Control and protection system for multi-terminal dc transmission in series

Abstract

This application proposes a series multi-terminal DC transmission control and protection system. Each pole of the series multi-terminal DC transmission system includes at least three converter stations and four converters. Two converters are distributed in series at two different converter stations on the sending or receiving side of each pole of the series multi-terminal DC transmission system. The two different converter stations include station 1 and station 2. Station 1 is a terminal station, and station 2 is an intermediate station with a three-station busbar. Station 1 is equipped with a station 1 control host to realize the converter layer control function and the bipolar layer control function of station 1. Station 2 is equipped with a station 2 first control host and a station 2 second control host. The station 2 first control host realizes the converter layer control function of station 2, and the station 2 second control host realizes the bipolar layer control function and the related pole layer control functions of station 1 and station 2.

Description

Technical Field

[0001] This application relates to the field of multi-terminal DC transmission, and more specifically, to a series multi-terminal DC transmission control and protection system. Background Technology

[0002] Currently, ultra-high voltage direct current (UHVDC) has been widely applied in engineering projects in China. Almost all existing UHVDC projects adopt a two-terminal converter station architecture, with each converter station containing two poles, and each pole consisting of two 12-pulse converters connected in series.

[0003] The large transmission capacity of ultra-high voltage direct current (UHVDC) at both ends, coupled with the concentrated sending and receiving points, places high demands on the interconnected AC systems. To improve the safety and stability of AC / DC system operation, some newly built UHVDC receiving stations in recent years have adopted a topology where high- and low-voltage converters are connected to different AC power grids in a hierarchical manner. This helps to improve the voltage support capability of the DC receiving system, but it is still limited to the scope of the two-end DC system, and the design flexibility is still insufficient.

[0004] The Wudongde DC project is my country's first multi-terminal ultra-high voltage DC project. It adopts a three-terminal converter station parallel architecture, with one sending-end converter station and two receiving-end converter stations. This multi-terminal architecture reduces the requirements for the receiving-end AC system and improves the operational flexibility of the DC system. However, the overall construction cost of parallel multi-terminal ultra-high voltage DC projects is relatively high.

[0005] Based on the existing two-terminal UHVDC transmission system, two converters connected in series on the sending or receiving side of each pole are arranged at two converter stations with different landing points. Together with the converter station on the other side, they form a series-type three-terminal or four-terminal UHVDC transmission system. This can improve the safety and flexibility of UHVDC aggregation and consumption of large-scale energy, and the construction cost is lower than that of parallel multi-terminal UHVDC projects. However, the difficulty of this topology lies in the close DC coupling relationship between the two converters connected in series on each side, which requires close coordination and control. After the two converters connected in series on the same side are placed at two converter stations with different landing points, the DC control and protection system on that side also needs to be redesigned to form a series multi-terminal UHVDC control and protection system, configured at different converter stations, and coordinated control of the two converters connected in series on the same side is achieved through the newly added inter-station communication.

[0006] The series multi-terminal UHVDC control and protection system is not a simple replication or splitting of the original two-terminal UHVDC control and protection system. Instead, it requires consideration of various limiting factors and extensive optimization design to achieve the best overall safety, reliability, flexibility, and economy for the series multi-terminal UHVDC system. These limiting factors include at least:

[0007] (1) To achieve all operating wiring modes of the series multi-terminal UHVDC system, as well as safe switching between various operating wiring modes;

[0008] (2) To reliably detect and handle all types of faults that may occur in a series multi-terminal UHVDC system, including the detection and handling of faults in DC tie lines newly introduced due to the addition of inter-station DC tie lines;

[0009] (3) To enable any converter in a series multi-terminal UHVDC system to be taken out of maintenance without affecting the reliable operation of the remaining parts of the system;

[0010] (4) The reliability of new inter-station communication is inevitably lower than that of the original intra-station communication. Under this constraint, the overall reliability of the series multi-terminal UHVDC transmission system should be maintained as much as possible through the optimized design of the series multi-terminal UHVDC control and protection system.

[0011] (5) While achieving the above requirements, it is also necessary to reduce the overall complexity of the series multi-terminal UHVDC control and protection system as much as possible.

[0012] Therefore, the design of series-connected multi-terminal UHVDC control and protection systems is challenging, and their operational reliability may be lower than that of two-terminal UHVDC control and protection systems due to limitations in inter-station communication. Currently, there are no reports on the application of series-connected multi-terminal DC projects domestically or internationally. However, due to their advantages in economy and flexibility, and with the continuous development of DC control and protection technology in my country, related preliminary research has been gradually carried out. However, current research mainly focuses on the coordinated control between series-connected multi-terminal DC converter stations, and there are no reports on the overall configuration methods of series-connected multi-terminal DC transmission control and protection systems. Summary of the Invention

[0013] This application proposes a series multi-terminal DC transmission control and protection system to better adapt to the impact of series converter substation layout on the design and functional configuration of DC control and protection system, and to meet the operation mode and reliability requirements of series multi-terminal DC transmission system without significantly increasing the complexity of DC control and protection system.

