A DC fault ride-through method for a sea-land integrated DC system of offshore wind power based on a fast communication link

Abstract

The application discloses a DC fault ride-through method of a sea-land integrated DC system of offshore wind power based on a fast communication link, and the method comprises the following steps: when a DC fault occurs, the voltage drop speed and the voltage drop amplitude of an onshore converter station are obtained; when the voltage drop speed is lower than a voltage drop speed threshold value and the voltage drop amplitude is lower than a voltage drop amplitude threshold value, a fan energy consumption input instruction is sent to an offshore converter station, so that the offshore converter station transmits the fan energy consumption input instruction to each communication forwarding device through a bidirectional ring network optical fiber channel, and then the fan energy consumption input instruction is transmitted to corresponding fan energy consumption devices by the communication forwarding devices, so that the fan energy consumption devices absorb the fault surplus power according to the fan energy consumption input instruction; wherein the time from the issuance of the fan energy consumption input instruction from the HVDC side to the start of the fan energy consumption device is not greater than the maximum allowable delay duration.

Description

Technical Field

[0001] This invention relates to the field of power electronics technology, and in particular to a DC fault ride-through method for an integrated onshore and offshore wind power DC system based on a fast communication link. Background Technology

[0002] my country boasts abundant offshore wind energy resources and significant development potential. Promoting high-quality development of offshore wind power is a crucial aspect of the dual-carbon strategy and a vital support for energy security in coastal areas. The National 14th Five-Year Plan outlines the exploration of new models for ultra-large-scale deep-sea wind power development, accelerating the construction of multiple 10-million-kilowatt-level offshore wind power bases in the Shandong Peninsula, the Yangtze River Delta, and eastern Guangdong. Currently, deep-sea wind power utilizes DC landing and then transmits power to load centers via AC overhead lines. To meet the development needs of the national 10-million-kilowatt-level offshore wind power bases, the existing model requires the construction of multiple new AC transmission lines to load centers, consuming substantial land resources and significantly increasing overall offshore wind power development costs. Technically, because existing offshore wind power DC cables immediately convert to AC after landing, DC fault crossing issues are generally not considered, as a DC cable fault is permanent and requires power outages for maintenance. Integrating large-scale offshore wind power with onshore and offshore integration, and using a hybrid overhead cable system for direct load absorption, can achieve intensive offshore wind power development, save land space, and reduce development costs. However, because there are overhead DC lines in the offshore wind power DC transmission system, it is necessary to overcome the problem of DC fault ride-through in the integrated onshore and offshore DC transmission system for offshore wind power. Summary of the Invention

[0003] This invention provides a DC fault ride-through method for an integrated onshore-offshore DC system for offshore wind power based on a fast communication link. By transmitting wind turbine energy consumption input commands through a bidirectional ring network optical fiber channel between the offshore converter station and several wind turbine energy consumption devices in the offshore wind farm, the speed at which wind turbine energy consumption input commands are sent to each wind turbine energy consumption device can be improved, the intervention of wind turbine energy consumption devices can be accelerated, DC faults can be responded to and handled more quickly, and the stable operation of the integrated onshore-offshore DC system for offshore wind power can be ensured.

[0004] One embodiment of the present invention provides a DC fault ride-through method for an integrated offshore wind power DC system based on a fast communication link. The method is applied to an integrated offshore wind power DC system comprising: an offshore wind farm, an offshore converter station, and an onshore converter station.

[0005] The offshore wind farm includes several wind power converters and several communication relay devices; each wind power converter is connected to a communication relay device, and each wind power converter includes a wind turbine energy consumption device; the offshore converter station and each communication relay device are connected sequentially through a bidirectional ring network optical fiber channel.

[0006] The DC fault ride-through method includes:

[0007] In the event of a DC fault, obtain the voltage drop rate and voltage drop magnitude of the onshore converter station;

[0008] When the voltage drop rate is lower than the voltage drop rate threshold and the voltage drop amplitude is lower than the voltage drop amplitude threshold, a wind turbine power consumption activation command is sent to the offshore converter station. The offshore converter station then transmits the wind turbine power consumption activation command to each communication forwarding device through a bidirectional ring network fiber optic channel. Each communication forwarding device then transmits the wind turbine power consumption activation command to the corresponding wind turbine power consumption device, so that each wind turbine power consumption device can absorb the fault surplus power according to the wind turbine power consumption activation command. The time from the issuance of the wind turbine power consumption activation command from the flexible DC side to the start-up of the wind turbine power consumption device shall not exceed the maximum allowable delay time.

[0009] Furthermore, the offshore wind power integrated onshore-offshore DC system also includes: a terminal converter station, a switch collection station and a receiving-end power grid. The terminal converter station includes a number of first high-speed DC switches, the switch collection station includes a number of second high-speed DC switches and a number of third high-speed DC switches, and the onshore converter station includes a number of fourth high-speed DC switches.

[0010] The offshore converter station is connected to the terminal converter station via a DC submarine cable;

[0011] Each of the first DC high-speed switches is connected to each of the second DC high-speed switches in a one-to-one correspondence via a first DC overhead line;

[0012] Each of the second DC high-speed switches is connected in parallel with each of the third DC high-speed switches;

[0013] Each of the third DC high-speed switches is connected to each of the fourth DC high-speed switches via the second DC overhead line;

[0014] The onshore converter station is connected to the receiving-end power grid via a third overhead DC line.

[0015] Furthermore, the onshore converter station includes a first DC control and protection system, and the offshore converter station includes a second DC control and protection system;

[0016] The first DC control and protection system and the second DC control and protection system communicate through a direct communication channel.

[0017] Furthermore, the offshore wind farm also includes several wind turbines; each wind turbine is connected to a wind power converter;

[0018] The bidirectional ring network fiber optic channel includes: a first transmitting fiber, a second transmitting fiber, a first receiving fiber, and a second receiving fiber.

