Multi-terminal flexible direct current power transmission system and offshore wind power converter station online putting-in method

Abstract

The present application relates to a kind of multi-terminal flexible HVDC transmission system and offshore wind power converter station online input method, belong to offshore wind power flexible HVDC transmission engineering technical field.The present application is by adding DC starting resistance and bypass circuit breaker in the DC side of offshore converter station, first by the DC bus of switch collection station to the DC side of offshore converter station through DC starting resistance charging, after charging is completed, this offshore converter station can be unlocked, realize online input.The starting resistance and bypass circuit breaker increased by the present application can be charged by DC, can be closed by DC bus high-speed isolating switch when other station is unlocked, will not cause the overcurrent problem caused by the voltage difference of high-speed isolating switch two ends too large, each in operation converter station does not need to be shut down in the whole input process, avoid the long-time power interruption of in operation converter, also avoid the phenomenon of wind power curtailment, improve the utilization of multi-terminal flexible HVDC transmission system.

Description

Technical Field

[0001] This invention relates to a multi-terminal flexible DC transmission system and an online commissioning method for offshore wind power converter stations, belonging to the field of offshore wind power flexible DC transmission engineering technology. Background Technology

[0002] Flexible DC transmission systems are widely used in offshore wind power DC transmission. Offshore wind power flexible DC transmission topologies are diverse, including multi-terminal systems. These multi-terminal systems (i.e., systems with multiple converter stations) further highlight the flexibility of power transmission. For offshore wind power systems with passive stations (offshore stations), putting them into operation requires locking the operating converter station. The converter station to be put into operation can only be connected to the DC bus (by closing the high-speed disconnect switches of the positive and negative buses) when there is no voltage on the DC bus. Closing the positive and negative bus switches of the operating converter station without locking it requires a specific control strategy. Without a control strategy, directly closing them can lead to overcurrent or overvoltage due to voltage inconsistencies on both sides of the high-speed disconnect switch. Therefore, the operating converter station must first be shut down. In the shutdown state, the DC high-speed disconnect switch is operated to connect the passive station, and then the active station is unlocked to DC charge the passive station. This process completes the unlocking and commissioning of the passive converter station. The control of passive station commissioning in multi-terminal systems is a critical issue that must be addressed and urgently needs to be solved in the application of offshore wind power flexible DC transmission projects.

[0003] Currently, commissioning an offshore converter station requires shutting down all existing stations, operating a DC high-speed disconnect switch to connect the station to be started, then unlocking the active station to DC charge the passive station, and finally unlocking and operating the passive station to complete the commissioning process. Therefore, the current scheme requires shutting down all operating converter stations, necessitating more time for equipment operation and unlocking, leading to prolonged power interruptions at the receiving end, wind curtailment, and economic losses. This also compromises the operational flexibility of the multi-terminal flexible DC transmission system. Summary of the Invention

[0004] The purpose of this invention is to provide a multi-terminal flexible DC transmission system and an online commissioning method for offshore wind power converter stations, so as to solve the problems of long time, low efficiency and low utilization rate of multi-terminal flexible DC transmission systems caused by the need to shut down the operating converter station when commissioning offshore wind power converter stations.

[0005] To solve the above-mentioned technical problems, this invention provides a method for putting an offshore wind power converter station into operation online, the method comprising: A DC starting resistor is installed in the DC circuit on the DC side of the offshore wind power converter station, and a bypass circuit breaker is connected in parallel across the DC starting resistor. Once the offshore wind power converter station is ready for commissioning, the bypass circuit breaker is opened and the high-speed disconnect switch is closed to connect the DC circuit on the DC side of the offshore wind power converter station to the DC busbar of the switch collection station. The DC busbar then charges the offshore wind power converter station via the DC starting resistor. The charging current of DC charging is detected, and after the charging current is less than a set threshold and continues for a set time, the bypass circuit breaker is controlled to close, the DC starting resistor is disconnected from the DC circuit, and the offshore wind power converter station is directly charged by the busbar until charging is completed. Once charging is complete, the offshore wind power converter station will be unlocked to enable its online operation.