[0014] According to one aspect of this application, a series multi-terminal DC transmission control and protection system is proposed. Each pole of the series multi-terminal DC transmission system includes at least three converter stations and four converters. Two converters are distributed in series at two different converter stations on the sending or receiving side of each pole of the series multi-terminal DC transmission system. The two different converter stations include station 1 and station 2. Station 1 is a terminal station, and station 2 is an intermediate station with a three-station busbar. Station 1 is equipped with a station 1 control host to realize the converter layer control function and the bipolar layer control function of station 1. Station 2 is equipped with a station 2 first control host and a station 2 second control host. The station 2 first control host realizes the converter layer control function of station 2, and the station 2 second control host realizes the bipolar layer control function and the related pole layer control functions of station 1 and station 2.

[0015] According to some embodiments, a protection host is configured at station 1 to realize the converter layer protection function of station 1, the pole layer protection function within the area of ​​station 1, the bipolar layer protection function of station 1, and the DC tie line protection function between station 1 and station 2; a first protection host and a second protection host are configured at station 2, wherein the first protection host realizes the converter layer protection function of station 2, and the second protection host realizes the bipolar layer protection function of station 2, the pole layer protection function within the area of ​​station 2, the DC tie line protection function between station 1 and station 2, and the DC pole line protection function between the rectifier side and the inverter side.

[0016] According to some embodiments, inter-station communication is configured between the control host of station 1 and the second control host of station 2 to realize the coordinated operation of control functions between station 1 and station 2.

[0017] According to some embodiments, inter-station communication is configured between the protection host of station 1 and the second protection host of station 2 to realize the coordinated cooperation of protection functions between station 1 and station 2.

[0018] According to some embodiments, the station 1 control host includes converter trigger control, control pulse generation unit, switch sequence control, mode sequence control, preparation sequence control, converter transformer tap control, unlocking and locking sequence control, inter-station communication and / or station 1 reactive power control.

[0019] According to some embodiments, the first control host of station 2 includes converter trigger control, control pulse generation unit, switching sequence control, mode sequence control, preparation sequence control, converter transformer tap control and / or unlocking / locking sequence control.

[0020] According to some embodiments, the second control host of station 2 includes pole power / current control, overload limiting, DC power modulation, switching sequence control, mode sequence control, preparation sequence control, voltage angle reference value calculation, open circuit test control, inter-station communication and / or reactive power control of station 2.

[0021] According to some embodiments, the control host of station 1 further includes backup pole power / current control, backup overload limitation and / or backup DC power modulation, so as to realize the pole layer backup control function related to the two stations, station 1 and station 2.

[0022] According to some embodiments, the protection functions of the converter layer include valve short-circuit protection, commutation failure protection, and / or converter differential protection; the protection functions of the pole layer include pole bus differential protection, pole-neutral bus differential protection, pole differential protection, DC harmonic protection, DC overvoltage protection, DC undervoltage protection, and / or grounding electrode lead open-circuit protection; the protection functions of the bipolar layer include bipolar bus differential protection, grounding electrode lead unbalance protection, and / or metallic return line grounding protection.

[0023] According to some embodiments, the DC tie line protection function and the DC pole line protection function respectively include DC line traveling wave protection, DC line voltage surge protection, DC line undervoltage protection and / or DC line differential protection.

[0024] According to some embodiments, a first protection host and a second protection host are configured in the station 2. The first protection host implements the converter layer protection function of the station 2 and the DC tie line protection function between the station 1 and the station 2. The second protection host controls and implements the bipolar layer protection function of the station 2, the pole layer protection function within the area of ​​the station 2, and the DC pole line protection function between the rectifier side and the inverter side.

[0025] According to some embodiments, the protection host of station 1 and the first control host of station 2 are configured with inter-station communication to realize the coordinated cooperation of protection functions between station 1 and station 2.

[0026] According to some embodiments of this application, the overall operation control of a series multi-terminal DC control and protection system is achieved with fewer inter-station communication channels.

[0027] According to other embodiments of this application, a smaller number of inter-station communication channels enable the overall protection and control of a series multi-terminal DC control and protection system.

[0028] According to some embodiments, by arranging fewer inter-station communication channels in the series multi-terminal DC control and protection system, various operation control modes and protection functions of the multi-terminal DC transmission system under the series converter substation layout structure are realized, and the series multi-terminal DC control and protection system as a whole has high reliability. Attached Figure Description

[0029] 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.

[0030] Figure 1 A schematic diagram of a series four-terminal DC transmission system is shown.

[0031] Figure 2 A schematic diagram of a series three-terminal DC transmission system is shown.

[0032] Figure 3 This diagram illustrates a single-pole configuration of a series multi-terminal DC control and protection system according to an example embodiment of this application.

