DC voltage control system and method

Abstract

The embodiment of the invention provides a direct-current voltage control system and method, and relates to the field of converter control, and the system comprises a pole control protection device which is configured in a converter station and is configured to determine a voltage control state of the corresponding converter station; the direct current station control device is configured in a direct current bus converter station, is electrically connected with each pole control protection device in a direct current bus control area, and is configured to obtain a voltage control state of each converter station and issue a voltage control instruction to the corresponding pole control protection device, and the voltage control instruction is used for indicating the corresponding converter station to take over direct current voltage control; and the coordination control device is configured in any direct current bus converter station, is electrically connected with each direct current station control device, and is configured to issue a voltage control instruction to the corresponding direct current station control device based on the voltage control state of each converter station. According to the system, a three-layer control architecture can be realized, so that each control device does not need to communicate with all other control devices, and the communication traffic and the load rate can be greatly reduced.

Description

Technical Field

[0001] This application relates to the field of converter control technology, specifically to a DC voltage control system and method. Background Technology

[0002] In flexible DC transmission systems, ensuring stable DC voltage control is crucial for normal system operation. Multi-terminal flexible DC transmission systems involve complex scenarios with multiple DC buses and branch lines, making coordinated DC voltage control even more complex. Under steady-state conditions, DC voltage control mainly relies on communication mechanisms, while under transient conditions, it primarily relies on margin control and droop control.

[0003] Typically, the DC voltage control system of a multi-terminal flexible DC transmission system mainly adopts a single-layer control architecture. This requires that the devices at each port must communicate with the devices at all other ports, resulting in a large amount of communication and a high load rate. Summary of the Invention

[0004] This application provides a DC voltage control system and method to reduce the communication volume and load rate of DC voltage control in a multi-terminal flexible DC transmission system.

[0005] In a first aspect, embodiments of this application provide a DC voltage control system for controlling a multi-terminal flexible DC transmission system. The multi-terminal flexible DC transmission system includes multiple converter stations, each converter station comprising a DC bus converter station and branch converter stations. The DC bus converter stations are connected to a DC bus, and the branch converter stations are connected to branch lines. The DC voltage control system includes:

[0006] A voltage control protection device, configured in one of the converter stations, is configured to determine the voltage control state corresponding to the converter station;

[0007] A DC station control device, configured in a DC bus converter station and electrically connected to each of the pole control and protection devices within the DC bus control area, is configured to acquire the voltage control status of each converter station and issue voltage control commands to the corresponding pole control and protection devices, wherein the voltage control commands are used to instruct the corresponding converter station to take over DC voltage control.

[0008] A coordination control device, configured at any of the DC bus converter stations and electrically connected to each of the DC station control devices, is configured to issue voltage control commands to the corresponding DC station control device based on the voltage control status of each converter station.

[0009] In some embodiments, the coordination control device is configured to issue voltage control commands to the corresponding DC station control device based on the voltage control status of each converter station, including:

[0010] Based on the voltage control status and DC voltage takeover strategy of each converter station, a first target device for the voltage to be taken over is determined from the multiple DC station control devices;

[0011] The voltage control command is sent to the first target device.

[0012] In some embodiments, the plurality of converter stations include a DC voltage control station and a power control station; the coordination control device is configured to determine a first target device for the voltage to be managed from among the plurality of DC station control devices, including:

[0013] If any of the power control stations is found to have a communication failure, the DC voltage control station shall remain unchanged.

[0014] In some embodiments, upon determining that any of the power control stations is experiencing a communication anomaly, the coordination control device is further configured to perform the following steps:

[0015] In the event that the power control station, which is determined to have communication failure, is lost, a second target converter station whose power needs to be adjusted is determined from among the multiple converter stations based on the active power allocation strategy.

[0016] A power control command is issued to the DC station control device corresponding to the second target converter station. The power control command is used to instruct the corresponding converter station to redistribute active power.

[0017] In some embodiments, the coordination control device is further configured to determine that the power control station has lost communication by means of the following steps:

[0018] If the DC voltage deviation slope control strategy of all converter stations with normal communication is enabled, and the DC line current value of the power control station with abnormal communication is less than the preset current value, then the power control station with abnormal communication is deemed to be out of service.

[0019] In some embodiments, the coordination control device is configured to determine a first target device for the voltage to be managed from among a plurality of DC station control devices, and further includes:

[0020] In the event that the DC voltage control station is found to be in communication failure and the DC voltage control station is lost, a first target converter station to be taken over voltage is determined from among the multiple power control stations.

[0021] The DC station control device corresponding to the first target converter station is identified as the first target device.

