Extra-high voltage flexible direct current transmission system and starting method thereof

Abstract

The application discloses an extra-high voltage flexible direct current power transmission system and a starting method thereof, and belongs to the technical field of extra-high voltage power transmission. The method acquires the connection state of each converter valve group and a direct current line and the live state of a polarity converter valve group. In response to the existence of induced voltage risk, the method sequentially performs: charging and unlocking the polarity converter valve group, charging and unlocking the low-end converter valve group of the self-polarity, and unlocking the high-end converter valve group of the self-polarity in an online input mode. Through the technical scheme, the converter valve group of the polarity is first charged and unlocked, a stable polarity voltage is established, then the low-end converter valve group of the self-polarity is charged and unlocked, and then the high-end converter valve group of the self-polarity is unlocked in an online input mode. Thus, after the polarity voltage of the polarity is established, the influence of the induced voltage on the high-end converter valve group of the self-polarity which is not charged is reduced, and the converter valve group of the self-polarity can sequentially complete charging and unlocking under the condition that the voltage has been established, and the converter valve group can complete charging and input.

Description

Technical Field

[0001] This application relates to the field of ultra-high voltage power transmission technology, and in particular to an ultra-high voltage flexible DC power transmission system and its starting method. Background Technology

[0002] In an ultra-high voltage flexible direct current transmission system, two converter stations are connected by a DC line. Each converter station includes a local pole and a counterpart pole. Each local pole and counterpart pole includes a low-end converter valve group and a high-end converter valve group connected in series. The converter valve groups need to be charged before being put into operation.

[0003] During system startup, if the converter valve group of this pole is connected to the DC line and there is a energized converter valve group in the opposite pole, the energized converter valve group of the opposite pole will generate an induced voltage on the uncharged converter valve group of this pole, causing the uncharged converter valve group to fail to complete charging normally, and the startup process will be difficult to complete normally. Summary of the Invention

[0004] This application provides an ultra-high voltage flexible direct current transmission system and its startup method to solve the technical problem that the converter valve group cannot be charged normally due to induced voltage during the startup process of the ultra-high voltage flexible direct current transmission system.

[0005] To achieve the above objectives, according to a first aspect of this application, a startup method for an ultra-high voltage flexible direct current transmission system is provided, comprising: the ultra-high voltage flexible direct current transmission system including two converter stations and a DC line connecting the two converter stations; each converter station including a local pole and a counterpart pole, wherein each local pole and the counterpart pole include a low-end converter valve group and a high-end converter valve group connected in series; The startup method of the ultra-high voltage flexible DC transmission system includes: Obtain status information, which includes: the connection status of the two converter valve groups of this pole to the DC line, the connection status of the two converter valve groups of the opposite pole to the DC line, and the energized status of the two converter valve groups of the opposite pole. In response to the risk of induced voltage, the following unlocking sequence control steps are executed in sequence: the two converter valve groups of the opposite pole are charged and unlocked; the low-end converter valve group of the local pole is charged and unlocked; and the high-end converter valve group of the local pole is unlocked in an online-connected manner.

[0006] Optionally, the two converter stations of the ultra-high voltage flexible DC transmission system are a sending-end converter station and a receiving-end converter station, respectively. The sending-end converter station is connected to the sending-end power grid, and the receiving-end converter station is connected to the receiving-end power grid. Charging and unlocking the two commutation valve assemblies of the opposite pole includes: The converter valve group of the opposite pole of the sending-end converter station and the converter valve group of the opposite pole of the receiving-end converter station are charged and unlocked. The sending-end converter station is controlled to charge the converter valve group of its opposite pole, and the charging is carried out through the sending-end power grid; The receiving-end converter station is controlled to charge the converter valve group of its opposite pole, and the charging is carried out through the receiving-end power grid; When both the converter valve groups of the sending-end converter station and the receiving-end converter station have completed charging, the valves are unlocked to establish a stable pole voltage between the sending-end converter station and the receiving-end converter station.

[0007] Optionally, the two converter stations of the ultra-high voltage flexible DC transmission system include a sending-end converter station and a receiving-end converter station, wherein the sending-end converter station is connected to the sending-end power grid; Charging and unlocking the two commutation valve assemblies of the opposite pole includes: The converter valve group of the opposite pole of the sending-end converter station and the converter valve group of the opposite pole of the receiving-end converter station are charged and unlocked. The sending-end converter station is controlled to charge the converter valve group of its opposite pole, and the charging is carried out through the sending-end power grid; The sending-end converter station is controlled to transmit electrical energy to the receiving-end converter station via the DC line in order to charge the converter valve group of the opposite pole of the receiving-end converter station. When both the converter valve groups of the sending-end converter station and the receiving-end converter station have completed charging, the valves are unlocked to establish a stable pole voltage between the sending-end converter station and the receiving-end converter station.

[0008] Optionally, charging and unlocking the low-end converter valve group of the local pole includes: Charge and unlock the low-end converter valve group of the local pole of the sending-end converter station and the low-end converter valve group of the local pole of the receiving-end converter station. With the two converter valve groups of the opposite pole unlocked, the sending-end converter station is controlled to charge the low-end converter valve group of its own pole, and the charging is carried out through the sending-end power grid; The receiving-end converter station is controlled to charge its low-end converter valve group at its own pole, and the charging is carried out through the receiving-end power grid; Unlocking is performed when both the low-end converter valve group of the sending-end converter station and the low-end converter valve group of the receiving-end converter station have completed charging.

[0009] Optionally, charging and unlocking the low-end converter valve group of the local pole further includes: While the low-end converter valve group of the local pole is being charged, the bypass switch of the high-end converter valve group of the local pole is closed to bypass the high-end converter valve group.

[0010] Optionally, unlocking the high-end converter valve assembly of the local pole in an online engagement manner includes: With the low-end converter valve group of the pole unlocked, the high-end converter valve group of the pole is pre-charged. When the voltage of the high-side converter valve group of the local pole matches the voltage of the DC line, the high-side converter valve group of the local pole is unlocked.