[0019] The first transmitting end of the offshore converter station is connected to the first receiving end of the first communication forwarding device through the first transmitting optical fiber. The first transmitting ends of the remaining communication forwarding devices, except for the first communication forwarding device and the terminal communication forwarding device, are connected to the first receiving ends of the next communication forwarding device in sequence through the first transmitting optical fiber. The first transmitting end of the terminal communication forwarding device is connected to the first receiving end of the offshore converter station through the first receiving optical fiber.

[0020] The second transmitting end of the offshore converter station is connected to the second receiving end of the terminal communication forwarding device via the second transmitting optical fiber. The second transmitting ends of the other communication forwarding devices, except for the first communication forwarding device and the terminal communication forwarding device, are connected to the second receiving ends of the previous communication forwarding device in sequence via the second receiving optical fiber. The second transmitting end of the first communication forwarding device is connected to the second receiving end of the offshore converter station via the second receiving optical fiber.

[0021] Furthermore, the capacity of each of the aforementioned wind turbine energy-consuming devices is determined according to the following formula:

[0022]

[0023] in, Indicates the capacity of the fan's energy-consuming device; This indicates the rated output power of the fan; This indicates the time margin, which is determined based on the DC fault ride-through time.

[0024] Furthermore, the maximum allowable delay duration is determined by the following formula:

[0025]

[0026] in, This is the maximum allowable delay duration; The capacitance value of the offshore converter station; This refers to the maximum permissible module voltage for offshore converter stations. This refers to the rated module voltage of the offshore converter station; The total number of bridge modules in the offshore converter station; This represents the maximum active power of the offshore converter station.

[0027] Furthermore, when the voltage sag rate is lower than the voltage sag rate threshold and the voltage sag amplitude is lower than the voltage sag amplitude threshold, the following is also included:

[0028] Send DC fault ride-through commands to onshore and offshore converter stations so that they can establish negative voltage, absorb fault current, and complete a DC fault clearing operation.

[0029] Furthermore, each wind turbine energy-consuming device absorbs surplus power from faults according to the wind turbine energy-consuming activation command, including:

[0030] The system obtains the real-time power of each wind turbine energy-consuming device from the previous moment according to the wind turbine energy consumption input command, and controls each wind turbine energy-consuming device to absorb the fault surplus power according to the real-time power of each wind turbine energy-consuming device from the previous moment, until the offshore wind power integrated onshore-sea DC system achieves surplus power balance.

[0031] Furthermore, after clearing a primary fault in the offshore wind power integrated onshore-offshore DC transmission system, the process also includes:

[0032] The offshore wind power integrated onshore-offshore DC system was restarted under its original pressure for the first time, controlling the offshore converter station to restore the first DC current and simultaneously controlling the onshore converter station to establish the first DC voltage.

[0033] If the first DC voltage is successfully established at the onshore converter station, the DC fault will be completely cleared.

[0034] If the first DC voltage of the onshore converter station fails to be established, the offshore wind power integrated onshore-offshore DC system will be restarted at the original voltage for the second time, controlling the offshore converter station to restore the second DC current, and at the same time controlling the onshore converter station to establish the second DC voltage.

[0035] If the second DC voltage at the onshore converter station is successfully established, the DC fault will be completely cleared.

[0036] Furthermore, after performing a second original-pressure restart on the offshore wind power integrated onshore-offshore DC system, controlling the offshore converter station to restore the second DC current, and simultaneously controlling the onshore converter station to establish the second DC voltage, the process also includes:

[0037] If the second DC voltage of the onshore converter station fails to be established, the wind turbines will be shut down and the energy-consuming devices of each wind turbine will be taken out of operation.

[0038] The following benefits can be obtained by implementing the present invention:

[0039] This invention provides a DC fault ride-through method for an integrated offshore wind power DC system based on a fast communication link. The integrated offshore wind power DC system includes an offshore wind farm, an offshore converter station, and an onshore converter station. The offshore wind farm includes several wind power converters and several communication relay devices. Each wind power converter is connected to a communication relay device, and each wind power converter includes a wind turbine energy dissipation device. The offshore converter station and each communication relay device are sequentially connected via a bidirectional ring network optical fiber channel. When a DC fault occurs, the voltage drop rate and voltage drop amplitude of the onshore converter station are obtained. When the voltage drop rate is lower than a voltage drop rate threshold and the voltage drop amplitude is lower than a voltage drop amplitude threshold, a wind turbine energy dissipation activation command is sent to the offshore converter station. This allows the offshore converter station to transmit the wind turbine energy dissipation activation command step-by-step to each communication relay device via the bidirectional ring network optical fiber channel. Each communication relay device then transmits the wind turbine energy dissipation activation command to the corresponding wind turbine energy dissipation device, enabling the wind turbine energy dissipation device to absorb the fault surplus power according to the wind turbine energy dissipation activation command within the maximum allowable delay time. By transmitting wind turbine energy consumption input commands through a two-way ring network fiber optic channel, the speed at which wind turbine energy consumption input commands are sent to each wind turbine energy consumption device can be improved, the intervention of wind turbine energy consumption devices can be accelerated, DC faults can be responded to and handled more quickly, and the stable operation of the offshore wind power integrated onshore-sea DC system can be guaranteed. Attached Figure Description

[0040] Figure 1 This is a flowchart illustrating a DC fault ride-through method for an integrated onshore and offshore wind power DC system based on a fast communication link, according to an embodiment of the present invention.

[0041] Figure 2 This is a schematic diagram of the structure of an integrated onshore and offshore wind power DC system provided in an embodiment of the present invention.