[0006] Furthermore, the DC starting resistor is installed in the terminal converter station on the DC side of the offshore wind power converter station.

[0007] Furthermore, the DC circuit on the DC side of the offshore wind power converter station includes a positive line and a negative line, and the positive line and the negative line are respectively equipped with corresponding DC starting resistors and corresponding bypass circuit breakers.

[0008] Furthermore, the completion of the preparation for commissioning of the offshore wind power converter station means that the offshore wind power converter station has energized all control and protection systems through backup power, the primary equipment is in normal condition, and the secondary control subsystem is operating normally.

[0009] This invention also provides a multi-terminal flexible DC transmission system, including an offshore wind power converter station and a receiving-end converter station. The offshore wind power converter station is used to connect to the receiving-end converter station through a terminal conversion station and a switchgear collection station. A DC starting resistor is provided in the DC circuit on the DC side of the offshore wind power converter station, and a bypass circuit breaker is connected in parallel across the two ends of the DC starting resistor. The bypass circuit breaker is used to open after the offshore wind power converter station is ready for commissioning, so as to connect the DC circuit on the DC side of the offshore wind power converter station to the DC bus of the switchgear collection station. The bus then charges the offshore wind power converter station through the DC starting resistor. After the charging current is less than a set threshold and continues for a set time, the circuit breaker closes, and the bus then directly charges the offshore wind power converter station until charging is complete. The offshore wind power converter station is unlocked after charging is completed, so as to realize the online commissioning of the offshore wind power converter station.

[0010] Furthermore, the DC starting resistor is installed in the terminal converter station on the DC side of the offshore wind power converter station.

[0011] Furthermore, the DC circuit on the DC side of the offshore wind power converter station includes a positive line and a negative line, and the positive line and the negative line are respectively equipped with a corresponding DC starting resistor and a corresponding bypass circuit breaker.

[0012] Furthermore, the completion of the preparation for commissioning of the offshore wind power converter station means that the offshore wind power converter station has energized all control and protection systems through backup power, the primary equipment is in normal condition, and the secondary control subsystem is operating normally.

[0013] Furthermore, the positive and negative busbars of the offshore station of the aforementioned switch collection station are equipped with high-speed disconnect switches, and the high-speed disconnect switches of the positive and negative busbars have the function of simultaneous opening and closing linkage.

[0014] Furthermore, the power devices of the offshore wind power converter station adopt a hybrid topology of full-bridge + half-bridge, half-bridge, or full-bridge topology.

[0015] The beneficial effects of this invention are as follows: By adding a DC starting resistor and a bypass circuit breaker to the DC side of the offshore converter station, the DC bus of the switchgear station first charges the DC side of the offshore converter station through the DC starting resistor. After the charging current is less than a set threshold, the DC starting resistor is bypassed through the bypass circuit breaker, and the DC bus of the switchgear station directly charges the DC side of the offshore converter station until charging is complete. After charging is complete, the offshore converter station can be unlocked and put into operation online. It is evident that the added starting resistor and bypass circuit breaker of this invention can perform DC charging and can be closed through the high-speed disconnect switch of the DC bus when other stations are unlocked, avoiding overcurrent problems caused by excessive voltage difference across the high-speed disconnect switch. Therefore, the entire commissioning process does not require shutting down any operating converter stations, and there is no power interruption in the operating converter stations during commissioning. This greatly reduces the operation time for putting passive stations into operation after each station is shut down, avoids long-term power interruptions in operating converter stations, and also avoids wind curtailment, improving the utilization rate of the multi-terminal flexible DC system and enhancing the economy and operational flexibility of the multi-terminal flexible DC transmission system. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the architecture of the multi-terminal flexible DC transmission system of the present invention; Figure 2 This is a flowchart of the online commissioning method for offshore wind power converter stations according to the present invention. Detailed Implementation

[0017] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings.

