Multi-terminal ultra-high voltage direct current power transmission topological structure and operation method

Abstract

The present application relates to a multi-terminal ultra-high voltage direct current power transmission topological structure and an operation method therefor. The multi-terminal ultra-high voltage direct current power transmission topological structure comprises at least one sending end high-voltage end converter station, at least one sending end low-voltage end converter station, and a receiving end converter station. The sending end high-voltage end converter station and the sending end low-voltage end converter station are connected in series by means of a medium-voltage direct current line. A first grounding electrode line which is coupled to a grounding electrode is provided in the sending end high-voltage end converter station, and a second grounding electrode line which is coupled to the grounding electrode is provided in the sending end low-voltage end converter station, respectively. The medium-voltage direct current line, the first grounding electrode line, and the second grounding electrode line form different grounding loops. A metal loop between the sending end low-voltage end converter station and the sending end high-voltage end converter station is a series loop formed by multiplexing the first grounding electrode line and the second grounding electrode line.

Description

A multi-terminal ultra-high voltage direct current transmission topology and operation method

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application is based on the Chinese patent application with application number 202311133224.5, application date September 4, 2023, and application name “A multi-terminal ultra-high voltage direct current transmission topology structure and operation method”, and claims the priority of the Chinese patent application. The entire content of the Chinese patent application is hereby introduced into this disclosure as a reference. Technical Field

[0003] The present application belongs to the technical field of direct current transmission systems, and relates to a cascade converter station for cascaded multi-terminal high-voltage direct current transmission, and a cascaded multi-terminal high-voltage direct current transmission system constructed using the cascade converter station, and specifically to a high-reliability multi-terminal ultra-high voltage direct current transmission grounding electrode line topology structure and operation method. Background Art

[0004] Since the end of the last century, China's direct current transmission industry has developed rapidly, from being technologically backward to being a technological leader, becoming the country in the world with the largest number of direct current projects, the highest voltage level (1100kV), and the most diverse technologies.

[0005] Direct current (HVDC) transmission is a backbone energy transportation channel in my country and plays an irreplaceable role in energy transportation. In response to the development of power electronics technology and the trend toward large-scale grid-connected renewable energy, cascaded multi-terminal HVDC transmission systems are increasingly being tested and applied in engineering applications. Compared to traditional two-terminal HVDC systems, cascaded multi-terminal HVDC transmission enables more flexible and economical power transmission. For example, power can be transmitted from multiple power sources using HVDC transmission technology, branched to connect power sources or loads, or supplied from a single power source to multiple load areas. This approach optimizes the allocation of power resources.

[0006] The equipment configuration in multi-terminal cascaded UHVDC transmission is essentially the same as that in traditional two-terminal DC transmission. For example, converters, smoothing reactors, DC filters, AC filters, and so on are core components of the converter station. These devices are subject to high voltage and high current for extended periods. Therefore, ensuring the operational reliability of the DC system after AC system or equipment failures is a key concern and consideration for multi-terminal DC transmission systems.

[0007] Summary of the Invention

[0008] In response to the above problems, the purpose of this application is to provide a high-reliability multi-terminal ultra-high voltage direct current transmission grounding electrode line topology structure and operation method. This topology structure has the advantages of flexible operation mode, high reliability and high economy, and can improve the direct current transmission operation efficiency of the direct current transmission system.

[0009] To achieve the above objectives, this application adopts the following technical solutions:

[0010] In a first aspect, the present application provides a multi-terminal ultra-high voltage direct current transmission topology structure, comprising: at least one sending-end high-voltage converter station, at least one sending-end low-voltage converter station and a receiving-end converter station; each of the sending-end high-voltage converter station and the sending-end low-voltage converter station is connected in series through a medium-voltage direct current line, and the sending-end high-voltage converter station and the sending-end low-voltage converter station are respectively provided with a first grounding electrode line and a second grounding electrode line coupled to the grounding electrode, the medium-voltage direct current line, the first grounding electrode line and the second grounding electrode line form different grounding loops, and the metal return line between the sending-end low-voltage converter station and the sending-end high-voltage converter station adopts a series loop composed of the reused first grounding electrode line and the second grounding electrode line.