[0033] Figure 4 This diagram illustrates a single-pole configuration of another series multi-terminal DC control and protection system according to an example embodiment of this application.

[0034] Figure 5 This diagram illustrates a single-pole configuration of another series multi-terminal DC control and protection system according to an example embodiment of this application. Detailed Implementation

[0035] Exemplary embodiments will now be described more fully with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many forms and should not be construed as limited to the embodiments set forth herein; rather, they are provided so that this application will be thorough and complete, and will fully convey the concept of the exemplary embodiments to those skilled in the art. The same reference numerals in the drawings denote the same or similar parts, and therefore repeated descriptions of them will be omitted.

[0036] The described features, structures, or characteristics can be combined in any suitable manner in one or more embodiments. Numerous specific details are provided in the following description to give a full understanding of embodiments of this disclosure. However, those skilled in the art will recognize that the technical solutions of this disclosure can be practiced without one or more of these specific details, or other methods, components, materials, apparatus, or operations may be employed. In these cases, well-known structures, methods, apparatuses, implementations, materials, or operations will not be shown or described in detail.

[0037] The flowcharts shown in the accompanying drawings are merely illustrative and do not necessarily include all content and operations / steps, nor do they necessarily have to be performed in the described order. For example, some operations / steps can be broken down, while others can be combined or partially combined; therefore, the actual execution order may change depending on the specific circumstances.

[0038] The terms "first," "second," etc., in the specification, claims, and accompanying drawings of this application are used to distinguish different objects, not to describe a specific order. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to these processes, methods, products, or apparatuses.

[0039] The following detailed description, with reference to the accompanying drawings, describes a series multi-terminal DC transmission control and protection system according to an exemplary embodiment of this application.

[0040] According to some embodiments of this application, each pole of a series multi-terminal DC transmission system includes at least three converter stations and four converters, wherein two converters are distributed in series at two different converter stations on the sending or receiving side of each pole of the series multi-terminal DC transmission system, and the two different converter stations include station 1 and station 2, station 1 being the terminal station, and station 2 being an intermediate station with three busbars within the station.

[0041] For example, each pole of a series multi-terminal DC transmission system includes four converters and four converter stations. Two converters are located at two different converter stations on the sending end side of each pole, and the other two are located at two different converter stations on the receiving end side of each pole. Figure 1 As shown.

[0042] For example, each pole of a series multi-terminal DC transmission system includes four converters and three converter stations. Two converters are located at two different converter stations on the sending end side of each pole, while the other two are located at the same converter station on the receiving end side of each pole. Figure 2 As shown.

[0043] For example, each pole of a series multi-terminal DC transmission system includes four converters, with two converters located at two different converter stations on the receiving end side of each pole, and the other two located at the same converter station on the sending end side of each pole.

[0044] According to some embodiments, for two converter stations distributed in series at the same end of each pole of a series multi-terminal DC transmission system, namely station 1 and station 2, station 1 is the terminal station and station 2 is the intermediate station with three busbars.

[0045] To distinguish between Station 1 and Station 2 on the sending and receiving sides, the two converter stations on the sending side of each pole of the series multi-terminal DC transmission system are defined as Sending-side Station 1 and Sending-side Station 2, and the two converter stations on the receiving side of each pole of the series multi-terminal DC transmission system are defined as Receiving-side Station 1 and Receiving-side Station 2.

[0046] Figure 1 A schematic diagram of a series four-terminal DC transmission system is shown. Figure 1 The series four-terminal DC transmission system shown includes four converter stations on pole 1, of which two are sending-end converter stations and two are receiving-end converter stations.

[0047] The sending-end converter station's pole 1 side includes stations A and B, and the receiving-end converter station's pole 1 side includes stations C and D. Each converter station includes one converter. Station A is the terminal station of the four-terminal DC system and is defined as sending-end station 1. The neutral bus area and pole bus area of ​​station B serve as the busbars for stations A, B, and C, and station B is defined as sending-end station 2. The neutral bus area and pole bus area of ​​station C serve as the busbars for stations B, C, and D, and station C is defined as receiving-end station 2. Station D is defined as receiving-end station 1. Sending-end station 1 and receiving-end station 1 are collectively referred to as station 1, and sending-end station 2 and receiving-end station 2 are collectively referred to as station 2.

[0048] According to some embodiments of this application, a station 1 control host is configured at each pole of the series four-terminal DC transmission system to realize the converter layer control function and the bipolar layer control function of station 1; a station 2 first control host and a station 2 second control host are configured at each pole of the series four-terminal DC transmission system, wherein the station 2 first control host realizes the converter layer control function of station 2, and the station 2 second control host realizes the bipolar layer control function and the pole layer control function related to stations 1 and 2.