[0018] This invention adds a DC starting resistor and a bypass circuit breaker to the DC side of the offshore converter station. The DC bus of the switchgear station first charges the DC side of the offshore converter station through the DC starting resistor. After the charging current is less than a set threshold, the DC starting resistor is bypassed through the bypass circuit breaker, and the DC bus of the switchgear station directly charges the DC side of the offshore converter station until charging is complete. After charging is complete, the offshore converter station can be unlocked and put into operation online.

[0019] Multi-terminal flexible DC transmission system embodiment This invention is suitable for systems with passive converter stations. Generally, offshore DC systems include multiple operating converter stations and the passive converter stations, while onshore DC systems are generally active. The multi-terminal flexible DC transmission system in this embodiment is as follows: Figure 1 As shown, the system includes three offshore converter stations. Each offshore converter station is connected to a terminal conversion station (completing the conversion from submarine cable to overhead line) via a corresponding DC submarine cable. The terminal conversion station is then connected to a switchgear collection station via overhead line zone I. The switchgear collection station is equipped with a DC bus to collect the DC lines from each offshore converter station. The switchgear collection station is then connected to the receiving-end converter station via overhead line zone II. The offshore station incoming lines and positive and negative buses of the switchgear collection station are equipped with high-speed disconnect switches (HSS). The positive and negative bus HSSs have simultaneous opening and closing linkage functions. The power devices of each offshore converter station and the receiving-end converter station can adopt a "full-bridge + half-bridge hybrid topology", "half-bridge topology", or "full-bridge topology". In addition, the multi-terminal flexible DC transmission system also includes an AC station, which can interact the energy of the converter inverter and rectifier with the AC grid. The AC station completes the aggregation of external AC lines and completes switching operations. It can be connected to the on-shore converter station through AC overhead lines, and after rectification by the on-shore converter station, it is connected to the DC bus of the switchgear collection station.

[0020] like Figure 1 As shown, this embodiment includes three offshore converter stations. The DC side of each offshore converter station is connected to the terminal converter station via a DC submarine cable. The line between the DC side of the offshore converter station and the terminal converter station is referred to as the DC circuit. This invention sets up a DC starting resistor in the DC circuit on the DC side of the offshore wind power converter station, and connects a bypass circuit breaker (also called a starting resistor bypass switch) in parallel across the DC starting resistor. To facilitate control of the bypass circuit breaker, this invention places both the DC starting circuit and the bypass circuit breaker at the terminal converter station. Since the DC circuit on the DC side of the offshore wind power converter station includes a positive line and a negative line, the positive line is used to connect to the positive bus in the switchgear station through the terminal converter station, and the negative line is used to connect to the negative bus in the switchgear station through the terminal converter station. To improve the safety of the line, both the positive and negative lines of the DC circuit are equipped with corresponding DC starting resistors and corresponding bypass circuit breakers. The following describes the online commissioning method of the offshore wind power converter station in the multi-terminal flexible DC transmission system of this invention. The specific implementation process of this method is as follows: Figure 2 As shown below, a detailed explanation will follow.

[0021] 1. Monitor the status of offshore wind power converter stations to determine if they are ready for operation.

[0022] If an offshore wind power converter station is not connected to the grid and is in a passive state, it can be simply referred to as a passive station. When a passive station needs to be put into operation online, it is first determined whether it is ready for operation. In this embodiment, when the passive station has energized all control and protection systems through the backup power supply, the primary equipment is in normal condition, and the secondary control subsystem is operating normally, it indicates that the primary and secondary systems are ready, that is, the passive station is ready for operation.

[0023] 2. Connect the DC circuit on the DC side of the offshore wind power converter station to the DC bus of the switchgear station, and then charge the offshore wind power converter station via the DC starting resistor through the bus.