[0011] Optionally, unlocking the high-end converter valve assembly of the local pole in an online engagement manner includes: When the low-end converter valve group of the pole is charged and the DC line has not yet established power transmission, Through the internal control of the sending-end converter station, the DC voltage of the high-end converter valve group of the local pole is gradually established; After the DC voltage matches the DC line voltage, the corresponding disconnect switch is closed to complete the commissioning of the high-end converter valve group.

[0012] Optionally, unlocking the high-end converter valve assembly of the local pole in an online engagement manner includes: With the low-end converter valve group of the aforementioned pole unlocked and in power transmission mode, The control system of the sending-end converter station is coordinated with the control system of the receiving-end converter station to perform pre-charging, voltage matching, bypass switch operation and unlocking, so as to connect the high-end converter valve group of the local pole in an uninterrupted manner.

[0013] Optionally, in response to the risk of induced voltage, the state of the local pole of the sending-end converter station is monitored; The unlocking restriction sequence will be exited if any of the following conditions are met: The local pole converter valve group of the sending-end converter station was successfully unlocked; Both converter valve groups at the local pole of the sending-end converter station have been issued charging commands; The local pole of the receiving-end converter station has completed charging of the converter valve group.

[0014] According to a second aspect of this application, an ultra-high voltage flexible direct current transmission system is provided, comprising: Sending-end converter station and receiving-end converter station, each of the converter stations includes a local pole and a counterpart pole, and each of the local pole and the counterpart pole includes a low-end converter valve group and a high-end converter valve group connected in series; A DC line connecting the sending-end converter station and the receiving-end converter station; The control device is configured to execute the startup method of the ultra-high voltage flexible DC transmission system described in any of the above embodiments.

[0015] Optionally, the control device includes a monitoring module and an interlocking control module; The monitoring module is configured to acquire status information, which includes: the connection status of the converter valve group of the local pole to the DC line, the connection status of the converter valve group of the opposite pole to the DC line, and the energized status of the converter valve group of the opposite pole. The interlocking control module is configured to, in response to the presence of an induced voltage risk, sequentially execute the following unlocking sequence control steps: charge and unlock the two converter valve groups of the opposite pole; charge and unlock the low-end converter valve group of the local pole; and unlock the high-end converter valve group of the local pole in an online-connected manner. The conditions under which there is a risk of induced voltage include: the converter valve group of the local pole is connected to the DC line, the converter valve group of the opposite pole is connected to the DC line, and at least one of the converter valve groups in the opposite pole is energized.

[0016] The startup method of the ultra-high voltage flexible direct current transmission system according to this application embodiment obtains the connection status of each converter valve group to the DC line and the energized status of the opposite pole converter valve group; in response to the risk of induced voltage, it sequentially executes: charging and unlocking the opposite pole converter valve group, charging and unlocking the low-end converter valve group of the current pole, and unlocking the high-end converter valve group of the current pole in an online connection manner. Through the above technical solution, the two converter valve groups of the opposite pole are first charged and unlocked to establish a stable pole voltage, then the low-end converter valve group of the current pole is charged and unlocked, and then the high-end converter valve group of the current pole is unlocked in an online connection manner. As a result, after the pole voltage of the opposite pole is established, the impact of induced voltage on the uncharged high-end converter valve group of the current pole is reduced, and the converter valve group of the current pole can sequentially complete charging and unlocking under the established voltage conditions, enabling the converter valve group to complete charging and connection, and the startup process to be completed normally.

[0017] The ultra-high voltage flexible direct current transmission system of this application includes a sending-end converter station, a receiving-end converter station, a DC line connecting the sending-end and receiving-end converter stations, and a control device configured to execute the above-described startup method. Through the above technical solution, the control device acquires the connection status of each converter valve group to the DC line and the energized status of the opposing pole converter valve group. In response to the risk of induced voltage, it sequentially executes: charging and unlocking the opposing pole converter valve group, charging and unlocking the low-end converter valve group of this pole, and unlocking the high-end converter valve group of this pole in an online-connected manner. Thus, a stable pole voltage is first established for the opposing pole, and then the charging, unlocking, and online connection of the low-end and high-end converter valve groups of this pole are completed sequentially. The impact of induced voltage on the uncharged high-end converter valve group of this pole is reduced, and the startup process can be completed normally.

[0018] Other features and advantages of this application will be described in detail in the following detailed description section. Attached Figure Description

[0019] 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 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.

[0020] To gain a more complete understanding of this application and its beneficial effects, the following description will be provided in conjunction with the accompanying drawings, wherein the same reference numerals in the following description denote the same parts.

[0021] Figure 1 This is a flowchart of the startup method of the ultra-high voltage flexible DC transmission system provided in the exemplary embodiments of this application; Figure 2 This is a flowchart illustrating the charging and unlocking of the opposite pole provided in an exemplary embodiment of this application; Figure 3 This is a flowchart of the charging and unlocking process of the ultra-low-end valve group provided in an exemplary embodiment of this application; Figure 4 This is a flowchart of the exit unlocking restriction sequence control provided in an exemplary embodiment of this application; Figure 5 This is a schematic diagram of the connection structure of an ultra-high voltage flexible DC transmission system provided in an exemplary embodiment of this application.

[0022] Explanation of reference numerals in the attached figures: 10a. Sending-end converter station; 10b. Receiving-end converter station; 20. Sending-end power grid; 30. Receiving-end power grid; 40. DC lines; 11. Opposite pole; 12. This extreme; 121. High-end converter valve assembly; 122. Low-end converter valve assembly. Detailed Implementation

[0023] 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 a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the protection scope of this application.

[0024] Reference Figure 1This application provides a startup method for an ultra-high voltage flexible direct current transmission system to solve the technical problem that during the startup process of the ultra-high voltage flexible direct current transmission system, the energized converter valve group of the opposite pole 11 generates an induced voltage to the uncharged converter valve group of the local pole 12 through the DC line 40, which causes the uncharged converter valve group to be unable to charge normally.