[0049] like Figure 1 As shown, one control host is configured at station 1 on the sending end side, namely the station 1 control host, as follows: Figure 3 or Figure 4 The CCP_S1 shown implements the converter layer control function and the bipolar layer control function of the sending-end station 1; a control host is configured in the receiving-end station 1, namely the station 1 control host, as shown in the figure. Figure 3 or Figure 4 The CCP_S1 shown implements the converter layer control function and the bipolar layer control function of the receiving-end station 1. Two control hosts are configured at the sending-end station 2, one of which implements the converter layer control function of the sending-end station 2. Figure 3 or Figure 4 In the CCP_S2 control unit, another control host implements the bipolar layer control function of sending-end station 2, and the related polar layer control functions of sending-end station 1 and sending-end station 2. Figure 3or Figure 4 In the PCP (Converter-on-Package) configuration, two control hosts are configured at the receiving-end station 2, one of which implements the converter layer control function of the receiving-end station 2. Figure 3 or Figure 4 In the CCP_S2 control unit, another control host implements the bipolar layer control function of receiving-side station 2, and the related polar layer control functions of receiving-side station 1 and receiving-side station 2. Figure 3 or Figure 4 PCP in China.

[0050] It should be noted that the two control hosts configured at the sending-end station 2 and the receiving-end station 2 are two different control hosts. One set is collectively referred to as the first control host of station 2, and the other set is collectively referred to as the second control host of station 2. Similarly, the control hosts configured at the sending-end station 1 and the receiving-end station 1 are different control hosts, but the control hosts configured at the sending-end station 1 and the receiving-end station 1 are collectively referred to as the station 1 control host.

[0051] According to some embodiments of this application, a protection host is configured at station 1 of each pole of a series four-terminal DC transmission system to realize the converter layer protection function of station 1, the pole layer protection function within the station 1 area, the bipolar layer protection function of station 1, and the tie line protection function between station 1 and station 2.

[0052] like Figure 1 As shown, one protection host is configured at station 1 on the sending end side, namely the station 1 protection host, as follows: Figure 3 or Figure 4 CPR_S1 in the configuration implements the protection functions of the converter layer at the sending-end station 1, the pole layer protection function within the area of ​​the sending-end station 1, the bipolar layer protection function of the sending-end station 1, and the DC tie line protection function between the sending-end station 1 and the sending-end station 2; a protection host is configured at the receiving-end station 1, namely the station 1 protection host, such as... Figure 3 or Figure 4 CPR_S1 in the middle realizes the protection function of the converter layer of the receiving end station 1, the protection function of the pole layer in the area of ​​the receiving end station 1, the protection function of the bipolar layer of the receiving end station 1, and the protection function of the DC tie line between the receiving end station 1 and the receiving end station 2.

[0053] It should be noted that the protection hosts configured at the sending end station 1 and the receiving end station 1 are different control hosts. The protection hosts configured at the sending end station 1 and the receiving end station 1 are collectively referred to as the station 1 protection host.

[0054] According to some embodiments, in each pole of the series four-terminal DC transmission system, a first protection host and a second protection host are configured at station 2. The first protection host at station 2 implements the converter layer protection function of station 2, and the second protection host at station 2 implements the bipolar layer protection function, the pole layer protection function within the area of ​​station 2, the DC tie line protection function between station 1 and station 2, and the DC pole line protection function between the rectifier side and the inverter side.

[0055] like Figure 1 As shown, two protection main units are configured at the sending-end station 2, one of which implements the converter layer protection function of the sending-end station 2, i.e. Figure 3 or Figure 4 In CPR_S2, another protection host implements the bipolar layer protection function of the sending-end station 2, the pole layer protection function within the area of ​​the sending-end station 2, the DC tie line protection function between the sending-end station 1 and the sending-end station 2, and the DC pole line between the rectifier side and the inverter side, that is... Figure 1 The protection functions for DC lines at pole 1 and pole 2, such as... Figure 3 or Figure 4 The PPR shown is used. Two protection units are configured at the receiving-end station 2, one of which implements the converter layer protection function at the receiving-end station 2. Figure 3 or Figure 4 In CPR_S2, another protection host implements the bipolar layer protection function of receiving-end station 2, the pole layer protection function within the area of ​​receiving-end station 2, the DC tie line protection function between receiving-end station 1 and receiving-end station 2, and the DC pole line between the rectifier side and the inverter side, that is... Figure 1 The protection functions for DC lines at pole 1 and pole 2, such as... Figure 3 or Figure 4 The PPR shown is shown in the image.

[0056] It should be noted that the two protection hosts configured at the sending end station 2 and the receiving end station 2 are two different protection hosts. One of them is collectively referred to as the first protection host of station 2, and the other is collectively referred to as the second protection host of station 2.

[0057] According to some embodiments, inter-station communication is configured between the control host of station 1 and the second control host of station 2 to achieve coordinated operation of control functions between station 1 and station 2.