[0022] In some embodiments, the coordination control device is further configured to perform the following steps:

[0023] Based on the active power allocation strategy, a second target converter station whose power needs to be adjusted is determined from among the multiple power control stations;

[0024] A power control command is sent to the DC station control device corresponding to the second target converter station.

[0025] In some embodiments, the coordination control device is configured to determine a first target device for the voltage to be managed from among a plurality of DC station control devices, and further includes:

[0026] If it is determined that the communication of the DC station control device corresponding to the voltage control area is abnormal and the DC voltage of the DC bus is abnormal, the first target device is determined from the DC station control devices corresponding to each non-voltage control area. The voltage control area is the DC bus control area corresponding to the DC voltage control station, and the non-voltage control area is other DC bus control areas besides the voltage control area.

[0027] In some embodiments, the coordination control device is configured to determine a first target device for the voltage to be managed from among a plurality of DC station control devices, and further includes:

[0028] If it is determined that the communication of the DC station control device corresponding to the non-voltage control area is abnormal and the DC voltage of the DC bus is abnormal, the DC voltage control station shall be kept unchanged.

[0029] In some embodiments, the coordination control device is configured to determine a first target device for the voltage to be managed from among a plurality of DC station control devices, and further includes:

[0030] If it is determined that the communication of the coordination control device is abnormal and the DC voltage of the DC bus is abnormal, the first target device is determined from the DC station control devices corresponding to each non-voltage control area.

[0031] In some embodiments, the coordination control device is configured to determine a first target device for the voltage to be managed from among a plurality of DC station control devices, including:

[0032] If it is determined that all the converter stations are communicating normally and there is no DC voltage control station at present, the first target device is determined from the multiple DC station control devices based on a first preset priority.

[0033] In some embodiments, the DC station control device is configured to issue voltage control commands to the corresponding pole control protection device, including:

[0034] Receive the voltage control command sent by the coordination control device;

[0035] Based on the voltage control status of each converter station, a second target device is determined from among the multiple pole control protection devices;

[0036] The voltage control command is sent to the second target device.

[0037] Secondly, embodiments of this application also provide a DC voltage control method, applied to the DC voltage control system described in any one of the first aspects, the method comprising:

[0038] The coordination control device issues voltage control commands to the corresponding DC station control device based on the voltage control status of each converter station. The voltage control commands are used to instruct the corresponding converter station to take over DC voltage control. The voltage control status of each converter station is obtained through the corresponding pole control protection device.

[0039] The DC station control device sends the voltage control command to the corresponding pole control and protection device so that the corresponding pole control and protection device can take over the DC voltage control.

[0040] The DC voltage control system provided in this application embodiment realizes a three-layer control architecture through a pole control protection device, a DC station control device, and a coordination control device. Each layer of control device only communicates with the adjacent layer of control device to realize the hierarchical transmission of data or instructions, thereby eliminating the need for each control device to communicate with all other control devices, which can greatly reduce the amount of communication and the load rate. Attached Figure Description

[0041] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0042] Figure 1 This is a schematic diagram of the structure of a multi-terminal flexible DC transmission system according to an embodiment of this application;

[0043] Figure 2 This is a schematic diagram of the DC voltage control system according to an embodiment of this application;

[0044] Figure 3 This is a schematic diagram illustrating the principle of the DC voltage deviation slope control strategy in the embodiments of this application;

[0045] Figure 4 This is a schematic diagram of an example structure of the DC voltage control system of the five-terminal flexible DC transmission system according to an embodiment of this application;

[0046] Figure 5 for Figure 4The waveform diagram of the system under normal communication conditions is shown in the simulation test.

[0047] Figure 6 for Figure 4 The waveform diagram of the system under communication failure conditions is shown in the simulation test.

[0048] Figure 7 This is a flowchart illustrating the DC voltage control method according to an embodiment of this application. Detailed Implementation

[0049] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0050] In the description of this application, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are used only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of the stated features. In the description of this application, "a plurality of" means two or more, unless otherwise explicitly specified.

[0051] "A and / or B" includes the following three combinations: A only, B only, and a combination of A and B.

[0052] The use of "applies to" or "configured to" in this application implies open and inclusive language, which does not exclude the applicability to or configuration to devices performing additional tasks or steps. Additionally, the use of "based on" implies openness and inclusivity, because processes, steps, calculations, or other actions "based on" one or more of the stated conditions or values ​​may in practice be based on additional conditions or values ​​beyond those stated.