[0011] In some embodiments, the sending-end high-voltage converter station includes a positive pole and a negative pole; the positive pole is provided with a high-voltage converter transformer and a high-voltage converter valve, one side of the high-voltage converter transformer is connected to the sending-end first AC system, and the other side is connected to the AC side of the high-voltage converter valve; the DC side of the high-voltage converter valve is provided with a first high-voltage PLC reactor, a second high-voltage PLC reactor, a first high-voltage smoothing reactor, a second high-voltage smoothing reactor, a high-voltage DC filter and a high-voltage bypass switch; the first high-voltage PLC reactor and the first high-voltage smoothing reactor are sequentially arranged at the high-voltage end of the DC side of the high-voltage converter valve, and the second high-voltage PLC reactor and The second high-voltage-end smoothing reactor is sequentially arranged at the low-voltage end of the DC side of the high-voltage-end converter valve; the high-voltage-end bypass switch is arranged in parallel between the high-voltage end and the low-voltage end of the high-voltage-end converter valve, and is located between the high-voltage-end PLC reactor and the high-voltage-end smoothing reactor; the high-voltage-end DC filter is arranged in parallel between the high-voltage end and the low-voltage end of the high-voltage-end converter valve, and is located after the high-voltage-end smoothing reactor; the high-voltage end of the high-voltage-end converter valve is connected to the receiving-end converter station via a high-voltage DC line, the low-voltage end of the high-voltage-end converter valve is connected to the sending-end low-voltage converter station, and the low-voltage end of the high-voltage-end converter valve is also coupled to the grounding electrode via the first grounding electrode line; the negative electrode structure is the same as the positive electrode structure.

[0012] In some embodiments, the sending-end low-voltage converter station includes a positive pole and a negative pole, and the positive pole is provided with a low-voltage converter transformer and a low-voltage converter valve; one side of the low-voltage converter transformer is connected to the sending-end first AC system, and the other side is connected to the AC side of the low-voltage converter valve; the DC side of the low-voltage converter valve is provided with a first low-voltage PLC reactor, a second low-voltage PLC reactor, a first low-voltage smoothing reactor, a second low-voltage smoothing reactor, a low-voltage DC filter and a low-voltage bypass switch; the first low-voltage PLC reactor and the first low-voltage smoothing reactor are sequentially arranged at the high-voltage end of the DC side of the low-voltage converter valve, and the second low-voltage PLC reactor is arranged at the high-voltage end of the DC side of the low-voltage converter valve. The high-voltage-end PLC reactor and the second low-voltage-end smoothing reactor are sequentially arranged at the low-voltage end of the DC side of the low-voltage-end converter valve; the low-voltage-end bypass switch is arranged in parallel between the high-voltage end and the low-voltage end of the low-voltage-end converter valve, and is located between the low-voltage-end PLC reactor and the low-voltage-end smoothing reactor; the low-voltage-end DC filter is arranged in parallel between the high-voltage end and the low-voltage end of the low-voltage-end converter valve, and is located after the low-voltage-end smoothing reactor; the high-voltage end of the low-voltage-end converter valve is connected to the low-voltage end of the sending-end high-voltage converter station via the medium-voltage DC line, and the low-voltage end of the low-voltage-end converter valve is coupled to the grounding electrode via the second grounding electrode line; the negative electrode structure is the same as the positive electrode structure.

[0013] In some embodiments, the voltage level of the sending-end low-voltage converter station is not less than 400kV, the low-voltage end of the DC side of the sending-end high-voltage converter station and the high-voltage end of the DC side of the sending-end low-voltage converter station are connected through a medium-voltage DC line with a voltage level of not less than 400kV, and isolation switches for isolation are provided at both ends of the medium-voltage DC line.

[0014] In some embodiments, the different grounding loops composed of the medium-voltage DC line, the first grounding electrode line, and the second grounding electrode line include: the low-voltage end of the DC side of the sending-end high-voltage converter station is grounded in series through the medium-voltage DC line and the second grounding electrode line; the low-voltage end of the DC side of the high-voltage converter station is grounded through the first grounding electrode line; the low-voltage end of the DC side of the high-voltage converter station is grounded through two parallel grounding loops, one parallel grounding loop is composed of the medium-voltage DC line and the second grounding electrode line in series, and the other grounding loop is composed of the first grounding electrode line alone.