[0042] Figure 3 This is a communication diagram of a land-based converter station and a marine converter station via a direct communication channel, provided in an embodiment of the present invention.

[0043] Figure 4 This is a schematic diagram of the internal structure of a wind power converter provided in an embodiment of the present invention.

[0044] Figure 5 This is a schematic diagram of a bidirectional ring network optical fiber channel provided in an embodiment of the present invention.

[0045] Figure 6 This is a schematic diagram of the DC fault ride-through stage provided in an embodiment of the present invention.

[0046] Figure 7 This is a schematic diagram illustrating the communication delay when calling a wind turbine energy-consuming device, provided in an embodiment of the present invention.

[0047] Figure 8This is a schematic diagram illustrating the calculation results of the fault current generated under the condition of DC fault caused by the DC overhead line between the terminal conversion station and the switch collection station, according to an embodiment of the present invention.

[0048] Figure 9 This is a schematic diagram illustrating the calculation results of the fault current generated under a DC fault caused by a DC overhead line between a switchgear station and an onshore converter station, according to an embodiment of the present invention. Detailed Implementation

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

[0050] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in this application will be clearly and completely described below with reference to the accompanying drawings of the embodiments of this application. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application pertains; the terminology used herein is for the purpose of describing specific embodiments only and is not intended to limit this application; the terms "comprising" and "having," and any variations thereof, in the specification, claims, and the foregoing description of the accompanying drawings of this application are intended to cover non-exclusive inclusion. In the description of the embodiments of this application, technical terms such as "first," "second," etc., are only used to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly indicating the number, specific order, or primary or secondary relationship of the indicated technical features. In the description of the embodiments of this application, "a plurality of" means two or more, unless otherwise explicitly specified. The reference to "embodiment" herein means that a specific feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art will understand, explicitly and implicitly, that the embodiments described herein can be combined with other embodiments. In the description of the embodiments of this application, the term "and / or" is merely a description of the association relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship. In the description of the embodiments of this application, the term "multiple" refers to two or more (including two); similarly, "multiple groups" refers to two or more groups (including two groups), and "multiple pieces" refers to two or more pieces (including two pieces). In the description of the embodiments of this application, unless otherwise expressly specified and limited, technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0051] like Figure 1The image shows a DC fault ride-through method for an integrated onshore and offshore wind power DC system based on a fast communication link, provided by an embodiment of the present invention. This method is applied to applications such as... Figure 2 The offshore wind power integrated onshore-sea DC system shown is illustrated.

[0052] The offshore wind power integrated DC system includes an offshore wind farm, an offshore converter station, and an onshore converter station. The offshore wind farm includes several wind power converters and several communication relay devices. Each wind power converter is connected to a communication relay device, and each wind power converter includes a wind turbine energy consumption device. The offshore converter station and each communication relay device are connected sequentially through a bidirectional ring network optical fiber channel.

[0053] In a preferred embodiment, the offshore wind power integrated onshore-offshore DC system further includes: a terminal converter station, a switchgear collection station, and a receiving-end power grid; the terminal converter station includes a plurality of first high-speed DC switches; the switchgear collection station includes a plurality of second high-speed DC switches and a plurality of third high-speed DC switches; and the onshore converter station includes a plurality of fourth high-speed DC switches; the offshore converter station is connected to the terminal converter station via a DC submarine cable; each of the first high-speed DC switches is connected to each of the second high-speed DC switches in the switchgear collection station via a first overhead DC line; each of the second high-speed DC switches is connected in parallel with each of the third high-speed DC switches; each of the third high-speed DC switches is connected to each of the fourth high-speed DC switches via a second overhead DC line; and the onshore converter station is connected to the receiving-end power grid via a third overhead DC line.

[0054] Specifically, the offshore wind power integrated onshore-offshore DC system proposed in this invention consists of an offshore wind farm, an offshore converter station, a terminal conversion station, a switchgear collection station, an onshore converter station, and a receiving-end power grid connected sequentially. Both the offshore and onshore converter stations are equipped with DC control and protection systems. The term "first DC control and protection system" refers to the DC control and protection system corresponding to the onshore converter station, and "second DC control and protection system" refers to the DC control and protection system corresponding to the offshore converter station. To achieve DC fault ride-through in the DC transmission system of this invention, both the offshore and onshore converter stations adopt a hybrid full-half-bridge topology. When a DC line fault occurs, the hybrid full-half-bridge converter allows the arm current to flow bidirectionally through the capacitor, effectively clamping the fault current and thus suppressing its further development. Preferably, considering the possibility of overvoltage in the MMC submodule of the offshore converter station due to the inability to transmit power externally, this invention eliminates centralized energy dissipation devices when constructing the offshore wind power integrated onshore-offshore DC system, utilizing the energy dissipation devices of the offshore wind farm's turbines themselves to balance the surplus power during faults.

[0055] To enable DC fault ride-through in the offshore wind power integrated onshore-sea DC system of this invention, a high-speed DC switch is installed at both ends of each overhead DC line. The high-speed DC switch is... Figure 1The HSS identifier in the diagram includes multiple high-speed DC switches in the terminal converter station, switchgear concentrator, and onshore converter station. The terminal converter station connects multiple first high-speed DC switches to multiple second high-speed DC switches in the switchgear concentrator, which then aggregate them into multiple third high-speed DC switches. Each third high-speed DC switch is connected to a fourth high-speed DC switch. It should be noted that the switchgear concentrator's function is to aggregate multiple second-order overhead DC lines passing through the second high-speed DC switches, thereby reducing the length of the second-order overhead DC lines. Therefore, the number of third high-speed DC switches in the switchgear concentrator is less than the number of second-order high-speed DC switches, thus achieving aggregation of the second-order overhead DC lines within the switchgear concentrator and further reducing the required length of overhead DC lines between the switchgear concentrator and the onshore converter station.