[0053] In this application, the term "exemplary" is used to mean "used as an example, illustration, or description." Any embodiment described as "exemplary" in this application is not necessarily to be construed as being more preferred or advantageous than other embodiments. The following description is provided to enable any person skilled in the art to make and use this application. Details are set forth in the following description for purposes of explanation. It should be understood that those skilled in the art will recognize that this application can be made without using these specific details. In other instances, well-known structures and processes are not described in detail to avoid obscuring the description of this application with unnecessary detail. Therefore, this application is not intended to be limited to the embodiments shown, but is consistent with the broadest scope of the principles and features disclosed in this application.

[0054] In flexible DC transmission systems, ensuring stable DC voltage control is crucial for normal system operation. Multi-terminal flexible DC transmission systems involve complex scenarios with multiple DC buses and branch lines, making coordinated DC voltage control even more complex. Under steady-state conditions, DC voltage control mainly relies on communication mechanisms, while under transient conditions, it primarily relies on margin control and droop control.

[0055] Please see Figure 1 , Figure 1 This is a schematic diagram of the structure of a multi-terminal flexible DC transmission system according to an embodiment of this application. The multi-terminal flexible DC transmission system includes N DC buses, denoted as DC bus x, where x is the DC bus number, 1 ≤ x ≤ N, x is an integer, and N is an integer greater than or equal to 2. Each DC bus x is connected to M branch lines, denoted as branch lines xy, where y is the branch line number, 1 ≤ y ≤ M, y is an integer, and M is an integer greater than or equal to 1. Each DC bus is connected via tie lines x1x2 (x1 = 1, 2, ..., N; x2 = 1, 2, ..., N, x1 ≠ x2). The multi-terminal flexible DC transmission system also includes multiple converter stations. The multiple converter stations S include DC bus converter stations Sx0 (x = 1, 2, ..., N) and branch converter stations Sxy (x = 1, 2, ..., N; y = 1, 2, ..., M). The DC bus converter station Sx0 is connected to the DC bus x, and the branch converter station Sxy is connected to the branch line xy.

[0056] Typically, the DC voltage control system of a multi-terminal flexible DC transmission system adopts a single-layer control architecture. This requires that devices at each port must communicate with devices at all other ports, resulting in high communication volume and high load factor. Furthermore, when the topology of a multi-terminal flexible DC transmission system changes, such as during renovation or expansion, the programs for devices at all ports need to be modified. This not only increases the workload of modifications but also raises the probability of errors. Margin control is related to the number of ports; when the number of ports exceeds three, designing margin reference values ​​for margin control becomes more difficult.

[0057] In view of this, embodiments of this application provide a DC voltage control system and method for controlling a multi-terminal flexible DC transmission system. A three-layer control architecture is achieved through pole control protection devices, DC station control devices, and coordination control devices. Each layer of control devices communicates only with adjacent layer control devices, enabling data or commands to be transmitted step-by-step. This eliminates the need for each control device to communicate with all other control devices, thereby reducing the communication volume and load rate of DC voltage control in the multi-terminal flexible DC transmission system, and thus solving at least some of the aforementioned technical problems.

[0058] Please see Figure 2 , Figure 2 This is a schematic diagram of the DC voltage control system according to an embodiment of this application. The DC voltage control system includes a pole control and protection device PCPxy (PCP stands for Pole Control & Protection), a DC station control device DCCx0 (DCC stands for Direct Current Control), and a coordination control device SCC (SCC stands for Inter-station Coordinated Control). The pole control and protection device PCPxy is configured to determine the voltage control state of the corresponding converter station S. The DC station control device DCCx0 is configured in a DC bus converter station Sx0 and electrically connected to each pole control and protection device PCPxy within the DC bus control area. It is configured to acquire the voltage control state of each converter station S and issue voltage control commands to the corresponding pole control and protection device PCPxy. The voltage control commands are used to instruct the corresponding converter station S to take over DC voltage control. The coordination control device SCC is configured at any DC bus converter station Sx0 and electrically connected to each DC station control device DCCx0. It is configured to issue voltage control commands to the corresponding DC station control device DCCx0 based on the voltage control status of each converter station S.

[0059] For example, multiple converter stations S include DC voltage control stations and power control stations. The voltage control status includes a DC voltage control status and a DC voltage takeover permission status. The DC voltage control status characterizes whether the DC voltage of the system is currently controlled. For example, if converter station S is a DC voltage control station, it means that converter station S controls the DC voltage of the system; if converter station S is a power control station, it means that converter station S does not control the DC voltage of the system. The DC voltage takeover permission status characterizes the ability to take over DC voltage control when needed. For example, if converter station S is locked, it means that converter station S does not allow takeover of DC voltage control; if converter station S is unlocked, it means that converter station S allows takeover of DC voltage control.