[0015] In some embodiments, the metal return line between the sending-end low-voltage converter station and the sending-end high-voltage converter station adopts a series loop composed of the reused first grounding electrode line and the second grounding electrode line, including: when the high-voltage end converter valve of any pole at the sending end operates alone, the low-voltage end of the high-voltage end converter valve is connected in series through the medium-voltage DC line, the low-voltage end bypass switch, the second grounding electrode line, the first grounding electrode line, and the other pole DC line to form a high-voltage end metal return line path; when the high-voltage end converter valve and the low-voltage end converter valve of any pole at the sending end operate in series, the low-voltage end of the low-voltage end converter valve is connected in series through the second grounding electrode line, the first grounding electrode line, and the other pole DC line to form a metal return line path.

[0016] In some embodiments, the receiving end converter station is provided with a metal return line transfer switch and an earth return line transfer switch. The metal return line transfer switch is arranged at one end of the grounding electrode line close to the positive and negative pole coupling point, and the earth return line transfer switch is arranged at one end of the positive and negative pole line jumper coupling point. The metal return line transfer switch and the earth return line transfer switch are used to realize the conversion between single-pole and single-pole metal operation modes.

[0017] In a second aspect, the present application provides an operating method for the multi-terminal ultra-high voltage direct current transmission grounding electrode line topology structure, comprising the following steps: determining the operating mode of the multi-terminal ultra-high voltage direct current transmission topology structure when only one of the grounding electrode lines of the high-voltage end converter station at the sending end or the grounding electrode lines of the low-voltage end converter station at the sending end is put into operation; determining the operating mode of the multi-terminal ultra-high voltage direct current transmission topology structure when both the grounding electrode lines of the high-voltage end converter station at the sending end or the grounding electrode lines of the low-voltage end converter station at the sending end are put into operation.

[0018] In some embodiments, when it is determined that only one of the grounding electrode lines of the sending-end high-voltage converter station or the sending-end low-voltage converter station is put into operation, the operating modes of the multi-terminal ultra-high voltage direct current transmission topology structure include 77 operating modes: full voltage of double-pole loop, full voltage of single-pole metallic loop, full voltage of single-pole loop, mixed voltage of double-pole loop, half voltage of double-pole loop, half voltage of single-pole metallic loop, and half voltage of single-pole loop.

[0019] In some embodiments, when the grounding electrode line of the sending-end high-voltage converter station or the grounding electrode line of the sending-end low-voltage converter station is determined to be put into operation, the operating mode of the multi-terminal ultra-high voltage direct current transmission topology structure includes at least 113 operating modes including bipolar, monopolar, and monopolar metal.

[0020] Due to the adoption of the above technical solution, this application has the following advantages:

[0021] 1. This application improves the traditional DC transmission system transmission topology with a multi-terminal form, which has the advantages of flexible operation, high reliability and high economy;

[0022] 2. The topological structure of the present application has the characteristics of simple and clear steps in use. It applies multiple operation modes for the two-terminal grounded electrode line, so that the DC transmission system can achieve high DC transmission operation efficiency.

[0023] 3. The topology structure and usage method of this application provide a very valuable reference for the subsequent main wiring design of multi-terminal DC and can be widely used in multi-terminal DC transmission systems.

[0024] Therefore, the present application can be widely applied in the technical field of direct current transmission systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] FIG1 is a schematic diagram of a high-reliability multi-terminal ultra-high voltage direct current transmission topology structure provided by an embodiment of the present application;

[0026] FIG2 is a simplified diagram of the main wiring of the sending-end DC system provided in an embodiment of the present application;

[0027] Figures 3-1 to 3-77 show 77 operating modes provided by the embodiments of the present application through the neutral line area equipment and grounding electrode lines of the high-end and low-end converter stations;

[0028] FIG4 is a simplified diagram of the main loop of the metal loop multiplexing grounding electrode line provided in an embodiment of the present application. DETAILED DESCRIPTION

[0029] To make the purpose, technical solutions, and advantages of the embodiments of the present application more clear, the technical solutions of the embodiments of the present application will be clearly and completely described below in conjunction with the drawings of the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the described embodiments of the present application, all other embodiments obtained by ordinary technicians in this field fall within the scope of protection of this application.

[0030] In the description of this application, it should be understood that the terms "upper", "lower", "inside", "outside", etc. indicate orientations or positional relationships based on the orientations or positional relationships 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, be constructed and operated in a specific orientation. Therefore, they cannot be understood as limitations on this application.