[0056] In a preferred embodiment, the onshore converter station includes a first DC control and protection system, and the offshore converter station includes a second DC control and protection system; the first DC control and protection system and the second DC control and protection system communicate with each other through a direct communication channel.

[0057] Specifically, the specific communication method of the system under DC fault conditions is as follows: Figure 3 As shown, this invention establishes a direct communication channel between the first and second DC control and protection systems. This DC communication channel is a 100 Mbps inter-station communication channel. Based on the construction of this communication channel, if the first DC control and protection system of the onshore converter station detects a fault, it can transmit the fault signal to the second DC control and protection system of the offshore converter station through the 100 Mbps inter-station communication channel between the onshore and offshore converter stations. The second DC control and protection system of the offshore converter station then issues a command to activate the wind turbine energy consumption device, which is transmitted to the corresponding wind turbine energy consumption device of each wind turbine through the optical fiber channel of the collector cable.

[0058] In a preferred embodiment, the offshore wind farm further includes a plurality of wind turbines; each wind turbine is connected to a wind power converter;

[0059] The bidirectional ring network optical fiber channel includes: a first optical fiber, a second optical fiber, a third optical fiber, and a fourth optical fiber;

[0060] The first transmitting end of the offshore converter station is connected to the first receiving end of the first communication forwarding device through the first optical fiber. The first transmitting ends of the remaining communication forwarding devices, except for the first communication forwarding device and the terminal communication forwarding device, are connected to the first receiving ends of the next communication forwarding device in sequence through the first optical fiber. The first transmitting end of the terminal communication forwarding device is connected to the first receiving end of the offshore converter station through the first optical fiber.

[0061] The second transmitting end of the offshore converter station is connected to the second receiving end of the terminal communication forwarding device via the second optical fiber. The second transmitting ends of the other communication forwarding devices, except for the first communication forwarding device and the terminal communication forwarding device, are connected to the second receiving end of the previous communication forwarding device in sequence via the second optical fiber. The second transmitting end of the first communication forwarding device is connected to the second receiving end of the offshore converter station via the second optical fiber.

[0062] The third transmitting end of the offshore converter station is connected to the third receiving end of the first communication forwarding device through the third optical fiber. The third transmitting ends of the remaining communication forwarding devices, except for the first and the last communication forwarding devices, are connected to the third receiving ends of the next communication forwarding device in sequence through the third optical fiber. The third transmitting end of the last communication forwarding device is connected to the third receiving end of the offshore converter station through the third optical fiber.

[0063] The fourth transmitting end of the offshore converter station is connected to the fourth receiving end of the terminal communication forwarding device via the fourth optical fiber. The fourth transmitting ends of the other communication forwarding devices, except for the first and terminal communication forwarding devices, are connected to the fourth receiving ends of the previous communication forwarding devices in sequence via the fourth optical fiber. The fourth transmitting end of the first communication forwarding device is connected to the fourth receiving end of the offshore converter station via the fourth optical fiber.

[0064] Specifically, such as Figure 4 The diagram shown is a schematic representation of the internal structure of a wind power converter provided by this invention. The wind power converter includes a turbine-side converter, a wind turbine energy dissipation device, and a grid-side converter. Offshore wind farms include multiple wind turbines, multiple wind power converters, and multiple communication relay devices.

[0065] like Figure 5 As shown in the figure, the present invention provides a schematic diagram of communication between the communication relay devices of the offshore converter station and each wind turbine through a bidirectional ring network optical fiber channel.

[0066] Taking a system containing n wind turbines as an example, the offshore converter station sends the wind turbine energy consumption input command from the first transmitting end TX1 of the offshore converter station to the first receiving end RX1 of the communication relay device 1 through the first optical fiber. After receiving the signal, the first receiving end RX1 transmits it through its internal signal and then sends it again through the first transmitting end TX1 of the communication relay device 1 to the first receiving end RX1 of the communication relay device 2 through the first optical fiber. After being sent to the first receiving end RX1 of the communication relay device n in this way, after the internal signal transmission of the communication relay device n, the response signal of each communication relay device to the wind turbine energy consumption input command is sent through the first transmitting end of the communication relay device n to the first receiving end RX1 of the offshore converter station through the first optical fiber.

[0067] Simultaneously, the offshore converter station transmits the wind turbine energy consumption input command from the second transmitting end TX2 to the second receiving end RX2 of the communication relay device n via the second optical fiber. After internal signal transmission of the communication relay device n, it is transmitted from the second transmitting end TX1 of the communication relay device n to the second receiving end RX2 of the communication relay device n-1 via the second optical fiber. This process is repeated sequentially until the command is transmitted to the second receiving end RX2 of the communication relay device 1. After internal signal transmission of the communication relay device 1, the response signals of each communication relay device to the wind turbine energy consumption input command are transmitted from the second transmitting end TX2 of the communication relay device 1 to the second receiving end RX2 of the offshore converter station via the second optical fiber.

[0068] Simultaneously, the offshore converter station transmits the wind turbine energy consumption input command from the third transmitting end TX3 of the offshore converter station to the third receiving end RX3 of the communication relay device 1 via the third optical fiber. After receiving the signal, the third receiving end RX3 transmits it through its internal signal transmission and then transmits it again through the third transmitting end TX3 of the communication relay device 1 to the third receiving end RX3 of the communication relay device 2 via the first transmitting optical fiber. After being transmitted to the third receiving end RX3 of the communication relay device n in this way, after the internal signal transmission of the communication relay device n, the response signals of each communication relay device to the wind turbine energy consumption input command are transmitted through the third optical fiber to the third receiving end RX3 of the offshore converter station via the first transmitting end of the communication relay device n.