[0060] Specifically, in a multi-terminal flexible DC transmission system, each converter station S is equipped with a pole control and protection device PCPxy. That is, each DC bus converter station Sx0 and each branch converter station Sxy is also equipped with a pole control and protection device PCPxy, and all pole control and protection devices PCPxy form the first-level control architecture. In addition, each DC bus converter station Sx0 is equipped with a DC station control device DCCx0, and all DC station control devices DCCx0 form the second-level control architecture. Furthermore, any one of the DC bus converter stations Sx0 is also equipped with a coordination control device SCC. Figure 2 The following is an example of a coordinated control device (SCC) configured in the DC bus converter station S10. The coordinated control device SCC forms the third layer of the control architecture.

[0061] During communication, the first-level control architecture communicates with the second-level control architecture, and the second-level control architecture communicates with the third-level control architecture. That is to say, the communication configuration principle is that devices within the same level do not communicate; specifically, the pole control protection devices PCPxy of different converter stations S, and the DC station control devices DCCx0 of different converter stations S, do not communicate. Devices across levels do not communicate; that is, the pole control protection device PCPxy does not communicate with the coordination control device SCC. Each control architecture only communicates with the adjacent control architecture.

[0062] The above scheme achieves a three-layer control architecture through the polar control protection device PCPxy, the DC station control device DCCx0, and the coordination control device SCC. Each layer of control device communicates only with the adjacent layer of control device, realizing the hierarchical transmission of data or commands. This eliminates the need for each control device to communicate with all other control devices, thereby reducing the communication volume and load rate of each layer of protection devices and better adapting to the needs of system transformation or expansion.

[0063] In some embodiments, the coordination control device SCC is configured to issue voltage control commands to the corresponding DC station control device DCCx0 based on the voltage control status of each converter station S in the following manner:

[0064] Step 1: Based on the voltage control status and DC voltage takeover strategy of each converter station S, determine the first target device for the voltage to be taken over from multiple DC station control devices DCCx0.

[0065] Step two: Send a voltage control command to the first target device.

[0066] In some examples, step one can be achieved in the following way:

[0067] If it is determined that the S-communication of each converter station is normal and there is no DC voltage control station at present, the first target device is determined from multiple DC station control devices DCCx0 based on the first preset priority.

[0068] Specifically, when the S-communication of each converter station is normal, the multi-terminal flexible DC transmission system is in steady-state operation mode. In steady-state operation mode, each pole control and protection device (PCPxy) sends the DC voltage control status and permitted DC voltage takeover status of its branch converter station (Sxy) to the superior DC station control device (DCCx0). The DC station control device (DCCx0) then sends the DC voltage control status and permitted DC voltage takeover status of its DC bus control area to the superior coordination control device (SCC). If the coordination control device (SCC) detects that there is currently no DC voltage control station in the multi-terminal flexible DC transmission system, it can determine the first target device (DCC1) according to a first preset priority. Correspondingly, it sends a voltage control command to the first target device (DCC1). Upon receiving this command, the first target device (DCC1) can determine the second target device (PCP2) from among the multiple pole control and protection devices (PCPxy) corresponding to the DC bus control area according to a second preset priority, and sends the voltage control command to the second target device (PCP2). After receiving the command, the second target device (PCP2) will take over the system DC voltage, achieving stable DC voltage control for the entire system.

[0069] With the above scheme, under steady-state operation, commands can be issued sequentially between the coordination control device SCC, the DC station control device DCCx0, and the pole control protection device PCPxy. This not only reduces the communication volume and load rate of each layer of protection devices, but also better adapts to the needs of system modification or expansion.

[0070] In other examples, step one can be achieved in the following way:

[0071] If any power control station is found to have a communication failure, the DC voltage control station shall remain unchanged.

[0072] Specifically, upon determining a communication anomaly at any power control station, if the DC voltage is normal, the DC voltage control station remains unchanged. If a DC voltage anomaly is determined, indicating that the power control station may be lost, the coordination control device SCC can also be configured to perform the following steps:

[0073] The first step, in the event that the power control station with communication failure is lost, is to determine the second target converter station whose power needs to be adjusted from multiple converter stations based on the active power allocation strategy.

[0074] Specifically, a power control station communication failure indicates a communication failure between the power control station and the corresponding pole control and protection device PCPxy.

[0075] For example, a power control station that has lost communication can be identified by the following methods:

[0076] If the DC voltage deviation slope control strategy of all converter stations S with normal communication is enabled, and the DC line current value of the power control station with abnormal communication is less than the preset current value, then the power control station with abnormal communication is determined to be lost.