[0031] The embodiment of the present application provides a multi-terminal ultra-high voltage direct current transmission topology structure. Taking the three-terminal project of the sending end as an example, it includes a sending end high-voltage end converter station, a sending end low-voltage end converter station, and a receiving end converter station. Among them, the sending end high-voltage end converter station and the sending end low-voltage end converter station are connected in series through a DC line, and the sending end high-voltage end converter station and the sending end low-voltage end converter station are both provided with a grounding electrode line coupled to the grounding electrode, with multiple grounding methods. At the same time, the metal return line reuses the grounding electrode line, and no separate metal return line is required. In this topology structure, any failure of the high-voltage end grounding electrode line or the low-voltage end grounding electrode line will not cause the DC system to stop operating.

[0032] Correspondingly, in other embodiments of the present application, a method for operating a multi-terminal ultra-high voltage direct current transmission topology structure is provided.

[0033] Example 1

[0034] As shown in Figures 1 and 2, this embodiment provides a multi-terminal UHVDC transmission topology. Taking a three-terminal project with a sending-end split-address cascade as an example, the structure includes a sending-end high-voltage converter station 1, a sending-end low-voltage converter station 2, and a receiving-end converter station 3. The sending-end high-voltage converter station 1 and the sending-end low-voltage converter station 2 are connected in series via a medium-voltage DC line. Each of the sending-end high-voltage converter station 1 and the sending-end low-voltage converter station 2 is provided with a first grounding electrode line 5 and a second grounding electrode line 6 coupled to a grounding electrode 4. The medium-voltage DC line, the first grounding electrode line, and the second grounding electrode line form different grounding loops. Meanwhile, the metallic return line reuses the series loop formed by the first grounding electrode line 5 and the second grounding electrode line 6, eliminating the need for a separate metallic return line.

[0035] In some embodiments, the sending-end high-voltage converter station 1 includes a positive pole and a negative pole, and the positive pole is provided with a high-voltage converter transformer 11 and a high-voltage converter valve 12, wherein one side of the high-voltage converter transformer 11 is connected to the sending-end first AC system 13, and the other side is connected to the AC side of the high-voltage converter valve 12; the DC side of the high-voltage converter valve 12 is provided with a first high-voltage PLC reactor 14, a second high-voltage PLC reactor 15, a high-voltage smoothing reactor 16, a high-voltage DC filter 17 and a high-voltage bypass switch 18, and the first high-voltage PLC reactor 14 and the high-voltage smoothing reactor 16 are sequentially arranged at the high-voltage end of the DC side of the high-voltage converter valve 12, and the second high-voltage PLC reactor 15 is connected to the AC side of the high-voltage converter valve 12. Two high-voltage PLC reactors 15 are installed on the low-voltage side of the DC side of the high-voltage converter valve 12. A high-voltage bypass switch 18 is installed in parallel between the high-voltage and low-voltage sides of the high-voltage converter valve 12, and between the high-voltage PLC reactor and the high-voltage smoothing reactor. A high-voltage DC filter 17 is installed in parallel between the high-voltage and low-voltage sides of the high-voltage converter valve 12, and after the high-voltage smoothing reactor 16. The high-voltage side of the high-voltage converter valve 12 is connected to the receiving-end converter station 3 via a DC line, and the low-voltage side of the high-voltage converter valve 12 is connected to the sending-end low-voltage converter station 2. The low-voltage side of the high-voltage converter valve 12 is also coupled to the ground electrode 4 via the first grounding electrode line 5. The negative electrode structure is the same as the positive electrode structure.

[0036] In practice, the smoothing reactor can be a single unit or multiple units connected in series; wherein, the smoothing reactor can be configured at each converter station or at some converter stations according to the length of the DC line.

[0037] In some embodiments, the sending-end high-voltage converter station 1 is an 800kV converter station, which is connected to the receiving-end converter station through an 800kV DC line.

