202 of the inverter station 200, no reverse DC current will flow, thus possessing DC fault ride-through capability.

[0149] When the bridge uncontrolled rectifier circuit 11 of rectifier station 100 is disconnected from the line, the first converter transformer incoming switch 131 is tripped, the bridge uncontrolled rectifier circuit 11 resumes current, and the first bypass switch 13 is closed. When the grid-commutated converter 1 of rectifier station 100 is disconnected from the line, the DC voltage is controlled to zero, the bypass switch 3 is closed, and the grid-commutated converter 1 is locked. When the third grid-commutated converter 201 of inverter station 200 is disconnected from the line, the DC voltage is controlled to zero, the third bypass switch 52 is closed, and the third grid-commutated converter 201 is locked.

[0150] When the bridge uncontrolled rectifier circuit 11 of rectifier station 100 fails and exits, the first converter transformer incoming line switch 131 is tripped, the first bypass switch 13 is closed, the first bypass disconnect switch 14 is closed, and the first bypass switch 13, the first isolation disconnect switch 15, and the first isolation disconnect switch 16 are separated. When the grid phase-commutation converter 1 of rectifier station 100 fails and exits, the bypass switch 3 is closed, the AC switch 132 of converter transformer 117 is tripped, the grid phase-commutation converter 1 is locked, the bypass disconnect switch 4 is closed, and the bypass switch 3, the first isolation disconnect switch 5, and the second isolation disconnect switch 6 are separated. When the third grid phase converter 201 of inverter station 200 fails and exits, the third bypass switch 52 is closed, the AC switch 231 of converter transformer 216 is tripped, the third grid phase converter 201 is locked, the third bypass switch 52 is closed, the third bypass disconnect switch 51 is closed, and the third bypass switch 52, the fourth first isolation disconnect switch 53 and the fourth second isolation disconnect switch 54 are separated.

[0151] When the bridge uncontrolled rectifier circuit 11 of rectifier station 100 is connected online, the first bypass switch 13 is opened, the current is transferred to the bridge uncontrolled rectifier circuit 11, and the first converter transformer incoming switch 131 is closed. When the grid-commutated converter 1 of rectifier station 100 is connected online, the grid-commutated converter 1 is unlocked, and after the current is transferred to the grid-commutated converter 1, the bypass switch 3 is opened. When the third grid-commutated converter 201 of inverter station 200 is connected online, the third grid-commutated converter 201 is unlocked, and after the current is transferred to the third grid-commutated converter 201, the third bypass switch 52 is opened.

[0152] Example 5:

[0153] Based on the control method disclosed in Embodiment 4, Embodiment 5 of this application provides a control device 300 for executing the method described in Embodiment 5, such as... Figure 15 As shown, the control device 300 includes:

[0154] The detection unit 310 is used to detect the operating parameters and fault data of the hybrid DC transmission valve group;

[0155] The control unit 320 is used to control the semi-controlled valve group or the fully controlled valve group to operate in rectification mode based on the operating parameters and fault data detected by the detection unit 310; control the uncontrolled valve group to operate in uncontrolled rectification mode; when an AC system fault may cause the DC voltage of the uncontrolled valve group to drop or rise, maintain the stability of the DC voltage or current in the hybrid DC transmission valve group by increasing or decreasing the DC voltage of the semi-controlled valve group or the fully controlled valve group; when a DC line fault occurs, suppress the current flowing into the fault point by controlling the firing angle of the grid commutation converter of the semi-controlled valve group, or by decreasing the DC voltage of the fully controlled valve group, or by controlling the DC circuit breaker of the fully controlled valve group or the semi-controlled valve group to turn off.

[0156] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0157] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working processes of the systems, devices, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here.

[0158] In the several embodiments provided in this application, it should be understood that the disclosed systems, apparatuses, and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between apparatuses or units may be electrical, mechanical, or other forms.

[0159] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0160] In addition, the functional units in the various embodiments of this application can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit.

[0161] If a function is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the methods of the various embodiments of this application.