[0077] For example, the preset current value can be set to 5% of the rated current value. Other preset current values ​​can also be set, but this application embodiment does not specifically limit this.

[0078] Specifically, when the DC voltage is abnormal, the DC voltage deviation slope control strategy of each converter station S will be automatically enabled, that is, the value of the DC voltage deviation slope control flag bit will be set to 1. At this time, each converter station S with normal communication will send the value of the DC voltage deviation slope control flag bit to 1. Then, after the DC voltage deviation slope control strategy of each converter station S is automatically enabled for a certain period of time (for example, it can be set to 10 seconds or more), the coordination control device SCC can determine that the DC voltage deviation slope control strategy of all converter stations S with normal communication is enabled. In this way, false judgments can be prevented and identification accuracy can be improved.

[0079] Please see Figure 3 , Figure 3 This is a schematic diagram illustrating the principle of the DC voltage deviation slope control strategy in the embodiments of this application. d1 ~U d3 P represents the voltage between S1 and S3. d1 ~P d3 This represents the power of S1 to S3. When the DC voltage control station stabilizes the DC voltage, each power control station operates stably at its set power value. When a disturbance occurs in the DC voltage, the power control station may enter the slope characteristic range, adjusting the output of converter S to assist in stabilizing the DC voltage. Once the DC voltage stabilizes again, each converter S in the system will return to constant power control mode. (Combined with...) Figure 3For example, in steady-state operation, taking S1 as the DC voltage control station and S2 and S3 as active power control stations, S1 controls the DC voltage, and S2 and S3 control the active power, with the system balanced at Udref1. When S1 is blocked, it loses DC voltage control, and the system has no DC voltage control station. The active power of S2 and S3 becomes negative, leading to an imbalance in the system's active power and a drop in DC voltage. In transient operation, under the influence of the DC voltage-active power relationship curve (i.e., the deviation slope curve), S2 and S3 reach the next system balance, that is, the system balances at a new Udref1, and the active power of S2 and S3 changes to a new value.

[0080] It should be noted that the specific settings of the active power allocation strategy are related to the current grid demand. The coordinated control device (SCC) does not perform calculations; it only needs to receive the corresponding command signals. This application will not elaborate on this aspect in the embodiments.

[0081] The second step is to send a power control command to the DC station control device DCCx0 corresponding to the second target converter station. The power control command is used to instruct the corresponding converter station to redistribute active power.

[0082] In some other examples, step one can be achieved in the following way:

[0083] The first step, in the event that the DC voltage control station is found to be in communication failure or lost, is to identify the first target converter station from among multiple power control stations to take over the voltage.

[0084] The second step is to identify the DC station control device DCCx0 corresponding to the first target converter station as the first target device.

[0085] Specifically, a communication failure at the DC voltage control station indicates a communication breakdown between the DC voltage control station and its corresponding pole control protection device, PCPxy. Upon confirming the communication failure, if the DC voltage control station is lost, the DC voltage deviation slope control strategy of each power control station will activate to maintain a transient stable balance of the DC voltage. The coordinated control device SCC can determine that the DC voltage deviation slope control strategy of each power control station is enabled after receiving the DC voltage deviation slope control flag value 1 from each power control station for a certain period (e.g., 10 seconds or more). Simultaneously, if the DC line current value of the DC voltage control station with the communication failure is less than a preset current value (e.g., 5% of the rated current value), it is determined that the DC voltage control station has been lost.

[0086] Furthermore, the coordinated control device SCC can send voltage control signals to power control stations with higher DC voltage control priority and perform active power redistribution. Specifically, the coordinated control device SCC can perform active power redistribution through the following steps:

[0087] The first step is to determine the second target converter station whose power needs to be adjusted from multiple power control stations based on the active power allocation strategy.

[0088] The second step is to send a power control command to the DC station control device DCCx0 corresponding to the second target converter station.

[0089] The active power allocation strategy can be found in the description of the aforementioned embodiments, and will not be repeated here.

[0090] In some other examples, step one can be achieved in the following way:

[0091] If the DC station control device DCCx0 corresponding to the voltage control area is found to have communication failure and the DC voltage of the DC bus is found to be abnormal, the first target device is determined from the DC station control devices DCCx0 corresponding to each non-voltage control area. The voltage control area is the DC bus control area corresponding to the DC voltage control station, and the non-voltage control area is the other DC bus control areas other than the voltage control area.

[0092] For example, if the DC voltage control station is a branch converter S11, then the area controlled by the DC bus 1 corresponding to the branch converter S11 is the voltage control area, and the areas controlled by the other DC buses 2 to x are the non-voltage control areas.