[0025] The ultra-high voltage flexible direct current transmission system includes two converter stations and a DC line 40 connecting the two converter stations. Both converter stations adopt a bipolar, two-terminal neutral-point grounding method. Each converter station includes a local pole 12 and a counterpart pole 11. Each local pole 12 and counterpart pole 11 includes a low-end converter valve group 122 and a high-end converter valve group 121 connected in series. The terms local pole 12 and counterpart pole 11 are relative designations; local pole 12 is the pole to be started within the converter station, and counterpart pole 11 is the other pole within the converter station opposite to local pole 12. The converter valve groups need to be charged before being put into operation.

[0026] During system startup, if both poles of the converter station are connected to DC lines 40, and one pole contains a energized converter valve group, the uncharged converter valve group on the other pole faces the risk of induced voltage. Specifically, the energized converter valve group on pole 11 induces a voltage in the uncharged converter valve group on pole 12. Under this induced voltage, the uncharged converter valve group on pole 12 is passively charged, preventing simultaneous charging and unlocking of both valve groups, thus hindering the normal startup process.

[0027] To address the aforementioned technical issues, this embodiment is implemented according to the following steps: S101, Obtain status information.

[0028] The status information includes the connection status of the two converter valve groups of the local pole 12 to the DC line 40, the connection status of the two converter valve groups of the opposite pole 11 to the DC line 40, and the energized status of the two converter valve groups of the opposite pole 11. The energized status includes charging in progress and charging completed.

[0029] S102. Determine whether there is a risk of induced voltage at pole 12.

[0030] When the two converter valve groups of the local pole 12 are connected to the DC line 40, the two converter valve groups of the opposite pole 11 are connected to the DC line 40, and at least one converter valve group in the opposite pole 11 is energized, it is determined that the local pole 12 has an induced voltage risk.

[0031] S103. In response to the risk of induced voltage, the commutation valve group of pole 11 is charged and unlocked.

[0032] After the two commutator valve groups of counter pole 11 have finished charging, unlocking is performed, and a stable pole voltage is established for counter pole 11.

[0033] S104. Charge and unlock the low-end converter valve group 122 of the local pole 12.

[0034] After establishing a stable voltage at pole 11, the low-end converter valve group 122 of pole 12 is charged, and unlocking is performed after the low-end converter valve group 122 of pole 12 is fully charged.

[0035] S105, the high-end converter valve group 121 of the pole 12 is unlocked by online engagement.

[0036] After the low-end converter valve group 122 of the pole 12 is unlocked, the high-end converter valve group 121 of the pole 12 is put into online operation, and then unlocked after the online operation is completed.

[0037] Through the above steps, the two converter valve groups of pole 11 are charged first and a stable pole voltage is established. The low-end converter valve group 122 and the high-end converter valve group 121 of pole 12 are put into operation in sequence under the condition that the pole voltage has been established. The high-end converter valve group 121 of pole 12 that has not been charged is less affected by the induced voltage, and the start-up process can be completed normally. The above technical problems are improved.

[0038] In some embodiments, refer to Figure 2 This paper provides a startup method for an ultra-high voltage flexible direct current transmission system to solve the technical problem that it is difficult for the converter valve group of pole pair 11 at the sending-end converter station 10a and the converter valve group of pole pair 11 at the receiving-end converter station 10b to coordinate the charging and unlocking of the two converter stations, thus making it impossible to establish a stable pole voltage.

[0039] The UHV flexible DC transmission system has two converter stations: the sending-end converter station 10a and the receiving-end converter station 10b. The sending-end converter station 10a is connected to the sending-end power grid 20, and the receiving-end converter station 10b is connected to the receiving-end power grid 30. The converter valve groups of pole pairs 11 at the sending-end converter station 10a and the receiving-end converter station 10b are located at the sending-end converter station 10a and the receiving-end converter station 10b, respectively. Both need to be charged through the sending-end power grid 20 and the receiving-end power grid 30, respectively. Only after both pole pairs 11 converter valve groups have been charged can they be unlocked at the same time to establish a stable pole voltage between the sending-end converter station 10a and the receiving-end converter station 10b.

[0040] Step S103 includes the following steps: The two converter valve groups of the pole 11 include the two converter valve groups of the pole 11 of the sending-end converter station 10a and the two converter valve groups of the pole 11 of the receiving-end converter station 10b. Both of them receive electrical energy from their respective AC sides to complete the charging process. The charging process is carried out separately.

[0041] S1031, the sending-end converter station 10a charges the two converter valve groups of its opposite pole 11, and the charging is carried out through the sending-end power grid 20. The AC side of both converter valve groups of the opposite pole 11 of the sending-end converter station 10a is connected to the sending-end power grid 20.

[0042] S1032, the receiving-end converter station 10b charges the two converter valve groups of its opposite pole 11, and the charging is carried out through the receiving-end power grid 30. The AC side of the low-end converter valve group 122 of the opposite pole 11 of the receiving-end converter station 10b is connected in parallel to the first receiving-end power supply, and the AC side of the high-end converter valve group 121 of the opposite pole 11 is connected in parallel to the second receiving-end power supply.

[0043] S1033. When both converter valve groups of pole pair 11 in the sending-end converter station 10a and the two converter valve groups of pole pair 11 in the receiving-end converter station 10b are fully charged, the converter valve groups are unlocked to establish a stable pole voltage between the sending-end converter station 10a and the receiving-end converter station 10b.

[0044] The charging of the two converter valve groups of pole 11 at the sending-end converter station 10a and the charging of the two converter valve groups of pole 11 at the receiving-end converter station 10b are carried out separately. After both are charged, the aforementioned converter valve groups are unlocked.

[0045] After a stable electrode voltage is established at electrode 11, the subsequent charging process of electrode 12 has a stable voltage reference, and the degree to which the induced voltage is borne by the uncharged converter valve group at electrode 12 is reduced.