[0058] For example, inter-station communication is configured between the control host CCP_S1 of sending-end station 1 and the control host PCP of sending-end station 2, which implements the related pole-level control functions of sending-end station 1 and sending-end station 2, to achieve coordinated operation of the control functions of sending-end station 1 and sending-end station 2. Similarly, inter-station communication is configured between the control host CCP_S1 of receiving-end station 1 and the control host PCP of receiving-end station 2, which implements the related pole-level control functions of receiving-end station 1 and receiving-end station 2, to achieve coordinated operation of the control functions of receiving-end station 1 and receiving-end station 2.

[0059] According to some embodiments, inter-station communication is configured between the protection host of station 1 and the second protection host of station 2 to achieve coordinated cooperation of protection functions between station 1 and station 2.

[0060] For example, inter-station communication is configured between the protection host CPR_S1 at the sending-end station 1 and the protection host PPR at the sending-end station 2, which implements the DC tie line protection function between sending-end station 1 and sending-end station 2, to achieve coordinated operation of the protection functions between sending-end station 1 and sending-end station 2. Similarly, inter-station communication is configured between the protection host CPR_S1 at the receiving-end station 1 and the protection host PPR at the receiving-end station 2, which implements the DC tie line protection function between receiving-end station 1 and receiving-end station 2, to achieve coordinated operation of the protection functions between receiving-end station 1 and receiving-end station 2.

[0061] According to other embodiments, a first protection host and a second protection host are configured at station 2. The first protection host implements the converter layer protection function and the DC tie line protection function between station 1 and station 2. The second protection host controls and implements the bipolar layer protection function, the pole layer protection function within the station 2 area, and the DC pole line protection function between the rectifier side and the inverter side. Inter-station communication is configured between the protection host at station 1 and the first control host at station 2 to achieve coordinated operation of the protection functions between station 1 and station 2.

[0062] For example, in the two protection main units configured at the sending-end station 2, one unit implements the protection function of the converter layer of sending-end station 2 and the protection function of the DC tie line between sending-end station 1 and sending-end station 2, such as... Figure 3 or Figure 4 In CPR_S2, another protection host implements the bipolar layer protection function of the sending-end station 2, the pole layer protection function within the area of ​​the sending-end station 2, and the DC pole line protection function between the rectifier side and the inverter side, such as... Figure 3 or Figure 4 In this configuration, inter-station communication is configured between the protection host CPR_S1 of the sending-end station 1 and the protection host CPR_S2 of the sending-end station 2, which implements the DC tie line protection function between sending-end station 1 and sending-end station 2, so as to achieve coordinated cooperation of the protection functions between sending-end station 1 and sending-end station 2.

[0063] For example, in the two protection main units configured at the receiving-end station 2, one unit implements the protection function of the converter layer of the receiving-end station 2 and the protection function of the DC tie line between the receiving-end station 1 and the receiving-end station 2, such as... Figure 3 or Figure 4 In CPR_S2, another protection host implements the bipolar layer protection function of the receiving-end station 2, the pole layer protection function within the area of ​​the receiving-end station 2, and the DC pole line protection function between the rectifier side and the inverter side, such as... Figure 3 or Figure 4In this configuration, inter-station communication is configured between the protection host CPR_S1 of the receiving-end station 1 and the protection host CPR_S2 of the receiving-end station 2, which implements the DC tie line protection function between the receiving-end station 1 and the receiving-end station 2, so as to achieve coordinated cooperation of the protection functions between the receiving-end station 1 and the receiving-end station 2.

[0064] It should be noted that the two protection hosts configured at the sending-end station 2 and the receiving-end station 2 are two different protection hosts. One set is collectively referred to as the first protection host of station 2, and the other set is collectively referred to as the second protection host of station 2. Similarly, the protection hosts configured at the sending-end station 1 and the receiving-end station 1 are different control hosts. The protection hosts configured at the sending-end station 1 and the receiving-end station 1 are collectively referred to as the protection host of station 1.

[0065] According to some embodiments, the control host CCP_S1, which implements the converter layer control and bipolar layer control functions of station 1, also known as the station 1 control host, includes converter trigger control, control pulse generation unit, switching sequence control, mode sequence control, preparation sequence control, converter transformer tap control, unlocking and blocking sequence control, inter-station communication and / or station 1 reactive power control.

[0066] According to some embodiments, the control host CCP_S2 that implements the control function of the converter layer of station 2, that is, the first control host of station 2, includes converter trigger control, control pulse generation unit, switching sequence control, mode sequence control, preparation sequence control, converter transformer tap control and / or unlocking sequence control.

[0067] According to some embodiments, the control host PCP that realizes the bipolar layer control of station 2 and the related pole layer control functions of station 1 and station 2, that is, the second control host of station 2, includes pole power / current control, overload limitation, DC power modulation, switching sequence control, mode sequence control, preparation sequence control, voltage angle reference value calculation, open circuit test control, inter-station communication and / or reactive power control of station 2.