[0024] Once the preparation for commissioning of an offshore wind power converter station (passive station) is completed, it is ready for commissioning. The bypass circuit breaker on the DC circuit of the passive station's DC side is opened, and a starting resistor is connected in series with the DC circuit. In specific control, the bypass circuit breakers on both the positive and negative lines of the DC circuit are opened simultaneously. After the bypass circuit breaker opens, the DC circuit of the offshore wind power converter station's DC side is connected to the DC busbar of the switchgear station. In this embodiment, the HSS (Hospital Switch System) installed on both the offshore station's incoming line and the positive and negative buses of the switchgear station is closed to connect the DC circuit of the offshore wind power converter station's DC side to the switchgear station's DC busbar. In this way, the busbar can provide DC charging to the corresponding offshore wind power converter station via the DC starting resistor.

[0025] 3. Disconnect the DC starting resistor from the DC circuit and directly charge the offshore wind power converter station via the busbar until charging is complete.

[0026] During the DC charging process of the offshore wind power converter station via the busbar and DC starting resistor, the charging current is detected. In this embodiment, the detected charging current is the current in the DC circuit from the DC starting resistor to the DC side of the passive station, i.e., the current in the DC circuit. Based on the detected charging current, a decision is made whether to close the bypass circuit breaker. If the charging current is less than a set threshold and remains below it for a set time, the bypass circuit breaker is closed, disconnecting the DC starting resistor from the DC circuit. This allows the busbar to directly charge the DC side of the offshore wind power converter station, enabling controlled charging until charging is complete. The set threshold and set time can be determined based on parameters such as the resistor parameters and the DC voltage level.

[0027] Once charging is complete, the valve control equipment of the offshore wind power converter station is ready. At this time, the converter outlet is not connected to the AC system, so the VF control mode (voltage frequency conversion control) is selected to unlock the passive station, thus realizing the online commissioning of the offshore wind power converter station.

[0028] As can be seen, the offshore wind power converter station of the present invention does not require power interruption during the online commissioning process, which greatly reduces the operation time of the passive station after each station is shut down, avoids long-term power interruption of the operating converter station, and also avoids wind curtailment at the offshore wind power converter station, thus improving the utilization rate of the multi-terminal flexible DC system.

[0029] Implementation Examples of Online Commissioning Methods for Offshore Wind Power Converter Stations The online commissioning method for offshore wind power converter stations in this embodiment first involves setting a DC starting resistor in the DC circuit on the DC side of the offshore wind power converter station, and connecting a bypass circuit breaker in parallel across the DC starting resistor. Once the offshore wind power converter station is ready for commissioning, the bypass circuit breaker is opened, and the DC circuit on the DC side of the offshore wind power converter station is connected to the DC bus of the switchgear station. The bus then charges the offshore wind power converter station via the DC starting resistor. The charging current is detected, and if the charging current is less than a set threshold and remains below it for a set time, the bypass circuit breaker is closed, disconnecting the DC starting resistor from the DC circuit. The bus then directly charges the offshore wind power converter station until charging is complete. After charging is complete, the offshore wind power converter station is unlocked, thus achieving online commissioning. The specific implementation process of this method has been detailed in the multi-terminal flexible DC transmission system embodiment and will not be repeated here.

[0030] This invention adds a DC starting resistor and a bypass circuit breaker to the DC side of the offshore converter station. The DC bus of the switchgear station first charges the DC side of the offshore converter station through the DC starting resistor. Once the charging current is less than a set threshold, the bypass circuit breaker disconnects the DC starting resistor, allowing the DC bus of the switchgear station to directly charge the DC side of the offshore converter station until charging is complete. After charging, the offshore converter station can be unlocked and put into operation online. It is evident that the entire commissioning process of this invention does not require the shutdown of any operating converter stations, and there is no power interruption among the operating converter stations during commissioning. This significantly reduces the operation time for commissioning passive stations after the shutdown of other stations, avoids prolonged power interruptions in operating converter stations, and also prevents wind curtailment. This improves the utilization rate of the multi-terminal flexible DC system and enhances the economy and operational flexibility of the multi-terminal flexible DC transmission system.