[0046] In some embodiments, a startup method for an ultra-high voltage flexible direct current transmission system is provided to solve the technical problem that charging of the receiving-end pole-to-pole 11 converter valve group via the receiving-end power grid 30 depends on the conditions of the receiving-end AC system and is difficult to complete when the conditions of the receiving-end AC system are not met.

[0047] The ultra-high voltage flexible direct current transmission system has two converter stations: a sending-end converter station 10a and a receiving-end converter station 10b. The sending-end converter station 10a is connected to the sending-end power grid 20. The converter valve groups of pole pairs 11 in the sending-end converter station 10a and the receiving-end converter station 10b are located in the sending-end converter station 10a and the receiving-end converter station 10b, respectively. The converter valve groups of pole pairs 11 in the receiving-end converter station 10b are not charged through the receiving-end power grid 30, but are charged by the power transmitted from the sending-end converter station 10a through the DC line 40.

[0048] Another implementation of step S103 includes the following steps: S1031, the sending-end converter station 10a charges the two converter valve groups of its opposite pole 11, and the charging is carried out through the sending-end power grid 20. The AC side of each converter valve group of the sending-end converter station 10a is connected to the sending-end power grid 20, and the two converter valve groups of the opposite pole 11 of the sending-end converter station 10a receive electrical energy from the sending-end power grid 20 through their respective AC sides to complete the charging.

[0049] S1032, The sending-end converter station 10a transmits electrical energy to the receiving-end converter station 10b via DC line 40. The two converter valve groups of the receiving-end converter station 10b opposite pole 11 receive the electrical energy transmitted by the sending-end converter station 10a through the DC side to complete the charging.

[0050] S1033. When both converter valve groups of pole pair 11 in the sending-end converter station 10a and the two converter valve groups of pole pair 11 in the receiving-end converter station 10b are fully charged, the converter valve groups are unlocked to establish a stable pole voltage between the sending-end converter station 10a and the receiving-end converter station 10b.

[0051] The charging of the two converter valve groups of pole 11 at the sending-end converter station 10a and the charging of the two converter valve groups of pole 11 at the receiving-end converter station 10b are carried out separately. After both are charged, the aforementioned converter valve groups are unlocked.

[0052] After a stable electrode voltage is established at electrode 11, the subsequent charging process of electrode 12 has a stable voltage reference, and the degree to which the induced voltage is borne by the uncharged converter valve group at electrode 12 is reduced.

[0053] In some embodiments, refer to Figure 3 This embodiment provides a startup method for an ultra-high voltage flexible DC transmission system to solve the technical problem that after the two converter valve groups of the opposite pole 11 are unlocked, the low-end converter valve group 122 of the pole 12 is located at the sending-end converter station 10a and the receiving-end converter station 10b, making it difficult to coordinate the charging and unlocking, and thus the DC voltage of the pole 12 is difficult to establish.

[0054] The ultra-high voltage flexible direct current transmission system has two converter stations: a sending-end converter station 10a and a receiving-end converter station 10b. The sending-end converter station 10a is connected to the sending-end power grid 20, and the receiving-end converter station 10b is connected to the receiving-end power grid 30. After the two converter valve groups of the opposite pole 11 are unlocked, the low-end converter valve group 122 of the local pole 12 needs to be charged through both the sending-end power grid 20 and the receiving-end power grid 30. The valve groups 122 at both ends of the local pole 12 are unlocked simultaneously after charging to establish the DC voltage of the local pole 12.

[0055] Step S104 includes the following steps: S1041, the sending-end converter station 10a charges the low-end converter valve group 122 of its local pole 12, and the charging is carried out through the sending-end power grid 20. The AC side of each converter valve group of the sending-end converter station 10a is connected to the sending-end power grid 20, and the low-end converter valve group 122 of the local pole 12 of the sending-end converter station 10a receives electrical energy from the sending-end power grid 20 through its AC side to complete the charging.

[0056] S1042, the receiving-end converter station 10b charges the low-end converter valve group 122 of its own pole 12, and the charging is carried out through the receiving-end power grid 30. The AC side of the low-end converter valve group 122 of the receiving-end converter station 10b's own pole 12 is connected in parallel to the first receiving-end power supply, and the low-end converter valve group 122 of the receiving-end converter station 10b's own pole 12 receives electrical energy through its AC side to complete the charging.

[0057] S1043. When both the low-end converter valve group 122 of the sending-end converter station 10a and the low-end converter valve group 122 of the receiving-end converter station 10b are fully charged, the aforementioned converter valve groups are unlocked.

[0058] The charging of the low-end converter valve group 122 of the sending-end converter station 10a pole 12 and the charging of the low-end converter valve group 122 of the receiving-end converter station 10b pole 12 are carried out separately. After both are charged, the converter valve group is unlocked.

[0059] After the low-end converter valve group 122 of the local pole 12 completes charging and unlocking, the DC voltage of the local pole 12 is established, providing voltage conditions for the subsequent online connection of the high-end converter valve group 121 of the local pole 12.

[0060] In some embodiments, a startup method for an ultra-high voltage flexible direct current transmission system is provided to solve the technical problem that the high-end converter valve group 121 of the local pole 12 is difficult to control during the charging of the low-end converter valve group 122 of the local pole 12, and the charging voltage and charging state are difficult to control.

[0061] After the two converter valve groups of pole 11 are unlocked, the low-end converter valve group 122 of pole 12 is charged and unlocked. In step S104, while charging the low-end converter valve group 122 of pole 12, the bypass switch of the high-end converter valve group 121 of pole 12 is closed, so that the high-end converter valve group 121 of pole 12 is bypassed.

[0062] The high-end converter valve group 121 of the local electrode 12 does not bear the charging voltage in the bypass state, and the charging voltage of the local electrode 12 only acts on the low-end converter valve group 122 of the local electrode 12.

[0063] After the low-end converter valve group 122 of pole 12 is fully charged, it is unlocked. After the low-end converter valve group 122 of pole 12 is unlocked, the high-end converter valve group 121 of pole 12 is connected to the system in an online manner.