[0068] According to some embodiments, the converter layer protection functions include valve short-circuit protection, commutation failure protection, and converter differential protection. The pole layer protection functions include: pole bus differential protection, pole-neutral bus differential protection, pole differential protection, DC harmonic protection, DC overvoltage protection, DC undervoltage protection, and grounding electrode lead open-circuit protection; the bipolar layer protection functions include bipolar bus differential protection, grounding electrode lead unbalance protection, and metallic return line grounding protection; the DC tie line protection function and the DC pole line protection function respectively include DC line traveling wave protection, DC line voltage surge protection, DC line undervoltage protection, and DC line differential protection.

[0069] According to other embodiments, the station 1 control host also includes backup pole power / current control, backup overload limiting, and backup DC power modulation to realize the pole-level backup control functions related to station 1 and station 2. When the control host PCP that implements the pole-level control functions related to station 1 and station 2 in station 2 fails, the backup pole power / current control, backup overload limiting, and backup DC power modulation functions in the station 1 control host CCP_S1 take effect.

[0070] It should be noted that stations A, B, C, and D are located on pole 1 of the series four-terminal DC transmission system. The converter stations on pole 2 of the series four-terminal DC transmission system need to maintain the same configuration as stations A, B, C, and D, which will not be elaborated here.

[0071] According to some embodiments of this application, the overall operation control of a series multi-terminal DC control and protection system is achieved with fewer inter-station communication channels.

[0072] According to other embodiments of this application, a smaller number of inter-station communication channels enable the overall protection and control of a series multi-terminal DC control and protection system.

[0073] According to some embodiments, by arranging fewer inter-station communication channels in the series multi-terminal DC control and protection system, various operation control modes and protection functions of the multi-terminal DC transmission system under the series converter substation layout structure are realized, and the series multi-terminal DC control and protection system as a whole has high reliability.

[0074] Figure 2 A schematic diagram of a series three-terminal DC transmission system is shown. Figure 2 The series three-terminal DC transmission system shown includes three converter stations on pole 1 side, including two sending-end converter stations and one receiving-end converter station. Each sending-end converter station includes one converter, and the receiving-end converter station includes two converters. Station A is the terminal station of the sending-end DC transmission and is defined as sending-end station 1. The neutral bus area and pole bus area of ​​station B serve as the busbars for stations A, B, and C, and station B is defined as sending-end station 2. There is only one converter station on the receiving-end side, namely station C. Its main wiring and DC control and protection system can follow the design of the single-sided converter station of the two-terminal UHVDC system.

[0075] The following is based on Figure 2 Taking the sending end side of pole 1 as an example, the configuration of each pole in the single-sided DC control and protection system will be explained. The configuration of the receiving end side is the same as that of the sending end side, and will not be repeated here. Similarly, the configuration of pole 2 side is the same as that of pole 1 side, and will not be repeated here either.

[0076] like Figure 2 As shown, at station 1, that is, station A-sending end station 1, one control host is configured, i.e. Figure 3 or Figure 4 CCP_S1 in the middle implements the converter layer control function and the bipolar layer control function of station 1; in station 2, that is, station B-sending end station 2, two control hosts are configured, one of which implements the converter layer control function of station 2, i.e. Figure 3 or Figure 4 In the CCP_S2 control unit, another control host implements the bipolar layer control function for station 2, and the related polar layer control functions for stations 1 and 2. Figure 3 or Figure 4 PCP in China;

[0077] One protection host is configured at station 1, namely Figure 3 or Figure 4 CPR_S1 is configured to implement the protection functions of the converter layer of station 1, the pole layer protection function within the station 1 area, the bipolar layer protection function of station 1, and the DC tie line protection function between station 1 and station 2. Two protection main units are configured in station 2, one of which implements the protection function of the converter layer of station 2. Figure 3 or Figure 4 In CPR_S2, another protection host implements the bipolar layer protection function of station 2, the pole layer protection function within the area of ​​station 2, the DC tie line protection function between station 1 and station 2, and the DC pole line between the rectifier side and the inverter side, i.e. Figure 1 The protection functions for DC lines at pole 1 and pole 2 are as follows: Figure 3 or Figure 4 PPR in China.

[0078] Inter-station communication is configured between the control host CCP_S1 of station 1 and the control host PCP of station 2, which implements the related polar layer control functions of station 1 and station 2, so as to realize the coordinated cooperation of the control functions of station 1 and station 2.

[0079] Inter-station communication is configured between the protection host CPR_S1 of station 1 and the protection host PPR of station 2, which implements the DC tie line protection function between station 1 and station 2, so as to achieve coordinated cooperation of the protection functions of station 1 and station 2.

[0080] The two protection units configured at station 2 can also be configured as follows: one unit can implement the protection functions for the converter layer of station 2 and the DC tie line protection function between station 1 and station 2, i.e. Figure 3 or Figure 4 In CPR_S2, another protection host implements the bipolar layer protection function of station 2, the pole layer protection function within the area of ​​station 2, and the DC pole line protection function between the rectifier side and the inverter side, that is... Figure 3 or Figure 4 In this configuration, inter-station communication is configured between the protection host CPR_S1 at station 1 and the protection host CPR_S2 at station 2, which implements the DC tie line protection function between station 1 and station 2, to achieve coordinated operation of the protection functions between station 1 and station 2.