[0069] Simultaneously, the offshore converter station transmits the wind turbine energy consumption input command from the fourth transmitting end TX4 to the fourth receiving end RX4 of the communication relay device n via the fourth optical fiber. After internal signal transmission in the communication relay device n, it is transmitted from the fourth transmitting end TX4 of the communication relay device n to the fourth receiving end RX4 of the communication relay device n-1 via the fourth optical fiber. This process is repeated sequentially until the command is transmitted to the fourth receiving end RX4 of the communication relay device 1. After internal signal transmission in the communication relay device 1, the response signals of each communication relay device to the wind turbine energy consumption input command are transmitted from the fourth transmitting end TX4 of the communication relay device 1 to the fourth receiving end RX4 of the offshore converter station via the fourth optical fiber.

[0070] In a preferred embodiment, the capacity of each of the wind turbine energy-consuming devices is determined according to the following formula:

[0071]

[0072] in, Indicates the capacity of the fan's energy-consuming device; This indicates the rated output power of the fan; This represents the time margin, measured in seconds (s). The value is determined based on the DC fault ride-through time.

[0073] Specifically, since this invention eliminates the centralized energy consumption device and only uses the wind turbine energy consumption device to balance the surplus power during DC fault ride, the capacity requirements of the wind turbine energy consumption device need to be reset when designing an integrated offshore wind power DC system to ensure that the wind turbine energy consumption device can meet the energy dissipation requirements during DC fault ride.

[0074] When designing the energy-consuming devices for wind turbines, it is necessary to focus on the capacity requirements of these devices, such as... Figure 6 As shown, DC fault ride-through takes 600-700ms. Considering the scenario of two restarts, the wind turbine energy-consuming device needs to absorb a maximum of "rated power * 2.1s" of surplus power. Under the condition of a certain power margin, this invention sets the capacity requirement for each wind turbine energy-consuming device as follows:

[0075] in, Indicates the capacity of the fan's energy-consuming device; This indicates the rated output power of the offshore wind turbine. Based on the value of the DC fault ride-through time, redundancy is added, and the value is set to 2.5s.

[0076] Existing wind turbines do not have the capacity to absorb surplus power. In engineering, they are usually designed according to "rated power * 1.5s". However, by resetting the capacity of the wind turbine's energy-consuming devices as described above, 2.5s zero voltage ride-through can be achieved, and the impact on the wind turbine converter, the structure of the offshore wind farm itself, and temperature control is minimal.

[0077] In a preferred embodiment, the maximum allowable delay duration is determined by the following formula:

[0078]

[0079] in, This is the maximum allowable delay duration; The capacitance value of the offshore converter station; This refers to the maximum permissible module voltage for offshore converter stations. This refers to the rated module voltage of the offshore converter station; The total number of bridge modules in the offshore converter station; This represents the maximum active power of the offshore converter station.

[0080] For example, as shown in the table below, the present invention takes typical values ​​according to actual engineering requirements. Calculations were performed based on the typical values ​​in the table below. That is, after a DC overhead line failure, the maximum allowable delay time from the issuance of the wind turbine energy consumption start command from the flexible DC side to the start of the wind turbine energy consumption device is 9.22ms. During the period when the DC overhead line fails and the wind turbine energy consumption device is not in operation, the surplus power is absorbed by the offshore converter station.

[0081]

[0082] Specifically, direct communication has not yet been established between the existing second DC control and protection system of the offshore converter station and the wind turbine converters of the offshore wind farm. Communication must be relayed through the offshore wind farm's SCADA system, with current communication times ranging from several hundred milliseconds to several seconds. Therefore, this significant communication delay severely impacts the stability of the DC transmission system, necessitating a redesign of the system's communication equipment to ensure sufficient communication time. The requirements stipulate that, under the constraint of the maximum allowable delay time, the bidirectional ring network fiber optic channel should enable the wind turbine energy-consuming devices to be put into operation in a timely and rapid manner to absorb the surplus power of the fault, thereby achieving rapid clearing of DC faults and restoring the system to stable operation.

[0083] Based on the above analysis, it can be seen that in an integrated onshore and offshore wind power DC system, the communication delay from the occurrence of a fault to the activation of the wind turbine energy-consuming devices mainly includes the following stages: fault characteristic transmission delay, line fault detection and communication delay, communication delay between the offshore converter station and each wind turbine converter, and the activation delay of the wind turbine energy-consuming devices. For example... Figure 7 As shown, based on the existing construction and operation of DC projects, it can be calculated that when a fault occurs in a remote overhead DC line, the transmission delay from the fault occurrence to the second DC control and protection system at the offshore converter station is approximately 5ms. The communication delay from the fault occurrence to the second DC control and protection system at the offshore converter station specifically includes: fault characteristic transmission delay of 1.5ms; line fault detection delay of 3ms; and protection host to control host delay of 0.5ms. Through bidirectional ring network fiber optic channels, communication signals can be transmitted, enabling the transmission from the offshore converter station issuing a wind turbine energy consumption activation command to the wind turbine energy consumption device activation control within 1ms. The communication delay between the offshore converter station and each wind turbine energy consumption device specifically includes: fiber optic fast communication delay between the flexible DC and the wind turbine converter of 100~200us; communication data packet length of 100~200us; and 500us within two cycles for the wind turbine converter to receive the control command and for the DSP to process the information. Considering the above communication delays, after a DC fault occurs, the fault information is transmitted to the wind turbine energy consumption device for activation, and the delay for a fault on a remote DC overhead line is about 6ms, which enables rapid communication in the DC transmission system.