[0093] Specifically, communication anomalies in the DC station control device DCCx0 corresponding to the voltage control area include communication anomalies between the DC station control device DCCx0 and the connected pole control protection device PCPxy, as well as communication anomalies between the DC station control device DCCx0 and the connected coordination control device SCC.

[0094] If the DC voltage remains normal, the DC voltage control station remains unchanged, meaning the coordinated control unit (SCC) maintains the control of the entire system unchanged. If the DC voltage is abnormal, the DC voltage deviation slope control of each converter S will activate, indicating that the voltage control area has lost its DC voltage control capability and the non-voltage control area needs to take over DC voltage control. At this time, the coordinated control unit (SCC) can determine that the DC voltage deviation slope control strategy of each power control station in the non-voltage control area has been enabled after receiving the value of the DC voltage deviation slope control flag bit sent by each power control station in the non-voltage control area for a certain period of time (e.g., it can be set to 10 seconds or more). It then determines the first target device from the DC station control devices (DCCx0) corresponding to each non-voltage control area, so that the first target device can take over DC voltage control and allocate DC voltage control rights to the corresponding converter station.

[0095] In some other examples, step one can be achieved in the following way:

[0096] If the DC station control device DCCx0 in the non-voltage control area is found to have communication failure and the DC voltage of the DC bus is found to be abnormal, the DC voltage control station shall be kept unchanged.

[0097] Specifically, communication anomalies in the DC station control device DCCx0 corresponding to the non-voltage control area include communication anomalies between the DC station control device DCCx0 and the connected pole control protection device PCPxy, as well as communication anomalies between the DC station control device DCCx0 and the connected coordination control device SCC.

[0098] If the DC voltage remains normal, the DC voltage control station remains unchanged, meaning the coordinated control unit SCC maintains the control of the entire system unchanged. If the DC voltage is abnormal, the DC voltage deviation slope control of each converter S will activate to assist in stabilizing the DC voltage.

[0099] In some other examples, step one can be achieved in the following way:

[0100] If it is determined that the communication of the coordination control device SCC is abnormal and the DC voltage of the DC bus is abnormal, the first target device is determined from the DC station control devices DCCx0 corresponding to each non-voltage control area.

[0101] Specifically, a communication failure in the coordination control unit SCC indicates a communication failure between the coordination control unit SCC and the connected DC station control unit DCCx0.

[0102] If the DC voltage remains normal, the DC voltage control station remains unchanged, meaning the coordination control device SCC maintains the control of the entire system unchanged. If the DC voltage is abnormal, the DC voltage deviation slope control of each converter S will activate, indicating that the voltage control area has lost its DC voltage control capability, and the non-voltage control area needs to take over DC voltage control. At this time, the DC voltage deviation slope control flag of the non-voltage control area is 1, with a delay time t (t≥10s). The DC station control device DCCx0 of the non-voltage control area takes over DC voltage control and allocates DC voltage control rights to the corresponding converter station.

[0103] It should be noted that in the embodiments of this application, communication software tools can be used to detect abnormal communication signals between the devices.

[0104] In some embodiments, the DC station control device DCCx0 can issue voltage control commands in the following manner:

[0105] Step 1: Receive voltage control commands sent by the coordination control device SCC.

[0106] Step 2: Based on the voltage control status of each converter station S, determine the second target device from multiple pole control protection devices PCPxy.

[0107] Step 3: Send a voltage control command to the second target device.

[0108] For example, the DC station control device DCCx0 can determine the highest priority pole control protection device PCPxy among multiple pole control protection devices PCPxy as the second target device based on a second preset priority.

[0109] The above solution enables stable DC voltage control of multi-terminal flexible DC transmission systems under communication anomalies. It not only reduces the communication load and load rate of protection devices at each level, but also determines stable DC voltage control under different communication conditions. It can cope with more scenarios and better adapt to the needs of system transformation or expansion.

[0110] To better illustrate the DC voltage control system of the embodiments of this application, specific examples are provided below.

[0111] Please refer to the following: Figure 4 , Figure 5 and Figure 6 , Figure 4 This is a schematic diagram of an example structure of the DC voltage control system of the five-terminal flexible DC transmission system according to an embodiment of this application. Figure 5 for Figure 4 The waveform diagram shown is from a simulation test of the system under normal communication conditions. Figure 6 for Figure 4 The diagram shows the simulation waveforms of the system under communication failure conditions. For example, a system like this can be built in the power system transient simulation software platform PSCAD / EMTDC. Figure 4 The diagram shows a detailed model of the DC voltage control system for a five-terminal flexible DC transmission system. The experimental waveforms are shown below. Figure 5 , Figure 6 As shown. Figure 5 and Figure 6 In this diagram, UdcB1 and UdcB2 represent the DC voltages of DC bus 1 and DC bus 2, respectively. S1, S2, S3, S4, and S5 represent S11, S10, S12, S20, and S21, respectively. Psys represents the active power of the converter station. TOORD represents the voltage control command received by the converter station. UdcIND represents the DC voltage control status of the converter station. DEBIND represents the unlocked status of the converter station. TOSCC represents the voltage control command sent from SCC10 to DCC.