[0162] The aforementioned storage media include: USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, optical disks, and other media that can store program code.

[0163] The above are merely specific embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A hybrid DC transmission valve assembly, characterized in that: include: An uncontrolled valve assembly, the uncontrolled valve assembly including a bridge-type uncontrolled rectifier circuit; And a semi-controlled valve group or a fully controlled valve group, wherein the semi-controlled valve group includes a grid phase-commutation converter; and the fully controlled valve group includes a voltage source converter. Wherein, when the semi-controlled valve group is connected in series with the uncontrolled valve group, the anode of the semi-controlled valve group is connected to the cathode of the uncontrolled valve group, or the cathode of the semi-controlled valve group is connected to the anode of the uncontrolled valve group; The fully controlled valve group is connected in series with the uncontrolled valve group. The negative terminal of the fully controlled valve group is connected to the cathode of the uncontrolled valve group, or the positive terminal of the fully controlled valve group is connected to the anode of the uncontrolled valve group. When the fully controlled valve group is connected in series with the uncontrolled valve group, if the fully controlled valve group cannot adjust the DC voltage to a negative voltage, both the fully controlled valve group and the uncontrolled valve group include a DC circuit breaker and a bypass diode valve. When the fully controlled valve group is connected in series with the uncontrolled valve group, if the fully controlled valve group can adjust the DC voltage to a negative voltage but cannot adjust the rated DC voltage of the uncontrolled valve group to a negative DC voltage, the uncontrolled valve group includes a DC circuit breaker and a bypass diode valve. The semi-controlled valve group, the fully controlled valve group, and the uncontrolled valve group all include a bypass isolation circuit; In the fully controlled valve group: the DC circuit breaker is connected in series with the positive terminal of the voltage source converter to form a series circuit of the voltage source converter and the DC circuit breaker; the bypass diode valve is connected in parallel with the voltage source converter and the DC circuit breaker, that is, the anode of the bypass diode valve is connected to the negative terminal of the voltage source converter, and the cathode of the bypass diode valve is connected to the other end of the series circuit of the voltage source converter and the DC circuit breaker; Alternatively, the DC circuit breaker is connected in series with the negative terminal of the voltage source converter to form a series circuit of the voltage source converter and the DC circuit breaker; the bypass diode valve is connected in parallel with the series circuit of the voltage source converter and the DC circuit breaker, that is, the cathode of the bypass diode valve is connected to the positive terminal of the voltage source converter, and the anode of the bypass diode valve is connected to the other end of the series circuit of the voltage source converter and the DC circuit breaker; In the uncontrolled valve group: the DC circuit breaker is connected in series with the positive terminal of the bridge uncontrolled rectifier circuit to form a bridge uncontrolled rectifier circuit and a DC circuit breaker series circuit; the bypass diode valve is connected in parallel with the bridge uncontrolled rectifier circuit and the DC circuit breaker series circuit, that is, the anode of the bypass diode valve is connected to the negative terminal of the bridge uncontrolled rectifier circuit, and the cathode of the bypass diode valve is connected to the other end of the bridge uncontrolled rectifier circuit and the DC circuit breaker series circuit; Alternatively, the DC circuit breaker is connected in series with the negative terminal of the bridge uncontrolled rectifier circuit to form a series circuit of the bridge uncontrolled rectifier circuit and the DC circuit breaker; the bypass diode valve is connected in parallel with the bridge uncontrolled rectifier circuit and the DC circuit breaker series circuit, that is, the cathode of the bypass diode valve is connected to the positive terminal of the bridge uncontrolled rectifier circuit, and the anode of the bypass diode valve is connected to the other end of the series circuit of the bridge uncontrolled rectifier circuit and the DC circuit breaker.

2. The hybrid DC transmission valve assembly according to claim 1, characterized in that: The fully controlled valve group or the uncontrolled valve group further includes a bypass diode valve and / or a DC circuit breaker.