[0064] After the high-end converter valve group 121 of the pole 12 is isolated by the bypass switch, it does not bear the charging voltage during the charging of the low-end converter valve group 122 of the pole 12. The charging process of the low-end converter valve group 122 of the pole 12 proceeds normally, and the low-end converter valve group 122 of the pole 12 can complete charging and unlocking.

[0065] In some embodiments, this embodiment provides a startup method for an ultra-high voltage flexible DC transmission system to solve the technical problem that after the low-end converter valve group 122 of the local pole 12 is unlocked, the voltage of the high-end converter valve group 121 of the local pole 12 is mismatched with the voltage of the DC line 40, making it difficult to complete the unlocking and connection.

[0066] After the low-end converter valve group 122 of pole 12 is unlocked, the high-end converter valve group 121 of pole 12 is unlocked in an online connection manner. That is, it is not directly unlocked by charging, but is unlocked after pre-charging and voltage matching to reduce the impact on the voltage of DC line 40 during connection. Step S105 includes the following steps: S1051, with the low-end converter valve group 122 of the local pole 12 unlocked, the high-end converter valve group 121 of the local pole 12 is pre-charged. The high-end converter valve group 121 of the local pole 12 gradually builds up DC voltage through pre-charging.

[0067] S1052. When the voltage of the high-side converter valve group 121 of the local pole 12 matches the voltage of the DC line 40, the high-side converter valve group 121 of the local pole 12 is unlocked. After the high-side converter valve group 121 of the local pole 12 is unlocked, it is connected to the system.

[0068] After the high-end converter valve group 121 of the pole 12 completes pre-charging and its voltage matches the voltage of the DC line 40, it performs unlocking.

[0069] After pre-charging, the voltage of the high-end converter valve group 121 of the pole 12 is consistent with the voltage of the DC line 40, thus reducing the disturbance to the voltage of the DC line 40 when unlocking and connecting.

[0070] In some embodiments, a startup method for an ultra-high voltage flexible direct current transmission system is provided to solve the technical problem that when the DC line 40 has not yet established power transmission, the high-end converter valve group 121 of the local pole 12 lacks the power matching conditions with the station and is difficult to complete online commissioning.

[0071] When the low-end converter valve group 122 of pole 12 is charged and the DC line 40 has not yet established power transmission, the high-end converter valve group 121 of pole 12 is put into online operation using an open-circuit test method. In the open-circuit test method, the load or station is not directly connected; the high-end converter valve group 121 of pole 12 is put into operation by the internal control of the sending-end converter station 10a. The open-circuit test implementation method in step S105 includes the following steps: S1051, when the low-end converter valve group 122 of the local pole 12 has been charged and the DC line 40 has not yet established power transmission, the DC voltage of the high-end converter valve group 121 of the local pole 12 is gradually established through the internal control of the sending-end converter station 10a, so that the DC voltage of the high-end converter valve group 121 of the local pole 12 rises to the rated value.

[0072] S1052. After the DC voltage of the high-end converter valve group 121 of the local pole 12 is matched with the voltage of the DC line 40, the corresponding disconnect switch is closed to complete the commissioning of the high-end converter valve group 121 of the local pole 12.

[0073] After the DC voltage of the high-end converter valve group 121 of the pole 12 is established to the rated value and matched with the voltage of the DC line 40, the disconnect switch is closed to complete the commissioning.

[0074] In this embodiment, the high-end converter valve group 121 of the local pole 12 is put into operation under the condition that the DC line 40 has not yet established power transmission. The operation process is completed by the internal control of the sending-end converter station 10a and does not depend on the power coordination of the receiving-end converter station 10b. The high-end converter valve group 121 of the local pole 12 can be put into operation online.

[0075] In some embodiments, a startup method for an ultra-high voltage flexible direct current transmission system is provided to solve the technical problem that when the low-end converter valve group 122 of the local pole 12 is unlocked and in power transmission state, the high-end converter valve group 121 of the local pole 12 is difficult to complete the connection under the condition of uninterrupted power transmission.

[0076] With the low-end converter valve group 122 of pole 12 already unlocked and in power transmission mode, the high-end converter valve group 121 of pole 12 is put into online operation using the normal two-end unlocked power transmission method. Under the normal two-end unlocked power transmission method, the high-end converter valve group 121 of pole 12 is put into operation according to a preset online operation procedure by coordinating the control systems of the sending-end converter station 10a and the receiving-end converter station 10b. The normal two-end unlocked power transmission implementation method in step S105 includes the following steps: S1051, when the low-end converter valve group 122 of the local pole 12 has been unlocked and is in power transmission state, coordinate the control system of the sending-end converter station 10a and the control system of the receiving-end converter station 10b.

[0077] S1052, the high-side converter valve group 121 of the local pole 12 is pre-charged, voltage matched, bypassed, and unlocked sequentially to connect the high-side converter valve group 121 of the local pole 12 to the system in an uninterrupted manner. The bypassed switch operation is used to release the bypass state of the high-side converter valve group 121 of the local pole 12.

[0078] After the high-end converter valve group 121 of the local pole 12 completes pre-charging, voltage matching, bypass switch operation and unlocking in sequence, it is connected to the system.

[0079] In this embodiment, the high-end converter valve group 121 of the local pole 12 is connected in the normal two-end unlocking power transmission mode under power transmission state. During the connection process, the power transmission remains continuous, and the high-end converter valve group 121 of the local pole 12 can be put into online operation.

[0080] In some embodiments, refer to Figure 4 This embodiment provides a startup method for an ultra-high voltage flexible DC transmission system to solve the technical problems of long-term occupation of unlocking restriction control affecting the conventional startup process and unclear exit timing and conditions.

[0081] During the unlocking restriction sequence control period in response to the risk of induced voltage, the status of the local pole 12 of the sending-end converter station 10a is continuously monitored. Step S106 includes the following steps: S1061. After determining that there is a risk of induced voltage, continuously monitor the status of the local pole 12 of the sending-end converter station 10a.