[0038] In some embodiments, the sending-end low-voltage converter station 2 includes a positive pole and a negative pole, and the positive pole is provided with a low-voltage converter transformer 21 and a low-voltage converter valve 22. One side of the low-voltage converter transformer 21 is connected to the sending-end first AC system 23, and the other side is connected to the AC side of the low-voltage converter valve 22; the DC side of the low-voltage converter valve 22 is provided with a first low-voltage PLC reactor 24, a second low-voltage PLC reactor 25, a first low-voltage smoothing reactor 26, a second low-voltage smoothing reactor 27, a low-voltage DC filter 28 and a low-voltage bypass switch 29, and the first low-voltage PLC reactor 24 and the first low-voltage smoothing reactor 26 are sequentially provided at the high-voltage end of the DC side of the low-voltage converter valve 22, and the second low-voltage PLC reactor 25 and A second low-voltage smoothing reactor 27 is sequentially arranged at the low-voltage end of the DC side of the low-voltage converter valve 22. A low-voltage bypass switch 29 is arranged in parallel between the high-voltage and low-voltage ends of the low-voltage converter valve, and between the low-voltage PLC reactor and the low-voltage smoothing reactor. A low-voltage DC filter 28 is arranged in parallel between the high-voltage and low-voltage ends of the low-voltage converter valve 22, and after the low-voltage smoothing reactor. The high-voltage end of the low-voltage converter valve 22 is connected to the low-voltage end of the sending-end high-voltage converter station 1 via a medium-voltage DC line, and the low-voltage end of the low-voltage converter valve 22 is coupled to the ground electrode 4 via a second grounding electrode line 6. The negative electrode structure is identical to the positive electrode structure and will not be further described in this application.

[0039] Bypass channels are set up in the positive and negative poles of the sending-end high-voltage converter station 1 and the sending-end low-voltage converter station 2, and the 800kV and 400kV and 400kV to neutral line areas. Bypass switches are set in the bypass channels. When the smoothing inductor, converter valve or DC filter of a converter station fails, the bypass channel can be opened to enable the high-end or low-end converter station to operate normally.

[0040] In some embodiments, in the sending-end high-voltage converter station 1 and the sending-end low-voltage converter station 2, the smoothing reactor can be a single unit or multiple units connected in series; wherein, the smoothing reactor can be configured at each converter station or at some converter stations according to the length of the DC line.

[0041] In some embodiments, the sending-end low-voltage converter station 2 is a 400kV converter station, and the low-voltage end of the DC side of the sending-end high-voltage converter station 1 is connected to the high-voltage end of the DC side of the sending-end low-voltage converter station 2 through a 400kV DC line, and an isolating switch 7 for isolation is provided at both ends of the DC line.

[0042] In some embodiments, the receiving-end converter station 3 is provided with a metal return line transfer switch and an earth return line transfer switch. The metal return line transfer switch is provided at one end of the grounding electrode line close to the positive and negative pole coupling point, and the earth return line transfer switch is provided at one end of the positive and negative pole line jumper coupling point; the sending-end high-voltage converter station 1 and the sending-end low-voltage converter station 2 are not provided with transfer switches, and the metal return line transfer switch and the earth return line transfer switch are used to realize the conversion between single-pole and single-pole metal operation modes.

[0043] In some embodiments, the different grounding loops formed by the medium voltage DC line, the first grounding electrode line, and the second grounding electrode line include:

[0044] The low-voltage end of the DC side of the high-voltage converter station at the sending end is grounded in series through the medium-voltage DC line and the second grounding electrode line;

[0045] The low-voltage end of the DC side of the high-voltage converter station is grounded through the first grounding electrode line;

[0046] The low-voltage end of the DC side of the high-voltage converter station is grounded through two parallel grounding loops. One parallel grounding loop is composed of a medium-voltage DC line and a second grounding electrode line in series, and the other grounding loop is composed of a first grounding electrode line alone.

[0047] In some embodiments, the metal return line between the sending-end low-voltage converter station and the sending-end high-voltage converter station adopts a series loop composed of the first grounding electrode line and the second grounding electrode line, including:

[0048] When the high-voltage converter valve at any pole of the sending end operates alone, the low-voltage end of the high-voltage converter valve is connected in series through the medium-voltage DC line, the low-voltage bypass switch, the second grounding electrode line, the first grounding electrode line, and the other pole DC line to form a high-voltage metal return path;

[0049] When the high-pressure end converter valve and the low-pressure end converter valve of any pole at the sending end are operated in series, the low-pressure side of the low-pressure end converter valve is connected in series through the second grounding electrode line, the first grounding electrode line, and the other pole DC line to form a metal return path.