3. The hybrid DC transmission valve assembly according to claim 1, characterized in that: Both the fully controlled valve group and the uncontrolled valve group further include a resistor or surge arrester, and a bypass switch connected in parallel across the resistor or surge arrester. The circuit consisting of the resistor or surge arrester and the bypass switch connected in parallel is connected in series with a bypass diode valve.

4. The hybrid DC transmission valve assembly according to claim 1, characterized in that: The grid phase-commutation converter, the voltage source converter, and the bridge uncontrolled rectifier circuit are all connected in parallel to a bypass isolation circuit.

5. The hybrid DC transmission valve assembly according to claim 4, characterized in that: The bypass isolation circuit includes a bypass circuit and an isolation circuit.

6. The hybrid DC transmission valve assembly according to claim 5, characterized in that: The bypass circuit includes a bypass switch and a bypass knife switch, which are connected in parallel.

7. The hybrid DC transmission valve assembly according to claim 6, characterized in that: The isolation circuit includes two isolation switches, and an isolation switch is provided at each of the two connection nodes of the bypass switch and the bypass switch.

8. The hybrid DC transmission valve assembly according to claim 7, characterized in that: In the semi-controlled valve group: the two isolating switches are connected in series with the cathode and anode of the grid phase-commutation converter, respectively; the two ends of the bypass switch are connected to the ends of the two isolating switches that are away from the grid phase-commutation converter, respectively. In the fully controlled valve group: the two isolating switches are connected in series with the positive and negative terminals of the voltage source converter, or the voltage source converter and the DC circuit breaker, respectively; the two ends of the bypass switch are connected to the ends of the two isolating switches that are away from the voltage source converter. In the uncontrolled valve group: the two isolating switches are connected in series with the positive and negative terminals of the bridge uncontrolled rectifier circuit, or the bridge uncontrolled rectifier circuit and the DC circuit breaker series circuit, respectively; the two ends of the bypass switch are respectively connected to the ends of the two isolating switches away from the bridge uncontrolled rectifier circuit.

9. The hybrid DC transmission valve assembly according to claim 1, characterized in that: The power grid phase-commutation converter includes a six-pulse bridge circuit or a twelve-pulse bridge circuit. The six-pulse bridge circuit or the twelve-pulse bridge circuit includes non-turn-off semi-controlled power semiconductors.

10. The hybrid DC transmission valve assembly according to claim 1, characterized in that: The voltage source converter includes 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 is composed of half-bridge sub-modules, full-bridge sub-modules, or a combination of hybrid sub-modules. The hybrid submodule includes the half-bridge submodule and the full-bridge submodule.

11. The hybrid DC transmission valve assembly 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. The six-pulse bridge circuit or the twelve-pulse bridge circuit includes uncontrolled power semiconductors.

12. A DC transmission system, characterized in that: Includes the hybrid DC transmission valve assembly as described in any one of claims 1 to 11.

13. The DC transmission system according to claim 12, characterized in that: The grid phase-commutation converter of the semi-controlled valve group, the voltage source converter of the fully controlled valve group, and the bridge uncontrolled rectifier circuit of the uncontrolled valve group are all connected to the AC system via converter transformers. The converter transformer includes a tap changer, which is used to adjust the grid-side voltage and valve-side voltage ratio.

14. A control method for a hybrid DC transmission valve group in a DC transmission system, characterized in that: The hybrid DC transmission valve assembly is a hybrid DC transmission valve assembly as described in any one of claims 1 to 11, and the control method includes the following steps: Semi-controlled or fully controlled valve groups operate in rectification mode, while uncontrolled valve groups operate in uncontrolled rectification mode. If the DC voltage of the uncontrolled valve group changes, the DC voltage of the semi-controlled valve group or the fully controlled valve group is adjusted to maintain the stability of the DC voltage or current in the hybrid DC transmission valve group. The adjustment direction of the DC voltage of the semi-controlled valve group or the fully controlled valve group is opposite to the direction of change of the DC voltage of the uncontrolled valve group. If a fault occurs in the DC line and an inrush current flows into the fault point, the firing angle of the grid commutation converter of the semi-controlled valve group is controlled, the DC voltage of the voltage source converter of the fully controlled valve group is reduced, and / or the DC circuit breaker of the fully controlled valve group or the uncontrolled valve group is turned off to suppress the inrush current flowing into the fault point.