[0084] After completing the construction of the aforementioned integrated onshore-sea DC system for offshore wind power and the rapid communication design of the bidirectional ring network fiber optic channel, a DC fault ride-through method is implemented on this system, including:

[0085] Step S1: When a DC fault occurs, obtain the voltage drop rate and voltage drop amplitude of the onshore converter station;

[0086] Step S2: When the voltage drop rate is lower than the voltage drop rate threshold and the voltage drop amplitude is lower than the voltage drop amplitude threshold, a wind turbine power consumption activation command is sent to the offshore converter station. This allows the offshore converter station to transmit the wind turbine power consumption activation command to each communication forwarding device through a bidirectional ring network fiber optic channel. Each communication forwarding device then transmits the wind turbine power consumption activation command to the corresponding wind turbine power consumption device, so that the wind turbine power consumption device can absorb the fault surplus power according to the wind turbine power consumption activation command. The time from the issuance of the wind turbine power consumption activation command from the flexible DC side to the start-up of the wind turbine power consumption device shall not exceed the maximum allowable delay time.

[0087] In step S1, after a DC fault occurs, the voltage at the fault point will drop instantaneously, while the DC current will rise. At this time, fault detection and location are performed on the offshore wind power integrated onshore-offshore DC system, and DC voltage data at the fault point from the onshore converter station is acquired. If the DC voltage does not reach the preset control start-up standard, it indicates a low fault severity, allowing for unnecessary system intervention and maintaining grid stability and security. The preset control start-up standard is that the voltage drop rate is lower than the voltage drop rate threshold and the voltage drop amplitude is lower than the voltage drop amplitude threshold. In this invention, the voltage drop rate threshold is a low voltage setpoint of 0.45 pu, and the voltage drop amplitude threshold is a voltage surge setpoint of -1.16 pu / ms. When the DC voltage data reaches the preset control start-up condition, a wind turbine energy consumption activation command needs to be sent to the offshore converter station. This command is then transmitted via a bidirectional ring network fiber optic channel to each wind turbine energy consumption device, allowing each device to absorb the surplus power from the fault according to the activation command.

[0088] For step S2, in a preferred embodiment, each wind turbine energy-consuming device absorbs the fault surplus power according to the wind turbine energy consumption input command, including: obtaining the real-time power of each wind turbine energy-consuming device at the previous moment according to the wind turbine energy consumption input command, and controlling each wind turbine energy-consuming device to absorb the fault surplus power according to the real-time power of each wind turbine energy-consuming device at the previous moment, until the offshore wind power integrated onshore-sea DC system achieves surplus power balance.

[0089] Specifically, after receiving the wind turbine energy consumption activation command, the wind turbine energy consumption device needs to absorb the surplus power due to the fault according to the command. Specifically, this involves obtaining the real-time power of each wind turbine energy consumption device at the previous moment, and controlling each wind turbine energy consumption device to consume the surplus power due to the fault based on the real-time power of each wind turbine energy consumption device at the previous moment, until the offshore wind power integrated onshore-sea DC system achieves surplus power balance.

[0090] In a preferred embodiment, when the voltage drop rate is lower than the voltage drop rate threshold and the voltage drop amplitude is lower than the voltage drop amplitude threshold, the method further includes: sending a DC fault ride-through command to the onshore converter station and the offshore converter station, so that the offshore converter station and the onshore converter station establish a negative voltage according to the DC fault ride-through command, absorb the fault current, and complete a DC fault clearing.

[0091] Specifically, when the DC voltage data reaches the preset control start-up conditions, it is also necessary to send a DC fault ride-through command to the offshore converter station and the onshore converter station. Upon receiving the DC fault ride-through command, the offshore converter station and the onshore converter station establish a negative voltage and actively absorb the fault current.

[0092] At this point, the first fault clearance of the offshore wind power integrated onshore-offshore DC system is completed. Preferably, after the first fault clearance, the offshore wind power integrated onshore-offshore DC system enters the deionization phase. During this period, the flexible DC system ensures that the DC current is zero, allowing the faulty line to be completely deionized, ensuring that the flashover arc disappears and the insulation performance returns to its original level. It is worth noting that the deionization time should not be too long, so as to avoid prolonged power surplus in the sending-end grid and prolonged power shortage in the receiving-end grid, thereby triggering stability control actions such as load shedding.

[0093] In a preferred embodiment, after clearing a fault in the offshore wind power integrated onshore-offshore DC system, the process further includes: performing a first on-state restart of the offshore wind power integrated onshore-offshore DC system, controlling the offshore converter station to restore the first DC current, and simultaneously controlling the onshore converter station to establish the first DC voltage; if the first DC voltage of the onshore converter station is successfully established, the DC fault is completely cleared; if the first DC voltage of the onshore converter station fails to be established, performing a second on-state restart of the offshore wind power integrated onshore-offshore DC system, controlling the offshore converter station to restore the second DC current, and simultaneously controlling the onshore converter station to establish the second DC voltage; if the second DC voltage of the onshore converter station is successfully established, the DC fault is completely cleared.

[0094] In a preferred embodiment, after performing a second original pressure restart on the offshore wind power integrated onshore-offshore DC system, controlling the offshore converter station to restore the second DC current, and simultaneously controlling the onshore converter station to establish the second DC voltage, the method further includes: if the onshore converter station fails to establish the second DC voltage, then disconnecting the wind turbine and controlling each wind turbine energy-consuming device to exit operation.