[0112] Simulation tests were conducted under normal communication conditions at each converter station. DC bus 1 and DC bus 2 were interconnected. S1 and S2 were both locked, while S3, S4, and S5 were unlocked. S3 controlled the DC voltage (25kV), and S4 and S5 controlled the active power (10MW). S3 locked after 3 seconds (S3DEBIND = 0). The SCC detected the lack of DC voltage control and took over. At this time, B1 had no DC voltage control capability, and the SCC issued a takeover command to region B2 (B2TOSCC = 1). Upon receiving the takeover command, S4 and S5 were prioritized, and S4 executed the takeover command (S4TOORD = 1), taking over the system DC voltage (S4UdcIND = 1). Simultaneously, S5 maintained the active power control mode. Throughout the entire DC voltage coordination control process, system fluctuations were minimal.

[0113] Simulation experiment under communication anomaly. DC bus 1 and DC bus 2 are interconnected. S1 controls the DC voltage, and S2, S3, S4, and S5 control the active power (10MW). S1 is blocked at 2s (S1DEBIND=0) and communication with S1 fails. SCC does not detect that the system needs to take over DC voltage control at this moment. The DC voltage deviation slope control strategy of S2, S3, S4, and S5 takes effect, adjusting the DC voltage and controlling it below 1.08pu (per unit). After a certain adjustment time, at 2.8s, SCC detects that the system needs to take over DC voltage and issues a takeover command to areas B1 and B2. According to the priority principle, area B1 receives the takeover command. S2 and S3 are sorted according to priority. S2 executes the takeover command (S2TOORD=1) and takes over the system DC voltage (S2UdcIND=1).

[0114] It is understood that the DC voltage control system of this application embodiment can not only reduce the communication volume and load rate of each control device, but also reduce the probability of errors during modification or expansion and adjustment, reduce the complexity of setting the margin reference value, and flexibly maintain stable DC voltage control in various scenarios.

[0115] On the other hand, this application also provides a DC voltage control method, applied to the DC voltage control system of the aforementioned embodiments.

[0116] Please see Figure 7 , Figure 7 This is a flowchart illustrating the DC voltage control method according to an embodiment of this application. The method specifically includes the following steps:

[0117] Step 701: Based on the voltage control status of each converter station, the coordination control device issues voltage control commands to the corresponding DC station control device. The voltage control commands are used to instruct the corresponding converter station to take over DC voltage control. The voltage control status of each converter station is obtained through the corresponding pole control protection device.

[0118] Step 702: Send a voltage control command to the corresponding pole control and protection device through the DC station control device so that the corresponding pole control and protection device takes over the DC voltage control.

[0119] It should be noted that the DC voltage control method of this application embodiment and the DC voltage control system of the foregoing embodiment can be referred to each other. For the contents not specifically described in the embodiments of this application, please refer to the corresponding description in the DC voltage control system of the foregoing embodiment.

[0120] Accordingly, this application also provides a multi-terminal flexible DC transmission system. This multi-terminal flexible DC transmission system includes the DC voltage control system described in the foregoing embodiments.

[0121] The above provides a detailed description of a DC voltage control system and method provided in the embodiments of this application. Specific examples have been used to illustrate the principles and implementation methods of this application. The description of the above embodiments is only for the purpose of helping to understand the method and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A DC voltage control system, characterized in that, For controlling a multi-terminal flexible DC transmission system, the multi-terminal flexible DC transmission system includes multiple converter stations, each converter station including a DC bus converter station and branch converter stations, the DC bus converter station being connected to a DC bus, and the branch converter station being connected to a branch line; the DC voltage control system includes: A voltage control protection device, configured in one of the converter stations, is configured to determine the voltage control state corresponding to the converter station; A DC station control device, configured in a DC bus converter station and electrically connected to each of the pole control and protection devices within the DC bus control area, is configured to acquire the voltage control status of each converter station and issue voltage control commands to the corresponding pole control and protection devices, wherein the voltage control commands are used to instruct the corresponding converter station to take over DC voltage control. A coordination control device, configured at any of the DC bus converter stations and electrically connected to each of the DC station control devices, is configured to issue voltage control commands to the corresponding DC station control device based on the voltage control status of each converter station.