[0082] S1062. Exit the unlock restriction sequence control when any of the following conditions are met: The converter valve group at pole 12 of the 10a local pole of the sending-end converter station has been successfully unlocked. Both converter valve groups of pole 12 of converter station 10a at the sending end have been issued charging commands; The converter valve group at the receiving end converter station 10b local pole 12 has completed charging.

[0083] The above three conditions correspond to the following scenarios: the local pole 12 converter valve group is unlocked, the charging commands for both local pole 12 converter valve groups have been issued, and the charging of the local pole 12 converter valve group at the other station is completed.

[0084] After the unlocking restriction sequence control is exited, each converter valve group completes the subsequent startup process according to the normal startup sequence control. In this embodiment, the time occupied by the unlocking restriction sequence control is shortened, reducing its impact on the normal startup process.

[0085] Among them, the unlocking limit sequence control refers to the charging unlocking operation of the converter valve group in a limited sequence when there is a risk of induced voltage, that is, the sequential control process of first the pole 11, then the low end of the pole 12, and finally the high end of the pole 12.

[0086] According to a second aspect of this application, an ultra-high voltage flexible direct current transmission system is provided, which includes the above-described startup method for an ultra-high voltage flexible direct current transmission system. The ultra-high voltage flexible direct current transmission system has all the beneficial effects of the above-described startup method for an ultra-high voltage flexible direct current transmission system, which will not be repeated here.

[0087] This embodiment provides an ultra-high voltage flexible direct current transmission system to solve the technical problems of converter valve groups failing to charge normally due to induced voltage and the lack of corresponding control devices during the startup process of the ultra-high voltage flexible direct current transmission system.

[0088] The ultra-high voltage flexible direct current transmission system includes a sending-end converter station 10a and a receiving-end converter station 10b. The sending-end converter station 10a is connected to the sending-end power grid 20, and the receiving-end converter station 10b is connected to the receiving-end power grid 30. A DC line 40 connects the sending-end converter station 10a and the receiving-end converter station 10b.

[0089] Both the sending-end converter station 10a and the receiving-end converter station 10b adopt a bipolar, two-terminal neutral-point grounding method. That is, each converter station includes two poles, namely the local pole 12 and the counterpart pole 11. The local pole 12 and the counterpart pole 11 each include a low-end converter valve group 122 and a high-end converter valve group 121 connected in series. In each pole, the low-end converter valve group 122 and the high-end converter valve group 121 are connected in series along the DC circuit to form the DC conduction circuit of that pole. The DC current flows through the high-end converter valve group 121 and the low-end converter valve group 122 in sequence.

[0090] The receiving-end power grid 30 includes two independent power sources: a first receiving-end power source and a second receiving-end power source. The AC sides of the low-end converter valve groups 122 of each pole 12 and pole 11 of the receiving-end converter station 10b are connected in parallel to the first receiving-end power source, and the AC sides of the high-end converter valve groups 121 of each pole 12 and pole 11 of the receiving-end converter station 10b are connected in parallel to the second receiving-end power source. That is, the low-end converter valve groups 122 of the receiving-end converter station 10b are powered by the first receiving-end power source, and the high-end converter valve groups 121 are powered by the second receiving-end power source, thus distinguishing the low-end converter valve groups 122 and high-end converter valve groups 121 of each pole of the receiving-end converter station 10b. The AC sides of each converter valve group of the sending-end converter station 10a are connected to the sending-end power grid 20, and the low-end converter valve groups 122 and high-end converter valve groups 121 of each pole 12 and pole 11 of the sending-end converter station 10a are all powered by the sending-end power grid 20.

[0091] The system also includes a control device connected to each converter valve group of the sending-end converter station 10a and the receiving-end converter station 10b. The control device is used to acquire the operating status of each converter valve group and control the charging, unlocking, and activation operations of each converter valve group. The control device is configured to execute the above-described startup method: the connection status of the two converter valve groups of the local pole 12 of the sending-end converter station 10a and the receiving-end converter station 10b to the DC line 40, the connection status of the two converter valve groups of the opposite pole 11 to the DC line 40, and the energized status of the two converter valve groups of the opposite pole 11; in response to the presence of induced voltage risk, sequentially executing the charging and unlocking of the two converter valve groups of the opposite pole 11, the charging and unlocking of the low-end converter valve group 122 of the local pole 12, and the unlocking of the high-end converter valve group 121 of the local pole 12 in an online activation manner; and exiting the unlocking restriction sequence control when the exit conditions are met.

[0092] In this embodiment, the control device executes the above-described startup method, and the system completes an orderly startup under the condition of induced voltage risk. The high-end converter valve group 121 of the local pole 12 that is not charged is less affected by the induced voltage.

[0093] In one embodiment, reference is made to Figure 5 This embodiment provides an ultra-high voltage flexible DC transmission system to solve the technical problems of modular implementation and division of labor and cooperation among the modules in the above-mentioned starting method.

[0094] The control device includes a monitoring module and an interlocking control module. The monitoring module is connected to the interlocking control module, and the monitoring module transmits the acquired status information to the interlocking control module.

[0095] The monitoring module is used to acquire status information, which includes: the connection status of the two converter valve groups of the local pole 12 of the sending-end converter station 10a with the DC line 40, the connection status of the two converter valve groups of the opposite pole 11 of the sending-end converter station 10a with the DC line 40, the energized status of the two converter valve groups of the opposite pole 11 of the sending-end converter station 10a, and the charging and unlocking status of each converter valve group.

[0096] The interlocking control module, in response to the presence of induced voltage risk, sequentially executes the following actions: charging and unlocking the two converter valve groups of the opposite pole 11 of the sending-end converter station 10a; charging and unlocking the low-end converter valve group 122 of the local pole 12 of the sending-end converter station 10a; and unlocking the high-end converter valve group 121 of the local pole 12 of the sending-end converter station 10a in an online-connected manner. The conditions for the presence of induced voltage risk include: the two converter valve groups of the local pole 12 of the sending-end converter station 10a are connected to the DC line 40; the two converter valve groups of the opposite pole 11 of the sending-end converter station 10a are connected to the DC line 40; and at least one converter valve group within the opposite pole 11 of the sending-end converter station 10a is energized.