[0095] Specifically, after a sufficient deionization process, a voltage restart is performed. The offshore converter station is controlled to restore the first DC current, while the onshore converter station is controlled to establish the first DC voltage. If the onshore converter station successfully establishes the first DC voltage, it indicates that the DC fault has been completely cleared, and each station will gradually restore DC power. If the onshore converter station fails to establish the first DC voltage, it indicates that the DC fault still exists, requiring a repeat of the deionization process, followed by a second voltage restart. The offshore converter station is controlled to restore the second DC current, while the onshore converter station is controlled to establish the second DC voltage. If the onshore converter station successfully establishes the second DC voltage, it indicates that the DC fault has been completely cleared, and each station will gradually restore DC power. If the onshore converter station fails to establish the second DC voltage, it indicates that the DC fault still exists and is a permanent fault. If the DC current of the DC transmission system is still outside the stable operating range after two restarts, a generator tripping operation is required. It should be noted that, for the offshore wind power integrated onshore-offshore DC system of this invention, considering the 600-700ms required for DC fault ride-through, the wind turbine energy dissipation device can absorb a maximum of "rated power * 2.5s" of surplus power. Considering the 600-700ms required for DC fault ride-through and the at least 150ms required for turbine tripping, two restarts are used as the tripping criterion for the offshore wind power integrated onshore-offshore DC system. When the number of DC transmission system restarts is less than or equal to two, the surplus power is absorbed through the offshore converter station, onshore converter station, and wind turbine energy dissipation device. When the number of DC transmission system restarts is greater than two, a turbine tripping operation is performed, and the wind turbine energy dissipation device is taken out of operation.

[0096] For example, a simulation study of DC fault ride-through in an integrated onshore and offshore wind power DC system is conducted. In steady state, three sets of flexible DC converter stations at sea transmit wind turbine power, using VF control, with a rated power of 2000MW each. The receiving-end converter station at the onshore station has two sets of converters connected to the HSS via a DC bus, controlling DC voltage and active power respectively in steady state. Two scenarios are considered: DC faults caused by overhead DC lines between the terminal conversion station and the switching collection station, and DC faults caused by overhead DC lines between the switching collection station and the onshore converter station. Simulation experiments are designed. The DC side positive and negative bus voltages of the receiving-end voltage station at the onshore converter station are ±500kV, and the DC current is approximately 2.6kA. The fault occurs at 5.1s. After the fault, the onshore converter station is put into control 5ms later, the offshore converter station 6ms later, and the wind turbine energy dissipation device is activated 7ms later. Specific results of the example are as follows: Figure 8 and Figure 9 As shown, where, Figure 8 This describes the fault current generated under a DC fault caused by an overhead DC line between the terminal conversion station and the switchgear collection station (Scenario 1). Figure 9This describes the fault current generated under a DC fault caused by an overhead DC line between the switchgear and the onshore converter station (Scenario 2). At the moment of the fault, the fault electrode capacitor discharges through the fault point, generating a large fault current. As the DC voltage and current are controlled to zero, the fault current rapidly decreases. Approximately 120ms (Scenario 1) / 200ms (Scenario 2) after the fault, the fault current exhibits AC fluctuations with a peak value less than 200A.

[0097] The table below compares key electrical parameters under different fault conditions. It can be observed that during the fault process, the maximum overvoltage of the submodule capacitor at the sending end (offshore converter station) does not exceed 1.30 pu, and the current does not exceed 2.5 kA; while at the receiving end (onshore converter station), the maximum overvoltage of the submodule capacitor does not exceed 1.20 pu, and the current does not exceed 3.5 kA. The calculation results demonstrate that the proposed offshore wind power integrated onshore-offshore DC transmission system and offshore wind power DC fault ride-through method can utilize distributed wind turbine energy consumption devices to consume surplus wind power, while the converter valves at both the sending and receiving ends have no overvoltage or overcurrent risk.

[0098]

[0099] It should be noted that the system embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate, and the components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs. Furthermore, in the accompanying drawings of the system embodiments provided by this invention, the connection relationships between modules indicate that they have communication connections, which can be specifically implemented as one or more communication buses or signal lines. Those skilled in the art can understand and implement this without any creative effort.

[0100] Those skilled in the art will clearly understand that, for convenience and brevity, the specific working process of the device described above can be referred to the corresponding process in the foregoing method embodiments, and will not be repeated here.

[0101] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A DC fault ride-through method for an integrated onshore and offshore wind power DC system based on a high-speed communication link, characterized in that, This invention relates to an integrated onshore-offshore DC system for offshore wind power, comprising an offshore wind farm, an offshore converter station, and an onshore converter station. The offshore wind farm includes several wind power converters and several communication relay devices. Each wind power converter is connected to a communication relay device, and each wind power converter includes a wind turbine energy consumption device. The offshore converter station and each communication relay device are sequentially connected through a bidirectional ring network optical fiber channel. The DC fault ride-through method includes: In the event of a DC fault, obtain the voltage drop rate and voltage drop magnitude of the onshore converter station; When the voltage drop rate is lower than the voltage drop rate threshold and the voltage drop amplitude is lower than the voltage drop amplitude threshold, a wind turbine power consumption activation command is sent to the offshore converter station. The offshore converter station then transmits the command through a bidirectional ring network fiber optic channel to each communication forwarding device. Each communication forwarding device then transmits the command to the corresponding wind turbine power consumption device, enabling the device to absorb surplus power from the fault. The time from the issuance of the wind turbine power consumption activation command to the activation of the wind turbine power consumption device must not exceed the maximum allowable delay. During the period when the DC overhead line fails and the wind turbine energy-consuming device is not in operation, the offshore converter station absorbs the surplus power. The maximum allowable delay duration is determined by the following formula: in, This is the maximum allowable delay duration; The capacitance value of the offshore converter station; This refers to the maximum permissible module voltage for offshore converter stations. This refers to the rated module voltage of the offshore converter station; The total number of bridge modules in the offshore converter station; This represents the maximum active power of the offshore converter station.