[0081] The control host CCP_S1, which implements converter layer control and bipolar layer control functions of Station 1, includes functional modules such as converter trigger control, control pulse generation unit, switching sequence control, mode sequence control, preparation sequence control, converter transformer tap control, unlocking and locking sequence control, inter-station communication and / or Station 1 reactive power control.

[0082] The control host CCP_S2, which implements the control functions of the converter layer of Station 2, includes functional modules such as converter trigger control, control pulse generation unit, switching sequence control, mode sequence control, preparation sequence control, converter transformer tap control and / or unlocking sequence control.

[0083] The control host PCP, which realizes bipolar layer control of station 2 and related pole layer control functions of stations 1 and 2, includes functional modules such as pole power / current control, overload limiting, DC power modulation, switching sequence control, mode sequence control, preparation sequence control, voltage angle reference value calculation, open circuit test control, inter-station communication and / or reactive power control of station 2.

[0084] The converter layer protection functions include valve short-circuit protection, commutation failure protection, and / or converter differential protection; the pole layer protection functions include pole bus differential protection, pole neutral bus differential protection, pole differential protection, DC harmonic protection, DC overvoltage protection, DC undervoltage protection, and / or grounding electrode lead open-circuit protection; the bipolar layer protection functions include bipolar bus differential protection, grounding electrode lead unbalance protection, and / or metallic return line grounding protection; the DC tie line protection function and the DC pole line protection function respectively include DC line traveling wave protection, DC line voltage surge protection, DC line undervoltage protection, and / or DC line differential protection.

[0085] Optionally, the station 1 control host also includes backup pole power / current control, backup overload limiting, and / or backup DC power modulation to realize the pole-level backup control functions related to stations 1 and 2. When the control host PCP that implements the pole-level control functions related to stations 1 and 2 in station 2 fails, the backup pole power / current control, backup overload limiting, and backup DC power modulation functions in the station 1 control host CCP_S1 take effect.

[0086] According to Figure 2 The series multi-terminal DC transmission control and protection system described above only requires a very small number of control and protection hosts and inter-station communication channels to realize various operation control modes and protection functions of the multi-terminal DC transmission system under the series converter substation structure. It can also flexibly handle various primary and secondary equipment faults and adapt to the maintenance needs of single station or single converter equipment.

[0087] It should be noted here that... Figure 3 , Figure 4This is a simplified configuration example of a series multi-terminal DC transmission control and protection system implemented according to the technical solution of this application. In practical engineering applications, dual or multiple redundancy configurations of the main unit can be adopted, i.e., adding redundancy, backup communication channels, etc., to further increase the reliability of the series multi-terminal DC transmission control and protection system. For example, in Figure 3 Based on the most basic configuration, Figure 5 An example of adding backup communication channels is given, which adds inter-station communication between PCP and CPR_S1 and intra-station host communication between PCP and CPR_S2, as well as inter-station communication between PPR and CCP_S1 and intra-station host communication between PPR and CCP_S2.

[0088] The following three examples illustrate the operation of the series multi-terminal DC transmission control and protection system of this application.

[0089] Implementation Example 1: When communication between a pole of Station 1 and Station 2 fails, or a grounding fault occurs in the DC primary system of a pole within Station 1, or the converter control host CCP_S1 of a pole of Station 1 fails, the pole of Station 1 can be taken out of operation, and the electrical connection of the DC primary system between Station 1 and Station 2 can be disconnected. At the same time, one converter on the opposite side of the pole will also be taken out of operation. By coordinating with the DC control and protection system configured in Station 2 and the opposite side, the remaining converters of Station 2 and the opposite side can continue to operate. At this time, maintenance of the primary and secondary equipment of Station 1 will not affect the normal operation of the remaining converters of Station 2 and the opposite side.

[0090] Implementation Example 2: When the converter control host CCP_S2 of a certain pole in station 2 fails, or a DC primary system fault occurs in the converter area, the converter of that pole in station 2 can be taken out of operation, and one converter on the opposite side of the pole will also be taken out of operation at the same time. The PCP and PPR hosts configured in station 2 can reliably control and monitor the three busbars in station 2, and together with the DC control and protection system configured in station 1, ensure that the remaining system on this side continues to operate reliably. At this time, station 2 can safely repair the equipment in the converter area of ​​the pole that has failed.

[0091] Operating Condition Example 3: Following Operating Condition Example 2 above, the converter at station 2 of a certain pole is in the off state, while the converter at station 1 is in the running state. If the control host PCP of that pole in station 2 fails, the backup pole power / current control, backup overload limit, and backup DC power modulation functions in the control host CCP_S1 of station 1 of that pole can take effect, maintaining the continued operation of that pole, and the DC power / current still has basic regulation capability.