[0097] The interlocking control module is also used to: when there is a charging converter valve group on pole 11 and the DC bus voltage of pole 12 of the sending-end converter station 10a is higher than a preset threshold, only allow charging and unlocking of one converter valve group of pole 12 of the sending-end converter station 10a, while the other converter valve group of pole 12 is unlocked in an online connection manner. In this embodiment, the preset threshold ranges from 800kV to 1600kV, for example, the preset threshold can be 800kV, 1200kV, or 1600kV.

[0098] The interlocking control module is also used to exit the unlocking restriction sequence control when any of the following conditions are met: the local pole 12 of the sending-end converter station 10a has successfully completed the unlocking of the converter valve group; both converter valve groups of the local pole 12 of the sending-end converter station 10a have issued charging commands; and the local pole 12 of the receiving-end converter station 10b has completed charging of the converter valve group.

[0099] In this embodiment, the monitoring module continuously acquires status information and transmits it to the interlocking control module. Under the above conditions, the interlocking control module performs a charging unlocking operation and exits the unlocking restriction sequence control. The control device completes the control of the system startup process under the induced voltage risk condition, and the high-end converter valve group 121 of the local pole 12 that is not charged is less affected by the induced voltage.

[0100] This embodiment provides a startup method for an ultra-high voltage flexible DC transmission system to solve the technical problems of lacking a quantitative threshold and having an unclear threshold value range for the charging and unlocking conditions of the pole 12 under induced voltage risk.

[0101] When a charging converter valve group exists at counter pole 11, the DC bus voltage of local pole 12 changes with the induced voltage. In this embodiment, the charging and unlocking of local pole 12 is limited by a preset threshold: when a charging converter valve group exists at counter pole 11 and the DC bus voltage of local pole 12 is higher than the preset threshold, only one converter valve group of local pole 12 is allowed to be charged and unlocked, while the other converter valve group of local pole 12 is unlocked in an online connection mode.

[0102] In this embodiment, the preset threshold value ranges from 800kV to 1600kV, specifically 800kV, 1200kV, or 1600kV. For example, when the preset threshold is 800kV, the DC bus voltage of pole 12 is higher than 800kV, meaning a single-valve group charging unlocking restriction is applied to pole 12; when the preset threshold is 1600kV, the DC bus voltage of pole 12 is higher than 1600kV, meaning a single-valve group charging unlocking restriction is applied to pole 12; when the preset threshold is 1200kV, the DC bus voltage of pole 12 is higher than 1200kV, meaning a single-valve group charging unlocking restriction is applied to pole 12. The specific value of the preset threshold is determined based on the system's rated voltage and operating conditions.

[0103] In this embodiment, the charging and unlocking limitation of a single valve group is quantified by a preset threshold, and the triggering time of the limitation action has a clear basis. The pole 12 can complete the charging and unlocking under the risk of induced voltage.

[0104] In the description of this application, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more features. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0105] In the above embodiments, the descriptions of each embodiment have different focuses. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions in other embodiments.

[0106] The embodiments, implementation methods, and related technical features of this application can be combined and substituted for each other without conflict.

[0107] The above are merely preferred embodiments of this application and are not intended to limit this application in any way. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of this application without departing from the scope of the technical solution of this application shall still fall within the scope of the technical solution of this application.

Claims

1. A startup method for an ultra-high voltage flexible direct current transmission system, characterized in that, The ultra-high voltage flexible DC transmission system includes two converter stations and a DC line (40) connecting the two converter stations; each converter station includes a local pole (12) and a counterpart pole (11), and each of the local pole (12) and the counterpart pole (11) includes a low-end converter valve group (122) and a high-end converter valve group (121) connected in series. The startup method of the ultra-high voltage flexible DC transmission system includes: Obtain status information, which includes: the connection status of the converter valve group of the local pole (12) and the DC line (40), the connection status of the converter valve group of the opposite pole (11) and the DC line (40), and the energized status of the converter valve group of the opposite pole (11). In response to the risk of induced voltage, the following unlocking sequence steps are executed in sequence: the two converter valve groups of the opposite pole (11) are charged and unlocked; the low-end converter valve group (122) of the local pole (12) is charged and unlocked; the high-end converter valve group (121) of the local pole (12) is unlocked in an online-connected manner. The conditions under which there is a risk of induced voltage include: the converter valve group of the local pole (12) is connected to the DC line (40), the converter valve group of the opposite pole (11) is connected to the DC line (40), and at least one of the converter valve groups in the opposite pole (11) is energized.

2. The startup method of the ultra-high voltage flexible DC transmission system according to claim 1, characterized in that, The two converter stations of the ultra-high voltage flexible DC transmission system are the sending-end converter station (10a) and the receiving-end converter station (10b). The sending-end converter station (10a) is connected to the sending-end power grid (20), and the receiving-end converter station (10b) is connected to the receiving-end power grid (30). Charging and unlocking the commutation valve assembly of the counter electrode (11) includes: Charge and unlock the converter valve group of the opposite pole (11) of the sending-end converter station (10a) and the converter valve group of the opposite pole (11) of the receiving-end converter station (10b); The sending-end converter station (10a) is controlled to charge the converter valve group of its opposite pole (11), and the charging is carried out through the sending-end power grid (20); The receiving-end converter station (10b) is controlled to charge the converter valve group of its opposite pole (11), and the charging is carried out through the receiving-end power grid (30); When both the converter valve group of the opposite pole (11) of the sending-end converter station (10a) and the converter valve group of the opposite pole (11) of the receiving-end converter station (10b) have been fully charged, the valves are unlocked to establish a stable pole voltage between the sending-end converter station (10a) and the receiving-end converter station (10b).