[0050] Example 2

[0051] Based on the multi-terminal UHVDC grounding electrode line topology structure provided in Example 1, this embodiment provides an operation method of the multi-terminal UHVDC topology structure, including the following steps:

[0052] 1) Determine the operating mode of the multi-terminal UHVDC transmission topology when only one grounding electrode line of the high-voltage converter station at the sending end or the grounding electrode line of the low-voltage converter station at the sending end is put into operation;

[0053] 2) Determine the operation mode of the multi-terminal UHVDC transmission topology when the grounding electrode line of the high-voltage converter station at the sending end or the grounding electrode line of the low-voltage converter station at the sending end are both put into operation.

[0054] In some embodiments, in the above step 1), when only the grounding electrode line of the sending-end high-voltage converter station or the grounding electrode line of the sending-end low-voltage converter station is put into operation, the operation modes of the DC transmission system include at least 77 types.

[0055] As shown in Figures 3-1 to 3-77, the embodiments of the present application provide that, without considering the simultaneous operation of the high-end and low-end converter station grounding electrode lines, the operating modes formed by the neutral line area equipment and the grounding electrode lines of the high-end and low-end converter stations can be divided into 7 categories, with a total of 77 operating modes. Specifically, they include: 1 type of full voltage of the double-pole loop; 2 types of full voltage of the single-pole metal loop; 2 types of full voltage of the single-pole loop; 12 types of mixed voltage of the double-pole loop; 36 types of half voltage of the double-pole loop; 12 types of half voltage of the single-pole metal loop; and 12 types of half voltage of the single-pole loop. Specifically, the various operating modes are shown in Table 1 below. The increase in operating modes greatly improves the reliability of DC power operation.

[0056] Table 1 77 operating modes

[0057] In some embodiments, in the above step 2), when only the high-end is in operation, the grounding electrode line of the high-voltage converter station at the sending end and the grounding electrode line of the low-end converter station at the sending end can be put into operation at the same time, so as to realize the parallel connection of the grounding electrode line impedance and effectively reduce the line loss during single-pole operation. At this time, there are as many as 113 operating modes.

[0058] The embodiment of the present application provides a classification of operation modes formed by the neutral line area equipment and the grounding electrode lines of the high-end and low-end converter stations when the grounding electrode lines of the high-end and low-end converter stations are operated simultaneously, as shown in Table 2 below.

[0059] Table 2 Classification of operation modes when grounding electrode line 1 and grounding electrode line 2 are in operation simultaneously

[0060] Please refer to FIG4 , which is a simplified diagram of the main circuit of the metal loop multiplexing grounding electrode line provided in an embodiment of the present application. The main circuit is marked with a dotted line 40 based on the simplified diagram of the main connection of the sending-end DC system provided in FIG2 .

[0061] In a high-reliability multi-terminal UHVDC transmission topology structure provided by the present application, when the normal single-pole double-valve group earth operation of the high-voltage converter station at the sending end and the low-voltage converter station at the sending end is switched to a single-pole double-valve group metal return operation, the high-voltage converter station at the sending end and the low-voltage converter station are connected to the earth of the grounding electrode through the first grounding electrode line, and then switched to the high-voltage converter station at the sending end and the low-voltage converter station being connected to the pole line of the other pole through the second grounding electrode line and the first grounding electrode line to form a metal return operation. At the same time, when the single-valve group of the high-end converter valve at any pole is in operation, it can be connected to the DC pole line of the other pole through the first grounding electrode line to form a metal return loop path, or it can be connected to the DC pole line of the other pole through the medium-voltage DC line, the second grounding electrode line, and the first grounding electrode line to form a metal return loop path.

[0062] Therefore, any fault in the high-voltage end grounding electrode line or the low-voltage end grounding electrode line will not cause the DC transmission system to stop operating; when the grounding electrode line of the high-voltage end converter station at the sending end fails, it will not affect the bipolar full-voltage operation of the DC transmission system; when the grounding electrode line of the low-voltage end converter station at the sending end fails, a current path can still be formed through the grounding electrode line of the high-voltage end converter station at the sending end, that is, bipolar high-half-voltage operation, and the DC power is consistent with the single-pole metal.