15. The control method for a hybrid DC transmission valve group in a DC transmission system according to claim 14, characterized in that: The control method further includes: If the semi-controlled valve group fails, the bypass circuit of the semi-controlled valve group is turned on, the grid-side AC switch of the semi-controlled valve group is turned off, the grid phase-commutation converter is locked, and the grid phase-commutation converter is isolated through the isolation circuit of the semi-controlled valve group.

16. The control method for a hybrid DC transmission valve group in a DC transmission system according to claim 14, characterized in that: The control method further includes: If the fully controlled valve group fails, disconnect the AC switch of the fully controlled valve group, control the bypass circuit of the fully controlled valve group to conduct, lock the voltage source converter, and isolate the voltage source converter through the isolation circuit of the fully controlled valve group.

17. The control method for a hybrid DC transmission valve group in a DC transmission system according to claim 14, characterized in that: The control method further includes: If the uncontrolled valve group fails, disconnect the AC switch of the uncontrolled valve group, control the bypass circuit of the uncontrolled valve group to conduct, and isolate the bridge uncontrolled rectifier circuit through the isolation circuit of the uncontrolled valve group.

18. The control method for a hybrid DC transmission valve group in a DC transmission system according to claim 14, characterized in that: The control method further includes: If the fully controlled valve group or the semi-controlled valve group fails, the DC circuit breaker in the fully controlled valve group or the semi-controlled valve group is disconnected, and the DC current of the fully controlled valve group or the semi-controlled valve group continues through the bypass diode valve of the fully controlled valve group or the semi-controlled valve group.

19. The control method for a hybrid DC transmission valve group in a DC transmission system according to claim 14, characterized in that: The control method further includes: If the hybrid DC transmission valve group is connected to a high-proportion new energy power system, the voltage source converter of the fully controlled valve group operates based on a grid-type control strategy.

20. The control method for a hybrid DC transmission valve group in a DC transmission system according to claim 14, characterized in that: The control method further includes: In the uncontrolled valve group: the tap of the uncontrolled valve group controls the valve-side voltage of the uncontrolled valve group: When the grid voltage increases, adjust the tap position to reduce the increase in valve-side voltage; when the grid voltage decreases, adjust the tap position to reduce the decrease in valve-side voltage, thereby controlling the DC voltage of the uncontrolled valve group within the specified range.

21. The control method for a hybrid DC transmission valve group in a DC transmission system according to claim 14, characterized in that: The control method further includes: The semi-controlled valve group reduces grid-side voltage fluctuations by adjusting the firing angle or switching AC filters; or the fully controlled valve group reduces grid-side voltage fluctuations by adjusting reactive power.

22. A control device, characterized in that: A control method for performing a hybrid DC transmission valve group in a DC transmission system as described in any one of claims 14 to 21, the control device comprising: The detection unit is used to detect the operating parameters and fault data of the hybrid DC transmission valve group; The control unit is used to control the semi-controlled valve group or fully controlled valve group to operate in rectification mode based on the operating parameters and fault data detected by the detection unit; to control the uncontrolled valve group to operate in uncontrolled rectification mode; when an AC system fault may cause the DC voltage of the uncontrolled valve group to drop or rise, to maintain the stability of the DC voltage or current in the hybrid DC transmission valve group by increasing or decreasing the DC voltage of the semi-controlled valve group or fully controlled valve group; when a DC line fault occurs, to suppress the current flowing into the fault point by controlling the firing angle of the grid commutation converter of the semi-controlled valve group, or by decreasing the DC voltage of the fully controlled valve group, or by controlling the DC circuit breaker of the fully controlled valve group or semi-controlled valve group to turn off.

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