3. The startup method of the ultra-high voltage flexible DC transmission system according to claim 1, characterized in that, The two converter stations of the ultra-high voltage flexible DC transmission system include a sending-end converter station (10a) and a receiving-end converter station (10b), wherein the sending-end converter station (10a) is connected to the sending-end power grid (20); Charging and unlocking the commutation valve assembly of the counter electrode (11) includes: Charge and unlock the converter valve group of the opposite pole (11) of the sending-end converter station (10a) and the converter valve group of the opposite pole (11) of the receiving-end converter station (10b); The sending-end converter station (10a) is controlled to charge the converter valve group of its opposite pole (11), and the charging is carried out through the sending-end power grid (20); The sending-end converter station (10a) is controlled to transmit electrical energy to the receiving-end converter station (10b) via the DC line (40) to charge the converter valve group of the opposite pole (11) of the receiving-end converter station (10b); When both the converter valve group of the opposite pole (11) of the sending-end converter station (10a) and the converter valve group of the opposite pole (11) of the receiving-end converter station (10b) have been fully charged, the valves are unlocked to establish a stable pole voltage between the sending-end converter station (10a) and the receiving-end converter station (10b).

4. The startup method of the ultra-high voltage flexible DC transmission system according to claim 2, characterized in that, Charging and unlocking the low-end converter valve group (122) of the local pole (12) includes: The low-end converter valve group (122) of the local pole (12) of the sending-end converter station (10a) and the low-end converter valve group (122) of the local pole (12) of the receiving-end converter station (10b) are charged and unlocked. When the converter valve group of the opposite pole (11) is unlocked, the sending-end converter station (10a) is controlled to charge the low-end converter valve group (122) of its own pole (12), and the charging is carried out through the sending-end power grid (20). The receiving-end converter station (10b) is controlled to charge the low-end converter valve group (122) of its local pole (12), and the charging is carried out through the receiving-end power grid (30); Unlocking is performed when both the low-end converter valve group (122) of the local pole (12) of the sending-end converter station (10a) and the low-end converter valve group (122) of the local pole (12) of the receiving-end converter station (10b) have been fully charged.

5. The startup method of the ultra-high voltage flexible DC transmission system according to claim 4, characterized in that, Charging and unlocking the low-end converter valve group (122) of the local pole (12) further includes: While the low-end converter valve group (122) of the local pole (12) is being charged, the bypass switch of the high-end converter valve group (121) of the local pole (12) is closed so that the high-end converter valve group (121) is bypassed.

6. The startup method of the ultra-high voltage flexible DC transmission system according to claim 1, characterized in that, Unlocking the high-end converter valve assembly (121) of the aforementioned pole (12) via online engagement includes: When the low-end converter valve group (122) of the pole (12) is unlocked, the high-end converter valve group (121) of the pole (12) is pre-charged. When the voltage of the high-side converter valve group (121) of the local pole (12) matches the voltage of the DC line (40), the high-side converter valve group (121) of the local pole (12) is unlocked.

7. The startup method of the ultra-high voltage flexible DC transmission system according to claim 4, characterized in that, Unlocking the high-end converter valve assembly (121) of the aforementioned pole (12) via online engagement includes: When the low-end converter valve group (122) of the local pole (12) of the sending-end converter station (10a) is charged and the DC line (40) has not yet established power transmission, Through the internal control of the sending-end converter station (10a), the DC voltage of the high-end converter valve group (121) of the local pole (12) is gradually established; After the DC voltage matches the DC line (40) voltage, the corresponding disconnect switch is closed to complete the commissioning of the high-end converter valve group (121).

8. The startup method of the ultra-high voltage flexible DC transmission system according to claim 4, characterized in that, Unlocking the high-end converter valve assembly (121) of the aforementioned pole (12) via online engagement includes: When the low-end converter valve group (122) of the pole (12) is unlocked and in power transmission mode, The control system of the sending-end converter station (10a) and the control system of the receiving-end converter station (10b) are coordinated to perform pre-charging, voltage matching, bypass switch operation and unlocking, so as to connect the high-end converter valve group (121) of the local pole (12) in an uninterrupted manner.

9. The startup method of the ultra-high voltage flexible DC transmission system according to claim 2, characterized in that, In response to the risk of induced voltage, the status of the local pole (12) of the sending-end converter station (10a) is monitored; The unlocking restriction sequence will be exited if any of the following conditions are met: The converter valve group of the local pole (12) of the sending-end converter station (10a) has been successfully unlocked; Both converter valve groups of the local pole (12) of the sending-end converter station (10a) have issued charging commands; The converter valve group of the receiving-end converter station (10b) has been charged.

10. An ultra-high voltage flexible direct current transmission system, characterized in that, include: Sending-end converter station (10a) and receiving-end converter station (10b), each of the converter stations includes a local pole (12) and a counterpart pole (11), each of the local pole (12) and the counterpart pole (11) including a low-end converter valve group (122) and a high-end converter valve group (121) connected in series; A DC line (40) connects the sending-end converter station (10a) and the receiving-end converter station (10b); The control device is configured to perform the startup method of the ultra-high voltage flexible DC transmission system as described in any one of claims 1 to 9.

11. The ultra-high voltage flexible DC transmission system according to claim 10, characterized in that, The control device includes a monitoring module and an interlocking control module; The monitoring module is configured to acquire status information, which includes: the connection status of the converter valve group of the local pole (12) and the DC line (40), the connection status of the converter valve group of the opposite pole (11) and the DC line (40), and the energized status of the converter valve group of the opposite pole (11). The interlocking control module is configured to, in response to the presence of an induced voltage risk, sequentially execute the following unlocking limit control steps: charge and unlock the two converter valve groups of the opposite pole (11); charge and unlock the low-end converter valve group (122) of the local pole (12); and unlock the high-end converter valve group (121) of the local pole (12) in an online-connected manner. The conditions under which there is a risk of induced voltage include: the converter valve group of the local pole (12) is connected to the DC line (40), the converter valve group of the opposite pole (11) is connected to the DC line (40), and at least one of the converter valve groups in the opposite pole (11) is energized.

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