[0063] The above embodiments are only used to illustrate the present application, and each step can be changed. On the basis of the technical solution of the present application, any improvements and equivalent transformations of individual steps based on the principles of the present application should not be excluded from the scope of protection of the present application. Industrial Applicability

[0064] The present application relates to a multi-terminal ultra-high voltage direct current transmission topology and its operation method, including: at least one sending-end high-voltage converter station, at least one sending-end low-voltage converter station and a receiving-end converter station; each sending-end high-voltage converter station and each sending-end low-voltage converter station are connected in series via a medium-voltage direct current line, and the sending-end high-voltage converter station and the sending-end low-voltage converter station are respectively provided with a first grounding electrode line and a second grounding electrode line coupled to a grounding electrode, the medium-voltage direct current line, the first grounding electrode line and the second grounding electrode line form different grounding loops, and the metal return line between the sending-end low-voltage converter station and the sending-end high-voltage converter station adopts a series loop composed of a reused first grounding electrode line and a second grounding electrode line. In the topology of the present application, any high-voltage end grounding electrode line or low-voltage end grounding electrode line failure will not cause the DC system to stop operating. The present application can be widely used in the field of direct current transmission technology.

Claims

1. A multi-terminal ultra-high voltage direct current transmission topology structure, wherein: The multi-terminal ultra-high voltage direct current transmission topology structure includes: at least one sending-end high-voltage converter station, at least one sending-end low-voltage converter station and a receiving-end converter station; each of the sending-end high-voltage converter station and the sending-end low-voltage converter station is connected in series through a medium-voltage direct current line, and the sending-end high-voltage converter station and the sending-end low-voltage converter station are respectively provided with a first grounding electrode line and a second grounding electrode line coupled to the grounding electrode, the medium-voltage direct current line, the first grounding electrode line and the second grounding electrode line form different grounding loops, and the metal return line between the sending-end low-voltage converter station and the sending-end high-voltage converter station adopts a series loop composed of the first grounding electrode line and the second grounding electrode line.

2. A multi-terminal ultra-high voltage direct current transmission topology structure according to claim 1, wherein the sending-end high-voltage converter station comprises a positive electrode and a negative electrode; The positive electrode is provided with a high-voltage end converter transformer and a high-voltage end converter valve, one side of the high-voltage end converter transformer is connected to the first AC system at the sending end, and the other side is connected to the AC side of the high-voltage end converter valve; The DC side of the high-voltage end converter valve is provided with a first high-voltage end PLC reactor, a second high-voltage end PLC reactor, a first high-voltage end smoothing reactor, a second high-voltage end smoothing reactor, a high-voltage end DC filter and a high-voltage end bypass switch; The first high-voltage-end PLC reactor and the first high-voltage-end smoothing reactor are sequentially arranged at the high-voltage end of the DC side of the high-voltage-end converter valve, and the second high-voltage-end PLC reactor and the second high-voltage-end smoothing reactor are sequentially arranged at the low-voltage end of the DC side of the high-voltage-end converter valve; The high-voltage side bypass switch is arranged in parallel between the high-voltage side and the low-voltage side of the high-voltage side converter valve, and is located between the high-voltage side PLC reactor and the high-voltage side smoothing reactor; The high-voltage DC filter is arranged in parallel between the high-voltage end and the low-voltage end of the high-voltage converter valve and is located after the high-voltage smoothing reactor; The high-voltage end of the high-voltage converter valve is connected to the receiving-end converter station via a high-voltage DC line, and the low-voltage end of the high-voltage converter valve is connected to the sending-end low-voltage converter station. The low voltage end is also coupled to the ground electrode via the first ground electrode line; The negative electrode structure is the same as the positive electrode structure.

3. A multi-terminal UHV DC transmission topology structure according to claim 2, wherein the sending-end low-voltage converter station comprises a positive electrode and a negative electrode, and the positive electrode is provided with a low-voltage converter transformer and a low-voltage converter valve; One side of the low-voltage end converter transformer is connected to the first AC system at the sending end, and the other side is connected to the AC side of the low-voltage end converter valve; The DC side of the low-voltage converter valve is provided with a first low-voltage PLC reactor, a second low-voltage PLC reactor, a first low-voltage smoothing reactor, a second low-voltage smoothing reactor, a low-voltage DC filter and a low-voltage bypass switch; The first low-voltage end PLC reactor and the first low-voltage end smoothing reactor are sequentially arranged at the high-voltage end of the DC side of the low-voltage end converter valve, and the second low-voltage end PLC reactor and the second low-voltage end smoothing reactor are sequentially arranged at the low-voltage end of the DC side of the low-voltage end converter valve; The low-voltage side bypass switch is arranged in parallel between the high-voltage side and the low-voltage side of the low-voltage side converter valve, and is located between the low-voltage side PLC reactor and the low-voltage side smoothing reactor; The low-voltage DC filter is arranged in parallel between the high-voltage end and the low-voltage end of the low-voltage converter valve and is located after the low-voltage smoothing reactor; The high-voltage end of the low-voltage converter valve is connected to the low-voltage end of the sending-end high-voltage converter station via the medium-voltage DC line, and the low-voltage end of the low-voltage converter valve is coupled to the grounding electrode via the second grounding electrode line; The negative electrode structure is the same as the positive electrode structure.