Claims

1. A method for online commissioning of an offshore wind power converter station, characterized in that, The method includes: A DC starting resistor is installed in the DC circuit on the DC side of the offshore wind power converter station, and a bypass circuit breaker is connected in parallel across the DC starting resistor. Once the offshore wind power converter station is ready for commissioning, the bypass circuit breaker is opened and the high-speed disconnect switch is closed to connect the DC circuit on the DC side of the offshore wind power converter station to the DC bus of the switch collection station. The DC bus then charges the offshore wind power converter station via the DC starting resistor. The charging current of DC charging is detected, and after the charging current is less than a set threshold and continues for a set time, the bypass circuit breaker is controlled to close, the DC starting resistor is disconnected from the DC circuit, and the offshore wind power converter station is directly charged by the busbar until charging is completed. Once charging is complete, the offshore wind power converter station will be unlocked to enable its online operation.

2. The method for online commissioning of an offshore wind power converter station according to claim 1, characterized in that, The DC starting resistor is installed in the terminal converter station on the DC side of the offshore wind power converter station.

3. The method for online commissioning of an offshore wind power converter station according to claim 1 or 2, characterized in that, The DC circuit on the DC side of the offshore wind power converter station includes a positive line and a negative line. The positive line and the negative line are respectively equipped with corresponding DC starting resistors and corresponding bypass circuit breakers.

4. The method for online commissioning of an offshore wind power converter station according to claim 1, characterized in that, The completion of the preparation for commissioning of the offshore wind power converter station means that the offshore wind power converter station has energized all control and protection systems through backup power, the primary equipment is in normal condition, and the secondary control subsystem is operating normally.

5. A multi-terminal flexible DC transmission system, comprising an offshore wind power converter station and a receiving-end converter station, wherein the offshore wind power converter station is used to connect to the receiving-end converter station via a terminal conversion station and a switchgear collection station, characterized in that, The DC circuit on the DC side of the offshore wind power converter station is equipped with a DC starting resistor, and a bypass circuit breaker is connected in parallel across the two ends of the DC starting resistor. The bypass circuit breaker is used to disconnect after the offshore wind power converter station is ready for commissioning, so that the DC circuit on the DC side of the offshore wind power converter station is connected to the DC bus of the switchgear station. The bus then charges the offshore wind power converter station via the DC starting resistor. The circuit breaker closes after the charging current is less than a set threshold and continues for a set time, so that the bus directly charges the offshore wind power converter station until charging is complete. The offshore wind power converter station is unlocked after charging is completed, so as to realize the online commissioning of the offshore wind power converter station.

6. The multi-terminal flexible DC transmission system according to claim 5, characterized in that, The DC starting resistor is installed in the terminal converter station on the DC side of the offshore wind power converter station.

7. The multi-terminal flexible DC transmission system according to claim 5 or 6, characterized in that, The DC circuit on the DC side of the offshore wind power converter station includes a positive line and a negative line, and the positive line and the negative line are respectively equipped with a corresponding DC starting resistor and a corresponding bypass circuit breaker.

8. The multi-terminal flexible DC transmission system according to claim 5, characterized in that, The completion of the preparation for commissioning of the offshore wind power converter station means that the offshore wind power converter station has energized all control and protection systems through backup power, the primary equipment is in normal condition, and the secondary control subsystem is operating normally.

9. The multi-terminal flexible DC transmission system according to claim 5, characterized in that, The positive and negative busbars of the offshore station of the aforementioned switch collection station are equipped with high-speed disconnect switches, which have the function of simultaneous opening and closing linkage.

10. The multi-terminal flexible DC transmission system according to claim 5, characterized in that, The power devices of the offshore wind power converter station adopt a hybrid topology of full-bridge + half-bridge, half-bridge, or full-bridge topology.

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