2. The DC voltage control system according to claim 1, characterized in that, The coordination control device is configured to issue voltage control commands to the corresponding DC station control device based on the voltage control status of each converter station, including: Based on the voltage control status and DC voltage takeover strategy of each converter station, a first target device for the voltage to be takenover is determined from the multiple DC station control devices; The voltage control command is sent to the first target device.

3. The DC voltage control system according to claim 2, characterized in that, The plurality of converter stations include DC voltage control stations and power control stations; the coordination control device is configured to determine a first target device for the voltage to be managed from among the plurality of DC station control devices, including: If any of the power control stations is found to have a communication failure, the DC voltage control station shall remain unchanged.

4. The DC voltage control system according to claim 3, characterized in that, In the event that any of the power control stations is found to have a communication anomaly, the coordination control device is further configured to perform the following steps: In the event that the power control station, which is determined to have communication failure, is lost, a second target converter station whose power needs to be adjusted is determined from among the multiple converter stations based on the active power allocation strategy. A power control command is issued to the DC station control device corresponding to the second target converter station. The power control command is used to instruct the corresponding converter station to redistribute active power.

5. The DC voltage control system according to claim 4, characterized in that, The coordination control device is also configured to determine that the power control station has lost communication by the following steps: If the DC voltage deviation slope control strategy of all converter stations with normal communication is enabled, and the DC line current value of the power control station with abnormal communication is less than the preset current value, then the power control station with abnormal communication is deemed to be out of service.

6. The DC voltage control system according to claim 3, characterized in that, The coordination control device is configured to determine a first target device for the voltage to be managed from among the plurality of DC station control devices, and further includes: In the event that the DC voltage control station is found to be in communication failure and the DC voltage control station is lost, a first target converter station to be taken over voltage is determined from among the multiple power control stations. The DC station control device corresponding to the first target converter station is identified as the first target device.

7. The DC voltage control system according to claim 6, characterized in that, The coordination control device is also configured to perform the following steps: Based on the active power allocation strategy, a second target converter station whose power needs to be adjusted is determined from among the multiple power control stations; A power control command is sent to the DC station control device corresponding to the second target converter station.

8. The DC voltage control system according to claim 3, characterized in that, The coordination control device is configured to determine a first target device for the voltage to be managed from among the plurality of DC station control devices, and further includes: If it is determined that the communication of the DC station control device corresponding to the voltage control area is abnormal and the DC voltage of the DC bus is abnormal, the first target device is determined from the DC station control devices corresponding to each non-voltage control area. The voltage control area is the DC bus control area corresponding to the DC voltage control station, and the non-voltage control area is other DC bus control areas besides the voltage control area.

9. The DC voltage control system according to claim 3, characterized in that, The coordination control device is configured to determine a first target device for the voltage to be managed from among the plurality of DC station control devices, and further includes: If it is determined that the communication of the DC station control device corresponding to the non-voltage control area is abnormal and the DC voltage of the DC bus is abnormal, the DC voltage control station shall be kept unchanged.

10. The DC voltage control system according to claim 3, characterized in that, The coordination control device is configured to determine a first target device for the voltage to be managed from among the plurality of DC station control devices, and further includes: If it is determined that the communication of the coordination control device is abnormal and the DC voltage of the DC bus is abnormal, the first target device is determined from the DC station control devices corresponding to each non-voltage control area.

11. The DC voltage control system according to claim 2, characterized in that, The coordination control device is configured to determine a first target device for the voltage to be managed from among the plurality of DC station control devices, including: If it is determined that all the converter stations are communicating normally and there is no DC voltage control station at present, the first target device is determined from the multiple DC station control devices based on a first preset priority.

12. The DC voltage control system according to claim 1, characterized in that, The DC station control device is configured to issue voltage control commands to the corresponding pole control and protection device, including: Receive the voltage control command sent by the coordination control device; Based on the voltage control status of each converter station, a second target device is determined from among the multiple pole control protection devices; The voltage control command is sent to the second target device.

13. A DC voltage control method, characterized in that, The method, applied to a DC voltage control system as described in any one of claims 1-12, comprises: The coordination control device issues voltage control commands to the corresponding DC station control device based on the voltage control status of each converter station. The voltage control commands are used to instruct the corresponding converter station to take over DC voltage control. The voltage control status of each converter station is obtained through the corresponding pole control protection device. The DC station control device sends the voltage control command to the corresponding pole control and protection device so that the corresponding pole control and protection device can take over the DC voltage control.

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