2. The DC fault ride-through method for an integrated onshore and offshore wind power DC system based on a fast communication link as described in claim 1, characterized in that, The offshore wind power integrated onshore-sea DC system also includes: a terminal converter station, a switch collection station and a receiving-end power grid. The terminal converter station includes a number of first high-speed DC switches, the switch collection station includes a number of second high-speed DC switches and a number of third high-speed DC switches, and the onshore converter station includes a number of fourth high-speed DC switches. The offshore converter station is connected to the terminal converter station via a DC submarine cable; Each of the first DC high-speed switches is connected to each of the second DC high-speed switches in a one-to-one correspondence via a first DC overhead line; Each of the second DC high-speed switches is connected in parallel with each of the third DC high-speed switches; Each of the third DC high-speed switches is connected to each of the fourth DC high-speed switches via the second DC overhead line; The onshore converter station is connected to the receiving-end power grid via a third overhead DC line.

3. The DC fault ride-through method for an integrated onshore and offshore wind power DC system based on a fast communication link as described in claim 2, characterized in that, The onshore converter station includes a first DC control and protection system, and the offshore converter station includes a second DC control and protection system. The first DC control and protection system and the second DC control and protection system communicate through a direct communication channel.

4. The DC fault ride-through method for an integrated onshore and offshore wind power DC system based on a fast communication link as described in claim 3, characterized in that, The offshore wind farm also includes several wind turbines; each wind turbine is connected to a wind power converter. The bidirectional ring network optical fiber channel includes: a first optical fiber, a second optical fiber, a third optical fiber, and a fourth optical fiber; The first transmitting end of the offshore converter station is connected to the first receiving end of the first communication forwarding device through the first optical fiber. The first transmitting ends of the remaining communication forwarding devices, except for the first communication forwarding device and the terminal communication forwarding device, are connected to the first receiving ends of the next communication forwarding device in sequence through the first optical fiber. The first transmitting end of the terminal communication forwarding device is connected to the first receiving end of the offshore converter station through the first optical fiber. The second transmitting end of the offshore converter station is connected to the second receiving end of the terminal communication forwarding device via the second optical fiber. The second transmitting ends of the other communication forwarding devices, except for the first communication forwarding device and the terminal communication forwarding device, are connected to the second receiving end of the previous communication forwarding device in sequence via the second optical fiber. The second transmitting end of the first communication forwarding device is connected to the second receiving end of the offshore converter station via the second optical fiber. The third transmitting end of the offshore converter station is connected to the third receiving end of the first communication forwarding device through the third optical fiber. The third transmitting ends of the remaining communication forwarding devices, except for the first and the last communication forwarding devices, are connected to the third receiving ends of the next communication forwarding device in sequence through the third optical fiber. The third transmitting end of the last communication forwarding device is connected to the third receiving end of the offshore converter station through the third optical fiber. The fourth transmitting end of the offshore converter station is connected to the fourth receiving end of the terminal communication forwarding device via the fourth optical fiber. The fourth transmitting ends of the other communication forwarding devices, except for the first and terminal communication forwarding devices, are connected to the fourth receiving ends of the previous communication forwarding devices in sequence via the fourth optical fiber. The fourth transmitting end of the first communication forwarding device is connected to the fourth receiving end of the offshore converter station via the fourth optical fiber.

5. The DC fault ride-through method for an integrated onshore and offshore wind power DC system based on a fast communication link as described in claim 4, characterized in that, The capacity of each of the aforementioned wind turbine energy-consuming devices is determined according to the following formula: in, Indicates the capacity of the fan's energy-consuming device; This indicates the rated output power of the fan; This indicates the time margin, which is determined based on the DC fault ride-through time.

6. The DC fault ride-through method for an integrated onshore and offshore wind power DC system based on a fast communication link as described in claim 1, characterized in that, When the voltage sag rate is lower than the voltage sag rate threshold and the voltage sag amplitude is lower than the voltage sag amplitude threshold, the following is also included: Send DC fault ride-through commands to onshore and offshore converter stations so that they can establish negative voltage, absorb fault current, and complete a DC fault clearing operation.

7. The DC fault ride-through method for an integrated onshore and offshore wind power DC system based on a fast communication link as described in claim 6, characterized in that, Each wind turbine energy-consuming device absorbs surplus power from faults according to the wind turbine energy consumption activation command, including: The system obtains the real-time power of each wind turbine energy-consuming device from the previous moment according to the wind turbine energy consumption input command, and controls each wind turbine energy-consuming device to absorb the fault surplus power according to the real-time power of each wind turbine energy-consuming device from the previous moment, until the offshore wind power integrated onshore-sea DC system achieves surplus power balance.

8. The DC fault ride-through method for an integrated onshore and offshore wind power DC system based on a fast communication link as described in claim 7, characterized in that, After completing the initial fault clearing of the offshore wind power integrated onshore-sea DC transmission system, the following is also included: The offshore wind power integrated onshore-offshore DC system was restarted under its original pressure for the first time, controlling the offshore converter station to restore the first DC current and simultaneously controlling the onshore converter station to establish the first DC voltage. If the first DC voltage is successfully established at the onshore converter station, the DC fault will be completely cleared. If the first DC voltage of the onshore converter station fails to be established, the offshore wind power integrated onshore-offshore DC system will be restarted at the original voltage for the second time, controlling the offshore converter station to restore the second DC current, and at the same time controlling the onshore converter station to establish the second DC voltage. If the second DC voltage at the onshore converter station is successfully established, the DC fault will be completely cleared.

9. The DC fault ride-through method for an integrated onshore and offshore wind power DC system based on a fast communication link as described in claim 8, characterized in that, After performing a second original-voltage restart of the offshore wind power integrated onshore-offshore DC system, controlling the offshore converter station to restore the second DC current, and simultaneously controlling the onshore converter station to establish the second DC voltage, the process also includes: If the second DC voltage of the onshore converter station fails to be established, the wind turbines will be shut down and the energy-consuming devices of each wind turbine will be taken out of operation.

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