4. A multi-terminal ultra-high voltage direct current transmission topology structure as described in claim 3, wherein the voltage level of the sending-end low-voltage converter station is not less than 400kV, the low-voltage end of the DC side of the sending-end high-voltage converter station is connected to the high-voltage end of the DC side of the sending-end low-voltage converter station through a medium-voltage DC line with a voltage level of not less than 400kV, and isolation switches for isolation are provided at both ends of the medium-voltage DC line.

5. The multi-terminal UHV DC transmission topology structure according to claim 3, wherein the different grounding loops formed by the medium voltage DC line, the first grounding electrode line, and the second grounding electrode line include: The low-voltage end of the DC side of the sending-end high-voltage converter station is connected to the ground in series via the medium-voltage DC line and the second grounding electrode line; The low voltage end of the DC side of the high voltage end converter station is grounded through the first grounding electrode line; The low-voltage end of the DC side of the high-voltage converter station is grounded through two parallel grounding loops, one of which is composed of a medium-voltage DC line and a second grounding electrode line in series, and the other grounding loop is composed of the first grounding electrode line alone.

6. A multi-terminal UHV DC transmission topology structure according to claim 3, wherein the metal return line between the sending-end low-voltage converter station and the sending-end high-voltage converter station adopts a series loop composed of the first grounding electrode line and the second grounding electrode line, comprising: When the high-voltage converter valve at any pole of the sending end is operated alone, the low-voltage end of the high-voltage converter valve is connected in series through the medium-voltage DC line, the low-voltage bypass switch, the second grounding electrode line, the first grounding electrode line, and the other DC line to form a high-voltage metal return line; When the high-voltage converter valve and the low-voltage converter valve at any pole of the sending end are operated in series, the low-voltage end of the low-voltage converter valve is connected in series through the second grounding electrode line, the first grounding electrode line, and the other pole DC line to form a metal return line.

7. A multi-terminal UHV DC transmission topology structure as claimed in claim 1, wherein the receiving-end converter station is provided with a metal return line conversion switch and an earth return line conversion switch, the metal return line conversion switch is arranged at one end of the grounding electrode line close to the positive and negative electrode coupling point, the earth return line conversion switch is arranged at one end of the positive and negative electrode line jumper coupling point, and the metal return line conversion switch and the earth return line conversion switch are used to realize the conversion between single-pole and single-pole metal operation modes.

8. An operating method of the multi-terminal UHV DC transmission grounding electrode line topology structure according to any one of claims 1 to 7, comprising the following steps: Determine the operation mode of the multi-terminal UHV DC transmission topology structure when only one grounding electrode line of the high-voltage converter station at the sending end or the grounding electrode line of the low-voltage converter station at the sending end is put into operation; Determine the grounding electrode line of the high-voltage converter station at the sending end or the grounding electrode line of the low-voltage converter station at the sending end The operating mode of the multi-terminal UHV DC transmission topology when all are put into operation.

9. The operating method of the multi-terminal UHV DC transmission grounding electrode line topology structure according to claim 8, when determining that only one grounding electrode line of the high-voltage end converter station at the sending end or the grounding electrode line of the low-voltage end converter station at the sending end is put into operation, the operating mode of the multi-terminal UHV DC transmission topology structure includes: There are 77 operating modes including double-pole large loop full voltage, single-pole metal loop full voltage, single-pole large loop full voltage, double-pole large loop mixed voltage, double-pole large loop half voltage, single-pole metal loop half voltage and single-pole large loop half voltage.

10. The method for operating a multi-terminal UHV DC transmission grounding electrode line topology structure according to claim 8, wherein when the grounding electrode line of the high-voltage end converter station at the sending end or the grounding electrode line of the low-voltage end converter station at the sending end is determined to be put into operation, the operating mode of the multi-terminal UHV DC transmission topology structure at least includes: 113 operating modes including bipolar, monopolar, and monopolar metal.

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