[0092] According to some embodiments of this application, only a very small number of control and protection hosts and inter-station communication channels are required to realize various operation control modes and protection functions of multi-terminal DC transmission systems under the series converter substation structure. It can also flexibly handle various primary and secondary equipment faults and adapt to the maintenance needs of single station or single converter equipment.

[0093] The embodiments of this application have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the embodiments above are only for the purpose of helping to understand the method and core ideas of this application. Furthermore, any changes or modifications made by those skilled in the art based on the ideas of this application, and on the specific implementation methods and application scope of this application, are all within the scope of protection of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A series multi-terminal DC transmission control and protection system, wherein each pole of the series multi-terminal DC transmission control and protection system includes at least three converter stations and four converters, wherein two converters are distributed in series at two different converter stations on the sending-end or receiving-end side of each pole of the series multi-terminal DC transmission control and protection system, the two different converter stations including station 1 and station 2, station 1 being a terminal station, and station 2 being an intermediate station with a three-station busbar, characterized in that: A station 1 control host is configured at station 1 to realize the converter layer control function and the bipolar layer control function of station 1; At station 2, a first control host and a second control host are configured. The first control host implements the converter layer control function of station 2, and the second control host implements the bipolar layer control function of station 2 and the related pole layer control functions of station 1 and station 2. A protection host is configured at station 1 to realize the converter layer protection function of station 1, the pole layer protection function within the area of ​​station 1, the bipolar layer protection function of station 1, and the DC tie line protection function between station 1 and station 2. The station 2 is equipped with a first protection host and a second protection host. The first protection host implements the converter layer protection function of the station 2, and the second protection host implements the bipolar layer protection function of the station 2, the pole layer protection function within the area of ​​the station 2, the DC tie line protection function between the station 1 and the station 2, and the DC pole line protection function between the rectifier side and the inverter side.

2. The series multi-terminal DC transmission control and protection system as described in claim 1, characterized in that: Inter-station communication is configured between the control host of station 1 and the second control host of station 2 to achieve coordinated operation of control functions between station 1 and station 2.

3. The series multi-terminal DC transmission control and protection system as described in claim 1, characterized in that: Inter-station communication is configured between the protection host of station 1 and the second protection host of station 2 to achieve coordinated cooperation of protection functions between station 1 and station 2.

4. The series multi-terminal DC transmission control and protection system according to claim 1, characterized in that, The station 1 control host includes: Converter trigger control, control pulse generation unit, switch sequence control, mode sequence control, preparation sequence control, converter transformer tap changer control, unlocking / locking sequence control, inter-station communication and / or station 1 reactive power control.

5. The series multi-terminal DC transmission control and protection system according to claim 1, characterized in that, The first control host of station 2 includes: Converter trigger control, control pulse generation unit, switching sequence control, mode sequence control, preparation sequence control, converter transformer tap control and / or unlocking / locking sequence control.

6. The series multi-terminal DC transmission control and protection system according to claim 1, characterized in that, The second control host of station 2 includes: Extreme power / current control, overload limiting, DC power modulation, switching sequence control, mode sequence control, preparation sequence control, voltage angle reference value calculation, open circuit test control, inter-station communication and / or station 2 reactive power control.

7. The series multi-terminal DC transmission control and protection system as described in claim 1, characterized in that: The station 1 control host also includes Backup pole power / current control, backup overload limitation and / or backup DC power modulation are used to realize the pole layer backup control functions related to the two stations, station 1 and station 2.

8. The series multi-terminal DC transmission control and protection system according to claim 1, characterized in that, The protection functions of the converter layer include: Valve short-circuit protection, commutation failure protection, and / or converter differential protection; The protective functions of the polar layer include: Differential protection for pole bus, differential protection for pole and neutral bus, pole differential protection, DC harmonic protection, DC overvoltage protection, DC undervoltage protection and / or grounding electrode lead open circuit protection; The bipolar layer protection functions include: bipolar bus differential protection, grounding electrode lead imbalance protection and / or metallic return line grounding protection.

9. The series multi-terminal DC transmission control and protection system according to claim 1, characterized in that, The DC tie line protection function and the DC pole line protection function respectively include: DC line traveling wave protection, DC line voltage surge protection, DC line undervoltage protection and / or DC line differential protection.

10. The series multi-terminal DC transmission control and protection system according to claim 1, characterized in that, At station 2, a first protection host and a second protection host are configured, wherein: The first protection host of station 2 implements the converter layer protection function of station 2 and the DC tie line protection function between station 1 and station 2. The second protection host of station 2 controls the implementation of bipolar layer protection function of station 2, pole layer protection function within the area of ​​station 2, and DC pole line protection function between rectifier side and inverter side.

11. The series multi-terminal DC transmission control and protection system according to claim 10, characterized in that: Inter-station communication is configured between the protection host of station 1 and the first control host of station 2 to achieve coordinated cooperation of protection functions between station 1 and station 2.

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